JP2000298270A - Wavelength selection filter and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a wavelength selective filter, which can select wavelengths with high accuracy by preparing at least a liquid crystal device, consisting of a pair of substrates disposed at a const. distance, a liquid crystal between the substrates, and a bubble left in the liquid crystal not to block off the optical path. SOLUTION: Quartz glass substrates 12, having high light-transmitting property, are disposed parallel to each other at a constant distance and laminated with an epoxy-based sealing agent 9. An antireflection film 11 is formed on one principal plane of the quartz glass substrate 12, and an ITO transparent electrode 13 and a dielectric multilayered film 14 are vapor deposited on the other principal plane. Furthermore, a liquid crystal alignment film 15 is formed on the inner face of the quartz glass substrate 12 facing each other. A liquid crystal 10 is injected into the cell surrounded by the liquid crystal alignment films 15 and the sealing agent 9, and the liquid crystal injection port is sealed with a sealing agent 16 such as a UV-curing adhesive. Moreover, a gas reservoir (bubbles) 17 is formed near the liquid crystal injection port. The amt. of gas sucked differs, depending on the kinds of the liquid crystal 10 and on the use environment of the wavelength selective filter. With such a constitution, the temp. control mechanism can be simplified, and a wavelength selective filter which is easily minimized is realized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a wavelength selective filter for selectively extracting an optical signal of an arbitrary wavelength from a wavelength multiplexed optical signal.

[0002]

2. Description of the Related Art In optical multiplex communication, a wavelength-multiplexed optical signal is transmitted, and an optical signal of an arbitrary wavelength is selectively extracted from the transmitted signal and received. Usually, a wavelength selection filter is used for selecting an optical signal. As a conventional wavelength selection filter, one described in, for example, JP-A-4-140714 is known. FIG. 11 is a diagram showing one configuration example of a conventional wavelength selection filter. As shown in FIG. 11, in the conventional wavelength selection filter, light incident from the optical fiber 3 via the collimating lens 4 is branched into two optical paths (P wave and S wave) by the birefringent crystal plate (calcite) 6. And both enter the liquid crystal element 1. S wave light is 1/2
After being rotated by 90 ° through the wave plate 7 and incident as a P-wave,
The P-wave light is directly incident on the liquid crystal element 1. Two P-wave lights incident on the liquid crystal element 1 are selectively output only at a desired wavelength, one P-wave light is directly incident on the birefringent crystal plate 6, and the other P-wave light is 1 / The light is rotated by 90 ° through the two-wavelength plate 7 and is incident on the birefringent crystal plate 6 as an S wave. The two lights incident on the birefringent crystal plate 6 merge again, and the merged light is emitted to the optical fiber 3 via the collimator lens 4. In the wavelength selection filter of FIG. 11, the polarization independence is achieved by using the birefringent crystal plate 6 and the half-wave plate 7 to keep the polarization state of light incident on the liquid crystal element 1 constant. .

FIG. 12 is a sectional view of a liquid crystal device having a Fabry-Perot ethane structure as an example of the liquid crystal device 1 of FIG. 11, and FIG. 13 is a sectional view taken along line BB of FIG. 178219, JP-A-4-220
618). The liquid crystal device shown in FIGS. 12 and 13 has a configuration in which quartz glass substrates 12 having high light transmittance are arranged in parallel at regular intervals and bonded with an epoxy sealant 9. On one main surface of the quartz glass substrate 12, an antireflection film 11 is formed, and on the other main surface, a transparent electrode 13 made of ITO and a reflection film 14 using a dielectric multilayer film are formed. Further, a liquid crystal alignment film 15 is formed on the opposite surfaces of the quartz glass substrate 12. Liquid crystal 1
Numeral 0 is injected into a space (hereinafter, referred to as a cell) surrounded by the liquid crystal alignment film 15 and the sealing agent 9, and the liquid crystal injection port is sealed with a sealing agent 16 such as a UV adhesive.

The liquid crystal device shown in FIGS. 12 and 13 operates as a wavelength selection filter by changing the refractive index of the liquid crystal 10 by applying a voltage between the transparent electrodes 13. That is,
The optical path length nd in the liquid crystal 10 (n: refractive index of the liquid crystal 10, d:
The relationship between the width of the liquid crystal 10) and the resonance wavelength λ is given by the following equation.

