WO2004023612A1 - Waveguide type light amplifier and method for manufacure thereof - Google Patents

Abstract

A waveguide type light amplifier which has a core (3) having a laminate structure comprising a rare earth element containing layer (301) having a film thickness of, for example, a one atom layer and a rare earth element free layer (302) having a film thickness of, for example, a four atom layer. The rare earth element containing layer (301) is, for example, a layer comprising a silica-based material and, added thereto, Er as a rare earth element, and having a film thickness of 0.3 nm, wherein the concentration of Er added is approximately 5 % relative to the amount of silicon constituting the rare earth element containing layer (301). The rare earth element free layer (302) is, for example, a layer comprising a silica-based material and having a film thickness of 1.5 nm. The waveguide type light amplifier allows the achievement of an enhanced gain.

Description

 Description: Waveguide optical amplifier and method of manufacturing the same Background of the invention

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

 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 having 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 optical amplifiers, pumping light is introduced into the optical amplifier from outside to excite rare-earth electrons, the electrons excited by signal light are relaxed, and the intensity of the original signal light is increased by induced emission, thereby increasing the optical intensity. The signal is being amplified.

 Therefore, 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. That is, in order to increase the gain efficiently, it is necessary to provide more excitation levels in the waveguide, and therefore, more rare earth elements such as erbium as sources for generating the excitation levels are provided in the waveguide. Introducing into the market makes it possible to achieve both miniaturization and high gain. .

However, rare earth elements have the property of clustering when added in a high concentration 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 clustering. 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 the 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 is introduced into the waveguide glass in order to suppress the clustering of the added rare earth and to broaden the band of the optical amplifier (Reference 1: JP-A-9-11010). No. 5,965,5). 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 sci. 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 added uniformly into the core.

 In addition, by forming a layer to which a rare earth element is added in the central portion of the core and forming a plurality of layers to which the rare earth element is added in the core, it is possible to obtain a wider band and a higher amplification effect. The following technology has also been proposed (Reference 2: Published Japanese Patent Application Laid-Open No. Hei 4-359230). In the technique disclosed in Reference 2, an auxiliary dopant for suppressing cluster unification and broadening the band is also added to the rare earth element-added layer, and neither the rare earth element nor the auxiliary element is introduced into the upper and lower adjacent layers. . Literature 2 indicates that the thickness of the rare earth element-added layer is about 0.5 zm to about 1.5 m.

 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

An object of the present invention is to obtain a higher gain in a waveguide-type optical amplifier. The waveguide type optical amplifier according to the present invention includes a clad formed on a substrate and a core disposed in the clad, and the core is formed of a material having a different refractive index from the clad. The first layer and the second layer made of a material having a refractive index different from that of the clad and to which a rare earth element is added are alternately stacked, and the second layer is composed of several tens of atoms. The layer is formed to have a thickness of, for example, 50 atomic layers or less. Here, one atomic layer has a thickness of one rare earth element.

 According to this waveguide type optical amplifier, the rare earth element is discretely present in the thickness direction of the core, and in the second layer formed thin at the atomic layer level, clustering in the thickness direction of this layer is performed. Is suppressed.

 In the above-mentioned waveguide type optical amplifier, the thickness of the second layer is thinner, for example, up to 15 atomic layers, more desirably 1 atomic layer, and the higher the number of atomic layers, the higher the clustering. Can be expected. The thickness of all the second layers to which the rare earth element is added may be set to several tens of atomic layers or less than the wave number atomic layer, but the thickness may be set to be at least one of the second layers as described above. .

 In the above waveguide type optical amplifier, the average concentration distribution of the rare earth elements in the core is higher at the center of the core at least in the height direction of the core, that is, in the stacking direction of the first and second layers. May correspond to the intensity distribution of light guided through the core. The above-mentioned average concentration distribution of the rare earth element refers to an average concentration within a predetermined range centered on an arbitrary point of the core. For example, in the thickness direction of the core, a plurality of layers including the arbitrary point (first layer) , Including the second layer).

