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Microcavity laser linewidth behavior close to the threshold transition region is investigated through high-resolution linewidth measurements. A local maximum is found for the linewidth of lasers operating slightly above threshold. The increase in laser linewidth close to threshold is explained by the effective contribution of the linewidth enhancement factor (alpha) to the laser linewidth. The Fokker-Planck model of laser noise is then solved using the eigenfunction expansion method to fit to the measured linewidth data. The behavior of the measured linewidth agrees with the model with an extracted linewidth enhancement factor (alpha) ranging between 3.5 and 5.0.

A detailed 3-D finite-difference time-domain analysis of photonic crystal double-heterostructure bound state resonances is presented along with supporting experimental results. The connection between different photonic crystal waveguide bands and the associated photonic crystal double-heterostructure bound states is made, and mode profiles are presented. We analyze the quality factors using the Pade interpolation method and directional radiation properties by calculating the time-averaged Poynting vector. We also present field profiles of higher order bound states and discuss cavity geometries to enhance a given bound state mode relative to neighboring modes. Experimental lasing results are presented demonstrating the utility of our approach.

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.

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).

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.

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.

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.

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.

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.

Polarization insensitivity of the gain saturation properties of a 1.3 /spl mu/m semiconductor amplifier with tensile and compressive strain quantum well active region are used to demonstrate a WDM wavelength conversion configuration in which the outputs at the two wavelengths are separated on the basis of polarization. Use of orthogonal polarizations allows operation of a wavelength converter without an optical frequency filter at the output. Alternatively, inherent polarization insensitivity of the device can be used for wavelength conversion of an arbitrarily polarized signal. >

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/. >

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.

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. >

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.

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.

Metalorganic chemical vapor deposition (MOCVD) has been used to grow low threshold 1.3 μm lattice matched and strained quantum well lasers. By careful optimization of growth conditions and growth interruptions between different layers, we have been able to grow good quality lattice matched and strained In x Ga 1- x As y P 1- y layers and quantum wells. This is demonstrated by achieving broad area lasers with threshold current densities as low as 190 A/cm 2 for a two quantum well device with 0.85% compressive strain.

One attraction of photonic crystals is the ability to control optical device characteristics by lithographically varying the geometry. In this letter, we demonstrate a 10/spl times/10 array of optically pumped two-dimensional (2-D) photonic crystal defect lasers with varying lattice parameters. By adjusting the photonic crystal interhole spacing as well as the hole diameter we are able to tune the laser wavelength from 1500 to 1625 nm on a monolithic InP-InGaAsP wafer. A wavelength resolution of 10 nm from device to device was obtainable, limited by the lithography and etching tolerances of our fabrication method.

Two-dimensional photonic crystal defect lasers in InGaAsP membranes directly bonded to a SiO(2)/Si substrate have been demonstrated. Lasing at wavelengths near 1550 nm was obtained with incident threshold pump powers as low as 1.5 mW. Good agreement between experimental data and three-dimensional finite-difference time-domain (FDTD) simulation was achieved. The thermal impedance of this laser is also characterized.

We have demonstrated high performance wafer-bonded bottom-emitting 850-nm vertical-cavity surface-emitting lasers (VCSEL's) on transparent substrates. The free-carrier absorption of the substrate was avoided by using undoped GaP or sapphire substrates. The maximum external quantum efficiency approaches 48% while the threshold current remains as low as 550 /spl mu/A for the 6/spl times/6 /spl mu/m/sup 2/ VCSEL's bonded on GaP substrates. VCSEL's with 8.6/spl times/8.6 /spl mu/m/sup 2/ aperture bonded on sapphire substrates also exhibit threshold currents of 800 /spl mu/A and external quantum efficiencies of 33.2%. The difference in efficiency between these two devices results from the change of the refractive index of the exit medium.

Techniques for fabricating a self-defined AlAs oxide-current-aperture that is applicable to very small stripe width edge emitting devices and small aperture vertical-cavity surface-emitting lasers are reported. InGaAs single-quantum-well buried-heterostructure edge-emitting lasers with a self-defined AlAs oxide-current-aperture were fabricated by a three-step metal-organic chemical vapor deposition growth to demonstrate the validity of the process. The AlAs layer for the AlAs oxide was grown by selective area growth techniques. The threshold current and differential quantum efficiency of 3-/spl mu/m stripe width, 446-/spl mu/m-long laser were 2 mA and 91%, respectively. The leakage current at -15 V was less than 20 nA.

