JP5432044B2 - Variable focus lens - Google Patents

Description

  The present invention relates to a variable focus lens, and more particularly to a polarization-independent variable focus lens that uses an optical material having an electro-optic effect to change the focal length and operates without polarization dependency. .

  Conventionally, optical components such as optical lenses and prisms are optical devices such as cameras, microscopes, and telescopes, electrophotographic recording devices such as printers and copiers, optical recording devices such as DVDs, optical devices for communication, industrial use, etc. It is used for. A normal optical lens has a fixed focal length. However, a lens that can adjust the focal length according to the situation, a so-called variable focus lens may be used in the above-described devices and apparatuses. The conventional variable focus lens mechanically adjusts the focal length by combining a plurality of lenses. However, such a mechanical variable focus lens has a limit in extending the application range from the viewpoint of response speed, manufacturing cost, miniaturization, power consumption, and the like.

  Therefore, a variable focus lens in which a material capable of changing the refractive index is applied to the transparent medium constituting the optical lens, a variable focus lens that mechanically deforms the shape of the optical lens, instead of moving the position of the optical lens, etc. It was issued. As the former variable focus lens, a variable focus lens using liquid crystal as an optical lens has been proposed. This variable focus lens encloses the liquid crystal in a container made of a transparent material by sandwiching the liquid crystal between two glass plates. When the inside of the container is processed into a spherical surface and the liquid crystal is molded into a lens shape, a variable focus lens can be configured. A transparent electrode is provided inside the container, and the refractive index is controlled by applying an electric field to the liquid crystal, and the focal length is variably controlled (see, for example, Patent Document 1).

  As the latter variable focus lens, liquid is often used as the material of the deformable lens. For example, the variable focus lens described in Patent Document 2 has a structure in which a liquid such as silicon oil is sealed in a space sandwiched between glass plates. The glass plate is thinly processed. By applying pressure to the glass plate with a lead zirconate titanate (PZT) piezo actuator from the outside, the lens composed of the oil and the entire glass plate is deformed, and the focal position is adjusted. Control. The operating principle of this variable focus lens is the same as that of the lens of the eyeball.

Japanese Patent Laid-Open No. 11-064817 JP-A-11-133210

  However, the conventional variable focus lens includes any one of a variable focus lens that mechanically adjusts the focal length, a variable focus lens that controls the refractive index by applying an electric field to liquid crystal, and a variable focus lens that deforms the lens by a PZT piezo actuator. However, the response speed required to change the focal length is limited, and there is a problem that it cannot be applied to a high-speed response of 1 ms or less.

  An object of the present invention is to provide a variable focus lens using an electro-optic effect so that the focal length can be changed at high speed. In addition, since many electro-optic effect devices operate depending on polarization, the object is to provide a polarization-independent variable focus lens while utilizing the electro-optic effect.

  In order to achieve such an object, an embodiment of the present invention includes an electro-optic material (1) made of a single crystal having inversion symmetry, and a first surface formed on a first surface of the electro-optic material. One anode (2), a first cathode (3) formed on a second surface facing the first surface and facing the first anode, and the first A second cathode (4) formed on a surface and spaced from the first anode; and formed on the second surface and at a position facing the second cathode. And a second anode (5) spaced apart from the first cathode, and when light is incident from a third surface orthogonal to the first surface, the first anode A second electrode consisting of the second anode and the second cathode is transmitted through the first electrode pair consisting of the anode and the first cathode. The first to fourth unit elements (12, 14, 17, 19) having an optical axis set so as to transmit light between the electrode pairs and emit light from the fourth surface opposite to the third surface. ) And the optical axis of the first unit element (12) and the optical axis of the second unit element (14), and between the first unit element and the second unit element The first half-wave plate (13) disposed on the optical axis, the optical axis of the third unit element (17) and the optical axis of the fourth unit element (19) are made to coincide with each other, A second half-wave plate (18) disposed on the optical axis between the third unit element and the fourth unit element, and the incident light is polarized into the first polarized light and the second polarized light. Polarization separating element (11) that separates the wave, makes the first polarized light incident on the first unit element (12), and makes the second polarized light incident on the third unit element (17) When, The polarization beam combining element (20) for combining the first emitted light emitted from the second unit element (14) and the second emitted light emitted from the fourth unit element (19). The voltage application direction by the first and second electrode pairs of the first unit element and the voltage application direction by the first and second electrode pairs of the second unit element are orthogonal to each other The direction of voltage application by the first and second electrode pairs of the third unit element is orthogonal to the direction of voltage application by the first and second electrode pairs of the fourth unit element. And the focal point of the light emitted from the polarization beam combiner is varied by changing the voltage applied between the first and second electrode pairs of the first to fourth unit elements. And

