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A type of As2S3 chalcogenide glass mid-infrared dual-core photonic crystal fiber has been proposed. The dual-core photonic crystal fiber (PCF) consists of two asymmetric cores. The high polarization property and the coupling characteristics have been studied by using the finite element method and mode coupling theory. Numerical results show that the birefringence at wavelength λ = 10 μm is up to 0.01386 and the coupling length can reach wavelength λ = 5 μm, 261 μm and 271.44 μm for x-polarized mode and y-polarized mode, respectively. It demonstrates that a 6.786-mm-long fiber can exhibit an extinction ratio of better than −10 dB and a bandwidth of 180 nm.

The dispersion characteristics of photonic crystal fibers are computed using the multipole method. Single-mode fiber with three zero-dispersion wavelengths is obtained by properly designing fiber structure parameters. The dispersion characteristics of photonic crystal fiber with a small air hole in the core are analyzed. Fibers with four zero-dispersion wavelengths are designed. The variation rules of zero-dispersion wavelength with fiber structure parameter are found. The locations and spacings of the zero-dispersion wavelengths can be adjusted flexibly in a large wavelength range. Closing to zero and flattened dispersion can be obtained in the fibers with multiple zero-dispersion wavelengths. The multiple zero-dispersion wavelengths can create a rich phase-matching topology, and enable better controlling the spectral locations of the four-wave-mixing and resonant-radiation bands emitted by solitons and short pulses.

Today, immersion precipitation is the most often used process for the preparation of gas separation membranes from polymeric materials. In this process a polymer solution in the form of a thin liquid film or hollow fiber is immersed in a nonsolvent bath where the polymer precipitates and forms a membrane. The immersion precipitation process can be performed by various means. The dual bath spinning process is one specific way which can be used, e.g., for the preparation of hollow fiber membranes for gas separation. In this process hollow fibers are spun by contacting the polymer solution with two properly chosen coagulents successively. The first coagulant is used to 'extract' solvent out of the polymer solution. The contact time is short in order to create a thin layer of high polymer concentration at the interface. The second coagulent is used to quickly precipitate the polymer solution to form the membrane. With this spinning process, hollow fibers with the intrinsic selectivity of the polymer material can be easily obtained without the necessity of coating. This thesis is aimed on extending the knowledge on membrane formation and on further developing the dual bath spinning process for the preparation of gas separation hollow fibers with both high selectivity and high flux.

Bandgaps of chalcogenide glass hollow-core photonic crystal fibers (GLS HC-PCFs) are analyzed by using the plane-wave expansion method. A mid-infrared laser can propagate in these low confinement loss fibers when the wavelength falls into the bandgaps. For enlarging the bandgap width, an improved GLS HC-PCF is put forward, the normalized frequency kΛ of the improved fiber is from 7.2 to 8.5 in its first bandgap. The improved GLS HC-PCF with pitch of 4.2 μm can transmit the lights with wavelengths ranging from 3.1 μm to 3.7 μm.

A terahertz photonic crystal fibre (THz-PCF) is designed for terahertz wave propagation. The dispersion property and model birefringence are studied by employing the finite element method. The simulation result reveals the changing patten of dispersion parameter versus the geometry. The influence of the large frequency band of terahertz on birefringence is also discussed. The design of low loss, high birefringence THz-PCFs with zero dispersion frequency at 0.3 THz is presented.

A real-coded genetic algorithm (GA) combined with a fully vectorial effective index method (FVEIM) is employed to design structures of photonic crystal fibers (PCFs) with user defined dispersion properties theoretically. The structures of PCFs whose solid cores are doped GeO2 with zero-dispersions at 0.7–3.9μm are optimized and the flat dispersion ranges through the R+L+C band and the negative dispersion is −1576.26 pskm−1nm−1 at 1.55 μm. Analyses show that the zero-dispersion wavelength (ZDW) could be one of many ZDWs for the same fiber structure; PCFs could alter the dispersion to be Battened through the R+L+C band with a single air-hole diameter; and negative dispersion requires high air filling rate at 1.55 μm. The method is proved to be elegant for solving this inverse problem.

