JP2012108428A - Optical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical element capable of obtaining a stable optical characteristic, even when a gravity direction and a temperature, etc. change.SOLUTION: This optical element 1 includes: a liquid lens 2 capable of changing refractive power by changing the shape of a boundary surface 7 formed by a plurality of liquid 5 and 6 having refractive indexes different from each other; an auxiliary unit 3 capable of changing the refractive index distribution on a light transmission surface; and control means 20 for controlling the liquid lens 2 and the auxiliary unit 3 so that a change in the optical characteristic of the liquid lens 2 is corrected when at least one of a gravity direction and a temperature changes.

Description

  The present invention relates to an optical element including a refractive power variable element using a liquid.

  Conventionally, a refractive power variable element (variable focus element, hereinafter simply referred to as “liquid lens”) that can change the refractive power by controlling the shape of the boundary surface of the liquid using electrowetting phenomenon is known. It has been. However, in this liquid lens, there is a possibility that the shape of the boundary surface is deformed due to the influence of gravity and the optical characteristics are deteriorated. Therefore, as a technique for suppressing the influence of gravity, Patent Document 1 discloses an optical scanning device that suppresses the distortion of the boundary surface due to gravity by matching the specific gravity of the two liquids forming the boundary surface to eliminate the difference in specific gravity between the two liquids. Is disclosed. Further, in Patent Document 2, there is usually one electrode for changing the shape of the boundary surface between two liquids, one of which is an electrolytic solution, whereas this electrode is divided into a plurality of electrodes. Discloses a variable optical system that corrects a boundary surface distorted by gravity by varying a voltage applied to the. Further, Patent Document 3 employs a liquid lens as a collimator lens, and further includes an optical scanning device in which a correction lens for correcting coma aberration generated due to distortion of the shape of the boundary surface due to gravity is installed in the unit. Disclosure.

Special table 2008-503016 gazette Special table 2008-53087 JP 2009-3053 A

  However, when the specific gravity of two liquids is made to coincide as in the optical scanning device shown in Patent Document 1, the difference in refractive index between the two liquids becomes small, and the function as a lens is likely to deteriorate. In addition, in the liquid lens, it is premised that two different liquids do not mix. However, if the specific gravity is matched, the liquid lens is easily mixed. Furthermore, for example, even if the specific gravity of the two liquids is matched in the normal temperature state, the specific gravity of the two gradually becomes different when the environment changes and becomes a low temperature state or a high temperature state.

  Moreover, in the variable optical system shown in Patent Document 2, a plurality of electrodes must be arranged, which complicates the mechanism. Furthermore, by actually installing a plurality of electrodes and correcting non-rotationally symmetric (refractive power component) on the distorted boundary surface, the spherical shape returns to some extent, but it is difficult to return it to the complete shape. Also, it is difficult to correct the aspherical surface.

  Furthermore, the correction lens in the optical scanning device shown in Patent Document 3 has only a function of correcting the influence of gravity in the vertical direction. Accordingly, in this correction lens, if the collimator lens unit is tilted, the gravity direction and the vertical direction of the correction lens do not coincide with each other, so that coma aberration cannot be corrected, and as a result, the optical characteristics of the optical scanning device deteriorate. To do. Furthermore, as described above, since the specific gravity of the two liquids gradually changes when the environment changes to a low temperature state or a high temperature state, the distortion of the shape of the boundary surface in the vertical direction also changes. However, since the non-rotationally symmetric aspherical shape of the correction lens is not affected by temperature, the optical characteristics of the optical scanning device also deteriorate as a result.

  The present invention has been made in view of such circumstances, and an object thereof is to provide an optical element capable of obtaining stable optical characteristics even when a change occurs in conditions such as the direction of gravity and temperature. To do.

