JP4025538B2 - Optical waveguide substrate - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical waveguide substrate used for optical communication.
[0002]
[Prior art]
With the rapid spread of the Internet, the increase in capacity of optical communication systems is proceeding at a great pace, and in trunk optical communication systems, a method for increasing the capacity of multiple times by wavelength multiplexing has already been put into practical use. Has reached the point. At present, high-density wavelength multiplexing systems up to 160 wave levels have been commercialized. In such a wavelength multiplexing optical communication system, a multiplexer for introducing a plurality of signal lights having different wavelengths into one optical fiber, and a demultiplexing for separating the wavelength multiplexed signal light into signals of different wavelengths A multiplexer / demultiplexer consisting of a multi-unit is used.
[0003]
In addition, an optical subscriber system that introduces an optical fiber to the vicinity of each home is also being introduced, and a single optical fiber is used by using different wavelengths for the downstream signal from the station side and the upstream signal to the station side. A system for performing uplink / downlink bidirectional communication has also been put into practical use. Also in this two-wavelength bidirectional communication, a multiplexer / demultiplexer is used for introducing a transmission signal into one optical fiber and separating the transmitted signal to the receiver side.
These multiplexers / demultiplexers are often composed of optical waveguides in which a wave plate, a wavelength selection filter, or the like for improving performance is inserted at a predetermined position.
[0004]
For example, a trunk-system multiplexer / demultiplexer or an arrayed waveguide grating (an arrayed waveguide having the same optical path length difference is formed between two input / output star couplers). In the case of the function of multiplexing / demultiplexing by taking the role of the next diffraction grating), a slit is provided in the waveguide section of the array, and a half-wave plate is inserted into this slit to rotate the polarization direction by 90 degrees. Thus, the polarization dependence caused by the optical waveguide is eliminated. In addition, in the multiplexer / demultiplexer used in the subscriber system, a Y-shaped optical waveguide is formed, a wavelength selection filter is inserted at a portion where the three optical waveguides intersect, and the signal light coming from one direction is converted into a wavelength. Accordingly, the light is folded or transmitted according to the above, and only the light having a predetermined wavelength is transmitted through the other two optical waveguides.
A common problem of these optical waveguides is miniaturization, and the relative refractive index difference Δ is increased to increase light confinement, and the optical waveguide is reduced in curvature to reduce the optical waveguide.
[0005]
[Problems to be solved by the invention]
However, in order to increase Δ in the optical waveguide to strengthen the light confinement and satisfy the single mode condition, it is necessary to reduce the core diameter. If the core diameter is reduced, the spot size of the propagation light is also reduced. In general, in the connection of single mode light, as the spot size becomes smaller, the connection loss increases with respect to the axial deviation and spacing deviation of the connection part.When inserting a filter with a slit in an optical waveguide with a large Δ, Furthermore, the loss becomes large.
[0006]
For example, in the case of an optical waveguide having a wavelength of about 0.4%, which is used in a normal silica-based optical waveguide, the spot size is usually about 4 μm, but Δ is 1.2% and the radius of curvature is 3 mm or less. In this case, the spot size is about 2 μm, and when Δ is 2.0% and the radius of curvature is 1.5 mm or less, the spot size is 2 μm. The allowable axis deviation value for obtaining the same connection loss is inversely proportional to the spot size. When the allowable axis deviation amount in a normal quartz waveguide is 1 μm, Δ is 1.2 to obtain the same connection loss. In the case of%, 0.5 μm , and in the case where Δ is 2%, the tolerance is very small, 0.38 μm , and high processing accuracy and mounting accuracy are required. In addition, the thickness of a film such as a filter is generally about 30 μm with respect to the gap, and a minimum interval of 50 μm is necessary to insert the filter into the optical waveguide portion, but in order to obtain the same connection loss. Since the allowable gap is proportional to the square of the spot size, when Δ is 1.2%, the required gap is about 12 μm or less, and filter insertion is theoretically impossible. For this reason, when the filter is inserted into the optical waveguide portion, there is a problem that the connection loss becomes larger than in the past. Further, in order to insert an optical element other than a thin film-like member such as a filter into the optical waveguide portion, it is necessary to provide a further space. Conventionally, this has not been realized because the increase in connection loss is too large. Therefore, the present invention is to provide an optical waveguide substrate that suppresses an increase in connection loss and realizes a reduction in size.
