JP4663578B2 - Electro-optic element and manufacturing method thereof - Google Patents

Description

  The present invention relates to an electro-optical element and a manufacturing method thereof, and more particularly to an electro-optical element that changes the direction of light by an electric signal using an electro-optical crystal and a manufacturing method thereof.

  Currently, there is an increasing demand for light control elements for deflecting laser light in projectors and other video equipment, laser printers, high-resolution confocal microscopes, barcode readers, and the like. Proposed technologies to deflect light include a technology that rotates a polygon mirror, a technology that controls the deflection direction of light with a galvanometer mirror, a light diffraction technology that uses the acousto-optic effect, and a micromachine technology called MEMS (Micro Electro Mechanical System). Has been.

  The polygon mirror mechanically rotates a mirror having a polyhedral shape, and deflects light by continuously changing the reflection direction of laser light. The method using a polygon mirror uses mechanical rotation. For this reason, the rotational speed is limited, and it is difficult to obtain a rotational speed of 10,000 rpm or more, and there is a drawback that it is not suitable for applications requiring high-speed operation. A method using a polygon mirror is used for deflection of laser light of a laser printer, and the rotational speed of the polygon mirror is a bottleneck in increasing the printing speed of the printer. In order to further improve the printing speed of the printer, a higher speed light deflection technique is required.

  Galvano mirrors are used in laser scanners that deflect and scan laser light. A conventional practical galvanometer mirror has a magnetic path composed of, for example, a movable iron piece that replaces a movable coil disposed in a magnetic field, and a magnetic body provided with two permanent magnets and four magnetic poles around it. Yes. By changing the magnetic flux between the magnetic poles according to the magnitude and direction of the current flowing through the drive coil wound around the magnetic body, the reflecting mirror is oscillated through the movable iron piece, and the laser beam is deflected and scanned. The method using the galvanometer mirror can operate at a higher speed than the polygon mirror. However, it is difficult to reduce the size of the conventional galvanometer mirror further because the drive coil is mechanically wound. Therefore, it is difficult to further reduce the size of a laser scanning system using a galvano mirror and a laser application device using this system. In addition, there is a disadvantage that the power consumption is large, and furthermore, it cannot be operated at a high speed in a cycle of MHz.

  An optical diffractive optical deflector utilizing the acousto-optic effect has also been put into practical use. However, this method using a light diffraction type optical deflector has the disadvantages of high power consumption, difficulty in miniaturization, and difficulty in obtaining a large deflection angle and high speed operation. Also, the method using MEMS has a limit of a response of several tens of microseconds because a fine mirror is electrostatically driven as an optical deflection element.

  As means for solving the above problems, a technique for deflecting a beam using an electro-optic crystal processed into a prism shape or an electro-optic crystal produced with a prism-shaped electrode has been developed (for example, Patent Document 1 and Patent). Reference 2). When a voltage is applied to the electrode of the electro-optic crystal, the refractive index can be changed by the electro-optic effect. The method using an electrode manufactured in a prism shape creates a region in which the refractive index changes in the electro-optic crystal and a region in which no refractive index is changed because no voltage is applied. The beam is deflected by the difference in refractive index formed at the boundary between these two regions to obtain a deflection angle.

The method using the electro-optic crystal can respond to the speed limit of the electro-optic effect, and a response exceeding GHz is possible. To date, there have been reports using LiNbO ₃ (hereinafter referred to as LN crystal) and PLZT as an optical deflection element using an electro-optic crystal. However, since an element using an LN crystal has a small electro-optic effect, there is a drawback that only a deflection angle of about 3 mrad can be obtained even when a voltage of about 5 kV / mm is applied. Furthermore, even in an element using PLZT, a deflection angle of about 45 mrad with respect to an applied electric field of 20 kV / mm is a limit (for example, see Non-Patent Document 1).

JP 09-159950 A Japanese Patent Laid-Open No. 10-239717 Akio Sakuma, 5 others, “Development of EO waveguide deflection type optical switch”, IEICE Technical Report, The Institute of Electronics, Information and Communication Engineers, October 2004, PN 2004-59, p. 61-64

  However, in the conventional method, the refractive index change due to the electro-optic effect of each prism region is small, and the deflection angle due to the refractive index change is also small. Therefore, in order to obtain a large deflection angle in the conventional method, it is necessary to arrange a plurality of prisms. However, when a plurality of prisms are arranged, there is a problem that a desired resolution cannot be obtained when light enters the prism at a large incident angle.

