JPH1062829A - Nonlinear optical element and method of manufacturing the same - Google Patents

Abstract

[PROBLEMS] To provide a nonlinear optical element having an optical waveguide structure and a desired crystal orientation, and a method for manufacturing the same. SOLUTION: A cladding 42 having a hole portion 41 whose both ends are opened is heated by a heating device 43 to a temperature higher than a melting point of a crystal material to be used as a core. A part of the liquid 45 is caused to enter the pore portion 41 by capillary action to form a melt 46 in the pore portion, and solidification of the crystal from the seed crystal 44, which maintains a crystalline state, toward the melt 46 in the pore portion. By moving the relative positions of the cladding 42 and the seed crystal 44 maintaining the crystalline state and the heating device 43 so as to proceed, the in-hole crystal 47 having the same crystal orientation as the seed crystal 44 is produced. .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical element having an optical waveguide structure and a desired crystal orientation, and more particularly to a nonlinear optical element exhibiting a second-order nonlinear optical effect and a method of manufacturing the same.

[0002]

2. Description of the Related Art First, a second-order nonlinear optical effect will be briefly described.

The second-order nonlinear optical effect causes an interaction between three lights, and wavelength conversion and application to various optical elements such as a switch element are being studied.

As is well known, the nonlinear optical effect means that the polarization P in a substance is P = ε _o · (x ⁽¹⁾ E + x ⁽²⁾ E ² + x ⁽³⁾ E ³ ,...) (1) This is an effect caused by having higher-order terms proportional to E ² and E ³ in addition to the term proportional to the electric field E of light as shown in FIG.

Here, the effect caused by the second term in the equation (1) is a second-order nonlinear optical effect, and x ⁽²⁾ is a second-order nonlinear susceptibility. In general, the second-order nonlinear susceptibility x ⁽²⁾ is 3
It is a rank tensor and is described as x ⁽²⁾ _ijk . here,
i, j, and k represent the components of the contributing electric field, respectively.

In the second-order nonlinear optical effect, it is common to use a second-order nonlinear optical constant d _ijk , but the second-order nonlinear optical constant _dijk is also a third-order tensor like the second-order nonlinear susceptibility. In general, there is a relationship of d _ijk = (１ ／) × x ⁽²⁾ _ijk . Of the three tensor d _{i jk,} Which component is larger Sadamari the symmetry of the medium, the traveling direction and the polarization direction of light with respect to the medium, so that the effective secondary nonlinear optical constant available is determined.

In order to efficiently generate the second-order nonlinear optical effect, it is necessary to use a larger effective second-order nonlinear optical coefficient and to satisfy a phase matching condition between three lights generally involved. There is. Here, the phase matching condition means that, when the wavelengths of the three light beams involved are λ ₁ , λ ₂ , and λ _{3 in the} order of longer wavelength, the energy conservation law 1 / λ ₁
For three lights satisfying + 1 / λ ₂ = 1 / λ ₃ , the effective refractive index of polarized light involved in wavelength conversion of the substance having the second-order nonlinear optical effect into three light wavelengths is N (λ ₃ ). / Λ ₃ -N (λ ₁ ) / λ ₁ -N (λ ₂ ) / λ ₂ = 0 (2) Where N (λ ₁ ), N
(Λ ₂ ) and N (λ ₃ ) are the effective refractive indices of polarized light involved in wavelength conversion of the nonlinear material with respect to three light wavelengths.

In order to satisfy the phase matching condition, a method generally used is a method using birefringence of a crystal having a second-order nonlinear optical effect. They try to meet the conditions. The outline of phase matching using birefringence will be described with reference to second harmonic generation (SHG), which is an example of wavelength conversion. SHG is
The wavelength conversion is λ ₁ = λ ₂ and λ ₃ = λ _1/2 .

Considering a biaxial optical crystal, the x-axis, y-axis,
z-axis direction of the polarizing each n _x a refractive index of, n _y when, was n _z, and a _{n x> n z> n y} . In this case, the wavelength dependency of the refractive index monotonically decreases with respect to the wavelength unless there is a large absorption, and the magnitude relation between the refractive indexes is maintained. Here, among the second-order nonlinear optical coefficients of this optical crystal, d _31
1 is relatively large, and this d ₃₁₁ is used for SHG generation.
Is, x-axis component, respectively, y-axis component, because it corresponds to the z-axis component, the light λ ₁ (= λ ₂₎ has a polarized light including x-axis component, lambda ₃ of (= λ _1/2) The light must have a polarization that includes the z-axis component.

