Equilateral pentagon polarization maintaining photonic crystal fibre with low nonlinearity

A new pentagon polarization maintaining photonic crystal fibre with low nonlinearity is introduced. The full vector finite element method was used to investigate the distribution and the effective area of modal field, the nonlinear properties, the effective indices of two orthogonal polarization modes and the birefringence of the new PM-PCF effectively. It is found that the birefringence of the new polarization maintaining photonic crystal fibre can easily achieve the order of 10^-4, and it can obtain higher birefringence, larger effectively mode-field area and lower nonlinearity than traditional hexagonal polarization maintaining photonic crystal fibre with the same hole pitch, same hole diameter, and same ring number. It is important for sensing and communication applications, especially has potential application for fibre optical gyroscope.     

Design and fabrication of Panda-type erbium-doped polarization-maintaining fibres

To obtain the stable operation of erbium-doped fibre laser, the simple and ideal technology is adopted by use of the erbium doped polarization maintaining fibre (EDPMF). The design criteria of the Panda-type EDPMF are presented, which take into account the cutoff wavelength, mode field diameter, modal birefringence and background loss. Four groups of optimum structural parameter combinations are determined in terms of the design criteria. Two kinds of the Panda-type EDPMFs are selected to be fabricated. The fabrication process and the parameter control of the Panda-type EDPMFs are presented in detail. Their refractive index profiles, birefringence and absorption spectra are experimentally investigated. The absorption coefficient of the EDPMF, whose core is co-doped with Bi, Ga, Al and Ge, is about 57.9dB/m at 1.53\mum. Co-doping Bi, Ga and Al can greatly increase the erbium concentration in the silica-based fibre. The high birefringence is obtained for the Panda-type EDPMF. The group birefringence of the EDPMF, whose outer cladding diameter is 125\mum, is about 4.8\ti10^-4.     

Analysis of bias thermal stability of interferometer fiber-optic gyroscope using a solid-core polarization-maintaining photonic crystal fiber

Bias thermal stability of a fiber-optic gyroscope using polarization-maintaining photonic crystal (PM-PCF) was studied. The thermal sensitivity of birefringence in PM-PCF and polarization cross talking in fiber coil was measured. Using an OCDP method, the polarization cross talking causing phase error of the fiber-optic gyroscope (FOG) was analyzed. The contrast experiment result of the FOGs with the PM-PCF coil and PMF coil showed that using PM-PCF instead of PMF can improve the FOG’s bias thermal stability by about 50 %.     

Birefringence sensitivity to temperature of polarization maintaining photonic crystal fibers

In this paper, we investigate the birefringence of polarization maintaining photonic crystal fibers (PM-PCFs) under thermal effect. Modeling and simulation of PM-PCFs under thermal effect are conducted. Birefringence in a PM-PCF as a function of the temperature is measured experimentally. The experimental results are in agreement with theoretical calculation, and show that the relative temperature dependent birefringence coefficient of the PM-PCF, dΔn/dT/Δn, is 2.93×10^?5/°C, which is typically ～35 times less than that of conventional panda fibers. The insensitivity of polarization properties in PM-PCFs to temperature is demonstrated. These findings have important benefits in fiber optic systems and sensors, especially in fiber optic gyroscopes (FOG) where it translates into a lower polarization error and thus a higher measurement precision.     

Temperature dependence of the PER in PM-PCF coil

A piece of domestic polarization-maintaining photonic crystal fiber (PM-PCF, 964 m in length) is made into a fiber coil, and its polarization extinction ratio (PER) is measured in a temperature range of -45- 80 C before and after PM-PCF is wound and solidified. A fiber coil made of commercial panda PM fiber (PMF) is also fabricated and measured for comparison. Our experiments show that the PER variation of the PM-PCF coil (2.25 dB) is far smaller than that of the panda PMF coil (10 dB) in the whole temperature range because PM-PCF is intrinsically insensitive to the temperature variation and stress in the fiber coil induced by the winding and solidification process. This characteristic is important for the real application of PM-PCFs in temperature-insensitive fiber interferometers, fiber sensors, and optical fiber gyroscopes.     

基于高双折射光子晶体光纤环镜的全光纤平顶梳状滤波器(英文)

A novel all-fibre flat-top comb filter based on a high birefringence photonic crystal fibre loop mirror is proposed and demonstrated. We simulate theoretically its output spectra and experimentally realize a flat-top output with a high extinction ratio. Compared to filters consisting of the conventional Panda polarization maintaining fibre, filters based on a high birefringence photonic crystal fibre loop mirror have better temperature stability. This kind of filter can be expected to be used widely in Wave...     

基于高双折射光子晶体光纤环镜的全光纤平顶梳状滤波器

A novel all-fibre flat-top comb filter based on a high birefringence photonic crystal fibre loop mirror is proposed and demonstrated. We simulate theoretically its output spectra and experimentally realize a flat-top output with a high extinction ratio. Compared to filters consisting of the conventional Panda polarization main- taining fibre, filters based on a high birefringence photonic crystal fibre loop mirror have better temperature stability. This kind of filter can be expected to be used widely in Wavelength-division-multiplexing（WDM） systems in the future.     

