A planar lightwave circuit comprising: a combined signal waveguide (128, 164, 174, 186; 213); a set of dispersed signal waveguides (130; 215); a first slab waveguide (112; 206); a second slab waveguide (114, 160, 178, 190; 208); a first mirror (118, 162, 180, 192; 218) optically connected to the second slab waveguide (114, 160, 178, 190; 208), a mirror assembly supporting the first mirror; and a waveguide array (116; 210); wherein the waveguide array (116; 210) optically connects the first slab waveguide (112; 206) and the second slab waveguide (114; 208) to provide an arrayed waveguide grating, wherein the combined signal waveguide or the set of dispersed signal waveguides (130; 215) is optically connected at an access edge (113, 168, 176, 188; 214) to the second slab waveguide (114; 208) and the other of the combined signal waveguide or the set of dispersed signal waveguides is optically connected to the first slab waveguide (112; 206), and wherein an optical path through the second slab waveguide (114; 208) from the access edge is folded by providing an optical reflection from the first mirror (118; 218) to an array edge (170, 182, 194) connecting the waveguide array (116; 210) and the appropriate element of the combined signal waveguide or the set of dispersed signal waveguides, the array edge being where the waveguide array interfaces with the second slab waveguide, with the access edge not displaced toward or away from the first mirror relative to the array edge or with the access edge displaced toward the mirror relative to the array edge or with the access edge displaced away from the mirror relative to the array edge, and wherein the configuration of the reflection off of the mirror is at a reflection angle of 5 to 60 degrees and the ratio of optical path distance from the access edge (113, 168, 176, 188) to the mirror (118, 162, 180, 192) as compared to the optical path distance from the array edge (170, 182, 194) to the mirror (118, 162, 180, 192) being from 0.5 to 2, and wherein the mirror assembly comprises an actuator that pivots the first mirror (118; 218) in response to a change in temperature to change the angle to provide effectively temperature compensated transmission of light through the planar lightwave circuit over a selected temperature range. a combined signal waveguide (128, 164, 174, 186; 213); a set of dispersed signal waveguides (130; 215); a first slab waveguide (112; 206); a second slab waveguide (114, 160, 178, 190; 208); a first mirror (118, 162, 180, 192; 218) optically connected to the second slab waveguide (114, 160, 178, 190; 208), a mirror assembly supporting the first mirror; and a waveguide array (116; 210); wherein the waveguide array (116; 210) optically connects the first slab waveguide (112; 206) and the second slab waveguide (114; 208) to provide an arrayed waveguide grating, wherein the combined signal waveguide or the set of dispersed signal waveguides (130; 215) is optically connected at an access edge (113, 168, 176, 188; 214) to the second slab waveguide (114; 208) and the other of the combined signal waveguide or the set of dispersed signal waveguides is optically connected to the first slab waveguide (112; 206), and wherein an optical path through the second slab waveguide (114; 208) from the access edge is folded by providing an optical reflection from the first mirror (118; 218) to an array edge (170, 182, 194) connecting the waveguide array (116; 210) and the appropriate element of the combined signal waveguide or the set of dispersed signal waveguides, the array edge being where the waveguide array interfaces with the second slab waveguide, with the access edge not displaced toward or away from the first mirror relative to the array edge or with the access edge displaced toward the mirror relative to the array edge or with the access edge displaced away from the mirror relative to the array edge, and wherein the configuration of the reflection off of the mirror is at a reflection angle of 5 to 60 degrees and the ratio of optical path distance from the access edge (113, 168, 176, 188) to the mirror (118, 162, 180, 192) as compared to the optical path distance from the array edge (170, 182, 194) to the mirror (118, 162, 180, 192) being from 0.5 to 2, and wherein the mirror assembly comprises an actuator that pivots the first mirror (118; 218) in response to a change in temperature to change the angle to provide effectively temperature compensated transmission of light through the planar lightwave circuit over a selected temperature range.