Application of the finite-difference vector beam propagation methodto directional coupler devices

The finite-difference vector beam propagation method (FD-VBPM) is applied to optical guided-wave devices based on two-dimensional directional couplers. The FD-VBPM is first validated for a parallel coupler made of two identical step-index slab waveguides by comparing with the exact analytical solutions. Subsequently, the polarization beamsplitters and wavelength filters based on directional couplers are simulated. The polarization properties of these devices are examined     

Determination of the coupling length in directional couplers fromspectral response

A novel technique to determine the coupling length as a function of wavelength in directional couplers, especially in the case of weakly coupled, symmetrical directional couplers is described. The technique is illustrated by using Ag⁺-Na⁺ ion-exchanged directional couplers in BK7 glass. Application of this technique to asymmetrical directional couplers is also addressed     

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     

Field Theory Design of Rectangular Waveguide Broad-Wall Metal-Insert Slot Coulplers for Millimeter-Wave Applications

A design theory for broad-wall metal-insert slot couplers suitable for an inexpensive and very accurate metal-etching manufacturing technique is described. The method of field expansion into suitable eigenmodes used considers the effects of finite insert thickness and higher order mode interaction at the step discontinuities. Computer-optimized design data for -3-dB couplers in the Ka- and W-bands are given. The data of the Ka -band design are transferable into the U- and V-bands by suitable frequency scaling calculation. Since the metal-etching technique is also advantageously applicable for couplers in the centimeter wavelength range, optimized design data for E-plane slot couplers in the often used Ku- and R120-waveguide-bands are included in the tables given. A Ku-band metal-etched four-slot coupler prototype achieves a +-1dB bandwidth of the -3-dB coupling of about 2 GHz, together with -36-dB isolation. The measurements show good agreement with theory.     

A new analytic design technique for two- and three-way warped modecombine directional couplers

An analytic technique of designing ultra-wideband warped-mode two way and three-way microwave directional couplers is presented. With this matrix method it is possible to design couplers for any level of coupling by choosing a warping angle appropriate to the desired output amplitudes. The design technique involves obtaining a wave propagation matrix in analytical form as a function of the taper parameter, which in turn is a function of distance along the coupler length. The line parameters and the forward scattering matrix are then determined from the wave propagation matrix at any distance from the beginning of the coupler. The method is demonstrated for couplers using microstrip coupled comblines. The computed and the measured performances of a two-way and a three-way microstrip combline are presented for equal power splitting. These couplers were found to work between 1.5 and 8.5 GHz     

The local absorption technique: A straightforward characterization method for many optical devices

A new technique is analyzed and demonstrated to characterize integrated optical directional couplers. It is based on the locally induced absorption caused by a sliding Mercury drop. This technique works at any wavelength, does not rely on specific material properties, and leads to very fast knowledge of the characteristic parameters of the directional couplers.     

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     

Three-dimensional electromagnetic modeling of fiber-core effects onthe coupling characteristics of weakly fused tapered fiber-opticcouplers

Based on the full-wave formulations, which combine the finite element method add the boundary element technique, and the step-like approximation method, a three-dimensional (3-D) electromagnetic modeling approach is proposed in this work to investigate the fiber-core effects on the coupling characteristics of the weakly fused tapered couplers. We find the fiber cores have significant effects on the mode field patterns, coupling coefficients, and birefringence for the coupler with large normalized frequencies. The influence of the fiber cores on the coupling behavior for the real couplers, such as 3 dB power dividers, polarization beam splitters, and wavelength demultiplexing/multiplexing couplers, are also studied in 3-D view. It is found that the effects of fiber-cores in the weakly fused tapered couplers have to be considered for accurately modelling their coupling behavior, although the model with no core assumption can predict the trend of the coupling characteristics for the real couplers     

Bandwidth of forward and backward coupling directional couplers

This paper deals with the filter properties of directional couplers. Formulas are derived for the bandwidth in wavelength units of couplers consisting of two waveguides that exchange their power either in the direction of the incident wave (forward couplers) or in the opposite direction (backward couplers). Backward couplers require the presence of a diffraction grating on one or both waveguides but they can achieve very much smaller bandwidth than forward couplers and hence are useful for constructing narrow-band optical wavelength filters.     

Wavelength-flattened fused couplers

A technique is reported for the fabrication of fused couplers, which yields devices having splitting ratios substantially independent of wavelength. A low-loss, stable, single-mode 2×2 port coupler has been fabricated using this technique. The coupler has 50/50% coupling at both 1.3 and 1.52 ?m and 50% ± 9% coupling over the wavelength range 1.23 to 1.57 ?m.     