  In order to solve the above-described problems, an optical element of the present invention includes a liquid lens capable of changing refractive power by changing the shape of a boundary surface formed by a plurality of liquids having different refractive indexes, and a light transmission Auxiliary unit capable of changing the refractive index distribution on the surface, and controlling the liquid lens and auxiliary unit to compensate for changes in the optical characteristics of the liquid lens when at least one of the direction of gravity and temperature changes And a control means.

  Furthermore, the optical element of the present invention has a liquid lens that can change the refractive power by changing the shape of the boundary surface formed by a plurality of liquids having different refractive indexes, and the refractive index distribution on the light transmission surface. An auxiliary unit that can be changed and a control unit that controls the liquid lens and the auxiliary unit so as to correct individual differences between the liquid lenses.

  According to the present invention, it is possible to provide an optical element capable of obtaining stable optical characteristics even when a change occurs in the direction of gravity or temperature.

It is the schematic which shows the structure of the optical element which concerns on 1st Embodiment of this invention. It is a flowchart which shows the flow of correction | amendment in the optical element of 1st Embodiment. It is the schematic which shows the structure of the optical element which concerns on 2nd Embodiment of this invention. It is the schematic which shows the structure of the optical element which concerns on 3rd Embodiment of this invention.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

(First embodiment)
First, the optical element according to the first embodiment of the present invention will be described. FIG. 1 is a schematic diagram showing the configuration of the optical element 1 according to the present embodiment and the peripheral configuration of the optical element 1. First, the optical element 1 of the present embodiment includes a liquid lens (refractive power variable element) 2 and a refractive optical element 3 adjacent to the transmission surface of the liquid lens 2 in order from the light incident side.

  The liquid lens 2 uses two types of liquids having different refractive indexes, and controls the shape of the boundary surface formed by the two types of liquids by electrowetting driving (EW driving). As shown in FIG. 1, the liquid lens 2 has a substantially cylindrical housing 4, and two types of first liquid 5 and second liquid 6 are arranged inside the housing 4 in order from the light incident side. Two layers of the liquid are arranged in the optical axis direction. As the 1st liquid 5 and the 2nd liquid 6, the substance which does not mix with each other in the interface 7 formed with both the liquids 5 and 6 and has a different refractive index is employ | adopted. For example, an electrolytic solution (refractive index: 1.4) centered on water is used as the first liquid 5, and a non-electrolytic solution such as silicon oil (refractive index: 1.6) is used as the second liquid 6. To do. The liquid lens 2 is formed in an annular shape on the inner peripheral portion of the housing 4, and has an insulating film 8 in contact with the first liquid 5 and the second liquid 6, and an electrode 9 located on the outer peripheral portion of the insulating film 8. And a power source 10 for applying a voltage between the electrode 9 and the first liquid 5 made of an electrolytic solution. In this case, the electrode 9 changes the shape (curvature radius) of the boundary surface 7 by controlling the contact angle with the boundary surface 7 by the applied voltage from the power supply 10. Furthermore, the liquid lens 2 includes a first protection plate 11 and a second protection plate 12 that seal the first liquid 5 and the second liquid 6 inside at both ends of the light incident side and the light emission side, respectively. Each of the protection plates 11 and 12 is formed of a transmissive member such as quartz glass.

  The refractive optical element 3 shares the second protective plate 12 and includes a substance 14 having a variable refractive index inside a casing 13 equivalent to the casing 4 of the liquid lens 2, and further includes the substance 14. It is an auxiliary unit provided with a third protective plate 15 equivalent to the second protective plate 12 sealed inside. In this case, as the substance 14, for example, liquid crystal can be used, but is not particularly limited as long as the refractive index changes. The refractive optical element 3 can be electrically driven by a matrix for each minute cell within the optically effective surface, and this specific portion (cell: light transmission) can be changed by changing the externally applied voltage for each cell. The refractive index distribution of the surface) can be changed.

