JP2003270404A - Antireflection film and optical parts using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an antireflection film which gives low reflectance in a wide band and which can be easily formed at a low cost and to provide optical parts using the antireflection film, relating to an antireflection film formed on the surface of a Bi substituted rare earth iron garnet material to be used for a Faraday rotator and to optical parts using the antireflection film. <P>SOLUTION: The antireflection film is obtained by successively depositing a first Ta<SB>2</SB>O<SB>5</SB>layer satisfying 0.17≤nd/λ≤0.8, a first SiO<SB>2</SB>layer satisfying 0.02≤nd/λ≤0.54, a second Ta<SB>2</SB>O<SB>5</SB>layer satisfying 0.16≤nd/λ≤0.38 and a second SiO<SB>2</SB>layer satisfying 0.20≤nd/λ≤0.29 on a substrate, wherein λ is the wavelength of transmitted light, n is the refractive index of each layer and d is the film thickness of each layer. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an antireflection film formed on the surface of a Bi-substituted rare earth iron garnet material used for a Faraday rotator and an optical component using the antireflection film.

[0002]

2. Description of the Related Art An antireflection film is an optical thin film formed on a light incident surface and an emission surface of an optical component for the purpose of preventing reflection of light generated at an interface where a substance having a different refractive index contacts an optical component. .

In various optical components used in optical communication systems, an antireflection film is formed on the interface through which light is transmitted to reduce the return light due to reflection. Even in the Faraday rotator used for optical isolators and optical attenuators, which are passive components for optical communication,
An antireflection film is formed on both sides of the light incidence / emission to be incorporated in the device. The antireflection film of the Faraday rotator is formed at the interface between the magnetic garnet, which is a constituent material of the Faraday rotator, and air, or the interface between the magnetic garnet and the epoxy resin. Epoxy resin is used for bonding the Faraday rotator and other optical components, and the light is transmitted to the bonding surface.

These antireflection films are disclosed in JP-A-4-230.
As disclosed in Japanese Patent No. 701, it is generally composed of a plurality of thin films of materials having different refractive indexes by using a vapor deposition method. The conventional antireflection film has a light wavelength λ of 131, for example.
It is formed so as to obtain a low reflectance for light of one specific wavelength used in an optical communication system such as 0 nm and 1550 nm.

[0005]

In response to the dramatic increase in the amount of communication data in recent years, the current optical communication technology employs a wavelength division multiplexing (WDM) optical communication system to provide a plurality of wavelengths λ of light used for communication. By doing so, the communication capacity is significantly increased. Light used in such wavelength-multiplexed optical communication has a plurality of wavelengths dispersed in a wide band and passes through an optical fiber and an optical passive component, as compared with the conventional light having a single wavelength.
However, in the current optical communication technology, for example, 1550 nm
The Faraday rotation angle is 45 degrees (de
g. In the Faraday rotator (4), an antireflection film having a low reflectance for light having a single wavelength of 1550 nm is formed. Therefore, with this antireflection film,
A sufficient antireflection function is not exhibited for light having a wavelength other than m. Therefore, there is a problem that light having a wavelength other than 1550 nm is reflected by the light incident surface of the Faraday rotator to generate return light, or the insertion loss of the Faraday rotator increases.

Further, since many wavelengths are used in the wavelength division multiplexing optical communication system, the Faraday rotator used for these light sources has a rotation angle of 4 with respect to light of a specific wavelength.
5 deg. It is manufactured so that The magnetic garnet has a characteristic that the Faraday rotation angle varies depending on the wavelength of the incident light, so that the rotation angle 45 deg. It is necessary to fabricate a Faraday rotator. Therefore, in the conventional antireflection film deposition process, an optimum antireflection film for each wavelength was formed for each Faraday rotator manufactured for each wavelength. Since the antireflection film is formed by a batch process by a vacuum film forming method such as vapor deposition, if the number of wavelengths increases, the number of times of film formation increases, the process of the antireflection film becomes complicated, and productivity decreases. The problem arises.

An object of the present invention is to provide an antireflection film which can obtain a low reflectance in a wide band and can be easily formed at a low cost, and an optical component using the antireflection film.

