JP2004170711A - Polarization reversed crystal, method for manufacturing and processing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polarization reversed crystal of which the mechanical strength hardly deteriorates even when the period of polarization reversal is small and a method for manufacturing the same. <P>SOLUTION: The polarization reversed crystal is constructed by forming a polarization reversal structure with polarization reversal regions and polarization nonreversal regions alternately appearing on one plate surface of a ferroelectric crystal substrate and is characterized by having recessing parts disposed at the positions corresponding to the polarization reversal regions on the other plate surface of the substrate. Thereby, in the case a polarization reversal voltage is applied for the purpose of manufacturing the polarization reversed crystal, the thickness w1 of the part to which the voltage is applied gets thin and, as a consequence, the polarization reversal region 11 is prevented from expanding in the substrate surface direction. Because the thickness w0 of the substrate in parts other than the recessing parts 10, on the other hand, remains thick, a deterioration in the mechanical strength of the obtained polarization reversed crystal 1 as a whole is not so significant as that of the conventional one and fracture caused by handling or heat treatment hardly occurs. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a domain-inverted crystal using a ferroelectric crystal substrate, a method for manufacturing the same, and a method for processing the domain-inverted crystal.
[0002]
[Prior art]
The domain-inverted crystal is a ferroelectric crystal in which a domain-inverted structure is formed (hereinafter, also simply referred to as “crystal”), and the domain-inverted structure reverses the direction of spontaneous polarization of a predetermined portion of the crystal. Usually, regions in different polarization directions are alternately arranged at a specific period in one crystal. By using the domain-inverted structure, quasi-phase matching becomes possible, and the second harmonic generation and optical parametric oscillation can be more efficiently achieved as compared with other conventional phase matching methods. Become.
[0003]
As a typical method of forming a domain-inverted structure, a method of arranging electrodes on the upper and lower surfaces of a substrate so as to face each other at a position directly opposite to each other, and applying a reversal voltage (electric field) to reverse the polarization direction. (Patent Document 1). In order to preferably apply the inversion voltage, various methods have been proposed, such as an external voltage application method using a liquid electrode. FIG. 7 is a diagram showing a domain-inverted crystal having a typical domain-inverted structure obtained by the above-described method. This domain-inverted crystal uses a crystal Z plate. The Z plate is a crystal substrate cut (so-called Z cut) such that the direction of the Z axis of the crystal is perpendicular to the substrate surface. In the embodiment of this figure, the Z plate is subjected to polarization reversal processing, and on the upper surface (+ Z plane in the example of the figure) of the Z plate, -Z polarization appears on the intended region surface, and the domain-reversed crystal is obtained. The middle region reaches the back surface of the crystal substrate. In the drawing, the hatched portion is the domain-inverted region 11, and the thick arrow drawn in the crystal goes from -Z to + Z.
[0004]
[Patent Document 1]
US Pat. No. 5,800,767.
Conventionally, as shown in FIG. 7 described above, electrodes are arranged on both upper and lower surfaces of a crystal substrate having a uniform substrate thickness, and a domain-inverted region is formed by applying an electric field between the two electrodes. . However, in this method, the domain-inverted region is likely to spread in the direction of the crystal substrate surface, and it has been difficult to accurately manufacture a domain-inverted crystal having a small inversion period. Therefore, when it is necessary to reduce the inversion cycle, the thickness of the entire crystal substrate is reduced to prevent the domain-inverted region from spreading in the crystal plane direction.
[0006]
[Problems to be solved by the invention]
However, if the thickness of the substrate is reduced uniformly over the entire crystal substrate, the mechanical strength of the substrate is reduced, handling during the manufacturing process becomes difficult, and the substrate is damaged. . Further, if the thickness of the substrate is uniformly reduced, the crystal may be damaged when the domain-inverted crystal is manufactured and then further processed such as, for example, performing a heat treatment to manufacture an optical waveguide. Was. An object of the present invention is to provide a domain-inverted crystal in which the mechanical strength is hardly reduced even when the inversion cycle is small, and a method for manufacturing the same.
[0007]
[Means for Solving the Problems]
The present inventors have completed the present invention based on the idea of providing a concave portion in a part of the crystal substrate instead of making the entire crystal substrate thinner. That is, the features of the present invention are as follows.
(1) A domain-inverted crystal having a domain-inverted structure in which domain-inverted regions and non-domain-inverted regions alternately appear on one surface of a ferroelectric crystal substrate,
A domain-inverted crystal, wherein a concave portion is provided at a position corresponding to the domain-inverted region on the other plate surface of the substrate.
