JP2000056148A - Polymer optical waveguide and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polymer optical waveguide which can reduce the connection loss between an optical waveguide and an optical fiber and the light loss of the optical waveguide and has a circularly sectioned core. SOLUTION: The core 1 of the polymer optical waveguide is circularly sectioned. The polymer material is, preferably, polyimide and, more preferably, polyimide fluoride. This polymer optical waveguide can be manufactured by forming a 1st polymer optical waveguide having a semicircilarly sectioned core 1 and a 2nd polymer optical waveguide having a semicircularly sectioned core 1 and putting them so that the cores face each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polymer optical waveguide and a method for manufacturing the same, and more particularly to a polymer optical waveguide having a structure that can be easily coupled to an optical fiber and a method for manufacturing the same.

[0002]

2. Description of the Related Art With the practical use of optical communication systems by the development of 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.

In general, an optical waveguide has a small optical loss,
Easy to manufacture, can control the refractive index difference between core and clad,
Characteristics such as excellent heat resistance are required.

[0004] As a low-loss optical waveguide, a quartz-based optical waveguide is mainly studied. Quartz has a very good light transmittance as demonstrated in an optical fiber. Therefore, when applied to an optical waveguide, a low optical loss of 0.1 dB / cm or less is achieved at a wavelength of 1.3 μm.

Polymer optical waveguides such as polymethyl methacrylate have advantages in that optical loss is inferior to that of silica-based optical waveguides, but the manufacturing process is simple, and the refractive index difference between the core and the clad can be made large.

[0006] Conventionally, the cross-sectional shape of the core of a silica-based optical waveguide or a polymer optical waveguide has been a square or a rectangle due to limitations in the manufacturing process. That is, in a general method for manufacturing an optical waveguide, a concave portion for burying a core is formed by applying plasma or light through a mask, so that the cross-sectional shape of the core becomes linear.
Therefore, those skilled in the art provided a core having a square or rectangular cross-sectional shape without adding any consideration to the cross-sectional shape, as if it were conventional to assume that the cross-sectional shape of the core is square or rectangular. Optical waveguides have been used. However, the present inventor has recognized that the fact that the cross-sectional shape of the core can be only square or rectangular is a serious problem in establishing optical wiring technology for mounting optical components at high density, particularly in establishing optical waveguide technology. . This is because an optical waveguide is generally used in combination with an optical fiber.If the cross-sectional shape of the core of the optical fiber is circular while the cross-sectional shape of the core of the optical fiber is square, the coupling efficiency is reduced. Despite how to increase the connection loss (that is, how to reduce the connection loss) is a major practical problem, it is difficult to achieve good coupling efficiency. Conventionally, in order to achieve such an improvement in the coupling efficiency, the core diameter is narrowed, or a delicate adjustment is performed so that the core having a square cross section and the optical fiber having a circular cross section overlap as much as possible. There is no other choice but to adopt such a method that wastes time and money because the cross-sectional shape of the core of the conventional optical waveguide is square or rectangular.

From the viewpoint of light loss, it is considered that the cross section of the core of the optical waveguide should be circular.
The optical loss of the silica-based optical fiber is said to be 0.2 dB / km, whereas the optical loss of the silica-based optical waveguide is 0.2 dB / km.
It is said to be 01 dB / cm. Indeed, the light loss differs by three to four orders of magnitude. Even if the cross-sectional shape of the core is made circular, the light loss is not improved by three to four orders of magnitude, but some improvement in light loss can be expected.

As described above, an optical waveguide having a circular core cross-section has not been known, despite the fact that many researchers conduct research and development of optical waveguides day and night.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide a polymer optical waveguide having a circular core having a circular cross section capable of reducing the connection loss between the optical waveguide and the optical fiber and reducing the optical loss of the optical waveguide. It is an object of the present invention to provide a manufacturing method thereof.

[0010]

In order to solve the above-mentioned problems, a polymer optical waveguide according to the present invention is a polymer optical waveguide having a core and a clad made of a polymer material, and has a cross-sectional shape of the core. Is circular.

[0011] Preferably, the polymeric material is a polyimide, more preferably a fluorinated polyimide.

A method of manufacturing a polymer optical waveguide according to the present invention is a method of manufacturing a polymer optical waveguide having a core and a clad made of a polymer material, wherein the core has a semicircular first cross section. Forming a second polymer optical waveguide having a semicircular cross-sectional shape of a core; and forming a first polymer optical waveguide and a second polymer optical waveguide. And overlapping the cores so that the cores face each other.

