JPH06347658A - Plastic optical waveguide - Google Patents

Abstract

PURPOSE:To provide such a plastic optical waveguide as to decrease the thermal strains generated by a temp. change during and after production. CONSTITUTION:This plastic optical waveguide is formed by using a plastic having >=1X10<-5> deg.C<-1> coefft. of thermal expansion and a substrate used for production of the optical waveguide has >=1X10<-5> deg.c<-1> coefft. of thermal expansion. The adequate plastic includes polyamide and more particularly polyimide fluoride. The adequate substrate for the production includes metallic plates consisting of aluminum, copper, etc., alloy plates inclding these metals, resin substrates consisting of polyimide, etc., or substrates having these plates formed on the substrates, and flexible substrates such as polyimide films. As a result, the plastic optical waveguide which is free from peeling and cracking and has high reliability is provided at a high yield.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide using plastic.

[0002]

2. Description of the Related Art With the practical use of an optical communication system by developing a low loss optical fiber, development of various optical communication parts is desired. Further, it is desired to establish an optical wiring technology for mounting these optical components at a high density, particularly an optical waveguide technology. So far, silica-based materials have been mainly studied as low-loss optical waveguides. As demonstrated by optical fiber, quartz has an extremely good optical transparency, so even when used as a waveguide, the wavelength is 1.3 μm.
A low loss of 0.1 dB / cm or less has been achieved at m. On the other hand, in recent years polymethylmethacrylate (PM
MA), polystyrene (PS), polycarbonate (P
Plastic optical waveguides such as C) and polyimide (PI) are being studied. Generally, these optical waveguides have high versatility as substrates, and have good matching with semiconductor components.
A silicon substrate is used because of its excellent surface smoothness. However, the thermal expansion coefficient (about 10 ⁻⁴ to 10 ⁻⁵ ° C. ⁻¹ ) of many of these optical waveguide plastics is larger than that of silicon (2 × 10 ⁻⁶ ° C. ⁻¹ ). Therefore, in a plastic optical waveguide manufactured on a silicon substrate, especially in an optical waveguide using a highly elastic polyimide as a material, thermal distortion occurs due to heat treatment during manufacturing or temperature change after manufacturing, and peeling from the substrate or The characteristics may change. In particular, a buried type single mode optical waveguide requires a cladding layer having a sufficient thickness to reduce optical loss. Further, even in a large-diameter multimode optical waveguide, it is necessary to increase the film thickness of the optical waveguide layer as the core diameter increases. However, in the conventional method for producing a plastic optical waveguide using a silicon substrate, as the film thickness of the optical waveguide layer increases, the thermal strain due to the difference in thermal expansion coefficient also increases.
There was a limit to the film thickness.

[0003]

As described in the prior art, in the plastic optical waveguide manufactured on the silicon substrate, thermal strain may occur due to the difference in the thermal expansion coefficient between the plastic and silicon. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a plastic optical waveguide in which thermal strain caused by temperature change during or after manufacturing is reduced.

[0004]

The present invention will be described in brief. The present invention relates to a plastic optical waveguide, and in the optical waveguide using a plastic having a thermal expansion coefficient of 1 × 10 ^-5 ° C ^-1 or more, The production substrate of the optical waveguide is 1 × 10
It is characterized by having a coefficient of thermal expansion of ^-5 ° C ^-1 or more.

The present invention will be specifically described below. Examples of the structure of the plastic optical waveguide include a flat type, a slab type, a ridge type, a lens type, and a buried type.

In the present invention, a substrate having a coefficient of thermal expansion of 1 × 10 ⁻⁵ ° C. ⁻¹ or more is used as the production substrate, and such production substrate is made of aluminum, copper or the like. A metal plate with a coefficient of 1 × 10 ^-5 ℃ ^-1 or more,
And a resin substrate such as an alloy containing these or a polyimide molded product, or various substrates having a thermal expansion coefficient of 1 × 10 ^-5 ℃ ^-1
A substrate on which the above materials are formed, or a flexible printed circuit board such as a polyimide film can be exemplified. Regarding the aluminum alloy, an aluminum alloy for a magnetic disk can be used because of its easy availability and easy handling. It does not particularly care about the alloy composition. As an example of a suitable fabrication substrate,
Examples thereof include an aluminum alloy plate whose surface has been nickel-phosphorus plated and then polished, or a polyimide molded plate whose surface has been polished.

