JP2008038027A - Organic polymer composition and optical waveguide and method for producing optical waveguide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic polymer composition which can match the thermal characteristics and birefringence of the core portion of an optical waveguide with those of its clad portion, can reduce the diffusion of light, can easily control refractive index, and can more simply form the optical waveguide at a lower cost in high accuracy, and to provide a method for producing an optical waveguide. <P>SOLUTION: This organic polymer composition comprising an organic polymer and fine light-transmitting particles for adjusting the refractive index of the organic polymer is characterized in that the average particle diameter of the fine light-transmitting particles is ≤20 nm. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an organic polymer composition, an optical waveguide, and an optical waveguide manufacturing method. More specifically, the present invention relates to an organic polymer mainly used for optical applications, and light transmission for adjusting the refractive index of the organic polymer. The present invention relates to an organic polymer composition containing conductive fine particles, an optical waveguide that is obtained by curing the organic polymer composition to form a core portion, and a method for manufacturing the optical waveguide.

In recent years, with the increase in Internet traffic, there has been a demand for higher speed and larger capacity for optical communication networks using optical fibers. In order to popularize this optical communication network, the cost of the system has been reduced. It has been demanded.
In order to reduce the price of this system, it is indispensable to reduce the price of various optical devices constituting the system, and manufacturing an optical device at a low cost is a major issue in reducing the price of the system.
In these optical devices, optical waveguides having a two-dimensional or three-dimensional structure are adopted, and these optical waveguides are formed in an optical waveguide formation region of a rigid substrate such as a quartz substrate by an ion exchange method or an impurity thermal diffusion method. It is formed by diffusing ions.
Although these conventional waveguide formation methods can provide low-loss optical waveguides, it is difficult to meet the demand for cost reduction due to the relatively high cost of materials such as quartz substrates and a large number of processes. It was.

Therefore, recently, an organic polymer (plastic) has been attracting attention as an alternative to these conventional optical waveguide materials.
An optical waveguide using an organic polymer (hereinafter referred to as an organic polymer waveguide) is composed of an organic polymer such as an acrylic resin, epoxy resin, polycarbonate, polystyrene, polyimide, etc., in the core and clad of the optical waveguide. It is easy to increase the area at low cost, and various optical devices with an optical waveguide structure can be manufactured at low cost because various optical printing methods such as various printing methods, stamping and embossing can be applied. It is expected as a material that can be manufactured.
Furthermore, since this organic polymer waveguide can form a flexible optical waveguide by using a film as a base material, it can be applied to a conventional optical waveguide using a rigid substrate. The present invention can be applied to applications that have not been used, for example, so-called optical interconnect applications in which electronic components are connected by light.

Examples of the method for forming the organic polymer waveguide include reactive ion etching (RIE), direct exposure (see, for example, Patent Document 1), irradiation with high energy rays such as an electron beam, stamping, embossing, and the like. Have been proposed, for example, a method for adding fine particles (see, for example, Patent Document 2).
The direct exposure method is a method in which a photosensitive resin precursor layer formed on a lower cladding layer is exposed and developed in a predetermined pattern using ultraviolet (UV) or the like to form a core layer. An optical waveguide can be manufactured by forming an upper cladding layer on the cladding layer.
In addition, the fine particle addition method is a method of forming, on a clad portion made of an organic polymer, a core portion containing light transmissive fine particles having a higher refractive index than the organic polymer. An optical waveguide can be produced by further forming a clad portion thereon.

In this method of adding fine particles, the core and the clad of the optical waveguide can be made of an organic polymer having the same composition, so that the thermal characteristics and birefringence of the core and the clad coincide with each other. It has excellent characteristics such that the waveguide characteristics are not deteriorated and the refractive index difference between the core and the clad can be arbitrarily adjusted by adding the fine particles.
In this fine particle addition method, fine particles having a particle size of 50 nm or less are used. The reason is that Mie scattering for purple to blue light, which is a short wavelength as visible light, can be almost ignored. It is thought that light loss is reduced.
JP 2005-165139 A JP 2005-121696 A

By the way, the conventional fine particle addition method has a problem in that scattering loss due to Rayleigh scattering remains even if the particle size of the fine particles of the organic polymer waveguide is 50 nm or less. Scattering loss due to Rayleigh scattering is not a problem when the optical path length is about several μm as in an optical thin film, but the optical path length is from several centimeters to several meters as in an optical waveguide element or an optical fiber. In the above case, it cannot be ignored.
In addition, since the conventional reactive ion etching method requires a vacuum process, the manufacturing process becomes complicated, and the structure of the manufacturing apparatus becomes complicated and expensive. Therefore, in terms of mass productivity and cost reduction. There was a problem.

