JP2004101876A - Optical waveguide and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new structure of an optical waveguide and its manufacturing method in which a groove having the core form of the optical waveguide is formed by a molding method to produce the core part without a process of removing an excess core material so as to easily mass-produce an optical waveguide with a small loss and high reliability at a low cost. <P>SOLUTION: The optical waveguide having a square core part with a flat upper face of the core is produced by forming a groove pattern deeper than the core depth by a glass molding method and then filling the groove with a resin material having large cure shrinkage. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
INDUSTRIAL APPLICABILITY The present invention is used for optical passive components such as a demultiplexer, a multiplexer, and optical switching in the field of optical communication, and is also applicable to an optical integrated circuit, particularly a single mode optical waveguide and a method for manufacturing the same It is about.
[0002]
[Prior art]
With the development of the optical communication market, optical components are required to have both performance and cost. In particular, optical passive components that do not operate by themselves, especially optical waveguides, are attracting attention, and demand for cost reduction is increasing.
[0003]
The optical waveguide is formed by covering a core made of a high refractive index material with a clad made of a low refractive index material. FIG. 5 is a plan view (FIG. 5A) and a cross-sectional view (FIG. 5B: AA cross-sectional view of FIG. 5A) of a general quartz-based single mode optical waveguide. Since the core 51 has a higher refractive index than the cladding 52, light satisfying a specific condition is confined in the core pattern and transmitted. An optical circuit can be formed by patterning the core 51 as shown in FIG. In the wavelength band of 1.3 to 1.55 μm, the core 51 generally has a square cross section with one side of about 6 to 8 μm. The core shape and the core surface roughness greatly affect the light propagation performance.
[0004]
Optical waveguides require very fine and accurate patterns. In particular, a pattern accuracy specification is strict for a single mode optical waveguide.
[0005]
Therefore, photolithography and dry etching, which are frequently used in semiconductor processes, are used for manufacturing optical waveguides.
[0006]
Hereinafter, a manufacturing process of a single mode optical waveguide for optical communication will be described with reference to the drawings.
[0007]
FIG. 6 is a process diagram showing a general method for manufacturing a conventional silica-based optical waveguide (for example, see Non-Patent Document 1). In the illustrated step, first, a core film 61 is formed by a flame deposition method on a quartz substrate 62 also serving as a lower cladding layer (FIG. 6A). When a substrate made of a material other than the quartz substrate is used, the lower cladding layer 63 is first formed by a flame deposition method. Next, the core film 61 is patterned into a predetermined pattern by using photolithography and dry etching (FIG. 6B). Further, an upper clad layer 63 is formed by a flame deposition method (FIG. 6C). By such a method, a low-loss optical waveguide has been manufactured.
[0008]
Also, in manufacturing an optical waveguide using a resin material, a core layer and a cladding layer are mainly formed by spin coating, and photolithography and dry etching are used for patterning of the core layer.
[0009]
As described above, in the production of a conventional optical waveguide, a clad, which is a thick film of 20 μm or more, is formed a plurality of times for both quartz and resin, and the core is patterned into a convex shape using photolithography and dry etching. In such a case, a complicated and expensive facility uses a process requiring a large number of facilities, and thus has a problem in cost and productivity.
[0010]
Since a resin material is easy to process, various studies have been made on a method of manufacturing a polymer optical waveguide using the resin material, aiming at low cost and high productivity. Above all, molding methods using dies are being actively studied because mass production is easy.
[0011]
For example, Patent Literature 1 proposes an optical waveguide in which a clad layer having a core-shaped groove is formed by press-molding a polyimide resin, and the groove is filled with a polyimide resin. However, in the above manufacturing method, although the groove shape of the core portion can be easily formed by the molding method, after the groove portion is filled with the polyimide resin, a polishing step or a reaction for newly removing excess core material remaining on the clad surface is performed. It was necessary to introduce a ionic ion etching step. However, it is difficult to remove only the surplus part without affecting the performance, and there is a limit.
[0012]
Further, in Patent Document 2, in order to remove excess core material, a mold having a transparent core portion is used, and a liquid photo-curing resin sealed in a recessed portion of the mold is cured to form a mold. There has been proposed a method of manufacturing an optical waveguide in which a photo-curing resin existing in portions other than the recesses is washed away with a solvent. However, since a special mold is used, the cost increases.
[0013]
Patent Document 3 proposes an optical waveguide having a two-step groove shape in order to reduce the influence of the residual resin after the removal processing using a squeegee. Although the removal of the surplus core material is facilitated, the cost increases because the upper surface of the core has a concave shape and a special mold is used.
