JP3709088B2 - Optical waveguide - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical waveguide used in an optical communication module and the like. More specifically, the optical waveguide has high optical transparency and is less likely to be softened or stretched under a high temperature environment. The shape of the optical waveguide and an optical circuit using the optical waveguide is good. The present invention relates to an optical waveguide using an organic material, which is kept at the above and does not increase in light propagation loss or deteriorate characteristics due to deformation or cracking.
[0002]
[Prior art]
Conventionally, as an optical waveguide, for example, a silica-based optical waveguide in which a three-dimensional clad and a core are formed using a silica film formed on a quartz glass substrate or a silicon substrate by a flame deposition method, or a lithium niobate single unit is used. There is an optical waveguide in which a crystal substrate is used as a cladding portion and Ti is thermally diffused on the substrate to form a core portion in a three-dimensional waveguide shape.
[0003]
However, since these optical waveguides require heat treatment at a high temperature of 1000 ° C. or higher at the time of production, they are replaced with these conventional silica-based optical waveguides that require high-temperature treatment at the time of production from the viewpoint of ease of production of the optical waveguide. Therefore, it has been studied to use an optical waveguide using an organic material that can be formed at a low temperature.
[0004]
For example, PMMA (polymethyl methacrylate) resin, polycarbonate resin, polyimide resin, siloxane resin, BCB (benzocyclobutene) resin, fluorine resin, and the like have been studied as organic materials used for the organic optical waveguide. .
[0005]
Among these optical waveguides using organic resin materials, those using organic materials having a CH group such as PMMA, polycarbonate, polyimide, siloxane, BCB, etc. are one of the near infrared light regions used in optical communication systems. Since the 1.55 μm wavelength band is located in the vibration absorption band of the CH group, there is a problem that the propagation loss in the 1.55 μm wavelength band becomes large.
[0006]
On the other hand, since the fluororesin does not have a CH group that causes such light absorption, a low-loss optical waveguide can be manufactured by using the fluororesin.
[0007]
As a method for producing these organic optical waveguides, a lower clad layer is formed on a silicon substrate or a glass substrate, and then a core layer having a refractive index larger than that of the lower clad layer is formed. After forming the core part by thin film microfabrication technology such as (Reactive Ion Etching), the upper cladding layer having a refractive index smaller than that of the core part is coated to form a three-dimensional optical waveguide. Forming is done.
[0008]
[Problems to be solved by the invention]
However, the fluororesin described above has a low Tg (glass transition temperature) and softening temperature of 100 to 120 ° C. Further, the amount of expansion and expansion of the resin due to softening in such a temperature range was large.
[0009]
As a specific example of such a conventional fluororesin, an example of an evaluation result of the amount of elongation with respect to temperature for a cyclized fluoroethylene resin is shown by a diagram in FIG. In FIG. 4, the horizontal axis represents measurement temperature (unit: ° C.), and the vertical axis represents TMA (Thermo-Mechanical Analysis) elongation (unit:%). And the characteristic curve B in the figure has shown the measurement result of the TMA elongation amount of the conventional fluororesin.
[0010]
From this result, it can be seen that the glass transition temperature Tg of this fluororesin is about 108 ° C., and that the TMA elongation amount suddenly increases at a temperature higher than this, and a large elongation occurs in the resin.
[0011]
For this reason, in the organic optical waveguide manufacturing process, the resin material is 100 in the RIE process of the core part, the process of forming a metal film used as a resist mask in the RIE process, and the process of covering the core part with the upper cladding layer. Since it is heated to about 250 ° C. to about 250 ° C., there is a problem that unevenness, strain, cracking, etc. occur in the fluororesin at such a high temperature.
[0012]
Therefore, the fluororesin does not have a CH group, so even if it has excellent transparency to near infrared light used in an optical communication system, unevenness, distortion, cracks, etc. that occurred during the production of the optical waveguide As a result, the light is scattered, which causes a problem that a large propagation loss occurs in the optical waveguide.
[0013]
In addition, when an optical circuit having a structure in which two core portions are close to about several μm, such as an optical directional coupler, is to be manufactured, submicron manufacturing accuracy is required. However, there has been a problem that it is difficult to realize the desired characteristics because the optical waveguide cannot be manufactured with the required accuracy due to the softening and extension of the core part due to heating during the manufacturing.
[0014]
The present invention has been devised in view of the above-mentioned problems of the prior art, and its purpose is excellent in light transmittance, and softening and elongation due to heating during production are small, and the shape of the optical waveguide is kept good. Another object of the present invention is to provide an organic optical waveguide that does not increase the propagation loss of light or deteriorate characteristics due to deformation or cracking.