In addition, although the conventional molding method is excellent in mass production, it is difficult to further improve the processing accuracy of the optical waveguide because the accuracy of the optical waveguide depends on the accuracy of the mold used for molding. There was a problem.
In addition, since this molding method requires changing the mold for each waveguide pattern, it is necessary to prepare a huge amount of molds in order to cope with a small variety of optical waveguides. There was also a problem in terms of cost.
Furthermore, since this mold is mainly made to order, there is also a problem that it takes a long time from ordering the mold to delivery, leading to a long lead time.

Further, the conventional direct exposure method is considered advantageous from the viewpoint of the balance between mass productivity and processing accuracy in consideration of the above-mentioned problems, but titanium oxide is added to fine particles added for adjusting the refractive index of the photosensitive resin. When a material having an energy gap Eg of less than 3.2 eV such as cerium oxide or cerium oxide is used, it absorbs ultraviolet rays during patterning and thus becomes opaque to ultraviolet rays.
For this reason, in the case where an optical waveguide is manufactured by exposing a waveguide pattern after applying a fine particle-added organic polymer for forming a core portion on a previously formed cladding portion, the interface with the cladding portion is sufficient. There is a problem that the amount of ultraviolet rays does not reach, the pattern transferability deteriorates, and the dimensional accuracy of the optical waveguide decreases.

  The present invention has been made in order to solve the above-described problems. The thermal characteristics and the birefringence of the core portion and the clad portion of the optical waveguide are matched, and the light scattering loss is low, and the refractive index is low. An object of the present invention is to provide an organic polymer composition, an optical waveguide, and a method for manufacturing the optical waveguide, which are easy to control and can form an optical waveguide more easily, at a lower cost, and with higher accuracy. .

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that an organic polymer and light-transmitting fine particles having an average particle size of 20 nm or less for adjusting the refractive index of the organic polymer If the core part of the optical waveguide is made from an organic polymer composition containing the same, it is possible to match the thermal characteristics and birefringence of the core part and the clad part, and to reduce the light scattering loss. In addition, the refractive index can be easily controlled by changing the content of the light-transmitting fine particles, and furthermore, an optical waveguide can be formed with higher accuracy at a simpler and lower cost. As a result, the present invention has been completed.

  That is, the organic polymer composition of the present invention is an organic polymer composition comprising an organic polymer and light-transmitting fine particles for adjusting the refractive index of the organic polymer, The average particle diameter of the permeable fine particles is 20 nm or less.

Preferably, the organic polymer is a photosensitive resin, and the energy gap Eg in the energy band of the light transmissive fine particles is set to 3.2 eV or more.
The light-transmitting fine particles are preferably fine particles composed of one or more selected from the group consisting of zirconia, barium titanate, calcium titanate, potassium tantalate, and gallium nitride.

  The optical waveguide of the present invention includes a core portion formed by curing the organic polymer composition of the present invention, and a cladding portion formed by curing an organic polymer having the same composition as the organic polymer contained in the organic polymer composition. It is characterized by comprising.

  In the method for producing an optical waveguide of the present invention, a coating film is formed by applying the organic polymer composition of the present invention on a clad layer, and then the coating film is patterned to form an optical waveguide region having a predetermined shape. In addition, the chemical reaction of the optical waveguide region is allowed to proceed, and then the optical waveguide region is cured to form a core portion.

The organic polymer is a photosensitive resin that is sensitive to ultraviolet rays. During the patterning, the optical waveguide region of the coating film is irradiated with ultraviolet rays, and the crosslinking reaction of the photosensitive resin in the optical waveguide region proceeds. It is preferable to make it.
The clad layer is preferably formed by curing an organic polymer having the same composition as the organic polymer contained in the organic polymer composition of the present invention.

According to the organic polymer composition of the present invention, since the average particle diameter of the light-transmitting fine particles for adjusting the refractive index of the organic polymer is 20 nm or less, the core portion is formed using this organic polymer composition. By forming the clad part using the organic polymer, the thermal characteristics and birefringence of the core part and clad part of the optical waveguide can be matched, and the light scattering loss due to Rayleigh scattering is reduced. Can be made.
Further, the refractive index of the organic polymer composition can be easily controlled by adjusting the content of the light transmissive fine particles.
Further, by patterning the coating film of the organic polymer composition, an optical waveguide can be formed with higher accuracy at a simpler and lower cost.

