LiDAR (light detection and ranging) technology has gained significant importance in various fields, including autonomous vehicles, environmental monitoring, and remote sensing. 905nm pulsed laser diodes are an essential component of a LiDAR system, which performance relies heavily on the laser power level and the characteristics of its emitted light beam. While the fabrication of high-power pulsed laser diodes is already mature, reliably combining a high-power level and a concentration of the laser beam (⪆90%) within a limited emitting width is an ongoing challenge. Another major concern is the development of facet coatings capable of withstanding the high-power density generated by these lasers. Facet degradation due to the excessive optical power leads to a reduced laser efficiency and a risk of increased failure rates. Here, we have devised novel optical waveguide designs for triple junction 905nm lasers with optimized mode profiles and an effective confinement structure. This enables lasers to have a power density that is four (4) times higher than the traditional ones and, to confine most of the beam energy within an emitting width of less than 60 µm. Furthermore, our research explores innovative approaches to facet coatings that enhance facet durability and minimize power-induced degradation. This results in exceptionally reliable lasers, as demonstrated by a thousand hours of life test data. Through this work, we have achieved significant advancements in design and fabrication of high-power laser diodes for LiDAR applications. Experimental results demonstrate improved power efficiency, reliable facet coatings, and effective energy confinement within the desired emitting width.
The micro-fabrication process for advanced GaAs-based Pulsed Laser Diodes (PLDs) necessitates the precise etching of trenches for patterning waveguides. Traditionally, we employed wet etching in our approach, which, unfortunately, does not allow for precise engineering of waveguide trench geometry. The isotropic nature of wet etching results in a sidewall angle of approximately 45°. To enhance device performance, achieving a steeper angle without compromising other process steps dry etching is preferable. Ideally, trenches with sidewall angles ranging from 60° to 70° would strike an optimal balance. In pursuit of this goal, we initiated a Design of Experiment (DoE) to optimize the etching by Inductively Coupled Plasma - Reactive Ion Etching (ICP-RIE). Through this experimentation, we identified an ICP-RIE recipe capable of producing trenches with sidewall angles within the desired range (60° to 70°), exhibiting low roughness and attaining a depth of 17 μm. After this optimization, we applied the new ICP-RIE process to fabricate PLDs and conducted a comparative analysis against devices produced using our conventional wet etching method. The PLDs etched with ICP-RIE showcased slightly superior performance compared to those etched with wet etching. The implementation of ICP-RIE not only enhances device performance but also allows for a reduction in footprint per device. Consequently, this optimization contributes to an increased yield of devices per wafer, thus demonstrating the potential for scalability and improved efficiency in our micro-fabrication process.
New generation of eye safe military applications such as range finding, short range illumination and friend or foe
identification have started to use the 1550nm wavelength region. This was encouraged by the advent of diode lasers
efficient enough to approach the output power of shorter wavelength, 850nm and 905nm devices. This paper will review
the actual performance and technologies of various commercially available 1550nm pulsed laser diodes. The
performance and reliability of a new high brightness 1550nm semiconductor laser diode are disclosed and compared.
Peak power of up to 35 Watts is achieved out of a single junction 350 micron stripe laser. Similarly, peak power in
excess of 20W is achieved with a 180 micron stripe laser. This represents an optical power density of 11.1M W/cm2.
Other key advantages of this new laser are a fast axis FWHM divergence of 25 degrees and less than a 10mRad
divergence after fast axis collimation. The new diode technology will be explained in some detail covering aspects of
design, fabrication and adaptation to meet its final target performances. A description of the optimization of chip
dimensions and laser packaging is also undertaken. Finally, various ideas are offered to further improve the laser
efficiency and power.
The 1550nm wavelength region is critical to the development of next generation eye safe military applications such as
range finding and friend or foe identification (FOE). So far the relatively low laser external efficiency was a strong
limiting factor favoring shorter wavelength diode lasers. We report on the development of a new monolithic multiple
junction pulsed laser diode offering an external efficiency of more than one Watt per Amp with high brightness. Peak
optical output power of more than 37 Watts has been achieved from a single multi-junction diode laser. Divergence is
narrow with less than 35 degrees (FWHM) in the fast axis direction. Starting from an AlGaInAs quantum well laser
structure, we show the criticality of the design of InP based tunnel junctions to the growth of the three layer epitaxial
monolithic laser. We then report on trenches employed to confine carriers under the contacting stripe and on growth
strategies used to decouple the multiple light sources resulting from the multi-junction design. A full set of
characterization data is presented concluding with a discussion on performance limitations and their potential causes.
William Meyer, Walther Tscharnuter, Andrew MacGregor, Henri Dautet, P. Deschamps, Jean-Francois Boucher, Jixiang Zhu, Padetha Tin, Richard Rogers, Rafat Ansari
We describe recent advancements in laser light scattering hardware including intelligent single card correlators, active quench/active reset avalanche photodiodes, laser diodes, and fiber optics which were used by or developed for a NASA Advanced Technology Development program. We then preview a space shuttle experiment which will employ aspects of these hardware developments.
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