JP2005140822A - Optical waveguide and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical waveguide of a spot size changeable structure which has high coupling efficiency with an optical fiber, LD, VCSEL, LED, etc., and also to provide the manufacturing method. <P>SOLUTION: The optical waveguide is composed of a lower clad layer 52, a core 55 which has, on this lower clad layer 52, an input section or an output section for connecting to an optical fiber, and an upper clad layer 56 covering this core 55. The light propagating direction of the core 55 continuously varies, with the cross section of the core 55 shaped differently in the input section and the output section of light and also shaped nearly circularly or elliptically. The diameter of the input section or the output section of the core 55 can be formed in roughly the same shape and size as the core diameter of the optical fiber or the diameter of the outgoing light of a light emitting element such as an LD, VCSEL and LED, so that the coupling efficiency with the optical fiber or such light emitting elements can be increased. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical waveguide used in the field of optical communications and a method for manufacturing the same, and more particularly to an optical waveguide having a spot size conversion structure in which a cross section of an input portion and an output portion of a core is formed in a substantially circular or elliptical shape and a manufacturing method thereof. Is.

  A conventional optical waveguide manufacturing process is shown in FIG.

  6A to 6D are cross-sectional views showing an example of a manufacturing process of a conventional optical waveguide.

First, a glass substrate 1 corresponding to the cladding of an optical waveguide is prepared. The glass substrate 1 is subjected to surface polishing. Next, a mold 2 is prepared in which a convex rectangular optical waveguide pattern 2b made of TiN and having a thickness of 6 μm is formed on the surface of a mold base material 2a of cemented carbide (WC 95-80%, Co 5-20%). . The convex rectangular optical waveguide pattern 2b made of TiN can be obtained by a photoresist etching method and a sputtering method, and the surface thereof is polished with diamond powder to a surface roughness R _max = 0.01 μm.

Therefore, as shown in FIG. 6 (a), the glass substrate 1 and the mold 2 are accommodated in a molding apparatus (not shown), which is heated in N ₂ gas to a temperature of 650 ° C. to be softened. By pressing the mold 2 against the surface and cooling, the glass substrate 1 on which the concave core pattern is formed as shown in FIG. 6B is obtained.

  A groove 3 having a depth of 6 μm was formed on the glass substrate 1 corresponding to the convex pattern 2b of the mold 2, and the bottom surface was observed with an electron microscope. As a result, a very fine mirror finish was obtained.

  Next, as shown in FIG. 6C, an optical element material 4 having a refractive index higher than that of the glass substrate 1 is deposited on the surface of the glass substrate 1 having the grooves 3 by sputtering.

  Then, as shown in FIG. 6D, a core 5 is formed by polishing the optical element material 4 until a portion other than the groove 3 of the optical element material 4 is removed using a polishing machine (not shown). Is done.

  The optical waveguide can be manufactured through the above steps.

  As prior art document information related to the invention of this application, for example, Patent Document 1 is known.

  FIG. 7 shows a conventional optical waveguide having a spot size conversion structure.

  FIG. 7 is a schematic view of a core of an optical waveguide having a conventional spot size conversion structure. As shown in FIG. 7, the input / output units 12 and 13 of the core 11 have a large connection loss with the optical fiber as the relative refractive index difference increases when the optical fiber and the element are mounted. A tapered portion 14 having a taper shape which is widened toward the input / output portions 12 and 13 in the width direction and the height direction of the core 11 is formed so as to be smaller. The angle of the taper portion 14 is in the range of 0.3 ° to 1 °. According to the above configuration, the core width and core height of the input / output portions 12 and 13 of the optical waveguide are equal to the core diameter of the optical fiber, and the core cross-sectional shape of the optical waveguide is close to the core cross-sectional shape of the optical fiber. . This increases the mode field diameter and reduces the connection loss with the optical fiber.

