JP6335111B2 - Variable focus lens - Google Patents

Description

  The present invention relates to a variable focus lens, and more particularly, to a variable focus lens using a single crystal material having an electro-optic effect, the focal length of which can be changed.

  Optical parts such as optical lenses and prisms are used in optical equipment such as cameras, microscopes, and telescopes, electrophotographic recording devices such as printers and copiers, optical recording devices such as DVDs, optical devices for communication, and industrial use. ing. For example, an optical lens made of a glass material has a fixed focal length. On the other hand, in the above devices and apparatuses, there are cases where a lens whose focal length can be adjusted according to the situation, a so-called variable focus lens is used. The conventional variable focus lens mechanically adjusts the focal length by combining a plurality of lenses. However, there is a limit to extending the application range of such a mechanical variable focus lens in terms of response speed, manufacturing cost, miniaturization, power consumption, and the like.

  Therefore, as described in Patent Document 1, there has been known a variable focus lens using a material capable of changing a refractive index for a transparent medium constituting an optical lens. Also, as described in Non-Patent Document 1, a variable focus lens that mechanically deforms the shape of an optical lens has been proposed.

  However, any of the variable focus lenses as described above has a problem in that the response time required to change the focal length is limited and cannot be applied to a high-speed response of 1 ms or less.

  Therefore, as described in Patent Document 2, a variable focus lens using an optical material having an electro-optic effect has been proposed, and a variable focus lens capable of high-speed response of 1 ms or less is actually used.

Japanese Patent Laid-Open No. 11-064817 JP 2014-26229 A

Takashi Kaneko et al., “Long focal depth visual mechanism using variable focus lens”, Denso Technical Review, Vol.3, No.1, p.52-58, 1998

  However, in the variable focus lens having the structure described in Patent Document 2, it is necessary to apply a large voltage to the electro-optic material in order to shorten the focal length. As the applied voltage increases, high-speed operation becomes difficult, and wavefront aberration, which is important for lens performance, deteriorates.

  If the control voltage of the varifocal lens described in Patent Document 2 can be controlled with the same level of voltage, and the reduction of the focal length and the deterioration of the wavefront aberration can be improved, the high-speed response can be maintained. A higher performance variable focus lens can be realized.

  The object of the present invention is that it can be controlled with a voltage comparable to the control voltage of a conventional variable focus lens, and has a high performance capable of high-speed response with improved focal length shortening and wavefront aberration degradation. It is to provide a variable focus lens.

In order to achieve the above object, according to one embodiment of the present invention, there is provided a substrate made of a single crystal material having an electro-optic effect, wherein two straight lines whose cross sections are opposed to each other and convex toward the outside of the substrate. When the light is incident from an incident surface which is a straight line in the cross section among the surfaces orthogonal to the first surface of the substantially quadrangle, the incident light is incident. A substrate, a first anode formed on one third surface in contact with the incident surface, and a fourth surface facing the third surface, from which light is emitted from an exit surface facing the surface A first electrode pair formed on the third surface and formed with a first cathode formed on a position facing the first anode, and spaced apart from the first anode. A second cathode disposed on the fourth surface; and the second cathode, Are formed at positions mutually paddle, wherein the first cathode comprises a second electrode pair consisting of a second anode spaced, said third surface and said fourth surface, said The cross-sectional surfaces are arcs opposed to each other, and when light is incident from the incident surface, the light passes through the first electrode pair and then passes through the second electrode pair. by varying the voltage applied between the first electrode and the second electrode pair, characterized by varying the focus of light emitted from the emitting surface.

  As described above, according to the present invention, the substrate made of a single crystal material having an electro-optic effect has a substantially rectangular shape having two straight lines facing each other and two arcs facing each other. By changing the applied voltage between the first and second electrode pairs by changing the electrode arrangement, the focal point of the light emitted from the substrate can be varied. A voltage equal to that of a conventional cuboid variable focus lens reduces the focal length and deteriorates the wavefront aberration, and enables a high-speed response of 1 ms or less.

