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Arrays of GaAs nanowires have been grown by selective-area metal–organic chemical-vapor deposition (MOCVD) onto photoactive planar Si substrates. This tandem, vertical-wire-array-on-planar absorber...

Efficient green emitting LEDs and monolithic white light emitting LEDs require the extension of the range of efficient light emission in the GaN/InGaN materials system. We demonstrate high efficiency green and yellow light emitting multiple quantum well (MQW) structures grown on GaN nanostripe templates. The structures show promise for realizing high efficiency phosphor – free white LEDs. The nanostripe dimensions range from 100 to 300 nm and have separations that range from 300 nm to 1 μm. The MOCVD growth conditions strongly affect surfaces expressed in the GaN nanostripes whose sidewalls can be controlled to be nearly vertical or inclined and intersecting. Single quantum well (QW) structures are grown on these different stripes. Photoluminescence (PL) measurement shows that QW grown on stripes with the {10−11} surfaces and triangular shape emit the longest peak wavelength and highly efficient PL emission peak wavelengths as long as 570 nm are realized. PL and electroluminescence (EL) spectra show narrow linewidth that is comparable to the planar case and CL studies further demonstrate the uniform emission wavelength along the sidewalls of the structures. Finally, we have grown and fabricated green emitting LEDs on {10−11} faceted nanostripes with promising device characteristics.

Transmission electron microscopy (TEM) is carried out to characterize the extended defect reduction in low-defect nonplanar GaN substrate templates grown by lateral epitaxial overgrowth (LEO). The LEO nonplanar GaN substrate template has a trapezoidal cross section with smooth (0 0 0 1) and { 1 1 2 ¯ 2 } facets. We demonstrate here the dislocation distribution and behavior in both ordinary LEO and two-step LEO. Penetration of threading dislocations (TDs) beyond mask windows is observed in ordinary LEO substrates. In two-step LEO substrates, which utilize the tendency for TDs to bend 90° at certain plane interfaces, only a type dislocations with Burgers vector b = 1 3 〈 1 1 2 ¯ 0 〉 are generated in the upper part above the TD bending zone between two mask windows with a density of ∼8×10 7 cm −2 , and there are almost no dislocations in the LEO wing region. This approach provides a promising path to produce low-defect GaN substrate templates for high-performance buried heterostructure lasers.

Transmission electron microscopy techniques are applied to investigate three-dimensional (3D) microstructures of the GaN nonplanar substrate selectively grown by metalorganic chemical vapor deposition. Two-step lateral epitaxial overgrowth (LEO) has been utilized and optimized to fabricate fully coalesced nonplanar mesa substrate templates with the trapezoidal cross-section. All threading dislocations (TDs) penetrating beyond the two adjacent mask windows are engineered to bend 90° in the lower TD bending layer after the first step of growth. The dislocations, which approach the GaN mesa top, are predominantly perfect a type dislocations with Burgers vectors of 1 3 〈 1 1 2 ¯ 0 〉 and a density of 8×10 7 cm −2 , which is reduced by three orders of magnitude compared with that of bulk GaN. The spatial distribution of different types of dislocations in the LEO nonplanar substrate is demonstrated herein. The main sources of a type dislocations in the post-bending layer are byproducts of dislocation reactions occurring at the TD bending layer.

We have examined in detail the optical properties of InGaN quantum wells (QWs) grown on pyramidal GaN mesas prepared by lateral epitaxial overgrowth (LEO) in a metalorganic chemical vapor deposition system that resulted in QWs on {1-101} facets. The effects of In migration during growth on the resulting QW thickness and composition were examined with transmission electron microscopy (TEM) and various cathodoluminescence (CL) imaging techniques, including CL wavelength imaging and activation energy imaging. Spatial variations in the luminescence efficiency, QW interband transition energy, thermal activation energy, and exciton binding energy were probed at various temperatures. Cross-sectional TEM was used to examine thickness variations of the InGaN/GaN QW grown on a pyramidal mesa. CL imaging revealed a marked improvement in the homogeneity of CL emission of the LEO sample relative to a reference sample for a conventionally grown In0.15Ga0.85N/GaN QW. The characteristic phase separation that resulted in ...