As prior art document information related to the invention of this application, for example, Patent Document 2 is known.
Japanese Unexamined Patent Publication No. 64-026806 Japanese Patent Application Laid-Open No. 2001-99772

  However, the conventional optical waveguide manufacturing process has a problem that the core of the optical waveguide can only be manufactured in a shape substantially equal to the shape of the mold. Further, the conventional optical waveguide having the spot size conversion structure has a problem in that since the cross-sectional shape of the core is rectangular, a connection loss with an optical fiber having a circular cross-section is increased.

  The present invention can produce an optical waveguide whose cross-sectional shape of the core of the optical waveguide is substantially circular or elliptical, and the size of the input portion or output portion of the core is the same as the core of an optical fiber, LD, VCSEL, LED, etc. It is possible to form an optical waveguide having a spot size conversion structure with high coupling efficiency with an optical fiber, LD, VCSEL, LED, and the like, and a method for manufacturing the same. It is the purpose.

  In order to achieve the above object, the present invention has the following configuration.

  The invention according to claim 1 of the present invention comprises a lower clad layer, a core having an input part or an output part connected to an optical fiber on the lower clad layer, and an upper clad layer covering the core, An optical waveguide in which the propagation direction of light of the core continuously changes, the cross-sectional shape of the core has different shapes at the light input portion and the output portion, and is substantially circular or elliptical, and the input portion of the core Alternatively, since the diameter of the output portion can be formed with a shape and size substantially equal to the core diameter of the optical fiber and the diameter of the emitted light of the light emitting element such as LD, VCSEL, LED, etc., the optical fiber, LD, VCSEL, LED The coupling efficiency with a light emitting element such as can be increased.

  The invention according to claim 2 is the optical waveguide according to claim 1, wherein the hardness of the core is larger than the hardness of the lower cladding layer, and the cross-sectional shape of the core of the optical waveguide is circular or elliptical, which is higher than the lower cladding layer. It can be easily machined approximately equal to the shape.

  According to a third aspect of the present invention, there is provided a step of heat-pressing a concave core pattern using a mold for the lower clad layer, and glass having a refractive index and hardness higher than that of the lower clad layer. A step of filling the material so as to overflow, a step of heating the glass material filled in the concave core pattern to form a core and removing the overflowed glass material, and covering the lower cladding layer and the core A step of forming an upper clad layer made of a glass material or a resin having a refractive index substantially equal to that of the lower clad layer, and the die has a cross-sectional shape perpendicular to the light propagation direction of the core continuously changing at least partially. Is a method of manufacturing an optical waveguide in which a circular arc or elliptical arc shape is formed in a field, such as an optical fiber or a light emitting element, which connects the cross-sectional shape of the core of the optical waveguide It can be prepared in the same shape as the turn.

  The invention according to claim 4 is the method of manufacturing an optical waveguide according to claim 3, wherein the step of forming the core comprises polishing the upper surface of the lower cladding layer and polishing to round the upper portion of the core. It can be manufactured in the same shape as the field pattern of an optical fiber, a light emitting element or the like that connects the cross sectional shapes of the cores.

  The invention according to claim 5 is the method for manufacturing an optical waveguide according to claim 3, wherein the upper surface of the core is formed to be higher than the surface of the lower cladding layer, and the light for connecting the cross-sectional shape of the core of the optical waveguide. It can be manufactured in the same shape as the field pattern of a fiber, a light emitting element or the like.

  The invention described in claim 6 is the method of manufacturing an optical waveguide according to claim 3, wherein heating is performed in vacuum, and mixing of bubbles into the core of the optical waveguide can be prevented.

  The invention according to claim 7 is the method of manufacturing an optical waveguide according to claim 3, wherein a glass material is filled into a concave core pattern by sputtering, and a glass material having a high softening point is used as the core material of the optical waveguide. Therefore, the influence on the core can be reduced in forming the upper cladding layer.

  The invention according to claim 8 is formed by any one of a sputtering method, a CVD method, press molding, or a method of applying and heating a glass material pulverized into a powder form. This is an optical waveguide manufacturing method, and the upper cladding layer of the optical waveguide can be easily formed of the third glass material.