[0008]

[Means for Solving the Problems] The above-mentioned object
The first Ta satisfying 0.17 ≦ nd / λ ≦ 0.80
₂O_FiveLayer, first satisfying 0.02 ≦ nd / λ ≦ 0.54
SiO₂A layer satisfying 0.16 ≦ nd / λ ≦ 0.38
Ta of 2₂O_FiveLayer, satisfying 0.20 ≦ nd / λ ≦ 0.29
2nd SiO₂Layers must be stacked in this order (however
Where λ is the wavelength of the transmitted light, n is the refractive index of each layer, and d is the refractive index of each layer.
Is achieved by an anti-reflective coating characterized by
It

In the antireflection film of the present invention, the surface opposite to the substrate surface is in contact with air.

The antireflection film of the present invention is characterized in that the reflectance is 0.1% or less in the wavelength band of λ ± 70 nm centered on the wavelength λ of the transmitted light.

In the antireflection film of the present invention, the wavelength λ is 1310 nm ≦ λ ≦ 1750 nm.

Further, the above object is an optical component using a garnet single crystal, wherein the antireflection film of the present invention is formed on the light incident surface and the light exit surface of the garnet single crystal. It is achieved by the optical component.

[0013] In the optical component of the present invention, the garnet single _{crystal, Bi a A 3-a Fe} 5- x M x O 12 ( wherein,
A is Y, Lu, Yb, Er, Ho, Dy, Tb, G
d, Eu, Sm, Nd, Pr, Ce, La, Pb, Ca
One or more elements, M is Ga, Al, Sc, In,
One or more elements of Si, Ge, Ti, Au, Ir,
a and x satisfy 1.0 ≦ a ≦ 2.4 and 0 <x ≦ 1.5. ) Is represented by.

[0014] In the optical component of the present invention, the garnet single _{crystal, Bi a A b B 3-} ab Fe 5-x M x O 12 ( wherein, A represents, Er, Dy, Tb, Sm, Nd, One or more elements of Pr, B is Y, Lu, Yb, Ho, Gd,
One or more elements of Ce, La, Pb and Ca, M is G
a, Al, Sc, In, Si, Ge, Ti, Au, Ir
One or more elements, a, b and x are 1.0 ≦ a ≦
2.4, 0 ≦ a ≦ 0.1, 0 <x ≦ 1.5 are satisfied. ) Is represented by.

The above-mentioned optical component of the present invention is characterized in that the light reflectance is 0.1% or less in the entire wavelength range λ of 1460 nm ≦ λ ≦ 1530 nm.

The above-mentioned optical component of the present invention is characterized in that the reflectance of light is 0.1% or less in the entire region where the wavelength λ of light is 1530 nm ≦ λ ≦ 1565 nm.

The above-mentioned optical component of the present invention is characterized in that the light reflectance is 0.1% or less in the entire region where the wavelength λ of light is 1565 nm ≦ λ ≦ 1625 nm.

In the above optical component of the present invention, the garnet single crystal is used as a Faraday rotator.

[0019] Further, the above-mentioned object is that the antireflection film is provided with light incident /
An optical isolator having a Faraday rotator formed on an emission surface, wherein the antireflection film is the antireflection film of the present invention.

Further, the above object is an optical attenuator having a Faraday rotator having an antireflection film formed on a light incident / exiting surface, wherein the antireflection film is the antireflection film of the present invention. Achieved by a featured optical attenuator.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION An antireflection film and a method for forming the same, and an optical component using the antireflection film according to an embodiment of the present invention will be described with reference to FIGS. First, the outline of the present embodiment will be described. Assuming that the central wavelength of the wavelength band of light used in optical communication systems such as WDM is λ, an antireflection film that has a light reflectance of 0.1% or less in at least the entire region of λ ± 70 nm is magnetic. By forming the garnet single crystal on the light incident surface and the light emitting surface, the problem that the reflectance of light becomes large at a wavelength other than the conventional specific wavelength is solved.

In wavelength division multiplexing optical communication, S band (1460n
m ≦ λ ≦ 1530 nm), C band (1530 nm ≦ λ
≦ 1565 nm), L band (1565 nm ≦ λ ≦ 16
Since a communication system is configured for each specific wavelength band such as 25 nm), if the reflectance of the antireflection film can be 0.1% or less in all those specific bands, a Faraday rotator suitable for each system. Can be provided. That is, even when a plurality of lights having different wavelengths are incident on the Faraday rotator provided with such an antireflection film, the reflected light on the surface of the Faraday rotator can be uniformly reduced, and a stable optical communication system can be provided. It is effective for operation.

