JP2014026229A - Variable focus lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a variable focus lens capable of varying a focal length at high speed.SOLUTION: A variable focus lens includes: an electro-optical material comprising a single crystal having inversion symmetry; a plurality of electrode pairs, in which each pair of electrodes is formed on a first surface of the electro-optical material and on a second surface opposing to the first surface, at positions opposing to each other; and a light-emitting element disposed so as to illuminate the electro-optical material. By changing a voltage applied between the electrode pair, the focus of light transmitted through the electro-optical material can be changed.

Description

  The present invention relates to a variable focus lens, and more particularly to a variable focus lens that can change a focal length using an optical material having an electro-optic effect.

  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 Non-Patent Document 1 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.

Japanese Patent Laid-Open No. 11-64817

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, 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 capable of changing the focal length at high speed.

  In order to achieve such an object, an embodiment of the present invention is directed to an electro-optic material made of a single crystal having inversion symmetry, a first surface of the electro-optic material, and facing the first surface. A plurality of electrode pairs formed at positions facing each of the second surfaces, and a light emitting element arranged to illuminate the electro-optic material, and changing an applied voltage between the electrode pairs The focus of the light transmitted through the electro-optic material is varied.

The electro-optic material is preferably a perovskite single crystal material, and typically, potassium tantalate niobate (KTN: KTa _1-x Nb _x O ₃ , 0 <x <1) can be used. 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.

  As described above, according to the present invention, an electro-optic material made of a single crystal having inversion symmetry and a plurality of electrode pairs formed on the surface of the electro-optic material, the applied voltage between the electrode pairs. Since the focal point of the emitted light is controlled by changing the focal length, the focal length can be changed at high speed.

  In addition, since the light-emitting element that can illuminate the electro-optic material is provided, the space charge generated inside the electro-optic material can be eliminated, and the desired focal length and the shape of the focused spot can always be obtained. .

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 1st Embodiment. It is a figure which shows the example of the optical path length of the variable focus lens concerning 1st Embodiment. It is a figure which shows an example of a structure which irradiates uniform light to a variable focus lens. It is a figure which shows the structure of the variable focus lens concerning the 3rd Embodiment of this invention. It is a figure which shows the structure of the variable focus lens concerning the 5th Embodiment of this invention. It is a figure which shows the structure of the variable focus lens concerning the 6th Embodiment 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 utilizing the electro-optic effect of the inorganic crystal, a much faster response speed can be obtained as compared with the conventional variable focus lens. First, a basic variable focus lens will be described.

(Configuration of cylindrical variable focus lens)
FIG. 1 shows the configuration of a variable focus lens according to the first embodiment of the present invention. Two electrode pairs 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 at positions facing each other. 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.

  Incident light 6 is incident from a surface (third surface) orthogonal to the surface on which the electrodes are arranged, travels in the x-axis direction inside the substrate 1, and between these anodes 2 and 3, It penetrates in a direction perpendicular to the longitudinal direction. Next, after passing between the cathode 4 and the anode 5, the outgoing light 7 is emitted from the surface (fourth surface) opposite to 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.

  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 element shown in FIG. 1 is a cylindrical variable focus lens and is a basic unit constituting various lenses. In order to realize a normal spherical lens, two cylindrical variable focus lenses and a half-wave plate inserted between them are combined as basic unit elements, and the two basic unit elements are 90.degree. Arrange them at an angle of degrees. In this way, the light is condensed or diverged in the biaxial direction, which is called biaxial modulation. 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 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.

(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 function as a lens 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)
Here, the optical path length modulation will be described in detail. 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 the y-axis direction and when the direction is the z-axis direction. In each case, the refractive index modulation Δn felt by the light is different, so the optical path length modulation Δs is also different.

  FIG. 3 shows an example of the optical path length of the variable focus lens according to the first embodiment. The vertical axis represents the optical path length modulation Δs obtained by numerical calculation when the direction of the optical electric field is the z-axis direction. 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 of FIG. 3 shows the displacement from the origin with the center of the substrate 1 in the z coordinate shown in FIG. 2 as the origin. The distribution of Δs forms an upward convex curve, and this element functions as a cylindrical convex lens. In this example, the lens is a convex lens. However, since the optical path length modulation differs depending on the polarization as described above, the lens may be a concave lens.