[0014]
Further, in Patent Document 4, a polymer material is applied to a core groove and a clad having an inverted W-shaped cross section having a convex shape on both sides thereof, and the polymer material is cured. A method of forming a polymer core portion and eliminating the need for removing excess polymer has been proposed, but there is a concave groove for the core on the substrate and convex protrusions on both sides thereof, so that the mold is formed. Is difficult and costly.
[0015]
On the other hand, Patent Document 5 proposes an optical waveguide formed of glass for the purpose of improving transmission performance, reliability, and heat resistance. The optical waveguide is formed by molding a glass material of a cladding material, forming a cladding having a core groove shape, and further pressing the glass material of the core material into a groove shape using the cladding as a mold.
[0016]
However, as for the glass overflowing from the groove-shaped portion, a grinding, polishing, and etching removing process is introduced as in the case of the resin.
[0017]
[Patent Document 1]
JP 2000-56147 A
[Patent Document 2]
JP-A-10-90544
[Patent Document 3]
JP-A-11-74247
[Patent Document 4]
JP-A-9-101425
[Patent Document 5]
JP-A-8-304649
[Non-patent document 1]
Kawauchi, Optronics, 1988 8, p. 85
[0018]
[Problems to be solved by the invention]
As described above, although the groove shape of the core portion can be easily formed by the molding method, the removal of the surplus core material is a problem in reducing the cost and ensuring the performance in the currently proposed optical waveguide fabrication by filling the groove. Has become.
[0019]
SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems and to provide an optical waveguide which has a small propagation loss and does not require removal of excess material, and a method for manufacturing the same.
[0020]
Another object of the present invention is to provide an optical waveguide having improved heat resistance, which is a problem of the polymer optical waveguide, and a method for manufacturing the same.
[0021]
[Means for Solving the Problems]
In order to achieve the above object, the optical waveguide of the present invention is such that an optical waveguide in which a groove is formed on a flat substrate surface and a core material is filled in the groove to form an optical waveguide core portion, wherein the groove is It has a desired width of the optical waveguide core portion and has a depth deeper than the core portion.
[0022]
In the optical waveguide of the present invention, the core material to be filled in the groove is made of a cured product of a resin having a large curing shrinkage.
[0023]
In the optical waveguide of the present invention, the core material is a cured product of a mixture of a branched polysilane and a polysiloxane.
[0024]
In the optical waveguide of the present invention, the core material is made of a resin thermoset at a temperature of 300 ° C. or higher.
[0025]
In the optical waveguide of the present invention, the depth of the groove is larger than the depth of the core by 0.5 μm or more.
[0026]
In the optical waveguide of the present invention, the substrate having the groove formed on the surface is made of glass.
[0027]
The optical waveguide of the present invention forms a groove on the surface of a glass substrate by a glass molding method.
[0028]
The optical waveguide of the present invention is obtained by forming a resin layer having a refractive index equivalent to that of the substrate on an optical waveguide core formed by filling a core material into a groove on the surface of the substrate.
[0029]
In the optical waveguide of the present invention, the resin layer having the same refractive index as the substrate is made of a thermosetting resin.
[0030]
Further, in the method for manufacturing an optical waveguide of the present invention, a groove having a desired optical waveguide core portion width is formed on the substrate surface, and a groove deeper than the depth of the core portion is formed, and the core material is filled in the groove. In the method of manufacturing an optical waveguide for forming an optical waveguide core portion, a mold having a convex portion corresponding to a groove shape and a glass substrate are heated to a temperature near a softening point, and the mold is pressed against the softened glass substrate. Pressing, forming a groove on the surface of the glass substrate; forming a first resin layer serving as a core material by curing the surface of the glass substrate; A curing step of curing the first resin layer, wherein the resin is cured and shrunk in the curing step to form an optical waveguide core.
[0031]
In the method of manufacturing an optical waveguide according to the present invention, the first resin which becomes a core material by curing has a curing shrinkage of 10 to 70%.
[0032]
In the method of manufacturing an optical waveguide according to the present invention, the coating method for forming the first resin layer is blade coating or bar coating.
[0033]
In the method for manufacturing an optical waveguide according to the present invention, the step of curing the first resin layer is a heat treatment.
[0034]
According to the method of manufacturing an optical waveguide of the present invention, after the step of curing the first resin layer, a second resin layer having a refractive index equivalent to that of the glass substrate is formed.
[0035]
In the method for manufacturing an optical waveguide according to the present invention, the second resin layer having a refractive index equivalent to that of the substrate is made of a thermosetting resin, and is formed at a temperature equal to or lower than the curing temperature of the first resin forming the optical waveguide core. Heat treatment is performed.