  The present invention has been made in view of such problems, and an object of the present invention is to provide an electro-optical element having a simple configuration and a manufacturing method thereof that can efficiently increase the deflection of the beam. There is to do.

In order to achieve such an object, the electro-optical element according to the present invention has an electro-optic effect of K _1-y Li _y Ta _1-x Nb _x O ₃ (0 <x <1 , 0 ≦ y <1), and an electrode pair consisting of a positive electrode and a negative electrode that generates an electric field inside the electro-optic crystal, and when a voltage is applied between the electrode pair, A carrier is injected into the electro-optic crystal, and a pressure applying means for applying a pressure parallel to a growth direction of the crystal of the electro-optic crystal , wherein the internal stress of the electro-optic crystal is caused by the pressure. And a pressure applying means that is relaxed .

The pressure applying means preferably applies a pressure perpendicular to the direction of the electric field, and further preferably applies a pressure of 1 × 10 ⁶ Pa or more.

  According to a fourth aspect of the present invention, the electrode pair according to the first, second, or third aspect is made of a material that is in ohmic contact with a carrier that contributes to electric conduction of the electro-optic crystal. .

The relative permittivity of the electro-optical crystal according to any one of claims 1 to 4, characterized in that 500 to 40,000.

When the carriers contributing to the electrical conduction of the electro-optic crystal are electrons, the material of the electrode pair preferably has a work function of less than 5.0 eV, and the material of the electrode pair is Cs, Rb, K, Sr. Ba, Na, Ca, Li, Y, Sc, La, Mg, As, Ti, Hf, Zr, Mn, In, Ga, Cd, Bi, Ta, Pb, Ag, Al, V, Nb , Zn, One of Sn, B, Hg, Cr, Si, Sb, W, Mo, Cu, Fe, Ru, Os, Te, Re, Be, and Rh. The material of the electrode pair may be either ITO or ZnO.

  When the carriers contributing to the electric conduction of the electro-optic crystal are holes, the material of the electrode pair preferably has a work function of 5.0 eV or more, and the material of the electrode pair is Co, Ge, Au, One of Pd, Ni, Ir, Pt, and Se.

The invention according to claim 11 is an electrode pair composed of a positive electrode and a negative electrode, which generates an electric field inside an electro-optic crystal having an electro-optic effect, and applying the voltage between the electrode pair Forming a pair of electrodes for injecting carriers into the electro-optic crystal on opposing surfaces of the electro-optic crystal, wherein the electro-optic crystal is K _1-y Li _y Ta _1-x Nb _x A first step of O ₃ (0 <x <1, 0 ≦ y <1), and a step of applying a pressure in parallel with the crystal growth direction of the electro-optic crystal, wherein the electric pressure is applied by the pressure. An electro-optic element manufacturing method comprising: a second step in which internal stress of the optical crystal is relaxed .

In the pressure application step, it is preferable to apply a pressure perpendicular to the direction of the electric field, and it is preferable to apply a pressure of 1 × 10 ⁶ Pa or more.

  As described above, according to the present invention, since the pressure is applied in parallel with the crystal growth direction of the electro-optic crystal, the refractive index distribution remaining after the voltage application is stopped by relaxing the internal stress of the crystal. Therefore, it is possible to efficiently increase the deflection of the beam and to respond at high speed, and it is possible to manufacture an electro-optic element having a simple configuration.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The electro-optical element according to the embodiment of the present invention generates an electric charge in the electro-optical crystal by causing an electric charge to be generated inside the electro-optical crystal. As a method for generating an electric field gradient in the electro-optic crystal, generation of space charges accompanying high electric field electric conduction of the crystal can be used. High electric field conduction here refers to electric conduction in a region in a space charge limited state where the relationship between voltage and current deviates from Ohm's law and the current increases nonlinearly with respect to voltage. In this space charge limited region, space charge is formed in the crystal when the bulk current in the crystal is smaller than the current injected from the electrode.

  The inclination of the electric field generated inside the electro-optic crystal causes the change in refractive index due to the electro-optic effect in the cross section perpendicular to the optical axis of the incident beam to be refracted according to the inclination of the electric field. A rate slope occurs. The inclination of the refractive index causes an inclination in the traveling speed distribution of light on a cross section perpendicular to the optical axis of the beam. As a result, while the light propagates through the crystal, the light traveling direction is continuously changed according to the gradient of the refractive index, and the deflection angle is accumulated. Thereby, a large deflection angle can be obtained with a simple configuration.

