JPH0677578A - Optical amplifier and manufacture thereof - Google Patents

Abstract

PURPOSE:To make it possible to lessen the connection loss of an optical amplifier with an optical fiber and a bending loss of the amplifier. CONSTITUTION:An optical amplifier is manufactured into a constitution, wherein a core 5, which consists of Al2O3 and has a rectangular section, is formed on a substrate 1 and at the same time, a rare earth element, such as Pr, Nd, Yb, Ho, Er, Tm and La, a transition metal, such as Cr and Ti, or an element for optical amplification use, which is these mixture, is added to the interior of the core 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical amplifier which is suitable for the fields of communication, measurement and information processing, and which constitutes a small-sized and multifunctional optical integrated circuit, and a method of manufacturing the same.

[0002]

2. Description of the Related Art In the fields of communication, measurement and information processing,
In order to use light in a higher degree, researches on optical integrated circuits having various functions are being actively conducted. An optical amplifier is one of the basic elements constituting such an optical integrated circuit. So far, the light amplification effect has been confirmed using the phosphate glass LHG5 doped with 3 wt% of Nd (H. Aok
i, O.Maruyama, Y.Asahara: Topical meeting on glasses
for optoelectronics. Extended abstracts, p69, Dec.
1, (1989)). This manufacturing method is as follows. First Nd
Ti is vapor-deposited on the surface of a phosphate glass LHG5 doped with 3 wt% of Al, an optical waveguide mask pattern is provided by the photolithography method, and Ag is vapor-deposited. Next, a voltage is applied for several hours in an electric furnace at about 400 ° C. to diffuse Ag ions through the gap between the Ti films into the glass to form a channel type optical waveguide having a semicircular cross section. An amplifier function has been confirmed by using a laser diode with a wavelength of 802 nm as a light source for excitation in this optical waveguide.

[0003]

By the way, in the optical amplification using the above-mentioned phosphate glass, since the cross section of the optical waveguide has a semicircular asymmetric structure, a large coupling loss occurs when connecting with an optical fiber. With. In addition, in an optical amplifier with bending, such as a loop ring laser, it is necessary to suppress increase in loss due to bending as much as possible. That is, the refractive index difference (Δ
It is important that n) is large. By increasing Δn, the light is strongly confined in the core, and the loss is small even if the optical waveguide is bent with a small curvature, and as a result, the element size can be reduced. In the above-mentioned conventional example, A
Although the refractive index is made higher than that of the peripheral portion by diffusing g ions, Δn cannot be essentially increased.

The object of the present invention is to solve the above problems.
An object of the present invention is to provide an optical amplifier having a small connection loss with an optical fiber and a bending loss, and a manufacturing method thereof.

[0005]

In order to achieve the above-mentioned object, one embodiment of the present invention is to form a core having a rectangular cross section made of Al ₂ O ₃ on a substrate and to form the core in the core. , A rare earth element such as Pr, Nd, Yb, Ho, Er, Tm, and La, a transition metal such as Cr and Ti, or a light amplification element which is a mixture thereof is added.

In another aspect, a part of the Al film formed on the substrate is removed to form an optical waveguide pattern having a rectangular cross section, which is converted into an oxide by anodic oxidation to form a core, Pr, Nd, Yb, Ho, Er, T
A rare earth element such as m or La, a transition metal such as Cr or Ti, or a light amplification element which is a mixture thereof is added.

In another embodiment, an Al film is formed on a substrate, a part of the Al film is removed to form an optical waveguide pattern having a rectangular cross section, and the optical waveguide pattern is converted into an oxide by anodic oxidation. It is impregnated with an alcohol solution containing an element.

In another embodiment, a core having a rectangular cross section made of Al ₂ O ₃ is formed on a substrate, and A is formed in the core.
A refractive index control element, which is a material having a lower refractive index than l ₂ O _3, and a rare earth element such as Pr, Nd, Yb, Ho, Er, Tm, La, or a transition metal such as Cr or Ti, or a mixture thereof. A certain light amplification element is added.

In another embodiment, a refractive index control element, which is a material having a lower refractive index after oxidation than an oxide of Al, and Pr, Nd, Yb, Ho, Er, Tm, La, etc. are formed on a substrate. An Al film added with a rare earth element or a transition metal such as Cr or Ti or a light amplification element which is a mixture thereof is formed, and a part of the Al film is removed to form an optical waveguide pattern having a rectangular cross section. Is converted into an oxide by anodic oxidation to form a core. The refractive index controlling element is S
It is preferably an element of i, B, Mg, P, Pb or a mixture thereof.

