Ridge-waveguide InGaAs/GaAs strained quantum-well lasers with high temperature (225 degree(s)C), high power (350 mW), and high reliability characteristics have been successfully demonstrated. The paper reviews recent progress in the laser design and performance with respect to temperature, power, and reliability for fiber-optic amplifier and avionics applications.

We described the successful development of planar, low dark current, and high sensitivity In0.4Ga0.6As p-i-n photodiode fabricated on a semi-insulating GaAs substrate with the aid of a multistage strain-relief buffer system. Without using surface passivation and antireflection coatings, the detector has a quantum efficiency of 42% and a peak responsivity of 0.45 A/W at 1.3 micrometers wavelength. The reverse leakage current for the mesa-etched photodiode with an active area of 2 X 10-4 cm2 is 5 X 10-9 A at -5 V, and the breakdown voltage exceeds 25 V. To further study the quality of the p-i- n photodiode prepared on the lattice mismatched In0.4Ga0.6As/GaAs material system, the generation lifetime profile in the i-region of the photodiode has been determined by using a differential current-voltage (I-V) and capacitance-voltage (C-V) technique. In addition, the generation lifetime and deep-level defects in these p-i-n photodiodes were also determined by the deep-level transient spectroscopy (DLTS) measurement.

A new stable fundamental mode operation of a ridge wave guide laser array has been fabricated by introducing absorption regions in the laser stripes except the central one. The structure may be considered as an integrated injection locking array or the distributed saturable absorption laser array. The threshold current is typically 40 mA and the maximum power is more than 150 mW for laser arrays with five elements. The single lobed far field pattern is centered at 0 degree(s) with a full width at half maximum of 2 degree(s) at I equals 1.5 Ith.

Single narrow stripe ridge-waveguide modified triple-quantum-well AlGaAs lasers were fabricated with high reflection and anti-reflection facet coatings. The maximum cw output power exceeded 100 mW and kink-free power was up to 80 mW. The device had a characteristic temperature of 320 degree(s)K and a threshold current density of 480 A/cm2. A lateral spreading current as large as 20 mA was found. The aspect ratio of the far-field beam pattern was four while the astigmatism was measured to be less than 5 micrometers . The dependence of the parallel beam divergent angle on the ridge width was also investigated.

The materials quality of the InxGa1-xAs epilayers with 0.28 xGa1-xAs were also grown on GaAs to study the strain relaxation process in the initial growth stage and their effects on the generation of dislocations. For the x equals 0.5 case, the thin InGaAs formed a high density and many small size coherent islands; while for x equals 1, they changed to a low density and much larger size relaxed islands. This shows that the growth of highly mismatched InxGa1-xAs/GaAs heterojunction (x >= 0.28) is a kinetically limited strain relaxation process. The large lattice mismatch (7.16%) between InAs and GaAs favors the early relaxation of InAs islands before they coalesce, this explains why the bulk material quality of the InAs is better than InxGa1-xAs with x equals 0.28, 0.5 and 0.75 in spit of its larger lattice mismatch.

Massively parallel computers raise a major challenge to the interconnection designer by asking for more than the electrical connector and PCB backplane technology are able to perform. Many new configurations are being explored in optics such as the fiber and holographic interconnects. We describe a third option: optical interconnects between adjacent boards by means of free space beams. They present the significant advantage of being possibly packed (4 to 16 per mm2) much more heavily than electrical interconnects because they can be put at the output of the processor, therefore decreasing delay. They are working with short wavelength (around 0.85 micrometers ) LEDs to decrease the cost, the sensitivity to temperature shift, and increase the reliability. Crosstalk can be kept below 20 dB and still have reduced sensitivity to misalignment of the boards. LEDs and microlenses are solder bumped which provide mounting accuracy of around one micron.

M X N generalized shuffle networks are generally constituted by arrays of m X n switches linked together by an interconnection network. The number of stages necessary to obtain all the possible input-output links is very low. Therefore, they can be easily implemented on LiNbO3 crystals because the overall network length is reduced even if the transversal dimension is slightly increased. The architecture of such a shuffle network is presented here and its performance, in terms of networks cost, throughput, and bandwidth, is evaluated. The possible elementary switches are outlined.

Broad-bandwidth substrate-mode holograms for optical interconnect applications are investigated. These devices use total internal reflection to translate optical beams, and holographic elements to couple light in and out of the guiding substrate. Transmission and reflection-types of substrate-mode holograms are compared, and the reflection-type of devices give a broader angular bandwidth. The fabrication technique of reflection substrate-mode holograms are discussed and experimental results are given.

