Very small oxide-confined vertical microcavity lasers withhigh-contrast AlGaAs-AlxOy mirrors

We report the photo-pumped lasing action from a very small oxide-confined 870-nm vertical microcavity lasers with high-contrast AlGaAs-Al_xO_y mirrors. The effective cavity length is as small as 0.37 μm, and the oxide aperture size is 0.73 μm, estimated from the blue-shift of lasing mode due to the lateral confinement. The observed blue-shift of the lasing mode is 13.4 nm, the largest one ever reported for vertical cavity lasers. The optical losses seem to be size-independent for these small microcavity lasers. Our results indicate the possibility of the ultimate microcavity of order of λ³     

Steady-state and transient characteristics of microcavitysurface-emitting lasers with compressively strained quantum-well activeregions

In conventional semiconductor lasers, the dimensions of the optical cavity greatly exceed the photon wavelength, and the photon density of states forms a continuum since it is essentially that of a bulk system. On the other hand, in an ideal laser, one would like to have a single optical mode coincident with the maximum in the gain spectrum of the active medium. We show that substantial density-of-states quantization and enhancement of the fraction of photons spontaneously emitted into the lasing mode can be obtained by reducing the lateral width of the surface-emitting laser. For emission at λ=0.954 μm, the threshold current density can be drastically reduced by increasing the coupling factor to a few percent. For a cavity structure width of 0.3 μm, the threshold current density is 50 A/cm², compared with 250 A/cm² for the 0.6-μm cavity. At lower still lateral widths, the cavity loses its vertical character, and confinement of the lateral optical mode rapidly deteriorates. The large-signal response of microcavity lasers is slightly improved primarily due to elimination of mode competition in intrinsically single-mode microcavities, with relaxation times close to 1 ns. The enhancement of the spontaneous emission coupling factor results in an increase of the relaxation oscillation frequency and improvement in the standard small-signal response of microcavity lasers. For J=10J_th, the -3 dB modulation frequency exceeds 40 GHz. Since low threshold current densities may be achieved in microcavity lasers, the gains in small-signal performance are primarily extrinsic, i.e., higher modulation bandwidths ace accessible for the same injection     

Analysis of microcavity VCSEL lasing modes using a full-vectorweighted index method

Presents a semi-analytic full-vector method for calculating the spatial profile, optical confinement factor resonant frequency, absorption loss, and mirror loss of lasing modes in cylindrically symmetric microcavity vertical-cavity surface-emitting lasers (VCSEL's). It can be shown that this method gives the best separable approximation for the electric and magnetic vector potentials. Our technique can model the entire VCSEL structure and can treat complex media. We apply the method to etched-post and oxide-apertured VCSEL's designed for 980-nm emission and find a blueshift in cavity resonance as the cavity radius shrinks. We also find a minimum optical cavity radius below which radially bound lasing modes cannot be supported. This radius depends on the device geometry and lies between 0.5 and 1 μm for the devices studied. Once this model is augmented to include diffraction losses-the dominant loss mechanism for conventional small aperture lasers-it will provide a complete picture of lasing eigenmodes in microcavity VCSEL's     

30°C CW operation of 1.52 μm InGaAsP/AlGaAs vertical cavitylasers with in situ built-in lateral current confinement by localisedfusion

1.52 μm double fused InGaAsP/AlGaAs vertical cavity surface emitting lasers with in situ built-in lateral current confinement were fabricated using a localised wafer fusion process. A threshold current of 2.5 mA at 4 V was obtained for devices with a 10×10 μm² current aperture. These devices operate CW up to 30°C. The width of the dominant mode is less than 0.1 nm and the sidemode suppression ratio is 30 dB     

Continuous operation of high-power (200 mW) strained-layerGa1-xInxAs/GaAs quantum-well lasers with emissionwavelengths 0.87⩽λ⩽0.95 μm

Separate confinement single-quantum-well lasers with 100-120 Å-thick strained Ga_1-xIn_xAs/GaAs active layers have been grown on (100) GaAs substrates by metalorganic chemical vapour deposition. Ten-stripe proton-implanted arrays with 90 μm-wide aperture and 250 μm cavity length emit 200 mW CW optical power at wavelengths 0.87⩽λ⩽0.95 μm. Lifetest data on an uncoated device emitting 90 mW/facet at 50°C and λ=0.95 μm suggest a mean-time-to-failure in excess of 2500 h at room temperature. The performance of lasers with strained Ga_1-xIn_xAs quantum wells is comparable to that of unstrained Al_xGa_1-xAs/GaAs quantum-well lasers without facet coating     

High-power single-mode simplified antiresonant reflecting opticalwaveguide (S-ARROW) distributed feedback semiconductor lasers