 In order to obtain such a distribution, for example, the first layer may be formed so as to be thicker away from the center of the core, and the second layer may be formed so as to be farther away from the center of the core. The concentration of the rare earth element added to the second layer may be low, and the second layer may be formed thin enough to be separated from the center of the core. .

In the above-mentioned waveguide type optical amplifier, a function of suppressing the class dissociation of the rare earth element added to the core, or an amplification band for amplifying the signal light by exciting the rare earth element added to the core with the excitation light. With one or both of the functions to expand The modifying element made of element may be added to the core, or the modifying element may be added only to the second layer. The modifying element is at least one of Al, B, Ga, In, Ge, Sn, Bi, N, P, and Yb. In the above-mentioned waveguide type optical amplifier, a diffusion prevention layer formed of an element arranged in the first layer and preventing diffusion of a rare earth element added to the second layer may be provided. Alternatively, the diffusion prevention layer may be provided in contact with the second layer. The diffusion preventing layer may be made of at least one of aluminum oxide, silicon nitride, and silicon oxynitride.

 In the above waveguide type optical amplifier, the rare earth element is at least one of Er, Tm, Pr, and Nd, and the main components of the core are silicon oxide, aluminum oxide, and oxide. The second layer contains at least one of bismuth, and a main component of the second layer is any one of a phosphate glass, a rare-earth oxide, and a rare-earth element.

 A method of manufacturing a waveguide-type optical amplifier according to the present invention includes a step of forming a lower clad on a substrate, a first target including a main component of a core, and a second target including a rare earth element on the lower clad. And a third target containing a modifying element, and the core is formed by one of sputtering, ion plating, and vapor deposition that changes the sputter state of the second target and the third target. A step of forming a core to which a correction element is added, comprising a laminated structure in which a first layer comprising a main component and a second layer to which a rare earth element is added are alternately stacked; Forming an upper clad, and forming the second layer to a thickness of several tens of atomic layers, for example, 50 atomic layers or less.

 In the method of manufacturing a waveguide optical amplifier, the second target and the third evening target may be targets each containing a rare earth element and a modifying element at the same time.

Also, a method of manufacturing a waveguide type optical amplifier according to another aspect of the present invention includes a step of forming a lower clad on a substrate, a first source gas containing a main component of a core on the lower clad, By a chemical vapor deposition method in which a second source gas containing a rare earth element and a third source gas containing a modifying element are introduced, a first layer composed of the main components of the core and the rare earth element are added. Alternately with a second layer of tens of atomic layers or less The method includes a step of forming a core made of a laminated structure and having a modifying element added thereto, and a step of forming an upper clad on the lower clad and the core. BRIEF DESCRIPTION OF THE FIGURES

 1A and 1B are schematic cross-sectional views schematically showing a configuration example of a waveguide type optical amplifier according to a first embodiment of the present invention.

 FIGS. 2A and 2B are schematic cross-sectional views schematically showing configuration examples of a waveguide optical amplifier according to another embodiment of the present invention.

 FIG. 3A 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.

 FIG. 3B is a distribution diagram showing a rare earth element concentration distribution in a core of an optical waveguide according to another embodiment of the present invention.

 FIG. 4 is a distribution diagram showing a concentration distribution of a rare earth element in a core of an optical waveguide according to another embodiment of the present invention.

 FIG. 5 is a distribution diagram showing a concentration distribution of a rare earth element in a core of an optical waveguide according to another embodiment of the present invention.

 FIG. 6 is a schematic sectional view schematically showing a configuration example of a waveguide type optical amplifier according to another embodiment of the present invention.

 FIG. 7 is a schematic sectional view schematically showing a configuration example of a waveguide type optical amplifier according to another embodiment of the present invention.

 FIG. 8A, FIG. 8B, FIG. 8C, and FIG. 8D are process diagrams for explaining a method of manufacturing an optical waveguide according to an embodiment of the present invention.

 FIG. 9 is a configuration diagram schematically showing a manufacturing apparatus for realizing the optical waveguide manufacturing method according to the embodiment of the present invention.