Further, the antireflection film composed of a thin film of an oxide is a phenomenon in which the band for preventing light reflection varies due to alteration of the film when subjected to a reliability test required for optical components for communication. Occurs. In order to obtain the required reflectance characteristics even if the wavelength band changes, the reflectance is less than 0 in a wavelength band wider than the entire wavelength band used in optical communication.
It is necessary to set it to 1% or less, and it is necessary to set the reflectance to 0.1% or less in the wavelength band of 140 nm, which is wider than the bandwidth of each of the S, C, and L bands.

The antireflection film increases the number of layers of oxide thin films having different refractive indexes and adjusts the film thickness of those thin films to an appropriate value so that the wavelength band and the reflectance for preventing the reflection of light can be more accurately defined. Can be controlled. In order to form a broadband antireflection film having a wavelength of 140 nm or more, which is useful in a wavelength division multiplexing optical communication system, on a magnetic garnet single crystal, it is necessary to form the antireflection film with four or more oxide thin films. .
When the number of layers is increased, a broader antireflection film can be obtained, which is advantageous in characteristics. However, if the number of layers increases, the film forming process becomes long, which is disadvantageous in terms of cost. Further, the light insertion loss of the Faraday rotator increases due to the light absorption of the material forming the antireflection film. Therefore, it is desirable that the number of oxide thin film layers constituting the antireflection film is 20 or less. Furthermore, considering that reliability can be guaranteed and that light is not absorbed, Ta ₂ O ₅ , SiO ₂ , TiO ₂ , ZrO ₂ ,
It is preferable that the antireflection film is made of a material such as Y ₂ O ₃ , LaF ₃ , Al ₂ O ₃ or MgF ₂ .

FIG. 1 shows an antireflection film 2 according to this embodiment.
Shows a state in which the magnetic garnet single crystal substrate 1 is formed on both sides of light incidence / emission. As shown in FIG. 1, 0.17 ≦ nd was applied to the first layer on both surfaces of the magnetic garnet single crystal substrate 1.
A first Ta ₂ O ₅ layer satisfying /λ≦0.80 is formed,
A first SiO ₂ layer satisfying 0.02 ≦ nd / λ ≦ 0.54 is formed thereon as a _second layer. The third layer on the second layer has a second layer satisfying 0.16 ≦ nd / λ ≦ 0.38.
Ta ₂ O ₅ layer is formed and a fourth layer of 0.2 is formed thereon.
A second SiO ₂ layer satisfying 0 ≦ nd / λ ≦ 0.29 is laminated. Here, λ is the wavelength of the transmitted light, n is the refractive index of each layer, and d is the film thickness of each layer.

When the refractive index of air is 1, the refractive index n of the first and second Ta ₂ O ₅ layers on the surface of the magnetic garnet single crystal substrate is in the range of 2.08 ≦ n ≦ 2.15. And the refractive index n of the first and second SiO ₂ layers is 1.45 ≦ n ≦
The range is set to 1.47.

The Faraday rotator on which the antireflection film 2 is applied is often composed of magnetic garnet, but Bi-substituted rare earth iron garnet produced by the liquid phase epitaxial method is more mass-producible than rare earth iron garnet such as YIG. It is preferable in terms. Further, for example, Tb is an element effective for improving the temperature characteristics and wavelength characteristics of the Faraday rotator, but C
Since the band and L band have the property of absorbing light, when a large amount is contained in the magnetic garnet, the insertion loss of the C band and L band rotator, which uses a plurality of wavelengths in combination with the broadband antireflection film, will occur. It becomes big and becomes a problem. For the same reason, a large amount of Er, Dy, Tb, Sm, Nd, and Pr, which have optical absorption in the wavelength band used for optical communication, is contained in the Faraday rotator. However, if the content of the magnetic garnet is 0.1 or less in the composition formula, the insertion loss is not so large and there is no problem in characteristics. Therefore, containing these elements in an amount of 0.1 or less is useful for fine adjustment of various characteristics such as wavelength characteristics, temperature characteristics, and saturation magnetic field. Then, Y, Lu, Yb, Ho, Gd, Ce, and L that do not absorb light in these wavelength bands
If a Faraday rotator is made from magnetic garnet that contains elements such as a, Pb, and Ca as the main components of the C site, and a broadband antireflection film is applied to it, both the Faraday rotator and its antireflection film will absorb light. It is possible to obtain a Faraday rotator for a broadband wavelength with very little reflection. Also,
The Fe element of the magnetic garnet is also an element with little light absorption, such as Ga, Al, Sc, In, Si, Ge, Ti and A.
Since the saturation magnetic field can be controlled by substituting with u and Ir, it is useful for designing a device such as an optical isolator. However, if the substitution is 1.5 or more, the Curie temperature will drop to around room temperature and the Faraday rotator cannot be used. Therefore, the substitution amount is preferably 1.5 or less.

