Low-threshold continuous-wave surface emitting lasers with etchedvoid confinement

Data are presented demonstrating low threshold continuous wave operation of AlAs/GaAs/InGaAs vertical cavity surface emitting lasers. Continuous wave thresholds of 470 μA have been realized for device diameters of ~4 μm, and 1.1 mA for a device diameter of 10 μm. A two-step molecular beam epitaxial growth process is used which results in a buried etched void surrounding the active cavity of the laser     

Effect of surface recombination velocity on the threshold currentand differential quantum efficiency of the surface-emitting laser diode

Threshold current and quantum efficiency of the surface-emitting laser diodes were calculated on the basis of a planar carrier diffusion model with cylindrical boundary and analytical electromagnetic field distribution in either a uniform core waveguide or Vainshtein's open cavity model. Surface recombination at the boundary of the quantum-well active region was much greater than the bulk recombination in both structures unless cavity diameter was greater than 50 μm. Diffraction loss was also significant in the open cavity structure as cavity diameter decreased. Reducing the surface recombination velocity leads to the reduction of threshold current and enhancement of differential quantum efficiency. In order to further reduce that current, using a buried heterostructure with a vertical waveguide structure is suggested     

Low-threshold, highly reliable 630 nm-band AlGaIP visible laserdiodes with AlInP buried waveguide

Low-threshold, highly reliable 630 nm-band AlGaInP visible laser diodes have been developed by employing a low-loss optical waveguide buried in the AlInP layer. A low-threshold current of 19 mA at 25°C is obtained with a cavity length of 310 μm. This current is the lowest value for 630 nm-band AlGaInP visible laser diodes, to our knowledge. Our AlInP-buried laser diodes with a cavity length of 500 μm operated over 7000 h without significant degradation at 60°C and 5 mW     

Vertical cavity surface-emitting laser with an AlGaAs/AlAs Braggreflector

The letter elucidates the room temperature pulsed operation of a vertical cavity surface-emitting laser with an electrically conductive AlGaAs/AlAs distributed Bragg reflector (DBR). The maximum reflectivity of a DBR grown by MOCVD was 96% at 0.88 μm wavelength. The threshold current of 30 μm diameter devices was 200 mA under room temperature pulsed condition, which is the lowest value for such a broad area structure     

Low threshold InGaAs/GaAs 45° folded cavity surface-emittinglaser grown on structured substrates

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 has been fabricated. Devices with threshold currents of 8 mA and CW wall plug efficiencies at 5% at 6 mW output power have been demonstrated at a wavelength of 0.99 μm. By combining a cleaved uncoated mirror with the 45° deflecting mirror the authors have obtained threshold current as low as 5 mA for a device 450 μm long     

Quantum-dot microlasers

Edge-emitting short-cavity lasers with deeply-etched Bragg mirrors were fabricated on a GaInAs/AlGaAs laser structure with a single active layer of self-organised GaInAs quantum-dots. Continuous wave operation has been achieved down to cavity lengths of 16 μm with a minimum threshold current of 1.2 mA for 30 μm-long devices     

Grating-assisted surface-emitting laser transmitter withimage-forming capability

A grating-assisted surface-emitting laser transmitter with image-forming capability has been fabricated. The laser transmitter consists of an InP-InGaAsP distributed Bragg reflector ridge laser emitting at 1.5 μm, a semiconductor optical amplifier and a computer-generated holographic out-coupler. The area of the out-coupler is 80 μm×80 μm. The image produced by the out-coupler is focused at 3 cm above the laser surface and each circular spot has a diameter of 0.6 mm     

2-μm GaInSb-AlGaAsSb distributed-feedback lasers

Room temperature continuous-wave operation of 2-μm single-mode InGaSb-AlGaAsSb distributed-feedback (DFB) lasers has been realized. The laser structure has been grown by solid source molecular beam epitaxy (MBE). Single-mode DFB emission is obtained by first-order Cr-Bragg gratings on both sides of the laser ridge. For a cavity with 900 μm length and 4 μm width, the threshold currents are around 20 mA and the continuous-wave output power is 10 mW at a drive current of 200 mA at 20°C. Monomode emission with sidemode suppression ratios of 31 dB has been obtained     