 FIG. 10 is a configuration diagram schematically showing a manufacturing apparatus for realizing the method for manufacturing an optical waveguide according to the embodiment of the present invention. Detailed description of the embodiment

Hereinafter, embodiments of the present invention will be described with reference to the drawings. <Example 1>

 FIG. 1A is a schematic cross-sectional view schematically showing a configuration example of a waveguide optical amplifier according to a first embodiment of the present invention. This waveguide type optical amplifier is composed of a lower cladding 2 formed on a substrate 1, a core 3 having a width and height of about 2 m, and an upper cladding 4 formed so as to cover the core 3. The region including the core 3 is doped with a rare earth element for amplifying the signal light propagating in the core 3. 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.

Further, in the present embodiment, as shown in the partially enlarged view of FIG. 1B, the core 3 is made of a rare-earth-containing layer (second layer) 301 having a thickness of, for example, 1 atomic layer containing Er and a rare-earth element. For example, a laminated structure including a rare-earth-free layer (first layer) 302 having a thickness of 4 atomic layers that does not contain elements is used. The rare earth-containing layer 301 has a thickness of 0.3 nm when, for example, Er is added as a rare earth to a silica-based material. The concentration of the added Er is about 5% with respect to the silicon constituting the rare earth-containing layer 301. When the rare-earth-free layer 302 is made of, for example, a silica-based material, the layer 302 has a thickness of 1.5 nm. The average concentration of Er in the entire core 3 is about 1 × 10 ^{2 ()} atoms Zcm ³ .

 According to the waveguide type optical amplifiers of FIGS. 1A and 1B in the present embodiment, the waveguide gain was 1.2 dBZcm. The waveguide gain was 1 dB / cm when Er was added uniformly in the conventional core, and the waveguide gain was improved by the waveguide-type optical amplifiers in Figs. 1A and 1B. Is obtained.

 The substrate 1 is made of, for example, silicon single crystal, the lower cladding 2 is made of a silicon oxide film having a thickness of about 15 m, and the upper cladding 4 is made of, for example, boron and phosphorus having a thickness of about 10 m. It is composed of silicon oxide (BPSG (boron phosp horous silicate glass)) to which is added.

 In the present embodiment, by forming the core 3 by a laminate of the extremely thin rare earth-containing layer 301 and the rare earth non-containing layer 302, the classifying of the rare earth element (Er) added to the core 3 can be performed. Suppressed and efficient light amplification was performed.

Reduce the thickness of the rare earth-containing layer 301 to about 1 atom, and By sandwiching the rare earth non-containing layer 302 in which no rare earth element is added, a distance is provided between the rare earth atoms in the thickness direction of the core 3 to reduce clustering. When the thickness of the rare earth-free layer 302 is about 4 atomic layers, the rare earth added to the rare-earth-containing layer 301 diffuses and leaks into the rare earth-free layer 302. However, it is also possible to suppress clustering of these in the rare-earth-free layer 302. Also, in the manufacturing process, a small amount of rare earth may be mixed in the rare earth-free layer 302, but even if a small amount of rare earth is present in the rare earth-free layer 302, the concentration is very low. Since it is small, there is almost no cluster unification and there is no problem.

 By the way, the rare earth added to the rare earth-containing layer 301 is not limited to Er, but has an action of amplifying the signal light due to the excitation radiation, such as thulium (Tm), praseodymium (Pr), neodymium (Nd). It may be an element. A combination of a plurality of these may be added to the rare earth-containing layer.

 In the present embodiment, the film thicknesses of the rare earth-containing layer 301 and the rare-earth non-containing layer 302 are described as 1 atomic layer and 4 atomic layers, respectively, but are not limited thereto. The rare earth-containing layer 301 may have about 2 atomic layers, and the rare earth non-containing layer 302 may have about 8 atomic layers.

 In addition, if the rare earth-containing layer 301 is formed to be thinner, for example, 1 to 15 atomic layers, more preferably 1 atomic layer, and a few atomic layers or less, higher suppression of clustering can be achieved. The effect can be expected. The thickness of all the second layers to which the rare earth element is added may be set to several tens of atomic layers or less than the wave number atomic layer. However, the thickness may be set to be as described above for at least one of the two layers.

