Low drive voltage directional coupler optical switch with reduced voltage-length product

The phase change*interaction length product needed to switch a directional coupler is shown to be reduced by decreasing the coupling coefficient at the middle of the interaction region. With this improved structure, a voltage-interaction length product of 3.6 V cm was achieved with a LiNbO/sub 3/ device at a 1.3 mu m wavelength.<>     

Directional coupler optical switch constructed from field-induced waveguides

A novel directional-coupler optical switch based on the concept of the field-induced guide is demonstrated for the first time. The device exhibits a good switching characteristic between two output ends with a crosstalk of -10 dB at a 1.15 mu m wavelength for a device with an 800 mu m coupling length.<>     

A Mach-Zehnder interferometer electro-optic switch with ultralow voltage-length product using poled-polymer/ silicon slot waveguide

By using poled-polymer/silicon slot waveguides in the active region and the Pockels effect of the poled-polymer, we propose a kind of Mach-Zehnder interferometer (MZI) electro-optic (EO) switch operated at 1 550 nm. Structural parameters are optimized for realizing normal switching function. Dependencies of switching characteristics on the slot waveguide parameters are investigated. For the silicon strip with dimension of 170 nm×300 nm, as the slot width varies from 50 nm to 100 nm, the switching voltage can be as low as 1.0 V with active region length of only 0.17–0.35 mm, and the length of the whole device is only about 770–950 μm. The voltage-length product of this switching structure is only 0.17–0.35 V.mm, and it is at least 19–40 times smaller than that of the traditional polymer MZI EO switch, which is 6.69 V.mm. Compared with our previously reported MZI EO switches, this switch exhibits some superior characteristics, including low switching voltage, compact device size and small wavelength dependency.     

Directional coupler with curved lines

A curved line directional coupler is designed and is found to give very good response. Substantial length reduction is obtained as compared to a quarter wave uniform line directional coupler.     

Directional coupler switches with optical gain

We discuss the design and characteristics of directional coupler switches in semiconductor materials (GaAs/GaAlAs) which exhibit optical gain by laser action. Equal gain in the bar and cross states is achieved by carrier-induced changes in the real as the well as the imaginary parts of the refractive index in directional coupler structures. Conditions for equal gain and crosstalk, design tradeoffs, and saturation characteristics in terms of amplified spontaneous emission in relation to saturation power are briefly discussed.     

Low-voltage vertical directional coupler switch with suppressedelectroabsorption

We have studied the performance of a vertical directional coupler in which a multiple quantum well and a bulk semiconductor material act as the cores of the two guides in two arms. The power output of the device is expected to be unaffected by the electroabsorption effect in a directional coupler based on quantum confined Stark effect even when operated very close to the excitonic absorption edge. The above principle is utilized in realizing low-voltage switching and almost equal power in bar and cross states in a multiple-quantum-well (MQW) vertical directional coupler. Our calculation for a vertical coupler composed of InGaAsP bulk and InGaAsP-InP MQWs show switching voltages comparable to that of a similar coupler composed of a more complex barrier reservoir and quantum well electron transfer (BRAQWET) structure, with a slightly lower value of power output     

Push-pull fused vertical coupler switch

A single-electrode push-pull fused vertical coupler (PVC) switch using macroscopic crystal inversion symmetry is demonstrated. The anisotropic linear electrooptic effect in a zinc-blende crystal is used to achieve optical switching under 12-V reverse bias for a 6.9-mm-long FVC whose two guiding layers have different crystal symmetries. No switching is observed for the identical structure in which the two guiding layers have the same crystal symmetry     

Directional coupler using acoustic surface waves

The properties of interdigital transducers have been used to construct a directional coupler. The coupler consists basically of an array of eight transducers etched from an aluminium film deposited on a lithium-niobate substrate. Experimentally, a directivity of 17 dB was obtained at 75 MHz.     

Remotely controlled integrated directional coupler switch

In this paper experimental results concerning the remote control of a bistable directional coupler switch are reported. It is shown that the output light from the coupler can be switched from one channel to the other via switching information contained in the incident light itself. The principle of operation of the device is demonstrated using a coupler fabricated in an LiNbO3substrate. A switching time of the order of 100 μs has been obtained, limited only by the electronic feedback loop used in the experiment.     