[0010] The phase-matching conditions at this _{time, N (λ 1) -N (} λ 3) = 0 , but the ... (3), and _{n x (λ 1) -n z} (λ 3) = 0 This is limited to a special case, so that the z-axis of the crystal is generally inclined with respect to the traveling direction of light. In this example, the light of lambda ₁ is placed in the x-axis polarization, and _{N (λ 1) = n x} (λ 1), the light of lambda ₃ enters to have a polarization in the yz plane, y The combined refractive index of the axis and the z axis is felt.

[0011] At this time, the effective refractive index is given by _{N (λ 3) = (sin} 2 θ / n z 2 + cos 2 θ / n y 2) -1/2 ...... (4). Then, by adjusting the angle θ at which the crystal axis is inclined, it is possible to satisfy Expression (3),
The phase matching condition can be satisfied, and relatively efficient wavelength conversion can be performed. This method is called angular phase matching and is generally used for wavelength conversion of a second-order nonlinear optical crystal.

As described above, in order to effectively utilize the second-order nonlinear optical effect, a crystal grown in a desired crystal orientation is definitely required. In addition, since the efficiency of the second-order nonlinear optical effect is proportional to the square of the second-order nonlinear optical constant, the light density, and the interaction length, a large second-order nonlinear optical constant is required to realize a highly efficient optical element. It is necessary to use a crystal having the light and to confine and propagate light propagating by the optical waveguide structure. For this reason, a crystal element having a desired crystal orientation and having an optical waveguide structure has been required for an organic crystal generally having a higher second-order nonlinear optical constant than an inorganic crystal.

Hereinafter, a conventional method for producing a single crystal having an optical waveguide structure will be described.

FIG. 1 shows a method of growing organic crystals in a glass capillary by the Bridgeman-Stockberger method.

First, as shown in FIG. 1 (a), one end of a glass capillary 1 is immersed in a crystal melt 2, and the melt 2 is sucked up into the pores of the glass capillary 1 by capillary action.
A melt 3 in the hole is formed. Subsequently, as shown in FIG. 1 (b), the glass capillary 1 was cooled, and the
To form Subsequently, as shown in FIG. 1 (c), the glass capillary 1 is heated by the heater 5 to form a fusion zone 6. Thereafter, the glass capillary 1 is pulled out from the heater 5 to be solidified from one end of the glass capillary 1. At this time, if the conditions such as the drawing speed are appropriate, the solidified crystal 7 becomes a single crystal.

However, the crystal orientation in the longitudinal direction of the glass capillary is an orientation unique to each crystal, which is called a natural growth orientation, and it has not been possible to control the light guiding direction to an arbitrary direction.

For example, 3,5-dimethyl-1- (4-nitrophenyl) pyrazole (hereinafter abbreviated as DMNP)
In the case of (2), the crystal grows such that the x-axis of the crystal is oriented in the longitudinal direction of the glass capillary. Grow to face.
The notation of the crystal axis is as follows:
da et al. Applied Physics Letters, Vol. 59, 199
1, pp. 1535-137, and for AANP, S. Tomaru et al., Applied Physics Letters, No. 58.
Vol., 1991, pp. 2585-2585.

For this reason, a highly efficient second-order nonlinear optical element cannot be realized except for a very special case such as a specific wavelength.

Next, a conventional single crystal growth method for realizing a desired crystal orientation will be described.

FIG. 2 shows an indirect heating laser melting pedestal (I
(LHPG) method is schematically shown.

In FIG. 2, a part of a straight pipe 11 made of quartz glass or the like is heated by infrared light 12 such as a CO ₂ laser, and the upper part of a base material 14 is heated by radiant heat 13 from a high temperature part of the straight pipe.・ It melts. The melted portion 15 is adhered to the seed crystal 16, the seed crystal 16 is moved at the speed V <b> 2, and the base material 14 is moved at the speed V <b> 1 to draw a single crystal 17. Here, the crystal orientation of the single crystal 17 is the same as the orientation of the seed crystal 16.

According to this method, the crystal can be grown in a desired crystal orientation, but it is difficult to reduce the crystal diameter to 10 μm or less, and an effective optical waveguide structure cannot be formed. Therefore, even when 2-adamantylamino 5-nitropyridine (AANP), which is an organic crystal having a large second-order nonlinear optical constant, is used, the second harmonic generation efficiency is about 0.001 / W, and high efficiency is obtained. A second-order nonlinear optical element could not be realized.

