Topband: Light fiber question

[Bruce]

>From Tom
"People forget, or don't know, fiber cables require modulators and 
demodulators. The modulators and demodulators are not simple, and have 
horrible dynamic range compared to a simple piece of coax."


>From Bill
"The important part would be that you'd need to run a feedback loop with the laser/LED and a photodiode monitoring the output. The combined system would be your fiber driver. The receiver would be simpler -- just a photodiode and an amplifier. "

"I see your point, since the signal is undergoing a conversion. My thinking was modulator = baseband to some kind of RF or digital signal, i.e. something very different from the original signal in terms of content of the waveform. I wasn't thinking of using a band-limited section of spectrum being converted to an amplitude-modulated light source as a "modulator" in this case.

What I had meant was that the electrical->optical conversion doesn't have to be a particularly fancy system when you're only trying to run about 200kHz of spectrum over the fiber in the 2(ish)MHz range. The basics I mentioned before and some op amps are all that are needed. The op amps will likely be the limiting factor for dynamic range. "


Comment: Improvements are very evident as we look back in time. When I was about 13 years old and interested in radio, I would spend time in the Belfast Library. Radio books were in the basement and most dated into the 1920's, some early 1930's. These books were lost to hurricane flooding years later. I remember a 1920's publication where the author talked about germanium diodes and cat whiskers, He concluded   that better diodes/rectifiers could come from other sources like silicon.   Well silicon did not come for about 30 years, think about the late 1950's but it came with an avalanche. 

Think of the wire recorders in the 1940's to todays improved advanced digital recordings. 

New Your city lost all its phone connections through the subways in hurricane Sandy. Now replaced with light fibers that are not sensitive to salt water, NYC has taken another step up. 

It was not that many years ago when LED's were invented. With further advances in LED's, types of lighting, and better forms of fiber optics, large signal connection efficiency should be possible.

With each improvement we have to somehow look beyond what we now know.

73
Bruce-K1FZ
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