JP2014153598A - Variable focus optical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a variable focus optical element capable of improving degree of freedom of optical design.SOLUTION: A variable focus optical element includes: a lens portion that reserves a dispersion medium and a dispersoid that is dispersed in the dispersion medium and has a different refraction factor from the dispersion medium in a region including a space between a first optical surface and a second optical surface; a container that is disposed around the lens portion and is connected to the lens portion via a transmission film that transmits the dispersion medium and does not transmit the dispersoid; and a mechanism for moving the dispersion medium between the container and the lens portion.

Description

  The present invention relates to a variable focus optical element, an image forming optical system used in a camera for forming a subject on a photoreceptor surface, and an image for optically scanning the surface of a photosensitive drum to form image information on the surface. It is suitable for a forming optical system.

  In an actual optical system, a method of changing the lens surface interval has been adopted to change the focal length. It is not sufficient to change the curvature of the lens surface in terms of accuracy, and since the refractive index of the lens is determined by the glass material, it is not easy to change. This is because it is simple and highly accurate. Recently, however, many optical systems using variable focus optical elements by changing the curvature of the lens surface and the refractive index of the lens have been proposed.

  As an example of changing the curvature of a lens surface, in a camera lens module for a mobile phone developed by Varioptic, a voltage is applied to a liquid lens to change the curvature of the surface (Non-Patent Document 1). Further, many methods for changing the curvature of the lens surface by applying a mechanical force to the lens have been disclosed (Patent Document 1). Examples of changing the refractive index of a lens include a method of changing the refractive index of all lenses by moving nanoparticles in a liquid by electrophoresis (Patent Document 2), and refracting in stages by moving liquid between lenses. A method of changing the rate (Patent Document 3) is disclosed.

JP-A-10-115809 JP 2006-285182 A JP 07-306360 A “Technical Information”, [online], Varioptic, [searched June 30, 2009] Internet <URL: http: // www. varioptic. com / en / products / products-liquid-lens. php>

  Since the focal length of the actual optical system depends on the curvature of the lens surface, the lens surface interval, and the lens refractive index, at least one of these three parameters must be changed in order to change the focal length. In general, the focal length of the actual optical system is changed by changing the distance between the lens surfaces in terms of the ease and accuracy of the drive mechanism. However, in an optical system that changes the focal length only by the lens surface interval, the change in the overall lens length is extremely large in zoom lenses that require a large change in focal length, making it difficult to make compact, etc. There is a problem that it is scarce.

  An object of the present invention is to provide a variable focus optical element capable of improving the degree of freedom in optical design.

  In order to achieve the above object, a variable focus optical element according to the present invention includes a dispersion medium, a dispersion medium dispersed in the dispersion medium, and a dispersion medium dispersed between the first optical surface and the second optical surface. Is a lens unit that stores dispersoids having different refractive indexes, and a container that is disposed on the outer periphery of the lens unit and connected to the lens unit through a permeable film that transmits the dispersion medium and does not transmit the dispersoid. And a mechanism for moving the dispersion medium between the container and the lens unit.

  In addition, another variable focus optical element according to the present invention is dispersed in the first dispersion medium and the first dispersion medium in a region including between the first optical surface and the second optical surface. A first lens unit that stores a first dispersoid having a refractive index different from that of the first dispersion medium, a region including a space between the third optical surface and the fourth optical surface, the second dispersion medium, A second lens part that is dispersed in a second dispersion medium and stores a second dispersoid having a refractive index different from that of the second dispersion medium; and a second lens part that is disposed on an outer periphery of the first lens part. A first container connected to the first lens part through a first permeable membrane that passes through the dispersion medium and does not pass through the first dispersoid, and is disposed on the outer periphery of the second lens part, A second container connected to the second lens portion through a second permeable membrane that passes through the second dispersion medium and does not pass through the second dispersoid; and the first container. A mechanism for moving the first dispersion medium and the second dispersion medium in conjunction with each other between the second lens section and the second lens section; and It is characterized by providing.