In another embodiment, a refraction index controlling element, a light amplifying element and Al are simultaneously vapor-deposited from different evaporation sources to form an Al film, a part of which is removed to obtain a rectangular cross section. A shaped optical waveguide pattern is formed and converted into an oxide by anodic oxidation.

Further, it is desirable that the substrate has a lower refractive index than the core, or that the surface of the substrate is covered with a layer having a lower refractive index than the core. Further, it is desirable that the substrate is made of a material having a lower refractive index than the oxide of Al, or the surface of the substrate is previously covered with a layer having a lower refractive index than the oxide of Al.

[0012]

Since the core, which is a light propagation region, is formed in a rectangular cross section and has a symmetrical cross section, the connection loss with the optical fiber is reduced. Al ₂ O ₃ is transparent over a wide wavelength range from the visible region to the mid-infrared region, and its refractive index is 1.75 near a wavelength of 1.3 μm, and the refractive index of SiO ₂ used as a material for the cladding region is 1.45. Big enough. For this reason, the refractive index difference (Δn) between the core through which the light propagates and the clad around it becomes large, so that the bending loss becomes small, and it can be applied to those with bending such as a ring laser. An optical amplifier capable of amplifying light of various wavelengths can be obtained by adding the use element.

When an Al ₂ O ₃ film is directly formed on a substrate and is subjected to three-dimensional patterning, the film forming speed is much slower than that of Al, and the costly film forming,
Although a microfabrication device is required, since an Al film is formed on a substrate by a vapor deposition method or a dipping method, and this is patterned and then converted into Al ₂ O ₃ , the Al film is different from the case of the Al ₂ O ₃ film. In addition to being formed quickly, the film can be formed into a transparent oxide film in a short time by anodic oxidation.
In the case of Al only, Al at a speed of about 1 μm / min
Conversion to ₂ O ₃ is possible. Therefore, it becomes possible to easily manufacture the Al ₂ O ₃ waveguide containing the optical amplifying element and the like with an inexpensive device.

Further, the Al film formed on the substrate is converted into an oxide by anodic oxidation, and then impregnated with an alcohol solution containing an element for optical amplification to obtain Al ₂ O ₃ obtained by anodic oxidation. Since the film is porous, the dopant can be added almost uniformly from the surface to the deep position with ease and control.

Furthermore, the optical amplification element, the refractive index control element, and Al are simultaneously vapor-deposited from different evaporation sources to form an Al film, thereby forming the optical amplification element or the refractive control element Al. The concentration added to the film can be easily controlled.

[0016]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a process chart of a method of manufacturing an optical amplifier according to an embodiment of the present invention.

First, on the SiO ₂ substrate 1 shown in FIG.
The Al film 2 is formed by the electron beam evaporation method as shown in FIG. The film thickness was 10 μm. The Al film 2 can be formed by a vacuum vapor deposition method such as electron beam vapor deposition, a sputtering method, or a direct immersion in an Al solution.

Next, as shown in (c), a portion of the Al film 2 formed on the substrate 1 is removed by photolithography to pattern a waveguide of 10 μm × 10 μm, and an Al rectangle is formed by etching. Form part 3. The Al film is
For example, etching can be easily performed with caustic soda and phosphoric acid, but a dry process using an etching gas of BCl ₃ or CCl ₄ may be used. Wet etching is advantageous in that it does not require expensive equipment, and dry etching is excellent in accurately forming a waveguide pattern.

Next, as shown in (d), the rectangular portion 3 of Al is rectangular portion 4 of oxide (Al ₂ O ₃ ) by anodization.
Convert to. Anodization is a method in which Al of a substrate immersed in an electrolytic solution such as sulfuric acid is used as an anode and a carbon plate or a platinum plate is used as a cathode to apply a voltage to convert the surface into Al ₂ O ₃ . In this embodiment, the electrolytic solution has a liquid temperature of 20 ° C. and a concentration of 20.
% Sulfuric acid and a platinum plate was used as the cathode. When the current density was 30 mA / cm ² , the Al rectangular portion 3 was oxidized at a rate of about 45 μm / h and converted into a transparent oxide rectangular portion 4.

