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A novel kind of As 2 Se 3 chalcogenide glass multi-ring photonic crystal fiber is proposed. The characteristics of multi-ring photonic crystal fiber have been studied by the finite element method. Compared with another two kinds of single-core photonic crystal fibers, the multi-ring PCF can make the perfect combination of the effective mode area, the nonlinearity coefficient and multi-zero dispersion. It can achieve high power supercontinuum generation in middle infrared band; It also can be used in high-power pulsed laser fiber amplifier and high-power ultra-short pulse laser transmission in far infrared band.

A novel kind of polarization splitter based on tellurite glass dual-core photonic crystal fiber is proposed. The characteristics of the polarization splitter have been studied by the finite element method. By adjusting the ellipticity of the dual-core PCF, a very high value of birefringence can be reached. The high birefringence can increase the D-value of coupling length in the two orthogonal polarization directions, then the polarization-independent splitter can be achieved. Comparing with the SF57 glass dual-core PCF, the tellurite glass dual-core PCF has higher extinction ratio, the extinction ratio can reach −31 dB at the wavelength λ = 1.55 μ m . The 0.36-mm-long splitter is proposed to achieve extinction ratio better than −10 dB and a bandwidth of 20 nm.

Characteristics of modal interference in two-mode air-silica microstructure fibers are discussed. The theoretical result agrees well with the experiment measurement. Furthermore, the fine structure of modal interference is predicted.

We demonstrate a novel method for the fabrication of glass photonic crystal fibers (PCFs) with a die-cast process. SF6 glass is used as the material for PCFs, and the die is made of heat-resisting alloy steel, whose inner structure matches the PCF's structure. The die is put vertically in the vessel with SF6 glass, and the vacuum hose is attached to the top of the die. The die and glass are put in the furnace to heat at 870 K. The die is slowly filled with the softening glass under vacuum conduction until it is full. It is kept in the furnace to anneal at a rate of 20 K/h to remove the thermal stress that could lead to cracks. The outer tube of the die is taken apart when its temperature is close to room temperature, and the fused glass bundle is etched in an acidic solution to remove the heat-resisting alloy steel rods. Thus, the etched bundle is ready to use as a PCF preform. The PCF is observed in the generation of a supercontinuum, with the flat plateau in the spectrum of the output emission stretching from 400 to 1400 nm by experimental measurement. The transmission loss is 0.2-0.3 dB/m at wavelengths of 420-900 nm.

This paper describes a novel method of fabrication for glass photonic crystal fibres (GPCF) with die-cast process. The die is made of the heat-resisting alloy steel, whose inner structure matches the GPCF's structure, and the SF6 glass is used as the material of GPCF. The die is vertically put in the vessel with SF6 glass, and the vacuum hose is attached to the top of the die, then put them in the furnace to heat at 870 K together. The die is slowly filled with the softening glass under vacuum condition till it is full. Keep it in the furnace to anneal at a rate of 20 K/h to remove thermal stress that could lead to cracks. The outer tube of the die is taken apart after its temperature is close to room temperature, and the fused glass bundle is etched in an acidic solution to remove the heat-resisting alloy steel rods, and the etched bundle is ready for use as a GPCF preform. The preform is thinned to a fibre. The GPCF is observed the generation of supercontinuum, with the flat plateau in the spectrum of output emission stretching from 400 to 1400 nm by experimental measurement. The transmission loss is 0.2-0.3 dB/m at the wavelength of 420-900 nm

We have proposed a novel kind of photonic crystal fiber which contains two asymmetric cores. The birefringence and the dispersion are numerically analyzed based on finite element method when the size of the air holes and the pitch of two adjacent air holes are changed. It is shown that the proposed photonic crystal fiber has high birefringence up to the order of 10−2 and double-zero dispersion points are at the wavelengths of 1310 nm and 800 nm, simultaneously. At the same time, the normalized power and the extinction ratios of the proposed photonic crystal fiber have been simulated. It is demonstrated that, at the wavelength of 1310 nm, the x-polarized mode and the y-polarized mode are separated when the propagation distance is 2.481 mm.

In this paper, we show experimentally that a pair of signal wave and idler wave bands is generated by four-wave mixing, and a pair of optical solitons and dispersion wave bands is induced by intrapulse Raman scattering and non-soliton radiation, and we also observe the power saturation phenomenon of the photonic crystal fiber (PCF) by using the incident femtosecond pulses in normal dispersion region away from the zero-dispersion wavelength of the PCF. The dispersion and nonlinear characteristics of the PCF are studied by the finite element method. The possible positions of the signal wave band and the idler wave band that is generated in the fiber satisfying the phase-matching condition are simulated by four-wave mixing phase matching, the results are in good agreement with the experimental results and show that even the pump laser pulse in the normal dispersion region can also produce the PCF four-wave mixing and optical solitons effects. In the present study it also revealed that the four-wave mixing experiment is generated by the fourth-order dispersion parameter β4, and the origins of optical solitons and dispersion wave bands generation are further explained.

