JP2003287635A - Optical waveguide component - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical waveguide which can efficiently be coupled with an optical fiber even when the difference in specific refractive index between a core and a clad or a substrate is large. <P>SOLUTION: The optical waveguide is equipped with the substrate 10, the core 20, a side core 30A, a side core 30B, a thin-film layer 40, and an upper clad 50. The side core 30A and side core 30B serve to horizontally increase a mode field diameter and the thin-film layer 40 serves to vertically increase the mode field diameter. Consequently, the optical waveguide can efficiently be coupled with the optical fiber. Further, the side core 30A, side core 30B, and thin-film layer 40 are formed of the same raw material with the core 20 and then the optical fiber can be manufactured which hardly has loss against ambient temperature variation and is easy to form. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide, and more specifically to an optical waveguide that propagates light by being optically coupled to an external optical fiber.

[0002]

2. Description of the Related Art In the field of optical communication, research and development of an optical integrated circuit having various functions for performing advanced optical signal processing has been actively conducted. Here, the optical waveguide is an important component in the optical integrated circuit. The optical waveguide is a waveguide in which light is confined and propagated in the core region by covering the core region having a relatively high refractive index with a clad layer having a relatively low refractive index.

FIG. 7 is a diagram showing a manufacturing process of a conventional embedded type three-dimensional optical waveguide. In the three-dimensional optical waveguide, as shown in FIG. 7D, a core 820 made of glass having a relatively high refractive index is covered with an upper clad layer 825 made of glass having a relatively low refractive index. Is.
The procedure for manufacturing the conventional embedded three-dimensional optical waveguide will be described below with reference to the drawings.

First, as shown in FIG. 7A, a lower cladding layer 805 having a predetermined refractive index and a core layer 810 having a higher refractive index than the lower cladding layer 805.
Are formed on the substrate 800 by the flame deposition method. Next, as shown in FIG. 7B, the metal thin film 815 is
It is formed on the core layer 810. After that, as shown in FIG. 7C, the core layer 81 other than directly below the metal thin film 815 is formed.
0 is removed by the etching process, and further the metal thin film 815 is removed. Finally, as shown in FIG. 7D, the upper clad layer 825 is formed on the lower clad 805 and the core 820 by the flame deposition method. As a result, the conventional embedded type three-dimensional optical waveguide shown in FIG. 7D is completed.

Here, as a method of forming the lower clad 805 and the core layer 810, in addition to the above-mentioned flame deposition method, CVD (Chemical Vapor Depo) is used.
Sitton method, vacuum deposition method, sputtering method, and the like have been proposed. However, all of these methods have a problem that it takes a long time to form a thick film of about 10 μm because the film forming rate is slow. Furthermore, in these methods, large stress is generated in the formed film,
There is also a problem that it is difficult to obtain a uniform film quality. From these, at present, it is considered that the flame deposition method is the most suitable as a method for manufacturing the above-mentioned conventional embedded three-dimensional optical waveguide.

[0006] In general, since the core shape is considered to be coupled with a single mode optical fiber, the height and thickness of the core are set to 7 to 8 µm. in this case,
The relative refractive index difference of the core with respect to the clad is often 0.3%, which is the same as in the single mode optical fiber. On the other hand, the relative refractive index difference between the clad and the core is 0.4 to 0.
In some cases, the radius of curvature of the bent portion of the core is reduced by increasing the confinement of light to the core by increasing the ratio to 75% to reduce the size and integration of the optical waveguide.

[0007]

By the way, in the above-mentioned flame deposition method, soot is deposited on the substrate or the oxyhydrogen burner while moving the substrate, so that it is difficult to control the film thickness. Therefore, when the flame deposition method is applied to the formation of the core layer that requires precise film thickness control, an expensive control mechanism for obtaining a uniform film thickness is required for the apparatus that performs the flame deposition method. Become. As a result, the manufacturing cost of the conventional embedded three-dimensional optical waveguide increases.

Therefore, as an invention for solving the above problems, there is an optical waveguide manufacturing method disclosed in Japanese Patent Laid-Open No. 11-52159. This publication discloses a method for manufacturing an inexpensive optical waveguide that can be mass-produced. More specifically, first, a groove having a core pattern shape is
It is formed on a glass substrate by stamping. Next, an ultraviolet curable resin is filled in the formed groove as a core material. Then, the core material is sandwiched between the second glass substrates and irradiated with ultraviolet light to be cured. The optical waveguide is manufactured through the above steps. According to the method for manufacturing an optical waveguide, an expensive device such as a flame deposition device is not required, and therefore it is possible to manufacture optical waveguides inexpensively and in large quantities.

