Optical head and information recording apparatus

An optical head comprising:

• a semiconductor laser;
• a focusing optical system for forming spot of outgoing beams from said semiconductor laser on the surface of an information medium;
• a beam separation optical system for separating reflected beams reflected by said information medium from said outgoing beams;
• optical detectors for receiving detection beams separated by said beam separation optical system;
• and
• an optical head body for fixing said semiconductor laser, said focusing optical system, said beam separation optical system and said optical detectors;
• wherein said semiconductor laser is sealed by said focusing optical system and said optical head body;
• and
• wherein said beam separation optical system further comprises a second beam separation optical system for separating said reflected beams reflected by said information medium in the direction different from said outgoing beam comprises a diffraction grating plate equipped on at least one of the surface thereof with a second diffraction grating made df a bi-refrigerence material and polarization-rotation means for rotating a polarizing direction so that said reflected beam becomes either an extraordinary beam or an ordinary beam when said reflected beam passes through said second diffraction grating, and the convexities and concavities of said diffraction grating have the difference of their optical path lengths which is substantially equal to (N+0.05).lambda. where N is an integer and .lambda. is the wavelength of said extraordinary beam of said ordinary beam, and their widths are substantially equal to each other.

An optical information processing apparatus comprising:

• a light source;
• an information medium;
• a focusing optical system for forming spots of a main beam emitted from said light source as a main spot on the surface of said information medium;
• a separation optical system for separating reflected beams from said information medium;
• optical detectors for receiving said reflected beams;
• a diffraction grating or a holographic device for generating sub-beams emitted in directions different by a very fine angle from said main beam, and having a positive focus error or an astigmatism and a negative focus error or an astigmatism;
• pits for modulating reflected light power of said sub-beams, recorded in advance on the surface of said information medium;
• two optical detection devices for receiving said sub-beams reflected from said information medium, respectively;
• two amplitude detection circuits for detecting the magnitudes of the amplitudes modulated by said pits from light power signals outputted by said two optical detection devices;
• and
• a subtraction circuit for obtaining a focus error signal by effecting subtraction between two amplitude detection signals outputted from said amplitude detection circuits;
• wherein said amplitude detection circuits each comprises a first sample and hold circuit for holding the output signal level of said optical detection device wherein a +1 order beam or a -1 order beam exists between said pits, a second sample and hold circuit for holding the output signal level of said optical detection device when said +1 order beam or said -1 order beam exists on said pits, a division circuit for effecting division between the output signal of said first sample and hold circuit and the output signal of said second sample and hold circuit, and a gain adjustable circuit for adjusting the gains between the output signal of said first sample and hold circuit and the output signal of said second sample and hold circuit.