Christian F. Schaus

Resonant periodic gain surface-emitting semiconductor lasers

A surface-emitting semiconductor laser structure with a vertical cavity, extremely short gain medium length, and enhanced gain at a specific design wavelength is described. The active region consists of a series of quantum wells spaced at one half the wavelength of a particular optical transition in the quantum wells. This special periodicity allows the antinodes of the standing-wave optical field to coincide with the gain elements, enhancing the frequency selectivity, increasing the gain in the vertical direction by a factor of two compared to a uniform medium or a nonresonant multiple quantum well, and substantially reducing amplified spontaneous emission. Optically pumped lasing was achieved in a GaAs/AlGaAs structure grown by molecular-beam epitaxy, with what is believed to be the shortest gain medium (310 nm) ever reported. >

Gain characteristics of strained quantum well lasers

InGaAs/AlGaAs laser diode arrays fabricated with differing amounts of In in the quantum well active layer are characterized by threshold currents of 115 A/cm2, transparency currents of 50 A/cm2, optical losses of 3 cm−1, and wavelengths to 960 nm for In compositions of 20%. Gain coefficient measurements indicate an increase from 0.0535 to 0.0691 cm μm/A for quantum well lasers with 0% InAs and 10–20% InAs, respectively. The maximum output power achieved for a device with a 100 μm aperture is 3 W cw.

Zinc and tellurium doping in GaAs and AlxGa1−xAs grown by MOCVD

Abstract Diethylzinc and diethyltellurium have been used as p-type and n-type dopants, respectively, for GaAs and Al x Ga 1 - x As epilayers grown by low-pressure metalorganic chemical vapor deposition. The influence of growth temperature, growth rate, and dopant mole fraction upon carrier concentration were investigated for both dopants under similar growth conditions. The V/III ratio was 50 for all the samples. It was observed that the growth parameters do not affect the mobility of doped samples for a given carrier concentration. For both Zn and Te doped layers, the carrier concentrations increased linearly with decreasing growth temperature and increasing mole fraction. For the undoped samples, higher growth rates resulted in lower background impurity incorporation and higher Hall mobilities. The Te incorporation increased with increasing growth rate; however, the Zn incorporation was reduced under similar conditions. The morphology of heavily-doped samples was found to be dependent upon growth temperature and growth rate. By varying these two parameters, mirror-smooth surface morphology was obtained for Zn-doped GaAs epilayers of 1 × 10 20 cm -3 and Te-doped GaAs epilayers of 1 × 10 19 cm -3 .

Cascadable, latching photonic switch with high optical gain by the monolithic integration of a vertical-cavity surface-emitting laser and a pn-pn photothyristor

The authors report the first demonstration of a cascadable, photonic switch based on the monolithic integration of a multi-quantum-well vertical-cavity surface-emitting laser (VCSEL) and a latching pn-pn photothyristor grown by low-pressure metalorganic vapor-phase epitaxy (LP-MOCVD). The VCSEL and pn-pn photothyristor structures can be independently optimized for optical switching, logic, and memory functions. Optical switching with high gain (30000), high contrast (30 dB), low switching power (11 nW), and latching memory have been demonstrated. The integrated pn-pn/VCSEL switch not only represents a volatile optical memory, but also can be used to implement a new class of optical logic gates with latching logic outputs.<<ETX>>

High‐power spatially coherent operation of unstable resonator semiconductor lasers with regrown lens trains

We have obtained high‐power spatially coherent operation in wide‐stripe InGaAs/GaAs/AlGaAs semiconductor lasers using a monolithic unstable resonator [consisting of diverging lens elements incorporated above an asymmetric graded‐index separate confinement heterostructure (AGRIN‐SCH)]. The fabrication involves MOCVD regrowth after wet‐chemical etching of lens‐like patterns in a GaAs layer above the active region. Pulsed output powers of 175 and 490 mW have been obtained in 170‐ and 100‐μm‐wide lasers, respectively, with spatial coherence in the near field exceeding 60%. We observe good lateral mode discrimination up to 3.5 times threshold in the 100‐μm stripes with a round‐trip magnification of 6.4.

