Single-mode optical Y-branching circuit using deposited silica guides (DS guides)

A new optical Y-branching circuit using embedded single-mode glass waveguides is presented. The glass waveguides were made by depositing core glass on a silica substrate after forming grooves to contain the core (DS guides). Waveguide transmission loss is 0.6 dB/cm. The loss caused at a branching point is 0.13 dB when the branching angle is 0.3°.     

Optical directional coupler based on Si-wire waveguides

We fabricated optical directional couplers with Si-wire waveguides and demonstrated their fundamental characteristics. Their coupling-length was extremely short, several micrometers, because of strong optical coupling between the waveguide cores. Wavelength demultiplexing functions were also demonstrated for devices with a long coupled waveguide. Optical output from a device 800 /spl mu/m long changed reciprocally with 2.5-nm wavelength spacing between the parallel and cross ports.     

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     

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     

基于缺陷地结构的三分支线定向耦合器设计

针对高特征阻抗微带传输线的线宽过窄难以加工实现以及器件耐功率性差的问题,提出了利用缺陷地结构(DGS)提高微带传输线特征阻抗的方法,在传统三分支线定向耦合器结构支节线下方接地平面设计蚀刻矩形DGS结构,实现高特征阻抗支节线,完成阻抗匹配,且实现了较大的工作带宽。采用电磁仿真软件进行建模仿真分析、参数优化并制作出实际电路进行测试验证,结果表明该定向耦合器在4.5~5.5 GHz频带内具有较低的插入损耗、较高的幅度和相位稳定度,性能良好,具有一定的实用价值。     

一种实现超微光子晶体型定向耦合器的方法

在光子晶体定向耦合器中,通过减小两耦合波导之间介电柱的折射率来增大耦合系数,从而获得更短的拍长,形成超微的器件尺寸。耦合器的奇模场随调制折射率的减小变化不敏感,偶模场向更高频率的方向移动。在同一频率范围内,调制折射率减小,导致拍长随频率变化的函数曲线的斜率随频率增加而增大,这一特性可以在波分复用器中用来减小相邻信号频率差,在相同的器件长度下,可获得更多的信道。采用时域有限差分法验证了拍长随调制折射率减小而减小的变化规律。     

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     

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.     

Genetic algorithm-based characterization of the optical properties of flame-hydrolysis deposited silica waveguides

Genetic algorithms have been demonstrated to be a robust method for the calculation of the refractive-index profile of annealed germanium-doped flame-hydrolysis deposited (FHD) silica layers using measurements of the effective refractive indexes of the different modes of propagation. A nonuniform refractive-index profile in depth was obtained, which agrees well with the germanium concentration and density profiles measured for the films.     

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.     

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.     

All-optical multiplexing of femtosecond signals using an AlGaAsnonlinear directional coupler

The authors demonstrate multiplexing of femtosecond signals without the usual 3 dB loss of conventional passive multiplexers using an AlGaAs nonlinear directional coupler controlled by strong pump pulses     

Ionization-induced refractive index and polarization effects inLiNbO3:Ti directional coupler waveguides

Exposure of an LiNbO₃:Ti directional coupler to pulsed 16-MeV electrons was observed to nonequivalently affect the transverse electric-transverse magnetic (TE-TM) polarized transmission of a continuous wave 1300-nm optical signal through the channel waveguides. Two distinct ionization-induced attenuation responses were observed to depend on the magnitude of the optical power in the guides and on the polarization states. An hypothesis for these phenomena is advanced based on the presence of localized space charge fields arising from ionization-induced transient color centers, free carriers within or near the light guiding regions, and polarization conversion initiated through decreased mode confinement and scattering. Transient space charge fields causing localized changes to the refractive indexes in and near the guiding regions are believed to have caused both the loss of guiding and the onset of photorefractive-like processes     

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     

Numerical and experimental investigation of a 5-port mitre-bend directional coupler for mode analysis in corrugated waveguides

A directional coupler array with 5 ports integrated into a mitre bend for corrugated waveguide transmission lines at 140 GHz has been manufactured. The design is reviewed, and calculations on the performance for in-situ power measurement and mode discrimination are shown. Emphasis is given on detection of errors in alignment of the transmission system. Experimental tests are performed to benchmark the calculations. The results confirm the predictions and show that such a coupler is a viable tool for power measurement and basic mode analysis in high-power transmission systems.     

Optical intensity modulators using diazo-dye-substituted polymerchannel waveguides

The electrooptic (EO) modulation of 1.32 μm laser light is measured in Mach-Zehnder channel waveguides fabricated with diazo-dye-substituted polymers with coplanar-waveguide (CPW) or microstrip (MS) electrodes. Two types of channel waveguide fabricated by photobleaching or O₂ reactive-ion etching (RIE) exhibit the same EO coefficients r₃₃ under the same poling condition. However, the photobleached waveguides show a lower half-wave voltage than the RIE-fabricated ones because of both the optical power concentration in a core layer and the existence of an EO active cladding layer. These tendencies are well explained by considering “effective” overlap integrals between the optical and electric fields, including the distribution of EO-active regions. The maximum r₃₃ value (26 pm/V) of the poled diazo-dye-substituted polymer is obtained with an RIE-fabricated MS-modulator     

New technique for 2-port measurement using an 8-port directional coupler

It is shown that the complex scattering parameters of an arbitrary 2-port can be determined using an 8-port microwave network of suitable design and five power sensors.     

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.