However, in the invention described in JP-A-11-52159, glass is used as the substrate material and polymer is used as the core material. As described above, the optical waveguide in which the substrate material and the core material are different from each other has a problem that loss is likely to occur due to a change in ambient temperature. More specifically, when the ambient temperature changes, the refractive indices of the substrate material and the core material reverse. As a result, large light leakage may occur in the optical waveguide. The details of the phenomenon will be described below with reference to the drawings.

First, the temperature characteristic of the refractive index of glass ng
(T) is the room temperature refractive index of ng ₀ , the temperature change amount is ΔT, and the glass refractive index temperature change coefficient is 5 × 10 ^−7.
, Ng (T) = ng ₀ × (1-5 × 10 ⁻⁷⁾
ΔT). On the other hand, the temperature characteristic np (T) of the refractive index of the polymer is np (T) = np ₀ when the room temperature refractive index of the polymer is np ₀ and the temperature change coefficient of the refractive index of the polymer is 6 × 10 ^−5. × (1-6 × 10 ^-5 Δ
T). Note that these numerical values show typical materials. Thus, the temperature change coefficient of the refractive index of the polymer is larger than the temperature change coefficient of the refractive index of glass. Therefore, when the ambient temperature rises, a phenomenon occurs in which the refractive index of the core made of polymer is smaller than the refractive index of the substrate made of glass, and light is no longer guided. For example, when the optical waveguide in which the substrate material is glass and the core material is a polymer is set to have the same relative refractive index difference (0.3%) and the same core diameter (8 μm square) as the single mode optical fiber, When the temperature becomes high, the refractive indices of the clad and the core are reversed, and the light is not guided. FIG. 8 shows that the glass substrate has a refractive index of 1.504 and the polymer core has a refractive index of 1.50 at room temperature.
7 is a graph showing the temperature characteristic of the coupling loss with the single mode optical fiber for the optical waveguide having the core width and the thickness of 8 μm. As shown in FIG. 8, it can be seen that the coupling loss rapidly increases from around 70 ° C. Note that the coupling loss increases at low temperature because the core refractive index becomes too large relative to the cladding refractive index, and higher-order modes are excited, resulting in loss due to mode mismatch with the single-mode optical fiber. Is increasing.

Therefore, as a method of preventing the above-mentioned increase in the coupling loss around 70 ° C., by increasing the relative refractive index difference between the core and the cladding at room temperature (for example, the relative refractive index difference from 0.3% is reduced). A method of preventing the reversal of the refractive index within the temperature change range where the optical waveguide is used can be considered. However, when the relative refractive index difference becomes large, the light is likely to be excited in the higher-order mode as shown in FIG. In FIG. 9, the relative refractive index between the clad and the core is 0.
It is a figure showing the simulation result of light intensity distribution when it was 47% and the shape of the core was 8 μm square. In order to prevent such excitation of higher order modes of light, there is a method of reducing the core width and the core height. However, if the relative refractive index difference is increased and the core width and the core thickness are decreased, the mode field diameter decreases as shown in FIG. As a result, the coupling loss with the single-mode optical fiber increases, and the optical axis adjustment becomes very difficult. FIG. 10 is a diagram showing a simulation result of the light intensity distribution when the relative refractive index difference between the clad and the core is 0.47% and the shape of the core is 4 μm square.

To solve the problem of narrowing the mode field diameter, Japanese Patent Laid-Open No. 2000-258648 discloses that side cores having a refractive index higher than that of the substrate are formed on both sides of the core formed on the substrate. By doing so, an invention for increasing the mode field diameter of the waveguide is disclosed.

However, JP-A-2000-25864
In the method described in Japanese Patent Publication No. 8, as shown in FIG. 11, the mode field diameter expands only in the horizontal direction of the substrate surface, and the mode field diameter in the vertical direction of the substrate surface remains small. is there. Therefore, the highly efficient coupling between the optical waveguide and the single mode optical fiber is
It remains difficult. Note that FIG. 11 is a diagram showing a simulation result of a light intensity distribution when the relative refractive index of the core and the side core and the clad is 0.47% in the optical waveguide having the side core.

Therefore, an object of the present invention is to provide an optical waveguide which can be coupled with a single mode optical fiber with high efficiency even when the relative refractive index difference between the core and the clad or the substrate is large.

Another object of the present invention is to provide an optical waveguide which can be manufactured by a simple processing method without using a complicated processing method such as a flame deposition method. Still another object of the present invention is to provide an optical waveguide in which light does not easily leak even when the ambient temperature changes.