It is a figure which shows the structure of the conventional variable focus lens. It is a figure for demonstrating the principle of the conventional variable focus lens. It is a figure which shows the structure of the variable focus lens concerning the 1st Embodiment of this invention. It is a figure for demonstrating the principle of the variable focus lens concerning the 1st Embodiment of this invention. It is a figure which shows the structure of the variable focus lens concerning the 2nd Embodiment of this invention. It is a figure for demonstrating the principle of the variable focus lens concerning the 2nd Embodiment of this invention. It is a figure which shows the structure of the variable focus lens concerning the 3rd Embodiment of this invention. It is a figure for demonstrating the principle of the variable focus lens concerning the 3rd Embodiment of this invention. It is a figure which shows the optical path length modulation of the variable focus lens concerning the 3rd Embodiment of this invention. It is a figure which shows the tangent angle dependence of the focal distance of a variable focus lens. It is a figure which shows the tangent angle dependence of the wavefront aberration of a variable focus lens.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. First, the electro-optic effect and the optical path length modulation will be described with reference to a conventional variable focus lens.

(Electro-optic effect)
FIG. 1 shows a configuration of a conventional variable focus lens. Two electrode pairs are formed at positions facing each other on the upper and lower surfaces of the substrate 1 obtained by processing the electro-optic material into a rectangular parallelepiped. An anode 2 is disposed as an upper electrode on the light incident side, and a cathode 3 is disposed as a lower electrode across the substrate 1. Further, another pair of electrodes is disposed on the light emission side with a distance from these electrode pairs, the upper electrode being the cathode 4 and the lower electrode being the anode 5. The four strip-shaped electrodes have a shape in which all the sides in the longitudinal direction are parallel.

  Incident light 6 is incident from a plane orthogonal to the plane on which the electrodes are arranged, travels in the x-axis direction inside the substrate 1, and is perpendicular to the longitudinal direction of these strip electrodes between the anode 2 and the cathode 3. Transparent in the direction. Next, after passing between the cathode 4 and the anode 5, the outgoing light 7 is emitted from the surface facing the incident surface into the air.

  In such a configuration, a voltage is applied between the anode and the cathode. The direction of applying a voltage (z-axis direction) is opposite between the light incident side electrode pair and the light emission side electrode pair. The potentials of the anode 2 and the anode 5 may be different, and the potentials of the cathode 3 and the cathode 4 are the same. The lower potential of the anodes 2 and 5 is set to be higher than the higher potential of the cathodes 3 and 4.

  At this time, an electric field distribution is generated between these electrodes, and the refractive index is modulated by the electro-optic effect of the substrate 1. When light is transmitted through the refractive index modulated portion, the light is bent by this refractive index distribution, and as a result, the light is condensed or diverged. When condensed, according to the structure of FIG. 1, it functions as a cylindrical convex lens, and when diverged, it functions as a cylindrical concave lens. In this way, the light is condensed or diverged in the uniaxial direction, and thus is called uniaxial modulation. Further, since the degree of bending of light changes depending on the applied voltage, the focal length can be controlled by the voltage.

  As for the electro-optical effect, as described in Patent Document 2, several electro-optical effects having different orders are included. In general, a material exhibiting a primary electro-optic effect (hereinafter referred to as Pockels effect) or a secondary electro-optic effect (hereinafter referred to as Kerr effect) is used. When the Pockels effect is used, the refractive index change is proportional to the applied electric field. Therefore, in the above variable focus lens, the direction of the electric lines of force between the electrode pair on the entrance side and the electrode pair on the exit side is opposite, so that the change in refractive index is canceled when a material having the Pockels effect is used. Does not function as a lens. On the other hand, when a material having a Kerr effect is used, the refractive index change is proportional to the square of the electric field. Therefore, even if the direction of the lines of electric force is reversed, the refractive index changes are equal, so that it functions as a lens.

As described in Patent Document 2, as a substance having a Kerr effect, there is a single crystal material having a perovskite structure. If the use temperature is appropriately selected, the phase can be changed to a cubic phase exhibiting the Kerr effect. For example, barium titanate (BaTiO ₃ ) undergoes a phase transition from a tetragonal phase to a cubic phase that exhibits the Kerr effect at around 120 ° C.

In addition, a single crystal material mainly composed of potassium tantalate niobate (KTN: KTa _1-x Nb _x O ₃ , 0 <x <1) is formed from barium titanate ( It has more preferable characteristics than BaTiO ₃ ). While barium titanate (BaTiO ₃ ) has a predetermined phase transition temperature, KTN can select the phase transition temperature based on the composition ratio of tantalum and niobium, that is, the value of x in the chemical formula. If KTN is a temperature higher than the phase transition temperature, it becomes a cubic phase exhibiting a large Kerr effect, and the Kerr effect becomes larger as it is closer to the phase transition temperature. For this reason, it is very important to select a phase transition temperature near room temperature by changing the composition ratio of tantalum and niobium in order to easily express a large Kerr effect.

