Switching characteristics of variable coupling coefficient nonlinear directional coupler

This paper analyzes the characteristics of the variable coupling coefficient nonlinear directional coupler (VCC NLDC) in detail. The self-switching transmission curves of three types of NLDC with different coupler length are compared. Their phase-controlled transmission curves are compared, and these device acting as pump-controlled switches are analyzed. It is found that the VCC NLDCs show digital characteristics with the increase of the input power. As phase-controlled devices, the response of the VCC NLDC is binarylike when the input power is high. As pump-controlled devices, the transmission curves of the signal are similar to their self-switching transmission curves, except for some specific details.     

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     

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     

Proposed semiconductor narrow-band wavelength filter using directional coupler

A GaInAsP/InP waveguide narrow-band wavelength filter is proposed and analysed. The proposed wavelength filter is based on an asymmetric semiconductor directional coupler having a step-index waveguide and a double clad waveguide. It is numerically shown that a bandwidth as narrow as 5.4 nm is feasible for 1.3 mm long devices at a 1.53 mu m centre wavelength.<>     

Design of rectangular directional coupler using simple numericalalgorithm

A simple numerical algorithm for the design of a rectangular directional coupler (RDC) with arbitrary couplings is proposed. The performance of a designed RDC is also described. It is seen that the measured data agree well with the results predicted by using the proposed algorithm     

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.     

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     

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.     

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.<>     

A 1.3-/spl mu/m wavelength laser with an integrated output power monitor using a directional coupler optical power tap

A 1.3-/spl mu/m Fabry-Perot laser with a directional coupler power tap inside the laser cavity, used for diverting optical power to an integrated waveguide monitoring photodetector is demonstrated. The monitoring detector provides photocurrent which is linear with the front facet output power, with responsivity as high as 0.37 mA/mW, depending on the length of the directional coupler coupling region.     

Grating-assisted directional coupler filters using AlGaAs/GaAs MQW waveguides

Wavelength demultiplexing in the 800 nm region is demonstrated using grating-assisted vertical codirectional coupler filters formed in two AlGaAs/GaAs multiple quantum well (MQW) ridge waveguides. A filter bandwidth as narrow as 3 nm (full width at half maximum) and interwaveguide coupling efficiency of 95% with a coupling length of only 430 mu m were achieved. Channel spacing of 4 nm was obtained for five-channel wavelength demultiplexing with crosstalk suppression in excess of 10 dB.<>     

Optical waveguide directional coupler measurements using amicrocomputer-assisted TV camera system

Characterization of optical waveguide directional couplers using a microcomputer-assisted TV camera system is reported. A fluorescent technique is employed to visualize wave propagation in the optical waveguides, which exhibit small scattering. The method is simple and reproducible, and can be used to estimate waveguide losses and evaluate various optical devices such as waveguide lenses and waveguide interferometers on substrates. As an example of its application, parallel and nonparallel dual-chamber directional couplers and parallel triple-channel directional couplers are measured. Power transfer between the coupled channel waveguides is observed clearly, and coupling coefficients of the couplers are obtained nondestructively. The measured performance of the couplers is in good agreement with that predicted by coupled-mode analysis     

Stepped-impedance directional coupler with enhanced isolation using interdigital capacitance compensation

A novel and successful stepped-impedance coupler with enhanced isolation is presented. By incorporating the distributed interdigital capacitance at the ends of the coupled section in the planar structure, the even- and odd-mode phase velocities can be equalised so as to enhance the isolation. Measured results show an enhanced isolation of 47.5 dB at the centre frequency 2.4 GHz and a size reduction of 30% when compared with the conventional parallel-line coupler. It is also shown that the coupling frequency flatness is as broadband as 3.1 GHz.     

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     

Traveling wave optical modulator using a directional coupler LiNbO3waveguide

Fabrication methods for low drive voltage and broad-band LiNbO3waveguide directional coupler optical modulator are described. Optical waveguides were prepared by conventionaly Ti in-diffusion into LiNbO3c-cut plate. To obtain wide-band frequency response, traveling wave electrodes were used. Electrode characteristic impedance measured by time domain reflectometry method coincided well with the calculated value by conformal mapping. Measured electrode conductor losses followed square root of frequency. To reduce electrode conductor losses, asymmetric and 3-μm thick Al electrodes were used. Directional coupler optical modulator frequency response was analyzed, using the phase difference average value along the propagation directions. Calculated value by this method coincided well with measured value obtained by a swept frequency technique. The characteristics of this modulator at the 1.317-μm wavelength are as follows: 100 percent modulation voltage is 4 V, extinction ratio is 17 dB, optical insertion loss is 5.4 dB, 3-dB bandwidth is 3.6 GHz, and rise time is about 400ps.     

Integrated bistable optical multivibrator using electrooptically controlled directional coupler switches

An integrated bistable optical multivibrator based on two electro-optical directional coupler switches has been realised for the first time using Ti: LiNbO3 waveguides with two crossed feedback loops. The analysis and operation of the basic optical flip-flop are presented, and different feedback conditions and loops should provide other types of optical multivibrators, e.g. monostable and astable.     

Microstrip directional coupler with nearly ideal TEM coupler performance

A meandered parallel coupled-line structure is proposed to achieve high directivity within a wide bandwidth. By properly increasing the meandered parallel coupled-line sections, the high-directivity bandwidth becomes much wider. An example coupler is fabricated to verify the theory. More than 50 dB of isolation is achieved over a bandwidth of zero to twice centre frequency.     

CPW multilayer slot-coupled directional coupler

A new 3 dB CPW multilayer slot-coupled directional coupler between two CPW lines coupled through a rectangular slot etched on a common ground plane located between these lines is presented. The proposed directional coupler showed promising results, especially in terms of bandwidth (/spl sim/80%). The simulated results are compared with the measured data, and good agreement is reported.