JP2004077757A - Y-branch optical waveguide and manufacturing method for same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a Y-branch optical waveguide superior in uniformity and a manufacturing method for the same. <P>SOLUTION: A Y-branch optical waveguide 1 comprises one linear optical waveguide 2, two branch optical waveguides 3 and 4 which are connected to the linear optical waveguide 2 and overlap each other in the vicinity of a connection part 10 to the linear optical waveguide 2, and is formed by condensing and radiating laser into a transparent material, and first curved parts 3a and 4a including an area 5 where branch optical waveguides overlap and second curved parts 3b and 4b having no overlap areas are given to branch optical waveguides 3 and 4 respectively, and a radius R<SB>1</SB>of curvature of the first curved parts 3a and 4a is made shorter than a radius R<SB>2</SB>of curvature of the second curved parts 3b and 4b. Thus length L of the area 5 where branch optical waveguides 3 and 4 overlap is shortened to reduce unevenness of the condensation and radiation quantity of laser, so that the Y-branch optical waveguide 1 superior in uniformity of a branch ratio can be obtained. <P>COPYRIGHT: (C)2004,JPO

Description

【００３２】
【表２】

【００３３】
表１および表２に示す結果から明らかなように、Ｒ_１を５０ｍｍとした試験例１〜５のＹ分岐光導波路１は、重なり領域５の長さＬが０．４ｍｍを超えることにより、分岐比の均一性に劣るものとなった。これに対して、Ｒ_１を１０ｍｍまたは２０ｍｍとした試験例６、７のＹ分岐光導波路１は、重なり領域５の長さＬが０．４ｍｍ以下であり、分岐比の均一性が１ｄＢ以下となり、等分岐性に優れるものとなった。また、それぞれの分岐光導波路の損失も、Ｒ_１が５０ｍｍであるものに比べて大差なく、挿入損失をあまり増大させることなく、等分岐性を向上させることができた。
【００３４】
【発明の効果】
以上説明したように、本発明のＹ分岐光導波路によれば、透明材料の内部にレーザを集光照射することにより形成されたＹ分岐光導波路において、分岐光導波路の互いに重なり合った領域の長さを短くし、等分岐比のＹ分岐光導波路の均一性を向上することができる。このようにして得られたＹ分岐光導波路は、等分岐性に優れるので、１×Ｎ光スプリッタなどの光導波路素子に用いることにより、特性の優れた光導波路素子を製造することができる。
本発明のＹ分岐光導波路の製造方法によれば、透明材料の内部にレーザを集光照射することによりＹ分岐光導波路を形成するに際し、分岐光導波路の互いに重なり合った領域の長さを短くすることにより、挿入損失をあまり増大させることなく、等分岐性に優れたＹ分岐光導波路を容易に製造することができる。
【図面の簡単な説明】
【図１】本発明のＹ分岐光導波路の一実施形態を示す平面図である。
【図２】レーザの集光照射により光導波路を形成する方法を説明する図である。
【図３】従来の製造方法で作製されたＹ分岐光導波路の一例の出力特性を示すグラフである。
【図４】試験例のＹ分岐光導波路の形状および寸法を模式的に示す平面図である。
【符号の説明】
１…Ｙ分岐光導波路、２…直線光導波路、３…第１の分岐光導波路、３ａ…第１の分岐光導波路の第１曲線部、３ｂ…第１の分岐光導波路の第２曲線部、４…第２の分岐光導波路、４ａ…第２の分岐光導波路の第１曲線部、４ｂ…第２の分岐光導波路の第２曲線部、５…第１および第２の分岐光導波路の重なり領域、１０…直線光導波路と第１の分岐光導波路との接続部、２０…透明材料、２１…集光レンズ、２２…レーザ、Ｒ_１…第１曲線部の曲率半径、Ｒ_２…第２曲線部の曲率半径。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a Y-branch optical waveguide used for an optical waveguide device such as an optical splitter in an optical communication field and used for equal branching of optical power, and a method of manufacturing the same.
[0002]
[Prior art]
As disclosed in Japanese Patent Application Laid-Open No. 9-311237 and the like, as a method of manufacturing an optical waveguide, a laser such as a femtosecond pulse laser is condensed and radiated inside a transparent material such as glass. There is known a method of inducing a refractive index increase near a point (this phenomenon is called “laser-induced refractive index change”) to form a core of an optical waveguide. According to this method, an optical waveguide having a desired shape can be manufactured by a simple process. Therefore, as described in Japanese Patent Application No. 2000-233632 and Japanese Patent Application No. 2001-230371, the applicant has excellent characteristics. This has the advantage that the optical waveguide element can be easily manufactured.
