JP2004170830A - Planar polymer optical waveguide and method of manufacturing the same - Google Patents

Abstract

A planar polymer optical waveguide which is easy to manufacture, has a simple structure, and has a good effect of suppressing a clad mode is provided.
A planar polymer optical waveguide is an optical waveguide in which the wavelength of transmitted light is set at around 850 nm, and each of the planar polymer optical waveguides is a 20 μm-thick plate-shaped core layer made of a high-molecular organic compound. And a flat clad layer 12 sandwiching the core layer 11 from above and below. The cladding layer 12 is characterized in that it has an absorption coefficient larger than the absorption coefficient of the high molecular compound forming the core layer 11 with respect to light having a wavelength of about 850 nm to be guided.
[Selection diagram] Fig. 1

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a planar polymer optical waveguide and a method for fabricating the same, and more particularly, to a planar polymer waveguide used for optical interconnection and optical communication, which is easy to produce, has a simple structure, and has a good cladding mode suppression effect. And a method of manufacturing the same.
[0002]
[Prior art]
In devices for optical interconnection and optical communication, it is important to increase the optical coupling efficiency between an optical element or an optical component and an optical waveguide. The light from the light source should be focused with a lens or the like with sufficient accuracy so that the light from the light source is incident only on the core layer of the optical waveguide as much as possible, and the optical waveguide and the light source should be arranged so as to exhibit high optical coupling efficiency. is necessary. In order for light from a light source to enter only the core layer, high-precision technology is required, so it is actually difficult to achieve this. Light may leak not only into the core layer but also into the cladding layer. is there.
The light leaking into the cladding layer and propagating in the cladding layer propagates in the optical waveguide as a cladding mode, and is extracted from the emission end as unnecessary light. Since the unnecessary light becomes noise in obtaining a desired signal, an optical waveguide for suppressing the cladding mode is required.
[0003]
In particular, in a parallel optical waveguide in which a plurality of optical waveguides are arranged in parallel, since a large number of beams are incident, many optical components such as lenses are required, and alignment is not easy. For this reason, it is necessary to prevent the cost from increasing by suppressing the cladding mode with a simple configuration that does not increase the number of components.
[0004]
To meet such demands, Japanese Patent Application Laid-Open No. 4-67103 discloses an optical waveguide that employs a clad layer containing an additive and suppresses the clad mode by absorbing or scattering the clad mode. I have.
Here, the configuration of the optical waveguide disclosed in the above-mentioned publication and a method of manufacturing the same will be described with reference to FIG. FIG. 4 is a cross-sectional view showing the configuration of the optical waveguide disclosed in the above-mentioned publication.
According to the above-mentioned publication, when manufacturing the optical waveguide 30, first, the additive 34 is dispersed in the material of the clad 31, and the clad 31 is formed to have a groove shape.
Next, the core material is filled in the groove-shaped portion to form the core 32.
Subsequently, the optical waveguide 30 shown in FIG. 4 is obtained by covering the clad 31 filled with the core 32 with the clad coating material 33 in which the additive 34 is dispersed.
According to the publication, an optical waveguide capable of eliminating a cladding mode can be easily provided by such a manufacturing method.
[0005]
[Patent Document 1]
JP-A-4-67103 (pages 2-3)
[0006]
[Problems to be solved by the invention]
By the way, according to Japanese Patent Application Laid-Open No. 4-67103, it is necessary to disperse an additive in the material of the cladding 31 and the cladding covering material 33 before forming the optical waveguide.
However, such dispersion of the additive 34 has a problem in uniformly dispersing the additive 34 in the liquid clad material as pointed out in the publication. Further, if the additive 34 is not uniformly mixed in the clad material, there is a problem that the effect of suppressing the clad mode is poor and a good optical waveguide may not be obtained.
[0007]
SUMMARY OF THE INVENTION It is an object of the present invention to provide a planar polymer optical waveguide having a simple structure and an excellent effect of suppressing a cladding mode, and a method for manufacturing the same.
[0008]
[Means for Solving the Problems]
The present inventor considered as follows in order to solve the above problem. The complex refractive index of each layer of the optical waveguide is represented by n + ki. Here, the real part n of the complex refractive index is a so-called refractive index. The imaginary part k is proportional to the absorption coefficient, means light absorption, and represents attenuation due to light propagation.
