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.<>     

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     

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.     

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.<>     

A new AlGaAs/GaAs/InAlGaP npn bulk-barrier optoelectronic switch

Two-terminal switching performance is observed in a new AlGaAs/GaAs/InAlGaP optoelectronic device. The device shows that the switching action takes place from a low current state to a high current state through a region of negative differential resistance (NDR). The transition from either state to the other may be induced by an appropriate optical or electrical input. It is seen that the effect of illumination increases the switching voltage V/sub S/ and decreases the switching current I/sub S/, which is quite different from other results reported. In addition, it possesses obvious NDR even up to 160/spl deg/C. This high-temperature performance provides the studied device with potential high-temperature applications.     

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.<>     

InGaAsP/InP MQW directional coupler switch with small and low-lossbends for fiber-array coupling

We report on a compact InGaAsP/InP MQW directional coupler switch with spacing between the waveguides at the input and the output facets larger than 125 μm, required for the fiber-array coupling, by employing small low-loss bends. The total device length, including both the coupling and the bending regions, with the different optical confinements in the lateral direction is 2 mm. The coupling region of the switch is 420 μm, and the voltage-length product at switching is around 6 Vmm     

High temperature MOVPE growth of GaAs/AlGaAs device structures with tertiarybutylarsine

The performance characteristics of epitaxial structures suitable for optoelectronic and electronic devices were investigated. These were fabricated by MOVPE using tertiary-butylarsine, a non-hydride arsenic source. Minority carrier diffusion lengths of 5μm at 3 × 10¹⁸/cm³ and 2μm at 2 × 10¹⁹/cm³ were achieved inp-type GaAs. Recombination velocities at the GaAs/AlGaAs interface are reduced to 1 × 10³ cm/sec by processing under appropriate conditions. Electron mobilities of 4000 cm²/V-sec inn-type (2 × 10¹⁷/cm³) layers resulted in transconductances of 120 mS/mm in 1.5μm gate depletion mode MESFETs. The above values are comparable to those obtained with arsine in this work and others reported in the literature.     

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.<>     

4*4 directional coupler switch matrix with an InGaAlAs/InAlAs multiquantum well structure

A 4*4 directional coupler switch matrix is developed which uses, for the first time, the quantum confined Stark effect of InGaAlAs/InAlAs multiquantum well structures. The rearrangeable nonblocking 4*4 network with six 2*2 switches is shown to be perfectly functional with switching voltages between 5 and 6 V and crosstalk below -17 dB in all the operation states.<>     

Extremely low loss 4*4 GaAs/AlGaAs optical matrix switch

A 4*4 GaAs/AlGaAs optical matrix switch with an extremely low loss of 1.6 dB has been developed. This low loss switch was achieved by layer structure modification, to reduce free-carrier absorption, reduction of plasma damage while dry etching, and an improvement in the crystal quality.<>     

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     

Efficient time-domain demultiplexing with separate signal andcontrol wavelengths in an AlGaAs nonlinear directional coupler

Efficient time-division demultiplexing using two different wavelengths, one for the signal and one for the control beam, has been implemented in an AlGaAs nonlinear directional coupler at 1550 nm. This all-optical demultiplexer makes use of cross-phase modulation and walk-off between the two wavelengths to give high contrast at both low and high powers and to eliminate the pulse break-up. Additionally, ultrafast wavelength shifting has been observed     

Novel GaAs/AlGaAs multiquantum-well Schottky-junction device andits photovoltaic LWIR detection

The authors have demonstrated photovoltaic detection for a multiple-quantum-well (MQW) long-wavelength infrared (LWIR) detector. With a blocking layer, the MQW detector exhibits Schottky I-V characteristics with extremely low dark current and excellent ideality factor. The dark current is 5×10^-14 A for a 100×100 μm² detector (designed for 10-μm response) at 40 K, nearly nine orders of magnitude lower than that of a similar MQW LWIR detector without the blocking layer. The ideality factor is ~1.01-1.05 at T=40-80 K. The measured Schottky-barrier height is consistent with the energy difference between first excited states and ground states, or the peak of spectral response. The authors also report a measured effective Richardson constant (A**) for a GaAs/AlGaAs heterojunction using this blocking layer structure. The A** is ~2.3 A/cm²/K ²     

Experimental study of AlGaAs/GaAs HBT device design for powerapplications

An experimental study of AlGaAs/GaAs heterojunction bipolar transistor (HBT) device design for optimizing key DC and RF performance parameters relevant to power device applications is reported. The design of the collector, base, and base-emitter junction is investigated for improved power device performance, and novel device structures are presented. Device scaling effects and the extent to which air-bridged interconnect can reduce parasitics in large power devices are also explored. Power HBTs employing some of the optimized design features have achieved a power output of 1.2 W (4 W/mm) with 43% power-added efficiency at 10 GHz     

New tri-state switch (TSS) using AlGaAs/GaAs/InGaAs double heterostructure

A new AlGaAs/GaAs/InGaAs heteroconfinement tri-state switch (TSS) prepared by metal organic chemical vapor deposition has been fabricated and demonstrated. This TSS exhibits the interesting multiple negative differential resistance (MNDR) characteristics. The NDR behavior is caused by a p ⁺ n junction and sequential two-stage barrier-lowering and potential-redistribution effect that resulted from the electron confinement at AlGaAs/GaAs/InGaAs heterointerface and lnGaAs quantum well, respectively.     

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.     

Method for narrowing the directional pattern of an InGaAs/GaAs/AlGaAs multiwell heterolaser

A semiconductor laser with a new waveguide is developed. It allows significant narrowing of the directional pattern (to 4° in the plane perpendicular to the p–n junction). In the used waveguide, the minimum excess of the effective refractive index n_eff of the excitation mode over the substrate refractive index n_s (n_eff–n_s ? 1) is provided by selecting the thickness of Al_0.3Ga_0.7As confinement layers, which significantly increases the waveguide mode size and leads to directional-pattern narrowing.     

The DC characteristics of GaAs/AlGaAs heterojunction bipolartransistors with application to device modeling

A complete DC model for the heterojunction bipolar transistor (HBT) is presented. The DC characteristics of the HBT are compared with the Ebers-Moll (EM) model used by conventional bipolar junction transistors (BJTs) and implemented in simulation and modeling programs. It is shown that although the details of HBT operation can differ markedly from those of a BJT, a model and a parameter extraction technique can be developed which have physical meaning and are exactly compatible with the EM models widely used for BJTs. Device I- V measurements at 77 and 300 K are used to analyze the HBT physical device performance in the context of an EM model. A technique is developed to extract the device base, emitter, and collector series resistances directly from the measured I-V data without requiring an ideal exp(qV_be/kT) base current as reference. Accuracies of the extracted series resistances are assessed. AC parameters of HBT are calculated numerically from the physical device structure. For modeling purposes, these parameters are shown to be comparable with those of conventional BJTs