JP2004095839A - Waveguide optical amplifier and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a higher gain in a waveguide optical amplifier. <P>SOLUTION: A core 3 is constituted of the laminated structure of a rare earth containing layer 301, containing Er and having a thickness of one atomic layer, for example, and a rare earth not containing layer 302, not containing rare earth element and having a thickness of 4 atomic layers, for example. The rare earth containing layer 301 is a layer, prepared by adding the rare earth or Er to a silica base material and having a thickness of 0.3nm. The concentration of the added Er is about 5% with respect to silicon constituting the rare earth containing layer 301. Further, the rare earth not containing layer 302 is a layer consisting of a silica base material and having a thickness of 1.5nm, for example. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD 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 manufacturing the same. It is about the method.
[0002]
[Prior art]
An optical amplifier directly amplifies light without passing through an electric circuit, and further, amplifies light over a wide wavelength range. Therefore, the optical amplifier has become a very important device in recent long-distance WDM communication. At present, optical amplifiers using fibers doped with a rare earth element such as erbium are mainly used, and high quality amplifiers having high amplification gain and low noise characteristics are provided.
[0003]
Under such circumstances, optical amplifiers in which a rare-earth element is added to a planar optical waveguide have been developed with the aim of further miniaturization, and the development of optical amplifiers aiming for higher gain and a wider amplification band has been developed. Is being done. In an optical amplifier, an excitation signal is introduced from the outside into an optical amplifier to excite rare-earth electrons, the electrons excited by the signal light are relaxed, and the intensity of the original signal light is increased by stimulated emission. Is amplified.
[0004]
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 a source for generating an excitation level are provided in the waveguide. , It is possible to achieve both miniaturization and high gain.
[0005]
However, rare earths have the property of clustering when added in a high concentration into the waveguide glass. When the rare earth is clustered, the excitation level changes, the number of rare earth elements contributing to excitation at a desired wavelength is substantially reduced, and the amplification gain is reduced. 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.
[0006]
Important characteristics required of an optical amplifier include a wide gain wavelength band as well as a high gain. In wavelength multiplex communication, for example, optical signals of 40 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 multiplex communication is required to have a function of amplifying a gain in a band of 32 nm or more.
[0007]
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 clustering of the added rare earth and broaden the band of the optical amplifier (Reference 1: Japanese Patent Application Laid-Open No. 9-105965). . In Document 1, at least two elements other than rare earth elements are added to the core of the waveguide. These two elements are elements belonging to the genus IIIB, IVB and IIIA, such as La, Al and Ga. Since these elements are present in the core at the same time as the rare earth element, the effect of suppressing the clustering of the rare earth element and broadening the excitation level to broaden the amplification wavelength band can be obtained. These elements are uniformly added in the core.
[0008]
In addition, by forming a layer to which a rare earth element is added at the center 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. There is also proposed a technique for performing the above (Reference 2: Japanese Patent No. 2842954). In the technique disclosed in Reference 2, an assisting dopant for suppressing clustering and broadening the band is also added to the rare earth element-added layer, and neither the rare earth element nor the assisting element is introduced into the upper and lower adjacent layers. Document 2 shows that the thickness of the rare earth element-added layer is about 0.5 μm to about 1.5 μm.
[0009]
[Problems to be solved by the invention]
By the way, while it is required to realize more functions with a smaller device, the above-described optical amplifier is also required to be smaller. In the waveguide-type optical amplifier as described above, the gain per unit length in the waveguide direction is increased to shorten and reduce the size of the optical amplifier. As described above, in order to meet the recent demand for miniaturization, it is necessary to further increase the gain of the optical amplifier.
[0010]
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.
[0011]
[Means for Solving the Problems]
A 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 refractive index different from that of the clad. A laminated structure in which layers and second layers 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 laminated, and the second layer is composed of several tens of atomic layers, for example, 50 atomic layers. It was formed to the following thickness. 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 occurs. Be suppressed.
