JP2009128819A - Electrode for periodic polarization reversal, and method for manufacturing periodic polarization reversed element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To further enlarge the diameter of a periodic polarization reversal region, in a bulk type periodic polarization reversed element. <P>SOLUTION: The electrode 1 for periodic polarization reversal includes an aligned electrode group 10, comprising a plurality of electrode pieces 101 aligned side-by-side with spacings on a principal surface of a ferroelectric single crystal base member, and an electrode 11 for feeding connected to the respective electrode pieces 101 constructing the aligned electrode group 10 and feeding currents to the respective electrode pieces 101. The electrode 11 for feeding is extended so as to incline toward the aligning direction of the plurality of electrode pieces 101. In all or in the majority of the plurality of electrode pieces 101 constructing the aligned electrode group 10, the polarization reversal region is formed on the ferroelectric single-crystal base member, extending from both-end portions 101a, 101a of the electrode piece 101 toward the center portion. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a periodic polarization reversal electrode and a periodic polarization reversal element that uses this periodic polarization reversal electrode to form a periodic polarization reversal structure in a Z-cut or Z-off cut ferroelectric single crystal substrate. Regarding the method.

  The periodic polarization reversal element can convert the oscillation wavelength of the laser light with high efficiency without impairing the coherence characteristics of the laser light by wavelength conversion based on nonlinear optics. In this periodic polarization reversal element, for example, a second harmonic is generated by quasi phase matching (QPM) when the laser beam is transmitted through the region of the periodic polarization reversal structure. The second harmonic generation (SHG: Second Harmonic Generation) has twice the frequency and half the wavelength of the incident laser light. For this reason, if a laser beam from a semiconductor laser or the like is incident on the periodic polarization reversal element, a short-wavelength laser beam having a half wavelength with respect to the incident laser beam can be emitted.

  The application range of the periodically poled elements having such wavelength conversion characteristics is diverse. For example, in the fields of optical information processing and applied optical measurement control, periodic polarization reversal elements are applied to optical disks and laser display light sources that use light in the visible wavelength region, molecular spectroscopy that uses light in the mid-infrared wavelength region, etc. Periodic polarization inversion elements can be applied to environmental measurements and the like.

Such a periodic polarization reversal element is a ferroelectric single crystal substrate such as lithium niobate (LN: LiNbO ₃ ) or lithium tantalate (LT: LiTaO ₃ ), for example, by a voltage application method using a periodic polarization reversal electrode. It is manufactured by forming a periodically poled structure inside. That is, the periodic polarization reversal structure in the periodic polarization reversal element is formed by periodically reversing the direction of spontaneous polarization of the nonlinear optical crystal having ferroelectricity.

  In the voltage application method using the periodic polarization reversal electrodes, a large number of electrode pieces are arranged side by side with a predetermined arrangement period on one main surface of the ferroelectric single crystal substrate. When a periodic polarization inversion structure is formed on an X-cut type or Y-cut type ferroelectric single crystal substrate, which will be described later, they are arranged side by side with a predetermined arrangement period on one main surface of the ferroelectric single crystal substrate. In addition, uniform flat plate-like second and third electrodes are disposed on the main surface and the back surface of the ferroelectric single crystal substrate so as to face a large number of electrode pieces. On the other hand, when a periodically poled structure is formed on a Z-cut type ferroelectric single crystal substrate, which will be described later, a large number of electrodes arranged side by side with a predetermined arrangement period on one main surface of the ferroelectric single crystal substrate A uniform flat plate-like second electrode is disposed on the back surface of the ferroelectric single crystal substrate so as to face the piece. A voltage is applied to these electrodes to apply an electric field in the direction opposite to the spontaneous polarization of the ferroelectric single crystal substrate. As a result, a domain-inverted region polarized in the direction opposite to the spontaneous polarization direction of the ferroelectric single crystal substrate is formed at a site corresponding to each electrode piece. As a result, a periodically poled structure in which polarization non-inversion regions whose polarization direction is the original spontaneous polarization direction and polarization inversion regions polarized in a direction opposite to the spontaneous polarization direction are alternately formed is formed. The

  In addition, the light which permeate | transmits a periodic polarization inversion element advances in the direction parallel or substantially parallel to the arrangement direction of a polarization non-inversion area | region and a polarization inversion area | region. Further, by selecting the inversion periods of the non-polarization region and the polarization inversion region, the phase matching wavelength can be selected and the operating wavelength can be set freely.

  Conventionally, as shown in FIG. 6, a comb-shaped periodic polarization reversal electrode 80 is known as a periodic polarization reversal electrode used in the voltage application method (see, for example, Patent Documents 1 and 2).

  In this comb-shaped periodic polarization reversal electrode 80, a large number of electrode pieces 81 having the same shape and size are arranged side by side with a constant arrangement period D, and the base ends of these electrode pieces 81 are arranged. They are connected by a common power supply electrode 82 extending in a strip shape.

  Here, the ferroelectric single crystal substrate is roughly classified into types called X-cut, Y-cut, and Z-cut depending on the direction of the crystal axis with respect to the main surface of the substrate. The X-cut type ferroelectric single crystal substrate is cut so that the X-axis of the crystal is perpendicular to the main surface of the substrate. The Y-cut type ferroelectric single crystal substrate is cut so that the Y-axis of the crystal is perpendicular to the main surface of the substrate. A Z-cut type ferroelectric single crystal substrate is cut so that the Z-axis of the crystal is perpendicular to the main surface of the substrate. The ferroelectric single crystal substrate is polarized in the Z-axis direction of the crystal, and the Z-axis direction and the polarization direction of the crystal coincide with each other.