Simplified antiresonant-reflective-optical-waveguide distributed-feedback semiconductor lasers based on Al-free InGaAs-InGaAsP-InGaP materials are reported for the first time. Devices with 6.5-μm-wide emitting apertures operate single-frequency (λ=0.968 μm) and single-spatial-mode to 157-mW continuous-wave output power. The full-width at half-maximum of the lateral far-field pattern is 4.5°, in excellent agreement with theory. Relative intensity noise values as low as -154 dB/Hz are measured between 500 MHz and 8 GHz     

High-temperature operation of InGaAs/InGaAsP compressive-strainedQW lasers with low threshold currents

We investigated the influence of the band gap wavelength of barrier layers and separate confinement heterostructure (SCH) layers λ_SCH on the high-temperature operation of InGaAs/InGaAsP compressive-strained quantum-well (QW) lasers. The optimum λ_SCH was 1.2 μm, at which carriers were sufficiently confined into quantum wells. The QW laser with λ_SCH = 1.2 μm exhibited low threshold currents of 2.3 mA at 20°C and 9.7 mA at 100°C and CW lasing up to 150°C     

Temperature dependence of the bandwidth of buried heterostructuredistributed feedback lasers

Reports that the etched-mesa buried-heterostructure distributed-feedback lasers (λ = 1.3 μm) fabricated using semi-insulating InP blocking lasers have bandwidths in the 12-17 GHz range at 20°C. 15 mW (18 GHz at 20 mW). The bandwidth decreases with increasing temperature at low powers. For the practical range of interest from 20°C to 40°C, the observed decrease in bandwidth is 1.0±0.5 GHz at 15 mW output power. A large sublinearity in the light-versus-current characteristics is generally associated with a rollover in the bandwidth power curve     

High T0 long-wavelength InGaAsN quantum-well lasersgrown by GSMBE using a solid arsenic source

We demonstrate high performance, λ=1.3- and 1.4-μm wavelength InGaAsN-GaAs-InGaP quantum-well (QW) lasers grown lattice-matched to GaAs substrates by gas source molecular beam epitaxy (GSMBE) using a solid As source. Threshold current densities of 1.15 and 1.85 kA/cm² at λ=1.3 and 1.4 μm, respectively, were obtained for the lasers with a 7-μm ridge width and a 3-mm-long cavity. Internal quantum efficiencies of 82% and 52% were obtained for λ=1.3 and 1.4 μm emission, respectively, indicating that nonradiative processes are significantly reduced in the quantum well at λ=1.3 μm due to reduced N-H complex formation. These Fabry-Perot lasers also show high characteristic temperatures of T₀ =122 K and 100 K at λ=1.3 and 1.4 μm, respectively, as well as a low emission wavelength temperature dependence of (0.39±0.01) nm/°C over a temperature range of from 10°C to 60°C     

High-speed modulation of 850-nm intracavity contacted shallowimplant-apertured vertical-cavity surface-emitting lasers

GaAs-AlGaAs quantum-well (850 nn) vertical-cavity surface-emitting lasers, with lateral current injection and shallow implanted apertures, show small signal modulation bandwidths of at least 11 GHz and large signal data rates of at least 10 Gb/s. The devices achieved a maximum output power of 2.1 mW, with a threshold current and voltage of 1 mA and 1.71 V, respectively. The shallow implantation step provides photolithographically precise aperture formation (using O⁺ ions), for efficient lateral current injection into the quantum-well active region of the laser, from intracavity contacts. The device aperture was 7 μm in diameter, and the opening in the annular top contact was 13 μm in diameter. The optical spectrum showed several transverse modes     

Low-threshold current, high-efficiency 1.3-μm wavelengthaluminum-free InGaAsN-based quantum-well lasers

We demonstrate high-performance Al-free InGaAsN-GaAs-InGaP-based long-wavelength quantum-well (QW) lasers grown on GaAs substrates by gas-source molecular beam epitaxy using a RF plasma nitrogen source. Continuous wave (CW) operation of InGaAsN-GaAs QW lasers is demonstrated at λ=1.3 μm at a threshold current density of only J_TH =1.32 kA/cm². These narrow ridge (W=8.5 μm) lasers also exhibit an internal loss of only 3.1 cm^-1 and an internal efficiency of 60%. Also, a characteristic temperature of T₀=150 K from 10°C to 60°C was measured, representing a significant improvement over conventional λ=1.3 μm InGaAsP-InP lasers. Under pulsed operation, a record high maximum operating temperature of 125°C and output powers greater than 300 mW (pulsed) and 120 mW (CW) were also achieved     

CW high power single-lobed far-field operation of long-cavityAlGaAs-GaAs single-quantum-well laser diodes grown by MOCVD