This paper presents a theoretical study on a photonic crystal fiber plasmonic refractive index biosensor. The proposed photonic crystal fiber sensor introduces the concept of simultaneous detection with the linearly polarized and radially polarized modes because the sensing performance of the sensor based on both modes is relatively high, which will be useful for selecting the modes to make the detection accurately. The sharp single resonant peaks of the linearly polarized mode and radially polarized mode, are stronger and more sensitive to the variation of analyte refractive index than that of any other polarized mode in this kind of photonic crystal fiber. For linearly polarized mode and radially polarized mode, the maximum sensitivities of 10448.5 nm per refractive index unit and 8230.7 nm per refractive index unit can be obtained, as well as 949.8 and 791.4 for figure of merits in the sensing range of 1.33–1.45, respectively. Compared with the conventional Au-metalized surface plasmon resonance sensors, our device is better and can be applied as a biosensor.

A kind of lead silicate Photonic crystal fiber (PCF) has been proposed in this paper. The dispersion characteristic of this SF57 PCF are studied by the finite element method. The reasults demonstrate that the PCF presents all-normal dispersion profiles in the visible and infrared spectral regions. We use an adaptive split-step Fourier method to study the propagation of the 1550 nm and 150 fs laser pulse in the PCF .The resulting spectral profiles are extremely flat from 1300 nm to 1900 nm and with excellent stability and coherence properties.

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.

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 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.

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.

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.

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 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.

In this paper a square-lattice photonic crystal fiber with gradually increasing air-holes in a silica matrix has been put forward for the first time. The model field, dispersion, birefringence and confinement loss of the fibre fundamental mode are simulated by multipole method. It is found that low confinement loss can be realized under condition of fewer rings of air holes. Simulation shows that birefringence and dispersion of this square-lattice PCF are dominated by inner-ring air holes in the fibre. The simulation results of this paper are highly instructive for the fabrication of birefringent photonic crystal fibers.

The dispersion compensating property in photonic crystal fibers (PCFs) is simulated with a vectorial effective=index approach in this paper. It is found that the dispersion, dispersion slope, and Kappa parameter of PCFs can be designed neatly by changing the air hole size and the pitch in PCFs cladding. We can obtain PCFs with large absolute value of normal dispersion and negative dispersion slope at the wavelength of 1.55μm.Conventional communication nonshifted single-mode fibers (G652) and nonzero-dispersion shifted fibers (NZ-DSF,G655) can be compensated efficiently at wavelengths around 1.55μm low-loss optical communication window. It is demonstrated that there are huge potentials in designing dispersion compensating PCFs.

It Is reported that the supercontinuum spectrum can be generated in holey microstructure fibers by femtosecond laser pulses with a 800nm center wavelength. Broadband continua extending from 440 to 890nm are generated in holey microstructure fibers. Based on the theory of scalar approximation, the effective refractive index of the cladding and effective area for the fundamental space-filling mode and chromatic dispersion of fibers are calculated. It is found that the holey microstructure fibers have specifically the ability of controlling dispersion and waveguide property.The mechanism of supercontinuum generation in holey microstructure fibers is explicated preliminarily. The theoretic analysis is in good accodance with the experimental result.It is considered that supercontinuum broadband spectrum can be generated in holey microstructure fibers even if their cladding constitutes of random gas-line.

The dispersions of the fundamental cladding mode in photonic crystal fibers(PCFs)are computed with a vectorial effective index approach in this paper. By comparing with the results obtained from biorthonormal-basis method or scalar effective method,it is found that the results of this paper are in accordance with that obtained from the biorthonormalbasis method, and that the scalar effective method is a good approximation at a lower air-filling fraction or higher normalized wave-number A/λ. For high accuracy at larger air-filling fraction or lower normalized wave-number A/λ,it is necessary to consider the vectorial method. The relation between effective index of cladding and microstructure of PCFs is discussed. The computation and analysis in this paper can provide a theoretic reference for designing of PCFs.

A random distributed microstructure fiber in which strong asymmetry was introduced around a puresilica core was reported. Femtosecond laser pulses with duration of 35?fs from a Ti:sapphire laser oscillator were coupled into this fiber, and then periodic color rings were observed from the side of the fiber when the supercontinuum light propagated along the fiber. We attributed this phenomenon to the polarization beating of the supercontinuum light in this highly birefringent microstructure fiber. Measurement showed that the fiber had a beat length of approximately 1?mm at a central wavelength of 600?nm, which is in good agreement with the result of calculation. A new method is proposed to measure the beat length directly in a highly birefringent microstructure fiber.

We report supercontinuum (SC) generation in a lead silicate SF57 photonic crystal fiber by using a 1550 nm pump source. The effective nonlinear coefficient of the SF57 fiber is simulated to be 111.5 W?1centerdotkm?1 at 1550 nm. The fiber also shows ultraflat dispersion from 1700 nm to 2100 nm. Our results reveal that with an increase of the average power of the incident pulse from 10 mW to 90 mW, the SC of the SF57 photonic crystal fiber is generated from 1300 nm to 1900 nm with high stability and without significant change in spectral broadening. Refereed/Peer-reviewed