[0003]
[Problems to be solved by the invention]
When an attempt is made to form a Y-branch optical waveguide having an equal branch ratio (branch ratio of 1: 1) using the above-mentioned laser-induced refractive index change, the branch ratio of light passing through the two branch optical waveguides is 1: 1. A deviation from 1 tends to result in poor uniformity (Uniformity). For this reason, it is difficult to manufacture a Y-branch optical waveguide having an equal branch ratio.
[0004]
Accordingly, it is an object of the present invention to provide a Y-branch optical waveguide having excellent branching ratio uniformity and a method for manufacturing the same.
[0005]
[Means for Solving the Problems]
The object is to provide a Y-branch optical waveguide including one linear optical waveguide and two branch optical waveguides connected to the linear optical waveguide and overlapping each other near a connection portion with the linear optical waveguide, When formed by condensing and irradiating a laser inside a transparent material, each of the branch optical waveguides includes a first curved portion including a region overlapping with the other branch optical waveguide, and the other branch optical waveguide. This problem is solved by providing a second curved portion that does not overlap with each other, and forming the branch optical waveguide such that the radius of curvature of the first curved portion is smaller than the radius of curvature of the second curved portion. According to the Y-branch optical waveguide obtained in this way, the length of the mutually overlapping region of the branch optical waveguide is shortened, and the asymmetry of the laser beam irradiation in the region can be reduced. This makes it possible to manufacture a Y-branch optical waveguide having excellent branching ratio uniformity.
Further, it is preferable that the length of the region where the first and second branch optical waveguides overlap each other is 0.4 mm or less.
[0006]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail based on embodiments.
FIG. 1 is a plan view illustrating an example of the Y-branch optical waveguide according to the present embodiment. The Y-branch optical waveguide 1 shown in FIG. 1 is connected to one linear optical waveguide 2 and this linear optical waveguide 2 and overlaps each other in the vicinity of a connection portion 10 with the linear optical waveguide 2 and has the same shape. It comprises first and second branch optical waveguides 3 and 4. The first branch optical waveguide 3 and the second branch optical waveguide 4 are formed symmetrically with respect to a straight line that extends the center line of the straight optical waveguide 2.
The straight optical waveguide 2 and the first and second branch optical waveguides 3 and 4 are formed by condensing irradiation of a laser, and have a substantially uniform width in all sections.
[0007]
In the Y-branch optical waveguide 1, the first branch optical waveguide 3 includes a first curved portion 3a, a second curved portion 3b, and a straight portion 3c.
The first curved portion 3a of the first branch optical waveguide 3 is smoothly connected to the straight optical waveguide 2 at the connection portion 10, and bends in a direction away from the second branch optical waveguide 4 as the distance from the connection portion 10 increases. I have.
The second curved portion 3b is smoothly connected to the first curved portion 3a at the connecting portion 11a, and is bent in a direction approaching the second branch optical waveguide 4 as the distance from the connecting portion 11a increases.
The straight portion 3c is smoothly connected to the second curved portion 3b at the connection portion 11b, and is parallel to the straight optical waveguide 2.
[0008]
Similarly, the second branch optical waveguide 4 includes a first curved portion 4a, a second curved portion 4b, and a straight portion 4c.
The first curved portion 4a of the second branch optical waveguide 4 is smoothly connected to the straight optical waveguide 2 at the connection portion 10, and bends away from the first branch optical waveguide 3 as the distance from the connection portion 10 increases. I have.
The second curved portion 4b is smoothly connected to the first curved portion 4a at the connection portion 12a, and is bent in a direction approaching the first branch optical waveguide 3 as the distance from the connection portion 12a increases.
The straight portion 4c is smoothly connected to the second curved portion 4b at the connection portion 12b, and is parallel to the straight optical waveguide 2.
[0009]
Also, the center lines of the first curved portions 3a, 4a and the second curved portions 3b, 4b of the first and second branch optical waveguides 3, 4 are connected to the respective connecting portions 10, 11a, 11b, 12a, 12b. Adjacent portions are smoothly connected so that the tangents of the center lines coincide with each other, in order to minimize radiation light loss in the bent optical waveguide.
