Optical receiver and modulator frequency response measurement with a Nd:YAG ring laser heterodyn technique

A description is given of how the frequency response of optical receivers can be accurately calibrated by measuring a heterodyne signal generated by mixing two Nd:YAG ring lasers. One laser signal passes through the modulator while the other functions as a local oscillator to convert one of the sidebands of the modulated carrier to a fixed intermediate signal. This heterodyne system offers more than 50 dB of dynamic range. Calibration of both optical phase and amplitude modulators is achieved. The technique presented eliminates the need for a high-speed photoreceiver, has a good signal-to-noise ratio, and makes measurement of phase modulator frequency response possible