[0012]
In the above waveguide type optical amplifier, the thickness of the second layer is thinner, for example, 1 to 15 atomic layers, more desirably 1 atomic layer, and if the second layer is formed to be several atomic layers or less, higher clustering can be achieved. A suppression effect can be expected. Although 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, the thickness may be set to be as described above for at least one second layer. .
[0013]
Further, in the above waveguide type optical amplifier, the average concentration distribution of the rare earth element 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-described 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) , And the second layer).
[0014]
In order to obtain such a distribution, for example, the first layer may be formed so thick that it is separated from the center of the core, and the second layer is 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 formed to be low, and the second layer may be formed thin enough to be separated from the center of the core.
[0015]
In the above-mentioned waveguide type optical amplifier, the function of suppressing the clustering of the rare earth element added to the core, or expanding the amplification band when amplifying the signal light by exciting the rare earth element added to the core with excitation light. A modifying element made of an element having one or both of the functions 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.
[0016]
In the above-mentioned waveguide type optical amplifier, a diffusion prevention layer made of an element which is disposed in the first layer and prevents diffusion of the 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 formed 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 component of the core is at least one of silicon oxide, aluminum oxide, and bismuth oxide. The main component of the second layer is any one of phosphate glass, rare earth oxides, and rare earth elements.
[0017]
The 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 containing a main component of a core, and a second target containing a rare earth element on the lower clad. And a third target containing a modifying element, and the main component of the core is formed by any one of a sputtering method, an ion plating method, and a vapor deposition method that changes the sputtering state of the second target and the third target. A step of forming a core to which a first element and a second layer to which a rare earth element is added are alternately stacked, and forming a core to which a correction element is added; and forming a lower clad and an upper clad on the core. And forming the second layer to a thickness of several tens of atomic layers, for example, 50 atomic layers or less.
In the above-described method for manufacturing a waveguide optical amplifier, the second target and the third target may be targets each containing a rare earth element and a modifying element at the same time.
[0018]
According to another aspect of the present invention, there is provided a method of manufacturing a waveguide type optical amplifier, comprising: forming a lower cladding on a substrate; forming a first source gas containing a main component of a core on the lower cladding; The first layer composed of the main components of the core and the number of rare earth elements added by a chemical vapor deposition method in which a second source gas containing an element and a third source gas containing a modifying element are introduced. It comprises a laminated structure in which ten or less atomic layers or less are alternately laminated, and includes a step of forming a core to which a modifying element is added, and a step of forming an upper clad on the lower clad and the core. It is a thing.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
<Embodiment 1>
FIG. 1A is a schematic cross-sectional view schematically showing a configuration example of the waveguide type optical amplifier according to the first embodiment of the present invention. This waveguide type optical amplifier comprises a lower cladding 2 formed on a substrate 1, a core 3 having a width and a height of about 2 μm, and an upper cladding 4 formed so as to cover the core 3. A rare earth element for amplifying the signal light propagating in the core 3 is added to the region including 3. The core 3 has a higher refractive index than the lower cladding 2 and the upper cladding 4 and extends in a direction parallel to the plane of the substrate 1.
[0020]
Further, in the present embodiment, as shown in a partially enlarged view of FIG. 1B, the core 3 is made of a rare earth-containing layer (second layer) 301 containing Er, for example, having a thickness of one atomic layer and containing Er. And a laminated structure including a rare earth-free layer (first layer) 302 having a thickness of, for example, 4 atomic layers containing no rare earth element. For example, when Er is added as a rare earth to a silica-based material, the rare earth-containing layer 301 has a thickness of 0.3 nm. 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, for example, a layer having a thickness of 1.5 nm when made of a silica-based material. The average concentration of Er in the entire core 3 is 1 × 10 ²⁰ Atom / cm ³ It is about.
