Optical properties of liquid-filled microstructured fiber with glass core

Dependence of the optical properties of a microstructured (holey) fiber with a silica glass core on the refractive index of a liquid that fills the channels in the cladding has been studied. Optimum conditions ensuring a single-mode regime, high degree of the interaction of radiation with the liquid, and low losses are determined for the fiber with a silica glass core and a microcapillary structure geometry parameter of d/Λ = 0.9.     

Study of birefringence of elliptical core photonic crystal fiber using Mathieu function

The birefringence of the elliptical core photonic crystal fiber with circular pores in the cladding has been studied by using higher order Mathieu functions. It is observed that the birefringence decreases with decreasing wavelength. Calculated results also indicate the sensitivity to the radius of the pores in the cladding. High birefringence up to 0.0079 is obtained. The efficacy of this proposed method is proved by comparing the results.     

Embedded multicore hollow fiber with high birefringence

We fabricate and demonstrate a hollow fiber with multiple embedded cores (MCHF) based on a modified "suspended core-in-tube" preform technique. Its birefringence properties are controlled by the MCHF core's ovality, which could be controlled by the applied pressure and drawing temperature in the MCHF preform. An in-fiber Mach-Zehnder interferometer with 90.38% visibility is built by fuse-tapering a single-mode fiber to the MCHF, and the splice loss is less than 2 dB. We expect that the proposed MCHF has some potential applications in in-fiber interferometers without the polarization-induced fading problem and in the biosensing area.     

Polarization properties of fiber lasers with twist-induced circular birefringence

We have experimentally observed and theoretically analyzed the polarization properties of fiber lasers with twist-induced birefringence. Twisting a fiber induces the circular birefringence of a fiber laser cavity, and this birefringence reduces the effects of intrinsic linear birefringence on the polarization properties of fiber lasers. The frequencies of their polarization eigenmodes coincide with each other gradually as the twist rate increases, and the directions of polarization eigenmodes deviate from the birefringence axis at a much larger twist rate than the magnitude of intrinsic linear birefringence. We describe the successful experimental results for Nd and Er fiber lasers.     

Effects of hydrostatic pressure on phase and group modal birefringence in microstructured holey fibers

We calculated the sensitivity of phase (dB/dp) and group (dG/dp) modal birefringence to hydrostatic pressure versus wavelength in two birefringent holey fibers of different construction, where B is the phase modal birefringence, G is the group modal birefringence, and p is the pressure applied to the fiber. The contributions of the geometrical effects that were related only to deformation of the holey structure and the stress-related contribution to the overall pressure sensitivities were analyzed separately. Our results show that these two factors decrease the phase modal birefringence in both structures, which results in negative signs of dB/dp and dG/dp. Furthermore, we demonstrate that the geometrical effects are much weaker than the stress-related effects and contribute only a few percent to the overall pressure sensitivity.     

Improving of high birefringence photonic crystal fiber with low confinement loss using small elliptical air holes in the core region

In this paper, a novel design double lattice photonic crystal fiber is proposed for achieving both high birefringence and low confinement loss. In this structure, circular air holes are arranged as octagonal lattice in the cladding and elliptical as rectangular lattice in the core region. Numerical results illustrate that the birefringence in such fibers is determined not only by the double lattice but also the changing of the shape and the arrangement of the air hole in the first inner rings of the cladding. The birefringence property and confinement loss are studied by employing the finite difference time domain method with transparent boundary condition. The numerical results demonstrate that the maximal birefringence and lowest confinement loss of our optimized structure PCF at the excitation wavelength of λ = 1550 nm can be achieved at 5.16 × 10^?2 and 0.003 dB/km, respectively.     

Dispersion control with use of long-period fiber gratings

Chirped long-period fiber gratings are analyzed for management of dispersion in optical fiber communications systems. A ray model is used to derive simple analytic expressions that describe the transmission, chromatic delay, and dispersion properties of chirped long-period fiber gratings. A numerical model based on coupled-mode theory is used to verify the accuracy of the analytic expressions and explore design issues of the chirped long-period grating. With certain reasonable restrictions, chirped long-period gratings are found to be a viable and desirable alternative to existing dispersion compensation techniques.     

