CCD measurements of guided optical mode attenuation in GaN layers

Abstract

The wide band gap and strong piezoelectric effects make GaN-based materials attractive for visible and ultraviolet optoelectronic applications, especially for optical integration devices. The optical waveguide is a fundamental component of integrated optical devices. The measurement of the propagation loss is essential for waveguide characterization, where the loss is due to absorption and scattering. The conventional methods require the measurement of the absolute optical power, polishing of sample edges, and, sometimes, the sliding of a coupling prism. Therefore, the conventional techniques are not very convenient or controllable. In this paper, a straightforward method has been proposed to characterize the attenuation of guided modes in GaN layer by employing a CCD system. As an optical mode propagates in the waveguide, the light is scattered and a characteristic light track appears on the waveguide surface. It is assumed that the scattered light is proportional to the guided mode intensity. By taking a digital picture of the track for each guided mode, the light intensity variation along the track is obtained. We used this technique to measure the attenuation of guided optical modes in multi-mode GaN layers grown by MOCVD on (0001) sapphire substrates. The results demonstrate that the CCD technique is a fast, convenient and reliable method to characterize attenuation in optical waveguides.