Optical device for recording and reading on a data carrier

An optical device for recording and reading a data carrier, of the type comprising two fixed radiant-energy sources of the semiconductor laser type having a predetermined wavelength, a first beam for reading data recorded on said data carrier being emitted by the first source aforesaid and a second beam for recording data on said data carrier being emitted by the second source aforesaid, wherein recording and reading are performed by means of a recording-reading head rigidly fixed to a moving system which is displaceable with respect to the data carrier and comprising an objective for focusing the reading and recording beams respectively on predetermined zones of the data carrier, said beams being also reflected from said predetermined zones, said optical device being further provided with first optical means consituting a composite radiant energy source comprising said first and second fixed semiconductor-laser sources which are each provided with stigmantic means for making said beams parallel, said sources being linearly polarized in first and second orthogonal directions and adapted to emit beam components in said first and second emission directions which are parallel respectively to first and second axes, said beam components being passed through an optical element of refractive material having a preferential optic axis parallel to one of said directions of polarization, the incident beam emitted by one of said sources and having a direction of polarization parallel to the preferential optic axis being transmitted by said optical element in a direction parallel to said first axis without modification whilst the incident beam emitted by the other source aforesaid is totally reflected in the same direction by said optical element, said optical device being further provided with second optical means placed on said first axis and comprising a second optical element of refractive material which also has another preferential optic axis, said second optical element being intended to transmit all or part of the composite beam in a direction parallel to said first axis, the direction of polarization of the emergent composite beam being parallel to the other optic axis aforesaid, provision being made for a quarter-wave plate having the function of converting the linear polarization to circular polarization, said polarized composite beam being transmitted to said recording-reading head, and for a convergent optical system placed on a third axis, said composite beam being totally reflected in a direction parallel to said third axis by said second optical element after reflection from the data carrier, the function of the convergent optical system aforesaid being to focus the two components of said beam to two separate and distinct points of impact on an optoelectronic detection device.