[0016]

The first invention of the present invention is as follows:
It is an optical waveguide that propagates light by being optically coupled to an external optical fiber, is formed with a substrate having a predetermined refractive index and a substrate embedded in the surface of the substrate, and has a refractive index larger than that of the substrate. A core that propagates light inside, an auxiliary core that is formed near the core and has a refractive index higher than that of the substrate, and a core that is formed on the substrate to cover the core and the auxiliary core. A thin film layer having a refractive index equal to or lower than the refractive index of.

According to the first aspect of the present invention, since the auxiliary core is provided in the vicinity of the core and the thin film layer is provided on the upper part of the core, the mode field diameter can be increased and the occurrence of multi-order modes can be prevented. It More specifically, even when the core is small, the mode field is expanded and can be efficiently coupled with the optical fiber. Further, even if the core is large, multi-order modes are prevented, so that the optical waveguide according to the present embodiment and the optical fiber can be efficiently coupled.

A second invention of the present invention is an invention subordinate to the first invention, further comprising a cladding layer formed on the thin film layer and having a refractive index smaller than that of the thin film layer.

According to the second aspect of the invention, since the clad is provided on the thin film layer, the thin film layer is protected. Further, since the air layer is not in contact with the thin film layer, total reflection at the boundary surface above the thin film layer is alleviated. As a result, the shape of the mode field is approximated to a circle, and the optical waveguide is easily and efficiently coupled with the optical fiber.

A third invention of the present invention is an invention subordinate to the first invention, wherein the auxiliary core is provided on both sides of the core in a cross section perpendicular to a traveling direction of light guided through the core. It is characterized in that it is formed so as to be located.

According to the third aspect of the invention, since the auxiliary core is formed so as to be positioned on both sides of the core in the cross section perpendicular to the traveling direction of the light guided through the core, the mode field diameter is reduced. Are expanded to both sides of the core. As a result, the shape of the mode field is approximated to a circle, and the optical waveguide is easily and efficiently coupled with the optical fiber.

A fourth invention of the present invention is an invention subordinate to the third invention, characterized in that the auxiliary core is formed in a state of being embedded in the surface of the substrate.

According to the fourth aspect of the invention, since the auxiliary core is formed by being embedded in the surface of the substrate, the auxiliary core can be easily formed. More specifically, the auxiliary core pattern can be formed by the process of forming the auxiliary core pattern on the substrate and filling the auxiliary core pattern with the optical member.

A fifth invention of the present invention is an invention subordinate to the fourth invention, characterized in that the core, the auxiliary core and the thin film layer are formed of the same material.

According to the fifth aspect, since the core, the auxiliary core and the thin film layer are made of the same material, they can be simultaneously formed by the same making method. More specifically, the core, the auxiliary core and the thin film layer can be simultaneously formed by the spin coating method.

A sixth invention of the present invention is an invention subordinate to the first invention, wherein the relative refractive index difference between the refractive index of the core and the refractive index of the substrate is the optical fiber core to be optically coupled. It is characterized in that it is larger than the relative refractive index difference with the clad.

According to the sixth aspect of the invention, since the relative refractive index difference between the refractive index of the core and the refractive index of the substrate is larger than the relative refractive index difference between the core and the clad of the optical fiber, the light to the core is It is possible to strengthen the containment. On the other hand, in the above-mentioned first invention, the mode field diameter is enlarged by providing the auxiliary core and the like. That is, by combining these, the shape of the mode field can be adjusted. As a result, it becomes possible to create an optical waveguide that can be efficiently coupled with an optical fiber.

A seventh invention of the present invention is an invention subordinate to the first invention, wherein the core, the auxiliary core and the thin film layer are formed of materials having substantially the same temperature change coefficient of refractive index. It is characterized by

According to the seventh aspect of the invention, since the core, the auxiliary core and the thin film layer are made of materials having the same temperature change coefficient of the refractive index, even if the ambient temperature changes, The difference between the refractive index of the substrate around the core and the refractive index of the core does not change significantly. As a result, light loss in the optical waveguide is less likely to occur.

An eighth invention of the present invention is an invention subordinate to the second invention, wherein the substrate is made of a polymer, and the core, the auxiliary core and the clad are glass containing SiO ₂ as a main component. It is characterized by being formed by.

According to the eighth aspect of the invention, since the substrate is made of polymer, the substrate can be manufactured at low cost. Further, since the core, the auxiliary core, and the clad are made of glass, it is possible to produce a highly reliable optical waveguide with little loss. Furthermore, since the core, the auxiliary core, and the clad are made of the same material, the difference between the refractive index of the substrate around the core and the refractive index of the core does not change significantly even if the ambient temperature changes. As a result, it becomes difficult for light to leak in the optical waveguide.