Λ = 2nd / m (m: positive order) (1) As is apparent from the above equation (1), the resonance wavelength λ of the liquid crystal 10 is proportional to the refractive index n of the liquid crystal 10. Therefore, FIG.
In the liquid crystal device shown in FIGS. 2 and 13, if a voltage is applied between the transparent electrodes 13 to change the refractive index n of the liquid crystal 10, the resonance wavelength λ also changes with the change.

[0006]

However, FIG.
In addition, in the liquid crystal element shown in FIG. 13, since the refractive index and volume of the liquid crystal 10 have a large temperature dependency, the resonance wavelength λ changes due to temperature fluctuation, and the distribution in the resonance wavelength plane decreases.
As a result, there is a problem that PDL (polarization dependence) becomes large. It is apparent from the above equation (1) that the resonance wavelength λ depends on the refractive index n. The reason why the volume fluctuation of the liquid crystal 10 changes the resonance wavelength λ is as shown in FIG.
The expansion and contraction of 0 raises and lowers the pressure in the sealed cell, and the distance between the quartz glass substrates 12, that is, the width d of the liquid crystal 10 differs during cooling (a), normal temperature (b), and heating (c). That's why. Further, the expansion and contraction of the liquid crystal 10 is not uniform as a whole, and the volume fluctuation near the center of the cell is particularly remarkable, so that the distribution in the resonance wavelength plane also changes.

For this reason, in the conventional wavelength selection filter shown in FIG. 11, a radiating fin 22 is provided on the liquid crystal element 1 and the temperature is controlled using the temperature control circuit 18 and the Peltier element 21 to thereby control the liquid crystal element 1. The temperature is stabilized.
Further, a heat insulating material 23 is provided on the inner wall of the housing 2 to suppress a temperature change of the liquid crystal element 1. However, the temperature control mechanisms such as the radiation fins 22, the temperature control circuit 18, the Peltier device 21, and the heat insulating material 23 necessary for controlling the temperature of the liquid crystal element 1 are very problematic in reducing the size of the wavelength selection filter. . In addition, the temperature controllability of the liquid crystal element 1 is not actually high precision. Furthermore, a method of keeping the pressure of the liquid crystal 10 constant by not sealing the injection port of the liquid crystal 10 can be considered. However, the liquid crystal 10 leaks or the liquid crystal 10 absorbs moisture, which causes deterioration of characteristics of the liquid crystal element 1. There is a possibility that it cannot be adopted in reality.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems and to provide a wavelength selection filter capable of minimizing a change in a resonance wavelength of a liquid crystal element due to a temperature change and realizing a highly accurate wavelength selection.

Another object of the present invention is to provide a wavelength selective filter in which the temperature control mechanism is simplified and the size of the filter is easily reduced.

[0010]

Means for Solving the Problems In order to solve the above problems, a first feature of the present invention is to block a pair of substrates arranged at regular intervals, a liquid crystal arranged between the substrates, and an optical path. The wavelength selection filter includes at least a liquid crystal element including a bubble provided in the liquid crystal so as not to have a liquid crystal element.

According to the first aspect of the present invention, the expansion and contraction of the bubbles absorbs the pressure fluctuation inside the cell due to the temperature change of the liquid crystal, and can suppress the deformation of the substrate. Therefore, the distance between the substrates does not greatly change due to the temperature change, and the change in the resonance wavelength with respect to the temperature change can be reduced. Further, a large-scale temperature control mechanism is not required, and the size of the apparatus can be easily reduced.

[0012] A second feature of the present invention is a step of bonding a pair of substrates via a sealant, and an opening formed in the sealant in a space surrounded by the pair of substrates and the sealant. A step of injecting liquid crystal from, a step of heating the liquid crystal and overflowing the opening, a step of removing the overflowing liquid crystal, a step of cooling the liquid crystal, and forming a bubble in the space, A method for manufacturing a wavelength selective filter, comprising at least a liquid crystal element manufacturing step including a step of applying a sealing agent to the opening and a step of cooling the liquid crystal and drawing the sealing agent into the opening. .

