W. F. Reichert

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.

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.

Demonstration of monolithic, grating-surface-emitting laser master oscillator-cascaded power amplifier array

The design, fabrication, and performance characteristics of a monolithic grating-surface-emitting master-oscillator-cascaded-power-amplifier laser array are reported. Light output from the amplifier chain was obtained using grating output couplers after each amplifier section. Power outputs of 80-100 mW per amplifier were measured, while the spectral purity of the master oscillator was maintained. The operating characteristics of these laser arrays demonstrate that the spectral characteristics determined by the laser oscillator and power control provided by the amplifier sections are independent.<<ETX>>

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.

Universality of mode-locked jitter performance

It is shown experimentally that the jitter of actively mode-locked laser pulses is determined by two factors: first, by spontaneous noise associated with cavity loss, and second, by round-trip propagation time. As the round-trip time is increased, a characteristic frequency which defines the high-frequency limit of phase noise decreases. For a comparable round-trip time and cavity loss, the jitter of mode-locked lasers based on diverse gain media, whether semiconductor or erbium ion is universal and independent of the upper-state transition lifetime.

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.

Lateral beam steering in mutual injection coupled Y‐branch grating‐surface‐emitting diode laser arrays

We have observed lateral electronic beam steering of light emitted by monolithic, two‐dimensional, grating‐surface‐emitting, mutually injection coupled arrays of diode lasers in the AlGaAs/GaAs system. Positionally staggered Y‐branch subarrays are optically connected through pumped waveguides which provide the required phase shift. These observations taken in conjunction with previously reported work on steering such arrays in the longitudinal direction now demonstrate, for the first time, monolithic, two‐dimensional‐coherent‐diode‐laser arrays that may be electronically steered in two orthogonal directions.