Optical modulators are used with superconductors which work properly only at low temperatures, generally just above absolute zero.
Optical modulators convert information carried by an electric current in an electromagnet into light.
The absorption coefficient of the material in the modulator can be manipulated by the Franz–Keldysh effect, the Quantum-confined Stark effect, excitonic absorption, changes of Fermi level, or changes of free carrier concentration.
The effect of a refractive modulator of any of the types mentioned above is to change the phase of a light beam.
The role of SLM is modification two dimensional distribution of amplitude and/or phase of an optical wave.