JP2847171B2 - Optical waveguide using perfluoro organic polymer material - Google Patents

Description

The present invention relates to an optical waveguide, and more particularly to a plastic optical waveguide that can be used as a circuit component in an optoelectronic integrated circuit (OEIC).

[Conventional technology]

Organic polymer materials (plastics) are lighter than inorganic materials, have excellent impact resistance, workability, and are easy to handle. It has been used for various optical applications such as substrates for optical and optical lenses. Among them, those having high transparency in the visible region (wavelength = 0.4 to 0.8 μm) such as polymethyl methacrylate (PMMA) and polystyrene (PS) have been mainly used as plastic optical materials.

On the other hand, with the practical use of optical communication systems due to the development of silica-based low-loss optical fibers, development of various optical communication components has been desired. It is also desired to establish an optical wiring technology for mounting these optical components at a high density, particularly an optical waveguide technology.

When plastic is used as an optical material in the near-infrared region (0.8 to 2.0 μm) such as an optical waveguide in OEIC, the first problem is a large light loss as compared with inorganic materials. There are two main causes of loss in plastics: light scattering and light absorption. Wavelengths used for optical communication will shift to longer wavelengths in the future (0.85 μm to 1.3 μm
It is thought that the latter cause, ie, the loss due to vibrational absorption, which is essential to the molecular structure, becomes dominant according to (up to 1.65 μm), and greatly imposes restrictions on the light-guiding properties of plastics. In particular, conventional plastics represented by PMMA and PS exhibit high light-guiding characteristics in the visible region, but cause a large light transmission loss (1 dB / cm or more) in the near-infrared region. This is because the harmonics of the carbon-hydrogen bond (CH bond) of the alkyl group or the phenyl group in the molecular chain exist in this wavelength range, but the fundamental vibration of the CH bond originally shifts to the lower wavelength side. The fact that the absorption intensity of those harmonics is hardly attenuated even when the order is high is a major cause of large optical loss.
In order to reduce the harmonic absorption due to the C—H bond and shift the absorption wavelength to longer wavelengths, it is necessary to replace hydrogen in the molecular chain with deuterium (D) or fluorine (F). Proposals have already been made on materials in which hydrogen in PMMA or PS has been replaced with deuterium or fluorine [for example, Toshikuni Kaino, Appl. Phys. (1986)
reference〕. Previous studies have shown that these plastics show good light-guiding properties in the near-infrared region.For example, fluorination and deuteration of PS have achieved a low loss of less than 0.04 dB / cm. Have been.

The next issue in applying plastic to OEIC optical waveguides is hygroscopicity. Many plastics have higher hygroscopicity than inorganic materials, and the adsorbed moisture has a large absorption peak in the near infrared region. Therefore, the plastic used for the optical waveguide must have low hygroscopicity. As described above, the light-guiding properties in the near-infrared region are significantly improved by deuterium substitution, but since they hardly affect the chemical properties of the material, for example, deuterated PMMA
The light-guiding properties of the chromium are greatly degraded by the absorption of moisture over time [for example, T. Kaino, Applied Optics, Appl. Opt. 24, 4192 (1985)]
reference〕.

[Problems to be solved by the invention]

That is, when plastic is applied to an optical waveguide for OEIC in the near-infrared region, there is a problem that a large light loss based on the existence of C—H bond and a temporal increase of the light loss due to moisture absorption. The present invention has been made in view of such circumstances, and an object of the present invention is to provide a plastic optical waveguide having very low light loss in the near infrared region and low hygroscopicity.

[Means for solving the problem]

In general, the present invention relates to an optical waveguide using a perfluoroorganic polymer material.In an optical waveguide having a core and a clad as main components, a carbon-carbon single bond and a carbon Characterized in that the core is an amorphous organic polymer material having a cyclic structure composed of an oxygen single bond and containing only carbon-fluorine engagement as a chemical bond between carbon and a monovalent element.

The present invention relates to an optical waveguide using a perfluoro organic polymer material, and uses an amorphous plastic containing only a carbon-fluorine bond as a chemical bond between carbon and a monovalent element in a molecular structure to form a core layer of the optical waveguide. It is characterized by using.

The present inventors measured the absorption spectra of various existing plastic optical materials in the infrared and near-infrared regions, calculated the light loss value in the near-infrared region, and studied the causes thereof. As a result, the first factors that cause a large light loss in the near infrared region are harmonic absorption of stretching vibration of C—H bond in an alkyl group or a phenyl ring, and C absorption.
It became clear that the harmonics of the stretching vibration of the -H bond and the bending vibration were absorbed by the combined sound.