According to the optical waveguide of the present invention, a core formed by curing the organic polymer composition of the present invention and an organic polymer having the same composition as the organic polymer contained in the organic polymer composition are cured. Since the cladding portion is provided, the thermal characteristics and birefringence of the core portion and the cladding portion can be matched, and the light scattering loss due to Rayleigh scattering can be reduced.
Further, the refractive index of the core part can be easily controlled by adjusting the content of the light transmissive fine particles.

  According to the method for producing an optical waveguide of the present invention, a coating film is formed by applying the organic polymer composition of the present invention on a clad layer, and then the coating film is patterned to form an optical waveguide region having a predetermined shape. In addition, the chemical reaction of the optical waveguide region is allowed to proceed, and then the optical waveguide region is cured to form a core portion. Therefore, a highly accurate optical waveguide can be manufactured more easily and at a lower cost.

The best mode for carrying out the organic polymer composition, the optical waveguide, and the method for producing the optical waveguide of the present invention will be described.
This embodiment is specifically described for better understanding of the gist of the invention, and does not limit the present invention unless otherwise specified.

"Organic polymer composition"
The organic polymer composition of the present invention is an organic polymer composition comprising an organic polymer and light-transmitting fine particles for adjusting the refractive index of the organic polymer. Is an organic polymer composition having an average particle size of 20 nm or less.
Here, the average particle diameter is an average particle diameter in a dispersion in which light-transmitting fine particles are dispersed in various solvents such as water, methyl ethyl ketone, toluene, propylene glycol monomethyl ether, and is measured by a dynamic light scattering method. Is.

The organic polymer is not particularly limited as long as it has a high transmittance with respect to light propagating through the core portion of the optical waveguide, and is sensitive to electromagnetic waves such as visible light and ultraviolet light. A photosensitive resin having a photosensitivity is preferable, and a photosensitive resin having sensitivity to ultraviolet rays is particularly preferable.
Examples of such photosensitive resins include acrylic resins such as polymethyl methacrylate, epoxy resins, polyimide resins, silicone resins, polystyrene resins, polyamide resins, polyester resins, phenol resins, and polyquinoline resins. Examples include resins, polyquinoxaline resins, polybenzoxazole resins, polybenzothiazole resins, polybenzimidazole resins, and the like.

As the light-transmitting fine particles, those having a refractive index higher than that of the organic polymer as a base material, and having an average particle diameter of 20 nm or less, more preferably 10 nm or less, are appropriately selected and used. it can.
Here, the reason why the average particle diameter of the light-transmitting fine particles is 20 nm or less is between the average particle diameter of the light-transmitting fine particles and the pattern reproducibility when patterning the coating film of the organic polymer composition. Because of the correlation, by making the average particle size of the light-transmitting fine particles 20 nm or less, it is possible to suppress pattern dullness caused by scattering of ultraviolet rays or the like used for patterning to be less than the line width accuracy of the photomask. Therefore, the optical waveguide can be formed with higher accuracy.

The light-transmitting fine particles are not particularly limited as long as the energy gap Eg in the energy band of the material constituting the fine particles is 3.2 eV or more, and are not particularly limited. The fine particles having a refractive index higher than that of the molecule can be appropriately selected and used.
Here, the reason why the energy gap Eg of the light-transmitting fine particles is set to 3.2 eV or more is that when the optical waveguide is formed by patterning the coating film of the above organic polymer composition with ultraviolet rays (UV), This is because it is possible to increase the transmittance of ultraviolet rays in the polymer composition and form an optical waveguide with good pattern accuracy.

The light-transmitting fine particles are preferably oxide or nitride fine particles in view of chemical stability and the like. For example, zirconia (ZrO ₂ ), barium titanate (BaTiO ₃ ), calcium titanate (CaTiO _3). ), Potassium tantalate (KTaO ₃ ), and gallium nitride (GaN) are preferably used.
In particular, zirconia (ZrO ₂ ) is preferable because the energy gap Eg is as extremely high as 5.0 eV and the oxide has a high refractive index (2.17).

