J. Guy wrote:
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very clever, a device that produces light from a current passing through a filament...BUT ITS PATENTED REMEMBER

I read that the diode laser was modulated.

But the method still requires high frequencies / and or precision period measurement, requiring external processing.
I don't see why it should need external processing. Admittedly the technique is RF design, but since frequency is the system output you have a wonderful o/p signal for further processing, and the signal is divided down into the interesting band.


What about the phase comparison method ? How is the comparison made ?

See my reply to Gil, for when you have a processor in the path. Otherwise a single logic gate can be used to make a phase sensitive detector.

Steve