Research On Novel Optical Fiber Gas Sensing Technology Based On Slow Light In Photonic Crystal Waveguide

With the development of optical fiber sensing technology, the optical fiber gas sensor based on the principle of infrared spectrum absorption has been developed drastically. However, the existing detection sensitivity is limited by the length of absorption path, so it is very important to study novel optical fiber gas sensing technology. By using photonic crystal waveguide, the light velocity could be reduced at room temperature. In addition, photonic crystal has the advantages of compact structure and diversity. If the gas cell is replaced by photonic crystal waveguide in optical fiber gas sensing system, the effective gas absorption factor would be greatly enhanced take advantage of slow light in photonic crystal waveguide, thus can simultaneously increase the detection sensitivity and decrease the volume of gas cell, which offers the possibility of high sensitivity and miniaturization gas sensor.This paper proposed a gas sensing system based on slow light in photonic crystal waveguide, which provides a new theory, new technology and new means for high sensitivity gas sensor. The main contents are as follows:(1) The design of novel optical fiber gas sensing based on slow light in photonic crystal waveguide. By analyzing the basic characteristic of photonic crystal and the generation principle of slow light in photonic crystal waveguide, the effect of slow light on the effective gas absorption factor was deduced. Then, an optical fiber gas sensing was designed with high sensitivity and miniaturization due to the introduction of slow light in photonic crystal waveguide. At last, some problems that may arise in practical application were analyzed.(2) The research on wideband slow light with low group velocity and low dispersion. By analyzing and summarizing the research status of slow light in photonic crystal waveguide, the wideband slow light was obtained in slotted photonic crystal waveguide by simply changing the positions of the first and second rows of air holes adjacent to the slot. Using the plane wave expansion method and finite differences time domain method, the properties of slotted photonic crystal waveguide were performed, optimized and designed. Numerical results demonstrated that slow light with group index of100over2.57nm bandwidth was achieved.(3) The research on low loss slotted photonic crystal waveguide. By summarizing and analyzing the existing method for efficient input and output fiber coupling to a slotted photonic crystal waveguide, a resonant coupling structure was proposed. Numerical results demonstrated that the coupling efficiency could reach to90%.(4) The design and building of optical fiber gas sensing system for the preliminary measurement experiment of gas concentration. First, the distribution gas system and chamber structure are devised. Then, the gas concentration was measured by using the correlation spectroscopy method. The experimental data showed that the system resolution could reach500ppm, the system stability was2.27%, and the system repeatability was3.38%.