A ninth invention of the present invention is an invention subordinate to the second invention, wherein the core, the auxiliary core and the clad are
It is characterized by being formed of a polymer.

According to the ninth aspect of the invention, since the core, the auxiliary core and the clad are made of polymer, they can be easily manufactured at low cost. Further, since the core, the auxiliary core, and the clad are made of the same material, even if the ambient temperature is changed, the difference between the refractive index of the substrate around the core and the refractive index of the core does not significantly change. As a result, it becomes difficult for light to leak in the optical waveguide.

[0034]

DETAILED DESCRIPTION OF THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an external perspective view of an optical waveguide according to an embodiment of the present invention. Figure 1
The optical waveguide shown in is provided with a substrate 10, a core 20, a side core 30A, a side core 30B, a thin film layer 40, and an upper clad 50. In the claims, the side cores 30A and 30B are referred to as auxiliary cores. On the substrate 10, the core 20, the side core 30A,
The side core 30B and the thin film layer 40 are formed. The material of the substrate 10 is quartz glass, LiNbO ₃ , L
iTaO ₃ , ZnO, PLZT, metal oxide (Ta
₂ O ₅ ) and organic polymers are used. Core 2
0 is made of a material that propagates light inside and has a refractive index larger than that of the substrate 10. As the material of the core 20, for example, Ge—SiO ₂ , acrylic ultraviolet curing resin, and fluorinated polyimide are used. The side cores 30A and 30B play a role of enlarging the mode field diameter in the horizontal direction with respect to the surface of the substrate 10, and are made of a material having a refractive index larger than that of the substrate 10 like the core 20. The thin film layer 40 plays a role of expanding the mode field diameter in the direction perpendicular to the surface of the substrate 10, and is made of a material having a refractive index larger than that of the substrate 10 like the core 20. The upper clad 50 is formed on the thin film layer 40, and the material thereof has a refractive index smaller than that of the core 20.

Here, the side core 30A and the side core 3
The reason why the mode field diameter increases when 0B and the thin film layer 40 are provided will be described. The mode field diameter depends on the relative refractive index difference between the substrate 10 and the core 20. More specifically, when the relative refractive index difference between the substrate 10 and the core 20 is large, light is strongly confined in the core 20, and the mode field diameter becomes small. On the other hand, when the relative refractive index difference between the substrate 10 and the core 20 is small, light is not strongly confined in the core 20, so the mode field diameter becomes large. Therefore, when it is desired to increase the mode field diameter, the substrate 10 and the core 20
It suffices to reduce the relative refractive index difference between and. However, as described in the related art, if the relative refractive index difference between the substrate 10 and the core 20 is reduced, the substrate 1 may be changed due to the ambient temperature change.
The magnitude of the refractive index of 0 and the magnitude of the refractive index of the core 20 are reversed, and the optical waveguide does not guide light. In order to solve this problem, in the optical waveguide according to this embodiment, the side core 30A, the side core 30B, and the thin film layer 40 are included.
Are provided around the core 20. According to this, the refractive index of the substrate 10 around the core 20 can be regarded as the refractive index in a state in which the side core 30A, the side core 30B, the thin film layer 40, and the substrate 10 are mixed, and is more than the original refractive index of the substrate 10. It can be regarded as a grown one. As a result, it can be considered that the relative refractive index between the core 20 and the substrate 10 around the core 20 is reduced, and the mode field diameter of the optical waveguide is expanded. Further, since the side core 30A, the side core 30B, and the thin film layer 40 are formed of the same optical member, even if the temperature around the optical waveguide changes, the substrate 10 around the core 20 does not change.
It becomes difficult for the magnitude of the refractive index of and the magnitude of the refractive index of the core 20 to be reversed. Therefore, even if the temperature around the optical waveguide changes, light loss is unlikely to occur in the optical waveguide. This can be regarded as the temperature change coefficient of the refractive index of the substrate 10 around the core 20 as the temperature change coefficient of the refractive index when the side core 30A, the side core 30B, the thin film layer 40 and the substrate 10 are mixed. As a result, the core 2
This is because the temperature change coefficient of the substrate around 0 and the temperature change coefficient of the refractive index of the core 20 do not significantly change.

The core 20, the side core 30A, the side core 30B, and the thin film layer 40 may be formed of different optical members. However, when they are formed of different materials, it is preferable that the temperature change coefficients of the refractive index of the optical members are similar to each other.

