Re: [time-nuts] a newbie question: where can I purchase 794.7 nm VCSEL for building CPT rubidium clock?
On 06/11/2018 09:52 AM, Attila Kinali wrote: > On Sat, 9 Jun 2018 23:28:29 +0800 > mimitech mimitech wrote: > >> Just do a little bit research on 1560nm telecom laser transceiver. The >> closest wavelength is 1560.61nm (DWDM channel 21) as defined by ITU. >> Usually telecom laser transceiver module uses DFB (distributed feedback) >> type laser diode instead of VCSEL laser. However, the DFB LD should be >> capable of direct modulation, so there maybe not much difference with VCSEL >> in terms of usage. For the modulation bandwidth, I guess a 2.5Gbps module >> should be OK for 1.71GHz analog modulation. > > A 2.5Gbps module should be good even for 3.4GHz modulation. The 3dB frequency > of should be higher than the baud rate used. Besides, even if the 3dB > frequency > is below 3.4GHz, that does not matter, it just means that your sidebands will > be damped (second order low pass, IIRC), but you don't need that much power > anyways. Considering that the bandwidth of the reference receiver for SDH/SONET is 3/4 of the baudrate, and then using a 4-pole Bessel-Thompson filter, I beg to differ regarding the expected bandwidth. The majority of the modulated energy will be inside those 3/4 and you don't want much more as it causes unnecessary problems. But sure, sidebands will be damped and you can expect 6 dB slope there from the bare diode. This is stuff I can actually measure at home as I come to think of it. >> So, imagine I modulated 1.71GHz microwave signal onto 1560nm laser wave, >> then used a KPT non-linear optical crystal to double the frequency, >> hopefully I could get 780nm laser with +/-3.42GHz sideband spectrum, that >> should be suitable to shine on a Rubidium vapor cell and trigger CPT >> effect. I don't know if I understand this process correctly, many details >> must be missed. > > Using a non-linear element will give you lots of intermodulation products. > Ie, your sidebands will be +/-1.71GHz, +/-3.42GHz, +/-6.84GHz,... > So you will have to be a bit carefull with the laser tuning in order to > get the right harmonics. Consider the roll-off of the diode/modulator. Also, expect to servo the amplitude of the modulation for stabilization. This is separate from the servo of the center of wavelength as well as the width of the modulation. CPT has more of these loops than a traditional rubidium. >> Another question is, after passing through the KPT doubler crystal, whether >> the light remains single mode and linear polarization mode or not? If >> someone could provide any relevant information and suggestion, thanks very >> much. > > If I understood the optical process correctly (disclaimer: I'm not > a physicst and have never worked with optical systems), then the multiple > modes are a problem of the laser source, not of the doubler. As multi-modes > are a problem for high speed communication, I expect telecom lasers to > be quite clean. You will have to ensure that you are not operating it > close to a mode jump, though. The DWDM lasers is quite clean and their temperature-stabilization is what you want to have to start with. However, I don't think any of the ones I have will match the frequency needed, but I may be lucky. Cheers, Magnus ___ 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] a newbie question: where can I purchase 794.7 nm VCSEL for building CPT rubidium clock?
On Sat, 9 Jun 2018 23:28:29 +0800 mimitech mimitech wrote: > Just do a little bit research on 1560nm telecom laser transceiver. The > closest wavelength is 1560.61nm (DWDM channel 21) as defined by ITU. > Usually telecom laser transceiver module uses DFB (distributed feedback) > type laser diode instead of VCSEL laser. However, the DFB LD should be > capable of direct modulation, so there maybe not much difference with VCSEL > in terms of usage. For the modulation bandwidth, I guess a 2.5Gbps module > should be OK for 1.71GHz analog modulation. A 2.5Gbps module should be good even for 3.4GHz modulation. The 3dB frequency of should be higher than the baud rate used. Besides, even if the 3dB frequency is below 3.4GHz, that does not matter, it just means that your sidebands will be damped (second order low pass, IIRC), but you don't need that much power anyways. > So, imagine I modulated 1.71GHz microwave signal onto 1560nm laser wave, > then used a KPT non-linear optical crystal to double the frequency, > hopefully I could get 780nm laser with +/-3.42GHz sideband spectrum, that > should be suitable to shine on a Rubidium vapor cell and trigger CPT > effect. I don't know if I understand this process correctly, many details > must be missed. Using a non-linear element will give you lots of intermodulation products. Ie, your sidebands will be +/-1.71GHz, +/-3.42GHz, +/-6.84GHz,... So you will have to be a bit carefull with the laser tuning in order to get the right harmonics. An alternative approach would be to use an EOM after the doubler to get the sidebands. These have bandwidths in the order of 10-20GHz, so applying 3.42GHz shouldn't be a problem. BTW: a lot of the frequency doubler