As a manufacturing method combining the above two conventional techniques, a manufacturing method as shown in FIG. 3 can be analogized. That is, a glass capillary containing a polycrystal is produced by the above-mentioned Bridgeman-Stockberger method, and this is used as a base material for the above-mentioned ILHPG method.

FIG. 3 schematically shows a manufacturing method in this case.

First, as shown in FIG. 3A, a part of a straight pipe 21 made of quartz glass or the like is heated by infrared light 22 such as a CO ₂ laser. The upper portion of the polycrystal 24 inside the glass capillary 23 is melted by the radiant heat from the high temperature portion of the straight tube to form a melted portion 25 in the capillary. The melted portion 25 in the capillary is connected to the seed crystal melted portion 27 at the lower end of the seed crystal 26.
Adhere to Subsequently, as shown in FIG. 3 (b), the seed crystal 26 and the glass
It is moved upward by 8 and 29 and solidified from the side of the seed crystal 26 to form a single crystal 30, and the solidification is advanced into the capillary 23.

The inventor of the present invention has actually carried out this method.
When contacted with air bubbles, as shown in FIG.
It can be seen that the crystal orientation of the seed crystal is hardly transmitted to the crystal in the capillary due to the bubbles 31 in the capillary, and the combination of the conventional crystal growth methods has the optical waveguide structure and the desired crystal orientation. It has been found that a single crystal having the same cannot be grown.

[0027]

As described above, in order to efficiently utilize the second-order nonlinear optical effect in a wavelength conversion element or the like, the second-order nonlinear optical crystal must have an optical waveguide structure and a desired structure. Although it is necessary to grow the crystal in the crystal orientation, conventionally, there is a problem that the crystal orientation is limited to a specific orientation in a method capable of producing an optical waveguide structure, and that the optical waveguide structure cannot be produced in a method capable of controlling the crystal orientation. Was.

An object of the present invention is to provide a nonlinear optical element having an optical waveguide structure and a desired crystal orientation, and a method of manufacturing the same.

[0029]

According to the present invention, in order to achieve the above object, there is provided a nonlinear crystal having an optical waveguide structure having an optical crystal having a second-order nonlinear optical effect as a core and surrounding the core with a cladding. The optical element has a nonlinear optical element in which a desired crystal orientation other than the natural growth orientation of the optical crystal coincides with a light guiding direction in the optical waveguide structure, and a second-order nonlinear optical effect composed of DMNP. In a nonlinear optical element having an optical crystal as a core and having an optical waveguide structure in which the periphery of the core is surrounded by a clad, a desired crystal orientation other than the x-axis of the optical crystal has a light guiding direction in the optical waveguide structure. And a light guide structure in which an optical crystal made of AANP having a second-order nonlinear optical effect is used as a core, and the core is surrounded by a clad. In the linear optical element, the desired crystal orientations other than the c-axis of the optical crystal, proposes a non-linear optical element coincides with the light propagation direction in the optical waveguide structure.

Further, in the present invention, in order to achieve the above object, a first step of heating a hollow body made of a material having a melting point higher than that of an optical crystal having a secondary nonlinear optical effect to a temperature equal to or higher than the melting point of the optical crystal; The seed crystal made of the optical crystal is brought into contact with the hollow body while making the desired crystal orientation of the seed crystal coincide with the direction in which the hollow part of the hollow body is formed, and is brought into contact with the hollow body of the seed crystal. A second step of melting the melted portion and its vicinity, and a third process of filling the hollow portion of the hollow body with a part of the melted seed crystal by capillary action.
And a fourth step of sequentially cooling and crystallizing the molten seed crystal from its solid-liquid interface to form an optical crystal having a desired crystal orientation in the hollow portion of the hollow body. A method for manufacturing a nonlinear optical element is proposed.

According to the present invention, a part of the seed crystal is melted,
This penetrates into the hollow portion of the hollow body constituting the clad due to the capillary phenomenon. However, since the hollow body is maintained at a temperature equal to or higher than the melting point of the crystal material, the crystal material exists in a molten state in the hollow portion. As described above, since a part of the seed crystal is used to introduce the crystal material into the hollow portion, the connection of the crystal material from the seed crystal to the hollow portion is continuously performed without a break, so that air bubbles can enter the hollow portion. By moving toward the remaining part of the seed crystal that can be suppressed and maintain the crystalline state without melting, the same crystal orientation as the seed crystal is continuously realized in the crystal in the hollow part of the hollow body And a crystal orientation control optical waveguide structure having the crystal in the hollow portion as a core can be obtained.

