Compact low-loss 8 × 8 silica optical switch based on large fan-in/fan-out couplers

An optical switch scheme based on large fan-in/fan-out multimode interference (MMI) couplers is proposed to enable compact, low-loss N × N switching with channel uniformity. Specifically, two identical 8 × 8 MMI couplers are connected via equal-path-length waveguides to form an 8 × 8 silica switch. With CMOS-compatible fabrication, the switch demonstrates an insertion loss of 2.7 ± 0.6 dB and a crosstalk of -14.7 ± 4 dB across all switching scenarios at 1550 nm. The 3-dB bandwidth with crosstalk < -10 dB covers the wavelength range 1535 - 1565 nm (~C-band), which exactly coincides with the theoretical expectation. This scalable design breaks the constraints of traditional switches and facilitates high-density photonic integration.