JPH09304637A - Optical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical device which is easy to manufacture and handle since an electromagnetic field can be expanded where a refractive index difference is small between two parts, by using a divergent optical waveguide element which is different in the refractive index difference between a core and a clad between the two parts without changing the shapes and components. SOLUTION: The cores 2 and 12 and clads 3 and 13 of divergent optical waveguide elements 1 and 11 are composed of optical glass which differs in transition temperature, and parts 4b and 14b of optical waveguide element main bodies 4 and 14 are thermally treated and different in refractive index between the cores 2 and 12 and clads 3 and 13 from thermally untreated parts 4a and 14a; and the electromagnetic field of waveguide light is expanded parts (electromagnetic field expansion part) which are smaller in refractive index difference between the thermally treated parts 4b and 14b and thermally untreated parts 4a and 14a. Projections films 5 and 15 are formed of materials which are properly selected from silicone resin, ultraviolet-ray setting resin, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dispersive optical waveguide device and an optical device using the same, and more specifically, to a difference in refractive index between a core and a clad of an optical waveguide from other parts locally. The present invention relates to an optical device using a dispersive optical waveguide element in which the electromagnetic field is increased or reduced by reducing or reversing the same.

[0002]

2. Description of the Related Art Conventionally, a quartz optical fiber has been used in a fiber type optical device as in an optical transmission line for communication.
However, since the silica optical fiber is made with emphasis on the band and the loss, the difference in the refractive index between the core and the clad does not depend on the wavelength of the light, and there is no diversity in the wavelength characteristics, so it was used. The types of fiber-type optical devices were also limited.

For example, as an optical branching / coupling device using an optical fiber, it is necessary to allow the electromagnetic field of the guided light to propagate to a core of another optical fiber in a certain region.
Therefore, as shown in FIG. 10, two quartz optical fibers 1
An optical branching / combining device 100 is used in which 1 and 121 are heated at a part E thereof and stretched while melting a part M to form a branch part 130. Quartz optical fiber 111,
121 is the clad 1 on the cores 112 and 122, respectively.
It is coated with 13,123. In this optical branching / coupling device 100, the electromagnetic field of the light L guided by the optical fiber 111 as shown by the arrow leaks from the core 112 toward the clad 113 at the narrow branching portion 130, and the optical fiber. 121 is also accessed and branched into lights L1 and L2. However, this optical branching / combining device 100 has a branching unit 1
It is necessary to make the outer diameter of 30 about 1/10 or less of the outer diameter of the portion F, and it is necessary to pay close attention so as not to damage it during manufacturing and use. Further, in order to obtain a practical element that can withstand normal handling, appropriate reinforcement is required, which is expensive. Further, therefore, advanced control technology and control device for controlling heating and stretching are also required for manufacturing.

Therefore, there has been proposed an optical waveguide which does not require such a stretching process and has no diameter-reduced portion, and a manufacturing method thereof. This optical waveguide is a quartz optical fiber
The dopant added to the core is diffused by heating to reduce the difference in the refractive index between the core and the clad, and the light that is confined in the core and guided is
The portion where the difference in the refractive index is reduced spreads toward the cladding (in other words, the electromagnetic field of the guided light is enlarged), so that the adjacent silica optical fiber is accessed. However, since the material is high-purity quartz, heating up to several thousand degrees centigrade is necessary for the desired diffusion of the dopant, and therefore the heating device and the optical fiber for melting the dopant are required. Requires a high-level control technique for diffusing, and about 1 hour of working time is required to obtain desired characteristics. Moreover, the concentration of the dopant diffusing from the core to the clad is in equilibrium when it reaches the concentration of the dopant remaining in the core, and does not exceed the equilibrium. Therefore, the refractive index of the clad cannot be made larger than that of the core. .

Further, in the silica optical fiber, the difference in the refractive index between the core and the clad is almost constant regardless of the wavelength, so that the difference in the refractive index is reduced as a whole even in the portion where the dopant is diffused. The difference in the refractive index does not differ depending on the wavelength of the wave that is oscillated, and it is difficult to obtain various characteristics according to the application.

Dispersive optical fibers in which the difference in the refractive index between the core and the clad greatly depends on the wavelength have been proposed to give various wavelength characteristics to an optical device (IEICE Transactions C-1, Vol. J78-C-1, No. 1
2, pp 658-663, December 1995). With such an optical fiber, it can be used as an optical fiber having an arbitrary difference in refractive index required for an optical device by selecting the wavelength. However, it is not easy to find a core material and a clad material having an appropriate refractive index dispersion that can be used for an optical device, and a manufacturing method for creating such an optical waveguide has not been found. It was rare.

