JP2005217007A - Plane optical waveguide for optical amplifier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a means for suppressing clustering of rare earth element ions, and realizing a higher optical amplification rate and a wide amplification band width in increasing an additive rate of the rare earth element ions added into a core base metal as an amplification medium in a plane optical waveguide that can be used for an optical amplifier. <P>SOLUTION: In the optical waveguide in this form, composition elements of a waveguide core are set to be a rare earth element and elements other than the base metal. At least one element among Sc, Y and La, which belong to a group IIIA is added, and the elements other than the group IIIA are not added. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical waveguide having a planar core / clad waveguide shape, and in particular, the planar waveguide core has an optical amplification function in a 1.5 μm band, for example, as an optical amplification medium in a base material glass material. The present invention relates to an optical waveguide that can be used in an optical amplifier for a 1.5 μm band to which a rare earth element is added.

  Unlike an O / E conversion type amplification method that converts an optical signal into an electrical signal and converts it again into an amplified optical signal for an optical signal in the form of converting information into light intensity change, an optical amplifier is an electrical signal. It is possible to directly amplify an optical signal without passing through a circuit. In addition, optical amplifiers can have a relatively wide amplification wavelength bandwidth, and amplify optical signals that are attenuated due to loss in the transmission path in recent long-distance wavelength division multiplexing communications. It has become a very important device. The optical amplifier used in the current optical transmission system is mainly a rare earth element-doped fiber type optical amplifier that uses a rare earth element such as erbium added to the core of the silica fiber as an amplification medium, and is involved in amplification. Although the fiber is long and difficult to reduce the size of the device itself, there is provided one that exhibits high quality amplification characteristics having high amplification gain and low noise characteristics.

  On the other hand, in the future, with the aim of downsizing the optical amplifier unit, including the laser light source for pumping optical amplifiers, and modularizing the integrated and integrated multiple optical amplifier units, In place of element-doped fiber optical amplifiers, planar optical waveguide-shaped optical amplifiers have been developed that use materials with rare-earth elements added to the core of planar optical waveguides as amplification media in the desired wavelength range. Is underway.

Even in a planar optical waveguide-shaped optical amplifier using a rare earth element-added material that can be used as an amplifying medium, the optical amplification principle itself is the same as that of a conventional rare earth element-added fiber optical amplifier. Specifically, an excited state ⁴ I _11/2 in which an optical transition is allowed from the ground state ⁴ I _15/2 to a rare earth element ion added to the core, for example, Er ³⁺ ions. Excitation to the excited state ⁴ I _11/2 , which is equivalent to the absorption of, is then converted to the metastable excited state ⁴ I _13/2 through a non-radiative relaxation process . The _probability of non-radiative relaxation from this metastable excited state ⁴ I _13/2 to the ground state ⁴ I _15/2 or spontaneous optical transition is low, so when excitation light with strong light intensity is irradiated, compared to occupation ratio in the state ⁴ I _15/2, it increases the ratio present in a metastable excited state ⁴ I _13/2, population inversion is achieved. In the state where this inversion distribution is achieved, stimulated emission occurs when light corresponding to the optical transition energy from the metastable excited state ⁴ I _13/2 to the ground state ⁴ I _15/2 is injected from the outside. Then, the induced radiation of the same wavelength as the light injected from the outside is generated. Such stimulated radiation itself also depends on the intensity of incident light, and optical amplification with high linearity is achieved.

On the other hand, rare earth element ions added to the base material, such as Er ³⁺ ions, have a microscopic variation in the coordination state of coordination negative ions occupying the periphery, and the microscopic variation. As a result, in each Er ³⁺ ion, a minute variation occurs in the energy of each level resulting from the Stark effect resulting from the coordination state of the coordination negative ion. By utilizing the energy distribution (expansion width) of each level derived from the coordination state of this coordinated negative ion, it is possible to make the amplification wavelength bandwidth relatively wide. Therefore, in order to increase amplification efficiency or increase the amplification wavelength bandwidth, it is necessary to increase the concentration of rare earth element ions added per unit volume, for example, Er ³⁺ ions. In this case, if a situation occurs in which a plurality of added rare earth element ions, for example, Er ³⁺ ions, are present in a cluster shape, improvement of amplification efficiency is hindered by the phenomenon introduced below.

That is, when a rare earth element ion to be added, for example, a plurality of Er ³⁺ ions is present in a cluster shape, energy transfer is more likely to occur between adjacent Er ³⁺ ions. For example, the energy transfer occurs between the Er ³⁺ ions two in metastable excited state ⁴ I _13/2, one Er ³⁺ ions lose excitation energy, ground state ⁴ I _15/2, and the other The Er ³⁺ ions are excited from the metastable excited state ⁴ I _13/2 to a higher excited state, for example, ⁴ I _9/2 , with energy transfer. Then, this high excitation state ⁴ I _9/2, by going through non-radioactive relaxation process, the process returns again to the metastable excited state ⁴ I _13/2, Overall, initially metastable excited state ⁴ Er ³⁺ ions two in I _13/2 is a result of energy transfer between them, in the end, and has a Er ³⁺ ions, one in the metastable excited state ⁴ I _13/2. Therefore, in the optical amplifier of the planar optical waveguide shape, in order to increase the amplification efficiency and increase the amplification wavelength bandwidth, the concentration of rare earth element ions added to the core, for example, Er ³⁺ ions is increased. At this time, it is necessary to suppress clustering of added rare earth element ions, for example, Er ³⁺ ions, and some studies have been made so far.

  At the same time, in a planar optical waveguide-shaped optical amplifier, it is necessary to achieve a state in which more internally amplified light is confined in the core and to reduce the overall loss. That is, it is necessary to achieve a favorable refractive index waveguide condition by forming a desired refractive index difference between the core and the cladding surrounding the core.

In order to achieve the various requirements described above, there are several techniques for co-adding other elements into the host base material in addition to the rare earth element ions added to the core, such as Er ³⁺ ions. Proposed. Table 1 summarizes typical conventional examples of techniques for co-adding other elements in addition to rare earth element ions.

In the first conventional example, phosphorus (P ₂ O ₅ ) is added to quartz glass as a core base material of a waveguide (see Patent Document 1 and Non-Patent Document 1). The addition of phosphorus (P ₂ O ₅ ) has the function of increasing the refractive index of the core base material and also has the effect of increasing the melting amount of the added rare earth element ions. For this reason, when the concentration of the rare earth element ions to be added is increased, the rare earth element ions are less likely to be clustered. By increasing the concentration of the rare earth element ions added along with the increase in the refractive index difference Δn between the core / cladding and the effect of preventing clustering of the rare earth element ions added at a high concentration, It is possible to increase the amplification factor.

In the second conventional example, a material in which Al (Al ₂ O ₃ ) and P (P ₂ O ₅ ) are added to quartz glass as a core material of a waveguide has been studied (Non-Patent Document 2, Non-Patent Document 3). The co-addition of Al (Al ₂ O ₃ ) and P (P ₂ O ₅ ) has an effect of suppressing clustering of added rare earth element ions, and therefore, when increasing the concentration of added rare earth element ions. Even when a high excitation light intensity is selected, the effect of suppressing deterioration of excitation efficiency characteristics is exhibited.

In a third conventional example, Al (Al ₂ O ₃ ) and La (La ₂ O ₃ ) are added to quartz glass as a core base material of a waveguide (see Patent Document 2). The addition of Al (Al ₂ O ₃ ) and La (La ₂ O ₃ ) has the effect of suppressing the clustering of rare earth element ions added to quartz glass in addition to the function of increasing the refractive index of the core. ing.

In the fourth conventional example, in order to increase the refractive index difference Δn between the core and the clad, the core base material itself is alumina (Al ₂ O ₃ ), and the optical amplification element is contained in the alumina (Al ₂ O ₃ ). As an example, a rare earth element or Cr or Ti ions are added (Patent Document 3).

Japanese Patent Laid-Open No. 9-021922 JP-A-9-105965 JP-A-6-77578 Kuniori Hattori et al., JOURNAL OF APPLIED PHYSICS, VOL. 80, 1996, pages 5301-5308 Fabrizio Di Pasquale et al., JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 13, no. 9, 1995, pages 1858-1864 C. E. Chryssou et al., IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL. 6, no. 1, 2000, 114-121 pages

The conventional method described above still has some problems to be improved. For example, in the first conventional example (Patent Document 1, Non-Patent Document 1) in which phosphorus (P ₂ O ₅ ) is added to quartz glass of the core material of the waveguide, the refraction between the grad and the core is performed. When the addition rate of phosphorus (P ₂ O ₅ ) into the core is increased in order to increase the rate difference Δn, a new problem arises that the amplification bandwidth is reduced as compared with the case of a low addition rate.

