Space-wavelength tradeoff in the design of nonblockingdirectional-coupler-based networks under crosstalk constraint

Directional couplers are electrooptical switching devices that are capable of switching multiple wavelength signals. Once the state of a coupler is set up, optical signals can pass through the coupler with the rate of terabits per second. A directional coupler-based photonic switching system, however, suffers from the intrinsic crosstalk problem. This shortcoming has been the most limiting factor in building a large switching network of this kind. It has been shown that by using more hardware (couplers) we can reduce the crosstalk inside a switching system. In this paper, we explore the wavelength approach to achieve the same goal. We show that if two wavelengths are available for sending data, the number of couplers suffering the first-order crosstalk can be reduced to zero while the total number of couplers remains the same as in a network without any crosstalk constraint     

Three-electrode Ti:LiNbO3optical switch

Modifications of the conventional electrode arrangement of electrooptic directional coupler switches are described. UniformDelta Betaelectrodes can be symmetrically shortened to ∼ 40 percent of their length without significant increase in electrical drive voltage. Based on this result, a new three-electrode switch is described which can be used to electrically adjust both the bar and the crossed states of the switch. It is also demonstrated that the three-electrode arrangement can be used to reduce or eliminate optical crosstalk in Ti : LiNbO3switches.     

基于正交定向耦合器组合的微波功率测量方法

定向耦合器广泛应用于微波系统的功率测量.但定向耦合器的方向隔离度有限,两个方向的耦合输出信号存在一定程度地串扰,影响功率测量的准确性.为了解决这一问题,本文提出一种正交耦合测量方法.该方法采用一对相位差为90°的定向耦合器同时测量功率,通过对测量结果的计算处理,可消除方向串扰的影响.推导了正反向传输功率与正交耦合器组合功率测量值的关系,分析了正交偏差所产生的误差.为了确定耦合器的正交状态,提出了一种准确测量两个定向耦合器之间相位差的方法.实测表明正交耦合方法可有效提高功率和驻波比测量的准确性.     

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.     

田口稳健设计优化之绝热式光方向完全耦合器

本研究利用田口实验优化法配合光束传播法设计优化光方向完全耦合器 sin-square 函数,能夠达到低串扰与短耦合器长度的目标,在田口实验优化法中我们选择直交表 L9 做为我们的实验平台.研究结果显示,使用 BPM 辅助设计方式配合田口方法可有效的减少设计优化光方向完全耦合器的实验数.在实验过程中我们尝试去找出并设定符合低串扰与短耦合器长度的绝热式光方向耦合器 sin-square 函数的结构参数范围,并且在田口实验优化法中的确认实验可以达到95%的信心指数.在这份研究中,我们证实利用田口实验优化法配合 BPM 辅助设计优化光方向完全耦合器 sin-square 函数是确实可行的.     

Hybrid-Ring Directional Coupler for Arbitrary Power Divisions

A directional coupler in the form of a hybrid ring is described in this paper. A theoretical analysis using the scattering matrix has been carried out and experimental verification of the theoretical result has been achieved in a stripline network. Simple design equations which enable one to design a directional coupler with any degree of coupling have been derived. This coupler differs from the commonly used couplers in that the voltages at the output arms are either in-phase or opposite-phase with respect to each other. In addition, its geometrical symmetry makes it very convenient for use in symmetrical networks, particularly as a power divider in antenna feeding systems.     

Further evidence of strong coupling effects in three-arm Ti:LiNbO3 directional couplers

The switch characteristics of three-arm integrated optic directional couplers with both symmetric and antisymmetric drive voltages are examined. The symmetry properties of these devices, predicted by previous theory, are shown to be violated and the reasons for this are discussed in terms of scalar strong coupling coefficients normally neglected as small. It is also shown that the inclusion of modal overlaps introduces additional coupling terms and causes significant power redistribution in the bend sections. Experimental measurements for the antisymmetric configuration are presented, and it is shown that different electrode loading of the center and outer guides affects device operation     

A new approach to grating-assisted couplers

A novel approach to the analysis and design of grating-assisted directional couplers is proposed. Power exchange between the waveguides is maximized through phase matching of two power-orthogonal modes of the parallel coupler. It is shown that either complete power transfer or zero crosstalk can be achieved at two different coupling lengths even when the two wavelengths are strongly coupled and/or close to synchronism. An analytical solution to the coupled-mode equations is obtained for the grating of rectangular shape. A grating-assisted coupler made of two slab waveguides is examined as an example to illustrate the salient features of the scheme     

Performance of field-induced directional coupler switches

Switching in a GaAs field-induced, three-waveguide straight directional coupler is studied theoretically. This device can be tuned externally by changing the voltage across the waveguides. Because of this tunability, the device has some very attractive features as a switching element. The performance change due to variations in the device parameters such as length, waveguide separation, waveguide width, and wavelength of operation is numerically computed. The effect of material absorption, input and output coupling, and asymmetric excitation are included in the performance evaluation. For a device length of 1400 μm, a crosstalk of -34 dB and a power transfer efficiency of -2 dB is predicted, while for the same device size a two-guide directional coupler is predicted a crosstalk of -13.4 dB. The device has a 400 nm voltage tunable bandwidth with a maximum crosstalk penalty of 3 dB     

Ka波段3dB定向耦合器的设计与仿真

定向耦合器广泛地用在现代微波系统中,文中介绍了两种应用在平衡式放大器中的3dB定向耦合器。首先对微带分支线耦合器与波导耦合器进行了理论分析,然后利用电磁仿真软件HFSS,对两种耦合器进行了建模仿真。仿真结果验证了这两种定向耦合器的可实现性,最后比较了两种耦合器的性能,并且总结了各自的特点。     