architectures for high stability lasers use resonant cavities, to increase efficiency and decrease noise. You will either have to tune the free spectral range of the cavity to a divisor of 6.84GHz or use a non-resonant one. > Another question is, after passing through the KPT doubler crystal, whether > the light remains single mode and linear polarization mode or not? If > someone could provide any relevant information and suggestion, thanks very > much. If I understood the optical process correctly (disclaimer: I'm not a physicst and have never worked with optical systems), then the multiple modes are a problem of the laser source, not of the doubler. As multi-modes are a problem for high speed communication, I expect telecom lasers to be quite clean. You will have to ensure that you are not operating it close to a mode jump, though. A side note on the doubler approach: The group at UniNE around Gaetano Mileti and Christoph Affolderbach focuses only on double-resonant Rb standards. That means they do not modulate the laser. As they have gotten the whole standard to the SNR limit, they are now focusing on getting the shifts due to laser (frequency and intensity shift) and cavity (low Q cavity to avoid pulling) down. The current state of affairs is quite nicely documented in their two papers at 8FSM[1,2,3]. Attila Kinali [1] Proceedings of the 8th Symposium on Frequency Standards and Metrology http://conferenceseries.iop.org/conferenceseries/issue/1742-6596/723/1 [2] "High performance vapour-cell frequency standards", Gharavipour, Affolderbach, Kang, Bandi, Buret, Pellaton, Mileti, 2015 http://iopscience.iop.org/1742-6596/723/1/012006/pdf/1742-6596_723_1_012006.pdf [3] "Pulsed Optically Pumped Rb clock", Micalizio, Levi, Godone, Calosso, François, Boudot, Affolderbach, Kang, Gharavipour, Gruet and Mileti, 2015 http://iopscience.iop.org/1742-6596/723/1/012015/pdf/1742-6596_723_1_012015.pdf -- It is upon moral qualities that a society is ultimately founded. All the prosperity and technological sophistication in the world is of no use without that foundation. -- Miss Matheson, The Diamond Age, Neil Stephenson ___ 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] a newbie question: where can I purchase 794.7 nm VCSEL for building CPT rubidium clock?
Just do a little bit research on 1560nm telecom laser transceiver. The closest wavelength is 1560.61nm (DWDM channel 21) as defined by ITU. Usually telecom laser transceiver module uses DFB (distributed feedback) type laser diode instead of VCSEL laser. However, the DFB LD should be capable of direct modulation, so there maybe not much difference with VCSEL in terms of usage. For the modulation bandwidth, I guess a 2.5Gbps module should be OK for 1.71GHz analog modulation. So, imagine I modulated 1.71GHz microwave signal onto 1560nm laser wave, then used a KPT non-linear optical crystal to double the frequency, hopefully I could get 780nm laser with +/-3.42GHz sideband spectrum, that should be suitable to shine on a Rubidium vapor cell and trigger CPT effect. I don't know if I understand this process correctly, many details must be missed. Another question is, after passing through the KPT doubler crystal, whether the light remains single mode and linear polarization mode or not? If someone could provide any relevant information and suggestion, thanks very much. On Date: Thu, 07 Jun 2018 21:18:59 +0200, "Henk Peek" wrote: > > Rb vapor-cell clock demonstration with a frequency-doubled telecom laser > > Applied Optics Vol. 57, Issue 16, pp. 4707-4713 (2018) • https://doi.org/10.1364/AO.57.004707 > > Abstract > > We employ a recently developed laser system, based on a low-noise telecom laser emitting around 1.56 μm, to evaluate its impact on the performance of an Rb vapor-cell clock in a continuous-wave double-resonance scheme. The achieved short-term clock instability below 2.5·10−13·𝜏−1/2 demonstrates, for the first time, the suitability of a frequency-doubled telecom laser for this specific application. We measure and study quantitatively the impact of laser amplitude and frequency noises and of the ac Stark shift, which limit the clock frequency stability on short timescales. We also report on the detailed noise budgets and demonstrate experimentally that, under certain conditions, the short-term stability of the clock operated with the low-noise telecom laser is improved by a factor of three compared to clock operation using the direct 780-nm laser. > > © 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement > > Henk Peek > > On Tuesday, June 5, 2018 11:11 CEST, Attila Kinali wrote: > > > On Mon, 4 Jun 2018 21:31:56 +0800 > > mimitech mimitech wrote: > > > > > I'm planning to build a CPT (coherent-population-trapping) rubidium clock > > > as my next hobby project. The main purpose is to learn the principles > > > behind CPT rubidium clock, and hopefully got similar or better performance > > > than commercial miniature rubidium clock such as FE-5680A. > > > > Building a CPT clock is slightly more involved than you might think > > at first. The laser diode is only one part of it. You will most likely > > be able to improve on the