公开(公告)号：DE1937842A1

公开(公告)日：1970-02-12

申请号：DE1937842

申请日：1969-07-25

Applicant: IBM

Inventor： BURNS GERALD ,  WILLIAM SMITH ARCHIBALD ,  VICTOR SHMITH WILLIAM

IPC: G02F1/05 ,  G09G3/34 ,  G11C11/22 ,  G11C11/23 ,  G11C13/04

Abstract: 1,253,168. Modulating light. INTERNATIONAL BUSINESS MACHINES CORP. 22 July, 1969 [7 Aug., 1968], No. 36770/69. Heading H4F. [Also in Division G4] An optical switch which may be used as a memory element comprises means for applying an electric field across a crystal of Gd 2 (MoO 4 ) 3 , parallel to its c-axis, the crystal being ferroelectric and showing reversible birefringence, i.e. it will remain in one of two birefringent states depending on the polarity of the last applied electric field above a threshold (switching) value, the two states being related in that the fast and slow axes are interchanged. In one embodiment the crystal is provided with transparent silver electrodes and forms a quarterwave plate so that linearly polarized input light emerges as circularly polarized, of a hand dependent on the state of the crystal. A further quarter-wave plate and an analyser will then block or pass the emergent light to a detector. An X-Y addressable array of such cells is also described and shown, and the subsequent quarter-wave plate and analyser may be formed as a unitary film over the array. In a second embodiment, one electrode is reflective, e.g. silver or copper, and the other is in the form of strips or is transparent, so that linearly polarized laser light directed by a beam splitter through the crystal is reflected back through the splitter with left or right circular polarization. An electron gun charges the reflective electrode either negatively, with a low voltage beam, or positively, by secondary emission, using a higher energy beam, and so switches the crystal. Light from the beam splitter is again passed through a quarter-wave plate and analyser. An array of such memory cells may be operated by a single electron beam and the analysed light passed to the photo-conductive layer of an electron beam scanning tube.