[time-nuts] ?==?utf-8?q? a newbie question: where can I purchase 794.7nm VCSEL for building CPT rubidium clock?

Henk Peek henkp at nikhef.nl
Fri Jun 15 08:52:41 EDT 2018


Cheap (CW) lasers such as CD and short distance 850 and 1300nm telecommunication laser have an optical spectrum 
of a few nm width. This optical spectrum width is filed width multiple optical frequencies. 
Distributed feedback-lasers generate a single optical frequency. They much more expensive.
The most distributed-feedback lasers have peltier temperature control to set the optical frequency. 
The laser output is proportional with the laser current.   This laser current modulation is called direct modulation.  
The simplicity of direct modulation has always offered most cost-effective transmitters compared to external 
modulation techniques using continuous-wave (CW) laser diodes followed by electro-optic (EO) modulators, 
or integrated external-modulated lasers (EML) with electro-absorption (EA) modulators. Direct modulation system performance, however, has been limited by the intrinsic chirp (FM) of directly modulated lasers (DMLs), and 
induced spectrum broadening.

Henk

On Friday, June 15, 2018 10:47 CEST, Dana Whitlow <k8yumdoober at gmail.com> wrote: 
 
> I don't know of any particular reason why a DVD-player laser should be
> faster,
> since neither CD nor DVD players need to deliberately modulate the lasers
> anyway.  At least, that's the first blush answer.
> 
> However, these diode lasers are generally noisy, apparently due to the
> inevitable presence of optical reflections back into the diodes.  I once
> read that deliberately FM'ing the laser by applying a high frequency RF
> tone along with the DC bias current could be helpful in mitigating the
> problem.  But this was in connection with the *analog* Laser Disk video
> recording format.  I don't know if the laser noise was ever much of a
> problem
> with reading the digital formats of CDs and DVDs.  If not, then surely the
> makers of diodes for these mass market applications would not be investing
> effort in making the lasers fast.
> 
> On additional factor is that CD players and DVD players use different light
> wavelengths: ~780 nm for CDs, ~650 nm for DVDs.  It might be that the
> difference in semiconductor composition between the two types makes
> a significant difference in the response speed.  However, I doubt that this
> would would be relevant for present purposes, unless Rb also has some
> *useful* transitions in the 650 nm regime.
> 
> Dana
> 
> 
> On Thu, Jun 14, 2018 at 11:25 PM, Hal Murray <hmurray at megapathdsl.net>
> wrote:
> 
> >
> > k8yumdoober at gmail.com said:
> > > I've been told that CD player type diodes can be successfully modulated
> > up to
> > > about 600 MHz, but that going much further is either difficult or perhaps
> > > impossible.
> >
> > Are DVD lasers faster?
> >
> >
> > --
> > These are my opinions.  I hate spam.
> >
> >
> >
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