Further, in the above method, if a hollow body having a tapered hollow portion extending toward one end with which the seed crystal comes into contact is used, crystal growth from the seed crystal into the hollow portion can be performed more smoothly. Therefore, the moving speed of the seed crystal and the hollow body can be increased, and the crystallinity can be further improved.

[0033]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The concept of the present invention will be briefly described with reference to FIGS.

First, an outline of a manufacturing method in which the position of the seed crystal and the hollow body (cladding) and the position of the heating device are relatively changed will be described with reference to FIG.

As shown in FIG. 4A, a cladding 42 having a hollow (hole) portion 41 having both open ends is heated by a heating device 43 to a temperature higher than the melting point of the crystal material to be used as a core. Then, the seed crystal 44 is made to approach one end of the clad 42.

Next, as shown in FIG.
The seed crystal 44 is brought into contact with one end of 2. At that time, seed crystal 4
The heating conditions are adjusted from the beginning so that only part of 4 is melted. A part of the melt 45 of the seed crystal 44 enters the hole 41 by capillary action, and becomes a melt 46 in the hole.
At this time, the seed crystal 44, the melt 45 of the seed crystal, and the melt 46 in the pore portion, which maintain the crystalline state, are continuously connected.

Next, as shown in FIG. 4C, the cladding 42 and the crystal state are changed so that the solidification of the crystal proceeds from the seed crystal 44 maintaining the crystal state toward the melt 46 in the void portion. The relative position between the maintained seed crystal 44 and the heating device 43 is moved.

As a result, as shown in FIG.
The melted portion of the seed crystal 44 is solidified, and subsequently, as shown in FIG. 4D, the solidification of the melt 46 in the pore portion continuously proceeds, and the crystal 47 in the pore portion is formed. At this time, since the solidification proceeds from the seed crystal melt to the pores continuously, the crystal 47 in the pores and the seed crystal 44 have the same crystal orientation.

Then, as shown in FIG. 4E, the melt in the pore portion is solidified, and the crystal 47 in the pore portion is formed.
As a result, the crystal 47 in the hole is used as a core,
An optical waveguide structure crystal in which the crystal orientation is controlled and which has a cladding can be manufactured.

Next, an outline of a manufacturing method for changing the heating state of the heating device will be described with reference to FIG.

As shown in FIG. 5A, a cladding 52 having a hole 51 whose both ends are opened is heated by a heating device 53 to a temperature higher than the melting point of the crystal material to be used as a core. Then, the seed crystal 54 is made to approach one end of the clad 52.

Next, as shown in FIG.
The seed crystal 54 is brought into contact with one end of the second crystal. At that time, seed crystal 5
The heating conditions are adjusted from the beginning so that only part of 4 is melted. A part of the melt 55 of the seed crystal 54 enters the pore portion 51 by a capillary phenomenon, and becomes a melt 56 in the pore portion.
At this time, the seed crystal 54, the melt 55 of the seed crystal, and the melt 56 in the pore portion, which maintain the crystalline state, are continuously connected.

Up to this point, the manufacturing method is the same as the above-described manufacturing method in which the positions of the seed crystal and the clad and the position of the heating device are relatively changed.

Next, as shown in FIG.
Change the heating conditions of 3 and gradually lower the heating temperature. Then, the temperature distribution of the seed crystal 54 and the clad 52 changes,
The position where the melting point of the crystalline material is lower than the melting point moves from the seed crystal 54 maintaining the crystalline state toward the melt 56 in the pore portion, solidification proceeds continuously, and the crystal 57 in the pore portion is formed. .

Then, as shown in FIG. 5D, the crystal 57 in the pore is formed in a state where the temperature of the entire melt in the pore is lower than the melting point of the crystal. As a result, the crystal 5
An optical waveguide structure crystal in which the crystal orientation is controlled, which has the core 7 and the clad 52, can be manufactured.

The present invention can be applied if the melting or softening temperature of the material forming the cladding is higher than the melting point of the crystalline material used as the core. For this reason, it can be said that it is particularly useful for an organic crystal having a low melting point.

