JPH11258446A - V-grooved substrate for optical fiber array and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a V-grooved substrate for an optical fiber array which is excellent in productivity, low-cost and high-accuracy. SOLUTION: An optical fiber array includes a V-grooved substrate 2 for an optical fiber array and a pressing plate. The V-grooved substrate 2 includes a V-groove group 14 formed by plural V-grooves 13 formed on the surface 12, a stepped part 15 positioned at the end of the V-groove group 14 end, and an extension part 16 continued to the stepped part 15. The V-grooves 13 are formed parallel to each other, and the non-coated optical fibers are arranged therein. The V-groove substrate 2 is formed by a substrate material made of silicon monocrystal with the (110) surface. The V-groove 13 is formed along the direction of <100> in the substrate material. The stepped part 15 is formed along the direction of <110> in the substrate material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a V-groove substrate for an optical fiber array used for, for example, an optical connection portion of an optical fiber for transmitting signal light used for optical communication and the like, and a method of manufacturing the same.

[0002]

2. Description of the Related Art In order to connect an optical fiber used for optical communication or the like to an optical waveguide, a laser diode (LD), a photodiode (PD), or to optically connect a plurality of optical fibers, The optical fiber array 51 shown in FIG. 10 may be used.

The conventional optical fiber array 51 illustrated in FIG. 10 has a structure in which a plurality of optical fibers 52 are held by a V-groove substrate 53 and a holding plate 54. The optical fibers 52 are integrally formed such that the respective wire portions 55 are covered with a covering portion 56 and the optical axes are substantially parallel to each other by the covering portion 56.

The V-groove substrate 53 is made of quartz glass or silicon single crystal or the like, and has a V-groove group 58 composed of a plurality of V-grooves 57 parallel to each other, and a step portion 59 located at an end of the V-groove group 58. , An extension 60 connected to the step 59
And are integrally provided.

The optical fiber array 51 includes a V-groove substrate 5
The V-groove substrate 53 and the holding plate 54 are sandwiched between the V-groove substrate 53 and the holding plate 54 in a state in which the wire portion 55 of the optical fiber 52 is disposed in the V-groove 57 and the covering portion 56 is disposed in the extension portion 60. And V
The optical fiber 52, the V-groove substrate 53, and the holding plate 54 are fixed to each other by filling the gap between the groove substrate 53 and the holding plate 54 with an adhesive or the like.

[0006]

In order to manufacture the above-described V-groove substrate 53 of the conventional optical fiber array 51 using glass as a substrate material, the glass substrate material is subjected to mechanical processing such as grinding. Then, the V-groove 57, the step 59, and the extension 60 are formed. Then, using a dicing apparatus or the like, the substrate material is cut into a predetermined shape to obtain individual V-groove substrates 53.

At the time of machining the V-groove 57, the machining speed of the grinding process is reduced so that the machining accuracy of the V-groove 57 falls within a desired range such as ± 0.5 μm of a design value. When the working tool is worn, the working tool must be re-sharpened even during the grinding process. For this reason, the working time required for machining becomes long, and the V-groove substrate 53
Has a tendency to decrease, and it has been difficult to reduce costs.

In the case where a silicon single crystal is used as the substrate material of the V-groove substrate 53, the substrate material made of the silicon single crystal is subjected to anisotropic etching using a potassium hydroxide (KOH) solution. V groove 57,
In some cases, a step 59 and an extension 60 may be formed.
Manufacturing the V-groove substrate 53 by forming the V-groove 57 and the like by this anisotropic etching is performed by one-time etching.
Since a plurality of V-groove substrates 53 can be formed, the productivity is excellent.

However, since the covering portion 56 of the optical fiber 52 is disposed on the step portion 59 as described above, the height V is set to, for example, 300 μm from the surface of the substrate material. In some cases, the groove must be formed deeper than the groove 57.

For this reason, for example, as shown in FIG.
0) Wafer 7 made of silicon single crystal whose surface is the surface
1 (hereinafter referred to as (100) Si wafer) is subjected to anisotropic etching using the above-mentioned aqueous potassium hydroxide solution using SiO ₂ having a thickness of 1 μm formed by performing a thermal oxidation process as a mask. Since the SiO ₂ is corroded by potassium hydroxide, the SiO ₂ is corroded and disappears before forming the step 59 having the height H described above, and this step 59 is formed. It was difficult.

