Optical element, optical head and optical information processor
A light beam reflected by an information medium is split by a diffraction optical system into first diffraction light and second diffraction light, which is not a complex conjugate wave of the first diffraction light, in a predetermined energy distribution ratio. The first diffraction light enters a first photodetector ( 195 ) of a photodetector and is used for reading out data information recorded on the information medium, while the second diffraction light enters second and third photodetectors ( 194, 195 ) and is used for obtaining a servo error signal. With this optical head device, the area of the first photodetector can be reduced, thus allowing a high-speed reproduction of a data signal. Further, the first photodetector becomes less susceptible to stray light. Moreover, the number of head amplifiers, which are needed for detecting the data signal, decreases, and the S/N ratio improves.
1. An optical element, transmitting a light beam polarized in a first direction, and bending a traveling direction of light beam polarized in a second direction that is perpendicular to the first direction and diffracting the light beam polarized in a second direction,
wherein the optical element generates a first diffraction light beam obtained by bending the traveling direction of an incident light beam polarized in the second direction and a second diffraction light beam, which is a +1-order diffraction light beam or a −1-order diffraction beam with respect to the first diffraction light beam comprising:
a first diffraction element system for transmitting the light beam polarized in the first direction and diffracting all the light beam polarized in the second direction, and
a second diffraction element for transmitting the light beam polarized in the first direction and diffracting the light beam polarized in the second direction at a predetermined efficiency,
wherein the first diffraction element comprises a first light-transmitting material and a second light-transmitting material,
a refractive index of the light-transmitting material and a refractive index of the second light-transmitting material are equal for the light beam polarized in the first direction and different for the light beam polarized in the second direction,
an interface between the first light-transmitting material and the second light-transmitting material has a sawtooth groove shape,
the second diffraction element comprises a third light-transmitting material and a fourth light-transmitting material,
a refractive index of the third light-transmitting material and a refractive index of the fourth light-transmitting material are equal for the light beam polarized in the first direction and different for the light beam polarized in the second direction,
an interface between the third light-transmitting material and the fourth light-transmitting material has a groove shape formed of periodic protrusions and depressions, and
the first diffraction element and the second diffraction element are fixed to each other in a predetermined relative positional relationship.
2. An optical element, transmitting a light beam polarized in a first direction, and bending a traveling direction of a light beam polarized in a second direction that is perpendicular to the first direction and diffracting the light beam polarized in the second direction,
wherein the optical element generates a first diffraction light beam obtained by bending the traveling direction of an incident light beam polarized in the second direction and a second diffraction light beam, which is a +1-order diffraction light beam or a −1-order diffraction beam with respect to the first diffraction light beam comprising:
a first diffraction element for transmitting the light beam polarized in the first direction and diffracting all the light beam polarized in the second direction, and
a second diffraction element for transmitting the light beam polarized in the first direction and diffracting the light beam polarized in the second direction at a predetermined efficiency,
wherein the first diffraction element comprises a first light-transmitting material and a second light-transmitting material,
a refractive index of the first light-transmitting material and a refractive index of the second light-transmitting material are equal for the light beam polarized in the first direction and different for the light bean polarized in the second direction,
an interface between the first light-transmitting material and the second light-transmitting material has a step-like shape,
the second diffraction element comprises a third light-transmitting material and a fourth light-transmitting material,
a refractive index of the third light-transmitting material and a refractive index of the fourth light-transmitting material are equal for the light beam polarized in the first direction and different for the light beam polarized in the second direction,
an interface between the third light-transmitting material and the fourth light-transmitting material has a groove shape formed of periodic protrusion and depressions, and
the first diffraction element and the second diffraction element are fixed to each other in a predetermined relative positional relationship.
3. An optical element, transmitting a light beam polarized in a first direction, and bending a traveling direction of a light beam polarized in a second direction that is perpendicular to the first direction and diffracting the light beam polarized in the second direction,
wherein the optical element generates a first diffraction light beam obtained by bending the traveling direction of an incident light beam polarized in the second direction and a second diffraction light beam, which is a +1-order diffraction light beam or a −1-order diffraction beam with respect to the first diffraction light beam comprising:
a first-light transmitting material, a second light-transmitting material and a third light-transmitting material,
wherein the first light-transmitting material and the second light-transmitting material are adjacent to each other via a first interface,
the second light-transmitting material and the third light-transmitting material are adjacent to each other via a second interface,
a refractive index of the first light-transmitting material and a refractive index of the second light-transmitting material are equal for the light beam polarized in the first direction and different for the light beam polarized in the second direction,
a refractive index of the second light-transmitting material and a refractive index of the third light-transmitting material are equal for the light beam polarized in the first direction and different for the light beam polarized in the second direction,
the first interface has a sawtooth groove shape, and
the second interface has a groove shape formed of periodic protrusions and depressions.