Further, since fluorine atoms have high water repellency, it is known that plastics containing a certain amount of fluorine or more show a very low moisture absorption rate. Therefore, it is considered that the moisture absorption rate can be reduced by replacing hydrogen in the molecular structure with fluorine, and the temporal change in the light guide characteristic in the near-infrared region can be suppressed to a very low level.

That is, all 1's bonded to carbon such as alkyl groups
By using fluorine as the valence element, it is possible to solve both the vibration absorption based on the C—H bond, which is the largest light loss cause, and the temporal change of the light guide characteristic due to moisture absorption.

Further, by eliminating the symmetry in the molecular structure of the plastic and by making it highly amorphous, light scattering due to orientation birefringence can be suppressed. The present inventors examined the degree of crystallinity of various perfluoroplastics, and found that a cyclic ether structure, that is, a cyclic structure composed of a carbon-carbon single bond and a carbon-oxygen single bond, was included in the main chain structure of the polymer. It has been found that the plastic has a particularly high amorphous property and a very low birefringence.

However, as the fluorine-containing plastic used for the optical waveguide of the present invention, any amorphous plastic having no C—H bond in the molecule and containing only a carbon-fluorine bond as a chemical bond between carbon and a monovalent element can be used. Can be used.

Hereinafter, the plastic optical waveguide of the present invention will be described in more detail.

The structure of the optical waveguide of the present invention may be the same as that of all optical waveguides generally manufactured, and for example, a fiber type, a planar type, a ridge type, a lens type, a buried type, and the like are possible. The manufacturing method of the ridge type shown in the embodiment is described in Japanese Patent Application No. 2-110500. The method for producing polyimide shown in Comparative Examples is described in Japanese Patent Application No. 1-1201170.

Examples of the amorphous organic polymer material used in the present invention include the following structural formula I or II: And an organic polymer material having a repeating unit represented by the following formula:

〔Example〕

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

In the following examples, the wavelength dependence (spectrum) of the light transmission loss of the optical waveguide is measured by a spectrum analyzer using a white light source, and the light transmission loss value at λ = 1.3 μm is the light incident on the film via the prism. Was calculated again by a method of taking out with a prism.

Example 1 A polyperfluoroallyl vinyl ether having a repeating structure of the formula I was converted to a perfluoro organic solvent (CT-solv 180,
(Asahi Glass Co., Ltd.) so as to have a concentration of 10%, spin-coated on a silicon plate, and heated at 40 ° C. for 1 hour, 100 ° C. for 1 hour, and 180 ° C. for 1 hour under a nitrogen atmosphere to remove the solvent Removed completely.

Aluminum was deposited on the entire surface of the sample as an etching mask. Next, coating, pre-baking, exposure, development, and post-baking of a positive resist were performed, and aluminum was patterned by wet etching. Further, using this aluminum as a mask, a polyperfluoroallyl vinyl ether film was patterned by dry etching. Finally, the remaining aluminum mask was removed by wet etching, and the width was 50 μm and the height was 10 μm.
A ridge type optical waveguide having a length of 5 μm and a length of 5 cm was obtained. When the wavelength dependence of the light transmission loss of this optical waveguide was measured in the range of 0.8 μm to 1.7 μm, no light absorbing peak appeared in all wavelength ranges as shown in FIG. In FIG. 1, the horizontal axis represents wavelength (μm), and the vertical axis represents absorbance.

The light transmission loss rate at 1.3 μm is 0.1 dB / cm or less, and shows sufficiently low light loss values in all three wavelength bands of 1.3, 1.55, and 1.65 to be used for optical communication.
No change in weight was observed after immersing this polyperfluoroallyl vinyl ether film in water at 60 ° C. for one week, and no change was observed in the wavelength dependence of light transmission loss of an optical waveguide made from this film. Was.

Example 2 Instead of the polyperfluoroallyl vinyl ether in Example 1, a perfluoropolymer having a repeating structure of the formula II (bis-2,2-trifluoromethyl-4,5-difluoro-1,3-dioxole and tetrafluoro 50 μm in width and height in the same manner as in Example 1 using a copolymer with ethylene).
A 10 μm-length, 5 cm long optical waveguide was obtained.

The wavelength dependence of the light transmission loss of this optical waveguide is 0.8 μm
When measured in the range of 1.7 μm, no light-absorbing peak appeared in all wavelength ranges as in Example 1. No change in weight was observed after immersing the film in water at 60 ° C. for one week, and no change was observed in the wavelength dependence of the light transmission loss of the optical waveguide made from the film.