Further, as described in Patent Document 2, as a single crystal material related to KTN, the main component of the crystal is composed of periodic group Ia group and Va group, group Ia is potassium, Va For the group, a material containing at least one of niobium and tantalum can be used. Moreover, 1 or more types of the periodic table group Ia except potassium as an additional impurity, for example, lithium, or a group IIa can also be included. As an example, a cubic KLTN (K _1-y Li _y Ta _1-x Nb _x O ₃ , 0 <x <1, 0 <y <1) crystal may be used.

(Optical path length modulation)
Next, optical path length modulation will be described. With reference to FIG. 2, the state of refractive index modulation and the function as a lens will be described in detail. FIG. 2 shows a side view of the variable focus lens shown in FIG. 1 as viewed from the y-axis direction. The substrate 1 has a uniform refractive index when no voltage is applied to the four electrodes, so that light passes through without being modulated. Therefore, there is no lens function. However, when a plane wave is incident, the wavefront of the light emitted from the substrate 1 remains a plane, and it can be regarded as a lens with an infinite focal length considering that the radius of curvature is infinite.

  When voltages are applied to the four electrodes, electric lines of force 11 as shown in FIG. 2 are generated between these electrodes. The lines of electric force 11 are generated not only between the anode 2 and the cathode 3 and between the cathode 4 and the anode 5 but also widely spread outside these electrodes. The generation of electric lines of force means that an electric field is generated. At this time, since the substrate 1 has an electro-optic effect, the refractive index is modulated at a portion where an electric field is generated inside the substrate 1. Inside the substrate 1, in the vicinity of the four electrodes, that is, in the vicinity of the surface of the substrate 1, the electric field is large and the refractive index change is large. On the other hand, in the central part of the substrate 1 (near the center in all axial directions), the electric field is relatively small and the refractive index change is small.

  The right side of FIG. 2 schematically shows a refractive index modulation curve 12 representing a distribution of refractive index change. The vertical axis of the refractive index modulation curve 12 is the z-axis coordinate, and the horizontal axis is the refractive index change Δn from when no voltage is applied. FIG. 2 shows that the refractive index changes in the negative direction as a whole, but the modulation is large in the vicinity of the surface of the substrate 1, and therefore the refractive index change Δn is small. On the other hand, the modulation is small in the vicinity of the central portion, and therefore the change in refractive index Δn is not as small as in the vicinity of the surface. When light passes through such a refractive index distribution, it functions as a convex lens because the speed of light near the surface is higher than the speed of light at the center of the substrate 1. That is, the focal point moves from an infinite focal length when no voltage is applied to a finite focal length.

  In the configuration of FIG. 2, the characteristics of the lens are evaluated by an optical path length modulation Δs obtained by integrating the refractive index change Δn over the light traveling path (length L) as in the following equation.

  However, in the configuration of FIG. 2, there are two types of polarized light when the direction of the optical electric field is in the y-axis direction and in the z-axis direction. In each case, the refractive index modulation Δn felt by the light is different, so the optical path The long modulation Δs is also different.

(First embodiment)
FIG. 3 shows the configuration of the variable focus lens according to the first embodiment of the present invention. In the single crystal substrate 21 having an electro-optic effect cut out in a rectangular parallelepiped, a surface parallel to the x-axis and the z-axis is defined as a first surface, a first surface, and a surface perpendicular to the surface on which the light 26 is incident and exit The surface facing the surface is defined as the second surface. The shape of the first and second surfaces is a quadrangle. Two pairs of electrodes are formed on the third surface parallel to the x-axis and the y-axis and the fourth surface facing the third surface at positions facing each other with a space therebetween. A first electrode pair 22, 23 is formed on the light incident side, and a second electrode pair 24, 25 is formed on the light output side. The electrodes 22, 25 are anodes, and the electrodes 23, 24 are cathodes.

