The influence of quantum-well composition on the performance ofquantum dot lasers using InAs-InGaAs dots-in-a-well (DWELL) structures

The optical performance of quantum dot lasers with different dots-in-a-well (DWELL) structures is studied as a function of the well number and the indium composition in the InGaAs quantum well (QW) surrounding the dots. While keeping the InAs quantum dot density nearly constant, the internal quantum efficiency η_i, modal gain, and characteristic temperature of 1-DWELL and 3-DWELL lasers with QW indium compositions from 10 to 20% are analyzed. Comparisons between the DWELL lasers and a conventional In_0.15Ga_0.85As strained QW laser are also made. A threshold current density as low as 16 A/cm² is achieved in a 1-DWELL laser, whereas the QW device has a threshold 7.5 times larger. It is found that η_i and the modal gain of the DWELL structure are significantly influenced by the quantum-well depth and the number of DWELL layers. The characteristic temperature T₀ and the maximum modal gain of the ground-state of the DWELL structure are found to improve with increasing indium in the QW It is inferred from the results that the QW around the dots is necessary to improve the DWELL laser's η_i for the dot densities studied     

Oxidation of (n)-InP by nitric acid

Au-oxide-semiconductor barriers have been studied in n-type InP. A comparison was made, using the ESCA technique and current/voltage characteristics, between different natural oxides obtained with nitric acid as reagent. With regard to the ideality factor, barrier height and oxide resistivity, the best oxide is obtained with acid in a gaseous phase, and the XPS spectra give an interpretation of the oxide composition.     

Performance tradeoffs of optical WDM switches using different shared limited-range wavelength conversion mechanisms

The effects of different wavelength conversion ranging configurations on the performance of Wavelength Division Multiplexing (WDM) optical switches are investigated. Any-to-Any, Any-to-Range, Range-to-Any, and Range-to-Range conversion ranging configurations are considered. These mechanisms provide important design alternatives for optical switches due to technological limitations in the implementation of full range wavelength conversion in an all-optical wavelength converter device. Limited-range wavelength converter (LRWC) is a more economical and practical solution for WDM based optical networks. Differences among the input and output side ranging mechanisms and their effects on conversion resource sharing, and consequently on performance, are investigated. Any- to-Range ranging configuration is the most efficient mechanism and it operates comparably to Any-to-Any, reducing the need for complex control algorithms. The results help determine the most efficient ranging configuration for all-optical crossconnect.     

Fabrication of electroabsorption optical modulators using laserdisordered GaInAs/GaInAsP multiquantum well structures

Electroabsorption optical modulators have been fabricated on GaInAs/GaInAsP multiquantum well structures whose bandgap had been increased by laser photoabsorption-induced disordering. Modulation depths of 20 dB have been obtained in material which has been bandgap blue shifted by as much as 120 nm, while samples shifted by 80 nm gave depths as high as 27 dB     

Harmonics suppression investigations of pHEMT single-pole-single-throw switches using multi-gate structures

In this study, multi-gate GaAs pseudomorphic high electron mobility transistor (pHEMT) single-pole-single-throw (SPST) microwave switches were implemented and characterized for high power operation. The switch size is not only minimized by employing the compact zigzag layout structure but also with gate finger parallel bar structure for increasing power handling capability. The measured RF and harmonic powers suppression results was analyzed, the parameters of OFF-state (gate bias = −3 V) small-signal model were extracted for single-, dual-, triple- and quadruple-gate switch devices individually. Under ON-state (gate bias = 0 V) operation, the insertion loss performance is slightly worse due to the increasing of gate number and results in the rising ON-state resistance (R_ON). However, the isolation performance can be enhanced by 4 dB from the single-gate device to the triple-gate one. The quadruple-gate device demonstrates only 0.2 dB improvement in isolation performance than the triple-gate one, but it slows the improvement of harmonic suppression level owing to the increasing of the gate-to-gate coupling capacitance.     

