Electrooptic cutoff modulator using diffused channel waveguide bends

Abstract

Electrooptic intensity modulators are important components for fiber-optic communication and high-speed signal processing. The on/off extinction ratio, drive voltage, and insertion loss are important parameters that determine the performance of the modulators. Recently, an electrooptic cutoff modulator using a Ti-indiffused LiNbO3 channel waveguide with asymmetric strip electrodes was demonstrated with an extinction ratio of >56 dB.1 When a voltage is applied, the asymmetric configuration prevents most of the radiated light from being transferred back to the guide, thus greatly improving the on/off extinction ratio. The drive voltage of such a device, however, is quite high since the gap between the electrodes is considerably wider than the channel width. We propose an electrooptic cutoff modulator using low-loss-diffused channel waveguide bends. The proposed device shows an asymmetric effective index profile by which electrooptic modulation can be enhanced. Analysis based on the beam propagation method has shown that this device has a high extinction ratio with a low drive voltage. Design considerations are presented.