The electro-optic material is preferably a perovskite single crystal material, typically potassium tantalate niobate (KTN: KTa _1-x Nb _x O ₃ , 0 <x <1). In the electro-optic material, the main component of the crystal is composed of groups Ia and Va in the periodic table, group Ia is potassium, and group Va can contain at least one of niobium and tantalum. Furthermore, it is also possible to include one or more members of Group Ia of the periodic table excluding potassium as an additive impurity, for example, lithium, or Group IIa.

  It is preferable that the anode and the cathode on the same surface of the first to fourth variable focus lenses have a belt-like shape, and their longitudinal sides are all parallel. Further, when the distance G between the anode and the cathode on the first to fourth coplanar surfaces and the thickness T of the electro-optic material are satisfied, it is preferable that G <1.5T.

  As described above, according to the present invention, by arranging a plurality of basic unit elements of a variable focus lens having a desired electrode configuration and an electro-optic material made of a single crystal having inversion symmetry, it depends on polarization. It is possible to realize a variable focus lens that does not.

It is a figure which shows the structure of the basic unit element of the variable focus lens concerning the 1st Embodiment of this invention. It is a figure for demonstrating the principle of the basic unit element of a variable focus lens. It is a figure which shows the example of the optical path length modulation of the basic unit element of a variable focus lens. It is a figure which shows the electrode space | interval dependence of the focal distance of the basic unit element of a variable focus lens. It is a figure which shows the structure of the basic unit element of the variable focus lens concerning the 2nd Embodiment of this invention. It is a figure which shows the structure of the polarization independent variable focus lens concerning Example 1 of this invention. It is a figure which shows the structure of the polarization independent variable focus lens concerning Example 2 of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The variable focus lens of this embodiment is composed of an electro-optic material and an electrode attached thereto. By using the electro-optic effect, it is possible to obtain a much faster response speed than a conventional variable focus lens and to obtain a variable focus lens that does not depend on polarization.

(Basic unit element of variable focus lens)
FIG. 1 shows a configuration of basic unit elements of a variable focus lens according to the first embodiment of the present invention. Four strip-shaped electrodes are formed on the upper surface (first surface) and the lower surface (second surface) of the substrate 1 obtained by processing the electro-optic material into a plate shape. An anode 2 (first anode) is disposed as an upper electrode on the light incident side, and a cathode 3 (first cathode) 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 (second cathode), and the lower electrode being the anode 5 (second anode). It is. The four strip-shaped electrodes have a shape in which all the sides in the longitudinal direction are parallel.

  Light enters from a surface (third surface) perpendicular to the surface on which the electrodes are arranged, travels in the x-axis direction inside the substrate 1, and between the anode 2 and the cathode 3, the longitudinal direction of these strip electrodes Transmits in the vertical direction. Next, after passing between the cathode 4 and the anode 5, it is set so as to be emitted into the air from the surface (fourth surface) opposite to the incident surface.

  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. Further, since the degree of bending of light changes depending on the applied voltage, the focal length can be controlled by the voltage.

