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.
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Surface roughness determines mirror reflectivity.
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Mechanical constraints on membrane create distortions in reflected images.
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Integrated waveguides in optical Microsystems must have reproductive refractive index and optical losses.
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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.