short-term stability of the FE-5680 (which > > is rather poor). But I doubt you will be able to improve much on > > the long term stability, which is where things actually become interesting, > > if you use a naive approach. > > > > Nevertheless, I have not seen many 794/795nm diodes around. The only > > one that I have the datasheet of is the one from Vixar. > > You might want want to consider going for the D2 line instead of the > > D1 line, as 780nm diodes are more commonly available than 795nm. You will > > also need to buy several of those and select the ones that come closest > > to the wavelength at the desired opearating conditions (usuall spread > > is +/-1nm to +/-10nm). Do not assume you can tune more than 0.1nm with > > temperature and current (rule of thumb is that you get about 10GHz > > per °C and mA). If you need more tuning range, you will need to add an > > external cavity (can give you up to 5nm range), which then needs to be > > tuned to the 3.45GHz (ie it's length needs to be approximately 8-9cm). > > > > Alternatively, you can get two S1-0780-XXX from Sacher Laser > > (cost IIRC 2500€ each) and keep them 6.9GHz apart (using an optical PLL). > > If you have enough money to spend, I'd go for two Cateye diode laser CEL's > > from Moglabs (cost AFAIK 5000€ each) > > > > No matter what you choose, you will need some wavelength stabilization > > scheme. You can either do that with the vapor cell itself or use > > an additional cell and do a DVALL or a saturated absorption locking. > > Note that this addtional cell will need to be without buffer gas. > > An external cell will offer better stability and thus lower noise, > > which directly translates into higher stability. > > > > As polarisation scheme, I suggest using σ+/σ- as it seems to be more > > robust than the lin/lin schemes. > > > > Attila Kinali > > -- > > It is upon moral qualities that a society is ultimately founded. All > > the prosperity and technological sophistication in the world is of no > > use without that foundation. > >
Re: [time-nuts] a newbie question: where can I purchase 794.7 nm VCSEL for building CPT rubidium clock?
Thanks, Henk. This is a very interesting paper. The 1560nm VCSEL is indeed very easy to source thanks to widely application in Telecom, but the frequency double and stabilization scheme in the paper is very complex. the purpose of this paper to use 1560nm is because of its higher spectral purity than customized and small-scale manufactured 780/795nm VCSEL, to achieve better atomic clock performance (short-term stability). If I could find some simple frequency multiplier schemes, it is worth considering using a 1560 nm VCSEL. Anyway, I need to do further research on it. Thanks. mimitech. On Thu, 07 Jun 2018 21:18:59 +0200, "Henk Peek" wrote: > > Rb vapor-cell clock demonstration with a frequency-doubled telecom laser > > Applied Optics Vol. 57, Issue 16, pp. 4707-4713 (2018) • https://doi.org/10.1364/AO.57.004707 > > Abstract > > We employ a recently developed laser system, based on a low-noise telecom laser emitting around 1.56 μm, to evaluate its impact on the performance of an Rb vapor-cell clock in a continuous-wave double-resonance scheme. The achieved short-term clock instability below 2.5·10−13·𝜏−1/2 demonstrates, for the first time, the suitability of a frequency-doubled telecom laser for this specific application. We measure and study quantitatively the impact of laser amplitude and frequency noises and of the ac Stark shift, which limit the clock frequency stability on short timescales. We also report on the detailed noise budgets and demonstrate experimentally that, under certain conditions, the short-term stability of the clock operated with the low-noise telecom laser is improved by a factor of three compared to clock operation using the direct 780-nm laser. > > © 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement > > Henk Peek > > On Tuesday, June 5, 2018 11:11 CEST, Attila Kinali wrote: > > > On Mon, 4 Jun 2018 21:31:56 +0800 > > mimitech mimitech wrote: > > > > > I'm planning to build a CPT (coherent-population-trapping) rubidium clock > > > as my next hobby project. The main purpose is to learn the principles > > > behind CPT rubidium clock, and hopefully got similar or better performance > > > than commercial miniature rubidium clock such as FE-5680A. > > > > Building a CPT clock is slightly more involved than you might think > > at first. The laser diode is only one part of it. You will most likely > > be able to improve on the short-term stability of the FE-5680 (which > > is rather poor). But I doubt you will be able to improve much on > > the long term stability, which is where things actually become interesting, > > if you use a naive approach. > > > > Nevertheless, I have not seen many 794/795nm diodes around. The only > > one that I have the datasheet of is the one from Vixar. > > You might want want to consider going for the D2 line instead of the > > D1 line, as 780nm diodes are more commonly available than 795nm. You will > > also need to buy several of those and select the ones that come closest > > to the wavelength at the desired