Switching power reduction using a pumped nonlinear directional coupler

We show that in a nonlinear directional coupler (NLDC) in which the signal is controlled by a pump of appropriate and different wavelength, the power needed for full switching is 3 times lower than for the same device used as a self switch. This power requirement is only /spl radic/3 times higher than for a Mach-Zehnder switch, which makes the NLDC even more appealing for practical multiplexing and switching applications.     

三分支可变阻抗任意分贝集总元件定向耦合器

通过奇偶模分析方法,得到了可变阻抗任意分贝二分支集总元件定向耦合器的设计公式,并给出了8种拓扑结构,然后通过级联得到了三分支可变阻抗任意分贝集总元件定向耦合器的设计公式及拓扑结构.经ADS仿真验证,设计所得结果与仿真结果完全一致,隔离度和反射都在20 dB以上,(3±0.5)dB带宽达到了20 MHz.     

The calculation of switching power of symmetric and asymmetric nonlinear directional couplers with variable coupling coefficient

It is proposed that the switching power of symmetric one-coupling-length nonlinear directional couplers (NLDC) with variable coupling coefficient (VCC) can be calculated as the weighted average of the local critical power of the coupler. Further, it is shown that the switching characteristics of a one-coupling-length VCC NLDC are determined mainly by the first half of the coupler and the switching power of an asymmetric VCC NLDC can be calculated as the weighted average of the local critical power over the first half of the coupler. Both symmetric and asymmetric examples are presented.     

Slotted waveguide directional coupler characteristics

A moment method (MoM) solution for slotted waveguide directional couplers which is sufficiently accurate for predicting the couplers' characteristics is demonstrated. The slot length in the waveguide directional couplers considered is about four wavelengths and the wall thickness is about 0.27 λ. To simplify the numerical computation, the formulation assumes a uniform field across the slot aperture and utilizes Galerkin's method with the entire domain sinusoidal basis. A self-consistent method taking the finite wall thickness into account avoids an additional matrix equation, as in other MoM formulations. The final solution forms the basis for an efficient computer code applicable to dielectric-loaded slotted waveguide directional couplers. The uniform field assumption restricts the present solution to narrow slots. Numerical results verify, by comparisons with published analytical and experimental data, that this solution is valid for slot lengths as long as 4λ. A detailed discussion of the characteristics of narrow-wall and broad-wall slotted waveguide directional couplers is presented     

Optical bistability in a nonlinear directional coupler

In the nonlinear directional coupler, the optical field and the nonlinear material usually interact in a spatially and temporally local fashion and the device exhibits a nonlinear transmission characteristics, but it is not bistable. In this paper, it is shown theoretically that optical bistability in the input optical power is possible for the nonlinear directional coupler if the local phase change of the optical mode propagating through tile coupler is influenced by the excitation over the whole coupler. This condition can be satisfied in a coupler based on biased-pin-diodes comprising coupled asymmetric quantum wells in the i-region, Calculations show that in this configuration, the nonlinear directional coupler can exhibit sharp switching characteristics, low switching optical powers, optical bistability or bifurcation     

Leaky mode directional coupler for prism coupling interconnection

A leaky mode directional coupler was fabricated with its beam shaped into a Gaussian-like profile and was experimentally demonstrated for suppressing the diffraction of an out-coupled beam. The demonstrated coupler consists of a multilayered waveguide with six layers that are embedded in a symmetric slab waveguide. The out-coupled beam profile was measured to be shaped into a Gaussian function by using the prism coupling method. There was an excellent agreement between the measured and theoretically predicted coupling angles, and it was also confirmed that the diffraction was suppressed.     

Microstrip directional coupler with flat coupling and high isolation

Based on the open-circuited slotline to realise capacitive compensation, a microstrip directional coupler with high isolation is investigated. Meanwhile, by adding external matching networks at the input/output ports, bandwidth is enhanced and a flat coupling is obtained. Centred at 2.4 GHz, a 3 dB directional coupler is designed, fabricated and examined. Both simulated results and measured data are presented, and good agreement between them is observed     

Very low power nonlinear directional coupling in a p-i (MQW)-nvertical coupler using an electrooptic feedback

An optically controlled 1×2 optical switch based on a vertically arranged directional coupler in which the guiding regions are GaAs/GaAlAs multiple quantum wells is discussed. The device can be switched electrically in a very efficient way (5-V driving voltage for a 330-μm-long sample) as well as optically. When connected to a constant-current source, the system shows high optical nonlinearities and can be all-optically switched with very low incident optical power on the order of 0.1 mW     

Broadband microstrip directional coupler

A nonuniform microstrip directional coupler with sinusoidally modulated coupling function is presented. The ripple and the amplitude response are controlled by the index of modulation m and the periodicity P of the function. For demonstration, a 20 dB ± 6% coupler is constructed on two different substrates and the experiment shows much flatter coupling response than the uniform or exponential line directional couplers.     

Active surface-wave directional coupler

We report experimental results which show that noncollinear surface-wave mixing on [111]-cut bismuth?germanium oxide can be used to realise an active, switchable directional coupler. For low-level inputs, the coupling is enhanced by as much as 20 dB by a semiconductor placed over the interaction region. The directivity is found to be greater than 40 dB.     

