Polarization-dependent coupling in twin-core photonic crystal fibers

The polarization dependence of light coupling in photonic crystal fibers (PCFs) with sixfold symmetric dual cores and highly birefringent dual cores are numerically investigated. The characteristics of PCF-based couplers, such as coupling length, extinction ratio and form birefringence, are examined as functions of the air-hole size and pitch. The silica bridges between air holes take an important role in the energy transfer across the two cores. We believe that the mechanism of light coupling in PCF-based couplers is different from that of conventional waveguide couplers. The polarization dependent coupling can be reduced by adjusting the air holes around the cores of PCFs. On the other hand, the polarization dependent coupling can be enhanced by introducing high birefringence in the two cores.     

A novel polarization splitter based on the photonic crystal fiber with nonidentical dual cores

A novel polarization splitter based on photonic crystal fibers (PCFs) with two nonidentical cores is proposed. The two highly birefringent cores are vertically arranged to obtain polarization selective coupling. The horizontal polarization exchanges its energy between the two cores. However, the vertical polarization shows little coupling between the two cores. This is achieved in single-material glass waveguides for the first time to our knowledge. The PCF-based polarization splitter exhibits many advantages such as shorter length, high extinction ratio, and wide bandwidth over its counterparts.     

基于液体选择填充光子晶体光纤的波分解复用器研究

设计了一种基于液体选择填充三芯光子晶体光纤的1.31/1.55um波分解复用器。中间为缺失一个空气孔的普通二氧化硅纤芯,左右两纤芯填充了不同折射率的液体材料。根据光纤的消逝场耦合的模式理论,不对称相邻波导存在波长相关耦合。不同填充折射率的两纤芯与中间纤芯分别耦合,构成两个不同响应波长的光滤波器。通过选择合适光纤长度,可实现不同波长光的分离。采用全矢量有限元法分析了光纤的传输特性,讨论了填充不同折射率液体时波导间的模式耦合,得到了其匹配波长与耦合长度。基于光束传播法仿真发现,长度为4.88 mm的光纤能实现1.31/1.55 um波长光的解复用。     

A novel polarization splitter based on three-core photonic crystal fibers

A novel polarization splitter based on photonic crystal fibers(PCFs) with three cores of high birefringence is proposed.The 45o linearly polarized light is launched into a core.After a coupling length(about 1500 μm),the xand y-polarized light beams are separated into different cores.When the light is launched into another core,the xand y-polarized light from different cores can be obtained and the degree of separation can be also adjusted.The polarization splitter is highly flexible and adjustable.The lengt...     

Three-dimensional electromagnetic modeling of fiber-core effects onthe coupling characteristics of weakly fused tapered fiber-opticcouplers

Based on the full-wave formulations, which combine the finite element method add the boundary element technique, and the step-like approximation method, a three-dimensional (3-D) electromagnetic modeling approach is proposed in this work to investigate the fiber-core effects on the coupling characteristics of the weakly fused tapered couplers. We find the fiber cores have significant effects on the mode field patterns, coupling coefficients, and birefringence for the coupler with large normalized frequencies. The influence of the fiber cores on the coupling behavior for the real couplers, such as 3 dB power dividers, polarization beam splitters, and wavelength demultiplexing/multiplexing couplers, are also studied in 3-D view. It is found that the effects of fiber-cores in the weakly fused tapered couplers have to be considered for accurately modelling their coupling behavior, although the model with no core assumption can predict the trend of the coupling characteristics for the real couplers     

基于谐振耦合现象的三芯光子晶体光纤偏振分束器

设计了一种三芯光子晶体光纤(PCFs)偏振分柬器.利用光纤的谐振现象,实现了偏振状态的分离.当三芯光子晶体光纤中三个超模式的模式折射率满足一定条件时,将产生谐振现象.通过选择合适的光纤结构参数,可使某一偏振方向的光接近谐振条件,而另一偏振方向的光远离谐振条件.在光纤的输出端,由于耦合的程度不同,两个偏振光的功率集中在不同的纤芯区,从而达到分离偏振光的目的.应用有限元法(FEM)计算了三芯光子晶体光纤中的模式折射率,选择了合适的光纤结构参数.应用全矢量光束传播法(BPM)分析了这种光纤偏振分束器的性能.结果表明,在1.55 μm工作波长上,长度为1.039 mm的光纤即能实现偏振状态的隔离,隔离度达到-36.98 dB,隔离度<-11 dB的带宽可达到24 nm.     