Further, silicon nitride (Si ₃ N ₄ ), titanium (Ti), chromium (Cr), etc., which are not corroded by an aqueous solution of potassium hydroxide or the like, are produced by PVD (Physical Vapor Deposition).
ition: Physical vapor deposition) or CVD (Chemical Vapor)
Deposition: A film is formed on the surface of the (100) Si wafer 71 by a film forming method such as a chemical vapor deposition method, and then formed into a predetermined pattern by dry etching such as RIE (Reactive Ion Etching). Must.

For this reason, in order to use Si ₃ N ₄ , Ti, Cr or the like, which has corrosion resistance to the above-mentioned potassium hydroxide, as a mask for anisotropic etching, it is necessary to use the above-mentioned PV.
Relatively expensive equipment is required for film formation by the D method or the CVD method and pattern formation such as RIE, and relatively long operation time is required for film formation and pattern formation. Therefore, the productivity of the V-groove substrate 53 tends to decrease, and it has been difficult to reduce the cost of the V-groove substrate 53.

In the case where SiO ₂ is deposited to a thickness not corroded and disappears until the stepped portion 59 is formed and anisotropic etching is performed, for example, the SiO _{2 having} a desired thickness of 1 μm or more is used. A long operation time is required when forming a film by thermal oxidation, and the productivity of the V-groove substrate 53 tends to decrease. Accordingly, an object of the present invention is to provide a highly accurate V-groove substrate for an optical fiber array which is excellent in productivity and low in cost.

[0014]

In order to solve the above-mentioned problems and achieve the object, a V-groove substrate for an optical fiber array according to the present invention comprises a plurality of parallel V-shaped substrates on which a plurality of optical fibers are arranged. A V-groove group consisting of a groove, a flat reference surface along the V-groove, a step portion located at an end of the V-groove group, and an extension portion connected to the step portion and extending along the optical fiber. A V-groove substrate for an optical fiber array, the surface of which is (11)
0) plane is formed from a substrate material made of silicon single crystal, and the step portion is formed on the surface of the substrate material by <110>
Direction and <100> orthogonal to the <110> direction.
The V-groove is formed along one of the directions, and the V-groove is formed along the other direction.

According to a second aspect of the present invention, in the V-groove substrate for an optical fiber array according to the first aspect, the step portion is formed along the <110> direction. The V-groove is formed along a <100> direction orthogonal to the <110> direction.

According to a third aspect of the present invention, in the V-groove substrate for an optical fiber array according to the second aspect, the step portion formed along the <110> direction is flat. The V-groove formed along the <100> direction is flat and has an angle of 45 degrees with respect to the reference plane. It is characterized by comprising a (111) plane formed at an angle of 35.3 degrees.

According to a fourth aspect of the present invention, there is provided a method of manufacturing a V-groove substrate for an optical fiber array, comprising: a V-groove group comprising a plurality of V-grooves in which a plurality of optical fibers are arranged; A method for manufacturing a V-groove substrate for an optical fiber array, comprising: a reference surface, a step portion located at an end of the V-groove group, and an extension portion connected to the step portion and extending along the optical fiber. Performs anisotropic etching on a substrate material made of silicon single crystal having a (110) plane,
The step portion and the V-groove are formed along a <100> direction orthogonal to the <110> direction.

According to a fifth aspect of the present invention, in the method of manufacturing a V-groove substrate for an optical fiber array according to the fourth aspect, the substrate material is subjected to anisotropic etching. Forming the step portion along the <110> direction, performing anisotropic etching on the substrate material, and forming the V-groove along a <100> direction orthogonal to the <110> direction. It is characterized by doing.

The method of manufacturing a V-groove substrate for an optical fiber array according to claim 6 is the method of manufacturing a V-groove substrate for an optical fiber array according to claim 4 or 5, wherein the substrate material is anisotropic. When performing etching, as a mask
Using a film made of SiO ₂ or Si ₃ N ₄ , and using KOH, CsOH, N
aqueous solution of either aOH or NH ₄ OH, or tetramethylammonium hydroxide (TMAH)
Characterized by using an aqueous solution consisting of

That is, the optical fiber array V of the present invention
The grooved substrate and the method of manufacturing the same include forming a V-groove group including a plurality of V-grooves, a step portion, and an extended portion by using a difference in etching rate caused by a difference in crystal orientation of a substrate material made of silicon single crystal. It is characterized by.