  Further, the optical element 1 includes a control unit 20 as control means for controlling the EW drive of the liquid lens 2 and the matrix electric drive of the refractive optical element 3, and further includes a temperature sensor 21 and a gravity direction detection sensor 22 as detection means. With. The control unit 20 creates the table 23 in advance based on the temperature information (temperature) acquired by the temperature sensor 21, the gravity direction detected by the gravity direction detection sensor 22, and the voltage information (signal) applied by the power supply 10, Refer to each drive control. Further, the control unit 20 determines the rotationally symmetric refractive power component, the non-rotational symmetric refractive power component, the non-rotational symmetric aspherical component, and the rotationally symmetric aspherical component from the data indicating inappropriate optical characteristics in the table 23. The information extraction part 24 which extracts each of these is provided. The information extraction unit 24 may be installed in a control device different from the control unit 20.

  Next, the operation of the optical element 1 will be described. In the present embodiment, the optical element 1 is shared by both the liquid lens 2 and the refractive optical element 3 when a change in shape occurs on the boundary surface 7 of the liquid lens 2 due to environmental changes and the optical characteristics deteriorate. Various values indicating optical characteristics are corrected to normal values. Here, “environmental change” indicates a change in the temperature of the external environment of the liquid lens 2 and a change in the direction of gravity. In addition to this environmental change, the optical element 1 of the present embodiment can cope with the influence of individual differences (drive voltage values) of the liquid lens 2, for example. Furthermore, various numerical values indicating optical characteristics are, for example, aberration amounts such as coma aberration.

  First, the temperature change in the external environment affects the difference in specific gravity between the first liquid 5 and the second liquid 6 and also moves the focus due to the influence of the entire liquid lens 2 that is not related to the direction of gravity (a rotationally symmetric refractive power component). ) And optical characteristics such as aberration (rotationally symmetric aspheric component). Therefore, in the present embodiment, the control unit 20 acquires data indicating inappropriate optical characteristics of a rotationally symmetric refractive power component and a rotationally symmetric aspherical component in advance as correction data at each temperature, and stores the data in the table 23. Remember and refer to it as appropriate.

  In addition, the change in the gravity direction affects the shape change of the boundary surface 7 due to the difference in specific gravity between the first liquid 5 and the second liquid 6 and the temperature change. Therefore, in the present embodiment, the control unit 20 refers to the correction data at each temperature in the table 23 from the measurement data of the gravity direction and temperature, and adjusts the correction amount of the boundary surface 7 and the refraction according to the gravity direction. The correction amount of the mold optical element 3 is output and transmitted to the information extraction unit 24.

  Furthermore, the influence of the solid difference of the liquid lens 2 is as follows. Normally, in a liquid lens, if the insulating film (corresponding to the insulating film 8 of the present embodiment) has a uniform thickness, the radius of curvature is the same in any azimuth (azimuth) direction within the boundary surface, and the boundary surface Is a perfect spherical shape. Therefore, in this case, even if the applied voltage is changed, the spherical shape of the boundary surface only changes to a spherical shape having a completely different curvature radius. However, when there is variation in the film thickness of the insulating film, the contact angle θ differs in the azimuth direction within the boundary surface when a voltage is applied, and the boundary surface is non-rotationally symmetric with a different curvature radius depending on the azimuth direction. As a result, distortion occurs. In general, since the film thickness of the insulating film is almost uniform, this hardly distorts the boundary surface and affects the optical characteristics. However, the liquid lens using a special insulating film has a variation in film thickness. It is likely to occur. Therefore, in this embodiment, the control unit 20 acquires data indicating inappropriate optical characteristics due to film thickness variations in individual liquid lenses in advance as correction data for each drive voltage, and stores the data in the table 23 as appropriate. refer.