(2) The domain-inverted crystal according to (1), wherein the ferroelectric crystal substrate is a substrate cut so that the X-axis direction of the crystal is parallel to the substrate surface.
(3) The domain-inverted crystal according to (1) or (2), wherein an optical waveguide is formed so as to pass through the domain-inverted structure.
(4) The domain-inverted crystal according to (1) or (2), wherein the space inside the concave portion is filled with a heat transfer compound.
(5) Further, the domain-inverted crystal is provided with an electric field applying means, and the electric field applying means is provided inside and outside the concave portion so as to sandwich the domain-inverted region in the thickness direction of the ferroelectric crystal substrate. The domain-inverted crystal according to the above (1) or (2), comprising an electrode arranged at
(6) When further processing the domain-inverted crystal according to any of (1) to (3) using a processing tool, an alignment guide for positioning the processing tool on the domain-inverted crystal is provided. A method for processing a domain-inverted crystal, wherein the method is fitted into the recess.
(7) When forming a domain-inverted structure such that domain-inverted regions and non-domain-inverted regions alternately appear on one plate surface of a ferroelectric crystal substrate to obtain a domain-inverted crystal,
Of the other plate surface of the substrate, a concave portion is provided at a position corresponding to a region to be the domain-inverted region,
A method for manufacturing a domain-inverted crystal, comprising: arranging electrodes in a region to be the domain-inverted region and in a recess, and applying a domain-inverted voltage between the two electrodes.
(8) The manufacturing method according to (7), wherein the ferroelectric crystal substrate is a substrate cut so that the X-axis direction of the crystal is parallel to the substrate surface.
[0008]
In the present specification, for clear explanation, the front and back substrate surfaces of the crystal substrate are referred to as “upper surface” and “lower surface”, respectively, and the electrodes arranged on each surface are referred to as “upper electrode” and “lower electrode”. In. These names using the upper and lower sides are merely for simply and clearly associating the front and back substrate surfaces with the electrodes arranged on each surface, and are described, for example, as “upper surface” and “lower surface”. "Has the same meaning as" one surface "and" the other surface. "
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a schematic view of a domain-inverted crystal of the present invention. FIG. 1B is a sectional view taken along line BB of FIG. 1A, and FIG. 1C is a diagram of FIG. 1A viewed from the direction of arrow C. The domain-inverted crystal is obtained by applying an electric field (domain-inverted voltage) to one plate surface (upper surface) of the ferroelectric crystal substrate so that the domain-inverted regions 11 and other portions are alternately formed, preferably, in a stripe having a constant period. The structure (polarization inversion structure) that appears in the shape is formed. In this specification, a portion 12 other than the domain-inverted region 11 in the ferroelectric crystal substrate is referred to as a “non-domain-inverted region”. As shown in FIG. 1, the domain-inverted region 11 may reach not only the one plate surface (upper surface) but also the substrate. On the other surface (lower surface) of the domain-inverted crystal 1 of the present invention, a concave portion 10 is provided at a position corresponding to the domain-inverted region 11 described above. In the illustrated embodiment, the recess 10 is illustrated in FIGS. 1B and 1C.
[0010]
The “position corresponding to the domain-inverted region 11” is a preferred mode in which the opening of the concave portion is made to coincide with a region appearing when the domain-inverted region 11 is projected on the lower surface. Within the range achieved, the size and center position of the opening may be shifted from the domain-inverted region. For example, in the embodiment shown in FIG. 1, the opening of the recess 10 is larger than the region that appears when the domain-inverted region 11 is projected onto the lower surface.
[0011]
As will be described later, when the polarization inversion voltage is applied, the thickness w1 of the portion to which the voltage is applied is reduced due to the presence of the concave portion 10 in the ferroelectric crystal substrate. Spreading in the direction can be prevented. On the other hand, since the thickness w0 of the substrate other than the concave portion 10 remains large, the mechanical strength of the obtained domain-inverted crystal 1 as a whole is not reduced as much as in the past, and it is hard to be broken by handling or heat treatment. Become.
[0012]
In order to obtain the above-described effects, the substrate thickness w1 of the portion where the domain-inverted regions 11 are formed is formed to be smaller than the substrate thickness w0 of the portion other than the concave portion 10 (that is, w0−w1> 0). ) Is necessary, preferably w0-w1 is 0.1-0.8 mm, more preferably w0-w1 is 0.2-0.4 mm.
