Abstract
In this paper, a bicharacteristic waveguide (BW) is proposed for fundamental-mode phase-matched second harmonic generation (SHG) from mid-infrared (MIR) to near-infrared (NIR). The required phase matching condition (PMC) is satisfied between the fundamental plasmonic mode at 3100 nm and the photonic mode at 1550 nm. With 1 W pump power, the SHG conversion efficiency of 4.173% can be obtained in 90.3 μm length waveguide. Moreover, the SHG conversion can be enhanced by using a microring resonator (MRR). By optimizing the MRR, the SHG conversion efficiency is increased to 8.30%. The proposed waveguide can also provide a promising platform for upconversion detection. By using an on-chip cascaded configuration, a gas sensor with the capability of MIR absorption and NIR detection is proposed. It is found that the detection limit (DL) can reach 1.04 nmol/L with 100 mW pump power, which shows significant enhancement compared with direct MIR absorption and detection.
Highlights
Second-order nonlinear optical processes such as second harmonic generation (SHG) have significant applications in various fields e.g. all-optical signal processing [1], wavelength conversion [2], optical switch [3], etc
In summary, we theoretically propose a bicharacteristic waveguide for SHG from MIR to NIR
Leveraging the unique dispersion relation of cadmium oxide (CdO), the phase matching condition (PMC) for SHG can be satisfied between the fundamental plasmonic mode at fundamental frequency (FF) and photonic mode at second harmonic frequency (SHF), respectively
Summary
Second-order nonlinear optical processes such as second harmonic generation (SHG) have significant applications in various fields e.g. all-optical signal processing [1], wavelength conversion [2], optical switch [3], etc. Compared to the high performance NIR photodetection, the MIR photodetector usually shows much higher noise and lower sensitivity [19] and limiting the implementation of MIR sensors To overcome this challenge, upconverting the MIR signal to NIR by using nonlinear parametric process is a potential method [20]. Perfect phase matching between fundamental modes and MIR-to-NIR conversion are two challenges for waveguide-based SHG. Transparent conductive oxides (TCOs), such as indium cadmium oxide (CdO) and indium tin oxide (ITO), have attracted important research interests as alternative materials for plasmonics This is because the dispersion relation can be tailored through their carrier concentrations [21,22]. A microring resonator (MRR) is employed to further enhance the conversion efficiency Based on this waveguide, we further propose an on-chip gas sensor integrated with the capability of MIR-to-NIR upconversion detection. The results show that the detection limit (DL) of methane can achieve the order of 10−9 mol/L which is significantly enhanced comparing to direct MIR detection
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