Stabilizer + Pounder wiring diagram check

tomhepz

Hi all,

I was hoping to confirm the intended inputs+outputs of the Stabilizer+Pounder combination for offset PDH locking as I cannot seem to find any documentation regarding the use of the inputs/outputs? Perhaps my diagram would be a useful addition to the docs if confirmed.

Qs:

We are considering using the Stabilizer+Pounder combination to perform an offset PDH lock, but also wish to get access to the demodulated PDH signal (that I believe travels via the mezanine interconnect) for a feedfoward scheme which may not be possible in this setup. Is this correct?
I also believe in this setup an offset lock requires an extra external oscillator still, unless you use up Ch1 out perhaps?
Is there a status on the compatability of Pounder with the newer fast stabilizer card (Sinara 8462 Fast DSP "Fast Servo")?
Are you able to confirm the wiring diagram below?
As an aside, does anyone have opinionated reccomendations on other PDH hardware, in the past we have just used the toptica FALC module but I am not aware of many alternatives.

Below is the intended schematic of the setup, and below that is what I believe to be the wiring diagram where the OUT is the \omega_{ref}, the IN is the input of the photodiode, the demodulated PDH error signal travels via the mezanine interconnect, and then the output of the stabilizer card is the feedback +/- 10V to the laser.

Cheers,
Tom

sb10q

tomhepz also wish to get access to the demodulated PDH signal (that I believe travels via the mezanine interconnect) for a feedfoward scheme which may not be possible in this setup. Is this correct?

The PDH signal is available on the ADC0 connector of Stabilizer, which acts as an output when the Pounder mezzanine is present.

tomhepz Is there a status on the compatability of Pounder with the newer fast stabilizer card (Sinara 8462 Fast DSP "Fast Servo")?

It has never been done and there is at least a software and gateware problem.

tomhepz Are you able to confirm the wiring diagram below?

Looks good. I'm not familiar with the offset part, but this looks like an interesting trick. How do you tell if the laser is locking on the fundamental or the offset though?

sb10q

tomhepz I also believe in this setup an offset lock requires an extra external oscillator still, unless you use up Ch1 out perhaps?

Maybe you can do something using the phase modulation modes of the AD9959 inside Pounder, though (if it works at all) the maximum offset frequency is likely pretty limited.

tomhepz

sb10q Hi, thanks for your reply! That's very useful information.

You can check if you're locked to the fundemental or the offset when locking by turning the offset frequency tone on/off. When off the offset PDH signal will dissapear and the fundemental will get larger (and vice versa when on).

While locked a wavemeter is typically good enough to differentiate too.

We typically use a cheap RF source (https://windfreaktech.com/product/microwave-signal-generator-synthhd/) to generate the offset tone. It needs to generate tones up to the FSR/2 of the cavity though, typically _GHz, so I imagine the modulation you suggests wouldn't modulate that hard. It also has to apply solely to the EOM.

Regardless of testing pounder with the Fast stabilizer, are you aware of any testing of it's specs? (particularly loop delay) We're locking to a low expansion cavity and trying to get the best lock with digitally controlled servo where the servo loop is fast (typically reserved to analogue loops).

Thanks again!

sb10q

tomhepz You can check if you're locked to the fundemental or the offset when locking by turning the offset frequency tone on/off. When off the offset PDH signal will dissapear and the fundemental will get larger (and vice versa when on).

Well, yes, with the caveat of unlocking the laser.

tomhepz It also has to apply solely to the EOM.

Not an issue - the modulation and demodulation channels are already separated in the DDS so the phase between them can be tuned. GHz optical sidebands out of AD9959+EOM - maybe with some tricks (e.g. deeper phase modulation than is normally applied for PDH), but this is more like a sport at this stage and something you may not want to play around with 🙂

tomhepz Regardless of testing pounder with the Fast stabilizer, are you aware of any testing of it's specs? (particularly loop delay)

It should be the same as Linien.

And I think you probably don't need Pounder with Fast-Servo anyway, you could use a fully digital PDH. The offset could be applied with DSP as well, though again not GHz unless special tricks are employed and turn out to work.