On the other hand, in the second conventional example (Non-Patent Document 2 and Non-Patent Document 3) in which Al (Al ₂ O ₃ ) and P (P ₂ O ₅ ) are co-added into the quartz glass of the core base material, As reported in Patent Document 3, the increase in the refractive index is about 2% of the refractive index n _SiO2 (about 1.46) of the quartz glass of the clad base material. Furthermore, in the case reported in Non-Patent Document 3, when Al (Al ₂ O ₃ ) and P (P ₂ O ₅ ) are co-added to the quartz glass of the core base material, optical amplification is performed. The emission cross section of the photoluminescence in the rare earth element ions used, such as Er ³⁺ ions, is smaller than when added to other core materials such as alumina. In general, when the light emission cross-sectional area of photoluminescence is reduced, the optical amplification factor tends to decrease, which is not desirable for achieving a high optical amplification factor.

  As described above, in a planar optical waveguide type optical amplifier in which a rare earth element ion is added to the core, which is being developed with the goal of downsizing the optical amplifier unit, the rare earth element ion added to the core It is necessary to increase the amplification factor per unit length by increasing the concentration. At the same time, in order to maintain the optical confinement ratio in the core, it is also necessary to set the refractive index difference Δn between the core and the clad within a predetermined range. On the other hand, when considering use in a wavelength division multiplexing optical communication system, in addition to a high amplification gain, a wider amplification bandwidth is required. There is a need to search for elemental ions that have the effect of increasing the width. That is, in the planar optical waveguide type optical amplifier, when the concentration of the rare earth element ions added to the core is increased, it contributes to the suppression of clustering of the rare earth element ions added, and the appropriate core / cladding Through the formation of the refractive index difference Δn between them, the suppression of clustering of the added rare earth element ions, the achievement of high amplification gain, and the effect of increasing the amplification bandwidth. It is necessary to search for element ions that can be added.

  The present invention solves the above-mentioned problems, and the object of the present invention is to add to the core base material so that it can be used to form an appropriate refractive index difference Δn between the core and the clad. It contributes to the achievement of high amplification gain through suppression of clustering of rare earth ions, and also has the effect of increasing the amplification bandwidth in the optical amplification process by added rare earth ions. An object of the present invention is to provide an optical waveguide that can be used for an optical amplifier that uses an element ion that can be co-added with a rare earth element ion serving as an amplification medium. In particular, when a quartz glass layer is used for the cladding, a quartz material is used as a base material of the core, and for example, the above-mentioned characteristics are achieved in order to achieve an optical waveguide that can be used for an optical amplifier for a 1.5 μm band. It is an object of the present invention to provide an optical waveguide having a core region using element ions that can be added together with rare earth element ions serving as an optical amplification medium.

In order to solve the above problems, the present inventors first studied to clarify the problems in the conventional method. Materials in which Al (Al ₂ O ₃ ) was co-added at various ratios in addition to Er ³⁺ ions in the core quartz glass were prepared by sputtering. That is, the Er ³⁺ ion concentration, 0.5 mol% as Er ₂ O _3, while keeping the host _{(SiO 2 + Al 2 O 3} ) in a ratio of 99.5 mol%, in the host _{(SiO 2 + Al 2 O 3} ) Sputter-grown films with various ratios of SiO ₂ and Al ₂ O ₃ were prepared, and the photoluminescence was measured. When the excitation light is measured at a wavelength of 980 nm and an intensity of 200 mW, the photoluminescence intensity at a wavelength of 1.55 μm is plotted against the content ratio of Al ₂ O _{3 in} the host (SiO ₂ + Al ₂ O ₃ ). The result shown in FIG. 2 was obtained. Increasing the ratio of Al ₂ O ₃ added to the host (SiO ₂ + Al ₂ O ₃ ) increases the refractive index and has the effect of suppressing clustering of the added Er ³⁺ ions, It was found that as the content ratio of Al ₂ O ₃ increases, the photoluminescence intensity at a wavelength of 1.55 μm derived from Er ³⁺ ions decreases. In the results shown in FIG. 2, when the content ratio of Al ₂ O _{3 in} the host (SiO ₂ + Al ₂ O ₃ ) exceeds 15 mol%, the photoluminescence intensity at a wavelength of 1.55 μm derived from Er ³⁺ ions. Is not yet reduced, but the content ratio of Al ₂ O ₃ in the host is 100 mol%, that is, the photoluminescence intensity at a wavelength of 1.55 μm derived from Er ³⁺ ions when the core base material is alumina. Also turned out to be this low water collection. In conclusion, it is judged that the addition of Al ₂ O ₃ to the core base material is not always preferable for the purpose of improving the optical amplification efficiency.

In addition, when the planar optical waveguide is manufactured, the Si substrate 1 is used as a substrate. For example, as shown in FIG. 1, the periphery of the core 3 having a rectangular cross section is formed as the lower cladding layer 2 and the upper cladding layer 4. When using a quartz glass material in which Al (Al ₂ O ₃ ) or P (P ₂ O ₅ ) is added at a high ratio as a host material constituting the rectangular cross-section core 3 when the shape is surrounded by a quartz glass layer, A large strain stress is applied to the rectangular core 3 in a direction parallel to the substrate surface. That is, a large strain stress is applied to the Si clad 1 on the lower clad layer 2 itself made of a quartz glass film formed on the Si substrate 1 in a direction parallel to the substrate surface. In addition, there is a strain stress in the same direction between the quartz glass material to which Al (Al ₂ O ₃ ) or P (P ₂ O ₅ ) is added at a high ratio and the quartz glass material due to the difference in composition. As a whole, a larger strain stress is applied to the core 3 having a rectangular cross section surrounded by the lower cladding layer 2 and the upper cladding layer 4 in a direction parallel to the substrate surface. As a result, the large strain stress applied in the direction parallel to the substrate surface causes anisotropy of the dielectric constant tensor and birefringence, that is, the optical waveguide characteristics in the core region of the planar optical waveguide. It also becomes a factor causing polarization dependence.

Therefore, when a planar optical waveguide having a cross-sectional shape shown in FIG. 1 is produced, when a quartz glass layer is used as the lower cladding layer 2 and the upper cladding layer 4, addition to the quartz glass (SiO ₂ ) as a core base material is added. As a necessary component, it is possible to achieve a desired refractive index difference Δn between the clad and the core with a lower addition amount. 1, a strain stress opposite to the direction of the strain stress received by the lower cladding layer 2 made of a quartz glass film is generated, and as a result, in the core region, the strain is applied in a direction parallel to the substrate surface. It is desirable to add a component that can relieve strain stress. Of course, such an additive component has an effect of suppressing a decrease in light amplification efficiency due to clustering of rare earth element ions, for example, Er ³⁺ ions, which are light amplification media added in the core, and has a high effect. It is more desirable to be an element ion that can be co-added into the core, which is suitable for both achieving the amplification gain and increasing the amplification bandwidth.

For example, when the clad is formed using quartz glass, the inventors of the present invention add light of element ions selected from the group consisting of Sc, Y, La, and Ac among group IIIA elements to the core. As in the case of rare earth ions, for example, Er ³⁺ ions, which are amplification media, they can be added together in the form of oxides to the core matrix quartz glass (SiO ₂ ) to satisfy the above requirements. It discovered that it functions as an auxiliary element ion, and came to complete this invention.

That is, the optical waveguide that can be used in the optical amplifier according to the present invention is:
An optical waveguide capable of guiding light having a wavelength included in a specific wavelength band,
The optical waveguide includes a flat substrate,
A planar optical waveguide comprising at least a clad provided on the substrate and a core disposed in the clad;
The clad is composed of an oxide exhibiting light transmittance at a wavelength included in the specific wavelength band,
The core is added to the oxide constituting the clad, in the form of an oxide, a rare earth element ion having a transition state capable of inductive light emission at least at a wavelength included in the specific wavelength band, Furthermore, in addition to the rare earth element ions, one of the element ions selected from the group consisting of Sc, Y, and La among the group IIIA (group 3) elements is added as an auxiliary element ion in the form of an oxide. Composed of an oxide having a mixed composition of
At least at the core / cladding interface where the core and the clad contact each other, the refractive index of the mixed composition oxide constituting the core at the wavelength included in the specific wavelength band is the refractive index of the oxide constituting the clad. The optical waveguide is characterized in that the addition ratio of the assisting element ions in the core is selected so as to exhibit a refractive index higher by 1% to 20%. In that case, it is preferable that the addition ratio of the assisting element ions in the mixed composition oxide constituting the core is selected in the range of 2 mol% or more and 20 mol% or less.

