A transmitter for an optical device includes semi-conductor waveguides, each incorporating an electro-optic phase-shifter in the semi-conductor waveguide that is operable to change the refractive index of the waveguide to thereby introduce a phase shift in the light propagated through the waveguide. The electro-optic is connected to a phase shift controller and to a temperature measurement component, such as a PTAT circuit, that is integrated into the electronic or photonic chip carrying the waveguide. Temperature measurement by the measurement component can be multiplexed with the normal operation of the phase-shifter so that the temperature measurement function does not interfere with the phase shifting function.