JPH04340934A - Light wavelength converting element and its manufacture - Google Patents

Abstract

PURPOSE:To obtain the light wavelength converting element which is high in the degree of freedom of selection for a nonlinear optical material and easily manufactured and has periodic structure. CONSTITUTION:An embedded optical waveguide 13 is formed in the surface 11a of a 1st glass substrate 11 and single crystal 14 of MNA as the organic nonlinear optical material is charged in plural grooves 12b formed in the surface 12a of a 2nd glass substrate 12 at a specific period. Then those substrates 11 and 12 are joined so that the optical waveguide 13 contacts the MNA single crystal 14.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical wavelength conversion element for wavelength converting a fundamental wave into a second harmonic or the like, and more particularly to an optical wavelength conversion element having a periodic structure of a nonlinear optical material.

The present invention also relates to a method of manufacturing the above-mentioned optical wavelength conversion element using an organic nonlinear optical material.

0003

[Prior Art] Conventionally, nonlinear optical materials have been used to
Various attempts have been made to convert the wavelength of laser light into a second harmonic or the like (shorten the wavelength). As one of the optical wavelength conversion elements that perform wavelength conversion in this way, for example,
As shown in Japanese Patent No. 35424, a three-dimensional optical waveguide made of a nonlinear optical material is embedded in a substrate serving as a cladding layer. Since this optical waveguide type optical wavelength conversion element can easily achieve phase matching between the fundamental wave and the wavelength-converted wave, research on this optical waveguide type optical wavelength conversion element has been actively conducted recently. ing.

Recently, various proposals have been made to use single-crystal organic nonlinear optical materials as nonlinear optical materials in such optical waveguide type optical wavelength conversion elements. Since this organic nonlinear optical material has a significantly larger nonlinear optical constant than an inorganic material, high wavelength conversion efficiency can be achieved by using this organic nonlinear optical material.

This organic nonlinear optical material is disclosed in, for example, Japanese Patent Application Laid-Open No. 60-250334 and "Nonline
r Optical Properties of
Organic and Polymeric M
material”ACS SYMPOSIUM
SERIES 223, David J. Will
iams (American Chemical)
Society, 1983), “Organic Nonlinear Optical Materials” supervised by Masao Kato and Hachiro Nakanishi (CMC Publishing Co., Ltd., 1983).
985), “Nonlinear Optica
l Properties of Organic
Molecules and Crystals
” edited by D. S. Chemla and J. Zyss (
Academic Press Inc. , 1987
Annual), R. T. “The
Quality and Performance of
TheOrganic Non-Linear O
ptical Material (-)2-(α-
Methylbenzylamino)-5-Nitr
Opyridine (MBA-NP)” (Optics
Communications, Vol. 65
, No. MNA (2-
Methyl-4-nitroaniline), mNA (methanitroaniline), POM (3-methyl-4-nitropyridine-
1-oxide), urea, NPP[N-(4-nitrophenyl)-(S)-prolinol], NPAN{2-[
N-(4-nitrophenyl)-N-methylamino]acetonitrile}, DAN (2-dimethylamino-5-nitroacetanilide), MBA-NP[2-N(α-methylbenzylamino)-5-nitropyridine] , NPRO
(1-(4-nitrophenyl)pyrazole), and 3,5-dimethyl-1-(4-nitrophenyl)pyrazole shown in JP-A-62-210432, 3,
5-dimethyl-1-(4-nitrophenyl)-1,2,
4-triazole, 2-ethyl-1-(4-nitrophenyl)imidazole, 1-(4-nitrophenyl)pyrrole, 2-dimethylamino 1-5-nitroacetanilide, 5-nitro-2-pyrrolidinoacetanilide, 3 −
Methyl-4-nitropyridine-N-oxide, JP-A-2
Examples include TRI shown in Japanese Patent Application No. 28-28 and ENIM shown in Japanese Patent Application No. 2-58654 by the present applicant.

