Abstract: There is described a signalling device having a plurality of electro-optic elements and a lens system which is operable to receive a plurality of incoming free-space light beams from respective different light sources and direct the received light beams to respective ones of the electro-optic elements. The layout and/or shape of the electro-optic elements in the signalling device is adapted in accordance with a predetermined distribution of light sources. In this way, the number of electro-optic elements can be reduced. In an alternative embodiment, there is provided a signalling device having an electro-optic device, a plurality of lens systems having respective different fields of view, and a plurality of reflecting surfaces. Each reflecting surface is associated with a corresponding one of the plurality of lens systems, and the associated reflecting surface and lens system pairs are arranged so that the electro-optic device is provided in common to the plurality of lens systems.

Abstract: An optical communications system is provided comprising first and second signalling devices in which a duplex communications link between the signalling devices can be established. The first signalling device includes a retro-reflector and the second signalling device includes at least one light source for directing light towards the retro-reflector. Half-duplex embodiments and full-duplex embodiments are described. A wave division multiplex retro-reflecting communication system is also described.

Abstract: An optical instrument, such as a microscope or a camera, is provided for forming a viewable image of an object. The optical instrument comprises an objective lens for forming the viewable image at an image plane, an eye sensor for sensing the direction of gaze of a user viewing the viewable image and means for controlling a controllable function of the optical instrument in dependence upon the sensed direction of gaze. The eye sensor comprises a sensor lens for focusing light reflected from the retina of the user, an imaging transducer located at a plane which is conjugate to the image plane with respect to the sensor lens, for generating an electrical image sign of a portion of the user's retina, a memory for storing retinal image information of the user and circuitry for comparing the retinal image signal generated by the imaging transducer with the stored retinal image information to generate gaze information indicative of the direction of gaze of the user.