Investigation Of Photonic Crystal Fiber Characteristics And Sensing Applications

Photonic crystal fiber (PCF) has great application prospect in the field of fiber sensing and communication, due to the special air-hole structure and light guiding mechanism. Being aimed at the characteristics and sensing applications of PCF, the mode characteristics of PCF, sensing applications of PCF long-period grating (PCF-LPG) and PCF Mach-Zehnder interferometer (MZI, PCF-MZI) are investigated in this dissertation. The main achievements of our study have been summarized as following:1. Adjusting PCF dispersion by optimizing structural parameters has been studied based on vectorial effective index method. It is found that zero dispersion wavelength (ZDW) has a dual-extreme characteristic, presenting a maximum value and a minimum value with the variation of air filling factor and scaling parameter, respectively. These discoveries can be used to design PCF with special dispersion curve. Three special PCFs are designed around the 800 nm working wavelength of fetosecond laser, which have flattened anomalous dispersion, normal dispersion and nearly zero dispersion, respectively. Each has a bandwidth about 602. Through numerical modeling, method of writing out PCF-LPG with suitable resonant wavelength by choosing appropriate grating period based on structure parameters is investigated, and also enhancing the inner refractive index (nin) sensitivity characteristic of PCF-LPG by optimizing structural parameters. The nin sensitivity characteristic of PCF-LPG working in antiresonant reflecting optical waveguide is exploited, and it is found that the refractive index sensitivity can reach to 10-7 RIU/pm. A dual-channel method based on PCF-LPG which is able to measure refractive index is proposed and proved, in which medium surrounding PCF-LPG and filled in air holes simultaneously interact cladding mode. Thus, the sensitivity characteristic can be enhanced and refractive index sensor with great sensitivity can be manufactured.3. HE11cl, mode with its dispersive characteristic and nin sensitivity characteristic in PCFs with variant radii are studied. It is found that there are evolving phenomena among ring mode, HE11cl mode, and HE12cl mode with the variation of cladding radius, wavelength and nin, respectively. Several similar modes vary in a similar way with the decrease of cladding radius. The dispersive characteristic and nin sensitivity characteristic are different with different cladding radius, even under the same mode. The dispersive characteristic and nin sensitivity characteristic are changed and enhanced as a whole when the mode order rises. It is found that the nin sensitivity characteristic of PCF-LPG can be enhanced through reducing cladding radius appropriately.4. The factors which can affect the strain characteristic of PCF-MZI are theoretically and experimentally analyzed. The fiber loop mirror strain sensor is made of PCF-MZI. The test results show that the visibility of transmission spectrum can be enlarged, which can reduce bandwidth and improve the precision, with the strain sensitivity of -2.53 pm/??. A large-diameter PCF-MZI with streamline shape splicing region is designed. It is indicated that the strain sensitivity is -1.77 pm/??, however, the refractive index sensitivity characteristic is very weak. Thus, this large-diameter PCF-MZI could be used in index-insensitive strain sensor.5. A large lateral offset structure (LLOS) staged fiber MZI (LLOS-MZI) refractive index sensor is proposed and fabricated. The interference principle, spectrum characteristics and refractive index sensing characteristics are studied. The staged fiber LLOS-MZI sensor owns high refractive index sensitivity. The sensitivity of 327 ?m length staged LLOS-PCF-MZI sensor is 2.17*10-7 RIU/pm, and the sensitivity of 436 ?m length staged Single mode fiber LLOS-MZI sensor is 3.12*10-8 RIU/pm. And the sensitivity will increase with the decrease of MZI length. The LLOS-PCF-MZI sensor is fabricated. The interference principle and refractive index sensing mechanism are also theoretically analyzed. The refractive index sensitivity of 330 ?m length LLOS-PCF-MZI is 6.62* 10-8 RIU/pm. These two kinds of fiber LLOS-MZI are appropriate to make high sensitivity refractive index sensor for rapid measurement.