[0013] Preferably, the polymeric material is a polyimide, more preferably a fluorinated polyimide.

Preferably, the step of superposing includes a step of thermocompression bonding the first polymer optical waveguide and the second polymer optical waveguide.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a polymer optical waveguide and a method for manufacturing the same according to the present invention will be described.

The polymer optical waveguide according to the present invention is a polymer optical waveguide having a core made of a polymer material and a clad, and the core has a circular cross section. Although there is no particular limitation on the polymer material, polymethyl methacrylate, polycarbonate, aromatic polyester, polyarylate, epoxy resin, silicone resin, acrylic resin, and their fluorinated and deuterated compounds that have been proven as optical waveguide materials Is opened. Preferably, a polymer material having excellent heat resistance is preferable, and polyimide is most preferable. Further, among polyimides, a fluorinated polyimide which is excellent in light transmittance and moisture resistance is more preferable.

The cross section of the core is preferably a perfect circle,
It may be slightly distorted, for example, elliptical. The dimensions of the core can be determined according to the application,
A diameter between a few μm and a few 100 μm is most common.

The above-structured polymer optical waveguide can be manufactured as follows. Here, a case where the polymer optical waveguide is a polyimide optical waveguide will be described.

First, a convex mold having a semicircular cross section is prepared. A polyimide precursor solution having a relatively small refractive index is uniformly applied on a substrate such as a silicon wafer by a method such as spin coating. This is heated and cured to obtain a polyimide film. Next, this polyimide film is mounted on a press capable of controlling the temperature, and is set at a temperature equal to or higher than the glass transition temperature of the polyimide film and equal to or lower than the thermal decomposition starting temperature. A convex mold having a semicircular cross section is mounted on the polyimide film, and pressure is applied at a set temperature. Next, after the press is cooled, the convex mold is removed from the polyimide film to obtain a polyimide film having a semicircular cross section. This becomes the lower cladding layer. A polyimide precursor solution having a relatively large refractive index serving as a core portion is applied thereon by spin coating or the like, and then cured by heating to obtain a polyimide film. The polyimide of the core, whose cross-sectional shape of the cladding protrudes from the semicircular portion, is removed. Reactive methods
Although there is a dry etching method such as ion etching, it is preferable to polish and remove it in order to realize a low manufacturing cost. In this way, a polyimide optical waveguide in which the core is embedded in the semicircular portion where the cladding has a semicircular cross section can be obtained. Two polyimide optical waveguides having a core embedded in a semicircular portion having a cross-sectional shape of this clad were formed, and 1
Turn the sheets upside down and adjust them so that the cores overlap, and stack the two sheets. This is mounted on a press capable of controlling the temperature, and pressure is applied at a temperature equal to or higher than the glass transition temperature of the polyimide film and equal to or lower than the thermal decomposition starting temperature. Next, after cooling the press machine,
By removing the polyimide optical waveguide from the press, the core has a circular cross section.

Hereinafter, specific examples of a polymer optical waveguide and a method of manufacturing the same according to the present invention will be described with reference to the drawings. FIG. 1 is a schematic sectional view showing an example of a polymer optical waveguide according to the present invention. FIG. 2 is a sectional view of a convex mold having a semicircular convex portion used in the method for manufacturing a polymer optical waveguide according to the present invention. further,
FIG. 3 is a cross-sectional view illustrating each step of the method for manufacturing a polymer optical waveguide according to the present invention.

The polymer optical waveguide according to the present invention is shown in FIG.
As shown in FIG. 2, a core 1 having a circular cross section and a clad 2 surrounding the core 1 are provided. A polymer optical waveguide having such a structure can be manufactured as follows.

Here, a fluorinated polyimide optical waveguide will be described. First, a lower clad layer 4 made of a polyimide film is formed on one surface of the substrate 3. That is, a fluorinated polyamic acid produced from 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride and 2,2'-bis (trifluoromethyl) -4,4'-diaminobiphenyl N, N-dimethylacetamide (hereinafter abbreviated as DMAc) solution (fixed concentration 15 wt%, viscosity 80 poise) was spin-coated on the substrate 3, and the temperature was gradually increased in an oven. For 1 hour, and the lower cladding layer 4 made of a polyimide film (low refractive index polyimide layer)
Is formed (FIG. 3A).