Comparative Example 1 Polycarbonate having the following structure Was dissolved in dimethylacetamide to a concentration of 10%, and spin-coated on a silicon plate. Then, the mixture was heated at 70 ° C. for 3 hours in a nitrogen atmosphere to completely remove the solvent, thereby obtaining a film. The width of this film is determined in the same manner as in Example 1.
A ridge-type optical waveguide having a size of 50 μm, a height of 10 μm, and a length of 3 cm was prepared, and the wavelength dependence of light transmission loss was measured in the range of 0.8 μm to 1.7 μm. The results are shown in FIG. 2 as a graph of the relationship between wavelength (μm, horizontal axis) and absorbance (vertical axis).

The light transmission loss rate at 1.3 μm was 0.4 dB / cm. This material is already used as an optical material in the visible light range, but as shown in FIG.
2. At each wavelength of 1.4 to 1.65 μm, harmonic of stretching vibration of C—H bond, stretching vibration harmonic of C—H bond and C
A coupled sound of the -H coupled bending vibration appears. The 1.65 μm band to be used for optical communication in the future completely overlaps the second harmonic absorption of C—H coupling, and is 1.3 μm, 1.55 μm
Although the band is located in the "window" where light loss is relatively small, since the above-mentioned large vibration absorption hem is applied,
The light loss value cannot be said to be sufficiently small.

Comparative Example 2 N-polyamide acid synthesized from 2,2- (34-dicarboxyphenyl) -hexafluoropropane dianhydride and 2,2'-bis (trifluoromethyl) -4,4'-diaminobiphenyl A methyl-2-pyrrolidone solution was spin-coated on a silicon plate, and the solution was stirred at 70 ° C. for 2 hours under a nitrogen atmosphere.
Heating was carried out at 0 ° C. for 1 hour, at 250 ° C. for 30 minutes, and at 350 ° C. for 1 hour to completely imidize, thereby obtaining a polyimide film having the following structure.

A ridge-type optical waveguide having an axis of 50 μm, a height of 10 μm, and a length of 5 cm was prepared from the polyimide film in the same manner as in Example 1, and the absorption spectrum measured at 0.8 μm to 1.7 μm was shown in FIG. (Μm, horizontal axis) and absorbance (vertical axis) as a graph.

The light transmission loss rate at 1.3 μm was 0.3 dB / cm. This material is a polyimide having a higher light transmittance in the near-infrared region than the conventional polyimide, and is promising as an optical material. However, as shown in FIG. Harmonics of stretching vibration of H bond,
The combined sound of the stretching vibration harmonic of the C—H bond and the bending vibration of the C—H bond, and the harmonic of the oxygen-hydrogen bond (O—H bond) caused by the moisture contained in the film slightly appear. I have. In particular, the 1.65 μm band overlaps the second harmonic absorption of the C—H bond, and the light loss value in this wavelength region is as large as about 5 dB / cm.

〔The invention's effect〕

As described above in detail, an optical waveguide manufactured using an amorphous plastic containing only a carbon-fluorine bond as a chemical bond between carbon and a monovalent element in a molecular structure as a core has a near-infrared light range. Absorption peak is absent and has very low moisture absorption. ADVANTAGE OF THE INVENTION According to this invention, the novel optical waveguide excellent in both the light transmittance of near infrared region and moisture absorption resistance is provided.

[Brief description of the drawings]

FIG. 1 is a graph showing an example of an optical waveguide according to the present invention, and FIGS. 2 and 3 are graphs showing wavelength dependence of light transmission loss in an optical waveguide of a conventional example.

────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Toru Matsuura 1-6, Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (56) References JP-A-63-261204 (JP, A) (58) Field surveyed (Int.Cl. ⁶ , DB name) G02B 6/12

Claims (3)

(57) [Claims] An optical waveguide having a core and a clad as main constituents, wherein the molecular structure has a cyclic structure comprising a carbon-carbon single bond and a carbon-oxygen single bond, and a chemical bond between carbon and a monovalent element. An optical waveguide using a perfluoro organic polymer material characterized by having a core made of a non-quality organic polymer material containing only a carbon-fluorine bond. 2. The following structural formula I: The optical waveguide using a perfluoro organic polymer material according to claim 1, wherein the core is an organic polymer material having a repeating unit represented by the following formula. 3. The following structural formula II: The optical waveguide using a perfluoro organic polymer material according to claim 1, wherein the core is an organic polymer material having a repeating unit represented by the following formula.