That is, the present inventor considers not only the real part n of the complex refractive index but also the imaginary part k involved in absorption as a material for forming the cladding layer, so that not only the refractive index is smaller than the core layer but also the absorption. By adopting a high molecular organic compound having a large coefficient to attenuate and suppress the cladding mode, the present invention has been completed.
[0009]
Therefore, in order to achieve the above object, based on the above findings, the planar polymer optical waveguide according to the present invention (hereinafter, referred to as the first invention) includes a core layer made of a polymer organic compound, And in a planar polymer optical waveguide having a cladding layer enclosing or sandwiching the core layer, the cladding layer absorbs a wavelength of light to be guided that is larger than the absorption coefficient of the polymer organic compound constituting the core layer. It is characterized by being composed of another high molecular weight organic compound having a coefficient.
[0010]
In the first invention, the cladding layer is made of another polymer organic compound having an absorption coefficient larger than the absorption coefficient of the polymer organic compound constituting the core layer with respect to the wavelength of the guided light. , Ie, the cladding mode can be attenuated and suppressed. That is, it is possible to attenuate the cladding mode by selecting the high molecular weight organic compound with the same structure as the conventional one. Thereby, noise mixed in the signal extracted from the emission end of the optical waveguide can be reduced. As a material constituting these planar polymer optical waveguides, for example, fluorinated polyimide (manufactured by NTT Advanced Technology Co., Ltd., manufactured by Hitachi Chemical Co., Ltd.), gracia (polysilane) (manufactured by Nippon Paint Co., Ltd.), oxetane resin ( Sony Chemical Co., Ltd.). In the first invention, the cladding layer may be formed of a high molecular weight organic compound having a property of being cured by ultraviolet irradiation.
[0011]
In the first invention, for example, for guided light having a wavelength of around 850 nm, it is possible to employ Gracia for the core layer and fluorinated polyimide for the cladding layer. Since the fluorinated polyimide has a smaller refractive index than that of Gracia and has a larger absorption coefficient for guided light having a wavelength of around 850 nm, it can be suitably applied to the planar polymer optical waveguide of the first invention.
[0012]
Another planar polymer optical waveguide according to the present invention (hereinafter referred to as a second invention) is formed in a lower clad layer, an intermediate clad layer, and an intermediate clad layer, respectively, made of a polymer organic compound. Core layer, and a planar polymer optical waveguide having an upper cladding layer,
An intermediate cladding layer is formed of the same high molecular organic compound as the core layer, with a high molecular organic compound modified to have a refractive index smaller than the refractive index of the core layer by ultraviolet irradiation,
The lower and upper cladding layers are made of a polymer organic compound having an absorption coefficient larger than the absorption coefficient of the polymer organic compound forming the core layer with respect to the wavelength of light to be guided.
[0013]
In the second invention, the lower and upper cladding layers are made of a polymer organic compound having an absorption coefficient larger than the absorption coefficient of the polymer organic compound forming the core layer with respect to the wavelength of light to be guided. In addition, the cladding mode propagating in the upper cladding layer can be attenuated and suppressed. Further, since the intermediate cladding layer has a refractive index smaller than the refractive index of the core layer, a good lateral light confinement effect can be obtained. According to the second aspect, the absorption coefficient of the intermediate cladding layer is equal to the absorption coefficient of the core layer and smaller than the cladding mode propagating in the lateral direction, but the above configuration allows the signal taken out from the output end of the optical waveguide to have a smaller value. Mixed noise can be sufficiently reduced.
[0014]
In the preferred embodiment of the second invention of the present invention, the core layers extend in parallel, so that the optical waveguide can be made denser.
[0015]
The method for producing a planar polymer optical waveguide according to the present invention forms a lower clad layer on a substrate,
On the lower cladding layer, for light of a specific wavelength, to form a core forming layer with a high molecular organic compound having an absorption coefficient larger than the absorption coefficient of the high molecular organic compound constituting the lower cladding layer,
Place a photomask having a band-shaped pattern on the core forming layer, irradiate with ultraviolet light, lower the refractive index of the ultraviolet irradiation area to make the intermediate cladding layer, the ultraviolet non-irradiation area as the core layer,
An upper clad layer made of the same high molecular weight organic compound as the lower clad layer is formed on the intermediate clad layer and the core layer.
