Re: [time-nuts] Photodiodes for high frequency OPLL
On Monday 01 April 2013, Attila Kinali wrote: > On Mon, 1 Apr 2013 14:24:58 +0100 > > Wolfgang wrote: > > Anyway, each of these down-mixing approaches needs to resolve the > > mirror frequency problem. I.e. if you modulate your receiver with > > 7.1 GHz (or use an EOM to do that optically) and detect at 100 MHz, > > you do not know whether the input signal has an offset of 7.2 GHz > > or 7.0 GHz. > > So you might be locking on the wrong one. > > If i'm not mistaken, this shouldn't be a problem > I'm not demodulating the laser, but using a PLL to fix the difference > frequency. Being on the wrong side would invert the sign on the loop > gain, thus the mirror freuquency would be an unstable point. > Without too much of thinking it seems to me that there are 4 cases that show up as 100 MHz. Only 2 of them without the RF mixing. 2 will have the same loop sign (only 1 without RF mixing). A-B = 7.2 GHz A-B = 7.0 GHz A-B = -7.0 GHz A-B = -7.2 GHz BTW, what's the linewidth of your lasers? -Wolfgang DL1SKY ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Photodiodes for high frequency OPLL
Reverse biased diodes are not very low impedance. You can't really drive a low impedance with them. In fact, the high impedance of the photodiode leads to all sorts of ugliness in noise analysis. This is well documented in Graeme's book. I think TI also has an app note on feedback networks for the best SNR, though Graeme has a technique to get optimal bandwidth and noise performance. A lot of people make a living just designing front ends for high impedance devices. They are really hard to do optimally since high impedance is bad for bandwidth, noise, and all things nice. There is also a book by Hobbs on photodiode interfaces. Much of the book is unfortunately filler, though parts are very good. I found a pirated copy online and decided not to buy the real thing. Graeme's book is much more detailed. The derivations of the equations are shown in painful detail. [My dislike of Gain Technology comes from dealing with the company. I have no personal knowledge of Graeme other than buying his books.] You might want to track down the pirated version of Hobbs before spending $150. I did, then deleted it since I already owned Graeme's book. Building Electro-Optical Systems: Making It all Work On 4/1/2013 10:30 AM, J. Forster wrote: I think that you should be able to take the signal right out of the backbiased diode and run it straight into a microwave mixer w/ a fixed 7 GHz LO and frequency discrimitate the IF output from the mixer to generate a control signal for your LASER. In theory, if your LASERS were very, very, very good, you might be able to achieve phase lock, but I'd not hold my breath. A discriminator can give you frequency lock. YMMV, -John ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Photodiodes for high frequency OPLL
I think that you should be able to take the signal right out of the backbiased diode and run it straight into a microwave mixer w/ a fixed 7 GHz LO and frequency discrimitate the IF output from the mixer to generate a control signal for your LASER. In theory, if your LASERS were very, very, very good, you might be able to achieve phase lock, but I'd not hold my breath. A discriminator can give you frequency lock. YMMV, -John = > On Mon, 1 Apr 2013 14:24:58 +0100 > Wolfgang wrote: > >> On Monday 01 April 2013, Attila Kinali wrote: >> >> [APD...] >> > >> > I think the gain modulated approach to downconvert the signal should >> work. >> > >> Anyway, each of these down-mixing approaches needs to resolve the >> mirror frequency problem. I.e. if you modulate your receiver with >> 7.1 GHz (or use an EOM to do that optically) and detect at 100 MHz, >> you do not know whether the input signal has an offset of 7.2 GHz >> or 7.0 GHz. >> So you might be locking on the wrong one. > > If i'm not mistaken, this shouldn't be a problem > I'm not demodulating the laser, but using a PLL to fix the difference > frequency. Being on the wrong side would invert the sign on the loop > gain, thus the mirror freuquency would be an unstable point. > > Attila Kinali > > -- > The people on 4chan are like brilliant psychologists > who also happen to be insane and gross. > -- unknown > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Photodiodes for high frequency OPLL
On Mon, 1 Apr 2013 14:24:58 +0100 Wolfgang wrote: > On Monday 01 April 2013, Attila Kinali wrote: > >> [APD...] > > > > I think the gain modulated approach to downconvert the signal should work. > > > Anyway, each of these down-mixing approaches needs to resolve the > mirror frequency problem. I.e. if you modulate your receiver with > 7.1 GHz (or use an EOM to do that optically) and detect at 100 MHz, > you do not know whether the input signal has an offset of 7.2 GHz > or 7.0 GHz. > So you might be locking on the wrong one. If i'm not mistaken, this shouldn't be a problem I'm not demodulating the laser, but using a PLL to fix the difference frequency. Being on the wrong side would invert the sign on the loop gain, thus the mirror freuquency would be an unstable point. Attila Kinali -- The people on 4chan are like brilliant psychologists who also happen to be insane and gross. -- unknown ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Photodiodes for high frequency OPLL
On Mon, 1 Apr 2013 14:28:49 +0100 Wolfgang wrote: > On Saturday 30 March 2013, Attila Kinali wrote: > > So far, i figured out that PIN photodiodes can go up to several 100MHz > > transition frequency and avalanche photodiodes are available up to 2GHz. > > The only photodiodes that go higher are those for the telecom range > > at 1-1.5um, which is a bit low for my needs. > > > Took me about 15 Seconds of googling to find this: > > http://search.newport.com/?x2=sku&q2=818-BB-45 > > Biased Photodetector, 400-900nm, GaAs, 12.5 GHz, for $ 940 Yes. I found these as well. There are tons of such photodetectors, but their price is almost always above 1000USD. I'm doing this on my own and thus am a little bit constraint on money. Beside i hope to get the whole thing done for under 2000USD. Hence i hope to be able to use some of the shelf photodiodes and build the electronics myself. Attila Kinali -- The people on 4chan are like brilliant psychologists who also happen to be insane and gross. -- unknown ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Photodiodes for high frequency OPLL
This thread has already drifted a bit, but as an aside, the "sky UV" filters sold for photography are a joke. (Easily verified with UV diodes and any material that reacts to UV.) The Andover 400nm long pass actually DOES filter UV. A 400nm is nearly cast free. A 420nm does have a bit of a cast, but can be useful at times. These UV filters reduce the effect of airborne water vapor in long distance photography/remote-sensing. -Original Message- From: Attila Kinali Sender: time-nuts-boun...@febo.com Date: Mon, 1 Apr 2013 11:12:26 To: Discussion of precise time and frequency measurement Reply-To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Photodiodes for high frequency OPLL On Sun, 31 Mar 2013 20:31:58 -0700 gary wrote: > On 3/31/2013 5:52 AM, Attila Kinali wrote: > > > > Probably. But as steep filters for optics are kind of hard to come by, > > i think a super heterodyne design isn't realy going to work. > I've bought optical filters from Andover. They are pretty cheap, at > least compared to the rest of the industry. > > http://www.andovercorp.com/Web_store/index.php Yes, but the usual optical filters are not steep enough for this application. They are specified to a few nm, while we are talking here about GHz. At those wavelengths this is IIRC a factor 100'000. But thanks for the page anyways.. they might come handy as an ambient light filter for the photodiodes. Attila Kinali -- The people on 4chan are like brilliant psychologists who also happen to be insane and gross. -- unknown ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Photodiodes for high frequency OPLL
On Monday 01 April 2013, Bruce Griffiths wrote: > Back to the original problem: > > An AOM could be used to generate a sideband 7GHz above (or below) the > output of 1 laser which could then be mixed with the output of the other > laser using a narrow bandwidth photodiode. > That's going to get tough. AOMs usually stop at some hundret MHz and even if you do quad-pass (2 polarizations, 2 directions), you will have a hard time getting to 7 GHz. So you'd have to cascade several ones. You could, however, use an EOM theoretically, but again, considering price and bandwidth constraints, you will only find suitable ones for telecom wavelengths. On Monday 01 April 2013, Attila Kinali wrote: >> [APD...] > > I think the gain modulated approach to downconvert the signal should work. > Anyway, each of these down-mixing approaches needs to resolve the mirror frequency problem. I.e. if you modulate your receiver with 7.1 GHz (or use an EOM to do that optically) and detect at 100 MHz, you do not know whether the input signal has an offset of 7.2 GHz or 7.0 GHz. So you might be locking on the wrong one. The AOM would not have that issue because it is single sideband. --Wolfgang, DL1SKY ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Photodiodes for high frequency OPLL
On Saturday 30 March 2013, Attila Kinali wrote: > So far, i figured out that PIN photodiodes can go up to several 100MHz > transition frequency and avalanche photodiodes are available up to 2GHz. > The only photodiodes that go higher are those for the telecom range > at 1-1.5um, which is a bit low for my needs. > Took me about 15 Seconds of googling to find this: http://search.newport.com/?x2=sku&q2=818-BB-45 Biased Photodetector, 400-900nm, GaAs, 12.5 GHz, for $ 940 -Wolfgang, DL1SKY ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Photodiodes for high frequency OPLL