  ADVANTAGE OF THE INVENTION According to this invention, the variable focus optical element which can improve the freedom degree of optical design can be provided.

It is sectional drawing containing the optical axis of the variable focus optical element which concerns on the 1st Embodiment of this invention. It is the figure which looked at the variable focus optical element which concerns on 1st Embodiment from the optical axis direction. It is the graph which showed the focal length change of the variable focus optical element concerning a 1st embodiment. It is sectional drawing containing the optical axis of the variable focus optical element which concerns on the 2nd Embodiment of this invention. It is the graph which showed the focal distance change of the variable focus optical element which concerns on 2nd Embodiment. It is sectional drawing containing the optical axis of the variable focus optical element which concerns on the 3rd Embodiment of this invention. It is sectional drawing containing the optical axis of the variable focus optical element which concerns on the 4th Embodiment of this invention. It is the graph which showed the focal distance change of the variable focus optical element which concerns on 4th Embodiment.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

<< First Embodiment >>
1 and 2 are diagrams of a variable focus optical element according to the first embodiment of the present invention. As shown in FIG. 1, the variable focus optical element of the present embodiment is an optical element in which a dispersoid 1 as particles is dispersed in a dispersion medium 2. Here, the particles have a size of about the wavelength used in the optical system. The dispersoid 1 is a nanoparticle formed of silica, alumina, titanium oxide or the like and floats, and is different from the refractive index of the dispersion medium 2 (water or the like). In general, if the difference in refractive index between the dispersoid 1 and the dispersion medium 2 is small, the floatability of the dispersoid 1 becomes high.

  In the present embodiment, the lens portion is formed by the transparent container shown in 3, and the radius of curvature of the lens surface of the lens portion 3 is determined by the wall surface of the transparent container 3, and the surface shape of the lens surface does not change. Here, the term “transparent” refers to a state where the wavelength used in the optical system is sufficiently transmitted at a level required by the optical system.

  Inside the lens barrel indicated by 5 is a container indicated by 6 and filled with the dispersion medium 2. FIG. 2 is a view of the lens unit 3 in a cross section that crosses the container 6 and is perpendicular to the optical axis. The container 6 is connected to the lens unit 3 through a permeable membrane indicated by 4. In this way, the permeable membrane 4 that partitions the lens unit 3 and the container 6 that stores the dispersion medium 2 transmits only the dispersion medium 2 among the dispersoid 1 and the dispersion medium 2.

  In the present embodiment, the permeable membrane 4 is movable in the radial direction (optical axis vertical direction) when the optical axis is set in the lens unit 3. In other words, in the present embodiment, from the state of FIG. 1A, the first optical surface (the left surface of the optical element) and the second optical surface (the left surface of the optical element) are the transmission film 4 that is the wall surface of the transparent container 3 as the lens unit. It is possible to displace from between the right side surface of the optical element in the direction of the outer peripheral portion of the lens portion (upward direction in FIG. 1).

  As a result, the volume of the region occupied only by the dispersion medium in the container 6 is variable (decreases), and the amount of dispersoid between the first optical surface and the second optical surface is variable (decreases). This is because the floating space has expanded. As described above, FIGS. 1 and 2 show that the volume concentration of the dispersoid 1 with respect to the entire lens unit 3 is changed from a high state (A) to a low state (A).

  Specifically, the displacement of the permeable membrane 4 is dynamically performed by rotating a screw indicated by 7 as a mechanism for moving the dispersion medium. By such a mechanism for moving the dispersion medium, a change in volume concentration of the dispersoid between the first optical surface and the second optical surface with respect to the dispersion medium of the dispersoid causes a change in the refractive index between the first optical surface and the second optical surface. A change is caused to change the power (refractive power) of the lens unit. It is to be noted that the excess permeable membrane 4 when moved from the state (a) to the state (a) in FIG. 1 is solved by giving a slack as shown by 9 in FIG.

