Michael Jansen, Szutsun Ou, Jane Yang, Moshe Sergant, Cynthia Hess, Chan Tu, Phillip Hayashida, D. Bowier, Fernando Alvarez, George Harpole, Mark Emanuel
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.
Semiconductor lasers with dry etched facets are of interest for monolithic 2-D coherent applications such as optical interconnects and optoelectronic integrated circuits. This paper reports recent development on this area including high-performance 3 X 3 individually addressable InGaAs/GaAs single-mode surface emitting laser diodes, 630 nm GaInP/GaAlInP surface-emitting laser diodes, and 1.3 micrometers InGaAsP/InP surface-emitting laser diodes grown on Si substrate.
In this paper a beam propagation model used to compute model reflectivities of HC SELs, amplifiers, and SLEDs will be presented. These devices all employ an intracavity 45 degree(s) micromirror which causes the light to propagate in a direction perpendicular to the epilayers. The lack of a waveguide structure for propagation perpendicular to the epilayers and the broad angular spectrum produced by highly confined transverse modes of GRINSCH-SQW devices must be considered when analyzing folded-cavity devices. The model includes Fresnel reflections from multilayer thin-films, angular errors in the 45 degree(s) micromirror, the dependence on the horizontal reflector separation, Fresnel beam propagation, and waveguide coupling losses of the reflected field. The model predicts good conversion efficiencies, despite low effective reflectivities from the folded-end-mirror. There is good agreement with experimental data.
We report on the first demonstration of high power, short-wavelength, in-plane, horizontal cavity ion-beam-etched surface-emitting lasers with emission wavelengths of 740 nm and 635 nm, and surface-emitting output powers of 850 mW and 170 mW from GaAlAs/GaAs and GaInP/GaAlInP laser diodes, respectively.
Michael Jansen, Szutsun Ou, Jane Yang, Moshe Sergant, Cynthia Hess, Chan Tu, Phillip Hayashida, Dennis Bowler, Fernando Alvarez, George Harpole, Mark Emanuel
We review in-plane surface-emitting laser diode arrays and their applications. Efficient operation of monolithic, large area (0.54 cm2, 108 emitters) two-dimensional surface- emitting GaAlAs laser diode arrays mounted junction-down on microchannel heat exchangers has been demonstrated. Devices with 1.5 micrometers thick cladding layers were operated quasi- continuous-wave to high peak output power densities (> 100 W/cm2), exhibited high power conversion efficiencies (22%), and full width emission spectra of < 4 nm at 2% - 5% duty cycles. Arrays with a 2.5 micrometers thick cladding region were operated under continuous wave conditions to 46 W/cm2 power density levels. This corresponded to a 550 W/cm2 heat flux extracted by microchannel heat exchanges.
A novel GaAs/GaAlAs quantum well optoelectronic switching device, which exhibits an s-type negative differential resistance at room temperature and emits high performance stimulated emission, was demonstrated. The device structure is similar to the conventional separate confinement heterojunction quantum well laser, and thus can be easily integrated with state-of-the-art optoelectronic integrated circuits. The devices can be switched optically and/or electrically. Threshold current densities of 1.2 kA/sq cm, differential quantum efficiencies as high as 67 percent (0.5 W/A slope efficiency per facet) and output power in excess of 50 mW per facet were obtained.
The fabrication, performance characteristics, and applications of monolithic in-plane surface-emitting lasers (IPSELs) with dry-etched 45-degree micromirrors are reviewed. Several types of such laser diode structures in both junction-up and junction-down configurations are considered. The performance goals for IPSELs with 45-degree micromirrors are high power and efficiency, high duty cycle and CW operation, good reliability, and high fabrication yields. The proposed approach for achieving these goals includes uniform quantum well material growth and dry etching of the laser micromirrors with tight fabrication tolerances.
Monolithic in-plane surface emitting laser diode arrays with 45 degree(s) micromirrors offer great promise for both coherent and incoherent applications. This paper describes several such laser diode structures in both the junction-up and junction-down configurations, and summarizes their design, fabrication and performance characteristics.
High-power visible laser diodes operating at 630 - 640 nm have been demonstrated. The devices have a GaInP/GaAlInP single quantum well, graded-index separate confinement heterojunction. For 100-micrometers -broadstripe uncoated lasers, pulsed threshold current of 740 A/cm2 and output powers as high as 1.5 W/facet (total 3 W) at room temperature were achieved by optimizing the device cavity length. For 10-micrometers -ridge-waveguide lasers, 40 mW CW output powers with single-longitudinal mode and stable transverse mode have also been demonstrated. We also present, for the first time, high power 635 nm surface-emitting lasers with pulsed output powers of 170 mW.
Low-threshold, high-performance dry-etched ridge waveguide lasers with dry etched facets are of interest for monolithic two-dimensional coherent applications such as optical interconnects and optoelectronic integrated circuits. We report on low threshold current and wavelength emission < 8000 angstroms laser diodes with short cavity and dry etched facets. The facets are fabricated by reactive ion etching, which provides nearly vertical walls. For the first time, coherent GaAlAs/GaAlAs laser diodes (emission wavelength 7940 angstroms at room temperature) with cw threshold currents as low as 4 mA (room temperature) and 0.8 mA (at 77 degree(s)K) were achieved on a 4-micrometers -wide, 100-micrometers -long device.
Monolithic in—plane surface emitting laser diode arrays with 45° micromirrors offer great promise for both coherent and incoherent applications. This paper describes several such laser diode structures in both the junction-up and junction-down configurations, and summarizes their design, fabrication and performance characteristics.
Twenty element resonant optical waveguide (ROW) antiguided arrays were locked to 2.6 times above the threshold level (2.6 x Ith) by injecting light from a master oscillator in a direction normal to the diode facet and only in one element of the array. The spectra and far-field output pattern of the SL were found to be independent of the MO beam position on the SL facet, and the far-field pattern was stable with wavelength detuning (i.e. no steering) . Single frequency tuning was achieved over a < 30 A spectral range, and the beam pattern was found to be stable and diffraction-limited for nearly resonant devices. Two and four coupled ROW arrays on a bar were also injection—locked by injecting an external MO into one element of one of the arrays. Two locked arrays were wavelength tuned over a 12 A spectral range.
Recent work has demonstrated high power, spatially coherent operation of on-the-chip unstable resonator diode lasers. The unstable resonators were fabricated in SQW-GRINSCH material using photolithography and a dry chemical etch technique. The unstable resonator design provides mode selectivity in broad area devices by suppressing higher order lateral modes. These devices demonstrated twice diffraction limited far fields with high average power and strong lateral coherence.
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.
The small signal modulation characteristics, large signal modulation characteristics and dc noise spectra on 70 micron-wide 20-element high-power phase-locked arrays of antiguides are reported. The relaxation resonance frequency at 1.5 times threshold is found to be 1.65 GHz. Large-signal pulse modulation produced no distortion to the far-field characteristics. The dc noise spectra showed a damped shot noise resonance at 1.32 GHz for a dc bias level of 1.18 times threshold.
Stabilized in-phase mode oscillation is demonstrated from large-aperture 20-element antiguided diode laser arrays. 20-element resonant optical waveguide arrays emit 160 mW total power at 2.8 x I(th) in a diffraction-limited beam and have high spatial coherence across the entire array. CW operation of nonresonant 20-element array structures is demonstrated to high output power levels.
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