JPH09311232A - Optical waveguide, manufacturing method thereof, and optical module - Google Patents

Abstract

(57) 【Abstract】 PROBLEM TO BE SOLVED: A low-cost optical waveguide with a wide spot. SOLUTION: Between a core 23 and clads 22, 26,
A layer 25 having a refractive index intermediate between the two is provided. The layer having the intermediate refractive index may be realized as the intermediate layer 25 made of the third substance having the intermediate refractive index between the core and the clad, and both materials are formed at the interface between the core and the clad. It may be realized as a dispersed layer. The core 23, the clads 22 and 26, and the intermediate layer 25 / dispersion layer are all made of polyimide.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide, a method for manufacturing the optical waveguide, and an optical module using the optical waveguide.

[0002]

2. Description of the Related Art Laser diodes, photodiodes,
When an optical module is manufactured by mounting an optical element such as a modulator or a coupling element and a waveguide for optically coupling these elements on a substrate, these elements and the waveguide are used. High-precision alignment is required to align the central axes of the. When the alignment of the central axes is incomplete, optical loss occurs at the connection portion, and it causes deterioration of the optical signal due to interference light. In particular, when a single mode optical waveguide is used as the waveguide, highly accurate alignment of ± 1 μm or less is required to achieve good optical coupling.
However, the implementation with such high precision alignment is
The process takes time, increases the cost, and lowers the yield.

Therefore, in order to improve this problem and further improve the optical coupling efficiency, "optical" (199)
5 years) Vol. 24, No. 5, 270-275 and 282-
283, JP-A-5-150135, JP-A-5-150135
No. 323139, JP-A-6-18737, JP-A-7-84146, etc., a waveguide in which the shape of the core at the tip is tapered or a waveguide in which the refractive index of the core at the tip is changed Is proposed.

These are intended to enlarge the spot by making the shape of the core at the tip of the waveguide or the refractive index tapered, thereby improving the optical coupling efficiency and relaxing the required accuracy of optical coupling. is there. Therefore, if such a tapered waveguide is used, the alignment process time is shortened,
Since the yield is improved, the cost of the optical module can be reduced.

[0005]

In the above-mentioned tapered waveguide, the core shape is usually tapered by a selective growth mask, an epitaxial selective growth technique, or a photolithography technique, or a carbon dioxide gas laser or an electron beam is used. It is manufactured by changing the refractive index by irradiation of a beam. However, many of these processes require heating in a vacuum atmosphere or high temperature, and the number of processes is long, which causes an increase in cost.

Therefore, an object of the present invention is to provide a waveguide having a wide spot at the entrance end and / or the exit end which can be easily manufactured at low cost, a method for manufacturing the same, and an optical module using the same. .

[0007]

In order to achieve the above object, as a result of intensive studies, the present inventors have found that a layer having an intermediate refractive index is provided at the interface between the core and the clad, and the layer is made of resin. It has been found that a waveguide with an enlarged spot can be easily obtained without going through a vacuum process or a high temperature heating process. The region having the intermediate refractive index may be realized as an intermediate layer made of a third substance having an intermediate refractive index between the core and the clad, and both materials are dispersed at the interface between the core and the clad. It may be realized as a dispersed layer. The layer having an intermediate refractive index has a predetermined length including the optical waveguide end (light incident end or light output end) (similar to a normal tapered waveguide, the refractive index of the core and the clad, and the core If it is provided within a range of a length determined by design according to the diameter) (hereinafter referred to as a taper region), it is sufficient for spot expansion. Further, if a layer having an intermediate refractive index is provided over the entire length of the optical waveguide, it is possible to transmit multimode light without phase shift.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Among the optical waveguides of the present invention, the optical waveguide of the first embodiment is (a-1) a core made of a first organic polymer compound, and (a-2) An intermediate layer made of a third organic polymer compound having a small refractive index, and (a-3) a clad made of a second organic polymer compound having a smaller refractive index than the intermediate layer.

The second embodiment of the optical waveguide is (b-
1) A core composed of a first organic polymer compound having a first repeating unit, and (b-2) a dispersion composed of a third organic polymer compound containing a first repeating unit and a second repeating unit. Layer (b-3): a clad made of a second organic polymer compound having a second repeating unit. Here, the refractive index of the clad is smaller than the refractive index of the core. Also,
The refractive index of the third organic polymer compound is lower than that of the core and higher than that of the clad.