  In the above, the permeable membrane 4 is displaced from the state of FIG. 1A to the upper side of FIG. 1 so that the volume concentration of the dispersoid 1 with respect to the entire optical element is lower than the state of FIG. However, conversely, it can be displaced from the state of FIG. In this case, the volume concentration of the dispersoid 1 with respect to the entire optical element is made higher than the state (a).

  In the present embodiment, as described above, the transmission film 4 moves in the direction perpendicular to the optical axis, so that the entire volume of the lens unit 3 in the effective area of the optical element (between the first optical surface and the second optical surface) is reduced. The volume concentration of the dispersoid 1 changes, and the refractive index of the entire lens unit 3 changes. Here, the effective region is a portion of the lens unit 3 through which light passes.

As a method for expressing the refractive index of the entire lens unit 3 when the dispersoid is dispersed in the dispersion medium, there is an effective medium approximation theory. In particular, when the dispersoid is particles and the volume concentration of all particles relative to the entire lens unit 3 is 0.3 or less, there is Maxwell-Garnett theory expressed by the following equation, which was used for the calculation shown below.

  Here, Neff is the refractive index of the entire lens unit 3, Ne is the refractive index of the dispersion medium, Na is the refractive index of the particles, and f is the volume concentration of the particles with respect to the total volume of the lens unit 3. Here, examples of particles are given as the dispersion medium 2, but molecules, salts, ions, and the like can also be adopted. In this case, a reverse osmosis membrane, a nanofiltration membrane, a semipermeable membrane, etc. are used as the permeable membrane 4. Can be adopted.

  Table 1 shows the parameters used for the calculation, and the particles are used so that the above equation holds as the dispersoid. At this time, the refractive index of the entire lens unit 3 when the volume concentration with respect to the total volume of the lens unit 3 of dispersoid is changed by moving the transmission film 4 in a direction away from the optical axis from the edge of the lens unit 3. The change in focal length is shown in FIG. As can be seen from FIG. 3, it is possible to configure a variable focus optical element that changes the focal length with a single lens unit.

  In this embodiment, compared to the one disclosed in Patent Document 2 (Japanese Patent Laid-Open No. 2006-285182), since no voltage application is used for the displacement of the dispersoid in the direction perpendicular to the optical axis, the durability for maintaining the dispersion state There is an effect that it is easy to control the concentration. Further, in Patent Document 2, even if the density can be lowered from the reference density, it cannot be raised from the reference density, and the present embodiment can lower or raise the density from the reference density. It can be said that (displacement from the state (a) to the upper side or the lower side in FIG. 1) is excellent.

<< Second Embodiment >>
Next, a variable focus optical element according to a second embodiment of the present invention will be described with reference to FIG. As shown in FIG. 4, the variable focus optical element of the present embodiment is a lens unit in which the dispersoid 1 as particles is dispersed in the dispersion medium 2, and the curvature radius of the surface of the lens unit is set by the transparent container shown in 3. The surface shape of the lens portion does not change. Note that the dispersoid 1 and the dispersion medium 2 are the same as those shown in the first embodiment. In the lens barrel indicated by 5, there is a container indicated by 6, which is filled with the dispersion medium 2. The lens portion and the container 6 are partitioned by a permeable membrane indicated by 4, and the permeable membrane 4 transmits only the dispersion medium 2 among the dispersion medium 2 and the dispersoid 1.

In the present embodiment, the region occupied by the dispersoid 1 is set to change in the optical axis direction when the optical axis is set in the lens unit. Specifically, the transparent container 3 is movable back and forth by a screw indicated by 8. That is, the permeable membrane 4 is fixed, the volume of the dispersion medium 2 in the container 6 is variable, and the amount of the dispersion medium 2 between the first optical surface and the second optical surface is variable in FIG. It shows that the volume concentration of the entire quality lens unit 3 has changed from a high state (A) to a low state (A). In FIG. 4, as a mechanism for moving the dispersion medium, the dispersion medium 2 is moved from the space 6 by the screw 7 (the refractive index of the effective region between the first optical surface and the second optical surface changes), and at the same time, the screw 8 The distance between the surfaces is changed by moving the transparent container 3 back and forth in conjunction with each other.