On 30 March 2013 11:48, Attila Kinali wrote: > So far, i figured out that PIN photodiodes can go up to several 100MHz > transition frequency and avalanche photodiodes are available up to 2GHz. It might be worth Picosecond Pulsed Labs to. I can't see it on their web site, but I would not be surprised if they sell very high speed diodes - it is sort of the market they aim at. Dave ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Photodiodes for high frequency OPLL
Attila Kinali wrote: On Mon, 01 Apr 2013 22:32:11 +1300 Bruce Griffiths wrote: Attila Kinali wrote: On Mon, 01 Apr 2013 09:08:51 +1300 Bruce Griffiths wrote: Nothing to do with laser line width. Merely indicating that the photodiode mixer can be used with a suitable LO to build an optical spectrum analyser front end. Are you refering to heterodyne spectrum analyser? Essentially, however if the photdiode has say a 1GHz bandwidth the LO could be stepped in say 1GHz steps with subsequent circuitry providing finer resolution. The difficulty here is to get an LO laser that can be stepped in 1GHz steps and keep it there, stable. The only way i have seen sofar is using a mode locked laser and referencing/stabilizing the LO to one of the comb tooths. Technically seems to be relatively simple, but unfortunately a mode locked laser is financially out of the reach of a mere mortal. Constructing an optoelectronic version of either an LSB or USB converter may be interesting. Yes, an optoelectronical I/Q mixer would be very intersting. But also very difficult and fragile to build, considering that you have to keep the distances stable down to a couple of 10nm. Attila Kinali Back to the original problem: An AOM could be used to generate a sideband 7GHz above (or below) the output of 1 laser which could then be mixed with the output of the other laser using a narrow bandwidth photodiode. How do ensure a suitably wide mode hop free tuning range for the lasers to be locked to the first laser? Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Photodiodes for high frequency OPLL
On Mon, 01 Apr 2013 22:32:11 +1300 Bruce Griffiths wrote: > Attila Kinali wrote: > > On Mon, 01 Apr 2013 09:08:51 +1300 > > Bruce Griffiths wrote: > > > > > >> Nothing to do with laser line width. > >> Merely indicating that the photodiode mixer can be used with a suitable > >> LO to build an optical spectrum analyser front end. > >> > > Are you refering to heterodyne spectrum analyser? > > > Essentially, however if the photdiode has say a 1GHz bandwidth the LO > could be stepped in say 1GHz steps with subsequent circuitry providing > finer resolution. The difficulty here is to get an LO laser that can be stepped in 1GHz steps and keep it there, stable. The only way i have seen sofar is using a mode locked laser and referencing/stabilizing the LO to one of the comb tooths. Technically seems to be relatively simple, but unfortunately a mode locked laser is financially out of the reach of a mere mortal. > Constructing an optoelectronic version of either an LSB or USB converter > may be interesting. Yes, an optoelectronical I/Q mixer would be very intersting. But also very difficult and fragile to build, considering that you have to keep the distances stable down to a couple of 10nm. Attila Kinali -- The people on 4chan are like brilliant psychologists who also happen to be insane and gross. -- unknown ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Photodiodes for high frequency OPLL
Attila Kinali wrote: On Mon, 01 Apr 2013 09:08:51 +1300 Bruce Griffiths wrote: Nothing to do with laser line width. Merely indicating that the photodiode mixer can be used with a suitable LO to build an optical spectrum analyser front end. Are you refering to heterodyne spectrum analyser? Attila Kinali Essentially, however if the photdiode has say a 1GHz bandwidth the LO could be stepped in say 1GHz steps with subsequent circuitry providing finer resolution. Constructing an optoelectronic version of either an LSB or USB converter may be interesting. Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Photodiodes for high frequency OPLL
On Mon, 01 Apr 2013 09:08:51 +1300 Bruce Griffiths wrote: > Nothing to do with laser line width. > Merely indicating that the photodiode mixer can be used with a suitable > LO to build an optical spectrum analyser front end. Are you refering to heterodyne spectrum analyser? Attila Kinali -- The people on 4chan are like brilliant psychologists who also happen to be insane and gross. -- unknown ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Photodiodes for high frequency OPLL
On Sun, 31 Mar 2013 10:47:29 -0400 Mike S wrote: > On 3/30/2013 7:48 AM, Attila Kinali wrote: > > So far, i figured out that PIN photodiodes can go up to several 100MHz > > transition frequency and avalanche photodiodes are available up to 2GHz. > > The only photodiodes that go higher are those for the telecom range > > at 1-1.5um, which is a bit low for my needs. > > > > But, i have seen descriptions of such OPLL that work with multi GHz > > offsets in the 700-800nm range. > > Maybe you can find something here: > http://www.gcsincorp.com/optical_chips/GaAs%20&%20InGaAs%20PIN%20Photodetectors.php > > They have ones which have a wavelength range of 760-860 nm, and go up to > 14 GHz. Interesting! thanks! Attila Kinali -- The people on 4chan are like brilliant psychologists who also happen to be insane and gross. -- unknown ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Photodiodes for high frequency OPLL
On Sun, 31 Mar 2013 20:31:58 -0700 gary wrote: > On 3/31/2013 5:52 AM, Attila Kinali wrote: > > > > Probably. But as steep filters for optics are kind of hard to come by, > > i think a super heterodyne design isn't realy going to work. > I've bought optical filters from Andover. They are pretty cheap, at > least compared to the rest of the industry. > > http://www.andovercorp.com/Web_store/index.php Yes, but the usual optical filters are not steep enough for this application. They are specified to a few nm, while we are talking here about GHz. At those wavelengths this is IIRC a factor 100'000. But thanks for the page anyways.. they might come handy as an ambient light filter for the photodiodes. Attila Kinali -- The people on 4chan are like brilliant psychologists who also happen to be insane and gross. -- unknown ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Photodiodes for high frequency OPLL
On Sun, 31 Mar 2013 15:27:02 +0100 David Kirkby wrote: > You can't modulate the sensitivity of a PIN diode by an adjustable > bias like you can in an APD. For a PIN diode, at the wavelengths you > are talking of, you basically get around 0.5 Amps/Watt from the diode. Right.. Forgot about that ^^' > APDs are not that expensive, especially the small ones you will need > for this. Well.. an APD is about 60-100USD while PIN photodiodes start from 10USD. Ok, considering that the rest will be probably in the 2000-5000USD range, this isn't much :-) > But I still can't really see a solution - I was just > clutching at straws. I think the gain modulated approach to downconvert the signal should work. Taking the beat signal of the two lasers and applying it to the APD will get me an approx 7GHz signal. Gain modulating the the APD with an 1-2GHz sinusoidal should downconvert it to something below 1GHz. The frequency of the modulation signal is low enough to "pass" trough the APD unperturbed (the APD is specified for 2.5Gbps). That the gain of an APD is an exponential function of the applied bias voltage should make the bias modulation "sharp" enough to approximate it with a pulse train. Ie it should "nicely" downconvert the beat signal to something below 1GHz. Attila Kinali -- The people on 4chan are like brilliant psychologists who also happen to be insane and gross. -- unknown ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Photodiodes for high frequency OPLL
I've bought optical filters from Andover. They are pretty cheap, at least compared to the rest of the industry. http://www.andovercorp.com/Web_store/index.php On 3/31/2013 5:52 AM, Attila Kinali wrote: Probably. But as steep filters for optics are kind of hard to come by, i think a super heterodyne design isn't realy going to work. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Photodiodes for high frequency OPLL
Noise adds in a RMS fashion unless it is correlated. So a differential amplifier can cancel common mode noise, but that is about it. The diode, being a single ended device, seems to me to be impossible to bias in a manner where the noise from the bias circuitry will cancel out. Note it may not be the case you need the full 7GHz if it is only the mixer product you are feeding the photodiode. That is, the diode will see the difference prouct. You can get gain and bandwidth in multiple stages. The first stage will determine the noise if you do it correctly. It has been my experience that anything high gain I try to build oscillates. [And of course intentional oscillators just sit there.] You will need to insure there is no feedback through the supply rails. In this respect, going fully differential will be better. I can't speak for JFET at high frequencies, but there is a lumped model for the BF862. You need to create a subcircuit for it. I had spent quite a bit of time designing a high speed photodiode front end, but junked the design when a different part of the system couldn't be made in a cost effect manner. Anyway, you need to check the limits of the manufacturers lumped circuit. The JFET bootstrap really has two functions. That of a low capacitance high impedance input and a low impedance output. If you read the literature, there are multiple transistor circuits used to get the output impedance lower. There isn't much that can be done regarding input impedance. Trolling the net, RF transformers seem to have an upper limit of 5GHz. Just thinking out loud here, you can get a little gain with a transformer, get rid of DC, bias the diode, and generate a fully differential signal. It is a route worth looking into. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Photodiodes for high frequency OPLL