融熔型窄复用信道间隔波分复用器的研制

对如何实现偏振不敏感的窄复用信道间隔波分复用器进行了分析,采用熔融拉锥技术,实现了复用信道间隔为２５ｎｍ,波长隔离度为１８ｄＢ的波分复用器,并预计可以实现具有更窄复用信道间隔的波分复用器。     

Optical multi-mode interference devices based on self-imaging:principles and applications

This paper presents an overview of integrated optics routing and coupling devices based on multimode interference. The underlying self-imaging principle in multimode waveguides is described using a guided mode propagation analysis. Special issues concerning the design and operation of multimode interference devices are discussed, followed by a survey of reported applications. It is shown that multimode interference couplers offer superior performance, excellent tolerance to polarization and wavelength variations, and relaxed fabrication requirements when compared to alternatives such as directional couplers, adiabatic X- or Y-junctions, and diffractive star couplers     

A novel all-fiber optical interleaver with flat-top passband

An all-fiber optical interleaver with almost rectangular wavelength response is developed by using a new configuration. The device consists of a 2/spl times/2 and a 3/spl times/3 directional fiber coupler. Based on the digital approximation method of Fourier series, the relationships among the splitting ratios of the couplers, the length difference of interference arms, and the intensity transmission spectrum are analyzed. The results indicate that a uniform flattop spectral response can be obtained by the configuration when the length difference of interference arms and the coupling coefficient of the couplers, with some certain values, are given. The passband and stopband of optical interleaver are improved remarkably. The coupling ratio of couplers and the proportion of the length differences can be controlled accurately in the course of fabricating the interleaver. A novel structure of an interleaver is fabricated by using the fused biconical taper technics in experiment. The experimental results are in good agreement with the analytical ones.     

Waveguide input grating coupler for wavelength-divisionmultiplexing and wavelength encoding

We demonstrate the wavelength-division multiplexing (WDM) and wavelength-encoding capability of input waveguide grating couplers. The couplers are designed to have a predetermined wavelength response in addition to their conventional function of coupling an incident beam from, e.g., an optical fiber into a planar waveguide. The first example shows the WDM function: separating each of four input wavelengths into a different focus position in the waveguide. The second example shows wavelength encoding: translating a certain wavelength into a desired configuration of focus positions that is different for four different input wavelengths. The couplers were fabricated in an InP waveguide for ~1550-nm wavelength and the separation between the wavelengths was 10 nm. A WDM coupler with a narrower channel separation of 2 nm was also fabricated and successfully demonstrated     

Variational analysis of fused tapered couplers

A variational technique is used to evaluate the coupling ratio of a fused coupler. The technique can be used for both strongly and lightly fused couplers. Simple formulas are presented for use in regions of high V-value and are shown to be in agreement with the more lengthy beam propagation calculations. The importance of the fibre core in determining the field shape is highlighted. A realistic coupler model containing a gradual taper is presented and the strong wavelength response of the coupling ratio is confirmed by numerical means.     

Design of grating-assisted waveguide couplers with weightedcoupling

The design of grating-assisted, channel waveguide codirectional couplers is demonstrated using the Gel'fand-Levitan-Marchenko inverse scattering method. Weighted coupling coefficients are computed from rational expression for the desired wavelength response. Approximate formulas that relate the waveguide and grating geometries to the computed coupling coefficients are derived. The technique is illustrated by designing a directional coupler with a third-order Butterworth filter characteristic and a 130 Å full-width-half-maximum bandwidth     

玻璃基离子交换型宽带22 3dB耦合器研究

为满足2N光功率分配器的制作和应用的需求,对宽带集成化22 3dB耦合器进行了深入的理论和实验研究。采用3-D光束传播法,对传统的非对称X结进行了模拟改进,设计了低损耗且具有较宽工作带宽的22 3dB耦合器。采用Ag+-Na+离子交换技术在玻璃基上成功制作了非对称X结结构的宽带22 3dB耦合器。通过对1260nm~1360nm和1460nm~1600nm两个波段宽带光源的光谱测试,得到在宽带范围内小于4.0dB的插入损耗,光谱谱线相对平坦,波长依赖性较小,均匀性小于0.5dB。结果表明,采用这种非对称X结并结合离子交换工艺,可以在玻璃基上制作出宽带的22 3dB耦合器,这为进一步优化器件性能,研制成功具有应用价值的器件奠定了基础。     

Integrated directional couplers with photodetectors by hydridevapour phase epitaxy

The hydride vapour-phase-epitaxial crystal growth technique has been used to realise integrated waveguide-photodetectors and, for the first time, integrated directional coupler-photodetectors for detection in the 1.3 μm to 1.55 μm wavelength range. The GaInAsP waveguides which formed the directional couplers had propagation losses of 2±0.5 dB/cm and more than 90% of the guided light was coupled into the photodetectors. The directional couplers were symmetric with respect to the launch port and had 3 dB coupling lengths of about 1.45 mm     

An Analytical Method for Calculating Microstrip Transmission Line Parameters

When finite difference techniques are applied to the solution of coupled-line parameters for microstrip transmission lines, the computation times become prohibitively long. This paper describes an analytical method for calculating such parameters if TEM propagation is assumed. The method is applicable to a wide range of planar TEM mode transmission line calculations where the boundaries and dielectric interfaces are rectilinear. The accuracy of the analytical technique has been verified by experimental work on 10 dB and 6 dB coupled-line directional couplers and a parallel-coupled Cohn type 6 resonator filter.     

Asymmetric multimode couplers

An asymmetric multimode coupler consists of two dissimilar multimode fibers. A simple theoretical analysis of asymmetric multimode couplers that will enable couplers to be designed with specific performance parameters is presented. The theoretical predictions are compared with the measured behavior of specially fabricated couplers. A novel technique to determine the performance of a linear bus of identical asymmetric couplers from measurements on a single coupler is introduced