Phase and group modal birefringence of an index-guiding photonic crystal fibre with helical air holes

In this paper, we propose a novel photonic crystal fibre (PCF) with high phase birefringence and very low group birefringence. It is composed of a solid silica core and a cladding with helix-pattern air holes. Using a full-vector finite-element method, we study the phase and group modal birefringence of such PCF at various air-hole sizes, pitches and wavelengths. Owing to this innovative structure of air holes, a high phase to group modal birefringence rate is obtained. Its phase modal birefringence is as large as 10⁻⁴ magnitude; however, the group modal birefringence of this PCF is at 10⁻⁷-10⁻⁶. The phase birefringence is 2 orders of magnitude larger than group birefringence over a broad wavelength span, which means that the light with different polarization and effective index has almost a same group velocity. As a result, the group modal birefringence that closely relates to the polarization modal dispersion is negligible.     

重频应用下等离子体电光开关热退偏损耗分析

 基于有限元数值方法,给出电光晶体KDP在高平均功率激光负载下温度场分布和应力场分布。在此基础上得到了折射率随温度变化、电光系数随温度变化、及应力双折射引入的退偏损耗。数值模拟显示：电光系数随温度变化和应力双折射是引起开关退偏损耗的主要因素。当入射激光平均功率为40 W、辐照时间为420 s时,KDP晶体最高温度为38.43 ℃,电光系数随温度变化及应力双折射引入的最大退偏损耗分别为2.38%和4.04%。实验测量了应力双折射导致的退偏损耗,实验结果和理论结果符合较好。     

Analysis of thermal property in hollow-core polarization maintaining photonic crystal fibers

We study the thermal-induced variance of effective refractive indices (ERIs) and birefringence in several kinds of polarization maintaining fibers (PMF) and carry out numerical simulations by utilizing the finite element method (FEM). Responses under varying temperatures in these fibers are analyzed thoroughly. According to our computational results, hollow-core photonic crystal fibers (HC-PCFs) exhibit much more stable temperature-dependent ERIs and birefringence among these PMFs.     

高数值孔径双芯光纤的双折射研究

具体分析了具有高数值孔径的双芯光纤的双折射特性。首先利用超格子正交函数法和耦合模理论分析了双芯光纤的几何双折射,并将两种方法计算的几何双折射进行了比较分析。数值计算结果表明双芯光纤在两纤芯非常接近的情况下,几何双折射仍较小,只能到10-5量级。利用超格子正交函数法计算了双椭圆芯光纤的双折射,改变结构参量可使几何双折射达到10-4量级。高的数值孔径需要高的掺锗量,理论上分析了高数值孔径时双芯光纤功率集中区域的应力双折射,应力双折射接近10-4量级。设计制作出了具有良好保偏性能的双芯掺铒光纤,测试、分析了它的几何参量和折射率分布;双芯光纤双折射系数达到了8.4×10-5。双芯掺铒光纤可以作为保偏掺铒光纤,应用到制作具有稳定的单一偏振态输出的光纤激光器。     

Design of temperature-compensated elliptical core birefringent fibres

A new type of temperature compensated birefringent optical fibre is reported. The proposed fibre is designed aiming to minimising the stress birefringence by matching the thermal expansion coefficients between the core and the cladding and maximising the geometric birefringence by increasing the refractive index difference between the core and the cladding and increasing the core ellipticity. The optimum dopant concentrations satisfying the requirements is determined by solving a set of nonlinear algebraic equations. The fibre aimed at satisfying the requirements is fabricated and characterised. The experimental results show that the temperature dependence of the fibre birefringence is 6.97 × 10⁻⁴/°C. Methods of further improvement of the compensation are discussed and an alternative dopant material, titanium, for the improvement is suggested.     

A novel photonic crystal fiber with near-circular mode field distribution for the application of fiber optic gyroscope

In this letter, we reported on a polarization-maintaining photonic crystal fiber (PM-PCF) with near-circular mode field distribution. The modal field distribution of the proposed PM-PCF is near-circular, which enhanced the mode field compatibility between PM-PCFs and traditional polarization-maintaining fibers (PMFs). And the birefringence of the novel PM-PCF can easily achieve the order of 10⁻³–10⁻², which is at least 1–2 order of magnitude higher than that of commonly used Panda or Bow-tie PMFs. Additionally, the diameter of this PM-PCF is much smaller than traditional PM-PCFs. It can well satisfy the application of fiber optic gyroscope (FOG) which need high polarization-maintaining, high-precision and miniaturization.     

