JP2001033640A - Optical waveguide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical waveguide formed of an organic optical material excellent in moisture resistance reliability in which the increase in propagation loss of light or the deterioration of characteristics under high humidity environment is restrained by covering the exposed surface of a clad part with an amorphous fluororesin layer. SOLUTION: An optical waveguide to be formed on a substrate 1 is a three- dimensional waveguide-shaped optical waveguide comprising a clad part 5 formed of an organic optical material consisting of a lower clad layer 2 and an upper clad layer 4, and a core part 3 formed of an organic optical material having a refractive index larger than this clad part 5. An amorphous fluorine resin layer 6 is formed so as to cover the exposed surface of the clad part 5 or the upper clad layer 4. As the fluorine resin usable for the amorphous fluorine resin layer 6, cyclized polyfluoride ethylene resin, polytetrafluoroethylene, and tetrafluoroethylene-hexafluoropropylene copolymer are preferably used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide used for an optical communication module or the like, and more particularly, to an optical waveguide which suppresses an increase in light propagation loss and deterioration of characteristics in a high humidity environment.
The present invention relates to an optical waveguide having excellent moisture resistance reliability.

[0002]

2. Description of the Related Art Conventionally, as an optical waveguide, for example, a quartz-based optical waveguide in which a three-dimensional clad and a core portion are formed by using a quartz film formed by a flame deposition method on a quartz glass substrate or a silicon substrate is used. There is an example in which a lithium niobate single crystal substrate is used as a clad portion, and titanium is thermally diffused on the substrate to form a core portion in a three-dimensional waveguide shape.

However, since these optical waveguides require a high-temperature heat treatment of 1000 ° C. or more to produce them, from the viewpoint of easy production of optical waveguides, these conventional quartz-based optical waveguides that require high-temperature treatment during production are required. Instead of the optical waveguide, an optical waveguide made of an organic optical material that can be formed at a low temperature has been studied. Examples of the organic optical material used for this optical waveguide include PMMA (polymethyl methacrylate), polycarbonate, polyimide, polysiloxane, and BC.
B (benzocyclobutene) and fluororesin are being studied.

In manufacturing an optical waveguide using these organic optical materials, a lower cladding layer is formed on a silicon substrate or a glass substrate, and a core layer having a higher refractive index than the lower cladding layer is formed thereon. Next, the core layer is processed by RIE (reactive ion etching) or the like using a thin film microfabrication technique to form a core portion, and then the upper clad layer having a lower refractive index than the core portion is covered. 2. Description of the Related Art A three-dimensional optical waveguide having a core portion formed in a clad portion formed thereon has been formed.

[0005]

However, an optical waveguide made of an organic optical material is more likely to absorb moisture than an optical waveguide using a quartz optical waveguide or a lithium niobate single crystal substrate. Since the refractive index changes and the propagation loss of light increases, there has been a problem in that long-term reliability is poor not only in a high humidity environment but also in a low humidity environment.

The present invention has been devised in view of the above-mentioned problems of the prior art, and has as its object to improve the moisture resistance reliability in which an increase in light propagation loss and deterioration of characteristics in a high humidity environment are suppressed. An object of the present invention is to provide an optical waveguide made of an excellent organic optical material.

[0007]

According to the optical waveguide of the present invention, a core made of an organic optical material having a higher refractive index than that of the clad is formed in a clad made of an organic optical material formed on a substrate. And the exposed surface of the cladding is covered with an amorphous fluororesin layer.

In the optical waveguide according to the present invention, the cladding and the core are made of a siloxane-based polymer in the above structure.

According to the optical waveguide of the present invention, since the exposed surface of the organic optical waveguide formed on the substrate is covered with the amorphous fluororesin layer, the excellent water repellency of the fluororesin is obtained. The penetration of moisture into the optical waveguide made of an organic optical material that easily absorbs moisture due to the water blocking is suppressed, and the absorption of moisture in the optical waveguide can be suppressed. An increase in light propagation loss can be suppressed, and an optical waveguide having excellent moisture resistance reliability can be obtained.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an optical waveguide according to the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view of an essential part showing an example of an embodiment of an optical waveguide according to the present invention. In FIG. 1, 1 is a substrate,
Reference numeral 2 denotes a lower cladding layer of an optical waveguide formed of an organic optical material formed on a substrate 1, and reference numeral 3 denotes a core formed of an organic optical material having a higher refractive index than the lower cladding layer 2 formed on the lower cladding layer 2. Reference numeral 4 denotes an upper cladding layer formed of an organic optical material having the same refractive index as that of the lower cladding layer 2 formed so as to cover the core 3. By these, the substrate 1
In a clad portion 5 composed of a lower clad layer 2 and an upper clad layer 4 formed thereon, a core portion 3 made of an organic optical material having a higher refractive index than the clad portion 5 is formed.