Next, the reason why the average particle diameter of the light-transmitting fine particles is set to 20 nm or less will be described by taking zirconia (ZrO ₂ ) fine particles having no absorption edge in the visible light region as an example.
FIG. 1 is a graph showing the visible light transmittance depending on the difference in the average particle diameter of zirconia (ZrO ₂ ) fine particles.
Here, two kinds of zirconia fine particles having an average dispersed particle diameter of 9 nm and 40 nm when used as a dispersion are used, and two kinds of zirconia fine particles dispersed in toluene at a concentration of 0.8 v / v% are used. Zirconia fine particle dispersions were prepared, and these zirconia fine particle dispersions were sealed in quartz cells adjusted to have an optical path length of 10 mm, respectively, and then transmission spectra at wavelengths of 400 nm to 800 nm were measured.
In the figure, a solid line (-) indicates a transmission spectrum of a dispersion having an average dispersed particle diameter of 9 nm, and a broken line (...) indicates a transmission spectrum of a dispersion having an average dispersed particle diameter of 40 nm.

As is clear from FIG. 1, when the average dispersed particle size of the zirconia fine particles is 9 nm, the light transmittance in the visible light region is 93%, whereas when the average dispersed particle size is 40 nm, the light transmittance in the visible light region. Is 6%, and there is a clear difference in the transmittance in the visible light region.
This difference in light transmittance can be regarded as a difference in the magnitude of Rayleigh scattering by the zirconia fine particles, so by setting the average dispersed particle size of the zirconia fine particles, that is, the average particle size of the light transmissive fine particles to 20 nm or less, It has become clear that light scattering loss can be reduced.

"Optical waveguide"
FIG. 2 is a cross-sectional view showing an optical waveguide according to an embodiment of the present invention. In the figure, 1 is a substrate, 2 is an organic high polymer contained in the organic polymer composition of this embodiment formed on the substrate 1. A lower clad layer formed by curing an organic polymer having the same composition as the molecule, 3 is a striped core portion formed by curing the organic polymer composition of the present embodiment formed on the lower clad layer 2, and 4 is This is an upper cladding layer formed by curing an organic polymer having the same composition as that of the lower cladding layer 2.

The substrate 1 may be any substrate that can withstand the temperature during drying or heat treatment, and a glass substrate, a translucent ceramic substrate, a silicon substrate, or the like is preferably used.
In the case where the heat treatment temperature is about 200 ° C. to 250 ° C., a heat resistant plastic substrate can also be used as long as thermal deformation does not occur.

This optical waveguide can be manufactured as follows.
On the substrate 1, an organic polymer having the same composition as the organic polymer contained in the organic polymer composition of the present embodiment is applied to form a coating film, and this coating film is heated and cured to form the lower cladding layer 2 And
Next, the organic polymer composition of the present embodiment is applied onto the lower cladding layer 2 to form a coating film, and the coating film is patterned into a core shape using photolithography or the like. The coating film is heated and cured to form the core portion 3 which is an optical waveguide region having a predetermined shape.

During this patterning, a chemical reaction in the optical waveguide region is advanced.
As this chemical reaction, the above organic polymer is made a photosensitive resin that is sensitive to ultraviolet rays, and the optical waveguide region of the coating film is irradiated with ultraviolet rays at the time of patterning, and the photosensitive resin in the optical waveguide region is irradiated. It is preferable to advance the crosslinking reaction.
Next, an organic polymer having the same composition as the organic polymer contained in the organic polymer composition of the present invention is applied onto the core 3 and the lower cladding layer 2 to form a coating film, and the coating film is heated. Curing to form the upper clad layer 4

  Examples of the coating method include a spray coating method, a bar coating method, a spin coating method, a dip coating method, a screen printing method, a roll coating method, a meniscus coating method, a gravure printing method, an inkjet method, and a slip die coating method. A normal wet coating method applied to the surface of the substrate can be used. Among these, the spray coating method, the bar coating method, and the spin coating method are particularly preferable coating methods because a thin film can be formed in a short time.

The atmosphere for heating and curing is preferably in the air because it is necessary to advance the chemical reaction of the organic polymer.
The temperature and time for heating and curing are preferably temperatures sufficient to advance and cure the organic polymer chemical reaction, and are preferably 75 ° C. or higher and 5 to 30 minutes, for example.

EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention concretely, this invention is not limited by these Examples.
"Example"
As the light-transmitting fine particles, zirconia fine particles having an extremely high energy gap Eg of 5.0 eV and a high refractive index of 2.17 as the oxide and having an average particle diameter of 10 nm are used. ) Using a positive type photosensitive acrylic resin precursor excellent in transparency in the visible light region, and the content ratio of the zirconia fine particles and the photosensitive acrylic resin precursor to the photosensitive acrylic resin precursor of the zirconia fine particles is An organic polymer composition was prepared by dispersing in methyl ethyl ketone (MEK) so as to be 0.7 v / v%.