In the optical waveguide according to the present invention, depending on the case,
The oxide having a mixed composition constituting the core may further contain a small amount of group IIIB (group 13) element ions or group IVB (group 14) element ions other than silicon ions.
The trace amount of group IIIB (group 13) element ions or group IVB (group 14) element ions other than silicon ions are limited to oxides with a total content ratio of 1 mol% or less. Is desirable.

In particular, in the optical waveguide according to the present invention,
The oxide constituting the clad is preferably silicon dioxide. Further, the oxide constituting the cladding is quartz glass,
The mixed composition oxide constituting the core is preferably a mixed composition glass in which both the rare earth element ions and the auxiliary element ions are added in the form of an oxide to the quartz glass.

In the optical waveguide according to the present invention,
The core disposed in the cladding is
In the core cross section in the direction perpendicular to the substrate surface, the additive element ion concentration added in the core is at least from the center of the core toward the core / cladding interface in the perpendicular direction. , It can have a uniform distribution.

On the other hand, in the optical waveguide according to the present invention,
The core disposed in the cladding is
In the core cross section in the direction perpendicular to the substrate surface, the additive concentration of the rare earth element ions added in the core is at least from the center of the core toward the core / cladding interface in the perpendicular direction. Also, it can be in a form having a uniform distribution.

Alternatively, the core disposed in the cladding is
In the core cross section in the direction perpendicular to the substrate surface, the addition concentration of the rare earth element ions added in the core gradually increases from the center of the core toward the core / cladding interface in the perpendicular direction. It is also possible to adopt a form having a distribution that decreases to a minimum. At that time, the core disposed in the clad,
In the core cross section in the direction perpendicular to the substrate surface, the addition concentration of the rare earth element ions added in the core has a distribution close to a Gaussian distribution having a maximum at the center of the core. Is preferred.

The present invention also provides an invention of a method of manufacturing an optical waveguide that can be used in the optical amplifier according to the present invention.
That is, the method for manufacturing an optical waveguide according to the present invention is as follows.
A method of manufacturing an optical waveguide capable of guiding light having a wavelength included in a specific wavelength band,
The optical waveguide includes a flat substrate,
A lower clad provided on the substrate;
A core having a rectangular cross-sectional shape provided on the lower clad and patterned into a predetermined plane pattern shape;
The lower clad upper surface, and the upper clad formed in a form covering the side surface and upper surface of the core subjected to patterning,
At least, it has a form of a planar optical waveguide composed of a core disposed in a clad composed of a lower clad and an upper clad,
The lower clad and the upper clad are made of an oxide exhibiting optical transparency at a wavelength included in the specific wavelength band,
The core is added to the oxide constituting the clad, in the form of an oxide, a rare earth element ion having a transition state capable of inductive light emission at least at a wavelength included in the specific wavelength band, Furthermore, in addition to the rare earth element ion, as a supporting element ion, one of element ions selected from the group consisting of Sc, Y, and La among group IIIA elements is added in the form of an oxide. Composed of oxides,
At least at the wavelength included in the specific wavelength band at the core / upper clad upper interface and the side interface where the core upper surface and the upper clad are in contact, and at the core / lower clad lower interface where the core lower surface and the lower clad are in contact, The refractive index of the mixed composition oxide constituting the core is 1% to 20% higher than the refractive index of the oxide constituting the cladding. Having a selected structure,
The method of manufacturing the optical waveguide is as follows:
A lower clad film forming step of forming an oxide layer having a predetermined thickness on the substrate at a wavelength included in the specific wavelength band constituting the lower clad;
A rare earth element ion having a transition state capable of inductively emitting light at least at a wavelength included in the specific wavelength band with respect to the oxide constituting the clad and constituting the core on the lower clad film. Is added in the form of an oxide, and in addition to the rare earth element ion, one of the element ions selected from the group consisting of Sc, Y, and La among the group IIIA elements is an oxide of the group IIIA element. A mixed composition oxide constituting the core layer at a wavelength included in the specific wavelength band at least in the core layer, the core layer having a predetermined film thickness made of an oxide having a mixed composition added in a form The refractive index of the auxiliary element ions in the core layer thickness direction is such that the refractive index is 1% to 20% higher than the refractive index of the oxide constituting the cladding. A core layer forming step of forming on-option has been that structure,
A resist mask forming step of forming a resist pattern of the predetermined plane pattern shape on the surface of the core layer by photolithography;
Using the resist mask as an etching mask, the core layer is etched by a dry etching method to form a core having a rectangular cross-sectional shape and patterned into the predetermined planar pattern shape Process,
An oxide layer exhibiting optical transparency at a wavelength included in the specific wavelength band constituting the upper clad, in a form covering the upper surface of the lower clad and the side surface and upper surface of the patterned core. Including an upper clad film forming step for forming a predetermined film thickness,
This is a method for manufacturing an optical waveguide.

As described above, in the planar optical waveguide according to the present invention, a core composition to which rare earth element ions are added to the quartz glass (SiO ₂ ) cladding constituting the optical waveguide is added to the core matrix. Rare earth element ions (R ₂ O ₃ ; R represents a rare earth element) and quartz glass (SiO ₂ ) as a core base material, Sc, Y of group IIIA (group 3) elements substantially. , And a core element ion selected from the group consisting of La is selected in the form of its oxide (M ₂ O ₃ ; M represents any one of Sc, Y, and La). The planar optical waveguide is excellent in photoluminescence emission characteristics from rare earth element ions added to the base material. Furthermore, when producing such an optical waveguide on a silicon substrate, the strain stress applied to the core region is made of a quartz glass material to which conventional Al (Al ₂ O ₃ ) or P (P ₂ O ₅ ) is added in a high ratio. Compared with what is used for a core base material, it can reduce significantly. With these advantages, when the planar optical waveguide according to the present invention is used as a waveguide type optical amplifier, a higher optical amplification effect can be obtained.

In the present invention, in the core base material, among the group IIIA (group 3) elements, only the assisting element ions selected from the group consisting of Sc, Y, La are oxides thereof (M ₂ O ₃ ; By adding in the form of Sc, Y, or La), a desired refractive index difference is formed between the refractive index of the core and the refractive index of the clad constituting the planar optical waveguide. Therefore, the addition ratio of the above-mentioned assisting element ions necessary to achieve a desired refractive index difference can be significantly reduced as compared with the conventional addition ratio of Al (Al ₂ O ₃ ). At the same time, among the group IIIA (group 3) elements, the use of an auxiliary element ion selected from the group consisting of Sc, Y, and La is used as an optical amplifying medium, and the addition concentration of rare earth element ions added to the core The function to suppress the decrease in luminous efficiency due to the clustering is shown, and the intensity of photoluminescence from rare earth ions is not decreased so much, and the amplification wavelength bandwidth is increased. doing.

  Hereinafter, the optical waveguide according to the present invention will be described in more detail.

The optical waveguide according to the present invention employs a planar optical waveguide composed of at least a clad and a core containing rare earth element ions arranged in the clad on the substrate. When used as an optical amplifier, rare earth element ions added to the core are used as an optical amplification medium. For example, Er ³ for optical amplification in the 1.5 μm band depending on the target amplification wavelength band. ⁺ Ions, Ho ³⁺ ions, Tm ³⁺ ions, Yb ³⁺ ions, etc. In addition, for light amplification in the 1.3 μm band, suitable rare earth element ions such as Pr ³⁺ ions and Nd ³⁺ ions are used. select. Of the rare-earth element ions added to the core used as these optical amplification media, among the group IIIA (group 3) elements, at least one of the auxiliary element ions selected from the group consisting of Sc, Y, and La Are co-added.

For example, when quartz glass (SiO ₂ ) is used as a grad, the core is composed of rare earth element ions (R ₂ O ₃ ; R represents a rare earth element) added to the core matrix, and quartz as the core matrix. Only an auxiliary element ion selected from the group consisting of Sc, Y, and La among Group IIIA (Group 3) elements is converted into glass (SiO ₂ ) with its oxide (M ₂ O ₃ ; M is Sc, Y, It is preferable to select a configuration to be added in the form of (indicating one of La). At that time, the rare earth element ion is in the form of an oxide (R ₂ O ₃ ; R represents a rare earth element), and the addition ratio depends on the excitation wavelength of the excitation light source for light amplification and the intensity of the incident excitation light. The light absorption intensity (absorption cross section) of the rare earth element ion at the excitation wavelength is also selected as appropriate. On the other hand, the auxiliary element ions that are co-added with the rare earth element ions exhibit substantially no light absorption at the excitation wavelength to be used, and among the group IIIA (group 3) elements, Sc, Y, La Selected from the group consisting of In addition, the auxiliary element ions co-added with the rare earth element ions are substantially free of light absorption even in a target amplification wavelength band, for example, 1.5 μm band or 1.3 μm band, Among group IIIA (group 3) elements, selected from the group consisting of Sc, Y, and La.