High-quality-factor vertically coupled InP microdisk resonators have been fabricated. The devices exhibit smooth sidewalls, single-mode operation, high-quality factors Q in excess of 7000, and finesse of 50. The influence of different structural parameters on the device performance is investigated both theoretically and experimentally. These include the disk radius R, the coupling separation d/sub c/, the thickness of the thin membrane between the waveguides and resonator that remains after fabrication t, and the waveguide etch depth d/sub WG/ (defined as the distance between the core layer of the waveguides and the thin membrane).

InAs/InGaAsP quantum dots (QD) grown on InP substrates show strong photoluminescence (PL) signals, with peaks from 1.4 to 1.6 µm at room temperature. Time-resolved PL measurements reveal that carrier lifetimes are the same across the entire PL band at low temperature, as well as at room temperature. This is strong evidence that the PL originates from the inhomogeneously broadened states of well-isolated QDs even at room temperature. These good characteristics, with the availability of additional InGaAsP confinement layers of different band gaps, make the present QD system a good candidate for low threshold lasers at 1.5 µm.

The design of active semiconductor microdisk switches, modulators, or wavelength routers enabled by modulating the transfer characteristics of a resonant cavity is investigated. A simple theoretical model based on coupled-mode theory is used to elucidate design trends and constraints in the cases where electroabsorption, gain, and free carrier injection are employed to modulate the resonator characteristic.

InGaN/GaN quantum wells (QW) were grown by metalorganic chemical vapor deposition (MOCVD) on pyramids of epitaxial lateral overgrown (ELO) GaN samples. The ELO GaN samples were grown by MOCVD on sapphire (0001) substrates that were patterned with a SiNx mask. Scanning electron microscopy and cathodoluminescence (CL) imaging experiments were performed to examine lateral variations in structure and QW luminescence energy. CL wavelength imaging (CLWI) measurements show that the QW peaks on the top of the grooves are red-shifted in comparison with the QW emission from the side walls. The results show that In atoms have migrated to the top of the pyramids during the QW growth. The effects of V/III ratio, growth temperature as well as ELO GaN stripe orientation on the QW properties are also studied.

Gain compression factor and thermal properties of a photonic crystal microcavity laser bonded on a sapphire substrate are extracted by analyzing wavelength shifts under different duty cycles. A high thermal resistance of 43 K/mW and a gain compression factor of 1.2 times 10-16 cm3 are obtained.

An in depth study of aperture placement relative to the electric field standing wave of oxide aperture vertical-cavity surface-emitting lasers (VCSELs) is presented. VCSELs with oxide apertures placed at a node and at an antinode are studied for their dependence of internal loss, far field, threshold current, and efficiency on the position of a thin AlO/sub x/ current aperture relative to the longitudinal standing wave in the cavity.

GaAs/AlGaAs quantum wells (QWs), selectively disordered using an AlAs native oxide and thermal annealing technique, were studied using spectrally, spatially, and temporally resolved cathodoluminescence (CL). The spectral shift of the QW luminescence was determined as a function of annealing temperature in the oxide and nonoxide regions. Time-resolved CL was used to assess the impact of defects and the built-in field near the oxide/nonoxide transition region on the carrier lifetime. Spatially resolved CL spectroscopy was used to examine changes in the QW luminescence intensity near the transition region. The carrier lifetime was found to increase in the transition region, owing to the enhanced spatial separation of electrons and holes in this region. From CL images and line scans of three samples annealed at different temperatures, a partial dead region is found between oxide and nonoxide regions. Details of the native oxide formation are discussed.

