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Total internal reflection mirrors with ultra-low losses in 3 µm thick SOI waveguides

Total internal reflection (TIR) mirrors represent an ultra-compact and flexible method to turn light in a photonic integrated circuit (PIC). These can also have very broadband and polarisation independent operation. This paper presents results from 90 degree strip waveguide turning mirrors with novel geometry on a 3 μm SOI waveguide platform. The new TIR mirrors have record-low insertion loss of 0.08 dB/mirror. They are compared with previous designs that have demonstrated insertion losses down to 0.15 dB/mirror. The test structures consisted of up to 96 consecutive mirrors and were fabricated in a multi-project wafer run. The multi-moded test devices only propagate light in the fundamental mode. The mirrors can be used in single-mode PICs that combine low losses, small polarisation dependency, wide bandwidth and small footprint.