Investigation Of Fluoride & Chalcogenide Glass Based Photonic Devices

Silica glass materials have excellent optical properties from ultraviolet to near-infrared wavelength region,and silica glass-based fibers have been widely used in a range of important applications,including optical communications,laser processing etc.However,the transmission loss of silica glass increases exponentially when the working wavelength of the silica glass materials exceeds 2.5 microns,and the optical performance of silica material therefore greatly reduces,induced by the infrared band absorption.Non-oxide glass compound glass materials,for example fluoride glass and chalcogenide glass,have attracted much interests in recent years.Compared with the traditional silica glass-based fiber optic devices,fluoride glass and chalcogenide glass-based fiber optic devices have a number of advantages of optical properties,such as high rare earth ion-doped concentrations,broad infrared spectroscopy and fluorescence spectroscopy,lower phonon energy and high nonlinearity etc.So far,fluoride glass and chalcogenide glass devices have been widely investigated in the research areas of mid-infrared fiber lasers,high-nonlinearity devices,fiber optic sensors,and high-efficiency photoluminescent devices etc.This thesis has developed several fiber optic devices based on fluoride and chalcogenide glass materials for the applications of mid-infrared lasers and supercontinuum light sources.The main content of this thesis is shown as follows:1.A home-made single-mode fluoroaluminate fiber was fabricated first,and the fabrication of fiber Bragg gratings（FBGs）was achieved using femtosecond（fs）laser inscription method at 800 nm.The grating strength of the FBGs was investigated for different pulse energies and different orders,and a 3rd-order FBG with Bragg wavelength at 1557 nm was found to have the highest reflectivity of 99.5%.In addition,the reflectivity of the mid-IR grating peaks for different orders was also studied,and a 2nd-order FBG with a reflectivity of 98.8%was obtained at 2864 nm.Finally,the temperature dependent characteristics of a mid-IR FBG were studied between 30℃ and 150℃,showing a linear wavelength dependence and an excellent stability for the refractive index modulation of the proposed FBG.2.A long-period fiber grating（LPFG）was fabricated in a home-made fluoroindate fiber using a femtosecond laser,and attenuation peaks as strong as-17 dB,with sharp and predictable spectral resonances,were obtained over the transmission spectrum.A strain up to 2000με applied on the LPFG yielded a resonant wavelength redshift of circa 8.46 nm.The strain sensitivity of this LPFG in fluoroindate fibers could pave the way for a new range of applications in the mid-infrared wavelength regions,such as tunable optical rejection band filters in fiber amplifiers and sensing devices.3.The theoretical analysis of traditional single-mode-multimode-single-mode fiber mode was studied in detail,mode interference effects in multimode fibers had been investigated,and the well-known Beam Propagation Method had been adoped for describing the light propagation in the multimode fiber.Based on theoretical analysis,we had fabricated the structure of silica single-mode fiber-chalcogende glass multimode fiber-silica single-mode fiber,and such structure could be usded for temperature sensing device at the wavelength of 2μm.4.A novel solid core chalcogenide glass photonic crystal fiber（PCF）was designed and fabricated,and the PCF fiber was tapered using a CO₂ laser scanning method,the diameter of tapered was 55μm and the uniform tapered length was 3 cm.An ultra broadband mid-infrared supercontinuum source was achieved with a spectral coverage of 1500 nm～6200nm at the level of-20 dB,using the custormised femtosecond laser operating at 2.87μm, combined with a space pumping method.The repetition frequency of the femtosecond laser is 42 MHz,and the pulse width is 173 fs,The theoretical model had a good agreement with the experimental data.