JP2001264562A - Polymer optical waveguide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polymer optical waveguide having high reliability without generating cracks even when it is used for a long time in a general environment accompanied with changes in temperature or changes in humidity. SOLUTION: The optical waveguide has a stress relief layer 12 consisting of a polymer material and a lower clad layer 13 formed on a substrate 11 and has an upper clad layer 15 which covers a core part 14 formed on the lower clad layer 13.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a highly reliable polymer optical waveguide formed by providing a lower clad layer, a core portion and an upper clad layer on a substrate, and more particularly to the field of general optics and micro optics and to the field of optical optics. The present invention relates to a polymer optical waveguide that can be used for various optical waveguide components used in the fields of communication and optical information processing.

[0002]

2. Description of the Related Art A polymer material is easy to form a thin film by a spin coating method or a dipping method, and is suitable for producing a large-area optical component. In addition, since the film does not include a high-temperature heat treatment step, an optical waveguide is formed on a substrate such as a semiconductor substrate or a plastic substrate, which is difficult to heat-treat at a high temperature, as compared with a case where an inorganic glass material such as quartz is used. There is an advantage that you can. Therefore, it is expected that optical integrated circuits and optical waveguide components used in the field of optical communication can be manufactured in large quantities and at low cost using polymer optical materials.

Conventionally, polymer optical materials have been problematic in terms of environmental resistance such as heat resistance and moisture resistance, or transparency in an optical communication wavelength band from the visible region to the near infrared region. In recent years, fluorinated polyimides (for example, refer to JP-A-4-8734) and polysilsesquioxanes (for example, JP-A-3-43423 and Electronics Letters (Electron. Lett.), Vol. 30,
No. 12, pages 958 to 959 (1994)), a polymer material having both heat resistance and transparency has been developed, and by stacking them, a practical polymer optical waveguide can be manufactured. became.

FIG. 2 is a cross-sectional view of a polymer optical waveguide having a core / cladding structure which has been generally manufactured conventionally. In FIG. 2, reference numeral 1 denotes a substrate, 2 denotes a lower cladding layer, 3 denotes a core portion, and 4 denotes an upper cladding layer. To produce an optical waveguide by laminating polymer materials,
The following methods are the most common. First, a solution of a clad material is applied on the substrate 1 by spin coating or dipping to form a film, thereby forming a lower clad layer 2 which is a polymer layer having a low refractive index. Next, a solution of a core material having a higher refractive index than that of the lower cladding layer 2 is applied on the lower cladding layer 2 by spin coating or dipping to form a high refractive index polymer layer. Form a core layer. Subsequently, this core layer is processed into a desired pattern by a fine processing technique such as photolithography and etching to form a core portion 3. Finally, on this core part 3,
A polymer optical waveguide as shown in FIG. 2 is completed by applying a solution of a clad material by spin coating or dipping to form a film and forming an upper clad layer 4.

The polymer optical waveguide component manufactured in this manner includes a branch element, a multiplexing / demultiplexing element, a thermo-optic switch,
An arrayed waveguide grating (AWG), an optical transceiver module, an optical termination unit (ONU), and the like can be given.

[0006]

The conventional polymer optical waveguide component manufactured as described above has a problem that cracks occur when used for a long time.

[0007] That is, stress is repeatedly generated and lost inside the component due to repetitive environmental changes such as a temperature cycle between a low temperature and a high temperature, and a cycle of humidity between a dry state and a wet state. The elimination and reproduction of the existing residual stress are repeated, causing a kind of fatigue in a long period of time, and there is a problem that the element is destroyed due to a crack generated when the limit is exceeded.

This problem can be solved to some extent by reducing the generated stress. For example, since the generated stress increases with the thickness of the polymer layer, reducing the thickness of the entire optical waveguide is considered as one of the solutions.

