Modal noise in single-mode fibres operated slightly above cutoff

If a single-mode fibre is operated slightly above the theoretical cutoff frequency, at every discontinuity like a misaligned joint, a part of the LP01-mode will be converted to the LP11-mode. At a following discontinuity, the LP11-mode will be partly reconverted to the LP01-mode, e.g. a source wavelength shift will then cause modal noise.     

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.     

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.     

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.     

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.     

一种X波段GW级TE21模耦合器的设计

针对目前高功率微波(HPM)传输与发射系统无法实现自跟踪的问题,引入TE21模耦合器,使HPM系统具备自跟踪能力。由于现有的TE21模耦合器应用到HPM中会面临功率容量的问题,为此设计一种X波段GW级TE21模耦合器,以探索其在HPM系统中的应用。仿真结果表明：设计的TE21模耦合器在9.0~10.0 GHz频率范围内,对TE21模的耦合度大于-0.5 dB,对TE11模的耦合度小于-40 dB,功率容量可达到GW量级。     

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.     

Analytical form of EM fields radiated by circular aperture antennas of various current distributions

~~Analytical form of EM fields radiated by circular aperture antennas of various current distributions[1] Schelkunoff S. A., Advanced Antenna Theory, John Wiley &Sons, 1952. [2] E|liott R.S., Antenna Theory and Design, Prentice-Hall, Engie-wood Cliffs, N J, 1981. [3] R.W.P. King and G.S. Smith, Antennas in Matter: fundamen-tals, Theory and Applications, MIT Press, Cambirdge, MA,1981. [4] W.L. Stutzman and G.A. Thiele, Antenna Theory and Desigrn,John Wiley & S…     

A simple circular-to-rectangular waveguide transition

We describe a novel one-step TE/sub 11/-mode circular waveguide to TE/sub 10/-mode rectangular waveguide transition. The primary advantage of this device over existing transitions is its ease of fabrication. We have incorporated our transition into a number of waveguide components operating at V-band. The transition's measured return loss exceeds 15 dB over a 12% bandwidth centered near 60 GHz.     

Nanodeposition of materials with complex refractive index in long-period fiber gratings

An overlay of higher refractive index than the cladding is deposited on a long-period fiber grating (LPFG). This causes large attenuation-band shifts in the transmission spectrum, which permits the improvement of the sensitivity of the device to ambient and overlay refractive-index changes. To obtain maximum sensitivity for specific overlay and ambient refractive indexes, an optimum overlay thickness (OOT) must be selected. For complex overlay refractive indexes, there is an additional phenomenon of vanishing of the attenuation bands. This occurs for specific overlay-thickness values. The problem is analyzed with a numerical method based on linearly polarized (LP)-mode approximation and coupled-mode theory. Experimental results are contrasted with theoretical ones.     

Slot-Coupled T-junction of TE/sub 11/ Coaxial to TE/sub 10/ Rectangular Waveguide

A solution is presented to the problem of a slot-coupled T-junction of a TE/sub 11/ -mode coaxial to a TE/sub 10/ -mode rectangular waveguide. A variational technique is employed which combines the reaction concept with the field representation of a waveguide slot and leads to a closed-form solution for the junction scattering matrix. Numerical examples illustrate the characteristics of such a junction in practical applications. Good agreement between theory and experiment is obtained. Design criteria and examples are presented and discussed.     

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.     

Admittance of Irises in Coaxial and Circular Waveguides for TE/sub 11/-Mode Excitation

The admittance of irises in both coaxial and circular waveguides is deduced from a mode-matching technique. Design data for the effective admittance to TE/sub 11/ -mode excitation are given for a range of waveguide and iris dimensions.     

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。     

Broadband conical microstrip antenna

Conical patch antennas, excited on TE11-mode are studied and their resonance frequencies are computed. These antennas present a broader bandwidth compared to classical microstrip antennas and, furthermore, good impedance matching can be easily obtained.     

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....     

Steady-State Responses of NRD-Guide LSE/LSM Mode Oscillators in MM-Wave Bands

The analysis methods for the steady-state responses of the mm-wave band NRD-guide negative impedance oscillators based on nonlinear microwave autonomous circuits harmonic balanced method are presented in the paper in details. Firstly, the large-signal nonlinear lumped equivalent circuits of the Gunn diode are studied in mm-wave bands. Then, the performances of two kinds of NRD-guide autonomous circuits, the probe-exciting LSM ₁₁ ^o-mode oscillator and the LSE ₁₁ ^o-mode oscillator, are analyzed by the way of extracting the large-signal dynamic harmonic admittance (conductance) of the Gunn diode or directly configuring the harmonic balance equations for the oscillator. The input impedance of the exciting probe in the oscillator and the performances of the load-pulling and the local stability of the NRD-guide oscillator are also involved.     

Design formulae of unsymmetrical double-gap output cavities of klystrons

A new perspective is proposed that unsymmetrical double-gap output cavities of klystrons will have greater energy conversion efficiency of beam to microwave than the conventional symmetrical double-gap output cavities. The equivalent circuit method is used to get the relationships of the two gap electric fields in π-mode and 2π-mode unsymmetrical double-gap cavities in the case that the two gaps of the unsymmetrical double-gap cavities are approximately regarded as parallel grid gaps. The energy conversion efficiency in the process of an ideal bunching beam passing through the π-mode or 2π-mode unsymmetrical double-gap cavity is calculated by simulating the ideal cluster beam with a succession of periodically repeated electrons; then, the formulae of the optimal gap width, the optimal length of the drift tube between two gaps and the optimal gap voltage amplitude corresponding to the maximal conversion efficiency are obtained, which can be used to design π-mode and 2π-mode unsymmetrical double-gap output cavities of klystrons.