  FIG. 1 shows the principle of the generation of an electric field gradient due to charges inside the crystal. Each of the elements shown in FIGS. 1A and 1B includes an electro-optic crystal 1 sandwiched between a positive electrode 2 and a negative electrode 3 in parallel. 1C and 1D are graphs in which the vertical axis represents the distance from the negative electrode 3 to the positive electrode 2 and the horizontal axis represents the strength of the electric field in the electro-optic crystal 1. FIG. 1A shows a case where there is no space charge in the electro-optic crystal 1 and the electric field is constant. In this case, the electric field is constant over the entire space between the positive electrode 2 and the negative electrode 3. On the other hand, FIG. 1B shows a case where the space charge limited state is generated by the space charge in the electro-optic crystal 1. In the space charge limited state, the electric field is terminated by the space charge generated in the electro-optic crystal 1, and the electric field distribution in the electro-optic crystal 1 is inclined. This space charge can be either a positive charge or a negative charge, or both a positive charge and a negative charge, depending on the composition of the electro-optic crystal 1.

  FIG. 2 shows the principle of light deflection according to an embodiment of the present invention. In FIG. 2, the x-axis direction is the thickness direction of the electro-optic crystal 1 (the direction from the positive electrode 2 to the negative electrode 3 or from the negative electrode 3 to the positive electrode 2 in FIG. 1). The refractive index n (x) that linearly changes in the thickness direction (x-axis direction) of the electro-optic crystal 1 is set to n as the refractive index at x = 0, and the amount of change in the refractive index from the refractive index n at x is Δn. As (x), n (x) = n + Δn (x). When a beam having a diameter D in the cross section perpendicular to the optical axis passes through the electro-optic crystal 1, the difference in refractive index between the upper end and the lower end of the beam is Δn (D) −Δn (0). Given in. If the length of the part where the refractive index through which the beam passes is inclined, that is, the interaction length L, a shift 5 occurs in the equiphase surface 4 between the upper and lower ends of the beam after propagation of the length L. The distance of the deviation 5 of the equiphase surface 4 between the upper end and the lower end is given by the following equation.

  At this time, if the inclination θ of the beam propagation direction 6 is sufficiently smaller than the diameter in the cross section perpendicular to the optical axis of the beam, the following equation is obtained.

  When this is emitted from the end face of the electro-optic crystal 1 to the outside where the refractive index can be approximated to 1, it is refracted at the boundary surface between the electro-optic crystal 1 and the outside, and the total deflection angle of the incident light from the optical axis is .

  Here, a change in refractive index due to the electro-optic effect is considered. The change in the refractive index due to the electro-optic effect is given by the following equations for the first-order Pockels effect and the second-order Kerr effect, respectively.

Here, r _ij is a primary electro-optic constant, s _ij is a secondary electro-optic constant, and E is an electric field inside the crystal.

  When the electric field is changed in the thickness direction of the crystal by generating an electric charge in the crystal and terminating the electric field generated by the electric charge before reaching the ground electrode, the electric field is E (x) Is expressed by the following equation.

  These equations show that a non-zero deflection angle can be obtained if the electric field E (x) varies depending on x.

  As shown in FIG. 1B, when a voltage V is applied between the positive electrode 2 and the grounded negative electrode 3 to the electro-optic crystal 1 having a thickness d in a space charge limited state, it is expressed by the following equation. A spatial distribution of the electric field E appears.

Here, x is a position from the side surface of the electro-optic crystal 1 in contact with the negative electrode in the direction from the negative electrode to the opposite positive electrode, and x ₀ is a constant determined by the material of the electro-optic crystal and the electrode.

  Here, when the electric field E is approximated by the following equation,

The refractive index change Δn induced through the electro-optic effect can be expressed by the following equation by substituting equation (8) into equations (4) and (5) in the case of the primary Pockels effect and the secondary Pockels effect. Given.

  Therefore, from the equations (6), (7), (10), and (11), the deflection angle θ (x) becomes the following equation.

  As described above, by generating an electric charge inside the electro-optic crystal, a gradient is generated in the electric field generated by the voltage applied to the crystal from the outside, and the beam is generated by the electro-optic effect using the gradient of the electric field. It is possible to deflect.

