High-quality extended cavity ridge lasers fabricated by impurity-free vacancy diffusion with a novel masking technique

By using phosphorous doped (5% wt P) silica as masking material and standard silica capping to promote quantum well interdiffusion, GaAs-AlGaAs ridge waveguide QW lasers with integrated transparent waveguides were fabricated. With a selective differential blue-shift of 30 nm in the absorption edge, devices with 400-/spl mu/m/2.73-mm-long active/passive sections exhibited threshold currents of 8 mA in CW operation, only 1 mA higher than that for normal lasers of the same active length and from the same chip. This 14% increase in threshold current was accompanied by a slope efficiency decrease of 40%. Losses of 3.2 cm/sup -1/ were measured in the passive waveguides at the lasing wavelength using the Fabry-Perot resonance method. This value is among the lowest reported so far using an impurity-free disordering technique.     

Low-threshold lasers fabricated by alignment-free impurity induceddisordering

An Si/SiN_x/Si trilayer diffusion source and mask is described and applied to an alignment-free process for fabricating lasers by impurity-induced disordering (IID). Edge-emitting lasers with continuous wave threshold currents of 4.8 mA were achieved, and folded-cavity surface-emitting lasers with Si disordered waveguides were demonstrated for the first time with a threshold of 11 mA. The process that makes possible self-aligned-metallization on a diffusion defined stripe will be useful in fabricating narrow stripe IID lasers and simplify processing for integration of IID waveguide devices     

Monolithic integration of curved waveguides and channeled-substrate DH lasers by wet chemical etching

Integration of AlGaAs/GaAs curved waveguides and other two-dimensional waveguides with DH lasers and detectors is demonstrated. Devices are fabricated from LPE AlGaAs/GaAs layers by wet chemical etching processes. Differential transfer efficiencies ofeta_{t}= 5percent are routinely achieved in a structure consisting of an integrated laser, a 90° curved waveguide with 150μm radius, and a detector, for the case where one laser mirror is etched and one cleaved. This value iseta_{t}= 4percent if both mirrors are etched. A comparison of waveguide attenuation between straight and curved rib waveguides is given, along with the transfer characteristics of curved waveguides. The loss coefficient of curved rib waveguides with 150-μm radius is about two times that of a straight waveguide of the same length. The fabrication and properties of channeled-substrate crescent (CSC) lasers and detectors with transverse single-mode confinement, monolithically integrated by means of passive CSC interconnecting waveguides, is also described.     

Improvements in mode-locked semiconductor diode lasers using monolithically integrated passive waveguides made by quantum-well intermixing

By using the technique of quantum-well intermixing (QWI), monolithically integrated passive, and active waveguides can be fabricated. It is shown that mode-locked extended cavity semiconductor lasers with integrated low-loss passive waveguides display superior performance to devices in which the entire waveguide is active: the threshold current is a factor of 3-5 lower, the pulsewidth is reduced from 10.2 ps in the all active laser to 3.5 ps in the extended cavity device and there is a decrease in the free-running jitter level from 15 to 6 ps (10 kHz-10 MHz).     

High-temperature operating 1.3-μm quantum-dot lasers fortelecommunication applications

High-performance 1.3-μm-emitting quantum-dot lasers were fabricated by self-organized growth of InAs dots embedded in GaInAs quantum wells. The influence of the number of quantum-dot layers on the device performance was investigated. Best device results were achieved with six-dot layers. From the length dependence; a maximum ground state gain of 17 cm^-1 for six dot layers could be determined. Ridge waveguide lasers with a cavity length of 400 μm and high-reflection coatings show threshold currents of 6 mA and output powers of more than 5 mV. Unmounted devices can be operated in continuous wave mode up to 85°C. A maximum operating temperature of 160°C was achieved in pulsed operation for an uncoated 2.5-mm-long ridge waveguide laser     

Growth and characterization of continuously graded index separateconfinement heterostructure (GRIN-SCH) InGaAs-InP long wavelengthstrained layer quantum-well lasers by metalorganic vapor phase epitaxy

A report is presented on the growth and characterization of the first InGaAs-InP-based graded-index separate-confinement-heterostructure (GRIN-SCH) strained quantum-well lasers operating near 1.47 μm. The structure features linearly graded InGaAsP waveguide layers for both optical and carrier confinement in a very narrow, strained quantum-well layers. The excellent structural quality of the active and waveguide regions has been confirmed by transmission electron microscopy (TEM) and secondary ion mass spectroscopy (SIMS) analysis results. Strained quantum-well lasers with well widths as narrow as 5-6 nm were fabricated with threshold current densities as low as 750 A/cm². Buried-heterostructure lasers based on strained quantum-well active lasers exhibit threshold currents as low as 10-15 mA with quantum efficiency of 70-80%. With antireflection coating on one side of the sample, the laser shows threshold current of 35 mA with highest output power of 160 mW     

