VCSEL Light Coupling to a Waveguide to Interconnect XPUs and HBMs on Interposer Chips

Multimode VCSELs coupled into waveguides can be a practical path toward realizing commercially viable photonic interposer chips. The experimental coupling of multimode VCSEL light to a non-silicon waveguide fabricated using a CMOS-compatible process is demonstrated. The GaP prism was tested and adopted as a coupling method. Both conventional and cavity-type optical waveguides, fabricated from CMOS-compatible PECVD SiO2, Si3N4, and SiOxNy materials, were evaluated. The average propagation loss transmitted through the cavity-type waveguide was measured as 0.444 dB/cm. A polyimide micro-lens, cavity-type waveguide, and a GaP prism coupler are developed to inject the multimode VCSEL light into the waveguide measuring the net coupling loss of 0.762 dB. The packaged size of VCSEL has an area of 0.4 mm2 and a height of 0.64 mm. MUX/DeMUX was designed on the bottom of the prism. A light source, a modulator, and MUX/DeMUX are all located in the same area of the prism bottom in VCSEL-based interconnections.