J. B. Kirk

Two-dimensional coherent laser arrays using grating surface emission

The concepts, fabrication, and operating characteristics of monolithic two-dimensional, coherent AlGaAs laser arrays are presented. The arrays consist of 100 (10*10) active elements fabricated from a single-quantum-well graded-index separate-confinement heterostructure laser geometry. A surface relief grating is used for feedback and outcoupling. The elements of the array are index-guided ridge lasers with evanescent or Y coupling in the lateral direction and injection coupling longitudinally. The far field emanating from a 60- mu m*5-mm aperture, measures 0.01 degrees *1 degrees . These arrays emit more than 1 W peak power into a 2-AA wavelength interval. By adjusting the drive current to the electrically independent gain sections of these arrays, the angular position of the far-field beam can be steered. >

Coherent, monolithic two-dimensional (10×10) laser arrays using grating surface emission

Two‐dimensional, coherent AlGaAs laser arrays consisting of 100 (10×10) active elements have been fabricated using single quantum well laser structures. A surface relief grating is used both for feedback and outcoupling. The elements of the array are index‐guided ridge lasers. In one array design, the elements are coupled laterally by evanescent field overlap while in the second design, the coupling is by Y branches. Longitudinal coherence is achieved by injection coupling. The far field, emanating from a 60 μm by 5 mm aperture, measures 0.01°×1°. Both types of arrays emit more than 1 W peak power. The mode spectrum of the emitted power is contained in a ∼2–3 A wavelength interval at ∼1 W.

Characteristics of coherent two-dimensional grating surface emitting diode laser arrays during CW operation

Recent progress in the development of monolithic two-dimensional coherent grating surface emitting (GSE) laser arrays is presented. Such GSE arrays have operated continuously to more than 3 W/surface and pulsed to more than 30 W/surface. They have achieved continuous wave (CW) threshold current densities of under 140 A/cm/sup 2/ with CW differential quantum efficiencies of 20-46% per surface. Linewidths in the 40-100 MHz range were obtained with output powers of 100-300 mW per surface. The arrays typically consist of 10-30 mutually injection coupled gain sections with 10 laterally coupled ridge-guided lasers in each gain section. A single GaInAs strained-layer quantum well with a graded-index separate confinement heterostructure (GRINSCH) geometry allows junction down mounting with light emission through the transparent GaAs substrate. A surface relief grating is used for feedback and outcoupling. >

Electronic beam steering in monolithic grating‐surface‐emitting diode laser arrays

Electronic beam steering has been demonstrated in both one‐ and two‐dimensional injection‐coupled grating‐surface‐emitting diode laser arrays. By appropriately varying the drive current to the electrically independent gain sections of an injection‐coupled grating‐surface‐emitting laser array, the angular position of the far‐field output can be steered. Experimental results for two‐dimensional surface‐emitting arrays are presented, as well as a theoretical model which shows that beam steering is a general property of injection‐coupled surface‐emitting arrays.

High‐power seven‐element grating surface emitting diode laser array with 0.012° far‐field angle

A coherent seven‐element grating surface emitting diode laser array with a predominant single‐lobe far‐field pattern having an angular divergence of 0.012° has been demonstrated. The extent of the emitting aperture was 4 mm, and the beam divergence was within 10% of the diffraction limit. Under pulsed operation the array had a peak output power of over 400 mW and a differential quantum efficiency of 15%.

Coherent, monolithic two-dimensional strained InGaAs/AlGaAs quantum well laser arrays using grating surface emission

Two‐dimensional coherent strained‐layer InGaAs/AlGaAs quantum well laser arrays consisting of 100 (10×10) active elements have been fabricated and characterized. The central lobe of the far field has a full width at half power of 0.04°×1°. Observation of about 2 W peak power from either the substrate or the junction surface, with differential quantum efficiencies from each side of about 40%, is reported. The mode spectrum of the emitted power is contained in a ∼2 A wavelength interval at ∼2 W.

Efficient, high-power (>150 mW) grating surface emitting lasers

Surface emitting AlGaAs second‐order distributed Bragg reflector lasers using a superlattice graded‐index separate confinement heterostructure with a single quantum well have been fabricated. The total peak power is emitted coherently from both gratings into a 0.06° full width half‐power single lobe far field pattern. Peak powers are in excess of 150 mW. The external differential quantum efficiency is as high as 30%. Under severe current modulation conditions, the stable single longitudinal mode had 20–45 dB wavelength side mode rejection.

Single frequency 1550-nm AlGaInAs-InP tapered high-power laser with a distributed Bragg reflector

A strained-layer multiple-quantum-well tapered laser with single-frequency operation near 1550 nm and with 20-dB sidemode suppression, for continuous-wave power levels up to 0.6 W is reported. At a power level of 0.5 W, 80% of the power from this device remains in the central lobe of the far-field. Increased lateral mode stabilization was observed in devices having both a Gaussian-patterned contact and a distributed Bragg reflector (DBR) compared to those without a DBR. An increase by a factor of five in the power level obtainable, with at least 80% of that power in the central lobe of the far-field pattern, was obtained using the DBR reflector.

MOCVD Regrowth over GaAs/AIGaAs Gratings for High Power Long-Lived lnGaAs/AIGaAs Lasers

Buried second-order Bragg gratings have been fabricated in GaAs/AlxGa1-xAs (x ⩾ 0.4) near the active region of InGaAs/AlGaAs lasers. we discuss a GaAs periodic wire grating for which mass transport is suppressed, materials analysis, and the metalorganic chemical vapor deposition (MOCVD) regrowth techniques used to address damage and contamination of the grating layer in these laser structures. The effect of the grating/regrowth interface on CW laser performance and reliability is described.

High-power semiconductor red laser arrays for use in photodynamic therapy

Semiconductor laser ridge arrays emitting 250 mW at a wavelength of 635 nm are designed for photodynamic therapy applications. Although ridge laser arrays are less efficient than broad area lasers, they are more reliable and can produce higher power from the same lateral width due to thermal considerations. An analytic expression for the active layer temperature of the laser array as a function of the ridge spacing, number of ridges, and width is derived and has excellent agreement with a finite-element analysis. This analytic expression allows optimization of the laser and the submount geometry to minimize the active region temperature with the constraint of a small submount, heat sink, and package.