On the other hand, in order to compensate for the phase mismatch between the fundamental wave and the wavelength-converted wave, it has been proposed to introduce a periodic structure in which states of different refractive indexes or nonlinear polarizations (domains) periodically repeat in the optical waveguide section. has been done. This periodic structure allows the amount of phase mismatch to be compensated to be Δn(Δn=n2 −n
1, where n1 is the refractive index of the optical waveguide that is felt by the fundamental wave, and n2 is the refractive index of the optical waveguide that is felt by the wavelength-converted wave), then the above refractive index or nonlinear polarization is

0007
]

[Math 1]

It is repeated at a period Λ that satisfies the following. Conventionally, as such an optical wavelength conversion element, specifically, one having a periodic structure in which LiNbO3 domains are inverted is known.

[0009]

However, the conventional optical wavelength conversion element having a domain inversion type periodic structure as described above has a problem in that the nonlinear optical materials that can be used are severely limited.

In particular, organic nonlinear optical materials such as MNA and NPRO in which the diagonal term d11, d22, or d33 of the nonlinear optical constant is the largest cannot achieve angular phase matching, so it is difficult to effectively utilize the large nonlinear optical constant. Therefore, it is desired to introduce the above-mentioned periodic structure, but hitherto no method has been established for producing a nonlinear optical material having a periodic structure using an organic nonlinear optical material.

The present invention has been made in view of the above circumstances, and provides an optical wavelength conversion element with a periodic structure that has a high degree of freedom in selecting the nonlinear optical material used and can be easily manufactured. The purpose is to provide the following.

Another object of the present invention is to provide a method for easily manufacturing an optical wavelength conversion element having a periodic structure using an organic nonlinear optical material having a large nonlinear optical constant. be.

[0013]

[Means for Solving the Problems] An optical wavelength conversion element according to the present invention includes a first substrate on which a buried optical waveguide is formed, and a plurality of grooves formed on the surface at a predetermined pitch. A second substrate filled with a material is bonded to the optical waveguide such that the optical waveguide is in contact with each of the nonlinear optical materials in the plurality of grooves.

[0014] Furthermore, the method for manufacturing an optical wavelength conversion element according to the present invention includes: ◆ forming an embedded optical waveguide on the surface of a first substrate; and ◆ forming a plurality of grooves at a predetermined pitch on the surface of a second substrate. , ◆ these substrates are integrated with the optical waveguide facing each of the plurality of grooves, and ◆ the plurality of grooves are filled with a crystalline organic nonlinear optical material having a higher refractive index than the substrate material. After that, ◆ By gradually pulling out both of these substrates from the inside of the furnace kept at a temperature higher than the melting point of the organic nonlinear optical material to the outside of the furnace kept at a temperature lower than the melting point, the organic nonlinear optical material in the molten state is This method is characterized in that the optical material is single-crystalized from the part drawn out of the furnace.

[0015]

[Operations and Effects of the Invention] In the optical wavelength conversion element of the present invention having the above configuration, when the fundamental wave is guided through the optical waveguide,
The light (evanescent wave) seeping out from the optical waveguide passes through the nonlinear optical material filled in each groove, and is wavelength-converted into a second harmonic or the like by the nonlinear optical material. Since the above-mentioned leaked light and wavelength-converted wave alternately pass through the nonlinear optical material section and the substrate section whose refractive index is different from the nonlinear optical material section, there is a phase mismatch in the same way as when passing through an optical waveguide with a periodic structure. Can be compensated.

Note that if the amount of phase mismatch to be compensated is Δn, then the period Λ of the periodic structure is

[0017]

[Math 2]

In the case of [0018], it becomes a waveguide-waveguide type optical wavelength conversion element in which phase matching is achieved between the fundamental wave of the waveguide mode and the wavelength-converted wave of the waveguide mode,

[0019]

[Math 3]

In the case of [0020], it becomes a so-called Cerenkov radiation type optical wavelength conversion element in which phase matching is achieved between the fundamental wave in the waveguide mode and the wavelength-converted wave in the radiation mode.