  The invention according to claim 9 is the method of manufacturing an optical waveguide according to claim 3, wherein the upper cladding layer is formed by using one of a spin coating method and a dropping method using a resin, and the upper cladding layer of the optical waveguide is formed. Since the layer can be formed of a resin, the cost can be reduced.

  The present invention comprises a lower clad layer, a core having an input part or an output part connected to an optical fiber on the lower clad layer, and an upper clad layer covering the core, and perpendicular to the light propagation direction of the core. An optical waveguide having a continuously changing cross-sectional shape and having different shapes at a light input portion and an output portion, and wherein the cross-sectional shape of the core is substantially circular or elliptical. Alternatively, since the diameter of the output portion can be formed with a shape and size substantially equal to the core diameter of the optical fiber and the diameter of the emitted light of the light emitting element such as LD, VCSEL, LED, etc., the optical fiber, LD, VCSEL, LED The coupling efficiency with a light emitting element such as can be increased.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1)
1A to 1E are cross-sectional views showing an example of a manufacturing process of an optical waveguide according to Embodiment 1 of the present invention, and FIG. 2 is a perspective view showing an example of a mold according to Embodiment 1 of the present invention. FIGS. 3A to 3C are cross-sectional views showing the shape of the mold in the first embodiment of the present invention.

  As shown in FIGS. 1A to 1E and FIG. 2, 41 is a convex core pattern of a mold, 42 and 43 are light input portions or output portions, 44 is a mold base material, and 51 is a mold. , 52 is a lower cladding layer, 53 is a concave core pattern, 54 is a core layer, 55 is a core, and 56 is an upper cladding layer.

  It is desirable to use a cemented carbide made of WC—Co or the like for the mold base 44 and an alloy made of WC—Co, TiN, Ni—P or the like for the core pattern 41. The shape of the light input or output units 42 and 43 includes a semicircular shape or a semielliptical shape.

  Hereinafter, an example of the manufacturing process of the optical waveguide having the spot size conversion structure of the present invention will be described.

  As shown in FIG. 3B, the shape of the CC ′ cross section of the convex core pattern 41 formed on the mold 51 is 6 μm in diameter on the short side of a rectangle having a short side of 6 μm and a long side of 15 μm. The shape is like a hemisphere. Further, as shown in FIG. 3C, the shape of the DD ′ cross section of the convex core pattern 41 formed on the mold 51 is 10 μm in diameter on the short side of a rectangle having a short side of 10 μm and a long side of 15 μm. The shape is such that a hemisphere is formed.

The lower cladding layer 52 is made of a first glass material having a softening point of about 600 ° C. or less in consideration of moldability in the mold 51. Such a mold 51 and the lower clad layer 52 are accommodated in a press molding machine (not shown), and this is heated above the softening point of the first glass material used for the lower clad layer 52 in N ₂ gas. .

  Then, as shown in FIG. 1A, the mold 51 is pressed against the lower clad layer 52 or the core pattern 53 is formed on the lower clad layer 52 by the dead weight of the mold 51, and then cooled, as shown in FIG. Thus, the lower clad layer 52 obtained by molding the concave core pattern 53 is obtained.

  Next, in the first embodiment of the present invention, the core material has a refractive index higher than that of the lower cladding layer 52, a softening point of about 450 ° C. or less, and a second glass whose hardness is higher than that of the lower cladding layer 52. Use materials. A powder obtained by pulverizing the second glass material is applied onto the lower cladding layer 52 formed with the concave core pattern 53. At this time, the second glass material in a powder form is applied sufficiently so as to overflow other than the concave core pattern 53.

  Then, the lower clad layer 52 coated with the second glass material is heated to a temperature of about 500 ° C. to soften the second glass material, and as shown in FIG. A core layer 54 is formed on the layer 52. The removal of bubbles inside the core layer 54 can be promoted by performing this heating step in a vacuum.

  Next, the lower clad layer 52 on which the core layer 54 is formed is removed by using a polishing machine (not shown), and the core layer 54 overflowing from the concave core pattern 53 is removed, and about 10 to 15 μm from the surface. The lower cladding layer 52 is removed to the depth. Here, since the hardness of the core layer 54 is larger than the hardness of the lower cladding layer 52, the shape of the core layer 54 is convex upward with respect to the surface of the lower cladding layer 52. Accordingly, as shown in FIG. 1D, a core 55 having a cross-sectional shape that is substantially circular or elliptical can be formed.

