Design Of Terahertz Piece Of Optical Fiber SPR Sensor And Achromatic Compound

The surface-plasmon-resonance(SPR) fiber optic sensor technology has become one of the hot researches in recent years. The SPR fiber optic sensor is studied in this thesis.In this thesis, based on the Fresnel theorem and the transfer matrix method, the principle of the SPR fiber optic sensor is described and a theoretical model is established. The angle modulation and the wavelength modulation which are the two basic modulations used in the SPR fiber optic sensor are explained in this model. The influence of the coating thickness, sensor probe geometry and the refractive index ratio of cladding to core on the sensor sensitivity and accuracy of the sensor are simulated. It is shown that the thickness of the coating will affect the sensor’s sensitivity and accuracy at the same time; the length and the core diameter of the sensor will affect the sensor’s accuracy and the emitted light intensity, but it do not affect the sensor’s sensitivity; the refractive index ratio of cladding to core will increase the sensor’s sensitivity within a certain range.A new type of high sensitivity tapered probe is studied in this thesis. The influence of different taper ratios (TR) on the sensitivity and accuracy of the sensor is analyzed. It is shown that the tapered probe can increase the sensitivity of the sensor effectively. The sensor with tapered probe has a good performance when TR is between1.2to1.8.Two types of SPR fiber optic sensor probe (cylindrical probe and tapered probe) are fabricated in the experiment. Experiment system is set up and the test on the refractive index of the solution using these two probes is realized. The experimental results showed that the sensitivity of the cylindrical probe is2510nm/RIU and the tapered probe is3940nm/RIU, both of which are well consistent with the result of theoretical simulation. Especially, the sensitivity of tapered probe is1.6times than ordinary probe, which has an important significance for the fabrication of high sensitivity probe.Based on the composite wave plate theory, the terahertz composite achromatic quarter-wave plate is designed using the simulated annealing algorithm in this thesis and remarkable design results (retardation deviation is2%from0.2THz to2THz and retardation deviation is4%from0.2THz to3THz) are got. The influence of different numbers of quartz plates on the key parameters of the quarter-wave plate are analyzed, such as achromatic performance, thickness and absorption loss. It is shown that with the increase of the number of quartz plates, the achromatic performance of the quarter-wave plate will be improved and phase delay detuning will also be reduced; however, the thickness of the quarter-wave plate is increased, leading to the increase of the absorption loss. It is also shown that the optimized quartz plate number is five, with which we can get good achromatic performance, and the thickness and the loss are also practical for THz application.