In wavelength division multiplexing optical communication, light is often amplified by a fiber amplifier in the middle of an optical fiber, and very strong light passes through the fiber.
When such high-intensity light is inserted into the Faraday rotator, if there is resin on the light transmitting surface of the Faraday rotator, the resin is burned by the heat of the light, resulting in device failure. For this reason, the Faraday rotator used in optical passive components such as polarization-dependent isolators used in the middle of optical fibers requires that the light-transmitting surface be in contact with air without being bonded with resin. It is necessary to form an antireflection film for the air. Therefore, by forming an antireflection film in the wide wavelength band against air on the light passage surface of the Faraday rotator, it is possible to prevent defects of the optical passive component and improve the characteristics in the wavelength division multiplexing optical communication system in which high intensity light is inserted. It is very effective.

Further, for example, at various wavelengths used in the C band, the rotation angle is 45 deg. When manufacturing the Faraday rotator of, if an antireflection film having a reflectance of 0.1% or less is formed in the entire C band, the Faraday rotators for the C band are simultaneously formed in the same batch film forming process. An antireflection film can be applied. Thus, by simultaneously forming a broadband antireflection film on multiple types of Faraday rotators for each wavelength, it is possible to reduce the light reflectance at any wavelength. It is possible to simplify the complicated process and improve the productivity.

Hereinafter, the antireflection film according to the present embodiment and the optical component using the same will be described more specifically by way of examples. The main points of each example are:
A Faraday rotator made of a Bi-substituted rare earth iron garnet material was formed with four thin films on both sides of light incidence / emission.
An antireflection film having a light reflectance of 0.1% or less in a wavelength band of 0 nm was obtained. Such an antireflection film can reduce the reflection of light in all wavelength bands of S band, C band and L band used in wavelength division multiplexing optical communication, and is effective for improving the performance of optical passive components. is there. Further, an antireflection film can be simultaneously formed on a plurality of types of Faraday rotators for each wavelength, which improves productivity.

[Embodiment 1] FIG. 2 shows a state in which an antireflection film 2 according to this embodiment is formed on both the light incident / exiting surfaces of a magnetic garnet single crystal substrate 1. As shown in FIG.
A first Ta ₂ O ₅ layer of nd / λ = 0.19 is formed on the first layer on both sides of the magnetic garnet single crystal substrate (Faraday rotator) 1, and nd / λ = of the _second layer is formed thereon. 0.44
A first SiO ₂ layer is formed. Further, a second Ta ₂ O ₅ layer having a third layer of nd / λ = 0.33 is formed on the second layer.
A layer is formed, and nd / λ = 0.2 as a fourth layer on the layer.
A second second SiO ₂ layer is formed.

When the refractive index of air is 1, the refractive index n of the first and second Ta ₂ O ₅ layers on the surface of the magnetic garnet single crystal substrate is 2.10, and the first and second SiO ₂
The refractive index n of the layer is 1.46.

The structure shown in FIG. 2 was formed as follows. First, by liquid phase epitaxial method, CaMgZr
The composition formula is Bi _1.1 Tb _1.4 Y _0.2 Yb _0.1 Ho _0.15 on a substituted gadolinium gallium garnet (GGG) single crystal substrate.
A magnetic garnet single crystal of Pb _0.05 Fe _4.85 Ga _0.1 Ge _0.03 Pt _0.02 O ₁₂ was grown. Next, the wavelength λ = 131
The rotation angle is 45 deg. For 0 nm light. The Faraday rotator 1 was formed by processing the magnetic garnet single crystal so that A thin film is vapor-deposited on both sides of the Faraday rotator 1 processed into a plate by a vacuum vapor deposition method in which Ta ₂ O ₅ , SiO ₂ , Ta ₂ O ₅ , and SiO ₂ are ion-assisted in that order.
The value of nd / λ of each layer is 0.190 in the first layer, 0.443 in the second layer, 0.325 in the third layer, and 0.
It was adjusted to 217, and an antireflection film for air was formed to obtain an optical component.

