A "bel", https://en.wikipedia.org/wiki/Decibel is a logarithmic measure of relative amplitude, most commonly used when values vary by many factors of 10. While most people think of it in terms of sound intensity, it is also a description of radio signal strength, antenna gain, and other values.

a "3 decibel" difference is approximately a factor of 2 in power. So, if an optical fiber has an optical loss of "0.15 dB/kilometer", that means that 20 kilometers of fiber has about 20 kilometers x 0.15 dB/kilometer = 3 dB loss, or a factor of 2 in power.

Despite the fact that I had absolutely nothing to do with selecting my name, I can manage a minor gloat by saying that I am one of few people whose name is also the name of an ASCII character: https://en.wikipedia.org/wiki/ASCII

(Jim) Bel(l)

Tab (Hunter)

Del (Webb, or Shannon)

On Sunday, January 5, 2020, 02:06:11 PM PST, \0xDynamite <dreamingforward@gmail.com> wrote:

> But even at about 1550 nanometers, 50 kilometers of fiber has: 50 km x 0.15 dB/km = 7.5 dB of optical loss

Isn't there a better unit than Bells (dBs) for optics, like
transparency or opacity? It seems Bells are directly related to air
pressure....

Mark