Next, as shown in (e), the substrate 1 on which the rectangular portion 4 (waveguide) of Al ₂ O ₃ is formed is impregnated with an alcohol solution containing Er, which is an element that provides a light amplification effect. Then, Er ions are doped. In the present embodiment, Er was used as an element that brings about a light amplification effect, but other than this, rare earth elements such as Pr, Nd, Yb, Ho, Tm, etc. are not limited to one element by substantially the same method. It is possible to easily dope several kinds of elements simultaneously. Also, Al ₂ O doped with a transition metal such as Cr or Ti
₃ is known as a ruby or sapphire laser, and these materials can also be applied to the present invention.

After the dope is sufficiently dried, 1300 to 1500
Heat treatment is performed in an atmosphere of O ₂ and He-Cl at 0 ° C. O ₂
The heat treatment in the atmosphere aims to completely oxidize the residual Al, and the heat treatment in the He—Cl atmosphere aims to remove water. As a result, Al ₂ O ₃ becomes a dense film (core) 5 and the scattering loss can be made sufficiently small.

Finally, as shown in (f), on the Er-doped Al ₂ O ₃ (core 5), S as a clad is formed.
The iO ₂ layer 6 is formed. The SiO ₂ layer 6 is formed by a flame deposition method, a CVD method, or the like. This makes A
It is possible to obtain a stable optical waveguide which is hardly affected by the roughness of the side surface of the core (rectangular portion) 5 containing l ₂ O ₃ as a main component or the external environment. The SiO ₂ clad layer 6 may be added with any dopant for adjusting the refractive index or stress.
Although the glass substrate of SiO ₂ is used as the substrate, it is effective when integrating other elements such as a light source and a light receiving element in an optical integrated circuit, and the Si substrate is easily oxidized by thermal oxidation on its surface. _{Since two} films can be formed, it is also possible to form a waveguide for an optical amplifier on the SiO ₂ film by using the same process as described above.

FIG. 2 is a process chart of a method of manufacturing an optical amplifier according to another embodiment of the present invention.

First, as shown in FIG.
A low refractive index layer 11 containing SiO ₂ as a main component is formed thereon by thermal oxidation or the like. On the Si substrate 10, as shown in (b), an Al film 12 added with Er, which is an element that causes a light amplification effect, and Si, which is an element for controlling the refractive index, is formed by an electron beam evaporation method. To do. Film thickness is 10μ
m. Here, the film formation by electron beam evaporation is
1 tablet, an Er tablet that is an element for light amplification, and a Si tablet that is an element for controlling the refractive index were evaporated from different evaporation sources. By this method, it was possible to control the concentration of Er, which is an element that causes a light amplifying action in Al, and the concentration of Si, which is an element for controlling the refractive index, with good controllability. The method of forming the Al film to which an element that causes a light amplification effect and an element that controls the refractive index is added is not limited to high vacuum evaporation such as electron beam evaporation, and a sputtering method may be used. When using the sputtering method,
A film can be formed by co-sputtering or cross-sputtering by attaching an Al target and a target of an element that provides a light amplifying action or a target of an element for controlling the refractive index to the two cathodes. It is also possible to form the film by a single sputtering using a target in which a desired amount of an element that causes a light amplification effect to Al and an element that controls the refractive index is mixed. In addition, as an element that brings about the light amplification effect, E
r was used, but other than this, Pr, Nd, Yb, Ho, T
A rare earth element such as m or Ka can be easily doped by the same method, and an element that promotes the amplification effect of light can be easily doped by the same method. In addition to Si, the elements for controlling the refractive index include B and Mg.
Can be used. In addition, Cr and Ti
Al ₂ O ₃ doped with a transition metal such as is known as a ruby or sapphire laser, and these materials are also applicable to the present invention. Furthermore, of these, two or more kinds of elements can be used as a dopant.

Next, as shown in (c), a part of the film 12 formed by the above method is removed by photolithography to pattern the waveguide, and the rectangular portion 13 of Al is etched. Form. The size of the waveguide (core) at this time is, considering the coupling with the optical fiber,
The size was 10 μm × 10 μm. The Al film is, for example, caustic soda,
Can be easily etched with phosphoric acid, but BC
A dry process using an etching gas such as l ₃ or CCl ₄ may be used. Wet etching is advantageous in that it does not require expensive equipment, and dry etching is
It is excellent for accurately forming a waveguide pattern. However, when the ratio of Er and Si in Al is high, etching roughness and the like occur. Therefore, the concentration in the Al film is preferably 10 mol% or less.