[0007]

DISCLOSURE OF THE INVENTION The present invention has been made as a result of earnest research to solve the above-mentioned problems and meet the needs. The inventions according to claims 1 and 2 are the shape and composition of an optical waveguide device. It is an object of the present invention to provide an optical device which is easy to manufacture and handle by using an optical waveguide element in which the electromagnetic field of guided light is expanded or the guided light is radiated at a part thereof without changing the above.

According to a third aspect of the present invention, in addition to the problems of the first and second aspects of the present invention, the electromagnetic field is enlarged at the end of the optical waveguide element, the axis alignment is easy, and the optical loss is small. The challenge is to provide connectors.

According to a fourth aspect of the present invention, in addition to the problems of the first and second aspects of the present invention, the guided light can be generated by simply bringing the electromagnetic field expanding portions of a plurality of dispersive optical waveguide elements into contact with or close to each other. An object is to provide an optical branching / combining device that is distributed or combined.

An object of the invention of claim 5 is to provide an optical branching / coupling device in which the branching ratio can be easily set, in addition to the object of the invention of claim 4.

In addition to the object of the invention described in claim 4, it is an object of the invention in claim 6 to provide an inexpensive optical branching / coupling device.

In addition to the problems of the inventions of claims 1 and 2, the invention of claim 7 is to provide an inexpensive sensor with good detection sensitivity.

In addition to the problems of the inventions of claims 1 and 2, the invention of claim 8 is to provide a high-order mode elimination filter capable of eliminating any high-order mode from multimode guided light. To do.

[0014]

DISCLOSURE OF THE INVENTION The present invention has been made as a result of earnest research to solve the above-mentioned problems and meet the needs, and the optical device of the invention according to claim 1 comprises a core made of optical glass. An optical waveguide in which the core is covered with a cladding made of optical glass with a different transition temperature, and the difference in the refractive index between the core and the cladding of one part is different from that of the other part without changing its shape and composition. An element is provided with a dispersive optical waveguide element for expanding an electromagnetic field of guided light in a portion having a small difference in refractive index among the portion or the other portion. The electromagnetic field of the guided light is expanded in a portion of the dispersive optical waveguide element or a portion having a small difference in refractive index among other portions, and coupling with other optical waveguide elements is easy,
Moreover, since the shape and components are not changed, the manufacturing and handling are easy and the cost is low. Here, the refractive index difference means a difference obtained by subtracting the refractive index of the clad from the refractive index of the core, and does not mean the absolute value thereof.

According to a second aspect of the present invention, in the optical device according to the first aspect, the dispersive optical waveguide element heat-treats the part, so that the difference in refractive index between the core and the clad in the heat-treated part is changed to another value. The dispersive optical waveguide element is different from the non-heat-treated portion. Since the core material and the clad material are made of optical glass with different transition temperatures, an optical waveguide device with a different refractive index difference between the core and the clad can be obtained only by heat treatment. The electromagnetic field of the guided light is expanded.

An optical connector according to a third aspect of the present invention includes two optical waveguide elements each having a connection end face capable of abutting each other.
In an optical connector having a connector for abutting both connection end faces and detachably connecting the two optical waveguide elements, at least one of the optical waveguide elements is the dispersive optical waveguide element, and an electromagnetic field expansion portion thereof is provided. Is used as a connection end face with another optical waveguide device. Since the end face of the electromagnetic field expansion portion of the dispersive optical waveguide device is used as the connection end face, the connection loss due to the axis shift is small and the axis alignment is easy.

Further, the optical branching / coupling device of the present invention is an optical branching / coupling device comprising a plurality of optical waveguide devices, wherein the optical waveguide device has a core and a clad component at the center thereof. A dispersive optical waveguide device having an electromagnetic field expanding portion whose refractive index difference is reduced without making it different from other portions, wherein the central electromagnetic field expanding portions are in contact with or close to each other. It is characterized in that guided light is distributed or coupled in an electromagnetic field expansion portion of the dispersive optical waveguide device of the present invention. The guided light is distributed or combined only by bringing the electromagnetic field expansion portions of a plurality of dispersive optical waveguide elements into contact with or close to each other, and there is no need to reduce the diameter or change the component, so that manufacturing and handling are easy. . In addition, in this specification, the central part means an appropriate part excluding both end parts, and does not mean a geometrical central part.

The invention according to claim 5 is the same as claim 4
In the optical branching / coupling device described above, a plurality of dispersive optical waveguide elements having an electromagnetic field expanding portion in the central portion are brought into contact or close to each other, and the refractive index difference of the electromagnetic field expanding portion is made. Alternatively, the lengths are different. If the difference in the refractive index or the length of the electromagnetic field expanding portion of the dispersive optical waveguide element is different, the spread of the electromagnetic field at the end face of the electromagnetic field expanding portion is different, and the branching ratio to another waveguide element is different. Therefore, it is possible to arbitrarily select a waveguide element to be distributed to other waveguide elements at a desired branching ratio from a plurality of dispersive optical waveguide elements.

