Designing Ultra-High-Birefringent Photonic Crystal Fibers with Circular Air Holes in the Cladding

Abstract

This article reports a new air-silica photonic crystal fiber structure of high birefringence (~10^?2). The birefringence is due to large axial anisotropy introduced in the fiber geometry by a preferred arrangement of circular air holes of different sizes in the cladding structure along orthogonal directions. A series study of birefringence and cut-off properties of the fiber that leads to optimization of geometrical parameters toward maximized birefringence achievable in the single-mode regime through this micro-structure is provided. Also, other inherently related modal properties of the fiber and the stack design toward preform realization are investigated. The findings should be useful in realizing high-performance high-birefringence fiber.     

一种高双折射光子晶体光纤的模式特性分析

应用全矢量频域有限差分法,分析了所提出的一种高双折射光子晶体光纤的模式截止、损耗、模场半径及数值孔径等特性.数值模拟结果表明,通过设置合适的结构参量,可使这种高双折射光子晶体光纤在保持模式双折射为10-3量级的前提下,能够在600～1800 nm波长范围内保持单模传输,并且限制损耗可低于10-4dB/m量级,同时还可以获得较大的数值孔径,因而聚光能力增强,此外,通过采用高斯曲线拟合基模的模场分布,得到的模场半径与实际模场半径吻合得很好.     

Influence of the polarization mode dispersion on the propagation of ultrashort optical pulses in single-mode fiber lightguides with very weak linear birefringence and random inhomogeneities

We consider the influence of the polarization mode dispersion, which is stipulated by the presence of random inhomogeneities in single-mode fiber lightguides, on the propagation of ultrashort optical pulses in the fiber communication lines with very weak linear birefringence. Evolution of the envelope of ultrashort optical pulses and their spectra as functions of the length of a single-mode fiber lightguide with very weak linear birefringence and random inhomogeneities are obtained by the method of mathematical simulation. An increase in the pulse duration is shown to be proportional to the square root of the length of a single-mode fiber lightguide. The numerical-simulation results are compared with the results of experimental measurements of the polarization mode dispersion.     

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。     

Reflectometric measurement of birefringence rotation in single-mode optical fibers

We present a novel reflectometric technique for the measurement of orientation and modulus of the linear birefringence vector in single-mode optical fibers. The technique provides information also on circular birefringence, although this component, if present, appears as a rotation of the linear birefringence. A detailed theoretical analysis is reported and validated by experimental results.     

Stress-induced birefringence in microstructured optical fibers

We present a numerical study of stress-induced birefringence in microstructured optical fibers (MOFs), using a finite-element method. MOFs under lateral forces and twists are considered separately. Compared with that in standard single-mode optical fibers, stress-induced linear birefringence in MOFs under a lateral force is reduced with increasing air-hole size, whereas twist-induced circular birefringence in MOFs is enhanced when the air-hole size is small.     

Mathematical modeling of random coupling between polarization modes in single-mode optical fibers: XII. Dependence of the zero drift in fiber ring interferometers in orthogonal polarization modes on the range of temperature variation in an optical fiber

Temperature dependences of the zero drift in a fiber ring interferometer (FRI) without a polarizer in the presence of random inhomogeneities in a single-mode optical fiber in the FRI loop are obtained by numerical simulation. The results are compared with known experimental data. It is shown that FRIs using a superluminescent diode as a source of nonmonochromatic radiation and a loop made of a single-mode optical fiber with weak linear birefringence can find application as low-accuracy fiber-optic gyroscopes and FRIs with a loop made of a single-mode optical fiber with strong linear birefringence can be used as medium-accuracy fiber-optic gyroscopes.     

Novel single-mode and polarization maintaining photonic crystal fiber

In this paper, we present and propose a novel structure for improved birefringence and single-mode propagation condition photonic crystal fiber (PCF) in a broad range of wavelength. The birefringence of the fundamental mode and single mode property in such a PCF is numerically estimated by employing full vector finite element method (FVFEM) and anisotropic perfectly matched layers (APML). The simulation results illustrate that we can achieve a high birefringence and perfect single-mode condition by employing silica-filled into one-line elliptical air holes parallel to x-axis and rotated by an angle. Obviously, the proposed PCF is quite useful for optical devices.     

Elliptical-hole photonic crystal fibers

We study the dispersive properties of photonic crystal fibers (PCF's) with elliptical air holes. The unusual guidance of PCF leads to novel behavior of the birefringence, group-velocity walk-off, and dispersion parameters, including the possibility of zero walk-off with high birefringence in the single-mode regime. A number of these effects are closely tied to the underlying radiation states of the air-hole lattice.     