For example, as shown in FIG. 11, a <110>
Forming a pattern extending along a direction along arrow C in the drawing along the direction and a direction along arrow D along the direction perpendicular to the arrow C and along the <110> direction. When anisotropic etching is performed using a potassium aqueous solution, V grooves 73 and 74 shown in FIGS. 11 to 13 are formed. The (100) Si wafer 7
1, an orientation flat 75 (a flat surface provided for facilitating discrimination of the crystal orientation and the like and alignment) is formed in the <110> direction.

The V-grooves 73 and 74 are such that their inner side surfaces 73a and 74a are (111) planes and the (10)
0) Angles Θ3, Θ4 with the surface 72 of the Si wafer 71
Is 54.7 degrees.

Table 1 below shows the etching rates of SiO ₂ and a wafer made of a silicon single crystal having different crystal planes when an aqueous solution of potassium hydroxide at 80 ° C. is used.

[0024]

[Table 1]

In Table 1, the (110) Si wafer indicates a wafer 41 (shown in FIG. 7) made of a silicon single crystal having a (110) surface. According to Table 1, for example, a SiO ₂ film having a thickness of 1 μm is formed on the surface of a (100) Si wafer 71 by a thermal oxidation process.
When O ₂ is used as a mask, this SiO ₂ is corroded and disappears in about 5 hours. For this reason, the (10)
0) Even if an attempt is made to form a step portion 59 having a height of, for example, 300 μm on the Si wafer 71, the step portion 59 can be formed only up to a height of about 250 μm because SiO ₂ has only 5 hours.

On the other hand, since the etching rate of the (110) Si wafer 41 is twice the etching rate of the (100) Si wafer, the time required for forming the step having a height of 300 μm is as follows. , About 3 hours. For this reason, even if SiO ₂ having a thickness of 1 μm, which can be formed by thermal oxidation at a relatively low cost, is used as a mask,
A step can be formed by the anisotropic etching described above,
The V-groove, the step portion, and the extension portion can be formed at the same time.

Further, the above-mentioned (110) Si shown in FIG.
On the surface 42 of the wafer 41, a direction along an arrow A in the figure along the <110> direction, and a direction along an arrow B in the figure as a <100> direction orthogonal to the <110> direction. When each of the extended patterns is formed and anisotropically etched, the V-grooves 43, 43 shown in FIGS.
44 are respectively formed. The (110) Si
An orientation flat 45 is formed on the wafer 41 in the <110> direction.

The groove 43 shown in FIG.
a is the (100) plane and the (110) Si wafer 4
1 with respect to the surface 42 is 45
It is formed in degrees. The groove 44 shown in FIG.
The inner surface 44a is the (111) plane and
0) An angle Θ6 with the surface 42 of the Si wafer 41 is formed at 35.3 degrees (degree) over the longitudinal direction.

For this reason, according to the V-groove substrate for an optical fiber array according to any one of claims 1 to 3, since the substrate material having a high etching rate is a (110) silicon single crystal substrate material, For example, the V-groove group, the step portion, and the extension portion can be simultaneously formed by anisotropic etching using a mask made of SiO ₂ or the like having a thickness of 1 μm by thermal oxidation.

Therefore, by applying anisotropic etching or the like to the above-described substrate material, an intermediate product having a plurality of sets of the V-groove group, the step portion, and the extension portion can be obtained. Then, a plurality of V-groove substrates for an optical fiber array can be obtained at one time by cutting the intermediate product for each of the V-groove group, the step portion, and the extension portion.

In the above-described V-groove substrate for an optical fiber array, the V-groove group, the step portion, and the extension portion can be formed by anisotropic etching. The positional relationship between them is determined by the accuracy of the photomask, and these positional relationships can be maintained with high accuracy.

According to the method of manufacturing a V-groove substrate for an optical fiber array according to any one of claims 4 to 6, the surface may be (11)
Since the substrate material made of silicon single crystal, which is the 0) plane, is subjected to anisotropic etching, the etching rate of the substrate material is reduced even if a mask made of SiO ₂ or the like having a thickness of 1 μm by thermal oxidation is used. Since it is early, it becomes possible to form the V-groove group, the step portion and the extension portion before the mask is corroded.