The manufacturing process of the optical waveguide configured as described above will be described below with reference to the drawings. FIG. 2 is a diagram showing a manufacturing process of the optical waveguide.

First, as shown in FIG. 2A, a concave core pattern 100, side core patterns 110A and side core patterns 110B are formed on the substrate 10. As a method for forming these grooves, there is used a method in which a mold having a convex pattern is pressed onto the substrate 10 to transfer the pattern. The substrate 1
As described above, the material of No. 0 is silica glass, LiNb.
O ₃ , LiTaO ₃ , ZnO, PLZT, metal oxide (T
a ₂ O ₅ ) and organic polymers are used.

Next, as shown in FIG. 2B, the concave core pattern 100 is filled with an optical member having a refractive index larger than that of the substrate 10 to form the core 20. Incidentally, in the optical member, as described above, Ge-SiO ₂
System optical members, acrylic ultraviolet curable resins, fluorinated polyimides and the like are used. Here, as a method of filling the optical member, a spin coating method can be mentioned.
In addition to the spin coating method, a flame deposition method or a vapor deposition method may be used as a method for filling the optical member. Now, the filling of the optical member will be described in detail below.

First, the optical member is applied onto the substrate 10 by the spin coating method. As a result, not only the core pattern 100 but also the side core patterns 110A and 110B can be filled with the optical member at the same time. In addition, since the thin film layer 40 can be formed at the same time, the manufacturing time of the optical waveguide according to this embodiment can be shortened. Also, core 2
0, the side core 30A, and the side core 30B are formed of the same optical member, so that the temperature change coefficients of the refractive indexes thereof are the same. As a result, the temperature conversion coefficient of the refractive index of the substrate 10 around the core 20 approaches the temperature change coefficient of the refractive index of the core 20. Further, according to the spin coating method, the apparatus is simpler than that of the flame deposition method and the like, so that the manufacturing cost can be reduced. The film thickness of the thin film layer 40 can be controlled by the viscosity coefficient of the applied optical member and the rotation speed of the spinner. In addition, Ge-SiO
_{When a 2-} system optical member is used as the material of the core 20 or the like, Ge-Si gelated by the sol-gel method is used.
The O ₂ based optical member is formed on the substrate 10 by spin coating.
Applied over.

Finally, as shown in FIG. 2C, the upper cladding 50 is formed on the thin film layer 40. As described above, the upper clad 50 is made of an optical member having a lower refractive index than the core 20, the side core 30A and the side core 30B. This is the end of the description of the manufacturing process of the optical waveguide according to the present embodiment.

Here, optimization of the size and position of each component will be described. First, the width of the side core has to be optimized. This is because if the width of the side core is too large, light is also guided to the side core, while if the width of the side core is too small, the mode field diameter cannot be effectively expanded. Also, the distance between the side core and the core must be optimized. This is because if the side cores are too close to each other, the light couples with the side cores, resulting in a large light propagation loss.
This is because if the distance between the side cores is too large, the mode field diameter cannot be effectively expanded.
Also, the thickness of the thin film layer must be optimized. This is because if the thin film layer is too thick, light leaks into the thin film layer and causes loss, while if the thin film layer is too thin, it is not possible to effectively increase the mode field diameter. In addition, the upper cladding thickness must also be optimized. This is because if the upper cladding is too thin, the shape of the mode field is distorted due to the influence of the air layer, while if the upper cladding is too thick, light easily leaks to the upper cladding.

Here, the reason why the thickness of the upper cladding needs to be optimized will be described in detail. As described above, if the upper clad is too thick, light easily leaks into the upper clad. This is because the difference in the refractive index between the thin film layer and the upper cladding near the thin film layer becomes small, and the light confinement in the thin film layer becomes weak. More specifically, the difference in the refractive index between the thin film layer and the upper clad near the thin film layer is affected by the refractive index of the air layer above the upper clad. Therefore, when the upper clad is thin, the refractive index of the upper clad near the thin film layer is strongly influenced by the refractive index of the air layer, and can be regarded as decreased. On the other hand, when the upper clad is thick, the refractive index of the upper clad near the thin film layer is not affected by the refractive index of the air layer so much that the refractive index is the original refractive index of the upper clad.
Therefore, if the upper clad is too thick, the difference in refractive index between the thin film layer and the upper clad in the vicinity of the thin film layer becomes small, and light easily leaks to the upper clad. From this, it can be said that the upper clad needs to be made thin to some extent. However, if the upper clad is too thin, the difference in refractive index between the thin film layer and the upper clad in the vicinity of the thin film layer becomes large, and light is confined too much in the thin film layer and the core. As a result, the shape of the mode field becomes distorted. From the above, it can be said that the thickness of the upper clad needs to be optimized.

