Guowen Yang

Highly reliable high-power 980-nm pump laser

We report on highly reliable, high-power, and high-performance 980-nm quantum-well laser chips and modules. Ridge waveguide laser diode chips with 750-mW output power and 500-mW fiber Bragg grating stabilized modules have been achieved and Telcordia-qualified. Long-term reliability tests show a very low failure rate of 400 FIT (failures in time) at 900-mA operating current or 500-mW module power. The kink-free fiber coupled module output power can be as high as 640 mW with grating stabilization, which produces very good wavelength stability and power stability. A further improved structure shows a record continuous-wave rollover chip power of 1.6 W for the 5-/spl mu/m-wide ridge waveguide laser diodes.

High-performance 980-nm ridge waveguide lasers with a nearly circular beam

We report high-performance 980-nm ridge waveguide quantum-well lasers with extremely low vertical beam divergence of 13/spl deg/. A very small aspect ratio of 1.6 is obtained at high operating power of 900 mW. In addition to the more circular beam, low threshold, high efficiency, high characteristic temperature, and high output power of over 1.18 W are achieved. The fiber coupled output power can be as high as 680 mW with fiber Bragg grating stabilization. Excellent wavelength and power stability are also demonstrated.

Theoretical investigation on quantum well lasers with extremely low vertical beam divergence and low threshold current

A specially designed quantum well laser for achieving extremely low vertical beam divergence was reported and theoretically investigated. The laser structure was characterized by two low index layers inserted between the waveguide layers and the cladding layers. The additional layers were intended to achieve wide optical spread in the cladding layers and strong confinement in the active region. This enabled significant reduction of beam divergence with no sacrifice in threshold current density. The numerical results showed that lasers with extremely low vertical beam divergence from 20° down to 11° and threshold current density of less than 131 A/cm2 can be easily achieved by optimization of the structure parameters. Influences of individual key structure parameters on beam divergence and threshold current density are analyzed. Attention is also paid to the minimum cladding layer thicknesses needed to maintain low threshold current densities and low internal loss. The near and far field patterns are given...

Conduction-band offset in a pseudomorphic GaAs/In0.2Ga0.8As quantum well determined by capacitance–voltage profiling and deep-level transient spectroscopy techniques

The conduction-band offset Delta E-C has been determined for a molecular beam epitaxy grown GaAs/In0.2Ga0.8As single quantum-well structure, by measuring the capacitance-voltage (C - V) profiling, taking into account a correction for the interface charge density, and the capacitance transient resulting from thermal emission of carriers from the quantum well, respectively. We found that Delta E-C = 0.227 eV, corresponding to about 89% Delta E-g, from the C - V profiling; and Delta E-C = 0.229eV, corresponding to about 89.9% Delta E-g, from the deep-level transient spectroscopy (DLTS) technique. The results suggest that the conduction-band discontinuity Delta E-C obtained from the C-V profiling is in good agreement with that obtained from the DLTS technique

Impact of near-end residual reflectivity on the spectral performance of high-power pump lasers

Abnormal spectral characteristics are observed in high-power semiconductor pump laser modules with ultralow chip front-facet reflectivity levels. We have identified the root cause as destructive interference in an external-cavity reflection from an antireflection (AR) coated fiber tip. This suppressive external cavity imposes a practical limit on the lower desirable bound for front-facet AR coatings for high-power lasers and uncooled fiber Bragg grating stabilized semiconductor devices.

Recent progress in fiber-coupled multi-mode pump module and broad-area laser-diode performance from 800-1500 nm

We present performance improvements of fiber-coupled pump modules and broad-area lasers at 8xx nm, 9xx nm and 14xx nm wavelengths. Broad-area lasers with a 200 μm aperture at 808 nm for direct diode applications emit 11W CW and 30W pulsed. Pump modules at 830 nm for printing applications show excellent linearity, power stability of 2% and 95% of the power within 0.12 NA into a 50 μm core fiber at 1W CW. Broad-area lasers at 880 nm for pumping applications emit 18W CW with a peak wallplug efficiency of 64%. An improved design of 9xx pump modules is demonstrated with built-in feedback-protection (>30 dB at 1060 nm) that allows safe operation in multi-kW peak-power fiber lasers. Up to 3W of optical power with slope efficiency and peak wallplug efficiency of 0.64 W/A and 46%, respectively, is presented for 14xx nm broad-area lasers with a 100 μm wide aperture.

Grating Stabilized High Power 980nm Pump Modules

We describe the next generation high power, single-mode 980 nm laser diode for EDFA pumping. The FBG-stabilized pump modules produce 0.7 W kink-free power with superior reliability and performance.

Design and fabrication of 980-nm InGaAs/A1GaAs quantum well lasers with low beam divergence

We report on the design and fabrication of 980nm InGaAs/AlGaAs double quantum well lasers with low vertical beam divergence. The specially designed structure, which characterized by two low refractive index layers inserted between the cladding and waveguide layers, was theoretically studied using the shooting method and systematic calculation. Results for the beam divergence and far-field distribution are given, and the physical concepts are discussed. Experimental investigation by molecular beam epitaxy was performed. For the fabricated as-cleaved 3micrometers - wide ridge waveguide structure lasers having a cavity length of 800micrometers , a threshold current of 30mA and an external quantum efficiency of 0.8mW/mA were achieved. The measured far field pattern has a vertical divergence of 21 degrees and a horizontal divergence of 8 degrees.

Growth and fabrication of high performance 980nm strained InGaAs quantum well lasers using novel hybrid material system of InGaAsP and AlGaAs

In this paper, we report on the design, growth and fabrication of 980 nm strained InGaAs quantum well lasers employing novel material system of Al-free active region and AlGaAs cladding layers. The use of AlGaAs cladding instead of InGaP provides potential advantages in laser structure design, improvement of surface morphology and laser performance. We demonstrate an optimized broad-waveguide structure for obtaining high power 980 nm quantum well lasers with low vertical beam divergence. The laser structure was grown by low-pressure metalorganic chemical vapor deposition, which exhibit a high internal quantum efficiency of approximately 90% and a low internal loss of 1.5 - 2.5 cm-1. The broad-area and ridge-waveguide laser devices are both fabricated. For 100 micrometers wide stripe lasers with cavity length of 800 micrometers , a low threshold current of 170 mA, a high slope efficiency of 1.0 W/A and high output power of more than 3.5 W are achieved. The temperature dependences of the threshold current and the emitting spectra demonstrate a very high characteristic temperature coefficient (T0) of 200 - 250 K and a wavelength shift coefficient of 0.34 nm/ degree(s)C. For 4 micrometers - width ridge waveguide structure laser devices, a maximum output power of 340 mW with COD-free thermal roll-over characteristics is obtained.

Threshold reduction in strained-layer InGaAs/GaAs quantum well lasers by liquid phase epitaxy regrowth

When liquid phase epitaxy regrowth at 780 degrees C for 2 h is applied to the samples after molecular beam epitaxy, a decrease of the threshold current density in strained InGaAs/GaAs quantum well lasers by a factor of 3 to 4 is obtained. We suggest that this improvement is attributed to the reduction of nonradiative centers associated with deep levels at the three regions of the active region, the graded layer and the cladding layer. Indeed, a significant reduction of deep center densities has been observed by using minority and majority carrier injection deep level transient spectroscopy measurements