[0036]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
[0037]
(Embodiment 1)
First, the optical waveguide of the present invention will be described.
[0038]
FIG. 1 shows a cross-sectional configuration of the optical waveguide of the present invention. As a lower clad, a glass substrate 11 having a groove 14 deeper than the optical waveguide core depth, as an upper clad, a second resin layer 12 having a refractive index equivalent to that of the glass substrate 11, and as a core, It is made of a cured first resin 13 having a large refractive index.
[0039]
The dimension of the optical waveguide core is 8 μm square, and the refractive index difference between the core and the clad, that is, the relative refractive index difference between the glass substrate 11, the cured resin layer 12, and the cured first resin 13 is 0.25%. Such an optical waveguide becomes a single mode at wavelengths of 1.3 μm and 1.55 μm which are often used for optical communication.
[0040]
As the first resin 13 as the core material, a mixture of a branched polysilane and a polysiloxane is appropriate. This resin causes a curing reaction by heating or irradiation with ultraviolet rays. That is, desorption of organic components in the molecule and decomposition of the SiSi bond in the polysilane molecule cause a three-dimensional reaction. As a result, the refractive index decreases and the center wavelength of optical communication becomes 1.3 to 1.55 μm. In addition, the reduction in waveguide loss can be realized, and the increase in the SiO component due to the curing reaction improves the adhesion to the glass substrate, advances the mineralization, and increases the reliability. .
[0041]
A curing temperature of 300 ° C. or higher is desirable in terms of light transmittance, heat resistance, and reliability.
[0042]
Below 300 ° C., the curing reaction becomes insufficient.
[0043]
Polysiloxane in the resin component has a low surface tension, and at the beginning of the curing process, reduces the adhesive force with the groove wall surface and reduces the shearing force of the resin. Occur, and the adhesion to the groove wall surface is small, so that there is no dent due to shrinkage.
[0044]
However, as the heating temperature rises, the effect is reduced due to volatilization and decomposition of polysiloxane, and the decomposition reaction of branched polysilane is accelerated. Strongly adhered to.
[0045]
By the effect of the above two components, the groove is filled with a cured resin having a flat upper surface, and a rectangular core portion is formed.
[0046]
The curing shrinkage of the resin is preferably from 10 to 70%, more preferably from 20 to 50%. If it is less than 10%, the separation of the cured resin between the core portion and the flat portion becomes insufficient, and if it is more than 70%, a deep groove is required to form the core portion with good separation from the flat portion. It becomes difficult to fill the groove of the resin and form the groove by glass molding.
[0047]
The cure shrinkage of the resin can be changed by changing the resin composition and heating conditions.
[0048]
The curing shrinkage ratio is obtained by dividing the film thickness reduced by the curing shrinkage after the curing treatment by the thickness of the resin layer before the curing treatment. When the resin layer was formed from the resin solution, after preheating (residual rate of the solvent was 10% or less) was regarded as before the curing treatment. In the case of a non-solvent type cured resin, the coating film thickness was determined before the curing treatment.
[0049]
Optical glass is used as a glass substrate on which a groove is formed as a lower clad. For optical lenses, optical glass whose refractive index is precisely controlled and which can be formed into a glass is commercially available and can be used. Since glass has a coefficient of thermal expansion one order of magnitude smaller than resin, glass substrates manufactured by glass molding can realize core shapes and core patterns with high dimensional accuracy, enabling optical waveguides with high performance. is there.
[0050]
As the second resin of the upper clad, a resin having the same refractive index as that of the glass plate as the lower clad and capable of precisely controlling the refractive index is used. Further, a cured resin is desirable for obtaining environmental reliability, and a thermosetting resin is desirable for securing heat resistance. The same type of resin of a mixture of a branched polysilane and a polysiloxane used as a core material has good adhesion to a glass substrate as a lower clad and a cured product of a mixture of a branched polysilane and a polysiloxane (resin 1) as a core. It is optimal to have.
[0051]
The depth of the groove formed in the glass substrate 11 is desirably 0.5 μm or more deeper than the depth of the core. If the thickness is less than 0.5 μm, the structure becomes continuous with the surplus cladding material in the flat portion of the glass substrate 11, causing light leakage and deteriorating the waveguide performance.
[0052]
Next, a method for manufacturing an optical waveguide will be described with reference to examples.
[0053]
【Example】
(Example 1)
FIG. 2 shows a method of manufacturing an optical waveguide for realizing the optical waveguide of FIG. FIG. 3 shows the press forming apparatus used this time.
