Polarization-independent switching operation in directional couplerusing tensile-strained multi-quantum well

Polarization-independent switching operation in a multi-quantum well directional coupler is obtained for the first time, with a bar-state crosstalk of -12 dB. By introducing tensile strain in an InGaAs-InP multi-quantum well, polarization-independent switching voltage is as small as 3 V, with the coupling length being 1.2 mm. The cross-state crosstalk that is obtained at zero-applied voltage, is less than -8 dB with respect to TE and TM polarized lights     

Y-cut LiNbO3 directional coupler with a self-alignedelectrode

A 2×2 Y-cut LiNbO₃ directional coupler switch using a self-aligned uniform Δβ electrode is fabricated by the proton diffusion method. Our design method makes it possible to form the electrode without the delicate alignment of the electrode pattern mask and optical waveguide. The switching voltage is also reduced due to the enhanced electro-optic efficiency by using the self-aligned electrode. To achieve the initial cross state of the uniform Δβ switch that is essential for low crosstalk, we control the proton diffusion time successively after the proton exchange. The measured crosstalk level of the directional coupler switch is -23 dB~-29 dB and its voltage-length product is as small as 9.6 Vmm     

Low crosstalk 4 × 4 TiLiNbO3optical switch with permanently attached polarization maintaining fiber array

Several low crosstalk 4 × 4 crossbar optical switch arrays have been fabricated for use atlambda = 1.3 mum. Each array consists of 16 independently functioning directional coupler switches. We describe the typical device performance characteristics. The average insertion loss is 5.2 dB. Crosstalk levels routinely measured < -35 dB. The voltage required to operate the device is ≈ 13 V. The inputs to one of the device arrays were permanently attached to four laser transmitters using lensed polarization maintaining fiber at the laser end and an array of polarization maintaining fibers at the device end.     

1550nm低推挽电压聚合物定向耦合电光开关的设计

应用保角变换法、镜像法、耦合模理论和电光调制理论设计了一种推挽电极聚合物脊形波导定向耦合电光开关,阐述了基本结构和工作原理,给出了器件的设计和优化过程,主要分析了耦合长度、开关电压、输出光功率、插入损耗、串扰等特性.为了实现正常的开关功能,讨论了制作公差、波谱漂移以及单模光纤耦合损耗对器件性能的影响.模拟结果表明,所设计的开关的耦合长度为3082μm,开关电压为2.14V;插入损耗小于1.14dB,串扰小于-30dB.与BPM仿真结果以及实验结果的对比表明,文中提出的波导和电极的理论分析与计算方法具有较高的精度和可行性.     

宽频太赫兹非对称主副波导定向耦合器设计

基于微型无人机雷达、精确制导武器雷达及无线通信终端设备的应用前景,设计了一种非对称主副波导定向耦合器。该耦合器采用主副波导为不同形状的等间距多孔耦合结构,将主矩形波导TE10模的信号耦合到副圆形波导TE11模中,利用相位叠加原理使得隔离端口相位达到反向相消的效果,能够得到良好的耦合度和隔离度。该耦合器中心频率为400 GHz,相对带宽为40 GHz,结果表明,定向耦合器耦合度达到-13.8～-12.8 d B,实现了弱耦合效果且耦合度稳定性较好,隔离度优于-24.5dB,直通插入损耗为-3～-2.5 dB,性能良好。     

多孔耦合型太赫兹波导定向耦合器的设计

设计了一种结构紧凑、工作频带较宽、耦合平稳、高方向性的十字形多孔耦合的太赫兹波导定向耦合器。基于多孔耦合原理,利用HFSS软件对太赫兹波导定向耦合器进行了模型仿真和结构优化。仿真结果表明:在325~475 GHz带宽范围内,该多孔耦合太赫兹波导定向耦合器耦合度达到7.50.8 dB,隔离度达到30 dB,即方向性优于20 dB,各端口回波损耗小于-20 dB。通过对该波导定向耦合器进行高温高压模拟仿真,确定了使用负性光刻胶SU-8作为结构材料的可行性,提出应用MEMS工艺在硅衬底上进行加工,将牺牲层工艺应用到波导腔结构的制作中。利用光刻在直通波导和耦合波导公共宽壁上形成的十字形等间距排列耦合孔结构,可以实现较宽的带宽和良好的耦合平坦度。该方法提高了耦合孔尺寸和位置的精度,减小了反射损耗,为太赫兹波导结构的加工提供了新思路。     

