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Lang, Robert J.

Publications and source records attributed to Lang, Robert J..

33 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Pseudomorphic Single-Quantum-Well Lasers Emit At 980 Nm

Narrow-stripe semiconductor lasers emitting at 980 nm include pseudomorphic In0.2Ga0.8As/GaAs/AlxGa1-xAs graded-index-of-refraction, separate-confinement-heterostructure single quantum well(GRINSCH SQW) with overlaid ridge waveguide. 980 nm chosen as one that yields most efficient pumping because there is no absorption in excited states at this wavelength. Suitable for pumping Er(Sup3+)-doped optical-fiber amplifiers in optical-fiber communication systems and optical phased-array ranging systems.

Larsson, Anders↗
NASA NTRS1992

Laterally Coupled Distributed-Feedback Lasers

Distributed-feedback semiconductor lasers of proposed design called "laterally coupled" features Bragg gratings located on top surfaces next to sides of ridge waveguides overlying gain regions of laser resonators.

Lang, Robert J.↗
NASA NTRS1991

Two-Period Gratings For Surface-Emitting Lasers

Grating surfaces having two spatial periods tailored to obtain desired proportions of output coupling and inward reflection. Solid-state lasers of type emitting light perpendicularly to their broad surfaces made more efficient. Same principle also applicable to "Annular-Bragg-Grating Surface-Emitting Laser", (NPO-17912).

Lang, Robert J.↗
NASA NTRS1991

High-Power AlGaAs Quantum-Well Lasers On Si Substrates

AlxGa1-xAs lasers of graded-index-of-refraction, separate-confinement-heterostructure, single-quantum-well type fabricated on silicon substrates by migration-enhanced molecular-beam epitaxy followed by metalorganic vapor-phase epitaxy. They are intermediate products of continuing effort to develop low-threshold-current, high-efficiency lasers for parallel optical interconnections between large-scale optoelectronic integrated circuits.

Kim, Jae-Hoon↗
NASA NTRS1991

Geometric formulation of unstable-resonator design and application to self-collimating unstable-resonator diode lasers

A new set of design parameters for unstable resonators is presented that yields simpler expressions for the mirror and beam radii and magnification than those given by the usual g parameters. The new formalism is applied to determine the design of a solid unstable resonator of index n with a self-collimated output beam, applicable to unstable-resonator diode lasers.

Lang, Robert J.↗
NASA NTRS1991

Lateral modes of broad area semiconductor lasers - Theory and experiment

Calculations of the lateral modes of an ideal broad area laser, including the nonlinear interaction between the carriers and the optical field, are made. The results include periodically modulated near fields and single- and double-lobed far fields similar to those previously measured. The unsaturable losses are higher and quantum efficiencies are lower than those determined from plane-wave approximations. Broad area InGaAs-GaAlAs-GaAs quantum-well lasers were fabricated and measured and found to closely agree with the theory in near, far, and spectrally resolved near fields. An occultation experiment on the far field confirms previously predicted unstable resonatorlike modes with V-shaped fronts.

Lang, Robert J.↗
NASA NTRS1991

Semiconductor Laser With Multilayer Dielectric Reflector

Multilayer dielectric reflector included in proposed surface-emitting, distributed-feedback, grating semiconductor laser (e.g., a GaAlAs device). Contributes to efficiency and output power of laser by reducing amount of light entering substrate, where wasted by absorption. Index of refraction in reflector sublayers alternates between higher and lower value. Higher value less than effective index of refraction of waveguide layer.

Lang, Robert J.↗
NASA NTRS1990

Annular-Bragg-Grating Surface-Emitting Laser

Proposed semiconductor laser emits radiation perpendicularly to its broad surface by use of annular Bragg grating as output coupler. Produces narrow output beam. Advantages include lower threshold current, smaller size, and increased efficiency.

Lang, Robert J.↗
NASA NTRS1990

Unstable-Resonator Distributed-Bragg-Reflector Laser

Proposed distributed-Bragg-reflector (DBR) semiconductor laser has wide curved gratings favoring single-mode operation, even with relatively wide laser stripe, enabling use of higher power. Consists of semiconductor double heterostructure laser bounded at each end by region of passive waveguide.

