JP2004233468A - Optical ferrule, optical device and optical module using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical ferrule which is easily manufactured, has greatly increased anti-breaking strength and does not deteriorate optical coupling efficiency at a joint surface. <P>SOLUTION: Equal to or more than one notched part, which reaches a through-hole, is arranged in the middle section of the optical ferrule which has the through-hole and has an approximately cylindrical shape and a boundary section between the bottom surface of the notched part and the both side surfaces is made into a curved shape or a chamfering shape. Moreover, the corner section of an optical element or an optical ferrule fixing means is made into the curved shape or the chamfering shape to fit with the above boundary section. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００６８】
ここで表１より、従来の光フェルールでは破壊荷重の平均値、ばらつきが７．６３Ｎ、０．２４Ｎという結果に対して、本発明の光フェルール１での平均値、ばらつきが８．８５Ｎ、０．１０Ｎという値を示し、平均値で約１６％向上し、ばらつきも大幅に小さくすることができた。
【００６９】
【発明の効果】
以上のように本発明によれば、貫通孔を有する略円筒状の光フェルールの中間部に、貫通孔まで到達する切欠部を１つ以上有し、該切欠部の底面とその両側面との境界部が曲面状または面取形状であることにより、作製容易で抗折強度が大幅に強い光フェルール及びそれを用いた光デバイスを提供することができる。
【００７０】
また、光学素子または光フェルール固定手段の角部が、上記境界部と勘合する曲面状または面取形状であることにより、側面と光学素子の光学面または光フェルール固定手段とを隙間なく接合することが可能となり、接合面における光結合効率を悪化させることがなくなった。
【図面の簡単な説明】
【図１】（ａ）は本発明の光フェルールを示す断面図であり、（ｂ）、（ｃ）は（ａ）の境界部１ｆにおける断面詳細図である。
【図２】（ａ）〜（ｄ）は本発明の光フェルールの切欠部のさまざまな形状を示す断面図である。
【図３】（ａ）〜（ｃ）本発明の光フェルールを示す断面図である。
【図４】本発明の光デバイスを示す断面図である。
【図５】本発明の光デバイスを示す図であり、（ａ）は斜視図であり、（ｂ）は側面図である。
【図６】本発明の光フェルールの抗折強度測定方法を示す断面図である。
【図７】従来の光デバイスを示す断面図である。
【図８】従来の光デバイスを示す図であり、（ａ）は斜視図であり、（ｂ）は側面図である。光デバイスを示す断面図である。
【符号の説明】
１ 光フェルール
１ａ 貫通孔
１ｂ 切欠部
１ｃ 底面
１ｄ 側面
１ｆ 境界部
１ｇ 外周平坦部
２ 補強部材
３ 光ファイバ
３ａ 第１シングルモード光ファイバ
３ｂ 第１マルチモード光ファイバ
３ｃ コアレス光ファイバ
３ｄ コアレス光ファイバ
３ｅ 第２マルチモード光ファイバ
３ｆ 第２シングルモード光ファイバ
３ｇ 先球
４ 光学素子
４ａ 角部
１０ 光デバイス
２０ 光ファイバスタブ
３０ 光モジュール
３１ ＰＬＣ
３２ シリコン基板
３２ａ 基板表面
３３ 光導波構造
３４ 光導波路コア部
３５ Ｖ溝
３６ 溝
３７ 光導波路フラット部
３８ 光フェルール固定手段
４０ プッシュプルゲージ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical ferrule used for optical communication, and an optical device and an optical module using the same.
[0002]
[Prior art]
BACKGROUND ART An optical ferrule and an optical device using the same are used as an optical bonding part with an optical semiconductor element (light emitting element or light receiving element) and an optical connector. The surface to be connected to the optical connector is PC-polished and optically polished to obtain optimal optical coupling.
[0003]
Further, there is also a structure having an optical connector using an FC connector, an SC connector, an MU connector, an LC connector, or the like having a fixed length of a single mode optical fiber on the optical connector connection surface side.
[0004]
Further, there is also a structure in which an optical fiber having a lens portion for optically connecting an optical semiconductor element to one end is projected.
[0005]
Still further, some optical ferrules have at least one cutout in which optical elements such as an optical isolator, an attenuator, a filter, and a lens can be disposed.
