WO2004006394A1

WO2004006394A1 - Optical wave guide and method for manufacture thereof

Info

Publication number: WO2004006394A1
Application number: PCT/JP2003/008241
Authority: WO
Inventors: Akio Furukawa; Tuyoshi Shimoda; Yukari Deki
Original assignee: Nec Corporation
Priority date: 2002-07-05
Filing date: 2003-06-27
Publication date: 2004-01-15
Also published as: JP2004037990A

Abstract

An optical waveguide type amplifier which has a core (3) containing a rare earth element having a concentration distribution such that the concentration is high in a central portion of the core and become gradually lower toward the perimeter and also a modifying element for preventing the rare earth element from forming a cluster and for expanding the wavelength region for a light capable of being amplified having a concentration distribution similar to that of the rare earth element, wherein the concentration of the rare earth element is gradually decreased both in the X direction and the Y direction in a coordinate system formed, in a plane perpendicular to the light guiding direction of the core (3), by an X axis of the direction of the surface of a substrate (1) (the width direction of the plane) and a Y axis of the direction of the normal to the surface of a substrate (1) (the height direction of the plane). The optical waveguide type amplifier allows the achievement of an enhanced gain.

Description

BACKGROUND OF THE INVENTION

The present invention relates to an optical waveguide using a planar waveguide and a method for manufacturing the same, and more particularly to an optical waveguide having an optical amplification effect by adding a rare earth element to a glass waveguide.

It relates to the manufacturing method.

Fine

Optical amplifiers are a very important device in recent long-distance WDM communications because they directly amplify light without passing through electric circuits and amplify over a wide wavelength range. At present, optical amplifiers using fibers doped with rare earth elements such as erbium are mainly used, and high quality amplifiers with high amplification gain and low noise characteristics are provided.

Under these circumstances, optical amplifiers with rare-earth elements added to planar optical waveguides have been developed with the aim of further miniaturization, and optical amplifiers aiming for higher gain and wider amplification band have been developed. Is being done. In order to achieve both miniaturization and high gain of the optical amplifier, the concentration of the rare earth element to be added may be increased.

In an optical amplifier, pumping light is introduced from the outside into an optical amplifier to excite rare-earth electrons, which are relaxed by signal light, and the intensity of the original signal light is increased by stimulated emission. Therefore, in order to increase the gain efficiently, more pump levels should be provided in the waveguide. Therefore, by introducing more rare earth elements such as erbium as a source for generating an excitation level into the waveguide, both miniaturization and high gain can be achieved.

However, rare earths have the property of clustering when added at high concentrations into the waveguide glass. When the rare earths are clustered, the excitation level changes and the number of rare earth elements contributing to excitation at the desired wavelength is substantially reduced, reducing the amplification gain. Therefore, in order to achieve both miniaturization and high gain, it is only necessary to increase the rare-earth concentration in the waveguide glass while suppressing clusters. Important characteristics required for optical amplifiers include high gain and a wide amplification wavelength band. In wavelength multiplex communication, for example, optical signals of 40 kinds of wavelengths are used at 0.8 nm intervals, and a total of 32 nm wavelength band is used. An optical amplifier used in such wavelength division multiplexing communication is required to have a function of amplifying a gain in a band of 32 nm or more.

Here, there has been reported an example in which an element other than the rare earth element is introduced into the waveguide glass to suppress the disintegration of the added rare earth class and broaden the bandwidth of the optical amplifier (Reference 1: Japanese Unexamined Patent Application Publication No. 9-11-1). No. 0 595 6). In Reference 1, at least two elements other than rare earths are added to the core of the waveguide. These two elements are elements of the genus IIB, IVB, and IIA, such as ゃ & ゃ '1 ゃ 0. The presence of these elements in the core at the same time as the rare-earth elements suppresses the clustering of the rare-earth elements, broadens the excitation level, and broadens the amplification wavelength band. These elements are uniformly added in the core.

Also, a technique has been proposed in which a rare-earth fS element is added only to the central layer of the core to obtain a wider band and a higher amplification effect (Reference 2: Japanese Patent Application Laid-Open No. 4-3599230). No.). In the technology shown in Reference 2, an auxiliary element for suppressing cluster unification and broadening the band is also added only to the central layer of the core at the same time, and neither the rare earth element nor the auxiliary element is introduced into the upper and lower core portions. I have to. This is because the intensity distribution of the excitation light for exciting the rare earth element is high at the center of the core, and the rare earth is selectively added to the center of the core to increase the excitation efficiency and increase the gain. Things. Even if there are many Er elements in a region where the light intensity is weak, all the Er elements added to this region cannot be excited enough and conversely contribute to light absorption. For this reason, in the above technique, Er is not added except for the central part where the light intensity is strong. Further, the assisting element only needs to be in the rare earth-containing layer, and in the above technique, it is not added to a region other than the center of the core because it contributes to light absorption.

