Comprehensive design and simulation of a composite reflector for mode control and thermal management of a high-power VCSEL

Abstract

We propose a composite top reflector composed of a distributed Bragg reflector (DBR) and a subwavelength high-contrast grating (HCG) for a high-power 808-nm vertical-cavity surface-emitting laser (VCSEL). The DBR and HCG in the reflector are connected by an indium tin oxide (ITO) surrounding layer, which makes it possible for the reflector to improve current injection uniformity and reduce heat generation while providing high reflectivity. The angle-dependent reflectivity of the composite reflector is optimized to suppress the high-order transverse modes of VCSEL while ensuring sufficient fundamental mode feedback. The number of top DBR periods and the thickness of the ITO surrounding layer are optimized to reduce the loss and provide high out-coupling efficiency. The double resonator coupled by top DBR is designed to provide optimal resonant wavelength stability, longitudinal optical confinement factor, and thermoelectric characteristics. Optical simulation results demonstrate that the well-designed configuration can provide a highest fundamental mode reflectivity of 99.7%, an out-coupling efficiency of 65%, a wavelength stability rate of 0.011 with the thickness of the ITO layer, and a confinement factor of 0.05. The transverse modes with order greater than 2 are effectively suppressed. The result of the thermoelectric model shows that the composite reflector-based VCSEL has low operating temperature and uniform current injection; thermal resistance of 0.87 K/mW is realized. In this context, devices with high emission efficiency and beam quality can be expected.