[0006]
FIG. 7 shows an example of the optical device 10 using the above-mentioned conventional optical fiber stub 20. The optical device 10 using the conventional optical fiber stub 20 is different from the first single mode optical fiber 3a provided with a lens-shaped tip 3g at one end for optically connecting an optical semiconductor element (light emitting element or light receiving element). At the end, a first multimode optical fiber 3b, a coreless optical fiber 3c, 3d, a second multimode optical fiber 3e, and a second single mode optical fiber 3f are sequentially connected in a line to form a through hole of an optical ferrule 1 as a base. An optical element 4 such as a polarizer or a Faraday rotator is placed in a cutout 1b formed between the coreless optical fibers 3c and 3d. In some cases, a light-transmitting refractive index matching adhesive whose refractive index is matched with that of the coreless optical fibers 3c and 3d is provided between the optical fibers 3c and 3d.
[0007]
As shown in FIGS. 8A and 8B, the optical module 30 includes a PLC (planar optical waveguide circuit) 31 and an optical fiber stub 20 (see Patent Document 1).
[0008]
The PLC 31 has an optical waveguide structure 33 formed on a silicon substrate 32.
[0009]
The optical waveguide structure 33 includes an optical waveguide core 34 and an optical waveguide clad 37 covering the optical waveguide core 34. The optical waveguide core section 34 has a rectangular shape with one side of about 8 μm in cross section, and an optical signal propagates through the optical waveguide core section 34 having a high refractive index.
[0010]
At one end of the silicon substrate 32, the substrate surface 32a is exposed, and a V groove 35 is formed by anisotropic etching of silicon. When the optical fiber 3 having a circular cross section with a diameter of 125 μm is mounted in the V-groove 35, the center of the optical fiber 3 core (the diameter of 9.5 μm) and the center of the optical waveguide core 34 coincide with each other. The position and size of the groove 35 are selected.
[0011]
A groove 36 having a rectangular cross section orthogonal to the V groove 35 is formed by cutting the silicon substrate 32 with a dicing saw.
[0012]
After the V-groove 35 is formed by anisotropic etching of silicon, the silicon substrate 32 is mechanically cut with a dicing saw to form the groove 36, so that the optical fiber 3 mounted in the V-groove 35 is formed into an optical waveguide. It can be abutted against the core part 34.
[0013]
The optical fiber stub 20 includes an optical ferrule 1 having a through hole 1a and an optical fiber 3 inserted and fixed in the through hole 1a. The optical ferrule 1 further has a cutout 1b such that the optical fiber 3 inserted and fixed in the through hole 1a is half exposed.
[0014]
At one end of the optical ferrule 1, the optical fiber 3 is held by the optical ferrule 1 all around. Further, an outer peripheral flat portion 1g is formed at one end. The outer peripheral flat portion 1g has a length of about 300 μm in the axial direction and a height of about 250 μm from the notch 1b. For this reason, the outer peripheral flat portion 1g fits into the groove 36 of the PLC 31 with a sufficient margin, and does not hinder the alignment by the optical fiber 3.
[0015]
To assemble the optical module 30, the optical fiber stub 20 is turned over, and the outer flat portion 1g of the optical ferrule 1 is inserted into the groove 36 so that one end of the optical fiber 3 abuts against one end of the optical waveguide core 34. At the same time, the optical fiber 3 is inserted into the V-shaped groove 35, and the optical fiber stub 20 is bonded to the substrate surface 32a by the cutout 1b.
[0016]
With such a structure, a receptacle-type optical module suitable for cost reduction and miniaturization can be obtained.
[0017]
[Patent Document 1]
JP-A-2002-90578
[Problems to be solved by the invention]
However, in the conventional optical ferrule 1 and the optical device 10 using the same as shown in FIGS. 7 and 8, when one end is held and a load is applied to the other end, the bottom surface of the cutout 1b of the optical ferrule 1 is formed. There is a problem in that it breaks at the boundary 1f between the side face 1d and the two side faces 1d located on both sides of the side face 1c.