  The electro-optic effect responds in a time of 1 μs or less even if it is late estimated from the application of the voltage. Therefore, it is possible to realize a variable focus lens that responds significantly faster than the conventional variable focus lens. As described above, the basic unit element shown in FIG. 1 is a cylindrical variable focus lens, which is a basic unit constituting various lenses. In order to realize a normal spherical lens, it is only necessary to combine two elements as the basic unit. That is, a function equivalent to a spherical lens can be realized by arranging the two basic unit elements so as to form an angle of 90 degrees with respect to the optical axis. In the present embodiment, the material of the substrate 1 is characterized by using a material made of a crystal having inversion symmetry, among materials having an electro-optic effect, and the reason will be described later.

  Hereinafter, the state of refractive index modulation and the function as a lens will be described in detail with reference to FIG. FIG. 2 shows a side view of the basic unit element 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 6 as shown in FIG. 2 are generated between these electrodes. The electric lines of force 6 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 portion of the substrate 1 (near the center in the thickness (z-axis) direction), 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 7 representing a distribution of refractive index change. The vertical axis of the refractive index modulation curve 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.

(Electro-optic material)
The electro-optic effect includes several different-order electro-optic effects, but generally, a first-order electro-optic effect (hereinafter referred to as Pockels effect) is used. In the Pockels effect, the refractive index change is proportional to the electric field. In the configuration shown in FIGS. 1 and 2, the direction of the electric field is reversed and the refractive index distribution is also reversed between the anode 2 and the cathode 3 and between the cathode 4 and the anode 5. Therefore, when the Pockels effect is used, when light passes between these two electrode pairs, the deflection of the light due to the refractive index distribution is canceled out between positive and negative, and the lens function is not achieved.

  On the other hand, when the secondary electro-optic effect (hereinafter referred to as the Kerr effect) is used, the refractive index change is proportional to the square of the electric field. Therefore, even if the direction of the electric field is reversed between the anode 2 and the cathode 3 and between the cathode 4 and the anode 5, the refractive index distribution is the same, so that the light deflection is canceled out. We will strengthen each other.

  Many electro-optic materials do not have inversion symmetry and develop a Pockels effect. On the other hand, some electro-optic materials have inversion symmetry, do not exhibit the Pockels effect, and the Kerr effect is dominant. Therefore, it is important to use a material having inversion symmetry as the electro-optic material constituting the substrate 1 of the present embodiment.

  In general, when an electric field is applied from the outside to a dielectric, polarization proportional to the electric field is generated, but when the electric field is removed, the polarization returns to zero. However, there are substances that retain finite polarization even when the electric field is removed. Polarization that exists even without an external electric field is called spontaneous polarization. There exists a substance capable of reversing the direction of this spontaneous polarization by an external electric field, which is called a ferroelectric.

  A single crystal having inversion symmetry refers to a crystal that has the same arrangement as the original arrangement of atoms when the arrangement of atoms is inverted in the x, y, z coordinate system around a certain origin. When a crystal having spontaneous polarization is inverted on the coordinate axis, the direction of spontaneous polarization is inverted, so that such a crystal cannot be said to have inversion symmetry. Therefore, since the ferroelectric has spontaneous polarization, it does not have inversion symmetry.

  On the other hand, there are substances that have spontaneous polarization but cannot be inverted by an external electric field. Such a material does not have inversion symmetry, but is not a ferroelectric material. Therefore, not all materials that do not have inversion symmetry are ferroelectric materials. Further, it cannot be a ferroelectric and has inversion symmetry.

As an electro-optic material having inversion symmetry, there is a single crystal material having a perovskite crystal structure. The perovskite single crystal material becomes a cubic phase having inversion symmetry in the use state if the use temperature is appropriately selected. In the cubic phase, the Pockels effect is not expressed and the Kerr effect is dominant. For example, even the most well-known barium titanate (BaTiO ₃ , hereinafter referred to as BT) may exceed the temperature at which the phase transition from the tetragonal phase to the cubic phase (hereinafter referred to as the phase transition temperature) occurs at around 120 ° C. For example, it becomes a cubic phase and exhibits the Kerr effect.

