Optical Heterodyne Method for Amplitude and Phase Response Measurements for Ultrawideband Electrooptic Modulators

We present an optical heterodyne method for measuring amplitude and phase responses of electrooptic modulators over an ultrawide frequency range. The microwave input signal for the modulator under test (MUT) is produced by heterodyning the outputs of two lasers. The output of one of these two lasers is modulated by a subcarrier to produce dual tones separated by twice the subcarrier frequency. The output of the MUT is optically filtered to extract the components carrying the amplitude and phase information. Experimental results of measurements made up to 50GHz are presented