With respect to the above problem, in the optical waveguide in which the relative refractive index difference between the substrate and the core is about 0.5%, the width of the side core is about 2 to 4 μm, and the width of the side core is about 2 μm. The distance between the end face and the end face of the side core is 2 to
It is known from the simulation result that it is appropriate that the thickness of the thin film layer is about 4 μm, the thickness of the thin film layer is about 1 to 3 μm, and the upper cladding is about 3 to 4 μm.

The first embodiment of the present invention will be described below.
An explanation will be given based on the simulation results. First, FIG.
Is the result of simulating the light intensity distribution of the single mode optical fiber. The contour line circles show contour lines of the intensity distribution of the output light, and the numerical value is a numerical value showing the intensity of the output light of each part when the intensity of the input light is 1. The meanings of the contour lines and numerical values are common in the following simulations. The diameter of the single mode optical fiber is 8 μm, and the relative refractive index difference is 0.3%. On the other hand, FIG. 10 is a result of simulating the light intensity distribution of the optical waveguide including only the core and the clad. The core is 4 μm square,
The relative refractive index difference between the core and the clad is 0.47%. Comparing FIG. 3 and FIG. 10, it can be seen that the mode field diameter of the optical waveguide is smaller than the mode field diameter of the single mode optical fiber. Therefore, if these are combined, a large coupling loss occurs.

Therefore, the thin film layer 40 and the side cores 30A and 30B provided in order to increase the mode field diameter of the optical waveguide are the optical waveguides according to the first embodiment of the present invention shown in FIG. is there. FIG. 4 is a result of simulating the light intensity distribution of the optical waveguide according to the first example of the present invention. The first aspect of the present invention
The core 20 of the optical waveguide according to the specific example is 4 μm square, the relative refractive index difference between the core 20 and the substrate 10 is 0.47%, and the widths and thicknesses of the side cores 30A and 30B are 3 μm and 4 μm, respectively. , The distance between the core 20 and the side cores 30A and 30B is 3 μm, the thickness of the thin film layer is 1 μm, and the thickness of the upper clad 50 is 3 μm.
μm.

It can be seen from FIG. 4 that the mode field diameter can be increased by providing the side core 30A, the side core 30B and the thin film layer 40 in the optical waveguide. Moreover, by adopting the above-mentioned configuration, the size of the mode field diameter of the optical waveguide of this example and the size of the mode field diameter of the single mode optical fiber can be made close to each other. as a result,
It has become possible to improve the coupling efficiency between the optical waveguide and the single mode optical fiber.

Further, according to this example, the refractive index of the substrate 10 and the refractive index of the upper clad 50 are equal, and the thickness of the upper clad 50 is 3 μm. In this specific example, by setting the thickness of the upper clad 50 to 3 μm,
It was possible to prevent light from leaking into the clad 50 and to make the mode field diameter of the optical waveguide close to the field diameter of the single mode optical fiber.
When the refractive index of the upper clad 50 is larger than that of the substrate 10, the upper clad 50 is thin, and when the refractive index of the upper clad 50 is larger than that of the substrate 10, the upper clad 50 is The clad 50 becomes thicker.
This is because, as described above, the refractive index of the upper clad 50 is affected by the air layer on the upper clad 50. In this way, when the thickness of the upper clad 50 changes, it can be considered that the refractive index of the upper clad 50 near the thin film layer 40 changes. Therefore, these are adjusted to adjust the mode field diameter of the optical waveguide. Good.

Next, a second specific example of the present invention will be described based on simulation results. First, FIG.
Is the result of simulating the light intensity distribution of an optical waveguide consisting of a core and a clad. The core is 8 μm square, and the relative refractive index difference between the core and the clad is 0.47%. As shown in FIG. 9, when the core becomes large, light of a multi-order mode is excited. When such an optical waveguide and a single mode optical fiber are coupled, mode mismatch occurs and a large coupling loss occurs.

Therefore, the thin film layer 40 and the side cores 30A and 30B provided in order to prevent the excitation of the multimode light are the optical waveguides according to the second embodiment of the present invention shown in FIG. is there. FIG. 5 is a result of simulating the light intensity distribution of the optical waveguide according to the second example of the present invention. The width of the core 20 of the optical waveguide according to the second example of the present invention is 7 μm, and the height of the core 20 is 6 μm.
μm, and the relative refractive index difference between the core 20 and the substrate 10 is 0.
47%, and the width and thickness of the side cores 30A and 30B are 3 μm and 6 μm, respectively.
The distance between the side cores 30A and 30B is 3 μm, the film thickness of the thin film layer is 1 μm, and the film thickness of the upper clad 50 is 4 μm.