When used as an optical amplifier, the concentration of rare earth element ions added to the core is, for example, 1.5 μm band, especially for light amplification in the C-band band (1530 to 1565 nm) Er ^3+. Ions, Ho ³⁺ ions, Tm ³⁺ ions, Yb ³⁺ ions, etc. under the conditions of a waveguide length of 10 cm, a core cross-sectional shape of 4 μm × 4 μm, an excitation wavelength of 980 nm for the light source for optical amplification, and an incident excitation light intensity of 200 mW On the other hand, the oxide (R ₂ O ₃ ; R represents a rare earth element) can be selected in the range of 0.05 mol% to 1.0 mol%.

The optical waveguide according to the present invention aims to achieve a desired gain even when the waveguide length is shortened as described above, and the addition concentration of rare earth element ions added to the core. Is an oxide (R ₂ O ₃ ; R represents a rare earth element), and in the range of 0.05 mol% to 1.0 mol%, 0.2 mol% to 1.0 mol% After selecting the above high concentration range, a mode of increasing the light amplification factor per unit length by selecting the following addition rate of the assisting element ions becomes more suitable.

Further, the assisting element ions added to the core are added to quartz glass (SiO ₂ ) in the form of an oxide (M ₂ O ₃ ; M represents any one of Sc, Y, La, and Ac). This constitutes the core base material and is used for adjusting the refractive index. Therefore, the additive element ion addition ratio is appropriately selected according to the refractive index difference provided between the refractive index of the core and the refractive index of the cladding. That is, at least at the core / cladding interface where the core and the clad are in contact, the refractive index of the mixed composition oxide constituting the core is 1 than the refractive index of the oxide constituting the clad in the target amplification wavelength band. The addition rate of the assisting element ions in the core is selected so as to show a refractive index higher by 20% to 20%.

For example, in the wavelength range 1.55μm band, the refractive index n _core of the core, silica glass (SiO ₂₎ relative refractive index difference to the refractive index of the cladding n _SiO2 (about _{1.45) Δ (≡ (n core} -n It is possible to design an optical waveguide by setting _SiO2 ) / _ncore ) in the range of 2% to 17%. Correspondingly, among group IIIA (group 3) elements, Sc, Y, La The addition ratio of an auxiliary element ion selected from the group consisting of, for example, La ³⁺ ions can be selected in the range of 2 mol% to 20 mol% as lanthanum oxide (La ₂ O ₃ ). In general, it is desirable to design the optical waveguide by setting the relative refractive index difference Δ between the core and the quartz glass (SiO ₂ ) clad in the wavelength region in the range of 3% to 10%, It is more desirable to select the addition ratio of the assistant element ions, for example La ³⁺ ions, in the range of 4 mol% to 10 mol% as lanthanum oxide (La ₂ O ₃ ). In some cases, Ac ³⁺ ions can also be used as auxiliary element ions by selecting the same additive concentration in the form of oxide (Ac ₂ O ₃ ).

Specifically, a planar optical waveguide is used to reduce the size and integration of the optical amplifier, so that the waveguide satisfies the refractive index guiding conditions in the core and the total reflection conditions at the core / cladding interface. Is made into a spiral optical waveguide. At this time, quartz having a refractive index n _core of the _core is set so that the minimum value of the radius of curvature r of the waveguide bend portion becomes a desired value according to the cross-sectional shape size of the rectangular core, in particular, the lateral width (W). An optical waveguide plane having a spiral shape as a whole after selecting a relative refractive index difference Δ (≡ (n _core −n _{SiO 2} ) / n _core ) with respect to the refractive index n _SiO2 (about 1.45) of the glass (SiO ₂ ) cladding. Design the pattern. For example, in a rectangular core, when the vertical thickness (T) × width (W) is set to 4 μm × 4 μm, the quartz bend portion has a minimum radius of curvature r of 2 mm (r ≧ 2 mm). In order to achieve a relative refractive index difference Δ of 1.5% or more with respect to the refractive index n _SiO2 (about 1.45) of the glass (SiO ₂ ) clad and a minimum value 1 mm (r ≧ 1 mm) of the curvature radius r, The relative refractive index difference Δ with respect to the refractive index n _SiO2 (about 1.45) of the quartz glass (SiO ₂ ) clad needs to be selected in the range of 3.0% or more. In order to satisfy the above requirement, in order to achieve the minimum value 2 mm (r ≧ 2 mm) of the radius of curvature r, correspondingly, among the group IIIA (group 3) elements, a group consisting of Sc, Y, La As a lanthanum oxide (La ₂ O ₃ ), the addition ratio of a donor element ion selected from the group ^consisting of La ³⁺ ions is in a range of 2 mol% or more, and the minimum value of the curvature radius r is 1 mm (r ≧ 1 mm). ), For example, it is desirable to select the addition ratio of La ³⁺ ions in the range of 3 mol% or more as lanthanum oxide (La ₂ O ₃ ). In some cases, Ac ³⁺ ions can also be used as auxiliary element ions by selecting the same additive concentration in the form of oxide (Ac ₂ O ₃ ).

For example, FIG. 3 shows a case where alumina (Al ₂ O ₃ ) is added as a material containing group IIIB (group 13) element ions to an Er ³⁺ ion-doped quartz (SiO ₂ ) film prepared by sputtering. The refractive index of an oxide film having a mixed composition is shown in comparison with the case where lanthanum oxide (La ₂ O ₃ ) is added as a material containing group IIIA (group 3) element ions. The right axis of FIG. 3 shows the relative refractive index difference Δ with respect to the quartz glass (SiO ₂ ) clad for reference. When alumina (Al ₂ O ₃ ) is added, even if the addition ratio reaches 20 mol%, the relative refractive index difference Δ is less than 4%, and the refractive index cannot be increased so much. When (La ₂ O ₃ ) is added, the same increase in refractive index can be achieved even if only a few percent is added. Further, in place of La ³⁺ ions, among group IIIA (group 3) elements, Sc, Y, and in some cases, when Ac is added as an ^auxiliary ion, Sc ³⁺ ions, Y ³⁺ ions, Ac ³⁺ ions are added to the main quartz glass (SiO ₂ ) in the form of oxides (Sc ₂ O ₃ , Y ₂ O ₃ , Ac ₂ O ₃ ), respectively. Each of these oxides itself has a high refractive index (Sc ₂ O ₃ : about 1.95, Y ₂ O ₃ : about 1.87). For example, the relative refractive index difference Δ achieves 7%. necessary to, the addition ratio, for the principal of the quartz glass (SiO _2), with respect to the La ³⁺ ions, 8 mol% in the form of an oxide (La ₂ O _3), with respect to Sc ³⁺ ions The oxide (Sc ₂ O ₃ ) may be selected to be 8 mol%, and the Y ³⁺ ion may be selected to be 8 mol% in the form of the oxide (Y ₂ O ₃ ). Further, Ac ³⁺ ions may be selected to have the same concentration in the form of oxide (Ac ₂ O ₃ ). In any case, the desired relative refractive index difference Δ can be achieved at a much lower addition ratio as compared with the case where alumina (Al ₂ O ₃ ) is added as a material containing group IIIB (group 13) element ions. . That is, in the optical waveguide according to the present invention, among the group IIIA (group 3) elements added to the core base material, the addition ratio of the auxiliary element ions selected from the group consisting of Sc, Y and La is mainly In quartz glass (SiO ₂ ), it is appropriate to select an oxide (M ₂ O ₃ ; M represents any one of Sc, Y, and La) in the range of 2 mol% to 20 mol%. More preferably, it is selected in the range of 4 mol% to 10 mol%. Alternatively, depending on the case, Ac ³⁺ ions may be used as the auxiliary element ions in the form of an oxide (Ac ₂ O ₃ ) with a similar addition concentration and utilized.

On the other hand, a group IIIA (3) added as a form of an oxide (M ₂ O ₃ ; M represents any one of Sc, Y, and La) in the main base material, quartz glass (SiO ₂ ). Among the group elements), the auxiliary element ions selected from the group consisting of Sc, Y, and La do not weaken the intensity of photoluminescence from the rare earth element ions added to the core so much even if the addition ratio increases. However, as the addition ratio increases, the photoluminescence emission intensity tends to gradually weaken, so from this point of view, by selecting the above addition ratio range, it is possible to avoid an extreme decrease in the photoluminescence emission intensity. can do. In addition, among the group IIIA (group 3) elements, the auxiliary element ions selected from the group consisting of Sc, Y, and La usually use one kind, but within the range satisfying the above-described requirements, two or more kinds are used. , And can be used together so that the sum of the addition ratios falls within the above range. In that case, depending on the case, it is also possible to use Ac ³⁺ ions in the form of oxides (Ac ₂ O ₃ ) in the form of oxides (Ac ₂ O ₃ ) as the auxiliary element ions and use them together.

