Single and multi-section CTL and branch-line CPW directional couplers with broadband performances for SIMMWIC

Single and multisection branch-line and coupled transmission line (CTL) directional couplers have been implemented in coplanar waveguide (CPW)-technology, showing broadband performances. The branch-line and CTL couplers had a phase balance of ±5° and a power variation of ≤1.5 dB in the coupling over a bandwidth of greater than 25% and 75% respectively. The experimental values for the couplers were found to agree well with simulated results. The CPW couplers provide larger bandwidth than comparable microstrip couplers. Investigation on different feeding structure for the branch-line couplers is also presented.     

Nonuniform transmission line codirectional couplers for hybridMIMIC and superconductive applications

A new design approach for thin-film codirectional quadrature couplers and their applications is described. An in-depth analysis and semi-empirical design curves are presented for these couplers. Forward-wave coupling is achieved by making use of the difference between even- and odd-mode phase velocities. Modified nonuniform codirectional couplers with a dummy channel for continuously decreasing or increasing taper and employing wiggly, serpentined and smooth coupled edges have been designed and tested. It is found that a wiggly coupler can achieve a 50% length reduction compared to a smooth-edge coupler. A further 60% length reduction compared to a wiggly coupler is achieved by a serpentine coupler. Coupler performance for wiggly and serpentined configurations is computed by choosing a realizable phase velocity function for a given coupler length. Either constant 90° or -90° phase shift is possible with these couplers giving significant design flexibility in some applications. The results for a K_u-band Σ-Δ magic-T circuit employing a 0 dB wiggly coupler and a -3 dB smooth-edge coupler are also presented in the paper     

E面分支波导耦合器的遗传算法优化设计

介绍了E面分支波导耦合器基于遗传算法的优化设计方法。详细讨论了遗传算法的优化策略和一个四端口5dB五分支波导耦合器设计实例，及该实例的等效网络综合结果和优化策略和一个四端口5dB五分支波导耦合器设计实例，及该实例的等效网络综合结果和优化后的HFSS软件仿真结果。通过比较可以发现，遗传算法优化结果完全满足期望的优化目标，经过优化设计，耦合器的频响特性有了明显改善。     

宽频带槽波导定向耦合器的分析与设计

用微波网络方法讨论了宽频带槽波导定向耦合器的分析和设计问题.使用部分介质填充非对称双槽波导的横向等效网络,编制了相应求解程序.计算表明,本文设计的两种3mm波段耦合器的相对带宽都在24%以上,是常规的对称双槽波导耦合器带宽的5倍,而它们的长度却比文献中已有的设计都大为缩短.     

Reduction of motion artifacts using a two-frequency impedanceplethysmograph and adaptive filtering

The authors measured transthoracic impedance in nine presumed healthy adult subjects with a two-frequency plethysmograph at 57 kHz and 185 kHz. The measurement protocol included periods of normal breathing without motion and periods of motion without breathing. The authors analyzed the cross-correlation and the ratio between the signals at both frequencies for all the different maneuvers. The correlation coefficient was between 0.97 and 1 for breathing, the minimal cross-correlation (0.81) was for simulated obstructive apnea. The authors found that the amplitude ratio between the two-frequency signals was different for normal breathing and for motion. Based on these results, the authors designed and tested an adaptive filter to increase the signal-to-artifact ratio (SAR). The increase in SAR (mean±standard deviation) compared with the signal at 57 kHz was: 183%±117% for arm movement, 133%±93% for leg movement, and 34%±62% for simulated obstructive apnea     

Analysis of generalized Mach-Zehnder interferometers forvariable-ratio power splitting and optimized switching

The nonideal integrated optical N×N generalized Mach-Zehnder interferometer (GMZI) employing multimode interference (MMI) couplers is analyzed using transfer matrix techniques. Deviations in the phase relations and the power splitting ratio of the MMI couplers are included in the theory, along with the effects of phase errors in the interferometer arms. The predictions of the theory are compared to the response of a 4×4 GMZI which has been fabricated. The device is operated as both a variable-ratio power splitter and a switch by compensating for the phase errors in the interferometer arms, but the performance is ultimately limited by the nonideal imaging in the MMI couplers. The practicality of these applications is investigated by performing a tolerance analysis for the operation of 1×N power splitters and switches for N up to 10     