Effect of birefringence on the bandwidth of noise-like pulse in an erbium-doped fiber laser

We report on the generation of superbroad spectrum bunched noise-like pulses from a passively mode-locked erbium-doped fiber laser, in which the cavity is made of purely anomalous dispersion fibers. The maximum 3 dB spectral bandwidth of the pulse is about 98 nm. We show numerically that the superbroad spectrum of the pulse is caused by the fiber birefringence.     

液芯有机光纤的研制

研制出了液态有机光纤.结果表明,有机溶液的拉曼光谱与普通样品池的方法相比,其强度增加102倍以上.     

一种高双折射低限制性损耗光子晶体光纤设计

本文设计了一种适用于长距离光纤通信的新型光子晶体光纤。该光纤包层内椭圆形和圆形空气孔呈交错排列,纤芯两侧为两个小椭圆空气孔。利用有限元分析方法对所设计光纤的传输特性进行分析并对其结构进行了优化,确定了最佳结构。结果表明,波长为1550 nm时,此新型光子晶体光纤在最佳结构下可提供高达3.51×10^-2的高双折射和低至1.5×10^-9 dB/m的限制性损耗。与现存的引入椭圆形空气孔的光子晶体光纤相比,本文中的光子晶体光纤的双折射系数有较大提高,限制性损耗系数降低了5个数量级。另外,本文还详细研究了光子晶体光纤的色散随光子晶体光纤结构的变化以及其布里渊增益特性,并分析了其可制造性。基于其高双折射和低限制性损耗特性,此种光纤可应用于长距离光纤通信系统。     

Thermal stress induced birefringence in double cladding fiber with non-circular inner cladding

Thermal stress induced birefringence due to the thermoelastic difference between the outer cladding and the non-circular inner cladding of a double cladding fiber (DCF) is theoretically investigated. A modified slab model is proposed to estimate the influence of the outer cladding on the birefringence property of the core. Numerical simulation is carried out to investigate the thermoelastic and geometric contributions of the cladding to thermal induced birefringence in rectangular and D-shaped ytterbium-doped DCFs. The thermoelastic relations deduced in the modified slab model are also qualitatively verified. Research shows that the influence of the outer cladding on the thermal-induced birefringence in DCF varies greatly depending on the choice of outer cladding materials, inner cladding shapes and temperature variation.     

Gas Raman sensing with multi-opened-up suspended core fiber

Gas sensing and fluid-guiding response properties of a suspended core fiber Raman analyzer with side-opened and strut microfluid-guiding array are explored. A Raman sensing model is introduced for effective mode area optimization and normalized intensity overlap enhancement between Raman sensing light and analyte. Calculations predict that there is a trade-off between the overlap and the effective mode area, while the optimal trade-off depends on the refractive index of the background material, core diameter, and strut's thickness. Furthermore, the multi-opened-up structure ensures a fast gases diffusing into/out of each hole for real-time Raman sensing. Simulation results confirm a limited gas sensing response time of less than 6 s could be feasible and, thus, a new approach to real-time gas sensing applications is identified.     

Transmission of linearly polarized light through a single-mode fiber with random fluctuations of birefringence

A simple theoretical formalism is developed to describe the effect of transmission on linearly polarized light through a fiber with random fluctuations of birefringence. We conclude that, for any optical fiber that does not experience polarization-dependent gain or loss, there exist two orientations for linearly polarized light input into the optical fiber that will also exit the fiber linearly polarized. We report experimental results that verify this prediction and also investigate its practical implications and limitations; in particular we investigate the stability of these linearly polarized output states in laboratory conditions.     

Wavelength-spacing switchable multiwavelength fiber lasers based on nonlinear polarization rotation with cascaded birefringence fibers

A wavelength-spacing switchable multiwavelength erbium-doped fiber lasers incorporating a highly nonlinear fiber (HNLF) based on nonlinear polarization rotation (NPR) has been demonstrated. The intensity-dependent transmission effect originating from NPR ensures room-temperature multi-wavelength lasing, which is further self-stabilized by the four-wave mixing in the HNF. Moreover, the equivalent Lyot birefringence fiber filter with two cascaded birefringence fibers makes the wavelength spacing switchable depending on the effective length of the birefringence fiber. The experimentally obtained multiwavelength outputs agree well with the simulation filter transmission spectra.     