Next, an acrylic resin precursor having the same composition as the photosensitive acrylic resin precursor contained in the organic polymer composition was applied onto the substrate by a spin coating method, and then heated and cured to form a lower cladding layer. .
Next, the organic polymer composition is applied onto the lower clad layer by a spin coating method, pre-baked at 80 ° C. for 5 minutes to form a coating film, and a linear waveguide having a core diameter of 10 μm is formed on the coating film. A predetermined optical waveguide pattern was transferred by ultraviolet irradiation using a photomask, and then developed.
Subsequently, it heated at 80 degreeC in air | atmosphere for 30 minutes, the organic polymer composition was hardened | cured completely, and the core part of a stripe shape whose core diameter is 10 micrometers was formed. As a result of measuring the width of this core part at 10 points, it was 9.8 μm on average.

Next, the acrylic resin precursor is applied onto the core portion and the lower clad layer by a spin coat method, and then heated and cured to form an upper clad layer to produce a three-dimensional embedded optical waveguide. .
As a result of measuring the light propagation loss at a wavelength of 1.3 μm of this three-dimensional embedded optical waveguide, it was 0.02 dB / cm.

"Comparative Example 1"
A three-dimensional embedded optical waveguide was produced according to the example except that the average particle diameter of the zirconia fine particles was 40 nm in the example.
As a result of measuring the width of the core portion after development and curing of this three-dimensional embedded optical waveguide, the average was 9.4 μm.
The light propagation loss at a wavelength of 1.3 μm of this three-dimensional embedded optical waveguide was measured and found to be 0.3 dB / cm.

"Comparative Example 2"
A three-dimensional embedded optical waveguide was produced in the same manner as in the examples except that the zirconia fine particles were replaced with titanium oxide fine particles having an average particle diameter of 10 nm.
As a result of measuring the width of the core portion after development and curing of this three-dimensional embedded optical waveguide, the average value was 9.2 μm.
Further, the optical propagation loss at a wavelength of 1.3 μm of this three-dimensional embedded optical waveguide was measured and found to be 0.03 dB / cm.

  The organic polymer composition of the present invention contains an organic polymer and light-transmitting fine particles having an average particle diameter of 20 nm or less for adjusting the refractive index of the organic polymer. As well as the thermal characteristics and birefringence of the cladding and the birefringence, the light scattering loss is reduced and the refractive index is easily controlled. Even in an optical device such as a Mach-Zehnder type optical waveguide, an optical coupler, a slab type waveguide, or an optical fiber, the effect is great.

It is a figure which shows the visible light transmittance | permeability by the difference in the average particle diameter of a zirconia microparticle. It is sectional drawing which shows the optical waveguide of one Embodiment of this invention.

Explanation of symbols

1 Substrate 2 Lower clad layer 3 Core part 4 Upper clad layer

Claims (7)

An organic polymer composition comprising an organic polymer and light-transmitting fine particles for adjusting the refractive index of the organic polymer,
The average particle diameter of the said light transmissive fine particle is 20 nm or less, The organic polymer composition characterized by the above-mentioned.   The organic polymer composition according to claim 1, wherein the organic polymer is a photosensitive resin, and an energy gap Eg in an energy band of the light-transmitting fine particles is 3.2 eV or more.   The light transmissive fine particles are fine particles composed of one or more selected from the group consisting of zirconia, barium titanate, calcium titanate, potassium tantalate, and gallium nitride. The organic polymer composition described.   A core portion formed by curing the organic polymer composition according to claim 1, 2, or 3, and a clad portion formed by curing an organic polymer having the same composition as the organic polymer contained in the organic polymer composition An optical waveguide comprising:   A coating film is formed by applying the organic polymer composition according to claim 1, 2 or 3 on the cladding layer, and then the coating film is patterned to form an optical waveguide region having a predetermined shape. A method of manufacturing an optical waveguide, wherein a chemical reaction of the region is allowed to proceed, and then the optical waveguide region is cured to form a core portion. The organic polymer is a photosensitive resin having sensitivity to ultraviolet rays,
6. The method of manufacturing an optical waveguide according to claim 5, wherein, during the patterning, the optical waveguide region of the coating film is irradiated with ultraviolet rays to cause a crosslinking reaction of the photosensitive resin in the optical waveguide region.   The optical waveguide according to claim 5 or 6, wherein the cladding layer is formed by curing an organic polymer having the same composition as the organic polymer contained in the organic polymer composition according to claim 1, 2 or 3. A method for manufacturing a waveguide.

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