4 March 2016 Reliability of high power laser diodes with external optical feedback
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Abstract
Direct diode laser systems gain importance in the fields of material processing and solid-state laser pumping. With increased output power, also the influence of strong optical feedback has to be considered. Uncontrolled optical feedback is known for its spectral and power fluctuation effects, as well as potential emitter damage. We found that even intended feedback by use of volume Bragg gratings (VBG) for spectral stabilization may result in emitter lifetime reduction. To provide stable and reliable laser systems design, guidelines and maximum feedback ratings have to be found. We present a model to estimate the optical feedback power coupled back into the laser diode waveguide. It includes several origins of optical feedback and wide range of optical elements. The failure thresholds of InGaAs and AlGaAs bars have been determined not only at standard operation mode but at various working points. The influence of several feedback levels to laser diode lifetime is investigated up to 4000h. The analysis of the semiconductor itself leads to a better understanding of the degradation process by defect spread. Facet microscopy, LBIC- and electroluminescence measurements deliver detailed information about semiconductor defects before and after aging tests. Laser diode protection systems can monitor optical feedback. With this improved understanding, the emergency shutdown threshold can be set low enough to ensure laser diode reliability but also high enough to provide better machine usability avoiding false alarms.
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Dennis Bonsendorf, Dennis Bonsendorf, Stephan Schneider, Stephan Schneider, Jens Meinschien, Jens Meinschien, Jens W. Tomm, Jens W. Tomm, } "Reliability of high power laser diodes with external optical feedback", Proc. SPIE 9733, High-Power Diode Laser Technology and Applications XIV, 973302 (4 March 2016); doi: 10.1117/12.2205296; https://doi.org/10.1117/12.2205296
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