[0054]
As shown in FIG. 2A, a groove 24 having a depth of 8.9 μm for an optical waveguide was formed in a glass substrate 21 by using a glass molding method.
[0055]
Details will be described with reference to FIG. 3 includes a pair of upper and lower heater blocks 31 and 32. The upper heater block 31 is vertically movable, and the lower heater block 32 is fixed.
[0056]
The 20 mm square upper die 33 has a convex optical waveguide pattern finely processed by dry etching on the molding surface, and has a noble metal-based protective film on the surface for mold release from glass and corrosion resistance. Have. The cross-sectional size of the groove of the waveguide pattern is 8 microns in width and 8.9 microns in depth, and is 0.9 microns deeper than the core.
[0057]
A 15 mm square glass substrate 34 (optical glass 1 having a refractive index of 1.581 and a softening point of 520 ° C.) was placed on a flat lower mold 35 fixed on a lower heater block 32.
[0058]
Nitrogen was charged into the chamber 36, and the upper heater block 31 to which the upper mold 33 was fixed was moved downward so that the molding surface of the mold was in contact with the glass substrate 34 with a low load of 50 kg / cm 2 or less. In this state, the upper and lower heater blocks 31 and 32 were energized to heat and soften the glass substrate 34 to 520 ° C. near the softening point of the glass substrate. Next, the load was increased to 400 kg / cm 2, and when it was deformed by 0.2 mm, the load was stopped, power supply to the heater was stopped, and cooling was started. Thereafter, the glass substrate was cooled to around room temperature and the glass substrate was taken out of the molding machine.
[0059]
Observation of the surface and cross section of the molded glass substrate taken out with an optical microscope and an electron microscope confirmed that a groove of a fine pattern in which the convex pattern of the mold was accurately transferred over the entire surface of the glass substrate.
[0060]
Next, a resin solution composed of a mixture of a branched polysilane and a polysiloxane (composition 1: cure shrinkage of 10%) is applied by a blade coating method to a glass substrate 21 on which an optical waveguide groove is formed as shown in FIG. The resin layer 23 was formed in the groove 24. Although the flat portion has some unsweeped portions, the film thickness of the flat portion after preheating at 120 ° C. for 30 minutes is 0.1 μm or less.
[0061]
In this embodiment, the blade coating method is used, but a method of sweeping out a solution dropped on the substrate surface or a bar coating method can also be used. In these coating methods, the resin in the groove can be filled with a very thin or thin resin layer in the flat portion of the substrate, and the effect of the excess core material can be prevented.
[0062]
Next, after the preliminary heating, the temperature was raised to 350 ° C., and the resin was cured by a heat treatment at 350 ° C. for 30 minutes.
[0063]
After curing, when observed with an optical microscope, no formation of bubbles or foreign matters due to insufficient filling of the groove or poor adhesion was observed, and the cured resin was filled in the optical waveguide groove. At this stage, when the cross section was observed with an electron microscope, as shown in FIG. 2 (c), the resin layer of the flat portion 22 and the groove 24 was separated by the curing shrinkage of the resin, and the upper surface was a flat 8-micron square rectangle. Was formed.
[0064]
Note that the heat treatment temperature is preferably higher within a range that does not adversely affect the film from the viewpoint of optical characteristics, heat resistance, and reliability, and is preferably in a range of 300 to 400 ° C. When the temperature is lower than 300 ° C., transparency becomes insufficient and the waveguide loss is large. When the temperature exceeds 400 ° C., cracks are easily generated.
[0065]
Although the resin can be cured by irradiation with ultraviolet rays, curing by heating is highly uniform and also has an annealing effect, so that it is suitable for a method for curing an optical waveguide with less distortion and defects.
[0066]
Next, a 20-micron-thick resin layer 26 (composition 5) made of a mixture of branched polysilane and polysiloxane was formed on the surface of the glass substrate 21 on which the core 25 was formed (FIG. 2D). Further, heat treatment was performed at 350 ° C. for 30 minutes to form an upper clad 27 whose refractive index was adjusted to be equal to that of the glass plate as the lower clad.
[0067]
Observation with an optical microscope showed no formation of bubbles or foreign matter due to insufficient filling of the grooves or poor adhesion.
[0068]
After the first resin forming the core portion is cured, the second resin layer is formed. Therefore, the influence of the second resin solution on the core portion during coating, the roughening of the film surface and the mixing of the resin components are caused. Can be prevented.
[0069]
Further, when the refractive index of the resin layer 25 in the core portion was measured before and after the formation of the resin layer 26, no change was observed.