The intermediate layer and the dispersion layer are provided between the core and the clad and provided in at least the tapered region, but may be provided over the entire length of the optical waveguide. The spots can be more effectively enlarged by making the intermediate layer and the dispersion layer thicker toward the ends.
Further, similarly to the ordinary tapered waveguide, if the cross-sectional area of the core (the area of the cross-section perpendicular to the extending direction) in the tapered region is made smaller toward the end, the spot can be further expanded.

The first, second and third organic polymer compounds are preferably thermosetting resins, especially polyimides, and are represented by the following general formula (Formula 1) or the following general formula (Formula 3). One or more polyimides selected from the organic polymer compounds having the repeating unit represented by are particularly suitable. This is because these polyimides can be easily molded and have high transparency. In addition, polyimide is particularly suitable as a material for the optical waveguide of the present invention because it can easily form a dispersion layer.

[0012]

Embedded image

(In the formula, R ¹ is at least one group of —H and —CF ₃ , and R ² is the following chemical formula group:

[0014]

Embedded image

At least one of the organic groups represented by any of the formulas )

[0016]

Embedded image

(Wherein R ³ is —O— and —C (CF ₃ ))
_2- at least one of the groups, R ⁴ is the following chemical formula group

[0018]

Embedded image

At least one of the organic groups represented by any of the formulas The weight average molecular weight of the polyimide used in the optical waveguide of the present invention is usually about 10,000 to 100,000, and it is desirable to use one having a weight average molecular weight of about 50,000.

Which of these compounds is used for which layer is appropriately selected and determined according to the required refractive index. Generally, the larger the number of fluorine atoms in the repeating unit, the lower the refractive index. Therefore, it is desirable to use a polyimide containing more fluorine than the polyimide used for the core in the cladding. Further, it is desirable to use polyimide for the intermediate layer, which contains more fluorine than the core polyimide and less than the clad polyimide.

The optical waveguide of the first embodiment described above is (A-
1) A first clad forming step of forming a first clad layer made of an organic polymer compound having a first refractive index on the substrate surface, and (A-2) a first clad layer surface A core forming step of forming a core made of an organic polymer compound having a second refractive index higher than the refractive index of 1;
3) Formation of an intermediate layer for forming an intermediate layer made of an organic polymer compound having a third refractive index larger than the first refractive index and smaller than the second refractive index so as to cover the core in a predetermined region. Step and (A-4) Second cladding for forming a second cladding layer made of an organic polymer compound having a first refractive index so as to cover exposed portions of the surfaces of the core and the intermediate layer. The forming step and the (A-5) end surface forming step of forming an end surface by processing at least one of the both ends by dry etching, ion beam, excimer laser, or the like are performed in this order. Manufactured by.

Here, the region forming the intermediate layer is at least one of a tapered region (that is, a region having a predetermined length from the light incident end and a region having a predetermined length from the light emitting end). Area). Further, in the core forming step, the core may be formed such that in the tapered region, the area of the cross section perpendicular to the extending direction of the core becomes smaller as it is closer to the end.

The optical waveguide of the above-mentioned second form is (B-
1) A layer composed of the first polyimide precursor composition is formed on the surface of the substrate by, for example, coating, and prebaked,
A first pre-baking step of forming a first polyimide precursor layer, and (B-2) excluding a predetermined region (that is, a region where the dispersion layer is formed), the first polyimide precursor layer is formed. A first clad layer forming step of heating and curing to form a first clad layer made of a first polyimide; and (B-3) a step of forming a first clad layer on the surfaces of the first clad layer and the first polyimide precursor layer. A second polyimide precursor layer is formed by forming a layer of the second polyimide precursor composition by, for example, coating and prebaking.
And (B-4) a core forming step of (B-4) heat-curing the second polyimide precursor layer to form a core made of the second polyimide, except for the region where the dispersion layer is formed, -5) Surfaces of the first cladding layer and the first polyimide precursor layer, the core and the second layer
Of the third polyimide precursor layer so as to cover the surface of the polyimide precursor layer of
Forming a third polyimide precursor layer composed of the polyimide precursor composition, and heating and curing at least the first polyimide precursor layer, the second polyimide precursor layer, and the third polyimide precursor layer. And a final curing step of obtaining a final cured product, and (B-6) at least one of both ends of the final cured product is processed by dry etching, an ion beam, an excimer laser, or the like to form an end face. It is manufactured by performing the forming process in this order. In forming each precursor layer, a varnish of the precursor composition may be directly formed into a film by a method such as coating or spin coating, or a precursor composition which is formed into a film shape in advance may be attached. Good.

