Patent ID: 8305502

Claim:
A beam combiner for combining a plurality of light beams onto an optical path, comprising: a first dichroic element having a dichroic coating that is disposed to transmit light of a first wavelength band along the optical path and to reflect light of a second wavelength band onto the optical path, and which imparts a phase difference to polarization states of the transiting light; a second dichroic element having a dichroic coating that is disposed to transmit the light of the first and second wavelength bands along the optical path and to reflect light of a third wavelength band onto the optical path, and which accumulates an additional phase difference for the polarization states of the transiting light; and wherein a surface of either the first or second dichroic element further comprises a phase difference compensation multilayer thin-film stack that provides at least one positive or negative reflectance edge transition that lies outside any of the first, second, and third wavelength bands for light incident on said surface, the phase difference compensation multilayer thin-film stack providing compensation for the accumulated phase difference in at least one of the first, second, and third wavelength bands.