[0019]
For example, in the case of a small-diameter ferrule having an outer diameter of φ1.25 mm of the optical ferrule 1, the optical ferrule 1 may be broken from the boundary 1 f of the optical ferrule 1 during assembly into the optical device 10. The light output from the light emitting element may fluctuate after being assembled into the optical device 10 or the optical module 30. This is because the optical ferrule 1 is deformed without being broken by the stress applied to the optical ferrule 1 during assembly, and the optical ferrule 1 is assembled into the optical device 10 or the optical module 30 in the deformed state, and then the stress is removed. Then, the deformation returns to the original state, which causes a problem that the light output fluctuates.
[0020]
[Means for Solving the Problems]
In view of the above problem, the present invention has at least one notch reaching the through hole in the middle of a substantially cylindrical optical ferrule having a through hole, and has a boundary between a bottom surface of the notch and both side surfaces thereof. The portion is characterized by a curved surface or a chamfered shape.
[0021]
Further, the present invention is characterized in that a substantially cylindrical reinforcing member surrounding the periphery of the notch is provided.
[0022]
Further, the present invention is characterized in that an optical element or an optical ferrule fixing means is provided in a cutout portion of the optical ferrule, and an optical fiber is held and fixed in the through hole.
[0023]
Further, the present invention is characterized in that a corner of the optical element or the optical ferrule fixing means has a curved surface or a chamfered shape to be fitted with the boundary.
[0024]
Furthermore, the present invention is characterized by using the above optical device.
[0025]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings schematically showing the embodiments. In the drawings, the same members are denoted by the same reference numerals and description thereof will be omitted.
[0026]
FIG. 1A is a cross-sectional view of an optical ferrule 1 according to the present invention. The optical ferrule 1 has at least one notch 1b reaching the through hole 1a at an intermediate portion of the substantially cylindrical optical ferrule 1 having the through hole 1a. The boundary 1f between the bottom surface 1c of the notch 1b and both side surfaces 1d has a curved or chamfered shape.
[0027]
That is, in the optical ferrule 1 of the present invention, when the boundary portion 1f between the bottom surface 1c of the cutout portion 1b and both side surfaces 1d is curved or chamfered, when the optical ferrule 1 is subjected to a bending load. This has the effect of reducing the stress applied to the boundary 1f and increasing the bending strength.
[0028]
As shown in FIGS. 1 (b) and 1 (c), assuming that the size of the chamfered shape or the curved shape, which is the cross-sectional shape of the boundary portion 1f of the present invention, is a C surface c and a radius of curvature r, respectively, c and r are both 0. It is desirable to be within the range of 01 mm to 1.0 mm. If it is less than 0.01 mm, there is no effect of increasing the bending strength, and if it is more than 1.0 mm, it is too large and restricts the optical element or the ferrule fixing means on the other side and becomes unsuitable as an optical device. It is. Here, it is desirable that the size of the curved or chamfered shape is appropriately selected within the above range according to the material and shape of the mating member and the structure of the optical device.
[0029]
In order to make the cross-sectional shape of the boundary 1f a curved surface or a chamfered shape, it is desirable to finish the outer periphery of the optical ferrule 1 and the through hole 1a and then to grind the notch 1b. This is because the shape of the grindstone is transferred to the notch portion 1b by performing a curved surface or chamfering on the corner portion which is a portion corresponding to the above.
[0030]
The part to be ground of the grinding wheel is desirably made of diamond.
[0031]
The optical ferrule 1 of the present invention can be made of glass or resin besides zirconia and alumina ceramics.
[0032]
Next, FIGS. 2A to 2D are cross-sectional views showing various shapes of the cutout portion 1b of the optical ferrule 1 according to the present invention, and FIG. 2A shows that the boundary portion 1f has a curved surface shape. The portion 1b has a shape in which a part of the through hole 1a is left. In FIG. 2B, the boundary 1f has a curved surface, and the cutout 1b has a shape in which the through hole 1a is divided.
[0033]
In FIG. 2C, the boundary 1f has a chamfered shape, and the cutout 1b has a shape in which a part of the through hole 1a is left. In FIG. 2B, the boundary portion 1f has a chamfered shape, and the cutout portion 1b has a shape obtained by dividing the through hole 1a.
[0034]
In the optical ferrule 1 of the present invention, the cutout 1b is located on the bottom surface 1c of the cutout 1b and on both sides thereof even when the cutout 1b partially leaves the through hole 1a or when the cutout 1a is divided. If the cross-sectional shape of the boundary 1f between the two side surfaces 1d is a curved surface or a chamfered shape, the effects of the present invention can be achieved.
