Spectral vs. Coherent Beam Combining: How Do They Compare?

Partial reflectors in interferometers and polarization-sensitive devices (beam splitters used in reverse) such as beam-splitting cubes are common examples of systems that combine two beams (adding beams so that they are co-linear). While these components perform beam combining, they typically are inefficient and/or limited in the number of beams that can be combined. Polarization beam combining, for instance, only works with two beams because the light has only two distinguishable states.