Optical detection system for simultaneously interrogating a plurality of tracks

Claim 1

In an optical playback apparatus, an optical detection system for deriving a baseband signal comprising a time-varying information signal which baseband signal had been employed to modulate a carrier that was recorded upon a record disc in the form of a single plane elongated spiral track, which track comprises a sequence of light scattering elements arranged in a predetermined distribution along said track so that said elements collectively constitute a spatial counterpart of the modulated carrier, said optical detection system comprising: means for supporting said record disc in a reading plane; means for developing an optical read beam; means, including an objective lens, disposed in the path of said beam for focusing said read beam into a reading spot of an area sufficient to interrogate, simultaneously, a plurality of said light scattering elements in at least two adjacent co-planar segments of said spiral track, said adjacent segments extending parallel in the direction of said elongated track, said reading spot further having a dimension in the longitudinal direction of said track such that such said spot is incapable of resolving said recorded carrier; drive means for displacing said record support means at a predetermined velocity relative to said reading spot to effect interrogation of said light scattering elements of said track segments by said spot so as to cause to be developed a diffraction pattern of said spot, said diffraction pattern comprising a time-varying distribution of scattered and non-scattered light, said non-scattered light being representative of said baseband signal; and light responsive means, disposed adjacent said disc and in the center of the far field of said reading spot for intercepting the non-scattered portion of said time-varying diffraction pattern and for averaging the light content of said intercepted portion to derive an electrical signal representative of the stored information in said baseband signal.