Here, the region forming the dispersion layer is at least one of a tapered region (that is, a region having a predetermined length from the light incident end and a region having a predetermined length from the light emitting end). Area). The heating temperature in the pre-baking step is usually about 90 to 180 ° C, and the heating temperature when heat-cured to obtain the final cured product (polyimide) is usually about 300 to 400 ° C.

In the final curing step, when heating the region where the dispersion layer is formed, the heating amount is increased as the region includes the incident end, the closer to the incident end, and when the region includes the outgoing end, the closer to the outgoing end. (That is, the heating temperature is increased and / or the heating time is increased). This is because the dispersion layer at the end can be thickened in this way.

Further, in the second pre-baking step, the second polyimide precursor layer may be formed in the taper region such that the area of the cross section perpendicular to the extending direction of the core becomes smaller toward the end. Good.

Further, according to the present invention, there is provided an optical module comprising the above-mentioned optical waveguide of the first or second aspect and an optical element connected to an incident end or an output end of the optical waveguide. Since the optical module of the present invention has a wide spot diameter of the optical waveguide, it is easy to align and the optical coupling efficiency is high. In the optical waveguide of the present invention, either one of the light emitting end and the light incident end may constitute an optical element such as a semiconductor laser. In this case, the tapered region has a predetermined length including the other end that does not form the optical element.

Further, in the optical module of the present invention, the space between the optical element and the incident end or the emitting end of the optical waveguide to which the element is connected may be filled with a filling material. If a transparent material having a refractive index of 1.1 to 2.1 at room temperature for light having a wavelength of 500 nm to 1600 nm is used as the filling material, the spread of the light at the connection portion is suppressed, and further, the reflection at the end face is performed. Since the light loss due to can be reduced, the optical coupling efficiency can be improved. For example, the above-mentioned polyimide (one or more polyimides selected from organic polymer compounds having a repeating unit represented by the general formula (Chemical formula 1) or the general formula (Chemical formula 3)), a silicone-based resin, or the like, It can be used as this filler.

[0029]

【Example】

<Synthesis example> Using the diamine component and acid dianhydride component shown in Table 1, the polyimide precursor composition for core, the polyimide precursor composition for clad, and the following:
A polyimide precursor composition for the intermediate layer was prepared.

First, the diamine component was mixed with N, N-dimethylacetamide and 1-methyl-2-, under a nitrogen stream at room temperature.
It was added to 420 g of a 1: 1 (weight ratio) mixed solvent with pyrrolidone while stirring and dissolved. To the obtained solution, acid dianhydride (the same mole as the diamine component) was added, and the mixture was stirred and dissolved under a nitrogen stream, further stirred at room temperature for 6 hours, and then heated at 55 to 70 ° C. for 6 hours. Thus, a varnish-shaped polyimide precursor composition was obtained. The solid content concentration and viscosity of the obtained composition are shown in Table 1. The amounts of the diamine component and the acid dianhydride added are determined so that the solid content concentration in the obtained composition becomes the predetermined concentration shown in Table 1.

[0031]

[Table 1]

The polyimide obtained by curing the obtained polyimide precursor composition had a weight average molecular weight of about 50,000. Repeating unit of each polyimide and wavelength is 633n
Table 2 shows the refractive indexes of m and 1300 nm light at 25 ° C.

[0033]

[Table 2]

<Example 1> 3 obtained as described above
An optical waveguide having an intermediate layer in a taper region was produced using one kind of polyimide precursor composition, and an optical module was produced using the optical waveguide. The manufacturing process of the optical waveguide in this example is shown in FIG. 1 (a), (b), (d),
(E) And (g) is a cross-sectional view of the end portion, FIG.
1 (c) and 1 (f) are partial cross-sectional perspective views with an end portion as a cross section, and FIG. 1 (h) is an external perspective view of the end portion.
(I) is a sectional view of an end portion. Although only one end is illustrated in FIGS. 1A to 1I, the other end of the optical waveguide of the present embodiment is the same as the illustrated end except that the substrate 21 is not cut. Has the same structure. The structure of the obtained optical module is shown in FIG.