[0016]
In the method of the present invention, since the core layer and the intermediate cladding layer are formed by irradiating ultraviolet rays using a photomask having a belt-like pattern, an optical waveguide can be easily manufactured. Further, the same effect as that of the second invention can be obtained.
[0017]
In the second invention and the method of the present invention, for example, for guided light having a wavelength of around 850 nm, gracia can be used for the core forming layer, and fluorinated polyimide can be used for the lower and upper cladding layers. Fluorinated polyimide has a smaller refractive index than that of Gracia and has a large absorption coefficient for guided light having a wavelength near 850 nm. Gracia is suitable for the second invention and the method of the present invention, since the refractive index of the guided light having a wavelength of about 850 nm is reduced by the irradiation of ultraviolet rays.
[0018]
In the method of the present invention, core layers extending in parallel can be formed. This makes it possible to realize a high-density optical fiber.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in more detail based on exemplary embodiments with reference to the accompanying drawings.
Embodiment 1
This embodiment is an example of an embodiment of a planar polymer optical waveguide according to the present invention. FIG. 1 is a side sectional view showing a configuration of a planar polymer optical waveguide according to the present embodiment.
The planar polymer optical waveguide 10 of the present embodiment is an optical waveguide in which the wavelength of the guided light is set to around 850 nm, and as shown in FIG. This is a planar polymer optical waveguide comprising a flat core layer 11 and a flat clad layer 12 sandwiching the core layer 11 from above and below.
[0020]
In this embodiment, the core layer 11 is made of gracia, and the cladding layer 12 is made of fluorinated polyimide. The refractive index of gracia in the core layer 11 is 1.58, and the refractive index of fluorinated polyimide in the cladding layer 12 is 1.52. The refractive index of the gracia of the core layer 11 is about 3.8% larger than the refractive index of the fluorinated polyimide of the cladding layer 12, and the light incident on the core layer 11 travels by totally reflecting the boundary surface of the core layer 11. .
For light having a wavelength around 850 nm, the propagation loss of glacia is 0.1 dB / cm, and the propagation loss of fluorinated polyimide is 2.5 dB / cm. This propagation loss is proportional to the absorption coefficient. Therefore, the absorption coefficient of Gracia is smaller than the absorption coefficient of fluorinated polyimide.
[0021]
In the present embodiment, since the absorption coefficient of the cladding layer 12 is large, the cladding mode incident on the cladding layer 12 can be attenuated and suppressed.
By applying the planar polymer optical waveguide 10 of the present embodiment, even when the alignment accuracy of the optical system is coarse and the optical coupling between the light source and the optical waveguide is low, the cladding mode leaking into the cladding layer 12 and entering. Attenuates and reduces noise.
It should be noted that such an effect of suppressing the cladding mode can be obtained not only in the multi mode and the single mode.
[0022]
The method of manufacturing the planar polymer optical waveguide 10 according to the present embodiment is as follows. First, a substrate (not shown) made of polyimide, glass, quartz, Si, GaAs, InP, SOI (Silicon on Insulator), or the like is coated with fluorine. Is applied to form a fluorinated polyimide film. Next, the fluorinated polyimide film is cured by ultraviolet irradiation and post-baking to form a lower cladding layer 12a.
[0023]
Subsequently, gracia is applied on the lower cladding layer 12a to form a gracia film. Subsequently, the core layer 11 is cured by baking to form the core layer 11.
[0024]
Subsequently, a fluorinated polyimide is applied on the core layer 11 to form a fluorinated polyimide film, and the fluorinated polyimide film is cured by ultraviolet irradiation and post-baking to form an upper clad layer 12b. Subsequently, through a process such as removing the substrate, the planar polymer optical waveguide 10 of the present embodiment can be completed. Note that the substrate may be left attached without being removed.
[0025]
According to the manufacturing method of the optical waveguide of the present embodiment, the selection of the high molecular organic compound specified in the present invention makes it possible to easily manufacture the optical waveguide of the present embodiment using the same manufacturing method as the conventional one. It is possible. In addition, using a photomask having a mask pattern of a predetermined shape, ultraviolet rays are irradiated only to a predetermined region of the core layer 11 to reduce the refractive index, and an optical waveguide having a complicated shape such as a Y-branch or an S-shaped curve can be manufactured. It is possible.