In addition, a technique for distributing rare earth elements in a core to increase the excitation light efficiency has been proposed (Reference 3: Japanese Patent Application Laid-Open No. 6-281977). In the technology shown in Reference 3, Er is added at a high concentration at the center of the core and at a low concentration at the periphery of the core. ing. This is because the excitation light intensity distribution that excites the Er element is high at the center of the core and weak at the periphery, so adding a large amount of Er at the center of the core and a small amount of Er around the core increases the excitation light rate and increases the gain. It is made to aim at. According to this technology, the concentration of Er in the core is distributed so that the ratio of the highest concentration to the lowest concentration is more than twice. By the way, while it is required to realize more functions with a smaller device, the above-mentioned optical amplifier is also required to be smaller. In the waveguide-type optical amplifier described above, the gain per unit length in the waveguide direction is increased to shorten and reduce the size of the optical amplifier. Thus, in order to meet the recent demand for miniaturization, it is necessary to further increase the gain of the optical amplifier. Summary of the Invention

The present invention has been made to solve the above problems, and has as its object to obtain a higher gain in a waveguide-type optical amplifier. An optical waveguide according to the present invention is an optical waveguide composed of a substrate, a clad formed on the substrate, and a core disposed in the clad, wherein the core has a rare-earth element having a predetermined concentration distribution. Element and a correction element that has at least one of the function of suppressing rare earth element class disintegration and the function of exciting the rare earth element with excitation light to broaden the signal light amplification band. is there.

Here, the rare earth element may have a concentration distribution in which the concentration gradually decreases from the center to the periphery, and the concentration is uniform from the center to the periphery in the substrate plane direction, and is perpendicular to the substrate plane. In any direction, a density distribution may be provided in which the density gradually decreases from the center to the periphery.

Further, the modifying element may be added uniformly in the core, or may be added in the core in a distribution similar to the concentration distribution of the rare earth element in the core. The correction element may be any one of A 1, B, G a, In, G e, S n, B i, N, P, and Y b. In this optical waveguide, the concentration distribution of the rare earth element in the core is the same as the intensity distribution of light propagating through the core, the Gaussian distribution that becomes maximum at the center of the core and becomes smaller toward the periphery, It is sufficient that the ratio of the deviation from the Gaussian distribution which becomes the maximum and becomes smaller toward the periphery is within the range of any distribution within 30%. The concentration distribution of the modifying element may be uniform or similar to the light intensity distribution. In the optical waveguide, the rare earth element may be any one of Er, Tm, Pr, and Nd. The main component of the core may be any of silicon oxide, aluminum oxide, and bismuth oxide.

The method for manufacturing an optical waveguide according to the present invention includes a step of forming a lower clad on a substrate; and a step of forming a core containing a rare earth element and a modifying element at a high concentration in the center on the lower clad; A step of forming an upper cladding on the lower cladding and the core, wherein the modifying element has a function of suppressing clustering of the rare earth elements added to the core and a function of suppressing the rare earth elements added to the core. It was made of an element having at least one of the functions of expanding the signal light amplification band by being excited by the excitation light.

Here, the step of forming the core includes a step of forming a film to be a core on the lower clad, and a step of injecting a rare earth element and a correction element into the film while scanning a focused ion beam. A step of providing a concentration distribution in which the concentration gradually decreases from the central portion to the peripheral portion of the core.

Alternatively, a film formation method using a first target including a main component of the core, a second target including a rare earth element, and a third target including a correction element on the lower clad is performed. However, the concentration of the rare earth element gradually decreases from the center of the film to the upper and lower peripheral parts, and the concentration of the correction element gradually decreases in the film and gradually decreases from the center to the upper and lower peripheral parts. A step of forming a layer having a certain concentration distribution may be provided. In the step of forming the core, the core may be formed by a sputtering method that changes the sputtered state of the second target and the third target, or the second target and the third target may be formed by a sputtering method. The target may be formed by an ion plating method that changes the evaporation state of the target, or may be formed by an evaporation method that changes the evaporation amount of the second target. In addition, the second target and the third target may be composed of the same evening target containing a rare earth element and a modifying element at the same time.

In the step of forming the core, a first source gas containing a main component of the core, a second source gas containing a rare earth element, and a third source gas containing a correction element are introduced on the lower clad. , The concentration of rare earth elements gradually decreases from the center of the film to the upper and lower peripheries, and the concentration of the correction element remains constant inside the film. A step may be provided for forming the density distribution so that the density distribution is one of a state and a state where the density gradually decreases from the central part to the upper and lower peripheral parts.

Further, a step of heating the core to diffuse the rare-earth element and the modifying element to provide a state in which the rare-earth element and the modifying element have a concentration distribution in which the concentration gradually decreases from the central portion to the peripheral portion of the core. It may be provided.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1A is a cross-sectional view schematically illustrating a configuration example of an optical waveguide according to an embodiment of the present invention.

1B and 1C are distribution diagrams showing the concentration distribution of rare earth elements in the core of the optical waveguide according to the embodiment of the present invention.

FIG. 2A and FIG. 2B are distribution diagrams showing the concentration distribution of the modifying element in the core of the optical waveguide in the example of the present invention.