[0021]
According to the waveguide type optical amplifier of FIG. 1 in the present embodiment, the waveguide gain was 1.2 dB / cm. In the conventional case where Er was uniformly doped in the core, the waveguide gain was 1 dB / cm, so that the waveguide type optical amplifier of FIG. 1 improved the waveguide gain.
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 μm, and the upper cladding 4 is made of, for example, boron and phosphorus having a thickness of about 10 μm. It is made of silicon oxide (BPSG).
[0022]
In the present embodiment, by forming the core 3 with a laminate of the extremely thin rare earth-containing layer 301 and the rare earth non-containing layer 302, clustering of the rare earth element (Er) added to the core 3 is suppressed, This is to efficiently perform optical amplification.
By setting the thickness of the rare-earth-containing layer 301 to about 1 atom and sandwiching the rare-earth-non-containing layer 302 to which the rare-earth element is not added between the other rare-earth-containing layers 301, the rare-earth atoms in the thickness direction of the core 3 are formed. Spacing was used to reduce clustering.
[0023]
Note that the thickness of the rare earth-free layer 302 is about 4 atomic layers, even if the rare earth added to the rare-earth-containing layer 301 diffuses and leaks into the rare-earth-free layer 302, but the rare-earth non-containing layer 302 becomes thin. Clustering in the containing layer 302 can be suppressed. In the manufacturing process, a small amount of rare earth may be mixed into the rare-earth-free layer 302. Even if a small amount of rare earth is present in the rare-earth-free layer 302, the concentration is very small. There is little to do and there is no problem.
[0024]
Incidentally, the rare earth added to the rare earth containing layer 301 is not limited to Er, and may be an element having a signal light amplifying effect by excitation radiation, such as thulium (Tm), praseodymium (Pr), and neodymium (Nd). Good. Further, a combination of a plurality of these may be added to the rare earth-containing layer.
[0025]
In this embodiment, the thickness of the rare earth-containing layer 301 and the thickness of the rare-earth non-containing layer 302 are described as 1 atomic layer and 4 atomic layers, respectively. However, the present invention is not limited to this. May be about 2 atomic layers, and the rare earth-free layer 302 may be about 8 atomic 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. In addition, each dimension described above is an example, and is not limited thereto.
[0026]
The effect of suppressing clustering increases as the number of atoms in the thickness direction of one layer 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 clustering is the highest.
By the way, even if the rare-earth-containing layer 301 is formed under the condition that the film thickness is 1 atomic layer, the current manufacturing technology may be about 5 atomic layers. As described above, the rare-earth-containing layer 301 is substantially formed of about several atomic layers.
[0027]
However, forming the rare earth-containing layer 301 into several atomic layers is not suitable for mass production in 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, if the thickness of the rare-earth-containing layer 301 is about 50 atomic layers, there is no difficulty, and the above-described laminated structure is mass-produced. In addition, gain can be improved by the effect of suppressing clustering. For example, when the rare earth-containing layer was a 50 atomic layer, the waveguide gain was 1.01 dB / cm.
[0028]
<Embodiment 2>
Next, another embodiment of the present invention will be described. In the waveguide type optical amplifier shown in FIG. 1, 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, but is not limited thereto. It 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 is changed in the core 3 will be described.
[0029]
FIG. 2A is a schematic cross-sectional view schematically illustrating a configuration example of a waveguide type optical amplifier according to another embodiment of the present invention, and FIG. 2B is an enlarged view of a core 3. FIG. This waveguide type optical amplifier comprises a lower clad 2 formed on a substrate 1, a core 3 having a width and a height of about 2 μm, and an upper clad 4 formed so as to cover the core 3. A rare earth element for amplifying signal light propagating in the core 3 is added to a region including the core 3. The core 3 has a higher refractive index than the lower cladding 2 and the upper cladding 4 and extends in a direction parallel to the plane of the substrate 1.