According to FIG. 5, the side core 30 is originally provided under the condition that the excitation of the light of the multimode is generated.
It can be seen that since the A, the side core 30B, and the thin film layer 40 are provided in the optical waveguide, the excitation of the multi-order mode light is not generated. Moreover, by adopting the above-mentioned configuration, the size of the mode field diameter of the optical waveguide of this example and the size of the mode field diameter of the single mode optical fiber can be made close to each other. As a result, it has become possible to improve the coupling efficiency between the optical waveguide and the single-mode optical fiber.

As described above, according to the optical waveguide of the present invention, the relative refractive index difference between the substrate 10 and the core 20 of the optical waveguide is equal to the relative refractive index difference (0 between the core and the clad of the single mode optical fiber). .3%), it is possible to adjust the mode field diameter of the optical waveguide by providing the side core 30A, the side core 30B and the thin film layer 40. Also, the core 20 and the side core 3
If the materials of 0A, the side core 30B, and the thin film layer 40 are the same, processing by the spin coating method becomes possible. The spin coating method is a cheaper and simpler processing method than the flame deposition method, so that the optical waveguide can be easily manufactured at a low cost.

Further, the optical waveguide according to the present invention can be applied to an optical waveguide having a large bending waveguide portion in order to miniaturize the optical waveguide. More specifically, in the large curved waveguide portion, the relative refractive index difference between the substrate 10 and the core 20 of the optical waveguide is set to be large,
The side core 30A and the side core 30B are not provided. On the other hand, the coupling part of single mode optical fiber and LD
Alternatively, in a place where the mode field diameter is desired to be increased, such as a coupling portion with a light emitting element such as an LED, the side core 3
0A and the side core 30B are provided. By adopting such a configuration, it is possible to reduce the loss at the bent portion and to improve the coupling efficiency with the optical element. The thin film layer 40 has the effect of expanding the mode field diameter in the direction perpendicular to the surface of the optical waveguide. Therefore, the provision of the thin film layer 40 does not cause a loss of light for the waveguide that bends in the horizontal direction with respect to the surface of the optical waveguide. Therefore, the thin film layer 40 may be formed over the entire area of the optical waveguide. Thereby, the thin film layer 4
The formation of 0 can be realized only by a spin coating method, and a complicated processing technique such as a photolithography method is unnecessary.

Further, in the optical waveguide according to the present invention, even if the temperature around the optical waveguide rises, the magnitude of the refractive index of the substrate 10 and the magnitude of the refractive index of the core 20 are not easily reversed.
As a result, the optical waveguide according to the present invention functions without problems even at a high temperature at which a large loss of light occurs in the conventional optical waveguide. Further, even if the temperature around the optical waveguide is lowered, the magnitude of the refractive index of the substrate 10 and the core 2
The difference from the size of the refractive index of 0 does not become extremely large. As a result, in the conventional optical waveguide, the coupling loss due to the mode mismatch generated at a low temperature is improved. If the optical waveguide has the configuration shown in FIG.
It is known that the light can be guided by the single mode in the range from to 80 ° C.

In the optical waveguide according to this embodiment,
Although the upper clad 50 is provided on the thin film layer 40,
The upper clad 50 may be omitted. This is because the refractive index of the air layer on the thin film layer 40 is lower than that of the thin film layer 40, so that the light guided in the core 20 can be confined also by the air layer. However, in this case, it is necessary to make the film thickness of the thin film layer 40 larger than that of the optical waveguide in which the upper clad 50 is provided. This is because when the thin film layer 40 is too thin, the refractive index of the thin film layer 40 is strongly influenced by the air layer, and the light confinement in the core 20 and the thin film layer 40 is strengthened too much, and the mode field shape is distorted. Because.

As an example of the combination of the materials of the optical waveguide according to this embodiment, the substrate 10 is made of polymer, and the core 20, the side core 30A, and the side core 30 are formed.
In some cases, B and the upper clad 50 are made of glass containing SiO ₂ as a main component. According to this, since the substrate 10 is made of a polymer, the substrate 10 can be provided at low cost. Further, since the core 20 is made of glass, loss is reduced and a highly reliable optical waveguide is produced. Further, since the core 20, the side core 30A, the side core 30B, and the upper clad 50 are made of glass of a material close to each other, it is possible to create an optical waveguide having stable characteristics with respect to temperature changes.