[0035]
Next, FIGS. 3A to 3C show another embodiment of the optical ferrule 1 of the present invention.
[0036]
FIG. 3A shows a case where there are several notches 1b. FIG. 3B shows an optical ferrule 1 in which an outer peripheral flat portion 1g is provided on the outer periphery. When mounting on an optical device or an optical module, a flat portion may be provided as described above, since it is difficult to fix the optical device with a curved outer peripheral shape.
[0037]
FIG. 3 (c) is provided with a reinforcing member 2 so as to cover the periphery of the cutout 1b, whereby the bending strength of the optical ferrule 1 having the cutout 1b can be easily increased.
[0038]
Here, the shape of the cylindrical reinforcing member 2 is a shape having at least one annular protrusion on the outer peripheral surface of the reinforcing member 2, and at least one notch is formed on the outer peripheral surface of the cylindrical reinforcing member 2. Having at least one hole in a part of the cylindrical reinforcing member 2, having at least one concave portion or at least two convex portions on the inner peripheral surface, or having a longitudinal shape of the inner peripheral surface. Various shapes such as those having at least three convex portions and concave portions in the direction can be used.
[0039]
As the material of the cylindrical reinforcing member 2, ceramic such as zirconia or alumina, glass, or the like can be used in addition to metal such as stainless steel. If the material is made of stainless steel, the optical module and the reinforcing member 2 can be laser-welded. Laser welding is a simpler and shorter process than solder encapsulation, and generates heat only locally, so it can be used for optical elements built into optical devices (not shown) and semiconductor elements in laser modules. Has little effect.
[0040]
Next, FIG. 4 shows a cross-sectional view of an optical fiber stub 20 according to an embodiment of the present invention and an optical device 10 using the same.
[0041]
The optical device 10 includes a first single mode optical fiber 3a, a first multimode optical fiber 3b, a coreless optical fibers 3c and 3d having no core, and a second multimode light in a through hole 1a of an optical ferrule 1 serving as a base. An optical fiber 3 in which a fiber 3e and a second single mode optical fiber 3f are sequentially connected in a line is housed. One end of the first single-mode optical fiber 3a protruding from the optical ferrule 1 has a tip sphere 3g processed for coupling with an optical semiconductor element (light-emitting element or light-receiving element), and one end of a second single-mode optical fiber 3f. Is polished at the other end of the optical ferrule 1.
[0042]
The coreless optical fibers 3c and 3d split in the optical ferrule 1 are optically connected via an optical element 4 (for example, an optical isolator) mounted in the cutout 1b.
[0043]
Here, a notch 1b reaching at least one or more through holes 1a is provided at an intermediate portion of the optical ferrule 1, and a boundary 1f between a bottom surface 1c of the notch 1b and two side surfaces 1d located on both sides thereof. The cross-sectional shape is a curved shape or a chamfered shape.
[0044]
Further, the cross-sectional shape of the corner 4a of the optical element 4 at the portion fixed to the notch 1b is a curved surface or a chamfered shape that fits into the curved surface or the chamfer of the boundary 1f of the notch 1b, thereby forming the side surface 1d. And the optical surface of the optical element 4 can be joined without a gap.
[0045]
Although not shown, a module equipped with an optical semiconductor element (light emitting element or light receiving element) (not shown) is optically connected to the first single mode optical fiber 3a provided with the tip sphere 1g of the optical device 10 for signal transmission. Light can be transmitted. In order to maintain a low connection loss with the optical connector, it is desirable that the optical connector connecting side of the optical device 10 be subjected to PC polishing in which a deteriorated layer is removed, or oblique PC polishing in which the tip surface is inclined.
[0046]
Further, there is also a structure having an optical connector using an FC connector, an SC connector, an MU connector, an LC connector, or the like having a fixed length of a single mode optical fiber.
[0047]
In addition to the optical isolator, various optical elements 4 such as an attenuator, a filter, and a lens can be placed in the notch 1b.
[0048]
Next, an optical module which is a kind of an optical device using the optical ferrule 1 of the present invention will be described with reference to FIGS.