The gain saturation behavior of semiconductor traveling-wave optical amplifiers has been analyzed using a model that includes the specific dependence of gain on carrier concentration. Under the condition of a specific gain at a particular current, it is found that the saturation power strongly depends on the choice between quantum well (QW) or bulk amplifying medium but weakly on the detailed design of the device such as the number of QW's or the thickness of the bulk layer. The higher saturation power of the QW-based amplifier is caused by its logarithmic gain-current relation rather than its low optical confinement factor. Also, when the unsaturated device gain is specified, the designed saturation power can be obtained with the lowest drive current by using the highest optical confinement.

Linewidth and small-signal modulation response measurements are reported for room-temperature-operating microcavity two-dimensional photonic crystal lasers. The measured optical linewidth versus the output power was found to saturate at values on the order of 1 GHz. The modulation bandwidth for these low-power lasers was demonstrated to be on the order of 10 GHz

Sapphire-bonded photonic crystal laser cavities with varying number of photonic crystal periods were studied in order to determine the optical loss in these cavities. The lasing threshold increases as the number of lattice periods decreases, and the quality factors of these cavities were calculated from the lasing threshold data. Continuous-wave operation was achieved for cavities with eight or more cladding periods

A procedure for fabricating vertical-cavity surface-emitting lasers (VCSELs) with oxide-based distributed Bragg reflectors (DBRs) is presented. An in-depth analysis of parameters and behavior unique to oxide VCSELs determines the device design. The development cycle time for these devices is reduced through development of a method for post-growth analysis of the epitaxial stack reflectivity before device processing. Threshold currents as low as 160 /spl mu/A and resistances as low as 80 /spl Omega/ are demonstrated using different device designs. The total optical loss of low-doped oxide VCSEL structures is 0.163% which is comparable to VCSEL designs based on all-semiconductor DBRs. The thermal resistance of an 8/spl times/8 /spl mu/m VCSEL is measured to be 2.8/spl deg/C/mW, demonstrating that the presence of oxide layers does not act as a barrier to heat flow out of the active region.

Laterally tapered waveguide structures have been fabricated using a novel, though simple fabrication technique to achieve spot-size transformation. The effect of mesa shape on the far-field pattern and the coupling efficiency to a single-mode fiber (SMF) is reported. A tapered active region having both tensile and compressive quantum wells has been used and dual polarization characteristics are observed for the first time. An experimental analysis of the waveguide losses due to the taper has also been shown.

Polarization resolved photoluminescence from a cleaved sample edge (edge photoluminescence) is shown to be a useful tool for characterization of complex multiple quantum well InP based structures with wells of different strains. The polarization resolved luminescence resulting from the heavy- and light-hole transitions of In0.51Ga0.49As0.78P0.22 tensile and In0.9Ga0.1As0.52P0.48 compressive wells are found to match closely with theoretical values, validating assignments applied to the peaks obtained from photoluminescence. Strain distribution is shown to be an important effect when quantum wells of opposite strain are mixed together in the growth structure. The overlap of the transverse-electric (TE) and transverse-magnetic (TM) emissions found from edge photoluminescence on a mixed strain quantum well structure is shown to have an excellent match with the overlap of the TE and TM modes of a laser which uses the same structure in its active region.

We demonstrate a very high quality (Q) factor wavelength filter based on a buried heterostructure (BH) microresonator platform technology. A 200-/spl mu/m-radius BH ring resonator is integrated with a semiconductor optical amplifier (SOA) using offset quantum wells for loss-cancellation. The resonator is operated near critical coupling at I/sub SOA/=29 mA, which yields a coupling-limited Q of 2.0/spl times/10/sup 5/ with an extinction of -26 dB at the resonant wavelength.

We have demonstrated the ability to selectively modify the mode structure of a multimoded photonic crystal laser cavity, based on the detailed knowledge of resonant modes in a suspended membrane D/sub 3/ microcavity. We have designed a microcavity in which the margins between the highest Q mode and the next highest Q modes have been increased. This modified cavity has been shown to have an improved sidemode suppression ratio under high power pumping condition.