As another example of the combination of materials of the optical waveguide according to the present embodiment, the substrate 10 is made of glass, and the core 20, the side core 30A, the side core 30B, and the upper clad 50 are made of polymer. There is. According to this, since the core 20 is made of a polymer, the core 20 can be provided at low cost. Further, the side core 30A, the side core 30B, and the upper clad 50 are formed of a polymer of a material close to each other, so that an optical waveguide having stable characteristics with respect to temperature changes can be created.

The optical waveguide according to the present embodiment can also have the structure shown in FIG. Figure 1
The optical waveguide of FIG. 6 differs from the optical waveguide of FIG. 6 in that in the optical waveguide of FIG.
Is embedded in the substrate 10. Also with such a configuration, the mode field diameter can be expanded in the vertical direction and the horizontal direction.

[0059]

As described above, according to the present invention, the thin film layer is provided on the core and the side core is provided in the vicinity of the core, whereby the mode field of the optical waveguide is expanded and the multi-order in the core is increased. Since the generation of modes is prevented, the optical waveguide and the optical fiber can be efficiently coupled.

[Brief description of drawings]

FIG. 1 is an external perspective view of an optical waveguide according to an embodiment of the present invention.

FIG. 2 is a diagram showing a manufacturing process of the optical waveguide according to the embodiment of the present invention.

FIG. 3 is a result of simulating a light intensity distribution of a single mode optical fiber.

FIG. 4 is a result of simulating the light intensity distribution of the optical waveguide according to the first example of the present invention.

FIG. 5 is a result of simulating the light intensity distribution of the optical waveguide according to the second example of the present invention.

FIG. 6 is an external view showing the configuration of another example of the optical waveguide according to the embodiment of the present invention.

FIG. 7 is a diagram showing a manufacturing process of a conventional embedded three-dimensional optical waveguide.

FIG. 8: The glass substrate has a refractive index of 1.5 at room temperature.
No. 04, the polymer core is 1.507, and the core width and the thickness are 8 μm, respectively, and are graphs showing the temperature characteristics of the coupling loss with the single mode optical fiber for the conventional optical waveguide.

FIG. 9 shows a relative refractive index of 0.47% between the clad and the core,
It is the figure which showed the simulation result of the light intensity distribution of the conventional optical waveguide which consists only of a core and a clad when the shape of a core was set to 8 micrometers square.

FIG. 10 is a diagram showing a simulation result of a light intensity distribution of a conventional optical waveguide when the relative refractive index difference between the clad and the core is 0.47% and the shape of the core is 4 μm square.

FIG. 11 shows an optical waveguide having a side core, in which the relative refractive index between the core and the side core and the clad is 0.47%.
It is a figure showing the simulation result of light intensity distribution when it was.

[Explanation of symbols]

10 substrates 20 cores 30A, 30B Side core 40 thin film layers 50 upper clad 100 core pattern 110A, 110B Side core pattern 800 substrates 805 Lower cladding layer 810 core layer 815 Metal thin film 820 core 825 Upper clad layer

Claims (9)

[Claims] 1. An optical waveguide that propagates light when optically coupled to an external optical fiber, the substrate having a predetermined refractive index, and the substrate formed to be embedded in the surface of the substrate. A core having a refractive index larger than that of the core, which propagates light inside, an auxiliary core formed near the core and having a refractive index larger than that of the substrate, and covering the core and the auxiliary core. Thus, an optical waveguide comprising a thin film layer formed on the substrate and having a refractive index equal to or lower than the refractive index of the core. 2. The optical waveguide according to claim 1, further comprising a cladding layer formed on the thin film layer and having a refractive index smaller than that of the thin film layer. 3. The auxiliary core is formed so as to be located on both sides of the core in a cross section perpendicular to a traveling direction of light guided through the core. The optical waveguide described in. 4. The auxiliary core is formed in a state of being embedded in the surface of the substrate.
The optical waveguide described in. 5. The optical waveguide according to claim 4, wherein the core, the auxiliary core, and the thin film layer are formed of the same material. 6. The relative refractive index difference between the refractive index of the core and the refractive index of the substrate is larger than the relative refractive index difference between the core and the cladding of the optical fiber to be optically coupled.
The optical waveguide according to claim 1. 7. The optical waveguide according to claim 1, wherein the core, the auxiliary core, and the thin film layer are formed of materials having substantially the same temperature change coefficient of refractive index. 8. The substrate is made of a polymer, and the core, the auxiliary core and the clad are made of SiO 2.
The optical waveguide according to claim 2, wherein the optical waveguide is formed of glass containing ₂ as a main component. 9. The core, the auxiliary core, and the clad are formed of a polymer.
The optical waveguide according to claim 2.