Nothing to do with laser line width. Merely indicating that the photodiode mixer can be used with a suitable LO to build an optical spectrum analyser front end. Bruce Attila Kinali wrote: Moin, On Sun, 31 Mar 2013 12:28:59 +1300 Bruce Griffiths wrote: With a suitable low noise tunable LO (laser) the frequency spectrum beyond the photodiode electrical bandwidth can be explored. I don't exactly get how the laser spectrum (line width?) can be exploited to go beyond the photodiode bandwidth? Could you explain that a little bit? Attila Kinali ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Photodiodes for high frequency OPLL
On 3/30/2013 7:48 AM, Attila Kinali wrote: So far, i figured out that PIN photodiodes can go up to several 100MHz transition frequency and avalanche photodiodes are available up to 2GHz. The only photodiodes that go higher are those for the telecom range at 1-1.5um, which is a bit low for my needs. But, i have seen descriptions of such OPLL that work with multi GHz offsets in the 700-800nm range. Maybe you can find something here: http://www.gcsincorp.com/optical_chips/GaAs%20&%20InGaAs%20PIN%20Photodetectors.php They have ones which have a wavelength range of 760-860 nm, and go up to 14 GHz. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Photodiodes for high frequency OPLL
On 31 March 2013 13:52, Attila Kinali wrote: > > But probably using an APD with gain modulation at 1GHz or so, i could > down modulate the signal to something that is easier to handle > (ie something similar as a direct conversion software defined radios). > > I wonder if this would work with normal PIN photodiodes as well, as > their price is much lower than APDs. > > Attila Kinali You can't modulate the sensitivity of a PIN diode by an adjustable bias like you can in an APD. For a PIN diode, at the wavelengths you are talking of, you basically get around 0.5 Amps/Watt from the diode. APDs are not that expensive, especially the small ones you will need for this. But I still can't really see a solution - I was just clutching at straws. Dave ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Photodiodes for high frequency OPLL
On Sat, 30 Mar 2013 20:45:43 + David Kirkby wrote: > Fulll thesis here > http://www.medphys.ucl.ac.uk/research/borl/docs/dkirkby.pdf > > I have seen systems where one sinusoidally modulates the voltage of a > photomultipler tube. You could do the same with an APD. Then it acts a > a mixer. Essentially > > 1) Modulate laser at 100 MHz > 2) Modlulate the APD bias voltage at 100.01 MHz > 3) Detect light from laser on an APD. > 4) Output of the APD is a sine wave at 10 kHz. Thanks! I had a short look at your thesis and i think the idea is not bad. I would need to calculate/simulate what that actually does. > > There has been a similar idea around, using a third laser that > > is pulsed with the desired offset frequency. > > I was wondering if it could be done in more than one stage. A bit like > a superhetrodyne receiver. Probably. But as steep filters for optics are kind of hard to come by, i think a super heterodyne design isn't realy going to work. But probably using an APD with gain modulation at 1GHz or so, i could down modulate the signal to something that is easier to handle (ie something similar as a direct conversion software defined radios). I wonder if this would work with normal PIN photodiodes as well, as their price is much lower than APDs. Attila Kinali -- The people on 4chan are like brilliant psychologists who also happen to be insane and gross. -- unknown ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Photodiodes for high frequency OPLL
Moin, On Sun, 31 Mar 2013 12:28:59 +1300 Bruce Griffiths wrote: > With a suitable low noise tunable LO (laser) the frequency spectrum > beyond the photodiode electrical bandwidth can be explored. I don't exactly get how the laser spectrum (line width?) can be exploited to go beyond the photodiode bandwidth? Could you explain that a little bit? Attila Kinali -- The people on 4chan are like brilliant psychologists who also happen to be insane and gross. -- unknown ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Photodiodes for high frequency OPLL
On Sat, 30 Mar 2013 21:40:47 + li...@lazygranch.com wrote: > The circuit is something like the instrumentation amplifier. > The description starts on page 207 with a schematic on page 208. > I can scan it later, but the circuit is easy to describe. Think of two > op amps in the classic current multiplication (I to V) circuit, that is > positive input to ground and a resistor from output to negative input. > Now place the diode between the two negative inputs. The current flow > will cause the outputs of the op amp to move differentially, which can > then be made single ended with an op amp circuit. But the thing to keep > in mind is that the voltage potential across the photodiode has been kept > to zero, so the capacitance doesn't matter. But it is only held to zero > as long as the amplifier has loop gain, that is create the virtual ground, > hence you need a high GBP for the capacitance to be neutralized. And here comes the problem: At 7GHz the amplifier will be build from discrete components. And i'm not sure that i can acheive high enough gain to cancel the capacitance. But then, the differential approach in itself might be benefitial. > Since the bootstrap needs to "sample" the virtual ground, it itself can't > steal any current from that point, so it usually employs a JFET. I might be mistaken, but i think 1GHz is about the maximum one can get out of modern JFETs? At least the discrete ones. > Linear Technology app notes use the bootstrap often. They use a common > low noise JFET from NXP. Noise from the bootstrap adds right to the diode, > so the bootstrap components need to be low noise. Yes, i've read a couple of Appnotes, and at least one from Linear describing something of that kind. > The fully differential > circuit doesn't have the bootstrap noise source, but it has two amplifiers > on the front end, hence two uncorrelated noise sources. I wonder, if i build a difference amplifier by hand and a seperate bias circuit, can get away with less noise? The noise from the bias circuit should should cancel out in the difference amplifier. Or am i missing something? > When you read the photodiode literature, bandwidth is stated into an > impedance, so I think they just treat the capacitance as the limiting > factor. Maybe that is real life, or maybe it is oversimplified. At that > point this is a solid state physics problem and not a circuit design issue. > (I'd have to crack a book on the physics.) That's one of my issues: I have not found much usuefull literature on photodiodes. Most deal with detecting on-off signals with very low frequency (a couple of kHz at most). There are some good papers from the telecom industry dealing with signal detection at high frequencies, but they always use an custom build IC as amplifier and bias stage, which limits their applicability to my case. Attila Kinali -- The people on 4chan are like brilliant psychologists who also happen to be insane and gross. -- unknown ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Photodiodes for high frequency OPLL
OK, so if you just need to detect the mixer difference, the band limiting of the photodiode is a feature. ;-) -Original Message- From: Bruce Griffiths Date: Sun, 31 Mar 2013 12:28:59 To: ; Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Photodiodes for high frequency OPLL Yes, the beat (difference) frequency of the 2 lasers has to lie within the photodiode electrical passband. With a suitable low noise tunable LO (laser) the frequency spectrum beyond the photodiode electrical bandwidth can be explored. Bruce li...@lazygranch.com wrote: > If I can rephrase that it it, the diode needs to see the difference signal of > the mixer? > -Original Message- > From: Bruce Griffiths > Sender: time-nuts-boun...@febo.com > Date: Sun, 31 Mar 2013 11:43:48 > To: Discussion of precise time and frequency measurement > Reply-To: Discussion of precise time and frequency measurement > > Subject: Re: [time-nuts] Photodiodes for high frequency OPLL > > The detectors don't have to be fast enough to keep up with optical > carrier frequency as long as the incident optical power has a component > at a much lower frequency. > > Bruce > > ed breya wrote: > >> Ooops - never mind. I wrote before my memory was updated. My >> experience in E-O stuff was years ago using AM at relatively low >> frequency, and nowhere near the lasers and microwave/gigabit/sec stuff >> - I didn't think the detectors were fast enough to actually keep up >> with the optical carrier frequency. I was also picturing >> wavelength/spatial separation with interference in order to allow >> relatively slow detectors to see it, or mixing in nonlinear optical >> materials. >> >> Ed >> >> Bruce Griffiths wrote: >> >> A photodiode is in fact a nonlinear device for optical fields as it is >> essentially a linear optical power detector. >> The output is proportional to the incident optical power not the field >> amplitude. >> Photomixers are routinely used in wide range of diverse application such >> as translating the frequency fluctuations of the (Mie) scattered light >> due to Brownian motion of the colloidal particle sizes to baseband. The >> size of the scattering particles can be inferred from the shape of the >> resultant frequency spectrum. >> >> An interferometer of itself (without a detector) is a linear device that >> merely superimposes optical fields and will of itself produce no >> difference frequency output. >> >> Bruce >> >> ed breya wrote: >> >>> I don't think that you can effectively directly mix two laser >>> wavelengths in a semiconductor light detector and get a useable IF - >>> it's hard enough just to get the tens of GHz modulation signals out >>> above the noise floor, let alone a tiny difference signal between >>> hundreds of THz. You need an optical interference or nonlinear device >>> up front to do the "mixing" and get the wavelength discrimination, >>> while the optical detector(s) serve as the first IF O-E transducer. >>> >>> My knowledge of this stuff isn't up to date - maybe nowadays there are >>> detector devices and methods that take care of this directly, but I >>> don't think so. >>> >>> >> >> >> ___ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> >> > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Photodiodes for high frequency OPLL