 Further, the concentration of the rare earth element in the plane direction of the rare earth containing layer 301 does not need to be uniform, and may be changed. Further, the dimensions described above are merely examples, and the present invention is not limited to these dimensions.

 The effect of suppressing clustering increases as the number of atoms in the thickness direction of the rare earth-containing layer 301 decreases. Therefore, theoretically, when the thickness of the rare earth-containing layer 301 is one atomic layer, the effect of suppressing cluster unification is the highest.

By the way, even if the rare earth-containing layer 301 is formed under the condition that the film thickness becomes one atomic layer, the current manufacturing technology may have a thickness of about five atomic layers. Thus, the rare earth-containing layer The layer 301 is formed substantially in the order of several atomic layers. '

 However, forming the rare earth-containing layer 301 into several atomic layers is not suitable for mass production with the current manufacturing technology. Increasing the thickness of the rare earth-containing layer 301 reduces the effect of suppressing clustering.However, in the current manufacturing technology, the rare earth-containing layer 301 has a thickness of several tens of atomic layers, for example, about 50 atomic layers. With this, it is possible to mass-produce the above-mentioned laminated structure without difficulty, and it is also possible to obtain an improvement in gain due to the effect of suppressing clustering. Here, one atomic layer has a thickness equivalent to one rare earth element. For example, when the rare earth-containing layer was a 50 atomic layer, the waveguide gain was 1.01 dB / cm.

 As described above, according to this waveguide type optical amplifier, the rare-earth element is discretely present in the thickness direction of the core, and in the second layer formed thin at the atomic layer level, the film of this layer is formed. Cluster unification in the thickness direction is suppressed.

Example 2>

 Next, another embodiment of the present invention will be described. In the waveguide-type optical amplifier shown in FIGS. 1A and 1B, the thickness of each of the plurality of rare earth-containing layers 301 and the plurality of non-rare earth-containing layers 302 is uniform in the core 3. However, the present invention is not limited to this, and each may be different. Hereinafter, an example in which the thickness of each of the plurality of rare earth-containing layers 301 and the plurality of non-rare earth-containing layers 302 changes in the core 3 will be described.

 FIG. 2A is a schematic cross-sectional view schematically illustrating a configuration example of a waveguide optical amplifier according to another embodiment of the present invention, and FIG. 2B is a cross-sectional view illustrating a core 3 in an enlarged manner. . This waveguide type optical amplifier comprises a lower cladding 2 formed on a substrate 1, a core 3 having a width and height of about 2 m, and an upper cladding 4 formed so as to cover the core 3. The region including the core 3 is doped with a rare earth element for amplifying the signal light propagating in the core 3. 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.

Further, in the present embodiment, as shown in the partial enlarged view of FIG. 2B, the core 3 is made of a rare earth-containing layer 301 having a thickness of, for example, 1 atomic layer containing Er, and containing no rare earth element. The laminated structure with the rare-earth-free layer 302 was formed, and the thickness of the rare-earth-free layer 302 was increased toward both ends in the vertical direction of the core 3. Thus, the thickness of the rare earth-free layer 302, That is, by making the interval between the rare earth-containing layers 301 different, the average concentration distribution of the rare earth element in the height direction of the core 3 is changed, and for example, the concentration distribution of light propagating in the core 3 is changed. It becomes possible to correspond.

The rare earth-containing layer 301 is, for example, a 0.3-nm-thick layer obtained by adding Er as a rare earth to a silica-based material. The concentration of the added Er is about 5% with respect to the silicon constituting the rare earth-containing layer 301. The rare-earth-free layer 302 is made of, for example, a silica-based material. The average concentration of Er in the entire core 3 is about 1 × 10 ^{2 ()} atoms Z cm ³ . is there.

