[time-nuts] Photodiodes for high frequency OPLL

Bruce Griffiths bruce.griffiths at xtra.co.nz
Mon Apr 1 06:00:48 EDT 2013


Attila Kinali wrote:
> 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
>    
Back to the original problem:

An AOM could be used to generate a sideband 7GHz above (or below) the 
output of 1 laser which could then be mixed with the output of the other 
laser using a narrow bandwidth photodiode.

How do ensure a suitably wide mode hop free tuning range for the lasers 
to be locked to the first laser?

Bruce


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