A very wide-band frequency response measurement system using optical heterodyne detection

A very-wide band frequency response measurement system for optical devices has been established using the optical heterodyne detection method utilizing two distributed feedback-laser diodes (DFB-LDs). By controlling the laser diode (LD) temperature, the beat frequency is swept from DC to beyond several tens of gigahertz and the measurable bandwidth can be extended to that frequency without any additional calibration. In this system, the spectral linewidth of each LD is stabilized by the two-stage optical isolator and the lightwaves are mixed with the same polarization by a polarization-maintaining optical coupler. The optical frequency fluctuation of the LD is detected by the change of the transmitted optical power through Fabry-Perot etalon and the frequency is controlled by the negative feedback to the LD temperature. Included are a comparison of measurement methods, features of the developed measurement system, and the measurement results.<
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