  The first electrode pairs 22 and 23 are also formed continuously on the surface (incident surface) on which the light 26 is incident, and the second electrode pairs 24 and 25 are surfaces (emitted surfaces) on which the light 27 is emitted. It is also formed continuously. That is, the first electrode pair 22, 23 is formed on the incident surface, the third surface orthogonal to the incident surface, and the fourth surface opposite to the third surface, and the first anode 22 3 is formed on the third surface and the incident surface across the side where the third surface and the incident surface are in contact, and the first cathode 23 is formed across the side where the fourth surface and the incident surface are in contact with each other. And light are formed on the incident surface.

  The second electrode pair 24, 25 is formed on the emission surface and the third surface and the fourth surface orthogonal to the emission surface, and the second anode 25 is in contact with the fourth surface and the emission surface. The second cathode 24 is formed on the third surface and the emission surface across the side where the third surface and the emission surface are in contact with each other. .

  With reference to FIG. 4, the state of refractive index modulation and the function as a lens will be described in detail. FIG. 4 shows the shape of the electric lines of force inside the crystal when the single crystal substrate 21 is viewed from the y-axis direction, and the refractive index modulation amount Δn in the z-axis direction is schematically shown on the right side thereof. The first and second electrode pairs have an L-shaped cross-sectional shape when viewed from the y-axis direction, and have a structure surrounding the four corners of the single crystal substrate 21. The principle of the lens function is the same as that of a conventional variable focus lens. Comparing FIG. 2 and FIG. 4, it can be seen that the curvature of the electric lines of force is larger in the variable focus lens of the present embodiment. When the curvature of the electric lines of force increases, the electric field distribution inside the crystal increases, and as a result, the refractive index change near the electrode becomes larger than the refractive index change at the center of the light incident surface. That is, in the zx plane, the difference between the refractive index change at z = 0 and the refractive index change in the vicinity of the electrode becomes large. As a result, the curvature of the parabola becomes larger than the conventional one, and a greater lens effect is exhibited.

(Second Embodiment)
FIG. 5 shows a configuration of a variable focus lens according to the second embodiment of the present invention. The substrate 31 is made of a single crystal material having an electrooptic effect, and has an octagonal prism shape whose cross section parallel to the optical axis viewed from the y-axis direction is an octagon. An octagonal surface parallel to the x-axis and the z-axis is defined as a first surface, and a surface facing the first surface is defined as a second surface. When the incident light 36 is incident from the incident surface among the surfaces orthogonal to the octagonal first and second surfaces, the emitted light 37 is emitted from the emission surface facing the incident surface. On the anode 32 (first anode) formed on the third surface on one side (upper side in the drawing) that contacts the incident surface and on the fourth surface on the other side (lower side in the drawing) that contacts the incident surface A first electrode pair composed of the formed cathode 33 (first cathode), a cathode 34 (second cathode) formed on one fifth surface in contact with the emission surface, and in contact with the emission surface And a second electrode pair including an anode 35 (second anode) formed on the other sixth surface.

  When the incident light 36 is incident from the incident surface, it passes through the first electrode pair, then passes through the second electrode pair, and the applied voltage between the first and second electrode pairs. By changing the focal point of the outgoing light 37 emitted from the outgoing surface.

  With reference to FIG. 6, the state of refractive index modulation and the function as a lens will be described in detail. FIG. 6 shows a state where the first surface (cross section of the octagonal prism) of the variable focus lens shown in FIG. 5 is viewed from the y-axis direction. The substrate 31 has a uniform refractive index when no voltage is applied to the four electrodes, so that light is transmitted without being modulated. Therefore, there is no lens function. However, when a plane wave is incident, the wavefront of the light emitted from the substrate 31 remains a plane, and it can be regarded as a lens with an infinite focal length considering that the curvature radius is infinite.

  When voltages are applied to the four electrodes, electric lines of force 41 as shown in FIG. 6 are generated between these electrodes. The electric lines of force 41 are generated not only between the anode 32 and the cathode 33 and between the cathode 34 and the anode 35 but also widely spread outside these electrodes. Compared with the conventional example of FIG. 2, it can be seen that the curvature of the electric lines of force is increased in the second embodiment. As the curvature of the lines of electric force increases, the electric field distribution inside the substrate 31 increases, and as a result, the refraction near the electrode surface (the third and fourth surfaces) compared to the change in the refractive index at the center of the incident surface. The rate change increases.

