Fabrication Of Mach-Zehnder Cavity Infiber By Femosecond Laser And Its Temperature-Salinit Sensing Properties

As the tunable photonic devices, high performance sensors, in-line Mach Zehnder interferometers(MZIs) have attracted considerable interests for their excellent properties such as simple, compact structure, immunity to electromagnetic radiation, high resolution, high sensitivity, tunability. In recent years, a number of techniques have been proposed to fabricate the MZIs with high performance, such as utilizing the fiber tapering, micro-cavity etching, fiber splicing. These MZIs are divided into two groups involving in-core, core-cladding interferences, respectively. The phase of MZI based on the double openings micro-cavity was modulated directly by the change of liquid refractive index because the liquid could flow into the micro-cavity freely. Therefore the double open micro-cavity structure in optical fiber can have great application in temperature, liquid refractive index sensing due to their higher sensitivities.In this thesis, a MZI sensing structure in optical fibers was fabricated by using femtosecond laser-induced water breakdown. Sensing properties of the double open micro-cavity in optical fiber was investigated theoretically, experimentally. The research work has been summarized in details as follows.Firstly, we studied the principle of MZI briefly, simulated the spectrum of interference with different parameters of double open micro-cavity structure in optical fiber by using Matlab, Beam PROP including of Rsoft. The influence of the microcavity length L, core-cavity β, transmission loss on MZI interference spectrum were analyzed under the simulation.Secondly, we analyzed the phenomenon of femtosecond laser-induced water breakdown, established the femtosecond laser induced water breakdown method for fiber optic micro machining system. Based on the theoretical analysis results, the MZI double open micro-cavity structure in optical fiber with the advantage of compact, good parallelism, high performance was fabricated by using femtosecond laser-induced water breakdown. We investigated the temperature, liquid refractive index sensing properties of the double open MZI micro-cavity Structure in optical fiber theoretically, experimentally. The experiment result shows that the temperature, refractive index sensitivity arrive 0.035 nm/°C,-13055.16 nm/RIU, respectively.Finally, we sealed the liquid in the micro-cavity by using the capillary tube, obtained an ultrasensitive temperature sensor with the maximum sensitivity of 1.60 nm/?C in the range of 30–44 °C, a fiber optic sensor composed of two Mach-Zehnder interferometers were proposed for simultaneous measurement of temperature and salinity.