JPH03225327A - Second harmonic generating element and production thereof - Google Patents

Abstract

PURPOSE:To obtain a second harmonic generating element ensuring a satisfactory wave front of Cerenkov radiation and having superior light convergency by filling an org. nonlinear optical material into a glass capillary tube having >=1,000 ratio of the outside diameter to the inside diameter. CONSTITUTION:A glass tube 3 is concentrically set in a glass tube 1, the resulting multi-tubed structure is fitted to a prescribed drawing device used to produce a capillary tube and a glass capillary tube having >=1,000 ratio of the outside diameter to the inside diameter is formed by heating and drawing the structure. An org. nonlinear optical material such as 2-methyl-4-nitroaniline is sucked into the hollow 6 of the capillary tube by capillarity and converted into a single crystal. Second harmonics SH whose wavelength is 1/2 of that of fundamental waves FW are radiated into the clad part 40 of the resulting element at a certain Cerenkov angle theta and second harmonics having a ring- shaped wave front 45 of radiation are taken out from the emergence end 40b.

Description

[Detailed description of the invention] [Industrial application field] The present invention is in the field of information processing that uses laser light.

Regarding second harmonic generation elements (hereinafter referred to as SHG elements) used in the measurement control field, etc., and their manufacturing methods, fiber-type SHG elements that can obtain particularly good Cerenkov radiation wavefronts and high output, and their manufacturing methods. Regarding.

[Summary of the invention]

The present invention uses a glass capillary tube with an extremely large ratio of outer diameter to inner diameter of 1000 or more as a cladding part surrounding a core part made of an organic nonlinear optical material.
The present invention aims to provide a fiber-type SHG element that has a good Cerenkov radiation wavefront and is suitable for uses such as light collection.

Furthermore, the present invention makes it possible to create the glass capillary tube constituting the cladding portion of the SHG element by so-called coaxial simultaneous stretching.

Furthermore, the present invention provides a tapered portion at one end of the core portion for increasing the fundamental wave incidence efficiency by heating the glass capillary while increasing the internal pressure in the hollow portion of the glass capillary to locally expand the glass capillary. High-output type SH
The purpose is to manufacture a G element.

[Conventional technology]

In the field of optoelectronics, which uses laser light to perform information processing, measurement control, etc., there is an increasing demand for shorter wavelengths (higher frequencies) and higher output light sources. Semiconductor lasers, which are small and whose price has fallen in recent years, are widely used as this light source. However, 700
When short-wavelength light of 0 Å or less is required, it is difficult to oscillate with conventional semiconductor lasers, so gas lasers have to be used, making it inevitable to increase the size of related equipment.

Therefore, SHG elements that can convert the wavelength of the fundamental wave from the light source to 172 nm using the phenomenon of second harmonic generation (SHG) are being researched. The SHG element is constructed using a nonlinear optical material, and generates a second harmonic with an angular frequency of 2ω from nonlinear polarization generated inside the material by a fundamental wave with an angular frequency of ω. By using such elements, we can visualize infrared lasers that are invisible to the naked eye and provide a new type of display device, or quadruple the recording density of optical information storage media by reducing the beam spot diameter. It becomes possible to do things like this.

The above-mentioned SHO element can be roughly divided into a bulk type using a bulk nonlinear optical crystal and a waveguide type having a waveguide. Considering that semiconductor lasers have been widely used as light sources in recent years, waveguides have been developed from the viewpoint of making devices smaller and lower in cost, and efficiently generating second harmonics from semiconductor lasers with relatively low power. Type is advantageous.

Furthermore, the waveguide type includes lithium niobate (LiNbO,
There are various types, such as a ridge type in which a ridge is formed on a substrate made of a nonlinear optical material such as ), and a fiber type in which a core made of a nonlinear optical material is arranged in a suitable rad material. Among these, the fiber type has advantages such as being suitable for miniaturization and having a highly symmetrical beam shape of the obtained second harmonic.

In addition to the conventionally known inorganic compounds such as potassium dihydrogen phosphate and the above-mentioned lithium niobate, the nonlinear optical materials mentioned above include inorganic compounds that have nonlinear optical effects that significantly exceed those of these inorganic compounds. Organic compounds that exhibit high-speed response have been discovered, and various molecular designs are being attempted by taking advantage of the diversity of organic molecular structures.

Therefore, a fiber-type SHG element having a core made of organic nonlinear optical material is suitable for its applications.

