GB924774A - Improvements in or relating to optical devices - Google Patents

Abstract

924,774. Light guides. T. B. CLERK. (American Optical Co.). July 17, 1961, No. 25857/61. Class 97 (1). [Also in Group XXIII] An image transfer device comprises a bundle of light conducting fibres of high refractive index each provided with a cladding of lower index transparent material, the claddings at at least one end of the device being coated with a layer of light shielding material so as to prevent light from entering said end and passing through the said claddings. The device may be made by assembling side by side a group of fibres 10, Fig. 1, the high index cores 11 of which have been provided with claddings 12, for example of borosilicate glass. One end of the fibre bundle is then clamped as at 13 and is heated with a ring-like heating element 14 to a temperature at which the bundle can be drawn so as to form a tapered device which is subsequently sheared off as at 16. Opposite ends of the device so formed are then cut and/or ground to provide flat surfaces which are substantially parallel and disposed substantially normal to the central longitudinal axis of the device, the distance between the opposite ends being chosen in accordance with the desired magnification. Thereafter the claddings 12, Fig. 4, at one or both ends of the device are removed, as by etching with hydrochloric acid, so as to provide recesses and then the whole of the or each end of the device is coated with light reflective material, such as silver or aluminium. The end faces of the tapered device are then polished so as to remove the reflective material from the ends of the fibre cores and simultaneously optically finish those faces. Finally, the sides of the tapered device may be provided with an opaque coating as of metal or opaque or light absorbent glass. Reference has been directed by the Comptroller to Specification 895,368.