High-Index-Contrast AlGaAs Waveguide Scattering Loss Reduction via Oxidation Smoothing of Sidewall Roughness

As technology continues to advance, there is a clear drive toward smaller, faster devices with more functionality. When it comes to lightwave technologies, this has created the need for photonic integrated circuit (PICs) which integrate a large number of optical components into continually decreasing spaces. This has brought about the need for high index contrast (HIC) devices which allow for greater optical confinement and bending radii several orders of magnitude smaller than conventional technology. Traditionally, the drawback of such HIC devices is their greater susceptibility to scattering losses from etch-induced sidewall roughness (s) and the greater index step (dn), losses which scale with at least s2 and dn2.

To combat these higher losses, a novel non-selective O2-enhanced oxidation smoothing technique has been used to significantly reduce the loss of passive AlGaAs ridge waveguide (RWG) structures. Using the Fabry-Perot loss measurement technique, this work shows that this non-selective oxidation smoothing technique can reduce the propagation loss of a 1 cm HIC RWG by almost 3 orders or magnitude when compared to waveguides clad by a SiO2 dielectric deposited via PEVCD. Through optimized processing to reduce the initial sidewall roughness before oxidation, further loss reductions should be achievable for HIC structures, as well as possible loss reduction in more conventional low-index-contrast structures commonly used in many photonic devices