D. B. Gilbert

High-power superluminescent diodes

By inclining the active stripe of a planar AlGaAs double heterojunction structure by 5 degrees with respect to the facets, reflection feedback has been eliminated and high-power superluminescent diodes emitting 28 mW with less than 5% spectral modulation have been obtained. >

Low degradation rate in strained InGaAs/AlGaAs single quantum well lasers

A 10000 h, 30 degrees C constant-current lifetest performed on five strained In/sub 0.2/Ga/sub 0.8/As/AlGaAs single-quantum-well lasers, with lambda approximately 930 nm, is discussed. The devices are 90- mu m*400- mu m oxide-stripe lasers with facet coatings, grown by atmospheric pressure organometallic vapor-phase epitaxy. For each diode, the current was maintained at a constant value of approximately 300 mA, corresponding to approximately 100 mW of output power. After 10/sup 4/ h, thresholds increased from an average of 84 mA to 108 mA, while quantum efficiencies were essentially unchanged. In relation to a typical 100-mW constant-power lifetest, this is equivalent to a degradation rate of less than 1%/kh.<<ETX>>

High-power separate-confinement heterostructure AlGaAs/GaAs laser diodes with broadened waveguide

AlGaAs/GaAs graded-index separate-confinement heterostructure single quantum well (GRINSCH-SQW) lasers with different waveguide thickness have been analyzed experimentally and compared with results from modeling using transverse optical field distributions. We have found that for GRINSCH lasers the halfwidth of near-field and far-field patterns depends very weakly on the waveguide thickness due to the focusing of the optical field in the transverse direction by the graded-index waveguide. At the same time, the mode intensity in the cladding layers is reduced by two orders of magnitude as the waveguide thickness is increased from 40 nm to 1200 nm. As a result, a 20% improvement in the differential quantum efficiency ((eta) d) is realized, while the threshold current density remains unchanged. Differential quantum efficiency as high as 78% and output power exceeding 4 W cw have been obtained for broadened waveguide lasers.

Operating characteristics of InGaAs/AlGaAs strained single quantum well lasers

The performance of a series of InxGa1−xAs/AlGaAs (x=0.20 and 0.25) strained single quantum well (SSQW) lasers with lasing wavelengths in the range 930≤λ≤1000 nm is discussed. Less‐strained devices, with x=0.20 and QW thickness 7 nm (λ∼930 nm), perform comparably with GaAs QW lasers. Longer wavelength (λ>950 nm), more highly strained lasers exhibit poorer performance. Our results suggest that interfacial recombination limits the performance at the longer wavelength structures.

Continuous, high‐power operation of a strained InGaAs/AlGaAs quantum well laser

Continuous wave (cw), high‐power operation of a strained In0.2Ga0.8As/ AlGaAs quantum well laser, grown by atmospheric pressure organometallic vapor phase epitaxy, is reported. The laser active region consists of a single 70 A In0.2Ga0.8As/Al0.2Ga0.8As quantum well, with optical confinement provided by a graded index separate confinement heterostructure. The threshold current density and differential quantum efficiency of a 90 μm×600 μm stripe with uncoated facets are ∼200 A/cm2 and 46%, respectively. Lasing wavelength is ∼930 nm, and the cw single ended power versus current characteristic is linear up to 250 mW (1 A current). In the short‐cavity (<300 μm) regime, these devices have high thresholds and have been observed to lase at shorter wavelength, presumably due to a saturation of gain at the lowest energy transition. The characteristic temperature is 150 K and decreases somewhat with cavity length. This suggests that some nonradiative process, most likely Auger recombination, contributes significantl...

High-power conversion efficiency in a strained InGaAs/AlGaAs quantum well laser

A strained quantum well laser with a front‐end power conversion efficiency exceeding 33% under continuous‐wave operation is demonstrated. The laser structure, grown by atmospheric pressure organometallic vapor‐phase epitaxy, consists of a 70‐A In0.2Ga0.8As quantum well active region with graded index separate confinement heterostructure. Lasing wavelength is 930 nm, and the front‐end differential quantum efficiency is 58% for broad‐area oxide stripe lasers with a high‐reflection coating on the rear facet. Front‐end, continuous power outputs greater than 1 W are available. Although these strained quantum well lasers have threshold currents as low as lattice‐matched GaAs quantum well lasers, their internal quantum efficiencies appear to be reduced, thus limiting the maximum attainable conversion efficiency.

980 nm diode laser for pumping Er/sup 3+/-doped fiber amplifiers

A high-power 980-nm diode laser, whose performance satisfies the requirements for pumping Er/sup 3+/-doped optical fiber amplifiers, is described. The device is grown by atmospheric pressure organometallic vapor-phase epitaxy and contains a strained, step-graded In/sub 0.25/Ga/sub 0.75/As/AlGaAs single-quantum-well active region. The threshold current of the ridge-waveguide laser is 8 mA, and a CW power output of 125 mW with a different quantum efficiency of 59% is demonstrated.<<ETX>>

Improving the performance of strained InGaAs/AlGaAs single quantum well lasers

By adjusting the carrier confining structure and the optical confining structure of strained InGaAs/AlGaAs single quantum well (QW) lasers, an improvement in performance has been obtained. First, the influence of optical confinement was examined by comparing two graded‐index confining structures. For InxGa1−xAs QWs with either x=0.20 or x=0.25, lasers with greater optical confinement factor had improved performance, with both lower threshold (180 A/cm2 for x=0.20) and higher characteristic temperature (250 K for x=0.20), despite their reduced carrier confining potentials. Second, experiments on graded‐composition quantum wells show that thin step‐grading layers result in improved performance. In this structure, where the QW has x=0.35, and the step layers have x=0.15, the optimum step thickness is 30–40 A. Thicker step layers appear to create too much strain, degrading the laser operation. These results indicate that step grading of strained QWs produces active region interfaces with lower defect density,...

The effect of facet mirror reflectivity on the spectrum of single-mode CW constricted double-heterojunction diode lasers

In this paper we show that the spectral mode content of mode-stabilized constricted douhle-heterojunction lasers can be altered by changes in facet reflectivity. If the facet reflectivity is substantially reduced below the nominal value of 30 percent, then the lasers will exhibit multilongitudinal mode operation. Nearly planar-geometry lasers that show instabilities can be made to operate in a stable single mode by increasing the facet reflectivity to values above 50 percent.

Investigation of active antenna arrays at 60 GHz

There has been a significant effort to develop millimeter-wave active-array antennas for communications and radar applications. A dielectric waveguide is a promising medium for this application. However, the integration of active devices, transmission media, and antennas has been difficult to achieve. This paper presents the first successful demonstration of a phase locked array of millimeter wave grating surface emitters (MMWGSE). We discuss three aspects of MMWGSE: (1) The achievement of an optically steered millimeter wave grating surface emitter. (2) The demonstration of a frequency locked array of millimeter wave grating surface emitters. (3) Rigorous analytical studies of efficiently coupling power from a millimeter wave semiconductor device, to a waveguide which incorporates grating surface emitters. This work leads to a full monolithic array using pseudomorphic high electron mobility transistor (PHEMT)-devices. >