Disc phonograph record playback by laser generated diffraction pattern

Abstract

A laser beam is directed at the groove of a conventional disc phonograph record as it rotates, creating a reflected interference/diffraction pattern of the groove walls. The magnitude and rate of displacement of the interference/diffraction pattern is sensed and converted into an audio reproduction signal of the original phonograph recording.

What is claimed is: 
     
       1. Apparatus for the playback of conventional disc phonograph records comprising a spiral recording groove having intersecting groove walls engraved in the disc surface and where flat land separates adjacent portions of the spiral groove, comprising: a. a laser for providing a laser beam of light;   b. means for rotating a disc phonograph record to be played at the required rotational velocity;   c. means for directing said laser beam to illuminate the record groove to create an interference-diffraction pattern comprising an arc of light of variable radius which is radially displaced along a vector, above and below a middle unmodulated position, and whose maximum-to-minimum radial displacement relative to its unmodulated position is proportional to the actual groove wall displacement relative to its unmodulated position and represents the amplitude of the recorded signal, and wherein the rate of change of the radial displacement of the arc of light corresponds to the frequency of the recorded signal;   d. tracking means for maintaining said laser beam directed within the record groove as the disc phonograph record rotates;   e. means positioned to intercept the interference-diffraction pattern for detecting the displacements of the interference-diffraction pattern created by the reflected laser beam; and   f. means responsive to said detecting means for converting said displacement variations of the interference-diffraction pattern into an electrical sound reproduction of the recording.   
     
     
       2. Apparatus as in claim 1 including means for narrowing the laser beam to provide a beam width no wider than the width of the combination of the record groove and the flat land areas adjacent thereto at the intersection of the beam and the disc phonograph surface. 
     
     
       3. Apparatus as in claim 2 wherein said laser beam narrowing means comprises a convex lens situated in the path of the laser beam between said laser and the disc phonograph record. 
     
     
       4. Apparatus as in claim 3 including means for positioning said convex lens so that the focal point thereof is situated beyond the intersection of the laser beam and the record surface. 
     
     
       5. Apparatus as in claim 4 wherein said tracking means includes beam centering means responsive to light reflected from the flat land areas adjacent each side of the groove for centering the laser beam within the groove, said beam centering means being sensitive to relative imbalance in the amount of light reflected from the respective adjacent lands. 
     
     
       6. Apparatus as in claim 2 wherein said tracking means includes beam centering means responsive to light reflected from the flat land areas adjacent each side of the groove for centering the laser beam within the groove, said beam centering means being sensitive to relative imbalance in the amount of light reflected from the respective adjacent lands. 
     
     
       7. Apparatus as in claim 1 including means for converting said arc displacements to an electrical signal which is proportional to the amplitude and frequency of the recorded signal. 
     
     
       8. Apparatus as in claim 1 wherein said detecting means includes means for converting the variable radial arc displacement to light whose brightness is variable and proportional thereto. 
     
     
       9. Apparatus as in claim 8 including photo detecting means responsive to said displacement-to-brightness means for converting said light of variable brightness to an electrical signal whose amplitude is proportional to the displacement of the light arc. 
     
     
       10. Apparatus as in claim 9 wherein said displacement-to-brightness means comprises end-to-end wedge-shaped fiber-optical bundles with the ends thereof located at the unmodulated position of the interference-diffraction pattern and wherein for each wedge the number of fibers therein increases proportionally in number with the displacement distance from the unmodulated position. 
     
     
       11. Apparatus as in claim 1 including means for preventing interfering cross talk from the diffraction patterns of the two groove walls forming the recording groove. 
     
     
       12. Sound reproduction apparatus for the playback of conventional disc phonograph records having grooves containing sound signal information recorded therein comprising: means for directing a laser beam along and within the grooves of a rotating disc phonograph record to create a dynamic interference-diffraction light pattern comprising an arc of light of variable radius which is radially displaced along a vector, above and below a middle unmodulated position, and whose maximum-to-minimum radial displacement relative to its unmodulated position is proportional to the actual groove wall displacement relative to its unmodulated position and represents the amplitude of the recorded signal, and wherein the rate of change of the radial displacement of the arc of light corresponds to the frequency of the recorded signal; and   means for detecting said radial displacements of said dynamic interference-diffraction light pattern and converting the same to an electrical sound signal reproduction of the original disc phonograph recording. .Iadd. 13. Apparatus for the playback of conventional disc phonograph records comprising a spiral recording groove having intersecting groove walls engraved in the disc surface and where flat land separates adjacent portions of the spiral groove, comprising:   (a) a laser for providing a laser beam of light;   (b) means for rotating a disc phonograph record to be played at the required rotational velocity;   (c) means for directing said laser beam to illuminate the record groove to create an interference-diffraction pattern comprising an arc of light defined by the groove wall which is positionally related to a vector, above and below a middle unmodulated position, and whose maximum-to-minimum positional variation relative to its unmodulated position is proportional to the actual groove wall displacement relative to its unmodulated position and represents the amplitude of the recorded signal, and wherein the rate of change of the positional variation of the arc of light corresponds to the frequency of the recorded signal;   (d) tracking means for maintaining said laser beam directed within the record groove as the disc phonograph record rotates;   (e) means positioned to intercept the interference-diffraction pattern for detecting the positional variations in the interference-diffraction pattern created by the reflected laser beam; and,   (f) means responsive to said detecting means for converting said positional variations of the interference-diffraction pattern into an electrical   
     
     
        sound reproduction of the recording. .Iaddend..Iadd. 14.  Sound reproduction apparatus for the playback of conventional disc phonograph records having grooves containing sound signal information recorded therein comprising: means for directing a laser beam along and within the grooves of a rotating disc phonograph record to create a dynamic interference-diffraction light pattern comprising an arc of light defined by the groove wall which is positionally related to a vector, above and below a middle unmodulated position, and whose maximum-to-minimum positional variations relative to its unmodulated position is proportional to the actual groove wall displacement relative to its unmodulated position and represents the amplitude of the recorded signal, and wherein the rate of change of the positional variations of the arc of light corresponds to the frequency of the recorded signal; and   means for detecting positional variations of said dynamic interference-diffraction pattern and converting same to an electrical sound signal reproduction of the original disc phonograph recording. .Iaddend.