Reference numeral 6 denotes an amorphous fluororesin layer, which covers the exposed surface of the clad 5. Although illustration of both side surfaces of the clad portion 5 is omitted in FIG. 1, when the clad portion 5 is formed independently on the substrate 1, similarly, the exposed side surfaces of the clad portion 5 are similarly formed. An amorphous fluororesin layer 6 is formed so as to cover these two side surfaces.

The substrate 1 includes various substrates used as substrates for handling optical signals, such as an optical integrated circuit substrate and a photoelectric mixed substrate, such as a silicon substrate and an alumina ceramic substrate.
A glass ceramic substrate, a multilayer ceramic substrate, an electric wiring substrate made of an organic insulating resin and the like can be used.

An optical waveguide formed on a substrate 1 comprises a lower cladding layer 2 and an upper cladding layer 4 made of an organic optical material.
This is a three-dimensional waveguide-shaped optical waveguide in which a core part 3 made of an organic optical material having a higher refractive index than the clad part 5 is formed in a clad part 5 made of the following. An optical waveguide made of fluorinated polyimide, siloxane-based polymer, PMMA, olefin-based resin, polycarbonate, BCB, or the like may be used.
Since an optical waveguide made of such an organic optical material absorbs moisture more easily than a quartz optical waveguide, the exposed surface of the optical waveguide is covered with an amorphous fluororesin as proposed in the present invention, so that moisture resistance is improved. The effect of improving reliability is great.

In manufacturing the optical waveguide of the present invention, first, a lower cladding layer 2 is formed on a substrate 1. The lower cladding layer 2 is formed by applying an organic solvent solution of an organic optical material such as polyimide, fluorinated polyimide, siloxane-based polymer, PMMA, olefin-based resin, polycarbonate, or BCB to the substrate 1 to a predetermined thickness by, for example, spin coating. And heat-treated.

Next, the core 3 is formed on the lower cladding layer 2 by a polyimide / fluorinated polyimide / siloxane-based polymer.
An organic solvent solution of an organic optical material having a higher refractive index than that of the lower cladding layer 2 such as PMMA / olefin resin is similarly applied to a predetermined thickness by a spin coating method or the like and formed by heat treatment, followed by photolithography or RIE. And the like, and may be formed into a predetermined shape by using a known thin film microfabrication technique.

After the core 3 is formed, the upper cladding layer 4 covers the core 3 so as to cover the same organic layer as the lower cladding layer 2 such as polyimide, fluorinated polyimide, siloxane-based polymer, PMMA, or olefin-based resin. It is formed by applying an organic solvent solution of a system optical material to a predetermined thickness by a spin coating method or the like and performing a heat treatment.

Here, the height, width and refractive index of the core portion 3, the thickness and refractive index of the lower cladding layer 2, and the thickness and refractive index of the upper cladding layer 4 are respectively determined by using a well-known optical waveguide theory. What is necessary is just to design according to a desired specification.

As described above, a buried optical waveguide having the core portion 3 formed in the clad portion 5 is manufactured.

Next, an amorphous fluororesin layer 6 is formed so as to cover the exposed surface of the clad portion 5 of the manufactured optical waveguide, that is, the upper clad layer 4 in the example of FIG. The formation of the amorphous fluororesin layer 6 is performed by applying an organic solvent of the fluororesin onto the upper cladding layer 4 by a spin coating method or the like, and then performing a heat treatment to evaporate the organic solvent. The layer 6 is formed. Here, by heating at a temperature higher than the glass transition point or the softening point to soften the resin, an amorphous fluororesin layer 6 having a flat and smooth surface and an amorphous layer can be formed.