(1) Formation of Optical Waveguide First, a substrate (Si or SiO ₂ plate) 2 on which electrodes made of a conductor and alignment marks are already formed 2
1, the above-mentioned clad polyimide precursor composition was applied, and the temperature was 140 ° C. for 30 minutes and 200 ° C. for 30 minutes.
Sequentially heat at 0 ° C for 30 minutes to completely cure, thickness 1
After forming the clad layer 22 of 5 μm, the core polyimide precursor composition is applied to the surface of the clad layer 22,
C. for 30 minutes, 200.degree. C. for 30 minutes, and 350.degree. C. for 30 minutes in order to completely cure and form a core layer 23 having a thickness of 8 .mu.m.

The surface of the obtained core layer 23 was subjected to oxygen plasma treatment, a negative resist having high dry etching resistance was applied, prebaked at 90 ° C. and developed, and further prebaked at 140 ° C. for 30 minutes. A resist layer 24 having a predetermined pattern was formed (FIG. 5A). As a result, the resist layer 2 has a pattern in which the shape of the tapered region (in this embodiment, the region having a length of 1 mm from the entrance end and the exit end) becomes narrower toward the end face later.
4 was obtained (FIG. 1 (a)).

Then, a pattern is formed on the core layer 23 by a reactive dry etching method using oxygen gas (see FIG. 1).
(B)), the resist layer 24 was peeled off (FIG. 1 (c)).
As a result, the core 23 was obtained in which the shape of the tapered region was a tapered shape in which the cross section narrowed toward the tip.

Next, the intermediate layer polyimide precursor composition is applied so as to cover the patterned core layer 23, and the temperature is set at 140 ° C. for 30 minutes, 200 ° C. for 30 minutes, and 350 ° C.
Sequentially heat at 30 ℃ for 30 minutes to completely cure, thickness 5μ
m after forming the intermediate layer 25 (FIG. 1D), the intermediate layer 2
A resist layer 24 having a high dry etching resistance was formed on the surface of No. 5 in a pattern that widens toward the end face later, up to a position 1 mm from the end face (FIG. 1).
(D)). Next, the intermediate layer 25 is patterned by a reactive dry etching method using oxygen gas (see FIG.
(E)), the resist 24 was peeled off (FIG. 1 (f)). As a result, in the tapered region, a tapered intermediate layer 25 having a cross section that widens toward the tip is formed.

The polyimide precursor composition for cladding is applied so as to cover the surfaces of the obtained core 23 and intermediate layer 25, and the temperature is set at 140 ° C. for 30 minutes and 200 ° C. for 30 minutes.
Sequentially heat at 0 ° C for 30 minutes to completely cure, thickness 1
A clad layer 26 having a thickness of 5 μm was formed (FIG. 1 (g)), and finally, predetermined portions to be the end faces of the incident end and the emission end were processed by using an excimer laser to form end faces to obtain an optical waveguide. .

FIG. 1H shows a perspective view of the end portion of the obtained optical waveguide, and FIG. 1I shows a cross section which is parallel to the laminating direction and the extending direction of the optical waveguide and which passes through the core. In addition,
Also in FIG. 1 (h), the optical waveguide extends toward the right rear side of the drawing, but is illustrated in a form cut near the end for easy viewing. In this embodiment, as shown in FIG. 2, two sets of electrodes 45 and alignment marks 46 are provided on the substrate 21, and one waveguide 42 is formed corresponding to each of them.

(2) Assembly of Optical Module Next, as shown in FIG. 3A, the semiconductor laser element 47 was mounted on the surface of the substrate 21. That is, the alignment mark 48 of the semiconductor laser element 47 and the electrode 4 are provided on one of the two sets of the alignment mark 46 and the electrode 45.
4 and 4 were aligned and connected using solder 50. As a result, the semiconductor laser device 47 was mounted on the substrate 21 so that the light emitting section 49 and the core 23 of the waveguide 42 were opposed to each other. The alignment marks 46 and 48 and the electrodes 44 and 48 are made of a three-layer film in which Ti, Pt, and Au are stacked in this order.

Similarly, the other alignment mark 4
6 and the electrode 45 were aligned with the alignment mark of the photodiode element and the electrode, and were connected using solder.

