JPH03233412A - Optical connecting method and laser etching method - Google Patents

Abstract

PURPOSE:To facilitate optical connections and to reduce connection loss by forming an optical waveguide on a substrate by mechanical grinding and groov ing, then inserting and fixing optical fibers in guide grooves. CONSTITUTION:The guide groove 14 whose center axes are aligned with the light transmission directions of optical waveguides 12 and 13 are formed on a lithium niobate crystal substrate 11 where the optical waveguides 12 and 13 are formed. The optical fibers 17 are inserted into the guide grooves 14 and slid until connection end surfaces 25 of the optical fibers are connected to connection end surface 24 of the optical waveguides to adjust the positions of the optical fibers. Further, the guide grooves 14 restrain the positions of the optical fibers 17, so there is no increase in connection loss due to a position sift until the optical fibers 17 and guide grooves 14 are fixed completely with and adhesive, etc. Consequently, the optical waveguides 12 and 13 and fibers 17 are connected optically in a short time with ease and the connection loss is reducible.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an optical connection method and a laser etching method, and more specifically to an optical connection method and a laser etching method for optical fibers and optical waveguides formed on a substrate such as a lithium niobate crystal. This invention relates to a connection method and a laser etching method for forming optical fiber guide grooves on a substrate.

(Conventional technology) With the development of optical communication technology, advanced systems with large capacity and multiple functions are required, and new functions such as generation of more advanced optical signals and switching and exchanging of optical transmission lines are required. addition is required. For example, in order to switch optical transmission lines or obtain network switching functions, a highly functional optical control device such as an optical switch is required.

The light control devices currently in use are mainly bulk type devices using prisms, lenses, mirror fibers, etc., which have the disadvantages of slow speed, insufficient reliability, large size, and unsuitability for matrix formation. be. A waveguide type optical control device using an optical waveguide is being developed as a means to solve this problem, and has features such as high speed, ability to integrate multiple elements, and high reliability. In particular, those using ferroelectric materials such as lithium niobate (LiNbOa) crystals have features such as low light absorption and low loss, and high efficiency because they have a large electro-optic effect. Various optical control devices have been reported in the past, such as a directional coupler type optical modulator, an optical switch, a total internal reflection type optical switch, or a Matsuhatsu Enda type optical modulator.

When applying such a waveguide type optical control device to an actual optical communication system, it is practically essential to connect the connecting end surfaces of the guiding waveguides corresponding to the human output part of each device to each other via optical fibers. In order to achieve low-loss optical coupling at the connection part, the connection end surface of the optical waveguide formed on the substrate is processed into a high-precision surface with no chips.
It is necessary to connect the optical waveguide and the optical fiber by aligning their central axes in the light transmission direction with high precision.

Generally, optical waveguides are made of −z(
0001), and the ±x planes (2110) and (2110) of the substrate become connection end faces of the optical waveguide. Conventionally, the connection end surface is mechanically cut using a grindstone, and then the cut end surface is polished using free abrasive grains to achieve high precision processing. In addition, to connect the optical waveguide and optical fiber, after processing the connecting end face of the arrayed optical fiber with high precision in the same way as the connecting end face of the optical waveguide, the position is adjusted so that the central axes in the light transmission direction match, and then the adhesive A method of fixing is used.

(Problems to be Solved by the Invention) When connecting an optical waveguide and an optical fiber, the spread of the optical field distribution of the optical waveguide or the optical fiber is often 10 pm or less. Therefore, in order to achieve a low-loss optical connection, it is necessary to adjust the positions so that the central axes of both in the light transmission direction coincide with each other with an accuracy of about 111 m or less. According to the conventional technology, there is a problem in that a large number of adjustment steps and a long adjustment time are required in order to achieve a highly accurate optical connection as described above. Furthermore, after the position adjustment, the central axis tends to be misaligned until the optical waveguide and the optical fiber are completely fixed to each other, resulting in an increase in connection loss.

Furthermore, the lithium niobate crystal substrate is a hard and brittle material, and is easily chipped and cracked. For this reason, when the ±x plane, which is the connection end surface of the guiding waveguide, is mechanically cut with a grindstone, a large-scale chip is created at the end of the cut surface, that is, the connection end surface 24 of the optical waveguide, as shown in FIG. 2(b). 18 occurs frequently. This large-scale chip 18 significantly increases connection loss with the optical fiber. For this reason, conventionally, it took a long time to remove the generated large-scale chipping 18 by polishing after cutting.

