The Fabry-Perot electrooptic modulator

The Fabry-Perot modulator, consisting of Fabry-Perot etalon plates separated by an electrooptic material such as KDP, is analyzed in detail. Time-dependent perturbation theory is used to describe the coupling of the axial modes by spatial and time varying perturbations in the dielectric constant. The perturbations are produced by the applied microwave modulating field. It is shown that the correct choice of the spatial variation of the microwave modulating field is essential to achieve efficient modulation and the choice is equivalent to matching the phase velocities of the microwaves and the light. Power requirements, heating, and bandwidth are discussed and a comparison is made to the traveling-wave modulator described by Kaminow. Calculations indicate that bandwidths of several hundred megacycles, centered at any microwave frequency, can be obtained with the expenditure of several watts of modulating power.