As the optical waveguide material, plastics having a coefficient of thermal expansion such as polymethylmethacrylate, polystyrene, polycarbonate, polyimide or the like of 1 × 10 ^-5 ° C ^-1 or more can be used, but polyimide is preferable from the viewpoint of heat resistance. In addition, fluorinated polyimide is preferable from the viewpoint of light transmittance. In this way, a plastic optical waveguide having a small thermal strain can be provided.

The present invention will be described in detail below with reference to the drawings. The method for manufacturing the planar plastic optical waveguide of the present invention can be realized through the steps shown in FIG. 1 as an example. In FIG. 1, reference numeral 1 is a substrate and 2 is an optical waveguide layer. After applying a resin solution or a precursor solution of a resin to be an optical waveguide layer to the substrate 1 having a thermal expansion coefficient of 1 × 10 ^-5 ° C ^-1 or more, heat treatment such as solvent removal is performed to form the optical waveguide layer 2. . The above-mentioned materials are used as the substrate material and the optical waveguide material, and a flat plastic optical waveguide having a small thermal strain can be produced on the substrate by the above operation.

Next, the method of manufacturing a slab type plastic optical waveguide according to the present invention can be realized through the steps shown in FIG. 2 as an example. In FIG. 2, reference numeral 1 is synonymous with FIG. 1, 3 is a lower clad layer, 4 is a core layer, and 5 is an upper clad layer. After coating the resin solution or the precursor solution of the resin to be the clad on the substrate 1 having a thermal expansion coefficient of 1 × 10 ⁻⁵ ° C. ⁻¹ or more, heat treatment such as solvent removal is performed to form the lower clad layer 3. Next, after coating a resin solution or a resin precursor solution for the core layer on the lower clad layer 3, heat treatment such as solvent removal is performed to form the core layer 4. After coating the resin solution for forming the clad layer again, heat treatment is performed to form the upper clad layer 5. In this way, a slab-type plastic optical waveguide with a small thermal strain can be manufactured on the substrate.

Next, the method of manufacturing the ridge type plastic optical waveguide according to the present invention can be realized through the steps shown in FIG. 3 as an example. In FIG. 3, reference numerals 1 and 2 have the same meaning as in FIG.
6 means a mask layer. Thermal expansion coefficient is 1 × 10 ^-5 ℃ ^-1
After applying a resin solution or a resin precursor solution for forming an optical waveguide layer on the above substrate, heat treatment such as solvent removal is performed to form the optical waveguide layer 2. Next, a mask layer is formed, and the mask layer 6 patterned by photolithography using a photoresist or the like is obtained. Next, this mask layer 6
Using the mask as a mask, the optical waveguide layer 2 is processed by dry etching using oxygen plasma or wet etching using an etching solution. Here, instead of using a metal mask such as aluminum as a mask for etching the optical waveguide layer 2, a silicon oxide film or an oxygen plasma resistant resist may be used. After that, the mask layer 6 is removed by peeling liquid or dry etching. In this way, a ridge type plastic optical waveguide can be manufactured on the substrate.

Further, as shown in FIG. 4, before forming the optical waveguide layer 2 in FIG. 2, after applying a resin solution or a resin precursor solution to be the lower clad, heat treatment such as desolvation is performed to remove the lower part. After forming the clad layer 3, the core layer 4 is formed, and thereafter, the same manufacturing process as that after forming the optical waveguide layer of FIG. 3 is performed to manufacture a ridge-type plastic optical waveguide having a lower clad layer on the substrate. it can. Note that each symbol in FIG. 4 has the same meaning as in FIGS. 2 and 3.

Next, the method of manufacturing the embedded plastic optical waveguide as shown in FIG. 5 according to the present invention can be realized through the following steps. In FIG. 5, reference numerals have the same meaning as in FIG. First, as described with reference to FIG. 4, a ridge-type plastic optical waveguide having a lower clad layer on a substrate is manufactured,
After coating the resin solution for forming the clad layer again, heat treatment is performed to form the upper clad layer 5. In this way, an embedded plastic optical waveguide with small thermal strain can be manufactured on the substrate.

