S. L. Palfrey

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.

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.

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.

Phase‐locked operation of a grating‐surface‐emitting diode laser array

A linear array of surface‐emitting distributed Bragg reflector AlGaAs diode lasers has been demonstrated. The intensity pattern for five emitting elements had structure with an angular divergence as low as 0.05°, indicating phase locking between the elements of the array.

Grating-surface-emitting lasers in a ring configuration

A monolithic grating‐surface‐emitting ring laser has been fabricated and its spectral properties and far‐field radiation pattern studied. The ring laser was configured from two columns of two‐dimensional grating‐surface‐emitting diode laser arrays. The columns were optically linked at each end with total‐internal‐reflection corner turning mirrors formed by micromachining grooves in the wafer with a focused ion beam. Single longitudinal mode operation with a high degree of spatial coherence between the two columns and a narrowing of the lateral far‐field pattern were observed.

Spectral locking in an extended area two-dimensional coherent grating surface emitting laser array

The spectral properties of a monolithic pair of two-dimensional coherent grating surface emitting (GSE) laser arrays optically coupled by means of total-internal-reflection corner turning mirrors are discussed. Each of the pair consists of six groups of ten laterally Y-coupled, index-guided ridge lasers interspersed with second-order distributed Bragg reflector (DBR) grating sections in the longitudinal direction to provide feedback and surface emitting output coupling. The turning mirrors were formed by focused-ion-beam micromachining channels in the wafer angled at 45 degrees to the laser waveguide. Locking of the emission spectra of the pair of GSE arrays and shifting of the spectrum of one of the pair by varying the drive current to one gain section in the other have been demonstrated.<<ETX>>

Network analysis of the modes of two-dimensional grating-surface-emitting diode laser arrays

The modes and threshold gain characteristics of two-dimensional grating-surface-emitting diode laser arrays that are evanescently coupled in the lateral direction and mutually injection coupled in the longitudinal direction are analyzed. The ratio of the grating transmissivity to reflectivity is found to be a critical parameter in obtaining uniform power distribution inside the array. Good qualitative agreement between the theory and experimentally measured near-field patterns and threshold currents is obtained. >

Efficient 30 mW grating surface-emitting lasers

A surface‐emitting AlGaAs second‐order distributed Bragg reflector laser using a graded index separate confinement heterostructure with a single quantum well has been fabricated. The surface emitted power is in excess of 30 mW with an external differential quantum efficiency of 20%. These values approach the performance of present commercially available edge‐emitting diode lasers. Under severe current modulation conditions, the stable single longitudinal mode had nearly 30 dB wavelength sidemode rejection, and a near diffraction limited 0.51° full width half‐power beam divergence of the single‐lobe far‐field pattern.

Low spectral modulation high-power output from a new AlGaAs superluminescent diode/optical amplifier structure

A double‐heterojunction angled stripe AlGaAs device consisting of an index‐guided ridge waveguide with gain‐guided facet regions has produced cw output powers of 20 mW with less than 1% spectral modulation from a 300‐μm‐long diode. These properties enable these devices to have important use in high‐sensitivity fiber optic gyroscopes and as broadband traveling‐wave optical amplifiers.