[0030]
In the present embodiment, as shown in a partially enlarged view of FIG. 2B, the core 3 is made of a rare-earth-containing layer 301 containing Er, for example, having a thickness of one atomic layer, and containing no rare-earth element. The laminated structure with the rare earth non-containing layer 302 was formed, and the film thickness of the rare earth non-containing layer 302 was increased toward both ends in the vertical direction of the core 3. By making the thickness of the rare earth-containing layer 302 different, that is, the interval between the rare earth-containing layers 301, the average concentration distribution of the rare earth element in the height direction of the core 3 is changed. It is possible to correspond to the density distribution of light propagating inside.
[0031]
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, and the average concentration of Er in the entire core 3 is 1 × 10 ²⁰ Atom / cm ³ It is about.
[0032]
In the waveguide type optical amplifier of FIG. 2, the thickness of the rare-earth-free layer 302 is, for example, 1 nm at the center of the core 3, is increased toward the upper and lower periphery, and is 5 nm at the upper and lower ends of the core 3. . As described above, since the distance is provided between the rare earth atoms in the thickness direction of the core 3, clustering of the rare earth element added to the core 3 can be suppressed even in the waveguide type optical amplifier of FIG. .
According to the waveguide type optical amplifier according to the present embodiment, 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, so that the waveguide type optical amplifier of FIG. 2 improved the waveguide gain.
[0033]
<Embodiment 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 becomes weaker toward the periphery of the core. When the light intensity is low, light may not be amplified by a high concentration of rare earth element, and light may be absorbed. 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. When the light guided in the core has the above-described light intensity distribution in a plane perpendicular to the waveguide direction, the rare earth element distribution in the height direction (y direction) of the core 3 (FIG. 2) is determined. As shown in FIG. 3 (b), the number may be increased at the center and decreased toward the periphery.
[0034]
In the present embodiment, in the waveguide type optical amplifier having the structure shown in FIG. 2 described above, the thickness of the rare-earth-free layer 302 is, for example, 1 nm at the center of the core 3 and becomes thicker toward the upper and lower periphery. The upper and lower ends of the core 3 were set to 5 nm. 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 the rare earth element in the core 3 can be formed.
[0035]
In forming the average concentration distribution of rare earth elements in the core 3 as shown in FIG. 3B, the rare earth containing layer 301 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 that is farther from the center of the core 3 may be formed thinner.
[0036]
As shown in FIG. 2, the thickness of the rare-earth-free layer 302 is 1 nm at the center of the core 3, is increased toward the upper and lower sides, and is 5 nm at the upper and lower ends of the core 3. The average concentration of Er per volume near the center is 2 × 10 ²⁰ Atom / cm ³ As a result, the waveguide gain could be set to 1.7 dB / cm. Conventionally, when Er is uniformly added into the core, the waveguide gain is 1 dB / cm. Therefore, according to the waveguide type optical amplifier of the present embodiment, the waveguide gain can be greatly improved. Can be.
[0037]
<Embodiment 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. 2, the concentration (average concentration) of Er per unit volume near the center of the core 3 is 2 × 10 ²⁰ Atom / cm ³ In the peripheral portion of the core 3, that is, in the boundary portion between the core 3 and the clad, the concentration (average concentration) of Er per unit volume is 2 × 10 ¹⁹ Atom / cm ³ And it is sufficient.
[0038]
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 dB / cm. Since the waveguide gain was 1 dB / cm when Er was uniformly added to the core in the related art, according to the waveguide type optical amplifier of the present embodiment, the waveguide gain was greatly improved. Can be.
[0039]
The average concentration distribution of the rare earth element in the core 3 does not need to be exactly Gaussian, but as shown in FIG. 5, if the error is within ± 30% of the Gaussian distribution, We have confirmed that the effect of the increase does not worsen. Therefore, in FIG. 5, the dotted lines indicate distributions that are increased by + 30% and decreased by −30% with respect to the Gaussian distribution, respectively, and may be any rare earth element distribution that changes as indicated by the solid line in these ranges.