[0010]
The straight portions 3c and 4c of the first and second branch optical waveguides 3 and 4 are parallel to the linear optical waveguide 2. This is because the Y-branch optical waveguides 1 are connected in multiple stages and This is because it becomes easy to manufacture a 1 × N optical splitter such as a × 4 branch, a 1 × 8 branch, and a 1 × 16 branch.
However, in the present invention, it is not essential that the straight portions 3c and 4c are parallel to the straight optical waveguide 2, and for example, the straight portions 3c and 4c may be expanded through a predetermined opening angle. Also, the second curved portions 3b, 4b may be directly connected to other optical waveguides without providing the linear portions 3c, 4c in the first and second branch optical waveguides 3, 4.
The first curved portions 3a, 4a and the second curved portions 3b, 4b are directly connected, but the first branch optical waveguide 3 and the second branch optical waveguide 4 have the same shape and symmetry with each other. For example, between the first curved portion 3a, 4a and the second curved portion 3b, 4b, a straight portion having the same length or another curve having a radius of curvature is interposed to smoothly connect. You may.
[0011]
In Y-branch optical waveguide 1 of the present embodiment, the first curved portion 3a of the first and second branched optical waveguides 3, 4, 4a center line of a circular arc of curvature radius R _1. The second curved portion 3b, 4b center line of a circular arc of curvature radius _{R 2.}
Here, the radius of curvature R ₁ is a smaller than the radius of curvature R _2. This is because when R ₁ and R ₂ are both large, as described above, on which causes the branching ratio deviates, the length required for the separation of the first and second branched optical waveguides 3 and 4 is long It is because. When both R ₁ and R ₂ are small, the loss of radiation light increases, which is not preferable.
[0012]
In the following description, for the sake of convenience, the first branch optical waveguide 3 will be described as being formed earlier than the second branch optical waveguide 4. The order of forming the second branch optical waveguides 4 is not limited. Even if the second branch optical waveguide 4 is formed before the first branch optical waveguide 3, it goes without saying that the following description is similarly established.
[0013]
When the second branch optical waveguide 4 is formed after the first branch optical waveguide 3 is formed by the condensing irradiation of the laser, when the second branch optical waveguide 4 is formed, It is necessary to irradiate and condense light on the formed first branch optical waveguide 3 in the vicinity of the connecting portion 10 described above. For this reason, the first branch optical waveguide 3 and the position 13 where the first branch optical waveguide 3 and the second branch optical waveguide 4 are completely separated from the connection portion 10 with the straight optical waveguide 2 are connected. A region 5 where the second branch optical waveguide 4 overlaps (hereinafter, referred to as an “overlap region”) is generated.
[0014]
In order to form a low-loss optical waveguide and to reduce the difference in loss between the first branch optical waveguide 3 and the second branch optical waveguide 4, the case where the first branch optical waveguide 3 is formed; It is preferable that the irradiation conditions such as the irradiation intensity and the irradiation time of the laser be the same when the second branch optical waveguide 4 is formed. When the irradiation conditions are the same, in the overlapping region 5, the laser is combined with a laser beam necessary for forming the first branch optical waveguide 3 and a laser beam necessary for forming the second branch optical waveguide 4 in the overlap region 2. Double irradiation is performed.
[0015]
As a result of the inventor's diligent studies, when the Y-branch optical waveguide 1 is formed in this way, the distribution of the increase in the refractive index in the overlapping region 5 becomes asymmetric, and the insertion of the first branch optical waveguide 3 formed earlier is performed. It was found that the difference between the loss and the insertion loss of the second branch optical waveguide 4 formed later tends to be large.
Although the cause is not clear, the laser-induced refractive index change occurs with a distribution centered on the focal point, and decreases with distance from the focal point. The difference in the amount of increase in the refractive index between the case where the laser beam is focused and the case where the laser beam is focused and irradiated where the change in the refractive index is induced, even when the same laser irradiation condition is used. it is conceivable that.
[0016]
3 shows an example of an insertion loss in a case where the _{R 1} and 50 mm. As shown in FIG. 3, the insertion loss of the first branch optical waveguide 3 formed earlier is equal to the insertion loss of the second branch optical waveguide 4 formed later over the entire wavelength range of 1520 to 1630 μm. It is about 2 dB smaller than that. That is, the uniformity of the branching (the absolute value of the difference between the insertion loss of the first branching optical waveguide 3 and the insertion loss of the second branching optical waveguide 4) deteriorates, and the output cannot be equally branched.