  Table 2 shows the parameters used in the calculation, and particles are used so that the above equation holds as the dispersoid. At this time, the dispersion medium in the space 6 is put into the optical element, the transparent container 3 is moved, and the refractive index and the focal length of the entire lens unit when the volume concentration with respect to the total volume of the lens unit of the dispersoid is changed. The change is shown in FIG.

When the thickness of the lens unit 3 changes due to the movement of the dispersion medium, Neff depends on d because f depends on d. Here, f is the volume concentration of the dispersoid with respect to the total volume of the optical element, d is the thickness of the optical element, and Neff is the refractive index of the entire lens unit 3. Such a focal length of the lens unit 3 is expressed by the following equation.

  Here, F is the focal length of the lens unit 3, and r1 and r2 are the radii of curvature of the first and second surfaces of the lens unit, respectively. By changing both Neff and d, the focal length F changes greatly. For comparison, the case where only the dispersion medium was added without dispersing the dispersoid was also calculated. In the lens portion containing only the dispersion medium, only the surface spacing changes, so the focal length of the entire lens portion hardly changes around 30.5 mm. On the other hand, when the dispersoid is added, the focal distance of the entire lens unit changes from approximately 23.0 mm to 26.0 mm because the surface spacing and the refractive index of the entire lens unit change.

<< Third Embodiment >>
Next, a variable focus optical element according to a third embodiment of the present invention will be described with reference to FIG. As shown in FIG. 6, the varifocal optical element of the present embodiment has a lens part in which the dispersoid 1 as particles is dispersed in a dispersion medium 2 (the left side is the first lens part and the right side is the second lens part). It is. When the optical axis is set in the lens unit, the region occupied by the dispersoid is set so as to change in the optical axis direction as in the second embodiment.

  3, the radius of curvature of the surface of the lens portion is determined, and the radius of curvature of the surface of the lens portion does not change. The two variable focus optical elements are arranged side by side by a partition member 11. In the lens barrel indicated by 5, there is a container indicated by 6, which is filled with the dispersion medium 2.

  The lens portion and the container 6 are partitioned by a permeable membrane indicated by 4, and the permeable membrane 4 passes through the dispersion medium 2 and does not pass through the dispersoid 1. The partition member 11 includes a protrusion-shaped member indicated by 10, and the partition member 11 is set to move back and forth by a screw 8 as a mechanism for moving the dispersion medium. The first lens part on the left side of the partition member 11 is a positive lens, and the second lens part on the right side is a positive lens.

  The change from (a) to (b) in FIG. 6 shows how the dispersion medium in the second lens unit moves to the first lens unit in the container 6 by moving the partition member 11 from left to right. It is a thing. An arrow 12 represents the flow of the dispersion medium at that time. In the present embodiment, the left surface of the first lens unit is the first optical surface, the right surface is the second optical surface, the left surface of the second lens unit is the third optical surface, and the right surface is the fourth optical surface. It is.

<< Fourth Embodiment >>
Next, a variable focus optical element according to a fourth embodiment of the present invention will be described with reference to FIG. In the present embodiment, unlike the third embodiment, the transparent container 3 and the partition member are formed such that the first lens portion has a positive lens (convex lens) shape and the second lens portion has a negative lens (concave lens) shape. 11 (cavity) was set. One of the first lens part and the second lens part may be a positive lens (convex lens), and the other may be a negative lens (concave lens), and the first lens part may be a negative lens (concave lens). The second lens unit may be a positive lens (convex lens).

  In FIG. 7, the lens portion and the container 6 are partitioned by a permeable membrane indicated by 4, and the permeable membrane 4 passes through the dispersion medium 2 and does not pass through the dispersoid 1. The partition member 11 includes a protrusion-shaped member indicated by 10, and the partition member 11 is set to move back and forth by a screw 8 as a mechanism for moving the dispersion medium.

