Non-Linear Response Characteristics of Optical Directional Coupler Modulators.

Waveguide electro-optic modulators are of much interest for multi-channel CATV applications because of the advantages they offer in relation to direct modulation of lasers. These include frequency independence of the distortion characteristics, negligible second harmonic distortion if suitably biased, and the ability to increase the output optical power level independent of the modulation depth. The latter provides the possibility of a larger signal-to-noise ratio and makes broadcasting to several receivers a feasibility. Additionally, these modulators exhibit a virtually chirp-free optical spectrum and thereby avoid distortions that might otherwise arise from optical reflections.