When the beam is deflected by the Pockels effect, an element whose deflection angle changes depending on the position of the beam is realized. On the other hand, when the beam is deflected using the Kerr effect, an element having a constant deflection angle can be realized regardless of the position of the beam. In order to increase the beam deflection angle, it is desirable to use an electro-optic crystal having a large electro-optic constant r _ij or s _ij . Examples of such an electro-optic crystal having a large electro-optic constant include a ferroelectric phase KLTN crystal having a large Pockels constant r _ij and a paraelectric phase KLTN crystal having a large Kerr constant s _ij . The KLTN crystal is a crystal of K _1-y Li _y Ta _1-x Nb _x O ₃ (0 <x <1, 0 <y <1).

Other electro-optic crystals having a large electro-optic constant include LiNbO ₃ , LiTaO ₃ , LiIO ₃ , KNbO ₃ , KTiOPO ₄ , BaTiO ₃ , SrTiO ₃ , Ba _1-x Sr _x TiO ₃ (0 <x <1), _{Ba 1-x Sr x Nb 2} O 6 (0 <x <1), Sr 0.75 Ba 0.25 Nb 2 O 6, Pb 1-y La y Ti 1-x Zr x O 3 (0 <x <1,0 < y <1), Pb (Mg _1/3 Nb _2/3 ) O ₃ —PbTiO ₃ , KH ₂ PO ₄ , KD ₂ PO ₄ , (NH ₄ ) H ₂ PO ₄ , BaB ₂ O ₄ , LiB ₃ O ₅ , CsLiB ₆ O ₁₀ , GaAs, CdTe, GaP, ZnS, ZnSe, ZnTe, CdS, CdSe, and ZnO.

(Internal stress of crystal)
An internal stress always acts on the KLTN crystal, and its direction is perpendicular to the crystal growth direction. The composition of the KLTN crystal changes in the process of growing from a small crystal (seed crystal) serving as a nucleus to a large crystal. For this reason, crystals having different lattice constants are generated in one individual, and stress strain is generated perpendicular to the crystal growth direction. Hereinafter, the principle of changing the crystal composition will be described.

FIG. 3 is a thermal equilibrium diagram during the growth of a KTN single crystal. The KTN crystal is a kind of KLTN crystal and does not contain Li (y = 0 in the above composition formula, KTa _1-x Nb _x O ₃ (0 <x <1) crystal. The horizontal axis represents the composition x. The ratio of the number of moles of Nb to the total number of moles of Ta and Nb is the vertical axis is the temperature, and the KLTN crystal containing KTN is cooled after mixing the raw materials and heating and melting them in an electric furnace or the like. Then, a crystal is grown from the seed crystal serving as a nucleus.

First, assume that the composition of the raw material is _xl . When this raw material is heated and melted and cooled, it reaches the liquidus at temperature T ₀ . On the other hand, the composition x _{s at} the temperature T ₀ on the solidus is a solid composition in equilibrium with the melt. The composition of the first growing crystal is the composition x _s. Since the solid in the composition x _s contains Ta at a higher ratio than the melt, the ratio of Nb decreasing from the melt is higher than that of the Ta. As a result, the composition of the melt changes to the larger composition x.

If the composition _{x l} of the melt is increased by [Delta] x _l, the temperature of the liquidus in the _{x l} + [Delta] x _l is, [Delta] T only lower. Therefore, crystal growth stops if this condition is maintained. Therefore, in order to continue crystal growth, it is necessary to lower the temperature to T ₀ -ΔT at the composition x ₁ + Δx ₁ . When the crystal is grown in this way, the composition of the melt changes along the liquidus line as the crystal grows due to the continuous decrease in temperature. Therefore, the composition of the precipitated crystals changes to a composition having a high Nb concentration along the solid phase line.

  On the other hand, the lattice constant of the KTN crystal at room temperature increases as the Nb concentration increases. Within the grown crystal, the portion grown later has a higher Nb concentration than the portion grown earlier in time. Therefore, the lattice constant of the later grown portion is larger and is distorted by receiving compressive stress. The direction of the stress is perpendicular to the crystal growth direction.

  The KTN crystal changes its phase from cubic, tetragonal, orthorhombic and rhombohedral depending on the temperature range, but the electro-optic effect is the largest in the case of cubic. In a cubic crystal, there is theoretically no optical anisotropy, but ions such as Ta and Nb in the crystal lattice are displaced due to the strain described above, and the crystal refractive index is changed to cause birefringence. In the above description, the KTN crystal has been described as an example, but the same applies to the KLTN crystal.

