High-power spatially single-mode diode lasers at 1.4 - 1.5 μm wavelength are of interest as pump lasers for Raman and rare-earth doped fiber amplifiers as well as for material processing and for Light Detection and Ranging (LIDAR) at eye-safe wavelengths. A cost-efficient way to realize high-power high-brightness devices is the tapered resonator concept.
We demonstrate InGaAsP/InP based diode lasers with compressively strained quantum wells and wavelengths around 1480 nm which were grown by solid source MBE. From broad area lasers with variations in quantum well number and waveguide layer thickness, parameters for the logarithmic gain model are deduced. With their implementation in 2-dimensional BPM simulations, an optimized resonator geometry is derived. Devices employ a 500 μm ridge section followed by a 2000 μm taper section with 6° angle. Continuous-wave (cw) output powers reach more than 1.5 W. Beam quality is characterized in terms of near field and far field distribution, M2, and astigmatism. An excellent agreement is found between measurement and simulation.
For narrow-linewidth operation, devices are provided with anti-reflection coatings on both facets and spectrally stabilized with an external grating. We achieve 0.7 W single mode power and a side mode suppression ratio (SMSR) of 42 dB.
Reliability is tested in terms of facet stability and lifetime. Pulsed measurements reveal a power stability up to more than 5 MW/cm2. From cw aging tests at 1 W output power, lifetimes of about 6,000 h are extrapolated.
Semiconductor lasers with high beam quality and high optical output power are very attractive for a variety of applications such as molecular spectroscopy, fiber optic communication and frequency conversion. In the used power regime, devices based on tapered gain sections are the most promising candidates to reach these demands. However, two disadvantages of the tapered laser concept are the reduced output power provoked by their additional resonator losses and the astigmatism of these diode lasers. In case of high brightness diode lasers it is important to discuss the methods needed for an advanced output power also from the point of view of beam quality. The knowledge about astigmatism is essential for designing micro-optics. For the experimental results low modal gain, single quantum well InGaAs/AlGaAs devices emitting at 980 nm were grown by molecular beam epitaxy. The influence of the thermal resistance and of the tapered section length on the output power as well as on the beam quality has been investigated. In addition the impact of these parameters on the astigmatism of tapered diode lasers has been analysed. The experimental results have been correlated with simulations of the current-power curves and BPM simulations of the nearfield behaviour.