An apparatus, comprising: a substrate that is transmissive of electromagnetic energy of at least a plurality of wavelengths, the substrate having a first end, a second end, a first major face, a second major face, at least one edge, a length, a width, and a thickness, the second end opposed to the first end across the length of the substrate, the second major face opposed across the thickness of the substrate from the first major face, the at least one edge which extends between at least a portion of the first major face and a portion of the second major face, the width of the substrate greater than the thickness of the substrate; at least a first input optic (104, 302, 408, 502) oriented and positioned to provide electromagnetic energy into the substrate via at least one of the first or the second major face of the substrate without total internal reflection therein; at least a first output optic (110, 306, 410, 506, 604, 802) spaced along at least one of the length or the width of the substrate from the first input optic; a number of first reflective portions (124A, 124B) that extend at least partially along the first major face of the substrate, the number of first reflective portions oriented and positioned to control a propagation direction of electromagnetic energy along a folded optical path, at least a portion of which extends through the substrate between the first input optic and the first output optic when electromagnetic energy is incident on the first input optic; at least two second reflective portions (124C, 124D) that extend at least partially along the second major face of the substrate, the second reflective portions oriented and positioned to control the propagation direction of electromagnetic energy along the folded optical path when electromagnetic energy is incident on the first input optic; a number of non-reflective portions (120A-C) that extend at least partially along the first major face of the substrate, at least one of said non-reflective portions positioned laterally adjacent to at least a portion of at least one of the first reflective portions; and a number of non-reflective portions (120D-F) that extend at least partially along the second major face of the substrate, at least one of said non-reflective portions positioned laterally adjacent to at least a portion of at least one of the second reflective portions, characterised in that each of the non-reflective portions comprises an absorptive portion, a spatial extent of at least one of the first reflective portions or the second reflective portions spatially limits the electromagnetic energy along the folded optical path, and the at least one of the first reflective portions or the second reflective portions limits a range of propagation angles of the electromagnetic energy along the folded optical path. a substrate that is transmissive of electromagnetic energy of at least a plurality of wavelengths, the substrate having a first end, a second end, a first major face, a second major face, at least one edge, a length, a width, and a thickness, the second end opposed to the first end across the length of the substrate, the second major face opposed across the thickness of the substrate from the first major face, the at least one edge which extends between at least a portion of the first major face and a portion of the second major face, the width of the substrate greater than the thickness of the substrate; at least a first input optic (104, 302, 408, 502) oriented and positioned to provide electromagnetic energy into the substrate via at least one of the first or the second major face of the substrate without total internal reflection therein; at least a first output optic (110, 306, 410, 506, 604, 802) spaced along at least one of the length or the width of the substrate from the first input optic; a number of first reflective portions (124A, 124B) that extend at least partially along the first major face of the substrate, the number of first reflective portions oriented and positioned to control a propagation direction of electromagnetic energy along a folded optical path, at least a portion of which extends through the substrate between the first input optic and the first output optic when electromagnetic energy is incident on the first input optic; at least two second reflective portions (124C, 124D) that extend at least partially along the second major face of the substrate, the second reflective portions oriented and positioned to control the propagation direction of electromagnetic energy along the folded optical path when electromagnetic energy is incident on the first input optic; a number of non-reflective portions (120A-C) that extend at least partially along the first major face of the substrate, at least one of said non-reflective portions positioned laterally adjacent to at least a portion of at least one of the first reflective portions; and a number of non-reflective portions (120D-F) that extend at least partially along the second major face of the substrate, at least one of said non-reflective portions positioned laterally adjacent to at least a portion of at least one of the second reflective portions, characterised in that each of the non-reflective portions comprises an absorptive portion, a spatial extent of at least one of the first reflective portions or the second reflective portions spatially limits the electromagnetic energy along the folded optical path, and the at least one of the first reflective portions or the second reflective portions limits a range of propagation angles of the electromagnetic energy along the folded optical path.