High-Speed Modeling of Ultracompact Electrooptic Modulators

The technology for compact thin-film lithium niobate electrooptic modulators has made significant advances recently. With achieving high levels of maturity for such platforms, a model is now required in order to accurately design the devices and reliably predict their performance limits. In this paper, a general transmission-line model is developed for predicting the frequency-dependent response of the compact modulators. The main radio frequency (RF) parameters of the modulators, such as characteristic impedance, effective index, and attenuation constant are calculated as a function of the coplanar waveguide dimensions, and validated by using numerical simulations. The accuracy of the model in predicting the 3-dB modulation bandwidth of the devices is verified by comparison with experimental results. Finally, guidelines for device design with significant improvement in the attainable modulation bandwidth are also presented by optimization of RF and optical parameters, predicting > 100 GHz modulation bandwidth. The presented model is not limited to emerging thin-film lithium niobate devices, and is applicable to any type of ultracompact electrooptic modulator.