[time-nuts] Photodiodes for high frequency OPLL

Attila Kinali attila at kinali.ch
Mon Apr 1 09:43:50 UTC 2013


On Mon, 01 Apr 2013 22:32:11 +1300
Bruce Griffiths <bruce.griffiths at xtra.co.nz> wrote:

> Attila Kinali wrote:
> > On Mon, 01 Apr 2013 09:08:51 +1300
> > Bruce Griffiths<bruce.griffiths at xtra.co.nz>  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



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