Next, as shown in (d), the rectangular portion 13 of Al is converted into a rectangular portion (core) 14 of oxide (Al ₂ O ₃ ) by an anodic oxidation method. The anodic oxidation is a method of converting the surface into Al ₂ O ₃ by applying a voltage with Al or the like of a substrate immersed in an electrolytic solution such as sulfuric acid as an anode and a carbon plate or a platinum plate as a cathode. In this example, the rectangular portion 13 of Al containing Er was used as an anode and the platinum plate was used as a cathode, and anodization was carried out in sulfuric acid having a liquid temperature of 20 ° C. and a concentration of 20% as an electrolytic solution. As a result, when the current density is 30 mA / cm ² , it is about 45 μm.
The rectangular portion 13 of Al to which Er was added was oxidized at a rate of / h and converted into a rectangular portion 14 of transparent oxide.

Finally, as shown in (e), the rectangular portion 14 which is the anodized oxide ridge portion is covered with the SiO ₂ clad layer 15 by the flame deposition method or the CVD method to form a waveguide. By this, the roughness of the side surface of the rectangular portion 14,
Alternatively, a stable optical waveguide that is not easily affected by the external environment is obtained. Some kind of dopant may be added to the SiO ₂ clad layer 15 in order to adjust the refractive index or stress.
As the substrate, Si having a low refractive index layer containing SiO ₂ as a main component was used. This is effective when integrating other elements such as a light source and a light receiving element in the optical integrated circuit. Even if SiO ₂ is used as the substrate, it is possible to form a waveguide for an optical amplifier by using the same process.

The optical amplifier is manufactured as described above, and the cores 5 and 14 which are light propagation regions on the substrates 1 and 10 are manufactured.
Is formed to have a rectangular cross section and has a symmetrical cross section, and since the periphery is covered with the SiO ₂ layers 6 and 15 which are uniform media, the connection loss with the optical fiber is reduced. Moreover, since the cores 5 and 14 are doped with the optical amplification element, it is possible to amplify light of various wavelengths. Furthermore, Al ₂ O ₃ is transparent over a wide wavelength range from the visible to the mid-infrared region, and its refractive index is 1.75 at a wavelength of around 1.3 μm, and the refractive index of SiO ₂ used as a cladding material is 1.45. Is also big enough. As a result, the refractive index difference (Δn) between the cores 5 and 14 through which light propagates and the clads 6 and 15 around them increases,
Bending loss is reduced. As a result, it is possible to obtain an optical amplifier that can be applied to a bending laser such as a ring laser and that can amplify light of various wavelengths.

When an Al ₂ O ₃ film is directly formed on a substrate and is subjected to three-dimensional patterning, the film forming speed is much slower than that of Al, and the expensive film forming,
Although a microfabrication device is required, Al films 2 and 12 are formed on the substrates 1 and 10 and patterned, and then Al is formed.
_Since the Al films 2 and 12 are converted into ₂ O ₃ , the film forming speed is faster than that in the case where the Al ₂ O ₃ film is directly formed on the substrate, and the film is a transparent oxide film in a short time by anodic oxidation. Can be Therefore, it is possible to dope various optical waveguides (cores 5 and 14) with an element that exerts a light amplifying effect and an element that controls the refractive index with an efficient and inexpensive device.

Furthermore, after converting the Al film 3 on the substrate 1 into an oxide by anodic oxidation, and impregnating this with an alcohol solution containing an element for light amplification, it is possible to control easily and well from the surface to a deep position. It is possible to add the dopant uniformly. That is, Al ₂ directly on the substrate
When the O ₃ film is formed, the Al ₂ O ₃ film becomes dense and the dopant cannot be uniformly added at a deep position from the surface in the film. On the other hand, the Al ₂ O ₃ film (rectangular part 4) obtained by anodic oxidation is porous and has micropores called pores of several tens to several hundred angstroms perpendicular to the substrate 1. Therefore, by utilizing the fine pores, the dopant can be added almost uniformly from the surface to the deep position with good control.

Furthermore, the optical amplification element, the refractive index control element and Al are simultaneously vapor-deposited from different evaporation sources to form the Al film 12, whereby the optical amplification element or the refraction control element is formed. The concentration added to the Al film 12 can be easily controlled. Therefore, the optical amplification element and the refractive index control element are uniformly distributed in the Al ₂ O ₃ optical waveguide (core 14).
Can be added in. Further, amplification of light of various wavelengths and refractive index can be arbitrarily controlled by changing the kind of dopant.