[0049]
As shown in FIGS. 5A and 5B, the optical module 30 includes a PLC (planar optical waveguide circuit) 31 and an optical fiber stub 20, and the optical ferrule fixing means 38 of the PLC 31 and the cutout of the optical fiber stub 20. The portion 1b is fixed by fitting.
[0050]
The PLC 31 has an optical waveguide structure 33 formed on a silicon substrate 32.
[0051]
The optical waveguide structure 33 includes an optical waveguide core 34 and an optical waveguide clad 37 covering the optical waveguide core 34. The optical waveguide core section 34 has a rectangular shape with one side of about 8 μm in cross section, and an optical signal propagates through the optical waveguide core section 34 having a high refractive index.
[0052]
At one end of the silicon substrate 32, the substrate surface 32a is exposed, and a V groove 35 is formed by anisotropic etching of silicon. When the bare optical fiber 3 having a circular cross section with a diameter of 125 μm is mounted in the V-shaped groove 35, the center of the core portion (9.5 μm in diameter) of the bare optical fiber 3 matches the center of the optical waveguide core portion 34. Thus, the position and dimensions of the V-groove 35 are selected.
[0053]
A groove 36 having a rectangular cross section orthogonal to the V groove 35 is formed by cutting the silicon substrate 32 with a dicing saw. The width W of the groove 36 is about 320 μm, and the depth D is about 300 μm.
[0054]
After the V-groove 35 is formed by anisotropic etching of silicon, the silicon substrate 32 is mechanically cut with a dicing saw to form the groove 36, so that the optical fiber 3 mounted in the V-groove 35 is formed into an optical waveguide. It can be abutted against the core part 34.
[0055]
The optical fiber stub 20 includes an optical ferrule 1 having a through hole 1a and an optical fiber 3 inserted and fixed in the through hole 1a. The optical ferrule 1 further has a cutout 1b such that the optical fiber 3 inserted and fixed in the through hole 1a is half exposed.
[0056]
The optical fiber 3 is held at both ends of the optical ferrule 1. Further, an outer peripheral flat portion 1g is formed at one end. The outer peripheral flat portion 1g fits into the groove 36 of the PLC 31 with a sufficient margin, and does not hinder the alignment by the optical fiber 3.
[0057]
To assemble the optical module 30, the optical fiber stub 20 of FIG. 5A is turned upside down and the outer periphery of the optical ferrule 1 is flattened so that one end of the optical fiber 3 abuts against one end of the optical waveguide core 34. The portion 1g is inserted into the groove 36 and the optical fiber 3 is inserted into the V-groove 35, and the optical fiber stub 20 is fitted into the optical ferrule fixing means 38 of the PLC 31 at the notch 1b and is bonded to the substrate surface 32a.
[0058]
With such a structure, a receptacle-type optical module suitable for cost reduction and miniaturization can be obtained.
[0059]
Here, since the cross-sectional shape of the boundary portion 1f of the optical ferrule 1 is a curved surface or a chamfered shape, even after the optical module 30 is assembled, the strength against the bending stress applied to the optical ferrule 1 is improved. There is no fluctuation in optical output, and stable optical module characteristics can be obtained.
[0060]
Also, the cross-sectional shape of both corners 4a of the substrate surface 32a, which is the optical ferrule fixing means of the portion fixed to the notch 1b, is a curved or chamfered shape corresponding to the curved surface or chamfer of the boundary 1f of the notch 1b. By doing so, it is possible to join the side surface 1d and the optical surface of the core 34 without a gap, so that the optical coupling efficiency at the joining surface does not deteriorate.
[0061]
As described above, according to the present invention, the cross-sectional shape of the boundary 1f between the bottom surface 1c of the cutout portion 1b and the two side surfaces 1d located on both sides of the cutout portion 1b is curved or chamfered. It is possible to provide an optical ferrule 1 which is easy to manufacture and has a significantly high bending strength, and an optical device 10 using the same.
[0062]
【Example】
Here, a comparison was made of the breaking strength between the optical ferrule of the present invention and the conventional optical ferrule.
