Research On Novel Gas Sensors With Photonic Crystal Fibers

Monitoring pollutant gases such as methane, acetylene, ammonia is essential inmany industrial, biomedical and environmental applications. Optical fiber sensorsoffer clear advantages such as immunity to electromagnetic interference, small size,low cost and, most important, the possibility for distributed.This paper tightly around the theme of the photonic crystal fiber optical fiber gassensing. The main contents and major innovations of this paper are as follows:1) A full-vector-element method with perfect matching layer boundaries is usedto simulation the single-mode condition and power fraction of an air cladding totalinternal reflection guided porous polymer THz fiber. We show that single modecondition and a high fraction of power in the air holes cannot be simultaneously metin porous fibers. Finally, employing the V parameter and the Lorentz-Lorenz formula,we analyze this problem theoretically.2) We researched dielectric function of ferroelectric PVDF in THz region andthe surface plasmon resonance-like excited in the interface between a ferroelectricPVDF layer and gaseous analyte. A simplest sensor based surface plasmonresonance-like is proposed to measure a particle change in real part of refractive indexof gas. The detection limit of the amplitude-based sensor for measuring changes in thegaseous analyte at304μm was found to be1.45104RIU, assuming a1%amplitudechange detection limited.3) Employing the unique properties of HC-PCF in guiding light within a hollowcore, we designed an absorption spectroscopy gas sensor with HC-PCF as gas cell.The transmission spectrum of13band of acetylene was obtained and theP11-branch was selected for sensing purpose. A minimum detective sensitivity of143ppmv for the system configuration is estimated.4) The action of an Er-doped fiber laser intra-cavity absorption gas sensor istheoretical investigated using two-level system rate equations. The results show thatchanging the reflectivity of cavity mirrors can change the frequency of laser reflection.And detective sensitivity will be enhanced by increasing the path of interaction. Thenonlinear characteristic of laser gain near the threshold affects detective sensitivity ina non-linear manner. The effect of mode competition amounts to the rise of absorption coefficient of gas in increasing the detective sensitivity. So the detective sensitivity ofa laser under multi-mode operation is much better than that of a laser under singlemode operation.5) We have investigated the output power characteristics of a dual-wavelengthoperating Er-doped fiber laser, and proposed a dual-wavelength Er-doped fiber laserintra-cavity absorption gas sensor. The sensitivity of the fiber laser sensor enhancedby the relative cavity loss and pump power is discussed experimentally. Usingcentre wavelength of the FBG can be fine tuned by temperature controller; anabsorption peak of NH3around1531.68nm is measured and matched absorption crosssection of NH3in HITIRN database very well.