[0017]
Therefore, by making the length of the overlapping region 5 shorter than the predetermined length, the uniformity of the branching ratio can be improved.
Specifically, the length of the overlapping region 5 is preferably set to 0.4 mm or less. Thereby, the uniformity of the branching ratio can be made as low as 1 dB or less.
The first curved portion 3a, the radius of curvature R ₁ of 4a is large, the length L of the overlap region 5 is increased, by a sufficient reduction in R _1, it is possible to shorten the length L of the overlap region 5 it can.
In general, in a circular arc, as is well known, the radius of curvature is always equal to the radius of the circular arc at any point on the circular arc.
[0018]
Next, a method of manufacturing the Y-branch optical waveguide 1 will be described.
As shown in FIG. 2, the linear optical waveguide 2 and the first and second branch optical waveguides 3 and 4 of FIG. 1 condense a laser 22 via a condenser lens 21 inside a transparent material 20 such as glass. Irradiation can be performed by inducing a change in the refractive index at the converging point 23.
That is, as shown in FIG. 2A, the laser 22 is condensed and radiated onto the transparent material 20, whereby an increase in the refractive index is induced near the converging point 23. Then, as shown in FIG. 2B, by scanning the focal point 23 of the laser 22 and continuously forming the refractive index increasing region 24 by the light focusing, the refractive index is higher than that of the original transparent material 20. High regions can be continuously formed to be the core of the optical waveguide. A method for manufacturing such an optical waveguide is described in, for example, Japanese Patent Application Laid-Open No. 9-31237.
[0019]
In the present embodiment, as long as the material causes a laser-induced refractive index change, the transparent material 20 can be used without any particular limitation. Examples of such a transparent material 20 include quartz glass, fluoride glass, chalcogenide glass, silicate glass, phosphate glass, fluorophosphate glass, borate glass, chloride glass, and sulfide glass. And the like. Further, examples of the polymer material include optical polyimide and acrylic resin.
[0020]
The laser 22 preferably has a high peak output as disclosed in Japanese Patent Application Laid-Open No. 9-311237. Specifically, the laser 22 has a pulse width of 1 ps or less, preferably 10 kHz or more. More preferably, a femtosecond laser having a repetition frequency of 100 kHz or more and having a peak power intensity at a focal point of 10 ⁵ W / cm ² or more is exemplified.
[0021]
Then, by scanning the converging point 23 along the center line of the linear optical waveguide 2 and the first and second branch optical waveguides 3 and 4 constituting the Y-branch optical waveguide 1, the Y-branch optical waveguide 1 is formed. It is formed.
As a method of scanning the light converging point 23, a method of appropriately moving the transparent material 20 on a computer-controlled precision stage, a method of changing the light converging direction of the light converging lens 21 by controlling, and a method of condensing by a galvanomirror A known method such as a method of moving the point 23 can be adopted.
The cross-sectional shape of the optical waveguide formed by the irradiation of the laser 22 is not particularly limited, but may be, for example, a substantially circular shape, an elliptical shape, or a teardrop shape. Further, in order to adjust the refractive index of the optical waveguide to a desired value, it is also possible to collectively irradiate the laser 22 several times.
[0022]
The order in which the straight optical waveguide 2 and the first and second branch optical waveguides 3 and 4 are formed and the direction in which the light converging point 23 is scanned are not particularly limited, and all the optical waveguides are finally formed. What should I do?
In this case, in order to surely converge and irradiate the laser 22 to a portion other than the overlapping region 5 and to induce a sufficiently large change in the refractive index, the laser 22 must be provided at least to the overlapping region 5. The irradiation for forming the branch optical waveguide 3 and the irradiation for forming the second branch optical waveguide 4 need to be combined and irradiated twice in total.
At this time, in order to reduce the influence of the asymmetry of the amount of change in the refractive index of the overlapping region 5 described above, the length L of the overlapping region 5 is shortened to produce the Y-branch optical waveguide 1 having a high uniformity of the branching ratio. can do.
