Thermal Characteristics of Mirror-based Optical Redistribution for Co-packaged Optics

Because traffic toward and inside datacenters is increasing, the power consumption of electrical wiring in ethernet switches for datacenter should be addressed. Co-packaged optics (CPO) is a promising solution, where optical components are integrated into the same package substrate as electrical elements. We have proposed one of the CPO modules, where micro-mirror- based optical redistribution is adopted for low-loss and broadband optical coupling. CPO is required to operate at high temperatures; however, this redistribution uses materials with different coefficients of thermal expansion; thus, there is concern about its operation. In this study, the thermo-optical characteristics in the C-band were analyzed by the finite element method for thermal deformation and physical optical propagation analysis. The coupling efficiency of more than 85% was obtained at 1550 nm in the specified temperature range of 15-85°C, and the difference in the average coupling loss between 20°C and 85°C was 0.49 dB in the calculation. The temperature-dependent transmittance was experimentally demonstrated using fabricated optical redistribution, and the average loss difference in C-band was 0.80 dB at 25°C, 55°C, and 85°C.