On 30 March 2013 19:50, Attila Kinali wrote: > On Sat, 30 Mar 2013 18:43:03 + > David Kirkby wrote: > >> I would contact Hammamatsu Photonics >> >> http://www.hamamatsu.com > This might be a good idea. Thanks! >> I played tricks during my Ph.D. of gain-modulating an APD with a step >> recovery diode. > You mean pulsing the bias voltage at about 7GHz and see whether > i can get a something out of that? I did not really have anything in mind specifically. I was just wondering if there was anything could do modulating the gain of a detector so forming a non-linear detector. I pulsed the voltage on an APD to buid a cross correlator. By doing that I was able to get better temporal resolution than the basic APD. Quick summary here: http://www.medphys.ucl.ac.uk/research/borl/research/phd_projects/davek_phd.htm Fulll thesis here http://www.medphys.ucl.ac.uk/research/borl/docs/dkirkby.pdf I have seen systems where one sinusoidally modulates the voltage of a photomultipler tube. You could do the same with an APD. Then it acts a a mixer. Essentially 1) Modulate laser at 100 MHz 2) Modlulate the APD bias voltage at 100.01 MHz 3) Detect light from laser on an APD. 4) Output of the APD is a sine wave at 10 kHz. > There has been a similar idea around, using a third laser that > is pulsed with the desired offset frequency. I was wondering if it could be done in more than one stage. A bit like a superhetrodyne receiver. I've had quite a few beers tonight (OK, I am ed) so my mind is not thinking too straight. >> Have you considered using a photomultiplier tube? I think there are >> some fast PMTs around, though perhaps not fast enough. 20 years I used >> to know what was state of the art in this area, but not any more. > > Not really. I am mostly looking at stuff i can easily get my hands on. > If possible without using ebay (other should be able to build the > system as well). PMTs are available new. Hamamatsu has almost 100 different types. http://www.hamamatsu.com/eu/en/product/category/3100/3003/index.html so there is no need to trawl ebay. Using PMTs you can easily get sub ns temporal response. Dave ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Photodiodes for high frequency OPLL
Yes, the beat (difference) frequency of the 2 lasers has to lie within the photodiode electrical passband. With a suitable low noise tunable LO (laser) the frequency spectrum beyond the photodiode electrical bandwidth can be explored. Bruce li...@lazygranch.com wrote: If I can rephrase that it it, the diode needs to see the difference signal of the mixer? -Original Message- From: Bruce Griffiths Sender: time-nuts-boun...@febo.com Date: Sun, 31 Mar 2013 11:43:48 To: Discussion of precise time and frequency measurement Reply-To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Photodiodes for high frequency OPLL The detectors don't have to be fast enough to keep up with optical carrier frequency as long as the incident optical power has a component at a much lower frequency. Bruce ed breya wrote: Ooops - never mind. I wrote before my memory was updated. My experience in E-O stuff was years ago using AM at relatively low frequency, and nowhere near the lasers and microwave/gigabit/sec stuff - I didn't think the detectors were fast enough to actually keep up with the optical carrier frequency. I was also picturing wavelength/spatial separation with interference in order to allow relatively slow detectors to see it, or mixing in nonlinear optical materials. Ed Bruce Griffiths wrote: A photodiode is in fact a nonlinear device for optical fields as it is essentially a linear optical power detector. The output is proportional to the incident optical power not the field amplitude. Photomixers are routinely used in wide range of diverse application such as translating the frequency fluctuations of the (Mie) scattered light due to Brownian motion of the colloidal particle sizes to baseband. The size of the scattering particles can be inferred from the shape of the resultant frequency spectrum. An interferometer of itself (without a detector) is a linear device that merely superimposes optical fields and will of itself produce no difference frequency output. Bruce ed breya wrote: I don't think that you can effectively directly mix two laser wavelengths in a semiconductor light detector and get a useable IF - it's hard enough just to get the tens of GHz modulation signals out above the noise floor, let alone a tiny difference signal between hundreds of THz. You need an optical interference or nonlinear device up front to do the "mixing" and get the wavelength discrimination, while the optical detector(s) serve as the first IF O-E transducer. My knowledge of this stuff isn't up to date - maybe nowadays there are detector devices and methods that take care of this directly, but I don't think so. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Photodiodes for high frequency OPLL
If I can rephrase that it it, the diode needs to see the difference signal of the mixer? -Original Message- From: Bruce Griffiths Sender: time-nuts-boun...@febo.com Date: Sun, 31 Mar 2013 11:43:48 To: Discussion of precise time and frequency measurement Reply-To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Photodiodes for high frequency OPLL The detectors don't have to be fast enough to keep up with optical carrier frequency as long as the incident optical power has a component at a much lower frequency. Bruce ed breya wrote: > Ooops - never mind. I wrote before my memory was updated. My > experience in E-O stuff was years ago using AM at relatively low > frequency, and nowhere near the lasers and microwave/gigabit/sec stuff > - I didn't think the detectors were fast enough to actually keep up > with the optical carrier frequency. I was also picturing > wavelength/spatial separation with interference in order to allow > relatively slow detectors to see it, or mixing in nonlinear optical > materials. > > Ed > > Bruce Griffiths wrote: > > A photodiode is in fact a nonlinear device for optical fields as it is > essentially a linear optical power detector. > The output is proportional to the incident optical power not the field > amplitude. > Photomixers are routinely used in wide range of diverse application such > as translating the frequency fluctuations of the (Mie) scattered light > due to Brownian motion of the colloidal particle sizes to baseband. The > size of the scattering particles can be inferred from the shape of the > resultant frequency spectrum. > > An interferometer of itself (without a detector) is a linear device that > merely superimposes optical fields and will of itself produce no > difference frequency output. > > Bruce > > ed breya wrote: > > I don't think that you can effectively directly mix two laser > > wavelengths in a semiconductor light detector and get a useable IF - > > it's hard enough just to get the tens of GHz modulation signals out > > above the noise floor, let alone a tiny difference signal between > > hundreds of THz. You need an optical interference or nonlinear device > > up front to do the "mixing" and get the wavelength discrimination, > > while the optical detector(s) serve as the first IF O-E transducer. > > > > My knowledge of this stuff isn't up to date - maybe nowadays there are > > detector devices and methods that take care of this directly, but I > > don't think so. > > > > > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Photodiodes for high frequency OPLL
The detectors don't have to be fast enough to keep up with optical carrier frequency as long as the incident optical power has a component at a much lower frequency. Bruce ed breya wrote: Ooops - never mind. I wrote before my memory was updated. My experience in E-O stuff was years ago using AM at relatively low frequency, and nowhere near the lasers and microwave/gigabit/sec stuff - I didn't think the detectors were fast enough to actually keep up with the optical carrier frequency. I was also picturing wavelength/spatial separation with interference in order to allow relatively slow detectors to see it, or mixing in nonlinear optical materials. Ed Bruce Griffiths wrote: A photodiode is in fact a nonlinear device for optical fields as it is essentially a linear optical power detector. The output is proportional to the incident optical power not the field amplitude. Photomixers are routinely used in wide range of diverse application such as translating the frequency fluctuations of the (Mie) scattered light due to Brownian motion of the colloidal particle sizes to baseband. The size of the scattering particles can be inferred from the shape of the resultant frequency spectrum. An interferometer of itself (without a detector) is a linear device that merely superimposes optical fields and will of itself produce no difference frequency output. Bruce ed breya wrote: > I don't think that you can effectively directly mix two laser > wavelengths in a semiconductor light detector and get a useable IF - > it's hard enough just to get the tens of GHz modulation signals out > above the noise floor, let alone a tiny difference signal between > hundreds of THz. You need an optical interference or nonlinear device > up front to do the "mixing" and get the wavelength discrimination, > while the optical detector(s) serve as the first IF O-E transducer. > > My knowledge of this stuff isn't up to date - maybe nowadays there are > detector devices and methods that take care of this directly, but I > don't think so. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Photodiodes for high frequency OPLL