[0040]
<Embodiment 5>
Next, another embodiment of the present invention will be described.
In the present embodiment, an element that suppresses clustering of a rare earth element or a correction element that expands an amplification band when a signal light is amplified by exciting an added rare earth element with excitation light is added to the core. Here is an example.
The materials of the substrate, the lower cladding, and the upper cladding, the film thickness, and the dimensions of the core are the same as those of the waveguide type optical amplifier shown in FIGS. 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.
[0041]
In addition, in this embodiment, aluminum (Al) and phosphorus (P) are added to the core 3 (FIG. 1) as modifying elements. The concentration (average concentration) of Er per unit volume of the rare earth-containing layer 301 and the rare-earth non-containing layer 302 constituting the core 3 is maximum (2.5 × 10 4) near the core center. ²⁰ Atom / cm ³ ), Gradually decreasing toward the periphery of the core, and 2.5 × 10 at the interface between the core and the clad. ¹⁹ Atom / cm ³ Until gradually decreased. As described above, the concentration of Er added is higher than that in the above-described embodiment, but in this embodiment, clustering can be suppressed because the correction element is added.
[0042]
The concentration of Al, which is a correction element, depends on the SiO 2 constituting the core. ₂ A concentration of 10% is added to the Si inside, and the concentration of phosphorus is ₂ A concentration of 5% was added to the Si inside. SiO constituting the core ₂ Al has an effect of suppressing clustering when a rare earth element is added at a high concentration and of expanding an amplification wavelength band. As an element having such an action, besides Al, boron (B), gallium (Ga), indium (In), germanium (Ge), tin (Sn), bismuth (Bi), nitrogen (N), phosphorus (P), yttrium (Yb), oxides thereof, and the like.
[0043]
Although these elements have different degrees of effect on both functions, any element has both functions of suppressing clustering and expanding the amplification band. One or two 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 Er concentration, the modifying element to be added, the substrate, the cladding material, the size, and the like are merely examples, and are not limited thereto.
According to this embodiment, clustering 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 the present embodiment, the waveguide gain was increased to 2.0 dB / cm. The amplification band of 1 dB / cm or more was expanded by 30 nm or more.
[0044]
<Embodiment 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 correction element is added only to the rare-earth-containing layer 301, the waveguide gain becomes 2.2 dB / cm. Therefore, according to the present embodiment, the waveguide gain is increased with respect to 2.0 dB / cm when a correction element such as Al or P is uniformly added in the core.
[0045]
<Embodiment 7>
Next, another embodiment of the present invention will be described.
FIG. 6 is a cross-sectional view schematically showing a partial configuration of the waveguide optical amplifier according to the present embodiment, that is, a core portion. The other configuration is the same as that of the waveguide type optical amplifier shown in FIGS.
In the core configured as shown in FIG. 6, a diffusion prevention layer 303 made of aluminum oxide is newly provided.
[0046]
The diffusion preventing layer 303 is provided in the rare-earth-free layer 302. By providing the diffusion preventing layer 303 in this manner, the diffusion of the rare earth element in the rare earth containing layer 301 can be suppressed as compared with the above-described embodiment. With the configuration of the present embodiment in which the diffusion preventing layer 303 made of aluminum oxide having a thickness of 0.2 nm is provided, the waveguide gain is increased to 2.4 dB / cm.
[0047]
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 the rare earth from the rare earth-containing layer 301 can be further suppressed. As a result, the waveguide gain increased to 2.5 dB / cm. Note that the rare earth-free layer may serve as a diffusion preventing layer.
[0048]
Hereinafter, a method of manufacturing the waveguide type optical amplifier according to the above-described embodiment, particularly, a portion of the waveguide will be described. First, as shown in FIG. 8A, a lower clad 2 is formed on a substrate 1, and then, as shown in FIG. 8B, a film 3a to be a core 3 is formed on the lower clad 2. . Next, the film 3a is processed by known photolithography and reactive ion etching (RIE), and the core 3 is formed on the lower clad 2 as shown in FIG. 8C.
