An optical device for combining RGB optical signals in a single waveguide, the single waveguide comprising a plurality of diffractive optical elements DOEs, including: a first DOE comprising a first linear grating on a front surface of the grating and having a first grating period and a second linear grating on the back of the grating and having a second grating period, the first DOE being configured to receive an optical signal at input propagation angles and to diffract the optical signal based on spectrum such that a +1 diffraction order of a predominately first spectrum of light is diffracted by the first linear grating in a first direction and a -1 diffraction order of the predominantly first spectrum of light is diffracted in a second direction by the first linear grating; and a +1 diffraction order of a predominately second spectrum of light is diffracted by the second linear grating and a -1 diffraction order of the predominantly second spectrum of light is diffracted by the second linear grating, such that different portions of optical signal take different paths, including four different paths; a second DOE and a third DOE, the second DOE comprising four wings with different expansion gratings, each expansion grating being oriented to diffract light toward the third DOE, wherein the first DOE is configured to diffract the optical signal of the predominantly first spectrum of light diffracted in the first direction toward a first wing, the optical signal of the predominantly first spectrum of light diffracted in the second direction toward a second wing, the +1 diffraction order of the predominately second spectrum of light toward a third wing, and the -1 diffraction order of the predominantly second spectrum of light toward a fourth wing; the third DOE configured to diffract light into an eye box keeping output propagation angles within some predetermined threshold of the input propagation angles; wherein the second and third DOE are configured to cause expansions that are substantially non-parallel; wherein the plurality of DOEs are associated with grating vectors and wherein a summation of grating vectors for each of the paths in the four different paths is substantially equal to zero. a first DOE comprising a first linear grating on a front surface of the grating and having a first grating period and a second linear grating on the back of the grating and having a second grating period, the first DOE being configured to receive an optical signal at input propagation angles and to diffract the optical signal based on spectrum such that a +1 diffraction order of a predominately first spectrum of light is diffracted by the first linear grating in a first direction and a -1 diffraction order of the predominantly first spectrum of light is diffracted in a second direction by the first linear grating; and a +1 diffraction order of a predominately second spectrum of light is diffracted by the second linear grating and a -1 diffraction order of the predominantly second spectrum of light is diffracted by the second linear grating, such that different portions of optical signal take different paths, including four different paths; a second DOE and a third DOE, the second DOE comprising four wings with different expansion gratings, each expansion grating being oriented to diffract light toward the third DOE, wherein the first DOE is configured to diffract the optical signal of the predominantly first spectrum of light diffracted in the first direction toward a first wing, the optical signal of the predominantly first spectrum of light diffracted in the second direction toward a second wing, the +1 diffraction order of the predominately second spectrum of light toward a third wing, and the -1 diffraction order of the predominantly second spectrum of light toward a fourth wing; the third DOE configured to diffract light into an eye box keeping output propagation angles within some predetermined threshold of the input propagation angles; wherein the second and third DOE are configured to cause expansions that are substantially non-parallel; wherein the plurality of DOEs are associated with grating vectors and wherein a summation of grating vectors for each of the paths in the four different paths is substantially equal to zero.