  Then, as shown in FIG. 1E, an upper clad layer 56 made of a third glass material is formed on the lower clad layer 52 on which the core 55 is formed by using a sputtering method. The sputtering method is characterized in that a glass material having a high softening point can be formed at a low temperature. Therefore, the third glass material only needs to have a refractive index substantially equal to that of the lower cladding layer 52, and the first glass material may be used as it is.

  Through the above manufacturing process, an optical waveguide having a spot size conversion structure that can be used for, for example, a core of an optical waveguide having a diameter of 6 μm and a single mode optical fiber having a diameter of 10 μm can be manufactured.

  Note that the core layer 54 may be formed on the lower cladding layer 52 by sputtering. In this case, there is an advantage that even a material having a high softening point can be used as the second glass material. Further, by performing film formation while applying an RF bias to the lower clad layer 52 which is a film formation material, it is possible to improve the embedding property of sputtered particles in the concave core pattern 53.

  Further, although the upper clad layer 56 made of the third glass material is formed by the sputtering method, a method such as a CVD method or a press molding method may be used.

  Furthermore, although the third glass material is used for the upper clad layer 56, the present invention is not limited to this, and a resin may be used as the second clad layer 56. For example, fluorinated polyimide can be used.

  When fluorinated polyimide is used, it can be formed on the lower clad layer 52 by spin coating or dropping.

  In addition, although the fluorinated polyimide was demonstrated to the upper clad layer 56 as an example to resin, it is not restricted to this material, Various resin, such as PMMA and photosensitive polysilane, can be used.

(Embodiment 2)
FIG. 4 is a schematic diagram showing the configuration of the single-fiber bidirectional optical transceiver module according to Embodiment 2 of the present invention.

  As shown in FIG. 4, 21 is a cladding layer, 22 is a core, 23a and 23b are spot size converters, 24 is a groove, 25 is a wavelength selection filter, 26 is a single mode optical fiber, 27 is an LD, 28 is a PD, 29 Is a substrate, and 30 is a light branching portion.

  The function of this single fiber bidirectional optical transceiver module will be briefly described.

  First, an optical signal having a wavelength of 1.55 μm emitted from the optical fiber 26 propagates through the core 22 via the spot size conversion unit 23a, passes through the wavelength selection filter 25 inserted in the optical branching unit 30, and passes to the PD 28. Incident light is converted into an electrical signal. On the other hand, the 1.3 μm wavelength optical signal emitted from the LD 27 serving as a light emitting element propagates through the core 22 via the spot size conversion unit 23 b, is reflected by the wavelength selection filter 25, and passes through the optical branching unit 30. 26 propagates through the core 22 connected to the optical fiber 26 through the spot size converter 23a.

  A clad layer 21 is formed on a substrate 29, and a core 22 having a substantially circular cross section is formed on the clad layer 21. An optical branching portion 30 is formed in the core 22, and the optical branching portion 30 is configured by using a Y branch having a low loss and a simple structure. Further, a groove 24 is formed in the vicinity of the light branching portion 30 so as to intersect the core 22, and a wavelength selection filter 25 is inserted into the groove 24. The PD 28 is coupled to the output portion of the core 22 on the non-branching side. Further, one of the branch sides of the core 22 is used as an input unit, and a spot size conversion unit 23b is formed at an end thereof and coupled to the LD 27. The other side of the branch side of the core 22 is used as an input / output unit, and a spot size conversion unit 23 a is formed at the end, which is coupled to the single mode optical fiber 26. It should be noted that an electric circuit (not shown) for driving the LD 27 and the PD 28 is disposed close to the LD 27 and the PD 28.