Monolithic fabrication of 2 × 2 crosspoint switches inInGaAs-InAlGaAs multiple quantum wells using quantum-well intermixing

In this letter, we report the fabrication of 2 × 2 crosspoint switches, which monolithically integrate passive waveguides, electro-absorption modulators and optical amplifiers onto one chip using sputtered SiO₂ quantum-well intermixing technique. The switches have low insertion loss to be about 4-5 dB and extinction ratios up to 26 dB     

Resonant-tunnelling hot-electron transistor (RHET) using a GaInAs/(AlGa)InAs heterostructure

A common-emitter current gain of 10 has been measured at 77 K for a 100 nm-base resonant-tunnelling hot-electron transistor (RHET) using a GaInAs/(AlGa)InAs heterostructure. The current gain for 25 nm-base RHETs has reached 25, which is the highest value yet reported for hot-electron transistors, and the collector current peak-to-valley ratio has reached 15.0 for the same device.     

Linear electrooptic effect in HgS (Cinnabar) at 0.63 and 3.39 microns

Nonlinear optical properties of HgS have been of interest lately. The electrooptic effect has been measured in a natural crystal and values for the two independent coefficients are reported here at wavelengths of 0.63 and 3.39 microns. The results agree well with predictions of purely electronic theories, but the wavelength dependence indicates an appreciable contribution of ionic motion to the optical polarizability.     

Characteristics of super structure grating (SSG) DBR lasers underbroad range wavelength tuning

Spectral characteristics of the super structure grating (SSG) distributed Bragg reflector (DBR) lasers under broad range wavelength tuning are discussed. SSG DBR lasers show good spectral characteristics with broad range wavelength tunability. Under the directly intensity modulated condition, stable single longitudinal mode oscillations are also obtained over the broad wavelength tuning range     

High quality compressively strained InP-based GaInAs(P)/GaInAsP multi-quantum well laser structures grown by metalorganic vapor phase epitaxy

The growth and characterization of strained GaInAs and GaInAsP multiquantum well (MQW) laser structures has been investigated. The use of triple axis x-ray diffraction (XRD), in addition to the conventional high resolution double crystal XRD, yields further information about the structural integrity of these complex structures. Buried heterostructure lasers with eight GaInAsP wells (+1.0% strain, 80Å thick) exhibit a record low threshold current of 3.1 mA. By using a constant As/P ratio in the wells and barriers of an MQW laser structure, we have shown that the structure can be annealed at 700°C for 1 h with only a minimal shift (-4 nm) in the photoluminescence emission wavelength. Conventional lattice-matched GaInAs/GaInAsP MQW structures exhibit a shift of-46 nm under the same conditions.     

Field effect transistor-self electrooptic effect device (FET-SEED)differential transimpedance amplifiers for two-dimensional optical datalinks

A 4×18 two-dimensional array of GaAs FET-SEED (field effect transistor-self electrooptic effect device) differential transimpedence receivers has been fabricated for application in massively parallel optical data link board-to-board interconnections. Several FET-SEED receiver arrays were tested and displayed a mean response of ~0.7 mV/μW, and were capable of >100 Mbps per channel operation. The mean receiver sensitivity for a BER of <10^-9 was calculated from the measured noise spectrum to be -26.8 dBm at the system design rate of 40 Mbps (18 k-22 MHz bandwidth), and -23.2 dBm for a 100 Mbps rate (dc-66 MHz bandwidth). A sensitivity of approximately -25 dBm for the 40 Mbps rate was confirmed using a bit-error-rate test set. The theoretical noise is compared to measured values with good agreement assuming a FET channel noise factor of 1.4. The 1/f noise corner frequency of ~13 MHz was found to cause a ~1.2 dB degradation in sensitivity for the 100 Mbps rate. The differential amplifier mean dc output offset voltage was measured to be 10 mV, and displayed a large sigma due to parameter variations in the active devices. Two receiver arrays were successfully used in a demonstration of a fully differential parallel optical small computer system interface (SCSI) data link     

Material characterization of an ion-implantation process for p-type (InGa)As/GaAs quantum-well structures

We have performed a detailed study of the formation of Be⁺-implanted contacts to modulation-doped, p-channel, (InGa)As/GaAs, single-strained quantum wells. Photoluminescence at 4 K from these structures is shown to be an excellent monitor of implant and annealing effects, as corroborated by Hall-effect measurements. Rapid thermal annealing produced higher electrical activation of the Be implants than did arsine-over-pressure annealing at comparable temperatures, similar to the trend in bulk GaAs. In contrast to conventional, alloyed-contact technologies, the rapid-annealed, implanted structures provided ohmic contact to the quantum well even at 4 K.     