Use of retinal nerve fiber layer birefringence as an addition to absorption in retinal scanning for biometric purposes

We built a device sensitive to the birefringence of the retinal nerve fiber layer for biometric purposes. A circle of 20 degrees diameter on the retina was scanned around the optic disk with a spot of light from a 785 nm laser diode. The nonbirefringent blood vessels indenting or displacing the retinal nerve fiber layer were seen as "blips" in the measured birefringence-derived signal. For comparison, the reflection-absorption signature of the blood vessel pattern in the scanned circle was also measured. The birefringence-derived signal proved to add useful information to the reflectance-absorption signature for retinal biometric scanning.     

Intermodal interferometer for strain and temperature sensing fabricated in birefringent boron doped microstructured fiber

We present a compact in-line fiber interferometric sensor fabricated in a boron doped two-mode highly birefringent microstructured fiber using a CO(2) laser. The intermodal interference arises at the fiber output due to coupling between the fundamental and the first order modes occurring at two fiber tapers distant by a few millimeters. The visibility of intermodal interference fringes is modulated by a polarimetric differential signal and varies in response to measurand changes. The proposed interferometer was tested for measurements of the strain and temperature, respectively, in the range of 20-700?°C and 0-17?mstrain. The sensitivity coefficients corresponding to fringe displacement and contrast variations are equal respectively for strain -2.51 nm/mstrain and -0.0256 1/mstrain and for temperature 16.7 pm/°C and 5.74×10(-5) 1/°C. This allows for simultaneous measurements of the two parameters by interrogation of the visibility and the displacement of interference fringes.     

Electromagnetic field calculations for an irregularly shaped,near-spheroidal particle with arbitrary illumination

A spheroidal coordinate separation-of-variables solution has been developed for the determination of the internal, near-surface, and far-scattered electromagnetic fields for irregularly shaped elongated (prolatelike) and irregularly shaped flattened (oblatelike) particles with arbitrary monochromatic illumination. Calculated results are presented, for both plane-wave and focused-Gaussian-beam illumination, which demonstrate the effects of particle geometry on the internal, near-surface, and far-scattered-field distributions.     

碳纳米管的分散性研究及其对复合电纺纤维的影响

将多壁碳纳米管(MWNTs)在硝酸中回流纯化,使用不同类型的表面活性剂将纯化后的MWNTs功能化分散,再将其加入到聚乙烯醇(PVA)和聚氧化乙烯(PEO)物理共混纺丝溶液中进行静电纺丝。利用扫描电子显微镜(SEM)、红外光谱仪(IR)、X衍射射线仪(XRD)和分光光度计等对纯化和功能化分散的MWNTs以及得到的超细纤维进行表征。结果表明,通过硝酸回流纯化处理,MWNTs的杂质被去除,晶格结构变得更加完整。在超声波作用下,十二烷基硫酸钠使纯化后的MWNTs在水溶液中具有较好的分散稳定性。进行功能化分散的MWNTs的加入使静电纺超细纤维的平均直径减小。     

High birefringence photonic crystal fiber with a complex unit cell of asymmetric elliptical air hole cladding

High birefringence induced by elliptical air hole photonic crystal fibers (EHPCFs) is analyzed numerically using the finite-element method. Statistical correlations between the birefringence and the various parameters are obtained. We found that the complex elliptical air hole is better than that of a circular one to obtain high birefringence in photonic crystal fibers. Our suggested structures can considerably enhance the birefringence in EHPCFs and show that the birefringence can be as high as 1.1294 x 10(-2), which is higher than the birefringence obtained from conventional step-index fiber (5 x 10(-4)), circular air holes PCF (3.7 x 10(-3)), and elliptical hollow PCF (2.35 x 10(-3)).