[0023]
As a procedure for forming each optical waveguide, for example, the incident point 14 of the linear optical waveguide 2, the connection portions 10, 11a, 11b of the first branch optical waveguide 3, and the emission point of the first branch optical waveguide 3 The laser beam 22 is condensed and irradiated along a line connecting 15 to form the linear optical waveguide 2 and the first branch optical waveguide 3, and then the connecting portions 10, 12 a, and 12 b of the second branch optical waveguide 4 are connected to each other. A method of forming the second branch optical waveguide 4 by condensing and irradiating the laser 22 along a line connecting the emission points 16 of the second branch optical waveguide 4 is exemplified.
[0024]
As another procedure, along a line connecting the incident point 14 of the linear optical waveguide 2, the connection parts 10, 11 a, 11 b of the first branch optical waveguide 3 and the emission point 15 of the first branch optical waveguide 3. After forming the linear optical waveguide 2 and the first branch optical waveguide 3 by condensing and irradiating the laser 22, the connection point 10 between the incident point 14 of the linear optical waveguide 2 and the second branch optical waveguide 4, A method of forming the second branched optical waveguide 4 by condensing and irradiating the laser 22 along a line connecting 12a, 12b and the emission point 16 of the second branched optical waveguide 4 is exemplified.
When this procedure is used, the number of irradiations of the laser 22 is not limited to the overlapping region 5 but also twice in the portion of the linear optical waveguide 2. However, since the linear optical waveguide is used, the refractive index induced distribution is asymmetric. Gender does not grow to a problem.
[0025]
As described above, in the Y-branch optical waveguide and the method of manufacturing the same according to the present embodiment, by setting the length L of the overlap region 5 to 0.4 mm or less, the laser is focused on the overlap region 5 twice or more. The asymmetry of the amount of increase in the refractive index due to irradiation can be reduced, and the uniformity of the branching ratio of the Y-branch optical waveguide 1 can be improved.
[0026]
In the above description, an arc is used as the curve that is the center line of the first curved portions 3a, 4a and the second curved portions 3b, 4b, but the present invention is not limited to this. The present invention can be applied to any curve as long as the radiation loss of the curved waveguide can be formed relatively low.
For example, a well-known sine curve (y = 1-cosx type) or a y = x-sinx type curve is preferable because a low-loss curved waveguide can be obtained. Further, a combination of an arc and a non-arc curve, a combination of two or more types of non-arc curves, and the like can be appropriately designed and adopted.
Even in such a curve other than the arc, the length L of the overlapping region 5 is shortened by reducing the radius of curvature of the branch optical waveguides 3 and 4 only at the branch portions, as in the case of using the above-described arc. The Y-branch optical waveguide 1 having high uniformity of the branch ratio can be manufactured.
[0027]
The Y-branch optical waveguide 1 of the present invention manufactured as described above can be used as a 1 × 2 optical splitter, and by connecting the Y-branch optical waveguides 1 in multiple stages, a 1 × N optical splitter (N: 4, 8, ...) can be manufactured.
[0028]
Hereinafter, test examples of the present invention will be described.
As shown in FIG. 2, a quartz glass is used as the transparent material 20, and a femtosecond pulse laser 22 is condensed and irradiated through a condensing lens 21 to form an optical waveguide having a width of 8 μm as shown in FIG. A Y-branch optical waveguide 1 having the shape shown was manufactured. The manufacturing conditions at this time are shown below.
[0029]
-Irradiation intensity of laser 22: 780 mW
・ Pulse width of laser 22: 400 fs
-NA of the condenser lens 21: 0.5
Focusing depth of laser 22: 20 μm (equivalent to the amount of movement from the surface of transparent material 20)
-Scanning speed of the focal point 23: 50 μm / s
[0030]
For each of the obtained Y-branch optical waveguides 1, the insertion loss (measurement wavelength: 1550 nm) of the first and second branch optical waveguides 3 and 4 is measured, and from the difference between these insertion losses, the uniformity of the branch ratio is determined. Calculated. The results are shown in Tables 1 and 2.
Note that the data shown in FIG. 3 described above was measured for the Y-branch optical waveguide of Test Example 4 in Table 1.
