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Cable Asylum Interconnects, speaker wire, power cords. Ask the Cable Guys. |
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Cable Asylum Interconnects, speaker wire, power cords. Ask the Cable Guys. |
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In Reply to: I'm with you on this one posted by Dave Kingsland on March 11, 2005 at 12:35:59:
I have never seen or measured these cables -- nor have I seen measurements posted.However, the technology seems to me to be something you would use for long distance transmission, not a short interconnect. As Dave says, you are adding two extra stages of electronics into the system.
I do have a Ph.D. in opto-electronic devices, and I can imagine whipping up a design for such a cable. I'm sure it could do an "okay" job, but I can think of a number of "gotchas" already.
First, both laser and LEDs are nonlinear output vs. input. LEDs tend to drop off a bit with current, and sometimes have a slight turn-on threshold of a few millivolts (usually because of non-ohmic contacts or some non-radiative recombination). Lasers have a turn-on threshold that is not constant with temperature, and their output past threshold is more non-linear than LEDs. This means that they need feedback to operate without severe harmonic distortions.
The feedback on a laser module is often a silicon photodetector measuring light coming out of the back laser facet. This does a pretty good job, but not perfect. The detected light does not always exactly correspond to the light getting coupled to the fiber, as the exact beam shape changes slightly with output intensity.
A solution is to use the feedback from the fiber itself -- by using a splitter. You would want to do mode stripping of the cladding first, to make sure you are getting light just through the fiber core.
The feedback detector could theoretically have nonlinearity, but you can get pretty linear ones these days -- providing you don't use too high an optical signal.
The detector circuit is just done with a high quality reverse-biased photodetector. Running it in photovoltaic mode would be too slow, and likely less linear.
This would be the way to go for long distance signals! In fact, the battery power is definitely the way to go. I always used battery power for my high-sensitivity photodectors. It reduces noise considerably.
However, it would be very easy to get high amounts of harmonic distortion if these cables are not done right. I would be very interested in seeing distortion figures. That would be the proof needed to determine if this was a technology that made sense. If the harmonic distortion is low, then they could have a winner. The rest of the sound quality lies in the electronics at each end.
Neil
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Follow Ups
- Analog optical transmission very hard to do without distortion - audioNeil 12:28:44 03/12/05 (0)
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