The thickness of the amorphous fluororesin layer 6 is desirably about 0.2 μm or more in order to form a layer having no defects such as pinholes, and 1 μm in order to obtain a sufficient water shielding effect. It is desirable that the thickness be not less than the above. Also,
If the thickness exceeds 100 μm, the water blocking effect reaches a plateau, and even if the thickness is larger than this, the total film stress increases, which causes factors such as film peeling. Therefore, the thickness is preferably about 100 μm or less.

The use of an amorphous fluororesin for the layer 6 effectively suppresses the permeation of moisture to the clad portion 5 and the core portion 3 in the optical waveguide due to excellent water repellency and water shielding. This is because moisture absorption of the optical waveguide can be effectively suppressed. When the layer 6 has crystallinity, the crystalline portion is a factor that scatters light, and scattering loss increases when light is propagated.
On the other hand, when the layer 6 is amorphous, there is no light scattering, so that there is an advantage that light propagation loss is small and the propagation characteristics are excellent.

Further, the thickness of the upper cladding layer 4 is small,
If there is a layer made of a material having a higher refractive index than the upper cladding layer 4 outside the upper cladding layer 4, light in the optical waveguide is radiated toward the layer having the higher refractive index, and the light is emitted as an optical waveguide. Therefore, the refractive index of the amorphous fluororesin layer 6 needs to be smaller than that of the upper cladding layer 4. However, the refractive index of the amorphous fluororesin is the smallest among various organic optical materials. Is preferable because it is easy to set the refractive index smaller than that of the upper cladding layer 4.

Further, the amorphous fluororesin layer 6 is formed by applying a solution of a fluororesin in an organic solvent to the optical waveguide substrate by spin coating or the like, and then performing a heat treatment at a low temperature of about 100 to 300 ° C. Is evaporated, and the film stress generated due to small shrinkage at the time of film formation is small, so that the layer can be formed without damaging the underlying substrate. is there.

The fluororesin which can be used for the amorphous fluororesin layer 6 in the present invention includes, for example, cyclized polyfluoroethylene resin, polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), tetrafluoroethylene. Ethylene-hexafluoropropylene copolymer (FEP) / polyvinylidene fluoride (PVD)
F), polyvinyl fluoride (PVF), tetrafluoroethylene-ethylene copolymer, chlorotrifluoroethylene-ethylene copolymer, tetrafluoroethylene-perfluorovinyl ether copolymer (PFA), and the like. Among them, cyclized polyfluoroethylene PTFE and FEP are excellent in transparency among amorphous fluororesins, have small loss even when light propagates, and are formed into a film by a spin coating method using an organic solvent solution. This is preferable in that it can be easily formed.

It is needless to say that these fluororesins should not be limited to one kind, but several kinds of resins may be used in combination or mixed.

Next, in the optical waveguide of the present invention, when a siloxane-based polymer is used for the clad portion 5 and the core portion 3, an organic solvent of the siloxane-based polymer is applied to the substrate by a spin coating method or the like, and then 100 to 300 ° C. The clad part 5 and the core part 3 can be formed by a low-temperature heat treatment to a certain degree, and the refractive index can be easily controlled by using a siloxane-based polymer containing a metal by mixing a metal alkoxide. Therefore, the optical waveguide can be manufactured easily and accurately. In addition, since the shrinkage during layer formation is small, it is excellent in flatness and smoothness of the substrate surface, and has good characteristics even on a substrate having a large surface roughness or an electric wiring substrate having a large undulation due to wiring. This is because the optical waveguide of (1) can be manufactured. Furthermore, siloxane-based polymers have excellent thermal stability because they have siloxane bonds.

The siloxane-based polymer preferably used for the clad portion 5 and the core portion 3 of the optical waveguide of the present invention may be any resin having a siloxane bond in the polymer skeleton, such as polyphenylsilsesquioxane. San polydiphenylsilsesquioxane and polymethylphenylsilsesquioxane.

[0029]

Next, specific examples of the optical waveguide of the present invention will be described.