  The space charge in the space charge limited state described above consists of free carriers (electrons or holes) in the electro-optic crystal. When the voltage applied to the electro-optic crystal is turned off, these free carriers are instantaneously diffused and emitted from the electrode to the outside. If the space charge limited state disappears instantaneously, it is considered that the deflection of the light beam also disappears instantaneously. However, when the above-described internal stress of the crystal exists, polarization due to ion displacement is induced in the KLTN crystal, interacts with the polarization generated by the application of voltage, and binds free carriers to the field. The constrained carriers remain in the form of space charges after the application of voltage is stopped, the refractive index distribution remains, and the deflection angle does not return to zero. The deflection angle disappears in a few minutes at the earliest, but it may take one day when it is late. Therefore, when used as a light beam deflector, the deflection angle and the applied voltage cannot be made to correspond one-to-one due to the influence of the past deflection state.

  Therefore, in this embodiment, by applying pressure from the outside of the crystal, the internal stress is relaxed, thereby suppressing the refractive index distribution remaining after the voltage application is stopped. As described above, the internal stress is perpendicular to the crystal growth direction. When pressure is applied in parallel with the crystal growth direction, a force that expands the crystal acts in a direction perpendicular to the crystal growth direction, and internal stress can be relaxed. In addition, when the direction of the electric field generated by the voltage applied to the electro-optic crystal from the outside and the internal stress are the same, the above-mentioned interaction is likely to occur, so it is also possible to apply pressure in a direction perpendicular to the electric field. This is effective for suppressing the refractive index distribution.

The electro-optic crystal may be used with pressure applied, but once the pressure is applied, the effect will persist even after the pressure is removed. Just add. Although depending on the crystal material, if the applied pressure is 1 × 10 ⁶ Pa or more, the refractive index distribution immediately after the voltage is turned off is reduced to less than half of the state where no pressure is applied. The influence of stress can be reduced.

  Here, the light beam deflector has been described as an example, but the present invention can also be applied to electro-optic elements for other purposes. Applying pressure to the electro-optic crystal can suppress the space charge remaining in the electro-optic crystal, and thus is effective for a light beam deflector that actively uses the space charge limited state. On the other hand, even in a light intensity modulation element that does not use deflection, that is, its characteristics deteriorate due to deflection, residual space charge may be generated. Therefore, by applying pressure to the electro-optic crystal, the space charge can be quickly lost when the voltage is turned off, and the refractive index distribution can be returned to the state before the voltage is applied.

(Work function of electrode material)
Next, paying attention to Equation (8), x ₀ is an amount that depends on the efficiency of carrier injection from the electrode to the electro-optic crystal, and the smaller the x _{0, the} higher the injection efficiency. If small x _0, the difference of the electric field between the positive electrode and the negative electrode becomes large, since the greater inclination of the refractive index with it, it is possible to increase the deflection of the beam efficiently.

FIG. 4 is a diagram showing the relationship between x ₀ and the spatial distribution of the electric field E. FIG. 5 shows the distribution of the refractive index change Δn due to the Kerr effect. An electro-optic crystal having a refractive index of 2.2 made of KLTN crystal was used, and the distance between the positive and negative electrodes was 0.5 mm and the electrode length was 5.0 mm. The applied voltage is 100 V, 2-order electrooptic constant _{s ij} is ^{2.85 × 10 15 m 2 / V} 2. It can be seen that when x ₀ = 0, the gradient of the refractive index becomes the largest. x ₀ = 0 may be an ideal ohmic contact between the electrode and the electro-optic crystal, as can be seen from the fact that the electric field is 0 at the negative electrode when x = 0 in FIG.

  An electro-optic crystal composed of a KLTN crystal is cut into a length of 6 mm, a width of 5 mm, and a thickness of 0.5 mm, and an electrode having a length of 5 mm and a width of 4 mm is attached to the opposing surface. Carriers that contribute to electrical conduction in KLTN crystals are electrons. Four types of electrode materials, Ti, Cr, Au, and Pt, are prepared. When a voltage of 100 V is applied between the positive and negative electrodes, the deflection angle of light traveling in the vertical direction is measured.

  FIG. 6 shows the relationship between the work function of the electrode material and the deflection angle. The dotted line A in the figure is the deflection angle when the electron injection efficiency is maximum, that is, the deflection angle when x = 0 shown in FIG. Therefore, when the electrode material is Ti or Cr, ideal ohmic contact is realized and the injection efficiency is maximized. As the work function of the electrode material increases, the Schottky contact is approached and the carrier injection efficiency decreases. From this, when the carrier contributing to the electric conduction of the electro-optic crystal is an electron, the work function of the electrode material is preferably less than 5.0 eV. Therefore, when the carrier contributing to the electric conduction of the electro-optic crystal is a hole, the work function of the electrode material is preferably 5.0 eV or more.

