M. T. Asom

Optical injection induced polarization bistability in vertical-cavity surface-emitting lasers

We report the observation of bistable polarization switching in a vertical‐cavity surface‐emitting laser under optical injection. The wavelength dependence of the switching is measured. It is found that this polarization switching is achieved through injection locking where both the wavelength and the polarization of the vertical‐cavity laser are locked to the injected optical signal.

Transverse mode control of vertical-cavity top-surface-emitting lasers

Transverse mode characteristics and control for vertical-cavity top-surface-emitting lasers (VCSELs) are discussed. A spatial filtering concept for the control of VCSEL transverse modes that allows over 1.5-mW single TEM/sub 00/ transverse mode emission to be routinely achieved from continuous-wave electrically excited VCSELs is introduced. Without spatial filtering, L-I and V-I kinks are observed.<<ETX>>

Interstitial defect reactions in silicon

Deep level transient spectroscopy has been employed in a study of impurity‐interstitial defect reactions in silicon following room‐temperature electron irradiation. Three defects have been isolated and identified from their reactions and electrical properties as Cs‐Ci, Ci‐Oi, and Ps‐Ci. The Cs‐Ci, ME[(0.10), (0.17)] and Ps‐Ci, ME[(0.21), (0.23), (0.27), (0.30)] defects exhibit metastable structural transformations. Our results reveal the multistructural nature and chemical reactivity of the silicon self‐interstitial.

High‐power coherently coupled 8×8 vertical cavity surface emitting laser array

We demonstrate record high pulsed output power exceeding 530 mW from an electrically pumped phase‐coupled 8×8 vertical cavity surface emitting laser array (SELA) at room temperature. Three array types are compared: an 8×8 pixellated SELA(PSELA), an 8×8 grid contact SELA(CSELA), and a 78 μm×78 μm single broad area SEL(BSEL) emitter. The CSELA operating in a phase‐coupled supermode exhibits the lowest threshold current (100 mA) and voltage (1.6 V), highest damage threshold and a smooth L‐I characteristic with differential quantum efficiency ηd≳27%, the BSEL has the largest output power≳580 mW and a large ηd≳48%, the PSELA exhibited a large voltage with the largest ηd≳80%.

Top‐surface emitting lasers with 1.9 V threshold voltage and the effect of spatial hole burning on their transverse mode operation and efficiencies

The fabrication and operating characteristics of a 1.9 V top surface emitting laser are presented. A planar fabrication process with a modified ion implantation mask is used to achieve gain guided lasers operating up to 90 °C. The laser operates in the fundamental mode up to 0.7 mW with 3.2 mW total peak optical output power. Direct evidence of spatial hole burning for the fundamental and the next higher mode is observed. This spatial hole burning puts a limit on the fundamental mode operation and efficiency of the lasers.

High-power cw vertical-cavity top surface-emitting GaAs quantum well lasers

We have devised a novel vertical‐cavity top surface‐emitting GaAs quantum well laser structure which operates at 0.84 μm. The laser combines peripheral current injection with efficient heat removal and uses only the epitaxially grown semiconductor layers for the output mirrors. The structure is obtained by a patterned deep H+ implantation and anneal cycle which maintains surface conductivity while burying a high resistance layer. Peripheral injection of current occurs from the metallized contact area into the nonimplanted nonmetallized emission window. For 10‐μm‐diam emitting windows, ∼4 mA thresholds with continuous‐wave (cw) room‐temperature output powers ≳1.5 mW are obtained. Larger diameter emitting windows have maximum cw output powers greater than 3 mW. These are the highest cw powers achieved to date in current injected vertical‐cavity surface‐emitting lasers.

Progress in planarized vertical-cavity surface-emitting laser devices and arrays

We report batch-processed, totally planar, vertical-cavity top surface emitting GaAs/AlGaAs laser devices and arrays. Different size devices are studied experimentally. We measure continuous-wave threshold currents down to 1.7 mA and output powers > 3.7 mW at room temperature. We also discuss interesting characteristics such as differential quantum efficiencies exceeding unity and multi-transverse mode behavior. An array having 64 X 1 individually-accessed elements is characterized and shown to have uniform room-temperature continuous-wave operating characteristics in threshold current approximately equals 2.1 +/- 0.1 mA, wavelength approximately equals 849.4 +/- 0.8 nm, and output power approximately equals 0.5 +/- 0.1 mW.

Low‐voltage, high‐saturation, optically bistable self‐electro‐optic effect devices using extremely shallow quantum wells

Symmetric self‐electro‐optic effect devices (S‐SEEDs) using extremely shallow GaAs/Al0.04Ga0.96As multiple quantum wells are demonstrated. By exploiting mainly exciton ionization, rather than the usual quantum‐confined Stark shift, room‐temperature optical bistability is obtained with no applied bias. The extremely shallow symmetric‐SEED (symmetric E‐SEED) exhibits contrast ratios (CRs)≂3.5, with biasses<5 V, demonstrating system applicability and compatability with electronics. Large system tolerances Δλ≂6 nm and maximum bistability loop width ≂70% are also obtained. Moreover, due to fast carrier escape times, the symmetric E‐SEED exhibits useful CRs≳2 even at continuous‐wave intensities ≳70 μW/μm2.

Interface disorder in AlAs/(Al)GaAs Bragg reflectors

We have investigated the structural properties of Bragg reflectors grown by molecular beam epitaxy. The reflectors consist of quarter‐wavelength stacks of AlAs/ AlxGa1−xAs. We find a strong dependence of the interface quality on the substrate growth temperature, the Al composition in the ternary alloy, and the presence of impurities in AlAs. We have classified the interface disorder into two categories: interface roughness and structural waviness. We ascribe interface roughness to the segregation of oxygen during AlAs growth. The structural waviness originates from differing surface migration kinetics of Al and Ga which results in phase separation during growth of AlGaAs.

Progress and properties of high-power coherent vertical-cavity surface-emitting laser arrays

We discuss the potential of using coherently-coupled vertical cavity surface emitting laser arrays as high-intensity light sources. In particular, the design and performance of a novel two-dimensional phase-coupled grid Contact vertical cavity Surface Emitting Laser Array (C- SELA) is reported. We discuss the optical properties of the C-SELA; in addition to the usual out-of-phase array mode, we demonstrate in-phase SELA coupling. We introduce a simple physical model to describe our experimental results. Over 1.2 Watt optical power emission is obtained at room temperature from an electrically-excited 10 X 10 C-SELA. This laser array exhibited a low threshold current density of only 600 Amps/cm2 and over 60% single-ended differential quantum efficiency.