 In the waveguide type optical amplifiers shown in FIGS. 2A and 2B, the film thickness of the rare-earth-free layer 302 is, for example, 1 nm at the center of the core 3, and is increased toward the upper and lower periphery. The upper and lower ends were set to 5 nm. As described above, since the distance is provided between the rare earth atoms in the thickness direction of the core 3, even in the waveguide type optical amplifiers of FIGS. 2A and 2B, the rare earth element added to the core 3 is removed. Cluster unification can be suppressed. According to the waveguide type optical amplifier according to the present example, the waveguide gain was 1.5 dB / cm. Conventionally, when Er was uniformly added to the entire core, the waveguide gain was 1 dB / cm.Therefore, the waveguide-type optical amplifier shown in FIGS. 2A and 2B improved the waveguide gain. Is obtained.

<Example 3>

 Next, another embodiment of the present invention will be described. As shown in Fig. 3A, the intensity distribution in the cross-sectional direction of the light guided through the core of the waveguide-type optical amplifier is strong at the center of the core and weaker toward the periphery of the core. When the light intensity is low, light may be absorbed without the amplification of light by the high concentration of rare earth elements. Therefore, if a rare earth element is added to the core in accordance with the distribution of the light intensity, the waveguide gain can be further improved. If the light guided in the core has the above-mentioned light intensity distribution in a plane perpendicular to the waveguide direction, the height direction (y direction) of core 3 (Fig. 2A, Fig. 2B) As shown in Fig. 3B, the distribution of the rare earth elements should be increased at the center and decreased toward the periphery.

In this embodiment, in the waveguide type optical amplifier having the structure shown in FIGS. 2A and 2B described above, the thickness of the rare-earth-free layer 302 is set to, for example, 1 at the center of the core 3. The thickness was made thicker toward the upper and lower periphery, and 5 nm at the upper and lower ends of the core 3. The thickness of the rare earth-containing layer 301 is about 1 to 10 atomic layers. In this way, as shown in FIG. 3B, an average concentration distribution of rare earth elements in the core 3 can be formed.

 In forming the average concentration distribution of the rare earth elements in the core 3 as shown in FIG. 3B, the rare earth-containing layer 301 located farther from the center of the core 3 has a rare earth content (concentration). It may be made lower, and the rare earth-containing layer 301 farther from the center of the core 3 may be formed thinner.

As shown in FIGS. 2A and 2B, the thickness of the rare-earth-free layer 302 is 1 nm at the center of the core 3, and is increased toward the upper and lower sides, and 5 nm at the upper and lower ends of the core 3. By setting the average concentration of Er per volume near the center of the core 3 to 2 × 10 2 ^Q atom Zcm ³ , the waveguide gain was able to be 1.7 dBZcm. Conventionally, when Er was uniformly added into the core, the waveguide gain was 1 dBZcm, so the waveguide type optical amplifier of the present embodiment can greatly improve the waveguide gain. .

<Example 4>

Next, another embodiment of the present invention will be described. As described above, when increasing the concentration of the rare earth element in the rare earth-containing layer toward the center of the core, the concentration of the rare earth element per unit volume in the core may have a Gaussian distribution as shown in FIG. . For example, in the waveguide type optical amplifier whose structure is shown in FIG. 2A, the concentration per unit volume of Er near the center of the core 3 (average concentration) is 2 × 10 2 ^10atom / cm ³ , That is, at the boundary between the core 3 and the clad, the concentration of Er per unit volume (average concentration) may be set to 2 × 10 ¹⁹ atoms Zcm ³ .

 As described above, by setting the average concentration distribution of the rare earth elements in the core 3 to a Gaussian distribution or a state similar thereto, the waveguide gain could be set to 1.7 dBZcm. Conventionally, when Er was uniformly added into the core, the waveguide gain was Id B Zcm.Therefore, according to the waveguide type optical amplifier of the present embodiment, the waveguide gain could be greatly improved. it can.

The average concentration distribution of rare earth elements in Core 3 is exactly Gaussian. As shown in Fig. 5, it has been confirmed that the effect of increasing the gain does not deteriorate if the error is within ± 30% of the Gaussian distribution. Therefore, in FIG. 5, the dotted lines indicate distributions that increase by + 30% and decrease by 30%, respectively, with respect to the Gaussian distribution.

 <Example 5>

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

 In this embodiment, the core contains an element that suppresses clustering of the rare earth element or a correction element that expands the amplification band when the added rare earth element is excited by the excitation light to amplify the signal light. This is an example of addition.

