High-brightness lasers on silicon by beam combining

High-brightness lasers are widely used in fields such as spectroscopy, infrared countermeasures, free-space communication, and industrial manufacturing. Integration of a broad-band, multi-spectral laser is made possible by heterogeneously integrating multiple gain materials on one silicon (Si) substrate chip. A single multi-spectral output with high beam quality can be achieved by wavelength beam combining in multiple stages: within the gain bandwidth of each laser material and then coarsely combining each spectral band to a single output waveguide. To make power scaling feasible with this system, heterogeneously integrated lasers spanning the nearto the mid-infrared with corresponding low-loss wavelength beam combining elements on chip must be demonstrated. In this work, a review of multi-spectral lasers integrated on Si is presented and various waveguide materials are discussed for spanning the visible to the mid-infrared. Recent work integrating 2.0-μm diode and 4.8-μm quantum cascade lasers on Si extend the previously available 1.3-μm and 1.5-μm diode lasers on Si to the mid-infrared. Spectral beam combining elements for spanning the visible to the mid-infrared with low loss are discussed.