[0013]

EXAMPLES The present invention will be described in more detail with reference to some examples. It is obvious that an unlimited number of plastic optical waveguides of the present invention can be manufactured by combining various optical waveguide materials and substrates, and the present invention is not limited to these examples. Table 1 shows the structures of the polyimides and polyimide copolymers used in this example (indicated by the acid dianhydride and diamine of their raw materials), the thermal decomposition temperature, the refractive index, and the average thermal expansion coefficient.
It was shown to.

[0014]

[Table 1]

6FDA: 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride PMDA: pyromellitic dianhydride P3FDA: trifluoromethylpyromellitic dianhydride P6FDA: 1,4- Bis (trifluoromethyl) pyromellitic dianhydride TFDB: 2,2'-bis (trifluoromethyl)-
4,4'-diaminobiphenyl 4,4'-6F: 2,2-bis (4-aminophenyl)
Hexafluoropropane DPTP: 4,4 "-diamino-p-terphenyl DMDB: 2,2'-dimethyl-4,4'-diaminobiphenyl

The thermal decomposition temperature is shown as the temperature at the time of 10 wt% weight loss when the temperature was raised at a rate of 10 ° C./min in a nitrogen stream. The refractive index is shown by a refractive index at a wavelength of 589 nm at 23 ° C. using an Abbe type refractometer. A polyimide film having an average thermal expansion coefficient of 5 mm in width and a film thickness of about 15 μm is used as a sample, and a load of 3 is applied in a nitrogen atmosphere using a thermomechanical tester.
g, tensile mode, 50 to 30 when heated at 5 ° C./min
The average value in the range of 0 ° C is shown. In Table 1, Nos. 1 and 9 to 13 are polyimides having a single composition, and Nos. 2 to 8
Is a polyimide copolymer.

Example 1 An aluminum alloy for a magnetic disk having a diameter of 3.5 inches and a thickness of 0.8 mm, whose surface was polished, was used as a substrate. , N-dimethylacetamide 15 wt% solution was applied by spin coating so that the film thickness after heating was 80 μm. This coating film was heat-treated at a maximum of 350 ° C. to form an optical waveguide layer. Finally, both ends of the optical waveguide on the substrate were cut together with the substrate with a band saw to process the input / output surface. Thus, a planar optical waveguide using polyimide on the aluminum alloy was obtained. Since this optical waveguide has a small thermal strain with the substrate, no peeling from the substrate occurred even if it was allowed to stand at room temperature for 10 days or more after fabrication.

Examples 2 to 13 Dimethylacetamide of polyamic acid, which is a precursor of the polyimide No. 1 in Table 1 used in Example 1, 15
A method similar to that of Example 1 using a 15 wt% N, N-dimethylacetamide solution of a polyamic acid, which is a precursor of a polyimide or polyimide copolymer selected from Nos. 2 to 8 in Table 1, instead of the wt% solution. Then, a planar optical waveguide using polyimide on an aluminum alloy for a magnetic disk was obtained (Table 2). Since these optical waveguides have a small thermal strain with the substrate, no peeling from the substrate occurred even when left at room temperature for 10 days or more after fabrication.

[0019]

[Table 2]

Example 14 The same as in Example 1 except that the aluminum alloy used in Example 1 was replaced by a polyimide molded plate having a diameter of 3 inches and a thickness of 10 mm [Yupimol-R, Ube Industries, Ltd.]. By the method, a planar optical waveguide using polyimide on a polyimide molded substrate was obtained (Table 2). Since these optical waveguides have a small thermal strain with the substrate, no peeling from the substrate occurred even when left at room temperature for 10 days or more after fabrication.

Example 15 An aluminum alloy for a magnetic disk having a diameter of 3.5 inches and a thickness of 0.8 mm, the surface of which was polished, was used as a substrate. , 15-wt% N-dimethylacetamide solution was applied by spin coating so that the film thickness after heating was 50 μm. This coating film was heat-treated at a maximum of 350 ° C. to form a lower clad layer. Subsequently, 15 wt% of N, N-dimethylacetamide of polyamic acid, which is a precursor of the polyimide copolymer of No. 2 in Table 1, was deposited on the lower clad layer.
The solution was applied by spin coating so that the film thickness after heating was 10 μm. This coating film was heat-treated at a maximum of 350 ° C. to form a core layer. Further, a 15 wt% solution of N, N-dimethylacetamide of polyamic acid, which is the same polyimide precursor as the lower clad layer, was applied onto this core layer by spin coating so that the film thickness after heating was 50 μm. This coating film was heat-treated at a maximum temperature of 350 ° C. to form an upper clad layer. Finally, both ends of the optical waveguide on the substrate were cut together with the substrate with a band saw to process the input / output surface.
Thus, a slab type optical waveguide using polyimide on an aluminum alloy was obtained. Since this optical waveguide has a small thermal strain with the substrate, no peeling from the substrate occurred even if it was allowed to stand at room temperature for 10 days or more after fabrication.