Directional couplers using fluorinated polyimide waveguides

Optical properties of directional couplers using a fluorinated polyimide waveguide were demonstrated. At a wavelength of 1.3 μm, directional couplers with the refractive index difference of 0.3% between the core and cladding have a maximum power coupling ratio of more than 97 and 96% for TE and TM polarisations, respectively. The excess loss for a 3-dB coupler was as low as 0.3 dB. Moreover, the change in the coupling ratio of the 3-dB couplers remained within 0.5% between 25 and 100°C     

Low-loss highly overcoupled fused couplers: fabrication andsensitivity to external pressure

A flame brush technique for fabrication of optical directional couplers that maintain low loss over many coupling cycles is discussed. Couplers with excess losses less than 3% and with 2500 power transfer cycles in the coupling are reported. Such couplers, which have a narrow wavelength band transmission (0.12 nm), can be tuned by applying an external hydrostatic pressure. The long fused couplers can also have application as optical fiber sensors     

Polarization independent narrow channel wavelength divisionmultiplexing fiber couplers for 1.55 μm

A polarization-independent narrow-channel (PINC) wavelength division multiplexing (WDM) coupler for operation at 1.55 μm has been designed based on the birefringent properties of fused single-mode couplers. These couplers are made from both conventional single-mode fiber (SMF) and dispersion shifted fiber (DSF). The couplers are designed so that the coupling-coefficient-length products for the two orthogonal polarizations are π out of phase. As a result of the long coupling lengths required, these couplers have very small cross-sectional dimensions, typically on the order of 10 μm     

Monolithic GaAs interdigitated couplers

This paper described the design, fabrication, and performance of two monolithic GaAs C-band 90° interdigitated couplers with 50- and 25-ω impedances, respectively. A comparison of the performance of these two couplers show that the 25-ω coupler has the advantages of lower loss and higer fabrication yield. the balanced amplifier configuration using 25-ω couplers will require a fewer member of elements in the input-output matching circuit of the FET amplifier. The fewer number of matching elements results in great savings in the GaAs real estate for microwave monolithic integrated circuits (MIMIC's). Both the couplers have been fabricated on a 0.1-mm-thick GaAs SI substrate. The measured results agree quite well with calculated results. The losses of the 50- and 25-ω couplers are 0.5 and 0.3 dB, respectively, over the 4-8-GHz frequency band.     

Wavelength sensitivity in directional couplers

Measured and calculated crosstalk ratios as a function of wavelength are compared for proton exchanged and annealed LiNbO₃ directional couplers at λ=1550 nm. The analytical technique employed models the experimentally determined wavelength sensitivities reasonably well. The analytical technique is further used to predict comparable functions for titanium indiffused couplers, and these results are compared to other calculations taken from the literature. No significant difference in sensitivity is noted between the two waveguide forming techniques     

Analysis of detuned second-order grating output couplers with an integrated superlattice reflector

Analysis is presented of second-order gratings at wavelengths detuned from the reflection bandwidth. These gratings have applications, for example, as surface-emitting output couplers in monolithic integrated master oscillator power amplifier (M-MOPA) configurations. The grating output couplers have reflectivities below 10/sup -4/ at an emission wavelength of 874 nm when the Bragg condition of the second-order grating occurs at 904 nm. When used in conjunction with a superlattice reflector integrated into the substrate, the surface emission can exceed 85% of the radiation incident on a 250 mu m long grating. Consequently, these gratings can act as nearly ideal output couplers in a M-MOPA without introducing undesirable feedback to the amplifier or master oscillator.<>     

Three-guide optical couplers in GaAs

Three-guide optical couplers consisting of three 4.75-μm-wide slab-coupled rib guides separated by 4.25μm have been fabricated in GaAs. The performance of these couplers at 1.28 μm is in close agreement with that predicted using a modified effective-index method to obtain an approximate analytical solution for this type of coupler. The coupling length needed to symmetrically transfer power from the center guide to the two outside guides was 3.2 mm. At this length, less than 1 percent of the power remained in the center guide. The length needed to transfer power from one outside guide to the other outside guide was ≈ 6.4 mm, which isapprox sqrt{2}- times that of a similar two-guide coupler and twice that required to couple power from the center guide to the two outside guides. The power transfer efficiency in this case is not as good as when power was inputted into the center guide. Three-guide couplers of this type should prove useful as power dividers and combiners, especially in cases where waveguide bend losses preclude the use of"Y"- junctions. They may also prove useful as replacements for two-guide couplers where either sharper transfer characteristics are desired or where losses due to waveguide bends are again unacceptable.     