Optical modulation using a depletion width translation mechanism in microdisk devices is investigated. The devices are designed to operate at low drive voltages and have high bandwidths. Analog modulators that operate at drive voltages below 1 V with a 3-dB bandwidth of over 8 GHz were achieved. Eye diagrams showed that the device is capable of operating as a digital switch with speeds up to 10 Gb/s. Since the speed in the case of depletion width modulation is essentially determined by the junction area of the device, it can be improved by further reduction in the active area.

Optical InP-based microresonator modulators which achieve low-voltage high-bandwidth modulation are presented, where resonant wavelength tuning of a circular resonator by free carrier injection is used as the modulation mechanism. Since thermal effects in small resonant cavities and switching speed limitations posed by minority carrier lifetime are the primary concerns in such types of devices, ion bombardment in microtoroidal structures is used to increase the speed of response. The modulation speed is enhanced by an order of magnitude.

Channel configurable optical filters are realized by using buried heterostructure semiconductor ring resonators. Two rings having slightly different radii are laterally coupled to bus waveguides in a cascaded manner, which affords free spectral range (FSR) expansion and channel configuration by Vernier effects. The effective FSR and spectral linewidth at resonance measured from a drop port are 10.2 and 0.017 nm, respectively, that corresponds to a finesse (F) of 600. By shifting the resonant wavelength of one of the resonators with free carrier injection, we demonstrate digital tuning filters where a distinct channel isolation of 15-20 dB is achieved with 0.68-nm spectral spacing.

Room-temperature continuous-wave lasing was demonstrated in photonic crystal microcavities with diameters of approximately 3.2 /spl mu/m. Far-field radiation patterns of these lasers were experimentally measured and compared with numerical simulation predictions.

Tertiarybutylarsine and tertiarybutylphosphine are less hazardous alternatives to arsine and phosphine as group V sources for crystal growth of In/sub x/Ga/sub 1-x/As/sub y/P/sub 1-y/ alloys by metalorganic chemical vapor deposition. Compressive and tensile-strained quantum-well lasers emitting at 1.55 /spl mu/m have been fabricated using these sources. Threshold current density as low as 93 A/cm/sup 2/, transparency current density as low as 38 A/cm/sup 2/ and internal efficiency of 91% were obtained for 1.5% compressive-strained single quantum-well lasers. These devices represent the best lasers emitting at this wavelength that have been reported in the literature. An analysis of some of the characteristics of these devices such as transparency current, differential gain and nonradiative recombination is also presented in this paper.

We demonstrate a 1.6-nm spectrally spaced eight-channel demultiplexer using active semiconductor microdisk resonators as a platform technology. Taking full advantage of the active microdisks, we are able to switch on and off a resonator individually and tune the resonant wavelength as well by controlling the current injection levels. The use of active microdisks affords narrow spectral linewidth ( 15 dB) for the demultiplexed output signals.

All-buried InP-InGaAsP ring resonators laterally coupled to bus waveguides are demonstrated. The buried configurations offer a lower built-in refractive index step along the resonator periphery, which affords enhanced optical coupling coefficients between the waveguides and reduced scattering losses caused by the resonator sidewall imperfections. Very low optical intensity attenuations of 0.4 cm/sup -1/ and coupling-limited quality factors of greater than 10/sup 5/ are observed from 200-/spl mu/m-radii ring resonators. The measured spectral linewidth is as narrow as 0.0145 nm.

1.6-nm spectrally spaced eight-channel semiconductor microdisk laser arrays are presented, where high-Q disk lasing modes are vertically coupled out through a common bus waveguide. The spectral channel spacing is achieved by varying the disk resonator radii from 10.6 to 10.95 /spl mu/m. Typical linewidth of 0.25 nm and side-mode suppression ratio of -20dB are observed under continuous-wave lasing operation near /spl lambda/=1.51 /spl mu/m. This is the first demonstration of integrated microresonator laser arrays.

Mach–Zehnder interferometers were fabricated from suspended membrane photonic crystal waveguides. Transmission spectra were measured and device operation was shown to be in agreement with theoretical predictions.