 The materials of the substrate, the lower cladding, the upper cladding, the film thickness, and the dimensions of the core are the same as those of the waveguide optical amplifier shown in FIGS. 1A and 2A described above. In the core, a rare-earth-containing layer 301 having a thickness of 0.3 nm and an in-plane Er concentration of 5% with respect to Si is spaced apart as shown in FIG.1B. Things.

 In addition, in this example, aluminum (A1) and phosphorus (P) were added to the core 3 (FIG. 1B) as modifying elements. Concentration of Er converted to unit volume in the rare earth-containing layer 301 and the rare-earth-free layer 302 constituting the core 3

(Average concentration) is maximized near the center of the core ( ^2.5 x 10 ^{2 ()} atoms / cm ³ ), gradually decreases toward the periphery of the core, and decreases at the core-cladding interface. It was gradually reduced to 2.5 × 10 ¹⁹ atoms / cm ³ . As described above, the concentration of Er added is higher than that in the above-described embodiment, but in this embodiment, since the modifying element is added, cluster unification can be suppressed.

 The concentration of A1, which is a modifying element, is 10% of the concentration of Si in S i〇2 constituting the core, and the concentration of phosphorus is A 5% concentration was added. A1 added to Si〇2 constituting the core has the effect of suppressing cluster unification when a rare earth element is added at a high concentration and expanding the amplification wavelength band. As elements having such an action, in addition to A1, boron (B), gallium

(Ga), indium (In), germanium (Ge), tin (Sn), bismuth

(B i), Nitrogen (N), Phosphorus (P), Itbium (Yb) and their oxides Etc.

 Although these elements have different degrees of effect on both functions, any element has both the function of suppressing cluster unification and the function of expanding the amplification band. One or more of these elements for suppressing clustering and for improving the amplification band may be added, and other elements having the same function may be added. The above Er concentration, the modifying element to be added, the substrate, the clad material, the size, and the like are merely examples, and are not limited thereto.

 According to the present embodiment, the class unification can be further suppressed as compared with the above-described embodiment, so that the concentration of Er that can be added can be increased. As a result, according to this example, the waveguide gain was increased to 2.0 dB / cm. In addition, the amplification band of 1 dBZ cm or more was expanded by 30 nm or more.

<Example 6>

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

 The above-mentioned modifying element may be added only to the rare earth-containing layer 301 constituting the core 3. When the modifying element is added only to the rare earth-containing layer 301, the waveguide gain is 2.2 dB / cm. Therefore, according to the present embodiment, the waveguide gain is increased with respect to 2. O dB / cm when a correction element such as A 1 P is uniformly added in the core.

<Example 7>

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

 FIG. 6 is a cross-sectional view schematically showing a part of the configuration of the waveguide optical amplifier according to the present embodiment, that is, a core portion. Other configurations are the same as those of the waveguide type optical amplifier shown in FIGS. 1A and 2A.

 In the core having the configuration shown in FIG. 6, a diffusion prevention layer 303 made of aluminum oxide is newly provided.

The diffusion preventing layer 303 is provided in the rare-earth-free layer 302. By providing the diffusion preventing layer 303 in this way, diffusion of the rare earth element in the rare earth containing layer 301 can be suppressed as compared with the above-described embodiment. According to the configuration of the present embodiment in which the diffusion preventing layer 303 made of aluminum oxide having a thickness of 2 nm is provided, the waveguide gain is 2.4 dB / cm increased.

 Further, as shown in FIG. 7, the diffusion preventing layer 303 may be provided in contact with the rare earth-containing layer 301. By doing so, the diffusion of rare earth from the rare earth-containing layer 301 can be further suppressed. As a result, the waveguide gain increased to 2.5 dB Zcm. Note that the rare earth-free layer may serve as a diffusion preventing layer. Hereinafter, a method of manufacturing the waveguide-type optical amplifier in the above-described embodiment, particularly, a waveguide portion will be described. First, as shown in FIG. 8A, a lower clad 2 is formed on the substrate 1, and then, as shown in FIG. 8B, a film 3 a to be the core 3 is formed on the lower clad 2 by RIE (reactive ion etching). )) To process the film 3 a, so that the core 3 is formed on the lower clad 2 as shown in FIG. 8C.

