Re: optical spectrum analyzer in zero span mode


The photoreceiver circuit on a standard OSA will be relatively slow, i.e it
will only have a small bandwidth. This is desirable in order to make wide
dynamic range measurements.

If you want to measure power- use a power meter, or if just interested in
power let your OSA scan and integrate under the curve.

If you want to measure your modulated waveform then use an appropriate
photoreceiver circuit. You can roll own for <$5 plus the cost of the
photodiode. A basic transimpedance amplifier circuit will easily meet what
looks to be fairly modest requirements, and there are plenty of examples in
IC manufacturers app notes. TI/burr brown in particular have some decent
information.


Thank you for the advices. I just want to add further details and
maybe you can give me some more information.
The instrument is an Agilent 86142B. So it's probably not designed for
pulsed application. Moreover the data*** claims a very large dynamic
range and as Helmut suggests, this might hamper the bandwidth.
I missed to tell you that I want to measure the lifetime of ytterbium
doped glass samples, hence I need to monitor the dynamics of the
collected power at specific wavelength. I then need a monochromator
or a selective filter prior to the photodiode, and cannot use that of
the OSA, since I would fall into the same situation. Am I right? Do
you know about other OSAs that have better performance in zero-span
mode? I can have access to an ANDO (I do not know what type it is) and
an old HP71450B.

Thank you very much
.