Data on long-cavity 100-μm-wide broad-stripe laser diodes that lase with a barrow single-lobed far-field pattern in continuous room-temperature operation are presented. Diodes with a cavity length of 1250 μm emit a power of 200 mW per facet into a 2.5° lobe (full width at half maximum). Short-cavity devices (cavity length of 350 μm) lase with a continuously increasing number of lateral modes right from threshold, and exhibit a far-field divergence that is over three times greater than that of 1250-μm diodes. Explanations for the effect of increasing cavity length on the field patterns of these devices are proposed, based on the measured increase in injected carrier diffusion length in long-cavity diodes and the influence of thermal waveguiding and mirror losses on intermodel discrimination     

Characteristics of a photonic bandgap single defect microcavityelectroluminescent device

A microcavity surface-emitting coherent electroluminescent device operating at room temperature under pulsed current injection is described. The microcavity is formed by a single defect in the center of a 2-D photonic crystal consisting of a GaAs-based heterostructure. The gain region consists of two 70-Å compressively strained In_0.15Ga_0.85As quantum wells, which exhibit a spontaneous emission peak at 940 nm. The maximum measured output power from a single device is 14.4 μW. The near-field image of the output resembles the calculated TE mode distribution in a single defect microcavity. The measured far-field pattern indicates the predicted directionality of a microcavity light source. The light-current characteristics of the device exhibit a gradual turn-on, or a soft threshold, typical of single- or few-mode microcavity devices. Analysis of the characteristics with the carrier and photon rate equations yields a spontaneous emission factor β≈0.06     

Dependence of differential quantum efficiency on the confinementstructure in InGaAs/InGaAsP strained-layer multiple quantum-well lasers

An internal efficiency of 91% was obtained with In_0.7Ga _0.3As/InGaAsP strained-layer multiple quantum well (MQW) lasers emitting at a wavelength of 1.5 μm. The dependence of the reciprocal differential quantum efficiency on the length of the laser cavity shows that the absorption loss in the InGaAsP (λ=1.3 μm) confinement layer caused by carrier overflowing into the confinement layer reduces the internal efficiency     

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     

Scanning near-field millimeter-wave microscopy using a metal slitas a scanning probe

In this paper, a novel type of scanning near-field millimeter-wave microscopy using a metal slit-type probe is proposed. A tapered reduced-height rectangular waveguide forms the slit aperture, which has a width much smaller than one wavelength λ and length of the order of λ. The slit probe can be operated in the TE₁₀ mode and, thus, results in high transmission efficiency, even when the width is exceedingly small. An image reconstruction algorithm based on computerized tomographic imaging is used to obtain two-dimensional near-field images. Experiments performed at 60 GHz (λ=5 mm) show that image resolution equal to the slit width (~80 μm) is achieved. As an application of this scanning slit microscopy, visualization of transition phenomena of photoexcited free carriers in silicon have been successfully demonstrated, yielding useful information on the dynamics of free carriers in semiconductor materials     

Improved catastrophic optical mirror damage level in InGaAs/AlGaAslaser diodes

9.2 W continuous wave (CW) optical power at a heatsink temperature 10°C and 12.2 W in a regime with stabilised temperature of the laser chip is demonstrated from a 100 μm aperture InGaAs/AlGaAs (λ=1.03 μm) laser diode with 0.4 μm wide GaAs waveguide. Thus, record-high optical power densities of 30 MW/cm² and 40 MW/cm² correspondingly are achieved at the front facet without catastrophic optical mirror damage (COMD)     

Very-low-threshold index-confined planar microcavity lasers

A fabrication process for laterally index-confined planar microcavity lasers is given that results in continuous-wave thresholds as low as 59 μA for a properly tuned cavity (T=250 K). Characterization of the spontaneous emission mode shows that the lateral confinement, when reduced to the mode size expected for the planar cavity, appears to increase the spontaneous emission coupling to the lasing mode     

Half-symmetric cavity tunable microelectromechanical VCSEL withsingle spatial mode

A new class of microelectromechanically tunable vertical-cavity surface-emitting lasers with a half-symmetric cavity structure is described. The cavity is realized by inducing a curvature (R~320 μm) in the top movable dielectric mirror. The microcavity forces lasing oscillations in a single fundamental spatial mode of approximately 6 μm despite the 20 μm electrical aperture of the device. The device wavelength was tunable from 863 to 833 nm under a 13-V voltage swing. The device operates in a single fundamental mode with sidemode supression ratio of >20 dB throughout the tuning range     

Monolithic super-bright red resonant cavity light-emitting diodegrown by solid source molecular beam epitaxy

Monolithic super-bright resonant-cavity light-emitting diode operating at λ=663 nm has been developed. The diode consisted of a 1λ-thick AlGaInP active region sandwiched between AlAs-AlGaAs distributed Bragg reflectors. The device structure was grown by solid source molecular beam epitaxy. The current aperture of the emitter was created by lateral selective wet thermal oxidation. A record-high peak wall-plug efficiency of 2.2% and a continuous-wave output power of 1.4 mW were attained without heatsinking at room temperature from a diode having a diameter of 80 μm. The emission linewidth was as narrow as 4.5 nm