  The right side of FIG. 6 schematically shows a refractive index modulation curve 42 representing the distribution of refractive index change. The vertical axis of the refractive index modulation curve 42 is the z-axis coordinate, and the horizontal axis is the change in refractive index Δn from when no voltage is applied. Compared to the conventional example of FIG. 2, in the second embodiment, the difference between the refractive index change at z = 0 (near the center line (optical axis) of the substrate 31) and the refractive index change near the electrode is large. ing. As a result, the curvature of the parabola of the refractive index change Δn is increased, and a greater lens effect can be exhibited.

  In the cross section of the substrate 31, an angle formed by the third to sixth surfaces with respect to the optical axis is defined as an electrode surface angle θ (see FIG. 6). Although the focal length increases as the electrode surface angle θ increases, it can be seen that the focal length is shorter than the conventional variable focal length lens, and the lens performance is improved. In addition, since the wavefront aberration is minimized when the electrode surface angle θ is between 20 ° and 30 °, in order to obtain a variable focus lens in which the focal length is shortened and the wavefront aberration is improved, the electrode surface The angle θ is preferably 20 ° to 30 °.

(Third embodiment)
FIG. 7 shows a configuration of a variable focus lens according to the third embodiment of the present invention. The substrate 51 is made of a single crystal material having an electro-optic effect, and has a substantially rectangular shape in which a cross section parallel to the optical axis viewed from the y-axis direction has two opposing straight lines and two opposing arcs. ing. A substantially quadrangular surface parallel to the x-axis and the z-axis is defined as a first surface, and a surface facing the first surface is defined as a second surface. When incident light 56 is incident from an incident surface that is a straight line in a cross section parallel to the optical axis viewed from the y-axis direction, out of the substantially quadrangular surfaces orthogonal to the first and second surfaces, it faces the incident surface. Outgoing light 57 is emitted from the emission surface.

  Two electrode pairs are formed at opposing positions on the upper surface (third surface) and the lower surface (fourth surface) that form an arc in a cross section parallel to the optical axis as viewed from the y-axis direction. An anode 52 (first anode) is disposed as an upper electrode on the light incident side, and a cathode 53 (first cathode) is disposed as a lower electrode across the substrate 51. Further, another pair of electrodes is disposed on the light emission side, with a distance from these electrode pairs, the upper electrode being the cathode 54 (second cathode), and the lower electrode being the anode 55 (second anode). It is. The four strip-shaped electrodes have a shape in which all the sides in the longitudinal direction are parallel.

  When the incident light 56 is incident from the incident surface, it passes through the first electrode pair, then passes through the second electrode pair, and the applied voltage between the first and second electrode pairs. By changing, the focus of the outgoing light 57 emitted from the outgoing surface can be varied.

  With reference to FIG. 8, the state of refractive index modulation and the function as a lens will be described in detail. FIG. 8 shows a state in which the side surface of the variable focus lens shown in FIG. 7 is viewed from the y-axis direction. Since the refractive index of the substrate 51 is uniform when no voltage is applied to the four electrodes, the light is transmitted without being modulated. Therefore, there is no lens function. When a plane wave is incident, the wavefront of light emitted from the substrate 51 remains a plane, and it can be regarded as a lens with an infinite focal length considering that the radius of curvature is infinite.

  When voltages are applied to the four electrodes, electric lines of force 61 as shown in FIG. 8 are generated between these electrodes. The electric lines of force 61 are generated not only between the anode 52 and the cathode 53, between the cathode 54 and the anode 55 but also widely spread outside these electrodes. Compared with the conventional example of FIG. 2, it can be seen that the curvature of the lines of electric force is larger in the third embodiment. As the curvature of the electric lines of force increases, the electric field distribution inside the substrate 51 increases, and as a result, the refractive index change near the electrode surface becomes larger than the refractive index change at the center of the light incident surface.

  On the right side of FIG. 8, a refractive index modulation curve 62 representing the distribution of refractive index change is schematically shown. The vertical axis of the refractive index modulation curve 62 is the z-axis coordinate, and the horizontal axis is the refractive index change Δn from when no voltage is applied. Compared to the conventional example of FIG. 2, in the third embodiment, the difference between the refractive index change at z = 0 (near the center line (optical axis) of the substrate 51) and the refractive index change near the electrode is large. ing. As a result, the curvature of the parabola of the refractive index change Δn is increased, and a greater lens effect can be exhibited.

