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To address the issues of low ratio of evanescent field (γ) and high reflectivity between waveguide cross‐section and gas for the mid‐infrared waveguide sensors, we propose a chalcogenide (ChG) suspended waveguide with Ge28Sb12Se60 as the core layer and silica (SiO2) as the buffer layer. The SiO2 beneath the waveguide core ridge structure is removed to create suspended structure. The waveguide sensing performance is obtained using a 10% methane (CH4) sample. The fabricated waveguide exhibits a γ of 112%, which is a 10% improvement compared to a free‐space optical sensor with the same optical path length. The good agreement between the theoretical and experimental results of γ confirms the reliability of our theoretical investigation approach. The influences of fabrication error, environmental temperature, and pressure on sensing performances are discussed. This work provides theoretical guidance for designing waveguide structures with large γ, contributing to the further enhancement of on‐chip sensor performance. [ABSTRACT FROM AUTHOR]

A novel double‐slot subwavelength grating with high sensitivity and small size was presented for the detection of carbon dioxide (CO2). Compared with single‐slot structure, the proposed double‐slot structure reduces the influence of slot width on the transmission intensity and thus improves the sensor performance. For enabling selectivity and sensitivity, the gap of the grating is filled with polyhexamethylene biguanide (PHMB). The refractive index of PHMB decreases after the absorption of CO2 molecules, which changes the effective refractive index of the waveguide mode. For getting the highest sensitivity, the proposed sensor was numerically simulated and optimized. The limit of detection for CO2 can be as low as 6.3 parts per million (ppm), which is lower than other reported waveguide CO2 sensors based on PHMB. The proposed sensor is capable of atmospheric CO2 monitoring with an acceptable limit of detection. [ABSTRACT FROM AUTHOR]