FIG. 3A and FIG. 3B are distribution diagrams showing the concentration distribution of the modifying element in the core of the optical waveguide in the example of the present invention.

FIGS. 4A and 4B are distribution diagrams showing the concentration distribution of rare earth elements in the core of the optical waveguide according to another embodiment of the present invention.

FIGS. 5A and 5B are distribution diagrams showing the concentration distribution of the modifying element in the core of the optical waveguide according to another embodiment of the present invention.

FIG. 6A is a distribution diagram showing a distribution of light intensity in a core of an optical waveguide according to another embodiment of the present invention.

FIGS. 6B and 6C are distribution diagrams showing the concentration distribution of rare earth elements in the core of the optical waveguide according to another embodiment of the present invention.

FIGS. 7A and 7B are distribution diagrams showing the concentration distribution of rare earth elements in the core of the optical waveguide according to another embodiment of the present invention.

FIG. 8A and FIG. 8B are distribution diagrams showing the concentration distribution of rare earth elements in the core of the optical waveguide according to another embodiment of the present invention.

FIG. 9A, FIG. 9B, FIG. 9C, and FIG. 9D are process diagrams for explaining a method of manufacturing an optical waveguide according to the embodiment of the present invention.

FIG. 10 is a view for explaining a method of partially manufacturing an optical waveguide in an embodiment of the present invention. It is a perspective view.

FIG. 11 is a configuration diagram schematically showing a manufacturing apparatus for realizing the method of manufacturing an optical waveguide according to the embodiment of the present invention. .

12A, 12B, 12C, 12D, 12E, 12F, 12G, 12H, 12I and 12J illustrate a method of manufacturing an optical waveguide according to another embodiment of the present invention. FIG.

Detailed description of the embodiment

FIG. 1A is a schematic sectional view schematically showing a configuration example of an optical waveguide according to a first embodiment of the present invention. This optical waveguide is composed of a lower clad 2 formed on a substrate 1, a core 3, and an upper clad 4 formed so as to cover the core 3, and propagates in the core 3 to a region including the core 3. A rare earth element for amplifying signal light is added. The refractive index of the core 3 is larger than that of the lower cladding 2 and the upper cladding 4, and extends in a direction parallel to the plane of the substrate 1.

1B and 1C are distribution diagrams showing the concentration distribution (profile) of a rare earth element in a cross section of the optical waveguide shown in FIG. 1A. FIG. 1B shows a direction in which the core 3 is disposed in a direction perpendicular to the waveguide direction of the core 3 in a plane perpendicular to the optical waveguide direction of the core 3, that is, the substrate 1 is located downward with the information of the substrate 1. The density distribution in the width direction of the core 3 is shown. FIG. 1C shows the concentration distribution of the core 3 in the height direction.

As shown in FIGS. 1B and 1C, in the optical waveguide of the present example, the concentration of the rare earth element added to the core 3 was high near the center and gradually decreased toward the periphery. The concentration of the rare earth element is defined as the X-axis (width direction) in the plane direction of the substrate 1 and the Y-axis (height direction) normal to the surface of the substrate 1 in a plane perpendicular to the optical waveguide direction of the core 3. In the coordinate system formed by, it gradually decreases in both the X and Y directions. The concentration of the rare earth element does not need to be rapidly reduced to zero outside the core 3 and may be gradually reduced. In this embodiment, a modifying element is added together with the rare earth element. First, A1 and P were added, and this concentration distribution was uniform in the X and Y directions as shown in Figs. 2A and 2B. Also, the concentration of the correction element suddenly becomes zero outside the core. It does not need to be, and may gradually decrease. In addition, in the optical waveguide of this embodiment, as shown in FIGS. 3A and 3B, the concentration distribution of A 1 and P in the core 3 is set to be substantially equal to the concentration distribution of Er. Good.

Hereinafter, a specific example of the optical waveguide shown in FIG. 1A will be described. First, the substrate 1 is a silicon substrate. Lower clad 2 is the also constructed from S I_〇 ₂ having a thickness of 1 5 m, the upper cladding 4 is a S i O 2 of boron and phosphorus having a thickness of 1 0 is added (BPSG). The core 3 is a square having a cross section of 2 m square and is composed mainly of a silicon-based material such as silicon oxide to which erbium (Er) is added as a rare earth element, aluminum oxide, bismuth oxide, and the like. It was done. As described above, the concentration of Er added to Core 3 reaches a maximum near the center of Core 3 (1 × 10 20 atoms Z cm ³ ) and gradually decreases toward the periphery of Core 3. are doing. The concentration of Er gradually decreases to 1 × 10 19 atoms / cm ³ at the interface between the core 3 and the clad. In addition, the concentration of Er decreases in both the X and Y directions. As described above, in this embodiment, the rare earth element concentration distribution is high at the center of the core, and does not become zero on the way to the periphery, but decreases so as to decrease.

