High-power, high-gain, diffraction-limited emission from single-mode tapered semiconductor optical amplifiers

The realization of high-power (over 1 Watt), coherent diode lasers will open up new possibilities in printing, biomedicine, efficient pumping of solid state lasers and rare-earth doped fiber amplifiers, free-space optical communication, and nonlinear frequency conversion to the blue spectral region.; The most successful approach toward high-power coherent light sources to date is the master oscillator power amplifier (MOPA) configuration which consists of a single-mode master laser source and a large-area traveling-wave-amplifier (TWA). The design and fabrication of this large-area TWA plays a determining role in the overall characteristics and performance of the device.; In my research work, high-power tapered semiconductor optical amplifiers have been investigated and fabricated. High-power, high-gain, single-mode and diffraction-limited emission has been obtained. Several approaches to improve the amplifier's performance have been proposed and demonstrated, including: (1) the integration of a single-mode preamplifier with the tapered amplifier leads to single-mode operation even when the amplifier is pumped at high currents, (2) a self-aligned dissipating grid efficiently suppresses high-order spatial modes oscillation and reduces amplified spontaneous emission power, and (3) an angled-facet tapered amplifier with very low effective reflectivity was demonstrated. As much as 5-W pulsed power with a 0.94-W/A slope efficiency was achieved from a 2-mm-long amplifier, by injecting an incident power of only 20-mW from a laser diode. Low effective reflectivity of less than 4 {dollar}times{dollar} 10{dollar}sp{lcub}-5{rcub}{dollar} can be obtained routinely. Record high gains have been achieved, including an internal small-signal gain of 35-dB, and external and internal saturated gains of 23 dB and 29 dB, respectively. The far-field pattern was found to be dominated by a diffraction-limited single lobe containing more than 85% of the total emitted output power. Additionally, we have developed a new die attach process. CW powers of 400 mW and 800 mW were obtained from a 1-mm-long and 2-mm-long amplifier, respectively, when injected with an incident power of 10 mW.