  Next, the flow of optical property correction in the optical element 1 will be described. FIG. 2 is a flowchart showing a flow of optical characteristic correction in the optical element 1 of the present embodiment. First, the control unit 20 executes EW driving in the liquid lens 2 in a room temperature state (about 23 ° C.) and in a state where the vertical direction of the optical element 1 and the direction of gravity are matched. At this time, the control unit 20 acquires data indicating the optical characteristics of the optical element 1 as reference data for the following steps in association with voltage information applied by the power supply 10 (step S101). Note that this step is not necessary if the reference data has been measured in advance or if various numerical values are considered to be normal values, such as when no aberration has occurred. Next, the control unit 20 executes EW driving in the liquid lens 2 in a state where the optical element 1 is used. At this time, the control unit 20 obtains performance data indicating the optical characteristics of the optical element 1, temperature information of the external environment acquired by the temperature sensor 21, gravity direction information detected by the gravity direction detection sensor 22, and further during EW driving. Is acquired while associating with the voltage information (step S102). Next, the control unit 20 creates and stores the table 23 including the performance data acquired in step S102 and each piece of information (measurement data) (step S103). Next, the control unit 20 compares the reference data acquired in step S101 with the table 23 to select data indicating inappropriate optical characteristics that are different from the reference data (step S104). Here, “data indicating inappropriate optical characteristics” corresponds to, for example, an aberration amount when a large amount of aberration occurs and a voltage value applied by the power supply 10 when the aberration amount occurs. Furthermore, when selecting data indicating this inappropriate optical characteristic, the control unit 20 also refers to the correction data due to the environmental change described above. Next, the information extraction unit 24 in the control unit 20 corrects the component that can be corrected by the spherical curvature of the boundary surface 7 that is the rotationally symmetric boundary surface from the data indicating the inappropriate optical characteristics selected in step S104, that is, Then, the correction amount of only the rotationally symmetric refractive power component is extracted (step S105). Here, the correction amount of the rotationally symmetric refractive power component to be extracted is preferably 10λ or more, more preferably 30λ or more as the amount of wavefront aberration. Next, the information extraction unit 24 determines the components other than the rotationally symmetric refractive power component, that is, the non-rotational symmetric refractive power component, the non-rotational symmetric power, from the data indicating the inappropriate optical characteristics selected in Step S104. Each correction amount of the aspheric component and the rotationally symmetric aspheric component is extracted (step S106). Then, the information extraction unit 24 transmits the correction amount of the rotationally symmetric refractive power component extracted in step S105 when the liquid lens 2 is EW driven, and performs control by appropriately changing the applied voltage of the power source 10. Optical characteristic correction is executed (step S107). At the same time, the information extraction unit 24 transmits the correction amount of each component extracted in step S106 to the refractive optical element 3 and controls the matrix drive, thereby executing optical characteristic correction (step S108).

  As described above, according to the optical element 1 of the present embodiment, even when the optical characteristics are deteriorated due to changes in the direction of gravity, temperature, or the like, the liquid lens 2 and the refractive optical element 3 correspond to these changes. Correction can be made by sharing, and stable optical characteristics can be obtained. In the present embodiment, the refractive optical element 3 is disposed behind the liquid lens 2 with respect to the light incident side. Therefore, for example, when the optical element 1 is used in an image pickup optical system, the refractive optical element 3 is on the image pickup element side, so that the light received by the image pickup element has good optical characteristics and is efficient. .

(Second Embodiment)
Next, an optical element according to a second embodiment of the present invention will be described. FIG. 3 is a schematic diagram illustrating the configuration of the optical element 30 according to the present embodiment and the peripheral configuration of the optical element 30. In this optical element 30, the configurations of the liquid lens 2 and the refractive optical element 3 are the same as those of the optical element 1 of the first embodiment. In addition, the optical element 30 is characterized by a table 23 included in the control unit 20 of the first embodiment, a first table 23a for correcting rotationally symmetric refractive power components, and a second table 23b for correcting other components. It is in the point to divide into and.