The excitation light introduced into the optical waveguide composed of the core 3 has an intensity distribution in the core 3 of the waveguide, the intensity is strong at the center, the intensity decreases near the core 3, and the intensity around the core 3 is reduced. Part of the lower cladding 2 and upper cladding 4 also penetrate. Since the amplification of the optical signal is caused by the relaxation of the energy of the rare earth element excited by the excitation light, it is preferable to excite all the added rare earth elements for the most efficient optical amplification. If some of the rare earth elements added to the core 3 are not excited, they contribute to the absorption of the signal light and contribute to the attenuation of the optical signal, and thus become an inhibiting factor of the optical amplification. On the other hand, if the amount of the rare earth element added to the core 3 is too small, the amplification factor per unit length of the optical waveguide decreases, and the amplifier becomes long and large. Here, in the embodiment of the present invention, as described above, the distribution of the rare earth element in the core 3 is configured to be higher toward the center of the core 3 and decrease toward the periphery of the core 3, and the excitation light inside the core 3 is reduced. It corresponded to the light intensity distribution.

As a result, the portion near the periphery of core 3 is excited by the excitation light guided through core 3. As a result, the number of rare earth elements that are not excited is reduced, and the excitation light can effectively contribute to the excitation throughout the core 3. Since the light intensity distribution in the core 3 is basically close to the Gaussian distribution, the concentration distribution of the rare earth element in the core 3 may be substantially Gaussian distribution. Also, the concentration distribution range may have an appropriate width and deviate from the Gaussian distribution so as to cope with a case where the light intensity distribution deviates from the Gaussian distribution due to deformation of the core 3 or the like. The gain is reduced by the deviation, but it is not a significant decrease.

The rare earth element added to the core 3 is not limited to Er, but may be thulium (Tm), plunge (Pr), neodymium (Nd), or any other element capable of amplifying signal light by excitation radiation. Or a plurality of them may be added. The above Er concentration, substrate and cladding materials, dimensions and the like are examples of the present invention and are not limited thereto.

The elements to be added to the core 3 are as follows: £ 1 "and 8 1, P are added in a uniform concentration distribution in the core 3. The concentration of A 1 is determined by the S i in the core 3 consisting of S i〇2. And the concentration of P was 5% with respect to the Si in core 3.

A 1 was added to the S i 0 ₂ suppresses cluster Ichika when doped with a rare earth element at high concentration, there is the action of both expanding the amplification wavelength band. As elements having such a function, instead of A1, boron (B), gallium (Ga), indium (In), germanium (Ge), tin (Sn), bismuth (Bi), nitrogen (N ), Phosphorus (P), itridium (Yb) and oxides thereof, and these may be added to the core 3. Each element has both functions, although the degree of effect on both functions is different.

One or two or more of these elements for suppressing clustering and for improving the amplification band may be added to the core 3, and other elements having the same function may be added. It may be added. The above Er concentration, the modifying element to be added, the material and dimensions of the substrate and the cladding are merely examples, and are not limited thereto.

According to the present example, the Er concentration that can be added without clustering was doubled compared to the case without the correction element, and a waveguide gain of 2. O dBZcm was obtained. An amplification band of 1 dBZ cm or more was obtained at 30 nm or more. The concentration distribution of A 1, 添加 added to the core 3 together with Er in the core 3 may be substantially equal to the concentration distribution of Er. In this case, the concentration distribution of A 1 in core 3 is such that, in the vicinity of the center of core 3, a concentration of 10% is added to S i in S i 0 ₂ , and the concentration distribution of P is In the vicinity of the center, it is set to 5% of S i 〇.

In the present embodiment, the inventors have found that the corrected element concentration distribution does not necessarily need to be exactly proportional to the rare earth element concentration distribution, and that the corrected element concentration distribution is 30% or less of the proportional value of the rare earth element concentration distribution. It has been confirmed that the effect does not deteriorate within the error range. In this case, the waveguide gain of the optical waveguide was increased to 2.5 dB / cm, compared to 2.0 dB / cm when a correction element such as A1, P was added uniformly in the core 3. .

Next, another embodiment of the present invention will be described. In this embodiment, the optical waveguide has the configuration shown in FIG. 1A.

In this example, the concentration distribution of the rare earth element in the core 3 was as shown in FIGS. 4A and 4B. First, the concentration distribution in the width direction of the core 3, that is, in the substrate plane direction, was made uniform as shown in FIG. 4A. The concentration distribution in the height direction of the core 3, that is, the direction perpendicular to the plane of the substrate, was high near the center of the core 3 and gradually decreased toward the periphery as shown in FIG. 4B.

The correction elements added together with the rare earth elements were A1 and P, and the concentration distribution was uniform in the X and Y directions as shown in Figs. 2A and 2B. A 1 and P may be added in the same manner as the concentration distribution of the rare earth element. The concentration distribution in the plane direction of the substrate is made uniform as shown in FIG. That is, the concentration distribution in the direction perpendicular to the substrate plane may be high near the center of the core 3 and gradually decrease toward the periphery, as shown in FIG. 5B.