  Among these, in the case of an X-cut type or Y-cut type ferroelectric single crystal substrate, a polarization inversion portion by voltage application is formed on the surface layer portion of the single crystal substrate. For this reason, the X-cut type and Y-cut type ferroelectric single crystal substrates are suitable for the production of waveguide-type periodic polarization reversal elements. This type is disclosed in Patent Document 1 and Patent Document 2.

On the other hand, in the case of a Z-cut type ferroelectric single crystal substrate, it is polarized in the thickness direction of the single crystal substrate, and polarization reversal by voltage application occurs along the thickness direction of the single crystal substrate. It is also suitable for manufacturing a bulk-type periodic polarization reversal element that is not limited. Even in the case where the periodic polarization reversal structure is formed on the Z-cut type ferroelectric single crystal substrate, a comb-shaped periodic polarization reversal electrode or the like is used as a conventional technique.
JP 2003-287779 A JP 2003-307757 A

  By the way, in recent years, in a periodic periodic polarization reversal element of a bulk type (periodic polarization reversal element using a Z-cut type ferroelectric single crystal substrate), the periodicity is related to the combination with a high-power laser and the improvement of wavelength conversion efficiency. There is a demand for increasing the diameter of the domain-inverted region (that is, the area of the periodically domain-inverted region is large in a cross section perpendicular to the laser incident direction).

  However, the conventional method using a comb-shaped periodic polarization reversal electrode has a problem that it cannot sufficiently meet this requirement. Specifically, in the conventional method, when forming a periodically poled region having the same thickness in the vertical direction (substrate thickness direction) and the same width in the horizontal direction, a 2 mm square (vertical thickness of 2 mm × horizontal direction). The production of a bulk-type periodic polarization reversal element having a periodic polarization reversal region having a diameter of about 2 mm in the direction was a substantial limit. According to the research of the present inventor, the cause of such a problem in the conventional method is as follows.

  FIGS. 7A to 7C are cross-sectional views illustrating a state in which a periodic polarization reversal structure is formed by a voltage application method using a conventional comb-shaped periodic polarization reversal electrode, and X1-X1 in FIG. It corresponds to a line cross-sectional view. However, the comb-shaped periodic polarization reversal electrode 80 is disposed on one main surface 90a of the Z-cut type ferroelectric single crystal substrate 90, and the periodic polarization is disposed on the back surface 90b of the ferroelectric single crystal substrate 90. Opposite to the inversion electrode 80, for example, a flat uniform back electrode 83 is provided.

  As shown in FIG. 7A, when a necessary voltage is applied between the periodic polarization reversal electrode 80 and the back electrode 83, charges are concentrated on the edge portion of the electrode, whereby the tip 81a of the electrode piece 81 is collected. The polarization inversion starts from the portion of FIG. 7, and the polarization inversion region 91 is first in the Z-axis direction of the substrate 90 (in the thickness direction of the Z-cut type ferroelectric single crystal substrate 90, in the direction of arrow h1 in FIG. 7A). Then, as shown in FIG. 7B, the electrode 90 extends in the plane direction of the one main surface 90a of the substrate 90 (in the direction of the arrow h2).

  However, the extension width of the domain-inverted region 91 in the plane direction of the substrate 90 has a certain limit (limit width WL) (see FIG. 7C). Therefore, the limit of increasing the diameter of the domain-inverted region 91 in the case shown in FIGS. 7A to 7C is the vertical thickness in the maximum expanded cross-sectional area of the domain-inverted region 91 shown in FIG. (The thickness of the substrate 90) and the lateral width (WL) in the maximum expanded cross-sectional area of the domain-inverted region 91. The thickness in the vertical direction in the cross-sectional area of the domain-inverted region 91 can be adjusted to some extent by setting the thickness of the substrate 90, although there is a certain limit. However, since the extension width of the domain-inverted region 91 starting from the tip 81a of the electrode piece 81 has a certain limit width WL as described above, the lateral width in the cross-sectional area of the domain-inverted region 91 is expanded beyond WL. Difficult to do.

  As shown in FIG. 7A, the domain-inverted region 91a is also formed in the portion of the substrate 90 immediately below the power supply electrode 82. However, the power supply electrode 82 extends in a strip shape along the arrangement direction of the electrode pieces 81 (the depth direction in FIG. 7A), and does not have a periodic arrangement structure. For this reason, in a portion immediately below the power supply electrode 82, a polarization inversion region 91 a extending continuously in the arrangement direction of the electrode pieces 81 is formed without leaving a non-polarization inversion region, and periodic polarization is performed in the arrangement direction of the electrode pieces 81. It is not an inverted structure. Therefore, the domain-inverted region 91a formed in the portion immediately below the power supply electrode 82 cannot be used as a region for converting the wavelength of the laser light.

  In this way, in the bulk type periodic domain inversion element, in order to increase the diameter of the domain inversion region substantially effectively, the lateral direction is equivalent to the thickness in the vertical direction (substrate thickness direction) of the domain inversion region. However, the increase in diameter is substantially defined by the limit width WL of the domain-inverted region 91. In the prior art, although there are some differences depending on the implementation conditions, for example, a bulk-type periodic polarization reversal element having a periodic polarization reversal region having a diameter of about 2 mm square is full.

  On the other hand, in order to cope with the problem of the comb-shaped periodic polarization reversal electrode 80 shown in FIG. 7, a periodic polarization reversal electrode 84 as shown in FIG. 8 can be assumed. In this periodic polarization reversal electrode 84, a large number of electrode pieces 81 are arranged side by side with a constant arrangement period D, and the central part of these electrode pieces 81 is connected by a common feeding electrode 82 extending in a strip shape. ing. In this case, since the domain-inverted regions 91 extend from the both ends 81a, 81a of the electrode pieces 81 toward the center, respectively, in accordance with the case shown in FIG. 7C, it is twice the limit width WL. A domain-inverted region 91 having a width of 10 mm should be formed.