For this reason, an intermediate product is obtained in which a plurality of sets of V-groove groups, steps and extensions are formed in the substrate material, and this intermediate product is cut into V-groove groups, steps and extensions, for example. A plurality of V-groove substrates for an optical fiber array can be obtained by one etching.

The positional relationship between the V-groove group formed by the above-described anisotropic etching, the stepped portion, and the extended portion is determined by the accuracy of a photomask or the like.
It is possible to obtain a V-groove substrate for an optical fiber array in which the positional relationship among the groove group, the step portion, and the extension portion is high.

[0035]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. For example, in optical communication, an optical fiber for signal light transmission is connected to an optical waveguide, a laser diode (LD), a photodiode (PD), or the like, or a plurality of optical fibers are optically connected to each other. The optical fiber array 1 shown in FIG.

The optical fiber array 1 includes an optical fiber array V-groove substrate 2 and a flat holding plate 3 and the like. A plurality of optical fibers 4 are held between the V-groove substrate 2 and the holding plate 3. It has become.

The optical fiber 4 is covered with a sheath 5 or the like for protection. These optical fibers 4
Has a covering portion 6 covered by the sheath 5 and a wire portion 7 not covered by the sheath 5.
The optical fibers 4 are integrated by the coating 6 so that their optical axes are substantially parallel to each other. Although the number of optical fibers 4 in the illustrated example is six, it is needless to say that the number is not limited.

As shown in FIGS. 2 to 4, the V-groove substrate 2 has a V-groove group 14 composed of a plurality of V-grooves 13 formed in parallel with one surface 12 located on the upper surface in the illustrated example. And a step portion 15 located at an end of the V groove group 14,
A flat extension 16 connected to the step 15 is integrally provided.

The V-groove group 14 has a number of V-grooves 13 corresponding to the number of the optical fibers 4. The V-shaped groove 13 has a V-shaped cross section so that the opening gradually narrows as the distance from the surface 12 of the V-groove substrate 2 for an optical fiber array increases.
It is formed in a character shape. The V-grooves 13 are configured to arrange the strands 7 of the optical fibers 4, respectively, and hold the optical fibers 4 together with the holding plate 3. The surface 12 of the V-groove substrate 2 is formed flat along the V-groove 13 and forms a reference plane described in this specification.

The inner surfaces 17, 17 of the V-groove 13 which are in contact with the strand 7 of the optical fiber 4, as shown in FIG.
The angle Θ1 with the surface 12 is formed to be constant over the longitudinal direction. This angle Θ1 is such that the V-groove 13 is perpendicular to the <110> direction as described below.
100> direction, 35.3 degrees (degr
ee).

The step 15 is formed along a direction substantially orthogonal to the transmission direction of the optical fiber 4 arranged in the V-groove 13. As shown in FIG. 4, the step 15 is formed such that the angle Θ2 with the surface 12 is constant over the width direction of the V-groove substrate 2. The angle Θ2 becomes 45 degrees when the step portion 15 is formed along the <110> direction as described later. The height H of the step 15 is 300 μm in the illustrated example.
It has become. The extension 16 is formed substantially parallel to the surface 12 and flat along the optical fiber 4 arranged in the V-shaped groove 13.

According to the above-described configuration, the wire 7 of the optical fiber 4 is arranged in the V-groove 13 of the V-groove substrate 2 and the extension 16
The optical fiber 4 is sandwiched between the V-groove substrate 2 and the holding plate 3 in a state in which the covering portion 6 is disposed. And V-groove substrate 2
An optical fiber array 1 is obtained by fixing the optical fiber 4, the V-groove substrate 2, and the holding plate 3 to each other by filling an adhesive between the holding plate 3 and the holding plate 3.

Next, an example of a method for manufacturing the optical fiber array V-groove substrate 2 having the above-described configuration will be described below. First, as shown in FIG. 5, SiO ₂ or Si is formed on a surface 42 of a substrate material 41 (hereinafter referred to as a (110) Si wafer) made of a silicon single crystal having a (110) surface by using a photolithography technique. _A mask 46 made of ₃ N ₄ or the like is formed and patterned 46 shown by hatching in FIG.
Is applied. The (110) Si wafer 41 includes:
An orientation flat 45 is formed in the <110> direction.