This is something that holds great promise for future development.

A typical configuration of such a fiber-type SHG element and peripheral optical system is shown in FIG. 7. This SHG element has an organic nonlinear optical material such as 2 A core portion (41) filled with methyl-4-nitroaniline (MNA) is arranged. Here, the refractive index of the cladding part (40) is selected to be lower than the refractive index of the core part (41). A semiconductor laser (42), a collimator lens (43), a condensing lens (44), etc. are placed outside this SHG element, and the fundamental wave FW emitted from the semiconductor laser (42) is transmitted through each of the lenses. The light enters the core portion (41) from the incident side end surface (40a). While the fundamental wave FW propagates inside the core part (41) while repeating total reflection, the second harmonic SH having half the wavelength of the fundamental wave FW enters the cladding part (40) with a constant Cerenkov angle θ. Only the radiated and mode-matched components are emitted into the air from the emission side end face (40b). At this time, if a filter or the like is provided after the output side end face (40b) to block the fundamental wave, a ring-shaped radiation wavefront (
45) can be selectively extracted.

By the way, in order to condense the second harmonic SH obtained from the SHG element as shown in FIG. 7 and form a fine beam spot, the coherence of the second harmonic SH must be good. Therefore, it is necessary to allow single mode propagation. The waveguide itself of the second harmonic SH is
It is also possible to use a mode that propagates within the cladding part (40) by total reflection using the refractive index between the cladding part (40) and air, but in this case, the second harmonic SH is transmitted to the core part (41 ), there are many practical problems, such as a decrease in propagation efficiency and the fact that light with a uniform emitted wavefront cannot be obtained, making it unsuitable for the purpose of condensing light.

Due to these circumstances, the dimensions of the fiber type SHG element are 2r for the outer diameter and 2.2r for the total length. When the Cerenkov radiation angle is θ, I! It is set to satisfy the relationship: -tan θ>r, and typically, when the Cherenkov radiation angle θ is 9 to 10'', the outer diameter is 2r-1 to 2 mm.

full length! =3 to 5 mm. Furthermore, in order to realize single mode propagation, it is necessary to narrowly define the angle of incidence of the fundamental wave FW on the core part (41), and therefore the inner diameter of the cladding part (40) [i.e. Diameter] is l
It is said to be about um. In other words, the ratio of the outer diameter to the inner diameter of the glass capillary tube constituting the cladding part (40) is 1.
More than 1,000 materials are required.

However, it is technically difficult to actually manufacture a glass capillary tube with such an extremely large ratio of inner diameter to outer diameter. Therefore, one way to solve this problem is to
After filling the hollow part of a glass capillary with an inner diameter of several μm and an outer diameter of about several tens of μm with an organic nonlinear optical material and crystallizing it, the glass capillary is inserted into the hollow part of a glass tube with a larger diameter, and both A structure has been considered in which the gap is filled with a molding resin having a melting point lower than the crystallization temperature of the organic nonlinear optical material, so that the outer diameter of the material is apparently increased.

[Invention tries to solve! II! However, the SHG element using molded resin as described above has several drawbacks. First, since it is difficult to form a smooth interface between the glass tube and the molded resin, the Cerenkov radiation wavefront is disturbed and the light focusing performance is deteriorated. Second, since the mold resin has absorption in the wavelength band of the fundamental wave, when the power of the incident light is large, the mold resin burns out or scatters, and there is a large possibility of contaminating the end face on the incident side. With the above configuration, the SHG has excellent practicality.
The reality is that we cannot provide the elements.

The above is a study on the ratio of the inner and outer diameters of the glass capillary when single mode propagation is taken into account, but improvement of the incidence efficiency is also important.
This is an important issue for HG devices. Conventional fiber type 5)
In the IG element, since the inner diameter of the glass capillary is constant over the entire length, the incidence efficiency when a fundamental wave is incident using a condensing lens with a large numerical aperture is extremely low, and therefore high output cannot be obtained.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a second harmonic generation element that can obtain a good Cerenkov radiation wavefront and high output, and a method for manufacturing the same.

[Problem to be solved by the invention]

As a result of repeated studies to achieve the above-mentioned object, the present inventors took a hint from the rod-in glass method used in the field of optical fiber manufacturing, and found that by coaxially drawing glass tubes of different diameters simultaneously. , the ratio of the outer diameter to the inner diameter is 1
We have discovered that it is possible to manufacture glass capillaries as large as 000 or more with high precision, and that by filling the hollow part of such glass capillaries with an organic nonlinear optical material, it is possible to provide a fiber-type SHG element with a good Cerenkov radiation wavefront and excellent light focusing ability. Ta.