Examples 16 to 24 N, N-dimethylacetamide of polyamic acid, which is the precursor of the polyimide of No. 1 in Table 1 used as the lower clad layer and the upper clad layer in Example 15, 15
N, N- of polyamic acid which is a precursor of a polyimide copolymer selected from Nos. 2 to 8 in Table 1 instead of the wt% solution.
Using a 15 wt% solution of dimethylacetamide and using a 15 wt% solution of N, N-dimethylacetamide of polyamic acid, which is a precursor of the polyimide copolymer of No. 2 in Table 1 used as the core layer, the numbers 2 to 2 of Table 1 were used. A 15 wt% N, N-dimethylacetamide solution of polyamic acid, which is a precursor of a polyimide copolymer having a refractive index larger than that of the lower clad layer selected from No. 8, was applied on the aluminum alloy in the same manner as in Example 15. A slab type optical waveguide using polyimide was obtained (Table 3). Since these optical waveguides have a small thermal strain with the substrate, no peeling from the substrate occurred even when left at room temperature for 10 days or more after fabrication.

[0023]

[Table 3]

Example 25 The surface of an aluminum alloy having a diameter of 3.5 inches and a thickness of 0.8 mm was used as a substrate, and N, N-dimethyl polyamic acid, which is a precursor of polyimide No. 1 in Table 1, was placed on the substrate. The film thickness after heating the acetamide 15 wt% solution is 50μ
It was applied by a spin coating method so as to have a thickness of m. This coating film was heat-treated at a maximum of 350 ° C. to form an optical waveguide layer. Next, an aluminum layer having a film thickness of 0.3 μm was formed by an electron beam vapor deposition machine. Next, a positive photoresist was applied by spin coating and then prebaked at 95 ° C. Next, the resist was irradiated with ultraviolet rays using a photomask having a line width of 50 μm and a length of 60 mm and an ultra-high pressure mercury lamp, and then developed using a developer for a positive type resist. Next, the aluminum layer was wet-etched by using the patterned resist as a mask to pattern the aluminum. After washing and drying, the patterned aluminum was used as a mask to etch the core layer with oxygen using a parallel plate type dry etching apparatus. After the etching was completed, the aluminum remaining on the core was removed. This coating film was heat-treated at a maximum of 350 ° C. to form an optical waveguide layer. Finally, both ends of the optical waveguide were cut on the substrate together with the substrate with a band saw to process the input / output surface. In this way, a ridge type optical waveguide using polyimide on an aluminum alloy was obtained. Since this optical waveguide has a small thermal strain with the substrate, no peeling from the substrate occurred even if it was allowed to stand at room temperature for 10 days or more after fabrication.

Examples 26 to 29 Instead of the 15 wt% N, N-dimethylacetamide solution of polyamic acid, which is the precursor of the polyimide No. 1 in Table 1 used in Example 25, selected from Nos. 2 to 8 in Table 1. N, N-dimethylacetamide of polyamic acid which is a precursor of polyimide or polyimide copolymer
A ridge type optical waveguide using polyimide on an aluminum alloy was obtained in the same manner as in Example 25 using the t% solution (Table 4). Since these optical waveguides have a small thermal strain with the substrate, no peeling from the substrate occurred even when left at room temperature for 10 days or more after fabrication.

[0026]

[Table 4]

Example 30 A film after heating a 15 wt% solution of N, N-dimethylacetamide of polyamic acid, which is a precursor of the polyimide copolymer of No. 1 in Table 1, before forming an optical waveguide layer in Example 26. It was applied by spin coating so as to have a thickness of 50 μm. This coating film was heat-treated at a maximum of 350 ° C. to form a lower clad layer. A 15 wt% N, N-dimethylacetamide solution of polyamic acid, which is a precursor of the polyimide copolymer of No. 2 in Table 1, was heated to a film thickness of 1
It was applied by spin coating so as to have a thickness of 0 μm. This coating film was heat-treated at a maximum of 350 ° C. to form an optical waveguide layer. After this, the line width used in Example 26 was 50 μm.
m, line width 10μ instead of 60mm photomask
By performing the same method as in Example 26 using a photomask having a length of m and a length of 60 mm, a ridge type optical waveguide including a lower clad layer and a core layer made of polyimide on an aluminum alloy was obtained. Since these optical waveguides have a small thermal strain with the substrate, no peeling from the substrate occurred even when left at room temperature for 10 days or more after fabrication.