Next, the substrate 21 produced as described above is adhered to the case 52, the terminals of the substrate 21 and the terminals of the case 52 are connected by wire bonding, and then the optical fiber 43 formed on the substrate 21 has an optical waveguide end. The parts were aligned, adhered and fixed. Next, the case 52, which was covered and sealed, was connected to the module substrate 51 as shown in FIG.

Next, as shown in FIG.
Connect the other end of 3 to the connector 56, respectively, and
The I (large-scale integrated circuit) 54 and the driving IC (integrated circuit) 55 for the semiconductor laser device 47 were mounted at predetermined positions to manufacture an optical transceiver module.

When the semiconductor laser 47 was operated, the optical coupling between the semiconductor laser 47 and the waveguide 42 was excellent. Further, when light was made incident through the connector 56 and the optical fiber 43, the photodiode element operated well.

<Example 2> An optical module was formed in the same manner as in Example 1. However, in this embodiment, the optical waveguide 4
The connecting portion between the semiconductor laser element 47 and the semiconductor laser element 47 was filled with the silicone resin 53. When the semiconductor laser 47 of the obtained optical module was operated, the optical coupling efficiency between the semiconductor laser 47 and the waveguide 42 was much better than in Example 1.

<Example 3> In this example, an optical waveguide having a dispersion layer in the tapered region was produced, and an optical module was produced using the optical waveguide. The manufacturing process of the optical waveguide in this embodiment is shown in FIG. 5 (a), (b) and (d) are cross-sectional views of the end portion, and FIGS. 5 (c) and (e) are partial cross-sectional perspective views with the end portion as a cross section. In FIGS. 5A to 5E, only one end is illustrated, but in the optical waveguide of this embodiment, the other end is also the substrate 2.
It has the same structure as the illustrated end except that 1 is not cut. The structure of the obtained optical module is the same as that of the first embodiment.

(1) Formation of Optical Waveguide First, the above-mentioned polyimide precursor composition for cladding is applied to the surface of the substrate 21 and the whole is heated (prebaked) at 150 ° C. for 30 minutes, and then a dispersion layer forming region (later) is formed. Except for a region (illustrated by an arrow 37 in FIG. 5 (e)) within 1 mm or more from the position where the end faces of the emitting end and the incident end are formed, only the range shown by the arrow 36 in FIG. 5 (c),
It was heated by the heating wire of a heat gun to cure it almost completely. As a result, the clad polyimide layer 32 (shown in FIG. 5C) was formed in the region where the dispersion layer was not formed, and the clad polyimide precursor layer 32a was left in the dispersion layer formation region.

Polyimide precursor layer 3 for cladding obtained
2a and the surface of the polyimide layer 32 for cladding are subjected to oxygen plasma treatment, and then the polyimide precursor composition for core is applied and heated at 140 ° C. for 30 minutes (prebaking),
A polyimide precursor layer 33a for core was formed.

After the surface of the obtained precursor layer 33a was subjected to oxygen plasma treatment, a negative resist layer 24 having the same pattern as in Example 1 was formed in the same manner as in Example 1 (FIG. 5).
(A)), after removing the resist residue in a portion other than the predetermined pattern by oxygen plasma treatment, the core polyimide precursor layer 33a is etched using an organic alkali aqueous solution (FIG. 5 (b)), and the resist layer 24 was peeled off.
As a result, a core polyimide precursor layer 33a having the same pattern as that of Example 1 was obtained. Next, the clad layer 3
Similar to the case of 2, only the region excluding the dispersion layer forming region of the precursor layer 33a was heated by the heating wire of the heat gun to be cured almost completely. As a result, the core polyimide layer 33 was formed in the region where the dispersion layer was not formed, and the core polyimide precursor layer 33a was left in the dispersion layer formation region (FIG. 5C).

The obtained core polyimide precursor layer 33a
After the surface of the core polyimide layer 33 is treated with oxygen plasma, the cladding polyimide precursor composition is applied, and the whole is sequentially heated at 140 ° C. for 30 minutes, 200 ° C. for 30 minutes, and 350 ° C. for 30 minutes. Completely cured (Fig. 5 (d)).

At this time, in the dispersion layer forming region (the region shown by the arrow 36 in FIG. 5 (e)), the interface consisting only of the uncured polyimide precursor layer is heated at the curing temperature, so that the core Dispersion of the precursor occurs between the clad and the clad. Therefore, between the core and the clad in the dispersion layer forming region, a mixture of both polyimide precursors obtained by curing, has a refractive index intermediate between the core and the clad,
A very thin dispersion layer (not shown in FIG. 5) will be formed.

