Wafer-scale silicon photonic switches beyond die size limit

Fast optical switches have been proposed as a promising alternative to enable continual scaling of data centers with increasing size and data rates. Silicon photonics is a compelling platform for large-scale integrated photonic switches, leveraging advanced manufacturing foundries for electronic integrated circuits. In the past decade, the port counts of silicon photonic switches have increased steadily to 128×128. Further scaling of the switch is constrained by the maximum reticle size (2–3 cm) of lithography tools. Here, we propose to use wafer-scale integration to overcome the die size limit. As a proof of concept demonstration, we fabricated a 240×240 switch by lithographically stitching a 3×3 array of identical 80×80 switch blocks across reticle boundaries. Stitching loss is substantially reduced (0.004 dB) by tapering the waveguide width to 10 μm. The fabricated switch on a 4 cm×4 cm chip exhibits a maximum on-chip loss of 9.8 dB, an ON/OFF ratio of 70 dB, and switching times of less than 400 ns. To our knowledge, this is the largest integrated photonic switch ever reported. The loss-to-port count ratio (0.04 dB/port) is also the lowest.