  However, in this case, the central portion of each electrode piece 81 is connected by the power supply electrode 82. Therefore, even if the domain-inverted region 91 is formed twice the limit width WL, as shown in FIG. 9 corresponding to the cross-sectional view taken along the line X2-X2 in FIG. This is a portion that does not have a periodic polarization reversal structure (cannot be used as a region for converting the wavelength of laser light) in the arrangement direction of the pieces 81 (the depth direction in FIG. 9). That is, the periodically poled structure itself has a defect in the center.

  Accordingly, an object of the present invention is to solve the problem of further increasing the diameter of a periodically poled region in a bulk type periodically poled device. Here, “increasing the diameter” means that the area (aperture) of the periodically poled region in the cross section perpendicular to the laser incident direction is large.

(1) An electrode for periodic polarization reversal of the present invention that solves the above-described problems includes an array electrode group composed of a plurality of electrode pieces arranged side by side at an interval on one main surface of a ferroelectric single crystal substrate. A feeding electrode connected to each of the electrode pieces constituting the array electrode group and feeding power to the electrode pieces, wherein the feeding electrode is inclined with respect to the arrangement direction of the plurality of electrode pieces. It is characterized by extending.

  In the periodic polarization reversal electrode according to the present invention, the power feeding electrodes respectively connected to the electrode pieces constituting the array electrode group extend in an inclined manner with respect to the array direction of the electrode pieces. For this reason, in all or most of the plurality of electrode pieces constituting the array electrode group, the feeding electrode is connected to a portion closer to the center than the end of the electrode piece. Therefore, in all or most of the plurality of electrode pieces constituting the array electrode group, both end portions of the electrode pieces function as electrode ends. Therefore, in all or most of the plurality of electrode pieces constituting the array electrode group, the domain-inverted regions can be formed on the ferroelectric single crystal base material from both end portions to the central portion of the electrode pieces. As a result, the domain-inverted region can be extended about twice as long as the conventional one in the length direction of the electrode piece, that is, in the lateral direction (width direction of the ferroelectric single crystal substrate).

  On the other hand, in a portion immediately below the power feeding electrode in the ferroelectric single crystal substrate, a polarization inversion region is also formed in a portion between adjacent electrode pieces (a portion that is originally desired to be a polarization non-inversion region). If only such an extra domain inversion region is focused on microscopically, it does not have a periodic domain inversion structure. However, in the periodic polarization reversal electrode of the present invention, the feeding electrode is disposed in an oblique direction with respect to the arrangement direction of the electrode pieces, that is, in an oblique direction with respect to the incident direction of the laser light. For this reason, the extra domain inversion region is formed at a position that is sequentially offset with respect to the incident direction of the laser beam. That is, the extra domain-inverted region is formed at a position sequentially shifted by a constant amount or a substantially constant amount in the width direction of the base material in the laser light incident direction. Therefore, the extra domain-inverted region is uniformly or substantially uniformly distributed in the length direction of the periodic polarization reversal element (parallel to the incident direction of the laser beam), and is also uniform or substantially uniform in the width direction of the periodic polarization reversal element. Distributed. As a result, when used as a periodic polarization reversal element, these extra polarization reversal regions do not substantially become an obstacle.

  Therefore, when the periodic polarization reversal electrode of the present invention is used, the critical width WL is doubled (a value twice is based on a simple calculation without actually forming a defective portion. It is possible to form a domain-inverted region having a width that can be twice or more of w1, and to increase the diameter of the periodically domain-inverted region.

Therefore, according to the periodic polarization reversal electrode of the present invention, a bulk-type periodic polarization reversal element in which the periodic polarization reversal region is enlarged to about 5 mm square, for example, is manufactured although there are some differences depending on the implementation conditions. It becomes possible.
(2) In the configuration of (1), it is preferable that an arrangement form of the power feeding electrode is a diagonal line. Here, “the arrangement form of the power feeding electrodes is diagonally straight” means that the power feeding electrodes are arranged on a straight line extending obliquely in a straight line.

According to this configuration, the portion of the extra domain-inverted region formed in the portion immediately below the feeding electrode in the ferroelectric single crystal substrate is the width of the substrate in the arrangement direction of the electrode pieces, that is, the laser light incident direction. It is in a position sequentially shifted by a certain amount in the direction. Therefore, the extra domain-inverted regions are uniformly distributed in the length direction of the periodic polarization reversal element (parallel to the incident direction of the laser beam) and uniformly distributed in the width direction of the periodic polarization reversal element. Further, when viewed from the incident direction of the laser light, unnecessary polarization inversion regions do not overlap. Therefore, at the time of use as a periodic polarization reversal element, it is possible to minimize an obstacle due to an extra polarization reversal region.
(3) In the configuration of (1) or (2), the feeding electrode is connected to all the electrode pieces constituting the arrayed electrode group at a portion closer to the center than the end portion. Is preferred.

According to this configuration, in all electrode pieces constituting the array electrode group, since both end portions of the electrode pieces are not connected to the power feeding electrode, each end portion of the electrode piece functions as an electrode end. For this reason, in all the electrode pieces constituting the array electrode group, the domain-inverted regions can be formed in the ferroelectric single crystal substrate from the respective end portions to the center portion of the electrode pieces. Therefore, in the entire range in the arrangement direction of the array electrode group, it is twice the limit width WL (the value twice is based on a simple calculation and may actually be more than twice the limit width WL). A domain-inverted region having a width can be formed.
(4) In the method for manufacturing a periodic polarization reversal element of the present invention that solves the above-mentioned problem, a periodic polarization reversal structure is formed in a Z-cut or Z-off cut ferroelectric single crystal substrate, and a periodic polarization reversal region is formed. A method of manufacturing a bulk type periodic polarization reversal element having a periodic polarization reversal electrode according to any one of claims 1 to 3 on one main surface of the ferroelectric single crystal substrate. And a back electrode opposite to the periodic polarization reversal electrode is provided on the back surface of the ferroelectric single crystal substrate opposite to the one main surface, and the periodic polarization reversal electrode and the back electrode A periodic polarization reversal structure is formed in the ferroelectric single crystal substrate by applying a voltage to the ferroelectric single crystal substrate.

