Thermal impedance of VCSELs with AlOx-GaAs DBRs

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-μm oxide aperture shows a thermal impedance of 2.8°C/mW. By varying the aperture size, the thermal conductance of the material below the active area is 0.255 W/cm°C. These results demonstrate that the oxide is not a major barrier to heat transport out of the active region     

Transverse modes under external feedback and fiber couplingefficiencies of VCSEL's

We report a detailed study on the transverse mode behavior of vertical-cavity surface-emitting lasers (VCSEL's) under strong external feedback. Backreflections from a glass facet result, periodically depending on the feedback phase, in variations of the transverse mode pattern of strongly index guided multitransverse-mode-emitting lasers. As a result, butt-coupling efficiencies of these lasers strongly depend on laser-fiber distance. For typical active VCSEL diameters around 15-μm fiber-coupled powers into standard 50 μm-core diameter graded-index (GI) silica fibers vary by nearly 10 dB. Even for high-numerical aperture 100-μm-core diameter fibers, power variations of up to 2 dB are observed     

Self-defined AlAs oxide-current-aperture buried-heterostructureridge waveguide InGaAs single-quantum-well diode laser

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-μm stripe width, 446-μm-long laser were 2 mA and 91%, respectively. The leakage current at -15 V was less than 20 nA     

Single-mode power dependence on surface relief size formode-stabilized oxide-confined vertical-cavity surface-emitting lasers

We have studied the mode behavior of oxide-confined vertical-cavity surface-emitting lasers (VCSELs) with a surface relief for fundamental mode selection. The dependence of single-mode power on the surface relief diameter was measured and compared with numerically calculated values. VCSELs with diameters of 9 and 12 μm were equipped with surface reliefs with diameters in the range 4-10 μm. The results show that there exists an optimum relief diameter for each VCSEL size. A maximum single-mode power of 2.2 mW was achieved for a 9-μm-diameter VCSEL with a 4-μm-diameter surface relief     

Single transverse mode operation of 1.55-μm buriedheterostructure vertical-cavity surface-emitting lasers

In this letter, we report the single-mode operation of 1.55-μm buried heterostructure vertical-cavity surface-emitting lasers (VCSELs) fabricated on a GaAs-AlAs distributed Bragg reflector using thin-film wafer fusion. A 7-μm VCSEL exhibits a single transverse mode at up to about 0.1-mW maximum optical output power and 75°C maximum operation temperature under continuous-wave operation     

Analog Modulation of 650-nm VCSELs

Small-signal properties of 650-nm vertical-cavity surface-emitting lasers (VCSELs) with different oxide aperture sizes were measured. A small diameter VCSEL of 3.5 /spl mu/m has a maximum resonance frequency of 5.7 GHz. The photon density determines the maximum resonance frequency. Modeling also indicates higher photon densities in the small VCSEL due to better thermal behavior.     

Low resistance intracavity-contacted oxide-aperture VCSELs

The authors study, analytically and experimentally, the extrinsic series resistance in intracavity-contacted vertical-cavity surface-emitting lasers (VCSEL's). Low resistance, low threshold-current, intracavity-contacted VCSELs are fabricated, with resistances ranging from 355 Ω for 4-μm square apertures to 80 Ω for 12-μm square apertures and threshold voltages as low as 1.35 V. To the best of our knowledge, these are the lowest values reported for this type of VCSEL. The threshold currents range from 270 μA for 4 μm×4 μm apertures to 850 μA for 12 ×12 μm. From a comparison of the resistance as a function of oxide aperture radius, the measured data follows closely with the calculated data, demonstrating the validity of the derived expressions for series resistance     

Few-mode vertical-cavity surface-emitting lasers for space-division multiplexing

In order to choose the proper radius of oxide aperture for few-mode vertical-cavity surface-emitting lasers (VCSELs), the influences of oxide aperture size on the multi-transverse-mode behaviors are investigated in detail. By establishing the effective refractive index model to simulate VCSELs with different radii of oxide apertures, the wavelength and corresponding order of different modes are obtained. VCSELs with three kinds of oxide apertures are manufactured. Then the multi-transverse-mode spectra and near-field are measured. It is found that when the radius is between 1.5 and 4.5 μm, few-mode VCSELs can be implemented. The 2.5 μm VCSEL manufactured in this paper only emits LP01 mode and LP21 mode. Since the space distance between the two modes is 2 μm, it is expected to realize direct-modulation few-mode VCSELs by channel etching or ion implantation between the two modes.     