(Initialization function)
The principle of the variable focus lens of the present embodiment has been described above, but this variable focus lens has one problem. An electro-optic material having inversion symmetry typified by KTN may generate a space charge inside when an electric field is applied to the electro-optic material. The space charge is generated when free carriers (electrons or holes) generated for some reason in the electro-optic material move inside the electro-optic material and are trapped (trapped) by local defects therein. The space charge generates an electric field distribution around the space charge and disturbs the electric field distribution suitable for moving the focal point. That is, even when a predetermined voltage is applied, the desired focal length and the shape of the focused spot may not be obtained. Therefore, it is important not to generate space charges in applications to variable focus lenses.

  Free carriers may be generated from the outside by an electrode or generated by photoexcitation or thermal excitation inside the crystal. About the former, generation | occurrence | production can be suppressed with an electrode material so that it may mention later. However, when a voltage is applied for a long time, the accumulation of carriers injected with a slight leakage current may not be ignored. Of the latter factors, it is very difficult to avoid thermal excitation. Although the degree of generation of photoexcitation varies depending on the wavelength of light, it is unavoidable that it is an element that controls light.

  Therefore, in the present embodiment, a light emitting element having a short wavelength is provided as a part of the variable focus lens element, and the problem is solved by using light excitation in reverse. When the electro-optic material is partially irradiated with light, free carriers are generated in that portion. The generated free carriers move to another place in the electro-optic material due to diffusion or drift due to an electric field, and are trapped there. That is, it becomes space charge and generates non-uniform charge distribution.

  However, when the electro-optic material is uniformly irradiated with light, even if the photo-excited carriers are trapped in another place, they are photo-excited again there. When carriers are injected from the outside through an electrode, etc., and the whole is in a charged state that is positively or negatively biased, surplus carriers will leave the electrode after a certain period of time has passed since this uniform light irradiation was started. Return to the electrically neutral state before carrier injection. In addition, even if there is no external carrier injection and the average charge of the entire electro-optic material is not biased, even if space charges are generated due to partial bias, the neutral charge state is uniformly uniform as a whole. Return to. That is, the space charge disappears and is initialized, and when a predetermined voltage is applied, the desired focal length and the shape of the focused spot can always be obtained.

  As the light emitting element, any kind of incandescent bulb, fluorescent tube or laser can be used. A light emitting diode (LED) or a semiconductor laser (LD) can be suitably used as it is small in size, has high luminous efficiency, and has small temperature fluctuation due to heat generation. Furthermore, the shorter the wavelength of the light source, the higher the photon energy, the higher the efficiency of initialization, and the initialization time can be shortened. In particular, LEDs and LDs that contain gallium nitride as a main component and generate ultraviolet rays in the vicinity of 405 nm are manufactured as general-purpose products, and when these are used, initialization efficiency is high. When the wavelength becomes shorter than this, the photon energy exceeds the band gap of KTN, so that the absorption becomes very strong, and the light is completely absorbed near the surface of KTN and does not reach the inside. For this reason, uniform light irradiation cannot be performed and it is unsuitable for initialization.

  If you start using the varifocal lens from a state where it has not been used for a long time, if you apply voltage for a long time, or if you use a strong light with non-uniform intensity on the electro-optic material, the space charge will be lost. It is assumed that it has occurred. Therefore, it is a preferred usage of the present embodiment that the space charge is erased and initialized by irradiating the LED or LD provided in the variable focus lens for a certain period.

  FIG. 4 shows an example of a configuration for irradiating the variable focus lens with uniform light. The relationship between the light source 21 and the substrate 1 of the electro-optic crystal constituting the variable focus lens, the electrode, the luminous flux (incident light 6 and outgoing light 7) receiving the lens effect is shown. Although the example which illuminates uniformly from the downward direction of the board | substrate 1 is shown, it is not limited to this figure, You may arrange | position the light source 21 of uniform illumination in which direction. The light source 21 may be a single light emitting element or may be an integrated plurality of light emitting elements.

(Place electrode)
In the varifocal lens of the first embodiment shown in FIG. 1, the anode 2 and the cathode 4 are arranged on the upper surface of the substrate 1 and the cathode 3 and the anode 5 are arranged on the lower surface as basic unit elements. However, the basic unit element may have a configuration in which both the electrodes on the upper surface are anodes and the electrodes on the lower surface are both cathodes. The lens effect is small compared to the variable focus of the first embodiment, but the function is the same (second embodiment).