On the crosstalk of reversed-Δβ directional couplerswitches

Coupled-mode theory applied to reversed-Δβ parallel directional coupler switches with tapered-sections input and output waveguide predicts a residual crosstalk in the straight through (bar) state due to coupling within the tapered regions which could be as low as 10-15 dB. Complete switching to the cross state, however, can be achieved assuming ideal conditions. Means of reducing the crosstalk in the bar state using phase control are presented     

Mesh waveguide optical star coupler

A new multimode optical star coupler with a mesh waveguide configuration is proposed to reduce the device length by stimulating light mixing in a short waveguide. A 4×4 optical star coupler has been fabricated and its branching variation of 2.8 dB is realised with the device length as short as 14.5 mm.     

GaAs/AlGaAs directional coupler switch with submillimetre device length

A GaAs/AlGaAs directional coupler switch, for the first time with a device length shorter than 1 mm, has been fabricated by utilising the good controllability of molecular beam epitaxy and reactive ion beam etching. The switching voltage is as low as 5V. The extinction ratio is 17dB for a crossover state and 14dB for a straight-through state.     

Two-section reversed /spl Delta//spl beta/ switch with uniform electrodes and domain reversal

The performance of the reversed-/spl Delta//spl beta/ LiNbO/sub 3/ optical directional coupler (DC) switch with electrodes of opposite polarity is known to be more tolerant to variations in coupling length than that of the single-section DC. However, sectioned electrodes are incompatible to a single microwave source and, therefore, preclude the use of the device in high-speed applications. In this letter, we discuss the operation and results of a modified DC that uses a domain reversal and uniform electrodes that can be readily matched to a microwave source. A crosstalk of -34 dB was measured in an experimental device, fabricated in Z-cut LiNbO/sub 3/. Factors which improve device performance are also discussed.     

Modified 1×2 directional coupler waveguide modulator

A novel 1×2 Ti:LiNbO3 modified directional coupler modulator is demonstrated. The 3 dB operating point requires no bias voltage. The device has a lower switching voltage requirement than a conventional directional coupler.     

Carrier-injected GaInAsP/InP directional coupler optical switchwith both tapered velocity and tapered coupling

For most applications, a quasi-digital switching response is desired. The authors report on the design and fabrication of a 2×2 `digital' optical switch in GaInAsP/InP based on a directional coupler with both tapered velocity and tapered coupling and designed to be in the cross state at the zero bias condition. Complete power transfer to the cross output port for both TE and TM polarizations has been realized in the passive couplers for a wide range of device lengths proving the theoretically predicted fabrication tolerances. In the very first controllable device, switching operation with a crosstalk of -7 dB has been achieved using carrier injection     

An acoustooptical directional coupler for an optical time-domain reflectometer

An optical directional coupler in which a TeO2acoustooptical deflector (AOD) is employed has been designed and developed for use in an optical time-domain reflectometer (OTDR). A low round-trip insertion loss of 4.6 dB and low crosstalk of below -48 dB were attained for the fabricated coupler. Signals of large amplitude, such as Fresnel reflection, could be suppressed to less than - 33 dB by switching of the optical directional coupler. Amplitude fluctuation of the back-scattered signal due to polarization fluctuation in single-mode fibers is reduced to a negligible extent.     

