- single axis : mirror can be tilted with single axis freedom
- two axis : mirror can be tilted with two axis freedom
since the mirror has to be tilted precisely, piezoelectric actuators are usually used. Piezoelectric actuators uses "inverse piezo effect" i.e, when exposed to an electric potential, piezoelectric materials change shape. The precise motion that results when an electric potential is applied to a piezoelectric material is used for tilting the mirror. fast steering mirrors can be used for laser beam steering mechanism.