[0026]
As shown in FIG. 5, when the optical waveguide 10 is curved in an S shape near the emission end 14, a part of the light 13 leaked from the optical waveguide 10 conventionally propagates through the cladding layer 12, It was taken out from the emission end 14 and became noise. However, by applying the planar polymer optical waveguide 10 of this embodiment, the noise light 13 transmitted through the cladding layer 12 can be attenuated, and the noise can be reduced.
[0027]
Embodiment 2
This embodiment is an example of an embodiment of a planar polymer optical waveguide according to the present invention. FIG. 2 is a perspective view showing the configuration of the planar polymer optical waveguide according to the present embodiment.
The planar polymer optical waveguide 20 of the present embodiment is a planar parallel optical waveguide in which the wavelength of guided light is set to around 850 nm and a plurality of core layers are arranged in parallel in a plane. As shown, a lower cladding layer 21, a 20 μm-thick intermediate cladding layer 23, a plurality of core layers 22 formed in a strip shape in the intermediate cladding layer 23, and an upper cladding layer 24 each made of a high-molecular organic compound. Is a planar polymer optical waveguide provided with:
[0028]
In the present embodiment, the core layer 22 and the intermediate cladding layer 23 are made of gracia, and the lower cladding layer 21 and the upper cladding layer 24 are made of fluorinated polyimide. The refractive index of the core layer 22 is 3.8% larger than that of the lower cladding layer 21 and the upper cladding layer 24. The refractive index of the intermediate cladding layer 23 is 1.0% smaller than that of the core layer 22 due to the irradiation of ultraviolet rays. For this reason, the incident light on the core layer 22 travels by totally reflecting the boundary surface of the core layer 22.
For light having a wavelength around 850 nm, the propagation loss of glacia is 0.1 dB / cm, and the propagation loss of fluorinated polyimide is 2.5 dB / cm. This propagation loss is proportional to the absorption coefficient. Therefore, the absorption coefficient of Gracia is smaller than the absorption coefficient of fluorinated polyimide.
[0029]
In this embodiment, since the lower cladding layer 21 and the upper cladding layer 24 have a large absorption coefficient, the light incident on the lower cladding layer 21 and the upper cladding layer 24 is attenuated. For this reason, it is possible to suppress cladding modes that propagate by reflecting air and waveguides in the vertical direction. In the present embodiment, although the absorption coefficient of the intermediate cladding layer 23 is small with respect to the cladding mode that propagates by reflecting in the lateral direction, noise can be sufficiently reduced by such a configuration.
[0030]
First, as shown in FIG. 3A, a method for manufacturing the planar polymer optical waveguide 20 according to the present embodiment uses polyimide, glass, quartz, Si, GaAs, InP, SOI (Silicon on Insulator), or the like. A fluorinated polyimide film is formed by applying fluorinated polyimide on the substrate 25 to be formed. Next, the fluorinated polyimide film is cured by ultraviolet irradiation and post-baking to form a lower cladding layer 21.
[0031]
Subsequently, gracia is applied on the lower cladding layer 21 to form a gracia film, thereby forming a core forming layer 22a.
Subsequently, as shown in FIG. 3B, a photomask 26 having a band-shaped pattern composed of a region 26a transparent to ultraviolet rays and an opaque region 26b is placed on the core forming layer 22a, and irradiated with an illuminance of 250 W and irradiation. Ultraviolet irradiation is performed for an amount of 30 minutes. As shown in FIG. 3 (c), the core forming layer 22a below the region 26a irradiated with the ultraviolet rays has a lower refractive index and becomes the intermediate cladding layer 23 due to the irradiation of the ultraviolet rays. The lower core forming layer 22a becomes the core layer 22. Subsequently, post baking is performed.
[0032]
Subsequently, as shown in FIG. 3D, the photomask 26 is removed, and a fluorinated polyimide is applied on the core layer 22 and the intermediate cladding layer 23 to form a fluorinated polyimide film. Subsequently, the fluorinated polyimide film is cured by ultraviolet irradiation and post-baking to form the upper clad layer 24. Subsequently, through a process of removing the substrate 25, etc., the planar polymer optical waveguide 20 of the present embodiment can be completed. The substrate 25 may be left attached without being removed.