[0015]
[Means for Solving the Problems]
The optical waveguide of the present invention is a mixture of a uniform organic material in which a fluororesin and a siloxane resin are mixed in a clad portion made of a mixed resin that is a uniform organic material in which a fluororesin and a siloxane resin are mixed. A core portion made of a resin and having a refractive index larger than that of the cladding portion is formed.
[0016]
According to the optical waveguide of the present invention, since a mixed resin that is an organic material in which a fluororesin and a siloxane resin are mixed is used, the fluororesin does not have a CH group, so that it is used in an optical communication system. Excellent transparency can be obtained even in the 1.55μm wavelength band, which is one of the light regions, and the siloxane resin has a siloxane bond (-Si-O-) as the main skeleton and excellent thermal stability. As a result, it has excellent light transmission, and even if the resin material is heated during the production of the optical waveguide, the optical waveguide will not be uneven, distorted, cracked, etc. It is possible to obtain an organic optical waveguide that can be maintained and has no increase in light propagation loss or deterioration of characteristics due to deformation or cracking.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
The optical waveguide of the present invention will be described below with reference to the drawings.
[0018]
FIG. 1 is a sectional view showing an example of an embodiment of an optical waveguide according to the present invention. In FIG. 1, 1 is a substrate for forming an optical waveguide, 2 is a lower cladding layer of the optical waveguide, 3 is a core portion of the optical waveguide, 4 is an upper cladding of the optical waveguide covering the lower cladding layer 2 and the core portion 3 The core portion 3 is formed in a clad portion composed of the lower clad layer 2 and the upper clad layer 4.
[0019]
The substrate 1 functions as a support substrate of the optical waveguide, and various substrates used as optical signal processing substrates such as an optical integrated circuit substrate and an optoelectronic mixed substrate, such as silicon substrates, alumina ceramic substrates, glass ceramic substrates, A multilayer ceramic wiring board, a plastic electric wiring board, etc. can be used.
[0020]
The lower cladding layer 2 is made of a mixed resin of a fluororesin and a siloxane resin. After the fluororesin and the siloxane resin are mixed at a predetermined ratio, the substrate 1 is applied to the substrate 1 by a spin coat method or the like and cured. Form.
[0021]
The core portion 3 is made of a mixed resin of a fluororesin and a siloxane resin, and has a higher refractive index than the lower cladding layer 2 and the upper cladding layer 4 in order to function as a core portion of the optical waveguide. The core 3 is formed by mixing a fluororesin and a siloxane resin at a predetermined ratio, and then applying a predetermined thickness to the substrate 1 by a spin coating method or the like to cure, thereby forming a resin layer having a predetermined thickness. It is formed with a predetermined shape and dimensions using a well-known thin film microfabrication technique such as lithography or RIE.
[0022]
The upper clad layer 4 is formed by forming the core portion 3, mixing fluororesin and siloxane resin at a predetermined ratio, and applying and curing to a predetermined thickness by a spin coat method or the like.
[0023]
The fluororesin is used as the resin material for forming the optical waveguide of the present invention because it does not have a CH group, so that it has a wavelength of 1.55 μm, which is one of near infrared light regions used in an optical communication system. However, it has excellent transparency and is advantageous in forming a complicated optical circuit with a long transmission distance. Further, dry etching is easier than quartz glass, which is most recognized as an optical waveguide material, and fine processing of the core portion 3 requiring high accuracy of submicron or less is easy. In addition, in optoelectronic mixed circuits, high-density integrated mounting of electronic components and optical components is desired, so stacking of electrical wiring and optical circuits is required, but the formation of the fluororesin layer is about 100 ° C to 300 ° C. Since the process can be performed at the processing temperature, the damage to the substrate 1 as a base is small, and it can be laminated on the electric wiring board.
[0024]
On the other hand, the use of a siloxane resin as a resin to be mixed with a fluororesin has excellent thermal stability because it has a siloxane bond as a skeleton, and the glass transition point Tg of the mixed resin by mixing with a fluororesin. And the softening temperature can be increased, and the amount of extension of the resin due to softening during heating can be kept small. In addition, siloxane resins are one of the near infrared light regions used in optical communication systems compared to fluororesins that do not have a CH group because the main component is a siloxane bond and the functional group has a small amount of CH. Although the transmittance of light in the 1.55 μm wavelength band is inferior, it has light transmittance that can be used satisfactorily. Furthermore, since the siloxane resin layer can be formed at a processing temperature of about 150 to 300 ° C., damage to the base substrate 1 is small, and it can be laminated on various electric wiring substrates. Moreover, due to the characteristics of these siloxane resins, even when mixed with a fluororesin, the optical transparency and low-temperature film-forming properties of the fluororesin are not significantly impaired.