For example, when alumina (Al ₂ O ₃ ) is added as a group IIIB (group 13) element ion in the core to which the rare earth element ion is added, it exhibits an action of weakening the photoluminescence emission intensity from the rare earth element ion. In addition, it is desirable that the core formed on the substrate does not contain IIIB group element ions or IVB group element ions having an effect of increasing the strain stress applied to the film. In some cases, a small amount of group IIIB element ions or group IVB element ions may be mixed in the core to an impurity level. However, due to the above-mentioned problems and undesirable functions / functions, the optical amplification characteristics, etc. In order to eliminate the influence, the content ratio of the group IIIB element ions and the group IVB element ions in the core is preferably limited to a range of 1 mol% or less as the oxide.

  In the planar optical waveguide according to the present invention, as shown in FIG. 1, a core layer having a uniform film thickness is once formed on a lower clad formed on a substrate, and then a desired width is obtained. Patterning is performed to make the cross-sectional shape of the core rectangular. After that, it is preferable that an upper clad is formed so as to cover both side surfaces and the upper surface portion of the core, and the core is installed in the clad. At that time, since the core is an optical waveguide, the refractive index of the mixed composition oxide constituting the core constitutes the clad in the target amplification wavelength band at the core / cladding interface where the core and the clad contact each other. The addition rate of the assisting element ions in the core is selected so that the refractive index is 1% to 20% higher than the refractive index of the oxide, and the addition rate of the assisting element ions in the core is uniform. It is preferable to do. In an optical waveguide having such a contrasting boundary condition, the intensity distribution of propagating light usually shows a distribution that can be approximated to a Gaussian distribution having a maximum at the core center.

When using such a planar optical waveguide as an optical amplifier, the signal light to be amplified and the pumping light used for amplification are combined in advance by an optical directional coupler and then transmitted from an optical fiber. It is incident on the core end face of the optical waveguide. The signal light amplified while passing through the optical amplifier and the remaining pump light are guided from the core end face of the optical waveguide to the optical directional coupler via the optical fiber, and are demultiplexed (wavelength separation). Is done. Accordingly, the vertical thickness (T) and width (W) in the cross-sectional shape of the rectangular core take account of the core diameter, aperture ratio, etc. of the optical fiber to be optically bonded at the entrance end and the exit end. It is appropriately selected within an allowable range. Further, the thickness (T _clad ) of the lower clad and the upper clad takes into consideration the vertical thickness (T) and the horizontal width (W), particularly the vertical thickness (T) in the cross-sectional shape of the rectangular core. Considering the refractive index difference between the core and the clad, the dielectric constant (refractive index) of the substrate under the lower clad or the space above the upper clad becomes the optical waveguide characteristic or optical amplification characteristic in the core. It can be selected as appropriate so as not to affect.

  On the other hand, the concentration distribution of rare earth element ions added to the core used as an optical amplification medium can be made uniform in the core, but is similar to the intensity distribution of light propagating in the core. It is also possible to provide a concentration distribution. That is, in the light intensity distribution of the excitation light in the core, in the region where the light intensity is low, the excitation light intensity rapidly increases due to absorption by the rare earth element ions while traveling through the waveguide when the concentration of the rare earth element ions is uniform. The ratio between the ground state and the excited state falls below the range in which optical amplification is possible, and conversely, the absorber for the amplified signal light, that is, the light of the rare earth element ions in the ground state This is a light propagation loss due to absorption. In order to reduce this light propagation loss, in the optical waveguide according to the present invention, it is preferable that the concentration distribution of the rare earth element ions contained in the core is close to the light intensity distribution in the core. For example, a concentration distribution in which the concentration is high in the center of the core in a direction perpendicular to the substrate surface and gradually decreases toward the upper and lower core / cladding interfaces is provided. At this time, the intensity distribution of the propagating light is generally a distribution that can be approximated to a Gaussian distribution having a maximum at the core center, and therefore the concentration distribution of rare earth element ions is also the central portion of the core in the longitudinal direction (thickness direction). It is preferable to use a distribution similar to a Gaussian distribution having a local maximum.

In the optical waveguide for an optical amplifier according to the present invention, the core has its supporting element ions from Sc, Y, and La in the group IIIA (group 3) element with respect to the rare earth element ions added to the base material. Choose from the group of This addition of the aid element ions is used to make the difference in refractive index between the core and the clad within an appropriate range, and at that time, the effect of reducing the emission intensity of photoluminescence from the rare earth element ions is exhibited. Yes. FIG. 4 shows a case where alumina (Al ₂ O ₃ ) is added as a material containing group IIIB (group 13) element ions to an Er ³⁺ ion-doped quartz (SiO ₂ ) film prepared by sputtering, and IIIA When a lanthanum oxide (La ₂ O ₃ ) is added as a material containing group (group 3) element ions, the relative refractive index difference Δ of the obtained mixed composition oxide film with respect to the quartz glass (SiO ₂ ) clad Shows the results of plotting the photoluminescence emission intensity of Er ³⁺ ions in the oxide film of the mixed composition. Even when lanthanum oxide (La ₂ O ₃ ) is added, the relative refractive index difference Δ is increased and the emission intensity is decreased, but the decrease when alumina (Al ₂ O ₃ ) is added is larger, at least, It can be seen that when the relative refractive index difference Δ is in the range of 2% to 10%, the decrease in emission intensity when lanthanum oxide (La ₂ O ₃ ) is added is significantly small.

As described above, in order to at least achieve the minimum value 2 mm (r ≧ 2 mm) of the radius of curvature r of the waveguide bend portion, in order to increase the relative refractive index difference Δ to be in the range of 2% or more, Among the group IIIA (group 3) elements, when increasing the addition ratio of an auxiliary element ion selected from the group consisting of Sc, Y, La, for example, La ³⁺ ions, as shown in FIG. As Δ increases, the photoluminescence emission intensity of Er ³⁺ ions decreases. Sc, Y, La, Ac among the group IIIA (group 3) elements based on the photoluminescence emission intensity of Er ³⁺ ions in quartz glass (SiO ₂ ) (corresponding to a relative refractive index difference Δ = 0%) When the relative refractive index difference Δ is increased to 15% by increasing the addition ratio of an auxiliary element ion selected from the group consisting of, for example, La ³⁺ ions, the emission intensity decreases to about 60%. In view of this point, in order to make the emission intensity decrease not to exceed 50%, among group IIIA (group 3) elements, auxiliary element ions selected from the group consisting of Sc, Y, La, for example, When increasing the addition ratio of La ³⁺ ions, the relative refractive index difference Δ of the quartz glass (SiO ₂ ) cladding with respect to the refractive index n _SiO2 (about 1.45) is at least 17% or less, usually 15% or less. It is desirable to keep it within a range, more preferably within 10% or less. Correspondingly, among the group IIIA (group 3) elements, the addition ratio of the ^auxiliary element ions selected from the group consisting of Sc, Y and La, for example, La ³⁺ ions, is defined as lanthanum oxide (La ₂ O ₃ ). However, it is desirable to keep at least 20 mol% or less, usually 18% or less, more preferably 10% or less.

In addition, when an optical waveguide is produced on a Si substrate, when Al (Al ₂ O ₃ ) or P (P ₂ O ₅ ) is added at a high ratio in quartz glass (SiO ₂ ) as a core base material. In addition, compressive (plus) strain stress is applied to the core layer, but when lanthanum oxide (La ₂ O ₃ ) is added, tensile (minus) strain stress is applied to the core layer. found. In the core layer formed on the Si substrate, for example, when 20 mol% of alumina (Al ₂ O ₃ ) is added to quartz glass (SiO ₂ ), the thickness is 1 micron and the stress is about 200 MPa. On the other hand, when 20 mol% of lanthanum oxide (La ₂ O ₃ ) was added to quartz glass (SiO ₂ ), the stress was about −200 MPa at a thickness of 1 micron. When a quartz clad film (lower clad) is formed on the Si substrate, the lower clad film itself is positively stressed against the Si substrate, and quartz glass (SiO ₂ ) is formed thereon. If a core film to which lanthanum oxide (La ₂ O ₃ ) is added is formed, the stress applied to the core can be alleviated as a whole. Regarding the relaxation effect of the stress applied to the core, not only lanthanum oxide (La ₂ O ₃ ) but also Sc, Y, and optionally used Ac among the Group IIIA (Group 3) elements. Since oxides (Sc ₂ O ₃ , Y ₂ O ₃ , Ac ₂ O ₃ ) have similar properties and functions, they can be suitably used in the same manner.

