Low‐Stress Silicon Nitride Platform for Mid‐Infrared Broadband and Monolithically Integrated Microphotonics

Implementation of mid-infrared (mid-IR) chip-scale microphotonic circuits is critical to advancing the science for applications such as (i) ultra-fast telecommunications that require wider bandwidth and (ii) integrated biochemical sensors which can fi nger-print using infrared absorption signatures. Though substantial progress has been made in the development of light sources and detectors, a monolithic mid-IR Si-CMOS-compatible platform remains a challenge. Here we experimentally demonstrate a sophisticated mid-IR microphotonics platform adopting engineered Si-rich and low-stress silicon nitride (SiN x ) thin fi lms where an extensive infrared transparency up to λ = 8.5 μ m is achieved. Furthermore, because of the designed low-stress property, the SiN x deposition is able to reach a thickness > 2 μ m that signifi cantly reduces mid-IR waveguide loss to less than 0.2 dB/cm. We show directional couplers functioning over a broad infrared spectrum, thus enabling monolithic mid-IR multiplexing schemes for integrated linear and nonlinear photonics leading to sophisticated label-free sensing.

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