An optical device implemented on a substrate (such as silicon) is described. This optical device includes a wavelength-sensitive optical component with a high thermal resistance to a surrounding external environment and a low thermal resistance to a localized thermal-tuning mechanism (such as a heater), which modifies a temperature of the wavelength-sensitive optical component, thereby specifying an operating wavelength of the wavelength-sensitive optical component. In particular, the thermal resistance associated with a thermal dissipation path from the thermal-tuning mechanism to the external environment via the substrate is increased by removing a portion of the substrate to create a gap that is proximate to the thermal-tuning mechanism and the wavelength-sensitive optical component. Furthermore, the optical device includes a binder material mechanically coupled to the substrate and proximate to the gap, thereby maintaining a mechanical strength of the optical device.