[0049]
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 forming each layer, for example, a CVD method, a sputtering method, an evaporation method, a flame deposition method, or the like may be used.
Next, a method of 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 becomes the core 3, will be described. This may be achieved, for example, by manufacturing a film having a laminated structure by a sputtering method using a sputtering apparatus schematically shown in FIG.
[0050]
For example, first, the film 3a shown in FIG. 8B is formed by the sputtering device shown in FIG. In this sputtering apparatus, SiO ₂ Target and Er ₂ O ₃ Target and Al ₂ O ₃ And a target. 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 Al only to a specific layer. Since the film is formed by the sputtering method in units of planes, the elements to be added are uniformly distributed in the x direction (the plane direction of the film).
[0051]
For example, the substrate was heated to 300 ° C., the power supply power was set to 2 kW, the gas pressure in the chamber of the sputtering apparatus was set to 3 mTorr, and the flow rate was adjusted so that the Er concentration was 5% and the film formation rate was 0.2 nm / s. As a result, the film thickness could be controlled within 1 nm, and a film having a thickness of 5 atomic layers or less could be formed. Note that the film formation rate is not limited to this, and controllability can be improved by adjusting the flow rate and lowering the rate.
[0052]
According to the above-described sputtering method, it is possible to realize 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. it can.
Further, a film having the above-described laminated structure can be formed by a CVD method. Hereinafter, a case where the film 3a shown in FIG. 8B is formed by the plasma CVD apparatus shown in FIG. 10 will be described.
[0053]
In this plasma CVD apparatus, silane, trimethylaluminum, 2,2,6,6-tetramethyl-3,5-heptanedioene erbium is used as a source gas. By changing the supply amount of each source gas while forming the film 3a (FIG. 8) using such a plasma CVD apparatus, Er or Al can be added only to a specific layer. It becomes. Since the film formation by the plasma CVD method is performed on a plane basis, the elements to be added are uniformly distributed in the x direction (the plane direction of the film).
[0054]
The substrate was heated to 420 ° C., the plasma power 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 nm / s. As a result, the film thickness could be controlled within 2 nm, and a film having a thickness of 10 atomic layers or less could be formed. Note that 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.
[0055]
The formation of such a film is not limited to the sputtering method and the CVD method, but can also be realized by a film forming method such as an evaporation method and a flame deposition method. In any of the methods, the desired concentration distribution can be formed by supplying Er and Al from different decreases and changing the supply amounts as the film is formed.
[0056]
【The invention's effect】
As described above, according to the present invention, since the rare earth elements are discretely present in the core, clustering of the rare earth elements can be suppressed. An excellent effect that a high gain can be obtained is obtained.
[0057]
Further, for example, a higher gain can be obtained by setting the average concentration distribution of the rare earth element in the stacking direction of the core such that the concentration is higher toward the center of the core. For example, a 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 the concentration distribution in this manner, 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 to be thinner as being away from the center of the core.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view schematically showing a configuration example of a waveguide type optical amplifier according to a first embodiment of the present invention.
FIG. 2 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. 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, and FIG. 3B is a distribution diagram showing a concentration distribution of a rare earth element.
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. 8 is a process chart illustrating a method for 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 a method of manufacturing an optical waveguide according to an embodiment of the present invention.
FIG. 10 is a configuration diagram schematically showing a manufacturing apparatus for realizing a method for manufacturing an optical waveguide according to an embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Substrate, 2 ... Lower clad, 3 ... Core, 4 ... Upper clad, 301 ... Rare earth containing layer, 302 ... Rare earth non-containing layer.