  As an electrode material having a work function of less than 5.0 eV, Cs (2.14), Rb (2.16), K (2.3), Sr (2.59), Ba (2.7), Na (2 .75), Ca (2.87), Li (2.9), Y (3.1), Sc (3.5), La (3.5), Mg (3.66), As (3. 75), Ti (3.84), Hf (3.9), Zr (4.05), Mn (4.1), In (4.12), Ga (4.2), Cd (4.22). ), Bi (4.22), Ta (4.25), Pb (4.25), Ag (4.26), Al (4.28), V (4.3), Nb (4.3) , Ti (4.33), Zn (4.33), Sn (4.42), B (4.45), Hg (4.49), Cr (4.5), Si (4.52), Sb (4.55), W (4.55), Mo (4. ), Cu (4.65), Fe (4.7), Ru (4.71), Os (4.83), Te (4.95), Re (4.96), Be (4.98) , Rh (4.98) can be used. Figures in parentheses indicate work functions. Further, an alloy using a plurality of the above materials may be used. For example, since a Ti single-layer electrode is oxidized and becomes high resistance, generally, a Ti layer and an electro-optic crystal are bonded using an electrode in which Ti / Pt / Au is laminated. Furthermore, transparent electrodes such as ITO (Indium Tin Oxide) and ZnO can also be used.

  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. Further, an alloy using a plurality of the above materials may be used.

(Dielectric constant of electro-optic crystal)
FIG. 7 shows the relationship between the relative dielectric constant of the electro-optic crystal and the deflection angle. An electro-optic crystal composed of a KLTN crystal is cut into a length of 6 mm, a width of 5 mm, and a thickness of 0.5 mm, and an electrode having a length of 5 mm and a width of 4 mm is attached to the opposing surface. The electrode material is Cr. When an electric field of 200 V / mm is applied between the positive and negative electrodes, the deflection angle of light traveling in the vertical direction is measured. At this time, the measurement result is shown while changing the dielectric constant by changing the temperature of the electro-optic crystal.

  The deflection angle is proportional to the difference in refractive index change between the positive electrode and the negative electrode, that is, the slope of the straight line shown in FIG. In the case of a secondary electro-optic effect, the refractive index change amount is proportional to the square of the dielectric constant. Accordingly, since the deflection angle is proportional to the square of the relative dielectric constant, the result of fitting the actual measurement value shown in FIG. 7 with a quadratic function is also shown. In the case of the secondary electro-optic effect, the refractive index change amount is proportional to the square of the applied electric field. Therefore, based on the result shown in FIG. 7, the ratio of the deflection angles when the applied electric field is changed. The dielectric constant dependency is shown in FIG.

A prism made of traditional LN, a deflection angle = 0.3 mrad upon application of an electric field of 500V / mm. Therefore, if an electro-optic crystal composed of a KLTN crystal having a relative dielectric constant of 500 or more is used in a space charge limited state, an equivalent deflection angle can be obtained with the same applied electric field. Further, when the relative dielectric constant exceeds 10,000, the dependency of the deflection angle on the relative dielectric constant becomes small, and therefore the relative dielectric constant of the electro-optic crystal may be 40000 or less.

  FIG. 9 shows a conventional light beam deflector for comparison. In the light beam deflector, a positive electrode 2 and a negative electrode 3 are formed on opposite surfaces of a rectangular electro-optic crystal 1. The electro-optic crystal 1 made of a KLTN crystal is cut into a length (z-axis direction) 6 mm × width (x-axis direction) 5 mm × thickness (y-axis direction) 1 mm, and a positive electrode 2 and a negative electrode 3 having a length 5 mm × width 4 mm are obtained. Attach to the opposite surface. Here, the crystal growth direction is made parallel to the x-axis direction so that compressive stress exists in the y-axis direction and the z-axis direction. The traveling direction of the light beam is the z-axis direction, and the direction in which the voltage is applied is the y-axis direction.

FIG. 10 shows the distribution of the refractive index variation of the conventional light beam deflector. When a voltage of 400 V is applied between the positive and negative electrodes, a refractive index distribution felt by light traveling in the z-axis direction is shown. The vertical axis represents the amount of change with respect to the refractive index when no voltage is applied, and the horizontal axis represents the distance from the positive electrode. It can be seen that with application of voltage, the refractive index near the positive electrode greatly changes in the negative direction, but hardly changes near the negative electrode. That is, it can be seen that the ideal ohmic contact (x ₀ = 0) shown in FIGS. The gradient of the refractive index is 7 × 10 ⁻³ per mm at the midpoint between the positive electrode and the negative electrode. Since the electrode length in the traveling direction of light is 5 mm, the light wavefront is inclined at a rate of 35 × 10 ⁻³ mm per 1 mm thickness. Therefore, the deflection angle of the incident light from the optical axis can be 35 mrad.

