BrianHG:
Modulated source sounds more promising, when doing AC gain stages. I'm actually going through some beginner's growing pains, in more specialized aspects of (so-called) nano-photonics, so I'm way behind the usual skill set, in that.
Right now encountering the, (what's it called?), the effects of drastic size scale changes, or rather, the drastic effects of scale changes, where nonlinear 'squares' or roots might cause an impractically low amplitude, compared with moderate small.
That means nano-scale, vs. something like 0.5 mm on your bench. The tiny scale would be implemented on a silicon wafer, but much of this is older, circa 1990's.
Educating myself there, but seems like a scale change also affects mechanical forces being at a different proportional effectiveness, at various scales.
Witness the tiny ANT, carrying and impossibly large stick, or piece of food (relative to ant size). So there's that.
My guess is, might be photodiode detection, but vet little signal, (guess at 4 mV type of small), vs MOSFET switch requiring 0.4 V gate to drain.
Overall, attempt is to piece together some working devices, using mostly light beams, analog and digital formats. Electronics sensing is for taking over at the end of chain, in COMPARATOR mode, as a crude Analog to Digital stage; detecting resulting counts (optical amplitudes), but at only one analog level...that being detection of a low 'count' that crosses a low threshold, for digital 'zero'.
It's a mix and confusing mess, both formats, digital and analog, (but fun). Please also refer to that Optical Bench monster of a thread,...dodgy thread.