A study of the influence of oxide apertures on the internal loss in vertical-cavity surface-emitting lasers (VCSEL's) is performed for two different aperture placements within the VCSEL cavity. It is found that when apertures are placed at a node in the standing wave of a VCSEL cavity there are negligible aperture dependent losses. However, when apertures are placed at an antinode there is a clear relationship between aperture dimension and internal loss.

The effect of the carrier capture into quantum wells on the modulation response of semiconductor laser is investigated. It is shown that the capture limits the maximum possible modulation speed by increasing gain nonlinearities.

In this report, microdisk lasers with -3dB small-signal modulation bandwidths in excess of 17 GHz are demonstrated. Linewidth of these lasers are also measured and a minimum linewidth of 85 MHz is achieved.

An array of double-heterostructure photonic crystal QW membrane lasers was fabricated in which number of cladding periods was varied. 60 muW peak output power was collected from the facet of one device by a bare fiber.

A study of the effects of aperture placement on the properties of vertical-cavity surface-emitting lasers (VCSELs) is presented. When thin apertures are placed at the peak of the electric field standing wave optical losses are very high for small apertures. The threshold current increases with decreasing aperture size and two-dimensional diffraction like patterns are evident in the far field. For apertures placed at a node, optical losses appear to be negligible, and loss of optical confinement is apparent for apertures below 2 /spl pi/m.

We have created bidirectional high-performance top- and bottom-emitting vertical-cavity surface-emitting lasers (VCSELs) from a single epitaxial wafer. Using a spatially selective oxidation of AlAs layers in hybrid distributed Bragg reflectors (DBRs) of a VCSEL structure, devices processed for top emission had threshold currents of 100-110 /spl mu/A with slope efficiencies of 18%-20%. Devices from the same wafer processed for bottom substrate emission had thresholds of 110-120 /spl mu/A and slope efficiencies of 17% and 18%. This technology will greatly simplify the use of VCSEL's in large three-dimensional (3-D) parallel interconnects, photonic repeaters, and smart pixels.

The authors have measured the thermal impedance of vertical-cavity surface-emitting lasers (VCSELs) with oxide/GaAs DBRs and shown that it is comparable to that of VCSELs with all-semiconductor DBRs. A VCSEL with an 8-/spl mu/m oxide aperture shows a thermal impedance of 2.8/spl deg/C/mW. By varying the aperture size, the thermal conductance of the material below the active area is 0.255 W/cm/spl deg/C. These results demonstrate that the oxide is not a major barrier to heat transport out of the active region.

We describe the demonstration of sapphire-bonded photonic crystal lasers operating under room temperature CW conditions and characterize the modal properties and small-signal modulation response of these lasers. In addition, we describe progress in photonic crystal nanocavity lasers which have InAs QD active material, and investigate the optical properties of passive photonic crystal waveguide components.)

We report for the first time polarization-insensitive, mixed-strain quantum-well semiconductor optical amplifiers (QW SOAs) with monolithically integrated laterally tapered section for mode transformation. This taper section improves coupling efficiency to cleaved single-mode fibers by 3-4 dB compared to an untapered linear waveguide. We have demonstrated 18 dB chip gain with less that 1-dB polarization sensitivity of the gain. We also found that the output saturation power is about 10 dBm for all polarizations. The gain bandwidth was estimated to be 45 nm.

A new class of an all-optical switch-the wavelength recognizing switch is proposed and experimentally demonstrated. The device uses a control signal to sense the wavelength of the input packet and taps a portion of the data packet to the appropriate output port. The device is based on noncollinear four-wave mixing in a broad-area traveling-wave semiconductor optical amplifier. Measured switching efficiency is +8.2 dB with -28.8 dB of crosstalk. The recognition bandwidth is as narrow as 0.03 /spl Aring/ and the 3-dB switching bandwidth is 42 nm.