Design of a Polarization Insensitive Triplexer Using Directional Couplers Based on Submicron Silicon Rib Waveguides

An ultracompact triplexer which could be used for both polarizations is designed by utilizing directional couplers based on submicron silicon rib waveguides. First, the polarization insensitive directional couplers are realized by carefully choosing cross-sectional geometry of the waveguide. The length of the coupling region in the first directional coupler is chosen to separate the three wavelengths (i.e., 1490 nm to one port, 1310 and 1550 nm to the other port). The second directional coupler separates the wavelengths of 1310 and 1550 nm. For the channel of 1490 nm, an additional directional coupler is used to reduce the crosstalk from the 1310 and 1550 nm channels. The total length of the present triplexer is only 400 $mu{rm m}$, and simulation with three-dimensional Beam Propagation Method shows good performances for both polarizations.      

Effect of intrinsic phase mismatch on linear modulator performanceof the 1×2 directional coupler and Mach-Zehnderinterferometer

The performance of 1×2 directional couplers and Mach-Zehnder interferometers as linear modulators is compared. Models describing the operation of each device, incorporating the intrinsic phase mismatch Δβ₀ which is present in nonideal devices, are developed. Distributions of Δβ₀ are obtained for each device and are shown to be independent of device type. Linear dynamic range and sensitivity measurements showing how Δβ₀ affects performance agree with theory. The additional effect of the coupling coefficient in the 1×2 directional coupler is demonstrated. This information can be used to predict device yield when combined with the measured Δβ₀ distributions     

Optical wavelength filter with tapered couplers

Optical wavelength filters based on tapered directional couplers are analyzed by nonorthogonal coupled-mode theory. The nonorthogonal coupled-mode formulation in general yields more accurate results than the conventional orthogonal coupled-mode theory. The focus is on the novel features of the tapered couplers used as wavelength filters. It is demonstrated that, in addition to reducing the crosstalk and suppressing the sidelobes, the tapered structure can also make the filtering response independent of the device length beyond a critical coupling length,.<>     

Crosstalk of passive directional couplers

Crosstalk in directional couplers (DC's) is an important parameter for device and system performance. Although various crosstalk mechanisms have been studied through the course of integrated optics, the fundamental lower limit for crosstalk is still uncertain. In this paper, crosstalk mechanisms are reviewed and fundamental limits are discussed. A new model for optical scattering is presented, and the effect of bending loss variation between the two propagating modes in the taper region on the crosstalk is discussed     

Digital and quasi-linear electrooptic modulators synthesized from directional couplers

By synthesizing from cascaded directional couplers, we propose new designs to achieve digital and quasi-linear electrooptic modulations. For the digital modulator, a nearly perfect on-state or off-state can be obtained in a broad range of modulation voltages. The calculated switching voltage can be as low as the drive voltage of a conventional directional coupler. The quasi-linear modulator is achieved by adding a set of compensating electrodes to a foreshortened directional coupler. Deviation from a linear voltage-intensity relationship of less than 1 percent can be obtained over a 93.5 percent modulation depth. The calculated second harmonic and the third order intermodulation distortions are -18.3 and -32.6 dB, respectively.     

Slot-coupled directional couplers between double-sided substratemicrostrip lines and their applications

A slot-coupled microstrip directional coupler and its application to a planar multiport directional coupler (MDC) are described. This coupler can be applied to both loose coupling (e.g. 10 dB) and tight coupling (e.g. 3 dB). A four-port planar MDC fabricated by combining these couplers is described. Measured and calculated results are in agreement for both couplers     

光纤耦合器与速度干涉仪的灵敏度

通过改进光纤定向耦合器的结构,可以显著提高光纤速度干涉仪的灵敏度.该文从熔融拉锥型光纤定向耦合器的数学模型出发进行研究,详细分析了2×2和3×3型光纤定向耦合器在全光纤速度干涉仪(AFVISAR)中的具体作用,并对此两种结构的光纤速度干涉仪的性能(主要是灵敏度)的优劣进行了对比分析,表现出3×3型光纤定向耦合器构成的两端探测系统的优越性.最后提出采用N×N型光纤定向耦合器可能带来的光纤速度干涉仪性能的提高和适用局限性.     

The crosstalk in three-waveguide optical directional couplers

An expression for the crosstalk in three-waveguide directional couplers is derived. The crosstalk is found to be due to the uneven spacing in the distribution of the propagation constants of the three eigenmodes of the couplers. Similar to the crosstalk in the two-waveguide directional couplers, it is also proportional to the square of the field overlap of the two neighboring waveguides. This feature seems to be universal in the straight couplers.     

Frequency domain analysis of RF and microwave circuits using SPICE

The SPICE circuit analysis program has limited math capability and, in general, cannot be used for RF and microwave simulation because complex arithmetic is required to compute S-parameters from node voltages. This paper presents two models of a directional coupler that can be used to obtain node voltages proportional to incident, reflected, and transmitted signals. These models are based on a previously developed multiple coupled transmission line (MTL) SPICE model. From SPICE computed node voltages, S-parameters are computed using the math capability of the PSPICE post processor, PROBE, as an example for a low-pass filter consisting of transmission line sections. The results of this example are compared with another high-frequency circuit analysis program, TOUCHSTONE. The difference between the results of these two programs in magnitude was less than 0.005 and in phase was a few tenths of a degree. By using these couplers to simulate a network analyzer, RF and microwave analysis can be made with SPICE, which can be a cost-effective and readily available computational tool for educators and practicing engineers