Furthermore, the rare earth element ions added to the core used as an optical amplification medium are, for example, Er ³⁺ ions for optical amplification in the 1.5 μm band, depending on the target amplification wavelength band, Ho ³⁺ ion, Tm ³⁺ ion, Yb ³⁺ ion, etc. Also, for light amplification in 1.3 μm band, Pr ³⁺ ion, Nd ³⁺ ion, etc. are co-added with these rare earth element ions Among the group IIIA (group 3) elements, the auxiliary element ions selected from the group consisting of Sc, Y, La, and Ac are all in the form of R ₂ O ₃ in quartz glass (SiO ₂ ). To be added. Moreover, the ionic radius etc. are also similar and take the same behavior in quartz glass (SiO ₂ ). For example, when rare earth element ions added to the core cause clustering, the rare earth element ions and these group IIIA (group 3) auxiliary element ions are incorporated into the generated clusters with almost equal probability. become. As a result, the ratio between the rare earth element ions and the IIIA (Group 3) auxiliary element ions contained in the generated cluster is equal to the ratio of the addition ratios. As a result, when the ratio of the addition ratio of rare earth element ions / addition ratio of IIIA (Group 3) auxiliary element ions is smaller than 1/4, the ratio of rare earth element ions adjacent to each other in the cluster is extremely high. Lower. Accordingly, when a plurality of added rare earth element ions, for example, Er ³⁺ ions, are present in a cluster, energy transfer is more likely to occur between adjacent Er ³⁺ ions. The reduction process will be greatly suppressed.

  That is, when the rare earth element ions and these group IIIA (group 3) auxiliary element ions are co-added, the ratio of the addition ratio of the rare earth element ions / group IIIA (group 3) auxiliary element ions is set to 1/4. Selecting a smaller value provides an effect of avoiding a substantial portion of the decrease in optical amplification efficiency caused by clustering. In particular, it is more preferable to select the ratio of the addition ratio of rare earth element ions / addition ratio of IIIA (Group 3) auxiliary element ions in the range of 1/4 to 1/27.

Incidentally, on the basis of the photoluminescence spectrum of the Er ³⁺ ions observed upon addition of the silica glass (SiO ₂₎ oxide Er ³⁺ ions in (Er ₂ O _3), C--band (1530～ 1565 nm) region, the wavelength band width (bandwidth) equal to or higher than half the peak intensity is 35 nm.
Er ³⁺ ions are added to quartz glass (SiO ₂ ) as oxides (Er ₂ O ₃ ), and La ³⁺ ions are added in the form of oxides (La ₂ O ₃ ) as 6 mol% as auxiliary element ions. Or when 10 mol% is added, when the wavelength band width (bandwidth) of half or more of the peak intensity is evaluated with respect to the C-band band (1530 to 1565 nm), 35 nm is maintained.
When Er ³⁺ ions are added as oxides (Er ₂ O ₃ ) to quartz glass (SiO ₂ ) and 7 mol% of phosphorus (P ₂ O ₅ ) is added as an auxiliary element ion, the C-band Regarding the band (1530 to 1565 nm) region, when the wavelength band width (bandwidth) of half or more of the peak intensity was evaluated, it was 24 nm, and the bandwidth was reduced.

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

(First embodiment)
FIG. 1 is a cross-sectional view schematically showing a configuration example of a planar optical waveguide in the first embodiment according to the present invention.

  The optical waveguide shown in FIG. 1 includes 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. The lower clad 2 and the upper clad 4 are formed using quartz glass, and the core 3 is a material having a refractive index higher than that of the quartz glass constituting the lower clad 2 and the upper clad 4 surrounding the core. It is formed with. Due to the refractive index difference Δn at the core / cladding interface, the laser light incident into the core from the end of the optical waveguide constitutes a planar optical waveguide guided through the core by refractive index guiding.

  In the form in which the light to be guided is a semiconductor laser beam in the 1.55 μm band, in such a wavelength band, silicon dioxide, which is a light transmitting oxide, in this case, quartz glass is used as a material constituting the cladding. Has been. The substrate 1 is a silicon substrate that does not exhibit optical transparency with respect to 1.55 μm band semiconductor laser light. The cross-sectional shape of the core 3 is selected to be a rectangle (square) of 4 μm in both the vertical thickness (T) and the horizontal width (W), and the lower cladding 2 and the upper cladding 4 both use an isotropic deposition method. Thus, the side surface of the core 3 is also uniformly coated with the upper clad 4. At this time, the deposition conditions (deposition time, etc.) are set so that the thicknesses of the lower cladding 2 and the upper cladding 4 are both 15 μm at the core / cladding interface parallel to the substrate 1.

A rare earth used as an optical amplifying medium in a rectangular core 3 extending in parallel with the upper surface of the substrate 1 and amplifying signal light propagating in the core 3 constituting a planar optical waveguide. For amplification of element ions, for example, 1.55 μm band semiconductor laser light, Er ³⁺ ions and the like are oxides (R ₂ O ₃ ; R represents a rare earth element) and the mother constituting the core 0.5 mol% is uniformly added to the material. The base material constituting the core 3 has a mixed composition in which La ³⁺ ions are uniformly added in the form of lanthanum oxide (La ₂ O ₃ ) to quartz glass (SiO ₂ ) as a main component. There is a relative refractive index difference Δ (≡ (≡ ()) of the refractive index n _core of the core 3 to the refractive index n _SiO2 (about 1.45) of the quartz glass (SiO ₂ ) clad in the wavelength region of the 1.55 μm band semiconductor laser light. n _core −n _{SiO 2} ) / n _core ) corresponds to 7%. That is, in a planar optical waveguide that can be used for an optical amplifier of a 1.55 μm band semiconductor laser light, the mixed composition oxide constituting the core 3 oxidizes Er ³⁺ ions in quartz glass (SiO ₂ ). 0.5 mol% as a product (Er ₂ O ₃ ), 8 mol% of La ³⁺ ion as lanthanum oxide (La ₂ O ₃ ) as a ^supporting element ion, and the composition added uniformly. Yes. Therefore, in this core, group IVB (group 14) element ions other than Si ⁴⁺ ions and group IIIB (group 13) element ions such as Al ³⁺ ions, which are contained as quartz glass (SiO ₂ ), are contained. Not included.

In the above embodiment, the relative refractive index of the refractive index n _core of the core 3 to the refractive index n _SiO2 (about 1.45) of the quartz glass (SiO ₂ ) clad in the wavelength region of 1.55 μm band semiconductor laser light. As the difference Δ (≡ (n _core −n _{SiO 2} ) / n _core ) is selected to be 7%, the addition ratio of La ³⁺ ions added as the auxiliary element ions is expressed as lanthanum oxide (La ₂ O ₃ ). The relative refractive index difference Δ of the refractive index n _core of the core 3 to the refractive index n _SiO2 (about 1.45) of the quartz glass (SiO ₂ ) clad in the wavelength region is It is also possible to design the optical waveguide by setting it in the range of 2% to 17%. Correspondingly, the addition ratio of La ³⁺ ions is 2 mol% to 2% as lanthanum oxide (La ₂ O ₃ ). It can also be selected in the range of 20 mol%. In general, the relative refractive index difference Δ between the core and the quartz glass (SiO ₂ ) clad in the wavelength region is 3% to about the refractive index n _SiO2 (about 1.45) of the quartz glass (SiO ₂ ) clad. It is desirable to design the optical waveguide by setting it in the range of 10%. Correspondingly, the addition ratio of La ³⁺ ions is in the range of 4 mol% to 10 mol% as lanthanum oxide (La ₂ O ₃ ). It is more desirable to choose.

In the first embodiment, when configuring a planar optical waveguide that can be used as an optical amplifier in the wavelength region of 1.55 μm band semiconductor laser light, high-power semiconductor laser light having a wavelength of 980 nm can be used as an excitation light source. As an optical amplifying medium, Er ³⁺ ions are added as oxides (Er ₂ O ₃ ) into the core, and as the core base material, quartz glass (SiO ₂ ) as a main material, La ³⁺ as an ^auxiliary element ion Although ions are mixed in the form of lanthanum oxide (La ₂ O ₃ ), Sc, Y, and Ac among the Group IIIA (Group 3) elements are used as the supporting element ions instead of La. A similar effect can be achieved.