Therefore, it is possible to obtain an optical amplifier which can efficiently and inexpensively dope the optical waveguide (cores 5 and 14) with an element or the like which has a function of amplifying light and which has a small connection loss with an optical fiber and a small bending loss. Will be done.

[0034]

As described above, according to the present invention, the following effects are exhibited.

(1) An optical amplifier which has a small bending loss and can be applied to a bending type such as a ring laser and which is doped with an element for optical amplification can be obtained.

(2) An Al ₂ O ₃ waveguide containing an optical amplification element or the like can be easily manufactured with an inexpensive device.

(3) The Al film formed on the substrate is converted into an oxide by anodic oxidation, and then an element for optical amplification is added to this to easily and well controllably and substantially uniformly from the surface to the deep position. Further, a light amplification element can be added to the Al ₂ O ₃ film.

(4) An optical amplification element, a refractive index control element and Al are simultaneously vapor-deposited from different evaporation sources to form Al.
By forming the film, it is possible to control the addition of the light amplification element and the refractive index control element into the Al ₂ O ₃ optical waveguide, and it is possible to arbitrarily control the light amplification and the refractive index. .

[Brief description of drawings]

FIG. 1 is a process drawing showing an embodiment of the present invention.

FIG. 2 is a process drawing showing another embodiment of the present invention.

[Explanation of symbols]

 1 substrate 5 cores

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location H01S 3/07 8934-4M 3/10 Z 8934-4M (72) Inventor Akifumi Hongo Tsuchiura City, Ibaraki Prefecture 3550 Kita Yomachi, Hitachi Cable Advanced Research Center (72) Inventor Katsuyuki Imoto 3550, Kida Yomachi, Tsuchiura City, Ibaraki Hitachi Cable Advanced Research Center

Claims (9)

[Claims] 1. A core having a rectangular cross section made of Al ₂ O ₃ is formed on a substrate, and Pr, Nd,
An optical amplifier comprising a rare earth element such as Yb, Ho, Er, Tm and La, a transition metal such as Cr and Ti, or an optical amplification element which is a mixture thereof. 2. A portion of the Al film formed on the substrate is removed to form an optical waveguide pattern having a rectangular cross section, which is converted into an oxide by anodic oxidation to form a core. An optical amplifier, wherein a rare earth element such as Pr, Nd, Yb, Ho, Er, Tm, La, etc., a transition metal such as Cr, Ti, etc., or an optical amplification element which is a mixture thereof is added. 3. An Al film is formed on a substrate, a part of the Al film is removed to form an optical waveguide pattern having a rectangular cross section, and the optical waveguide pattern is converted into an oxide by anodic oxidation. A method for manufacturing an optical amplifier, which comprises impregnating with an alcohol solution. 4. A core having a rectangular cross section made of Al ₂ O ₃ is formed on a substrate, and a refractive index control element which is a material having a refractive index lower than that of Al ₂ O ₃ is formed in the core. P
An optical amplifier, wherein a rare earth element such as r, Nd, Yb, Ho, Er, Tm, La, or a transition metal such as Cr or Ti, or an optical amplification element which is a mixture thereof is added. 5. A refractive index control element, which is a material having a lower refractive index after oxidation than an oxide of Al, and Pr, N on a substrate.
An Al film to which a rare earth element such as d, Yb, Ho, Er, Tm, La or the like or a transition metal such as Cr or Ti or a light amplification element which is a mixture thereof is added is formed, and a part thereof is removed. An optical amplifier characterized in that a core is formed by forming an optical waveguide pattern having a rectangular cross section and converting it into an oxide by anodic oxidation. 6. The element for controlling the refractive index is Si, B, M
5. An element of g, P, Pb or a mixture thereof.
Alternatively, the optical amplifier according to item 5. 7. An optical film having a rectangular cross section is formed by simultaneously vapor-depositing a refractive index control element, a light amplification element and Al from different evaporation sources on a substrate to form an Al film. A method for manufacturing an optical amplifier, which comprises forming a waveguide pattern and converting it into an oxide by anodic oxidation. 8. The method according to claim 1, wherein the substrate has a lower refractive index than the core, or the surface of the substrate is covered with a layer having a lower refractive index than the core. Optical amplifier. 9. The method according to claim 3, wherein the substrate is made of a material having a lower refractive index than the Al oxide, or the surface of the substrate is previously covered with a layer having a lower refractive index than the Al oxide. 7. The method for manufacturing an optical amplifier according to 7.