However, when fabricating an ordinary optical waveguide, it is necessary to form a thin film having a certain thickness or more. For example, a single mode optical waveguide in which the cross section of the core part 3 is a square of 8 μm square is
In the case where the lower cladding layer 2 is formed on the lower cladding layer 2 to prevent light from leaking from the core portion 3 to the silicon substrate 1,
It is necessary to have a film thickness not less than about. The upper cladding layer 4
In order to prevent the influence of dust and dirt on the surface and the stress from the outside from affecting the light guided through the core part 3,
The upper cladding layer 4 needs to have a thickness of about 8 μm or more from the upper surface of the core portion 3. For this reason, there is a limit to solving the problem of crack generation only by thinning.

[0010] The present invention has been made in view of the above,
Its purpose is that it does not crack even if used for a long time in a general environment with temperature change and humidity change,
An object of the present invention is to provide a polymer optical waveguide having high reliability.

[0011]

According to a first aspect of the present invention, there is provided a polymer optical waveguide having a lower clad layer, a core portion and an upper clad layer provided on a substrate. Thus, the gist is that a stress relaxation layer is provided between the substrate and the lower cladding layer.

According to the first aspect of the present invention, unlike a conventional polymer optical waveguide in which a lower clad layer is directly provided on a substrate, a stress relaxation layer is provided between the substrate and the lower clad layer. Therefore, even if used for a long period of time in an environment with fluctuations in temperature and humidity, the performance is not significantly deteriorated and cracks do not occur.

[0013] The present invention described in claim 2 provides the present invention in claim 1.
In the invention described above, the gist is that the stress relaxation layer is made of a polymer material having rubber elasticity.

According to the second aspect of the present invention, since the stress relaxation layer is made of a polymer material having rubber elasticity, the stress generated by fluctuations in temperature and humidity is absorbed by the rubber elasticity of the polymer material. However, this makes it possible to avoid the occurrence of cracks and to manufacture a highly reliable polymer optical waveguide.

Further, the present invention described in claim 3 provides the invention according to claim 1.
In the invention described above, the gist is that the lower clad layer, the core portion, and the upper clad layer are each made of polyimide, silicon, or epoxy resin.

According to the present invention, the lower cladding layer, the core portion and the upper cladding layer are each made of polyimide, silicon or epoxy resin.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view schematically showing a structure of a polymer optical waveguide according to an embodiment of the present invention. The polymer optical waveguide shown in FIG. 1 includes a stress relaxation layer 12 made of a polymer material and a lower
And an upper clad layer 15 covering the core portion 14 formed thereon. That is, the polymer optical waveguide of the present embodiment differs from the conventional polymer optical waveguide in which the lower cladding layer is formed directly on the substrate as shown in FIG. In which a stress relaxation layer 12 is formed.

The substrate 11 on which the stress relaxation layer 12 is formed is not particularly limited as long as it has a smooth surface. For example, a silicon wafer, quartz glass,
Multicomponent glass, ceramics, metal plates, minerals, combinations of these materials, and the like can be used.

The stress relaxation layer 12 formed thereon is a polymer that exhibits rubber elasticity in the operating temperature range of the device and can be formed into a smooth film by a method such as spin coating, dipping, or spraying. Although not particularly limited, for example, block copolymers such as styrene-butadiene and styrene-isobutylene, hydrogenated products thereof, ABA-type block copolymers such as styrene-butadiene-styrene and styrene-isoprene-styrene, hydrogenated products thereof and the like Styrene-based thermoplastic elastomer, olefin-based thermoplastic elastomer composed of polypropylene-ethylene propylene rubber, PVC-based thermoplastic elastomer composed of crystalline polyvinyl chloride-amorphous polyvinyl chloride, other, ester-based, urethane-based,
An amide-based or imide-based thermoplastic elastomer or the like, and those further modified by graft polymerization, thermosetting silicone rubber or silicone elastomer, room temperature curing silicone rubber or silicone elastomer, etc. can be used.