The circuit I've seen is: |--||--- +Vb---o--|<> amp |--||-o- Vb gnd--| The diode is reverse biased by 50 to several hundred volts. The two caps are DC bypass caps w/ very short leads. The output is a 50 Ohm coax to a broadband amp w/ 50 Ohm input. In the limit, the amp is put right at the detector and has near-zero input Z. Best, -John = > On Sat, 30 Mar 2013 10:52:54 -0700 (PDT) > "J. Forster" wrote: > >> My understanding is that you want to operate photodiodes with high >> reverse >> bias for the best frequency response. The bias widens the space charge >> layer, thereby reducing the capacitance of the device. The high electric >> fields in the SCL region also sweeps the hole-electron pairs, produced >> by >> photon injection, out faster, hence improving the response as well. Such >> devices are best operated with very low capacity wiring into a virtual >> ground. > > Could you elaborate on this circuit a little bit? > Some terms i could google for or pointers to books/papers to read? > > >> Of course, there are limits as, at some point, the device will >> avalanche. >> When that ocurrs, the device will have gain akin to a photomultiplier. >> >> Some devices are actually designed to operate in this mode, but, since >> the >> thing is so near to unstable requires careful control of temperature and >> oher parameters. > > Yes, the avalanche photodiodes are meant for this operation. > Yes, there are kind of sensitive. But i think that's managable. > > Attila Kinali > > -- > The people on 4chan are like brilliant psychologists > who also happen to be insane and gross. > -- unknown > > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Photodiodes for high frequency OPLL
Ooops - never mind. I wrote before my memory was updated. My experience in E-O stuff was years ago using AM at relatively low frequency, and nowhere near the lasers and microwave/gigabit/sec stuff - I didn't think the detectors were fast enough to actually keep up with the optical carrier frequency. I was also picturing wavelength/spatial separation with interference in order to allow relatively slow detectors to see it, or mixing in nonlinear optical materials. Ed Bruce Griffiths wrote: A photodiode is in fact a nonlinear device for optical fields as it is essentially a linear optical power detector. The output is proportional to the incident optical power not the field amplitude. Photomixers are routinely used in wide range of diverse application such as translating the frequency fluctuations of the (Mie) scattered light due to Brownian motion of the colloidal particle sizes to baseband. The size of the scattering particles can be inferred from the shape of the resultant frequency spectrum. An interferometer of itself (without a detector) is a linear device that merely superimposes optical fields and will of itself produce no difference frequency output. Bruce ed breya wrote: > I don't think that you can effectively directly mix two laser > wavelengths in a semiconductor light detector and get a useable IF - > it's hard enough just to get the tens of GHz modulation signals out > above the noise floor, let alone a tiny difference signal between > hundreds of THz. You need an optical interference or nonlinear device > up front to do the "mixing" and get the wavelength discrimination, > while the optical detector(s) serve as the first IF O-E transducer. > > My knowledge of this stuff isn't up to date - maybe nowadays there are > detector devices and methods that take care of this directly, but I > don't think so. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Photodiodes for high frequency OPLL
The circuit is something like the instrumentation amplifier. The description starts on page 207 with a schematic on page 208. I can scan it later, but the circuit is easy to describe. Think of two op amps in the classic current multiplication (I to V) circuit, that is positive input to ground and a resistor from output to negative input. Now place the diode between the two negative inputs. The current flow will cause the outputs of the op amp to move differentially, which can then be made single ended with an op amp circuit. But the thing to keep in mind is that the voltage potential across the photodiode has been kept to zero, so the capacitance doesn't matter. But it is only held to zero as long as the amplifier has loop gain, that is create the virtual ground, hence you need a high GBP for the capacitance to be neutralized. Now I haven't seen this published, but it seems to me if you wanted a negative bias across the diode, you could just use a transformer. I ran into a patent on transformer coupled photodiode circuitry. It was for high speed flash detection. (Amazing was common sense obvious design technique can be patented.) The bootstrap technique basically takes the virtual ground signal of the current multiplier circuit and replicates the AC portion of the virtual ground on the other side of the photodiode, keeping the AC signal across the diode at zero volts, but letting the current flow into the circuit to be multiplied by the op amp&resistor. Since the bootstrap needs to "sample" the virtual ground, it itself can't steal any current from that point, so it usually employs a JFET. These amplifier circuits usually go down to DC, so they will also have response to ambient light, which could eat into the dynamic range of the circuit. Linear Technology app notes use the bootstrap often. They use a common low noise JFET from NXP. Noise from the bootstrap adds right to the diode, so the bootstrap components need to be low noise. The fully differential circuit doesn't have the bootstrap noise source, but it has two amplifiers on the front end, hence two uncorrelated noise sources. Going back to the fully differential circuit, you could bias the diode by placing the positive inputs of the I to V circuits at different potentials, then reject the DC components at the double ended to single ended converter by capacitive coupling. You would probably want to meditate on start up issues if the DC bias is large, that is use clamping diodes on the double ended to single ended converter if it looks like something will be stressed on start up. When you read the photodiode literature, bandwidth is stated into an impedance, so I think they just treat the capacitance as the limiting factor. Maybe that is real life, or maybe it is oversimplified. At that point this is a solid state physics problem and not a circuit design issue. (I'd have to crack a book on the physics.) --Original Message-- From: Attila Kinali To: li...@lazygranch.com To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Photodiodes for high frequency OPLL Sent: Mar 30, 2013 12:03 PM On Sat, 30 Mar 2013 17:29:45 + li...@lazygranch.com wrote: > You lose me at damping per decade? Is damping the right word? > Do you mean high frequency rolloff? Er.. yes. Frequency rolloff... Sorry, my native language got the better of me. > Most texts on photodiodes go into bootstrapping them to reduce the > effect of capacitance. But if you design fully differential amplifier > circuits, they have the same effect as bootstrapping. Jerald Graeme's > "Photodiode Amplifiers" goes into this. I'm not a fan of Gain technology > as a company, but Graeme's book are good texts. Thanks! I just ordered this book. Although i will have to build a discrete amplifier for the first stage until i can mix the signal down to something that can be handled easier. > The bootstrapping circuits use simpler buffers to keep the voltage > potential across the diode low, while the fully differential circuits > depend on gain bandwidth product to do the same. Well, as i currently lean torwards using an avalanche photodiode, which needs an operating voltage in the range of 100V, keeping the potential accross the diode low is not really an issue :-) How do the fully differential circuits get to keep the potential low? As far as i can tell, from the circuits i've seen so far, the differential circuits just use the single ended signal from the diode take the difference to a bias voltage. Attila Kinali -- The people on 4chan are like brilliant psychologists who also happen to be insane and gross. -- unknown ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Photodiodes for high frequency OPLL
A photodiode is in fact a nonlinear device for optical fields as it is essentially a linear optical power detector. The output is proportional to the incident optical power not the field amplitude. Photomixers are routinely used in wide range of diverse application such as translating the frequency fluctuations of the (Mie) scattered light due to Brownian motion of the colloidal particle sizes to baseband. The size of the scattering particles can be inferred from the shape of the resultant frequency spectrum. An interferometer of itself (without a detector) is a linear device that merely superimposes optical fields and will of itself produce no difference frequency output. Bruce ed breya wrote: I don't think that you can effectively directly mix two laser wavelengths in a semiconductor light detector and get a useable IF - it's hard enough just to get the tens of GHz modulation signals out above the noise floor, let alone a tiny difference signal between hundreds of THz. You need an optical interference or nonlinear device up front to do the "mixing" and get the wavelength discrimination, while the optical detector(s) serve as the first IF O-E transducer. My knowledge of this stuff isn't up to date - maybe nowadays there are detector devices and methods that take care of this directly, but I don't think so. Most really high speed diodes are optimized for the 1550 nm region where EDFAs work, but maybe they have usable response at other ranges. It depends on your particular application and wavelength. I think detectors are usually specified over the entire IR region, so datasheets may tell enough. Here's link to some good info, but not current state of the art: http://e-collection.library.ethz.ch/eserv/eth:28429/eth-28429-02.pdf There are various methods that use lower frequency modulation techniques so that regular detectors can be used directly. If you study up on related patents, you may find some ideas and leads to appropriate actual devices. Ed ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Photodiodes for high frequency OPLL