Bottom-emitting VCSEL's for high-CW optical output power

Bottom-emitting vertical-cavity surface-emitting InGaAs MQW lasers operating in the 980-nm wavelength regime have been designed for high continuous-wave optical output power. Devices of 200-μm active diameter and optimized performance reach 350-mW maximum output power when mounted on a heat sink. 50-μm-size lasers produce 100 mW at 25% electrical to optical power conversion efficiency. Thermal properties and size dependent basic characteristics are investigated in detail     

Single-mode operation in an antiguided vertical-cavitysurface-emitting laser using a low-temperature grown AlGaAs dielectricaperture

Data are presented on a single mode InGaAs DBR MQW vertical-cavity surface-emitting laser that uses a low temperature growth of a highly resistive AlGaAs dielectric aperture. An epitaxial regrowth is used to contact the laser active region, with the AlGaAs aperture resulting in cavity-induced antiguiding. Antiguiding is observed in 6-μm diameter devices, with single-mode operation obtained over the range of continuous-wave operation (about 8× threshold). Pulsed operation shows lowest order transverse mode profiles up to 24× threshold     

1.55-μm buried-heterostructure VCSELs with InGaAsP/lnP-GaAs/AlAsDBRs on a GaAs substrate

We demonstrate 1.55-μm buried-heterostructure (BH) vertical-cavity surface-emitting lasers (VCSELs) on a GaAs substrate. Thin-film wafer-fusion technology enables InP-based BH VCSELs to be fabricated on GaAs/AlAs distributed Bragg reflectors. Detailed investigations of the device resistance are also described. As a result of introducing BH and obtaining low device resistance, the threshold current density under CW operation shows the independence of mesa size due to a strong index guide and small noneffective current. A 5-μm VCSEL exhibits a record threshold current of 380 μA at 20°C. This VCSEL also operates with single transverse mode up to the maximum optical output power     

Intracavity contacts for low-threshold oxide-confinedvertical-cavity surface-emitting lasers

Very low threshold vertical-cavity surface-emitting lasers are demonstrated using intracavity contacts, an upper dielectric Bragg reflector, and an undoped lower AlAs-GaAs Bragg reflector. The undoped lower mirror allows the demonstration of the highest differential efficiency yet achieved for sub-100-μA threshold, which is 60% for a 67-μA threshold. Devices with smaller output coupling show threshold current densities as low 98 A/cm², and a minimum threshold current of 23 μA for a small aperture     

The use of spatially ordered arrays of etched holes for fabrication of single-mode vertical-cavity surface-emitting lasers based on submonolayer InGaAs quantum dots

To suppress the generation of high-order modes in vertical-cavity surface-emitting lasers based on submonolayer InGaAs quantum dots, the method of formation of a spatially ordered array of etched holes in the upper distributed Bragg reflector was used. Single-mode vertical-cavity surface-emitting lasers for spectral region of 990 nm with current-aperture diameter of 20 μm, threshold current 0.9 mA, and maximum output power 3.8 mW at room temperature were demonstrated. Single-mode lasing with the coefficient of side-mode suppression in excess of 35 dB is retained in the entire range of pump currents. A decrease in the current oxide aperture to sizes that are close to those of the optical aperture brings about an increase in the external quantum efficiency; however, in this case, the transition to the multimode of lasing is observed at high pump currents.     