A single crystal material mainly composed of potassium tantalate niobate (KTN: KTa _1-x Nb _x O ₃ , 0 <x <1) has more preferable characteristics. BT has a predetermined phase transition temperature, whereas KTN can select a phase transition temperature depending on the composition ratio of tantalum and niobium. Thereby, the phase transition temperature can be set near room temperature. KTN has a cubic phase at a temperature higher than the phase transition temperature, has inversion symmetry, and has a large Kerr effect. Even in the same cubic phase, the Kerr effect becomes overwhelmingly closer to the phase transition temperature. For this reason, setting the phase transition temperature around room temperature is very important for easily realizing a large Kerr effect.

Further, 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, and group Va includes at least one of niobium and tantalum. Materials can be used. Moreover, 1 or multiple types of periodic table group Ia except potassium as an additional impurity, for example, lithium, or IIa group can also be included. For example, a cubic phase 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)
The optical path length modulation will be described in detail for the case of KTN. In the configuration of FIG. 2, there are two types of polarization, 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 [Delta] n _y and [Delta] n _z where light feel,

It becomes different. Here, n ₀ is a refractive index before modulation, and s ₁₁ and s ₁₂ are electro-optic coefficients. While s ₁₁ is a positive value, s ₁₂ has a negative value, and s ₁₁ has a larger absolute value. The characteristic of the lens is evaluated by an optical path length modulation Δs obtained by integrating the change in refractive index over the light traveling path (length L) as in the following equation.

FIG. 3 shows an example of optical path length modulation of basic unit elements. The distribution of the optical path length modulation Δs _y and Δs _z is obtained by numerical calculation. The relative dielectric constant is 20,000, the length L of the substrate 1 is 7 mm, the thickness of the substrate in the z-axis direction is 4 mm, the width of the four electrodes is 0.8 mm, the distance between the electrodes on the same plane is 4 mm, and the voltage is It was calculated as 1000V. The horizontal axis in FIG. 3 indicates the z coordinate shown in FIG. 2, and the origin is at the center of the substrate 1. The distribution of Δs _y forms a downwardly convex curve, which indicates that this element functions as a cylindrical concave lens. On the other hand, the distribution of Δs _z forms an upwardly convex curve, indicating that this element functions as a cylindrical convex lens. As in this KTN example, the lens may become a convex lens or a concave lens depending on the polarization.

(Place electrode)
In the basic unit element, the anode 2 and the cathode 4 are disposed on the upper surface of the substrate 1, and the cathode 3 and the anode 5 are disposed on the lower surface. As a configuration similar to this, a configuration in which both the upper electrode is an anode and the lower electrode is both a cathode is conceivable. This configuration also functions as a variable focus lens, but the first embodiment is superior in the following points.

  When considering miniaturization of the element, in the configuration of FIG. 2, even if the substrate 1 is reduced in the z-axis direction, that is, the thickness of the substrate 1 is reduced, it is limited by the size of the light beam transmitted through the substrate 1. Will be. Therefore, when trying to reduce the size in the x-axis direction, in a configuration in which both electrodes on the upper surface are anodes and both electrodes on the lower surface are cathodes, the effect of the lens is reduced if the electrode spacing is reduced. The limit in which the electrode interval is narrowed becomes an electrode in which the interval is zero and both the upper electrode and the lower electrode are integrated. In this case, the electric field inside the substrate 1 becomes uniform, the refractive index distribution becomes uniform, and the lens effect is almost lost.

  On the other hand, in the first embodiment, the anode 2 and the cathode 4 on the upper surface have different potentials to be applied. Therefore, the limit in which the electrode interval is narrowed does not cause the electrodes to be integrated. If the electrode interval is reduced in the first embodiment, the electric field increases, so that the lens effect increases.