The stress relaxation layer 12 is formed, for example, by applying a solution or a stock solution containing these materials or precursors to the substrate 11.
It can be formed by a method such as spin-coating and then heating and drying, or immersing the substrate 11 in the solution and then heating and drying. Heating may not be required depending on the material. That is, the method of forming the stress relaxation layer in the present invention is not limited.

The lower cladding layer 13 formed on these
The polymer material for use is not particularly limited as long as it has a lower refractive index than the polymer material to be used for the core portion 14 described below, but anhydrides of aromatic dibasic acids and their partial fluorines Acid anhydrides such as chlorides or perfluorides;
Aromatic diamines, polyimide intermediates, fluorinated polyimide intermediates obtained by reacting partially fluorinated or fully fluorinated compounds thereof at an appropriate mixing ratio, or phenyltrichlorosilane, diphenyldichlorosilane, methyltrichlorosilane, dimethyldiamine Siloxane-based oligomers, high-molecular-weight substances, photocurable resins, and the like, which can be obtained by using chlorosilanes, their deuterated products, their corresponding alkoxides, and mixtures thereof in various ratios as starting materials, can be used.

Lower cladding layer 13 on stress relaxation layer 12
For example, the solution containing the polymer material for the lower cladding layer 13 is spin-coated on a substrate and then dried by heating, or the substrate is immersed in the solution, dried by heating, or applied, and then irradiated with ultraviolet rays. Such a method can be used. When a silicon-based material is used as the stress relaxation layer 12, the surface of the stress relaxation layer 12 is subjected to corona discharge treatment, plasma treatment, silane coupling, in order to improve the adhesion between the stress relaxation layer 12 and the lower cladding layer 13. A surface treatment using an agent may be performed. That is, the method of forming the lower cladding layer 13 in the present invention is not limited. Lower cladding layer 13 formed on stress relaxation layer 12
May be a single composition or a mixture of a plurality of polymer materials.

A core layer is formed on lower clad layer 13 formed by the above method. The polymer material necessary for forming the core layer is not particularly limited as long as it has a higher refractive index than the lower cladding layer 13 described above. For example, the fluorinated polyimide used for the lower cladding layer is used. For example, fluorinated polyimides having a lower fluorine content than those of the lower cladding layer, and siloxane-based materials having a lower phenyl and higher methyl content than the siloxane-based material used for the lower cladding layer 13 can be used. The composition of the core layer may be a single material or a mixture of a plurality of materials.

The formation of the core layer can be carried out by spin coating or immersion in a solution, followed by drying by heating or irradiation with ultraviolet rays, as in the case of the lower cladding layer 13. The formed core layer is processed into a desired core shape using a conventional photolithography technique, and the core portion 14 is formed. When a photocurable resin is used, direct patterning is possible by using a pattern mask.

The upper cladding layer 15 formed on these
The polymer material for use is not particularly limited as long as it has a lower refractive index than the polymer material used for the above-described core portion 14, but it is preferable to use the same material as the lower cladding layer 13. The upper cladding layer 15 is, for example, spin-coated with a solution containing a polymer material for the upper cladding layer and then dried, or is immersed in the solution and dried, or is coated and irradiated with ultraviolet light. And the lower clad layer 13 and the core layer. That is, the method for forming the upper cladding layer 15 is not limited in the present invention. The formed upper cladding layer 15 may be a single composition or a mixture of a plurality of materials.

Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.

Example 1 A polyimide material, a clad material,
A polymer optical waveguide using a silicon-based material as a core material was manufactured. First, a polyimide paste SN-9000 manufactured by Hitachi Chemical Co., Ltd. was dissolved in γ-butyrolactone as a stress relaxation layer material, and a predetermined amount of a curing agent was added (solution A).
Next, as a cladding material solution, deuterated phenyltriethoxysilane and deuterated methyltriethoxysilane were dissolved in ethanol in a molar ratio of 50:50, and polycondensation was performed using an acid catalyst. Was converted to methyl isobutyl ketone to prepare a solution (solution B). Similarly, a core material solution was prepared from a raw material in which deuterated phenyltriethoxysilane and deuterated methyltriethoxysilane were mixed at a molar ratio of 55:45 (solution C).