According to the second feature of the present invention, it is possible to easily manufacture a wavelength selective filter which can obtain the above-mentioned effects.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. In the following drawings, the same parts are denoted by the same reference numerals. FIG. 1 is a diagram showing a configuration of a wavelength selection filter according to an embodiment of the present invention. As shown in FIG. 1, in the wavelength selection filter according to the embodiment of the present invention, light incident from an optical fiber 3 via a collimator lens 4 passes through a birefringent crystal plate (calcite) 6 through two optical paths (P-waves). And S waves), and both are incident on the liquid crystal element 1. The S-wave light is rotated as 90 degrees through the half-wave plate 7 and is incident as a P-wave.
Is incident on. Two P-wave lights incident on the liquid crystal element 1 are selectively output only at a desired wavelength, one P-wave light is directly incident on the birefringent crystal plate 6, and the other P-wave light is 1 / The light is rotated by 90 ° through the two-wavelength plate 7 and is incident on the birefringent crystal plate 6 as an S-wave. The two lights incident on the birefringent crystal plate 6 merge again, and the merged light is emitted to the optical fiber 3 via the collimator lens 4. FIG.
In the wavelength selection filter described above, the polarization state of light incident on the liquid crystal element 1 is made constant by using the birefringent crystal plate 6 and the half-wave plate 7, thereby achieving polarization independence.

FIG. 2 is a cross-sectional view of the liquid crystal device 1 having the Fabry-Perot ethane structure of FIG. 1, and FIG. 3 is a cross-sectional view taken along line AA of FIG. The liquid crystal device shown in FIGS. 2 and 3 has a configuration in which quartz glass substrates 12 having high light transmittance are arranged in parallel at a predetermined interval, and are bonded with an epoxy-based sealant 9. An anti-reflection film 11 is provided on one main surface of a quartz glass substrate 12, and a transparent electrode 13 made of ITO and a reflection film 14 using a dielectric multilayer film are provided on the other main surface.
Has been deposited. Further, a liquid crystal alignment film 15 is deposited on the opposite surfaces of the quartz glass substrate 12. The liquid crystal 10 is injected into a cell surrounded by a liquid crystal alignment film 15 and a sealant 9, and the liquid crystal injection port is provided with a sealing agent 16 such as a UV adhesive.
It is sealed with.

In the embodiment of the present invention, as shown in FIGS. 2 and 3, a gas reservoir (hereinafter, simply referred to as a bubble) 17 is provided near the liquid crystal inlet. The amount of gas to be drawn in varies depending on the type of the liquid crystal 10 and the use environment (use temperature range) of the wavelength selection filter. For example, considering that the volume change of the liquid crystal with respect to temperature is about + 0.08% / ° C. and that the liquid crystal 10 expands by about 2.4% by a temperature change of 30 ° C., the amount of gas to be drawn in is 20 ° C. and 1 atmosphere. The volume of the liquid crystal 10 is preferably 0.5% to 20%, and practically 2% to 12%. This is because, if the amount of gas is too small, the volume expansion of the liquid crystal 10 due to the temperature rise cannot be absorbed by the shrinkage of the bubbles 17. Conversely, if the amount of gas is too large, bubbles 17
This will block the optical path in the liquid crystal 10. 2 and 3, the bubble 17 is located near the liquid crystal injection port, but may be located at any position other than the center of the liquid crystal 10 through which light passes.

The bubbles 17 expand and contract due to temperature fluctuations, thereby preventing fluctuations in the distance between the quartz glass substrates 12. As shown in FIG. 4, during cooling (a), the pressure in the liquid crystal 10 decreases, but the bubbles 17 expand, thereby causing the liquid crystal 1 to expand.
Suppress the fluctuation of the width of 0. At the time of heating (c), the liquid crystal 1
Although the pressure in 0 increases, the fluctuation of the width of the liquid crystal 10 is similarly suppressed by compressing the bubble 17. That is, the bubbles 17 absorb the pressure fluctuation inside the cell due to the temperature change of the liquid crystal 10 and play the role of suppressing the deformation of the quartz glass substrate 12. Therefore, in the embodiment of the present invention, the distance between the quartz glass substrates 12 does not greatly change even when the use temperature changes, and the change in the resonance wavelength with respect to the temperature change can be reduced.

