Ultra Low-Loss Ion-Exchange Waveguides in Optimized Alkali Glass for Co-Packaged Optics

Glass provides high dimensional stability and flatness, enabling high-throughput electronic assembly with high precision optical alignment for co-packaged optics (CPO) applications. Optical waveguides can be integrated in the glass core material by thermal silver ion-exchange (IOX) process at temperatures around 350°C for fiber to chip connectivity. The waveguides must be stable over a lifetime of five years at an elevated temperature of 85°C without performance degradation which could impact the integrity of the optical signal. An alkali glass and a SiO2 barrier layer are demonstrated to meet the elevated temperature requirements for CPO applications and to overcome reliability risks of alkali migration into attached components. With SiO2layer thickness values <200nm, evanescent coupling between IOX and attached Si3N4 waveguides of the photonic integrated circuit (PIC) can be achieved with losses <0.5 dB. Record low loss IOX waveguides were fabricated with propagation loss of only 0.034 dB/cm.