Furthermore, the present inventors have found that the incidence efficiency of the fundamental wave can be improved by providing an appropriate taper in the core part so that the inner diameter of the cladding part, that is, the diameter of the core part expands toward the incidence side end face. It was discovered that such a glass capillary tube can be manufactured by local heating expansion using the difference in internal and external pressure.

The present invention was completed based on the above-mentioned findings.

That is, the SHG element according to the first aspect of the present invention is
It is characterized in that an organic nonlinear optical material is filled in a glass capillary tube having an outer diameter to inner diameter ratio of 1000 or more.

Furthermore, the method for manufacturing an SHG element according to the second aspect of the present invention includes heating and stretching a multi-tube structure formed by coaxially arranging a plurality of glass tubes having different diameters, and at the same time integrating them by heat fusion. This method is characterized by comprising a step of forming a glass capillary tube having an outer diameter to inner diameter ratio of 1000 or more, and a step of filling the hollow part of the glass capillary tube with an organic nonlinear optical material.

Furthermore, the method for manufacturing an SHG element according to the third aspect of the present invention includes heating and stretching a multi-tube structure formed by coaxially arranging a plurality of glass tubes having different diameters, and at the same time integrating them by heat fusion. a step of forming a glass capillary having an outer diameter to inner diameter ratio of 1000 or more; a step of sealing a predetermined amount of liquid into the hollow part of the glass capillary and increasing the internal pressure by heating vaporization; The method is characterized by comprising a step of heating the heated portion to a temperature higher than its softening point to expand the heated portion, and a step of removing the liquid from the hollow portion of the glass capillary and filling it with an organic nonlinear optical material. be.

The cladding portion of the SHC element of the present invention is composed of a glass capillary tube. In general, the raw material glass for the above-mentioned glass capillary has a lower refractive index than the organic nonlinear optical material used for the core, which will be described later, is transparent to the second harmonic, and is in a molten state in the hollow part during the manufacturing process. Since it is necessary to fill the glass with an organic nonlinear optical material to be described later, a glass having a melting point higher than that of the organic nonlinear optical material, sufficient strength, and excellent moldability is preferred. However, in the present invention, since the glass capillary tube is manufactured by simultaneous coaxial stretching, an important property is that it is less likely to generate striae. For this purpose, lead glass having a refractive index of 1.40 to 1.98 is particularly suitable.

As the organic nonlinear optical material filled in the hollow part of the glass capillary to form the core part, known compounds having high SHG activity can be used.

For example, 2-methyl-4-nitroaniline (MNA
), 2. N-dimethyl-4-nitroaniline (MNMA
), 1-dimethylamino-2-acetamido-4-nitrobenzene (DAN), methyl-(2,4-dinitrophenyl)aminopropionate (MAP), l(α-methylbenzylamino)-5-di Tropyridine [MBA-
NP]2-(2-hydroxymethylpyrrolidino)-5nitropyridine (PNP), 3-methyl-4-nitropyridine-N-oxide (POM), and the like.

In addition, in order to realize SHG, the second-order nonlinear susceptibility χ
First of all, it is necessary that I) be large. From this point of view, all of the above-mentioned compounds have in common a structure in which an electron-withdrawing group and an electron-donating group are arranged with an aromatic ring in between.

However, there are some compounds, such as p-nitroaniline and 4'-dimethylamino-4-nitrostilbene, which do not express SHG because they have inversion symmetry even if they have the above-mentioned structure. For such compounds,
It can be applied to the present invention by means such as introducing a substituent with large steric hindrance, introducing an optically active group, introducing a hydrogen bond, and reducing a permanent dipole.

In order to create the above-mentioned glass capillary tube, a multi-tube structure consisting of a plurality of glass tubes having different diameters arranged coaxially is heated and stretched, and at the same time, integrated by heat fusion. The temperature during heating and stretching is selected to be higher than the yield point and lower than the softening point. Glass in the temperature range mentioned above, where the glass tubes arranged coaxially do not fuse to each other at temperatures lower than the yielding point, and the hollow portion collapses due to the glass material flowing under its own weight at temperatures higher than the softening point. The viscosity of the material is approximately 10'~IQ
I l boys.