Comparison of heterostructure-emitter bipolar transistors (HEBTs) with InGaAs/GaAs superlattice and quantum-well base structures

The characteristics of InGaP/GaAs heterostructure-emitter bipolar transistors (HEBTs) including conventional GaAs bulk base, InGaAs/GaAs superlattice-base, and InGaAs quantum-well base structures are presented and compared by two-dimensional simulation analysis. Among of the devices, the superlattice-base device exhibits a highest collector current, a highest current gain and a lowest base–emitter turn-on voltage attributed to the increased charge storage of minority carriers in the InGaAs/GaAs superlattice-base region by tunneling behavior. The relatively low turn-on voltage can reduce the operating voltage and collector–emitter offset voltage for low power consumption in circuit applications. However, as to the quantum-well base device, the electrons injecting into the InGaAs well are blocked by the p⁺-GaAs bulk base and it causes a great quantity of electron storage within the small energy-gap n-type GaAs emitter layer, which significantly increases the base recombination current as well as degrades the collector current and current gain.     

Theory of electric field-induced optical modulation in single and multiquantum well structures using a Monte Carlo approach

A Monte Carlo approach is used in conjunction with the variational method to calculate quasi-bound levels in arbitrary quantum wells in the presence of transverse electric field. This approach is expected to be superior to the conventional variational approach since the results do not depend upon the choice of any starting wave solution. The technique is applied to Al0.3Ga0.7AS/GaAs quantum wells. The shift in the ground state level energies is calculated, along with the tunneling rates for the electrons and holes. We find that the tunneling rates are very sensitive to the band edge discontinuity distribution and to the barrier width in the case of multiquantum wells. The exciton binding energy is also calculated. Due to high tunneling rates at high electric fields, the photoluminescence is expected to be quenched. Consequences of these results are examined.     

Extended range interrogation of wavelength division multiplexed fibre Bragg grating sensors using arrayed waveguide grating

A technique for interrogating multiplexed fibre Bragg grating (FBG) sensors using an arrayed waveguide grating (AWG) is described. The approach considerably extends the sensing range from that achieved previously, while providing a strain resolution of 17n/spl epsiv///spl radic/Hz at 30 Hz.     

Digitally tunable optical filters using arrayed-waveguide grating(AWG) multiplexers and optical switches

Two novel configurations for digitally tunable optical filters based on arrayed-waveguide grating (AWG) multiplexers are described in detail with emphasis on the connection of the AWG multiplexer and optical switches. Performance comparisons show that conventional configurations are disadvantaged by the switch size required and loss imbalance among the optical frequency-division-multiplexed (FDM) channels; the proposed configurations require only O(√(N)) switch elements to select one of N FDM channels, and the loss imbalance is lower by up to 75% in decibel     

Structural characterization of InGaAs/InAlAs quantum wells grown on 0 (111)-InP substrates

Recent studies on HEMT structures according to their growth orientation have attracted much interest from the viewpoint of physics and novel device applications. However, the optimization of their properties needs a high degree of crystalline quality. In this work, the structural characteristics of the layers present on InGaAs/InAlAs HEMT structures grown on (111)-InP substrates have been analyzed by atomic force and transmission electron microscopies. The presence of a strained quantum well induces a defect structure and surface morphology quite different from those observed in similar samples without the quamtum well. These results show that an accurate control of the growth conditions is necessary to obtain acceptable structural quality for (111) devices.     

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     

W/WSi gate self-aligned HIFETs (heterointerface FETs) using anAlInAs/GaInAs heterostructure grown by MOCVD

An undoped AlInAs/GaInAs heterostructure was grown by MOCVD and a W/WSi gate self-aligned HIFET (heterointerface FET) structure was made by ion implantation and rapid thermal annealing. The HIFET, 5 μm in gate length, was of an enhancement-type with a threshold voltage of about 0 V and with a transconductance of 280 mS/mm at room temperature. This result confirms the very high potential of this device for direct coupled FET logic (DCFL)     

Predicted performance of quantum-well GaAs-(GaAl)As opticalamplifiers

The gain, noise, and saturation performance of GaAs-(GaAl)As quantum-well laser amplifiers is calculated. A single-quantum-well amplifier with 100-mA injection should achieve similar gains to those of present devices with bulk active regions, but with improved saturation output powers and near-ideal noise performance. A low-current amplifier with a 2.5-mA injection current is investigated for varying well thickness and number of wells