Polarization independent, integrated optical, acoustically tunablewavelength filters/switches with tapered acoustical directional coupler

Enhanced sidelobe suppression of the filter characteristics of tunable acousto-optical mode converters in LiNbO₃ has been achieved using for the first time tapered acoustical directional couplers. A sidelobe suppression of more than 15.5 dB could be demonstrated in a single stage device. By combining the mode converter with two integrated optical polarization splitters a polarization independent filter/wavelength selective switch has been fabricated with less than 3 dB intrinsic insertion loss, a polarization dependence of less than 1 dB, and a sidelobe suppression exceeding 14 dB     

Monopulse Networks for Series Feeding an Array Antenna

Series networks for feeding an array antenna are attractive because they can be designed compactly. A series "ladder" network is available which is particularly applicable for feeding a monopulse array antenna since it has complete independent control of the sum and difference excitations, minimum dissipative loss, and physical symmetry. This network consists of primary and secondary transmission lines feeding two sets of directional couplers that are interconnected to resemble a ladder. To obtain physical symmetry, the ladder is fed at the center by two hybrid junctions and an additional directional coupler. An experimental array fed by a ladder network was fabricated and tested. The design objectives of 25 dB sidelobe suppression for the sum and difference mode patterns were achieved.     

Tapered mismatched couplers

The criteria for adiabatic power flow along tapered mismatched directional couplers are discussed. The authors present the coupled local normal mode equations for tapered mismatched directional couplers. From these, the authors derive an optimally short profile for obtaining quasi-adiabatic power propagation. Apart from the trivial case where the mismatch is a constant, this is the only known mismatch profile for which analytical solutions of the coupled local normal mode equations exist. Conditions for which an adiabatic coupler can be used to obtain approximately 100% power transfer from one core to the other are also given     

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.     

Signal bandwidth of general n×n multimode interferencecouplers

Analytical expression of signal bandwidth of general straight and tapered N×N multimode interference (MMI) couplers is presented. The signal bandwidth is characterized as a function of mode relative energy, mode propagation delay time, and mode pulse broadening in the multimode section of MMI coupler. The model is used to evaluate the signal bandwidth of specific couplers. Results indicate that the signal bandwidth decreases seriously with the increase of channel number and channel guide space. Compared with the straight MMI coupler, the tapered MMI coupler has an improved signal bandwidth     

Ultralow sidelobe-level integrated acoustooptic tunable filtersusing tapered-gap surface acoustic wave directional couplers

We propose a new weighted-coupling scheme using tapered-gap surface acoustic wave directional couplers for realization of ultralow sidelobe-level integrated acoustooptic tunable filters (IAOTF's). Appropriate design analysis has been carried out for 30-mm-long filters operating at an optical wavelength of 1.55 μm in an X-cut Y-propagating LiNbO₃ substrate. New synthesized weighting functions have been used for the improvement of sidelobe level suppression over existing single-stage filters by as much as 27 dB. The -20 dB mainlobe width of the resulting IAOTF's varies from 2.7 to 3.9 nm only for the worst sidelobe levels ranging from -30.6 to -44.7 dB, respectively. It has also been shown that further suppression of sidelobe levels by 3-9 dB is possible if the filter is underdriven at 80% mode-conversion efficiency     

Directly Connected Image Guide 3-dB Couplers with Very Flat Couplings

The design and evaluation of the directly connected image guide 3-dB directional coupler is described. These couplers have several useful features as a component for millimeter-wave integrated circuits because of broadband and flat coupling characteristics, mechanical stability, and compactness. The bandwidth of the directly connected image guide coupler with proper dimensions and the nearly optimixed value of h extends to about 28 percent under the tolerance limits of +-0.25 dB of deviation in coupling from 3 dB. Furthermore, experimental verification has been performed, and, hence, the usefulness of the proposed directly connected couplers with appropriate tapered sections was confirmed, even at frequencies where higher modes could be excited.     

A new multiple-tuned six-port Riblet-type directional coupler in rectangular waveguide

Directional couplers are fundamental components for the realization of power splitting and combining networks. A basic component is the four-port coupler realized in a wide range of different electrical and geometrical configurations. Using multiport directional couplers, with six or more ports, compact power splitting and combining networks can be designed. Most of the multiport directional couplers in a rectangular waveguide found in literature use an E-plane branch-line layout. A special configuration of a six-port narrow-wall short-slot directional coupler (Riblet type) is presented here. The coupler has only one central coupling region, following the Riblet concept based on the differences among the propagation constants of the modes through the coupling region. A number of different solutions have been investigated and some examples are presented here. Moreover, a multituning realized by using input resonators permits one to significantly enlarge the bandwidth. A six-port coupler equally splitting on the output ports the power injected at each input port has been designed for a 8.4% working band. The theoretical and measured responses presented here prove the effectiveness of the multituning concept.     

Analysis of a Two-Section Coupler (Correspondence)

The use of single-section quarter wavelength TEM mode directional couplers having excellent wide-band performance is well known. A method for decreasing the coupling variation with frequency by cascading three quarter wavelength couplers has also been described. The purpose of this note is to analyze, for loose coupling, the behavior of a two quarter wave section coupler and compare the results with a coupler consisting of three sections.     

