Thermal Characteristics of a Double Intra-Cavity Contact VCSEL for Cryogenic Optical Links

Abstract

Cryogenic computing systems, including quantum computers, cryo-CMOS and superconducting processors, necessitate efficient optical data links capable of operation at temperatures as low as 4 K. Vertical-cavity surface-emitting lasers optimized for cryogenic conditions (cryo-VCSELs) present a promising high-bandwidth, efficient, and scalable technology for such optical interconnections. This study focuses on a comprehensive characterization of intra-cavity contact cryo-VCSELs, investigating laser behavior over an extensive temperature range from 6 K to 200 K. Accurate design of VCSEL structure for operation at low temperatures requires precise knowledge of cavity temperature at varying bias currents, to account for the shifts occurring in the resonance mode wavelength and gain spectra. To this end, the lasing wavelength shifts corresponding to different junction temperatures across multiple bias current levels were investigated. Additionally, a thermal analysis employing finite element simulation was conducted to accurately estimate actual cavity temperatures, ensuring informed detuning decisions. Furthermore, we demonstrate that double IC contact design significantly reduces series resistance and thermal load to cryostat compared to conventional conducting distributed Bragg reflector (DBR) configurations.