GB1289285A - - Google Patents

Abstract

1289285 Light deflection apparatus INTERNATIONAL BUSINESS MACHINES CORP 12 March 1970 [7 April 1969] 12040/70 Heading G2J [Also in Division B6] Light deflection apparatus in which astigmatic aberrations caused by the propagation of extraordinary rays through birefringent elements is avoided comprises a transparent medium (e.g. an oil bath) of refractive index Á enclosing two negative birefringent plates 20, 21 of ordinary refractive index Á (e.g. calcite) and two adjustable isotropic plates 22, 23 of refractive index less than Á (e.g. sodium fluoride) arranged as in Fig.3, and polarizing means (not shown) located on the side of plate 20 remote from plate 22 to direct on to plate 20 light polarized either in the ordinary or in the extraordinary sense at an angle of incidence greater than the critical angle for the extraordinary refractive index. The optic axes 24, 25 of plates 20, 21 are disposed in perpendicular planes and the polarizing means (e.g. a KDP crystal) presents a light beam 26 having a linear polarization in one of two orthogonal states. When beam 26 has a polarization in a plane corresponding to the plane of axis 24, it encounters the lower (extraordinary) refractive index of plate 20 and is thus reflected as beam 27; this encounters the higher (ordinary) refractive index p of plate 21 and passes through without refraction to be reflected at the incident face of plate 23 as beam 28. If the polarization of beam 26 is in a perpendicular plane it encounters first the higher index Á of plate 20 and then the lower index of plate 21. To ensure that both possible output beams have the same pathlength, an optical element 34 of refractive index greater than Á is inserted in the path of beam 31, and each output beam is controlled only by altering the difference between distances h 1 and h 2 (which may be adjusted so that plate 23 can be formed as a coating on plate 21). Any number of such arrangements may be assembled, n such arrangements in any one plane yielding 2<SP>n</SP> possible output beams Fig. 4 (not shown). Alternative arrangements are illustrated in Figs. 5 and 7 (not shown). A number of the above arrangements 85-88 (Fig.8) may be assembled together with a laser input 80 and a number of telescoping lenses 90-95 in order to select a character from a matrix 82 and to position it at a desired location on an output medium 84.