[0013]
The relationship between w1 and w0 can also be expressed by a thickness ratio (w1 / w0). In order to obtain the above-described effects, w1 / w0 needs to be greater than 0 and less than 1, preferably w1 / w0 is 1/10 to 2/3, and more preferably w1 / w0 is 1/5. ~ 1/3.
[0014]
Further, within the above-described range, preferred ranges of w1 and w0 are as follows. That is, w1 is preferably 0.1 to 0.2 mm, w0 is preferably 0.3 mm or more, and more preferably 0.3 to 1.0 mm.
[0015]
FIG. 1 shows a domain-inverted crystal in which the concave portion 10 has a rectangular shape. However, the shape of the concave portion 10 is not particularly limited, and may be, for example, a columnar shape, an elliptical columnar shape, a polygonal columnar shape, or a concave portion having a V-shaped cross section as shown in FIG. In the embodiment shown in FIG. 3, the substrate thickness at the portion where the domain-inverted region 11 is formed is not uniform. In this case, w1 in the above description of the preferred thickness is replaced by w1 in the portion where the domain-inverted region 11 is formed. It is regarded as the average value ((w11 + w12) / 2) of the maximum value (w12) and the minimum value (w11) of the thickness.
[0016]
Further, the recess 10 may be (i) a single mode or (ii) a collective mode.
In the one-shot mode (i) as shown in FIG. 1, the recess 10 has a ratio of 1 (upper electrode) to 1 (recess) or 1 (upper) with respect to the upper electrode (arranged according to the polarization inversion period). Electrodes) are provided corresponding to a plurality of (concave portions). In this case, the concave portions 10 are preferably arranged on the lower surface in a pattern similar to the arrangement pattern of the upper electrodes.
Further, in the collective aspect (ii), the recesses are provided in a groove shape such that adjacent ones of the recesses 10 arranged in (i) communicate with each other. The communication between the concave portions 10 may be only a few communication (the rest remains single shot), a communication every few, an irregular communication, or all communication. When the concave portion 10 is formed in a groove shape, a plurality of grooves extending in parallel with each other may be used. Further, as a combination of the above (i) and (ii), a mode in which a single concave portion 10 is further provided on the inner bottom surface of the collective groove may be adopted.
[0017]
By forming the recess 10 in the one-shot mode of (i), the main electric field between the upper and lower electrodes is generated individually, and the directionality of the electric field becomes clearer, and the mechanical strength of the entire substrate is reduced. Although there is an advantage that it is not damaged, processing of the concave portion 10 is troublesome. On the other hand, in the collective mode (ii) described above, in particular, in the mode in which all of the recesses 10 are communicated and formed in a groove shape, it is possible to form a groove through which the polishing tool is passed from one end face to the other end face. Is much easier. Further, in the above-mentioned embodiment (i), when the recesses 10 are closely arranged close to each other, even if they are connected to form a groove, the directionality of the main electric field does not greatly deteriorate, and processing is easy. Often only gender is significant. The mode of the recess 10 may be selected in consideration of these individual features.
[0018]
FIG. 2 is a diagram schematically showing a step of forming a domain-inverted structure on one plate surface (upper surface in the illustrated embodiment) of a ferroelectric crystal substrate in the method of manufacturing a domain-inverted crystal of the present invention. In the manufacturing method of the present invention, a concave portion 10 is provided at a position corresponding to a region to be a domain-inverted region 11 on the other plate surface (lower surface) of the substrate, and a region to be a domain-inverted region 11 is formed. The electrodes 21 and 22 are arranged in the recess 10 and a polarization inversion voltage is applied between the electrodes. The "position corresponding to the region to be the domain-inverted region 11" is as described above. As described above, by disposing one electrode 22 in the concave portion 10, the distance (w1) between the two electrodes can be reduced, so that even if the domain-inverted structure has a short period, it can be manufactured accurately. . When disposing the electrodes 21 and 22 on the ferroelectric crystal substrate, the electrodes may be brought into contact with the crystal substrate directly or via a conductive film (such as a metal thin film) with reference to a known technique. .
[0019]
The lower electrode 22 disposed in the concave portion 10 may be disposed at an arbitrary portion (the bottom surface of the concave portion, etc.) in the concave portion 10 by using a conventionally known electrode. The filling mode is preferred. The mode using the liquid electrode is preferable in that the arrangement (filling) into the concave portion 10 and the removal from the concave portion 10 are easy, and the shape follows the shape of the concave portion 10 well. Here, as the liquid electrode, an electrolytic solution used in a known liquid electrode method may be used, but if an electric field is applied at a high temperature, it does not boil depending on the temperature and can be used. What is necessary is just to choose. For example, examples of the solvent constituting the electrolyte include water, polyol, and a mixture thereof. Examples of the electrolyte material include lithium chloride, sodium chloride, and potassium chloride. It is also possible to use liquid metals such as gallium, indium, and mercury.
