Liquid crystal optical element, optical device, and aperture control method
The present invention is intended to provide a liquid crystal optical element that is compatible with a plurality of types of recording media and that can compensate for aberration occurring during reading. The liquid crystal optical element in accordance with the present invention includes a first substrate, a second substrate, a liquid crystal provided between the first and second substrates, an electrode pattern formed on one of the first and second substrates and having an aperture control field and an aberration compensation field, and an opposite electrode, which is formed on the other one of the first and second electrodes, for applying a voltage between the electrode pattern and itself.
1 . A liquid crystal optical element for controlling an aperture through which incident light passes, comprising:
a first substrate;
a second substrate;
a liquid crystal provided between the first and second substrates;
an electrode pattern formed on one of the first and second substrates and having an aperture control field and an aberration compensation field;
an aperture control electrode disposed in the aperture control field;
an aberration compensation electrode disposed in the aberration compensation field; and
an opposite electrode, which is formed on the other one of the first and second substrates, for applying a voltage between the electrode pattern and itself.
2 . The liquid crystal optical element according to claim 1 , wherein the aperture control electrode is used to perform both aperture control and aberration compensation.
3 . The liquid crystal optical element according to claim 2 , wherein the aperture control electrode includes a plurality of electrodes, and the plurality of electrodes are driven under substantially the same condition for the purpose of aperture control and are driven under different conditions for the purpose of aberration compensation.
4 . The liquid crystal optical element according to claim 2 , wherein the aperture control electrode change the refractive index of the liquid crystal so as to allow incident light passing through the aperture control field to diverge.
5 . The liquid crystal optical element according to claim 4 , wherein the aperture control electrode includes a plurality of electrodes and a refractive-index distribution induced by the plurality of electrodes is used to directly modulate incident light passing through the aperture control field so that the incident light passing through the aperture control field diverges.
6 . The liquid crystal optical element according to claim 2 , wherein the aperture control electrode induces an aberration in the portions of the liquid crystal corresponding to the position of the aperture control electrode so as to allow the incident light passing through the aperture control field to diverge.
7 . The liquid crystal optical element according to claim 6 , wherein the aperture control electrode induces an aberration equivalent to approximately a quarter of the wavelength of incident light.
8 . The liquid crystal optical element according to claim 2 , wherein the aperture control electrode includes a plurality of electrodes and the plurality of aperture control electrodes induce a diffraction pattern, which brings about a phase difference, in the portions of the liquid crystal corresponding to the positions of the aperture control electrodes so that the incident light passing through the aperture control field diverges.
9 . The liquid crystal optical element according to claim 8 , wherein the diffraction pattern induced by the plurality of aperture control electrodes optically serves as a Ronchi grating.
10 . The liquid crystal optical element according to claim 1 , wherein the aberration compensation field is defined inside the aperture control field.
11 . The liquid crystal optical element according to claim 1 , wherein a plurality of coma compensation electrodes is disposed in the aberration compensation field.
12 . The liquid crystal optical element according to claim 1 , wherein a plurality of spherical aberration compensation electrodes is disposed concentrically in the aberration compensation field.
13 . An optical device comprising:
a light source;
a liquid crystal optical element including a first substrate, a second substrate, a liquid crystal provided between the first and second substrates, an electrode pattern formed on one of the first and second substrates and having an aperture control field and an aberration compensation field, an aperture control electrode disposed in the aperture control field, an aberration compensation electrode disposed in the aberration compensation field, and an opposite electrode, which is formed on the other one of the first and second substrates, for applying a voltage between the electrode pattern and itself; and
an objective lens for focusing light passing through the liquid crystal optical element.
14 . The optical device according to claim 13 , wherein the liquid crystal optical element uses the aperture control field thereof to control an aperture through which incident light emanating from the light source passes, and uses the aperture control field and aberration compensation field thereof to compensate for aberration.
15 . The optical device according to claim 14 , further comprising a driver that drives the aperture control electrodes for the purpose of aperture control, and drives the aperture control electrode and the aberration compensation electrode for the purpose of aberration compensation.
16 . The optical device according to claim 15 , wherein the aperture control electrode includes a plurality of electrodes and the driver drives the plurality of electrodes under substantially the same condition for the purpose of aperture control, and drives the plurality of electrodes under different conditions for the purpose of aberration compensation.
17 . An aperture control method in an optical device comprising a first light source, a second light source, a liquid crystal optical element including a first substrate, a second substrate, a liquid crystal provided between the first and second substrates, an electrode pattern formed on one of the first and second substrates and having an aperture control field and an aberration compensation field, an aperture control electrode disposed in the aperture control field, an aberration compensation electrode disposed in the aberration compensation field, and an opposite electrode, which is formed on the other one of the first and second substrates, for applying a voltage between the electrode pattern and itself, an objective lens for focusing light passing through the liquid crystal optical element, and a driver for driving the electrode pattern, the method comprising the steps of:
lighting the first light source;
driving the aperture control electrode by using the driver, and focusing light, which emanates from the first light source and passes through the aperture control field and aberration compensation field in the liquid crystal optical element, on the first recording medium by using the objective lens;
lighting the second light source; and
driving the aperture control electrode by using the driver, and focusing only light, which emanates from the second light source and passes through the aberration compensation field in the liquid crystal optical element, on the second recording medium by using the objective lens.
18 . The aperture control method according to claim 17 , wherein at the step of focusing light on the first recording medium, light emanating from the first light source and passing through the aberration compensation field in the liquid crystal optical element is compensated for aberration.
19 . The aperture control method according to claim 18 , wherein at the step of focusing light on the first recording medium, light emanating from the first light source and passing through the aperture control field in the liquid crystal optical element is compensated for aberration.
20 . The aperture control method according to claim 19 , wherein the aperture control electrode includes a plurality of electrodes, and at the step of focusing light on the first recording medium, the driver drives the plurality of electrodes under different conditions and at the step of focusing light on the second recording medium, the driver drives the plurality of electrodes under substantially the same condition.