Photonic Switching: How Feeble can you get, when using MOS switching ? - Page 1
Forum section: electronics / general

author: RJSV
author_rank: Super Contributor
timestamp: January 28, 2023, 09:42:04 am
content: Hello there, and Happy New Year everyone!I'm just wondering, how low can a circuit go, when MOS gate isn't getting all that much signal ?Looking at some simple arrangements, such as a fiber optic 'splitter'...(OK that's a decorative optic 'bush' for backyard...).My bench-top optic fiber bunch has many strands, about 90, so any light beams would potentially be diminished quite a bit simply due to lots of division factor, down at small scales of construction.Like, I guesstimate something like 20 mW (laser diode at maybe 1500 nM), but divided down drastically by factor of several hundred.

author: RJSV
author_rank: Super Contributor
timestamp: January 28, 2023, 09:59:26 am
content: - - -:Have done some reading, as it looks like the 'vertical stressed' MOS switches turn at around 0.4 volts gate to drain input. Seems like miniature optical sensing would have severe reduction in signals, something like related to square of device area...So, if you reduce sensor and fiber optic size by half, then sensor to MOS gate voltage is going down to 1/4 or one over square (of size reduction in devices).

author: AVGresponding
author_rank: Super Contributor
timestamp: January 28, 2023, 10:59:46 am
content: You might have to amplify the signal before you can use it to switch a MOSFET.

author: BrianHG
author_rank: Super Contributor
timestamp: January 28, 2023, 04:19:19 pm
content: What are you using to sense the source light?Is the source light modulated?

author: RJSV
author_rank: Super Contributor
timestamp: January 28, 2023, 05:49:05 pm
content: 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.