Study On Mechanical Characteristics And Interferometric Sensoring Characteristics Of Photonic Crystal Fibers

In this thesis, the mechanical, micro-bend and interferometric sensing characteristics of photonic crystal fibers (PCFs) are studied.The study mainly includes:1. Mechanical characteristics of the total internal reflection photonic crystal fiber (TIR-PCF), including its transverse load, twist and bend characteristics.2. Micro-bend sensing characteristics of the TIR-PCF.3. Interferometric sensing characteristics of the photonic crystal fibers, including its temperature and strain characteristics.The study on the mechanical characteristics of the TIR-PCF shows that in a definite wavelength, the effective refracting index of the TIR-PCF presents a regular movement with the change of the transverse load. The phase of interferometric fringes generated by the M-Z interferometer used to testing the TIR-PCF have, approximately, a linear relationship with the change in the transverse load applied to the M-Z interferometer arm and the amplitude of the interferometric fringes indicates, approximately, a sine relationship with the load.The phase of interferometric fringes has, approximately, a linear relationship with the change of twist angle of the TIR-PCF. In fact, it is found that the mechanical characteristics of the TIR-PCF are similar to that of a normal single-mode fiber.The study on micro-bend characteristics of the TIR-PCF shows that for different periods of bending teeth, the TIR-PCF has similar micro-bend characteristics trend to the single-mode fiber (SMF) and multi-mode fiber (MMF), i.e. shorter the period of the bend teeth is, higher the sensitivity of the micro-bend is. Because of the splicing loss between the TIR-PCF and SMF, the absolute loss of the TIR-PCF is smaller than that of the SMF and MMF. For the same period of the bend teeth, the TIR-PCF has the highest micro-bend sensitivity, while MMF has the lowest micro-bend sensitivity, and the micro-bend sensitivity of SMF is slightly lower than that of the TIR-PCF.The interferometric sensing characteristics of PCFs were investigated for the first time to our knowledge. It shows that by selecting appropriate splicing parameters, the splicing loss between PCFs and SMF can be reduced to less than 1dB. The temperature coefficient of one-end spliced Fabry-Perot (F-P) cavity formed by the TIR-PCF and SMF is 7.24nm/℃, and the cavity length of the F-P sensor has a good linear relationship with temperature when the temperature varies from -20℃to 100℃. The temperature coefficient of two-end spliced F-P cavity formed by a photonic band gap photonic crystal fiber (PBG-PCF) and SMF is 13nm/℃, and within the range of 0～1000 , the cavity of the F-P sensor has a linear relationship with the change of strain applied.The temperature coefficient of in-fiber micro F-P interferometric sensor which is fabricated on the TIR-PCF by a femtosecond laser is -0.0017nm/℃, and its strain sensitivity is 0.0036nm/ ? . This is the first fs-laser micro-machined micro F-P sensor to the best of our knowledge.The characteristics of PCFs are also analyzed qualitatively by using the equivalent-index model in this thesis.