High performance buried heterostructure InGaAs-GaAs-AlGaAs quantum-well lasers and laser arrays with tight spatial confinement of the electrical current and the optical fields have been fabricated by metalorganic chemical vapor deposition. The lasers ace fabricated in a single growth step, using nonplanar substrates as a template for the active region definition. CW room temperature threshold currents, as low as 0.5 mA and 0.6 mA, are obtained for as-cleaved double and single quantum-well lasers, respectively. External quantum efficiencies exceeding 80% are obtained in the same devices. High-reflectivity facet-coated lasers have room temperature CW threshold currents as low as 0.145 mA with 10% external quantum efficiency. Lasers made by this technique have high yield and uniformity, and are suitable for low threshold array applications. >

A theoretical approach to nonplanar wave propagation through Bragg reflector multilayer structures is presented. The theory is applied to the optical coupling and feedback in a folded cavity surface emitting laser using a 45/spl deg/ deflection mirror-epitaxial Bragg reflector arrangement. The effects of the nonplanar wave propagation on the Bragg mirror reflectivity in vertical cavity surface emitting lasers is also examined. Experimental verification of the theory is presented in a novel folded cavity surface emitting laser structure integrating a horizontal cavity InGaAs-GaAs laser grown on a structured substrate with a high reflectivity Bragg reflector. >

Semiconductor microdisk resonator lasers vertically coupled to bus waveguides are demonstrated for the first time. These structures have many of the characteristics required for a light source in photonic integrated circuits because they can be coupled to other optical elements (switches, routers, filters, etc.) through common bus lines. A continuous-wave single-mode laser at 1579 nm with a side-mode suppression ratio greater than 30 dB has been achieved for an 8-/spl mu/m-radius microdisk. For larger disks, mode competition between modes near the maximum gain wavelength is observed from the light output-current (L-I) characteristics. Improved heat sink design is required for future devices.

GaN nanorods and nanosheets with non-polar facets are used as templates to form InGaN QW active regions for LEDs on the nonpolar facets. Uniform, narrow spectra light emitting regions are formed on the nonpolar facets.

Single-pulse ps-pump and ns-probe nonlinear transmission measurements provide carrier-density-dependent optical nonlinear spectra in GaAs/AlGaAs multiple quantum wells grown by metalorganic chemical vapor deposition. The use of the ps pump eliminates the need to know carrier lifetime to determine carrier density. The saturation behavior of changes in absorption coefficient and refractive index are modeled by a simple saturation equation to obtain saturation carrier density. The saturation spectra for different well thicknesses are obtained. The minimum saturation carrier density appears around 150 /spl Aring/. >

Gain saturation properties of a multiple-quantum-well structure with both tensile and compressively strained quantum wells are investigated analytically. This type of structure has recently been experimentally demonstrated to serve as a basis for the implementation of a two-polarization/two-frequency laser and polarization insensitive travelling wave(TW) amplifier. The performance of these devices strongly depends on the interaction between the TE and TM gains of the structure. The gain medium model appropriate for this type of structure is developed and the rate equation approach is used to describe the saturation properties of TE/TM gains and the coupling between the TE and TM gains due to gain saturation. The minimum amount of coupling between the two is governed by the basic symmetry of the light-hole wavefunction which interacts with photons of both polarization: photon cross-coupling. The finite rate of carrier escape from the quantum wells provides for carrier induced coupling between the populations of the two well types and therefore also couples TE and TM gains: carrier cross-coupling. The performance of a polarization insensitive amplifier, laser, and polarization control element is evaluated as a function of the amount of carrier cross-coupling, which is a structure dependent parameter. A structure with high degree of cross-coupling is desirable for polarization insensitive TW amplifier, while two-polarization lasers and polarization control elements require minimum cross-coupling. >

InP vertically coupled microdisk resonator/waveguide switching devices with an electroabsorptive (EA) active region are demonstrated for the first time. The devices exhibit single-mode operation, large free spectral range of 10.5 nm and a high quality factor of 5700. The EA effect provides a way of loss-trimming the resonant characteristics. Active switches, routers, and fast modulators based on these devices are envisioned as part of a WDM system.

