Orientation-dependent time delays of the first higher-order mode in elliptical-core fibres

Time delays of the differently orientated LP11 modes in elliptical-core fibres have been measured in dependence on the wavelength. These measurements permit one to determine the orientation-dependent effective cutoff wavelengths. An empirical expression relating LP11-mode delay splitting due to slight ellipticity and LP01-mode chromatic dispersion is obtained.     

Single-mode propagation in 2-mode region of optical fibre by using mode filter

The effect of a mode filter using fibre bend has been clearly shown experimentally. The mode filter effectively removes the LP11-mode, and has a negligibly small effect on the attenuation of the LP01-mode. The single-mode propagation was attained at the V-value of 2.8 by using the filter.     

Propagation mechanisms in quadruple-clad fibres: mode coupling, dispersion and pure bend losses

The steep LP01-mode waveguide dispersion in quadrupleclad fibres is due to a coupling process. Unlike W-profilcs, these fibres allow achievement of zero dispersion at two relatively remote wavelengths, with a very small sensitivity to curvature. Because of the coupling process, however, these fibres can also propagate the LP02 mode.     

Zero-mode dispersion in single-mode fibres

Near cutoff the loss of the LP11-mode in cladded optical fibres becomes very high in the presence of even slight bends. Singlemode operation can thus be achieved with zero-mode dispersion as well as zero material dispersion, thus promising enormously large bandwidths.     

Comparison between techniques for measuring the LP11-mode cutoff wavelength in monomode fibres

The LP11-mode cutoff wavelength ?c of a monomode fibre can be obtained by measuring changes in microbending loss or mode field width. These two methods have been compared and it was found that the presence of microbending in the latter technique resulted in a discrepancy of between 0.04 and 0.12 ?m in the measurement of ?c.     

一种基于三芯光纤的模式复用器/解复用器的设计

提出了一种基于三芯光纤的模式复用器/解复用器,三个纤芯包括两个相同的单模纤芯和一个少模纤芯,在少模纤芯中写入长周期光纤光栅以实现单模纤芯中LP01模与少模纤芯中LP11模间的转换。同时从两个单模纤芯输入LP01模,能激发少模纤芯中两个简并的LP11,a模和LP11,b模。采用光束传播法分析了该模式复用器/解复用器的耦合特性及串扰。数值模拟结果显示,若以少模纤芯中LP11模输出能量大于-1dB的波长范围作为该模式复用器/解复用器的工作带宽,则能够达到23nm,并且少模纤芯中生成的其他模式的输出能量皆比LP11模的输出能量小-21dB以上。该模式复用器/解复用器能够实现对少模光纤的模式复用与解复用,并具有极低的串扰。     

Streak camera study of ultrashort pulse propagation in a weakly multimode optical fibre

A mode-locked dye laser in conjunction with a synchronously operating streak camera has been used to study ultrashort light pulse propagation in a weakly multimode optical fibre. Measurements of the intermodal temporal dispersion allowed the effective core radius a, the refractive index difference ? and the cutoff wavelengths of the LP21 and LP11 mode groups to be determined. The LP21 cutoff wavelength was experimentally verified and the temporal dispersion of the LP01 and LP11 mode groups investigated as a function of the fibre length.     

降低模分复用传输中信号串扰的预编码技术

为降低点到多点短距离模分复用传输中的模式串扰,提出了一种基于系数回传的预编码方法.设计了联合控制任意波形发生器(AWG)和示波器(DS0)的控制台,以及连接500 m少模光纤(FMF)的光子灯笼强度调制直接检测(IM-DD)模分复用传输系统,并选用LP01-LP01模式信道和LP11a-LP11b模式信道进行对比实验....     

Millimeter Wave Multi-mode Transmission Line Components

The present paper reports on the recent development of several oversized millimeter wave transmission line components for different applications. The studies include a circular TE₁₁-to-Gaussian beam mode converting horn, a TM₀₁-to-rotating TE₃₁ mode converter, a TE₁₁-mode 90° bend, a series of different HE₁₁-mode transmission line components, a notch filter and a fast laser controlled semiconductor microwave switch.     

Broad-band LP/sub 02/ mode excitation using a fused-type mode-selective coupler

We demonstrate a novel fused-type directional coupler that couples the LP/sub 01/ mode in one fiber and the LP/sub 02/ mode in another using a few-mode fiber. The phase-matching condition was satisfied in the coupler waist by initially etching and prepulling portions of the fibers based on simple numerical calculation. A coupling efficiency of about 70% was maintained over 1515-1595-nm wavelength range, and the mode extinction ratios with LP/sub 01/, LP,/sub 11/, and LP/sub 21/ modes were measured to be 35,20, and 7 dB, respectively.     

H-plane Bends in Overmoded Rectangular Waveguide Systems†

The eigenvalue and eigenfunction of the fundamental wave propagating in an ff-plane bend of rectangular cross-section is solved approximately by means of a perturbation method. In an oversize system,H⁰¹-mode power is found to be most strongly coupled to the H⁰²-mode which is assumed to be propagating. This mode coupling can be greatly reduced within a limited band width by offsetting laterally, in the H -plane of the H⁰¹-mode, the adjacent straight waveguide sections. Theoretical study and experimental verification for such a system are given.     