A solution A of a stress relaxation layer material is spin-coated on a silicon substrate so that the film thickness after curing becomes 3 μm,
It was kept at room temperature for 24 hours to cure. Next, the clad material solution B was spin-coated thereon so that the film thickness after curing became 15 μm, and cured by heating at 250 ° C. for 1 hour. A core material solution C is applied thereon, and a film is formed under the same conditions to form a core material layer having a thickness of 8 μm. After that, the core portion is formed into a length of 50 mm and a width of 8 μm by ordinary fine processing using photolithography technology. And a straight rectangular pattern having a height of 8 μm. On this, the same clad material solution B as before
Was applied and cured by heating under the same conditions.

When a light having a wavelength of 1550 nm was made incident from one end of the polymer optical waveguide obtained as described above and the amount of light emitted from the other end was measured, the loss of the waveguide was measured. It was about 0.3 dB / cm. This polymer optical waveguide is placed in a thermo-hygrostat at 85 ° C. and 85% RH.
Even after holding for 000 hours, no crack generation or increase in waveguide loss was observed. The same applies when the temperature cycle between −40 ° C. and 75 ° C. is repeated 300 times.

COMPARATIVE EXAMPLE 1 A polymer optical waveguide in which the stress relaxation layer was not formed in Example 1 was manufactured and subjected to a constant-temperature and constant-humidity test at 85 ° C. and 85% RH. Was done. In the temperature cycle test between −40 ° C. and 75 ° C., cracks occurred within 10 cycles.

Example 2 A polymer optical waveguide using a polyimide-based material as a stress relaxation layer, a cladding material, and a core material was manufactured. First, polyimide paste SN manufactured by Hitachi Chemical Co., Ltd. was used as a stress relaxation layer material.
-9000 was dissolved in γ-butyrolactone, and a predetermined amount of a curing agent was added (solution D). Next, as a cladding material solution, 2,2′-bis (3,4-dicarboxyphenyl)
Equivalent mixture of hexafluoropropanoic acid dianhydride and 2,2'-bis (trifluoromethyl) -4,4'-diaminobiphenyl is dissolved in N, N-dimethylacetamide so as to have a solid concentration of 15% by weight. A solution was prepared (solution E). Further, as the core material solution, pyromellitic dianhydride, 2,2′-bis (3,4-dicarboxyphenyl) hexafluoropropanoic dianhydride and 2,2 ′
A solution was prepared by dissolving -bis (trifluoromethyl) -4,4'-diaminobiphenyl in N, N-dimethylacetamide at a molar ratio of 3: 7: 10 and a solid concentration of 15 wt%. (Solution F).

A solution D of a stress relaxation layer material is spin-coated on a silicon substrate so that the film thickness after curing becomes 3 μm.
It was cured by heating at 150 ° C. for 1 hour. Next, the clad material solution E was spin-coated thereon so that the film thickness after curing became 15 μm, and was cured by heating at 350 ° C. for 1 hour. A film was formed on this under the same conditions using the core material solution F, and after forming a core material layer having a thickness of 8 μm, the core portion was formed into a 50 mm long, 8 μm wide, by ordinary fine processing using photolithography technology. It was processed into a linear rectangular pattern having a height of 8 μm. On this, the same clad material solution E as before
Was applied and cured by heating under the same conditions.

When a light having a wavelength of 1550 nm was made incident from one end of the thus obtained polymer optical waveguide and the amount of light emitted from the other end was measured, the loss of the waveguide was measured. It was about 0.3 dB / cm. This polymer optical waveguide is placed in a thermo-hygrostat at 85 ° C. and 85% RH.
Even after holding for 000 hours, no crack generation or increase in waveguide loss was observed. The same applies when the temperature cycle between −40 ° C. and 75 ° C. is repeated 300 times.

