Photonic crystal fiber Mach-Zehnder interferometric refractive index sensor

A simple photonic crystal fiber (PCF) based Mach-Zehnder interferometric sensor is fabricated for sensing the Refractive index. The sensing head is formed by all-fiber in-line singlemode - multimode - photonic crystal - singlemode fiber structure, using the fusion splicing method. The fully collapse air holes of PCF make the coupling of the core and cladding mode in the splicing region which establish a Mach-Zehnder interferometer. The multimode fiber is used as a mode coupler. The intensity of output at the end of lead-out single mode fiber varies decreasing manner with increasing refractive index. Photonic crystal fiber sensors with length 5.5 cm exhibit refractive index sensing at 1550nm. . It is shown analytically that the intensity of output at the end of lead-out single mode fiber varies sinusoidally with the relative phase difference between core and cladding mode.