An optical rotator such as a Pechan rotator is arranged to rotate an image about a given axis. Light entering an input surface of the rotator is subjected to a number (e.g. five) of reflections, alternate reflections being total internal reflections and the intervening ones being mirror reflections....http://www.google.de/patents/US4948228?utm_source=gb-gplus-sharePatent US4948228 - Optical image rotators
