A device whose optical transmission properties (e.g. refractive index and polarizing properties) can be varied by an externally applied field or by some other external influence. Electric, magnetic, and surface acoustic wave techniques are all used for this purpose. By these means, light may be deflected away from a detector, thus switching the beam. LCD shutters are also used. The light that is processed in this way often originates in a laser source. Optical switches can be used, for example, as logic elements.