Study On Filter Characteristics Of Phase-Shifted Fiber Grating And Its Sensing Application

Since the 21st century, the rapid development of the fiber Bragg grating brought great changes to communication. As the requirement of practical production is more and more strict, application of the fiber Bragg grating in some ways also encounter bottlenecks. In order to overcome the use barrier in reality, by changing the structure and parameters, the researchers explored the characteristics and application of the fiber Bragg grating in different form. For periodic modulation of the fiber core refractive index in optical fiber, specific grating structure can be formed. Using the principle of reflection and transmission of incident light in grating, the introduction of the grating for optical fiber brought to the function of signal detection and identification. Fiber Bragg grating accelerate the development of optical fiber in various fields. Fiber Bragg grating as the main components of devices has the advantages of resistance to electromagnetic interference, corrosion resistance, electrical insulation, high sensitivity and low cost. As grating is carved in fiber, it can greatly reduce the loss of coupling and the attenuation of the signal light. According to the period of the carved grating in the optical fiber, the fiber grating is divided into short period and long period of fiber Bragg grating.Phase-shifted fiber grating is a kind of basic fiber Bragg grating. Through carved phase shift in the grating, it makes the original center of the fiber Bragg grating reflective spectrum peak to open a window, and then produced a similar transmission property with long period fiber grating. Understanding the principle of fiber Bragg grating and using multi-layer membrane method to analyze the filter principle of phase-shifted fiber grating, the transfer matrix can be get and can further understand its dispersion and time delay characteristics. The make of phase shift fiber grating has very important influence on its application. The introduction of phase shift is the key during the production process. In this paper, on the basis of fiber Bragg grating production, the phase-shifted fiber grating can be made through direct introduction method.The characteristics of phase-shifted fiber grating is the introduction of phase shift in grating. However, with the introduction of different phase shift number, location and size, phase-shifted fiber grating will show different characteristics. In this paper, by using MATLAB and OptiGrating to program, it analyzes the influence on the phase-shifted fiber grating filter function minutely with different grating parameters. The results showed that:1.The multiple parameters of grating are influence on the filtering properties, and the location of the transmission window has approximate linear change with the coupling coefficient and grating length; 2.For dual-phase shifted fiber grating, the transmission spectrum will collapse inward with the location change of the phase shift points from the inside out; 3. With the increase of phase shift point, the reflectivity of the center transmission window fall rapidly. By properly selecting the location of phase shift can be formed more transmission windows and super wide rectangular transmission window. Introduced phase shift in the fiber Bragg grating, a transmission window is narrower than the reflection peak of fiber Bragg grating can be get. Cutting the toe of phase-shifted fiber grating can eliminate the influence of sidelobe to grating filter and improve precision and signal quality.Phase-shifted fiber grating with the characteristics of high sensitivity, high precision, high resolution, low loss, low cost, that can be applied in the sensor and demodulation system to achieve the detection of external factors such as temperature, strain and refractive index. Phase-shifted fiber grating has a better filter properties than ordinary fiber Bragg grating. The successful application of fiber Bragg grating makes the phase shifted fiber grating instead of fiber Bragg grating in many ways can be used as system components to achieve real-time measurement of external signal.