[0070]
By performing the heat treatment at a temperature equal to or lower than the curing temperature of the first resin, an additional curing reaction of the core resin due to the heat treatment can be prevented, thereby preventing a change in the refractive index.
[0071]
In this example, the composition 5 was used as the upper clad, and the refractive index was controlled by the resin composition. However, the resin having the same composition 1 as the core material may be used, and the refractive index may be adjusted by the heating temperature.
[0072]
The optical waveguide sample thus produced was cut out at several locations by dicing, and the cross section was observed with an electron microscope. As a result, the upper surface of the core portion had a flat shape and a rectangular core portion of 8 μm square was formed.
[0073]
When a single-mode quartz optical fiber was connected to the manufactured single-mode optical waveguide, the measured value of the propagation loss at a wavelength of 1.55 μm was about 0.12 dB / cm, which confirmed that there was no practical problem.
[0074]
(Example 2)
In the same manner as in Example 1, the optical waveguide groove was formed on a 15 mm square glass substrate 34 (optical glass having a refractive index of 1.569 and a softening point of 542 ° C.) using the press forming apparatus shown in FIG. Formed. The cross-sectional size of the groove in the waveguide pattern is 8 microns wide and 10.5 microns deep, 2.5 microns deeper than the core.
[0075]
Observation of the surface and the cross section of the formed glass substrate with an optical microscope and an electron microscope revealed that a groove of a fine pattern in which the convex pattern of the mold was accurately transferred over the entire surface of the glass substrate.
[0076]
Next, as shown in FIG. 2B, a resin solution composed of a mixture of a branched polysilane and a polysiloxane (composition 2: cure shrinkage of 24%) is applied by a blade coating method to a glass substrate 21 on which an optical waveguide groove is formed. The resin layer 23 was formed. The film thickness of the flat portion after preheating at 120 ° C. for 30 minutes is 0.1 μm or less.
[0077]
Next, after preheating, the temperature was raised to 370 ° C., and the resin was cured by a heat treatment at 370 ° C. for 30 minutes. Observation with an optical microscope showed no formation of bubbles or foreign matter due to insufficient filling of the grooves or poor adhesion, and the cured resin was filled in the optical waveguide grooves. At this stage, when the cross section was observed with an electron microscope, the resin layer of the groove 24 was separated from the flat portion 22 due to the curing shrinkage of the resin as shown in FIG. Was formed.
[0078]
Next, a resin layer 26 (composition 6) having a thickness of 20 μm made of a mixture of branched polysilane and polysiloxane was formed on the surface of the glass substrate 21 on which the core 25 was formed (FIG. 2D). Further, heat treatment was performed at 350 ° C. for 30 minutes to form an upper clad 27 whose refractive index was adjusted to be equal to that of the glass plate as the lower clad.
[0079]
The optical waveguide sample thus produced was cut out at several locations by dicing, and the cross section was observed with an electron microscope. As a result, the upper surface of the core portion had a flat shape and a rectangular core portion of 8 μm square was formed.
[0080]
When a single-mode quartz optical fiber was connected to the manufactured single-mode optical waveguide, the measured value of the propagation loss at a wavelength of 1.55 μm was about 0.10 dB / cm, which confirmed that there was no practical problem. .
[0081]
(Example 3)
In the same manner as in Example 1, an optical waveguide groove was formed on a 15 mm square glass substrate 34 (optical glass 2 having a refractive index of 1.569 and a softening point of 542 ° C.) using a press forming apparatus shown in FIG. Formed by using The cross-sectional size of the groove of the waveguide pattern is 8 microns wide and 16 microns deep, which is 8 microns deeper than the core.
[0082]
Observation of the surface and the cross section of the formed glass substrate with an optical microscope and an electron microscope revealed that a groove of a fine pattern in which the convex pattern of the mold was accurately transferred over the entire surface of the glass substrate.
[0083]
Next, a resin solution composed of a mixture of a branched polysilane and a polysiloxane (composition 3: cure shrinkage of 50%) is applied to the glass substrate 21 on which the optical waveguide groove is formed as shown in FIG. The resin layer 23 was formed. After preheating at 120 ° C. for 30 minutes, the thickness of the flat portion 22 is 0.1 μm or less.
[0084]
Next, after preheating, the temperature was raised to 370 ° C., and the resin was cured by a heat treatment at 370 ° C. for 30 minutes. Observation with an optical microscope showed no formation of bubbles or foreign matter due to insufficient filling of the grooves or poor adhesion, and the cured resin 3 was filled in the optical waveguide grooves. At this stage, when the cross section was observed with an electron microscope, as shown in FIG. 2 (c), the resin layer of the flat portion 22 and the groove 24 was separated by the curing shrinkage of the resin, and the upper surface was a flat 8-micron square rectangle. Was formed.