Examples of the organic crystal applicable as the core include the following. That is, as a material,
-Nitroaniline (m-NA), 2-methyl-4-nitroaniline (MNA), 3-methyl- (2,4-dinitrophenyl) -aminopropanoate (MAP), 3-
Methyl-4-nitropyridine-1-oxide (PO
M), 3-aminophenyl (m-AP), 2-adamantylamino 5-nitropyridine (AANP), N- (4
-Nitrophenyl) -L-prolinol (NPP), N
-(Nitrophenyl) -N-methylaminoacetonitrile (NPAN), 4-nitrodimethylaniline (NDM
A), 4-N, N-dimethylamino-2-acetamide-
4-nitroaniline (DAN), 2- (N-prolinol) -5-nitropyridine (PNP), 2-cycloacetylamino-5-nitropyridine (COANP), 3,
9-dinitro-5a, 6,11a, 12-tetrahydro- [1,4] benzoxazino [3,2-b] [1,
4] Benzoxazine (DNBB), 4'-nitrobenzylidene-3-acetamino-4-methoxyaniline (MNBA), dicyanovinylanisole (DIV
A), (-) 4- (4'-dimethylaminophenyl)-
3- (2'-hydroxypropylamino) cyclobutene-3,4-dione (DAD), 2-methoxy-5-nitrophenol (MNP), stilbazolium-P-toluenesulfonic acid (SPTS), 3,5-dimethyl- 1-
(4-nitrophenyl) pyrazole (DMNP), N-
Methoxymethyl-4-nitroaniline (MMNA) and the like.

On the other hand, as described above, the melting temperature or the softening temperature of the material forming the clad is higher than the melting point of the crystalline material used as the core. The condition is that the refractive index of the cladding is lower than the refractive index of the core at at least one wavelength of the light associated with the conversion. If this condition is satisfied, a glass material, a polymer material, a crystal material, and other materials can be used as the cladding material.

Hereinafter, specific embodiments of the present invention will be described.

(First Embodiment) FIG. 6 schematically shows a first embodiment of the present invention. Here, a glass capillary 61 having an outer diameter of 1 mm and an inner diameter of 0.03 mm is used as a clad, and 3,5-dimethyl-
1- (4-Nitrophenyl) pyrazole (DMNP) is used, and a seed crystal 62 having a crystal orientation such that the longitudinal direction of the glass capillary 61 is perpendicular to the z-axis of the DMNP crystal and is 24 degrees with the x-axis is used.

The seed crystal 62 is held on a glass plate 65 by a support rod 63 and a seed crystal holding jig 64. The glass capillary 61 is held by the glass plate 6 by a capillary holding jig 66 so as not to block the holes of the glass capillary.
5 is held.

The heating state of the first heater 67 is set to be higher than the melting point of the crystal, and the second heater 68 is set to be lower than the melting point of the crystal. In this example, D
Since the melting point of MNP is 102 degrees, the first heater 67
Is set to 120 degrees, and the second heater 68 is set to 70 degrees.

In the first step, the glass capillary 61 is substantially contained in the first heater 67, and is heated to a temperature equal to or higher than the melting point of DMNP. At this time, the seed crystal 62 is in the second heater 68 and maintains the crystal state.

In the second step, the seed crystal 62 comes into contact with the glass capillary 61, a part of the seed crystal 62 is melted, and a part of the seed crystal melt 69 is formed in the hole of the glass capillary 61 by capillary action. Then, the melt 70 in the pore portion is formed. FIG. 6 shows the state at this time.

In the third step, the glass plate 65 is moved by the wire 71 in the direction of the second heater 68 together with the glass capillary 61 and the seed crystal 62 held. The moving speed is 1 mm / s in this example. As a result, the seed crystal melt 69 and the melt 70 in the void portion are continuously solidified from the seed crystal to the void portion, and the void portion crystal becomes the seed crystal 6.
2 will have the same crystallographic orientation.

As a result of this example, the hole D having an inner diameter of 0.03 mm was obtained.
It has an optical waveguide structure in which an MNP crystal is used as a core and a glass having an outer diameter of 1 mm is clad, and the crystal orientation is such that the longitudinal direction of the glass capillary is perpendicular to the z-axis of the DMNP crystal and is 24 degrees with the x-axis. Crystal optical waveguide has a length of 6m
m.

The crystal orientation is 1.32 μm wavelength.
The azimuth satisfying the phase matching condition of the second harmonic generation, and a second harmonic generation experiment with a wavelength of 1.32 μm was performed using the manufactured crystal optical waveguide.
W was obtained. Wavelength conversion efficiency 0.001 for bulk crystal
/ W, the efficiency was improved by about two orders of magnitude in this example.