Furthermore, the invention according to claim 6 is the invention according to claim 4.
In the optical branching / coupling device described above, a plurality of optical waveguide elements formed by coating a core made of optical glass and a clad made of optical glass having a transition temperature different from that of the core are bundled,
By heat-treating the central part at once, each of the optical waveguide elements becomes the dispersive optical waveguide element,
It is characterized in that they are mutually heat-sealed. Since the heat treatment and the heat fusion of each optical waveguide element can be performed at the same time, a separate step is not required to fix the positional relationship between the plurality of optical waveguide elements, and the number of manufacturing steps is small and the manufacturing can be performed at low cost.

According to a seventh aspect of the present invention, there is provided a sensor having the dispersive optical waveguide element and a measuring device for measuring a change in a parameter of light guided by the dispersive optical waveguide element, and the electromagnetic field is a clad. The electromagnetic field expansion portion of the dispersive optical waveguide device that is expanded to the outside is used as a detection unit to detect a detection target that changes the electromagnetic field in the detection unit. By appropriately selecting the refractive index difference in the electromagnetic field enlarged portion according to the detection target, the ratio of the radiation mode and the guided mode can be appropriately changed, and a sensor with high detection sensitivity can be obtained.

The high-order mode removing filter according to the invention of claim 8 is a filter which is inserted into an optical waveguide to remove a higher-order mode of guided light, wherein an electromagnetic field expanding portion is provided at a central portion of the dispersive optical waveguide element. The refractive index difference between the refractive index difference corresponding to the critical angle of the lowest mode of the modes whose minimum refractive index difference is to be eliminated and the refractive index difference corresponding to the highest order mode of the modes not to be eliminated. It is characterized by the difference.
Arbitrary higher-order modes can be eliminated by selecting the minimum refractive index difference in the electromagnetic field expansion portion provided in the central portion.

[0022]

Embodiments of the present invention will be described below. FIG. 1 is a schematic view of an optical connector 10 which is an example of the optical device of the present invention, and FIG. 2 is a cross-sectional view of dispersive optical waveguide elements 1 and 11 used in this connector 10. ) Is a vertical sectional view, and FIG. 7B is a YY sectional view thereof. In FIGS. 1 and 2, the dispersive optical waveguide elements 1 and 11 include protective films 5 and 15 (in FIG. 1), a dispersive optical waveguide element body 4 and 14 in which cores 2 and 12 are covered with claddings 3 and 13, respectively. It consists of a dispersive optical fiber coated with (not shown). Cores 2, 12 and clads 3, 13
Are made of optical glass having different transition temperatures, and the parts 4b and 14b of the optical waveguide element bodies 4 and 14 have been subjected to the heat treatment described later, and the difference in refractive index between the cores 2 and 12 and the clads 3 and 13 is not heat treated. Unlike the portions 4a and 14a, the electromagnetic field of the guided light is enlarged in the portion (electromagnetic field enlargement portion) having a small difference in refractive index among the heat treated portions 4b and 14b or the non-heat treated portions 4a and 14a. The protective films 5 and 15 are made of a material such as a silicone resin or an ultraviolet curable resin that is appropriately selected.

Reference numeral 20 is a connector for detachably connecting the dispersive optical waveguide elements 1 and 11, for example, plugs 21 and 2.
2 and sleeve 23. Dispersive optical waveguide device 1,
11 is the heat treatment part (electromagnetic field expansion part) 4b, 14
The plugs 21 and 22 are inserted and fixed so that b is the tip portions 6 and 16. The plugs 21 and 22 are fitted into the sleeve 23, for example. The fitting is performed, for example, by fitting the concave groove 21a provided in the plug 21 and the concave groove 22b provided in the plug 22, and the convex rings 23a and 23b provided in the sleeve 23, respectively. FIG. 1 shows a state in which the plug 22 is already fitted in the sleeve 23. When the plug 21 is inserted in the direction of the arrow I and fitted in the sleeve 23, the connection end face 6a of the dispersive optical waveguide device 1 is formed. Is brought into contact with the connection end face 16a of the dispersive optical waveguide device 11 to complete the connection.

FIG. 3 is a diagram showing the refractive index wavelength characteristics of the dispersive optical waveguide elements 1 and 11, FIG. 3 (a) is an example of the refractive index wavelength characteristics of the non-heat-treated portion 4a, and A ₁ is Core 2
, And B ₁ is the refractive index wavelength characteristic of the cladding 3. 3B shows an example of the refractive index wavelength characteristic of the heat-treated portion 4b, where A ₂ is the refractive index wavelength characteristic of the core 2 and B ₂ is the refractive index wavelength characteristic of the cladding 3. As is clear from a comparison between the two, the core 2b was
The refractive index wavelength curve of A is changed from A ₁ to A ₂ , and the refractive index wavelength curve of the clad 3b is changed from B ₁ to B ₂ . If the wavelength of the guided light is .lambda.1, the refractive index difference, a non-heat content is reduced to [delta] ₁₂ in the heat treatment section that was [delta] _11, also with respect to the wavelength .lambda.2, a non-heat amount [delta] ₂₁ However, in the heat-treated part, the reversed difference is δ ₂₂ .