[0020]
Ferroelectric crystal is used in the present invention may be a known, for _{example, LiNbO 3, LiTaO 3, X} A TiOX B O 4 (X A = K, Rb, Tl, Cs, X B = P, Typical examples include As) and those obtained by doping these with various elements such as Mg. LiNbO ₃ or LiTaO ₃ may have a congruent composition or a stoichiometric composition. Among these crystals, MgO-doped LiNbO ₃ is particularly excellent in light damage resistance.
[0021]
When cutting the substrate from the ferroelectric crystal, attention is usually paid to how to match the direction of the crystal axis with the direction of the substrate surface. In the domain-inverted crystal of the present invention, there is no particular problem even if a substrate cut in any direction is used, and a Z-cut plate (a crystal substrate cut so that the direction of the Z axis of the crystal is perpendicular to the substrate surface) is used. Alternatively, an X-cut plate (a crystal substrate cut so that the X-axis is perpendicular to the substrate surface) may be used. Furthermore, for example, a crystal substrate formed by a cut (off-cut about the X-axis) in which the X-axis makes a specific angle (off-angle) θ with the normal to the substrate surface may be used. . Usually, the ferroelectric crystal substrate is not a substrate cut so that the direction of the X-axis of the crystal is parallel to the substrate surface (that is, neither a X-cut plate nor a substrate off-cut about the X-axis). Substrate), and in particular, a Z-cut plate is preferably used.
[0022]
FIG. 3 is a diagram showing an embodiment in which an optical waveguide is formed on the domain-inverted crystal of the present invention. The optical waveguide is formed so as to pass through a domain-inverted structure in which domain-inverted regions 11 and non-domain-inverted regions 12 appear alternately. According to the present invention, the substrate thickness (w11, w12 in the figure) of the portion corresponding to the domain-inverted region 11 can be reduced, so that the thickness is suitable for an optical waveguide (preferably 2 to 100 μm, more preferably). Is 2 to 10 μm). In FIG. 3, a hatched circle in the domain-inverted region 11 schematically shows the waveguide propagation light. By reducing the thickness of the substrate corresponding to the domain-inverted region 11 as in the present invention, the substrate corresponding to the domain-inverted region 11 is confined in both the upper and lower directions by an air layer, and forms a strongly confined optical waveguide. There is an advantage that can be. After forming the domain-inverted structure, the prior art may be appropriately referred to for the means for changing the refractive index by ion exchange or the like in order to further form an optical waveguide. In the case where an optical waveguide is formed in the domain-inverted crystal of the present invention as in this embodiment, a waveguide region having a circular cross section is easily obtained, as shown in FIG. In the cross section, it is preferable to form a V-shaped concave portion such that the substrate thickness at the central portion of the substrate increases. By forming such a V-shaped concave portion, both sides of the optical waveguide are well confined under the influence of the air layer, and an optical waveguide having a cross section close to a circle (close to point symmetry) is easily formed. In this case, the difference (w12−w11) between the maximum value w12 and the minimum value w11 of the thickness of the substrate corresponding to the recess is preferably 2 to 20 μm, and more preferably 4 to 8 μm. The ratio (w12 / w11) between w12 and w11 is preferably 2 to 10, more preferably 3 to 5.
[0023]
FIG. 4 shows one embodiment of the domain-inverted crystal of the present invention, in which the space inside the concave portion is filled with the heat transfer compound 3. As the heat transfer compound, those commonly used in the field of semiconductor element production can be used without any particular limitation, but those having a high thermal conductivity (preferably 0.001 cal / ° C. or more) are preferable. , A silicone resin, and a silicone resin containing a metal (eg, aluminum, copper, etc.) powder. Since the heat capacity of the domain-inverted crystal of the present invention is particularly small in the concave portions, the temperature control of the crystal is facilitated by filling the heat transfer compound 3. In the embodiment of FIG. 4, the domain-inverted crystal filled with the heat transfer compound 3 is placed on the Peltier device 4 as a cold source. However, the Peltier device 4 is not essential and other cold sources (for example, water-cooled heat radiation Plate, etc.), and it is not particularly necessary to provide a cold source. Further, by providing a heater in place of the Peltier element 4, heating can be performed instead of cooling.