In addition, instead of La, among the group IIIA (group 3) elements, Sc, Y, Ac are added as ^auxiliary ions, and Sc ³⁺ ions, Y ³⁺ ions, Ac ³⁺ ions are added, Each is added to the main quartz glass (SiO ₂ ) in the form of oxides (Sc ₂ O ₃ , Y ₂ O ₃ , Ac ₂ O ₃ ). The addition ratio can be selected in the range of 2 mol% to 20 mol% when Sc ³⁺ ions are added in the form of oxide (Sc ₂ O ₃ ), but the 1.55 μm band semiconductor laser The relative refractive index difference Δ between the core and the quartz glass (SiO ₂ ) clad in the wavelength region of light is 3% to 10% with respect to the refractive index n _SiO2 (about 1.45) of the quartz glass (SiO ₂ ) clad. It is desirable to design the optical waveguide by setting to the range of, and correspondingly, the addition ratio of Sc ³⁺ ions is more preferably selected in the range of 4 mol% to 10 mol% as Sc ₂ O _3. desirable. In addition, when adding Y ³⁺ ions in the form of oxide (Y ₂ O ₃ ), the addition ratio can be selected in the range of 2 mol% to 20 mol%. Desirably, the relative refractive index difference Δ between the core and the quartz glass (SiO ₂ ) clad in the wavelength region of the laser light is set in the range of 3% to 10% to design the optical waveguide. The addition ratio of Y ³⁺ ions is more preferably selected in the range of 4 mol% to 10 mol% as Y ₂ O ₃ . Alternatively, when Ac ³⁺ ions are added in the form of an oxide (Ac ₂ O ₃ ), the addition ratio can be selected from the range of 2 mol% to 20 mol%. The relative refractive index difference Δ between the core and the silica glass (SiO ₂ ) cladding in the wavelength region of the laser light is 3% to 10% with respect to the refractive index n _SiO2 (about 1.45) of the silica glass (SiO ₂ ) cladding. It is desirable to design the optical waveguide by setting it in the range of%, and correspondingly, the addition ratio of Ac ³⁺ ions may be selected in the range of 4 mol% to 10 mol% as Ac ₂ O _3. More desirable.

On the other hand, the lower clad and the upper clad are made of quartz glass (SiO ₂ ). Instead of quartz glass (SiO ₂ ), quartz added with B (B ₂ O ₅ ), P (P ₂ O ₅ ), or both is added. By using glass (SiO ₂ ), the relative refractive index difference Δ between the core and the clad is set in the range of 3% to 10% with respect to the refractive index n _CLAD of the oxide constituting the clad, and the optical waveguide It is also possible to design.

As described above, in the first embodiment, La ³⁺ ions as the ^auxiliary element ions are mixed in the form of lanthanum oxide (La ₂ O ₃ ) as the core matrix and the main quartz glass (SiO ₂ ). In the manufacturing process, an impurity element may be mixed depending on circumstances. In particular, as a light amplification medium, a group IIIB such as an Al ³⁺ ion, which is an element ion having an action of weakening photoluminescence emission from a rare earth element ion such as an Er ³⁺ ion, which is added to the core. (Group 13) Element ions and group IVB (Group 14) element ions that have the effect of narrowing the optical amplification band are preferably avoided if possible, but if they are mixed as impurities, In order not to weaken the photoluminescence emission from the added rare earth element ions, for example, Er ³⁺ ions, the total addition concentration of the group IIIB (group 13) element ions and the group IVB (group 14) element ions is The oxide is preferably in the range of 1 mol% or less. In general, the action of weakening the photoluminescence emission from rare earth element ions such as Er ³⁺ ions added in the core is derived from an increase in the non-radiative deactivation process from the excited state to the ground state. In other words, it is not preferable because it causes a reduction in the ratio (inversion distribution) remaining in the excited state involved in the optical amplification process, resulting in a decrease in gain in optical amplification.

The optical waveguide according to the first embodiment described above having a relative refractive index difference Δ of 7% can increase the optical gain per unit length, the waveguide length is 10 cm, and the excitation light wavelength is 980 nm. In the optical waveguide containing Al (Al ₂ O ₃ ) having the same relative refractive index difference Δ at a high ratio and containing the same concentration of Er ³⁺ ions under the condition of 200 mW, the amplification factor is 1 dB / cm. On the other hand, it was 1.8 dB / cm.

(Process for producing a planar optical waveguide according to the first embodiment)
With respect to a method of manufacturing the optical waveguide according to the first embodiment, the manufacturing process will be described below with reference to FIG.

  First, as shown in FIG. 5A, a quartz glass layer (silicon oxide layer) is formed as a lower clad 2 on a Si substrate 1 using a CVD method. Next, as shown in FIG. 5B, as a core layer, a quartz glass layer to which erbium and lanthanum are added in the form of oxides is formed by a CVD method. A resist pattern is formed on the core layer by photolithography, and the core layer is etched by dry etching using the resist pattern as an etching mask. As shown in FIG. 5C, a desired lateral width (W) is obtained. A core 3 having a rectangular cross section is formed. Next, as shown in FIG. 5D, a quartz glass layer (silicon oxide layer) is formed by CVD as an upper clad 4 so as to cover the core 3 to form a planar optical waveguide. .

  In the manufacturing process described above, the CVD method is used to form the quartz glass layer (silicon oxide layer) for the lower cladding 2 and the upper cladding 4 and the core layer, but isotropic deposition is achieved. In addition, as long as the composition of the obtained deposited film can be a desired composition, other film forming methods can be used. Examples of usable film forming methods include various isotropic deposition methods such as sputtering, low pressure CVD, atmospheric pressure CVD, and ion plating.

  In the deposition method using the above-described CVD method, erbium and lanthanum added to the core layer are introduced into the source gas containing erbium and the source gas containing lanthanum in the process of forming the silicon oxide layer from the silicon source. At the same time, the oxide is added as an oxide, and a uniform concentration distribution is achieved. For example, when silicon oxide, which is the main material of the core base material, is deposited from a quartz target using a sputtering method, erbium and lanthanum added to the core layer are also preliminarily formed of erbium oxide or oxide. After the lanthanum oxide is formed, it can be added and deposited using a sputtering method.

(Second embodiment)
Hereinafter, a second embodiment according to the present invention will be described in detail with reference to the drawings.

The basic configuration of the planar optical waveguide according to the second embodiment of the present invention is almost the same as that of the first embodiment shown in FIG. The concentration distribution is not uniform, and the additive concentration in the vertical direction has a maximum at the center of the core, and the additive concentration decreases toward the interface between the lower cladding 2 and the upper cladding 4 positioned above and below the core. Is provided. On the other hand, the concentration of La ³⁺ ions added simultaneously in the form of lanthanum oxide (La ₂ O ₃ ) in the core is set to a uniform concentration in the longitudinal direction of the core. The structure of other parts is the same as that of the optical waveguide of the first embodiment.

As rare earth element ions, for example, Er ³⁺ ions in the direction perpendicular to the substrate surface (longitudinal direction), the addition concentration of the central portion of the core is 0.5 mol% as an oxide (Er ₂ O ₃ ), Decrease gradually toward the upper and lower interface direction. It is effective to select the distribution of the Er ³⁺ ion addition concentration to a distribution similar to the in-core light intensity distribution of the excitation light incident from the core end face for optical amplification. The in-core light intensity distribution of the excitation light incident from the end face of the core shows a distribution close to a Gaussian distribution showing a maximum at the center of the core. In this second embodiment, the addition concentration of Er ³⁺ ions The vertical distribution of was selected to be close to the Gaussian distribution. In the direction parallel to the substrate surface of the core, no distribution is provided in the Er ³⁺ ion addition concentration, and the concentration is uniform in the lateral width direction.

In the planar optical waveguide in the second embodiment, the Gaussian distribution type light intensity distribution in the core of the excitation light incident from the end face of the core, and the vertical distribution of the Er ³⁺ ion addition concentration in the core As a result, the ratio of Er ³⁺ ions in the excited state by the excitation light is larger than that in the case where the addition concentration of Er ³⁺ ions in the core is uniform. Reduction of light propagation loss due to light absorption of Er ³⁺ ions in the state is attempted.

(Process for producing a planar optical waveguide according to the second embodiment)
With respect to a method of manufacturing the optical waveguide according to the second embodiment, the manufacturing process will be described below with reference to FIG.

The optical waveguide manufacturing process according to the second embodiment is the same as the optical waveguide manufacturing process according to the first embodiment described above, except for the core layer manufacturing process for forming the core. Are the same. That is, in the core layer deposition step shown in FIG. 5B, the Er ³⁺ ion addition concentration is adjusted to a target distribution in the deposition thickness direction (vertical thickness direction).