Next, the mode of expansion of the electromagnetic field of light of wavelength λ1 propagating through the waveguide element in FIG. 2 will be described. In the non-heat-treated portion 4a, the refractive index of the core 2a is larger than that of the cladding 3a regardless of whether the wavelength is λ1 or λ2. Therefore, as shown in FIG. La is confined in the core 2a and propagated. However, when reaching the heat-treated portion 4b, since the refractive index difference δ ₁₂ is small, the electromagnetic field Lb of the guided light becomes wider than the electromagnetic field La at the non-heat-treated portion 4a. However, since the dispersive optical waveguide elements 1 and 11 are single-mode waveguide elements, the electromagnetic field expansion portions 4b and 14
If the refractive index difference δ ₁₂ and the length of b are properly selected, the spread of the electromagnetic field increases to Lb ₁ and Lb _{2 as} it progresses, then decreases again, enters the non-heat-treated portion 14a, and becomes the electromagnetic field La. Become.

In the butt connection of optical waveguides, there is a problem of connection loss due to axial misalignment, but especially in the case of a single mode optical waveguide, it is important to solve the problem because the core diameter is small, such as plugs and sleeves. It was necessary to pay close attention to the dimensional accuracy of the connector and the adjustment when the optical fiber was attached to the plug. However, when the above-mentioned optical connector 10 is used, the electromagnetic field is enlarged in the electromagnetic field enlarged portions 4b and 14b, so that it is effectively the same as when the core diameter is enlarged. Therefore, even if some axis deviation occurs, the rate of loss is much smaller, and axis alignment becomes easier.

In the above example, in FIG. 2A, the refractive index wavelength curve A ₁ of the core of the non-heat-treated portion 4a is larger than the refractive index wavelength curve B _{1 of the} clad, but the opposite is true. May be. In addition, the non-heat treated portion 4a is shown in FIG.
The refractive index wavelength curves may intersect as shown in (b), and the heat treated portion may have the two refractive index wavelength curves separated from each other as shown in FIG. 2 (a). As will be described later, depending on the properties of the core material and the clad material and the heat treatment method, the two refractive index wavelength curves may come close to each other, may intersect, or may come apart from each other, so depending on the materials of the core and the clad. The heat treatment method may be appropriately selected, and in short, the portion having a small difference in refractive index may be used as the electromagnetic field expansion portion. Further, in FIG. 1 and FIG. 2, the dispersive optical waveguide elements 1 and 11 are not limited to those in which the difference in the refractive index and the length of the electromagnetic field expanding portions 4b and 14b are equal, and the end surfaces 6a and 16a of the both portions are the same. It suffices that the spreads of the electromagnetic fields at are almost the same.

Therefore, in order to manufacture the optical connector 10, the tips 6a and 16a of the dispersive optical waveguide elements 1 and 11 may be heat-treated, but the core and the clad are made of optical glass having different transition temperatures. A part of which is heat-treated so that the length of the heat-treated portion is equal to that of the heat-treated portions 4b and 14b of the dispersive optical waveguide elements 1 and 11 and the length is equal to the sum of both 4b and 14b. The heat treated portions may be cut and the tips 6a and 16a may be used as the electromagnetic field enlarged portions 4a and 14b.

Next, an optical branching / combining device 30 as an example of the optical device of the present invention will be described with reference to FIG. In FIG. 4, the optical branching / coupling device 30 is composed of two dispersive optical waveguide elements 41 and 51, and the dispersive optical waveguide elements 41 and 51 are, for example, optical waveguide element bodies 44 and 54 and are coated thereon. And a protective coating (not shown). FIG. 4 shows a state where the optical waveguide element bodies 44 and 54 excluding the protective coating are in contact with each other. Dispersive optical waveguide device bodies 44, 54
Consists of cores 42 and 52 and clads 43 and 53,
They consist of optical glasses with different transition temperatures. The dispersive optical waveguide element bodies 44 and 54 are respectively formed in the central portion 44.
b and 54b are heat-treated to be electromagnetic wave expanding portions, and at least central electromagnetic field expanding portions 44b and 54b are in contact with each other.