  FIG. 4 shows the electrode spacing dependence of the focal length of the basic unit element. The focal length obtained by numerical calculation is plotted as a function of electrode spacing. Under the same conditions as the calculation conditions of FIG. 3, the length of the substrate 1 was increased or decreased by the same amount simultaneously with the increase or decrease of the electrode interval. The electric field of light is in the z-axis direction. The smaller the focal length of the vertical axis, the stronger the degree of light collection and the greater the effect. The plots with squares indicate that both the upper electrodes are anodes and the lower electrodes are both cathodes, and the effect deteriorates when the electrode spacing is small. Plots in the case of the first embodiment are more effective when the electrode spacing is small. As the distance between the electrodes increases, the interaction between the two electrode pairs becomes weaker, so that both configurations converge to the same effect. Since the thickness of the substrate 1 is 4 mm, referring to FIG. 4, the configuration of the first embodiment is advantageous when the electrode interval is smaller than 1.5 times the thickness (6 mm).

  As described above, when KTN is used, it can be used as a convex lens or a concave lens as long as the polarization is changed. On the other hand, it is known that when an electric field is applied to an electro-optic crystal, its physical shape changes due to a piezoelectric effect or an electrostrictive effect. The piezoelectric effect is a phenomenon in which strain is proportional to the applied electric field, and the electrostrictive effect is a phenomenon in which strain is proportional to the square of the applied electric field. The change in the physical shape is represented by the sum of the piezoelectric effect and the electrostrictive effect. In general, an electro-optic material having inversion symmetry has only an electrostrictive effect because a piezoelectric effect does not occur. Due to this electrostrictive effect, the refractive index distribution may slightly deviate from the distribution obtained from the above-described calculation of the electric field distribution.

At this point, Δn _z (or optical path length s _z ) is less shifted between the calculated value and the actual value than Δn _y (or optical path length s _y ). That is, according to the electrode configuration of the first embodiment, the z component of the electric field increases as a whole, but the refractive index distribution as calculated is better when the oscillating electric field of light is aligned parallel to the z axis. It is suitable because it is easy to match. Of course, the x component of the electric field also increases, but the oscillating electric field of the light cannot be made parallel to the x axis in the optical axis setting of the first embodiment.

(Electrode material)
When a high voltage is applied to the electro-optic material, charges are injected from the electrodes, and space charges can be generated in the crystal. This space charge causes a gradient in the magnitude of the electric field in the direction in which the voltage is applied, so that a gradient also occurs in the modulation of the refractive index. Therefore, in order to obtain a desired refractive index distribution for causing the electro-optic material to function as a lens, or to prevent light transmitted through the electro-optic material from being deflected, when a voltage is applied to the substrate 1, It is better that no space charge is formed inside the substrate 1.

  Since the amount of space charge depends on the carrier injection efficiency, the carrier injection efficiency injected from the electrode should be small. When the carriers contributing to electrical conduction in the electro-optic crystal are electrons, as the work function of the electrode material increases, the electrode and the substrate approach a Schottky junction and the carrier injection efficiency decreases. Therefore, the electrode is preferably a material that forms a Schottky junction with the electro-optic material. Specifically, when the carrier contributing to electrical conduction in the electro-optic crystal is an electron, the work function of the electrode material is preferably 5.0 eV or more. For example, as an electrode material having a work function of 5.0 eV or more, Co (5.0), Ge (5.0), Au (5.1), Pd (5.12), Ni (5.15), Ir (5.27), Pt (5.65), Se (5.9) can be used. The parentheses indicate work functions, and the unit is eV.