On the other hand, a region where the dispersion layer is not formed (see FIG.
In the area indicated by arrow 37 in (e)), since the first cladding 32 and the core 33 have already been hardened, there is no interface between the polyimide precursors. Therefore, the dispersion of the precursor as described above does not occur and the dispersion layer is not formed.

Finally, predetermined portions to be the end faces of the entrance end and the exit end were processed by using an excimer laser to form end faces to obtain an optical waveguide. FIG. 5 (e) is a perspective view showing the vicinity of the emission end of the obtained optical waveguide. In addition, in FIG. 5E, the optical waveguide extends toward the right rear of the paper,
In order to make the figure easy to see, it is shown in a cut form near the end. In this example, as in Example 1, two sets of electrodes 45 and alignment marks 46 were provided on the substrate 21, and one optical waveguide was produced corresponding to each of the electrodes.

(2) Assembly of Optical Module Next, as shown in FIG. 6A, the semiconductor laser element 47 and the photodiode element are formed on the surface of the substrate 21 on which the optical waveguide 61 is formed, as in the first embodiment. And an optical transceiver module was manufactured in the same manner as in Example 1. The obtained optical transceiver module operated well as in Example 1, and the optical coupling between each optical element and the waveguide 61 was good.

Incidentally, FIG. 6B is a partial sectional view showing a connecting portion between the optical waveguide 61 and the optical fiber 43 of this embodiment. In FIG. 6A and FIG. 6B, the thickness of the dispersion layer 38 is emphasized more than the actual thickness.

[0057]

According to the present invention, an optical waveguide having a wide spot can be obtained at low cost. Since the optical waveguide of the present invention has high optical coupling efficiency and relaxes the required alignment accuracy, throughput and yield are improved in manufacturing an optical module, and therefore, the cost of the optical module can be reduced. .

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a manufacturing process of an optical waveguide of Example 1.

FIG. 2 is a plan view of a substrate on which an optical waveguide is formed in Example 1.

FIG. 3 is a partial cross-sectional view showing a connecting portion of an optical waveguide in the first embodiment.

FIG. 4 is a plan view of the optical transmission / reception module manufactured in Example 1.

FIG. 5 is an explanatory diagram showing a manufacturing process of the optical waveguide of Example 2.

FIG. 6 is a plan view of a substrate on which an optical waveguide is formed in Example 2.

[Explanation of symbols]

21 ... Substrate, 22, 32 ... First clad layer, 23, 3
3 ... Core, 24 ... Resist, 25 ... Intermediate layer, 26, 35
... Second clad layer, 32a ... Clad precursor layer, 3
3a ... Precursor layer for core, 36 ... Arrow showing region where dispersion layer is not formed, 37 ... Arrow showing region where dispersion layer is formed,
38 ... Dispersion layer, 42 ... Optical waveguide, 43 ... Optical fiber, 4
4, 45 ... Electrodes, 46, 48 ... Alignment marks, 4
7 ... Semiconductor laser element, 49 ... Light emitting part, 50 ... Solder,
51 ... Module substrate, 52 ... Case, 53 ... Filling material, 54 ... Logic LSI, 55 ... IC, 56 ... Connector.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location H01S 3/18 H01L 31/02 C

Claims (12)