Hereinafter, a specific example of the optical waveguide in the present embodiment will be described. Basically, the same as the embodiment described before mentioned, the substrate 1 is a silicon substrate, the lower cladding 2 has been constructed from the S i 0 ₂ having a thickness of 1 5 m, the upper cladding 4 Is SiO 2 (BPSG) with a thickness of 10 m to which boron and phosphorus are added. The core 3 has a square cross section of 2 m square, and is a silica-based material to which Er is added as a rare earth element. It is composed of fees.

As described above, in this example, the Er concentration added to the silica-based core 3 was uniform in the X direction (width direction). Also, in the Y direction (height direction), the maximum is set near the center of the core 3 (1 × 10 20 atoms Z cm ³ ), and the density gradually decreases toward the periphery of the core 3. At the cladding interface, it was gradually reduced to 1 × 10 19 atoms Z cm ³ .

The correction elements to be added to core 3 are added at a uniform concentration distribution in core 3 using A 1 and P. The concentration of A 1 is 10% added to S i in S i 0 ₂ constituting core 3, and the concentration of P is 5% to S i in S i 0 _2. I made it. In this case, the waveguide gain of the optical waveguide was 1.5 dB / cm.

The concentration distribution of A 1 and P added together with Er to the core 3 in the core 3 may be substantially equal to the concentration distribution of Er. For example, the concentration distribution of Al and P in the core 3 may be uniform in the X direction of the core 3 and gradually decrease toward the periphery in the Y direction. The concentration of A 1 in the core 3 when distribution core 3 in the vicinity of the center and the 1 0% S i in S I_〇 _2, the concentration distribution of P is in the vicinity of heart in the core 3 S I_〇 ₂ 5% for S i in the table. In this case, the waveguide gain of the optical waveguide was 2.2 dB / cm.

In the present embodiment, the inventors have found that the corrected element concentration distribution does not necessarily need to be exactly proportional to the rare earth element concentration distribution, and that the corrected element concentration distribution is 30% or less of the proportional value of the rare earth element concentration distribution. It has been confirmed that the effect does not deteriorate within the error range. <Example 3>

Next, another embodiment of the present invention will be described.

In this example, the concentration distribution of the rare earth element in the core 3 was as shown in FIGS. 6B and 6C. In this embodiment, the concentration distribution in the height direction of the core 3 is increased near the center of the core 3 as shown in FIG. 6C in accordance with the light intensity distribution propagating in the core 3 as shown in FIG. 6A. However, the state gradually decreases toward the periphery. On the other hand, the concentration distribution of the rare earth element in the width direction of the core 3 was made uniform toward the periphery as shown in FIG. 6B. The concentration distributions of the modified elements A1 and P are uniform in the core 3 as shown in Figs. 2A and 2B, and similar to those of the rare earth elements as shown in Figs. 6B and 6C. In the distribution Just fine.

Hereinafter, a specific example of the optical waveguide in the present embodiment will be described. This embodiment also has the same configuration as that of the above-described embodiment. Substrate 1 is a silicon substrate, lower clad ₂ is made of Si 2 having a thickness of 15 m, and upper The cladding 4 is Si ₂ (BP SG) with a thickness of 10 zm to which boron and phosphorus are added. The core 3 has a square shape with a cross section of 2 m square, and is made of a silicon-based material to which Er is added as a rare earth element.

However, in this example, the Er concentration added to the silica-based core 3 is uniform in the X direction, and is maximum (1 × 1020 atoms Zcm ³ ) near the center of the core 3 in the Y direction. The configuration is such that it decreases in proportion to the intensity distribution of the signal light toward the periphery of the core 3. Regarding the concentration distributions of A l and P, in the case of A 1, a concentration of 10% is added to S i in S i 〇 ₂ near the center of core 3, and the concentration distribution of P is In the vicinity of the center, it is 5% of S i in S i 0 ₂ . When the distribution is uniform in the core 3, the distribution is at this concentration, and when the distribution is similar to the rare earth element distribution, the distribution is similar to the distribution of the excitation light in the Y direction.

The waveguide gain of the optical waveguide was 1.6 dBZcm when the concentration distribution of A 1 and P was uniform in the core, and 2.3 dBZcm was obtained when the concentration distribution was similar to the excitation light intensity. .

In the present embodiment, the rare earth concentration distribution is uniform in the X direction and similar to the excitation light intensity in the Y direction, but may be similar to the excitation light intensity in both directions. Example 4>

Next, another embodiment of the present invention will be described. In the present embodiment, in the core 3, the concentration distribution of the rare earth element in the height direction of the core 3 is high near the center of the core 3 as shown in FIG. The state was reduced to On the other hand, the concentration distribution of the rare earth element in the width direction of the core 3 was made uniform toward the periphery as shown in FIG. 7A. Therefore, the optical waveguide according to the present embodiment has substantially the same effect as the embodiment having the concentration distributions shown in FIGS. 6B and 6C. The concentration distributions of the correction elements A 1 and P may be uniform within the core 3 as shown in FIGS. 2A and 2B, and similar to those of the rare earth elements as shown in FIGS. 7A and 7B. Is also good. Hereinafter, a specific example of the optical waveguide in the present embodiment will be described. This embodiment also has the same configuration as that of the above-described embodiment. Substrate 1 is a silicon substrate, lower clad ₂ is made of Si 2 having a thickness of 15 m, and upper The cladding 4 is made of Si ₂ (BPSG) doped with boron and phosphorus to a thickness of 10 / m. The core 3 is a square having a cross section of 2 zm square and made of a silicic material to which Er is added as a rare earth element.