The cladding is 0.03 mm long,
When a DMNP crystal was produced in the same manner as in this example using a glass plate having a flat hole having a width of 2 mm,
A kind of slab waveguide having a core shape of 0.03 mm in length and 2 mm in width was produced. The wavelength conversion efficiency in this case is 0.01
/ W was lower than in the case where the glass capillary was used, because the core area was large in the slab shape.
As a result, the orientation control crystal optical waveguide in the form of a thin film is manufactured, and there is a possibility that a three-dimensional optical waveguide can be manufactured by performing the subsequent secondary processing. Therefore, the present invention is not limited to the shape of the clad, and can be applied as a clad as long as the clad has a hole portion open at both ends.

(Second Embodiment) FIG. 7 schematically shows a second embodiment of the present invention. Here, a glass capillary 82 having an outer diameter of 1 mm, an inner diameter of 0.01 mm, and a tapered shape 81 at one end of a hole is used as a clad, and 3,5-dimethyl-1- (4-nitrophenyl) is used as a crystal material. Using a pyrazole (DMNP), a seed crystal 83 having a crystal orientation such that the longitudinal direction of the glass capillary 82 is perpendicular to the z-axis of the DMNP crystal and is 24 degrees with the x-axis.

The seed crystal 83 is held on a glass plate 86 by a support rod 84 and a seed crystal holding jig 85. The glass capillary 82 is held by the glass plate 8 by a capillary holding jig 87 so as not to block the holes of the glass capillary.
6 is held.

The heating state of the first heater 88 is set to be higher than the melting point of the crystal, and the second heater 89 is set to be lower than the melting point of the crystal. In this example, D
Since the melting point of MNP is 102 degrees, the first heater 88
Is set to 120 degrees, and the second heater 89 is set to 70 degrees.

In the first step, the glass capillary 82 is substantially contained in the first heater 88, and is heated to a temperature equal to or higher than the melting point of DMNP. At this time, the seed crystal 83 is in the second heater 89 and maintains the crystalline state.

In the second step, the seed crystal 83 comes into contact with the glass capillary 82, a part of the seed crystal 83 is melted, and a part of the seed crystal melt 90 passes through the tapered portion 81 due to the capillary action, and the glass capillary. The melt enters into the hole portion 82 and becomes the melt 91 in the hole portion. FIG. 7 shows the state at this time.

In the third step, the glass plate 86 is moved in the direction of the second heater 89 together with the glass capillary 82 and the seed crystal 83 held by the wire 92. The moving speed is 4 mm / s in this example. As a result, the seed crystal melt 90 and the melt 91 in the void portion are continuously solidified from the seed crystal to the void portion, and the void portion crystal becomes the seed crystal 8.
3 will have the same crystal orientation.

As a result of this example, a hole D having an inner diameter of 0.01 mm was obtained.
It has an optical waveguide structure in which an MNP crystal is used as a core and a glass having an outer diameter of 1 mm is clad, and the crystal orientation is such that the longitudinal direction of the glass capillary is perpendicular to the z-axis of the DMNP crystal and is 24 degrees with the x-axis. 8m long crystal optical waveguide
m.

At this time, by having the tapered structure 81 at one end of the hole of the glass capillary 82, the continuity of crystal solidification from the seed crystal 83 to the hole becomes smoother,
Generally, the moving speed can be increased as compared with the case where there is no tapered shape.

This crystal orientation is 1.32 μm wavelength.
An orientation that satisfies the phase matching condition for second harmonic generation, and a second harmonic generation experiment with a wavelength of 1.32 μm was performed using the fabricated crystal optical waveguide.
W was obtained. Wavelength conversion efficiency 0.001 for bulk crystal
/ W, the efficiency was improved by about three orders of magnitude in this example.

(Third Embodiment) FIG. 8 schematically shows a third embodiment of the present invention. Here, a glass capillary 102 having an outer diameter of 1 mm and an inner diameter of 0.01 mm and having a tapered shape 101 at one end of a hole portion is used as a cladding, and 2-adamantylamino 5-nitropyridine (AANP) is used as a crystal material. Glass capillary 1
The seed crystal 103 having a crystal orientation such that the longitudinal direction of the crystal 02 is perpendicular to the c-axis of the AANP crystal and 30 degrees with the b-axis is used.

The seed crystal 103 is held on a glass plate 106 by a support rod 104 and a seed crystal holding jig 105.
The glass capillary 102 is connected to the capillary holding jig 10.
7, the glass capillary is held on the glass plate 106 so as not to block the holes.