[Claims] 1. A core comprising a first organic polymer compound having a first repeating unit and having a first refractive index, and a second refractive index having a second refractive index smaller than the first refractive index. And a clad made of a second organic polymer compound having a repeating unit of, wherein the clad is composed of the core and the clad within a predetermined length range including one of the light incident end and the light emitting end. The third organic polymer compound forming the interface between the two has the above-mentioned first repeating unit and the above-mentioned second repeating unit, and is an optical waveguide. 2. A core made of a first organic polymer compound having a first refractive index and a second organic polymer compound having a second refractive index smaller than the first refractive index. A clad, and at least within a predetermined length range including one of the light incident end and the light emitting end, between the core and the clad, the refractive index being smaller than the first refractive index; The optical waveguide further comprising an intermediate layer made of a third organic polymer compound having a third refractive index higher than 2. 3. The area according to claim 1 or 2, wherein within a predetermined length range including the end portion, the area of a cross section perpendicular to the extending direction of the core becomes smaller as the end portion is closer to the end portion. Optical waveguide to do. 4. The optical waveguide according to claim 1, wherein each of the first, second and third organic polymer compounds is made of polyimide. 5. The repeating unit according to claim 4, wherein the first, second and third organic polymer compounds each have a repeating unit represented by the following general formula (Formula 1) or the following general formula (Formula 3). An optical waveguide, which is one or more kinds of polyimide selected from organic polymer compounds. Embedded image (In the formula, R ¹ is at least one group of —H and —CF ₃ , and R ² is the following chemical formula group: At least one of the organic groups represented by any of the formulas. ) (In the formula, R ³ is at least one of —O— and —C (CF ₃ ) ₂ —, and R ⁴ is the following chemical formula group (Chemical Formula 4): At least one of the organic groups represented by any of the formulas. ) 6. The optical waveguide according to claim 1 or 2, wherein the third organic polymer compound layer is thicker toward the end. 7. (1) A first clad forming step of forming a first clad layer made of an organic polymer compound having a first refractive index on a substrate surface, and (2) the first clad layer. A core forming step of forming a core made of an organic polymer compound having a second refractive index higher than the first refractive index on the surface of, and (3) covering the surface of the core in a predetermined region. Is larger than the first refractive index,
An intermediate layer forming step of forming an intermediate layer made of an organic polymer compound having a third refractive index smaller than the second refractive index, and (4) the first and second intermediate layers so as to cover the surfaces of the core and the intermediate layer. A second clad forming step of forming a second clad layer made of an organic polymer compound having a refractive index of 1 and (5) an end face forming step of processing the end portion to form an end face in this order. And the predetermined region includes at least one of a region having a predetermined length from a light incident end and a region having a predetermined length from a light emitting end. And a method for manufacturing an optical waveguide. 8. The core forming step according to claim 7, wherein in the region including the incident end of the predetermined region, the area of a cross section perpendicular to the extending direction of the core is closer to the incident end. The step of forming the core so as to be small, and forming the core such that, in a region including the emission end, the area of a cross section perpendicular to the extending direction of the core becomes smaller as it is closer to the emission end. And a method for manufacturing an optical waveguide. 9. A first pre-baking step of forming a layer of a first polyimide precursor composition on a surface of a substrate and pre-baking to form a first polyimide precursor layer,
(2) A first clad layer forming step of forming a first clad layer made of the first polyimide by heating and curing the first polyimide precursor layer except for a region where a dispersion layer is formed, 3) Forming a layer made of the second polyimide precursor composition on the surfaces of the first cladding layer and the first polyimide precursor layer and prebaking it to form a second polyimide precursor layer Second Pre-baking process of (4)
A core forming step of forming a core made of a second polyimide by heating and curing the second polyimide precursor layer except for the region where the dispersion layer is formed, and (5) the first cladding layer and the first The surface of the polyimide precursor layer and the surface of the core and the second polyimide precursor layer, to form a third polyimide precursor layer consisting of the third polyimide precursor composition, A final curing step of heating and curing at least the first polyimide precursor layer, the second polyimide precursor layer, and the third polyimide precursor layer to obtain a final cured product; and (6) above. An end face forming step of forming an end face by processing at least one of both ends of the final cured product, and the region forming the dispersion layer is a region having a predetermined length from the incident end of light, and Light output end Luo predetermined length of the region, the manufacturing method of the optical waveguide, characterized in that it comprises at least one region of the. 10. The final curing step according to claim 9, wherein when the region forming the dispersion layer is heated, the region is closer to the incident end when the region includes the incident end, and is emitted when the region includes the emitting end. A method of manufacturing an optical waveguide, characterized in that the amount of heating is increased toward the edge. 11. The second prebaking step according to claim 9, wherein in the region including the incident end of the region forming the dispersion layer, the cross section perpendicular to the extending direction of the core is closer to the incident end. The second polyimide precursor layer is formed so that the area of the core becomes smaller, and in the region including the emitting end, the area of the cross section perpendicular to the extending direction of the core becomes smaller as it is closer to the emitting end, A method of manufacturing an optical waveguide, which is a step of forming the second polyimide precursor layer. 12. An optical module comprising the optical waveguide according to claim 1 and an optical element connected to an incident end or an output end of the optical waveguide.