On Sat, 30 Mar 2013 12:45:52 -0700 (PDT) Robert LaJeunesse wrote: > Maybe I'm jaded a bit, but in this town the sub-10GHz optical stuff is > considered kinda slow. The guys down the street, Picometrix, have been doing > 40+GHz optical receivers for over 15 years. They claim "1.5G to 100G and from > 400nm to 1650nm" so probably they can help. http://www.picometrix.com/ I stumbled over picometrix, but did not get much from their webside, beside that they are claiming to acheive GHz frequencies with PIN photodiodes. But nothing specific. I will contact them and see what they say. > As > background info they are a spinoff of the University of Michigan Center for > Ultrafast Optical Science. http://www.engin.umich.edu/research/cuos/ Interesting. Thanks! Attila Kinali -- The people on 4chan are like brilliant psychologists who also happen to be insane and gross. -- unknown ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Photodiodes for high frequency OPLL
On Sat, 30 Mar 2013 18:43:03 + David Kirkby wrote: > I would contact Hammamatsu Photonics > > http://www.hamamatsu.com > > and see if they can help. They might havae something in development, > that is not on the web site. If you are in a uni, they might be > especially helpful - they paid my salary for a couple of years as a > post-doc. This might be a good idea. Thanks! > I played tricks during my Ph.D. of gain-modulating an APD with a step > recovery diode. I was wondering if there is anything one could do to > gain modulate one at 7 GHz, but I can't think how one could achieve > anything useful by changing the gain, but it might be worth thinking > about. I'm just trying to "think out of the box" - I can't actually > see how it would help. You mean pulsing the bias voltage at about 7GHz and see whether i can get a something out of that? There has been a similar idea around, using a third laser that is pulsed with the desired offset frequency. Using this and the non-linear intensity response of the photodiode one can get a low frequency correlation signal out of the system. A Japanese group did something like this to acheive offset frequencies of 160GHz[1] and later of 1THz[2]. In [3] Aljunid describes how to build such a correlator for fs pulses using a simple LED. (yes, i came across some really weird stuff when i started digging into this) > Have you considered using a photomultiplier tube? I think there are > some fast PMTs around, though perhaps not fast enough. 20 years I used > to know what was state of the art in this area, but not any more. Not really. I am mostly looking at stuff i can easily get my hands on. If possible without using ebay (other should be able to build the system as well). Attila Kinali [1] "External Synchronization of 160-GHz Optical Beat Signal by Optical Phase-Locked Loop Technique" by Shigehiro et al, 2006 http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=4012083 [2] "Development of an Optical Phase-Locked Loop for 1-THz Optical Beat Signal Generation" by Shigehiro et al, 2008 http://www.furukawa.co.jp/review/fr033/fr33_02.pdf [3] "Optical Autocorrelation using Non-Linearity in a Simple Photodiode" by Aljunid, 2007 http://qolah.org/thesis/thesis-syed.pdf -- The people on 4chan are like brilliant psychologists who also happen to be insane and gross. -- unknown ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Photodiodes for high frequency OPLL
Maybe I'm jaded a bit, but in this town the sub-10GHz optical stuff is considered kinda slow. The guys down the street, Picometrix, have been doing 40+GHz optical receivers for over 15 years. They claim "1.5G to 100G and from 400nm to 1650nm" so probably they can help. http://www.picometrix.com/ As background info they are a spinoff of the University of Michigan Center for Ultrafast Optical Science. http://www.engin.umich.edu/research/cuos/ Bob L. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Photodiodes for high frequency OPLL
On Sat, 30 Mar 2013 10:52:54 -0700 (PDT) "J. Forster" wrote: > My understanding is that you want to operate photodiodes with high reverse > bias for the best frequency response. The bias widens the space charge > layer, thereby reducing the capacitance of the device. The high electric > fields in the SCL region also sweeps the hole-electron pairs, produced by > photon injection, out faster, hence improving the response as well. Such > devices are best operated with very low capacity wiring into a virtual > ground. Could you elaborate on this circuit a little bit? Some terms i could google for or pointers to books/papers to read? > Of course, there are limits as, at some point, the device will avalanche. > When that ocurrs, the device will have gain akin to a photomultiplier. > > Some devices are actually designed to operate in this mode, but, since the > thing is so near to unstable requires careful control of temperature and > oher parameters. Yes, the avalanche photodiodes are meant for this operation. Yes, there are kind of sensitive. But i think that's managable. Attila Kinali -- The people on 4chan are like brilliant psychologists who also happen to be insane and gross. -- unknown ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Photodiodes for high frequency OPLL
On 30 March 2013 11:48, Attila Kinali wrote: > Moin, > > I'm currently reading up some stuff on optical PLLs and am stuck with some > details i cannot find any data on. > > The goal is to make two lasers locked with about 7GHz of offset to eachother. > > So far, i figured out that PIN photodiodes can go up to several 100MHz > transition frequency and avalanche photodiodes are available up to 2GHz. I would contact Hammamatsu Photonics http://www.hamamatsu.com and see if they can help. They might havae something in development, that is not on the web site. If you are in a uni, they might be especially helpful - they paid my salary for a couple of years as a post-doc. I played tricks during my Ph.D. of gain-modulating an APD with a step recovery diode. I was wondering if there is anything one could do to gain modulate one at 7 GHz, but I can't think how one could achieve anything useful by changing the gain, but it might be worth thinking about. I'm just trying to "think out of the box" - I can't actually see how it would help. Have you considered using a photomultiplier tube? I think there are some fast PMTs around, though perhaps not fast enough. 20 years I used to know what was state of the art in this area, but not any more. Dave ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Photodiodes for high frequency OPLL
On Sat, 30 Mar 2013 13:46:51 -0400 "jmfranke" wrote: > I used UDT PIN10 photodiodes to observe the mode spacings in HeNe lasers. > The typical mode spacings were around 600 MHz. This sounds interesting. According to the datasheet i've found, the PIN10D has a response time of 25ns, which would suggest a maximum frequency around 40MHz. How does your circuit look like? How much signal do you get out of the photodiode? Attila Kinali -- The people on 4chan are like brilliant psychologists who also happen to be insane and gross. -- unknown ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Photodiodes for high frequency OPLL
On Sat, 30 Mar 2013 17:29:45 + li...@lazygranch.com wrote: > You lose me at damping per decade? Is damping the right word? > Do you mean high frequency rolloff? Er.. yes. Frequency rolloff... Sorry, my native language got the better of me. > Most texts on photodiodes go into bootstrapping them to reduce the > effect of capacitance. But if you design fully differential amplifier > circuits, they have the same effect as bootstrapping. Jerald Graeme's > "Photodiode Amplifiers" goes into this. I'm not a fan of Gain technology > as a company, but Graeme's book are good texts. Thanks! I just ordered this book. Although i will have to build a discrete amplifier for the first stage until i can mix the signal down to something that can be handled easier. > The bootstrapping circuits use simpler buffers to keep the voltage > potential across the diode low, while the fully differential circuits > depend on gain bandwidth product to do the same. Well, as i currently lean torwards using an avalanche photodiode, which needs an operating voltage in the range of 100V, keeping the potential accross the diode low is not really an issue :-) How do the fully differential circuits get to keep the potential low? As far as i can tell, from the circuits i've seen so far, the differential circuits just use the single ended signal from the diode take the difference to a bias voltage. Attila Kinali -- The people on 4chan are like brilliant psychologists who also happen to be insane and gross. -- unknown ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Photodiodes for high frequency OPLL
On Fri, 29 Mar 2013 17:20:35 -0700 ed breya wrote: > I don't think that you can effectively directly mix two laser > wavelengths in a semiconductor light detector and get a useable IF - > it's hard enough just to get the tens of GHz modulation signals out > above the noise floor, let alone a tiny difference signal between > hundreds of THz. Well, i'd like to stay at 7GHz. That should be doable. At least i have read at least a dozen papers who claim to have done that. Some even from the 80s. > My knowledge of this stuff isn't up to date - maybe nowadays there > are detector devices and methods that take care of this directly, but > I don't think so. According to some papers i've read, just pointing two lasers at a photodiode will do that. Most of those around 800nm do offsets of a couple 10MHz to a few 100MHz at most. The ones with the larger offsets are usually in the 1-1.5um region and talk about applications for long haul highspeed communication. > Most really high speed diodes are optimized for the 1550 nm region > where EDFAs work, but maybe they have usable response at other > ranges. It depends on your particular application and wavelength. I > think detectors are usually specified over the entire IR region, so > datasheets may tell enough. Wavelenght is 780-800nm which is outside of the detection range of those communcation photodiodes. > > Here's link to some good info, but not current state of the art: > > http://e-collection.library.ethz.ch/eserv/eth:28429/eth-28429-02.pdf Thanks. I have read this already. I thought about trying to contact the author, and ask him a few questions about this project. > There are various methods that use lower frequency modulation > techniques so that regular detectors can be used directly. If you > study up on related patents, you may find some ideas and leads to > appropriate actual devices. I have not come accross any that seemed simpler. Can you give me some pointers? Attila inali -- The people on 4chan are like brilliant psychologists who also happen to be insane and gross. -- unknown ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Photodiodes for high frequency OPLL
