METHOD AND DEVICE FOR REDUCING THE FORMATION OF SPECKLE ON A PROJECTION SCREEN

摘要

The invention relates to a method and a device for reducing the speckle that is formed on a projection display when a coherent light source (1) is used. Before being projected, the light coming from the light source strikes an electrically controllable optical element (4) with a spatially inhomogeneous index of refraction and penetrates said optical element, whereby the index of refraction within the period of projection is temporally altered. This leads to the averaging out of the speckle pattern on the projection screen (6). A multimode light source is preferably used for illumination and/or the light coming from the light source is split into several spatial modes in order to increase the effect. The light from the light source is preferably split by being coupled into a multimode light-conducting fibre. Said optical element is advantageously a liquid crystal element consisting of at least two liquid crystal layers, to which a position-dependent voltage is applied in order to produce a position-dependent index of refraction and whose birefringence is compensated by the appropriate alignment of the layers in relation to each other.