  On the other hand, when the carriers contributing to electrical conduction in the electro-optic crystal are holes, the work function of the electrode material is preferably less than 5.0 eV in order to suppress the injection of holes. For example, Ti (3.84) or the like can be used as an electrode material having a work function of less than 5.0 eV. Since the Ti single-layer electrode is oxidized and becomes high resistance, generally, the Ti layer and the electro-optic crystal are bonded using an electrode in which Ti / Pt / Au are sequentially laminated. Furthermore, transparent electrodes such as ITO (Indium Tin Oxide) and ZnO can also be used.

  FIG. 5 shows basic unit elements of a variable focus lens according to the second embodiment of the present invention. The basic unit elements described above are arranged in series along the optical axis direction. A plurality of electrodes 8a, 8b, 9a, 9b, 10a, 10b,... Are arranged on one substrate 6, and opposite voltages are applied to electrode pairs adjacent to each other. By configuring the element in this way, a large lens effect can be obtained even at a lower voltage. The number of electrode pairs may be even or odd as long as it is two or more.

  That is, 2N electrodes are provided on each of the first surface and the second surface of the substrate 6. When 1 ≦ k ≦ N−1, the k-th electrode from the light incident side is the k-th anode, formed on the second surface facing the first surface, and at the position facing the k-th anode. Let the formed electrode be the kth cathode. An electrode formed on the first surface and spaced apart from the kth anode is defined as a (k + 1) th cathode, formed on the second surface and formed at a position facing the (k + 1) th cathode, An electrode that is spaced apart from the (k + 1) th cathode is the (k + 1) th anode.

(Polarization-independent variable focus lens)
As described above, in order to realize a normal spherical lens, the optical axes of the two basic unit elements may be arranged in cascade and arranged at an angle of 90 degrees with respect to the optical axis. However, in the case of a single crystal material having inversion symmetry such as KTN, the lens effect may be completely reversed from a convex lens to a concave lens by polarization as shown in FIG. In order to realize a spherical lens, a light whose electric field oscillates in the z-axis direction is incident on the first basic unit element and is condensed in the z-axis direction. Incident on the basic unit element. However, according to this configuration, the light is diverged in the y-axis direction and does not function as a spherical lens.

  In order to function normally as a spherical lens, the polarization direction must also be rotated by 90 degrees in accordance with this element before entering the second basic unit element. Therefore, a structure in which a polarization rotation element is inserted between the first basic unit element and the second basic unit element is adopted. There are various types of polarization rotation elements, but a half-wave plate is most commonly used.

  The half-wave plate is an optical element that generates a phase shift corresponding to half the wavelength, that is, a phase shift of π radians, between two polarized waves orthogonal to each other. Typically, it consists of a birefringent material processed into a plate shape. A single crystal material having inversion symmetry such as KTN usually does not have birefringence. However, when an electric field is applied in one direction, birefringence occurs in a direction parallel to the electric field and in a direction perpendicular thereto. . By utilizing this property, a half-wave plate can be formed by KTN.

  FIG. 6 shows the configuration of a polarization-independent variable focus lens according to Example 1 of the present invention. The first polarized light separated by the polarization beam splitter (PBS) 11 is converted into a first basic unit element 12, a half-wave plate 13, and a second basic unit element 14 (first set) arranged in series. ). The second polarized light separated from the other polarization is passed through the optical mirror 16 through the third basic unit element 17, the half-wave plate 18 and the fourth basic unit element 19 (second Set). The voltage application direction by the electrode pair of the first basic unit element 12 and the voltage application direction by the electrode pair of the second basic unit element 14 are arranged so as to be orthogonal to each other. Similarly, the voltage application direction by the electrode pair of the third basic unit element 17 and the voltage application direction by the electrode pair of the fourth basic unit element 19 are arranged so as to be orthogonal to each other.

