Aland K. Chin

Temperature profile along the cavity axis of high power quantum well lasers during operation

Measurements of the temperature distribution along the cavity of 0.5 W AlGaAs quantum well lasers are presented. The spatial distribution of temperature was determined by measuring the spectral shift of electroluminescence emitted through a window in the GaAs substrate metallization. The average temperature of the active layer is 10–15 K higher than the heatsink temperature at 0.5 W output. Facet temperatures can exceed the average active layer temperature by over 100 K. Data are also presented illustrating the temperature profile at different drive currents between threshold and the maximum operating current. A temperature profile of a laser with a damaged front facet is presented, showing a hot region that is twice the size of the defect.

Gas source molecular beam epitaxy of GaN with hydrazine on spinel substrates

Growth of high quality wurtzite-structure GaN layers on (111) MgAl2O4 by gas source molecular beam epitaxy is described. Hydrazine was used as a source of active nitrogen. In situ reflection high energy electron diffraction was used to monitor the growth mode. Two-dimensional growth was obtained at temperatures above 750 °C on multi-step GaN buffer layers. The resulting GaN films show excellent luminescence properties.

High-power, reliable operation of 730 nm AlGaAs laser diodes

High-power operation of AlGaAs multi-quantum-well laser diodes emitting near 730 nm is reported. 1000 h, reliable operation at a power of 1.0 W for 100 μm emission aperture and 500 μm cavity length devices has been demonstrated at room temperature. These devices have threshold current densities of 770 A/cm2 with the characteristic temperature coefficients of threshold current, T0, and external differential quantum efficiency, T1, of 152 and 167 K, respectively.

Simultaneous cw dual-wavelength laser action and tunability performance of diode-pumped Yb3+:Sr5(VO4)3F

Abstract Simultaneous cw laser operation at 1044 and 1120 nm in Yb 3+ :Sr 5 (VO 4 ) 3 F (SVAP) under diode pumping has been achieved for the first time. Output powers of 29.9 mW at 1044 nm and 26.5 mW at 1120 nm were obtained under simultaneous operation. A maximum output for each transition operating separately was 103 mW at 1044 nm and 157 mW at 1120 nm. In addition, we demonstrate over 27 nm of wavelength tunability of the 1120 nm band.

Cubic zirconia as a high‐quality facet coating for semiconductor lasers

In this paper we describe the properties of high‐quality, semiconductor laser facet coatings based on yttria‐stabilizied cubic zirconia (90‐m% ZrO2/10‐m% Y2O3). We have found that cubic zirconia films can be reproducibly deposited by electron‐beam evaporation with an index of refraction of 1.98 at 6328 A, almost ideal for use as a single‐layer antireflection coating for GaAs/GaAlAs‐based lasers. ZrO2 has a monoclinic crystal structure at room temperature, but changes to tetragonal, hexagonal, and cubic phases upon heating to higher temperatures. However, the addition of the Y2O3 stabilizes ZrO2 in the cubic form, thus allowing electron‐beam deposition of thin films of this material to be more controllable and reproducible without the usual addition of oxygen into the vacuum chamber during deposition. Preliminary aging tests of high‐power GaAs/GaAlAs lasers show that cubic zirconia films suppress the photo‐enhanced oxidation of laser facets that degrades device performance.

Higher brightness laser diodes with smaller slow axis divergence

The slow axis (SA) divergence of 20% fill-factor, 980nm, laser diodes (LDs) have been investigated under short pulsed (SP) and continuous (CW) operation. By analyzing the data collected under these two modes of operation, one finds that the SA divergence can be separated into two components: an intrinsic divergence and a thermally induced divergence. At low injected current and power, the intrinsic SA divergence is dominant while at high power their magnitudes are approximately equal. The thermal gradient across the broad stripe is negligible under SP operation and, the SA divergence increased at a much slower rate as a function of injected current, thereby increasing the brightness of the LD by 2X. SRL has redesigned microchannel coolers that remove the thermal gradient under CW operation thereby eliminating the thermally induced SA divergence resulting in LDs that are 2X brighter at 300W/bar.

Record CW-brightness from a single 20% fill-factor 1-cm laser-diode bar at 20°C

A record, 250W, CW output-power has been achieved for a single, 1cm-wide, 3.5mm cavity-length, 20% fill-factor, 976nm, laser-diode bar operated at 20°C. The remarkable laser-bar performance was in part the result of a novel EPIC (Enhanced Performance Impingement Cooler) heat-sink with a thermal resistance of 0.16K/W. The superb thermal management resulted in record brightness for a laser bar, i.e. a slow-axis divergence of 10° (95% power containment angle) was achieved at 200W output-power. A coupling efficiency of ~74% into a 200μm core, 0.22NA fiber was achieved.

Zinc diffusion in III‐V semiconductors using a cubic‐zirconia protection layer

Zinc was diffused into GaAs, Al0.38Ga0.62As, and GaAs0.6P0.4 using a 2000–3000‐A‐thick yttria‐stabilized cubic‐zirconia (YSZ) protection layer to produce planar p‐n junctions. The YSZ layer greatly reduced thermal decomposition of the semiconductor while allowing zinc to diffuse into the III‐V semiconductors. The diffusion depth showed a square‐root‐of‐time dependence for all samples protected with YSZ. Characterization of the GaAs diffused with the YSZ protection process indicates that the YSZ layer has virtually no effect on either the carrier concentration profile or activation energy. No thermal decomposition was observed by visual inspection following a diffusion using only elemental Zn on the GaAs, Al0.38Ga0.62As, or GaAs0.6P0.4 samples protected with a YSZ layer. Photoluminescence analysis shows that the YSZ‐protected GaAs samples have higher luminescence efficiency relative to unprotected samples. Device fabrication has been demonstrated by combining the YSZ passivation process with selective area...

Narrow far fields from extended‐window broad‐area lasers

Broad‐area lasers are fabricated with a long (80–100 μm), nonabsorbing window at each end. The window is shown to dramatically improve the spatial mode properties, stabilizing and smoothing the near field, and reducing the far field from 5°–15° to as low as 2°. This improvement comes at the expense of an increase in threshold current and reduction of quantum efficiency.

Record-brightness laser-diode bars for fiber coupling

High brightness, laser-diode bars are required for efficient coupling into small-core optical-fibers. Record power and brightness results were achieved using 20% fill-factor, 980nm, 1cm-wide, 4mm cavity-length bars. Lifetimes of single bars, operated CW at 200W and 20°C, exceed 1000hr. Due to superb thermal management, the power conversion efficiency (PCE) exceeds 60% at 200W output power. Similar lifetime and PCE were obtained for a 3-bar stack emitting 600W output power.