Among the optical wavelength conversion elements of the present invention, those in which an organic nonlinear optical material is used as the nonlinear optical material have an extremely large diagonal term d of the nonlinear optical constant.
11, d22, or d33, thereby achieving high wavelength conversion efficiency.

[0022] The buried optical waveguide to be formed in the first substrate can be produced relatively easily by various currently established methods. On the other hand, filling the grooves of the second substrate with an organic or inorganic nonlinear optical material can be done relatively easily by various known methods without being subject to material limitations. The optical wavelength conversion element of the present invention is formed by directly bonding the first substrate on which the optical waveguide is formed in this way and the second substrate whose grooves are filled with a nonlinear optical material. Because of this, the nonlinear optical materials that can be used are not significantly restricted and can be manufactured relatively easily.

Furthermore, in the method for manufacturing an optical wavelength conversion element according to the present invention, filling the plurality of grooves in the second substrate with an organic nonlinear optical material is described in, for example, Japanese Patent Laid-Open No. 64-35424.
The method disclosed in the publication is to immerse the ends of the bonded first and second substrates in a melted organic nonlinear optical material or a solution of the organic nonlinear optical material, and to absorb the melt or solution by capillary action. This can be easily done by using a method of entering the groove. Also, forming an embedded optical waveguide in the first substrate can be easily done as described above.

Therefore, according to this method, it is possible to relatively easily manufacture an optical wavelength conversion element that has a periodic structure and performs wavelength conversion using an organic nonlinear optical material.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained in detail below based on embodiments shown in the drawings. FIG. 1 shows an optical wavelength conversion element 10 according to an embodiment of the present invention. This optical wavelength conversion element 10 includes a first glass substrate 11 and a second glass substrate 1.
2, and the surface (lower surface in the figure) 11 of the first glass substrate 11
A buried optical waveguide 13 formed in a portion a and an MNA single crystal 14 filled in a plurality of grooves 12b provided in a surface 12a of a second glass substrate 12 (upper surface in the figure).
It consists of This MNA is an organic nonlinear optical material as described above. The grooves 12b are each formed to extend perpendicularly to the direction in which the optical waveguide 13 extends. The grooves 12b are arranged at a predetermined period Λ and have a width of Λ/2. The optical waveguide 13 is obtained by forming a portion with a higher refractive index within the first glass substrate 11 by a known method such as an ion exchange method.

Both substrates 11 and 12 are connected to their respective surfaces 11a and 12 by, for example, optical contact.
A is integrated in a state where they are in close contact with each other. As a result, the optical waveguide 13 is in contact with each of the plurality of MNA single crystals 14.

When using the optical wavelength conversion element 10 having this configuration, the laser beam 16 as a fundamental wave with a wavelength of 1064 nm emitted from the Nd:YAG laser 15 is, for example,
The condenser lens 1 is configured to converge on the end face of the optical waveguide 13.
The light is focused by 7. As a result, this laser beam 16 enters the optical waveguide 13 and travels therein in a waveguide mode. FIG. 2 schematically shows the propagation state of the laser beam 16 in the optical waveguide 13. As shown in the figure, a portion of the laser beam 16 leaks out of the optical waveguide 13, and this leaked light passes through a portion of the MNA single crystal 14,
The MNA single crystal 14 reduces the wavelength to 1/2, that is, 532
The wavelength is converted to a second harmonic 18 of nm. This second harmonic 18 is radiated into the second glass substrate 12 at a predetermined angle (
(so-called Cherenkov radiation), phase matching is achieved between this radiation mode and the guided mode of the laser beam 16 in the optical waveguide 13. End face 1 of optical wavelength conversion element 10
A light beam 19 that is a mixture of a laser beam 16, which is a fundamental wave, and a second harmonic wave 18 is emitted from 0a. This light beam 19 is passed through, for example, a filter (not shown), and only the second harmonic wave 18 is extracted.