A kind of midinfrared As2S3 chalcogenide glass photonic crystal fiber is proposed in this paper. The characteristics of this fiber are studied by multipole method, including high birefringence, chromatic dispersion, and high nonlinearity. Through numerical simulation, it is found that at midinfrared wavelength λ = 3.625 μm, the birefringence of this fiber reaches up to 0.098 and nonlinear parameters are 1.69 m-1 ·W-1 and 0.78 m-1 ·W-1 for x-polarized mode and y-polarized mode, respectively. In addition, the fiber keeps normal dispersion in a wavelength range from 3 to 7 μm . In conclusion, the band of transmitted wavelength extends into a midinfrared wavelength range of 3—10 μm, and high birefringence and high nonlinearity in this photonic crystal fiber are perfectly combined. The results are significant for the further development of new photonic devices.

A kind of chalcogenide glass midinfrared dual-core photonic crystal fiber has been proposed in this paper. The coupling characteristic of this fiber has been studied by multipole method using the basic theory of coupling. It is found that the birefringence of dual-core PCF with pitch 5.4 μm, air-hole radius 1.35 μm and air-filling fraction 0.5 is 0.551×10-2 at normalized frequency λ/Λ = 2.04 μm. At normalized frequency λ/Λ = 0.93 μm, coupling lengths are 145.32 μm and 154.68 μm for x-polarized mode and y-polarized mode, respectively. The band extended to midinfrared. This dual-core photonic crystal fiber with coupling length and high polarization is useful for manufacturing midinfrared band optical fiber coupler.

This paper proposes three kinds of tapered holey fibres with a multi-layer of holes whose pitch of air holes at the end of untapered and tapered are 5.8 μm and 1.8 μm. The central wavelength which locates in the anomalous dispersion region is 1.55 μm. An adaptive split-step Fourier method is numerically used to study the pulse propagation in tapered holey fibres. For the considered convex tapered holey fibre, at a wavelength of 1.55 μm, a compression factor of 136.7 can be achieved by initial width of 800 fs propagation through a length of 0.8 m. It demonstrates that in anomalous dispersion region, pulse can be compressed with the increase of nonlinearity coefficient and the decrease of dispersion coefficient.

A kind of high birefringence SF6 soft glass photonic crystal fiber (HBSF6-PCF) is proposed. The properties of birefringence, dispersion, nonlinear coefficient and the transmission characteristics are studied by the multipole method and the adaptive split-step Fourier method. The numerical results show that the birefringence and the nonlinear coefficient reach the orders of 10-2 and 10-1, respectively. In addition, the HBSF6-PCFs can generate very smooth supercontinuum spectra when illuminated with femtosecond pulsed light of 1064 nm. It is found that up to 800 nm spectral width (evaluated at −5dB from the peak) is achieved. Therefore, the advantage of the HBSF6-PCFs is such that a high birefringence, a high nonlinearity and a smooth supercontinuum are perfectly combined in them.

A kind of linerly tapered microstructure fiber has been proposed in this paper. The central wavelength, which is located in the anomalous dispersion region, is 1550 nm. We use an adaptive split-step Fourier method to numerically study the propagation of 1 ps laser pulse in this microstructure optical fiber. For the tapered fiber under consideration, a compression factor of 56.9 and a quality factor of 27 can be achieved in a fiber 1 m long. With the pulse shape evolution in the fiber, we find that in anomalous dispersion region, the pulse can be highly efficiently compressed by the increasing of nonlinearity coefficient and the decreasing of dispersion coefficient. Compared with the normal photonic crystal fibers, the thicker end of the tapered fiber is apt to be coupled to the laser pulse which has a larger effective mode area.

Photonic crystal fibers（PCFs）with rectangle core and elliptical core have been designed.Their fundamental characteristics are studied by electromagnetic scattering theory of multipole method.It is found that the fiber birefringence,dispersion and nonlinear characteristics can be flexibly adjusted by changing the radius of the air holes in the core.The PCFs have the following characteristics: With the increase of radius r 1 of air holes in the core,the birefringence increases and the wavelength corresponding to the maximum birefringence shifts towards the longer wavelength region,the number of zero-dispersion-wavelengths increases from one to three and nonlinear coefficient of the short-wave band decreases while it increases in the longer wavelength region.The three zero-dispersion-wavelengths of elliptical core PCFs with r 1 = 0.4 μm are located in visible,near-infrared and mid-infrared band,respectively.For similar structural parameters,elliptical core PCFs can achieve high birefringence and high nonlinearity more readily than rectangular core PCFs.

