heterodyne fiber optic system?

Shigeyuki Otsuki has written:

'Development of a heterodyne harmonic analyzer in the audible frequency range with automatic sweep' -- subject(s): Physics Theses

its a radio! :D

A superheterodyne receiver is a Radio Frequency receiver method that multiplies the received signal frequency with a local oscillator frequency to get frequencies that are the sum and difference of the 2 frequencies. For example, if the received signal is 5MHz and the local oscillator frequency is 4MHz, they are multiplied together. 1MHz and 9MHz frequencies would be gotten. Usually the 1MHz is the Intermediate Frequency (IF). It will be admitted (through a band pass filter) later passed through the required electronic circuits for proper processing. There is also the method of the Variable Tuned Filter.

Het is short for heterosexual, heterogeneous, or even heterodyne.