Analysis of fiber-optic polarizing beam splitters consisting of fused-taper couplers

The characteristics of polarization splitting in fiber-optic couplers employing both nonbirefringent and birefringent fibers (PANDA fibers) are investigated. An analytical method that takes into account the cores, stress-applying parts, and stress birefringence in the coupling region is proposed. From comparison between the theory and experiments, the validity of the present analytical method is confirmed. It is shown that the length of the coupling region in birefringent-fiber polarizing beam splitters (BPBS) is several times shorter than that in nonbirefringent-fiber polarizing beam splitters (NPBS).     

Structural auto-optimization of integrated optical directional coupler polarization splitters and reflectors

The directional coupler is one of the most important devices in the field of integrated optics, from which other optical devices such as polarization splitters and reflectors are derived. In this paper, we present an autodesign method for polarization splitters and reflectors based on the beam propagation method and the golden section method, which can decrease the amount of computation greatly. Using this method, we analyze and discuss the influence of Ti-diffusion conditions on the structural optimization of polarization splitters and reflectors quantitatively. In addition, we have fabricated a series of polarization splitters and the experimental results are consistent with theoretical analysis.     

Analysis and Design of Photonic Crystal Fibers Based on an Improved Effective-Index Method

The modal characteristics of photonic crystal fibers (PCFs), with guiding cores consisting of one or seven missing airholes, are investigated with the finite element method and compared to those of step-index fibers (SIFs). To extend the applicability of the classical SIF theories to PCFs, the effective refractive index of photonic crystal cladding and the effective core radius of a PCF are studied systematically, based on simple physically consistent concepts. With the new effective cladding index and core radius of PCFs, the classical definition of the V parameter for SIFs is extended to PCFs, and a highly efficient approach based on the effective-index method is developed for the design of PCFs. The new design approach has been successfully employed to analyze the modal properties of PCF lasers with depressed-index cores and further tested by using it to effectively estimate the number of guided modes for PCFs with large cores     

Novel magnetic field sensor based on magnetic fluids infiltrated dual-core photonic crystal fibers

Novel magnetic field sensor based on magnetic fluids infiltrated dual-core Photonic Crystal Fibers (PCFs) is proposed in this paper. Inside the cross-section of the designed PCFs, the two fiber cores filled with magnetic fluids (Fe₃O₄) are separated by an air hole, and then form two independent waveguides with mode coupling. The mode coupling under different magnetic field strength is investigated theoretically. A novel and simple magnetic field sensing system is proposed and its sensing performances have been studied numerically. The results show that the magnetic field sensor with 15-cm PCFs has a large sensing range and high sensitivity of 4.80 pm/Oe. It provides a new feasible method to design PCF-based magnetic field sensor.     

A Design Method for Single-Polarization Holey Fibers With Improved Beam Quality Factor

Recently, there has been an increasing interest in developing single polarization fibers for applications such as polarization splitters, polarizers, high power lasers, etc. Usually, the polarization maintenance can be achieved by form birefringence, such as by creating elliptical cores, or material anisotropy, or by stress-applying parts inside the fiber. However, this results into the non-Gaussian field distributions due to the distortion of fiber core, therefore leading to the degradation of beam quality factor $M^{2}$. In this study, we propose a design method for single-polarization holey fibers with improved beam quality by introducing the resonant coupling phenomenon between the central depressed core and the elliptical cores arranged on either side of the central core. The proposed single-polarization holey fiber with 1-m length has the extinction ratio of 30 dB over 10-nm wavelength range and a good beam quality factor $M^{2}=1.31$.      

椭圆孔正方形点阵单偏振单模光子晶体光纤的设计

设计了一种椭圆空气孔正方形点阵单偏振单模光子晶体光纤,并以聚甲基丙烯酸甲酯为基材,利用基于棱边/节点混合元的全矢量有限元法对该光纤进行了数值模拟。结果发现,其偏振模场、快轴模和慢轴模截止波长完全依赖于光纤的结构参数;通过优化光纤的结构参数,发现该光纤传输基模的一个偏振态（慢轴模）在0.62μm至0.70μm可见光波长范围内;若调整该光纤结构具有9圈椭圆空气孔时,其偏振模约束损耗在波长0.65μm处可以降至0.13dB/m。该聚合物基低损耗单偏振单模光子晶体光纤可以有效消除传统保偏光纤固有的偏振串扰和偏振模色散。     