[0085]
Next, a resin layer 26 (composition 6) having a thickness of 20 μm made of a mixture of branched polysilane and polysiloxane was formed on the surface of the glass substrate 21 on which the core 25 was formed (FIG. 2D). Further, heat treatment was performed at 350 ° C. for 30 minutes to form an upper clad 27 whose refractive index was adjusted to be equal to that of the glass plate as the lower clad.
[0086]
The optical waveguide sample thus produced was cut out at several locations by dicing, and the cross section was observed with an electron microscope. As a result, the upper surface of the core portion had a flat shape and a rectangular core portion of 8 μm square was formed.
[0087]
When a single-mode quartz optical fiber was connected to the manufactured single-mode optical waveguide, the measured value of the propagation loss at a wavelength of 1.55 μm was about 0.008 dB / cm, which confirmed that there was no practical problem. Was.
[0088]
As described above, in Examples 1 to 3, the case where the resin was filled in the groove for the core by the blade coating method was described. However, in Examples 4 to 6, the conventional method for manufacturing a polymer optical waveguide was used. The case of the spin coating method used in the above will be described. FIG. 4 shows a manufacturing method.
[0089]
(Example 4)
In the same manner as in Example 1, an optical waveguide groove was formed on a 15 mm square glass substrate 34 (optical glass 2 having a refractive index of 1.569 and a softening point of 542 ° C.) using a press forming apparatus shown in FIG. (FIG. 4A). The cross-sectional size of the groove 44 of the waveguide pattern is 8 microns in width and 10 microns in depth, and is 2 microns deeper than the core.
[0090]
Observation of the surface and the cross section of the formed glass substrate with an optical microscope and an electron microscope revealed that a groove of a fine pattern in which the convex pattern of the mold was accurately transferred over the entire surface of the glass substrate.
[0091]
Next, as shown in FIG. 4B, a resin solution composed of a mixture of a branched polysilane and a polysiloxane (composition 3: cure shrinkage of 50%) is applied to the glass substrate 41 on which the optical waveguide groove is formed, by a spin coating method. The resin layer 43 was formed. After preliminary heating at 120 ° C. for 30 minutes, the thickness of the flat portion 42 was 6 μm.
[0092]
Next, after preheating, the temperature was raised to 370 ° C., and the resin was cured by a heat treatment at 370 ° C. for 30 minutes. Observation with an optical microscope showed no formation of bubbles or foreign matter due to insufficient filling of the grooves or poor adhesion, and the cured resin 3 was filled in the optical waveguide grooves. At this stage, when the cross section was observed with an electron microscope, as shown in FIG. 4 (c), the resin layer of the flat portion 46 and the groove portion 44 was separated by the curing shrinkage of the resin, and the flat upper surface was a square of 8 μm square. Was formed.
[0093]
The groove deeper than the core depth and the resin having a large curing shrinkage enable the resin layer to be separated from the groove portion and the flat portion, thereby preventing the leakage of light to the surplus core material remaining in the flat portion and the excess core. This eliminates the need for a material removal step.
[0094]
In the case of filling the groove portion with the resin by the spin coating method, there is a feature that the groove depth can be reduced. In other words, the groove depth is 6 microns smaller than that of the third embodiment.
[0095]
Next, a resin layer 47 (composition 6) having a thickness of 20 μm and made of a mixture of branched polysilane and polysiloxane was formed on the surface of the glass substrate 41 on which the core 45 was formed (FIG. 4D). Further, heat treatment was performed at 350 ° C. for 30 minutes to form an upper clad 48 whose refractive index was adjusted to be equal to that of a glass plate as a lower clad.
[0096]
The optical waveguide sample thus produced was cut out at several locations by dicing, and the cross section was observed with an electron microscope. As a result, the upper surface of the core portion had a flat shape and a rectangular core portion of 8 μm square was formed.
[0097]
When a single-mode quartz optical fiber was connected to the manufactured single-mode optical waveguide, the measured value of the propagation loss at a wavelength of 1.55 μm was about 0.08 dB / cm, which confirmed that there was no practical problem.
[0098]
(Example 5)
In the same manner as in Example 1, an optical waveguide groove was formed on a glass substrate (optical glass having a refractive index of 1.549 and a softening point of 536 ° C.) by a glass molding method using the press molding apparatus of FIG.
