A scheme by which information retrieved from holograms can be made in a true sequential fashion (no buffer storage) is described. By using a reduction lens and making the Fourier transform hologram only in the transverse direction, high information recording density can be achieved in both the longitudinal and transverse direction on a long tape. A tenfold or more increase in total information density as compared with direct recording methods is possible. The feasibility of using this scheme for audio recording is demonstrated. When fully implemented, a multitrack (two or more) and multichannel (four or more) audio system is possible. The hologram tape can be economically replicated.
C. S. Ih, "Sequential information retrieval from holograms," Appl. Opt. 15, 2698-2700 (1976)