Reminder
We have seen that micro-machining makes the manufacturing of miniature mobile structure suitable to optical applications possible. Very small movements, for instance of a quarter wavelength in an interferometer, can make an on/off switching or create modulation effects more important than in conventional electronic or electro-optical devices. Likewise, we saw that micro mirrors gratings can be the basis for display systems or optical routers.
At the same time, the miniature optical devices have to meet a certain number of dimensional and structural constraints that can be more important than those weighting on other Microsystems.
Exemple :
Surface roughness determines mirror reflectivity.
Mechanical constraints on membrane create distortions in reflected images.
Integrated waveguides in optical Microsystems must have reproductive refractive index and optical losses.
Actuators, which can be electrostatic, piezoelectric or thermo-mechanical, must have an actuation voltage and a weak energy dissipation while ensuring a reproductive performance on a large range of performance cycles.
So, it's really important to correctly choose the materials and manufacturing techniques.