Two-wavelength optical pickup device with step-like diffraction element
View Patent ↗An optical pickup device is equipped with a first light source that emits first light, a second light source that emits second light having a wavelength different from a wavelength of the first light, and a diffraction element that deflects the first light or the second light to match optical axes of the lights. The diffraction element is a step-like diffraction element in which one of an incident face and an emitting face thereof has a step-like grating face. A step difference of the step-like grating face is set to have a measurement that generates a phase difference of one wavelength of one of the first light and the second light, and the number of steps of the step-like grating face is set to maximize a (+) first order diffraction efficiency or a (−) first order diffraction efficiency for the other light.
1. An optical pickup device comprising:
a first light source that emits first light;
a second light source that emits second light with a wavelength different from a wavelength of the first light; and
a step-like diffraction element that deflects one of the first light and the second light to match optical axes of the first light and the second light,
the step-like diffraction element defining a light incident face and a light emitting face, one of the incident face and the emitting face having multiple sets of step-like grating faces,
wherein, when a wavelength λ 1 of the first light is longer than a wavelength λ 2 of the second light, a step difference between adjacent ones of the step-like grating faces has a measurement that generates a phase difference corresponding to one wavelength for the first light, and
the number of steps of each of the multiple sets of step like grating faces is set at an integer that is closest to a value α that satisfies an expression of λ 2/λ1=α/(α+1).
2. An optical pickup device according to claim 1 , wherein, when the wavelength λ 1 of the first light is about 785 nm, and the wavelength λ 2 of the second light is about 650 nm, the number of steps of each of the multiple sets of step-like grating faces is five.
3. An optical pickup device according to claim 1 , wherein, when the wavelength λ 1 of the first light is about 635 nm, and the wavelength λ 2 of the second light is about 470 nm, the number of steps of each of the multiple sets of step-like grating faces is three.
4. An optical pickup device comprising:
a first light source that emits first light;
a second light source that emits second light having a wavelength different from a wavelength of the first light; and
a step-like diffraction element that deflects one of the first light and the second light to match optical axes of the first light and the second light,
the step-like diffraction element defining a light incident face and a light emitting face, one of the light incident face and the light emitting face having multiple sets of step-like grating faces,
wherein, when a wavelength λ 1 of the first light is longer than a wavelength λ 2 of the second light, a step difference between adjacent ones of the step-like grating faces of each of the multiple sets of step-like grating faces has a measurement that generates a phase difference corresponding to one wavelength for the second light, and
the number of steps of each of the multiple sets of step like grating faces is set at a value in which one is added to an integer that is closest to a value α that satisfies an expression of λ 2/λ1=α/(α+1).
5. An optical pickup device according to claim 4 , wherein, when the wavelength λ 1 of the first light is about 785 nm, and the wavelength λ 2 of the second light is about 635 nm, the number of steps of each of the multiple sets of step-like grating faces is five.
6. An optical pickup device according to claim 4 , wherein, when the wavelength λ 1 of the first light is about 635 nm, and the wavelength λ 2 of the second light is about 470 nm, the number of steps of each of the multiple sets of step-like grating faces is four.
7. A method for designing an optical pickup device comprising a first light source that emits first light, a second light source that emits second light having a wavelength different from a wavelength of the first light, and a step-like diffraction element that deflects one of the first light and the second light to match optical axes of the first light and the second light, the step like diffraction element defining a light incident face and a light emitting face, one of the light incident face and the light emitting face having multiple sets of step-like grating faces, the method comprising the steps of:
when a wavelength λ 1 of the first light is longer than a wavelength λ 2 of the second light, setting a step difference between adjacent ones of the step-like grating faces to have a measurement that generates a phase difference corresponding to one wavelength for the first light; and
setting the number of steps of each of the multiple sets of step -like grating faces to be at an integer that is closest to a value α that satisfies an expression of λ2/λ1=α/(α+1).
8. A method for designing an optical pickup device comprising a first light source that emits first light, a second light source that emits second light having a wavelength different from a wavelength of the first light, and a step-like diffraction element that deflects one of the first light and the second light to match optical axes of the first light and the second light, the step-like diffraction element defining a light incident face and a light emitting face, one of the light incident face and the light emitting face having multiple sets of step-like grating faces, the method comprising the steps of:
when a wavelength λ 1 of the first light is longer than a wavelength λ 2 of the second light, setting a step difference between adjacent ones of the step-like grating faces of each of the multiple sets of step-like grating faces to have a measurement that generates a phase difference corresponding to one wavelength for the second light; and
setting the number of steps of each of the multiple sets of step-like grating faces to be at a value in which one is added to an integer that is closest to a value α that satisfies an expression of λ 2/λ1=α/(α+1).