Variable power optical element
View Patent ↗A variable power optical element is divided into cells which contain two liquid crystals mixed according to different proportions. The proportion of one of the liquid crystals in each cell increases on the basis of the radial distance between a central point of the optical element and said cell. An appropriate selection of the two liquid crystals results in a higher variation of the optical power between two control states of said optical element. More particularly, the optical element may consist of an ophthalmic lens which changes between a convergent lens state and a divergent lens state.
1. A variable power optical element, comprising:
a substrate;
a transparent set of cells separated and closed, juxtaposed substantially parallel to a face of the substrate; and
a controllable polarization system configured to cause changes between a homeotropic orientation and a planar orientation of nematic or cholesteric liquid crystals contained in the cells, wherein:
the set includes at least one first cell situated close to a central point of the face of the substrate and containing a nematic or cholesteric first liquid crystal, and second cells situated farther from said central point and containing a mixture of said first liquid crystal with a nematic or cholesteric second liquid crystal different from said first liquid crystal, respective proportions of said second liquid crystal in relation to said first liquid crystal in the mixture inside the second cells increasing as a function of radial distances between said second cells and the central point of the face of the substrate,
the proportions of the second liquid crystal in the second cells increase as a function of the radial distance such that said optical element has a first or a second optical power value for a light beam passing through the cell set, as a function of a command applied to the polarization system,
the polarization system comprises two transparent electrodes facing each other and each extending substantially parallel to the face of the substrate, and the cell set is situated between the two electrodes so that said electrodes produce an electric field in all of the cells when an electrical voltage is applied between said electrodes,
the first and second liquid crystals respectively have first and second dielectric anisotropies with opposite respective signs, and
the polarization system is configured to cause, in response to a variation of the electrical voltage applied between the two electrodes, a change between a planar type orientation and a homeotropic type orientation for one of the first and second liquid crystals, and simultaneously a reverse change of orientation between said types for the other of the first and second liquid crystals, in those cells containing the first liquid crystal without the second liquid crystal or the second liquid crystal without the first liquid crystal.
2. An optical element according to claim 1 , in which the at least one first cell contains the first liquid crystal without containing the second liquid crystal.
3. An optical element according to claim 1 , in which the set includes third cells situated near a perimeter edge of the substrate and containing the second liquid crystal without containing the first liquid crystal.
4. An optical element according to claim 1 , in which the first and second liquid crystals comply with the following conditions:
n o2 <( n 01 +ne2)/2 and
n o1 <( n 02 + n e2 )/2 where
n o1 and n e1 are respectively ordinary and extraordinary light-refractive indices for the first liquid crystal, and
n o2 and n e2 are respectively ordinary and extraordinary light-refractive indices for the second liquid crystal.
5. An optical element according to claim 1 , further comprising anchoring surface portions inside the cells and configured to fix an orientation of the first or second liquid crystal in those cells containing said liquid crystal without containing the other liquid crystal when the controllable polarization system is not activated.
6. An optical element according to claim 5 , in which said anchoring surface portions are adapted so that when the controllable polarization system is not activated, the orientation of the first liquid crystal is of the homeotropic type or of the planar type in those cells containing the first liquid crystal without containing the second liquid crystal and the orientation of the second liquid crystal is simultaneously the other of said types in those cells containing said second liquid crystal without the first liquid crystal.
7. An optical element according to claim 1 , in which the substrate comprises an optical lens or a portion of an optical lens.
8. An optical element according to claim 1 , in which the substrate comprises an ophthalmic lens or a portion of an ophthalmic lens.
9. An optical element according to claim 8 , in which:
the substrate comprises at least a first ophthalmic lens portion and a second ophthalmic lens portion,
the optical element is positioned on the first ophthalmic lens portion, so that said optical element has a first or a second optical power value for a first light beam passing through
the first ophthalmic lens portion, as a function of the command applied to the polarization system, and the optical element has a third optical power value for a second light beam passing through the second ophthalmic lens portion.
10. An optical element according to claim 9 , in which one of said first and second optical power values is equal to said third optical power value.