Optical collimator for visor of protective helmet etc. - comprises sequence of linear polariser, spherical mirror, slide and flat mirror, with reflection of mirrors controlled by surface coatings

摘要

The collimator consists of a linear polariser (8) followed along an optical axis by a spherical mirror (9) which is selectively semi-reflecting. A slide (10) and a selectively circular-polarising flat mirror (11) are located between the spherical mirror and the viewer. The flat mirror has a coating of cholesteric liquid crystal material. The spherical mirror has a semi-reflecting holographic coating which reflects light only of a specific range of frequencies corresponding to a range to which the flat mirror is sensitive. A selective mixing device may be interposed between the polariser and the spherical mirror. ADVANTAGE - Improved efficiency of light transmission, with compact construction.