<Example> On a silicon substrate, a step index type optical waveguide was formed in which a cladding portion was composed of a siloxane-based polymer and a core portion in the cladding portion was composed of a titanium-containing siloxane-based polymer. At this time, the refractive index of the core portion and the cladding portion were 1.44 and 1.440, respectively, the width of the core portion was 8 μm, the height was 8 μm, and the thickness of the cladding portion (upper cladding layer) above the core portion was 4 μm. The thickness of the cladding (lower cladding layer) between the substrate and the core was 12 μm. The waveguide length was 3 cm.

Next, using an organic solvent solution of cyclized polyfluorinated ethylene as a fluororesin, spin-coating to cover the substrate, and heat-treating at 300 ° C., so that the exposed surface of the clad has a thickness of 4 μm. And an amorphous fluororesin layer made of a cyclized polyfluoroethylene resin having a refractive index of 1.31.

After leaving the optical waveguide of the present invention thus manufactured in a constant temperature and constant humidity of 85 ° C. and 85% RH for 500 hours,
1.3 μm wavelength light from a laser diode passes through an optical fiber, enters from one end of this optical waveguide, propagates through the optical waveguide, and measures the light emitted from the other end through another optical fiber. The change in the propagation loss was examined by measuring the light intensity using a detector. As a result, 85
The change amount of the propagation loss between before and after the constant temperature and humidity treatment at 85 ° C. and 85% RH was 1 dB or less, and the change was at a level with no particular problem in characteristics.

<Comparative Example> For comparison with the optical waveguide of the present invention, an optical waveguide similar to the above was produced as follows.
A conventional optical waveguide in which the exposed surface of the clad was not covered with an amorphous fluororesin layer was prepared and evaluated.

On a silicon substrate, a step index type optical waveguide was formed in which a cladding portion was made of a siloxane-based polymer and a core portion was made of a titanium-containing siloxane-based polymer. At this time, the refractive indices of the core and cladding were 1.44 respectively.
4 and 1.440, the width of the core is 8 μm and the height is 8
μm, and the thickness of the cladding (upper cladding layer) above the core was 4 μm. The thickness of the cladding (lower cladding layer) between the substrate and the core was 12 μm. The waveguide length was 3 cm.

The conventional optical waveguide manufactured as described above is
After standing in a constant temperature and humidity of 85 ° C. and 85% RH for 100 hours, light having a wavelength of 1.3 μm from a laser diode is passed through an optical fiber and made incident from one end of the optical waveguide to propagate through the optical waveguide. Then, the light emitted from the other end was passed through another optical fiber, and the intensity of the light was measured using a light intensity measuring device to examine the change in propagation loss. As a result, 85 ℃ ・ 85% R
The propagation loss was degraded by about 2 dB between before and after the constant temperature and humidity treatment of H and after standing for 100 hours, which was a problematic characteristic.

As described above, according to the present invention, it is possible to manufacture an optical waveguide made of an organic optical material having excellent humidity resistance, in which an increase in light propagation loss and deterioration of characteristics in a high humidity environment are suppressed. It was confirmed that it was possible.

It should be noted that the present invention is not limited to the above examples, and various changes and improvements can be made without departing from the spirit of the present invention.

[0038]

As described above, according to the optical waveguide of the present invention, the exposed surface of the optical waveguide made of the organic optical material formed on the substrate is covered with the amorphous fluororesin layer. Therefore, the excellent water repellency and water blocking property of the amorphous fluororesin suppresses the permeation of moisture to the clad part and the core part in the optical waveguide, and reduces the moisture absorption of the optical waveguide made of organic optical material to its optical characteristics. It can be effectively suppressed without adverse effects, and as a result, it is possible to suppress changes in the refractive index and increase in light propagation loss due to moisture absorption,
An optical waveguide made of an organic optical material having excellent humidity resistance was obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part showing an example of an embodiment of an optical waveguide of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... Lower cladding layer of optical waveguide 3 ... Core part of optical waveguide 4 ... Upper cladding layer of optical waveguide 5 ... Cladding part of optical waveguide 6 ... Amorphous Fluororesin layer

Claims (2)

[Claims] 1. A core portion made of an organic optical material having a higher refractive index than a clad portion is formed in a clad portion made of an organic optical material formed on a substrate, and an exposed surface of the clad portion is formed. An optical waveguide, which is covered with an amorphous fluororesin layer. 2. The optical waveguide according to claim 1, wherein said clad portion and said core portion are made of a siloxane-based polymer.