  When the refractive index difference between the cladding layer 21 and the core 22 is increased to reduce the size of the optical waveguide, the diameter of the core 22 can be reduced. However, the spot size between the core 22 and the single mode optical fiber 26 is not reduced. Matching increases. For example, if the refractive index difference between the cladding layer 21 and the core 22 is 0.6%, the diameter of the core 22 is 6 μm, whereas the core diameter of the single mode optical fiber 26 is about 10 μm. The coupling loss with the mode optical fiber 26 is as large as about 2.0 dB.

  Therefore, in the present invention, the core 22 is coupled to the single mode optical fiber 26 using the spot size conversion portion 23a whose cross-sectional shape is substantially equal to a circle. For example, as a result of coupling using the spot size conversion unit 23a in which the diameter of the end of one core 22 is about 6 μm and the diameter of the other core 22 is about 10 μm, the coupling loss is about 0.5 dB. It was possible to greatly reduce. When coupling was performed using a rectangular spot size converter having a rectangular cross-sectional shape, the coupling loss was about 1.0 dB.

  The light emitted from the LD 27 generally has an elliptical polarization plane. Therefore, conventionally, the LD 27 and the optical waveguide are coupled using a lens. In the present invention, the spot size conversion unit 23 b is used for coupling the LD 27 and the core 22. For example, one end is processed into a substantially oval shape so that the length in the major axis direction is about 4.5 μm, the length in the minor axis direction is about 3.4 μm, and the other end is circular with a diameter of about 6 μm. When coupling was performed using the processed spot size conversion portion 23b, the coupling loss was as very small as 3 dB.

(Embodiment 3)
FIG. 5 is a schematic diagram showing a configuration of an LN (LiNbO ₃ ) optical modulator according to the third embodiment of the present invention.

  As shown in FIG. 5, 31 is a cladding layer, 32 is a core, 33a and 33b are spot size conversion units, 34 is an LD, 35 is an electrode, 36 is a single mode optical fiber, 37 is a substrate, and 38a and 38b are optical branching units. It is.

  The function of this LN optical modulator will be briefly described.

LN is a material having an electro-optic effect in which the refractive index of the medium changes when a voltage (electric field) is applied. When the refractive index changes, the optical path length also changes, so that it is converted into a phase change of light passing therethrough. That is, in the LN optical modulator of the present invention, when the voltage V = V ₀ is applied to the electrode 35, there is a phase difference in the light passing through the two optical waveguides that reach the optical branching portion 38b from the optical branching portion 38a. Therefore, the two lights are added as they are, and the signal is “1”. On the other hand, when the voltage V = V ₁ is applied to the electrode 35, the light passing through the two optical waveguides reaching the light branching portion 38 b from the light branching portion 38 a has a phase difference of 180 °. Therefore, the light waves cancel each other and the output becomes “0”. That is, the light emitted from the light branching portion 38b does not propagate through the core 22 but becomes diffused light.

  A clad layer 31 made of LN is formed on a substrate 37, and a core 32 is formed on the clad layer 31 by Ti thermal diffusion. Two optical branch portions 38a and 38b are formed in the core 32. The optical branch portions 38a and 38b are configured by using a Y branch having a low loss and a simple structure. In addition, an electrode 35 is provided to apply a voltage to the core 32 branched into two by the light branching portions 38a and 38b. Spot size converters 33a and 33b are provided in the input / output section of the core 32, respectively, and an LD 34 is coupled to the input section side and a single mode optical fiber 36 is coupled to the output section side.

  The diameter of the core 32 of the optical waveguide made of LN is about 4 μm. Therefore, the spot size mismatch with the single mode optical fiber 36 increases. Therefore, as a result of coupling the core 32 and the single mode optical fiber 36 using the spot size conversion unit 33a of the present invention, the coupling loss is about 0.7 dB, which is compared with the case where the spot size conversion unit 33a is not used. Thus, the coupling loss can be reduced by about 2 dB.

  In addition, the spot size conversion unit 33b is used for coupling the LD 34 and the core 32. For example, by using a spot size conversion unit 33b in which one end is processed into a substantially elliptic shape, the major axis is approximately 4.0 μm, the minor axis is approximately 3.4 μm, and the other end is processed into a circular shape having a diameter of approximately 4 μm. As a result of the coupling, the coupling loss was as small as 3.3 dB.