  FIG. 5 shows the configuration of a variable focus lens according to the third embodiment of the present invention. The arrangement of the electrodes 32-35 with respect to the substrate 31 is the same as in the first embodiment of FIG. The incident direction of the incident light 36 and the outgoing direction of the outgoing light 37 are different. As shown in FIG. 5, the incident light 36 is incident from between the anode 32 and the cathode 34 on the upper surface of the substrate 31, travels in the z-axis direction inside the substrate 31, and is formed between the cathode 33 and the anode 35 on the lower surface. It is emitted as emitted light 37 from the space to the air. According to the structure of FIG. 5, it functions as a cylindrical convex lens, and when divergent, it functions as a cylindrical concave lens.

  Further, in the third embodiment, both of the upper electrode may be an anode and both of the lower electrodes may be a cathode, and conversely, the upper surface may be a cathode and the lower surface may be an anode (fourth embodiment). Form).

  FIG. 6 shows a configuration of a variable focus lens according to the fifth embodiment of the present invention. This is a further application of the basic unit element of the first embodiment, in which a plurality of electrodes are arranged in series along the optical axis direction. A plurality of anodes 42a, 42b, 42c and cathodes 43a, 43b, 43c are arranged on one substrate 41, and voltages having opposite polarities are applied to electrode pairs adjacent to each other. Incident light 46 is incident from a surface orthogonal to the surface on which the electrodes are arranged, travels in the x-axis direction inside the substrate 41, and is emitted as emitted light 47 from the surface opposite to the incident surface into the air.

  When 2N electrodes are formed on the surface of the electro-optic material, the kth (1 ≦ k ≦ N−1) electrode from the light incident side on the upper surface (first surface) of the substrate 41 is the kth anode. And an electrode arranged at an interval from the kth anode is referred to as a (k + 1) th cathode. On the lower surface (second surface) of the substrate 41, an electrode formed at a position facing the kth anode is a kth cathode, and an electrode spaced from the k + 1th cathode is a k + 1th electrode. The anode is formed at a position facing each other.

  Similarly to the second embodiment, a voltage having the same polarity may be applied to all the electrode pairs on the upper surface, and a voltage having the same polarity may be applied to all the electrode pairs on the lower surface. Of course, the voltage may be applied in an arbitrary pattern. 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.

(Polarization rotation element)
As described above, a half-wave plate is necessary for biaxial modulation. This half-wave plate is generally a polarization rotation element that rotates polarized light by 90 degrees. Any element that rotates the polarized light by 90 degrees may be used. In addition to a half-wave plate as a representative example, a Faraday rotation element or the like can be used instead.

  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. KTN usually does not have birefringence, but 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. 7 shows the configuration of a polarization-independent variable focus lens according to the sixth embodiment of the present invention. The first basic unit element 51, the KTN half-wave plate 53, and the second basic unit element 52 are arranged in series along the optical axis direction. The shape of the KTN half-wave plate 53 is a rectangular parallelepiped shape, and an electrode film is formed over almost the entire surface on two surfaces facing each other. By applying a voltage to the electrode pair, an electric field perpendicular to these two surfaces is uniformly formed. By adjusting the magnitude of the voltage, a phase difference of π radians can be generated between the orthogonal polarizations. The direction of the electric field is arranged so as to form an angle of 45 degrees with respect to the voltage application direction of the first basic unit element 51 and the second basic unit element 52, that is, the normal line of the electrode surface. As a result, the polarization of the light transmitted through the first basic unit element 51 is rotated by 90 degrees.

  When the half-wave plate is also made of KTN like the cylindrical variable focus lens that is the basic unit element described above, a substrate made of three electro-optic materials is integrally molded, and an electrode for the first basic unit element 51; An electrode for the KTN half-wave plate 53 and an electrode for the second basic unit element 52 are attached in order. In this way, an integrated polarization-independent variable focus lens can be configured.

(Electrode material)
When a high voltage is applied to the electro-optic material, charges are injected from the electrodes, and space charges are generated in the crystal. As described above, this space charge disturbs the refractive index distribution and adversely affects the lens function.

  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.