Wavelength selection in an integrated multiwavelength ring laser

The wavelength selection mechanism of a compact integrated multiwavelength ring laser is demonstrated. The device contains four semiconductor optical amplifiers, a compact arrayed waveguide grating and passive waveguides integrated on a single InP wafer. The device can produce seven different wavelengths through biasing one or two out of the four amplifiers. Comparison of calculated and measured subthreshold laser spectra demonstrates the role of crosstalk in the arrayed waveguide grating in the laser and allows the crosstalk to be quantified. A rate-equation model of the laser and measurements are presented that describe the switching between wavelengths of the laser as a function of bias currents. A comparison between the measured data and the model is made.     

Tunable sampled-grating DBR lasers with integrated wavelengthmonitors

We report on the design and development of a wavelength monitor for use with tunable semiconductor lasers. The device is based on two-mode interference in an asymmetrically excited waveguide that is coupled to a Y-branch splitter. The monitoring range of the device is 30 nm. The wavelength monitor is capable of operating over an input power range of 34 dB, and the waveguide detectors do not saturate at photocurrents as high as 1.2 mA. The sensitivity of the monitor is only 1.24 nm for an isolated device, but improves to 0.44 nm when it is integrated on chip with the laser     

A Compact SOI-Integrated Multiwavelength Laser Source Based on Cascaded InP Microdisks

We report on the performance of a compact multi- wavelength laser (MWL) source heterogeneously integrated with and coupled to a silicon-on-insulator (SOI) waveguide circuit. The MWL consists of four InP-based microdisk lasers, coupled to a common SOI wire waveguide. The microdisk lasers operate in continuous-wave regime at room temperature, with a threshold current around 0.9 mA and a waveguide-coupled slope efficiency of up to 8 muW/mA, for a microdisk diameter of 7.5 mum. The output spectrum contains four laser peaks uniformly distributed within the free-spectral range of a single microdisk. While thermal crosstalk is negligible, laser peak output powers vary up to 8 dB for equal microdisk drive currents, as a result of loss due to coupling with higher order modes supported by the 1-mum-thick microdisks. This nonuniformity could be eliminated by reducing the microdisk thickness.     

Curved waveguides for spatial mode filters in semiconductor lasers

Curved waveguides are used as a lateral spatial mode filter to increase the threshold for the first-order mode in high-power narrow stripe semiconductor lasers. Beam propagation analysis is used to determine optimal waveguide geometries and radii of curvature to establish appropriate amounts of bend loss. Curved waveguide devices are fabricated and compared against conventional devices. Use of a curved waveguide increases the current level at which lateral beam instabilities occur from /spl sim/400 to /spl sim/700 mA with no decline in slope efficiency.     

Tapered polymer single-mode waveguides for mode transformation

This paper presents a tapered polymer waveguide structure for coupling light between optical waveguides with differing geometries. Optical fibers, lasers, and other photonic integrated circuit components can be coupled with tapered waveguides. The polymer waveguide performs a mode transformation between different mode shapes and sizes. For example, the mode transformation can be from an elliptical laser diode mode to that of a circular optical fiber mode. The input and output of a tapered waveguide structure are analyzed, for the case of laser to fiber coupling, in order to determine the effect of misalignments on the coupling efficiency. Adiabaticity in waveguide propagation is discussed. The fabrication of our polymer waveguides is also described     

Measurements of coupling and reflection characteristics of butt-joints in passive waveguide integrated laser diodes

Amplified spontaneous emission (ASE) spectra of passive waveguide integrated lasers have been studied to estimate the coupling efficiency and the reflectivity at the butt-joints between active and passive waveguides. A new method has been proposed for the analysis of ASE to extract the coupling efficiency and reflectivity at the butt-joints. This method was applied experimentally to estimate the coupling and reflection of the passive waveguide integrated lasers with different amounts of vertical misalignments of active and passive waveguides.     