  As described above, in the liquid lens 2, the temperature change in the external environment affects the optical characteristics such as focus movement and aberration, while the change in the gravity direction affects the distortion of the boundary surface 7. Here, if the temperature change of the external environment can be ignored, the distortion of the boundary surface 7 due to the influence of gravity can be corrected only by the non-rotation symmetric component (refractive power component and aspheric component). Therefore, in this case, the control unit 20 may perform correction by the refractive optical element 3 with reference to only the second table 23b excluding the rotationally symmetric refractive power component. However, in the refractive optical element 3, the amount of wavefront aberration (correction amount) when a liquid crystal is used as the material that changes the refractive index as in this embodiment is generally about several tens of λ. Accordingly, when the specific gravity difference between the two liquids employed in the liquid lens 2 is large and the non-rotationally symmetric component at the boundary surface 7 is large, the desired correction amount in the refractive optical element 3 is the maximum that can be corrected. A case where the correction amount is exceeded is also conceivable. In this case, the control unit 20 may perform allocation correction that combines correction of the rotationally symmetric refractive power component of the boundary surface 7 and correction by the refractive optical element 3.

  On the other hand, the influence of the temperature change of the external environment is mainly on the focus movement (rotationally symmetric refractive power component), and the influence on optical characteristics such as aberration (rotationally symmetric aspheric component) may be ignored. Therefore, in this case, the control unit 20 may perform correction of the rotationally symmetric refractive power component by the boundary surface 7 with reference to only the first table 23a. However, when high optical characteristics are required for the optical element 30, it may be necessary to correct the rotationally symmetric aspherical component. In this case, the control part 20 should just perform the allocation correction | amendment combined with the correction | amendment by the refractive optical element 3 with reference to the 2nd table 23b simultaneously.

  Thus, according to the optical element 30 of the present embodiment, the information extraction unit is not required in the control unit 20 as in the first embodiment, so that the configuration and operation of the first embodiment are simplified, The same effect as the first embodiment is achieved.

(Third embodiment)
Next, an optical element according to a third embodiment of the present invention will be described. FIG. 4 is a schematic diagram illustrating the configuration of the optical element 40 according to the present embodiment and the peripheral configuration of the optical element 40. The optical element 40 is characterized in that the arrangement positions of the liquid lens 2 and the refractive optical element 3 in the configuration of the optical element 1 of the first embodiment are reversed with respect to the light incident side. Other configurations are the same as those of the optical element 1 of the first embodiment. Here, although the refractive optical element 3 employs liquid crystal as a substance that makes the refractive index variable, the liquid crystal generally does not have good viewing angle characteristics, and the contrast may decrease depending on the incident angle. Therefore, in the optical element 40, the refractive optical element 3 may be disposed in front of the liquid lens 2, which may occur due to a change in the incident angle of the light beam due to a change in refractive power in the liquid lens 2. A change in contrast can be avoided. In this embodiment, since the optical characteristic deterioration due to the variation in the film thickness of the insulating film 8 in the liquid lens 2 described in the first embodiment is small, the individual difference data is excluded from the table 23 in this case. It doesn't matter.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary.

For example, in the above-described embodiment, the refractive optical element 3 using liquid crystal is employed as the auxiliary unit adjacent to the liquid lens 2, but the present invention is not limited to this. The auxiliary unit can achieve the same effects as those of the above embodiment as long as the refractive index can be appropriately changed. Therefore, for example, instead of the refractive optical element 3, an electro-optic effect that changes the refractive index by applying an electric field to a dielectric crystal, particularly a Pockels effect that changes the refractive index in proportion to the strength of the electric field is used. It is also possible to adopt an auxiliary unit that has been used. In this case, it is desirable to employ a lithium niobate (LiNbO ₃ ) crystal having a relatively large electro-optic constant as the dielectric crystal.

  In the above embodiment, the liquid lens 2 has been described as using two liquids having different refractive indexes and controlling the shape of the boundary surface 7 by EW driving. However, the present invention is not limited to this. Absent. The liquid lens 2 only needs to have at least two (plural) liquids. For example, three liquids may be used, and two boundary surfaces may exist along with the three liquids. Further, the driving of the boundary surface 7 is not EW driving. For example, the boundary surface may be formed of a transparent film, and the transparent film may be mechanically driven.