双折射光纤环镜应变灵敏度优化研究

灵敏度是衡量传感器的重要指标之一, 基于双折射光纤环镜(PM-FLM)应变传感器灵敏度理论模型,通过数值模拟与实验的方法,在不增加系统复杂性的前提下,通过自身性能优化PM-FLM轴向应变灵敏度;同时研究了双折射光纤(PMF)长度对PM-FLM轴向应变灵敏度的影响。研究结果表明：对于相同PM-FLM,可以选择长波长监测点优化轴向应变灵敏度;对于双折射率相同的PM-FLM,可以选择双折射应变系数较大的PMF优化轴向应变灵敏度。对于双折射应变系数相同的PM-FLM,可以选择双折射率较小的PMF优化轴向应变灵敏度。PM-FLM传感器应变灵敏度与PMF长度无关。     

波长间隔可调的可开关双波长掺铒光纤激光器

对两种波长间隔可调的可开关双波长掺铒光纤激光器结构进行了实验研究。一种结构应用保偏光纤中布拉格光栅作为波长选择器件，另一种结构则利用侧向压力下的常规单模光纤光栅作为波长选择器件。两种结构均利用了光纤光栅的双折射特性。在室温下，通过调整偏振控制器的状态可使两激光器工作在稳定的双波长状态或在两单波长之间转换。通过改变加在光纤光栅上侧向应力的大小和方向，可有效控制双波长激射的波长间隔。     

Automatic fringe analysis of the induced anisotropy of bent optical fibres

A new theoretical model considering the refraction of the incident light beam by the fibre is suggested to determine the refractive index profile of bent optical fibres. This new model (slabs model) considering the cross section of the bent optical fibre consists of large number of slabs. The slabs model bases on the refraction of the incident beam by the fibre. The refractive index profile of the optical fibre cladding before bending obtained using the automated Fizeau interferometer with the aid of suggested model is compared with other models such as, the homogenous model and the multilayer model to verify the ability of this slab model. The refractive index profile of the bent optical fibre cladding is investigated using this suggested model. In addition, the new model is used to obtain the induced birefringence and the guiding parameters. The bending radius is recommended to be greater than 7.1 mm for the used optical fibre. The consideration of the refraction increases the accuracy of the results.     

Interferometric studies on the influence of temperature on the optical and dispersion parameters of GRIN optical fibre

Opto-thermal device attached to automate Fizeau interferometer is used to investigate the influence of temperature on opto-thermal properties of multimode graded-index (GRIN) optical fibre in the range from 27 to 54 °C. The effect of temperature on the refractive index profile of fibre is studied. The optical parameters and the opto-thermal coefficient of this fibre are determined. Also the variation of oscillation and dispersion energies, zero dispersion wavelengths, coupling efficiency, normalised frequency, number of propagation modes with the temperature and the material dispersion with the wavelength at different temperatures are calculated. Microinterferograms are given for illustration.     

Three methods for improving an axial strain sensitivity of polarization maintaining fiber loop mirror

Sensitivity is one of the important performances for sensor. Theoretical results show that we can choose a long wavelength monitoring point, a high strain dependent birefringence coefficient polarization maintaining fiber (PMF) and a low birefringence PMF to improve the axial strain sensitivity of PMF loop mirror, and experimental results show that the axial strain sensitivity has respectively been improved by 8.06, 30.73, and 22.26% by these methods. The advantage of these methods is to improve the axial strain sensitivity without increasing system complexity. These results help to improve the temperature, displacement, torsion, curvature and liquid level sensitivities of PMF loop mirror. These results can also be applied in photonic crystal fiber loop mirror.     

Polarization-dependent two-color dispersion wave generation and evolution in polarization-maintaining photonic crystal fiber

We investigate the effect of the polarization state of the input pulses on the visible emissions in the anomalous dispersion region of polarization-maintaining photonic crystal fiber (PM-PCF), by using ～100 fs pump pulses whose central wavelength (1064 nm) is close to the second zero dispersion wavelength (1100 nm) of the fiber, where the soliton fission mechanisms play an important role. The experimental results show that the phase-matching two-color dispersive wave emission, one at 582 nm and the other at 600 nm, is polarization-dependent and frequency shift results from the different dispersion characteristics along the two orthogonal principal axes of PM-PCF. Furthermore, it is observed for the first time that the variation of the linear input polarization angles in 45° region almost has no influence on the output spectral profiles, and the break variation of the output spectrum exists when the angle between the polarization of the linear incident pulse and the fast-axis or the slow-axis of PM-PCF is 45°, which are attributed to the coupling between the two polarization modes in high birefringent PM-PCF.     

偏振保持光纤的模式双折射

偏振保持光纤是单模光纤的一种特殊类型,其模式双折射与温度、芯和皮折射率差及椭圆度、热膨胀系数、光纤直径、弹性模量、泊松比、频率、波长、拉丝张力等诸多因素有关,对与偏振保持光纤模式双折射相关的上述因素进行分析,指出光纤模式双折射越高,光纤的偏振态保持就越好,为更好地设计新型保偏光纤或合理选择保偏光纤类型奠定了基础.