Optical-fiber resonant rings based on polarization-dependentcouplers

A theoretical and experimental analysis has been carried out on optical-fiber resonant rings based on polarization-dependent couplers. The analysis includes the use of optical-fiber polarization splitters and polarization-preserving fiber as particular cases. Two resonant configurations are presented and their sensor applications discussed. The changes of polarizations that take place in the ring are used as an effective distributed coupling which in one configuration feeds power into a resonance, and in the other introduces a variable attenuation, changing the effective losses of the resonant mode. The experimental characteristics of the system enable detection of small polarization changes. The experimental characteristics of a resonant ring about 2.5-m long and a polarization-selecting coupler are presented     

基于Contourlet变换和压缩感知的实际光子晶体光纤光

为了准确估计实际光子晶体光纤（photonic crystal fibers,PCFs）的光特性,提出一种基于Contourlet变换的压缩感知重建方法来重建实际PCFs的截面,进而对实际PCFs的光特性进行快速评估。结合全变差去噪方法,对经典图像、商用大模场面积PCF和保偏PCF的光特性进行评估,结果表明,提出的方法可以有效保留PCFs截面空气孔多尺度多方向的特征,光特性的评估结果与产品参数相吻合。这也是目前首次将基于Contourlet变换的压缩感知应用于PCFs的光特性估计,研究工作为实际PCFs光特性的快速准确估计提供了有效的手段。     

Multichannel optical splitters based on planar multimode silica-glass waveguides

The calculated optical characteristics and the technology for the structure formation of multichannel optical splitters are presented. The splitters are based on planar optical waveguides made of silica glass obtained via microwave plasma chemical deposition. Multimode splitters of the 16 × 16 type for the fiber optic data-transmission systems are produced with the use of the planar waveguides.     

Design and realization of phase retardation-control polarization controllers based on artificial birefringence

Polarization controllers(PCs) are indispensable passive components for state of polarization(SOP) control in optical fiber communication systems.In order to overcome the disadvantages of existing polarization controller(PC),a novel PC based on the artificial birefringence is designed in this paper.The PC results from the concatenation of 3 phase retardation control units each of which consists of two polarization beam splitters,two prisms and one piezoz-lectric transducer(PZT) piezoelectric ceramic.The experimental results show that the proposed PC can convert an arbitrary input SOP to any expected output one with high accuracy under low control voltage.     

TE/TM mode splitters on InGaAsP/InP

In a monolithic heterodyne polarization diversity receiver, mode splitters which effectively separate the TE and TM polarization of the optical wave are required. For this purpose, a directional coupler which utilizes a metal cladding on one of its branches to separate both polarizations was investigated. The polarization splitters can act in two distinct modes of operation, depending on the degree of lateral confinement of the optical rib waveguide before an asymmetric coupler. For weak confinement, the metallized waveguide is guiding for TE- but nonguiding for TM-polarization, and negligible TM-crosstalk results     

基于亚波长偏振光栅的空间光桥接器设计

为了研究自由空间的相干光探测,基于亚波长偏振光栅的衍射和偏振特性,提出了一种新的24的90空间光桥接器。该桥接器主要由一个亚波长偏振光栅、两个/2波片和两个偏振分束器构成。结果表明,通过亚波长偏振光栅将信号光束和本振光束进行空间光桥接,通过左旋和右旋圆偏振光在偏光分离时的相位性质实现所需的相位关系,避免了传统空间光桥接器中对分光元件的相位要求,易于实现稳定的相位输出,在空间激光相干探测系统中有潜在应用。     

Photonic Crystal Fibers With a General Bravais Lattice

We present a systematic and comprehensive analysis of photonic crystal fibers with a general Bravais lattice and one hole per unit cell. We show how the lack of a proper separation of lattice shape effects from volume rescaling can lead to an incorrect assessment of the impact of lattice shape. We study and compare the endlessly single-mode, waveguide dispersion, and birefringence properties of the fundamental mode across all lattice shapes. For example, we show that the triangular and square lattice shapes offer the largest critical air-hole radius for the endlessly single-mode operation. We identify a general class of PCFs with large birefringence and show that the total birefringence of the fundamental mode is the result of the competition between two opposing effects: the cladding lattice shape and the asymmetry of the core and can vanish for some PCFs with even very nonsymmetric lattices. We show designs for which the birefringence vanishes even with nonsymmetric lattices and cores.     

硫系玻璃光子晶体光纤研究进展

硫系玻璃与石英玻璃相比具有折射率高(2.0～3.5)、声子能量低(小于350 cm-1)、优良的中远红外透过性能、较宽的组分可调等特性.近年来,硫系玻璃光子晶体光纤作为一种新型中红外光子晶体光纤备受关注.回顾了硫系玻璃光子晶体光纤研究历程,从玻璃组成选择、光纤制备与损耗的降低、传输特性和结构设计、色散特性及应用等方面总...