[0033]
In the method of manufacturing a planar polymer optical waveguide according to the present embodiment, the lower cladding layer 21 and the upper cladding layer 24 have a refractive index smaller than that of Gracia for light having a wavelength near 850 nm and a large absorption coefficient. Is adopted. In addition, by adopting gracia for the core forming layer 22a, irradiating the core forming layer 22a with ultraviolet rays using a photomask 26 to lower the refractive index, and forming the core layer 22 and the intermediate cladding layer 23, the present embodiment is performed. The planar polymer optical waveguide according to the embodiment can be easily manufactured.
[0034]
【The invention's effect】
According to the planar polymer optical waveguide of the present invention, the cladding mode can be attenuated and suppressed by employing a polymer organic compound having a larger absorption coefficient than the core layer for the cladding layer. Therefore, noise can be reduced even if the alignment accuracy between the light source and the optical waveguide is somewhat coarse. Further, the cladding mode can be suppressed with a simple configuration, and low-cost optical interconnection equipment and optical communication equipment can be realized.
According to the method of manufacturing a planar polymer optical waveguide of the present invention, the optical waveguide of the present invention can be easily manufactured by using the same manufacturing method as that of the related art by selecting the polymer organic compound specified in the present invention. It is possible.
[Brief description of the drawings]
FIG. 1 is a side sectional view showing a configuration of a planar polymer optical waveguide according to a first embodiment.
FIG. 2 is a perspective view illustrating a configuration of a planar polymer optical waveguide according to a second embodiment.
FIGS. 3A to 3D are cross-sectional views illustrating a method for manufacturing a planar polymer optical waveguide according to a second embodiment.
FIG. 4 is a cross-sectional view showing a configuration of an optical waveguide described in JP-A-4-67103.
FIG. 5 is a cross-sectional view showing the vicinity of a light emitting end of the planar polymer optical waveguide according to the first embodiment.
[Explanation of symbols]
10 ······················································································································································································ ···················································· sequence · [mm_low_low] ..., Upper cladding layer 13, (noise) light leaking from core layer 12, emission end 20,... , Lower clad layer, 22 core layer, 22a core formed layer, 23 intermediate clad layer , 24... Upper cladding layer, 25... Substrate, 26... Photomask, 26a. ... Area opaque to ultraviolet rays, 30 ... Optical waveguide described in JP-A-4-67103, 31 ... Cladding, 32 ...... core, 33 ...... cladding covering portion, 34 ...... additives.

Claims (6)

In each of the planar type polymer optical waveguides comprising a high-molecular organic compound, a core layer, and a cladding layer enclosing or sandwiching the core layer,
The cladding layer is made of another polymer organic compound having an absorption coefficient larger than the absorption coefficient of the polymer organic compound forming the core layer with respect to the wavelength of the light to be guided. Wave path. The planar polymer optical waveguide according to claim 1, wherein the cladding layer is formed of a polymer organic compound having a property of being cured by ultraviolet irradiation. In each of the lower clad layer, the intermediate clad layer, the core layer formed in a belt shape in the intermediate clad layer, and the planar polymer optical waveguide including the upper clad layer, each of which is made of a high-molecular organic compound,
An intermediate cladding layer is formed of the same high molecular organic compound as the core layer, with a high molecular organic compound modified to have a refractive index smaller than the refractive index of the core layer by ultraviolet irradiation,
A planar polymer, wherein the lower and upper cladding layers are made of a polymer organic compound having an absorption coefficient larger than that of the polymer organic compound constituting the core layer with respect to the wavelength of the guided light. Optical waveguide. 4. The planar polymer optical waveguide according to claim 3, wherein the core layers extend in parallel. Forming a lower cladding layer on the substrate,
On the lower cladding layer, for light of a specific wavelength, to form a core forming layer with a high molecular organic compound having an absorption coefficient larger than the absorption coefficient of the high molecular organic compound constituting the lower cladding layer,
A photomask having a band-shaped core layer pattern is placed on the core forming layer, ultraviolet irradiation is performed, the refractive index of the ultraviolet irradiation region is lowered to form an intermediate cladding layer, and the ultraviolet non-irradiated region is used as the core layer,
A method of manufacturing a planar polymer optical waveguide, comprising forming an upper clad layer made of the same high molecular organic compound as a lower clad layer on an intermediate clad layer and a core layer. The method for producing a planar polymer optical waveguide according to claim 5, wherein a core layer extending in parallel is formed.

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