The above phase matching will be explained below. In this embodiment, d22, which is the largest diagonal term among the nonlinear optical constants of MNA, is used. When the optical wavelength conversion element 10 is produced as described below, the MNA single crystal 14 is oriented such that the optical axis Y faces the longitudinal direction of the groove 12b (the optical axes X, Y, and Z are crystal axes a, b, and (corresponding to the c-axis). Therefore, when making the laser beam 16 enter the optical waveguide 13, its linear polarization direction indicated by the arrow P is
By matching the direction of the axis, the nonlinear optical constant d22 is utilized, and high wavelength conversion efficiency can be achieved. In this case, the second harmonic 18 is linearly polarized in the Y-axis direction. Further, the X and Z axes may be oriented in a direction other than that shown in FIG.

[0029] Laser beam 16 and second harmonic 1
In order to phase-match the grooves 12b, that is, the period Λ of the MNA single crystal 14, the period Λ of the MNA single crystal 14 is set to a value that satisfies the equation (3) above, where Δn is the amount of phase mismatch that occurs when a periodic structure is not applied. There is. In this way, MNA single crystal 14
By adopting a periodic structure in which the substrate 12 and the substrate 12 having a lower refractive index are repeated at a period Λ, the laser beam 16 and the second harmonic 18 are phase matched. If the above period Λ is a value that satisfies the formula (2) above, the waveguide-waveguide type in which phase matching is achieved between the fundamental wave of the waveguide mode and the wavelength-converted wave of the waveguide mode as well. It becomes an optical wavelength conversion element.

Next, a method for manufacturing the optical wavelength conversion element 10 will be explained with reference to FIG. First, as shown in FIG. 1 (1), on the surface 11a of the first glass substrate 11,
A portion 13 having a higher refractive index than other substrate portions, that is, an optical waveguide, is formed by ion exchange or the like. At the same time, as shown in FIG. 2(2), a plurality of grooves 12b are formed on the surface 12a of the second glass substrate 12 by photolithography, etching, or the like. Note that, as described above, these grooves 12b are formed to have a width of Λ/2 and to be lined up at a period of Λ.

Next, as shown in FIG. 3(3), the first glass substrate 11 and the second glass substrate 12 are connected to
a and the surface 12a are in close contact with each other, and the embedded optical waveguides 13 extend in a direction perpendicular to the plurality of grooves 12b. Note that these substrates 11 and 12 can be bonded together by, for example, optical contact.

Next, as shown in FIG. 4 (4), the MNA is kept in a melt state in a furnace or the like, and one end of the glass substrates 11 and 12 is immersed into the melt 14'. Then, due to capillarity, the MNA 14' in a molten state enters the plurality of grooves 12b. Note that the temperature of the melt is MNA
In order to prevent decomposition of , the temperature is slightly higher than its melting point (132°C). Thereafter, when the glass substrates 11 and 12 are rapidly cooled, the MNA that has entered the grooves 12b is solidified in a polycrystalline state.

Next, put the glass substrates 11 and 12 into a furnace,
Remelt the MNA. In this embodiment, a brass heating bath 22 in which an electric heating means 21 is embedded in a brass block 20 is used as the above-mentioned furnace, as shown in FIG. 3(5). An elongated hole 23 having a square cross-section is provided in the center of the brass heat bath 22. A current is supplied to the electric heating means 21 via a temperature control circuit 24, and the temperature inside the hole 23 is maintained at a desired temperature. Both glass substrates 11 and 12 are inserted into this hole 23.

