Optical head with polarized beam hologram

An optical head for optically recording and reproducing information on and from a recording medium, comprising:

• light source means;
• optical means for converging a light beam emitted from said light source means on said recording medium;
• beam splitter means provided between said light source means and said optical means for branching a light beam reflected from said recording medium;
• hologram means for producing diffracted lights of different diffraction order and of different focal points in an off-axis direction symmetrically arranged relative to said light source means and for causing transmission or reflection of the light beam branched by said beam splitter means as a zero-order light and .+-. first-order diffracted lights and for polarizing the light beam so that the zero-order light of P-polarization and the .+-. first-order diffracted light of S-polarization produced due to the polarization are cross polarized with respect to each other and the zero-order light of P-polarization and the - first-order diffracted light of S-polarization produced due to the polarization are cross polarized with respect to each other;
• and
• photodetector means for receiving the zero-order light, the + first-order diffracted light and the - first-order diffracted light from said hologram means,
• said photodetector means comprising diffracted light detecting means and zero-order detecting means, and
• differential means for performing a difference operation on outputs from said diffracted light detecting means and said zero-order detecting means to obtain a differential signal to control retrieval of said information from the recording medium.

An optical head for optically recording and reproducing information on and from a recording medium, comprising:

• light source means;
• optical means for converging a light beam emitted from said light source means on said recording medium;
• beam splitter means provided between said light source means and said optical means for branching a light beam reflected from said recording medium;
• hologram means for producing diffracted lights of different diffraction order and of different focal points in an off-axis direction symmetrically arranged relative to said hologram means and for causing transmission or reflection of the light beam branched by said beam splitter means as a zero-order light and .+-. first-order diffracted lights and for polarizing the light beam so that the zero-order light of P-polarization and the + first-order diffracted light of S-polarization produced due to the polarization are cross polarized with respect to each other and the zero-order light of P-polarization and the - first-order diffracted light of S-polarization produced due to the polarization are cross polarized with respect to each other;
• said hologram means including means for providing a P-polarization to the zero-order light and an S-polarization to the + and - first order diffracted light;
• and
• photodetector means for receiving the zero-order light, the + first-order diffracted light and the - first-order diffracted light from said hologram means,
• said photodetector means comprising diffracted light detecting means and zero-order detecting means, and
• differential means for performing a difference operation on outputs from said diffracted light detecting means and said zero-order detecting means to obtain a differential signal to control retrieval of said information from the recording medium.