[0063]
FIG. 6 schematically shows a method for measuring the breaking strength of the optical ferrule 1. A position 3 mm from one end of the optical ferrule 1 is firmly held by a fixing jig such as a chuck, and a load is applied to the optical ferrule 1 as a base from above by a push-pull gauge 40 at a position 2 mm from the end surface of the other end. The load up to this point was measured with a push-pull gauge 40, and the bending strength was measured.
[0064]
The optical ferrule 1 used for the measurement has an outer diameter of φ2.500 mm, a length of 16 mm, an inner diameter of the through hole 1a of φ0.126 mm, and is made of zirconia. The width of the cutout 1b is 1.5 mm and the depth is 1.5 mm. Was set to 1.300 mm.
[0065]
In the conventional example, the boundary 1f between the bottom surface 1c of the notch 1b and the two side surfaces 1d located on both sides of the notch 1b is a sharp corner, and the boundary 1f of the present invention is a curved surface having a radius of curvature of 0.1 mm. And
[0066]
Ten measurement samples were prepared, and the measurement results are shown in Table 1.
[0067]
[Table 1]

[0068]
From Table 1, it can be seen from the results that the average value and the variation of the breaking load of the conventional optical ferrule are 7.63N and 0.24N, whereas the average value and the variation of the optical ferrule 1 of the present invention are 8.85N and 0. .10N, which was improved by about 16% on average, and the variation was significantly reduced.
[0069]
【The invention's effect】
As described above, according to the present invention, the intermediate portion of the substantially cylindrical optical ferrule having the through-hole has one or more notches reaching the through-hole, and the bottom surface of the notch and the both side surfaces thereof Since the boundary portion has a curved surface or a chamfered shape, it is possible to provide an optical ferrule which is easy to manufacture and has a significantly high bending strength and an optical device using the same.
[0070]
Further, since the corners of the optical element or the optical ferrule fixing means have a curved surface or a chamfered shape to be fitted with the above-mentioned boundary portion, the side surface and the optical surface of the optical element or the optical ferrule fixing means can be joined without a gap. And the optical coupling efficiency at the joint surface is not deteriorated.
[Brief description of the drawings]
1A is a cross-sectional view showing an optical ferrule of the present invention, and FIGS. 1B and 1C are detailed cross-sectional views at a boundary 1f of FIG. 1A.
FIGS. 2A to 2D are cross-sectional views showing various shapes of cutout portions of the optical ferrule of the present invention.
3A to 3C are cross-sectional views illustrating an optical ferrule of the present invention.
FIG. 4 is a sectional view showing an optical device of the present invention.
5A and 5B are diagrams showing the optical device of the present invention, wherein FIG. 5A is a perspective view and FIG. 5B is a side view.
FIG. 6 is a cross-sectional view showing a bending strength measuring method of the optical ferrule of the present invention.
FIG. 7 is a sectional view showing a conventional optical device.
8A and 8B are views showing a conventional optical device, wherein FIG. 8A is a perspective view and FIG. 8B is a side view. It is sectional drawing which shows an optical device.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Optical ferrule 1a Through hole 1b Notch 1c Bottom 1d Side 1f Boundary part 1g Perimeter flat part 2 Reinforcement member 3 Optical fiber 3a First single mode optical fiber 3b First multimode optical fiber 3c Coreless optical fiber 3d Coreless optical fiber 3e 2 multi-mode optical fiber 3 f second single-mode optical fiber 3 g tip 4 optical element 4 a corner 10 optical device 20 optical fiber stub 30 optical module 31 PLC
32 Silicon substrate 32a Substrate surface 33 Optical waveguide structure 34 Optical waveguide core 35 V-groove 36 Groove 37 Optical waveguide flat 38 Optical ferrule fixing means 40 Push-pull gauge

Claims (5)

In the middle of the substantially cylindrical optical ferrule having a through hole, one or more notches reaching the through hole are provided. An optical ferrule, characterized in that: 2. An optical ferrule according to claim 1, further comprising a substantially cylindrical reinforcing member surrounding the cutout. 3. An optical device, wherein an optical element or an optical ferrule fixing means is provided in a cutout portion of the optical ferrule according to claim 1 or 2, and an optical fiber is held and fixed in the through hole. The optical device according to claim 3, wherein a corner of the optical element or the optical ferrule fixing means has a curved surface or a chamfered shape to be fitted with the boundary. An optical module using the optical device according to claim 3.

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