Surface Plasmon Resonance Sensor Based on Side-Polished D-Shaped Photonic Crystal Fiber With Split Cladding Air Holes

We present and numerically characterize a sidepolished D-shaped photonic crystal fiber (PCF) sensor based on plasmon. The coupling properties and sensing performance are investigated through the parameter study of metal thickness and polishing depth by the finite element method. With uniform metal evaporation, the metal-dielectric interfaces of the polished flat plane and inner surfaces of split first-cladding air holes can support two different kinds of surface plasmon polariton (SPP) modes. Each mode has its certain resonance wavelength, which is independent of polishing depth and side-polishing angle, and the resonance intensity of the two modes can be changed by polishing depth and the angle, respectively. In the process of measuring analytes with different refractive indexs (RIs), a two-axis detecting method has been presented to improve the sensitivity. The commercial PCF ESM-12 is used to fabricate the sensor probe with wheel-polishing system, and the experimentally detected data have a good agreement with theoretical simulation. As RI varies, both the resonance and intensity perform linear response with the sensitivity of 2.3319 × 10 ³ nm/RIU and -252.86%/RIU, respectively. By detecting the wavelength and intensity at the resonance, the two-axis method has obtained a sensitivity of 127.0902 CI/0.01RIU, which is 9% higher than the conventional method (116.595 CI/0.01RIU) that only measures wavelength shift. This study facilitates a new way for the analysis of D-shaped PCF sensor characteristics and provides a novel detecting method to improve the sensitivity of side-polished SPR sensor.