The heating state of the first heater 108 is set so as to be equal to or higher than the melting point of the crystal.
9 is set to be lower than the melting point of the crystal. Further, a third heater is provided between the first heater 108 and the second heater 109.
The heater 110 is set at an intermediate temperature between the set temperature of the first heater 108 and the set temperature of the second heater 109. In this example, since the melting point of AANP is 168 degrees, the first heater 108 is set to 190 degrees,
The second heater 109 is set at 100 degrees, and the third heater 110 is set at 154 degrees.

In the first step, the glass capillary 102
Is substantially in the first heater 108 and is heated to a temperature equal to or higher than the melting point of AANP. At this time, the seed crystal 103 is in the second heater 109 and maintains a crystalline state.

In the second step, the seed crystal 103 comes into contact with the glass capillary 102, a part of the seed crystal 103 is melted, and a part of the seed crystal melt 111 passes through the tapered portion 101 due to the capillary action, and the glass capillary. The melt enters into the hole portion 102 and becomes the melt 112 in the hole portion. FIG. 8 shows the state at this time.

In the third step, the wire 113
Glass capillary 102 and seed crystal 10 held
For every three, the glass plate 106 is moved toward the second heater 109. The moving speed is 4 mm / s in this example. As a result, the seed crystal melt 111 and the melt 112 in the pore portion are
The seed crystal is continuously solidified into the vacancy, and the vacancy crystal has the same crystal orientation as the seed crystal 103.

As a result of this example, a hole A having an inner diameter of 0.01 mm
It has an optical waveguide structure in which an ANP crystal is used as a core and a glass having an outer diameter of 1 mm is clad, and the crystal orientation is such that the longitudinal direction of the glass capillary is perpendicular to the c-axis of the AANP crystal and 30 degrees with the b-axis. 8m long crystal optical waveguide
m.

At this time, the tapered structure 101 is provided at one end of the hole portion of the glass capillary 102 so that the seed crystal 1 can be formed.
The continuity of crystal solidification from 03 to the hole becomes smoother, and the moving speed can be generally increased as compared with the case where there is no tapered shape. Further, by providing the third heater 110, the temperature gradient in the vicinity of solidification can be controlled more precisely, and the yield of crystal growth can be improved.

This crystal orientation is 1.32 μm wavelength.
An orientation that satisfies the phase matching condition for second harmonic generation, and a second harmonic generation experiment with a wavelength of 1.32 μm was performed using the fabricated crystal optical waveguide. The wavelength conversion efficiency was 1.8 /.
W was obtained. Wavelength conversion efficiency 0.001 for bulk crystal
/ W, the efficiency was improved by about three orders of magnitude in this example.

(Fourth Embodiment) FIG. 9 schematically shows a fourth embodiment of the present invention. Here, a glass capillary 122 having an outer diameter of 1 mm and an inner diameter of 0.01 mm and having a tapered shape 121 at one end of a hole portion is used as a cladding, and 2-adamantylamino 5-nitropyridine (AANP) is used as a crystal material. Glass capillary 1
A seed crystal 123 having a crystal orientation such that the longitudinal direction of the crystal 22 is perpendicular to the c-axis of the AANP crystal and 30 degrees with the b-axis is used.

As shown in FIG. 9A, the seed crystal 123
It is held from above by a support rod 125 in a straight glass tube 124. The glass capillary 122 includes a glass straight tube 124.
The glass capillary is held from below by a support rod 126 so as not to block the hole of the glass capillary.

The heating state of the heater 127 is set so as to be higher than the melting point of the crystal. In addition, the glass straight pipe 12
The portion above the fourth heater 127 is heated by carbon dioxide laser light 128 which is infrared light.

As shown in FIG. 9 (a), when the seed crystal 123 is brought close to the glass capillary 122 from above, the carbon dioxide laser light 1
The tip of the seed crystal 123 is melted by the radiation from the straight glass tube 124 heated by
29 are formed. In this state, as shown in FIG.
When the melting portion 129 is brought into contact with the tapered portion 121 at one end of the hole of the glass capillary 122, a part of the seed crystal melt 129 enters the hole of the glass capillary 122 through the tapered portion 121 due to a capillary phenomenon, and becomes empty. It becomes the melt 130 in the hole.

Thereafter, the glass capillary 122 and the seed crystal 123 are moved upward at the same speed. The moving speed is 4 mm / s in this example. As a result, the seed crystal melt 129 and the melt 130 in the void portion are continuously solidified from the seed crystal to the void portion, and the void portion crystal has the same crystal orientation as the seed crystal 123.