Furthermore, conventionally, as a laser etching method for making fine grooves and holes in substrates such as lithium niobate crystals, lithium niobate crystal substrates are etched in an etching solution that is thermally reactive to lithium niobate crystal substrates. A laser etching method is known in which the material is immersed and irradiated with a laser beam such as an argon laser or a YAG laser (for example, Japanese Patent Laid-Open No. 60-278362). However, since lithium niobate crystal substrates transmit argon laser beam light and YAG laser beam light, first, an etching solution containing a substance that absorbs laser beam light is heated by laser beam light, and the etching process is performed using the generated heat. I will let you do it. As described above, in the laser etching process of a lithium niobate crystal substrate, since the etching process indirectly utilizes the heat generated by the laser beam light, the process speed is low and there is a problem in productivity.

The purpose of the present invention is to solve the problems of the conventional optical connection method described above, and to enable optical connection between an optical waveguide formed on a substrate such as a lithium niobate crystal and a fiber easily and in a short time. The object of the present invention is to provide an optical connection method with low connection loss. A further object of the present invention is to provide a laser etching method that can form optical fiber guide grooves in a substrate on which an optical waveguide is formed in a shorter time than conventional techniques.

(Means for Solving the Problems) A first invention provides an optical connection method for optically coupling a leading waveguide formed on a substrate and an optical fiber, in which a central axis of the optical waveguide in the light transmission direction is formed on the substrate. An optical fiber guide groove that matches the above is formed by laser etching, and an optical connection end face perpendicular to the optical waveguide is formed on the substrate by mechanical grinding and grooving, and then the optical fiber is inserted into the guide groove and fixed. It is characterized by

A second invention provides an optical connection method for optically bonding an optical waveguide formed on a lithium niobate crystal substrate to an optical fiber, in which ±x planes (2110) serving as optical connection end faces of the lithium niobate crystal substrate (2110) is characterized by having the −z plane (000〒) on which the optical waveguide is formed as the upper surface, and is formed by grinding and grooving in the +y force direction from the −y direction of the crystal axis using the down cut grinding method. It is characterized by

A third invention is a laser etching method for forming fine grooves and holes in a substrate, in which the substrate is immersed in an etching solution that is thermally reactive to the substrate, and ultrasonic vibration is applied to the etching solution or the substrate. It is characterized by irradiating the laser beam without adding.

(Operation) First, regarding the operation of the first invention, FIGS. 1(a) and (b)
) and (c). In the optical connection method of the present invention, as shown in FIG. 1(c), optical waveguides 12 and 1
A guide groove 14 whose central axis coincides with the light transmission direction of the optical waveguides 12 and 13 is formed on the same substrate as the lithium niobate crystal substrate 11 on which the optical waveguides 3 are formed. Therefore, the position of the optical fiber can be easily adjusted by inserting the optical fiber 17 into the guide groove 14 and sliding the optical fiber 17 until the connecting end surface 25 of the optical fiber is connected to the connecting end surface 24 of the optical waveguide. Furthermore, since the guide groove 14 restricts the position of the optical fiber 17, an increase in connection loss due to positional deviation does not occur until the guide groove 14 and the optical fiber 17 are completely fixed with adhesive or the like.

Here, since the lithium niobate crystal substrate 11 transmits the argon laser beam 15, it is difficult to form the guide groove 14 by directly irradiating the lithium niobate substrate 11 with the laser beam 15. In dry etching such as ion beam etching and reactive plasma etching,
In order to obtain a guide groove of a desired depth, a long time of 10 hours or more is required, and a problem remains in terms of productivity. Furthermore, when the guide groove 14 is mechanically ground using a grindstone, it can be expected to be processed in a short time; however, when processing the end surface 29 of the guide groove, the outer peripheral part of the grindstone also removes the connection end surface 24 of the optical waveguide. This is not realistic as there is a risk of this happening. That is, as shown in FIG. 1(a), the guide groove 14 can be efficiently formed by a laser etching process in which the etching liquid 22 is heated with a laser beam 15 and the etching process is progressed by this heat. becomes.

Next, regarding the operation of the second invention, FIGS. 2(a) and (b)
). Lithium niobate crystal substrate 11
When forming the connecting end surfaces 24 of the optical waveguides 12 and 13 formed in the above by mechanical grinding using a grindstone 19,
According to the conventional technology, large-scale chips 18 frequently occur on the connection end surface 24 of the optical waveguide. Therefore, polishing is required to remove the generated chip 18, and it takes a long time to optically connect the optical waveguides 12 and 13 and the optical fiber 17. The lithium niobate crystal substrate 11 has two axes (C
cleavage plane (1102X1012X01
12), and the chip 18 generated on the connection end surface 24 of the optical waveguide during grinding and grooving grows along the cleavage plane. However, in the inventor's experiment, the optical waveguides 12 and 13 were formed on the connection end surface 24 of the optical waveguide.
When processing by grooving using the down cut grinding method with the z plane as the top surface, the connecting end surface 24 of the leading waveguide is It has become clear that the size and shape of the chipping 18 that occurs during the process change.