Comparative Example 2 A polymer optical waveguide in which the stress relaxation layer was not formed in Example 2 was manufactured and subjected to a constant temperature and constant humidity test at 85 ° C. and 85% RH. As a result, cracks were observed within 100 hours. Was done. In the temperature cycle test between −40 ° C. and 75 ° C., cracks occurred within 10 cycles.

Example 3 A polymer optical waveguide using a silicon-based material as a stress relaxation layer, a cladding material, and a core material was manufactured. First, a room temperature-curable silicon material Silpot 184 manufactured by Shin-Etsu Chemical Co., Ltd. as a stress relaxation layer material was dissolved in diglyme, and a predetermined amount of a curing agent was added (solution G). Next, as a clad material solution,
Phenyltriethoxysilane and methyltriethoxysilane were dissolved in ethanol at a molar ratio of 60:40 to carry out polycondensation using an acid catalyst, and then a solution was prepared in which the solvent was converted to methyl isobutyl ketone (solution H). ).
Similarly, a core material solution was prepared from a raw material in which phenyltriethoxysilane and methyltriethoxysilane were mixed at a molar ratio of 65:35 (solution I).

A solution G of a stress relaxation layer material is spin-coated on a silicon substrate so that the film thickness after curing becomes 3 μm.
It was kept at room temperature for 24 hours to cure. Next, the surface of the stress relaxation layer was subjected to a corona discharge treatment, and a clad material solution H was spin-coated thereon so as to have a cured film thickness of 15 μm, and was cured by heating at 250 ° C. for 1 hour. A core material solution I was applied thereon, and a film was formed under the same conditions to form a core material layer having a thickness of 8 μm. After that, the core portion was formed into a 50 μm long and 8 μm wide by ordinary fine processing using photolithography technology. And a straight rectangular pattern having a height of 8 μm. The same clad material solution H as above was applied on top of it and cured by heating under the same conditions.

When a light having a wavelength of 1550 nm was made incident from one end of the polymer optical waveguide thus obtained, and the amount of light emitted from the other end was measured, the loss of the waveguide was measured. It was about 0.5 dB / cm. This polymer optical waveguide is placed in a thermo-hygrostat at 85 ° C. and 85% RH.
Even after holding for 000 hours, no crack generation or increase in waveguide loss was observed. The same applies when the temperature cycle between −40 ° C. and 75 ° C. is repeated 300 times.

Comparative Example 3 A polymer optical waveguide in which the stress relaxation layer was not formed in Example 3 was manufactured and subjected to a constant temperature and constant humidity test of 85 ° C. and 85% RH. As a result, cracks were observed within 100 hours. Was done. In the temperature cycle test between −40 ° C. and 75 ° C., cracks occurred within 10 cycles.

Example 4 A polymer optical waveguide was manufactured using a silicon-based material as a stress relaxation layer, a clad material, and an epoxy-based material as a core material. First, two liquids of a silicon material SE1821 made by Toray Dow Corning Silicon as a stress relaxation layer material were mixed at a predetermined ratio (material J). Next, as a clad material solution, a UV curable resin (material K) having a refractive index after photo-curing of 1.52 at a wavelength of 850 nm and U having a refractive index of 1.54 at the same wavelength
A V-cured resin (material L) was prepared.

A stress relaxation layer material J is spin-coated on a silicon substrate so as to have a thickness of 3 μm after curing.
Cured by heating at ℃ for 1 hour. Next, the surface of the stress relaxation layer was subjected to a corona discharge treatment, and a clad material K was spin-coated thereon so as to have a cured film thickness of 15 μm, and was cured by irradiating the entire surface with ultraviolet rays. A core material L is coated thereon, irradiated with ultraviolet light through a pattern mask provided via a spacer, and then developed using a diglyme solvent to form a linear rectangular core having a length of 50 mm, a width of 8 μm, and a height of 8 μm. Part was produced. The same clad material K as above was applied thereon and cured under the same conditions.