opearating conditions (usuall spread > > is +/-1nm to +/-10nm). Do not assume you can tune more than 0.1nm with > > temperature and current (rule of thumb is that you get about 10GHz > > per °C and mA). If you need more tuning range, you will need to add an > > external cavity (can give you up to 5nm range), which then needs to be > > tuned to the 3.45GHz (ie it's length needs to be approximately 8-9cm). > > > > Alternatively, you can get two S1-0780-XXX from Sacher Laser > > (cost IIRC 2500€ each) and keep them 6.9GHz apart (using an optical PLL). > > If you have enough money to spend, I'd go for two Cateye diode laser CEL's > > from Moglabs (cost AFAIK 5000€ each) > > > > No matter what you choose, you will need some wavelength stabilization > > scheme. You can either do that with the vapor cell itself or use > > an additional cell and do a DVALL or a saturated absorption locking. > > Note that this addtional cell will need to be without buffer gas. > > An external cell will offer better stability and thus lower noise, > > which directly translates into higher stability. > > > > As polarisation scheme, I suggest using σ+/σ- as it seems to be more > > robust than the lin/lin schemes. > > > > Attila Kinali > > -- > > It is upon moral qualities that a society is ultimately founded. All > > the prosperity and technological sophistication in the world is of no > > use without that foundation. > > -- Miss Matheson, The Diamond Age, Neil Stephenson > > ___ > > 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] a newbie question: where can I purchase 794.7 nm VCSEL for building CPT rubidium clock?
On Mon, 4 Jun 2018 21:31:56 +0800 mimitech mimitech wrote: > I'm planning to build a CPT (coherent-population-trapping) rubidium clock > as my next hobby project. The main purpose is to learn the principles > behind CPT rubidium clock, and hopefully got similar or better performance > than commercial miniature rubidium clock such as FE-5680A. Building a CPT clock is slightly more involved than you might think at first. The laser diode is only one part of it. You will most likely be able to improve on the short-term stability of the FE-5680 (which is rather poor). But I doubt you will be able to improve much on the long term stability, which is where things actually become interesting, if you use a naive approach. Nevertheless, I have not seen many 794/795nm diodes around. The only one that I have the datasheet of is the one from Vixar. You might want want to consider going for the D2 line instead of the D1 line, as 780nm diodes are more commonly available than 795nm. You will also need to buy several of those and select the ones that come closest to the wavelength at the desired opearating conditions (usuall spread is +/-1nm to +/-10nm). Do not assume you can tune more than 0.1nm with temperature and current (rule of thumb is that you get about 10GHz per °C and mA). If you need more tuning range, you will need to add an external cavity (can give you up to 5nm range), which then needs to be tuned to the 3.45GHz (ie it's length needs to be approximately 8-9cm). Alternatively, you can get two S1-0780-XXX from Sacher Laser (cost IIRC 2500€ each) and keep them 6.9GHz apart (using an optical PLL). If you have enough money to spend, I'd go for two Cateye diode laser CEL's from Moglabs (cost AFAIK 5000€ each) No matter what you choose, you will need some wavelength stabilization scheme. You can either do that with the vapor cell itself or use an additional cell and do a DVALL or a saturated absorption locking. Note that this addtional cell will need to be without buffer gas. An external cell will offer better stability and thus lower noise, which directly translates into higher stability. As polarisation scheme, I suggest using σ+/σ- as it seems to be more robust than the lin/lin schemes. Attila Kinali -- It is upon moral qualities that a society is ultimately founded. All the prosperity and technological sophistication in the world is of no use without that foundation. -- Miss Matheson, The Diamond Age, Neil Stephenson ___ 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] a newbie question: where can I purchase 794.7 nm VCSEL for building CPT rubidium clock?
Hi, list member I'm planning to build a CPT (coherent-population-trapping) rubidium clock as my next hobby project. The main purpose is to learn the principles behind CPT rubidium clock, and hopefully got similar or better performance than commercial miniature rubidium clock such as FE-5680A. To build this clock, I think for the Rb 87 vapor cell I could use a cell removed from commercial rubidium clock. Another import component is 794.7 nm VCSEL laser diode. Does anyone know some good sources I could buy small quantities (< 5pcs) of this special wavelength VCSEL (perfer a model targeting for CPT rubidium clock applications), and what’s approximate price? if necessary you could send relevant information to my email . Has anyone else already done or is doing similar projects? I'd be very appreciative to know what your thoughts and suggestions for this project. Thanks very much. ___ 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.
