Moshe Sergant

HIGH PERFORMANCE SURFACE-EMITTING LASERS WITH 45 INTRACAVITY MICROMIRRORS

For the first time, high performance GaAs/GaAlAs surface‐emitting lasers with internal 45° micromirrors, which totally reflect and emit the beam from the substrate in junction‐down configuration, have been demonstrated. The 45° and 90° mirrors of the device were fabricated by using ion milling and reactive ion etching techniques, respectively. Typical threshold current density of 440 A/cm2, external differential efficiencies of 52%, and output power in excess of 1 W under quasi‐cw operation have been achieved.

High power cw operation of GaAs/GaAlAs surface‐emitting lasers mounted in the junction‐up configuration

High power cw operation of horizontal cavity monolithic GaAs/GaAlAs surface‐emitting lasers with all dry etched micromirrors in the junction‐up configuration has been demonstrated for the first time. The 45° and 90° mirrors of the devices were fabricated by ion beam etching and reactive ion etching techniques, respectively. Typical threshold current densities of less than 360 A/cm2, external differential efficiencies of 22% (0.34 W/A) from the emitting facet, and output powers in excess of 280 mW were achieved under cw operation.

Coherent operation of injection-locked monolithic surface-emitting diode laser arrays

A row of six surface‐emitting GaAlAs laser diode arrays was locked in a coupled resonator configuration by means of interconnecting waveguides. An external master oscillator was injected into the first array in order to achieve single longitudinal mode operation and wavelength tunability. Spectral data show all six devices were locked in a single longitudinal mode, with tunable operation of over 60 A. Far‐field fringe visibilities greater than 60% were achieved at 100 mW output powers.

Monolithic two‐dimensional surface‐emitting diode laser arrays mounted in the junction‐down configuration

We report on the first achievement of large area (0.5 cm2) monolithic two‐dimensional surface‐emitting arrays mounted in the junction‐down configuration. Device fabrication involves dry etching of 45°, and vertical micromirrors with ±2° tolerances and <0.2 μm RMS smoothness, integration of 100‐μm‐thick current‐spreading electrodes for minimizing ohmic loss, large area packaging, and mounting to heat exchangers for long pulse and minimum chirp operation. Uniform lasing is achieved from 0.2×0.5 cm2 and 0.5×1 cm2 active area junction‐down monolithic arrays (120 and 600 emitters, respectively) using 100 μs long pulses at a 1% duty cycle. Differential quantum efficiencies of ≥ (R18)40% and 7% are achieved for rows of 12 emitters, and for 0.2×0.5 cm2 active area arrays, respectively. The decrease in efficiency with increased area is found to be due to current leakage, which in turn limits the 2‐D array emitted optical‐power density to 150 W/cm2. Wavelength chirp in these devices is measured to be <4 nm at twice...

Supermode discrimination in diffraction‐coupled laser arrays with separate contacts

We show that in‐phase lasing is favored in diffraction‐coupled arrays with separate electrical contacts for the common unguided diffraction zone and for the waveguide section, if the common unguided section is biased above a critical level. Below that level, out‐of‐phase lasing will be favored. By varying the current about the critical level, the far‐field intensity switches from a wide far‐field pattern characterized by the admixture of several supermodes, to a near‐diffraction‐limited single peak.

Supermode selection in diffraction‐coupled semiconductor laser arrays

A modal gain analysis for diode laser diffraction‐coupled arrays which takes into account evanescent coupling in the waveguide section of an array is presented. Theoretical predictions are supported by comparisons of patterns from typical double‐heterostructure and large‐optical‐cavity lasers.

Leaky-wave interarray coupling for coherent-power scaling of phase-locked diode-laser arrays of antiguides

Long‐range coupling and phase locking of several 10‐element resonant antiguided arrays via (lateral) radiation leakage is demonstrated. Coupling occurs for interarray separations as large as 90 μm, as evidenced from far‐field patterns and spectrally resolved near‐field patterns. Diffraction‐limited‐beam operation is achieved from a 244‐μm aperture (four coupled 10‐element arrays) device. Intermodal discrimination between the in‐phase mode and adjacent higher‐order modes is shown to be maximized for a resonant ensemble.

High-power, high-duty-cycle operation of monolithic two-dimensional surface-emitting diode laser arrays in the junction-down configuration

High-power, high-duty cycle and continuous wave operation of large-area monolithic 2D surface-emitting GaAlAs laser diode arrays mounted junction-down on microchannel heat exchangers have been demonstrated. Devices mounted don 2-mm-thick Cu heat spreaders were operated to peak output power densities of > 100 W/cm2 at 35% duty cycles,a nd exhibited high power conversion efficiencies, and full width emission spectra of < 4nm. Arrays mounted on 1-mm-thick heat spreaders were operated under continuous wave operating condition to approximately equals 50 W/cm2 power density levels. Silicon microchannel heat exchangers with a measured thermal resistance per unit are of 0.0324 degree(s)C cm2/W were used to removed up to 550 W/cm2 of excess heat generated by the arrays.

High‐power coherent surface‐emitting antiguided diode laser arrays

High‐power coherent GaAs/GaAlAs surface‐emitting antiguided laser arrays with dry etched micromirrors have been demonstrated for the first time. Both the deflecting 45° and 90° micromirrors were fabricated by ion beam etching. Twice diffraction‐limited far‐field beam profiles were obtained to pulsed output powers as high as 550 mW, with 220 mW in the central lobe.

Monolithic two-dimensional surface-emitting laser diode arrays with 45 degree micromirrors

Development and performance of large area (0.5 cm2) junction-down monolithic two- dimensional surface-emitting arrays is reported. This involves fabrication of 45 degree(s) and vertical micromirrors with +/- 2 degree(s) tolerances and < 0.2 RMS smoothness, lapping and polishing of 2 in. diameter wafers with < 10 micrometers thickness tolerances, integration of 100 micrometers thick current spreading electrodes which minimize ohmic losses, large area packaging, and mounting to heat exchangers for long pulse operation and minimum chirp. Single monolithic surface emitter diodes exhibit superior performance (slope efficiencies of (eta) d > 50%, threshold currents of Ith equals 220 mA, and output powers in excess of 720 mW). This projects to power densities > 860 W/cm2 and > 50% differential slope efficiencies for arrays of devices. Large area array operation (scaling) was demonstrated. Uniform lasing was achieved from 0.2 cm X 0.5 cm and 0.5 cm X 1.0 cm active area junction-down monolithic arrays (120 and 600 emitters respectively) using 100 microsecond(s) ec long pulses at a 1% duty cycle. Differential slope efficiencies of > 40% were achieved for rows of 12 emitters, and 8% for the large area arrays. The drop in efficiency was due to current leakage, which limited the output power densities to 150 W/cm2. Chirp in these devices was measured to be < 4 nm at twice the threshold current.