In this embodiment, the Er concentration added to the silica-based core 3 is made uniform in the X direction, and is maximum (1 × 1020 atoms / cm ³ ) near the center of the core 3 in the Y direction. It was made to decrease in a Gaussian distribution toward the periphery of the core 3, and at the interface between the core 3 and the cladding, it became 1 × 1019 atoms Z cm ³ .

A 1, for the concentration distribution of P, in the case of A 1, in the vicinity of the core 3 around which the addition of a concentration of 10% with respect to S i in S i 0 _2, the concentration distribution of P, the core 3 in the vicinity of the center is 5% relative to S i in S I_〇 _2. If it is uniform in the core 3, it is distributed at this concentration, and if it is similar to the rare earth element distribution, it becomes Gaussian.

The waveguide gain of the optical waveguide is 1.6 dB / cm when the concentration distribution of A 1 and P is uniform in the core, and 2.3 dBZcm when the concentration distribution is similar to the excitation light intensity. Was done.

In this embodiment, the rare earth concentration distribution is uniform in the X direction and Gaussian in the Y direction, but may be Gaussian in both directions.

In addition, regarding the optical waveguide in which the rare earth element in the core 3 has the concentration distribution shown in FIGS.7A and 7B, the present inventors have confirmed that the Er concentration distribution does not necessarily have to be exactly Gaussian distribution. I have. 8A and 8B show examples in which the error range from the Gaussian distribution is in the X and Y directions. As shown in the X direction in Fig. 8A and the Y direction in Fig. 8B, it has been confirmed that the effect of the gain increase does not deteriorate if the error is within ± 30% of the Gaussian distribution. In FIGS. 8A and 8B, the dotted lines indicate distributions that increase by + 30% and decrease by 30%, respectively, with respect to the Gaussian distribution, and may be a rare earth element distribution that changes as indicated by the solid lines. 8A and 8B, the density is changed in both the X and Y directions. However, the density may be made uniform in one of the directions. Hereinafter, a method of manufacturing the optical waveguide in the above-described embodiment, particularly, the waveguide portion will be described. Will be described. First, as shown in FIG. 9A, a lower clad 2 is formed on a substrate 1, and then, as shown in FIG. 9B, a film 3a to be a core 3 is formed on the lower clad 2.

The film 3a is processed by E), and the core 3 is formed on the lower clad 2 as shown in FIG. 9C.

Next, as shown in FIG. 9D, if the upper clad 4 is formed so as to cover the core 3, the optical waveguide is completed. For the formation of each layer, for example, a CVD method, a sputtering method, an evaporation method, a flame deposition method, or the like may be used. According to the above-described manufacturing method, an efficient optical amplifier is realized by adding a rare earth element or a correction element into the core 3 with an appropriate concentration distribution.

Next, a description will be given of a manufacturing method in which the rare earth element and the modifying element in the core 3 are added at a high concentration near the center of the core 3 and are reduced toward the periphery of the core 3 and added. In order to add a rare earth element with such a distribution, for example, as shown in FIG. 10, each element may be added by a focused ion beam. In a focused ion beam, for example, the Er element is ionized into an ion beam, and this ion beam is irradiated inside the core 3 while scanning, thereby implanting the ionized Er into the core 3 with an appropriate energy. . Thus, a concentration distribution of Er in the core 3 can be formed. An Er element or an oxide thereof may be used as an ion beam. When A1 is used as a modifying element, the A1 element or its oxide molecule can be used as an ion beam. The concentration of the additive is controlled by adjusting the concentration of the additive to be ionized. By controlling the convergence position of the ion beam and the addition concentration, the concentration X-direction distribution of the rare earth element or the correction element added to the core 3 is controlled. Further, by controlling the beam energy, it is possible to control the Y-direction distribution of the additive concentration.

As described above, after changing the concentration in the X or Y direction and adding a rare earth element or a correction element in or near the core 3, the core 3 is buried in the upper cladding 4 to obtain light. An optical waveguide serving as an amplifier can be formed. The same method as for the lower cladding 2 and the core 3 can be used for forming the upper cladding 4.

