Study On Sensors And Demodulation Technology Based On Long-period Fiber Grating Written On Photonic Crystal Fibers

Long-period fiber grating (LPG) written in a photonic crystalfiber (PCF) is a novel kind of optical passive component with manyadvantages. The PCF-LPG is of great importance for many applications insensors and demodulation technology. The works done in this paper are basedon the PCF-LPG and focus on the applications in these two aspects.Following are the main contents：1, Study on tilt sensor with a compact dimension based on a LPG: due tothe LPG with a high sensitivity to liquid level, the LPG is fixed in aPlexi-glass tubular with a slant orientation and half of the LPG is immersedinto the NaCl aqueous solution, whereas the other half is exposed in air. Thedip wavelength of the LPG gradually changes when the immersed length ofthe LPG varies with the tilt angle. By monitoring the dip wavelength shift ofthe LPG, we can obtain the tested tilt angle. The proposed tilt sensor in themeasurement range from30oto30ois achieved, and the LPG based tiltsensor is simple and compact; whose dimension is only35cm3.2, Study on a fiber loop mirror (FLM) temperature sensor demodulationtechnique which use a PCF-LPG and a band-pass filter: By utilizing the stablefiltering function of the LPG in the PCF, the resonant wavelength variation ofthe FLM with temperature is transferred effectively to the intensity variationof the output light. By monitoring the light intensity of the band-pass of thefilter, temperature applied on the FLM is deduced by an optical power meter.The temperature sensitivity of the sensor is1.742dB/℃and the resolution is0.006℃.3, Study on a highly-birefringent fiber loop mirror temperature sensordemodulation based on a PCF-LPG with differential processing: theintensities of two signals located respectively within the positive andnegative linear region of the LPG’s transmission spectrum can be monitoredsimultaneously and accurately. The noise of fiber sensors is eliminated effectively by the algorithm of two signals, since the two signals (alsoincluding the noise of fiber sensors) transmit through the same way to themonitor. Compared with the sensing without the algorithm, the accuracyincreases from~97.3%to~99.7%.