  The first to fourth basic unit elements are basic unit elements according to the first embodiment described above. When a voltage is applied to each of the electrodes of these four basic unit elements, the first set efficiently functions as a variable focus spherical lens, and the first polarized light is used as the first outgoing light. The light enters the polarization beam splitter (PBS) 20 through the optical mirror 15. The second set also functions efficiently as a variable focus spherical lens, and the second polarized light is incident on the PBS 20 as the second outgoing light. The first and second outgoing lights are polarized and synthesized by the PBS 20 and function as a variable focus lens independent of polarization as a whole.

  Although PBS is exemplified as the polarization separation / combination element, any element having a 1 × 2 polarization separation function and a 2 × 1 polarization combination function may be used. For example, a commercially available fiber-type polarization separation / combination element can be mentioned.

  The half-wave plate can also be formed of KTN, similar to the cylindrical variable focus lens that is the basic unit element described above. Molded integrally with the substrates of the front and rear basic unit elements, and the electrodes for the front and rear basic unit elements and the electrodes for the KTN half-wave plate are sequentially arranged and attached. In this way, an integrated polarization-independent spherical variable focus lens can be configured.

  As shown in FIG. 1, each of the first to fourth basic unit elements includes an anode 2 and a cathode 3 on a top surface and a bottom surface of a substrate 1 obtained by processing an electro-optic material into a plate shape, and a cathode 4 and an anode 5. Form. The substrate 1 is cut out from a KTN single crystal and formed into a shape of 7 mm × 7 mm × (thickness T =) 4 mm. All six surfaces of the substrate 1 are parallel to the (100) plane of the crystal and optical polishing is performed. Since this KTN single crystal had a phase transition temperature of 35 ° C., it is used at 40 ° C., which is slightly higher than this. The relative dielectric constant at this temperature is 20,000. The four electrodes have a strip shape of 0.8 mm × 7 mm, and the distance between the electrodes on the same plane is 4 mm. The two electrode pairs are formed by depositing platinum (Pt) on the 7 mm × 7 mm surface of the substrate 1. Each side of the electrode is parallel to the side of the substrate 1.

  A collimated non-polarized laser beam is incident on the varifocal lens with the temperature controlled at 40 ° C. The laser beam that has passed through the PBS 11 is polarized and separated and emitted along two orthogonal optical paths. One polarized light (first polarized light) is incident on the first basic unit element 12, the half-wave plate 13, and the second basic unit element 14. When a voltage is applied between the upper and lower electrodes of the first and second basic unit elements, the first emitted light is condensed in the z-axis direction and functions as a spherical convex lens. On the other hand, the other second polarized light is incident on the third basic unit element 17, the half-wave plate 18, and the fourth basic unit element 19. When a voltage is applied between the upper and lower electrodes of the third and fourth basic unit elements, the second emitted light is condensed in the z-axis direction and functions as a spherical convex lens. Finally, the two outgoing lights that have passed through the PBS 20 are combined to function as a polarization-independent spherical convex lens capable of high-speed operation.

  FIG. 7 shows the configuration of a polarization-independent variable focus lens according to Example 2 of the present invention. The first polarized light separated by the polarization beam splitter (PBS) 31 is converted into a first basic unit element 32, a half-wave plate 33, and a second basic unit element 34 (first set) arranged in series. ). The other polarization-separated second polarized light passes through the optical mirror 36, and the third basic unit element 37, the half-wave plate 38, and the fourth basic unit element 39 (second array) arranged in series. Set). The voltage application direction by the electrode pair of the first basic unit element 32 and the voltage application direction by the electrode pair of the second basic unit element 34 are arranged so as to be orthogonal to each other. Similarly, the voltage application direction by the electrode pair of the third basic unit element 37 and the voltage application direction by the electrode pair of the fourth basic unit element 39 are arranged so as to be orthogonal to each other.

  The first to fourth basic unit elements are basic unit elements according to the second embodiment described above. When a voltage is applied to each of the electrodes of these four basic unit elements, the first set efficiently functions as a variable focus spherical lens, and the first polarized light is used as the first outgoing light. The light enters the polarization beam splitter (PBS) 40 through the optical mirror 35. The second set also functions efficiently as a variable focus spherical lens, and the second polarized light is incident on the PBS 40 as the second outgoing light. The first and second outgoing lights are combined by polarization by the PBS 40 and function as a variable focus lens independent of polarization as a whole.