DESCRIPTION OF SYMBOLS 1 Optical element 2 Liquid lens 3 Refraction type optical element 5 1st liquid 6 2nd liquid 7 Interface 20 Control part

Claims (14)

A liquid lens capable of changing the refractive power by changing the shape of the boundary surface formed by a plurality of liquids having different refractive indexes from each other;
An auxiliary unit capable of changing the refractive index distribution on the light transmitting surface;
Control means for controlling the liquid lens and the auxiliary unit so as to correct a change in optical characteristics of the liquid lens when at least one of the direction of gravity and temperature changes. element.   The optical element according to claim 1, wherein the control unit controls the liquid lens and the auxiliary unit so as to correct individual differences between the liquid lenses. A detecting means for measuring the direction of gravity or the temperature;
The control means acquires reference data indicating optical characteristics serving as a reference in advance,
Next, by changing the shape of the boundary surface in use, performance data indicating the optical characteristics in this case is acquired in association with the measurement data acquired by the detection means and a signal for driving the boundary surface And
Next, a table including the reference data and the performance data is created,
Next, referring to the table, by comparing the reference data and the performance data, select correction data that is different from the reference data in the performance data,
Next, from the correction data, a correction amount of a rotationally symmetric refractive power component and a correction amount of a component other than the rotationally symmetric refractive power component are extracted,
And based on the correction amount, the liquid lens or the auxiliary unit is driven and corrected.
The optical element according to claim 1 or 2.   The component other than the rotationally symmetric refractive power component includes at least one of a non-rotary symmetric refractive power component, a non-rotational symmetric aspherical component, or a rotationally symmetric aspherical component. Item 4. The optical element according to Item 3.   The optical element according to claim 3, wherein the liquid lens corrects the rotationally symmetric refractive power component.   5. The auxiliary unit corrects at least one of the non-rotationally symmetric power component, the non-rotationally symmetric aspheric component, or the rotation-symmetric aspheric component. An optical element according to 1. The control means includes an information extraction unit that extracts a correction amount of a rotationally symmetric refractive power component and a correction amount of a component other than the rotationally symmetric refractive power component from the correction data,
The information extraction unit transmits a correction amount of the rotationally symmetric refractive power component to the liquid lens,
The optical element according to claim 3, wherein a correction amount of a component other than the rotationally symmetric refractive power component is transmitted to the auxiliary unit. The table includes a first table including a correction amount of the rotationally symmetric refractive power component, and a second table including a correction amount of a component other than the rotationally symmetric refractive power component,
The control means transmits the correction amount of the first table to the liquid lens,
The optical element according to claim 3, wherein the correction amount of the second table is transmitted to the auxiliary unit. The detection means is a gravity direction detection sensor that measures a change in the gravity direction, or a temperature sensor that measures the temperature,
The optical element according to claim 3, wherein the measurement data is gravity direction information acquired by the gravity direction detection sensor or temperature information acquired by the temperature sensor. The control means or the information extraction unit refers to the temperature information when extracting the correction amount of the rotationally symmetric refractive power component,
10. The optical element according to claim 3, wherein the gravity direction information is referred to when a correction amount of a component other than the rotationally symmetric refractive power component is extracted.   The reference data is acquired in association with a signal for driving the boundary surface by changing the shape of the boundary surface in a normal temperature state and a state in which the direction of gravity coincides with the vertical direction of the optical element. The optical element according to claim 3.   The optical element according to claim 1, wherein the liquid lens changes a shape of the boundary surface by electrowetting driving.   The optical element according to claim 1, wherein the auxiliary unit is a refractive optical element that uses liquid crystal as a substance that changes the refractive power. A liquid lens capable of changing the refractive power by changing the shape of the boundary surface formed by a plurality of liquids having different refractive indexes from each other;
An auxiliary unit capable of changing the refractive index distribution on the light transmitting surface;
An optical element comprising: control means for controlling the liquid lens and the auxiliary unit so as to correct individual differences of the liquid lenses.

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