Optimized coupling loss between single mode fiber and hollow-core photonic crystal fiber for Raman gas detection

In this investigation, the coupling losses caused by Fresnel reflection, core misalignment between single mode fiber (SMF) and HC-PCF are analyzed. A novel solution proposed from this research will reduce the coupling losses by using a T-type tube as a connector. Meanwhile, the theoretically calculated optimized gaps are at 15 pm in SMF-HCPCF direction and 25 pm in HCPCF-SMF direction. Thus, an experiment has been carried out, and the results of the practical gap in the above mentioned two directions have also been obtained. Furthermore, compared with detection by traditional methods, the proposed new detection method with PCF can remarkably enhance the Raman spectroscopy signal. Finally, the prospect of using the combination of HC-PCF and Raman spectroscopy in gas-cell detection has been demonstrated by using oxygen and nitrogen.