That is, as shown in FIG. 2(a), from the -y direction to +y
When cutting in the + direction and as shown in Figure 2 (b)
In the case of cutting from the y direction to the −y force direction, the cleavage plane along which each generated chip 18 grows is (1102
) and (1012), it was experimentally confirmed that large-scale chipping 18 can be prevented by cutting from the -y direction to the +y direction. In this way, by forming the connecting end surface 24 of the optical waveguide by grinding and grooving from the -y force direction to the +y direction, large-scale chips 18 can be avoided compared to conventional techniques.
Since the polishing process for removing the optical fibers can be omitted, the time required for optical connection between the optical waveguides 12 and 13 and the optical fiber 17 can be significantly shortened.

Next, regarding the effect of the third invention, Fig. 3(a) and (b)
Explain with reference to. In the conventional laser etching method, the etching liquid 22 is heated by the laser beam 15, and the etching process is progressed by this heat, which is an indirect process, so the processing speed is low and there is a problem in productivity. When the inventor of the present invention closely inspected the vicinity of the laser etching processing point 27 in detail, it was found that in the conventional technique, the etching liquid 22 was removed by boiling of the etching liquid 22 due to the irradiation of the laser beam light 15.
2 bubbles 26 are generated, these bubbles 26 adhere to the vicinity of the surface of the lithium niobate crystal substrate 11, and the etching liquid 2
In addition, the etching solution 22 containing processing waste generated during the etching process stagnates around the laser etching processing point 27, slowing down the progress of the etching process, which lowers the processing speed. It turned out to be the main cause.

Therefore, in the laser etching method of the present invention, the third
As shown in Figure (a), a configuration was adopted in which ultrasonic vibration was applied to the lithium niobate substrate 11. By doing so, the etching reaction rate between the etching liquid 22 and the lithium niobate crystal substrate 11 at the laser etching processing point 27 is improved, and the scattering of the laser beam light 15 by the generated bubbles 26 can be suppressed.

That is, as shown in FIG. 3(b), the adhesion of air bubbles 26 to the lithium niobate crystal substrate 11 can be prevented by the stirring effect of ultrasonic vibration. Therefore, scattering of the laser beam 15 when repeatedly irradiated with the laser beam 15 can be prevented, and the etching liquid 22 can be sufficiently supplied to the laser etching processing point 27. Furthermore, since the etching reaction speed increases by applying minute vibrations to the etching liquid 22, the processing speed is improved. As a result,
It has been experimentally confirmed that by the laser etching method of the third invention, the processing speed is more than doubled compared to the conventional technology which had low processing speed and had problems with productivity.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIGS. 1(a), (b) and (e) are diagrams showing an embodiment of the optical connection method according to the present invention, and FIGS.
(c) is a cross-sectional view showing a method of processing the guide groove 14 of the optical fiber 17, and a perspective view showing a method of processing the connection end surface 24 of the optical waveguide.
7 is shown in a perspective view with the device inserted. Figure 2 (a), (
b) shows a perspective view in which the X plane of the lithium niobate crystal substrate 11 is ground and grooved in the -y to +y direction of the crystal axis, and a perspective view in which the X-plane is ground and grooved in the +y to -y direction of the crystal axis, respectively. FIGS. 3(a) and 3(b) are a front view and an enlarged sectional view of a processed portion, respectively, showing an embodiment of the laser etching method of the present invention.

In FIG. 1, −z of the lithium niobate crystal substrate 11
Optical waveguides 12 and 13 are formed on the surface by titanium diffusion. The width and depth of the optical waveguide are both 6 to 9 pm.
The top surfaces of the optical waveguides 12 and 13 are shown in FIG.
As shown in a) and (b), a SiO layer with a thickness of lpm is prepared in advance.
A protective film made of two vapor-deposited films 21 is provided. As the protective film, in addition to the SiO2 vapor deposited film 21, a sputtered film, an Al2O3 vapor deposited film, or a sputtered film can also be used to obtain the same effect. Note that the thickness of the protective film is preferably thicker from the viewpoint of preventing chipping 18 . However, the thicker the film, the longer the film formation time is required and the film formation cost increases.
Made thick.