At this time, as shown in FIG. 6, the non-mask portion 47 corresponding to the V-groove has a constant width corresponding to the opening width of the V-groove 13 along the arrow B in the <100> direction. And is formed on the surface 42. The non-mask portion 47
The portion of the non-mask 48 corresponding to the step portion located at the left end in the figure is formed along the arrow A in the <110> direction. The non-mask portion 49 corresponding to the extension is provided in a direction away from the non-mask portion 48 corresponding to the V-groove from the non-mask portion 48 corresponding to the step portion.

Also, one (110) Si wafer 41
Then, a plurality of sets of non-mask portions 47, 48, and 49 corresponding to the above-described V-grooves, step portions, and extension portions are formed. (1) provided with an orientation flat 45 in the <110> direction.
10) In the Si wafer 41, a non-mask portion 47 corresponding to the V-groove is formed along the orientation flat 45, and a non-mask portion 48 corresponding to the step portion is orthogonal to the orientation flat 45. It is formed along the direction in which

And KOH, Cs
Using an aqueous solution composed of OH, NaOH, NH ₄ OH or the like or an aqueous solution composed of tetramethylammonium hydroxide (TMAH) as an etchant, anisotropic etching is performed, and the V groove 13 and the step 15 are formed.
And a plurality of sets of extension portions 16 are formed at the same time.

Next, using a dicing device or the like, FIG.
Along the two-dot chain line P shown in FIG.
The optical fiber array V-groove substrate 2 is obtained by cutting the substrate 5 and the extension 16.

According to this embodiment, since the V-groove substrate 2 for an optical fiber array is formed from the substrate material 41 made of silicon single crystal having a (110) surface, a relatively low-cost thermal oxidation process is used as a mask. 1 μm thick Si
Even by anisotropic etching using O ₂ and an aqueous solution of alkaline potassium hydroxide or the like as an etching solution, before the SiO ₂ is corroded and disappears, the V groove 13 and the height H are set to, for example, 300 μm. Step 15 and extension 16 can be formed.

Further, as described above, the formation of the V-groove 13, the step portion 15, the extension portion 16, and the like of the V-groove group 14 can be performed by anisotropic etching. Since the V groove 13 is formed along the <100> direction and the step 15 is formed along the <110> direction, the machining accuracy of the V groove 13, the step 15 and the extension 16 is a desired value. For example, it can be kept small so as not to cause a problem such as a range of ± 0.5 μm or less.

Further, since the V-groove group 14, the step portion 15, the extension portion 16 and the like can be formed by using anisotropic etching, a plurality of sets of V-grooves can be formed on one (110) Si wafer 41 by one etching. By forming the group 14, the step portion 15, the extension portion 16, and the like, a plurality of V-groove substrates 2 can be obtained.

Therefore, it is possible to provide a highly accurate V-groove substrate for an optical fiber array, which is excellent in productivity and low in cost. In the present embodiment, the V-shaped groove 13 is formed on the surface 42 of the (110) Si wafer.
The step 15 is formed along the <100> direction.
The V-groove 13 is formed along the <110> direction, and the step 15 is formed along the <100> direction, depending on the accuracy required for the V-groove substrate 2. May be formed.

[0052]

According to the V-groove substrate for an optical fiber array of the present invention, a group of V-grooves, steps, and extensions can be formed by anisotropic etching. An accurate V-groove substrate can be obtained. In addition, at the time of anisotropic etching, a relatively low-cost thermal oxidation treatment is used as a mask, for example, the thickness is 1 μm
It is possible to use a SiO _2, with can be reduced to improve the productivity and production costs, by photolithography and anisotropic silicon etching,
The relative positions of the V-groove group, the step portion, and the extension portion can be maintained with high accuracy. Therefore, it is possible to reduce the cost of a highly accurate V-groove substrate for an optical fiber array.