[0024]
FIG. 5 also shows an embodiment of the domain-inverted crystal of the present invention, and the domain-inverted crystal is further provided with electric field applying means indicated by reference numerals 51 to 53. The electric field applying means includes electrodes 52 and 53 disposed inside and outside the recess so as to sandwich the domain-inverted region 11 in the thickness direction of the ferroelectric crystal substrate. FIG. 5 also shows a power supply 51 for supplying power to the electrodes 52 and 53. The materials and the like of the electrodes 52 and 53 are not particularly limited, and the upper electrode and the lower electrode used in manufacturing the domain-inverted crystal of the present invention may be used as they are. With such a configuration, it is possible to further apply an electric field to the domain-inverted region 11 and to modulate the wavelength conversion efficiency. In particular, when the domain-inverted crystal of the present invention is used, the distance between the electrodes is smaller than that in the case of using the conventional domain-inverted crystal. Modulation of the wavelength conversion efficiency becomes possible.
[0025]
FIG. 6 shows an embodiment of a method for further processing the domain-inverted crystal of the present invention. The processing method is characterized in that an alignment guide 6 of a processing tool (not shown) for processing is fitted into the recess described above. The alignment guide is a means for positioning the processing tool with respect to the domain-inverted crystal. As a positioning mode, an alignment guide (for example, etching on a Si base substrate) is formed in a rectangular or V-shaped groove or a cylindrical concave portion. And a self-alignment of an optimal optical coupling position with an optical component (for example, a lens, a mirror, an optical fiber, a laser diode, or the like) provided on the Si substrate. Can be On the lower surface of the domain-inverted crystal shown in FIG. 6, the collective concave portion described as (ii) above is formed in a groove shape. A member having a shape that can be fitted into the groove-shaped concave portion is fitted as an alignment guide 6 so that the alignment guide 6 can be positioned when processing (for example, modularizing) the domain-inverted crystal. Therefore, the position of a processing tool such as a condenser lens can be set with high reproducibility and high accuracy. Here, the concave portion does not necessarily have to be groove-shaped, and may be, for example, rectangular. The processing using the alignment guide can be appropriately selected from various known processing, and examples thereof include dicing processing and etching processing.
[0026]
【Example】
Hereinafter, the present invention will be described more specifically by showing examples, but the present invention is not limited to the description of the examples.
[0027]
[Example 1]
On the surface of the + Z plane of a lithium niobate crystal (length: 20 mm, width: 10 mm, thickness: 0.5 mm), electrodes having a period of 1 mm × 15 mm (interval between adjacent electrodes; 4 μm) were formed. Thereafter, only a portion of the -Z surface corresponding to the lower surface of the electrode region was cut by a dicing saw to form a rectangular recess having a substrate thickness of 0.2 mm at that portion. A LiCl electrolytic solution was introduced into the concave portion, and a voltage (electric field) of 10 kV was applied between the concave portion and the electrode to perform polarization inversion. Thus, a domain-inverted crystal as shown in FIG. 1 was obtained (w0 = 0.5 mm, w1 = 0.2 mm). When this polarization-inverted crystal was subjected to selective etching using hydrofluoric nitric acid to observe the inverted shape, it was confirmed that a domain-inverted structure almost as designed was obtained without causing substrate cracking.
[0028]
[Example 2]
A domain-inverted crystal was manufactured in the same manner as in Example 1, except that the substrate thickness (w1) of the domain-inverted region was 25 μm. It was confirmed that a domain-inverted structure almost as designed was obtained by the same method as in Example 1.
[0029]
[Example 3]
A domain-inverted crystal was manufactured in the same manner as in Example 1, except that the substrate thickness (w1) of the domain-inverted region was set to 0.1 mm. It was confirmed that a domain-inverted structure almost as designed was obtained by the same method as in Example 1. Further, the space in the recess was filled with a silicone resin to which metal aluminum powder was added as a heat transfer compound. When a thermocouple was installed inside the heat transfer compound to control the crystal temperature of the domain-inverted crystal, the temperature controllability was better than when a domain-inverted crystal having a uniform thickness of 0.5 mm was used, Improved responsiveness and stability of temperature control (for example, when the outside air temperature suddenly changed by 5 ° C, it took 1 minute to recover to the temperature to be controlled and stabilize if there was no heat transfer compound. However, it took only 10 seconds when there was a heat transfer compound).