The behaviors of frequency modulation induced by direct current modulation in the ridge guide DFB laser at 1.55 micrometers are investigated. The frequency deviation is measured by the gated delayed self-homodyne technique. A systematic approach using the small-signal model to predict the experimental results is also presented.

In this paper we report a method of designing integrated-mirror etalons for photonic switching without time-consuming numerical calculation. It consists of the following two-step process: (1) find the minimum reflectance to obtain the maximum allowable linewidth of an etalon, and (2) find the number of the quarter-wave layers in each mirror of the etalon to obtain the reflectance given by step 1. The condition for maximum transmission in an integrated-mirror etalon is also derived. Under this condition we can achieve the required linewidth with the minimum number of quarter-wave layers.

In practical applications, the resultant channel waveguide of LiNbO₃ substrate should be efficiently coupled to the single mode fiber. The core shape of single mode fiber is a circular distribution, but that of the conventional Ti:LiNbO₃ channel waveguide is a semi-elliptical distribution. Optical mode patterns of channel waveguide and single mode fiber can not achieve the mode matching conditions. To improve coupling efficiency between channel waveguide and single mode fiber with arbitrary dimensions, the refractive index profiles and associated fundamental mode patterns of buried Ti/Mg:LiNbO₃ channel waveguides are simulated and controlled from fabrication parameters. We have also investigated the dependences of coupling loss on radial and axial offsets.

A successful fabrication of semiconductor optical switch, similar in function to the self- electro-optic effect devices, is reported for the first time from MOCVD-grown GaAs/AlGaAs low barrier quantum well pin diodes (Al fraction, x equals 4%). A reflective 16 X 8 switch array and its performance are also reported. The maximum contrast ratio was found to be 2.9:1 at 5 V bias.

A novel 0.98/1.55 micrometers dichroic coupler with high extinction ratio and low insertion loss has been designed and implemented on LiNbO₃ for Erbium-doped fiber amplifier applications. The design of dichroic coupler is based on a modified directional coupler structure with a single bend in each channel. Beam propagation method is used to analyze the coupler performance to get the optimal parameters for device design, such as channel width, titanium thickness, channel gap, and interaction length. Samples with the signal coupling ratio as high as 100% and pumping power ratio as high as 95% have been obtained.

In this paper we report the fabrication of a planar optical waveguide lens on a Y-cut LiNbO₃ substrate by Ti-indiffusion and Ti-indiffused proton-exchange (TIPE). LiNbO₃ planar waveguides are fabricated and refractive indices of the waveguides are measured. Based on the measured indices, planar waveguide lenses are designed and fabricated. The measured focal point and spot size of the fabricated lens are in good agreement with those of the designed lens.

Instability in the output of dc-biased surface emitting lasers due to an external cavity effect was observed. The output power spectrum exhibited multiple peaks with spacing corresponding to exactly the round-trip delay in silica fibers with length ranging from 2 m to 2 km. The magnitude of the peaks was enhanced in the spectral region centered at the laser relaxation frequency. With increased feedback, the background of the output spectrum was found to increase, indicating the presence of optical chaos. Numerical simulation based on the rate equation analysis was found to agree with the experiment, indicating the surface emitting lasers are well described by the rate equation and are susceptible to feedback as the edge emitting lasers.

Thermal behavior of all-MBE surface-emitting lasers is studied for the temperature range of 80 - 310 K. Minimum threshold current observed around 200 K indicates a slight mismatch between gain maximum and Fabry-Perot resonance for the deep-red superlattice surface- emitting laser. The barrier heights for holes between hetero-interfaces of Al_0.3Ga_0.7As-Al_0.65Ga_0.35As and AlAs-Al_0.65Ga_0.35As are measured to be 77 meV for the deep-red surface-emitting laser.

A theoretical study on the central wavelength shifts of double-hetero structure AlGaAs LEDs along with the experimental results are reported herein. All measurements of the spontaneous emission spectra from the AlGaAs active layer are performed with dc and pulsed driving current at a temperature from 253 K to 343 K.

The structures and performances of surface emitting AlGaInP green light emitting diodes (LEDs) with emission wavelength around 565 nm were studied. The AlGaInP green LEDs with epitaxial structure grown on P-type GaAs substrate showed the best performance. This is the first paper ever reported for the fabrication of AlGaInP LEDs using P-type GaAs as a substrate. In AlGaInP LED structure using P-type GaAs substrate, the highly conductive n- type AlInP was consequently used as a top confining layer and the current crowding problem was significantly improved. Therefore, the green electroluminescence (EL) was uniformly emitted from the surface of LED dice.

