Thermal Scaling Analysis of Large Hybrid Laser Arrays for Co-Packaged Optics

Abstract

Optical transceivers for data center applications require multi-wavelength light sources, which can either be integrated or external from the transceiver die. Scaling up the number of communication channels implies the need for large laser arrays. Since the energy efficiency of semiconductor lasers is very sensitive to temperature, it is imperative to employ a thermal-aware design and minimize self-heating and thermal crosstalk. In this paper, a thermal scaling analysis is performed on hybrid, flip-chip integrated InP-on-Si lasers. A finite element thermal model of a single gain section laser is validated with experimental measurement of the laser thermal resistance and extrapolated to accomodate multi-section operation. The impact of adding a top-side heat sink as well as increasing laser length and width are investigated. The detailed 3D simulation results are used to build a compact, coupled thermo-optic model of a large array of multiple lasers, considering thermal crosstalk. Finally, this model is applied to a test case with 8 WDM channels and 8 ports. Depending on the configuration (integrated vs. external) and ambient temperature, different optimal designs arise based on both energy efficiency and module footprint. The presented modelling framework is generic; it can be applied to different types of lasers and systems.