[0025]
Examples of the fluororesin that can be used as the lower clad layer 2, core portion 3, and upper clad layer 4 of the optical waveguide of the present invention include cyclized polyfluorinated ethylene resin, polytetrafluoroethylene (PTFE), and polychlorotrifluoroethylene. (PCTFE)-Tetrafluoroethylene-hexafluoropropylene copolymer (FEP)-Polyvinylidene fluoride (PVDF)-Polyvinyl fluoride (PVF)-Tetrafluoroethylene-ethylene copolymer-Chlorotrifluoroethylene-ethylene A copolymer, tetrafluoroethylene-perfluorovinyl ether copolymer (PFA) and the like can be mentioned. Among these, cyclized polyfluorinated ethylene / polytetrafluoroethylene (PTFE) and tetrafluoroethylene-hexafluoropropylene copolymer (FEP) are desirable in that they can be easily prepared with a siloxane resin. It should be noted that these fluororesins should not be used only in one type, and it goes without saying that several types of resins may be used in combination.
[0026]
On the other hand, the siloxane resin that can be used as the lower clad layer 2, the core portion 3, and the upper clad layer 4 of the optical waveguide of the present invention may be any resin that contains siloxane in the polymer skeleton. Sesquioxane, polydiphenylsilsesquioxane, polymethylphenylsilsesquioxane, ladder type silicone resin, and the like can be used.
[0027]
Polysilane can be used in combination with the siloxane resin. Examples of such polysilane include polyvinyltrimethylsilane, polydihalosilane, polytrihalosilane, and polytetrahalosilane. These polysilanes have —Si—Si— as a skeleton, and have excellent heat resistance.
[0028]
Needless to say, these siloxane resins and polysilanes are not limited to one kind, and several kinds of resins may be used in combination.
[0029]
Further, those obtained by substituting a part of silicon atoms of these siloxane resins or polysilanes with other trivalent or tetravalent metal atoms can also be used. In this case, it is useful because the refractive index of the resin can be set to a desired value depending on the amount of the substituted metal atom.
[0030]
The weight ratio of mixing the fluororesin and the siloxane resin is preferably in the range of 8: 2 to 4: 6, that is, 80% by weight of fluororesin: 20% by weight of siloxane resin to 40% by weight of fluororesin: 60% by weight of siloxane resin. . When the fluororesin exceeds 80% by weight and the siloxane resin is less than 20% by weight, the glass transition temperature Tg and softening temperature of the mixed resin forming the lower cladding layer 2, the core portion 3, and the upper cladding layer 4 are effectively increased. In other words, the amount of extension of the resin due to softening tends to be small. On the other hand, when the fluororesin is less than 60% by weight and the siloxane resin is more than 40% by weight, the glass transition temperature Tg and softening temperature of the mixed resin forming the lower clad layer 2, the core part 3 and the upper clad layer 4 are determined. An effective increase is seen, and the amount of resin stretched by softening can be suppressed to a smaller value, which is preferable.
[0031]
On the other hand, when the fluororesin is less than 40% by weight and the siloxane resin is more than 60% by weight, the solid content tends to precipitate during the preparation of the mixed resin, and there is a tendency that a uniform layer of the mixed resin cannot be obtained. When an optical waveguide is manufactured with such a layer, light is scattered by the deposited solid content to cause a propagation loss, or the scattered light becomes stray light and crosstalk occurs between adjacent optical waveguides. So undesirable.
[0032]
In addition, the light absorption loss of the fluororesin is 0.01 dB / cm or less and the light absorption loss of the siloxane resin is about 2 dB / cm in the wavelength 1.55 μm band which is one of the near infrared light regions used in the optical communication system. However, when the fluororesin exceeds 50% by weight and the siloxane resin is less than about 50% by weight, the light absorption loss in the mixed resin can be suppressed to 1 dB / cm or less, and a low-loss optical waveguide can be manufactured. This is preferable in terms of points.