The new LED structure suitable for high power and narrow beam pattern is proposed composed of microlens and LED layer. The microlens is fabricated by the meltback etching and regrowth technique in LPE. To control the shape of microlens, meltback etching and regrowth technique is studied and nearly ideal hemisphere is obtained. The characteristics of the proposed LED structure is calculated based upon ray-tracing method. And the fabricated result is discussed.

Bulks layers of both GaSb and InGaSb have been successfully deposited by metal-organic chemical vapor deposition (MOCVD). The transition energies in the GaSb/In_xGa_1-xSb single quantum well have been calculated using a model which takes into account the elastic strain and quantum well effects. The shifts of transitions energies as a function of In solid compositions and well widths for 300 K and 12 K, respectively, were calculated. The transition energies from conduction bands to light holes at 12 K were found to be higher than the GaSb energy-gap with In composition below 0.3. Thus, the light hole band cannot be confined in the quantum wells with In composition between 0 and 0.3. The photoluminescence (PL) spectra of quantum well structures with different well widths were presented. The transition energies obtained from the PL spectra were compared with theoretical predictions.

A numerical program which solves Poisson equation and Schrodinger equation self- consistently was developed. Many structures of the delta-doped layers structures had been simulated including different dopant concentrations, different length scales of dopant confinement, and delta doping in quantum well structures. A quantum mechanical model of C- V profile was adopted to derive the 'apparent C-V profile' of the delta-doped layer and which is compared with the dopant distribution and free carrier distribution. The electron concentration saturation, enhanced electron mobility, and the condition for minimum FWHM (full width at half maximum) of electron distribution can be successfully explained with the results from our study. The analyses are consistent with the experiment results of other groups. This could provide a tool for the delta-doped quantum well HEMT.

The Nd³⁺-doped fiber ring laser consisting of a mechanically polished tunable directional coupler and the Nd³⁺-doped single mode fiber with 4 m long is pumped by Ti:Al₂O₃ tunable laser ranging from 800 nm to 840 nm in wavelength. The optimum pumping wavelength of this Nd³⁺-doped fiber ring laser for commercial semiconductor laser is selected. The fiber laser's output power of 5.8 mw and the single end output slope efficiency of 24% at pumping wavelength of 830 nm are also obtained.

A hybrid distributed-node fiber-optic passive coupler structure is constructed by distributing the 2 X 2 couplers of conventional central-node star in several nodes, and the configuration of 2 X 2 couplers in each distributed node is adopted a double-tree structure. Compared with other star topologies, all the number of 2 X 2 couplers, fiber length and conduit length required to build up this coupler structure can be greatly reduced. Additionally, this coupler structure has good expansibility and flexibility.

The operating characteristics of ridge-waveguide AlGaAs/GaAs lasers with conventional double heterostructure (DH), separate-confinement heterostructures (SCH), and graded-index separate-confinement heterostructure single quantum well (GRIN-SCH-SQW) active layer structures grown by metalorganic vapor phase epitaxy (MOVPE) technique are reported. For conventional DH and SCH structures, an undoped Al_0.15Ga_0.85As active layer was used for an emission wavelength of 780 nm. An undoped 30 angstroms GaAs quantum well was centered in the 3000 angstroms thick graded Al_xGa_1-xAs (x equals 0.2 - 0.55) GRIN-SCH region with linear Al profile. The lasers with GRIN-SCH-SQE active layer exhibited lowest threshold current density among these three structures. The conventional DH laser has been shown to have better beam qualities and lower astigmatism than the other two types of lasers. Reliable operation for more than 1500 hrs was achieved at 50 degree(s)C for conventional DH lasers. However, GRIN-SCH-SQW lasers with very thin active layer (<EQ 30 angstroms) showed much higher degradation rate.

A novel substrate-mode grating pair structure for wavelength-division-demultiplexing (DEMUX) application is presented. An input grating coupler diffracts normally incident beams at an angle beyond the critical angle in the dielectric substrate. The diffracted beams then propagate through the substrate with total internal reflection to the output coupling grating and are separated for different wavelengths. Normally incident coupling and output on- axis imaging with this structure provide easier alignment with optical fibers. Three types of substrate-mode grating pairs providing the property of polarization-insensitive high-efficiency are investigated.

In-situ monitoring of horizontal Bridgman (HB) growth of GaAs crystals through the furnace window can reveal whether the growth condition is good or not. Good growth conditions are characterized by straight melt/crystal interface and (111) facet growth striations on the grown crystal surface. Abnormal growth conditions including twinning, lineaging and polycrystallizing in the growing crystals usually show curved or irregular-shaped melt/crystal interface and various slanted lines distributed over the crystal surfaces. The monitoring process can spot these defective conditions in the early stage of their formations, and growth parameters thus can be adjusted in real time for correction. It provides a convenient way to help understand the relations between growth parameters and defects formation. The yield and quality of the M2T-HB grown crystals are both increased by this method.

