TE-TM模变换型光波导隔离器的理论研究

利用微扰理论研究了TE-TM模转换型光波导隔离器的自相位补偿. 从相位同步和功率转换解释了这种器件的工作原理, 揭示了两个模转换器相位 失配与模转换比例的关系, 数值仿真结果与理论分析相符, 证实了模转换型 波导隔离器中的自相位补偿理论.     

基于TE-TM模变换的新型相位自补偿磁光隔离器

讨论了由45°非互易模变换器与45°互易模变换器构成波导型光隔离器时两者之间须满足的条件,并由此设计了一种新型的相位自补偿磁光隔离器. 利用全矢量有限差分光束传输法对隔离器进行仿真,得到了插入损耗为-12dB,隔离度为-34dB的结果. 关键词： 集成光学 磁光隔离器 非互易模变换器 互易模变换器     

Elimination of phase-matching requirement for optical waveguide isolator

A novel optical waveguide isolator based on self-phase compensated TE–TM mode conversion was proposed. In this work, the troublesome phase-match condition for the TE–TM mode conversion is eliminated without degradation on the performances. An isolator based on this mechanism is designed and simulated. An insertion loss of −0.1 dB and an isolation of −25 dB was obtained. The tolerance of fabrication and bandwidth of the isolator was also discussed.     

Theoretical research on terahertz wave generation from planar waveguide by optimized cascaded difference frequency generation

A novel scheme for high-efficiency terahertz(THz)wave generation based on optimized cascaded difference frequency generation(OCDFG)with planar waveguide is presented.The phase mismatches of each-order cascaded difference frequency generation(CDFG)are modulated by changing the thickness of the waveguide,resulting in a decrement of phase mismatches in cascaded Stokes processes and an increment of phase mismatches in cascaded anti-Stokes processes simultaneously.The modulated phase mismatches enhance the cascaded Stokes processes and suppress the cascaded anti-Stokes processes simultaneously,yielding energy conversion efficiencies over 25%from optical wave to THz wave at 100 K.     

高功率圆波导TE0n-TE11模式变换研究

 在模式耦合理论的基础上，详细讨论了波导轴线弯曲与波导半径渐变的圆波导模式变换，并对TE_0n-TE₁₁模式变换器的几何结构进行了优化分析，采用不同的相位重匹配技术，得到了可靠的最优几何参量。以此数据设计的8mm回旋速调管TE₀₁-TE₁₁模式变换器的转换效率可达98%。     

掺Bi钇铁石榴石薄膜光波导的线性双折射及消除方法

分析了光的线性双折射对磁光波导ＴＥ－ＴＭ模式转换，法拉第旋转，波导光隔离器隔离比及插入损耗的影响。研究了掺Ｂｉ钇铁石榴石薄膜光波导中的形状线性双折射，应力感生线性双折射及生长感生线性双折射的来源，特性和消除方法。     

Compensation of thermal effects in Faraday isolator for high average power lasers

A Faraday isolator system with external compensation of thermally induced birefringence was investigated for the case when optical components of the Faraday isolator and the compensator are made of different materials. Simultaneous reduction of thermally induced depolarization and thermal lens in the Faraday isolator based on a TGG crystal was demonstrated experimentally for the first time using an Sm:CaF₂ crystal. A method of compensating thermally induced birefringence without reciprocal polarization rotator was described theoretically and demonstrated in experiments for the first time. It was used as a basis for a new scheme of Faraday isolator with external compensation of thermally induced birefringence.     

An improved design of an integrated optical isolator based on non-reciprocalMach–Zehnder interferometry

Non-reciprocal rib waveguide structures can be used to realize integrated optical isolators. In this paper, we propose a concrete design for a Mach–Zehnder interferometer type isolator for TM modes. Just one of the arms, which are of equal length, is a non-reciprocal magneto-optic waveguide. The rest of the interferometer is reciprocal. Required fabrication tolerances are estimated, and the entire isolator is simulated by applying a finite difference beam propagation method.     