  The change from (a) to (b) in FIG. 6 shows how the dispersion medium in the second lens unit moves to the first lens unit in the container 6 by moving the partition member 11 from left to right. It is a thing. An arrow 12 represents the flow of the dispersion medium at that time. In the present embodiment, the left surface of the first lens unit is the first optical surface, the right surface is the second optical surface, the left surface of the second lens unit is the third optical surface, and the right surface is the fourth optical surface. It is.

  When the focal length of the first lens unit is F1, the focal length of the second lens unit is F2, the thickness of the partition member 11 is d, and the refractive index of the partition member 11 is N, the following formula is satisfied. It can be changed greatly.

d / 2N ≦ | F1 + F2 | ≦ 3d / 2N
In the present embodiment, F1 + F2 = 3.420836 mm in a state where the thickness of the first lens portion is 2.310167 mm (state (A) in FIG. 7), and at that time, d / N = 6.495849 mm. Is satisfied.

  Here, by moving the partition member 11, the dispersion medium in the second lens unit is moved into the first lens unit through the container 6 (change from the state (A) to the state (A) in FIG. 7). Thereby, the volume concentration with respect to the total volume of each lens part of the dispersoid in the 1st lens part and the 2nd lens part was changed. FIG. 8 shows changes in the overall refractive index and focal length of each lens unit and two lens units at that time. As is apparent from FIG. 8, the entire focal length of the two lens portions is changed from about 130 mm to about 1850 mm while the entire length of the two lens portions is unchanged.

  Table 3 shows parameters used in the calculation, and particles are used as the dispersoid so that the formula described in the first embodiment is satisfied.

(Modification 1)
In the above-described embodiment, the lens unit including the first optical surface and the second optical surface as the variable focus optical element is shown as constituting the lens itself, but the present invention is not limited to this. As the variable focus optical element, a partition member provided between two adjacent lenses may be configured such that a lens portion including a first optical surface and a second optical surface is provided. In this case, the rear lens surface of the front lens may be considered as the first optical surface, and the front lens surface of the rear lens may be considered as the second optical surface.

(Modification 2)
In the above-described embodiment, the dispersion medium is moved in and out as a mechanism for moving the dispersion medium between the container connected to the lens unit and the lens unit through the permeable membrane that transmits the dispersion medium and does not transmit the dispersoid (transfer). A bi-directional mechanism for putting out and putting in) was used. However, the present invention is not limited to this, and a mechanism for putting out or putting in (one direction of moving out or putting in) may be used.

(Modification 3)
In the third and fourth embodiments described above, the container 6 for storing the dispersion medium is a single container commonly connected to the first lens unit and the second lens unit. You may comprise with two containers each corresponding to 2 lens parts.

  In this case, the first container corresponding to the first lens unit is disposed on the outer periphery of the first lens unit, and passes through the first permeable membrane that transmits the first dispersion medium and does not transmit the first dispersoid. Connected to the first lens unit. The first lens unit is dispersed in the first dispersion medium and the first dispersion medium in a region including the space between the first optical surface and the second optical surface, and the first dispersion medium is refracted. Store the first dispersoid with different rates.

  The second container corresponding to the second lens unit is disposed on the outer periphery of the second lens unit, and passes through the second permeable membrane that transmits the second dispersion medium and does not transmit the second dispersoid. 2 Connected to the lens unit. The second lens unit is dispersed in the second dispersion medium and the second dispersion medium in a region including the space between the third optical surface and the fourth optical surface, and the second dispersion medium is refracted. A second dispersoid with a different rate is stored.

  And when using the mechanism which moves the 1st dispersion medium and the 2nd dispersion medium between the 1st container and the 1st lens part, and between the 2nd container and the 2nd lens part, The movement of the first dispersion medium and the movement of the second dispersion medium may be linked using various linkage mechanisms.

(Modification 4)
In the above-described embodiment, the container 6 for storing the dispersion medium stores the dispersion medium along the entire circumference in the outer periphery of the lens unit. However, the present invention is not limited to this, and the container for storing the dispersion medium. 6 may store the dispersion medium in at least a partial region of the outer peripheral portion of the lens portion.