Enhanced soliton robustness to polarization mode dispersion by using degenerate four-wave mixing

We propose a new method to strengthen the nonlinear pulses robustness to polarization mode dispersion through modulating the breath oscillation behavior of two principal polarization components of optical pulses. The optical realization of the breath behavior modulation is based on the degenerate four-wave mixing effect in fibers with high birefringence. The breath intensity increases and the periodical breath oscillation distances shorten in the process of breath behavior modulation. It is proved that the breath-modulated pulses have stronger adaptive abilities to polarization mode dispersion than common solitons when propagating in conventional single-mode fibers with random birefringence.     

光纤拉曼放大器中增益的偏振相关特性研究

提出了一种改进的、可用于计算偏振相关拉曼增益的光纤拉曼放大器的非线性耦合波方程。建立了单模双折射光纤拉曼增益的数学模型,分析了线偏振抽运光以与光纤快轴成45°激励的单模双折射光纤拉曼放大器模型与实际具有随机双折射的光纤拉曼放大器的拉曼增益偏振相关特性的等价性。基于上述模型,提出了一个可定量表征单模光纤偏振模色散统计特性的拉曼增益偏振相关因子,用以替代常规的光纤拉曼放大器非线性耦合波方程中的偏振相关因子。计算结果与已报道文献的实验数据非常吻合。同时对抽运增益在同向和反向抽运方式下截然不同的增益偏振相关特性给出了合理的解释。     

Effects of induced birefringence on Brillouin dynamic gratings in single-mode optical fibers

The effects of linear or circular birefringence on the operation of Brillouin dynamic grating are experimentally investigated where the birefringence is induced by bending or twisting a single-mode optical fiber, respectively. Experimental results show that the reflection spectrum of the dynamic grating in a 5 m fiber is split by bend-induced linear birefringence with the separation frequency dependent on the bending diameter, matching well with the theoretical model. Meanwhile, the spectrum is almost immune to circular birefringence induced by twist with a rate of up to 24 turns/m.     

Statistical characterization of fiber random birefringence

The statistical properties of the random birefringence that affects long single-mode fibers are experimentally evaluated by means of a polarization-sensitive optical time-domain reflectometry. The measurements are in good agreement with theoretical predictions and show, for what we believe is the first time, that the components of the local birefringence vector are Gaussian random variables.     

单模光纤中线偏振皮秒脉冲光的光致多脉冲现象的新解释

结合单模光纤的本征线性双折射与非线性双折射效应，利用二偏振分量的耦合方程对单模光纤中线偏振皮秒脉冲光的光致多脉冲现象作出了解释，得到的计算结果与实验符合得很好。     

Stress distribution and birefringence measurement in double-clad fiber

Modal birefringence and stress distribution measurements in a single-mode double-clad Nd⁺³-doped fiber are reported. The contribution of different mechanisms, such as stress-induced birefringence, bending and core ellipticity, to the total birefringence is determined for a fiber wound onto a drum. A stress distribution pattern in the cross-section of the fiber is presented. The stresses are shown to be applied to a fiber core along the cladding minor axis.     

Evaluation of the residual birefringence of single-mode erbium-doped silica fibers

We present a nondestructive method that allows the spectral birefringence characterization of single-mode erbium-doped fibers within the amplification band. Using the same optical set up and the predicted polarization eigenmodes, the quality of the results has been verified. The results obtained for three commercial erbium-doped fibers with different erbium concentrations are shown. For two of them, the values measured for the elliptical birefringence shift, for different signal wavelengths, from having a dominant circular component to exhibit a dominant linear component.     

Propagation of nonmonochromatic radiation in isotropic single-mode fibers with weak induced anisotropy

The change in the degree of polarization of nonmonochromatic radiation in isotropic single-mode fibers with a large h-parameter and small birefringence is examined.     

Phase-matched four-photon mixing processes in birefringent fibers

We describe several new phase-matching processes for four-photon mixing in polarization-preserving birefringent fibers. The frequency shifts and polarization conditions of the waves involved in this nonlinear interaction are specified for a single-mode fused silica birefringent fiber. Our calculations include the effect of dispersion in the birefringence of the fibers.     

Polarization decorrelation in optical fibers with randomly varying elliptical birefringence

Polarization decorrelation in single-mode fibers with randomly varying elliptical birefringence is studied. It is found that the effects of ellipticity on the polarization decorrelation length depend on the relative sizes of the beat length and the autocorrelation length of the birefringence fluctuations in the fiber. However, the evolution of the differential group delay remains unaffected by ellipticity.     

单模光纤的磁光效应

本文利用琼斯(Janes)矩阵叙述了单模光纤磁光效应的理论,导出了既具有双折射又具有法拉第效应的琼斯矩阵形式,并利用Mueller矩阵导出电流传感器系统输出光强与法拉第旋转角之间的关系.