In addition, when the rare earth element and the modifying element are added while being changed in the Y direction as described above. The manufacturing method will be described below. In this case, for example, the core 3 may be manufactured by a sputter method using a sputter device schematically shown in FIG. For example, first, the film 3a shown in FIG. 9B is formed by the sputtering device shown in FIG. The sputtering in the evening apparatus is provided with a target of S I_〇 the _second evening one rodents Bok and E r ₂ 〇 ₃ target and A 1 ₂ 0 _3. Using such a sputtering apparatus, the amount of each additive is changed in the thickness direction of the film 3a by changing the amount of sputter at each get while the film 3a is being formed. it can.

Since film formation by such a sputtering apparatus is performed in units of the surface of the substrate, the concentration of each element is uniform in the X direction (the direction of the film surface). Since different sunsets are used in the Y direction (film thickness direction), it is possible to realize a desired density change such as the density distribution described in each of the above-described embodiments. Here, an oxide target of each element is used, but an element target instead of an oxide may be used. In addition, the film forming method is not limited to the sputtering method, and other methods such as a CVD method, an ion plating method, a vapor deposition method, and a flame deposition method can be used. In any case, the elements Er and A1 can be supplied from different raw materials, and the supply amount can be changed as the film is formed to achieve a desired concentration distribution.

Next, a manufacturing method for forming the distribution of the additional element in the core 3 by thermal diffusion will be described.

First, as shown in FIG. 1 2 A, forming a lower clad 2 on the substrate 1, and then, as shown in FIG. 1 2 B, £ 1 "Ya £]: ₂ 0 _3, A 1 and A 1 _A high-concentration layer 13a containing a high concentration of 成膜₃ is formed Next, the high-concentration layer 13a is formed into a rectangular cross section by using a known photolithography technique and an etching technique such as RIE. The core 3 is formed on the lower clad 2 as shown in FIG. 12C.

Next, as shown in FIG. 12D, an upper clad 4 is formed so as to cover the core 3. The lower cladding 2, the high concentration layer 13a, and the upper cladding 4 can be formed by, for example, a CVD method, a sputtering method, various vapor deposition methods, a flame deposition method, or the like. At this time, the thickness of the upper cladding 4 is adjusted so that the core 3 is substantially at the center of the layer composed of the lower cladding 2 and the upper cladding 4.

Next, as shown in FIG. 12E, a high-temperature annealing treatment is performed to To the surroundings. As a result, the concentration of the rare earth element and the modifying element uniformly added to the core 3 at the time of FIG. 12D is high near the center of the core 3 and gradually increases in the X and Y directions toward the periphery of the core 3. The structure is reduced.

By the way, in the above, the core 3 was formed by processing the high concentration layer 13a, but the present invention is not limited to this. For example, the core may be formed as follows. First, as shown in FIG. 12F, a lower cladding 2 a is formed on a substrate 1. The lower cladding 2a is formed, for example, to have a total thickness of the lower cladding 2 and the high concentration layer 13a shown in FIG. 12B. Next, a groove is formed in the lower clad 2a as shown in FIG. 12G by using a known photolithography technique and an etching technique such as RIE. Next, as filled grooves formed in the lower clad 2 a, to form a film added with E r and E r ₂ 〇 _3, A 1 and A 1 ₂ 0 ₃ at a high concentration on the lower clad 2 a. In order to fill the groove with this film, for example, reflow by heat or the like may be used. Next, excess portions other than the groove portions are removed by etch-back or polishing, so that the core 3 is formed in the grooves of the lower cladding 2a as shown in FIG. 12H.

Next, as shown in FIG. 121, an upper clad 4 a is formed so as to cover the core 3. The lower cladding 2a, the above-mentioned film, and the upper cladding 4a can be formed by, for example, a CVD method, a sputtering method, various vapor deposition methods, a flame deposition method, or the like. At this time, the thickness of the upper cladding 4a is adjusted such that the core 3 is substantially at the center of the layer composed of the lower cladding 2a and the upper cladding 4a.

Finally, as shown in FIG. 12J, a high-temperature annealing treatment is performed to diffuse the additives in the core 3 to the periphery. As a result, the concentration of the rare earth element and the correction element uniformly added to the core 3 at the time of Fig. 12I is high near the center of the core 3 and gradually increases in the X and Y directions toward the periphery of the core 3. The structure is reduced.

In the above description, after forming the upper cladding 4 (upper cladding 4 a), a high-temperature heat treatment for diffusion of Er and A 1 was performed, but after forming a low-concentration layer surrounding the core 3. Alternatively, the upper clad may be formed after heat treatment at a high temperature to diffuse Er and A1.

According to the above-described manufacturing method, for example, a high-concentration layer 13 a made of 3 × 10 ₂₀ atoms Z cm ³ , Si 1 added with 1 O wt% of 81 and 12 wt% of P, and To form This was processed to form a core 3 with a cross-sectional dimension of 0.8 x 0.8 m, and after forming the upper cladding 4, an annealing process of 100 in oxygen atmosphere was performed for 3 hours. An optical waveguide having the core having the concentration distribution shown in FIGS. 1B and 1C can be obtained. According to the above-described embodiment, the rare earth element in the core is provided with a concentration distribution such that the concentration decreases toward the periphery, so that the optical signal is mainly amplified at the center of the core. Become. As a result, according to the present invention, an excellent effect that higher gain can be obtained in the waveguide type optical amplifier can be obtained.