[0007]
[Means for Solving the Problems]
In order to solve such a problem, an optical waveguide substrate according to the present invention is an optical waveguide substrate in which a core and a clad are formed on the substrate. A first taper waveguide whose length is gradually decreased, and the first taper waveguide and the first taper waveguide which are arranged opposite to each other in the signal light guiding direction, and a part of the core has a width toward the signal light guiding direction. And a second taper waveguide having a gradually increased height, a first taper waveguide, and a third waveguide connected to the second taper waveguide, the third waveguide having an optical element It is characterized in that there is provided a slit for inserting. According to this optical waveguide substrate, the spot size of the signal light guided through the optical waveguide substrate is enlarged by the first taper waveguide, and is transmitted through the third waveguide and the slit without changing the size. It is returned to the size before being enlarged by the two tapered waveguides.
[0008]
In the optical waveguide substrate, the surrounding cladding layers except the bottom surfaces of the first tapered waveguide, the second tapered waveguide, and the third waveguide may be made of a polymer material. According to this optical waveguide substrate, the confinement of signal light in the core is enhanced by the polymer material.
[0009]
In another example of the optical waveguide substrate according to the present invention, in the optical waveguide substrate in which the core and the clad are formed on the substrate, the width of a part of the core gradually increases in the signal light guiding direction, The first taper waveguide whose height is gradually reduced, the first taper waveguide and the first taper waveguide are arranged to oppose the signal light waveguide direction, and a part of the core faces the signal light waveguide direction. A second taper waveguide having a width that gradually decreases and a height that gradually increases; a third waveguide that connects the first taper waveguide and the second taper waveguide; The waveguide is provided with a slit for inserting an optical element. According to this optical waveguide substrate, the spot size of the signal light guided through the optical waveguide substrate is enlarged by the first taper waveguide, and is transmitted through the third waveguide and the slit without changing the size. It is returned to the size before being enlarged by the two tapered waveguides.
[0010]
In the optical waveguide substrate, the surrounding cladding layers except the bottom surfaces of the first tapered waveguide, the second tapered waveguide, and the third waveguide may be made of a polymer material. According to this optical waveguide substrate, the confinement of signal light in the core is enhanced by the polymer material.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[Embodiment 1]
FIG. 1 is a perspective view showing a configuration of an optical waveguide substrate 1 according to the first embodiment of the present invention, and FIG. 2 is a diagram in which an optical element is inserted into the optical waveguide substrate 1 according to the first embodiment. is there.
As shown in FIG. 1, the optical waveguide substrate 1 in the present embodiment has a core 13 having a refractive index higher than that of a clad 12 whose periphery is covered with a clad 12 on a substrate 11.
[0012]
The core 13 includes a tapered portion 13a having a shape in which the width and height are gradually decreased from a predetermined portion, and a tapered portion 13b, a tapered portion 13a, and a taper having a shape in which the width and height are gradually increased from a predetermined portion. An insertion portion 13c that connects the portions 13b is provided. A slit 14 as shown in FIG. 2 is formed in the insertion portion 13c, and an optical element 15 such as a filter is inserted.
[0013]
When the signal light is guided in the direction from the taper portion 13a to the taper portion 13b, the spot size of the signal light is enlarged and enlarged by the taper portion 13a whose width and height are reduced in the signal light guide direction. The size is reduced by the tapered portion 13b that is transmitted through the optical element 15 and whose width and height are increased in the waveguide direction of the signal light, and returned to the size before entering the tapered portion 13a again. As described above, the optical waveguide substrate 1 increases the spot size of the signal light before the signal light passes through the optical element 15, thereby preventing the axial deviation and the gap deviation at the connection portion between the insertion portion 13 c and the optical element 15. Since the tolerance can be relaxed, an increase in connection loss can be prevented even if the relative refractive index difference Δ is large. As a result, it is possible to reduce the size of the optical waveguide substrate. Actually, the total length including the taper portions 13a and 13b and the insertion portion 13c for expanding and reducing the spot size described above is 200 μm to 2000 μm, which is a length that does not sacrifice the size of the entire optical waveguide.