Surface‐emitting, multiple quantum well GaAs/AlGaAs laser with wavelength‐resonant periodic gain medium

A novel surface‐emitting semiconductor laser with a vertical resonator, extremely short gain length, and enhanced gain at a specific design wavelength has been demonstrated. The gain medium consists of a series of GaAs quantum wells separated by AlGaAs spacers whose thicknesses are chosen to be one‐half the wavelength of a particular transition in the quantum wells. This structure forces the antinodes of the standing‐wave optical field to coincide with the gain elements, enhancing the gain and frequency selectivity in the vertical direction and substantially reducing amplified spontaneous emission. We have achieved optically pumped lasing with a threshold of 6 MW/cm2 at room temperature in a molecular beam epitaxially grown structure of thickness 4.3 μm, of which only 320 nm provided gain.

Lasing threshold in quantum well surface‐emitting lasers: Many‐body effects and temperature dependence

The geometry of quantum well surface‐emitting lasers has several important consequences. The ultrashort (∼1 μm) vertical cavity defines longitudinal modes with energy separation greater than the bandwidth of spectral gain. The optical confinement of these modes can approach unity. To achieve lasing, high carrier densities (∼1012 cm−2) in the quantum well are required. The confined carriers interact through enhanced many‐body exchange which influences both the lasing wavelength and threshold characteristics. Indeed, the exchange interaction can facilitate the lasing process. We theoretically and experimentally study the role of the short cavity and exchange interaction on the cw lasing threshold as a function of temperature. In constrast to edge emitters, the lasing threshold in these surface emitters exhibits a well‐defined minimum at a particular temperature. The temperature of the minimum can be designed by merely changing the active layer thickness.

Vertical cavity surface-emitting semiconductor laser with CW injection laser pumping

Room-temperature CW operation of a GaAs/AlGaAs vertical cavity surface-emitting laser with a resonant periodic gain medium, using a GaAs/AlGaAs diode laser array as a pump source, is discussed. Pumping thresholds as low as 11 mW at 730 nm, output powers as high as 10 mW at 856 nm, and external quantum efficiencies as high as 70% are obtained, with considerably improved temporal and spatial coherence properties compared to the pump laser. This is the first reported operation of such a laser with an efficient, compact pump source, demonstrating its suitability for efficient integration. >

Inverting and latching optical logic gates based on the integration of vertical-cavity surface-emitting lasers and photothyristors

Inverting optical logic gates based on the monolithic integration of a vertical-cavity surface-emitting laser (VCSEL) with a heterojunction photothyristor (PNPN) are described. Logic functions INVERT, NAND, and NOR are experimentally demonstrated for the first time using latchable and cascadable PNPN/VCSEL switches, which can be triggered with very low optical energy, while producing high optical gain and optical contrast. These gates are integrable on a single epitaxial structure to provide multifunctional logic and memory arrays.<<ETX>>

Highly stable strained layer leaky-mode diode laser arrays

A simple fabrication process for InGaAs strained quantum well leaky-mode laser arrays is demonstrated. The arrays are ten-element devices grown by two-step metal-organic chemical vapor deposition. The structure consists of a strained quantum well InGaAs graded index-separate confinement active region and a thin (0.12 mu m), transparent GaAs waveguide region. The near-field pattern typical of leaky-mode phase-locked arrays was measured. Fundamental mode oscillation was observed up to 2 A (threshold was as low as 175 mA). The authors observed a 1 mu s pulsed optical output power of 172 mW per facet and a far-field angle (full width at half maximum) of 1.6 times the diffraction limit at 1 A. This is the first reported operation of a strained quantum well leaky-mode laser utilizing a built-in index step.<<ETX>>