High-efficiency suspended silicon waveguide edge coupler operating at 3.3 um for methane detection

Efficient light coupling to on-chip waveguides remains a key challenge in integrated photonic platforms due to the strong mode mismatch between the external light source and waveguide modes. In this work, a suspended edge coupler composed of a fork-like shape and transition gratings is introduced and experimentally demonstrated at a wavelength of 3.3 μm. This design enables efficient mode conversion between a free-space Gaussian beam and a suspended waveguide. A coupling loss of 1.93 ± 0.09 dB was experimentally achieved, with a simulated coupling loss of 1.05 dB. The results demonstrate that the proposed structure provides an effective and practical solution for low-loss light coupling in suspended mid-infrared platforms.