The light reflectance of the antireflection film 2 on one side of this optical component was evaluated by a spectrophotometer. FIG. 3 shows the characteristics of the antireflection film 2 according to this example. The horizontal axis of FIG. 3 represents the wavelength (nm) of light incident on the antireflection film of this example, and the vertical axis represents the obtained reflectance (%). Figure 3
, The wavelength λ of light is 1240 nm ≦ λ ≦ 137
The reflectance was 0.02% in the entire region of 0 nm, and a characteristic of 0.1% or less was obtained. When the insertion loss of the obtained Faraday rotator was evaluated in the entire range of 1240 nm ≦ λ ≦ 1370 nm, the loss was 0.03 dB, which was a stable value. Therefore, 1240 nm ≦ λ ≦ 1370n
A Faraday rotator having excellent characteristics with low light reflectance and insertion loss in the entire region of m was obtained.

Example 2 A composition formula of Bi _1.0 Gd _1.5 Yb _0.3 Ho _0.15 P was prepared on a CaMgZr-substituted gadolinium gallium garnet single crystal substrate by a liquid phase epitaxial method.
A magnetic garnet single crystal that became b _0.05 Fe _4.85 Al _0.1 Ge _0.03 Pt _0.02 O ₁₂ was grown. Next, the wavelength λ = 1495
rotation angle of 45 deg. A Faraday rotator was formed by processing the magnetic garnet single crystal so that On both sides of the Faraday rotator processed into a plate, Ta
_{2 O 5, SiO 2, Ta} 2 O 5, by depositing a thin film by a vacuum deposition method in this order SiO ₂ was added ion-assisted, each of n
The value of d / λ is 0.190 for the first layer and 0.4 for the second layer.
43, the third layer was adjusted to 0.325, and the fourth layer was adjusted to 0.217, and an antireflection film for air was formed to obtain an optical component.

The light reflectance of the antireflection film on one side of this optical component was evaluated by a spectrophotometer. FIG. 4 shows the characteristics of the antireflection film according to this example. The horizontal axis of FIG. 4 represents the wavelength (nm) of light incident on the antireflection film of this example, and the vertical axis represents the obtained reflectance (%). As shown in FIG. 4, the wavelength λ of light includes the S band and the C band.
The reflectance is 0.0 in the entire region of 25 nm ≦ λ ≦ 1565 nm.
It was 2% and a characteristic of 0.1% or less was obtained. In addition, the insertion loss of the obtained Faraday rotator is 1425 nm ≦ λ ≦
When evaluated in the entire region of 1565 nm, the loss is 0.0
The value was stable at 3 dB. Therefore, 1425
A Faraday rotator having excellent characteristics with low light reflectance and low insertion loss was obtained in the entire range of nm ≦ λ ≦ 1565 nm.

[Embodiment 3] A composition formula of Bi _1.1 Gd _1.45 Yb _0.4 Pb _0.05 F was formed on a CaMgZr-substituted gadolinium gallium garnet single crystal substrate by a liquid phase epitaxial method.
A magnetic garnet single crystal that became e _4.95 Ge _0.03 Pt _0.02 O ₁₂ was grown. Next, with respect to the light having the wavelength λ = 1562 nm, the rotation angle is 45 deg. A Faraday rotator was formed by processing the magnetic garnet single crystal so that On both sides of the plate-shaped Faraday rotator, Ta ₂ O ₅ , SiO ₂ ,
A thin film is deposited by a vacuum deposition method with ion assist in the order of Ta ₂ O ₅ and SiO ₂ , and the nd / λ value of each layer is 0.190 for the first layer and 0.443 for the second layer. The third layer was adjusted to 0.325 and the fourth layer was adjusted to 0.217, and an antireflection film for air was formed to obtain an optical component.