Next, together with the mold 10 shown in FIG. 2, the substrate 3 on which the lower clad layer 4 is laminated is mounted on a heating press machine, and the press temperature and press pressure are gradually increased. , 60 kg / cm ² . Thereafter, the heating press is cooled and the mold 10 is removed to form a lower cladding layer 4 'made of a low refractive index polyimide layer having a concave portion having a semicircular cross section (FIG. 3B).

On the lower cladding layer 4 'having a concave portion,
0.7 mol of 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride, 0.3 mol of pyromellitic dianhydride and 2,2′-bis (trifluoromethyl) -4,4 ′ -Diaminobiphenyl 1 mo
l of a DMAc solution of fluorinated polyamic acid produced from the starting monomer (fixed concentration 15 wt%, viscosity 8
(0 poise), the temperature is gradually increased in an oven, and finally heated at 350 ° C. for 1 hour to provide a core layer 5 made of a polyimide film (high-refractive-index polyimide layer) (FIG. c)).

Lower cladding layer (low refractive index polyimide layer)
Core layer (high refractive index polyimide layer) 5 laminated on 4 '
Is polished to leave a core layer portion buried in the concave portion of the lower cladding layer 4 ', thereby forming a core 1' having a semicircular cross section (FIG. 3D). In this way, a polyimide optical waveguide (first optical waveguide portion) having a core having a semicircular cross section is obtained.

Similarly, the steps of FIGS. 3A to 3D are repeated to obtain a polyimide optical waveguide (second optical waveguide portion) having a core having a semicircular cross section.

The inverted second optical waveguide portion is superimposed on the first optical waveguide portion. That is, the lower clad layer 4 'and the core 6 are overlapped so as to face each other. The superposed first and second optical waveguide portions are mounted on a heating press machine, and the press temperature and press pressure are gradually increased, and finally, 380 ° C., 60 kg / c.
and m ^2. By heating and pressing in this manner, a polyimide optical waveguide having a core 1 having a circular cross-sectional shape and a clad 2 covering the core 1 is obtained.

The core diameter of the polyimide optical waveguide having the core 1 having a circular cross section is about 8 μm. When 1.3 μm wavelength TE wave light was passed through this waveguide and the optical loss was measured, it showed good characteristics of 0.2 dB / cm. 8 × 8 using core material and clad material of the same composition
The optical loss of a polyimide optical waveguide having a μm square core is 0.4 dB / cm. In addition, when connection with a single mode optical fiber having a core diameter of 8 μm was performed, the alignment of the core was smoothly performed.

[0029]

As described above, the polymer optical waveguide and the method of manufacturing the same according to the present invention have a circular cross section, so that the optical loss is small and the coupling with the optical fiber is easy. To

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a polymer optical waveguide according to the present invention.

FIG. 2 is a cross-sectional view of a convex mold applied to the method for manufacturing a polymer optical waveguide according to the present invention.

FIG. 3 is a cross-sectional view showing each step of the method for producing a polymer optical waveguide according to the present invention.

[Explanation of symbols]

 Reference Signs List 1 core 2 clad 3 substrate 4 clad layer 5 core layer 10 mold

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Noriyoshi Yamada 1-3-1 Gotenyama, Musashino-shi, Tokyo NTT Advanced Technology Corporation (72) Inventor Fumio Yamamoto Gotenyama, Musashino-shi, Tokyo 1-Chome 1-3-3 NTT Advanced Technology Co., Ltd. F-term (reference) 2H047 AA03 EE02 EE24 EE28 GG05

Claims (7)

[Claims] 1. A polymer optical waveguide having a core and a clad made of a polymer material, wherein the core has a circular cross-sectional shape. 2. The polymer optical waveguide according to claim 1, wherein the polymer material is polyimide. 3. The polymer optical waveguide according to claim 2, wherein the polyimide is a fluorinated polyimide. 4. A method for manufacturing a polymer optical waveguide having a core and a clad made of a polymer material, comprising: forming a first polymer optical waveguide having a semicircular cross-sectional shape of the core; Forming a second polymer optical waveguide whose core has a semicircular cross-sectional shape; and setting the first polymer optical waveguide and the second polymer optical waveguide such that their cores face each other. And superposing the same. 5. The method according to claim 4, wherein the polymer material is polyimide. 6. The method according to claim 5, wherein the polyimide is a fluorinated polyimide. 7. The method according to claim 4, wherein the step of superimposing includes a step of thermocompression bonding the first polymer optical waveguide and the second polymer optical waveguide. Item 13. The method for producing a polymer optical waveguide according to item 8.