Microwave modulation of optical signal by electro-optic effect in GaAs microstrips

A novel experimental scheme for detecting the electrooptic (EO) effect in a GaAs microstrip line is demonstrated. This scheme does not require the use of an analyzing polarizer but utilizes the modulation of the interference pattern generated by the multiple beams reflected from the top and bottom surfaces of the GaAs substrate. It is shown that even if an analyzing polarizer is used in the conventional EO sampling techniques, the interference effect has to be taken into account in order to explain the observed EO signal. For both detection schemes, it is demonstrated experimentally and theoretically that the amplitude of the EO signal varies very rapidly with the GaAs thickness. The absolute calibration in the electrooptic sampling technique for device or MMIC characterization is thus very difficult. In order to avoid the interference effect, laser pulses with a duration shorter than the round-trip time for the optical beam to travel through in the substrate must be used.<>