L波段紧凑型TEM-TE11模式转换器

设计了一种适用于窄带高功率微波源系统的紧凑型TEM-TE11模式转换器。该结构首先将同轴波导沿角向分区使微波在各分区内相位传播常数不同,然后将相位传播常数较大的分区进行横向折叠设计以缩短系统轴向长度。分区传播的微波在模式转换器末端相位差达到180时,合成同轴波导中TE11模式。为L波段磁绝缘振荡器设计了模式转换器,并采用数值仿真程序进行计算,在1.31 GHz中心频率上,模式转换器转换效率为95%;在1.23~1.40 GHz频率上,模式转换器效率大于90%,相对带宽13%。将模式转换器应用于磁绝缘振荡器,并测量了天线的定向辐射能力,所得结果与设计一致。     

圆波导TM_(01)-矩形波导TE_(10)模式转换器

设计了一种高功率圆波导TM01-矩形波导TE10模式转换器,可以实现圆波导TM01模式与矩形波导TE10模式之间的相互转换。仿真结果表明:中心频率为9.7GHz时该模式转换器转换效率大于99.99%,回波损耗小于-40dB,转换效率大于90%时的带宽大于0.4GHz。调节底面短路圆波导长度可以实现模式转换器在9.2~10.1GHz范围内调谐(模式转换效率大于99%)。在圆波导和耦合段连接处引入倒角可有效降低场强,提高功率容量,注入功率0.7GW,其表面场强小于1 MV/cm。     

高功率微波弯曲矩形波导设计

 利用模式耦合理论,在理论推导出弯曲矩形波导TE01模和高阶模之间耦合系数显式表达的基础上,对弯曲矩形波导进行了实例研究。HFSS软件数值仿真结果表明：设计的矩形波导TE01-TE02模式转换器在9.5 GHz转换效率达到99.9%,转换效率大于90%的工作带宽为8.60～10.48 GHz;设计的弯曲矩形波导传输线,可有效传输TE01模,不激励起高阶模式。HFSS数值仿真结果验证了所设计的传输线工作带宽和功率容量均能够满足使用要求。     

全腔输出相对论磁控管输出模式转换结构的理论设计和数值模拟

采用全腔输出结构后,相对论磁控管径向尺寸显著减小,轴向长度也有较大幅度的缩短.但是,由于输出结构为三个相对独立的扇形波导,实际应用时,一般需要对微波输出模式进行转换.针对全腔输出相对论磁控管,本文研究了两种输出模式转换结构并利用三维全电磁粒子模拟程序对其进行了研究.首先研究了将三个扇形波导角向增宽从而渐变或者突变为一个同轴波导的情况,研究结果表明,两种情况下输出微波功率均大于采用传统三个独立扇形波导输出时的90%,输出模式主要是TEM模.其次研究了输出区由三个扇形输出波导分别变换为三个截面大小与之接近的矩形输出波导的可行性,研究结果表明,注入扇形波导中的TE₁₁模式几乎全部转换为矩形波导中的TE₁₀模式.实际应用时,可根据需要选择上述输出模式转换结构.     

功率容量大于1GW的组合式旋转关节

用耦合波理论分析了过模圆波导中不同模式之间的转换和波导弯曲半径之间的关系,研制了弯曲角度为90°的过模圆波导弯头,设计了一种结构简单的TM01过模圆波导旋转结构。对圆波导弯头和旋转结构的高功率测试证明,它们在X波段功率容量均大于1 GW,微波传输效率均大于93%。在此基础上,提出了一种组合式旋转关节,该关节能够在方位和俯仰上实现360°旋转,可应用于高功率微波的发射天线。     

径向线型模式变换器

 研究了一种通过改变波导内场分布的旋转对称性,可将高功率微波源输出的TEM模或TM01模转换为TE11模的径向线型模式变换器。介绍了该模式变换器的基本原理,即采用金属插板将同轴波导TEM模变换为4路90°扇形波导TE11模,各路扇形波导间所需的输出相位差通过将扇形波导转换为双层径向线传输来实现。基于这一原理,设计了一个中心频率为1.6 GHz的同轴TEM-TE11模式变换器,并进行了数值模拟计算,结果表明该模式变换器具有较高的功率容量,中心频率处反射系数为0.05,模式转换效率为99%,在1.52~1.68 GHz的频带范围内,模式转换效率大于90%。     

一种耦合度可调节的微波脉冲压缩装置设计及实验

针对有源能量倍增器法(SLED)脉冲压缩实验中对储存能量阶段和释放能量阶段耦合度调节的需求,利用支臂短路波导H-T的调配功能,设计了一种耦合度可调节的SLED脉冲压缩装置。基于散射矩阵理论,分析了支臂短路波导H-T对SLED脉冲压缩装置耦合度的调节能力。利用大功率波导环形器代替3 dB耦合器,进行了基于单储能腔的无源SLED脉冲压缩实验,实验结果表明,支臂短路波导H-T对耦合度的调节能力与理论分析相吻合。     