The light reflectance of the antireflection film on one side of this optical component was evaluated by a spectrophotometer. FIG. 5 shows the characteristics of the antireflection film according to this example. The horizontal axis of FIG. 5 represents the wavelength (nm) of light incident on the antireflection film of this example, and the vertical axis represents the obtained reflectance (%). As shown in FIG. 5, the wavelength λ of light includes the C band and the L band.
The reflectance is 0.0 in the entire region of 92 nm ≦ λ ≦ 1632 nm.
2%, which is 0.1% or less, and the S band (1
0.1% even in the entire region of (460 nm ≦ λ ≦ 1530 nm)
The following characteristics were obtained. When the insertion loss of the obtained Faraday rotator was evaluated in the entire region of 1492 nm ≦ λ ≦ 1632 nm, the loss was a stable value of 0.03 dB. Therefore, 1492 nm ≦ λ ≦ 1632
A Faraday rotator having excellent characteristics with low light reflectance and insertion loss in the entire nm region was obtained.

[Embodiment 4] A composition formula of Bi _1.1 Gd _1.45 Yb _0.4 Pb _0.05 F on a CaMgZr-substituted gadolinium gallium garnet single crystal substrate was obtained by a liquid phase epitaxial method.
A magnetic garnet single crystal that became e _4.95 Ge _0.03 Pt _0.02 O ₁₂ was grown. Next, with respect to the light having the wavelength λ = 1615 nm, the rotation angle is 45 deg. A Faraday rotator was formed by processing the magnetic garnet single crystal so that On both sides of the plate-shaped Faraday rotator, Ta ₂ O ₅ , SiO ₂ ,
A thin film is deposited by a vacuum deposition method with ion assist in the order of Ta ₂ O ₅ and SiO ₂ , and the nd / λ value of each layer is 0.190 for the first layer and 0.443 for the second layer. The third layer was adjusted to 0.325 and the fourth layer was adjusted to 0.217, and an antireflection film for air was formed to obtain an optical component.

The light reflectance of the antireflection film on one side of this optical component was evaluated by a spectrophotometer. FIG. 6 shows the characteristics of the antireflection film according to this example. The horizontal axis of FIG. 6 represents the wavelength (nm) of light incident on the antireflection film of this example, and the vertical axis represents the obtained reflectance (%). As shown in FIG. 6, the wavelength λ of light is 1545 nm ≦ λ including the L band.
The reflectance was 0.02% in the entire region of ≤1685 nm, and a characteristic of 0.1% or less was obtained. In addition, the insertion loss of the obtained Faraday rotator was 1545 nm ≦ λ ≦ 1685n.
When evaluated in the entire range of m, the loss was a stable value of 0.03 dB. Therefore, 1545 nm ≦ λ ≦
A Faraday rotator having excellent characteristics with low light reflectance and low insertion loss in the entire region of 1685 nm was obtained.

[Embodiment 5] A composition formula of Bi _1.1 Gd _1.45 Yb _0.4 Pb _0.05 F was formed on a CaMgZr-substituted gadolinium gallium garnet single crystal substrate by a liquid phase epitaxial method.
A magnetic garnet single crystal that became e _4.95 Ge _0.03 Pt _0.02 O ₁₂ was grown. Next, with respect to the light having the wavelength λ = 1750 nm, the rotation angle is 45 deg. A Faraday rotator was formed by processing the magnetic garnet single crystal so that On both sides of the plate-shaped Faraday rotator, Ta ₂ O ₅ , SiO ₂ ,
A thin film is deposited by a vacuum deposition method with ion assist in the order of Ta ₂ O ₅ and SiO ₂ , and the nd / λ value of each layer is 0.190 for the first layer and 0.443 for the second layer. The third layer was adjusted to 0.325 and the fourth layer was adjusted to 0.217, and an antireflection film for air was formed to obtain an optical component.

The light reflectance of the antireflection film on one side of this optical component was evaluated by a spectrophotometer. FIG. 7 shows the characteristics of the antireflection film according to this example. The horizontal axis of FIG. 7 represents the wavelength (nm) of the light incident on the antireflection film of this example, and the vertical axis represents the obtained reflectance (%). As shown in FIG. 7, the wavelength λ of light is 1680 nm ≦ λ ≦ 1820 nm
The reflectance was 0.02% over the entire area, and a characteristic of 0.1% or less was obtained. Further, when the insertion loss of the obtained Faraday rotator was evaluated in the entire region of 1680 nm ≦ λ ≦ 1820 nm, the loss was a stable value of 0.03 dB. Therefore, a Faraday rotator having excellent characteristics with low light reflectance and insertion loss in the entire region of 1680 nm ≦ λ ≦ 1820 nm was obtained.