As described above, the optical waveguide using the planar waveguide according to the present invention is suitable for use in long-distance wavelength multiplex communication.

Claims

The scope of the claims

1. An optical waveguide comprising: a substrate; a clad formed on the substrate; and a core disposed in the clad,

In the core,

A rare earth element having a predetermined concentration distribution;

A correcting element having at least one of a function of suppressing clustering of the rare earth elements and a function of exciting the rare earth elements with excitation light to broaden an amplification band of signal light, is added. Optical waveguide.

2. The rare earth element is

2. The optical waveguide according to claim 1, wherein the optical waveguide has a concentration distribution in which the concentration gradually decreases from a central portion to a peripheral portion.

3. The rare earth element is

Wherein the substrate has a concentration distribution in which the concentration is uniform from the center to the periphery in the plane direction of the substrate, and the concentration gradually decreases from the center to the periphery in the direction perpendicular to the substrate plane. Item 2. An optical waveguide according to item 1.

4. The optical waveguide according to claim 1, wherein the modifying element is uniformly added in the core.

5. The optical waveguide according to claim 1, wherein the modifying element is added to the core in a distribution similar to the concentration distribution of the rare earth element in the core.

6. The concentration distribution of the rare earth element is

A distribution similar to the intensity distribution of light propagating through the core,

The distribution of the deviation from the Gaussian distribution which is maximum at the center of the core and becomes smaller toward the periphery and becomes smaller toward the periphery of the core within 30% of soil.

Range of any distribution of

The optical waveguide according to claim 1, wherein:

7. The correction elements are Al, B, Ga, In, Ge, Sn, Bi, N, P, Y. 2. The optical waveguide according to claim 1, wherein the optical waveguide is at least one of b.

8. The rare earth element is

2. The optical waveguide according to claim 1, wherein the optical waveguide is at least one of Er, Tm, Pr, and Nd.

9. The optical waveguide according to claim 1, wherein a main component of the core includes at least one of silicon oxide, aluminum oxide, and bismuth oxide.

10. Forming a lower cladding on the substrate;

Forming a core containing a rare earth element and a modifying element at a high concentration in a central portion on the lower clad;

Forming an upper cladding on the lower cladding and the core;

With

The modifying element has at least one of a function of suppressing class disintegration of the rare earth element added to the core and a function of exciting the rare earth element added to the core with excitation light to broaden an amplification band of signal light. A method for producing an optical waveguide, comprising: an element having:

1 1. The step of forming the core comprises:

Forming a film serving as a core on the lower clad,

A rare earth element and a correction element are implanted into the film while scanning the focused ion beam, and the rare earth element and the correction element have a concentration distribution in which the concentration gradually decreases from the center to the periphery of the core. And the process

10. The method for manufacturing an optical waveguide according to claim 10, comprising:

1 2. The step of forming the core includes:

On the lower clad, the concentration of the rare earth element is determined by a film forming method using a first target containing a main component of the core, a second target containing a rare earth element, and a third target containing a correction element. Concentration gradually decreases from the center to the upper and lower peripheral portions of the film, and the concentration of the correction element becomes one of a constant state inside the film and a state of gradually decreasing from the center to the upper and lower peripheral portions. 10. The method of manufacturing an optical waveguide according to claim 10, further comprising a step of forming the optical waveguide.

1 3. The step of forming the core includes: 13. The method of manufacturing an optical waveguide according to claim 12, further comprising a step of forming the second evening get and the third evening get by a sputtering method for changing a sputter state.

1 4. The step of forming the core includes:

13. The method of manufacturing an optical waveguide according to claim 12, further comprising a step of forming the second target and the third target by an ion plating method that changes an evaporation state of the third target.

1 5. The step of forming the core includes:

13. The method of manufacturing an optical waveguide according to claim 12, further comprising a step of forming the second evening get by an evaporation method that changes an amount of evaporation.

16. The method according to claim 12, wherein the second target and the third target are composed of the same target containing a rare earth element and the modifying element at the same time. Manufacturing method of optical waveguide.

1 7. The step of forming the core includes:

Chemical vapor deposition in which a first source gas containing a main component of a core, a second source gas containing a rare earth element, and a third source gas containing a correction element are introduced onto the lower clad. By the method, the concentration of the rare earth element gradually decreases from the central part of the film to the upper and lower peripheral parts, and the concentration of the correction element gradually decreases in a constant state inside the film and the upper and lower peripheral parts from the central part. 10. The method for manufacturing an optical waveguide according to claim 10, further comprising a step of forming the optical waveguide so as to have a concentration distribution in any of the following states.

18. By heating the core to diffuse the rare earth element and the modifying element, the core has a concentration distribution in which the concentration of the rare earth element and the modifying element gradually decreases from the central portion to the peripheral portion of the core. State

The method for manufacturing an optical waveguide according to claim 10, further comprising: