Optical head

An optical head comprising:

• a first grating element and a second grating element arranged in that order in a light path between a light source and an objective lens, the light path including an outgoing light path and a return light path;
• a light path alteration member for deflecting light arranged in the light path between said light source and said first grating element, wherein light emitted from said light source is deflected by said light path alteration member and then enters said first grating element, light diffracted by said first grating element enters the second grating element, and light diffracted by said second grating element enters the objective lens and is focused on a recording medium;
• and
• a photo-detector for detecting light reflected by the optical recording medium and deflected again by said light path alteration member,
• wherein light deflected by said light path alteration member is used as incident light on said first grating element or said objective lens on the outgoing light path, and is used as incident light on said photo-detector or said second grating element on the return light path, and
• wherein the first grating element is a reflection element;
• the light path alteration member is a first transparent substrate having a first surface;
• the first grating element and said light path alteration member are arranged so that an angle defined by the optical axis of light emitted from the light source and a normal on said first surface is at least the critical angle, and an angle defined by the normal on said first surface and the optical axis of light diffracted by said first grating element to said second grating element is smaller than the critical angle;
• light emitted from said light source is reflected from said first surface and enters said first grating element;
• light reflected and diffracted by said first grating element passes said first surface and enters said second grating element;
• and wherein
• the first transparent substrate is a triangular prism having a slanted face, a bottom face and a side face;
• said slanted face is the first surface;
• the first grating element is provided on said bottom face;
• and
• light emitted from the light source enters said first transparent substrate through said side face.

An optical head comprising:

• a first grating element and a second grating element arranged in that order in a light path between a light source and an objective lens, the light path including an outgoing light path and a return light path;
• a light path alteration member for deflecting light arranged in the light path between said light source and said first grating element, the lowest point of said objective lens being lower than the highest position of light which is emitted from said light source and which is incident on said light path alteration member in a height direction from said objective lens toward an optical recording medium of the optical head, and said objective lens is positioned such that light in the outgoing light path enters said objective lens through a side thereof containing the lowest point, or in the light path between said second grating element and said objective lens, the lowest point of said objective lens being lower than the highest position of light which is emitted from said light source and which is incident on said first grating element in the height direction from said objective lens toward an optical recording medium of the optical head, and said objective lens is positioned such that light in the outgoing light path enters said objective lens through the side thereof containing the lowest point;
• and
• a photo-detector for detecting light reflected by an optical recording medium and deflected again by said light path alteration member,
• wherein light deflected by said light path alteration member is used as incident light on said first grating element or said objective lens on the outgoing light path, and is used as incident light on said photo-detector or said second grating element on the return light path.

An optical head comprising:

• a first grating element and a second grating element arranged in that order in a light path between a light source and an objective lens, the light path including an outgoing light path and a return light path;
• a light path alteration member for deflecting light arranged in the light path between said light source and said first grating element, the lowest point of said objective lens being lower than the highest position of light which is emitted from said light source and which is incident on said light path alteration member in a height direction from said objective lens toward an optical recording medium of the optical head, and the lowest point of said objective lens faces the outgoing light path, or in the light path between said second grating element and said objective lens, the lowest point of said objective lens being lower than the highest position of light which is emitted from said light source and which is incident on said first grating element in the height direction from said objective lens toward an optical recording medium of the optical head, and the lowest point of said objective lens faces the outgoing light path;
• and
• a photo-detector for detecting light reflected by an optical recording medium and deflected again by said light path alteration member,
• wherein light deflected by said light path alteration member is used as incident light on said first grating element or said objective lens on the outgoing light path, and is used as incident light on said photo-detector or said second grating element on the return light path.