When the core layer is formed using the CVD method, erbium and lanthanum added to the core layer are formed in the process of forming the silicon oxide layer from the silicon-containing source gas, erbium-containing source gas, lanthanum. At the same time, the supply ratio of the source gas containing erbium / the source gas containing silicon is set to a small value at the start of the core layer film formation, and is gradually added as an oxide. And after a half of the core layer deposition time has elapsed, it is gradually decreased. In this way, by controlling the supply ratio of the source gas containing erbium / the source gas containing silicon in accordance with the intended concentration distribution of addition, Er ³⁺ ions in the film thickness direction (longitudinal direction) of the resulting core layer are controlled. An additive concentration distribution is formed. The supply ratio of the source gas containing lanthanum / the source gas containing silicon is kept constant, so that the concentration of La ³⁺ ions added in the form of lanthanum oxide (La ₂ O ₃ ) is substantially equal to the core. The density is uniform in the vertical direction of the layer.

  Also in the manufacturing process of the optical waveguide according to the second embodiment, the CVD method is used for forming the quartz glass layer (silicon oxide layer) for the lower cladding 2 and the upper cladding 4 and the core layer. However, other film forming methods can be used as long as isotropic deposition is achieved and the composition of the obtained deposited film can be a desired composition. Examples of the film forming method that can be used include various isotropic deposition methods such as a sputtering method, a low pressure CVD method, an atmospheric pressure CVD method, and an ion plating method.

  An optical waveguide having a planar core / cladding waveguide shape according to the present invention is mainly used for amplifying a laser light intensity in a 1.55 μm band in an optical communication network device constituted by an optical fiber transmission line. It can be used as an optical amplifier.

It is sectional drawing which shows typically the structural example of the planar optical waveguide concerning embodiment of this invention. The photoluminescence emission intensity from Er ³⁺ ions contained in the core base material used for the planar optical waveguide is that of alumina (Al ₂ O ₃ ) with respect to quartz glass (SiO ₂ ) in the core base material. It is a figure which shows an example of the result of having evaluated the dependence with respect to an addition ratio. Is used in planar optical waveguides, a silica glass (SiO ₂₎ refractive index n _SiO2 (about 1.45) of the cladding, the core base material for quartz glass (SiO _2), lanthanum oxide (La ₂ O ₃ ) or alumina (Al ₂ O ₃ ) added core base material refractive index n _core , quartz glass (SiO ₂ ) clad refractive index n _SiO2 (about 1.45) relative refractive index difference Δ (≡ ( of _{n core -n SiO2) / n core} ), it is a diagram showing a dependency on the addition ratio of lanthanum oxide (La ₂ O ₃₎ or alumina (Al ₂ O ₃₎ (mol%). Quartz glass (SiO ₂ ), lanthanum oxide (La ₂ O ₃ ) or alumina (photoluminescence emission intensity from Er ³⁺ ions contained in the core base material, which is used in the planar optical waveguide, is used. Results of evaluating the dependence on the relative refractive index difference Δ between the refractive index n _core of the _core base material added with Al ₂ O ₃ ) and the refractive index n _SiO2 (about 1.45) of the quartz glass (SiO ₂ ) clad It is a figure which shows an example. It is a figure which illustrates the process of manufacturing the planar optical waveguide in embodiment concerning this invention.

Explanation of symbols

1 Substrate 2 Lower clad 3 Core 4 Upper clad

Claims (10)

An optical waveguide capable of guiding light having a wavelength included in a specific wavelength band,
The optical waveguide includes a flat substrate,
A planar optical waveguide comprising at least a clad provided on the substrate and a core disposed in the clad;
The clad is composed of an oxide exhibiting light transmittance at a wavelength included in the specific wavelength band,
In the core, the rare earth element ion having a transition state capable of inductive light emission is added in the form of an oxide at least at a wavelength included in the specific wavelength band with respect to the oxide constituting the cladding. Furthermore, in addition to the rare earth element ion, as a supporting element ion, one of element ions selected from the group consisting of Sc, Y, and La among group IIIA elements is added in the form of an oxide. Composed of oxides,
At least at the core / cladding interface where the core and the clad contact each other, the refractive index of the mixed composition oxide constituting the core at the wavelength included in the specific wavelength band is the refractive index of the oxide constituting the clad. An optical waveguide characterized in that the additive element ion addition rate in the core is selected so as to exhibit a refractive index higher by 1% to 20%. The addition ratio of the promoting element ions in the oxide having the mixed composition constituting the core is selected in the range of 2 mol% or more and 20 mol% or less as the oxide. The optical waveguide according to 1. The oxide of the mixed composition constituting the core may further contain a small amount of group IIIB element ions or group IVB element ions other than silicon ions,
2. The trace amount of group IIIB element ions or group IVB element ions other than silicon ions are oxides, and the total content thereof is limited to a range of 1 mol% or less. 2. The optical waveguide according to 2. The optical waveguide according to any one of claims 1 to 3, wherein the oxide constituting the cladding is silicon dioxide. The oxide constituting the cladding is quartz glass,
The mixed composition oxide constituting the core is a mixed composition glass obtained by adding the rare earth element ions and the auxiliary element ions in the form of an oxide to the quartz glass. The optical waveguide as described in any one of 1-4. The core disposed in the cladding is
In the core cross section in the direction perpendicular to the substrate surface, the additive element ion concentration added in the core is at least from the center of the core toward the core / cladding interface in the perpendicular direction. The optical waveguide according to claim 1, wherein the optical waveguide has a uniform distribution. The core disposed in the cladding is
In the core cross section in the direction perpendicular to the substrate surface, the additive concentration of the rare earth element ions added in the core is at least from the center of the core toward the core / cladding interface in the perpendicular direction. The optical waveguide according to any one of claims 1 to 6, wherein the optical waveguide has a uniform distribution. The core disposed in the cladding is
In the core cross section in the direction perpendicular to the substrate surface, the addition concentration of the rare earth element ions added in the core gradually increases from the center of the core toward the core / cladding interface in the perpendicular direction. The optical waveguide according to any one of claims 1 to 6, wherein the optical waveguide has a distribution that decreases rapidly. The core disposed in the cladding is
In the core cross section in a direction perpendicular to the substrate surface, the addition concentration of the rare earth element ions added in the core has a distribution close to a Gaussian distribution having a maximum at the center of the core, The optical waveguide according to claim 8. A method of manufacturing an optical waveguide capable of guiding light having a wavelength included in a specific wavelength band,
The optical waveguide includes a flat substrate,
A lower clad provided on the substrate;
A core having a rectangular cross-sectional shape provided on the lower clad and patterned into a predetermined plane pattern shape;
The lower clad upper surface, and the upper clad formed in a form covering the side surface and upper surface of the core subjected to patterning,
At least, it has a form of a planar optical waveguide composed of a core disposed in a clad composed of a lower clad and an upper clad,
The lower clad and the upper clad are made of an oxide exhibiting optical transparency at a wavelength included in the specific wavelength band,
The core is added to the oxide constituting the clad, in the form of an oxide, a rare earth element ion having a transition state capable of inductive light emission at least at a wavelength included in the specific wavelength band, Furthermore, in addition to the rare earth element ion, as a supporting element ion, one of element ions selected from the group consisting of Sc, Y, and La among group IIIA elements is added in the form of an oxide. Composed of oxides,
At least at the wavelength included in the specific wavelength band at the core / upper clad upper interface and the side interface where the core upper surface and the upper clad are in contact, and at the core / lower clad lower interface where the core lower surface and the lower clad are in contact, The refractive index of the mixed composition oxide constituting the core is 1% to 20% higher than the refractive index of the oxide constituting the cladding. Having a selected structure,
The method of manufacturing the optical waveguide is as follows:
A lower clad film forming step of forming an oxide layer having a predetermined thickness on the substrate at a wavelength included in the specific wavelength band constituting the lower clad;
A rare earth element ion having a transition state capable of inductively emitting light at least at a wavelength included in the specific wavelength band with respect to the oxide constituting the clad and constituting the core on the lower clad film. Is added in the form of an oxide, and in addition to the rare earth element ion, one of the element ions selected from the group consisting of Sc, Y, and La among the group IIIA elements is an oxide of the group IIIA element. A mixed composition oxide constituting the core layer at a wavelength included in the specific wavelength band in the core layer at least in a core layer having a predetermined thickness made of an oxide having a mixed composition added in a form The refractive index of the auxiliary element ions in the core layer thickness direction is such that the refractive index is 1% to 20% higher than the refractive index of the oxide constituting the cladding. A core layer forming step of forming on-option has been that structure,
A resist mask forming step of forming a resist pattern of the predetermined plane pattern shape on the surface of the core layer by photolithography;
Using the resist mask as an etching mask, the core layer is etched by a dry etching method to form a core having a rectangular cross-sectional shape and patterned into the predetermined planar pattern shape Process,
An oxide layer exhibiting optical transparency at a wavelength included in the specific wavelength band constituting the upper clad, in a form covering the upper surface of the lower clad and the side surface and upper surface of the patterned core. Including an upper clad film forming step for forming a predetermined film thickness,
An optical waveguide manufacturing method characterized by the above.

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