Claims (19)

A clad formed on the substrate,
And a core disposed in the cladding,
The core is
A first layer made of a material having a different refractive index from the cladding;
A laminated structure in which the clad and a second layer to which a rare earth element is added, which is made of a material having a different refractive index, are alternately laminated;
A waveguide type optical amplifier, wherein the second layer has a thickness of several tens of atomic layers or less. The waveguide type optical amplifier according to claim 1,
The said 2nd layer is formed in thickness below several atomic layers, The waveguide type optical amplifier characterized by the above-mentioned. The waveguide type optical amplifier according to claim 1 or 2,
The waveguide type optical amplifier according to claim 1, wherein an average concentration distribution of the rare earth element in the core is higher at a center of the core at least in a stacking direction of the first and second layers. The waveguide type optical amplifier according to claim 3,
The waveguide type light, wherein an average concentration distribution of the rare earth element in the core corresponds to an intensity distribution of light guided through the core at least in a stacking direction of the first and second layers. amplifier. The waveguide type optical amplifier according to claim 3 or 4,
The waveguide type optical amplifier according to claim 1, wherein the first layer is formed so as to be thicker than a central portion of the core. The waveguide type optical amplifier according to claim 3 or 4,
The waveguide type optical amplifier, 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. The waveguide type optical amplifier according to claim 3 or 4,
The waveguide type optical amplifier, wherein the second layer is formed so as to be thinner than a center portion of the core. The waveguide optical amplifier according to any one of claims 1 to 7,
Either a function of suppressing clustering of the rare earth element added to the core, or a function of expanding an amplification band when amplifying signal light by exciting the rare earth element added to the core with excitation light or A waveguide type optical amplifier, wherein a correction element comprising both elements is added to the core. The waveguide type optical amplifier according to claim 8,
The said optical element is added only to the said 2nd layer, The waveguide type optical amplifier characterized by the above-mentioned. The waveguide type optical amplifier according to claim 8 or 9,
A waveguide type optical amplifier, wherein the modifying element is at least one of Al, B, Ga, In, Ge, Sn, Bi, N, P, and Yb. The waveguide-type optical amplifier according to any one of claims 1 to 10,
A waveguide type optical amplifier, 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. The waveguide type optical amplifier according to claim 11,
The said diffusion prevention layer is provided in contact with the said 2nd layer, The waveguide type optical amplifier characterized by the above-mentioned. The waveguide type optical amplifier according to claim 11 or 12,
The waveguide type optical amplifier according to claim 1, wherein the diffusion preventing layer is made of at least one of aluminum oxide, silicon nitride, and silicon oxynitride. The waveguide type optical amplifier according to any one of claims 1 to 13,
The rare-earth element is at least one of Er, Tm, Pr, and Nd. The waveguide-type optical amplifier according to any one of claims 1 to 14,
A main component of the core includes at least one of silicon oxide, aluminum oxide and bismuth oxide. The waveguide type optical amplifier according to claim 15,
A main component of the second layer is any one of phosphate glass, a rare earth oxide, and a rare earth element. Forming a lower cladding on the substrate;
A second target including a main component of a core, a second target including a rare earth element, and a third target including a modifying element, on the lower clad, the second target and the third target being used; A first layer composed of a main component of the core and a second layer of several tens of atomic layers or less to which a rare earth element is added, by any one of a sputtering method, an ion plating method, and a vapor deposition method for changing a sputtering state of the core. Comprises a laminated structure alternately laminated, the step of forming a core to which the correction element is added,
Forming an upper cladding on the lower cladding and the core. The method of manufacturing a waveguide type optical amplifier according to claim 17,
The method of manufacturing a waveguide-type optical amplifier, wherein the second target and the third target are targets containing a rare earth element and the modifying element simultaneously. Forming a lower cladding on the substrate;
By a chemical vapor deposition method in which 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 onto the lower clad. A first layer composed of a main component of the core, and a laminated structure in which a second layer of several tens of atomic layers or less to which a rare earth element is added is alternately laminated, and the correction element is added. Forming a core;
Forming an upper clad on the lower clad and the core.

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