[0014]
The optical waveguide substrate 1 described above can be easily produced by a generally well-known manufacturing method such as a photolithography method or a flame deposition method. For this reason, the optical waveguide substrate 1 that changes the spot size of the signal light only at the place where the optical element 15 is inserted is not only small and has low connection loss, but also can be manufactured at low cost and easily.
[0015]
The slit 14 for inserting the optical element 15 is formed so as to be orthogonal to the core 13 in FIG. 2, but may be formed obliquely with respect to the core 13. Even with such a structure, the same effect as described above can be obtained.
The optical element 15 inserted into the slit 14 is not limited to a thin film element such as a filter, but may be a bulk element depending on the application.
[0016]
[Embodiment 2]
Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 3 is a perspective view showing the configuration of the optical waveguide substrate 2 according to the second embodiment. Since the second embodiment is different from the first embodiment only in the clad configuration, the same components are denoted by the same names and reference numerals, and the description thereof is omitted as appropriate.
As shown in FIG. 3, in the optical waveguide substrate 2 in the present embodiment, a lower clad 12a is formed on a substrate 11, and a core 13 whose periphery is covered with an upper clad 12b is formed on the lower clad 12a. Yes.
[0017]
In the optical waveguide substrate 2 of the present embodiment, the upper clad 12b is made of a polymer member, and the other components are made of a normal quartz-based member. The polymer member has a property that the refractive index changes greatly in temperature compared to the quartz-based member, and generally has a property of decreasing at a high temperature and increasing at a low temperature. Therefore, the confinement of light at the spot size conversion portion in the core 13 depends on the refractive index of the polymer, and the confinement is strong at a high temperature and weak at a low temperature. In this way, by covering the weakly confined portion of the signal light with the polymer, temperature dependence can be imparted to the connection loss characteristic or the polarization characteristic. Thereby, in addition to the effects described in the first embodiment, the optical waveguide substrate 2 further changes the refractive index of the upper clad 12b formed of the polymer member by changing the temperature, thereby further increasing the signal light. The confinement is strengthened, and thereby further downsizing can be realized.
[0018]
Also in this embodiment, a slit equivalent to that described in the first embodiment can be provided, and an optical element can be inserted into this slit. Further, the slit for inserting the optical element can be formed orthogonally or obliquely with respect to the core 13 as in the first embodiment.
Furthermore, the optical element inserted into the slit may be not only a thin film element such as a filter but also a bulk element depending on the application.
[0019]
[Embodiment 3]
Next, with reference to FIGS. 4 and 5, an optical waveguide substrate 3 according to a third embodiment of the present invention will be described. FIG. 4 is a perspective view showing a configuration of the optical waveguide substrate 3 according to the third embodiment, and FIG. 5 is a diagram in which an optical element is inserted into the optical waveguide substrate 3 according to the third embodiment. Note that the third embodiment is different from the first embodiment only in the shape of the core, and therefore, the same components are denoted by the same names and reference numerals, and the description thereof is omitted as appropriate.
[0020]
The core 16 has a tapered portion 7a having a shape in which the width is gradually increased and the height is gradually decreased from a predetermined location, and a shape in which the width is gradually decreased and the height is gradually increased from a predetermined location. The taper portion 16b and the insertion portion 16c for connecting the taper portion 16a and the taper portion 16b are provided. A slit 14 as shown in FIG. 5 is formed in the insertion portion 16c, and an optical element 15 such as a filter is inserted.