  As shown in the first embodiment (FIG. 1), the anode 2, the cathode 3, the cathode 4, and the anode 5 are formed on the upper and lower surfaces of the substrate 1 obtained by processing the electro-optic material into a plate shape. 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.

  Further, an LED for illuminating the substrate 1 was installed at a position that does not block the optical path of the light to be modulated by the variable focus lens and in the vicinity of the substrate 1. The emission wavelength of the LED is 405 nm.

  Collimated laser light is incident on the cylindrical variable focus lens while the temperature is controlled at 40 ° C. The polarization of light is a straight line, and the direction of the oscillating electric field is the z-axis direction. When a voltage of 1000 V is applied between the upper and lower electrodes, the light emitted from the substrate 1 is condensed in the z-axis direction and functions as a cylindrical convex lens. The focal length is 59 cm.

  When this cylindrical variable focus lens was used at 1000 V for a long time, the focal length shifted from the original 59 cm to about 100 cm, and the shape of the focused spot was also deteriorated. Therefore, the initialization was performed by energizing the provided LED and irradiating the substrate 1 with 5 mW light for 1 minute. As a result, the focal length and the shape of the focused spot were restored.

  In the basic unit element fabricated in Example 1, as shown in the second embodiment, both the upper surface electrodes are used as anodes and the lower surface electrodes are both used as cathodes. Collimated laser light is incident on the cylindrical variable focus lens while the temperature is controlled at 40 ° C. The polarization of light is a straight line, and the direction of the oscillating electric field is the z-axis direction. When a voltage of 1000 V is applied between the upper and lower electrodes, the light emitted from the substrate 1 is condensed in the z-axis direction and functions as a cylindrical convex lens. The focal length is 115 cm.

  When this cylindrical variable focus lens was used for a long time under the same conditions, the focal length was shifted to about 160 cm, and the shape of the focused spot was deteriorated. Therefore, the initialization was performed by energizing the provided LED and irradiating the substrate 1 with 5 mW light for 1 minute. As a result, the focal length and the shape of the focused spot were restored.

  The basic unit element produced in Example 1 is used as the cylindrical variable focus lens shown in the third embodiment (FIG. 5). Collimated laser light is incident on the cylindrical variable focus lens while the temperature is controlled at 40 ° C. The polarization of light is a straight line, and the direction of the oscillating electric field is the x-axis direction. When a voltage of 1000 V is applied between the upper and lower electrodes, the light emitted from the substrate 31 is condensed in the x-axis direction and functions as a cylindrical convex lens. The focal length is 104 cm.

  When this cylindrical variable focus lens was used for a long time under the same conditions, the focal length was shifted to about 150 cm, and the shape of the focused spot was deteriorated. Therefore, the initialization was performed by energizing the provided LED and irradiating the substrate 31 with 5 mW light for 1 minute. As a result, the focal length and the shape of the focused spot were restored.

  In the basic unit element fabricated in Example 3, as shown in the fourth embodiment, both the upper surface electrodes are used as anodes and the lower surface electrodes are both used as cathodes. Under the same conditions as in Example 3, the focal length was 114 cm.

  When this cylindrical variable focus lens was used for a long time under the same conditions, the focal length was shifted to about 160 cm, and the shape of the focused spot was deteriorated. Therefore, the initialization was performed by energizing the provided LED and irradiating the substrate 31 with 5 mW light for 1 minute. As a result, the focal length and the shape of the focused spot were restored.

1, 31, 41 Substrate 2, 5, 32, 35, 42 Anode 3, 4, 33, 34, 43 Cathode 6, 36, 46 Incident light 7, 37, 47 Emitted light 11 Electric field lines 12 Refractive index modulation curve 21 Light source 51, 52 Basic unit element 53 KTN half-wave plate

Claims (15)