A kind of double-cladding photonic crystal fiber (DC-PCF) with high birefringence and two zero-dispersion wavelengths is proposed. It is found that the birefringence of DC-PCF with inner cladding air holes pitch 1.0 μm and diameter 0.8 μm is 1.001 × 10−2 in the optical communication band at wavelength 1.55 μm by the multipole method. It is demonstrated that two zero dispersion wavelengths can be achieved in the optical communication band between 0.8 μm and 1.7 μm, and the first zero-dispersion wavelength is in the working wave band of the Ti:sapphire oscillator, which contributes to the frequency conversion of the Ti:sapphire femtosecond laser. PCF with two zero-dispersion wavelengths can make strong power supercontinuum spectral in the near infrared band.

An all-optical high sensitivity atomic magnetometer is investigated and demonstrated experimentally, of which the principle is based on the interaction between laser beam and rubidium atoms in magnetic field. This interaction is dependent on the magnetic field surrounding the Rb atom cell, therefore the magnetic field information can be obtained simply by measuring the changes of the laser power transmitted through the Rb atom cell. The principle of the atomic magnetometer is analyzed and the performance of the experimental setup is investigated. The experimental result agrees well with the theoretical predictions. Furthermore, some important factors that may affect the performance of the magnetometer are discussed, and the ways to improve the sensitivity of the atomic magnetometer are also put forward.

A kind of high birefringence and highly nonlinear nano-structured photonic crystal fibers （N-PCFs） is proposed. The birefringence, fundamental mode field, dispersion and nonlinear characteristics of the fiber have been studied by electromagnetic scattering theory of multipole. It is found that the birefringence becomes larger by increasing the dissymmetry level of fiber core and air holes in cladding, and the largest birefringence reaches up to 1.918×10-2. With this type of high birefringence and highly nonlinear N-PCFs, the peak of birefringence can be moved to the required wavelength by adjusting the pitch value. The non-linear coefficient of N-PCF with pitch 400 nm reaches up to 0.2 m-1·W-1 in the wavelength of 800 nm.Meanwhile, the birefringence value is also very large in the wavelength range of 750—1000 nm. A perfect combination of high birefringence and high nonlinearity is realized in N-PCF. It is useful for manufacturing new type of nano-photonic apparatus and development of integrated optics.

A highly sensitive all-optical atomic magnetometer based on the magnetooptical effect which uses the advanced technique of single laser beam detection is reported and demonstrated experimentally. A sensitivity of 0.5 pT/Hz1/2 is obtained by analyzing the magnetic noise spectrum, which exceeds that of most traditional magnetometers. This kind of atomic magnetometer is very compact, has a low power consumption, and has a high theoretical sensitivity limit, which make it suitable for many applications.

Guided-mode characteristics of hollow-core photonic crystal fibre (HC-PCF) are experimentally and theoretically investigated. The transmission spectrum in the range from 755 to 845 nm is observed and the loss is measured to be 0.12 dB/m at 800 nm by cut-back method. Based on the full-vector beam propagation method and the full-vector plane-wave method, the characteristics of mode field over propagation distance 1 m are simulated, and the results show that the propagation efficiency can be above 80%. Compared with the fundamental guided mode well confined in air core within shorter propagation distance, the second-order guided mode leaks into the cladding region and gradually attenuates due to larger refractive index difference. The primary loss factors in HC-PCF and the corresponding solutions are elementarily discussed.

A kind of dual-core high birefringence photonic crystal fibers （DHB-PCFs） has been proposed in this paper. The birefringence， coupling length and dispersion characteristics of DHB-PCFs have been studied by multipole method using mode coupling theory. It is found that the birefringence of DHB-PCF with pitch 1.2 μm and air-hole diameter 1.0 μm is 1.24×10-2 in optical communication band of 1.55 μm wavelength. Correspondingly， dual-core coupling lengths are 21.6 μm and 24.3 μm for x-polarized mode and y-polarized mode， respectively. The DHB-PCF with high degree of polarization and very short coupling length is useful for manufacturing minitype photonic apparatus.