光纤激光器高阶模式对相干合成特性影响分析

为了分析光纤激光器中高阶模式对相干合成的影响,采用将光纤激光器的基模以及高阶模式近似表示为拉盖尔-高斯光束的线性叠加的方法,利用拉盖尔-高斯光束的传输特性,得到了当光纤激光器的输出光束包含高阶模式时,激光器阵列相干合成的远场光强分布模型。同时以光纤激光器中输出混合模式为LP01和 LP11以及输出混合模式为LP01和LP02两种情况为例,分析了存在高阶模式的远场相干条纹的峰值功率和条纹对比度。结果表明,当光纤激光器中高阶模式为 LP11模时,远场相干条纹的峰值能量随着LP11模的增加线性下降;当光纤激光器中高阶模式为LP02模时,远场相干条纹的条纹对比度随着 LP02模的增加线性下降。     

Bending characteristics of dual-hole PM-PCF based on LP01 and LP11 modal interference

The bending characteristics of dual-hole polarization maintaining photonic crystal fiber (PM-PCF) are demonstrated in this paper. The modal interference is induced by the LP01 mode and LP11 mode propagating in a single PM-PCF with the same polarization direction. Simulation results demonstrate that the bending radius induces the phase difference between LP01 mode and LP11 mode, which leads to the change of light interference intensity on the fiber output facet. The relationship between bending radius and normalized interference intensity with three different bending angles is discussed, where the bending angle is defined as the angle between hole axis and the x axis. The bending sensitivity is obtained to be about -188.78/m around the bending radius of 1.5 cm with the bending angle of 90°. The bending characteristics can contribute for online bending detection in widespread areas.     

Scalar finite-element analysis of optical-fiber facets

A numerically efficient scalar analysis of optical-fiber-facet problems based on the finite-element scheme is presented. By adopting the Taylor's series expansion of the characteristic matrix at the discontinuity plane, an accurate and yet numerically efficient approach is suggested for calculating the reflected and transmitted fields at discontinuities with circular symmetry. The scattering of the scalar LP/sub 01/ mode and higher order LP/sub 0m/ modes at both uncoated and coated optical-fiber facets has been analyzed, and the accuracy of the present finite-element approach is revealed through the excellent agreement of its results with those in the literature.     

Novel technique for measurement of wavelength of zero relative delay between modes of a dual-mode optical fibre

A simple method of determining the wavelength of zero relative time-delay between the LP01 and LP11 modes of short lengths of a dual-mode optical fibre is described. The measurement allows easy comparison of short and long lengths of fibre. The technique may prove to be more convenient and reliable than those presently used for characterising monomode fibres.     

基于少模光纤布拉格光栅的模分复用系统实验研究

本文提出了一种基于少模光纤布拉格光栅(Few-mode FBG)的模分复用通信系统,阐述了基于少模光纤布拉格光栅的模分复用/解复用原理,建立了2×2的模分复用实验系统,分别利用LP01和LP11模作为独立信道,实现了1.25 Gbps和622Mbps两路伪随机序列(PRBS)的10km传输实验,给出了传输后的眼图,分析了当激光器波长为1549.228nm时,实验系统的误码特性.实验验证了基于少模光纤布拉格光栅的模分复用通信系统的可行性,为进一步实现长距离高速率的模分复用通信奠定了实验基础.     

Measurement of intermodal delay in a dual-mode optical fibre

A novel measurement technique for intermodal dispersion between the LP01 and LP11 modes of a dual-mode optical fibre is described. A frequency-modulated optical source produces a beat frequency, proportional to intermodal delay, by interference of the two modes at the fibre output. Experimental results agree with theoretical predictions.     

Spatial Mode Division Multiplexing for High Speed Optical Coherent Detection Systems

Spatial mode-division multiplexing is emerging as a potential solution to further increasing optical fiber capacity and spectral efficiency. We report a dual-mode, dual-polarization transmission method based on mode-selective excitation and detection over a two-mode fiber. In particular, we present 107 Gbit/s coherent optical OFDM (CO-OFDM) transmission over a 4.5 km two-mode fiber using LP01 and LP11 modes in which mode separation is performed optically.     

Sinusoidal microbending loss of HE11-mode in step-index fibres

Sinusoidal microbending losses of the HE11-mode in step-index fibres are compared by using a perturbation solution of electromagnetic wave scattering theory. The HE11-mode in a multi-mode step-index fibre is found to suffer much higher bending loss than that in a single-mode step-index fibre, except that in nearly perpendicular directions and in the perpendicular direction with respect to the fibre axis the HE11-mode in the single-mode step-index fibre shows some higher bending loss than that in the multimode step-index fibre.     

Propagation in Doubly Clad Single-Mode Fibers

General propagation properties and universal curves are given for doubly clad single-mode fibers with inner cladding index higher or lower than outer cladding index, using the two parameters inner cladding/core radii ratio and inner cladding/core index differences ratio. LP01, LP11, and LP02 cutoff conditions are examined. It is shown that dispersion properties largely differ from the singly clad single-mode fiber case, leading to large new possibilities for low-loss dispersion-free fibers at any wavelength between 1.3 and 1.7 µm.