A portion of an optical waveguide extending laterally within a photonic integrated circuit (PIC) chip is at least partially freed from the substrate to allow physical displacement of a released waveguide end relative to the substrate and relative to an adjacent photonic device also fabricated in the substrate. The released waveguide end may be displaced to modulate interaction between the photonic device and an optical mode propagated by the waveguide. In embodiments where the photonic device is an optical coupler, employing for example an Echelle grating or arrayed waveguide grating (AWG), mode propagation through the coupler may be modulated via physical displacement of the released waveguide end. In one such embodiment, thermal sensitivity of an integrated optical wavelength division multiplexer (WDM) is reduced by displacing the released waveguide end relative to the coupler in a manner that counters a temperature dependence of the optical coupler.