By the way, a technique for manufacturing a glass capillary tube by coaxial simultaneous stretching can also be found in, for example, Japanese Patent Laid-Open No. 185838/1983. However, in the above publication, the refractive index is 1.5.
This disclosure discloses a technique for manufacturing a glass ferrule used for connecting optical fibers using quartz-based glass of approximately 100%, and is different in purpose and effect from the present invention.

In other words, coaxial simultaneous stretching of silica glass tends to cause striae due to stretching, and the ratio of the outer diameter to the inner diameter of the manufactured glass capillary is as small as about 8, so it is difficult to achieve a highly uniform refractive index distribution. SH that requires high performance and large inner/outer diameter ratio
This is because it is completely unsuitable for use as a cladding material for G elements.

In order to fill the hollow part of the glass capillary with an organic nonlinear optical material as described above, the organic nonlinear optical material is heated above its melting point to form a melt, and this is injected into the hollow part of the glass capillary. Alternatively, the tip of the glass capillary can be immersed into the melt and sucked up by capillary action. In the present invention, the latter method can be easily applied because the inner diameter of the glass capillary to be manufactured is extremely small. After filling the organic nonlinear optical material, it may be single-crystalized by a conventional method using a Bridgman furnace or the like. In this way, the core portion composed of a single crystal of an organic nonlinear optical material is formed under the above-mentioned conditions (j2・
tan θ>r), it does not necessarily have to be placed exactly at the center of the cladding part.

Finally, by cutting the glass capillary filled with the single crystal of the organic nonlinear optical material into a length that satisfies the above-mentioned condition (1-tan θ>r), a plurality of 5f (G elements) can be efficiently manufactured.

In the present invention, furthermore, in order to increase the incidence efficiency of the fundamental wave,
Consider providing an appropriate taper portion in the core portion so that the inner diameter of the cladding portion, ie, the diameter of the core portion, increases toward the incident end face. In order to form such a tapered portion, the present inventors sealed a predetermined amount of liquid into the hollow part of a glass capillary, increased the internal pressure by heating, and then locally heated the glass capillary to a temperature higher than its softening point. We proposed a method in which the heating section is expanded by heating. The internal pressure at this time is practically selected to be about 50 to 200 ate. Local heating can be performed by moving a ring-shaped heater or the like arranged coaxially around the glass capillary tube.

According to the above method, by optimally controlling the internal pressure, heating temperature, heating time, etc., expansion parts having various shapes can be formed with extremely high precision. Here, the length of the taper part is 1710 of the final total length l of the SHG element.
It is desirable that the opening diameter of the taper part on the entrance side end face is 1.5 to 1.5 of the inner diameter of the glass capillary.
It is desirable to make it about 4 times. If the aperture diameter is too small, the fundamental wave incidence efficiency will not be improved, and if it is too large, fundamental waves with a wide range of incident angles will be accepted, resulting in multimode propagation.

To actually manufacture such an SHG element, a large number of expansion parts are formed on a long glass capillary tube, the liquid used to increase the internal pressure is removed and dried, and then the above-mentioned method is performed. Mass production becomes possible by filling the organic nonlinear optical material to form a single crystal, and cutting the glass capillary to a predetermined length at a portion where a desired taper shape can be obtained.

Incidentally, an example in which a taper is provided at one end of the hollow portion of a glass capillary tube is also disclosed in the above-mentioned Japanese Patent Laid-Open No. 185838/1983. However, the taper processing in this case is performed by etching after cutting the glass capillary tube to a predetermined length, so both the processing accuracy and the surface quality of the taper part are insufficient for application to the manufacture of SHG elements. In addition, productivity is also poor.

It should be noted that the end face of the SHG element of the present invention is free from adhesion of dust, etc.
Alternatively, in order to prevent performance deterioration due to scratches and deterioration of the organic nonlinear optical material, a protective layer made of resin or the like may be provided as necessary. It is very effective in some cases.

[Effect]

The SHG element of the present invention has a ratio of the outer diameter to the inner diameter of 100.
The core part is formed by using zero or more glass capillaries as a cladding part, and filling the hollow part of the cladding part with an organic nonlinear optical material. The second harmonic radiated from the core portion of such an SHG element can propagate only inside the glass material constituting the cladding portion toward the output side end face, and is not affected by the interface between different materials. . Therefore, the obtained Cerenkov radiation wavefront is good and the light focusing property is excellent. If the outer diameter is specified small, the inner diameter can be correspondingly reduced to 1 μm, and single mode propagation can be realized.