[0021]
When the spot size is increased by gradually narrowing the core and increasing the signal light leakage, especially the light confinement in the width direction is affected by the shape of the side surface because the required accuracy of patterning in the manufacturing process is severe. It is easy to receive and it is difficult to strengthen the light confinement. However, as shown in FIG. 4, the optical waveguide substrate 3 of the present embodiment has a structure in which the width is gradually increased by the tapered portion 16a, the width is gradually decreased by the tapered portion 16b through the insertion portion 16c. Is less affected by the pattern accuracy of the side surface, and as a result, it is possible to increase the confinement of signal light.
[0022]
When the signal light is guided in the direction from the tapered portion 16a to the tapered portion 16b, the spot size of the signal light is enlarged by the tapered portion 16a, transmitted through the optical element 15 at the enlarged size, and reduced by the tapered portion 16b. Then, it is returned to the size before entering the tapered portion 16a again. As described above, the optical waveguide substrate 3 increases the spot size of the signal light before the signal light passes through the optical element 15, thereby preventing the axial deviation and the gap deviation at the connection portion between the insertion portion 16 c and the optical element 15. Since the tolerance can be relaxed, an increase in connection loss can be prevented even if the relative refractive index difference Δ is large. As a result, it is possible to reduce the size of the optical waveguide substrate. Actually, the total length including the taper portions 16a and 16b and the insertion portion 16c for expanding and reducing the spot size described above is 200 μm to 2000 μm, which is a length that does not sacrifice the size of the entire optical waveguide.
[0023]
The optical waveguide substrate 3 described above can be easily produced by a generally well-known manufacturing method such as a photolithography method or a flame deposition method. For this reason, the optical waveguide substrate 3 that changes the spot size of the signal light only at the place where the optical element 15 is inserted is not only small and has low connection loss, but also can be manufactured at low cost and easily.
[0024]
The slit 14 for inserting the optical element 15 is formed so as to be orthogonal to the core 16 in FIG. 5, but may be formed obliquely with respect to the core 16. Even with such a structure, the same effect as described above can be obtained.
The optical element 15 inserted into the slit 14 is not limited to a thin film element such as a filter, but may be a bulk element depending on the application.
[0025]
[Embodiment 4]
Next, a fourth embodiment of the present invention will be described with reference to FIG. FIG. 6 is a perspective view showing the configuration of the optical waveguide substrate 4 according to the fourth embodiment. Since the fourth embodiment is different from the third embodiment only in the clad configuration, the same components are denoted by the same names and reference numerals, and the description thereof is omitted as appropriate.
As shown in FIG. 6, in the optical waveguide substrate 4 in the present embodiment, a lower clad 12a is formed on a substrate 11, and a core 16 whose periphery is covered with an upper clad 12b is formed on the lower clad 12a. Yes.
[0026]
In the optical waveguide substrate 4 of the present embodiment, the upper clad 12b is made of a polymer member, and the other components are made of a normal quartz-based member. The polymer member has a property that the refractive index changes greatly in temperature compared to the quartz-based member, and generally has a property of decreasing at a high temperature and increasing at a low temperature. Therefore, the confinement of light at the spot size conversion portion in the core 16 depends on the refractive index of the polymer, and the confinement is strong at a high temperature and weak at a low temperature. In this way, by covering the weakly confined portion of the signal light with the polymer, temperature dependence can be imparted to the connection loss characteristic or the polarization characteristic. Thus, in addition to the effects described in the third embodiment, the optical waveguide substrate 4 further changes the refractive index of the upper clad 12b formed of the polymer member by changing the temperature, thereby further increasing the signal light. The confinement is strengthened, and thereby further downsizing can be realized.
[0027]
Also in this embodiment, a slit equivalent to that described in the third embodiment can be provided, and an optical element can be inserted into this slit. Further, the slit for inserting the optical element can be formed orthogonally or obliquely with respect to the core 16 as in the third embodiment.
Furthermore, the optical element inserted into the slit may be not only a thin film element such as a filter but also a bulk element depending on the application.