一种Q波段多孔耦合型定向耦合器

论述了一种宽带多孔耦合型定向耦合器,工作频段中心频率为40 GHz,相对带宽50%,拟用于射电望远镜Q波段接收机系统。该定向耦合器为一款结构紧凑的器件,采用对称的等间距多孔耦合形式,将主通道圆波导TE11模式信号耦合到耦合通道的矩形波导中,实现了小于-20 dB 耦合特性。为了对设计进行验证,对该定向耦合器进行了加工和测试。测试结果表明,在30~50 GHz 工作频段内,主通道反射系数小于-24.2 dB,且全频段内的端口耦合度保持在-20~-21 dB 之间。仿真与测试结果具有较高的吻合度,进一步证实了该设计可用于射电天文望远镜的Q波段接收机系统。     

Characteristics of S-shaped waveguide structures by the annealedproton exchange process in LiNbO3

The loss of S-shaped waveguide bends in annealed proton-exchanged LiNbO₃ integrated optical devices is found to be dependent on the length of thermal annealing time. The minimum transition length required in order to have losses as low as 0.2 dB is 2.0 mm for a 0.1-mm lateral offset. Intersecting waveguides based on S-shaped structures have been characterized for passive crossovers. An angle greater than 6° is required to provide a crosstalk of less than -30 dB. At a particular angle, intersecting waveguides offer the possibility of making a 3-dB coupler if an insertion loss of 1.2 dB is not a big concern. Zero-gap couplers based on S-shaped structures have been characterized for applications as 3-dB couplers as well. This type of 3-dB coupler has a much lower insertion loss of roughly 0.4-0.5 dB. Both 3-dB intersecting waveguides and 3-dB zero-gap couplers are less sensitive to wavelength variations     

光方向耦合器汉明函数之波导结构影响

在本文章中研究光方向耦合器汉明函数之波导结构影响.传统的光方向耦合器之理论是由绝热的条件下所获得之结果,因此在波道耦合长度不夠长时则变得可疑,有鑑于此需要依靠光束模拟软体.在文章中有两个主要的指标:第一个为理论所适用的范围,第二个为最佳化低串扰、宽频宽和较短的耦合器长度.最后由结果得知我们所提出使用的汉明权重函数在此架构下能获得较佳的设计结果.     

Analysis and Synthesis of Waveguide Multiaperture Directional Couplers

A precise method of analysis of multiaperture waveguide directional couplers has been developed and used to investigate the performance of couplers designed both by conventional theories and by a new synthesis technique. The analysis is based on the equivalent four-port network of the coupler, the apertures being represented by lumped reactances in series and/or shunt with dispersive transmission lines, representing the waveguides. The effects of finite aperture dimensions and common wall thickness are taken into account. Many couplers designed on the usual basis of a first-order loose-coupling approximation have good directivity, even for tight (3 dB) coupling, but previous theories do not give the predicted directivity and are often far from optimum in design. A new synthesis technique based on the distributed low-pass prototype filter has been devised, and shown to give results close to the predicted performance. It has led to the construction of compact multiaperture directional couplers having directivity greater than 43 dB over complete waveguide operating bands.     

A short polarization splitter without metal overlays on InGaAsP-InP

A new and very short polarization splitter on InGaAsP-InP is designed and realized for the first time. The component contains a ridge waveguide directional coupler of 0.4 mm length and an output section of 0.7 mm. It uses the large waveguide birefringence of the first-order TE and TM modes to obtain polarization selective directional coupling. In this way, additional metal layers on the waveguides to create birefringence are avoided and fabrication becomes very simple. Components are realized, which show splitting ratios close to -20 dB. Excess losses are below 1 dB. The polarization splitting is investigated in the wavelength region of 1525-1560 nm and found to be better than -9 dB.     

High performance dual directional couplers for near-mm wavelengths

A low loss, high directivity dual directional coupler has been developed suitable for fabrication in waveguide bands up to WR3 (220-325 GHz). The design uses waveguide split on the E plane centerline with three waveguides running side by side and coupling holes made by drilling through all three guides. Construction is relatively simple and the resulting structure is very robust mechanically. Typical coupling is 15 dB, directivity is 25-30 dB, and the insertion loss of the WR3 coupler is 0.5 dB     

A dual wavelength (1.32-1.56 μm) directional couplerdemultiplexer by ion exchange in glass

A 1.32-1.56-μm demultiplexer using a symmetrical directional coupler consisting of Ag⁺-Na⁺ exchanged channel waveguides in BK7 glass with a total insertion loss of 1.25 dB for a 14.5-mm-long device and a propagation loss of 0.15 dB/cm is demonstrated. The crosstalk at 1.315 and 1.561 μm and the cross power ratio at 1.315 μm were measured to be less than -40 dB for the TE mode