 Next, as shown in FIG. 8D, 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 chemical vapor deposition (CVD) method, a sputtering method, a vapor deposition method, a flame deposition method, or the like may be used.

 Next, a method for manufacturing a laminated structure of a layer to which the rare earth is added and a layer to which the rare earth is not added, which will be the core 3, will be described. This may be achieved, for example, by manufacturing a film having a multilayer structure by a sputtering method using a sputtering apparatus 400 schematically shown in FIG.

 For example, first, the film 3a shown in FIG. 8B is formed by the sputtering device 400 shown in FIG. The sputter device includes a target 410 for Si〇2, a target 420 for Er2〇3, and a target 430 for Al2O3. By using such a sputtering apparatus and changing the amount of sputtering in each target during the formation of the film 3a, it becomes possible to add Er or A1 only to a specific layer. Since film formation by sputtering is performed on a plane basis, the elements to be added are uniformly distributed in the X direction (film plane direction).

For example, substrate 1 is heated to 300 ° C, the power supply power is 2 kW, the gas pressure in the chamber of the sputtering device is 3 mTorr, the Er concentration is 5%, and the deposition rate is 0.2 nmZs. The flow rate was adjusted. As a result, the film thickness could be controlled within 1 nm, and a film with a thickness of 5 atomic layers or less could be formed. The deposition rate is It is not limited to this, but controllability can be improved by adjusting the flow rate and lowering the rate.

 According to the above-described sputtering method, a film having a laminated structure in which a rare earth-containing layer having a thickness of about 1 atomic layer and a rare earth non-containing layer having a thickness of about 4 atomic layers are alternately formed is realized. Can be.

 Further, a film having the above-described laminated structure can be formed also by the CVD method. Hereinafter, the case where the film 3a shown in FIG. 8A is formed by the plasma CVD apparatus 500 shown in FIG. 10 will be described.

 In this plasma CVD apparatus 500, silane 5100, trimethylaluminum 5200, 2,2,6,6-tetramethyl-3,5-heptanedionerbium 530, oxygen 540 is used. By using such a plasma CVD apparatus 500 and changing the supply amount of each source gas during the formation of the film 3a (FIG. 8B), Er or A 1 can be added. Since the film is formed on a plane basis by the plasma CVD method, the elements to be added are uniformly distributed in the X direction (film plane direction). The substrate 1 was heated to 42 Ot :, the plasma flow was set to 500 W, and the flow rate was adjusted so that the Er concentration was 5% and the film formation rate was 1 to 2 nmZs. As a result, the film thickness can be controlled within 2 nm, and a film having a thickness of 10 atomic layers or less can be formed. The film formation rate is not limited to this, and the controllability of the film thickness can be improved by adjusting the flow rate and lowering the rate.

 The formation of such a film is not limited to the sputtering method and the CVD method, but can be realized by a film forming method such as a vapor deposition method or a flame deposition method. In either method, the desired concentration distribution can be formed by supplying Er and A1 from different reductions and changing the supply amount as the film is formed.

 According to the above-described embodiment, since the rare earth elements are discretely present in the core, clustering of the rare earth elements can be suppressed, and higher gain can be obtained in the waveguide type optical amplifier. An excellent effect of being able to obtain is obtained.

Also, for example, the average concentration distribution of rare earth elements in the stacking direction of the core is calculated as follows. By setting the density to be higher at the center, higher gain can be obtained. For example, higher gain can be obtained by making the average concentration distribution in the stacking direction of the core correspond to the concentration distribution of light guided through the core. In order to form such a concentration distribution, for example, the first layer may be thicker as the distance from the center of the core is increased, and the concentration of the rare earth element in the second layer may be decreased as the distance from the center of the core decreases. Alternatively, the second layer may be formed thinner away from the center of the core.

 As described above, the waveguide type optical amplifier according to the present invention is suitable for use in long-distance WDM communication.