High-power temperature-insensitive gain-offset InGaAs/GaAsvertical-cavity surface-emitting lasers

The authors have grown 997 nm vertical-cavity surface-emitting lasers with an offset between the wavelength of the cavity mode and the quantum well gain peak to improve high temperature operation, and with higher aluminum-content barriers around the active region to improve the carrier confinement. They fabricated lasers of 8-15 and 20-μm diameters. The 8-μm-diameter devices exhibited CW operation up to 140°C with little change in threshold current from 15°C to 100°C, and the 20-μm-diameter devices showed CW output power of 11 mW at 25°C without significant heat sinking     

Transverse mode characteristics of vertical-cavity surface-emittinglasers buried in amorphous GaAs antiguide layer

We report the transverse mode characteristics of InGaAs-GaAs vertical-cavity surface-emitting lasers (VCSEL's) buried in a low-temperature-deposited amorphous GaAs (a-GaAs) layer. The maximum current maintaining a stable fundamental transverse mode is increased by the antiguide effect of the a-GaAs clad with a high refractive index. For 10- and 15-μm-diameter devices, we attain a stable single-mode emission over a wide range of current. The antiguide effects and transverse mode profiles in vertical cavity lasers buried in the high refractive index clad are calculated using a two-dimensional beam propagation method     

A comprehensive model for the modal dynamics of vertical-cavitysurface-emitting lasers

We present a quasi-3-D dynamic model of vertical-cavity surface-emitting lasers (VCSELs). The interdependent processes of carrier transport, heat generation and dissipation, and optical fields are solved self-consistently for each point in time and space. An effective index model is adopted for the evaluation of the optical fields in the complex layer structure. The inclusion of a temperature- and carrier-density-dependent refractive index, and its time dependence, allows us to study the evolution of the transverse optical field distributions under dynamic conditions. The model is applied to a typical index-guided structure with a 7-μm oxide aperture. A direct comparison is made using "cold" cavity modes, which is a normal technique when modeling the dynamics of VCSELs. Significant discrepancies are demonstrated both at smalland large-signal modulation, which indicates the need of a more sophisticated model for accurately predicting and understanding the geometry-dependent modal evolution     

High performance of 1.55-μm buried-heterostructurevertical-cavity surface-emitting lasers

We report a record low threshold current of 1.55-μm vertical-cavity surface-emitting laser (VCSEL). Thin-film wafer-fusion technology enables InP-based buried heterostructure VCSELs to be fabricated on GaAs-AlAs distributed Bragg reflectors. Threshold current density is independent of mesa size, and a 5-μm VCSEL exhibits a threshold current as low as 380 μA at 20°C and a single transverse mode up to the maximum optical output power under continuous-wave operation     

Low thermal resistance high-speed top-emitting 980-nm VCSELs

Increasing copper plated heatsink radii from 0 to 4 /spl mu/m greater than the mesa in vertical-cavity surface-emitting lasers (VCSELs) reduced the measured thermal resistance for a range of device sizes to values 50% lower than previously reported over a range of device sizes. For a 9-/spl mu/m diameter oxide aperture, the larger heatsink increases output power and bandwidth by 131% and 40%, respectively. The lasers exhibit a 3-dB modulation frequency bandwidth up to 9.8 GHz at 10.5 kA/cm/sup 2/. The functional dependence of thermal resistance on oxide aperture diameter indicates the importance of lateral heat flow to mesa sidewalls.     

Aperture placement effects in oxide-defined vertical-cavitysurface-emitting lasers

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 πm     

Continuous wave operation of 1.26 μm GaInNAs/GaAsvertical-cavity surface-emitting lasers grown by metalorganic chemicalvapour deposition

Electrically pumped near 1.3 μm GaInNAs/GaAs vertical-cavity surface-emitting lasers grown by metalorganic chemical vapour deposition are demonstrated for the first time. The threshold current and voltage under continuous wave operation of a 10×10 μm² oxide aperture device were 7.6 mA and 2.8 V, respectively. The output power exceeded 0.1 mW and the slope efficiency was ~0.1 W/A