The electromagnetic fields La ₁ and La ₂ of the light incident on the core 42 of the dispersive optical waveguide element body 44 spread as an electromagnetic field Lb ₁ in the electromagnetic field enlarged portion 44b, and some of them are adjacent to each other. It is distributed to the dispersive optical waveguide element body 54 and becomes two electromagnetic fields Lb ₂₁ and Lb ₂₂ , and when the distribution further proceeds, it becomes an electromagnetic field Lb _3, and most of the electromagnetic field shifts to the optical waveguide element body 54. In the illustrated example, all the electromagnetic fields are schematically moved to the dispersive optical waveguide element body 54, but actually, there is also an electromagnetic field propagating in the optical waveguide element body 44. Of the total optical power, the optical power transferred to the dispersive optical waveguide element 54 and the dispersive optical waveguide element 44 as they are.
The ratio with the optical power propagating through the is called a branching ratio, and this branching ratio is changed by making the difference in refractive index between the electromagnetic field expanding portions 44b and 54b different. Further, in the illustrated example, the lengths of both the electromagnetic field expanding portions 44b and 54b are made equal, but the branching ratio is also changed by changing them.

Further, in the illustrated example, both electromagnetic field expansion portions 44
b and 54b are in contact with each other, but in an approaching state, that is,
Even if they are separated by some distance, if the spread of the electromagnetic field is large, they are distributed to other optical waveguide elements. Therefore, the branching ratio also changes by adjusting the distance between the two optical waveguide element bodies 44 and 54. In this way, the electromagnetic field expansion portions 44b and 54b are provided in the dispersive optical waveguide elements, respectively.
The branching ratio can be easily adjusted by providing the above to bring them into contact with or close to each other. Although the distribution of light has been described, it goes without saying that the light incident on the two optical waveguide elements can be joined to the one optical waveguide element on the contrary.

FIG. 5 is a diagram showing another embodiment of the optical branching / coupling device. FIG. 5 (a) is a longitudinal sectional view thereof, and FIG. 5 (b) is a change in transverse section in the longitudinal direction. FIG. In FIG. 5, the optical branching / coupling device 30 is composed of two optical waveguide elements 44 and 54 as in the example of FIG. 4, and each optical waveguide element 44 and 54 is a core 42 made of optical glass.
A dispersive optical fiber is formed by covering the cores 52 and 52 with the clads 43 and 53 made of optical glass having different transition temperatures, and applying a protective film (not shown) thereon.
Then, the optical waveguide element bodies 44 and 54 are bundled and the central portions thereof are collectively heat-treated to form the electromagnetic field enlarged portions 44b and 54b in the respective optical waveguide element bodies 44 and 54.

Since the two optical waveguide elements 44 and 54 are heat-sealed to each other when collectively heat-treated, there is no need to separately provide a step for fixing the two optical waveguide elements 44 and 54. In addition, the two heat-sealed optical waveguide elements 4
The major axis of 4, 54 is slightly smaller than the major axis of the non-heat treated portion in the electromagnetic field enlarged portion. The description of the propagation of the electromagnetic field of light is omitted because it is the same as in the case of FIG. 4, but due to thermal fusion, the cross section is S1 ... As shown in FIG.
Since it changes to S5, in the electromagnetic field enlarged portions 44b and 54b, the cross section has a smaller major axis like S2, S3, and S4, and at the same time, the interval between the core 42b and the core 52b becomes smaller. Therefore, light can be easily distributed without greatly expanding the electromagnetic field. In the examples of FIGS. 4 and 5 described above, only the two-branch type optical branching / coupling device (optical directional coupler) has been described, but the number of optical waveguide elements is not limited to two. The present invention includes three or more multi-branching type optical branching / combining devices (optical star couplers).

FIG. 6 is an explanatory view showing an optical sensor which is an example of the optical device of the present invention. In FIG. 6, an optical sensor 60 is composed of a dispersive optical waveguide element 61, a light emitting element (not shown), a light receiving element, and a measuring instrument that analyzes changes in the light emitted from the light emitting element and the light received by the light receiving element. The dispersive optical waveguide element 61 is the dispersive optical waveguide element 1
Similarly to the above, the core 62 is composed of a dispersive optical waveguide element body 64 in which the clad 63 is coated, and a protective coating (not shown) coated thereon, and at least the electromagnetic field expansion portion 64b which is the sensor portion has the protective coating removed. ing. The dispersive optical waveguide device 61 is formed so that the refractive index difference between the core 62b and the clad 63b in the heat-treated portion 64b is reduced, and the waveguide mode leaks to the outside of the optical waveguide device main body 64.

The electromagnetic fields La ₁ and La ₂ of the light incident on the core 62a of the non-heat-treated portion 64a of the dispersive optical waveguide element 61 from the light emitting element spread to the heat-treated portion 64b and spread to the electromagnetic fields Lb ₁ and Lb _2. And becomes narrower again to Lb ₃ , and further becomes La ₃ and La _{4 in the} non-heat-treated portion 64a. Assuming that the substance including the detection target M is arranged so as to contact the electromagnetic field expanding portion 64b and absorbs the evanescent wave leaking from the electromagnetic field expanding portion 64b, the dispersive optical waveguide element is assumed. The optical power LP ₁ emitted from 61 is the optical power L incident from the light emitting element.
It should be smaller than P ₀ . Therefore, by measuring the amount of attenuation of the optical power of this absorption wavelength, the content of the detection target M contained in the detection target substance can be known.