Claims

The scope of the claims 1. The cladding formed on the substrate,  A core disposed in the cladding;  With  The core is  A first layer made of a material having a different refractive index from the cladding,  A second layer made of a material having a different refractive index from the cladding and doped with a rare earth element; Is a laminated structure alternately laminated,  The waveguide type optical amplifier, wherein the second layer has a thickness of several tens of atomic layers or less. 2. The waveguide type optical amplifier according to claim 1, wherein the second layer has a thickness of several atomic layers or less. 3. The waveguide type optical amplifier according to claim 1, wherein an average concentration distribution of the rare earth element in the core has a predetermined distribution at least in a stacking direction of the first and second layers. 4. The waveguide type optical amplifier according to claim 3, wherein an average concentration distribution of the rare earth element in the core is higher toward a center of the core. 5. The waveguide light according to claim 3, wherein the average concentration distribution of the rare earth element in the core corresponds to an intensity distribution of light guided through the core. 6. The first layer is formed thick enough to separate from the center of the core 4. The waveguide type optical amplifier according to claim 3, wherein: 7. The waveguide-type optical amplifier according to claim 3, wherein the second layer is formed such that the concentration of the rare earth element decreases as the distance from the center of the core increases. 8. The waveguide type optical amplifier according to claim 3, wherein the second layer is formed so as to be thinner than a center portion of the core. 9. At least one of a function of suppressing clustering of rare earth elements added to the core and a function of broadening an amplification band when amplifying signal light by exciting the rare earth elements added to the core with excitation light. 2. The waveguide type optical amplifier according to claim 1, wherein a correction element composed of an element having one of them is added to the core. 10. The waveguide type optical amplifier according to claim 9, wherein the modifying element is added only to the second layer. 11. The method according to claim 9, wherein the modifying element is at least one of Al, B, Ga, In, Ge, Sn, Bi, N, P, and Yb. Waveguide type optical amplifier. 12. A claim, comprising: a diffusion prevention layer disposed in the first layer and made of an element for preventing diffusion of a rare earth element added to the second layer. 2. The waveguide type optical amplifier according to 1. 13. The waveguide type optical amplifier according to claim 12, wherein the diffusion preventing layer is provided in contact with the second layer. 14. The diffusion prevention layer according to claim 12, wherein the diffusion prevention layer is made of at least one of aluminum oxide, silicon nitride, and silicon oxynitride. 2. The waveguide type optical amplifier according to 1. 15. The waveguide optical amplifier according to claim 1, wherein the rare earth element is at least one of Er, Tm, Pr, and Nd. 16. The waveguide light according to claim 1, wherein a main component of the core includes at least one of silicon oxide, aluminum oxide, and bismuth oxide. 17. The waveguide type optical amplifier according to claim 16, wherein a main component of the second layer is any one of a phosphate glass, a rare earth oxide, and a rare earth element. 18. Forming a lower cladding on the substrate;  On the lower cladding, a first target containing a main component of a core, a second target containing a rare-earth element, and a third target containing a modifying element, wherein the second target and the third target are used. By a sputtering method, an ion plating method, or a vapor deposition method that changes the sputtering state of the target, a first layer composed of the main components of the core and several tens of atomic layers or less to which a rare earth element is added. Forming a core comprising a laminated structure in which the second layer and the layer are alternately laminated, and wherein the core to which the modifying element is added is formed;  Forming an upper cladding on the lower cladding and the core;  A method of manufacturing a waveguide-type optical amplifier, comprising: 19. The method for manufacturing a waveguide-type optical amplifier according to claim 18, wherein the second target and the third target include a target containing both a rare earth element and the modification element. 20. The step of forming a core includes, on the lower clad, a first source gas containing a main component of the core, a second source gas containing a rare earth element, and a second source gas containing a correction element. The first layer composed of the main component of the core and the second layer of several tens of atomic layers or less to which the rare earth element is added are alternately formed by the chemical vapor deposition method in which the source gas is introduced. 19. The method for manufacturing an optical waveguide according to claim 18, wherein the method comprises a step of forming a core comprising a laminated structure having the modifying element added thereto.