Synthesis of optical directional coupler modulators with linear response

The variable coupling directional coupler modulator is of interest for analog RF/microwave links because it can be synthesized to give linear electrical to optical conversion. The synthesis methods are still relatively undeveloped, however. This paper introduces an improvement to the preferred synthesis technique, the iterative Newton's method, which allows a closer match to the desired modulator response. A variable coupling directional coupler modulator synthesized with this improved method is then introduced, which has a response substantially more linear than previously reported.