Diffractive optical element and optical head using the same

An optical head comprising

• a first light source emitting light with a first wavelength λ1 satisfying the relationship:
• 0.35 μm≦λ1≦0.45 μm,
• a second light source emitting light with a second wavelength λ2 satisfying the relationship:
• 0.6 μm≦λ2≦0.7 μm,
• an objective lens for converging light with the first wavelength λ1 and light with the second wavelength λ2 respectively onto a first information recording medium having a first transparent protective layer or a second information recording medium having a second transparent protective layer that is thicker than the first transparent protective layer,
• a photo-detector for detecting light from the first and second information recording media, and
• the diffractive optical element according to in claim 1, which is disposed in a common light path of light with both wavelengths between the light source and the objective lens, wherein
• when the light with the first wavelength λ1 is incident on the diffractive optical element, the diffractive optical element emits substantially zero-order diffracted light and the zero-order diffracted light is converged onto the first information recording medium by the objective lens, and
• when the light with the second wavelength λ2 is incident on the diffractive optical element, the diffractive optical element emits substantially first-order diffracted light and the first-order diffracted light is converged onto the second information recording medium by the objective lens.

An optical head comprising

• a first light source emitting light with a first wavelength λ1 satisfying the relationship:
• 0.35 μm≦λ1≦0.45 μm,
• a second light source emitting light with a second wavelength λ2 satisfying the relationship:
• 0.6 μm≦λ2≦0.7 μm,
• an objective lens for converging the light with the first wavelength λ1 and the light with the second wavelength λ2 respectively onto a first information recording medium having a first transparent protective layer or a second information recording medium having a second transparent protective layer that is thicker than the first transparent protective layer,
• a photo-detector for detecting light from the first and second information recording media, and
• the diffractive optical element according to claim 1, which is disposed in a common light path of light with both wavelengths between the objective lens and the information recording media, wherein,
• when the light with the first wavelength λ1 emitted from the objective lens is incident on the diffractive optical element, the diffractive optical element emits substantially zero-order diffracted light and the zero-order diffracted light is converged onto the first information recording medium, and
• when the light with the second wavelength λ2 emitted from the objective lens is incident on the diffractive optical element, the diffractive optical element emits substantially first-order diffracted light and the first-order diffracted light is converged onto the second information recording medium.

An optical head comprising

• a first light source emitting light with a first wavelength λ1 satisfying the relationship:
• 0.35 μm≦λ1≦0.45 μm,
• a second light source emitting light with a second wavelength λ2 satisfying the relationship:
• 0.6 μm≦λ2≦0.7 μm,
• an objective lens comprising first and second lenses for converging the light with a first wavelength λ1 and the light with a second wavelength λ2 respectively onto a first information recording medium having a first transparent protective layer or a second information recording medium having a second transparent protective layer that is thicker than the first transparent protective layer,
• a photo-detector for detecting light from the first and second information recording media, and
• the diffractive optical element according to claim 1, which is disposed in a common optical path between the first lens and the second lens, wherein
• when the light with the first wavelength λ1 emitted from the first lens is incident on the diffractive optical element, the diffractive optical element emits substantially zero-order diffracted light and the zero-order diffracted light is converged onto the first information recording medium by the second lens, and
• when the light with the second wavelength λ2 emitted from the first lens is incident on the diffractive optical element, the diffractive optical element emits substantially first-order diffracted light and the first-order diffracted light is converged onto the second information recording medium by the second lens.

An optical head comprising

• a first light source emitting light with a first wavelength λ1 satisfying the relationship:
• 0.35 μm≦λ1≦0.45 μm,
• a second light source emitting light with a second wavelength λ2 satisfying the relationship:
• 0.6 μm≦λ2≦0.7 μm,
• an objective lens for converging the light with a first wavelength λ1 and the light with a second wavelength λ2 respectively onto a first information recording medium or a second information recording medium,
• a photo-detector for detecting light from the first and second information recording media, and
• a diffractive optical element according to claim 1, which is disposed in a common light path of the light with both wavelengths between the light sources and the objective lens, wherein
• when the light with the first wavelength λ1 is incident on the diffractive optical element, the diffractive optical element emits substantially zero-order diffracted light and the zero-order diffracted light is converged onto the first information recording medium by the objective lens, and
• when the light with the second wavelength λ2 is incident on the diffractive optical element, the diffractive optical element emits substantially first-order diffracted light, and the optical axis of the first-order diffracted light is allowed to coincide substantially with the optical axis of the light with a first wavelength λ1 and thereafter converged onto the second information recording medium by the objective lens.