On Sat, 30 Mar 2013 10:00:08 -0800 David McQuate wrote: > You'll need a photodiode that can detect photons at your lasers' > wavelength. Yes, of course. > You may be able to use a photodiode at a shorter than its > design wavelength as long as there are not coatings (eg anti-reflection) > that block the wavelength of interest. The 1um photodiodes i had a look at, have all a very steep roll of above below 900nm, leading to 0 detection at 800nm. > You'll need to make sure that > both lasers illuminate the same photodiode area, or you won't get a > signal at the difference frequency. Yes. The current plan is to have the beams aligned on the same path. > The difference frequency power > level is generally pretty low, so operating above the photodiode > bandwidth is difficult. My work was at HP and Agilent, who manufactured > the photodiodes we used. Hmm.. that makes it sound more difficult than i anticipated. Any ballpark numbers i can expect? > The photodiode frequency response is primarily limited by the depletion > region's capacitance. The circuit model is simply a current source > shunted by a capacitor (perhaps with bond wire inductance to the RF > connector) so the RF output current falls with increasing signal > frequency. So, i can expect it to behave like a first order filter and assume about 20dB/decade? Attila Kinali -- The people on 4chan are like brilliant psychologists who also happen to be insane and gross. -- unknown ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Photodiodes for high frequency OPLL
Moin Peter, On Sat, 30 Mar 2013 09:47:26 -0700 Peter Monta wrote: > > The goal is to make two lasers locked with about 7GHz of offset to > > eachother. > > > > So far, i figured out that PIN photodiodes can go up to several 100MHz > > transition frequency and avalanche photodiodes are available up to 2GHz. > > > > If you need photodiode response only near 7 GHz, as seems likely, then > maybe the reactance of the 2 GHz diode can be tuned out with some sort of > matching circuit in the hope of getting usable response near 7 GHz. Better > and simpler to get a diode with flat response all the way from DC to 7 GHz, > though, of course. Yes, but they are not available. At least i have not been able to locate any in the 700-800nm range. > Depending on the application, you might be able to tolerate pretty high > mixer losses, as you mention, but if you do need the best possible SNR, an > I/Q configuration would give slightly lower noise at the cost of two diodes > and amplifiers. What do you exactly mean by I/Q mixing here? Using two beam paths with 90° out of phase onto two photodiodes? If i'm not mistaken this will still lead to 7GHz mixing signal, which i have to get out of the diodes. Attila Kinali -- The people on 4chan are like brilliant psychologists who also happen to be insane and gross. -- unknown ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Photodiodes for high frequency OPLL
You might take a look at these: http://www.ebay.com/itm/360601919160?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649#ht_780wt_911 They have a fiber terminated Avalanche PD and built in HV supply from 5 volts. Cheap at $5 each. Tom - Original Message - From: "J. Forster" To: ; "Discussion of precise time and frequency measurement" Sent: Saturday, March 30, 2013 1:52 PM Subject: Re: [time-nuts] Photodiodes for high frequency OPLL My understanding is that you want to operate photodiodes with high reverse bias for the best frequency response. The bias widens the space charge layer, thereby reducing the capacitance of the device. The high electric fields in the SCL region also sweeps the hole-electron pairs, produced by photon injection, out faster, hence improving the response as well. Such devices are best operated with very low capacity wiring into a virtual ground. Of course, there are limits as, at some point, the device will avalanche. When that ocurrs, the device will have gain akin to a photomultiplier. Some devices are actually designed to operate in this mode, but, since the thing is so near to unstable requires careful control of temperature and oher parameters. -John You lose me at damping per decade? Is damping the right word? Do you mean high frequency rolloff? Most texts on photodiodes go into bootstrapping them to reduce the effect of capacitance. But if you design fully differential amplifier circuits, they have the same effect as bootstrapping. Jerald Graeme's "Photodiode Amplifiers" goes into this. I'm not a fan of Gain technology as a company, but Graeme's book are good texts. The bootstrapping circuits use simpler buffers to keep the voltage potential across the diode low, while the fully differential circuits depend on gain bandwidth product to do the same. -Original Message- From: Attila Kinali Sender: time-nuts-boun...@febo.com Date: Sat, 30 Mar 2013 12:48:01 To: Reply-To: Discussion of precise time and frequency measurement Subject: [time-nuts] Photodiodes for high frequency OPLL Moin, I'm currently reading up some stuff on optical PLLs and am stuck with some details i cannot find any data on. The goal is to make two lasers locked with about 7GHz of offset to eachother. So far, i figured out that PIN photodiodes can go up to several 100MHz transition frequency and avalanche photodiodes are available up to 2GHz. The only photodiodes that go higher are those for the telecom range at 1-1.5um, which is a bit low for my needs. But, i have seen descriptions of such OPLL that work with multi GHz offsets in the 700-800nm range. Now the question is: Do these use special made photodiodes with a very high transition frequency or do they just treat the transition frequency as a 3dB point and amplify the signal after detection? (They do not describe the detection circuit at all, so i guess it must be something readily available) If it's the former, any idea where i could get such photodiodes? If it is the later, how much damping can i assume with PIN or avalanche photodiodes per decade? Thanks in advance! Attila Kinali -- The people on 4chan are like brilliant psychologists who also happen to be insane and gross. -- unknown ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Photodiodes for high frequency OPLL
I forgot to mention if you use the bootstrap technique, you can keep a negative
bias on the photodiode, which improves bandwidth by reducing capacitance. That
is, you drive the AC signal across the diode to zero, but not the DC bias. If
you use the fully differential amplifer, then the bias voltage is zero, hence
more capacitance.
I've looked into transformer coupling for photodiodes as a way to go fully
differential and still apply a bias. A few years ago, the idea would be silly,
but RF applications have created a supply of really high frequency
transformers.
The UDT diodes with the BNC attached are pretty common on ebay. I think the
company was bought out.
-Original Message-
From: "jmfranke"
Sender: time-nuts-boun...@febo.com
Date: Sat, 30 Mar 2013 13:46:51
To:
Reply-To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Photodiodes for high frequency OPLL
I used UDT PIN10 photodiodes to observe the mode spacings in HeNe lasers.
The typical mode spacings were around 600 MHz.
John WA4WDL
--
From: "ed breya"
Sent: Friday, March 29, 2013 8:20 PM
To:
Subject: Re: [time-nuts] Photodiodes for high frequency OPLL
> I don't think that you can effectively directly mix two laser wavelengths
> in a semiconductor light detector and get a useable IF - it's hard enough
> just to get the tens of GHz modulation signals out above the noise floor,
> let alone a tiny difference signal between hundreds of THz. You need an
> optical interference or nonlinear device up front to do the "mixing" and
> get the wavelength discrimination, while the optical detector(s) serve as
> the first IF O-E transducer.
>
> My knowledge of this stuff isn't up to date - maybe nowadays there are
> detector devices and methods that take care of this directly, but I don't
> think so.
>
> Most really high speed diodes are optimized for the 1550 nm region where
> EDFAs work, but maybe they have usable response at other ranges. It
> depends on your particular application and wavelength. I think detectors
> are usually specified over the entire IR region, so datasheets may tell
> enough.
>
> Here's link to some good info, but not current state of the art:
>
> http://e-collection.library.ethz.ch/eserv/eth:28429/eth-28429-02.pdf
>
> There are various methods that use lower frequency modulation techniques
> so that regular detectors can be used directly. If you study up on related
> patents, you may find some ideas and leads to appropriate actual devices.
>
> Ed
>
> ___
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>
___
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To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
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___
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and follow the instructions there.