  The optical waveguide and the manufacturing method thereof according to the present invention can manufacture an optical waveguide having a substantially circular or elliptical cross-sectional shape of the core of the optical waveguide, and the diameter of the input portion or the output portion of the core is an optical fiber. Can be formed with a size substantially equal to the diameter of the light emitted from the light emitting element such as LD, VCSEL, LED, etc., and the coupling efficiency with the light emitting element such as optical fiber, LD, VCSEL, LED, etc. It has the effect of providing an optical waveguide having a high spot size conversion structure and a method for manufacturing the same, and is useful for a single-fiber bidirectional optical transceiver module, optical modulator, AWG, coupler, and the like.

(A)-(e) Sectional drawing which shows an example of the manufacturing process of the optical waveguide in Embodiment 1 of this invention. The perspective view which shows an example of the metal mold | die in Embodiment 1 of this invention. (A)-(c) Sectional drawing which shows the shape of the metal mold | die in Embodiment 1 of this invention. Schematic which shows the structure of the single fiber bidirectional | two-way optical transmission / reception module in Embodiment 2 of this invention. Schematic diagram showing the configuration of a LN (LiNbO ₃₎ optical modulator according to the third embodiment of the present invention (A)-(d) Sectional drawing which shows an example of the manufacturing process of the conventional optical waveguide Schematic diagram of core of optical waveguide with conventional spot size conversion structure

Explanation of symbols

21 Clad layer 22 Core 23a, 23b Spot size converter 24 Groove 25 Wavelength selection filter 26 Single mode optical fiber 27 LD
28 PD
29 Substrate 30 Optical branching section 31 Cladding layer 32 Core 33a, 33b Spot size conversion section 34 LD
35 Electrode 36 Single mode optical fiber 37 Substrate 38a, 38b Optical branching part 41 Core pattern 42, 43 Light input part or output part 44 Mold base 51 Mold 52 Lower clad layer 53 Concave core pattern 54 Core layer 55 Core 56 Upper cladding layer

Claims (9)

It consists of a lower clad layer, a core having an input part or an output part connected to the optical fiber on the lower clad layer, and an upper clad layer covering the core. The light propagation direction of the core changes continuously. The optical waveguide has a shape in which the cross-sectional shape of the core is different between the light input portion and the light output portion, and is substantially circular or elliptical. The optical waveguide according to claim 1, wherein the hardness of the core is greater than the hardness of the lower cladding layer. A step of heat-pressing a concave core pattern using a mold for the lower clad layer, and a step of filling the concave core pattern with a glass material having a higher refractive index and hardness than the lower clad layer so as to overflow. Heating the glass material filled in the concave core pattern to form a core and removing the overflowed glass material, and having a refractive index substantially equal to that of the lower cladding layer so as to cover the lower cladding layer and the core. A step of forming an upper clad layer made of a glass material or a resin, wherein the light propagation direction of the core is continuously changed by the mold, and the cross-sectional shape forms an arc or elliptical arc shape at least partially. A method for manufacturing a waveguide. 4. The method of manufacturing an optical waveguide according to claim 3, wherein the step of forming the core comprises polishing the upper surface of the lower cladding layer and polishing to round the upper portion of the core. The method for manufacturing an optical waveguide according to claim 3, wherein the upper surface of the core is formed to be higher than the surface of the lower cladding layer. The method for manufacturing an optical waveguide according to claim 3, wherein the heating is performed in a vacuum. 4. The method of manufacturing an optical waveguide according to claim 3, wherein the glass material is filled into the concave core pattern by a sputtering method. 4. The method of manufacturing an optical waveguide according to claim 3, wherein the upper cladding layer is formed by any one of a sputtering method, a CVD method, press molding, or a method of applying and heating a glass material pulverized into a powder form. The method for manufacturing an optical waveguide according to claim 3, wherein the upper cladding layer is formed by using a resin by any one of a spin coating method and a dropping method.

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