The temperature of the brass heat bath 22 (more precisely, the temperature of the hole 23
The internal temperature) is maintained at approximately 141° C., which is slightly higher than the melting point of MNA. Note that if, for example, grease is injected into the holes 23 of the brass hot bath 22, heat conduction from the brass hot bath 22 to the glass substrates 11 and 12 will be improved, and the speed of substrate withdrawal, which will be described later, will be constant. It is preferable. The hole 23 is open on one end surface of the block 20 (the end surface on the near side in FIG. 3(5)), but the opposite side is closed. This closed portion is provided with a pore (not shown) that communicates with the hole 23, and a wire 26 is inserted through this pore. This wire 26 is fixed to a rack 27, and a pinion 29 rotated by a motor 28 with a reduction gear is meshed with the rack 27. Therefore, when the motor 28 is driven and the pinion 29 is rotated in the direction of arrow B, the wire 26 is moved in the direction of arrow C, and the hole 29 is rotated.
The inner substrates 11 and 12 are pushed out of the block 20. The temperature outside the brass hot bath 22 is set to be lower than the melting point of MNA (for example, about room temperature).

By placing the glass substrates 11 and 12 in the brass hot bath 22 as described above, the MNA in the groove 12b becomes molten again. From this state, the motor 28 is rotated at a low speed to move the wire 26 as described above. Thereby, the glass substrates 11 and 12 are gradually drawn out of the brass hot bath 22. This glass substrate 11,
The drawing speed of No. 12 is set, for example, to about several mm/hour. In this way, the MNA single crystal grows little by little at the interface between the liquid phase and the solid phase of MNA (which is naturally located outside the brass hot bath 22). Therefore, the glass substrate 12 pulled out from the brass hot bath 22
In the groove 12b, a solid MNA is formed in a single crystal state over a long distance (for example, several cm) and whose crystal orientation is uniformly aligned.

As explained above, an optical wavelength conversion element 10 having a periodic structure in which a single crystal 14 of MNA, which is an organic nonlinear optical material, and a glass substrate 12 having a lower refractive index than the single crystal 14 are repeated at a period Λ, is manufactured. can be created.

In the above embodiment, the MNA 14' in a molten state is introduced into the grooves 12b of the glass substrate 12, but the MNA solution is introduced into the grooves 12b, and then the solvent of the solution is Evaporate the MNA into groove 12.
b may be filled.

Although the embodiment using the organic nonlinear optical material MNA has been described above, the optical wavelength conversion element of the present invention can also be produced by the same method as above when using other organic nonlinear optical materials. can. Furthermore, the optical wavelength conversion element of the present invention is not limited to organic nonlinear optical materials.
It can also be formed using an inorganic nonlinear optical material.

[Brief explanation of drawings]

FIG. 1 is a partially cutaway perspective view showing an optical wavelength conversion element according to an embodiment of the present invention.

[Fig. 2] A schematic side view showing the optical wavelength conversion element of the above embodiment.

FIG. 3 is an explanatory diagram showing an example of a method for manufacturing an optical wavelength conversion element according to the present invention.

[Explanation of symbols]

10 Optical wavelength conversion element 11 First glass substrate 11a Surface of first glass substrate 12 Second glass substrate 12a Surface of second glass substrate 13 Embedded optical waveguide 14 MNA single crystal 14' MNA melt 20 Brass block 21 Electric heating means 22 Brass heating bath 24 Temperature control circuit 26 Wire 27 Rack 28 Motor 29 Pinion

Claims (2)

[Claims] 1. A first substrate having a buried optical waveguide formed on its surface, and a second substrate having a plurality of grooves formed at a predetermined pitch on its surface filled with a nonlinear optical material, respectively, An optical wavelength conversion element in which an optical waveguide is joined in contact with nonlinear optical materials in a plurality of grooves. 2. A buried optical waveguide is formed on the surface of a first substrate, a plurality of grooves are formed at a predetermined pitch on the surface of a second substrate, and the optical waveguide is connected to the plurality of substrates. After integrating the plurality of grooves so as to face each of the grooves, and filling the plurality of grooves with a crystalline organic nonlinear optical material having a higher refractive index than the substrate material, both substrates are bonded to the melting point of the organic nonlinear optical material. The optical material in a molten state is single-crystalized from the part drawn out of the furnace by gradually drawing it from the inside of the furnace kept at a higher temperature to the outside of the furnace kept at a temperature lower than the melting point. A method for manufacturing an optical wavelength conversion element.