[0028]
【The invention's effect】
As described above, the optical waveguide substrate of the present invention includes the first tapered waveguide in which a part of the core gradually decreases in width and height in the signal light guiding direction, and the first tapered waveguide. The second taper waveguide and the first taper guide, which are disposed so as to face the waveguide direction of the signal light and in which a part of the core gradually increases in width and height in the signal light waveguide direction. By connecting the waveguide and the second tapered waveguide and having a third waveguide provided with a slit, the spot size of the signal light is enlarged before passing through the optical element inserted in the slit. As a result, the tolerance for the axial deviation and the gap deviation at the connecting portion between the core and the optical element is alleviated, so that an increase in connection loss can be suppressed, and as a result, a reduction in size can be realized.
In addition, the clad layer covering the periphery excluding the bottom surface of the core is made of a polymer material, so that the confinement of signal light in the core can be strengthened, and as a result, downsizing can be achieved.
[0029]
Another configuration example of the optical waveguide substrate according to the present invention includes a first tapered waveguide in which a part of a core gradually increases in width and gradually decreases in height in a signal light guiding direction. The second taper is disposed opposite to the first tapered waveguide in the signal light guiding direction, and a part of the core gradually decreases in width toward the signal light guiding direction, and the height gradually increases. A third waveguide provided with a slit and connecting the first tapered waveguide and the second tapered waveguide, the spot size of the signal light is inserted into the slit. Enlargement before passing through the optical element reduces the tolerance for misalignment and spacing at the connecting portion of the core and the optical element, so that an increase in connection loss can be suppressed and the first taper guide is reduced. The width is gradually increased in the waveguide, passed through the third waveguide, and then the second table. By adopting a structure in which the width is gradually reduced in the waveguide, the optical waveguide substrate 3 of the present embodiment is less affected by the pattern accuracy of the side surface, and as a result, the confinement of signal light can be strengthened. As a result, downsizing can be realized.
In addition, by forming a clad layer covering the periphery excluding the bottom surface of the core from a polymer material, it is possible to increase the confinement of the signal light to the core and consequently to reduce the size.
[Brief description of the drawings]
FIG. 1 is a perspective view showing a configuration of an optical waveguide substrate 1 according to a first embodiment.
FIG. 2 is a diagram in which an optical element is inserted into the optical waveguide substrate 1 according to the first embodiment.
FIG. 3 is a perspective view showing a configuration of an optical waveguide substrate 2 according to a second embodiment.
FIG. 4 is a perspective view showing a configuration of an optical waveguide substrate 3 according to a third embodiment.
FIG. 5 is a diagram in which an optical element is inserted into an optical waveguide substrate 3 according to a third embodiment.
FIG. 6 is a perspective view showing a configuration of an optical waveguide substrate 4 according to a fourth embodiment.
[Explanation of symbols]
1, 2, 3, 4 ... Optical waveguide substrate, 11 ... Substrate, 12 ... Cladding, 12a ... Lower cladding, 12b ... Upper cladding, 13 ... Core, 13a, 13b, 16a, 16b ... Tapered portion, 13c, 16c ... Insertion Part, 14 ... slit, 15 ... optical element.

Claims (2)

In the optical waveguide substrate in which the core and the clad are formed on the substrate,
The core is
A first taper that gradually increases in width and gradually decreases in height toward the waveguide direction of the signal light, and expands the spot size of the signal light;
Arranged to face the first taper portion to the waveguide direction of the signal light, the width toward the guiding direction of the signal light is gradually decreased, the height gradually increases, the spot size of the signal light A second taper portion for reducing
An insertion portion connecting the first taper portion and the second taper portion on the side having a wide width and a low height ;
The joint surface of the first tapered portion with the insertion portion, the cross section of the insertion portion perpendicular to the waveguide direction, and the joint surface of the second taper portion with the insertion portion are congruent,
An optical waveguide substrate, wherein the insertion portion is provided with a slit for inserting an optical element. The optical waveguide substrate according to claim 1,
The surrounding clad layer excluding the bottom surface of the first taper portion , the second taper portion, and the insertion portion is made of a polymer material.

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