[0030]
[Example 4]
A domain-inverted crystal was manufactured in the same manner as in Example 1, except that the substrate thickness (w1) of the domain-inverted region was set to 0.15 mm. It was confirmed that a domain-inverted structure almost as designed was obtained by the same method as in Example 1. Further, when a metal electrode was formed in the recess by sputtering and an electric field was externally applied between the metal electrode and the electrode provided on the upper surface of the substrate, the SHG intensity could be modulated.
[0031]
[Example 5]
A domain-inverted crystal was manufactured in the same manner as in Example 1, except that the concave portions formed on the lower surface of the substrate were connected to each other to form a groove. It was confirmed that a domain-inverted structure almost as designed was obtained by the same method as in Example 1. Further, a concave / convex base plate made of Si as an alignment guide was fitted into the groove-shaped concave portion to obtain a state as shown in FIG. Thereafter, fiber alignment, bonding, and packaging were performed to assemble the module. At this time, high efficiency optical coupling was easily achieved by installing the input optical fiber and the condenser lens in accordance with the alignment guide made of Si. At this time, the assembling time is greatly reduced as compared with the case where the module is assembled without the alignment guide, and the assembly can be performed with good reproducibility. In other words, when alignment was performed without an alignment guide, it took 30 minutes, but when alignment was used, it was completed in 5 minutes. As described above, when 10 lots of modules were assembled, reproducibility was obtained with an optical insertion loss of 1 dB or less.
[0032]
【The invention's effect】
The domain-inverted crystal of the present invention can accurately form a domain-inverted region even with a small inversion period, and has excellent mechanical strength, so that damage during handling or further processing can be prevented. .
[Brief description of the drawings]
FIG. 1 is a diagram showing a domain-inverted crystal of the present invention. FIG. 2A is a view from above, FIG. 2B is a view showing a cross section taken along line BB in FIG. 2A, and FIG. It is the figure seen from the direction.
FIG. 2 is a view schematically showing a step of forming a domain-inverted region in the method for producing a domain-inverted crystal of the present invention.
FIG. 3 is a diagram showing one embodiment of the domain-inverted crystal of the present invention.
FIG. 4 is a diagram showing one embodiment of the domain-inverted crystal of the present invention.
FIG. 5 is a view showing one embodiment of the domain-inverted crystal of the present invention.
FIG. 6 is a diagram schematically showing a method of further processing a domain-inverted crystal of the present invention.
FIG. 7 is a diagram illustrating an example of a conventional domain-inverted crystal.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 domain-inverted crystal 10 concave portion 11 domain-inverted region 12 non-domain-inverted region 21 upper electrode 22 lower electrode 3 heat transfer compound 4 Peltier element 51 power supply 52 electrode 53 electrode 6 alignment guide

Claims (8)

A domain-inverted crystal in which a domain-inverted structure in which domain-inverted regions and non-domain-inverted regions alternately appear on one surface of the ferroelectric crystal substrate,
A domain-inverted crystal, wherein a concave portion is provided at a position corresponding to the domain-inverted region on the other plate surface of the substrate. The domain-inverted crystal according to claim 1, wherein the ferroelectric crystal substrate is a substrate cut so that the X-axis direction of the crystal is parallel to the substrate surface. 3. The domain-inverted crystal according to claim 1, wherein an optical waveguide is formed so as to pass through the domain-inverted structure. 3. The domain-inverted crystal according to claim 1, wherein a space inside the concave portion is filled with a heat transfer compound. Further, an electric field applying means is provided on the domain-inverted crystal, and the electric field applying means is arranged inside and outside the concave portion so as to sandwich the domain-inverted region in the thickness direction of the ferroelectric crystal substrate. 3. The domain-inverted crystal according to claim 1, further comprising an electrode provided. When further processing the domain-inverted crystal according to any one of claims 1 to 3, using a processing tool, an alignment guide for positioning the processing tool on the domain-inverted crystal is fitted into the recess. A method of processing a domain-inverted crystal. In forming a domain-inverted structure such that domain-inverted regions and non-domain-inverted regions alternately appear on one plate surface of the ferroelectric crystal substrate to form a domain-inverted crystal,
Of the other plate surface of the substrate, a concave portion is provided at a position corresponding to a region to be the domain-inverted region,
A method for manufacturing a domain-inverted crystal, comprising: arranging electrodes in a region to be the domain-inverted region and in a recess, and applying a domain-inverted voltage between the two electrodes. The manufacturing method according to claim 7, wherein the ferroelectric crystal substrate is a substrate cut so that the direction of the X axis of the crystal is parallel to the substrate surface.

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