A directional coupler acoustooptic filter with reduced sidelobelevels

A two-waveguide directional coupler filter with an acoustically induced grating structure is proposed. The directional coupler filter has the advantage that it does not require input and output polarizers and does not require specific birefringent material properties. Since multiple acoustic waves could be applied simultaneously, this property could be used to couple both TE and TM polarizations from one waveguide to the other. This allows for filtering the required optical wavelength from both polarizations simultaneously. A notable weakness of acoustooptical filters and all mode-coupling filters is the high sidelobe levels in their optical transmission spectrum. A technique to suppress these high sidelobe levels in the proposed acoustooptic filter is presented. It is based on simultaneous application of several acoustic waves on the optical waveguide. This technique could be applied to any existing configuration of acoustooptic filters     

GaAs/AlGaAs directional coupler switch with submillimetre device length

A GaAs/AlGaAs directional coupler switch, for the first time with a device length shorter than 1 mm, has been fabricated by utilising the good controllability of molecular beam epitaxy and reactive ion beam etching. The switching voltage is as low as 5V. The extinction ratio is 17dB for a crossover state and 14dB for a straight-through state.     

Fused coupler switch using a thermo-optic cladding

An optical switch based on a single-mode fused coupler has been fabricated. The switching is achieved by a thermal refractive index change of a silicone resin cladding material in the coupling region. Fabrication details and device characteristics are described     

Directional coupler with high directivity using metallic cylinders on microstrip line

A directional coupler with high directivity performance using metallic cylinders on the microstrip line is presented. By using two rows of periodic metallic cylinders on a microstrip coupler, the odd-mode phase velocity is slowed down, and thus the directivity can be greatly improved for equal odd- and even-mode phase velocities. The parameters of metalised cylinders, which have an effect on the coupler performance, are investigated. A 12 dB coupler at 2.41 GHz has been designed and measured, providing excellent directivity. Theoretical and experimental results are presented.     

Three-guide directional coupler as polarisation independent optical switch

The polarisation independent directional coupler switch with three coupled waveguides is demonstrated. The device exhibits improved voltage tolerance over existing designs.<>     

Miniaturized ring coupler of arbitrary reduced size

A simple and successful method for miniaturizing a ring coupler is proposed. The size of the ring coupler is reduced by connecting multiple open stubs on the inside of the ring. There is no need of any lumped element, via hole or wire bond, but only microstrip lines. The reduced size is arbitrary and the results of the miniaturized ring coupler coincide with that of the traditional one.     

A novel vertical directional coupler switch with switching-operation-induced section and extinction-ratio-enhanced section

A novel vertical directional coupler switch with a switching-operation-induced section and an extinction-ratio-enhanced section is proposed. Switching operation is achieved by changing the refractive indexes of both cores in the switching-operation-induced section, and an improvement of extinction ratios larger than 30 dB for both cross and bar states is achieved by controlling the asymmetry of the refractive indexes of two cores in the extinction-ratio-enhanced section without changing the refractive index of the inner-cladding layer between the two waveguides. The required refractive indexes for the cores in the switching-operation-induced and extinction-ratio-enhanced sections are calculated for various thickness of the inner-cladding layer.     

SSFLC optical directional coupler switch with a short devicelength: a proposal

A novel vertical directional coupler waveguide switch composed of ferroelectric liquid crystal (FLC) is proposed and analyzed. The surface stabilized ferroelectric liquid crystal break (SSFLC) is used as an active separation layer between passive waveguides. To decrease the switching length, the waveguide switch is based on the power crossing the separation layer rather than coupling between waveguides. The calculated results relevant to the switch parameters such as the switching length, switching time, capacitance, and extinction ratio are presented. Because of the large birefringence of FLC, a very short switching length, less than 60 μm, is possible     

Tunable MQW-DBR laser with monolithically integrated GaInAsP/InP directional coupler switch

The authors report the successful monolithic integration of a GaInAsP/InP single-mode Delta kappa directional coupler switch with a 4-section tunable multiple-quantum-well distributed Bragg reflector laser. They obtain several mW of output power through the switch, with approximately 10 dB crosstalk either from the internal laser source or with external light injected through the parallel input port.<>     

Semiconductor monolithic wavelength selective router using agrating switch integrated with a directional coupler

A semiconductor monolithic wavelength selective router is proposed. An electrically tunable grating switch is monolithically integrated with a directional coupler. The effect of sidelobe on the demultiplexing characteristics of the router is investigated, and it is shown that the sidelobes degrade the wavelength crosstalk and introduce a power penalty for demultiplexing characteristics. A phase-synchronized sampled grating is introduced to suppress the sidelobes, and wavelength router switching is observed in this structure. The extinction ratio is over 10 dB at a current injection of 25 mA. Using this structure, power-penalty-free wavelength selective routing at a 2.5 Gb/s wavelength-division-multiplexed NRZ random pattern is demonstrated     

X-band monolithic transmit-receive switch based on a stub directional coupler

A new circuit realization of X-band transmit-receive switch is proposed that is based on a PHEMT-controlled stub directional coupler. The operation of the switch is analyzed. The impedances of the stubs are optimized to yield a considerably larger bandwidth of the switch. It is shown that the circuit can serve as a building block for multithrow switches.