The glass capillary tube that becomes the cladding part of such an SHG element is
Coaxial simultaneous stretching allows production with extremely high precision. In other words, by heat-stretching a multi-tube structure made up of coaxially arranged glass tubes with different diameters and simultaneously integrating them by heat fusion, it is possible to This is nothing more than compensating for the wall thickness of the glass tube with a larger diameter surrounding it. therefore,
The present invention also makes it possible to manufacture a glass capillary tube having a large inner/outer diameter ratio that would be completely impossible by heating and stretching a single glass tube.

Furthermore, according to the method of the present invention in which a part of the taper is provided at one end of the core portion to increase the incidence efficiency of the fundamental wave, local heating is performed from the outside while the internal pressure of the glass capillary is uniformly rising. Therefore, the expanded portion formed is thick at the portion closest to the heating source and becomes gradually thinner as it moves away from the heating source. Moreover, the formation process is extremely controllable. The inner surface of this expansion part is
Since it is not mechanically damaged at the time of formation, it is extremely smooth, and even if it is made into a tapered part, it will not adversely affect the propagation of the incident fundamental wave.

Further, since the formation of this taper portion is performed before cutting the elongated glass capillary tube to match the entire length of the SHG element, productivity is also extremely high.

〔Example〕

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

Example 1 In this example, S
This is an example of an HG element.

The configuration of the SHG element is as shown in FIG. 7 described above, and the dimensions are outer diameter 2r=1 mm, inner diameter d=1 μm, and total length 1=3 mm.

Hereinafter, a method for manufacturing such an SHG element will be explained.

First, FIG. 1 schematically shows the configuration of a drawing device used to manufacture a glass capillary tube that will become a cladding part.This drawing device has a material feeding mechanism for first guiding a glass tube (1) into the device. (10), a softening furnace (11) for heating the glass tube (1) above its softening point, an air cooling fan (17) for cooling the glass tube (2), which has been softened by heating and falls under its own weight, to an appropriate temperature. ), a stretching mechanism (12) that stretches the glass tube (2) while defining its outer diameter; Always hold the glass tube (1)
coaxial holders (13), (15), which make it possible to maintain the coaxial holders (13), (15) at the center of the softening furnace (11), and a stretched glass tube provided between the two coaxial holders (13), (15) (3) Measuring device (14
), a cutter (16) for cutting the elongated glass tube (3) to a predetermined length, etc. are arranged along the feeding direction of the glass tube (direction of arrow A in the figure). . The above material feeding mechanism (10) and coaxial holder (13)
, (15) is composed of a hair ring mechanism etc. that can be supported at three points. The measuring device (14) is composed of, for example, a digital linear gauge, and a control signal generated based on the measurement result of the outer diameter controls the rotation speed of the motor of the stretching mechanism (12).

Next, a glass capillary tube was created using the above-mentioned drawing device.

First, lead-based glass (refractive index 1.90, softening point 390°C
) with an outer diameter of 10 mm and an inner diameter of 0.6 mm (
1) into the material feeding mechanism (10) of the stretching device,
The temperature of the softening furnace (11) was set to 420°C, and the glass tube (1
) was softened, the falling glass tube (2) was received by a stretching mechanism (12) to define the outer diameter, and a glass tube (3) with an outer diameter of 0.5 mm and an inner diameter of 30 μm was manufactured. This glass tube (
The outer diameter of glass (3) is smaller than the inner diameter of the original glass (1).

Next, the glass tube (3) is inserted into the hollow part of the glass tube (1) to form a multi-tube structure (4), which is held using a holding mechanism (18) as shown in FIG. It was fixed. This holding mechanism (18) has a groove (19) that contacts and holds the outer edge of the glass tube (1), and a center hole (20) that contacts and holds the outer circumference of the glass tube (3). The glass tube (1) and the glass tube (3) are held coaxially.

The end (3a) of the glass tube (3) is melt-sealed. An exhaust hole (21) connectable to a pressure reducing device (not shown) such as a vacuum pump is provided at one end of the holding mechanism (18). The exhaust hole (21) is connected to the holding mechanism (
18) communicates with the cavity (22) formed when holding the multi-tube structure (4). Therefore, by reducing the pressure in the cavity (22) through the exhaust hole (21), the gap (23) between the glass tubes (1) and (3) is reduced.
) while exhausting the air present in the glass tube (1),
(3) It becomes possible to fuse them together well.