An example of such an optical sensor is a methane gas concentration sensor. This uses a He-Ne laser having a wavelength of 3.39 μm as a light source, and a detecting portion is formed by processing and extending an optical fiber to have a diameter of several μm so that an evanescent wave is emitted from this portion. In this type, since the thinned portion is easily damaged, care must be taken to support that portion, but according to the present invention, since there is no thinned portion, it is necessary to support it. It's easy.

7A and 7B are explanatory views of a high-order mode elimination filter which is an optical device of the present invention. FIG. 7A is a longitudinal sectional view thereof, and FIG. 7B is a refractive index in the length direction thereof. It is a figure which shows the change of a difference. The high-order mode removal filter 70 is
It is composed of a dispersive optical waveguide device body 71 and a protective film (not shown). Similar to the dispersive optical waveguide device 1, the dispersive optical waveguide device body 71 is composed of a multimode dispersive optical fiber having a body 74 in which a clad 73 is coated on a core 72, and the refractive index n _{co of the} core 72 is The difference δ between the refractive index n _cl of the clad 73 and the refractive index n _cl of the clad 73 decreases in the electromagnetic field enlarged portion 74 b and changes in the longitudinal direction as shown in FIG.
The minimum refractive index difference is δ _min .

The critical angle θ _c corresponds to the refractive index difference δ, and as the refractive index difference δ becomes smaller, the critical angle θ _c also becomes smaller, so that higher-order modes are sequentially radiated. Figure 7
As shown in (a), modes LP ₀₁ , LP ₁₁ , LP ₂₁ ,
It is assumed that light including LP ₀₂ and LP ₃₁ is incident on the core 72a of the dispersive optical waveguide device 71, and as shown in FIG. 7B, the refractive index difference corresponding to the critical angle of the mode LP ₃₁ is δ.
_If the refractive index difference corresponding to the critical angle of ₁ and modes LP ₂₁ and LP ₀₂ is δ ₂ , and the refractive index difference corresponding to mode LP ₁₁ is δ ₃ , the mode LP ₃₁ is radiated at the refractive index difference δ ₁ ,
Modes LP ₂₁ and LP ₀₂ are radiated at δ ₂ and δ ₃
At that point, mode LP ₁₁ is radiated. In this way, only the fundamental mode LP ₀₁ whose refractive index difference corresponding to the critical angle is smaller than the minimum refractive index difference δ _min passes. If the minimum refractive index difference δ _min is between δ ₂ and δ ₃ ,
Mode LP ₁₁ also passes. Thus, the minimum refractive index difference δ
By selecting _min appropriately, any higher order mode can be removed.

Next, a method of manufacturing the dispersive optical waveguide element used in each of the above optical devices will be briefly described. FIG. 8 is an explanatory view of the method for manufacturing the dispersive optical waveguide device of the present invention. In FIG. 8, the dispersive optical waveguide device body 4 is
For example, by a rod-in-tube method or the like, a core 2 made of optical glass is coated with a clad 3 made of optical glass having a transition temperature different from that of the core 2. Further, a silicone resin, an ultraviolet curable resin, or the like, which is appropriately selected, is applied and cured thereon to form the protective coating 5, and the dispersive optical fiber 1 is formed. Core 2 and clad 3
The material may be any optical glass having a different transition temperature. For example, for the core material, BaCED4 (main component by HOYA)
SiO ₂ -B ₂ O ₃ -BaO) and the cladding material F made by Ohara Glass Co., Ltd.
It is preferable to use a multi-component glass such as 11 (main component SiO ₂ —B ₂ O ₃ —Na ₂ OK ₂ O—TiO ₂ ). Core 2 transition temperature T _A
The difference between the transition temperature T _B of the cladding 3 theta is, if 10 ° C. Although it is easy to change the refractive index difference δ by heating, giving a less than 10 ° C. in the core 2 and the cladding 3 heat treatment Since the difference in the influence of 1 is small, the change in the refractive index difference δ hardly occurs. Further, if the transition temperature difference θ is too large, it becomes difficult to manufacture the base material and the fiber. Therefore, it is preferably 100 ° C. or lower.

Next, the protective film 5 of the part 4c
Is removed to expose the dispersive optical waveguide device body 4. The exposed part 4b of the dispersive optical waveguide device body 4 is heat-treated under a predetermined condition by using a heater H, for example, an electric heater.
The heater H is not limited to the electric heater, but may be a gas burner or any other device capable of controlling the temperature. FIG.
Is an example of the temperature-time curve of the heat treatment process. The heat treatment process includes a heating step a for raising the temperature by heating from time t ₀ to time t ₁ , a holding step b for holding at a substantially constant temperature from time t ₁ to time t ₂ , and a time t _2.
Consisting cooling step c lowering the temperature by cooling to time t ₃ from.