An electro-optic material made of a single crystal having inversion symmetry;
A plurality of electrode pairs formed at positions facing the first surface of the electro-optic material and the second surface opposite to the first surface;
A light emitting element arranged to illuminate the electro-optic material,
A variable focus lens, wherein a focus of light transmitted through the electro-optic material is varied by changing an applied voltage between the electrode pair. The electrode pair is
A first anode formed on the first surface of the electro-optic material and a second surface formed on a second surface opposite to the first surface and facing the first anode. A first electrode pair composed of one cathode, a second cathode formed on the first surface and spaced from the first anode, and on the second surface A second electrode pair formed with a second anode formed at a position facing the second cathode and spaced apart from the first cathode;
When light is incident from a third surface orthogonal to the first surface, the light passes through the first electrode pair and then passes through the second electrode pair, so that the third Light is emitted from the fourth surface opposite to the surface of
The focus of light emitted from the fourth surface of the electro-optic material is varied by changing an applied voltage between the first and second electrode pairs. Variable focus lens. The electrode pair is
A first anode formed on a first surface of the electro-optic material;
A first cathode formed on a second surface opposite to the first surface and formed at a position facing the first anode;
A second cathode formed on the first surface and spaced from the first anode;
A second anode formed on the second surface, facing the second cathode, and spaced apart from the first cathode;
When light is incident on the first surface between the first anode and the second cathode and passes through the electro-optic material, the first cathode and the second anode Light is emitted from the second surface between
The focus of light emitted from the second surface of the electro-optic material is varied by changing an applied voltage between the two anodes and the two cathodes. Variable focus lens. The electrode pair is
A first anode formed on the first surface of the electro-optic material and a second surface formed on a second surface opposite to the first surface and facing the first anode. A first electrode pair comprising a first cathode; a second anode formed on the first surface and spaced apart from the first anode; and on the second surface A second electrode pair formed with a second cathode formed at a position facing the second anode and spaced apart from the first cathode;
When light is incident from a third surface orthogonal to the first surface, the light passes through the first electrode pair and then passes through the second electrode pair, so that the third Light is emitted from the fourth surface opposite to the surface of
The focus of light emitted from the fourth surface of the electro-optic material is varied by changing an applied voltage between the first and second electrode pairs. Variable focus lens. The electrode pair is
A first anode formed on a first surface of the electro-optic material;
A first cathode formed on a second surface opposite to the first surface and formed at a position facing the first anode;
A second anode formed on the first surface and spaced from the first anode;
A second cathode formed on the second surface and facing the second anode, and spaced apart from the first cathode;
When light is incident on the first surface between the first anode and the second anode and passes through the electro-optic material, the first cathode and the second cathode Light is emitted from the second surface between
The focus of light emitted from the second surface of the electro-optic material is varied by changing an applied voltage between the two anodes and the two cathodes. Variable focus lens. The electrode pair includes 2N electrodes formed on the surface of the electro-optic material,
When 1 ≦ k ≦ N−1, a second electrode is formed on the first surface of the electro-optic material, and the second electrode is opposite to the first surface with the kth electrode from the light incident side as the kth anode. The electrode formed on the surface and facing the kth anode is the kth cathode,
The electrode formed on the first surface and spaced apart from the kth anode is the (k + 1) th cathode, and is formed on the second surface and faces the (k + 1) th cathode. And the k + 1th anode is an electrode spaced from the (k + 1) th cathode,
When light is incident from a third surface orthogonal to the first surface, it is formed between the electrode pair composed of the kth anode and the kth cathode, and the Nth anode and the Nth cathode. Light is emitted from a fourth surface that passes between the electrode pair and faces the third surface,
2. The variable focus lens according to claim 1, wherein a focus of light emitted from the fourth surface of the electro-optic material is varied by changing an applied voltage between the k-th and N-th voltages. .   7. The variable focus lens according to claim 1, wherein the electro-optic material is a single crystal material having a perovskite crystal structure. The electro-optical material, potassium tantalate niobate _{(KTN: KTa 1-x Nb} x O 3, 0 <x <1) variable focus lens according to claim 7, 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 7.   10. The variable focus lens according to claim 9, 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.   3. The first and second anodes, the first and second cathodes, and the 2N electrodes are made of a material that forms a Schottky junction with the electro-optic material. The variable focus lens according to any one of 6.   The first and second anodes, the first and second cathodes, and the 2N electrodes have a strip shape, and all of the longitudinal sides thereof are parallel to each other. Item 12. The variable focus lens according to Item 11.   The variable focus lens according to claim 1, wherein the light emitting element is a light emitting diode.   The variable focus lens according to claim 1, wherein the light emitting element is a semiconductor laser.   15. The variable focus lens according to claim 13, wherein the light emitting element is mainly composed of gallium nitride.

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