[0099]
The cross-sectional size of the groove in the waveguide pattern is 8 microns wide and 12 microns deep, 4 microns deeper than the core.
[0100]
Observation of the surface and the cross section of the formed glass substrate with an optical microscope and an electron microscope revealed that a groove of a fine pattern in which the convex pattern of the mold was accurately transferred over the entire surface of the glass substrate.
[0101]
Next, as shown in FIG. 4B, a resin solution composed of a mixture of a branched polysilane and a polysiloxane (composition 4: cure shrinkage of 70%) is applied to the glass substrate 41 on which the optical waveguide groove is formed, by a spin coating method. The resin layer 43 was formed. After the preliminary heating at 120 ° C. for 30 minutes, the thickness of the flat portion 42 was 15 μm.
[0102]
Next, after preheating, the temperature was raised to 370 ° C., and the resin was cured by a heat treatment at 370 ° C. for 30 minutes. Observation with an optical microscope showed no formation of bubbles or foreign matter due to insufficient filling of the grooves or poor adhesion, and the cured resin 3 was filled in the optical waveguide grooves. At this stage, when the cross section was observed with an electron microscope, it was as shown in FIG. Due to the curing shrinkage of the resin, the resin layer of the flat portion 46 and the groove 44 was separated, and a rectangular core 45 having a flat upper surface of 8 μm square was formed.
[0103]
The optical waveguide sample thus produced was cut out at several locations by dicing, and the cross section was observed with an electron microscope. As a result, the upper surface of the core portion had a flat shape and a rectangular core portion of 8 μm square was formed.
[0104]
Next, a resin layer 47 (composition 7) having a thickness of 20 μm made of a mixture of branched polysilane and polysiloxane was formed on the surface of the glass substrate 41 on which the core 45 was formed (FIG. 4D). Further, heat treatment was performed at 350 ° C. for 30 minutes to form an upper clad 48 whose refractive index was adjusted to be equal to that of a glass plate as a lower clad.
[0105]
When a single-mode quartz optical fiber was connected to the manufactured single-mode optical waveguide, the measured value of the propagation loss at a wavelength of 1.55 μm was about 0.06 dB / cm, which confirmed that there was no practical problem.
[0106]
(Example 6)
In the same manner as in Example 1, an optical waveguide groove was formed on a 15 mm square glass substrate 34 (optical glass 2 having a refractive index of 1.569 and a softening point of 542 ° C.) using a press forming apparatus shown in FIG. Formed by using The cross-sectional size of the groove in the waveguide pattern is 8 microns wide and 8.5 microns deep, 0.5 microns deeper than the core.
[0107]
Observation of the surface and the cross section of the formed glass substrate with an optical microscope and an electron microscope revealed that a groove of a fine pattern in which the convex pattern of the mold was accurately transferred over the entire surface of the glass substrate.
[0108]
Next, as shown in FIG. 4B, a resin solution composed of a mixture of a branched polysilane and a polysiloxane (composition 2: cure shrinkage 24%) is applied to the glass substrate 41 on which the optical waveguide groove is formed by spin coating. The resin layer 43 was formed. After the preliminary heating at 120 ° C. for 30 minutes, the thickness of the flat portion 42 was 2 μm. Next, after preheating, the temperature was raised to 370 ° C., and the resin was cured by a heat treatment at 370 ° C. for 30 minutes. Observation with an optical microscope showed no formation of bubbles or foreign matter due to insufficient filling of the groove or poor adhesion, and the cured resin 3 was filled in the optical waveguide groove. At this stage, when the cross section was observed with an electron microscope, it was as shown in FIG. Due to the curing shrinkage of the resin, the resin layer of the flat portion 46 and the groove 44 was separated, and a rectangular core 45 having a flat upper surface of 8 μm square was formed.
[0109]
The optical waveguide sample thus produced was cut out at several locations by dicing, and the cross section was observed with an electron microscope. As a result, the upper surface of the core portion had a flat shape and a rectangular core portion of 8 μm square was formed.
[0110]
Next, a resin layer 47 (composition 7) having a thickness of 20 μm made of a mixture of branched polysilane and polysiloxane was formed on the surface of the glass substrate 21 on which the core 45 was formed (FIG. 4D). Further, heat treatment was performed at 350 ° C. for 30 minutes to form an upper clad 48 whose refractive index was adjusted to be equal to that of a glass plate as a lower clad.
[0111]
When a single-mode silica-based optical fiber was connected to the single-mode optical waveguide fabricated in this manner, the measured value of the propagation loss at a wavelength of 1.55 μm was about 0.10 dB / cm, which confirmed that there was no practical problem. Was done.