4. An optical element, transmitting a light beam polarized in a first direction, and bending a traveling direction of a light beam polarized in a second direction that is perpendicular to the first direction and diffracting the light beam polarized in the second direction,
wherein the optical element generates a first diffraction light beam obtained by bending the traveling direction of an incident light beam polarized in the second direction and a second diffraction light beam, which is a +1-order diffraction light beam or a −1-order diffraction beam with respect to the first diffraction light beam comprising:
a first light-transmitting material, a second light-transmitting material and a third light-transmitting material,
wherein the first light-transmitting material and the second light-transmitting material are adjacent to each other via a first interface,
the second light-transmitting material and the third light-transmitting material are adjacent to each other via a second interface,
a refractive index of the first light-transmitting material and a refractive index of the second light-transmitting material are equal for the light beam polarized in the first direction and different for the light beam polarized in the second direction,
a refractive index of the second light-transmitting material and a refractive index of the third light-transmitting material are equal for the light beam polarized in the first direction and different for the light beam polarized in the second direction,
the first interface has a step-like shape, and
the second interface has a groove shape formed of periodic protrusions and depressions.
5. An optical element, transmitting a light beam polarized in a first direction, and bending a traveling direction of a light beam polarized in a second direction that is perpendicular to the first direction and diffracting the light beam polarized in the second direction,
wherein the optical element generates a first diffraction light beam obtained by bending the traveling direction of an incident light beam polarized in the second direction and a second diffraction light beam, which is a +1-order diffraction light beam or a −1-order diffraction beam with respect to the first diffraction light beam comprising:
a first light-transmitting material and a second light-transmitting material,
wherein the first light-transmitting material and the second light-transmitting material are adjacent to each other via an interface,
a refractive index of the first light-transmitting material and a refractive index of the second light-transmitting material are equal for the light beam polarized in the first direction and different for the light beam polarized in the second direction, and
a shape of the interface is defined by a shape function expressed by a sum of a function d 1 representing a sawtooth groove shape or a step-like shape and a function d 2 representing a groove shape formed of periodic protrusions and depressions.
6. An optical element, transmitting a light beam polarized in a first direction, and bending a traveling direction of a light beam polarized in a second direction that is perpendicular to the first direction and diffracting the light beam polarized in the second direction,
wherein the optical element generates a first diffraction light beam obtained by bending the traveling direction of an incident light beam polarized in the second direction and a second diffraction light beam, which is a +1-order diffraction light beam or a −1-order diffraction beam with respect to the first diffraction light beam comprising:
a first light-transmitting material and a second light-transmitting material,
wherein the first light-transmitting material and the second light-transmitting material are adjacent to each other via an interface,
a refractive index of the first light-transmitting material and a refractive index of the second light-transmitting material are equal for the light beam polarized in the first direction and different by Δn for the light beam polarized in the second direction, and
when λ is a wavelength of the incident light, a shape of the interface is defined by a shape function expressed by a remainder obtained by dividing by λ/Δn a sum of a function d 1 representing a sawtooth groove shape or a step-like shape and a function d 2 representing a groove shape formed of periodic protrusions and depressions.
7. The optical element according to claim 1 , comprising as one piece a wave plate for converting the light beam polarized in the first direction into a circularly polarized light beam.
8. The optical element according to claim 2 , comprising as one piece a wave plate for converting the light beam polarized in the first direction into a circularly polarized light beam.
9. The optical element according to claim 3 , comprising as one piece a wave plate for converting the light beam polarized in the first direction into a circularly polarized light beam.
10. The optical element according to claim 4 , comprising as one piece a wave plate for converting the light beam polarized in the first direction into a circularly polarized light beam.
11. The optical element according to claim 5 , comprising as one piece a wave plate for converting the light beam polarized in the first direction into a circularly polarized light beam.
12. The optical element according to claim 6 , comprising as one piece a wave plate for converting the light beam polarized in the first direction into a circularly polarized light beam.