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 <[email protected]> Date: Sun, 31 Mar 2013 12:28:59 To: <[email protected]>; Discussion of precise time and frequency measurement<[email protected]> 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 [email protected] wrote: > If I can rephrase that it it, the diode needs to see the difference signal of > the mixer? > -----Original Message----- > From: Bruce Griffiths<[email protected]> > Sender: [email protected] > Date: Sun, 31 Mar 2013 11:43:48 > To: Discussion of precise time and frequency measurement<[email protected]> > Reply-To: Discussion of precise time and frequency measurement > <[email protected]> > 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 -- [email protected] >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> >> > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
