Optical analog to digital converter

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Discussion Overview

The discussion centers around the concept of an optical analog-to-digital (A/D) converter, exploring its design, functionality, and potential applications. Participants delve into the theoretical aspects of how such a device would operate, the materials involved, and the implications of using optical methods for conversion.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant describes a theoretical design for an optical A/D converter that aims for zero conversion time, relying on settling time for detector outputs.
  • Another participant seeks clarification on the function of an optical A/D, questioning the nature of the analog input and its isolation from the light source.
  • There is discussion about the type of analog information being sampled, with suggestions that it could be in the range of 0 to 10 VDC depending on the material being probed.
  • Some participants propose that the optical A/D would use a pulse input to achieve faster digital output compared to traditional A/D converters.
  • Concerns are raised regarding the measurement of input in volts if the device is optical, leading to a clarification that the conversion process is electro-optical.
  • Participants discuss existing A/D converter technologies, including successive approximation and flash conversion, with differing views on their speed and application.
  • One participant suggests that the proposed optical A/D could be faster and cheaper than existing electronic chips, while another expresses skepticism about the feasibility of the design.
  • There is a description of the proposed optical setup involving LEDs and photodetectors integrated into a substrate, with a focus on how light interacts with the materials to produce a digital output.
  • Participants debate the complexity of the proposed design compared to traditional methods, with one participant humorously questioning its simplicity.

Areas of Agreement / Disagreement

The discussion features multiple competing views regarding the feasibility and practicality of the proposed optical A/D converter. Participants express both interest and skepticism, and no consensus is reached on the validity of the design or its advantages over existing technologies.

Contextual Notes

Participants note various assumptions about the materials and methods involved in the optical A/D converter, including the potential differences affecting the index of refraction and the arrangement of photodetectors. There are unresolved questions about the operational specifics and the practicality of the proposed design.

  • #31
by NateTG
By varying the angle, one can vary the constant of proportionality s.t. it should be possible to get each bit individually without doing other comparisons.
My first idea was to use a wedge between the mirrors. But I think that would be to difficult to fabricate.
This particular device is probably not suitable to use as an A/D but it does provide a theoretically simple model.
Do you see any other applications for something like this?
 
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  • #32
by wimms
Then I don't grasp how do you produce binary code by 24 detectors that represents 16 million possible values. At which point does substraction and residue amplification happen? You can't produce binary code by proportioning alone. "Arranged in spiral" doesn't hit the light for me, but I'm curious.
Cut the angle of refraction in half and you get twice as many reflections and so on. The placement along the spiral should be such that the furthest detector will have twice as many reflections passing over it as the next closer one and so on. The inner most on will be off over the whole range of input voltages until all other bits are on. The placement is very critical.
by wimms
How large is enough? There is a need to illuminate detectors in precise pattern, and have no "dead-spots" between readings, as well as no garbage-spots. Thus detectors must be closely spaced, and you have issue with either false concurrent detection or transient where no detection happens. Difraction makes this worse, and it happens quite easily.
Larger than many wavelengths. Very precise pattern. Not close around the spiral but the distance to the center circle may overlap a little. There may be a little light but still be in a zero/off state.
 
  • #33
Originally posted by dlgoff
Yes. The higher the light source frequency the better. Can InGaAs/InAlAs detectors be integrated in an InP substrate?

Maybe some sort of temperature monitoring could be employed to bias the mirror to compensate? Wouldn't want to make it too expensive though.

Have you ever made a rib waveguide laser source, monolithically integrated to a multimode interference splitter? Sounds interesting.

Do you think the this idea is worth pursuing?

Thank you much for the info.

Yes, the alloy ratios to lattice match to InP are well known - 48%In for one, 53%In for the other, but I forget which is which.

Temperature monitoring and compensation is going to be uneconomical. Heat sinking would be the way to go. If heat sinking can't handle it, it probably is a no-go.

I have made a rib waveguide laser monolithically integrated to other devices, integrating one with the splitter mentioned should not be hard. The optical absorption in the material can't be too high, so making the laser with a quantum well, and destroying the well in all other regions would be the way to go. Using regrowth to make a non-absorbing spliter would be better, but getting regrowth to work well is hard.

Is the idea worthwhile? I don't know. Some of the other comments suggest problems. My suggestion would probably have "dead spots". It might do fine for exact resonances, but shut off completely in between - IE, the 1,2 4 and 8 work just fine, but at 2.5 there is no output. This might be alleviated with a broadened source, but that would make the splitter function poorly. You could also make the DBRs "sloppy", but then you'd have to threshold the throughput, and thresholding optical signals can slow things down if you have low optical power. If you're splitting the signal in 24, your power will be low. The only way to know if it is worthwhile is to estimate the numbers and compare best and worst case scenarios to existing electronic devices. That, I will not do. Not unless you pay me $350/hr.

Njorl

Njorl
 
  • #34
Slightly OT:

Njorl - are semiconductor lasers suitable for amplifying existing light signals?
 
  • #35
Njorl,

Thank you for explaining the ups and downs.
It might do fine for exact resonances...
Couldn't it be done with a large enough scale where resonance doesn't come into play? i.e. just reflections and not "standing waves"? Am I missing something here?
The only way to know if it is worthwhile is to estimate the numbers and compare best and worst case scenarios to existing electronic devices. That, I will not do. Not unless you pay me $350/hr.
Wish I could but I'll have to respectfully decline the offer.

Sincerely
 
  • #36
Originally posted by NateTG
Slightly OT:

Njorl - are semiconductor lasers suitable for amplifying existing light signals?

I only have passing experience with it, so I may get things wrong. I think the "Q" of a good semiconductor laser is not a good "Q" for a good amplifier. I know some people were working on the idea, but I don't know if they got it to work. Last I heard, the best course was to just make the most powerful laser you can, and use a modulator (no amplification) to get the signal level you wanted.

Njorl
 
  • #37
Originally posted by dlgoff
Njorl,

Thank you for explaining the ups and downs.

Couldn't it be done with a large enough scale where resonance doesn't come into play? i.e. just reflections and not "standing waves"? Am I missing something here?
Sincerely

I suppose so, I don't know. Maybe I've been working in waveguides so long I shy away from free space. Free space is messy. I worked with a lot of applications where we needed 80 dB of signal to noise, so free space was never any use. I may very well be falling prey to my own prejudices. It happens to us old folks. One of the best things about students is they suggest things that are just "unacceptably silly" but wind up working.

Njorl
 
  • #38
posted by Njorl
...It happens to us old folks. One of the best things about students is they suggest things that are just "unacceptably silly" but wind up working.
Know what you mean. I'm one of those semi-old folks.

Anyway. Thank you and everyone else for their input. Maybe some one will take this idea and do something with it.

regards
 

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