Non-evanescent adiabatic directional coupler

A directional coupling mechanism based on an adiabatic coupling between three optical modes is suggested. The optical power transfer between two waveguides which are far apart is mediated by adiabatic coupling between zero-order optical modes of the individual waveguides and a high-order intermediate mode. The analytical model for an adiabatic three-mode coupling based on a scalar wave equation is presented. The directional coupling via the adiabatic mode coupling between copropagating modes is described and compared with a nonadiabatic directional coupling assisted by periodic perturbation. It is shown that adiabatic directional coupling has much less sensitivity to the mode parameters and to the wavelength     

Dual adjacent directional coupler

The design of a compact dual directional coupler, which can be readily broadbanded using existing published data, is presented. The two coupled output transmission lines are laterally aligned on opposite sides of the main transmission line. Experimental results of a 0.3?2.0GHz 23dB coupler are presented.     

Single-mode fiber-film directional coupler

Directional coupling has been observed both from a single-mode fiber to a single mode planar polymer waveguide and vice versa. The fiber coupler was prepared by polishing. The matching of propagation constants was achieved by using a polymer film only a few hundred nanometers thick.     

New application for nonlinear directional coupler: intensity controlled tunable optical filter

A novel intensity controlled optical filter is proposed. A reduction in bandwidth and peak efficiency is observed with increase in power. The device can in special cases operate as a linear optically tunable filter with no reduction in bandwidth or efficiency.<>     

An analysis of a planar optical directional coupler with a losslessKerr-like coupling medium

The nonlinear all-optically controlled coupling characteristics are studied analytically and numerically for two planar optical waveguides coupled through a lossless Kerr-like slab. The exact dispersion equation for this waveguiding structure is derived in terms of Jacobian elliptic functions. The optical intensity-dependent coupling length is described as a combination of symmetriclike and antisymmetriclike modes of propagation, derived from the nonlinear combination of the independent modes of the structure. A simple analytical formula is derived for the critical power, defined as the power above which the antisymmetric mode disappears and complete energy transfer between the two waveguides is no longer possible. The analysis provides insight into the complicated nature of the waveguiding structure behavior, and it shows one possible approach to solving difficult propagation problems in nonlinear optical waveguides of this or similar configuration     

Mode excitation theory and experiment of single-mode fiber directional coupler with strong coupling

The mode excitation theory is presented to analyze single-mode optical fiber directional couplers with transverse strong coupling, which either the weakly coupling theory or the ray theory fails to expound. By using the equivalence between the waveguides with square and circular cross sections, regarding the coupling zone of the coupler as a single waveguide, the excitation coefficients of the propagation modes in the coupling zone excited by the modes in the input waveguide have been evaluated. The theoretical coupling amount and insertion loss have been studied. Using a special monitoring technique to control the coupling length, several couplers with various coupling amounts have been made by the polishing method. The spectral characteristic of the coupling amount has been measured and compared with the theoretically inferred result. The two are found to agree with each other. The offset effect on the coupling amount has also been measured and it is different from that of the weak coupling device-the Stanford coupler.     

Backward directional coupler for weak coupling of double-sided microstrip lines using longitudinal double-slots

A backward directional coupler for double-sided microstrip lines is presented. Aligned microstrip lines are coupled via two parallel slots in the common ground plane. This design works well for weak coupling smaller than 20 dB and has some advantages over the single-slot coupler. Geometrical dimensions of the proposed coupler design are presented for coupling values of 20, 25 and 30 dB, together with measurements for a 30 dB coupler.     

飞秒弧子脉冲在非线性定向耦合器中的传输控制研究

本文研究了超短脉冲在非线性定向耦合器中的传输控制。在飞秒级超短脉冲情况下 ,三阶色散效应变得很重要 ,需对在耦合器中的皮秒级脉冲传输控制方程进行修正。用对称分步傅里叶变换方法进行数值模拟分析 ,结果表明通过选择不同强度的正交极化同步控制脉冲 ,可对在NLDC中超短信号弧子脉冲的传输方向进行控制     

A novel mixed conventional microstrip and composite right/left-handed backward-wave directional coupler with broadband and tight coupling characteristics

A novel backward directional coupler, composed of a conventional microstrip (C/spl mu/S) line and composite right/left-handed (CRLH) line, is proposed. This coupler is functionally backward but it is based on a forward-type coupling phenomenon. The coupler is shown to exhibit broad bandwidth and tight coupling characteristics. The theoretical circuit-model results are supported by full-wave and experimental evidence. A quasi 0-dB prototype with more than 50% bandwidth is demonstrated.     

Switching characteristics of directional couplers with alongitudinal electrode gap

The effect of passive phase shift regions on the performance characteristics of parallel waveguide couplers is considered. In particular, a longitudinal electrode gap in addition to phase shifts in the adiabatic input and output taper regions is considered. Both types of phase shifts have a degrading impact on the accessibility of some switching states. However, an electrode gap combined with taper region phase shifts may be beneficial for certain traveling wave electrode configurations. For a certain combination of gap and electrode lengths a through state with better than 30 dB crosstalk over an extended voltage range has been identified