  That is, in the method for manufacturing a periodic polarization reversal element according to the present invention, a Z-cut or Z-off cut ferroelectric single electrode is formed by using a periodic polarization reversal electrode having any one of the configurations (1) to (3). A periodic polarization reversal element having a periodic polarization reversal region is manufactured by forming a periodic polarization reversal structure in the crystal substrate.

Therefore, according to the method for manufacturing a periodically poled device of the present invention, as described above, although there are some differences depending on the implementation conditions, the periodically poled region is large, for example, about 5 mm square (5 mm length, 5 mm width). It is possible to manufacture a bulk-type periodic polarization reversal element having a diameter. For this reason, compared with the conventional periodic polarization reversal element, the combination with a high output laser becomes easy, and the output of wavelength conversion can be improved. Further, alignment when using this element is facilitated.
(5) Here, when a periodically poled region is formed by a voltage application method on a ferroelectric single crystal substrate made of lithium niobate (LN) or lithium tantalate (LT), a considerably large applied voltage is required. It is said. For this reason, the thickness of a periodically poled region that can be formed on a ferroelectric single crystal substrate made of LN or LT (the thickness direction or the vertical direction thickness or height of the substrate; the same applies hereinafter). Conventionally, the limit was about 1 mm. On the other hand, in a ferroelectric single crystal substrate made of MgLN or MgLT in which magnesium is added to LN or LT, the applied voltage required for polarization inversion is reduced by adding Mg. For this reason, it is currently possible to form a periodically poled region having a thickness of about 5 mm for a ferroelectric single crystal substrate made of MgLN or MgLT. On the other hand, wavelength conversion is performed by a periodically poled device. The laser light is usually beam light having a perfect circular cross-sectional shape. For this reason, the periodically poled regions formed on the ferroelectric single crystal substrate usually have the same width (lateral width) and thickness.

  From the above, in order to increase the diameter of the periodically poled region, MgLN or MgLT, which is advantageous for extending the periodically poled region in the thickness direction of the substrate, is adopted as the ferroelectric single crystal substrate. In addition, it is important how to increase the width of the periodically poled region formed in the ferroelectric single crystal substrate. However, in the conventional voltage application method using a periodically poled electrode, as described above, there is a limit to extending the lateral width of the periodically poled region, so even if it is made of MgLN or MgLT and has a thickness of For example, when a ferroelectric single crystal substrate of 5 mm is employed, the size of the periodically poled region that can be formed as a range that is substantially effective for wavelength conversion of laser light is at most 2 mm square (thickness). 2 mm × width 2 mm).

  In this regard, according to the method for manufacturing a periodic polarization reversal electrode or periodic polarization reversal element of the present invention, as described above, the width of the periodic polarization reversal region is about twice the limit width WL (in some cases, twice or more). Can be extended.

  Therefore, according to the method for manufacturing a periodic polarization reversal electrode or a periodic polarization reversal element of the present invention, it is possible to manufacture a novel periodic polarization reversal element that could not be made by conventional techniques as shown below. It becomes.

  That is, the periodic polarization reversal element of the present invention is a bulk-type periodic polarization reversal element having a periodic polarization reversal region in a Z-cut or Z-off cut ferroelectric single crystal substrate, wherein the ferroelectric single crystal The substrate is made of lithium niobate containing magnesium or lithium tantalate containing magnesium, and has a thickness (H) of 3 mm or more. The full width at half maximum in the width direction of the ferroelectric single crystal substrate exceeds 2 mm and is 50 to 90% of the thickness (H).

  Here, “full width at half maximum” refers to the width of the distribution corresponding to ½ of the maximum value in a curve having a mountain-shaped distribution.

  In the periodic polarization reversal element of the present invention having a full width at half maximum exceeding 2 mm and 50 to 90% of the thickness (H) of the ferroelectric single crystal substrate, the ferroelectric having a thickness (H) of, for example, 5 mm By adopting the body single crystal substrate, the range of the periodically poled region that is substantially effective for converting the wavelength of the laser light can be at least about 4 mm square.

  According to the present invention, when the periodic polarization reversal structure in the bulk type periodic polarization reversal element is formed by the voltage application method, the periodic polarization reversal region in the periodic polarization reversal structure can be enlarged. Such large-diameter bulk-type devices are used in optical information processing, optical measurement control, etc., in the visible wavelength region for optical disk light sources and laser display light sources, and in the mid-infrared wavelength region for molecular spectroscopy and environmental measurement. Etc., and can make new technical contributions to society.

  Embodiments of a periodic polarization reversal electrode, a periodic polarization reversal element manufacturing method, and a periodic polarization reversal element according to the present invention will be described in detail below. The embodiment to be described is only one embodiment, and the periodic polarization reversal electrode, the method of manufacturing a periodic polarization reversal element, and the periodic polarization reversal element of the present invention are not limited to the following embodiments. The electrode for periodic polarization reversal, the method for manufacturing a periodic polarization reversal element, and the periodic polarization reversal element of the present invention are in various forms that have been modified or improved by those skilled in the art without departing from the gist of the present invention. Can be implemented.