  On the other hand, the refractive index distribution immediately after the voltage is turned off is also shown in FIG. It can be seen that Δn = 0 does not hold from the positive electrode to the negative electrode, and the refractive index distribution remains. This residual refractive index distribution disappears with time, and Δn = 0 from the positive electrode to the negative electrode, but it takes about 12 minutes to disappear. Therefore, it cannot be used as a high-speed light beam deflector.

FIG. 11 shows a light beam deflector according to the first embodiment of the present invention. In the light beam deflector, a positive electrode 2 and a negative electrode 3 are formed on opposite surfaces of a rectangular electro-optic crystal 1. The electro-optic crystal 1 made of a KLTN crystal is cut into a length (z-axis direction) 6 mm × width (x-axis direction) 5 mm × thickness (y-axis direction) 1 mm, and a positive electrode 2 and a negative electrode 3 having a length 5 mm × width 4 mm Attach to the opposite surface. The composition of the KLTN crystal of this example is K _0.99 Li _0.01 Ta _0.68 Nb _0.32 O ₃ . At a measurement temperature of 20 ° C., the KLTN crystal is cubic and the relative dielectric constant is 12000. The electrode material is Ti / Pt / Au.

  Here, the crystal growth direction is made parallel to the x-axis direction so that compressive stress exists in the y-axis direction and the z-axis direction. The traveling direction of the light beam is the z-axis direction, and the direction in which the voltage is applied is the y-axis direction. The electro-optic crystal 1 is placed on the concave portion of the concave housing 11 and is sandwiched between one wall of the concave and the pressing plate 12. Pressure is applied to the electro-optic crystal 1 by pressing the holding plate 12 against the one wall of the dent with the screw 13. The pressure is applied in parallel with the crystal growth direction, that is, in the x-axis direction.

FIG. 12 shows the distribution of the refractive index change amount of the light beam deflector according to the first embodiment of the present invention. When a voltage of 400 V is applied between the positive and negative electrodes, a refractive index distribution felt by light traveling in the z-axis direction is shown. The vertical axis represents the amount of change with respect to the refractive index when no voltage is applied, and the horizontal axis represents the distance from the positive electrode. 10 shows a state where no pressure is applied, a state where pressure = 2 × 10 ⁶ Pa is applied, and a state where pressure = 4 × 10 ⁶ Pa is applied. In the state where pressure is applied, the refractive index distribution immediately after the voltage is turned off is smaller than in the state where pressure is not applied. At pressure = 4 × 10 ⁶ Pa, Δn = 0 is almost obtained from the positive electrode to the negative electrode. You can see that In this way, by applying pressure to the electro-optic crystal 1, the refractive index distribution does not remain immediately after the voltage is turned off, so that it can be used as a high-speed light beam deflector.

  FIG. 13 shows a light beam deflector according to the second embodiment of the present invention. The configuration of the electro-optic crystal 1 is the same as that of the first embodiment shown in FIG. Here, the crystal growth direction is made parallel to the z-axis direction so that compressive stress exists in the x-axis direction and the y-axis direction. The traveling direction of the light beam is the z-axis direction, and the direction in which the voltage is applied is the y-axis direction. In Example 2, the pressure is applied in parallel with the crystal growth direction, that is, in the z-axis direction.

  The electro-optic crystal 1 is placed on the concave portions of the two concave casings 21a and 21b, and is sandwiched between one wall of the concave and the pressing plates 22a and 22b. At this time, the glass plates 24a and 24b are respectively inserted between the holding plates 22a and 22b and the walls of the recesses and the electro-optic crystal 1 to secure the optical path of the light beam. Pressure is applied to the electro-optic crystal 1 by pressing the holding plates 22a and 22b against one wall of the dent with the screws 23a and 23b.

In a state where a voltage of 400 V is applied between the positive and negative electrodes and a pressure = 4 × 10 ⁶ Pa is applied, the refractive index distribution immediately after the voltage is turned off is about 1/10 smaller than that in the state where no pressure is applied. can do.