First, the guide groove 14 for the optical fiber 17 was formed by laser etching as shown in FIG. 1(a). As shown in FIG. 3(a), the laser etching method uses an argon laser with an output of 1.5 W as the laser beam 15, condenses the beam diameter to 5 pm with a condenser lens 16, and etches the lithium niobate. Irradiation was performed from the back side of the crystal substrate 11. The etching solution 22 includes a potassium hydroxide aqueous solution (weight concentration 40%) that is thermally reactive with the lithium niobate crystal substrate 11, and carbon powder (weight concentration 1%) that acts as an absorber for the laser beam 15. A glass disk 23 mixed with lithium niobate crystal substrate 11 and rotates
It was supplied to the gap between

The laser beam 15 from the argon laser passes through the lithium niobate crystal substrate 11, but is absorbed by the etching liquid 22 containing carbon powder.
2 is heated and the etching process progresses. Here, the glass disk 23 has the effect of supplying fresh etching liquid 22 around the etching point 27 at an appropriate flow rate. The peripheral speed of the glass disk 23 at the laser etching point 27 was 1 mm/s. Also, lithium niobate crystal substrate 1
1, ultrasonic vibration with a frequency of 50 KHz and a vibration power of 7 W was applied by a Langevin type ultrasonic vibrator 28 and a high frequency power source 31. In order to prevent the generation of a large amount of bubbles due to cavitation, the vibration power was set to a level that would not cause cavitation. Note that the gap d between the lithium niobate crystal substrate 11 and the glass disk 23 is 2.
5 mm, and the lithium niobate crystal substrate 11 was repeatedly irradiated with the laser beam 15 while being scanned by the feeding table 20 at a feeding speed of 3 mm/min or more.

According to the above embodiment, the lithium niobate crystal substrate 11
Two guide grooves 14 having a depth of 65 pm, a width of 130 pm, and a length of about 4 mm were formed in the. The time required for machining was approximately 10 minutes, which was reduced to less than half of the time required to form the same guide groove using conventional techniques. In this example, ultrasonic vibrations were applied directly to the lithium niobate crystal substrate 11, but an ultrasonic vibrator 28 was applied to the etching container 30.
A similar effect was obtained by applying vibration to the etching solution 22.

Next, the X plane, which will become the connecting end surface 24 of the optical waveguides 12 and 13, was formed by grinding and grooving using a grindstone 19, as shown in FIG. 1(b). The processing was performed using a grindstone with a diamond abrasive grain diameter of approximately 311 m, an outer diameter of 76 mm, and a width of 0.5 mm. Depth of cut approximately 1mm, feed speed 6m
m/min, and optical waveguides 12 and 13 were formed.
Grooves were made in the -y to +y direction of the crystal axis of the lithium niobate crystal substrate 11 using the down-cut grinding method with the z-plane as the top surface. As shown in FIG. 2(a), the connection end surface 2 of the optical waveguide
4, no large-scale chipping 18 occurred, and the chipping 18 that did occur
Most of the SiO2 vapor deposited film 21 with lpm thickness is also formed in advance.
The connection end face 24 of the optical waveguide could be formed with high precision.

As a result, the connection loss is reduced to less than the desired 2 dB,
The polishing process required with conventional technology can be omitted, significantly reducing processing time. For comparison, Figure 2(b)
When the ±x plane was ground and grooved in the +y to -y direction as shown in , many large chips 18 were generated on the connection end surface 24 of the optical waveguide, penetrating the SiO□ vapor deposited film 21, and
The connection end face 24 of the optical waveguide was frequently damaged. In this embodiment, the connection end surface 24 of the optical waveguide was formed after the guide groove 14 was formed, but this order may be reversed.

Next, as shown in FIG. 1(C), an optical fiber 1 with a diameter of 125 pm and a core diameter of 1011 m or less is inserted into the guide groove 14.
7 was inserted and slid until the connecting end surface 25 of the optical fiber came into contact with the connecting end surface 24 of the optical waveguide, and was fixed with an adhesive. The guide groove 14 connects the optical fiber 17 and the optical waveguide 1.
The center axes of the light transmitting directions of the lenses 2 and 13 are set to substantially coincide with each other. Therefore, the position adjustment of the optical fiber 17, which was necessary in the conventional technology, can be largely omitted.
The time required for connection with the optical waveguides 12 and 13 could be significantly reduced. Further, when the optical fiber 17 is fixed with an adhesive, it is possible to prevent the optical fiber 17 from being displaced, which often occurs with conventional techniques, and it is also possible to reduce connection loss caused by positional displacement.