Low threshold current density operation of GaInAsP-InP laser withmultiple reflector microcavities

We propose and demonstrate a new type of semiconductor laser having multiple reflector microcavities for the purpose of low threshold current operation. Very uniform multiple reflector microcavity structure was fabricated by electron beam (EB) lithography and selective wet chemical etching. Due to multiple reflection effect, threshold current density as low as 310 A/cm² (threshold current of 30 mA) was obtained at room temperature with the total cavity length of 64 μm and the cavity width of 200 μm     

Low threshold current density operation of GaInNAs quantum welllasers grown by metalorganic chemical vapour deposition

A metal organic chemical vapour deposition grown GaInNAs quantum well laser emitting at 1.25 μm is reported. The lowest threshold current density obtained by 50 μm wide stripe lasers was 340 A/cm² for a cavity length of 1420 μm. Which is almost comparable to the lowest value reported for GaInNAs lasers grown by molecular beam epitaxy. The threshold current density per well was 170 A/cm², which is the lowest threshold value reported to date     

Extremely low threshold (0.56 mA) operation in 1.3 μmInGaAsP/InP compressive-strained-MQW lasers

A record low threshold current of 0.56 mA, as a long-wavelength laser, has been obtained in a 1.3 μm InGaAsP/InP strained-MQW laser, at room temperature (25°C), by optimising an active layer and by employing a short cavity with high-reflection coatings     

Design and realization of a 1.55-μm patterned vertical cavitysurface emitting laser with lattice-mismatched mirror layers

It is possible to grow defect-free strained layers on patterned substrates (mesas or grooves) up to thicknesses far exceeding the critical thickness. Defect nucleation and propagation are inhibited in such growth. We have exploited this property to propose a novel InP-based 1.55-μm vertical cavity surface emitting lasers (VCSEL's). Careful photoluminescence and transmission electron microscopy (TEM) studies have confirmed that there are no propagating defects in the GaAs/Al_xGa_1-xAs distributed Bragg reflector (DBR) grown on the patterned InP-based heterostructures, specifically in the multiquantum-well (MQW) region. Lasers were designed with InP/InGaAsP bottom mirrors, InAlAs-oxide current confinement and short-stack GaAs/Al _xO_y top DBR mirrors. An optimal reflectivity and a maximum wall plug efficiency are determined analytically for this structure. In addition, a theoretical analysis of the modulation response of this device is performed using a rate equation model. Both analyzes show the potential of such a device for implementation in practical designs where high power and modulation bandwidth are required. Lasers with 8-40 μm diameter have been fabricated and characterized. A threshold current of 5 mA is observed at 15°C for an 8 μm diameter device; and up to 60 μW of light output is recorded     

MOVPE growth of a monolithic VCSEL at 1.56 μm in theInGaAlAs-InAlAs system lattice matched to InP

The first demonstration of a one-step-growth vertical-cavity surface-emitting laser (VCSEL) at 1.56 μm by low-pressure metal-organic vapor phase epitaxy in the InGaAlAs (λ_gap=1.43 μm)-InAlAs system lattice matched to InP is presented. The VCSEL's threshold current density was 7.5 kA/cm² and pulsed lasing had been obtained up to +55°C for 45-μm diameter proton implanted devices. This material system represents a high potential for continuous-wave VCSELs at 1.55-μm wavelength using a simple approach for large-scale industrial production     

Low threshold current GaAs/AlGaAs GRIN-SCH lasers grown bymolecular beam epitaxy on Si3N4 masked substrates

