GB1133514A - System for operating an optical shutter - Google Patents

Abstract

1,133,514. Optical systems. UNITED STATES OF AMERICA, ARMY, SECRETARY OF. Aug.18, 1966, No.37142/66. Heading G2J. [Also in Division G1] In an optical viewing device means are provided to protect the observer against the blinding effects of intense light produced, e.g. by laser beams or atomic explosions, the means comprising an inertia free shutter in the form of a Kerr cell interposed in the optical path. As shown in Fig. 1 a periscope comprises an objective lens 12 through which light rays 11 enter and travel along an optical path to an eyepiece lens 23, the optical path including, in succession, prism 13, a bundle of optical fibers 14 to produce a time delay of about twenty nanoseconds, prism 15, lens 16, polarizer 17, Kerr cell 18 and an analyzer 22. Light rays 24 from the same source as rays 11 pass through lens 25, prism 26 and lens 27 to a photo-cell 28, the output of the photo-cell passing through a wideband amplifier 32 and rectifier 33 to an output amplifier 34, the amplifier 34 being biased by a voltage at terminal 35 to establish a threshold operating level. When the threshold is exceeded the amplifier 34 applies a voltage through wires 36, 37 across the capacitor plates 19, 21 of the Kerr cell 18, causing rotation of the plane of polarizaion of the polarized light and thereby varying the amount of light transmitted by the analyzer 22. Above a certain light intensity the light transmission is zero. The optical delay means 14 provides the necessary time for the optical shutter to be operated before the light reaches the observer's eyes. In a modification Fig. 3 (not shown) the optical delay means comprises multiple reflections from a pair of opposed mirrors. In another modification Fig. 4 (not shown) intended for protection against laser beams exhibiting a series of pulses, a pulse stretcher and an O R gate are interposed between the amplifiers 32, 34 to ensure that the shutter is kept closed for a period of time considerably longer than the duration of a single pulse.