1 .... dispersoid, 2 .... dispersion medium, 3 .... transparent container (lens part), 6 .... container (dispersion medium)

Claims (14)

In a region including between the first optical surface and the second optical surface, a lens unit for storing a dispersion medium and a dispersoid dispersed in the dispersion medium and having a refractive index different from that of the dispersion medium;
A container disposed on the outer periphery of the lens unit, connected to the lens unit through a permeable membrane that transmits the dispersion medium and does not transmit the dispersoid;
A mechanism for moving the dispersion medium between the container and the lens unit;
A variable focus optical element comprising:   2. The surface shape of the first optical surface and the second optical surface does not change even when the dispersion medium is moved between the lens unit and the container by the mechanism. Variable focus optical element.   3. The surface interval between the first optical surface and the second optical surface changes as the dispersion medium is moved between the lens unit and the container by the mechanism. The variable focus optical element as described.   4. The variable focus optical element according to claim 1, wherein the mechanism moves the dispersion medium by displacing the transmission film. 5.   4. The variable focus optical element according to claim 1, wherein the mechanism moves the dispersion medium while the permeable membrane is fixed. 5.   The variable focus optical element according to claim 1, wherein the lens unit constitutes a partition unit provided between two adjacent lenses. The first dispersion medium is dispersed in the first dispersion medium in a region including between the first optical surface and the second optical surface, and the first dispersion medium has a refractive index different from that of the first dispersion medium. A first lens unit for storing dispersoids;
The second dispersion medium is dispersed in the second dispersion medium in a region including between the third optical surface and the fourth optical surface, and the second dispersion medium has a refractive index different from that of the second dispersion medium. A second lens part for storing dispersoids;
A first container disposed on the outer periphery of the first lens unit and connected to the first lens unit through a first transmission film that passes through the first dispersion medium and does not pass through the first dispersoid. When,
A second container disposed on the outer periphery of the second lens unit and connected to the second lens unit via a second transmission film that transmits the second dispersion medium and does not transmit the second dispersoid. When,
The first dispersion medium and the second dispersion medium are interlocked between the first container and the first lens part, and between the second container and the second lens part. A moving mechanism;
A variable focus optical element comprising:   The first dispersion medium and the second dispersion medium are a common dispersion medium, and the first container and the second container are connected, and the first permeable film and the second permeable film are connected. 8. The variable focus optical element according to claim 7, wherein is a common transmission film.   The mechanism moves the first dispersion medium and the second dispersion medium between the first lens section and the first container and between the second lens section and the second container. The surface shape of the first optical surface and the second optical surface, and the surface shape of the third optical surface and the fourth optical surface are not changed even if they are used. Variable focus optical element.   The mechanism moves the first dispersion medium and the second dispersion medium between the first lens section and the first container and between the second lens section and the second container. The surface distance between the first optical surface and the second optical surface and the surface distance between the third optical surface and the fourth optical surface are changed in accordance with this. Variable focus optical element.   11. The mechanism moves the first dispersion medium and the second dispersion medium while fixing the first permeable membrane and the second permeable membrane. The variable focus optical element according to any one of the above.   12. The variable focus optical element according to claim 7, wherein one of the first lens unit and the second lens unit is a positive lens and the other is a negative lens.   Between the first lens part and the second lens part, it is transparent and displaced in the direction connecting the first optical surface and the second optical surface and in the direction connecting the third optical surface and the fourth optical surface. The variable-focus optical element according to claim 7, further comprising a partition member that performs the above-described operation. One of the first lens portion and the second lens portion is a positive lens, and the other is a negative lens. The focal length of the positive lens is F1, the focal length of the negative lens is F2, and the thickness of the partition member The variable focus optical element according to claim 13, wherein the following expression is satisfied, where d is a thickness and N is a refractive index of the partition member.
d / 2N ≦ | F1 + F2 | ≦ 3d / 2N