PHASE MODULATOR SYSTEM COMPRISING A BEAM SPLITTER AND A LINEAR POLARISATION MODE PHASE MODULATOR AND METHOD FOR SEPARATING A LIGHT BEAM TRAVELLING TOWARD AND REFLECTED BACK FROM SUCH A PHASE MODULATOR.

摘要

The object of the invention is a phase modulator system (20) comprising a beam splitter and a reflection mode phase modulator (8) suitable for modulating linearly polarised light of at least one specific polarisation state while maintaining said polarisation state. The beam splitter and the phase modulator (8) are arranged along an optical path of a light beam (1, 3, 5, 7, 9, 10, 11, 12). The beam splitter is a polarisation beam splitter (2) and the phase modulator system (20) further comprises an optical rotator (6) being arranged along the optical path between the polarisation beam splitter (2) and the phase modulator (8), and rotating the polarisation state of the light beam (5, 9) by 45° in a given sense, wherein the polarisation state of the light beam (7) incident upon the phase modulator (8) corresponds to said specific polarisation state. The invention further relates to a method for separating an input light beam from a phase modulated light beam in a phase modulator system comprising a phase modulator operable in reflection mode and suitable for modulating linearly polarised light of at least one specific linear polarisation state while maintaining said specific linear polarisation state. The method comprises the steps of a) providing a light beam having a first polarisation state by making an input light beam pass through a polarisation beam splitter; b) rotating said first polarisation state of said light beam by 45° in a first sense by an optical rotator; c) reflecting said light beam by the phase modulator to obtain a phase modulated reflected light beam, wherein the polarisation state of the light beam incident upon the phase modulator corresponds to said specific polarisation state; d) rotating the polarisation state of the reflected light beam by 45° in said first sense by the optical rotator to obtain a light beam having a polarisation state orthogonal to said first polarisation state; and e) separating said light beam having said second polarisation state from the input light beam by making the light beam pass through said polarisation beam splitter.