[0033]
Furthermore, according to the mixed resin of the fluororesin and the siloxane resin, the refractive index of the mixed resin can be changed by changing the mixing ratio of the fluororesin and the siloxane resin within the above range. It can also be used effectively in the production of an optical waveguide that needs to be controlled in refractive index with the portion (lower cladding layer 2 and upper cladding layer 4).
[0034]
It should be noted that the amount of various metal atoms, such as Ti, Ge, Al, Zr, P, Er, and Pr, is controlled with respect to such a mixed resin as in the case of conventional resin materials, for example, By adding about 0 to 10% by weight with respect to the total weight, the refractive index of the mixed resin can be further changed and accurately controlled.
[0035]
【Example】
Next, specific examples of the optical waveguide of the present invention will be described.
[0036]
Cyclic polyfluorinated ethylene having a refractive index of 1.31 is used as the fluororesin, and polyphenylsilsesquiosan having a refractive index of 1.49 is used as the siloxane resin, and the weight ratio of polyphenylsilsesquiosan is 0%, 15%, Both are mixed to 20 wt%, 40 wt%, 60 wt%, 65 wt% and 100 wt%, spin-coated on a silicon substrate, and heat-treated at 300 ° C. A membrane consisting of
[0037]
For these films, near-infrared light was incident on the film and the transmitted light intensity was measured with an optical power meter to evaluate the transmission loss of the transmitted light. The results shown in FIG. 2 were obtained.
[0038]
FIG. 2 is a diagram showing a change in transmission loss with respect to the weight ratio (wt%) of the siloxane resin in the mixed resin of the fluororesin and the siloxane resin, the horizontal axis represents the siloxane resin ratio (wt%), and the vertical axis represents The transmission loss (dB / cm) with respect to light having a wavelength of 1.55 μm is represented. The black squares indicate the measurement values of the transmission loss in each composition, and the characteristic curve indicates the change.
[0039]
As can be seen from the results of FIG. 2, when the weight ratio of the siloxane resin is 60% by weight or less, the transmission loss is as low as about 1.2 dB / cm or less, and particularly when the weight ratio is about 50% by weight or less, the transmission loss is 1 dB / cm. The result was as low as cm or less, and good light transmittance was obtained.
[0040]
Among these, when the weight ratio of the siloxane resin was 20% by weight, the transmission loss was 0.4 dB / cm or less, which was very low and good. On the other hand, in the TMA evaluation, there was almost no change in the glass transition point Tg, but an effect that the change in softening was moderate as compared with the conventional resin shown by the characteristic curve B in FIG. When optical waveguides were actually made using this material, some wrinkles occurred, but the level was small compared to the case of using conventional materials, so that it could be used for short propagation lengths and simple optical circuit formation. It was a thing.
[0041]
Incidentally, when the weight ratio of the siloxane resin was 0% by weight, the transmission loss was approximately 0 dB / cm, which was very low and good. However, the glass transition point Tg and the amount of elongation were insufficient, Deformation, cracking, and the like occurred in the process of manufacturing the optical waveguide, such as the formation of the lower cladding layer, the formation of the core layer to be the core portion, and the formation of the core portion by forming the core layer and the formation of the upper cladding layer.
[0042]
Further, when the weight ratio of the siloxane resin was 15% by weight, the transmission loss was about 0.3 dB / cm or less, which was very low and good, but effective in terms of the glass transition point Tg and the amount of elongation in TMA evaluation. The improvement was not seen and it was insufficient.
[0043]
On the other hand, when the weight ratio of the siloxane resin is 65% by weight, the solid content is precipitated when the resin is mixed. Therefore, when a film is formed using the mixed resin, the composition is non-uniform and the surface roughness is large. It became a film and was not a desirable film for forming an optical waveguide.
[0044]
Moreover, when the refractive index was measured about these films | membranes using the refractive index measuring apparatus using a prism coupler, the result as shown in FIG. 3 was obtained. FIG. 3 is a diagram showing a change in refractive index with respect to the weight ratio (wt%) of the siloxane resin in the mixed resin of the fluororesin and the siloxane resin, the horizontal axis represents the siloxane resin ratio (wt%), and the vertical axis represents The refractive index with respect to light having a wavelength of 1.55 μm is shown. The black squares indicate the measured refractive index values of the respective compositions, and the characteristic curve shows the change.
[0045]
As can be seen from FIG. 3, by changing the weight ratio of the siloxane resin in the mixed resin of fluororesin and siloxane resin, the refractive index of the mixed resin can be changed at a substantially constant change rate, which is necessary for the production of the optical waveguide. The results show that the refractive indexes of the core and clad can be controlled easily and accurately.
