a phase modulator for the modulation of the phase of circular polarised light which interacts with the phase modulator . the phase modulator has a first and a second substrate , an electrode arrangement and a liquid crystal layer with liquid crystal molecules . the first substrate is disposed adjacent to the second substrate . the liquid crystal layer is disposed between the two substrates . the first substrate has a first surface , and the second substrate has a second surface . the liquid crystal molecules situated next to the first surface are oriented substantially parallel to the first surface . the liquid crystal molecules situated next to the second surface are oriented substantially perpendicular to the second surface . an in - plane component of the liquid crystal molecule orientation can be set within an angular range of about 180 °, e . g . between − 90 ° and + 90 ° related to a specifiable central orientation .