The multi-tube structure (4) held as described above is set again in the aforementioned stretching device (not shown in FIG. 2), and the cavity (22) and the gap ( 23
) was stretched under reduced pressure. Here, softening furnace (11
) is 490°C, the hollow part (6) of the glass tube (1) will not be crushed, and both glass tubes (1)
(3) The two were integrated by heat fusion without leaving any air bubbles between them, and a glass capillary tube (5) having an outer diameter of 1 mm and an inner diameter of 1 μm was manufactured. The ratio of the outer diameter to the inner diameter of this glass capillary (5) is 1000. Further, in the glass capillary tube (5), the glass tube (1) maintained its perfectly circular state, and no defects such as striae were formed.

When the above thermal fusion process is viewed along a cross section perpendicular to the length direction, it becomes as shown in FIGS. 3(A) to 3(C). FIG. 3(A) is a cross section of the multi-tube structure (4) before heat fusion as seen along line aa in FIG. 2, and FIG. 3(B) is b-
Figure 3 (C) shows the cross section of the multi-tube structure (4) during thermal fusion as seen along line b, and the cross section of the glass capillary tube (5) after stretching as seen along line c-c. However, the scale of FIG. 3(C) is set larger than that of FIG. 3(A) and FIG. 3(B). It is clear that as the glass tubes (1) and (3) are fused together, the gap (23) disappears and the diameter of the hollow part (6) becomes smaller.

In addition, in the process of heat fusion described above, glass capillary tubes (5
) In order to further improve the controllability of the inner diameter of the glass tube (
The end portion (3a) of 3) may be connected to an appropriate pressurizing means without being melt-sealed to prevent the hollow portion (6) from collapsing.

The hollow part (6) of the glass capillary tube (5) produced as described above was filled with an organic nonlinear optical material according to a conventional method, and single crystallization was performed. That is, the lower end of the glass capillary tube (5) was immersed in a container filled with molten 2-methyl-4-nitroaniline (MNA), and the hollow portion (6) was filled by capillary action. At this point, the MNA filled in the hollow part (6) has been cooled and is in a polycrystalline state. MNA was single crystallized by moving this glass capillary tube (5) in a Bringeman furnace.

Finally, the glass capillary tube (5) was cut into a length of 3 mm to complete the SHG device as shown in FIG.

When a YAG laser beam with a wavelength of 11064 nm was input from the input end face of the SHG element, a second harmonic with a wavelength of 532 nm (green) was obtained from the output end face in a clean ring-shaped radiation wavefront.

Example 2 This example is an example of an SHG element in which a part of the taper is provided on the end face on the incident side of the fundamental wave.

FIG. 4 shows an example of the configuration of the SHG element of this embodiment.

This SHG element is constructed such that the inner diameter of the glass capillary constituting the cladding section (30), that is, the diameter of the core section (31) increases toward the incident end surface (30a).
31) is provided with an appropriate taper portion (32) to increase the incidence efficiency of the fundamental wave.

The dimensions of each part are outer diameter 2r = 1mm, inner diameter d1 - 1μm, total length f, = 3mm, length of the tapered part (32) j22 = 0
．． 3 mm, and the opening diameter d2 of the tapered portion (32) on the incident side end surface (30a) is 4 μm.

Hereinafter, a method for manufacturing this SHG element will be explained with reference to FIG.

First, the steps up to manufacturing the glass capillary (5) are as described above in Example 1.

The hollow part (6) of the glass capillary tube (5) was filled with ethanol by sucking it up to the middle part by capillary action, and both ends (5a) of the glass capillary tube (5) were melt-sealed.

Next, the glass capillary tube (5) is set in the cylindrical heater (33) with the part containing ethanol facing downward, and heated to 240°C to reduce the internal pressure of the hollow part (6) to 63°C.
It was called ATM. In this state, the portion of the glass capillary (5) exposed to the outside of the cylindrical heater (33) is locally heated using a ring-shaped heater (34) disposed coaxially with the glass capillary (5). Heated. A ceramic heater is used as the ring-shaped heater (34), and 5
The temperature was raised to 400°C in seconds.

Also, by moving this ring-shaped heater (34) up and down (in the direction of arrow B in the figure), the glass capillary (5
) were sequentially and locally heated.

As a result, the glass capillary (5) as shown in FIG.
A state was reached in which a plurality of expanded portions (7) were locally formed. The inner wall portion (7a) of the expansion portion (7) constitutes a tapered portion (32) of the SHG element.