(Embodiment 1)
In the present embodiment shown in FIG. 1 to FIG. 2, a periodic polarization reversal structure is formed in the ferroelectric single crystal substrate 3 by a voltage application method using the periodic polarization reversal electrode 1 and the back electrode 2. A bulk-type periodic polarization reversal element having a periodic polarization reversal region is manufactured.

  FIG. 1 is a plan view of the periodically poled electrode 1 according to this embodiment. FIGS. 2A to 2C are cross-sectional views for explaining the formation of a periodically poled structure by a voltage application method using the periodically poled electrode 1 according to this embodiment. a) and (b) correspond to the sectional view taken along line Y1-Y1 in FIG. 1, and FIG. 2C corresponds to the sectional view taken along line Y2-Y2 in FIG.

  As the ferroelectric single crystal base material 3, a Z-cut ferroelectric single crystal base material cut such that the Z axis of the crystal is perpendicular to the main surface 3a of the base material 3, or the Z axis of the crystal is A Z-off cut base material inclined at a predetermined angle (1 to 45 °) with respect to the main surface 3a of the base material 3 can be used.

The material of the ferroelectric single crystal substrate 3 is not particularly limited. For example, lithium niobate (LN), lithium tantalate (LT), KTP (KTiOPO ₄ ), KN (KNbO ₃ ), or the like is preferably used. it can. An appropriate metal element such as magnesium (Mg) or Zn, a metal compound, a rare earth element, or the like can be added to the ferroelectric single crystal substrate 3 as necessary. In particular, a ferroelectric single crystal substrate 3 made of MgLN or MgLT obtained by adding magnesium to lithium niobate (LN) or lithium tantalate (LT) can be suitably used.

  The size and shape of the ferroelectric single crystal substrate 3 are not particularly limited. For example, the width: W = 1 to 10 mm, the thickness (height): H = 1 to 10 mm, and the length: L = 1. A rectangular parallelepiped having a size of about 50 mm can be suitably used. However, considering the increase in the diameter of the domain-inverted region and the depth at which the domain-inverted region can be formed, the width: W = 1-5 mm, and the thickness (height): H = 1-5 mm. More preferred. Further, depending on the implementation conditions for increasing the applied voltage, the thickness (height): H may be about 5 mm or more.

  As shown in FIG. 1, the periodic polarization reversal electrode 1 includes an array electrode group 10 and a power feeding electrode 11. In FIG. 1 and FIG. 2, the size and shape of the periodic polarization reversal electrode 1 etc. are drawn so as to be different from the actual ones in order to clarify the features of the present invention.

  The array electrode group 10 includes a plurality of electrode pieces 101 arranged side by side at an interval on one main surface (+ Z plane or −Z plane) 3a of the ferroelectric single crystal substrate 3. In this array electrode group 10, a plurality of electrode pieces 101 having a predetermined width W1 are arranged in a predetermined array period D in accordance with the width and inversion period of the domain-inverted region and the domain-inverted region in the periodic domain-inverted structure to be formed. It is formed with.

  Each electrode piece 101 in the present embodiment has a long and narrow rectangular shape. In the array electrode group 10, the relationship between the width W1 of the electrode pieces 101 and the array period D can be set appropriately and arbitrarily. For example, the arrangement period D can be set to D = several μm to several tens μm (for example, about 30 μm), and the width W1 of the electrode piece 101 is set to a value of about W1 = D / 4 to D / 2. can do. In addition, the length L1 of the electrode piece 101 can be appropriately set according to the width of the periodic domain-inverted region to be formed, and can be, for example, about L1 = 1 to 10 mm.

  Here, it is preferable that the length L1 of each electrode piece 101 is a length that is not excessive or insufficient. That is, when it is assumed that the maximum expandable width of the domain-inverted region 4 formed from the end 101a of the electrode piece 101 toward the center of the electrode piece 101 is the critical width WL, the electrode piece 101 is too short. When the length of the electrode piece 101 is the critical width WL, for example, the technical significance of adopting the configuration of the present invention is reduced. On the contrary, when the electrode piece 101 is too long (for example, the length of the electrode piece 101 is more than several times the critical width WL), the domain-inverted regions generated from both end portions 101a and 101a of the electrode piece 101, respectively. A large polarization non-inversion region remains in the middle of 4 and may become an obstacle when used as a bulk type periodic polarization inversion element. Also, the critical width WL itself is a value that can vary depending on the implementation conditions and the like. Therefore, the length L1 of the electrode piece 101 is preferably about 1.5 to 3 times (more preferably about 2 to 2.5 times) the critical width WL, and is optimal within this range by trial and error. A value can be set.

  The shape of each electrode piece 101 is not particularly limited, and may be an elongated rectangular shape extending from one end to the other end with a constant width, or an elongated shape having a width continuously increasing from one end to the other end (relative to the bottom). And a trapezoidal shape with a high height), or a different shape with a partially increased or decreased width. In addition, the size of the arrangement period D may be partially different in the arrangement direction of the electrode pieces 101.

  For convenience of explanation, in FIG. 1, among the electrode pieces 101 constituting the array electrode group 10, the electrode piece 101 located at the left end in FIG. 1 is denoted by 101A, and the electrode piece 101 located at the right end in FIG. The remaining electrode pieces 101 are indicated as 101C.

  The power supply electrode 11 is for supplying power to each electrode piece 101 constituting the array electrode group 10, and is connected to each electrode piece 101. The feeding electrode 11 in the present embodiment extends while being inclined with respect to the arrangement direction of the plurality of electrode pieces 101 in the array electrode group 10, and the arrangement form of the feeding electrode 11 is an oblique straight line.

