Reducing Optical Losses in GaN Waveguides – Toward an Electro-Optic Phase Modulator

In recent years, gallium nitride (GaN) has been investigated as a potential material for various integrated photonic devices. A key component of integrated photonic devices is a voltage-controlled phase modulator in an optical waveguide (WG) design. To date, the main obstacles in the realization of such a device are significant optical losses that are related to various mechanisms. In this research, the main factors for optical losses in a GaN phase modulator are experimentally studied. The suggested design is based on a reverse-biased p–n junction ridge WG scheme. The losses are determined mainly using the Fabry–Perot method at a wavelength of 1064 nm, which is important for high-optical-power applications. The contribution of the ridge waveguide wall roughness losses, the p-doped layer absorption, and the metallic p-contacts is evaluated. Based on these results, an optimized structure of an electro-optical GaN phase modulator is proposed. The modulator voltage response is calculated while taking optical polarization effects into account.