This tapered portion (32) is required to be highly smooth because it will ultimately become a reflecting surface for the fundamental wave, but according to the method of the present invention, the expanded portion (7) may be damaged by physical damage. Since it is formed without undergoing any process, it is extremely advantageous over tapering by etching or the like.

Next, ethanol was removed from the hollow part (6) of the glass capillary (5) and dried, filled with MNA to form a single crystal in the same manner as in Example 1, and then cut into a length of 3 mm. The SHG device was completed.

Here, in this example, the incident side end face of the SHG element (
Since it is necessary to form a tapered portion (32) in 30a), the cutting to form the entrance side end surface (30a) must be performed at an appropriate portion of the expansion portion (7).
This cutting can be performed, for example, along line dd in FIG. 6, but may be changed as appropriate depending on the desired opening diameter, length of the tapered portion, etc.

In such an SHG element, the incidence efficiency of the fundamental wave increased, and the radiation wavefront (35) of the obtained second harmonic SH was also good.

In addition, in this example, the hollow part (6) of the glass capillary (5)
Ethanol was used as a liquid to increase the internal pressure of the
The internal pressure can also be about 200 atmospheres. These conditions may be appropriately set depending on the desired shape and dimensions of the taper.

Furthermore, as a local heating method for forming the expanded portion (7), rapid heating using a carbon dioxide laser (wavelength: 10 μm) can be used instead of the ring-shaped heater (34) as described above, to further improve controllability. It can also be improved.

Further, in each of the above embodiments, the number of glass tubes constituting the multi-tube structure (4) is two, but it goes without saying that the present invention can also be applied to cases where three or more glass tubes are used.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, it is possible to manufacture glass capillary tubes with an extremely large inner/outer diameter ratio, which has been difficult to manufacture with high precision in the past, with high reliability and productivity. A fiber-type SHG element having such a glass capillary as a cladding part has an extremely good Cerenkov radiation wavefront and is also excellent in light convergence after emission. Therefore, it can also meet the need for shorter wavelength light sources for high-density recording and reproduction.

Furthermore, according to the present invention, it is possible to easily perform taper processing on the incident side end face of the core portion, and a high output SHG element with excellent fundamental wave incident efficiency can be provided with high reliability and productivity. become.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram schematically showing an example of the configuration of a drawing device used for manufacturing a glass capillary tube. FIG. 2 is a schematic cross-sectional view showing the process of coaxial simultaneous stretching, and FIGS. 3(A) to 3(C) are schematic cross-sectional views showing the state of the multi-tube structure at each stage shown in FIG. It is a diagram. Figure 4 shows a fiber type SHG with a part of the taper on the input side end face of the core part.
FIG. 2 is a schematic cross-sectional view showing an example of the configuration of an element. FIG. 5 is a schematic view schematically showing a method of locally forming an expanded portion in a glass capillary, and FIG. 6 is an enlarged sectional view of a main part of a glass capillary in which an expanded portion is locally formed. FIG. 7 is a schematic diagram schematically showing the configuration of a general fiber type SHG element and a peripheral optical system. 1.3 30, 40 31, 41 2 Glass tube multi-tube structure Glass capillary hollow part Expansion part Clad part Core part Taper part

Claims (3)

[Claims] (1) A second harmonic generation element comprising an organic nonlinear optical material filled in a glass capillary tube having an outer diameter to inner diameter ratio of 1000 or more. (2) A multi-tube structure consisting of multiple glass tubes with different diameters arranged coaxially is heated and stretched, and at the same time is integrated by heat fusion to form a glass capillary tube with a ratio of the outer diameter to the inner diameter of 1000 or more. A method for manufacturing a second harmonic generating element, comprising the steps of: filling the hollow portion of the glass capillary with an organic nonlinear optical material. (3) A multi-tube structure consisting of multiple glass tubes with different diameters coaxially arranged is heated and stretched, and at the same time integrated by heat fusion to form a glass capillary tube with an outer diameter to inner diameter ratio of 1000 or more. a step of sealing a predetermined amount of liquid in the hollow part of the glass capillary and increasing the internal pressure by heating and vaporizing it; and a step of locally heating the glass capillary to a temperature higher than its softening point to expand the heated part. and a step of removing the liquid from the hollow part of the glass capillary to fill it with an organic nonlinear optical material.