FIG. 9 shows optical path length modulation of the variable focus lens according to the third embodiment of the present invention. FIG. 5 is a plot of optical path length modulation Δs _z when the optical electric field is in the z-axis direction using Equation 1. The curve of the optical path length modulation with z = 0 (optical axis) as the center almost coincides with the parabola (quadratic function), and it can be seen that it functions as an ideal convex lens. FIG. 9 also shows the optical path length modulation of the conventional variable focus lens shown in FIG. This is a comparison of optical path length modulations calculated assuming that the applied voltage applied to the first and second electrode pairs is 1 kV and the relative dielectric constant of the substrate is 20,000.

  It can be seen that the variable focus lens of the third embodiment has a larger curvature than the prior art. This indicates that the difference in refractive index between the vicinity of the electrode and the center of the crystal is larger than that in the prior art, and as a result, it has a large convex lens effect for polarized waves parallel to the z axis.

  FIG. 10 shows the tangential angle dependence of the focal length of the variable focus lens. As shown in FIG. 8, in a cross section parallel to the optical axis viewed from the y-axis direction, an angle with respect to the optical axis of a tangent formed by an arc constituting the third surface is defined as a tangential angle θ. Under the same conditions as in the calculation of FIG. 9, the change in focal length when the tangent angle θ of the third surface was changed was plotted by numerical calculation. As the tangent angle θ increases, the thickness of the substrate 51 increases.

  At this time, the voltage applied to the first and second electrode pairs is 1 kV, and the relative dielectric constant of the substrate 51 is 20,000. The light incident surface and the light emitting surface are parallel to each other and have a size of 3 mm in the z-axis direction and 4.5 mm in the y-axis direction. The distance between the entrance surface and the exit surface is 4.5 mm in the x-axis direction. The four electrodes 52 to 55 are band-like electrode surfaces having a length of 1.5 mm when projected onto the x-axis and 4.5 mm in the y-axis direction, and are curved. As shown in FIG. 10, as the angle of the tangent to the optical axis becomes smaller, the focal length becomes smaller and the focal length can be made smaller than in the prior art.

  FIG. 11 shows the tangential angle dependence of the wavefront aberration of the variable focus lens. The relationship between the change in the tangent angle and the wavefront aberration is calculated by numerical calculation and plotted under the same conditions as those in FIG. It can be seen that the wavefront aberration is 150 nm or less at any angle, but the tangent angle θ takes a minimum value around 50 ° and is about 60 nm. Referring to FIG. 10 and FIG. 11, the tangent angle θ that can reduce the maximum value of the wavefront aberration and reduce the focal length is preferably 40 ° to 60 °.

(Example 1 of the third embodiment)
As shown in FIGS. 7 and 8, KTN is used as a single crystal material having an electro-optic effect, and a substrate 51 processed into a quadrangular prism having a substantially rectangular cross section is cut out. The dimensions of the light incident surface and light output surface of the substrate 51 are 4.5 mm in the y-axis direction and 3.0 mm in the z-axis direction. The maximum thickness of the substrate 51, that is, the maximum distance on the z-axis of the cross section parallel to the optical axis viewed from the y-axis direction is 4.5 mm. In a section parallel to the optical axis viewed from the y-axis direction, the tangent angle θ with respect to the optical axis of the tangential line formed by the arc serving as the third surface is processed to be 26.5 °. Four electrodes in contact with the entrance surface and the exit surface are formed on the upper surface (third surface) and the lower surface (fourth surface) that form an arc in a cross section parallel to the optical axis viewed from the y-axis direction. The electrode is formed by vapor-depositing Pt so that the width of the electrode, that is, the length when projected onto the x-axis is 1.5 mm.

  All surfaces of the substrate are optically polished, and all surfaces other than the electrode surface are parallel to the (100) surface. Since the used KTN single crystal had a phase transition temperature of 35 ° C., it was used at 40 ° C., which is slightly higher than this. The relative dielectric constant at this temperature is 20,000.

  While the temperature of the variable focus lens of Example 1 is controlled at 40 ° C., collimated laser light having a wavelength of 633 nm is incident as incident light 56 from the incident surface. The polarization of incident light is a straight line, and the direction of the oscillating electric field is the z-axis direction. A voltage of 1 kV is applied to each of the first electrode pair of the anode 52 and the cathode 53 and the second electrode pair of the anode 55 and the cathode 54. The outgoing light 57 from the outgoing surface is condensed and functions as a cylindrical convex lens. The focal length is 30 cm. When no voltage is applied, there is no light collection effect and the focal length is infinite.