组合型TM01-TE11弯形圆波导模式转换器研究

 研究了组合型TM₀₁-TE₁₁弯形圆波导模式转换器（两弯曲段中间加一段直圆波导），在保持其输出与输入端口轴线平行的前提下，分别从理论推导、数值计算、软件模拟三个方面对此结构进行了分析，模拟结果与数值计算结果吻合得很好。结果表明：计及功率损耗，频率为3.75 GHz，铜波导内径为9.0 cm，轴向间距为10.57 m时，模式转换器总的功率转换效率为93.8%。     

Pilot-based cross-phase modulation compensation for coherent optical orthogonal frequency division multiplexing long-haul optical communications systems

A pilot-based nonlinearity compensator (PB-NLC) is shown in this Letter to be an effective method for compensating cross-phase modulation (XPM) in coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems. An unmodulated pilot tone is transmitted at the center of each OFDM channel to detect phase errors caused by the Kerr effect, which converts intensity fluctuations from all channels to phase errors. The pilots are then used to cancel the XPM phase errors for each OFDM channel at the receiver after each channel's self-phase modulation (SPM) has been compensated, using its intensity waveform to determine its SPM. Numerical simulations of a 58 Gb/s single polarization 2375 km system with inline dispersion compensation show that the signal quality, Q, at the optimal launch power is increased by 2.4 dB if SPM compensation is used before the PB-NLC. This contrasts with only a 0.9 dB improvement if the PB-NLC is used without an SPM compensator for the same link. This shows the PB-NLC can effectively mitigate XPM but not SPM.     

Analysis of High Power Millimeter Wave Waveguide Mode Converters with Input Mode Mixture

Based on the coupled mode theory, this paper presents the study on the influence of input mode mixture in circular oversized waveguide mode converters. Three kinds of commonly used waveguide mode converters, including the waveguide mode converters with varying wall radius or small axis perturbations, and the waveguide mode converters with bent structures, are taken as the examples. The results show that the spurious input modes do not simply superimpose onto the output modes, and in some cases they may deteriorate the conversion efficiency for the main output mode. Methods for transforming such spurious input mode mixture simultaneously into the main output mode are also presented in this paper.     

Broadband operation of a Ka-band tapered gyro-traveling waveamplifier

A wideband low-voltage millimeter-wave gyro-traveling wave tube (gyro-TWT) amplifier operating in the TE₁₀ rectangular waveguide mode at the fundamental cyclotron frequency is under investigation, The device incorporates precise axial tapering of both the magnetic field and the interaction circuit for broadband operation. Experimental results of a wide (33%) instantaneous bandwidth with a small signal gain in excess of 20 dB and saturated efficiency of ~10% were achieved and shown to be in good agreement with the theory. Reflective instability due to multi-pass effects by mismatches was observed and characterized. Gain and efficiency have been limited by this reflective instability rather than by absolute instabilities which limit the performance of gyro-TWT's with uniform cross-section. The start-oscillation current in terms of the relevant experimental parameters such as the beam velocity ratio (α), magnetic field detuning and reflection coefficient has been measured and compared with theory. Measurements of the phase variation in terms of the RF frequency have shown that the phase varies ±30° from fitted linear phase line     

Phase-matched second-harmonic generation in hybrid polymer-LN waveguides

Here we propose a hybrid polymer-LN waveguide for achieving phase-matched second-harmonic generation (SHG). From the aspect of super-mode theory, the geometric parameters of the hybrid semi-nonlinear waveguide were optimized to utilize both symmetric (even) and antisymmetric (odd) modes of the pump and SHG waves so as to facilitate phase matching with large modal overlap. Phase matching between a fundamental even (TE₀₀-like) mode at 1320 nm and a fundamental odd (TE₀₁-like) mode at 660 nm was found with a calculated modal overlap integral of 0.299, while utilizing the largest nonlinear coefficient d₃₃, and achieving an efficient calculated normalized conversion efficiency of 148% W^-1·cm^-2. Considering the fabrication feasibility of such hybrid waveguide with features including etchless, large dimension, and low structural sensitivity, we believe our findings would provide a useful reference for future on-chip efficient nonlinear conversion devices.