  Compared to Example 1, a large lens effect can be obtained even at a lower voltage. The number of electrode pairs may be even or odd as long as it is two or more.

1,6 substrate 2,5,8a, 9a, 10a anode 3,4,8b, 9b, 10b cathode 11, 20, 31, 40 polarization beam splitter (PBS)
12, 32 First basic unit element 13, 33, 18, 38 Half-wave plate 14, 34 Second basic unit element 15, 16, 35, 36 Optical mirror 17, 37 Third basic unit element 19, 39 4 basic unit elements

Claims (9)

An electro-optic material made of a single crystal having inversion symmetry, a first anode formed on the first surface of the electro-optic material, and a second surface facing the first surface. A first cathode formed at a position facing the first anode, a second cathode formed on the first surface and spaced from the first anode, and A second anode formed on a second surface and facing the second cathode, and spaced apart from the first cathode, orthogonal to the first surface When light is incident from the third surface, the light passes through the first electrode pair consisting of the first anode and the first cathode, and then the second anode and the second cathode. The optical axis is set so that light is transmitted through the second electrode pair consisting of the first electrode and the fourth surface facing the third surface. First to fourth unit elements are,
The first unit element is disposed on the optical axis between the first unit element and the second unit element by matching the optical axis of the first unit element with the optical axis of the second unit element. Half-wave plate,
The second unit element is arranged on the optical axis between the third unit element and the fourth unit element by matching the optical axis of the third unit element with the optical axis of the fourth unit element. Half-wave plate,
The incident light is polarized and separated into first polarized light and second polarized light, the first polarized light is incident on the first unit element, and the second polarized light is transmitted to the third unit. A polarization separation element incident on the element;
A polarization beam combining element that combines the first emitted light emitted from the second unit element and the second emitted light emitted from the fourth unit element;
The direction of voltage application by the first and second electrode pairs of the first unit element and the direction of voltage application by the first and second electrode pairs of the second unit element are orthogonal to each other, and The voltage application direction by the first and second electrode pairs of the third unit element and the voltage application direction by the first and second electrode pairs of the fourth unit element are arranged to be orthogonal to each other; A variable focus, wherein the focus of the light emitted from the polarization beam combiner is varied by changing an applied voltage between the first and second electrode pairs of the first to fourth unit elements. lens. Wherein at least one of the first to fourth unit elements as a pair of the first and second electrode pair along the direction of the optical axis, arranged in series along a plurality of sets in the direction of the optical axis The variable focus lens according to claim 1, wherein electrode pairs adjacent to each other have opposite polarities .   The variable focus lens according to claim 1, wherein the electro-optic material is a perovskite single crystal material. The electro-optical material, potassium tantalate niobate _{(KTN: KTa 1-x Nb} x O 3, 0 <x <1) variable focus lens according to claim 3, characterized in that the.   The electro-optic material is characterized in that the main component of the crystal is composed of groups Ia and Va in the periodic table, group Ia is potassium, and group Va includes at least one of niobium and tantalum. The variable focus lens according to claim 3.   6. The variable focus lens according to claim 5, wherein the electro-optic material further includes one or more members of Group Ia or Group IIa of the periodic table excluding potassium as an additive impurity.   The variable focus lens according to claim 1, wherein the anode and the cathode are made of a material that forms a Schottky junction with the electro-optic material.   The variable focus lens according to claim 7, wherein the anode and the cathode have a belt-like shape, and their longitudinal sides are all parallel.   The variable focus lens according to claim 7 or 8, wherein G <1.5T, where G is a distance G between the anode and the cathode and a thickness T of the electro-optic material.

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