A study has been carried out for the particle deposition during the Modified Chemical Vapor Deposition (MCVD) process. The analysis includes thermophoretic particle transport in the gas flow inside the tube and heat transfer through the solid layer with considering variable properties for both gas and solid regions. A notable feature of the study is to consider the effects of the periodic heating due to repeatedly traversing of the torch including the effects of the increasing solid layer thickness as the particles deposit. The localized heating of the moving torch is modelled as a gaussian heat flux boundary condition on the tube wall and the surface temperature distribution and the deposition efficiency results in good agreement with the existing experimental data. Of particular interest are the effects of torch speeds and solid layer thicknesses on the efficiency and the rate of deposition of particles, and the tapered length.

A systematic study in the growth of In_xGa_1-xAs_yP_1-y (0.53 < x < 1, 0 < y < 1) compound semiconductor and it's application to laser diode structure has been carried out by the low-pressure organometallic vapor phase epitaxy (LP- OMVPE) technique. The indium (In), gallium (Ga), arsenic (As) and phosphorus (P) incorporation efficiencies were studied by varying the flow-rate of source gases. At the optimized growth conditions, the In incorporation efficiency has been found about 0.7 as compared with Ga's in both In_.53Ga_.47As and InGaAsP epilayers, and the Ga composition can be adjusted simply by varying the trimethylgallium (TMG) flow-rate linearly. However, the P incorporation efficiency is found much lower than the A's. Furthermore, we found that the As composition in In_xGa_1-xAs_yP_1-y quaternary epilayer (Q layer) is determined by arsine (AsH₃) flow-rate not by the AsH₃/PH₃ flow-rate ratio in gas phase. The hydride flow-rates concerning in experimental growth of Q layer has been explained by the proposed As/P competition model and then formulated. According to this model, the AsH₃ flow-rate is found proportional to y^2.24259(1-y)^-0.27138. For the final purpose, the graded index- separate confinement heterostructure (GRIN-SCH) and quantum wells (QW) for laser diode structure have been grown and demonstrated.

In the paper, the optical properties of III-V compound semiconductor quantum well structures are studied theoretically. We take into account the nonparabolic valence band structure due to band mixing effect using multiband effective mass theory (K(DOT)P theory). A variational method is used to solve the exciton problem. The calculated exciton peak positions versus electric field show good agreement with the experimental results published in literatures. The optical absorption coefficient and spontaneous emission rate in quantum well structures are calculated using the formula derived by the density matrix formalism with intraband relaxation taken into account. The optical gain and refractive index variation in a quantum well laser structure are calculated by giving equal electron and hole density in the well region. The theoretical results show that the peak position of the gain spectra exhibits a red shift and its amplitude decreases with increasing electric field for both the TE and TM polarization. The gain spectra in our model shows remarkable difference both in the spectra shape and the peak amplitude as compared with those from the conventional models. The peak gain is reduced and the gain spectrum is more symmetric and closer to experimental observations. The refractive index variation in the active region will result in the defocusing effect and increase the optical loss.

One-dimensional simulation on quantum-well laser diodes in steady-state had been studied in this work. The electrical behaviors are obtained by solving Poisson's equation and current continuity equations for electrons and holes using a self-consistent method. Band parameters are added in the continuity equations for compositional change in each layer. Different forms of band parameters are used in quantum well regime. The recombination model are revised in the quantum well regime. After the electron and hole profiles are obtained, the peak gain in the quantum well regime are then calculated. The model for the optical matrix element used in this study includes intraband relaxation but without band mixing effects. Wave equation is solved to obtain the optical field intensity and the optical confinement factor. Modal gain and total loss are then calculated. This procedure proceeds until the modal gain is greater than the loss. We use this method to simulate both graded-index separate-confinement heterostructure (GRIN-SCH) quantum-well laser and separate-confinement heterostructure (SCH) quantum- well laser for AlGaAs-GaAs system. Results show that the carriers are well-confined in GRIN-SCH laser, thus less recombination current density present outside the quantum well regime in GRIN-SCH than in SCH. The optical confinement factor depends strongly on the waveguide structures. It may be better confined in GRIN-SCH than in SCH for a set of layer thickness and poorly confined for another set of layer thickness. Thus, the threshold current density depends on the structure. The calculated threshold current density is slightly lower than the experimental result.