The Ultra-Bandwidth Finline Coupler

The "finline coupler" is a recently developed microwave circuit element with which it has been possible to assemble hybrid junctions, directional couplers, and polarization-selective couplers capable of operating over bandwidths of at least three-to-one in frequency. Constructional details and experimental results are given.     

Synthesis of Symmetrical TEM-Mode Directional Couplers

Exact synthesis procedures are derived for symmetrical three-section and five-section TEM-mode directional couplers. These synthesis procedures are based on the equivalence between the theory of directional couplers and stepped quarter-wavelength filters as previously described by Levy and Young. Explicit formulas for the parameters of three-section couplers are presented. A realizable insertion-loss function is derived for the five-section coupler resulting in an equal-ripple response. Although this function has an equal-ripple characteristic, it is not expressible in terms of Chebyshev polynomials. Results obtained for the five-section coupler show considerable improvement in bandwidth over a three-section coupler. For example, a five-section coupler of -3 /spl plus mn/ 0.5 dB has a bandwidth of 9.6:1 as compared with 5.8:1 for a three-section coupler of -3 /spl plus mn/0.5 dB. A five-section coupler of -10 /spl plus mn/ 0.5 dB was designed on this theoretical basis for the 555-4000 Mc band, and the measured shows good agreement with the theoretical coupling sponse, yielding a minimum directivity of 18.0 dB at 3.7 Gc.     

A directional coupler acoustooptic filter with reduced sidelobelevels

A two-waveguide directional coupler filter with an acoustically induced grating structure is proposed. The directional coupler filter has the advantage that it does not require input and output polarizers and does not require specific birefringent material properties. Since multiple acoustic waves could be applied simultaneously, this property could be used to couple both TE and TM polarizations from one waveguide to the other. This allows for filtering the required optical wavelength from both polarizations simultaneously. A notable weakness of acoustooptical filters and all mode-coupling filters is the high sidelobe levels in their optical transmission spectrum. A technique to suppress these high sidelobe levels in the proposed acoustooptic filter is presented. It is based on simultaneous application of several acoustic waves on the optical waveguide. This technique could be applied to any existing configuration of acoustooptic filters     

The digital directional coupler: improved design

Using a simple analytic model (weak-coupled mode theory), a new design is presented for digital directional couplers (i.e., directional couplers with tapered velocity mismatch and tapered coupling). These have relative immunity to variations in fabrication and operating conditions, and have a steplike switch response. The analysis shows that significantly improved performance can be obtained by simple modifications to the device shape given by R.R.A. Syms and R.G. Peall (1989)     

The design of mode evolution couplers

The design of an optical switch based on a directional coupler with tapered velocity and tapered coupling is investigated. The physical principle is based on power transfer by the evolution of a single normal mode. We consider cases where the coupling coefficient and guide mismatch variation are determined by optimized shape functions related to rectangle, raised cosine, Hamming, and Blackman window functions. Following simplified analysis by coupled mode theory, the physical parameters of the device are determined and the predicted performance is verified by the method of lines. Significant improvement in sidelobe levels and coupling length ran be obtained by careful design     

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     

The design of a mode selective directional coupler for a high power gyroklystron†

The design method of mode selective directional couplers from a transverse electric mode in a circular waveguide to the fundamental mode in a rectangular wave guide is presented in this paper. The design results for a TE₀₁ circular mode coupler intended for use in the output power measurement of a high power gyroklystron are reported; these results indicate that more than 50-80dB directivity and sufficient suppression of unwanted modes can be obtained with a coupler less than 07m in length. The effects of frequency and rectangular wave guide size on coupler parameters are also discussed in this paper     

Broad-band high-silica optical waveguide star coupler withasymmetric directional couplers

A broadband optical waveguide star coupler with asymmetric directional couplers is proposed. A coupling or splitting ratio of the coupler is flattened with respect to wavelength by choosing appropriate values for Δβ and complete power transfer length. The wavelength characteristics of uniform and alternating Δ&thetas;b directional couplers are investigated, and their broadband operation is shown theoretically. To demonstrate the feasibility of the new proposal, 8×8 star couplers composed of such asymmetric directional couplers are fabricated by using high-silica waveguides on a silicon chip. A star coupler composed of asymmetric directional couplers exhibited 2-dB loss variation in the wavelength range of 1.3-1.55 μm, and this value was almost one fourth of that of a star coupler composed of symmetric directional couplers     

一种高方向性弱耦合同轴耦合器的设计

从同轴定向耦合器的基本原理出发,提出了一种比较实用的高方向性弱耦合的同轴定向耦合器的模型。针对同轴定向耦合器端面的特性阻抗以及如何提高耦合器方向性或隔离度等问题进行了探讨。模拟与测试后的结果显示,此模型结构的同轴定向耦合器符合CDMA、W-CDMA和DCS等微波射频通信系统对于耦合度为35dB、隔离度大于65dB和驻波比小于1.05的同轴定向耦合器的指标要求。     

集成光学声光可调谐滤波器中的权重切趾

理论分析了权重耦合的声指向耦合器的原理及其在滤波器切趾中的应用 ,并且根据理论设计了声波导的方案 ,分析了应用这种声波导的滤波器的转换特性。在X切Y传的LiNbO3基底上实际制作了这种滤波器。实验测定表明 ,侧瓣被抑制到 - 14dB ,- 3dB带宽为 2 0nm。