Grating resonators for surface acoustic waves or surface optical waves are coupled in cascade via a track changer external to the resonator cavities. At least one grating of each resonator is partially transmissive in the resonant band, allowing the interchange of energy therebetween via the track changer. The track changer is comprised of either two or three reflective racks angled such that the energy reflected therein propagates along zero-temperature-coefficient paths. The three-rack, three-bounce U-path filter used as a track changer minimizes resonant energy losses due to variations in reflected wave angles from their designed values.