In the above embodiments, a lithium niobate crystal was used as the substrate on which the optical waveguide was formed, but it was confirmed that the present invention can be applied to other substrates such as glass substrates and semiconductor substrates.

Next, a second embodiment of the laser etching method of the third invention will be described with reference to FIGS. 4(a) and 4(b). In this example, we used alumina titanium carbide (A1203-TiC), which is often used as a slider for magnetic heads.
) On the board 32, vertical L1 = 0.5 mm, horizontal L2 = 0.5 m
A rectangular groove 33 with a depth of about 40 pm and a depth of 40 pm was machined.

Here, since the alumina titanium carbide substrate 32 absorbs the argon laser beam 15, there is no need to mix carbon powder that absorbs the laser beam 15 into the etching solution 22, and as shown in FIG. A laser beam 15 was irradiated from above 23.

Argon laser output 1.5W, beam diameter 5p
m.

The power of the ultrasonic vibration is 7W, and the circumferential speed of the glass disk 23 is 1.
mm/min, the gap d between the alumina titanium carbide substrate 32 and the glass disk 23 was set to 2.5 mm, and the laser beam 15 was repeatedly irradiated and scanned at a feed rate of the feed table 20 of 3 mm/min or more.

As a result, the time required to process the groove 33 shown in FIG. 4(b) was reduced to 172 seconds or less compared to the conventional technique.

(Effects of the Invention) As described above, in the optical connection method of the present invention, optical connection between an optical waveguide formed on a substrate such as a lithium niobate crystal and an optical fiber can be performed more easily and in a shorter time than before. Connection loss can be reduced.

Furthermore, the laser etching method of the present invention allows optical fiber guide grooves and the like to be formed on the substrate in a shorter time than conventional laser etching methods.

[Brief explanation of drawings]

1(a), (b), and (C) are diagrams showing an embodiment of the optical connection method according to the present invention, and (a) and (b) are sectional views showing the guide groove processing method, respectively. , and a perspective view showing a method of processing an optical connection end face, and (C) shows a perspective view of an optical fiber inserted into a guide groove. FIGS. 2(a) and 2(b) are perspective views of a lithium niobate crystal substrate in which the X plane is ground and grooved in the -y to +y direction and the +y to -y direction of the crystal axis, respectively. Furthermore, FIGS. 3(a) and (b) are a front view and an enlarged cross-sectional view of a processed part, respectively, showing a first embodiment of the laser etching processing method of the present invention, and FIGS. 4(a) and (b) 2A and 2B are a front view showing a second embodiment of the laser etching method of the present invention and a perspective view showing the shape of the grooves formed, respectively. In the figure, 11... lithium niobate crystal substrate, 1
2, 13... Optical waveguide, 14... Guide groove, 15...
・Laser beam light, 16... Condensing lens, 17...
Optical fiber, 18...Chip, 19...Whetstone, 20
...Feeding table, 21...SiO2 vapor deposited film, 22
...Etching liquid, 23...Glass disk, 24...
- Connection end face of optical waveguide, 25... Connection end face of optical fiber, 26... Air bubble, 27... Loser etching processing point, 28... Ultrasonic transducer, 29... End face of guide groove, 30. ...Etching liquid container, 31...High frequency power supply, 32...Alumina titanium carbide substrate, 33...
・Show each groove.

Claims (1)

[Scope of Claims] 1) In an optical connection method for optically coupling an optical waveguide formed on a substrate and an optical fiber, an optical fiber guide groove is provided on the substrate, the optical fiber guide groove coinciding with the central axis of the optical waveguide in the light transmission direction. An optical connection formed by laser etching, and after forming an optical connection end face perpendicular to the optical waveguide on the substrate by mechanical grinding and grooving, an optical fiber is inserted into the guide groove and fixed. Method. 2) ±x which becomes the optical connection end face of the lithium niobate crystal substrate
The planes (2@11@0) and (@2@110) have the -z plane (000@1@) on which the optical waveguide is formed as the upper surface, and are cut from the -y direction of the crystal axis to the +y direction by the down-cut grinding method. 2. The optical connection method according to claim 1, wherein the optical connection method is formed by grinding and grooving. 3) In a laser etching method for forming fine grooves and holes in a substrate, the substrate is immersed in an etching solution that is thermally reactive to the substrate, and a laser is applied to the etching solution or the substrate while applying ultrasonic vibrations. A laser etching processing method characterized by beam irradiation.