  Specifically, one end of the electrode piece 101A of the array electrode group 10 in the arrangement direction (the left end of the array electrode group 10 shown in FIG. 1) and one end of the electrode piece 101A (the upper end of the electrode piece 101A shown in FIG. 1) The other end of the electrode piece 101 of the array electrode group 10 in the arrangement direction (the right end of the array electrode group 10 shown in FIG. 1) is connected to the other end of the electrode piece 101B (the lower end of the electrode piece 101B shown in FIG. 1). As described above, the array electrode group 10 extends in a diagonal line with a certain width on one diagonal line. In other words, in the present embodiment, the power supply electrode 11 is disposed on a diagonal line composed of one straight line portion that does not have a bent portion or a curved portion in the middle.

  And among each electrode piece 101 which comprises the array electrode group 10, in each electrode piece 101C other than electrode piece 101A and electrode piece 101B, it is the electrode 11 for electric power feeding in the site | part closer to the center than the edge part 101a of the electrode piece 101. Is connected. In addition, among the electrode pieces 101 constituting the array electrode group 10, in the electrode pieces 101A and 101B located at the ends in the arrangement direction, the power supply electrode 11 is placed on the upper end of the electrode piece 101A and the lower end of the electrode piece 101B. Is connected.

  Here, the width of the power supply electrode 11 is not particularly limited as long as power can be reliably supplied to the electrode pieces 101 constituting the array electrode group 10. However, from the viewpoint of minimizing an extra domain inversion region formed immediately below the power supply electrode 11, it is preferable to reduce the width of the power supply electrode 11 as much as possible within a range where power can be reliably supplied to each electrode piece 11. preferable. From the viewpoint of uniformly distributing the extra domain-inverted regions in the length direction and width direction of the ferroelectric single crystal substrate 2, the width of the power supply electrode 11 is constant in the length direction of the power supply electrode 11. Preferably there is. The width W2 of the power supply electrode 11 is preferably about W2 = 1 to 100 μm, and more preferably about W2 = 10 to 30 μm. However, as long as it is not disconnected, it is of course possible to set the width W2 of the power supply electrode 11 to less than 1 μm.

  In addition, the arrangement of the power supply electrodes 11 is not limited to an oblique straight line, and may be, for example, an arc line shape that draws a certain curve, a sine curve line shape, or a zigzag broken line shape. May be. However, when the arrangement form of the power supply electrode 11 is not diagonally linear, when laser light is incident as the periodic polarization reversal element, there is a possibility that a difference in strength is produced in the effect of the quasi phase matching depending on the portion of incidence.

  Even when one power supply electrode 11 is disconnected, a plurality of power supply electrodes 11 may be provided in order to supply power to each electrode piece 101. For example, the power supply electrodes 11 that extend diagonally in a straight line are provided on two diagonal lines of the array electrode group 10, or two power supply electrodes that extend in parallel in a diagonal line along one diagonal line of the array electrode group 10. The electrode 11 may be provided.

  The back electrode 2 has a flat plate shape, and as shown in FIG. 2, the entire surface of the back surface 3 b opposite to the main surface 3 a of the ferroelectric single crystal substrate 3 is opposed to the periodic polarization inversion electrode 1. It is provided uniformly.

  Here, the back electrode 2 is in uniform contact with the back surface 3b of the ferroelectric single crystal substrate 3 so as to face the electrode pieces 101 constituting the array electrode group 10 of the periodic polarization reversal electrodes 1. The configuration is not limited as long as it is an electrode. For example, as the back electrode 2, a liquid electrode (electrolyte solution) that contacts the entire back surface 3 b of the ferroelectric single crystal substrate 3 may be employed.

  The material for the periodically poled electrode 1 and the back electrode 2 is not particularly limited. For example, a metal such as aluminum (Al), titanium (Ti), gold (Au), or chromium (Cr) can be preferably used. . The periodic polarization reversal electrode 1 can be formed by forming a fine pattern by photolithography after film formation by vacuum deposition or sputtering, and the back electrode 2 can be formed by vacuum deposition or sputtering. Further, the thicknesses of the periodic polarization reversal electrode 1 and the back electrode 2 are not particularly limited, and can be, for example, about 10 to 100 nm.

  In order to form a periodic polarization reversal structure in the ferroelectric single crystal substrate 3 by a voltage application method using the periodic polarization reversal electrode 1 and the back electrode 2, the periodic polarization reversal electrode 1, the back electrode 2, A predetermined voltage is applied during the period. The implementation conditions for this voltage application method may be set as appropriate and are not particularly limited. For example, it is preferable to apply a pulse voltage, and the magnitude of the voltage, the interval of voltage application, and the like can be set as appropriate. The voltage application can also be performed under appropriate heating conditions.

  When a necessary voltage is applied between the periodic polarization reversal electrode 1 and the back electrode 2, charges are concentrated on the edge portion of the electrode, so that polarization reversal starts from the end portion 101 a of each electrode piece 101. .

  Here, in the electrode for periodic polarization reversal 1 in the present embodiment, among the electrode pieces 101 constituting the arrayed electrode group 10, the electrode pieces 101C other than the electrode pieces 101A and 101B are the ends of the electrode pieces 101. Since the feeding electrode 11 is connected at a position closer to the center than the portion 101a, both end portions 101a and 101a of the electrode piece 101 function as electrode ends. Therefore, as shown in FIG. 2A, polarization inversion starts from both end portions 101a and 101a of each electrode piece 101C. The domain-inverted region 4 extends in the Z-axis direction of the ferroelectric single crystal substrate 3 (the thickness direction of the Z-cut type ferroelectric single crystal substrate 3) and After reaching the back surface 3b, each of the ferroelectric single crystal base material 3 extends along the electrode piece 101 in the plane direction of the main surface 3a of the ferroelectric single crystal substrate 3 (in the direction of arrow h2 in FIG. 2A) to the limit width WL. Thus, the domain-inverted regions 4 having a total width of about twice the limit width WL are formed.

