Packaging and thermal management of high-power, slab-coupled optical waveguide laser arrays for beam combining

Linear arrays of slab coupled optical waveguide lasers (SCOWL) are nearly ideally suited for beam combining of array elements. SCOWL array elements have very high brightness, low divergence, nearly-diffraction-limited optical output beams with Watt-level performance. Both wavelength beam combining (WBC) and coherent beam combining (CBC) of SCOWL array elements have been successfully demonstrated. In this presentation, the packaging techniques developed to ensure proper performance of SCOWL arrays will be described, with particular emphasis on the application to beam combining. Arrays up to 1.2 cm wide, containing 120 elements on 100-mum element-to-element pitch have been demonstrated and used for WBC experiments. Aggressive thermal management was required in order to ensure optimum CW performance of these arrays and to minimize thermal cross talk between array elements. Commercial high performance micro impingement coolers (MIC) were used to accomplish this task. A numerical thermal model was constructed and used to investigate the thermal performance for several alternative packaging schemes using the MIC coolers. Assembly procedures were also developed in order to promote uniform optical performance of SCOWL array elements. These techniques resulted in minimal contraction (~2 mum) and smile (~1 mum) of the laser bar during the packaging process, which were sufficiently small to have minimal impact on the resultant WBC beam quality. CBC of SCOWL arrays required the ability to adjust the phase of the individual array elements. Packaging providing both individual electrical addressability of SCOWL array elements and good thermal performance has been developed and demonstrated, allowing for phase control by current adjustment. Individually addressable, 10-element SCOWL arrays have been demonstrated with total uncombined output power levels of >10 W CW. Coherent combining of ~7 W CW of optical power has been demonstrated from these 10-element SCOWL arrays.