Wavelength temperature insensitivity of surface-trapped optical modes in microcavities

We address theoretically lateral localization of surface-trapped optical modes in microcavities formed at a surface of a distributed Bragg reflector (DBR). GaAs-GaAlAs materials are considered as a model system. We analyze such modes and demonstrate that thick metal bars mounted on top of the DBR form a lateral cavity strongly localizing in plane the modes which exhibit in the vertical direction an evanescent decay in the air and an oscillatory decay in the DBR. Such TM-polarized modes are strongly confined between the bars, the fraction of the optical energy of the mode located in the air reaching similar to 90%. We show that the wavelength of such modes is nearly temperature-insensitive, the thermal shift can be as small as below 0.005 nm/K, which is an order-of-magnitude smaller than the typical value for vertical cavity surface emitting lasers (VCSELs). TE-polarized modes are observed only if the top layer of the DBR sequence has a thickness different from lambda/4 and a cavity layer is formed at the surface. The surface-trapped modes enable near-field outcoupling to an external waveguide or to an optical fiber placed closed to the DBR surface. In DBR structures incorporating an active medium these modes can be employed for construction of microlasers as well as for resonant semiconductor optical amplifiers (SOAs) having nearly temperature-insensitive lasing/resonance wavelength. In another approach applying a reverse bias to the active medium one can realize resonant intensity modulators. Surface-trapped modes can be employed in all-dielectric DBRs enabling low loss waveguides for silicon photonics. Further applications include using such modes at interfaces between a semiconductor DBR and a dielectric medium having a lower refractive index. (C) 2021 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

Automated summary

This study theoretically analyzes the lateral localization of optical modes in microcavities, focusing on a model system using GaAs-GaAlAs materials. It demonstrates that thick metal bars on top of the DBR can strongly localize the modes laterally, with a high fraction of optical energy located in the air. These modes are nearly temperature-insensitive and can be used in various applications such as microlasers and resonant semiconductor optical amplifiers.