Examples 31-36 Table 1 used as the lower cladding layer in Example 30
In place of the N, N-dimethylacetamide 15 wt% solution of the polyamic acid that is the precursor of the polyimide of No. 1, the polyamic acid N that is the precursor of the polyimide copolymer selected from Nos. 2 to 8 of Table 1, N-dimethylacetamide 15 wt% solution was used, and instead of the N, N-dimethylacetamide 15 wt% solution of polyamic acid, which is the precursor of the polyimide copolymer of No. 2 in Table 1 used as the core layer, the number of Table 1 was used. 15 wt% of N, N-dimethylacetamide of polyamic acid, which is a precursor of a polyimide copolymer having a refractive index larger than that of the lower clad layer selected from 2 to 8
% Solution was used in the same manner as in Example 30 to obtain a ridge-type optical waveguide composed of a lower clad layer and a core layer made of polyimide on an aluminum alloy (Table 5). Since these optical waveguides have small thermal strain with the substrate,
No peeling from the substrate occurred even if left at room temperature for more than one day.

[0029]

[Table 5]

Examples 37 to 43 N, N of polyamic acid which is a precursor of the same polyimide or polyimide copolymer as the lower clad layer is formed on the ridge type optical waveguide having the lower clad layer prepared in Examples 30 to 36. A 15 wt% solution of dimethylacetamide was applied by spin coating so that the film thickness after heating was 50 μm. This coating film was heat-treated at a maximum temperature of 350 ° C. to form an upper clad layer. Finally, both ends of the optical waveguide on the substrate were cut together with the substrate with a band saw to process the input / output surface. In this way, a buried optical waveguide using polyimide on the aluminum alloy was obtained (Table 6). Since this optical waveguide has a small thermal strain with the substrate, no peeling from the substrate occurred even if it was allowed to stand at room temperature for 10 days or more after fabrication.

[0031]

[Table 6]

Comparative Example 1 Instead of the aluminum alloy used as the substrate in Example 37, a silicon substrate having a diameter of 3 inches and a thickness of 0.38 mm was used, and polyimide was used on the silicon substrate in the same manner as in Example 37. An embedded optical waveguide was produced. This optical waveguide was peeled from the substrate 10 days after completion of the production due to a large thermal strain due to the difference in thermal expansion coefficient between polyimide and silicon.

[0033]

Since the optical waveguide of the present invention can reduce the thermal strain in the plastic optical waveguide, it has an effect of providing a highly reliable plastic optical waveguide with high yield without peeling or cracking.

[Brief description of drawings]

FIG. 1 is a process drawing showing an example of a method for producing a planar plastic optical waveguide of the present invention.

FIG. 2 is a process drawing showing an example of a method for manufacturing a slab type plastic optical waveguide of the present invention.

FIG. 3 is a process drawing showing an example of a method for manufacturing a ridge-type plastic optical waveguide of the present invention.

FIG. 4 is a process drawing showing another example of the method for producing the ridge-type plastic optical waveguide of the present invention.

FIG. 5: 1 of the embedded plastic optical waveguide of the present invention
It is sectional drawing which shows the structure of an example.

[Explanation of symbols]

1: substrate, 2: optical waveguide layer, 3: lower clad layer, 4:
Core layer, 5: upper clad layer, 6: mask layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shinji Ando 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation

Claims (3)

[Claims] 1. In an optical waveguide using a plastic having a coefficient of thermal expansion of 1 × 10 ⁻⁵ ° C. ⁻¹ or more, a substrate for producing the optical waveguide has a thermal expansion coefficient of 1 × 10 ⁻⁵ ° C. ⁻¹ or more. A plastic optical waveguide characterized in that 2. The plastic optical waveguide according to claim 1, wherein the substrate for producing the optical waveguide is a metal plate or an alloy plate containing the metal. 3. The plastic optical waveguide according to claim 1, wherein the substrate for producing the optical waveguide is a resin molding plate.