[0112]
ADVANTAGE OF THE INVENTION According to this invention, the groove | channel for core part formation can be created with high precision in a glass surface, and the core material of a flat part and a groove part can be isolate | separated by using resin with large hardening shrinkage, , And a high-performance optical waveguide can be formed without introducing a step of processing an excess core material.
[0113]
Although the present invention is most effective for a single mode optical waveguide, it is added that the present invention can be applied to a multimode optical waveguide.
[0114]
【The invention's effect】
As described above, the present invention can form a core groove with good dimensional accuracy by glass molding, and can fill a core material with good transmission characteristics without removing excess core material. In addition, it uses a glass substrate and a cured product of high-temperature treatment as the core material and the upper clad material, and has high heat resistance and high reliability, and has practical performance, economic efficiency, and productivity as a single mode optical waveguide. And very useful.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of an optical waveguide according to the present invention.
FIG. 2 is a diagram showing a manufacturing process of an optical waveguide in Examples 1 to 3.
FIG. 3 is a diagram showing a configuration of a press molding machine used for forming an optical waveguide groove in Examples 1 to 6.
FIG. 4 is a view showing a manufacturing process of an optical waveguide in Examples 4 to 6.
FIG. 5A is a plan view of a general single-mode optical waveguide.
(B) Cross-sectional view of a general single-mode optical waveguide
FIG. 6 is a process chart showing a conventional general optical waveguide manufacturing method.
[Explanation of symbols]
11,21,41 Glass substrate
12 resin layer
13 Resin
14, 24, 44 grooves
22, 42, 46 Flat part
23, 43 resin layer
25,45 core
26 resin layer
27 Upper cladding
31 Upper heater block
32 Lower heater block
33 Upper type
34 glass substrate
35 lower mold
36 chambers
47 resin layer
48 Upper cladding
51 core
52 clad
61 core film
62 quartz substrate
63 cladding layer

Claims (15)

In an optical waveguide in which a groove is formed on a flat substrate surface and a core material is filled in the groove to form an optical waveguide core portion, the groove has a desired width of the optical waveguide core portion, and An optical waveguide having a depth deeper than a core portion. 2. The optical waveguide according to claim 1, wherein the core material to be filled in the groove is made of a cured product of a resin having a large curing shrinkage. 3. The optical waveguide according to claim 1, wherein the core material is made of a cured product of a mixture of a branched polysilane and a polysiloxane. The optical waveguide according to claim 1, wherein the core material is made of a resin thermoset at a temperature of 300 ° C. or higher. The optical waveguide according to claim 1, wherein a depth of the groove is larger than a depth of the core by 0.5 μm or more. The optical waveguide according to claim 1, wherein the substrate having the groove formed on the surface is made of glass. The optical waveguide according to claim 5, wherein the substrate having a groove formed on the surface is manufactured by a glass molding method. 6. A resin layer having a refractive index equivalent to that of the substrate is formed on an optical waveguide core formed by filling a core material in a groove on the surface of the substrate. An optical waveguide as described. The optical waveguide according to claim 7, wherein the resin layer having the same refractive index as the substrate is made of a thermosetting resin. An optical waveguide having a desired width of an optical waveguide core portion on a flat substrate surface and a groove deeper than the depth of the core portion, and filling the groove with a core material to form an optical waveguide core portion. In the method of manufacturing a waveguide,
A glass forming step of heating a mold and a glass substrate having a convex portion corresponding to the groove shape to a temperature near the softening point, pressing the mold against the softened glass substrate and pressurizing, forming a groove on the surface of the glass substrate; ,
A coating step of forming a resin layer serving as a core material by curing on the surface of the glass substrate,
It comprises a curing step of curing a resin layer formed on the surface of the glass substrate,
In the curing step, a desired optical waveguide core is formed by curing and shrinking a resin. The method for manufacturing an optical waveguide according to claim 10, wherein the curing shrinkage of the resin is 10 to 70%. The method of manufacturing an optical waveguide according to claim 10, wherein the coating method of forming the resin layer is blade coating or bar coating. The method for manufacturing an optical waveguide according to claim 10, wherein the curing step of the resin is a heat treatment. 11. The method according to claim 10, wherein a second resin layer having a refractive index equivalent to that of the substrate is formed after the curing step of the resin. A second resin layer having a refractive index equivalent to that of the substrate is made of a thermosetting resin, and is heated at a temperature equal to or lower than a curing temperature of the first resin forming the optical waveguide core. Item 15. The method for manufacturing an optical waveguide according to Item 14.

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