The solubility of the gas in the bubbles 17 is preferably small, but is not particularly limited. It is not necessary to consider the temperature dependence of solubility. Indeed, there is a problem that the solubility of the gas in the gas bubbles 17 changes with the temperature change, and the gas in the gas bubbles 17 may be dissolved in the liquid crystal 10 due to a rise in the pressure in the cell. In that case, the amount of gas sealed in the cell decreases, and when the temperature decreases again, the volume of the gas becomes smaller than before the temperature decrease. This is because the effect of the present invention cannot be sufficiently exhibited.

However, for example, in the case of the liquid crystal element of the present invention having a bubble rate of 10% at 25 ° C., it has been confirmed by the present inventors that no change was observed in the amount of gas even when the temperature was increased to 110 ° C. I have. Further, if the gas is dissolved in the liquid crystal 10 and the volume is changed, the parallelism of the quartz glass substrate should be reduced and the half width should be changed. However, such a phenomenon is not seen.

Therefore, in the case of the liquid crystal device of the present invention, it is considered that gas is hardly dissolved in the liquid crystal 10.

The method for producing the bubbles 17 will be described with reference to FIG. Here, a case where the bubble 17 is provided near the liquid crystal injection port will be described. First, as shown in FIG. 5A, the liquid crystal 10 is injected into the cell.

Next, as shown in FIG. 5B, the cell is heated to cause the liquid crystal 10 to overflow from inside the cell. For example, 14
What is necessary is just to heat to 5 degreeC. The liquid crystal 10 expands about 10%,
This is because it overflows from the cell.

Next, as shown in FIG. 5C, after the overflowing liquid crystal 10 is removed, the cell is cooled and the liquid crystal 10 is contracted. When the liquid crystal 10 contracts, gas is drawn in from the outside by the amount of contraction of the liquid crystal 10. For example, the cell may be cooled to a temperature of about 35 ° C. Gas is drawn in from the outside. For example, in a nitrogen atmosphere, nitrogen is drawn in. The gas is preferably inert and less soluble. For example, an inert gas such as nitrogen or dry air may be used.

Next, as shown in FIG. 5D, a sealing agent 16 such as a UV adhesive is applied to the liquid crystal inlet. Sealing agent 16
Is applied, the liquid crystal 10 attached to the sealing portion is wiped off. For wiping, paper or cloth having good water absorption may be used, and the wiping can sufficiently adhere the sealing agent 16. Note that a solvent or the like should not be used for wiping. This is because wiping with a solvent or the like may cause the solvent to enter the liquid crystal 10 and alter the quality of the liquid crystal 10. Further, if the solvent has high volatility, dew condensation water adheres to the wiping portion, and the water enters the liquid crystal 10 to deteriorate the characteristics of the liquid crystal 10.

Next, as shown in FIG. 5E, the cell is further cooled to, for example, about 25 ° C. The liquid crystal 10 is further contracted by cell cooling, and the sealing agent 16 is drawn into the cell by the contracted amount. Then, sealing agent 1
By irradiating 6 with UV light and curing, a liquid crystal element provided with bubbles 17 is completed.

The heating temperature and the cooling temperature of the cell are not limited to the above values, since they vary depending on the size of the cell, the type of the liquid crystal 10, and the amount of gas drawn.
Further, the above-described method for producing the bubble 17 is merely an example, and any method may be used as long as the bubble 17 can be provided in the cell.

FIG. 6 is a view showing the result of measuring the change in the resonance wavelength and the half-width with respect to the temperature change of the liquid crystal element used in the wavelength selection filter according to the embodiment of the present invention, using an optical spectrum analyzer. FIG. 7 is a graph showing the results of FIG. 6. The measurement is performed in a constant temperature bath, and is performed in the order of normal temperature (25 ° C) → heating (40 ° C) → cooling (10 ° C) → normal temperature (25 ° C).
The temperature was changed in ° C steps. At each temperature, 30
After the resonance wavelength was stabilized, the measurement was performed.
The shape of the liquid crystal element according to the present invention used for the measurement is as follows.

