Photonic Crystal Fiber Based Refractive Index Sensors

摘要

In this work two methods of making Mach-Zehnder Interferometer (MZI) for sensitive ambient refractive index (IR) measurement have been proposed by using photonic crystal fiber (PCF). PCF-MZI is fabricated by fusion splicing a short length of PCF between two single-mode fibers (SMF) with fully collapsed air holes in splicing region. Consequently, the fundamental core mode of PCF can be coupled to cladding modes at the first coupling region and then re-coupled to the core mode at the second coupling region. Miniaturized MZI is constructed using sharply tapered PCF and influence of sharp-tapering of PCF is then studied. Sharp-tapering of PCF over a short length of PCF is utilized by using tiny flame geometry. Experimental results verifies that sharp-tapering has a greater impact on refractive index sensitivity enhancement compare to decreasing taper waist diameter. MZI with length of 3.8 mm and taper waist diameter of 65 urn shows RI sensitivity of 677 to the miniaturized MZI, two types of polymer-deposited PCF-MZI is fabricated. Chitosan with RI~1.54 and Polycaprolactone (PCL) with RI~1.15 was filled into the cladding air-holes of PCF using capillary force. Chitosan-filled PCF with length of 10 mm shows RI sensitivity of 198.6 nm/RIU for RI range of 1.3327-1.3556, 474.5 nm/RIU for RI range of 1.3556 to 1.3917 and 677.8 nm/RIU for RI range of 1.3917-1.4204.