The present invention relates to a coaxial type apparatus (1) for reading from and/or writing to holographic storage media (18) with multiple reference beams (7", 7"'). The invention further relates to a beam generator (21) and a filter (12) for use in such an apparatus (1).
According to the invention, in an apparatus (1) for reading from and/or writing to a holographic storage medium (18), with a coaxial arrangement of three or more reference beams (7", 7"') and an object beam (6) or a reconstructed object beam (26), the reference beams (7", 7"') are arranged on a circle around the object beam (6) in a Fourier plane of the apparatus (1). A beam generator (21) generates the three or more reference beams (7", 7"') from an incoming reference beam (7). A filter (12) low-pass filters the object beam (6) and rotates the polarization of the three or more reference beams (7", 7"').