Quartz glass substrate thickness: 2.3 mm Reflectivity of reflection film: 98% (＠ 1550 nm) Distance between reflection films: 12 μm Liquid crystal agent: ZLI-3103 manufactured by Merck Ltd. Size of liquid crystal element: 13 × 10 mm (outer shape) Cell size: 8 × 7 mm Cell area: 21 mm ² Width of liquid crystal injection port: about 0.5 mm Seal width: 1.5 mm Bubble ratio: 10% Gas taken in: dry air As a comparative example (conventional example) A liquid crystal element having the same shape as above and having a bubble rate of 0% (no bubbles) was also measured.

As shown in FIGS. 6 and 7, in a conventional liquid crystal element, for example, when the temperature rises by 10 ° C., the resonance wavelength λ2
Rises about 8 nm. Further, the half width FWHM2 changes by 1.5 nm with a temperature change of 10 ° C. to 40 ° C. On the other hand, in the liquid crystal device of the present invention, the resonance wavelength λ1 is about 4 under similar conditions.
The change in the half width FWHM1 is only a very small value of 0.1 nm. Here, the reason why the resonance wavelength λ2 of the conventional liquid crystal element greatly increases with the temperature rise is that the optical path in the liquid crystal has changed due to the expansion of the liquid crystal and the increase in the interval between the quartz glass substrates. Further, the change in the half width is large because the expansion and contraction of the liquid crystal mainly occurs near the center in the cell, thereby decreasing the parallelism of the quartz glass substrate.

At around 20 ° C., the half width is a small value even in the conventional example. This is because the liquid crystal was sealed at around 20 ° C. In addition, the resonance wavelength λ1 of the liquid crystal element of the present invention tends to decrease as the temperature rises, and the resonance wavelength λ2 of the conventional liquid crystal element tends to increase as the temperature rises.
This is because, in the liquid crystal element of the present invention, the expansion of the liquid crystal is absorbed by the contraction of the bubbles, and the distance between the quartz glass substrates and the parallelism do not change, but the refractive index of the liquid crystal decreases with increasing temperature (−0). 0.06% / ° C.), resulting in a shorter optical path length in the liquid crystal. On the other hand, in the conventional liquid crystal element, the refractive index of the liquid crystal decreases as the temperature rises. However, since the change in the distance between the quartz glass substrates is larger than that, the resonance wavelength λ2 tends to increase due to the influence.

6 and 7, 10 ° C. to 40 ° C.
The measurement was performed in the temperature range of This is usually 10 ° C. as an environment in which an optical component on which a wavelength selection filter is mounted is used.
This is because a temperature range of about to 40 ° C. may be considered.
However, the present invention is not limited to this temperature range.
For example, even at around 0 ° C., there is no significant temperature dependence of the resonance wavelength and the half-value width, and this is sufficiently applicable.

Here, the half width will be described. FIG. 8 shows a general resonance wavelength spectrum of the liquid crystal element. Also,
FIG. 9 shows the resonance wavelength spectrum of the liquid crystal device of the present invention, and FIG.
0 shows the resonance wavelength spectrum of the liquid crystal element of the conventional example. In FIG. 8, “half width FWHM” indicates a wavelength width at half the intensity of the peak value of the spectrum, and means the sharpness of the peak of the spectrum. As shown in FIG. 10, in the liquid crystal element of the conventional example, the parallelism of the quartz glass substrate decreases with a change in temperature, and the half width increases. On the other hand, as shown in FIG. 9, in the liquid crystal element of the present invention, the parallelism of the quartz glass substrate is kept high by the expansion and contraction action of the bubbles, and the half width does not change.

As described above, the temperature dependence of the resonance wavelength and the half-value width of the liquid crystal device according to the present invention is much smaller than that of the conventional liquid crystal device without bubbles. Therefore, the wavelength selection filter using this liquid crystal element can perform wavelength selection with high accuracy by a simple configuration in which bubbles are provided in the cell of the liquid crystal element. In addition, the size of the entire apparatus can be reduced. Therefore, even when used as a part of a device such as an optical exchange or an optical tuner, the appearance and design of the device are not impaired. Furthermore, it can be used for optical communication equipment in a wide field.

Further, since the temperature dependence of the half width is small,
If the conversion of the resonance wavelength by the temperature coefficient is performed, highly accurate resonance wavelength control can be performed. Further, if a temperature control mechanism similar to the conventional one is used, wavelength selection with higher accuracy can be performed.