Lang, Robert J.↗
NASA NTRS1990

Integrated Grating Spectrometer

Proposed integrated grating spectrometer made in waveguide layer on silicon wafer. Occupies area of about 2 centimeters to 2nd power on wafer 0.4 mm thick. Operates in visible spectrum (wavelengths of 400 to 700 nm) and blazed to diffract in first order. Array of integrated grating spectrometers performs spectral analysis of picture elements along line. Optical fiber couples light from each picture element into separate integrated spectrometer. Technique enables continous independent variation, along grating, of pitch, curvature, and blaze angle. Grating designed to have large numerical aperture, zero aberration at two selected wavelengths, and very low aberration at intermediate wavelengths.

Lang, Robert J.↗
NASA NTRS1989

Strained-layer InGaAs/GaAs/AlGaAs single quantum well lasers with high internal quantum efficiency

Low threshold current density strained-layer In(0.2)Ga(0.8)As/GaAs/AlGaAs single quantum well lasers, emitting at 980 nm, have been grown by molecular beam epitaxy. Contrary to what has been reported for broad-area lasers with pseudomorphic InGaAs active layers grown by metalorganic chemical vapor deposition, these layers exhibit a high internal quantum efficiency (about 90 percent). The maximum external differential quantum efficiency is 70 percent, limited by an anomalously high internal loss possibly caused by a large lateral spreading of the optical mode. In addition, experimental results supporting the theoretically predicted strain-induced reduction of the valence-band nonparabolicity and density of states are presented.

Larsson, Anders↗
NASA NTRS1989

High-power low-threshold graded-index separate confinement heterostructure AlGaAs single quantum well lasers on Si substrates

A high-power low-threshold graded-index separate confinement heterostructure AlGaAs single quantum well laser on Si substrates has been demonstrated for the first time by a hybrid growth of migration-enhanced molecular beam epitaxy followed by metalorganic vapor phase epitaxy. The quantum well laser showed an output power of more than 400 mW per facet under pulsed conditions. A room-temperature threshold current of 300 mA was obtained with a differential quantum efficiency of 40 percent without facet coating. The threshold current density was 550 A/sq cm for a cavity length of 500 microns. These results show the highest peak power reported to date for low-threshold lasers on Si substrates. The full width at half maximum of the far-field pattern parallel to the junction was 6 deg. Threshold current densities as low as 250 A/sq cm were obtained for lasers on GaAs substrates.

Kim, Jae-Hoon↗
NASA NTRS1988

Narrow far fields from extended-window broad-area lasers

Broad-area lasers are fabricated with a long (80-100 microns), nonabsorbing window at each end. The window is shown to dramatically improve the spatial mode properties, stabilizing and smoothing the near field, and reducing the far field from 5-15 deg to as low as 2 deg. This improvement comes at the expense of an increase in threshold current and a reduction of quantum efficiency.

Lang, Robert J.↗
NASA NTRS1988

High-peak-power low-threshold AlGaAs/GaAs stripe laser diodes on Si substrates grown by migration-enhanced molecular beam epitaxy

A high-peak-power low-threshold AlGaAs/GaAs double-heterostructure stripe laser diode on Si substrats, grown by hybrid migration-enhanced molecular beam epitaxy (MEMBE) and metalorganic chemical vapor deposition (MOCVD) has been demonstrated for the first time. These devices showed the highest peak powers of up to 184 mW per facet reported so far for double-heterostructure stripe laser diodes on Si substrates, room-temperature pulsed threshold currents as low as 150 mA, and differential quantum efficiencies as high as 30 percent without mirror facet coating. An intrinsic threshold current density has been estimated to be about 2 kA/sq cm when taking current spreading and lateral diffusion effects into account. Low dislocation density shows that MEMBE can be a useful method to grow high-quality GaAs and AlGaAs/GaAs layers on Si substrates by combining with MOCVD.

Kim, Jae-Hoon↗