(A) And (b) is a figure which shows the generation | occurrence | production principle of the electric field inclination by the electric charge inside a crystal, (c) And (d) is the distance from a negative electrode to a positive electrode, and the strength of the electric field in an electro-optic crystal. It is a figure which shows the relationship. It is a figure which shows the principle of the deflection | deviation of the light concerning one Embodiment of this invention. It is a thermal equilibrium diagram at the time of growth of a KTN single crystal. FIG. 6 is a diagram showing the relationship between x ₀ and the spatial distribution of the electric field E. It is a figure which shows distribution of refractive index change (DELTA) n by a Kerr effect. It is a figure which shows the relationship between the work function of an electrode material, and a deflection angle. It is a figure which shows the relationship between the dielectric constant of an electro-optic crystal, and a deflection angle. It is a figure which shows the dielectric constant dependence of the deflection angle when an applied electric field is changed. It is a perspective view which shows the conventional light beam deflector. It is a figure which shows distribution of the refractive index change amount of the conventional light beam deflector. It is a perspective view which shows the light beam deflector concerning Example 1 of this invention. It is a figure which shows distribution of the refractive index variation of the light beam deflector concerning Example 1 of this invention. It is a perspective view which shows the light beam deflector concerning Example 2 of this invention.

Explanation of symbols

1 Electro-optic crystal 2 Positive electrode 3 Negative electrode 11, 21 Case 12, 22 Holding plate 13, 23 Screw 24 Glass plate

Claims (13)

An electro _- optic crystal that has an electro-optic effect K _1-y Li _y Ta _1-x Nb _x O ₃ (0 <x <1, 0 ≦ y <1) ;
An electrode pair consisting of a positive electrode and a negative electrode that generates an electric field inside the electro-optic crystal, and when a voltage is applied between the electrode pair, carriers are injected into the electro-optic crystal. When,
Pressure applying means for applying a pressure parallel to the crystal growth direction of the electro-optic crystal , wherein the internal stress of the electro-optic crystal is relieved by the pressure. Electro-optic element.   The electro-optical element according to claim 1, wherein the pressure applying unit applies a pressure perpendicular to a direction of the electric field. The electro-optical element according to claim 1, wherein the pressure applying unit applies a pressure of 1 × 10 ⁶ Pa or more.   4. The electro-optic element according to claim 1, wherein the electrode pair is made of a material that is in ohmic contact with a carrier that contributes to electrical conduction of the electro-optic crystal.   5. The electro-optic element according to claim 1, wherein a relative dielectric constant of the electro-optic crystal is 500 or more and 40000 or less. 6. The electro-optic element according to claim 5 , wherein when the carrier contributing to the electrical conduction of the electro-optic crystal is an electron, the material of the electrode pair has a work function of less than 5.0 eV. The material of the electrode pair is Cs, Rb, K, Sr, Ba, Na, Ca, Li, Y, Sc, La, Mg, As, Ti, Hf, Zr, Mn, In, Ga, Cd, Bi, Ta , Pb, Ag, Al, V, Nb , Zn, Sn, B, Hg, Cr, Si, Sb, W, Mo, Cu, Fe, Ru, Os, Te, Re, Be, Rh The electro-optical element according to claim 6 . The electro-optic element according to claim 6 , wherein a material of the electrode pair is any one of ITO and ZnO. 6. The electro-optic element according to claim 5 , wherein when the carrier contributing to the electrical conduction of the electro-optic crystal is a hole, the material of the electrode pair has a work function of 5.0 eV or more. The electro-optic element according to claim 9 , wherein a material of the electrode pair is any one of Co, Ge, Au, Pd, Ni, Ir, Pt, and Se. An electrode pair composed of a positive electrode and a negative electrode that generates an electric field inside an electro-optic crystal having an electro-optic effect, and a carrier is injected into the electro-optic crystal by applying a voltage between the electrode pair. Forming an electrode pair on the opposing surfaces of the electro-optic crystal, wherein the electro-optic crystal comprises K _1-y Li _y Ta _1-x Nb _x O ₃ (0 <x <1, is 0 ≦ y <1), the first step,
A step of applying a pressure parallel to the crystal growth direction of the electro-optic crystal , wherein the internal stress of the electro-optic crystal is relieved by the pressure. A method for manufacturing an optical element. 12. The method of manufacturing an electro-optical element according to claim 11 , wherein the pressure applying step applies a pressure perpendicular to a direction of the electric field. It said pressure application step, the method of manufacturing an electro-optical device according to claim 11 or 12, wherein applying a pressure of more than 1 × 10 6 ^Pa.

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