[0046]
Next, TMA evaluation was performed on a sample in which a mixed resin film having a siloxane resin ratio of 40% by weight was formed on a silicon substrate by spin coating. The result is shown by a characteristic curve A in FIG.
[0047]
As shown in FIG. 4, this mixed resin film has a glass transition temperature Tg of about 120 ° C., which is an improvement of about 10 ° C. compared to the conventional fluororesin film shown by the characteristic curve B. As for the softening temperature, the temperature up to 300 ° C. showed no rapid softening, and the result was improved from the conventional fluororesin film showing the rapid softening at 110 ° C. Furthermore, from the result of FIG. 4, it can be seen that the TMA elongation amount is about 14% even at 300 ° C., and can be sufficiently reduced.
[0048]
Also, various widths and heights of 5 to 50 μm are obtained using a mixed resin with a siloxane resin ratio of 40% by weight for the lower clad layer and upper clad layer and a mixed resin with a siloxane resin ratio of 45% by weight for the core part. When the optical waveguide having the core part was produced, all showed a good shape and good results. Among these, when the propagation loss for light having a wavelength of 1.55 μm is measured for an optical waveguide having a core width and height of 8 μm, it is about 0.8 dB / cm, and exceeds 2 dB / cm for an optical waveguide using only a siloxane resin. Although it was a loss, it was a good result with a low loss.
[0049]
As described above, according to the present invention, the light transmission is excellent, the softening and elongation due to heating at the time of manufacture are small and the shape is kept good, and the increase in light propagation loss and the deterioration of characteristics due to deformation and cracking are caused. It was confirmed that a non-organic optical waveguide could be produced.
[0050]
It should be noted that the present invention is not limited to the above examples, and various modifications and improvements can be made without departing from the scope of the present invention.
[0051]
For example, if a mixed resin of fluororesin and siloxane resin is used for the lower clad layer and the core part, and the core part is formed in the groove provided in the lower clad layer, these thermal characteristics can be improved. A conventional fluororesin that is not mixed with a siloxane resin may be used for the upper clad layer that covers the surface.
[0052]
Further, as the siloxane resin, a fluorinated siloxane resin in which hydrogen atoms are partially substituted with fluorine atoms, or a deuterated siloxane resin in which hydrogen atoms are substituted with deuterium atoms may be used.
[0053]
【The invention's effect】
As described above, according to the optical waveguide of the present invention, a uniform mixture in which a fluororesin and a siloxane resin are mixed in a clad portion made of a mixed resin that is a uniform organic material in which a fluororesin and a siloxane resin are mixed. Because it is an organic optical waveguide made of an organic material made of a mixed resin, which is an organic material and having a core portion with a refractive index larger than that of the cladding portion, the fluororesin does not have a CH group, so optical communication Excellent transparency can be obtained even for light in the 1.55 μm wavelength band, which is one of the near-infrared light regions used in the system, and the siloxane resin mainly contains siloxane bonds (—Si—O—). Because it has excellent thermal stability in the skeleton, it does not generate irregularities, strains, cracks, etc. even if it is heated during the production of the optical waveguide, and it can maintain the core shape well and deform Crack The growth and characteristics organic optical waveguide is not deterioration of the propagation loss of light can be manufactured by.
[0054]
As described above, according to the present invention, the optical waveguide is excellent in light transmittance, softened and stretched by heating at the time of fabrication, and the shape of the optical waveguide is kept good, and an increase in light propagation loss and deterioration of characteristics due to deformation and cracking. It was possible to provide an organic optical waveguide that does not have any.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an example of an embodiment of an optical waveguide according to the present invention.
FIG. 2 is a diagram showing a change in transmission loss with respect to a siloxane resin ratio in a mixed resin used in the optical waveguide of the present invention.
FIG. 3 is a diagram showing a change in refractive index with respect to a siloxane resin ratio in a mixed resin used in the optical waveguide of the present invention.
FIG. 4 is a diagram showing changes in the amount of TMA elongation with respect to the temperature of the mixed resin and the conventional fluororesin used in the optical waveguide of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... Lower clad layer (clad part)
3 ... Core part 4 ... Upper clad layer (clad part)

Claims (1)

Some of the cladding portion made of homogeneous organic material is a mixed resin obtained by mixing the fluorine resin and siloxane resin composed of homogeneous organic material is a mixed resin obtained by mixing the fluorine resin and siloxane resin, wherein the cladding portion An optical waveguide characterized in that a core portion having a higher refractive index is formed.

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