High temperature, high power InGaAs/GaAs quantum-well lasers withlattice-matched InGaP cladding layers

The authors report the high-temperature and high-power operation of strained-layer InGaAs/GaAs quantum well lasers with lattice-matched InGaP cladding layers grown by gas-source molecular beam epitaxy. Self-aligned ridge waveguide lasers of 3-μm width were fabricated. These lasers have low threshold currents (7 mA for 250-μm-long cavity and 12 mA for 500-μm-long cavity), high external quantum efficiencies (0.9 mW/mA), and high peak powers (160 mW for 3-μm-wide lasers and 285 mW for 5-μm-wide laser) at room temperature under continuous wave (CW) conditions. The CW operating temperature of 185°C is the highest ever reported for InGaAs/GaAs/InGaP quantum well lasers, and is comparable to the best result (200°C) reported for InGaAs/GaAs/AlGaAs lasers     

Analysis of a phase mismatched three waveguide coupler with an optical amplifier

A novel optical amplifier is proposed and analyzed. This device consists of three parallel waveguides and each has a slightly different propagation constant, that is, each waveguide is slightly phase mismatched and couplings among these waveguides are weak. Two adjacent waveguides are passive and the third one is active and all end facets of waveguides are antireflection coated, so that optical feedback can be eliminated and the active waveguide is a traveling wave type amplifier. Because of a phase mismatched configuration, this device can be used to tap optical signals without much power reduction in optical transmission lines. Signals coming into the device are weakly coupled to the active waveguide via the passive waveguide in between and they are amplified through the active waveguide. Characteristics of this device are studied and parameters which are required to design the device are also given as an example.     

Tunable GaInNAs lasers with photonic crystal mirrors

We present results of tunable GaInNAs lasers with photonic crystal (PhQ mirrors, fabricated from GaAs-AlGaAs layers with a double GaInNAs quantum well emitting at IR wavelength. The devices are realized as ridge waveguide lasers with two coupled segments and a total length between 240 and 580 pm. PhC blocks with different thicknesses are used for the back and front mirror as well as for the intermediate reflector between the two segments. The lasers have threshold currents around 20 mA and output powers up to 6 mW. Tuning of the laser emission over 30 nm is achieved by a variation of the currents injected into the two segments.     

GaAs:GaAlAs ridge waveguide lasers and their monolithic integrationusing the ion beam etching process

The fabrication and performance characteristics of GaAs/GaAlAs ridge waveguide lasers are discussed. Threshold currents as low as 8 mA and differential quantum efficiencies as high as 90% were obtained for 250-μm-long graded-index separate-confinement heterostructure with single quantum well (GRINSCH SQW) lasers. High-speed short-cavity ridge waveguide lasers for which both the ridge stripe and one-mirror facet were formed by Ar-ion beam etching were achieved. The dependence of threshold current and lasing spectra on the cavity length were theoretically and experimentally investigated. This process was successfully used to integrate a laser diode monolithically with a photodiode or a field-effect transistor     

High reliability low-threshold InGaAsP ridge waveguide lasersemitting at 1.3 μm

The fabrication, performance, and reliability of InP/InGaAsP ridge waveguide lasers emitting at 1.3 μm is described. The structure requires only one stage of planar wafer growth and simple fabrication steps and is therefore an inherently low-cost product. Threshold currents are typically 25-30 mA, and the external quantum efficiency is 20-25% per facet. Output power in the fundamental mode is maintained to above 10 mW, while total power in excess of 100-mW CW at 20° has been obtained. The life test data have been fitted to a power-law drift model to predict long-term behavior and is consistent with total lifetimes in excess of 25 years. The device is eminently suited for applications in high-reliability high-capacity fiber-optic communications systems     

Low threshold ridge waveguide single quantum well laser processed by chemically assisted ion beam etching

Fundamental lateral mode ridge waveguide lasers have been developed utilizing chemically assisted ion beam etching. The lasers exhibited mean threshold currents of 12.6 mA with close to 100 percent yield and differential quantum efficiencies as high as 69 percent.     

Extremely low threshold operation of 1.5 mu m GaInAsP/InP buried ridge stripe lasers

1.5 mu m Fabry-Perot lasers exhibiting extremely low threshold currents have been obtained with a buried ridge stripe (BRS) structure. Threshold currents are 5.7 and 15.5 mA for 300 mu m and 1 mm cavity lengths, respectively, in CW operation. The optical losses of the buried waveguide have been determined from the external quantum efficiency dependence with cavity length.<>     

Monolithically integrated transverse-junction-stripe laser with anexternal waveguide in GaAs/AlGaAs

This device consists of a five-layer transverse-junction-stripe laser structure monolithically integrated with an external three-layer waveguide. The transverse p-n junction within the laser cavity permits the use of a vertical p-n junction in the external waveguide for future implementation of a modulator without disturbing the laser operation. As a result, this structure allows for flexibility in the design of the external waveguide/modulator without resorting to complicated regrowth procedures. Design curves for two different types of optical cavities are presented, and the reflectivity and transmission of the etched facet as a function of active layer thickness is modeled in detail using an excitation field approach. Finally, integrated laser/waveguide devices are fabricated based on this design and are compared to the theoretical curves. Most devices had threshold currents between 60 and 80 mA, while laser-to-waveguide transmission coefficients were as high as 38%