Double‐slot subwavelength grating waveguide for on‐chip carbon dioxide sensing.

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]