Optical player with half wave plate

Claim 1

A system for reading out a record by point optical scanning of a diffractive track carried by said record, and along which information items are transcribed, said system comprising: means causing said record to displace in front of a read-out head, said read-out head comprising a source furnishing monochromatic radiation, and optical means focussing said monochromatic radiation for forming a read-out beam; said read-out beam having a point of convergence positioned close to the optical axis of said optical means and in immediate proximity of the element of said diffractive track being read at the time; said read-out head further comrpising at least two photodetector elements picking up the radiation emerging from the illuminated portion of said diffractive track; said system further comprising deflection means for deflecting said read-out beam positioned between said source and said record for causing said point of convergence to displace transversely in relation to the longitudinal axis of said diffractive track; a half-wave plate intercepting one of the halves of said read-out beam; said halves being generated by said half wave plate, and obtained by partitioning said read-out beam with a plane containing said optical axis and perpendicular to the direction of displacement of said point of convergence; an electrical generator being connected to said deflection means for imparting to said point of convergence an oscillatory motion; synchronous detector means being connected to said electrical generator and to said photodetector elements for supplying signals representing positional errors on the part of said point of convergence, in relation to said longitudinal axis.

Claim 2

A system for reading out a record by point optical scanning of a diffractive track carried by said record, and along which information items are transcribed, said system comprising: means causing said record to displace in front of a read-out head, said read-out head comprising a source furnishing monochromatic radiation, and optical means focussing said monochromatic radiation for forming a read-out beam; said read-out beam having a point of convergence positioned close to the optical axis of said optical means and in immediate proximity of the element of said diffractive track being read at the time; said read-out head further comrpising at least two photodetector elements picking up the radiation emerging from the illuminated portion of said diffractive track; said system further comprising deflection means for deflecting said read-out beam positioned between said source and said record for causing said point of convergence to displace transversely in relation to the longitudinal axis of said diffractive track; a half-wave plate intercepting one of the halves of said read-out beam; said halves being generated by said half wave plate, and obtained by partitioning said read-out beam with a plane containing said optical axis and perpendicular to the direction of displacement of said point of convergence; an electrical generator being connected to said deflection means for imparting to said point of convergence an oscillatory motion; synchronous detector means being connected to said electrical generator and to said photodetector elements for supplying signals representing positional errors on the part of said point of convergence, in relation to said longitudinal axis.