  Of the electrode pieces 101 constituting the array electrode group 10, in the electrode piece 101A and the electrode piece 101B, one end of the electrode piece 101A (the lower end of the electrode piece 101A shown in FIG. 1) 101a and the electrode piece 101B. Of each of the electrodes 101a (the upper end portion of the electrode piece 101B shown in FIG. 1) 101a, polarization inversion starts, and a domain-inverted region having the limit width WL is formed.

  On the other hand, as shown in FIG. 2C, a sectional view corresponding to the sectional view taken along line Y2-Y2 of FIG. An extra domain-inverted region 4a is also formed at a portion of the interval between the pieces 101 (a portion that is originally intended to be a non-polarized region). However, in the periodic polarization reversal electrode 1 according to the present embodiment, the feeding electrode 11 is obliquely linear with respect to the arrangement direction of the electrode pieces 101, that is, the laser light incident direction (A arrow direction shown in FIG. 1). It is arranged. For this reason, the extra domain-inverted region 4a is formed at a position sequentially shifted by a certain amount in the width W direction of the ferroelectric single crystal substrate 3 in the incident direction A of the laser beam. Therefore, the extra domain-inverted regions 4 are uniformly distributed in the length L direction of the ferroelectric single crystal substrate 3 (parallel to the incident direction A of the laser light) and the width of the ferroelectric single crystal substrate 3 Evenly distributed in the W direction. Further, the extra domain inversion region 4a does not overlap two or more times when viewed from the incident direction A of the laser beam. As a result, when used as a periodic polarization reversal element, these extra polarization reversal regions 4a do not substantially become an obstacle.

  Therefore, by using the periodic polarization reversal electrode 1 according to the present embodiment, it is possible to form the polarization reversal region 4 having a width about twice the limit width WL without forming a substantial defect portion. It is possible to increase the diameter of the periodically poled region (that is, the periodically poled structure).

  Therefore, according to the present embodiment, although there are some differences depending on the implementation conditions, a bulk type periodic polarization reversal element in which the periodic polarization reversal region is increased to a diameter of about 4 mm square or more (for example, 5 mm square) is used. It can be manufactured. For this reason, compared with the conventional periodic polarization reversal element, the combination with a high output laser becomes easy, and the output of wavelength conversion can be improved. Further, alignment when using this element is facilitated.

(Embodiment 2)
In the present embodiment shown in FIG. 3, the structure of the periodic polarization reversal electrode 1 is changed in the first embodiment.

  That is, in the periodic polarization reversal electrode 1 according to this embodiment, the power feeding electrode 11 is connected to all the electrode pieces 101 constituting the array electrode group 10 at a portion closer to the center than the end portion.

  Therefore, in this embodiment, in all electrode pieces 101 constituting the array electrode group 10, both end portions 101 a and 101 a of the electrode piece 101 are not connected to the power supply electrode 11. Each of 101a functions as an electrode end. For this reason, in all the electrode pieces 101 which comprise the array electrode group 10, a polarization inversion area | region can be formed in the ferroelectric single crystal base material 3 toward the center part from each edge part 101a of the electrode piece 101, 101a. it can. Therefore, it is possible to form a domain-inverted region having a width about twice the limit width WL in the entire range of the array electrode group 10 in the array direction.

  Other configurations and operational effects are the same as those of the first embodiment.

(Embodiment 3)
In the present embodiment shown in FIG. 4, the structure of the periodically poled electrode 1 is changed in the first embodiment.

  That is, in the periodic polarization reversal electrode 1 according to this embodiment, the power supply electrode 11 has a folded portion 11a, and the arrangement of the power supply electrode 11 is an obliquely folded straight line that is folded halfway.

  Therefore, in the present embodiment, in the portion immediately below the feeding electrode 11 in the ferroelectric single crystal substrate 3, it is formed in the portion of the interval between the adjacent electrode pieces 101 (originally the portion that is desired to be a non-polarized region). The extra domain-inverted region 4a overlaps twice when viewed from the incident direction A of the laser beam. For this reason, when used as a periodic polarization reversal element, the possibility that these extra polarization reversal regions 4a become a substantial obstacle is higher than that of the first embodiment.

  Other configurations and operational effects are the same as those of the first embodiment.

(Embodiment 4)
In the present embodiment, a Z-cut or Z-off cut ferroelectric single crystal substrate 3 is made of lithium niobate (MgLN) containing magnesium or lithium tantalate (MgLT) containing magnesium. The ferroelectric single crystal substrate 3 made of MgLN or MgLT has a thickness (H) of 3 to 5 mm.

  Then, a periodic polarization reversal element can be obtained by forming a periodic polarization reversal region in accordance with the production method described in the first to third embodiments for the ferroelectric single crystal base material 3 to obtain a periodic polarization. In the inverting element, the full width at half maximum in the width direction of the ferroelectric single crystal substrate 3 of the light output after being wavelength-converted by the periodically poled region exceeds 2 mm and has a thickness (H) of 50 to 90. %.

  Hereinafter, an example of the present invention and a comparative example will be described.

(Example)
In this example, a Z-cut plate made of MgO-doped LN single crystal (MgO addition concentration: 5 mol%) was used as the ferroelectric single crystal substrate. The size of this Z-cut plate is: width: W = 5 mm, height (thickness): H = 5 mm, and length: L = about 36 mm.

  The periodic polarization reversal electrode 1 described in the first embodiment is formed on the main surface (+ Z surface) of the Z-cut plate by vacuum deposition and photolithography, and the Z-cut plate has the back surface (−Z surface). The back electrode 2 described in Embodiment 1 was formed by vacuum deposition. In this periodic polarization reversal electrode 1, the arrangement period: D in the array electrode group 10 is D = 32.3 μm, the width of the electrode piece 101: W1 is W1 = 9.7 μm, and the length of the electrode piece 101 is The length L1 is L1 = 5 mm, and the width W2 of the power supply electrode 11 is W2 = 50 μm. Further, the periodic polarization reversal electrode 1 and the back electrode 2 are both made of aluminum and have a thickness of 50 nm.

