S.K. Liew

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. >

Mode discrimination in distributed feedback grating surface emitting lasers containing a buried second-order grating

The operating characteristics of a novel grating surface emitting laser structure containing a buried second-order grating have been studied both experimentally and theoretically. This device consists of a pumped distributed feedback (DFB) section that is terminated at each end by unpumped distributed Bragg reflector (DBR) sections. A single continuous second-order grating layer and waveguide layer extend throughout the active and passive sections so that there is essentially no fabricated optical discontinuity at the interface between the active and passive end sections. Single mode operation (>30 dB side mode suppression) and single-lobed far fields with negligible sidelobes are observed up to more than 5*I/sub th/ with spectral linewidths as narrow as 1 MHz. >

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>>

Demonstration of a grating‐surface‐emitting diode laser with low‐threshold current density

This letter reports the demonstration of grating‐surface‐emitting (GSE) lasers with threshold current densities as low as 440 A/cm2. When the distributed‐Bragg‐reflector sections were cleaved from these lasers, the resulting edge‐emitting lasers had threshold current densities that were essentially unchanged from that of the GSE laser. However, the operating wavelength of the Fabry–Perot laser was typically 70 A shorter than that of the surface emitter.

Characteristics of active grating-surface-emitting amplified lasers

The design and characteristics of active-grating surface emitting amplifiers are discussed. Performance projections indicate coherent power outputs of more than I W should be possible from devices that are 1 cm long. Preliminary experimental results on an AIGaAs/InGaAs active-grating MOPA are presented.

Demonstration of InGaAs/AlGaAs strained‐layer distributed‐feedback grating‐surface‐emitting lasers with a buried second‐order grating structure

We have fabricated InGaAs/AlGaAs strained‐layer distributed‐feedback grating‐surface‐emitting lasers with a buried grating structure. The device consists of a pumped distributed‐feedback section terminated on both sides by unpumped distributed Bragg reflector sections. cw operation in a stable single longitudinal mode is achieved up to six times threshold. The threshold current density is ∼600 A/cm2. The far‐field beam divergence is predominantly single lobed and diffraction limited. The spectral linewidth is 1.0 MHz at an output power of 8 mW.

High-speed switching of monolithic arrays of grating-surface-emitting diode lasers

The electrooptic switching properties of injection-coupled coherent two-dimensional grating-surface-emitting (GSE) laser arrays with multiple gain sections and quantum-well active layers are discussed. Within such an array of injection-coupled GSE lasers, a single gain section can act as an intracavity saturable loss element that can modulate the output of the entire array. Experimental results demonstrate efficient subnanosecond switching of high-power GSE laser arrays by operating only one gain section as an intracavity loss modulator. >

Spectral linewidth narrowing in monolithic grating-surface-emitting laser arrays

Linewidth measurements of single-element grating-surface-emitting (GSE) lasers and coherent three-element GSE arrays have shown that a significant reduction in the spectral linewidth is possible in the case of the coherent array. A monolithic array of three injection-coupled GSE lasers had a linewidth less than 300 kHz, whereas a single-array element, operated by itself, typically had a linewidth of about 6 MHz.<<ETX>>

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.