[time-nuts] a newbie question: where can I purchase 794.7 nm VCSEL for building CPT rubidium clock?
mimitech at gmail.com
Sat Jun 9 11:28:29 EDT 2018
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
On Date: Thu, 07 Jun 2018 21:18:59 +0200, "Henk Peek" <henkp at nikhef.nl>
> Rb vapor-cell clock demonstration with a frequency-doubled telecom laser
> Applied Optics Vol. 57, Issue 16, pp. 4707-4713 (2018) •
> 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
> Henk Peek
> On Tuesday, June 5, 2018 11:11 CEST, Attila Kinali <attila at kinali.ch>
> > On Mon, 4 Jun 2018 21:31:56 +0800
> > mimitech mimitech <mimitech at gmail.com> wrote:
> > > I'm planning to build a CPT (coherent-population-trapping) rubidium
> > > as my next hobby project. The main purpose is to learn the principles
> > > behind CPT rubidium clock, and hopefully got similar or better
> > > 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
> > 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
> > 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
> > If you have enough money to spend, I'd go for two Cateye diode laser
> > 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
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