| 摘要 |
<p>THE In an optical playback apparatus: means for directing a reading beam along a first optical path extending between a source of coherent light and a storage track; means disposed in a first optical path for converging the reading beam to an intermediate light spot; and objective lens, included in said first optical path, for focusing the light energy emanating from said intermediate spot into a reading spot on said storage track, a beam-splitter, also included in the first optical path, for establishing a second optical path for light reflected from the track and for relaying a reflected image of the reading spot into the second path; a pair of spaced apart orthogonally disposed cylinder lenses of substantially identical focal lengths positioned along said second path and comprising, in conjunction with said light converging means, first and second telescopes of forming respective first and second astigmatic images of said reading spot along said second path, said images being spaced apart a distance substantially equal to the separation of said cylinder lenses, and the spatial positions of said astigmatic images of said reading spot along said second path, and the spatial positions of said astigmatic images being effectively displaceable along the second path distances proportional to a misregistration between the track and the reading plane; photoreceptor means for developing an error signal indicative of the sense and extent of such a departure from the optimum focusing condition; and means, responsive to the error signal, for effecting a relative displacement between the objective lens and the track to re-establish said optimum focusing condition.</p> |
