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Re: POS OC48 interfaces using different wave length

  • From: Steve Schaefer
  • Date: Fri Jun 08 13:25:30 2001

On Fri, 8 Jun 2001, Mikael Abrahamsson wrote:

>
> On Fri, 8 Jun 2001, John Fraizer wrote:
>
> > Attenuation has nothing to do with the reason the two cards won't work
> > together.  Think of the cards as color blind.  They can only see ONE
> > color.  They ignore all other colors.
>
> Have you actually tried this? I have personally gotten linkups between
> 1310 and 1550 GBICs. Just as someone said here before, the receivers are
> very wide-band.
>
> > 1550nm and 1310nm are different colors.
>
> Yes, but if your receiver picks up photons in a range from (just guessing)
> 1200 to 1700nm light, it doesn't matter.
>

Receivers convert light into electricity when a photon bumps an electron
through the semiconductor band gap.  There is a sharp cutoff at the low
energy side.  (If the photon energy is less than the band gap energy, it
can't push the electron to the higher energy state.)  The cutoff on the
high energy side is very broad.

Since shorter wavelengths means higher energy photons, the 1310 nm
transmitter will almost certainly work with the 1550 nm receiver.  It is
possible that the 1310 nm receiver might not work with the 1550 nm
transmitter.  This is because the efficiency of the reciever is best near
the band gap of the material.  It is possible to choose the material and
do some other structural things (multiple quantum wells) to the
semiconductor to boost the sensitivity at the desired wavelenth.

The manufacturer may have elected to use a receiver that was optimized for
1300 nm.  In that case, it may have no sensitivity to 1510 nm signal.
But it would still work for 800 nm.

BTW, the attenuators are only important for making sure you don't burn
out a receiver when you test the unsupported configuration.

-steve





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