Re: [time-nuts] Photodiodes for high frequency OPLL
My understanding is that you want to operate photodiodes with high reverse bias for the best frequency response. The bias widens the space charge layer, thereby reducing the capacitance of the device. The high electric fields in the SCL region also sweeps the hole-electron pairs, produced by photon injection, out faster, hence improving the response as well. Such devices are best operated with very low capacity wiring into a virtual ground. Of course, there are limits as, at some point, the device will avalanche. When that ocurrs, the device will have gain akin to a photomultiplier. Some devices are actually designed to operate in this mode, but, since the thing is so near to unstable requires careful control of temperature and oher parameters. -John > You lose me at damping per decade? Is damping the right word? Do you mean > high frequency rolloff? > > Most texts on photodiodes go into bootstrapping them to reduce the effect > of capacitance. But if you design fully differential amplifier circuits, > they have the same effect as bootstrapping. Jerald Graeme's "Photodiode > Amplifiers" goes into this. I'm not a fan of Gain technology as a company, > but Graeme's book are good texts. > > The bootstrapping circuits use simpler buffers to keep the voltage > potential across the diode low, while the fully differential circuits > depend on gain bandwidth product to do the same. > > -Original Message- > From: Attila Kinali > Sender: time-nuts-boun...@febo.com > Date: Sat, 30 Mar 2013 12:48:01 > To: > Reply-To: Discussion of precise time and frequency measurement > > Subject: [time-nuts] Photodiodes for high frequency OPLL > > Moin, > > I'm currently reading up some stuff on optical PLLs and am stuck with some > details i cannot find any data on. > > The goal is to make two lasers locked with about 7GHz of offset to > eachother. > > So far, i figured out that PIN photodiodes can go up to several 100MHz > transition frequency and avalanche photodiodes are available up to 2GHz. > The only photodiodes that go higher are those for the telecom range > at 1-1.5um, which is a bit low for my needs. > > But, i have seen descriptions of such OPLL that work with multi GHz > offsets in the 700-800nm range. > > Now the question is: Do these use special made photodiodes with a very > high transition frequency or do they just treat the transition frequency > as a 3dB point and amplify the signal after detection? > (They do not describe the detection circuit at all, so i guess it must > be something readily available) > > If it's the former, any idea where i could get such photodiodes? > > If it is the later, how much damping can i assume with PIN or avalanche > photodiodes per decade? > > > Thanks in advance! > > Attila Kinali > > > -- > The people on 4chan are like brilliant psychologists > who also happen to be insane and gross. > -- unknown > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Photodiodes for high frequency OPLL
I used UDT PIN10 photodiodes to observe the mode spacings in HeNe lasers. The typical mode spacings were around 600 MHz. John WA4WDL -- From: "ed breya" Sent: Friday, March 29, 2013 8:20 PM To: Subject: Re: [time-nuts] Photodiodes for high frequency OPLL I don't think that you can effectively directly mix two laser wavelengths in a semiconductor light detector and get a useable IF - it's hard enough just to get the tens of GHz modulation signals out above the noise floor, let alone a tiny difference signal between hundreds of THz. You need an optical interference or nonlinear device up front to do the "mixing" and get the wavelength discrimination, while the optical detector(s) serve as the first IF O-E transducer. My knowledge of this stuff isn't up to date - maybe nowadays there are detector devices and methods that take care of this directly, but I don't think so. Most really high speed diodes are optimized for the 1550 nm region where EDFAs work, but maybe they have usable response at other ranges. It depends on your particular application and wavelength. I think detectors are usually specified over the entire IR region, so datasheets may tell enough. Here's link to some good info, but not current state of the art: http://e-collection.library.ethz.ch/eserv/eth:28429/eth-28429-02.pdf There are various methods that use lower frequency modulation techniques so that regular detectors can be used directly. If you study up on related patents, you may find some ideas and leads to appropriate actual devices. Ed ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Photodiodes for high frequency OPLL
You lose me at damping per decade? Is damping the right word? Do you mean high frequency rolloff? Most texts on photodiodes go into bootstrapping them to reduce the effect of capacitance. But if you design fully differential amplifier circuits, they have the same effect as bootstrapping. Jerald Graeme's "Photodiode Amplifiers" goes into this. I'm not a fan of Gain technology as a company, but Graeme's book are good texts. The bootstrapping circuits use simpler buffers to keep the voltage potential across the diode low, while the fully differential circuits depend on gain bandwidth product to do the same. -Original Message- From: Attila Kinali Sender: time-nuts-boun...@febo.com Date: Sat, 30 Mar 2013 12:48:01 To: Reply-To: Discussion of precise time and frequency measurement Subject: [time-nuts] Photodiodes for high frequency OPLL Moin, I'm currently reading up some stuff on optical PLLs and am stuck with some details i cannot find any data on. The goal is to make two lasers locked with about 7GHz of offset to eachother. So far, i figured out that PIN photodiodes can go up to several 100MHz transition frequency and avalanche photodiodes are available up to 2GHz. The only photodiodes that go higher are those for the telecom range at 1-1.5um, which is a bit low for my needs. But, i have seen descriptions of such OPLL that work with multi GHz offsets in the 700-800nm range. Now the question is: Do these use special made photodiodes with a very high transition frequency or do they just treat the transition frequency as a 3dB point and amplify the signal after detection? (They do not describe the detection circuit at all, so i guess it must be something readily available) If it's the former, any idea where i could get such photodiodes? If it is the later, how much damping can i assume with PIN or avalanche photodiodes per decade? Thanks in advance! Attila Kinali -- The people on 4chan are like brilliant psychologists who also happen to be insane and gross. -- unknown ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Photodiodes for high frequency OPLL
I don't think that you can effectively directly mix two laser wavelengths in a semiconductor light detector and get a useable IF - it's hard enough just to get the tens of GHz modulation signals out above the noise floor, let alone a tiny difference signal between hundreds of THz. You need an optical interference or nonlinear device up front to do the "mixing" and get the wavelength discrimination, while the optical detector(s) serve as the first IF O-E transducer. My knowledge of this stuff isn't up to date - maybe nowadays there are detector devices and methods that take care of this directly, but I don't think so. Most really high speed diodes are optimized for the 1550 nm region where EDFAs work, but maybe they have usable response at other ranges. It depends on your particular application and wavelength. I think detectors are usually specified over the entire IR region, so datasheets may tell enough. Here's link to some good info, but not current state of the art: http://e-collection.library.ethz.ch/eserv/eth:28429/eth-28429-02.pdf There are various methods that use lower frequency modulation techniques so that regular detectors can be used directly. If you study up on related patents, you may find some ideas and leads to appropriate actual devices. Ed ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Photodiodes for high frequency OPLL
You'll need a photodiode that can detect photons at your lasers' wavelength. You may be able to use a photodiode at a shorter than its design wavelength as long as there are not coatings (eg anti-reflection) that block the wavelength of interest. You'll need to make sure that both lasers illuminate the same photodiode area, or you won't get a signal at the difference frequency. The difference frequency power level is generally pretty low, so operating above the photodiode bandwidth is difficult. My work was at HP and Agilent, who manufactured the photodiodes we used. The photodiode frequency response is primarily limited by the depletion region's capacitance. The circuit model is simply a current source shunted by a capacitor (perhaps with bond wire inductance to the RF connector) so the RF output current falls with increasing signal frequency. I don't see much possibility of improvement thru matching--though using an amplifier with very low input impedance might help. Dave On 3/30/2013 3:48 AM, Attila Kinali wrote: Moin, I'm currently reading up some stuff on optical PLLs and am stuck with some details i cannot find any data on. The goal is to make two lasers locked with about 7GHz of offset to eachother. So far, i figured out that PIN photodiodes can go up to several 100MHz transition frequency and avalanche photodiodes are available up to 2GHz. The only photodiodes that go higher are those for the telecom range at 1-1.5um, which is a bit low for my needs. But, i have seen descriptions of such OPLL that work with multi GHz offsets in the 700-800nm range. Now the question is: Do these use special made photodiodes with a very high transition frequency or do they just treat the transition frequency as a 3dB point and amplify the signal after detection? (They do not describe the detection circuit at all, so i guess it must be something readily available) If it's the former, any idea where i could get such photodiodes? If it is the later, how much damping can i assume with PIN or avalanche photodiodes per decade? Thanks in advance! Attila Kinali -- Clear Stream Technologies ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Photodiodes for high frequency OPLL
Hi Attila, > The goal is to make two lasers locked with about 7GHz of offset to > eachother. > > So far, i figured out that PIN photodiodes can go up to several 100MHz > transition frequency and avalanche photodiodes are available up to 2GHz. > If you need photodiode response only near 7 GHz, as seems likely, then maybe the reactance of the 2 GHz diode can be tuned out with some sort of matching circuit in the hope of getting usable response near 7 GHz. Better and simpler to get a diode with flat response all the way from DC to 7 GHz, though, of course. Depending on the application, you might be able to tolerate pretty high mixer losses, as you mention, but if you do need the best possible SNR, an I/Q configuration would give slightly lower noise at the cost of two diodes and amplifiers. Cheers, Peter ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
