Abstract: An optical intensity modulator is disclosed which comprises a waveguide containing a core adjacent to at least one cladding layer and exhibits a refractive index n(core) different from the refractive index n(cl) or the cladding layer, where the waveguide is a bent channel waveguide and the intensity modulator contains a heater or cooler for altering the temperature at or near the bend. The core and the cladding layer exhibit different thermo-optic coefficients at the bend such that the contrast between n(core) and n(cl) can be changed by altering the temperature. The optical intensity modulator is more compact in size and more efficient with regard to energy consumption. The invention also pertains to thermo-optic switches and thermo-optic cascaded switches comprising the optical intensity modulator and to the use of the optical intensity modulator as a tunable attenuator.