A new surface passivation technique using P₂S₅/(NH₄)₂S on GaAs Schottky barrier diodes formed by Au and Al contacts was investigated, and the results are compared with those of (NH₄)₂S_x-treated devices. With this new surface treatment, the effective barrier heights for both Al- and Au-GaAs Schottky diodes were found to vary with the work function of metals, which is clear evidence of the lower surface state density in these diodes. Results of I-V measurements shows that P₂S₅/(NH₄)₂S-passivated diodes have lower reverse leakage current and higher effective barrier height than that of the (NH₄)₂S_x-treated diodes. We also utilized RTA annealing and successive sulfurization to identify the characteristics of the sulfide film. Results show that the anneal at 250 degree(s)C to certain extent destroys the Ga-S (and/or As-S) bonding. Auger Electron Spectroscopy (AES), X-ray photoelectron spectroscopy (XPS) and Raman scattering measurements are done to characterize the surface compositions and surface band bending.

We have carried out a series of experiments on a gain-switched Ti:sapphire laser to investigate the temporal characteristics of the output pulses. In these experiments the minimum laser pulsewidth of shorter than 2 ns has been obtained and pulsewidth can be varied from 5 ns to 27.5 ns continuously under our experimental condition. Using only one output coupler the laser tunable range was greater than 2.1 X 10³ cm^-1 (from 720 nm to 850 nm). A maximum output pulse energy of 4.65 mJ at 780 nm was obtained. The spectral content of the output from the laser with three intracavity prisms was less than 0.14 nm (FWHM).

Two types of resonator configuration, i.e. the axis-asymmetric resonator and improved off- axis resonator are used to reduce the beam parameter product in the large direction of the slab. Experiments performed with a slab (Nd,Ce):YAG laser have shown remarkable improvement of beam quality.

Soliton switching based on spatial solution emission requires the cladding material has high enough nonlinear change of the index. We describe the design of a waveguide that has nonlinearity enhancement at the boundary due to deep level states excitation. The example material is the Al_xGa_1-xAs. This material has El₂ related deep level states which become deeper as the AlAs mole fraction increases so that we can suitably choose the bandgap, and therefore the deep levels to match the working wavelength. The distribution of the guided mode field is also modified by the design of the waveguide geometry to facilitate an inner built electric field which is responsible for the nonlinearity enhancement.

An optical fiber and on-chip waveguide interconnect system is presented. The method of mode propagation by Fourier expansion for our simulation and design to efficiently couple optical signals from single-mode optical fibers to on-chip waveguides is discussed. Simulation and experimental results will be given and the feasibility of this interconnect structure will be investigated.

Al_0.5Ga_0.5Sb/GaSb metal-semiconductor-metal (MSM) detectors have been prepared on semi-insulating InP substrates. The molecular beam epitaxially grown samples on differently orientated substrates exhibit different types of conductivity. The Schottky barrier height between Al and Al_0.5Ga_0.5Sb grown on (311)B oriented substrates is 0.6 eV, while the Al contacts on (100) sample exhibit ohmic behavior. The results show that the Sb- deficiency related p-type native defect density is significantly reduced in the samples grown on (311)B oriented substrates. The 3-dB device response bandwidth is about 1 GHz at room temperature and beyond 10 GHz at 77 K.

The reliability of continuously operating (cw) high power laser arrays is a critical factor for the acceptance of these devices in a wide range of applications. Extensive investigation into the reliability of semiconductor lasers has led to an improved understanding of failure mechanisms such as material defects, mirror damage and solder related failures as well as to methods which significantly suppress the occurrence of catastrophic failure. Furthermore, as a result of material quality improvements, laser arrays exhibit very low gradual degradation for high power operation up to 2 Watts cw. Long term lifetest data shows that the projected medium life at room temperature of such devices exceed 100,000 hours at 2 W cw.

High-power visible laser diodes operating at 630 - 640 nm have been demonstrated. The devices have a GaInP/GaAlInP single quantum well, graded-index separate confinement heterojunction. For 100-micrometers -broadstripe uncoated lasers, pulsed threshold current of 740 A/cm² and output powers as high as 1.5 W/facet (total 3 W) at room temperature were achieved by optimizing the device cavity length. For 10-micrometers -ridge-waveguide lasers, 40 mW CW output powers with single-longitudinal mode and stable transverse mode have also been demonstrated. We also present, for the first time, high power 635 nm surface-emitting lasers with pulsed output powers of 170 mW.

Monolithic in-plane surface emitting laser diode arrays with 45 degree(s) micromirrors offer great promise for both coherent and incoherent applications. This paper describes several such laser diode structures in both the junction-up and junction-down configurations, and summarizes their design, fabrication and performance characteristics.