High-performance single-quantum-well graded-refractive index separate confinement heterostructure (SQW GRINSCH) laser have been grown by molecular beam epitaxy on Si₃N₄ patterned GaAs (100) substrates. Lasers grown on stripe windows orientated in the [011] direction have optical waveguiding and current confinement supplied by facetting occurring during growth. Lasers fabricated on 10 μm wide Si ₃N₄ openings have threshold currents as low as 15 mA for a 500 μm-long cavity. The current density required to reach optical transparency is 144 A/cm²; an internal quantum efficiency of 81%, and a peak optical power of 70 mW per facet has been obtained. Device performance comparable to ridge lasers is observed in a self-aligned laser process     

Improved performance of GaAs-AlGaAs superlattice quantum cascadelasers beyond λ=13 μm

Highly improved quantum cascade lasers based on intraband transitions in a chirped AlGaAs-GaAs superlattice have been realized. Lasing in a liquid nitrogen environment with a laser wavelength centered at 13 μm and with a peak optical power per facet exceeding 80 mW is achieved. A threshold current density of 8.6 kA/cm² at 80 K has been measured. Multimode lasing spectra ranging from 12.4 to 13.3 μm and single mode spectra in a short cavity at 13 μm are obtained. To improve the gain in the structure, the design of the injector is optimized. The minibands in the active region are more strongly confined beneath the conduction band edge of the barriers to decrease electron losses into the continuum. The maximum operating temperature exceeds 230 K with T₀ values of 170 K     

1.15-μm wavelength oxide-confined quantum-dot vertical-cavitysurface-emitting laser

Low-threshold lasing is achieved at 1.154 μm for an oxide-confined quantum-dot (QD) vertical-cavity surface-emitting laser (VCSEL) grown on a GaAs substrate. The long wavelength emission is obtained through use of an InAs-GaAs QD active region. A continuous-wave (CW) threshold of 502 μA is obtained for a device size of 10-μm diameter, corresponding to a threshold current density of 640 A/cm²      

Grating-coupled surface-emitting laser with a hyperbolic unstableresonator producing a stable focused output beam

A grating-coupled surface-emitting semiconductor laser has been integrated with a focusing diffractive beamforming element. A hyperbolic unstable resonator is used to introduce mode discrimination and suppress filamentation in a broad geometry, resulting in a 200-μm-wide coherent output. The light is focused 500 μm above the laser surface to a spot size of 5×7 μm. A remarkable beam stability is observed with very small spot size variation and beam-steering up to three times the threshold current under continuous operation     

1.2-μm GaAsP/InGaAs strain compensated single-quantum-well diodelaser on GaAs using metal-organic chemical vapor deposition

We demonstrate here 1.2-μm laser emission from a GaAsP-InGaAs strain compensated single-quantum-well (SQW) diode. This development enables the fabrication of vertical-cavity surface-emitting lasers for optical interconnection through Si wafers. Strain compensation and low temperature growth were used to extend the wavelength of emission to the longest yet achieved on a GaAs substrate in this materials system. The minimum threshold density achieved was 273.4 A/cm² at a cavity length of 610 μm. We have also demonstrated an 1.144-μm lasing wavelength in a 820-μm-long cavity on a GaAs substrate with a strained InGaAs-GaAs SQW laser for comparison using a low-temperature metal-organic chemical vapor deposition growth technique. The threshold current density for a 590-μm-long cavity under CW operation was 149.7 A/cm²     

Pulse operation and threshold characteristics of 1.55-μmInAlGaAs-InAlAs VCSELs

All-monolithic air-post index-guided vertical-cavity surface-emitting lasers have been demonstrated under pulsed electrical injection at room temperature. The structure grown in single step by metal-organic chemical vapor deposition employs InP lattice matched InAlAs/InAlGaAs Bragg mirrors and a 2λ-thick periodic gain active region with 15 InGaAs quantum wells (QWs). We report threshold current characteristics of these devices grown on a 2-in wafer with wide emission wavelength range of 1.51~1.59 μm. For the devices larger than 30-μm in diameter, we found the minimum threshold current density of ~2.93 kA/cm² at the emission wavelength of 1.57 μm, corresponding to about 20 nm wavelength offset between photoluminescence peak of InGaAs QWs and resonant cavity wavelength