[time-nuts] Photodiodes for high frequency OPLL

[J. Forster]

I think that you should be able to take the signal right out of the
backbiased diode and run it straight into a microwave mixer w/ a fixed 7
GHz LO and frequency discrimitate the IF output from the mixer to generate
a control signal for your LASER.

In theory, if your LASERS were very, very, very good, you might be able to
achieve phase lock, but I'd not hold my breath. A discriminator can give
you frequency lock.

YMMV,

-John

=================

> On Mon, 1 Apr 2013 14:24:58 +0100
> Wolfgang <timenuts at triplespark.net> wrote:
>
>> On Monday 01 April 2013, Attila Kinali wrote:
>> >> [APD...]
>> >
>> > I think the gain modulated approach to downconvert the signal should
>> work.
>> >
>> Anyway, each of these down-mixing approaches needs to resolve the
>> mirror frequency problem. I.e. if you modulate your receiver with
>> 7.1 GHz (or use an EOM to do that optically) and detect at 100 MHz,
>> you do not know whether the input signal has an offset of 7.2 GHz
>> or 7.0 GHz.
>> So you might be locking on the wrong one.
>
> If i'm not mistaken, this shouldn't be a problem
> I'm not demodulating the laser, but using a PLL to fix the difference
> frequency. Being on the wrong side would invert the sign on the loop
> gain, thus the mirror freuquency would be an unstable point.
>
> 			Attila Kinali
>
> --
> The people on 4chan are like brilliant psychologists
> who also happen to be insane and gross.
> 		-- unknown
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