InP, vertically coupled microdisk resonator/waveguide switches with a gain active region are demonstrated. The devices exhibit single-mode operation, large free-spectral range of 10 nm, and a high-quality factor of 5700. The introduction of a quantum-well region inside the cavity provides a way of gain trimming the resonant characteristics. Active switches, routers, and filters with tunable bandwidth based on these devices are envisioned as part of a wavelength division multiplexing system.

Spectral equalization devices for an optical analog-to-digital (A-to-D) converting system have been theoretically analyzed and fabricated. Selective area growth was used to define a multiple-section active region. Two-segment semiconductor optical amplifier with current adjustable gain spectrum is demonstrated.

Room-temperature operation of two-dimensional photonic crystal lasers optically pumped by a vertical-cavity surface-emitting laser emitting at 860 nm is reported. The photonic crystal membrane is surrounded by air on both sides and consists of four compressively strained quantum wells as the active region. The incident threshold pump power of an approximately 2.6-/spl mu/m-diameter hexagonal defect cavity laser operating at 1.6 /spl mu/m is 2.4 mW.

High-quality factor vertically coupled InP microdisk resonators have been fabricated. Wafer bonding techniques have been used as a main approach to enable this three-dimensional structure. The devices exhibit smooth sidewalls, single mode operation, and high-quality factors in excess of 7000.

The effect of strain on Auger recombination has been studied using the differential carrier lifetime technique in both lattice matched InGaAs-InP and compressively strained quaternary quantum wells. It is found that Auger recombination is reduced in strained devices. The transparency carrier density and differential gain of both lattice matched and strained devices have been obtained by gain and relative intensity noise measurement. A reduction of the transparency carrier density is observed in the strained device. However, no differential gain increase is seen. The temperature sensitivity of the threshold current density of both lattice matched and strained devices has been fully studied. Physical parameters contributing to the temperature sensitivity of the threshold current density have been separately measured, and it is shown that the change in differential gain with temperature is a dominant factor in determining the temperature sensitivity of both lattice matched and strained devices. >

A comprehensive study of the effect of compressive strain on the threshold current performance of long-wavelength (1.5 mu m) quantum-well (QW) lasers is presented. Model predictions of threshold currents in such devices identify QW thickness as a parameter that must be considered in optimizing laser performance when Auger currents are present. Experimental comparisons between strained and unstrained devices reveal strain-induced reductions in internal transparency current density per QW from 66 to 40 A/cm/sup 2/, an increase in peak differential modal gain from 0.12 to 0.23 cm/A, and evidence for the elimination of intervalence band absorption as compressive strain increases from 0 to 1.8%. However, most of these improvements arise in the first approximately 1% of compressive strain. To fabricate low-threshold 1.5- mu m buried heterostructure (BH) devices in InP using the strained QW active regions an optimized design which shows that threshold current is at its lowest when the stripe width is approximately 0.6-0.7 mu m is derived. Results for uncoated BH lasers are reported. >

Strained InGaAs/GaAs quantum-well three-terminal lasers with monolithically integrated intracavity modulators were fabricated using low threshold current structures formed by the temperature engineered growth (TEG) technique. An on-off switching ratio of 556 was obtained for a 30-mV change in absorber voltage. An optical power contrast ratio of 7.5 was measured with a total DC power consumption of 25.3 mW. These results show a great improvement in the digital (on-off) switching performance of three-terminal lasers with intracavity modulators. >

It is shown that amplified spontaneous emission (ASE) can affect the measurement of nonlinear optical properties in semiconductors through its reduction of the excess carrier density. When the optical excitation area is large, lateral ASE can reduce the carriers within a much shorter period of time than the normal carrier lifetime. Just after ASE is over, the time-integrated surface photoluminescence signal may be used as a measure of the carrier density, which is the carrier density experienced by an ns probe in ps pump experiments. When the excited carrier density is at 10/sup 20/ cm/sup -3/, surface ASE is also possible and is observed, even with small spot sizes. >