  Then, under heating at 120 ° C., a pulse voltage of 16 kV is applied from the + Z plane to the −Z plane between the periodic polarization reversal electrode 1 and the back electrode 2 for a necessary time, and the bulk type according to this example is applied. A periodic polarization reversal element was created.

  After the voltage application process was finished, the obtained periodically poled device was cut, the cut surface was etched with acid, and the periodically poled region was observed with an optical microscope. As a result, the longitudinal direction (Z direction) was about 5 mm. Further, it was confirmed that a periodic domain-inverted region having a substantially rectangular shape of about 5 mm was also formed in the lateral direction.

  Further, the full width at half maximum was measured by conducting an optical parametric oscillation experiment on the obtained periodically poled device. As a result, the full width at half maximum of this periodic polarization reversal element was about 4 mm, and the thickness (height) of the ferroelectric single crystal substrate: about 80% of H = 5 mm.

(Performance evaluation)
FIG. 5 shows performance data of the periodic polarization reversal element obtained in this example in an optical parametric oscillation experiment.

  In the graph of FIG. 5, the horizontal axis represents the input excitation energy of the excitation light, and the vertical axis represents the output energy. As the excitation laser, a lamp excitation high-power pulse Nd: YAG laser system (Spectra Physics, LAB170-30) having a wavelength of 1.064 μm and a pulse width of 10 nanoseconds was used. In FIG. 5, the graph plotted with “●” represents the laser light output energy of wavelength 2.128 μm wavelength-converted by optical parametric oscillation.

  From FIG. 5, it can be seen that the periodic polarization reversal element obtained in this example functions effectively as a wavelength converter for large output utilizing the large diameter. In addition, when the excitation laser was input to the periodic polarization reversal element in a beam shape that was almost a perfect circle, the beam shape of the output light obtained was also a substantially circle. Thus, it can be seen that the periodic polarization reversal element obtained in this example can realize a uniform periodic polarization reversal structure over the entire area of the aperture of 5 mm × 5 mm.

It is a top view which shows the whole structure of the electrode for periodic polarization inversion which concerns on Embodiment 1 of this invention. 2A and 2B are cross-sectional views illustrating a method for manufacturing a periodically poled device according to Embodiment 1 of the present invention, wherein FIGS. 1A and 1B are views corresponding to a cross section taken along line Y1-Y1 in FIG. 1, and FIG. It is a figure equivalent to the Y2-Y2 line | wire cross section. It is a top view which shows the whole structure of the electrode for periodic polarization inversion which concerns on Embodiment 2 of this invention. It is a top view which shows the whole structure of the electrode for periodic polarization inversion which concerns on Embodiment 3 of this invention. It is a graph which shows the result of having evaluated the performance of the periodic polarization inversion element obtained in the Example of this invention. It is a top view which shows the whole structure of the conventional electrode for periodic polarization inversion. It is sectional drawing explaining the manufacturing method of the conventional periodic polarization inversion element, (a)-(c) is a figure corresponded to the X1-X1 line | wire cross section of FIG. It is a top view which shows the whole structure of the other conventional electrode for periodic polarization inversion. It is sectional drawing explaining the manufacturing method of the other conventional periodic polarization inversion element, and is a figure equivalent to the X2-X2 line | wire cross section of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Periodic polarization reversal electrode 2 ... Back electrode 3 ... Ferroelectric single crystal base material 3a ... Main surface 3b ... Back surface 4 ... Polarization inversion area | region 10 ... Array electrode group 11 ... Feed electrode 101 ... Electrode piece

Claims (5)

An array electrode group consisting of a plurality of electrode pieces arranged side by side on one main surface of the ferroelectric single crystal base material, and each electrode piece connected to each electrode piece constituting the array electrode group A power supply electrode for supplying power to the electrode piece,
The electrode for periodic polarization inversion, wherein the power feeding electrode extends in an inclined manner with respect to an arrangement direction of the plurality of electrode pieces.   The periodic polarization inversion electrode according to claim 1, wherein the feeding electrode is arranged in a diagonal line.   3. The periodic polarization inversion according to claim 1, wherein the feeding electrode is connected to a portion closer to the center than the end with respect to all of the electrode pieces constituting the array electrode group. Electrode. A method of manufacturing a bulk-type periodic polarization reversal element having a periodic polarization reversal region by forming a periodic polarization reversal structure in a Z-cut or Z-off cut ferroelectric single crystal substrate,
A periodic polarization reversal electrode according to any one of claims 1 to 3 is provided on one main surface of the ferroelectric single crystal substrate, and the one main surface of the ferroelectric single crystal substrate is provided. Providing a back electrode opposite to the periodic polarization reversal electrode on the back side opposite to the surface, and applying a voltage between the periodic polarization reversal electrode and the back electrode, thereby providing the ferroelectric single crystal substrate A method of manufacturing a periodic polarization reversal element, wherein a periodic polarization reversal structure is formed inside. A bulk-type periodic polarization reversal element having a periodic polarization reversal region in a Z-cut or Z-off cut ferroelectric single crystal substrate,
The ferroelectric single crystal substrate is made of lithium niobate containing magnesium or lithium tantalate containing magnesium, and has a thickness (H) of 3 mm or more,
The full width at half maximum in the width direction of the ferroelectric single crystal substrate of the light that is wavelength-converted and output by the periodic polarization inversion region exceeds 2 mm, and is 50 to 90% of the thickness (H). There is a periodic polarization reversal element.

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