According to the method of manufacturing a V-groove substrate for an optical fiber array of the present invention, V-groove groups,
Since the step portion and the extension portion can be formed, a plurality of high-precision V-groove substrates can be obtained by performing etching once on the substrate material. In addition, in the case of anisotropic etching, (110)
By using a Si wafer, the etching rate is doubled, and for example, SiO ₂ having a thickness of 1 μm can be used by a relatively low-cost thermal oxidation process, so that the productivity is not reduced and the cost is reduced. In addition, it is possible to provide a highly accurate V-groove substrate for an optical fiber array.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view showing an optical fiber array provided with a V-groove substrate according to an embodiment of the present invention.

FIG. 2 is a perspective view showing a V-groove substrate for an optical fiber array according to the present invention.

FIG. 3 is a front view of the optical fiber array V-groove substrate viewed from the direction of arrow iii shown in FIG. 2;

FIG. 4 is a side view of the optical fiber array V-groove substrate viewed from the direction of arrow iv shown in FIG. 2;

FIG. 5 is a plan view of a (110) Si wafer on which a plurality of sets of V-groove groups, steps and extensions are formed as intermediate products in a manufacturing process of the V-groove substrate for an optical fiber array according to the present invention.

FIG. 6 is an enlarged view showing a vi portion in FIG. 5;

FIG. 7 is a plan view showing a (110) Si wafer on which a V groove is formed.

FIG. 8 is a sectional view taken along the line viii-viii in FIG. 7;

FIG. 9 is a sectional view taken along line ix-ix in FIG. 7;

FIG. 10 is an exploded perspective view showing an optical fiber array provided with a conventional V-groove substrate.

FIG. 11 is a plan view showing a (100) Si wafer in which a V groove is formed.

FIG. 12 is a sectional view taken along the line xii-xii in FIG. 11;

FIG. 13 is a sectional view taken along the line xiii-xiii in FIG. 11;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Optical fiber array 2 ... V groove substrate for optical fiber arrays 4 ... Optical fiber 12 ... Surface (reference surface) of V groove substrate 13 ... V groove 14 ... V groove group 15 ... Stepped part 16 ... Extension part 41 ... Surface (110) plane Si wafer A ... <110> direction B ... <100> direction

Claims (6)

[Claims] 1. A V-groove group including a plurality of parallel V-grooves on which a plurality of optical fibers are arranged, a flat reference surface along the V-groove, and a step portion located at an end of the V-groove group. A V-groove substrate for an optical fiber array, comprising: a substrate material made of a silicon single crystal having a (110) plane; A portion is formed on the surface of the substrate material along one of a <110> direction and a <100> direction orthogonal to the <110> direction, and the V-groove is formed along the other direction. A V-groove substrate for an optical fiber array, wherein the substrate is formed. 2. The step portion is formed along the <110> direction, and the V-groove is <10 orthogonal to the <110> direction.
2. The semiconductor device according to claim 1, wherein the first direction is formed along the 0> direction.
The V-groove substrate for an optical fiber array according to the above. 3. The step portion formed along the <110> direction is a (100) plane which is flat and has an angle of 45 degrees with the reference surface, and the <100> direction. The inner surfaces of the V-grooves formed along the plane are flat and the angle between the inner surface and the reference surface is 35.
3. The V-groove substrate for an optical fiber array according to claim 2, comprising a (111) plane formed three times. 4. A V-groove group including a plurality of parallel V-grooves on which a plurality of optical fibers are arranged, a flat reference surface along the V-groove, and a step portion located at an end of the V-groove group. A V-groove substrate for an optical fiber array, the substrate comprising an (110) plane silicon single crystal. A step of forming a step and a V-groove along a <110> direction and a <100> direction orthogonal to the <110> direction by performing a reactive etching. Manufacturing method of grooved substrate. 5. An anisotropic etching is performed on the substrate material to form the step portion along the <110> direction.
The method for manufacturing a V-groove substrate for an optical fiber array according to claim 4, wherein the V-groove is formed along a <100> direction orthogonal to the <0> direction. 6. When anisotropic etching is performed on the substrate material, a film made of SiO ₂ or Si ₃ N ₄ is used as a mask, and alkaline KOH, Cs
An aqueous solution of any of OH, NaOH, and NH ₄ OH,
Or tetramethylammonium hydroxide (T
The method for producing a V-groove substrate for an optical fiber array according to claim 4 or 5, wherein an aqueous solution comprising MAH) is used.