In-Fiber M-Z Interferometer Based on Cascaded Long Period Gratings in Embedded-Core Fiber

A novel Mach-Zehnder interferometer (MZI) in an embedded-core hollow optical fiber (ECOF) was demonstrated, which was composed of a pair of long period gratings (LPGs). In order to form an in-fiber MZI in an ECOF, a high-frequency CO2 laser was used to fabricate two similar LPGs with their peak attenuation of approximate 3 dB. The responses of the MZI to the temperature, the axial strain, and the refractive index were measured and discussed. The temperature sensitivity of the MZI is about 48.8 pm/°C, and the sensitivity of the axial strain is 0.5 pm/με. The ECOF has a big air hole, which is easy to form a microfluidic channel. The sensitivity of the internal refractive index can be as high as 1437.4 nm/RIU in the refractive index range of 1.4248~1.4569. The proposed MZI has a high resolution and can be a potential candidate for sensing, especially for on-line microfluidics sensors.