  Therefore, compared with the conventional variable focus lens, an applied voltage capable of a high-speed response of 1 ms or less can reduce the focal length as shown in FIG. 10, and as shown in FIG. In addition, the wavefront aberration can be reduced.

(Example 2 of the third embodiment)
Using the substrate 51 processed into the same substantially rectangular column as in the first embodiment, both the first electrode pair (two electrodes in contact with the light incident surface) are anodes and the second electrode pair (on the light emitting surface). A voltage of 1 kV is applied with both of the two electrodes in contact as cathodes. At this time, the outgoing light 57 from the outgoing surface is condensed and functions as a cylindrical convex lens. At this time, the focal length is 40 cm, which is longer than that of Example 1, but is superior to that of the prior art, and the wavefront aberration can be reduced to 70 nm.

(Example 3 of the third embodiment)
In the third embodiment described above, the cross section (first and second surfaces) parallel to the optical axis viewed from the y-axis direction has a substantially rectangular shape having two opposing straight lines and two opposing arcs. The case is described. In the upper surface (third surface) and the lower surface (fourth surface) that are arcs in a cross section parallel to the optical axis as viewed from the y-axis direction, portions where no electrode is formed may be linear. That is, the cross section parallel to the optical axis viewed from the y-axis direction has a shape composed of four sides and four arcs connecting them, that is, a shape obtained by deforming four corners of a quadrangle into an arc shape. .

1, 21, 31, 51 Substrate 2, 5, 22, 25, 32, 35, 52, 55 Anode 3, 4, 23, 24, 33, 34, 53, 54 Cathode 6, 26, 36, 56 Incident light 7 27, 37, 57 Outgoing light

Claims (5)

A substrate made of a single crystal material having an electro-optic effect, having a substantially quadrangular shape having two straight lines whose cross-sections are opposed to each other and two opposed arcs that are convex toward the outside of the substrate , A substrate that emits light from an exit surface that faces the entrance surface when light is incident from an entrance surface that is a straight line in the cross section among the surfaces orthogonal to the first surface of the quadrangle;
A first anode formed on one third surface in contact with the incident surface and a fourth surface opposed to the third surface are formed at a position facing the first anode. A first electrode pair comprising a first cathode;
A second cathode formed on the third surface and spaced from the first anode, and formed on the fourth surface and in a position facing the second cathode. It is, and a second electrode pair consisting of a second anode and said first cathode arranged at intervals,
The third surface and the fourth surface are arc-shaped surfaces facing each other in the cross section,
Wherein when light is incident from the incident surface, from the transmission between the first electrode pair, it passes through between the second electrode pair, wherein the first electrode pair and said second pair of electrodes A variable focus lens, wherein the focus of the light emitted from the emission surface is varied by changing an applied voltage between the two.   2. The variable focus lens according to claim 1, wherein an application voltage application direction of the first electrode pair and an application voltage application direction of the second electrode pair are opposite to each other. A substrate made of a single crystal material having an electro-optic effect, having a substantially quadrangular shape having two straight lines whose cross-sections are opposed to each other and two opposed arcs that are convex toward the outside of the substrate , A substrate that emits light from an exit surface that faces the entrance surface when light is incident from an entrance surface that is a straight line in the cross section among the surfaces orthogonal to the first surface of the quadrangle;
A first anode formed on one third surface in contact with the incident surface, and a first cathode formed on the third surface and spaced from the first anode A first electrode pair comprising:
A second anode formed on the other fourth surface in contact with the incident surface, and a second cathode formed on the fourth surface and spaced from the second anode A second electrode pair comprising:
The third surface and the fourth surface are arc-shaped surfaces facing each other in the cross section,
When light is incident from the incident surface, from the transmission between said first anode and said second anode, passes through between the first cathode and the second cathode, the first by changing the electrode pairs and the voltage applied between the second electrode pair, variable focus lens, characterized by varying the focus of light emitted from the emitting surface. The single crystal material is potassium tantalate niobate (KTN: KTa _1-x Nb _x O ₃ ,
4. The variable focus lens according to claim 1, wherein 0 <x <1). In the single crystal material, the main component of the crystal is composed of periodic group Ia group and Va group,
a group is potassium, Va group niobium, comprises at least one of tantalum, 1 to claim characterized in that it comprises a periodic table group Ia or IIa group 1 or more, excluding potassium as dopant 4. The variable focus lens according to any one of 3 above.