[0031]
[Table 1]

[0032]
[Table 2]

[0033]
Table 1 and as is clear from the results shown in Table 2, Y branch optical waveguide 1 in Test Example 1-5 in which the _{R 1} and 50mm, by the length L of the overlap region 5 is more than 0.4 mm, branch The uniformity of the ratio was poor. On the other hand, in the Y-branch optical waveguides 1 of Test Examples 6 and 7 in which R ₁ is 10 mm or 20 mm, the length L of the overlapping region 5 is 0.4 mm or less, and the uniformity of the branching ratio becomes 1 dB or less. , And excellent branchability. Also, the loss of each of the branched optical waveguides even without much difference as compared with those wherein R ₁ is 50 mm, without much increasing insertion loss, it was possible to improve the equal branching property.
[0034]
【The invention's effect】
As described above, according to the Y-branch optical waveguide of the present invention, in the Y-branch optical waveguide formed by converging and irradiating a laser on the inside of the transparent material, the length of the mutually overlapping region of the branch optical waveguide And the uniformity of the Y-branch optical waveguide having an equal branch ratio can be improved. Since the Y-branch optical waveguide obtained in this way has excellent branching properties, an optical waveguide element having excellent characteristics can be manufactured by using it for an optical waveguide element such as a 1 × N optical splitter.
According to the method of manufacturing a Y-branch optical waveguide of the present invention, when forming a Y-branch optical waveguide by condensing and irradiating a laser to the inside of a transparent material, the length of the mutually overlapping regions of the branch optical waveguide is shortened. This makes it possible to easily manufacture a Y-branch optical waveguide having excellent equal-branch properties without significantly increasing insertion loss.
[Brief description of the drawings]
FIG. 1 is a plan view showing one embodiment of a Y-branch optical waveguide of the present invention.
FIG. 2 is a diagram illustrating a method of forming an optical waveguide by condensing irradiation of a laser.
FIG. 3 is a graph showing output characteristics of an example of a Y-branch optical waveguide manufactured by a conventional manufacturing method.
FIG. 4 is a plan view schematically showing the shape and dimensions of a Y-branch optical waveguide of a test example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Y branch optical waveguide, 2 ... linear optical waveguide, 3 ... first branch optical waveguide, 3a ... First curve part of 1st branch optical waveguide, 3b ... 2nd curve part of 1st branch optical waveguide, 4 2nd branch optical waveguide, 4a 1st curve part of 2nd branch optical waveguide, 4b 2nd curve part of 2nd branch optical waveguide, 5 ... Overlap of 1st and 2nd branch optical waveguide Region, 10: connection portion between the straight optical waveguide and the first branch optical waveguide, 20: transparent material, 21: condensing lens, 22: laser, R ₁ : radius of curvature of the first curved portion, R ₂ : second The radius of curvature of the curve.

Claims (7)

It is composed of one linear optical waveguide and two branch optical waveguides connected to the linear optical waveguide and overlapping each other in the vicinity of the connection with the linear optical waveguide, and focuses the laser inside the transparent material. A Y-branch optical waveguide formed by irradiation,
Each of the branch optical waveguides has a first curved portion including a region overlapping with the other branch optical waveguide, and a second curved portion not overlapping with the other branch optical waveguide,
A Y-branch optical waveguide, wherein a radius of curvature of the first curved portion is smaller than a radius of curvature of the second curved portion. 2. The Y-branch optical waveguide according to claim 1, wherein the mutually overlapping regions of the branch optical waveguide are formed by condensing and irradiating a laser at least twice. 3. 3. The Y according to claim 1, wherein the region of the linear optical waveguide and the region of the branch optical waveguide that overlap each other are formed by condensing and irradiating a laser at least twice. 4. Branch optical waveguide. The Y-branch optical waveguide according to any one of claims 1 to 3, wherein a length of the overlapping region of the branch optical waveguide is 0.4 mm or less. The Y-branch optical waveguide according to any one of claims 1 to 4, wherein the laser is a femtosecond pulse laser. By converging and irradiating a laser inside the transparent material, one linear optical waveguide and two branch optical waveguides connected to the linear optical waveguide and overlapping each other near the connection with the linear optical waveguide. And forming a Y-branch optical waveguide,
Each of the branch optical waveguides has a first curved portion including a region overlapping with the other branch optical waveguide, and a second curved portion not overlapping with the other branch optical waveguide,
A method of manufacturing a Y-branch optical waveguide, comprising forming the branch optical waveguide such that a radius of curvature of the first curved portion is smaller than a radius of curvature of the second curved portion. The method according to claim 6, wherein a femtosecond pulse laser is used as the laser.

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