Since the degree of influence on the core 2 and the cladding 3 can be changed by selecting the holding temperature T _MAX, the transition temperature closer to the holding temperature T _MAX of the core and the cladding is
Since the refractive index relatively greatly changes, the refractive index difference also changes. If the holding temperature T _MAX is too much higher than the lower one of the core transition temperature T _A and the clad transition temperature T _B , the material with the lower transition temperature may melt. Not preferable. The holding temperature T _MAX is appropriately selected in consideration of the above two points to obtain a desired refractive index difference.

In the cooling step c, the higher the cooling rate, the greater the decrease in the refractive index, and the degree of this decrease depends on the material of the glass. Therefore, the degree of the decrease in the refractive index changes depending on the selection of the cooling rate according to the material. . Therefore, the refractive index difference can also be adjusted by adjusting the cooling rate. When the cooling rate is slowed down, the difference in refractive index enlarged in the heating step and the holding step is easily maintained, which is preferable. Further, the cooling step includes a slow cooling step c1 of cooling from the maximum temperature T _MAX to the intermediate temperature T _MED at a relatively slow rate from time t ₂ to time t _m, and a cooling step from time t _m to time t ₃ . In between, the intermediate temperature T _MED to the room temperature T ₀ is relatively fast.
It is preferable to divide into a rapid cooling step c2 for cooling up to. By providing a gradual cooling process to the intermediate temperature, it becomes easier to maintain the refractive index difference expanded in the heating step and the holding step, making it easier to control the refractive index difference, and providing a quenching process from the intermediate temperature. Thereby, the heat treatment time can be shortened.

In the above embodiment, the dispersive optical fiber having one core is used as the optical waveguide element.
The type of optical waveguide element is not limited to this,
Various forms such as a plurality of cores, a clad having a rectangular shape, and an optical fiber array in which a plurality of horizontally arranged cores are covered with a clad in a rectangular shape are included.

[0044]

As described above, according to the invention described in claim 1 of the present invention, the difference in the refractive index between the core and the clad of one part of the present invention is changed to the other part without changing the shape and the component. By using different dispersive optical waveguide elements, it is possible to expand the electromagnetic field in that part and the other part where the difference in refractive index is small, so an optical device that is easy to manufacture and handle can be obtained. .

According to the invention of claim 2, in addition to the effect of the invention of claim 1, the electromagnetic field is expanded only by heating a part of the optical waveguide element in which the core material and the clad material are made of optical glass having different transition temperatures. Parts can be obtained at low cost.

According to the invention of claim 3, in addition to the effect of the invention of claim 1 or 2, by making the end face of the electromagnetic field expanding portion a connection end face, the connection loss due to axis deviation is small and the shaft An optical connector that can be easily aligned is obtained.

According to the invention described in claim 4, in addition to the effect of the invention described in claim 1 or 2, the electromagnetic field expansion portions of the plurality of dispersive optical waveguide elements are only brought into contact with or close to each other. An optical branching / combining device in which guided light is distributed or combined is obtained.

According to the invention of claim 5, in addition to the effect of the invention of claim 4, by making the difference in the refractive index or the length of the electromagnetic field expanding portion different, the end surface of the electromagnetic field expanding portion is changed. The spread of the electromagnetic field can be different,
Further, the degree of coupling can be changed by changing the spacing between the plurality of optical waveguide elements, and the branching ratio to other waveguide elements can be changed by using them, so that the other waveguide element can be obtained at a desired branching ratio. An optical branching / combining device is obtained.

Further, according to the invention of claim 6, in addition to the effect of the invention of claim 4, heat treatment and heat fusion of each optical waveguide element can be performed at the same time, so the number of manufacturing steps is small and the cost is low. An optical branching / combining device is obtained.

According to the invention of claim 7, in addition to the effect of the invention of claim 1 or 2, the evanescent wave of the evanescent wave can be generated by appropriately selecting the refractive index difference of the electromagnetic field enlarged portion according to the object to be detected. The amount can be adjusted, and an optical sensor with high detection sensitivity can be obtained.

According to the invention described in claim 8, in addition to the effect of the invention described in claim 1 or 2, the minimum refractive index difference in the electromagnetic field enlarged portion provided in the central portion of the optical waveguide element is removed. Since it is set between the refractive index difference corresponding to the critical angle of the lowest mode of the modes to be performed and the refractive index difference corresponding to the highest mode of the modes not to be removed, any higher order mode to be removed A high-order mode removal filter that can easily remove

[Brief description of drawings]

FIG. 1 is a schematic view of an optical connector of the present invention.

FIG. 2 is a cross-sectional view of a dispersive optical waveguide device used in the optical connector of the present invention.