[0035]

According to the present invention, it is possible to realize a wavelength selection filter that can easily increase the wavelength selection accuracy.

According to the present invention, it is possible to realize a wavelength selection filter in which the temperature control mechanism is simplified and the size of the filter is easily reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a wavelength selection filter according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of the liquid crystal device having the Fabry-Perot ethane structure of FIG.

FIG. 3 is a sectional view taken along line AA of FIG. 2;

FIG. 4 is a diagram for explaining the effect of the bubbles shown in FIGS. 2 and 3;

FIG. 5 is a diagram for explaining a method of creating the bubbles of FIGS. 2 and 3;

FIG. 6 is a diagram showing a result of measuring a change in a resonance wavelength and a half width with respect to a temperature change of a liquid crystal element used in the wavelength selection filter according to the embodiment of the present invention by using an optical spectrum analyzer.

FIG. 7 is a graph showing the results shown in FIG. 6;

FIG. 8 is a diagram showing a general resonance wavelength spectrum of a liquid crystal element.

FIG. 9 is a diagram showing a resonance wavelength spectrum of the liquid crystal element of the present invention.

FIG. 10 is a diagram showing a resonance wavelength spectrum of a conventional liquid crystal element.

FIG. 11 is a diagram illustrating a configuration example of a conventional wavelength selection filter.

12 is a cross-sectional view of a liquid crystal element having a Fabry-Perot ethane structure as an example of the liquid crystal element in FIG.

FIG. 13 is a sectional view taken along line BB in FIG. 12;

FIG. 14 is a diagram for explaining a problem of a conventional example.

[Explanation of symbols]

 Reference Signs List 1 liquid crystal element 2 housing 3 optical fiber 4 collimator lens 5 liquid crystal element control electric wire 6 birefringence crystal plate 7 1/2 wavelength plate 8 liquid crystal element control circuit 9 sealant 11 antireflection film 12 quartz glass substrate 13 transparent electrode 14 Reflection film 15 Liquid crystal alignment film 16 Sealant 17 Bubbles 18 Temperature control circuit 19 Thermocouple 20 Peltier device control wire 21 Peltier device 22 Heat dissipation fin 23 Heat insulation material

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H048 GA01 GA13 GA24 GA48 GA51 GA60 GA62 2H049 BA05 BA06 BA42 BB03 BB62 BC25 2H088 FA10 HA01 HA14 HA21 MA20 2H091 FA01Y FB07 FD02 GA09 GA17 LA04 LA05 LA11

Claims (9)

[Claims] 1. A liquid crystal device comprising at least a pair of substrates disposed at regular intervals, a liquid crystal disposed between the substrates, and a bubble provided in the liquid crystal so as not to block an optical path. A wavelength selection filter. 2. The wavelength selection filter according to claim 1, wherein the pair of substrates are formed by bonding with a sealant. 3. The wavelength selection filter according to claim 2, wherein the liquid crystal is disposed in a space surrounded by the pair of substrates and the sealant. 4. The wavelength according to claim 1, wherein the pair of substrates have a transparent electrode and a reflective film sequentially formed on opposing main surfaces, and an anti-reflection film formed on another main surface. Selection filter. 5. The liquid crystal device according to claim 2, wherein the liquid crystal is injected through an opening formed in the sealant.
2. The wavelength selection filter according to 1. 6. The wavelength selection filter according to claim 5, wherein the opening is sealed with a sealing agent. 7. A step of bonding a pair of substrates via a sealant, and a step of injecting liquid crystal into a space surrounded by the pair of substrates and the sealant from an opening formed in the sealant. A step of heating the liquid crystal to overflow the opening; a step of removing the overflowing liquid crystal; a step of cooling the liquid crystal to form bubbles in the space; and a sealing agent in the opening. A method for manufacturing a wavelength selective filter, comprising at least a liquid crystal element manufacturing step including a step of applying and a step of cooling the liquid crystal and drawing the sealing agent into the opening. 8. The method according to claim 7, wherein the bubbles are formed by drawing outside air into the space. 9. The method according to claim 7, wherein the sealing agent is cured after being drawn into the opening.