When a light having a wavelength of 850 nm was made incident from one end of the polymer optical waveguide thus obtained and the amount of light emitted from the other end was measured, the loss of the waveguide was measured. It was about 0.5 dB / cm. This polymer optical waveguide is placed in a thermo-hygrostat at 85 ° C. and 85% RH for 10 minutes.
Even after holding for 00 hours, no crack generation or increase in waveguide loss was observed. The same applies when the temperature cycle between −40 ° C. and 75 ° C. is repeated 300 times.

Comparative Example 4 A polymer optical waveguide in which the formation of the stress relaxation layer in Example 4 was omitted was manufactured and subjected to a constant temperature and humidity test at 85 ° C. and 85% RH. As a result, cracks were observed within 100 hours. Was done. In the temperature cycle test between −40 ° C. and 75 ° C., cracks occurred within 10 cycles.

As described in each of the above-described embodiments, the polymer optical waveguide of the present embodiment reliably avoids the occurrence of cracks. Because the lower cladding layer made of a polymer material that has a large expansion and contraction due to heat, easily expands due to moisture, or undergoes a large volume change during film formation, is directly formed on a substrate that has a small expansion and contraction due to In the present embodiment, a crack is generated in a part of the polymer material due to repeated generation and disappearance of stress due to a difference in expansion and contraction between the substrate and the polymer material. This is because cracks are avoided by absorbing stress in the layer of the polymer material exhibiting rubber elasticity.

[0044]

As described above, according to the present invention,
Unlike a conventional polymer optical waveguide in which a lower cladding layer is directly provided on a substrate, a stress relaxation layer is provided between the substrate and the lower cladding layer. It absorbs the generated stress, and thus does not crack even when used for a long period of time in an environment where the temperature and humidity fluctuate, so that the performance degradation is extremely small. For this reason, by using the polymer optical waveguide of the present invention for an optical waveguide component, it is expected that the reliability of various optical waveguide components used in the fields of optical communication and optical information processing will be dramatically improved.

Further, according to the present invention, since the stress relieving layer is made of a polymer material having rubber elasticity, the stress generated by fluctuations in temperature and humidity is absorbed by the rubber elasticity of the polymer material.
Thereby, generation of cracks can be avoided, and a highly reliable polymer optical waveguide can be manufactured.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing a structure of a polymer optical waveguide according to one embodiment of the present invention.

FIG. 2 is a cross-sectional view schematically showing a structure of a conventional polymer optical waveguide.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Substrate 12 Stress relaxation layer 13 Lower cladding layer 14 Core part 15 Upper cladding layer

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Seiji Toyoda 2-3-1 Otemachi, Chiyoda-ku, Tokyo Within Nippon Telegraph and Telephone Corporation (72) Inventor Toshio Watanabe 2--3, Otemachi, Chiyoda-ku, Tokyo No. 1 Within Nippon Telegraph and Telephone Corporation (72) Inventor Akira Tomaru 2-3-1 Otemachi, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Inventor Yujiro Kato Otemachi, Chiyoda-ku, Tokyo Chome 3-1, Nippon Telegraph and Telephone Corporation (72) Inventor Toru Maruno 2-3-1, Otemachi, Chiyoda-ku, Tokyo F-Term within Nippon Telegraph and Telephone Corporation 2H047 KA04 QA05

Claims (3)

[Claims] 1. A polymer optical waveguide comprising a substrate and a lower cladding layer, a core portion and an upper cladding layer, wherein a stress relaxation layer is provided between the substrate and the lower cladding layer. Characteristic polymer optical waveguide. 2. The polymer optical waveguide according to claim 1, wherein the stress relaxation layer is made of a polymer material having rubber elasticity. 3. The polymer optical waveguide according to claim 1, wherein the lower cladding layer, the core portion, and the upper cladding layer are made of polyimide, silicon, or epoxy resin, respectively.