As a result of this example, a hole A having an inner diameter of 0.01 mm
It has an optical waveguide structure in which an ANP crystal is used as a core and a glass having an outer diameter of 1 mm is clad, and the crystal orientation is such that the longitudinal direction of the glass capillary is perpendicular to the c-axis of the AANP crystal and 30 degrees with the b-axis. 8m long crystal optical waveguide
m.

At this time, by performing heating using infrared light in addition to the heater, it becomes possible to control the temperature in a minute area, and to improve the yield of crystal growth.

This crystal orientation is 1.32 μm wavelength.
An orientation that satisfies the phase matching condition for second harmonic generation, and a second harmonic generation experiment with a wavelength of 1.32 μm was performed using the fabricated crystal optical waveguide. The wavelength conversion efficiency was 1.8 /.
W was obtained. Wavelength conversion efficiency of 0.002 for bulk crystal
/ W, the efficiency was improved by about three orders of magnitude in this example.

[0085]

As described above, according to the present invention,
An extremely efficient second-order nonlinear optical element having an optical waveguide structure and a desired crystal orientation can be provided.

[Brief description of the drawings]

FIG. 1 is a process diagram showing an example of a conventional manufacturing method.

FIG. 2 is a process chart showing another example of a conventional manufacturing method.

FIG. 3 is a process chart showing still another example of the conventional manufacturing method.

FIG. 4 is a process chart showing an outline of a first manufacturing method of the present invention.

FIG. 5 is a process chart showing an outline of a second manufacturing method of the present invention.

FIG. 6 is a schematic diagram showing the first embodiment of the present invention.

FIG. 7 is a schematic view showing a second embodiment of the present invention.

FIG. 8 is a schematic diagram showing a third embodiment of the present invention.

FIG. 9 is a schematic view showing a fourth embodiment of the present invention.

[Explanation of symbols]

41, 51: hole portion, 42, 52: clad, 43, 5
3: heating device, 44, 54, 62, 83, 103, 12
3: seed crystal, 45, 55, 69, 90, 111, 12
9: seed crystal melt, 46, 56, 70, 91, 112,
130: melt in the pore, 47, 57: crystal in the pore, 6
1, 82, 102, 122: glass capillary, 63,
84, 104, 125, 126: support rods, 64, 85,
105: seed crystal holding jig, 65, 86, 106: glass plate, 66, 87, 107: capillary holding jig, 6
7, 88, 108: first heater, 68, 89, 10
9: second heater, 71, 92, 113: wire, 8
1, 101, 121: tapered portion, 110: third heater, 124: straight glass tube, 127: heater, 128: carbon dioxide gas laser.

Claims (5)

[Claims] 1. A nonlinear optical element having an optical waveguide structure in which an optical crystal having a second-order nonlinear optical effect is used as a core and the core is surrounded by a clad, wherein a desired orientation other than the natural growth orientation of the optical crystal is provided. The crystal orientation is
A nonlinear optical element, which coincides with a light guiding direction in the optical waveguide structure. 2. A nonlinear optical element having an optical waveguide structure comprising a core made of DMNP having a second-order nonlinear optical effect as a core and surrounding the core with a cladding, wherein the optical crystal has a structure other than the x-axis. A non-linear optical element, wherein a desired crystal orientation coincides with a light-guiding direction in the optical waveguide structure. 3. A non-linear optical element having an optical waveguide structure including an AANP having a second-order nonlinear optical effect as a core and surrounding the core with a cladding, wherein the c-axis of the optical crystal is other than a c-axis. A non-linear optical element, wherein a desired crystal orientation coincides with a light-guiding direction in the optical waveguide structure. 4. A first step of heating a hollow body made of a material having a higher melting point than an optical crystal having a second-order nonlinear optical effect to a temperature equal to or higher than the melting point of the optical crystal; The crystal is brought into contact with the direction in which the hollow portion of the hollow body is formed while the desired crystal orientation of the seed crystal is made to coincide with the crystal. And a third step of filling the hollow portion of the hollow body with a part of the melted seed crystal by capillary action, and cooling and crystallizing the melted seed crystal sequentially from its solid-liquid interface, A fourth step of forming an optical crystal having a desired crystal orientation in the hollow portion of the hollow body. 5. The method for manufacturing a nonlinear optical element according to claim 4, wherein a hollow body having a tapered hollow portion extending toward one end with which the seed crystal contacts is used.