GB1347511A - Apparatus for spatial and time modulation of a light beam - Google Patents

Abstract

1347511 Modulating light INTERNATIONAL BUSINESS MACHINES CORP 29 April 1971 [2 May 1970] 12122/71 Heading H4F The intensity of a plane polarized light beam 1 is modulated across the beam by passing it through one or more electro-optic KDP crystals 40a, 40b, to which an electric field is applied in such a manner that the relative phase of the E and O rays is varied across the beam, and then through an analyser 20. As shown, triangular electrode pairs 44, 45, and 54, 55 are energized individually or together to provide intensity graduation along a horizontal, vertical or diagonal line, the potential from source 52 being such as to produce a relative phase difference between the E and O rays varying from 0-180 degrees across each crystal. A further electro-optic cell S (3-5) may be activated to switch the plane of polarization of beam 1 through 90 degrees and so reverse the direction of the intensity gradation. Alternatively the voltage source 9 may be variable whereby the averaged beam intensity may be varied in addition to the spatial modulation. In a further embodiment, Fig. 9 (not shown), an additional analyser is placed between cell S and crystal 40a and the source 9 is variable to alter the average beam intensity. Additional pairs of electrodes complementary to pairs 44, 45 and 54, 55 are provided on crystals 40a, 40b for providing reversed intensity gradients. The source 52 is also shown as being variable for further modulation of the beam. In a modification of the system, Fig. 3 (not shown), operating on the longitudinal electro-optic effect, transparent electrodes are disposed adjacent each of the light transmitting surfaces of the electro-optic crystal but at an acute angle thereto, whereby the spatially varying electric field across the crystal gives a varying degree of birefringence. The system is said to be useful for spot shaping in phototracing machines, e.g. for integrated circuits, to compensate for uneven exposure normally obtained at the ends of lines and at angles with a uniform spot.