FIG. 3 is a diagram showing a refractive index wavelength curve of a dispersive optical waveguide device.

FIG. 4 is an explanatory diagram of an optical branching / coupling device of the present invention.

FIG. 5 is an explanatory diagram of another example of the optical branching / coupling device of the present invention.

FIG. 6 is an explanatory diagram of an optical sensor of the present invention.

FIG. 7 is an explanatory diagram of a high-order mode removal filter of the present invention.

FIG. 8 is an explanatory diagram of a method for manufacturing a dispersive optical waveguide device.

FIG. 9 is a diagram showing a temperature-time curve in a heat treatment process of a dispersive optical waveguide device.

FIG. 10 is a schematic diagram of a conventional optical branching / coupling device.

[Explanation of symbols]

1, 11, 41, 51, 61, 71 Dispersive optical waveguide element 2, 12, 42, 52, 62, 72 Dispersive optical waveguide element core 3, 13, 43, 53, 63, 73 Dispersive optical waveguide element Cladding 4, 14, 44, 54, 64, 74 Dispersive optical waveguide element body 4a, 14a, 44a, 54a, 64a, 74a Non-electromagnetic field expansion portion 4b, 14b, 44b, 54b of dispersive optical waveguide element body 64b, 74b Electromagnetic field expansion part of dispersive optical waveguide element body 5 Protective film 10 Optical connector 30 of the present invention 30 Optical branching / coupling device 60 of the present invention Optical sensor 70 of the present invention Higher-order mode elimination filter A1 of the present invention A1 non-electromagnetic The refractive index wavelength curve of the core in the field expansion portion B1 The refractive index wavelength curve of the cladding in the non-electromagnetic field expansion portion A2 The refractive index wavelength curve of the core in the electromagnetic field expansion portion B2 The electromagnetic field expansion portion Wavelength T _MAX holding temperature Rad refractive index wavelength curve δ refractive index difference λ guided wave

Claims (8)

[Claims] 1. A core made of optical glass is coated with a clad made of optical glass having a transition temperature different from that of the core, and the shape and composition of the refractive index difference between a part of the core and the clad are changed. The optical waveguide element which is different from the other portion, and which comprises a dispersive optical waveguide element for expanding the electromagnetic field of the guided light in the portion having a small refractive index difference among the portion or the other portion. Characteristic optical device. 2. The dispersive optical waveguide element is a dispersive optical waveguide element in which the difference in the refractive index between the core and the clad of the heat-treated portion is different from that of the other non-heat-treated portion by heat-treating the portion. The optical device according to claim 1, wherein: 3. An optical connector comprising: two optical waveguide elements having connection end surfaces capable of abutting each other; and a connector for abutting both connection end surfaces to detachably connect the two optical waveguide elements. An optical connector, wherein one of the optical waveguide elements is composed of the dispersive optical waveguide element, and an end face of the electromagnetic field expanding portion is a connection end face with another optical waveguide device. 4. An optical branch comprising a plurality of optical waveguide elements
In the coupler, the optical waveguide element is a dispersive optical waveguide element having an electromagnetic wave expanding portion in the central portion of which the refractive index difference is reduced without changing the components of the core and the clad from other portions. Of the plurality of dispersive optical waveguide elements contacting each other or approaching each other, and the light incident on one of the plurality of dispersive optical waveguide elements contact or approach the other dispersive optical waveguide portion. An optical branching / combining device characterized by being distributed to elements. 5. A plurality of dispersive optical waveguide elements having an electromagnetic field expanding portion in the central portion are formed by contacting or approaching the electromagnetic field expanding portion, and a difference in refractive index or length of the electromagnetic field expanding portion is The optical branching according to claim 4, characterized in that they are different.
Combiner. 6. A plurality of optical waveguide elements comprising a core made of optical glass and a cladding made of optical glass having a transition temperature different from that of the core are bundled together, and the central portion thereof is heat treated collectively. 5. The optical branching / coupling device according to claim 4, wherein each of the optical waveguide elements is used as the dispersive optical waveguide element, and the optical waveguide elements are thermally fused and fixed to each other. 7. The dispersive optical waveguide element and a measuring device for measuring a change in a parameter of light guided by the dispersive optical waveguide element, wherein the electromagnetic field is expanded to the outside of the clad. A sensor characterized in that an electromagnetic field expanded portion of a dispersive optical waveguide element is used as a detection unit to detect a detection target that changes the electromagnetic field in the detection unit. 8. A filter that is inserted into an optical waveguide to remove higher-order modes of guided light, wherein the dispersive optical waveguide element has an electromagnetic field expansion portion at the center thereof, and the minimum refractive index difference is removed. A high-order feature characterized in that the difference between the index of refraction corresponding to the critical angle of the lowest-order mode of the modes to be performed and the index of refraction corresponding to the highest-order mode of the modes not to be removed is set. Mode removal filter.