A novel AlGaAs optically controlled bistable vertical directional coupler was demonstrated. The optical input can be routed between two outputs by an optical pulse on the input signal or by optical set and reset pulses applied via fiber. Both modes have been experimentally demonstrated. Because of positive optical feedback, the device is bistable and will latch into the set state until assertively reset. The operation is based on electrooptic modification of the phase match between the two waveguides in the directional coupler. Since no Fabry-Perot resonances are involved, the device operates over a fairly wide wavelength (840-880 nm) and applied voltage (2-12 V) range. A switching contrast in the upper waveguide output of 14.7:1 and a throughput of 64% were observed. The critical input power to cause bistable switching is 17 mu W. The switching speed ( approximately 200 ns) is RC-limited and the set and reset energies are determined by the charging energy of the waveguide capacitance. >

Uniform bottom-emitting 850-nm vertical-cavity surface-emitting laser (VCSEL) arrays on sapphire substrates have been demonstrated using wafer bonding technology to transfer the epitaxially-grown VCSEL structures from GaAs substrates onto sapphire substrates. The uniformity of the VCSEL arrays were improved by placing thin oxide aperture at the standing wave node to reduce scattering loss for small aperture devices. The averaged threshold current of a 5/spl times/5 VCSEL array is as low as 346 /spl mu/A, while the averaged external quantum efficiency approaches 57%. The maximum wall-plug efficiency is 25% and the single-mode output power is more than 2 mW under continuous-wave current excitation at room temperature. We have also demonstrated a large (10/spl times/20) VCSEL array with variations of threshold current and external quantum efficiency less than 4% and 2%, respectively.

We experimentally demonstrate filtering based on the finite time response of the interband carrier nonlinearities in a direct bandgap semiconductor. The filter is implemented in a mixed strain polarization insensitive multiple-quantum-well, broad-area semiconductor amplifier. The key to the filter implementation is the separation of a four-wave mixing generated sideband from the linearly amplified inputs based on spatial filtering. Both spectrum analysis and channelizing of RF modulated optical carriers are demonstrated.

Recombination processes, gain, and loss have been comparatively studied in both strained and lattice-matched 1.5- mu m semiconductor quantum-well lasers using differential carrier lifetime techniques and other measurements. For the first time, some predicted strain benefits to 1.5- mu m semiconductor lasers have been verified, including (i) the reduction of the Auger recombination rate in devices with both 0.9% and 1.8% compressive strain; and (ii) a 33% reduction of transparency carrier density in lasers with 0.9% strain compared to lattice-matched lasers. The authors, however, did not observe an increase of the differential gain in strained devices as predicted. >

The issues involved in the growth of strained InGaAs/GaAs quantum well lasers integrated with AlAs/GaAs Bragg reflectors on nonplanar substrates is treated in this work. Under optimized conditions, controlled growth of uniform small area Bragg reflectors integrated with low threshold lasers has been achieved. An average pulsed threshold current of 2.9 mA/μm for edge emitting lasers at 0.98 μm with 90% external efficiency was obtained showing the potential for the use of this structures as 45° folded cavity surface emitting lasers.

A low-threshold current density (J/sub th/) of 140 A/cm/sup 2/ for broad-area 1.5- mu m semiconductor lasers with uncoated facets is demonstrated at a cavity length of 3.5 mm. This was achieved by the use of a single InGaAsP quantum well (QW) of 1.8% compressive strain inside a step-graded InGaAsP waveguide region. Low-cavity losses of 3.5 cm/sup -1/ and a relatively wide quantum well as compared to InGaAs wells of equivalent strain contribute to this high performance. Double QW devices of 2 mm length showed threshold current densities of 241 A/cm/sup 2/. Quaternary single and double QWs of similar width but only 0. 9% strain gave slightly higher threshold current density values, but allowed growth of a 4 QW structure with a J/sub th/ of 324 A/cm/sup 2/ at L=1.5 mm. >