Abstract
The performance of conventional gas sensors based on light absorption in the mid-infrared are limited by the high-cost and low efficiency of photon detection at these wavelengths. In this paper, cascaded suspended waveguides are proposed and analyzed for mid-infrared gas sensing with enhanced detection limit. The cascaded structure contains two sections in which the first part is optimized for light absorption and the other one is tailored to satisfy the phase matching condition for third harmonic generation toward near-infrared wavelengths. In this configuration, the input mid-infrared light firstly experiences “fingerprint” frequency absorption in the on-chip gas chamber. Consequently, the residuary light produces third harmonic radiation in the second section. Benefiting from the nonlinear relation between pump and harmonic power, the sensitivity of the sensor is significantly improved. Moreover, the signal is up converted from mid-infrared to near-infrared and thus it can be easily detected by efficient near-infrared detectors. The results show that the detection limit can reach the order of nmol/L and the absorption lengths can be reduced to three times shorter comparing to direct mid-infrared detection. The proposed configuration has great potential for high performance on-chip gas sensing.
Highlights
Detecting the concentration of chemical vapor mixtures is of great demand in many fields such as environmental monitoring [1], resource prospecting [2], and medical diagnoses [3]
The results show that the detection limit can reach the order of nmol/L and the absorption lengths can be reduced to three times shorter comparing to direct mid-infrared detection
Current absorption gas sensors usually operate in the near-infrared (NIR), where photon detection can be performed with high efficiency and resolution (∼fW)
Summary
Detecting the concentration of chemical vapor mixtures is of great demand in many fields such as environmental monitoring [1], resource prospecting [2], and medical diagnoses [3]. Current absorption gas sensors usually operate in the near-infrared (NIR), where photon detection can be performed with high efficiency and resolution (∼fW). In order to overcome these constrains, it is desirable that absorption occurs in the MIR while detection is performed in the NIR. Nonlinear parametric upconversion methods demonstrated great potential for ultra-low noise single-photon imaging [12]. Leveraging on parametric processes, the information carried by MIR light is efficiently converted to NIR to achieve high performance photon detection. This upconversion-detection method has already been adopted for MIR gas sensing [11]. It should be noted that most of the previous upconversion-detection schemes are still limited in free-space implementations which are in bulk scales and not suitable for large-scale on-chip integration
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