Wavelength-selective fused fiber couplers utilizing fielddifference between core and cladding modes

It is shown that wavelength-selective fused taper couplers can be made by using the large difference in field distribution, between core and cladding modes. It is evident from the calculation results that fibers with a high-index difference and a thin outside diameter are necessary to fabricate the couplers. Fused taper couplers are made of thin fibers with a cladding diameter of 66.0 μm and an index difference of 0.84%. The splitting ratio of the coupler obtained is more than 20 dB in the 1.53-μm region and less than -20 dB in the 0.8 to 1.0-μm region. The loss is less than 0.2 dB and 0.4 dB in the 1.53-μm and the 0.8 to 1.0-μm regions, respectively     

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     

Broadband overlaid inset dielectric guide coupler with very flatcoupling

In this paper overlaid parallel coupled inset dielectric guides are proposed for broadband applications to directional couplers. This structure provides much flatter and higher coupling than the conventional one without an overlay. The propagation and coupling characteristics of the coupled guides are obtained by using the integral equation formulation and Galerkin's procedure. Numerical results for two limiting cases are compared with available measured data, showing good agreement. Effects of thickness and dielectric constant of the overlay are examined on coupling and bandwidth. It is found that by suitable choice of these parameters very flat coupling can be achieved for a wide frequency range which is still within the fundamental-mode bandwidth. Examples of couplers with the bandwidth exceeding 45% for the coupling of 3±0.25 dB are presented     

Theoretical and experimental research on nonradiative dielectric waveguide directional couplers

A practical design of nonradiative dielectric (NRD) waveguide directional couplers is presented. The dispersion characteristics of coupled NRD-guides and the scattering coefficients of NRD-guide directional couplers are studied as well as the transitions from metal rectangular wave-guide to NRD-guide couplers. Experiments of 3-dB and 10-dB NRD-guide couplers in ka-band show that the couplers are of good performance and promise in millimeter-wave integrated circuits.     

Monolithic GaAs Interdigitated Couplers

This paper deseribes the design, fabrication, and performance of two monolithic GaAs C-band 90° interdlgitiited couplers with 50- and 25-Omega impedances, respectively. A comparison of the performance of' these two couplers shows that the 25-Omega coupler has the advantages of lower loss and bigher fabrication yield. The bafanced amplifier configuration rising 25-Omega couplers will require, a fewer number of elements in the input-output matching circuit of the FET amplifier. The fewer number of matcfdng elements results in great savings in the GaAs real estate for microwave monolithic intergrated circuits (MMIC's). Both the couplers have been fabricated on a 0.1-mm-thick GaAs S1 substrate. The measured results agree quite well with calculated results. The losses of the 50- and 25-Omega couplers are 0.5 and 0.3 dB, respectively, over the 4-8-GHz frequency band.     

Optimum field theory design of broad-band E-plane branchguide phase shifters and 180° couplers

Optimum rectangular waveguide E-plane branch guide phase shifters and 180° branch guide couplers are designed with the rigorous method of field expansion into normalized eigenmodes. The design includes both the higher order mode interaction between the step discontinuities and the finite step and branch heights. The phase shifter design applies the Schiffman principle to branch guide couplers where two ports are short-circuited. The 180° coupler design combines the advantage of the broadband potential of multiple-branch couplers with the low-insertion-loss qualities of E-plane stub-loaded phase shifters. A computer-optimized phase shifter prototype for the waveguide Ku-band (12-18 GHz) shows a 90°±1° differential phase shift with reference to an empty waveguide within about 23% bandwidth. Five-branch three-stub coupler prototypes, designed for 3±0.2 dB coupling, for the waveguide Ku- and Ka-bands (26-40 GHz) achieve a 180°±1° differential phase shift at the output ports within about 19% bandwidth, as well as more than 30 dB isolation and return loss. The theory is verified by measured results     

Novel mass-fabrication of fibre couplers using arrayed fibreribbons

To achieve high productivity and high density packaging of fibre couplers for practical systems, a novel mass-fabrication process using arrayed fibre ribbons has been developed. The fabricated arrayed-fibre coupler consists of four couplers which are all fabricated together from four-fibre ribbons. Each fibre coupler had 3 dB coupling ratio to within 49.3±2.1%. It has been confirmed that plural fibre couplers with equal coupling ratio can be simultaneously fabricated by the mass-fabrication process