Comparative Example 1 A composition formula of Bi _1.1 Gd _1.45 Yb _0.4 Fb _0.05 F was formed on a CaMgZr-substituted gadolinium gallium garnet single crystal substrate by a liquid phase epitaxial method.
A magnetic garnet single crystal that became e _4.95 Ge _0.03 Pt _0.02 O ₁₂ was grown. Next, with respect to the light having the wavelength λ = 1550 nm, the rotation angle is 45 deg. A Faraday rotator was formed by processing the magnetic garnet single crystal so that Thin films are vapor-deposited on both sides of the plate-shaped Faraday rotator by Ta ₂ O ₅ and SiO ₂ in this order with ion assist, to form an antireflection film against air to form an optical component. did.

The light reflectance of the antireflection film on one side of this optical component was evaluated by a spectrophotometer. FIG. 8 shows the characteristics of the antireflection film according to the comparative example. The horizontal axis of FIG. 8 represents the wavelength (nm) of the light incident on the antireflection film of this comparative example, and the vertical axis represents the obtained reflectance (%). As shown in FIG. 8, when the wavelength λ of light is 1480 nm, the reflectance is 0.16%.
And the reflectance was 0.15% or less at λ = 1620 nm. Further, when the insertion loss of the obtained Faraday rotator was evaluated in the entire region of 1480 nm ≦ λ ≦ 1620 nm, the loss was 0.03 dB, which was a stable value. Therefore, although the loss is good in the wavelength band of 1480 nm ≦ λ ≦ 1620 nm, the reflectance of light tends to increase at wavelengths near the band boundary, and return light is generated, which is a characteristic problem.

As described above, according to this embodiment, an antireflection film for a Faraday rotator having a low reflectance of 0.1% or less can be obtained in a broadband wavelength used in wavelength division multiplexing optical communication. . Further, since the same antireflection film can be formed on a plurality of types of Faraday rotators produced for each wavelength, productivity can be improved.

[0046]

As described above, according to the present invention, it is possible to realize an antireflection film which has a low reflectance in a wide band and can be easily formed at low cost, and an optical component using the antireflection film.

[Brief description of drawings]

FIG. 1 is a diagram showing a state in which an antireflection film according to an embodiment of the present invention is formed on both sides of light incidence / emission of a magnetic garnet single crystal substrate 1.

FIG. 2 is a diagram showing a state in which an antireflection film in Example 1 of one embodiment of the present invention is formed on both light incident / exiting surfaces of a magnetic garnet single crystal substrate 1.

FIG. 3 is a diagram showing characteristics of an antireflection film according to example 1 according to the embodiment of the present invention.

FIG. 4 is a diagram showing characteristics of an antireflection film according to example 2 according to the embodiment of the present invention.

FIG. 5 is a diagram showing characteristics of an antireflection film according to example 3 according to the embodiment of the present invention.

FIG. 6 is a diagram showing characteristics of an antireflection film according to example 4 according to the embodiment of the present invention.

FIG. 7 is a diagram showing characteristics of an antireflection film according to example 5 according to the embodiment of the present invention.

FIG. 8 is a diagram showing characteristics of an antireflection film according to a comparative example.

[Explanation of symbols]

1 Magnetic garnet single crystal substrate 2 Antireflection film

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kazuto Yamazawa             1-13-1, Nihonbashi, Chuo-ku, Tokyo             -In DC Inc. F-term (reference) 2H049 BA08 BA42 BB03 BC25                 2H099 AA01 BA02 CA05 CA11                 2K009 AA07 BB04 CC03 CC42 DD03                       EE00                 4K029 AA04 BA43 BA46 BB02 BC08                       BD00 CA09

Claims (13)

[Claims] 1. On the substrate surface, 0.17 ≦ nd / λ ≦ 0.8
First Ta ₂ O ₅ layer satisfying 0, 0.02 ≦ nd / λ ≦
First SiO ₂ layer satisfying 0.54, 0.16 ≦ nd /
Second Ta ₂ O ₅ layer satisfying λ ≦ 0.38, 0.20 ≦ n
A second SiO ₂ layer satisfying d / λ ≦ 0.29 is laminated in this order (where λ is the wavelength of transmitted light, n is the refractive index of each layer, and d is the film thickness of each layer). Characteristic anti-reflection film. 2. The antireflection film according to claim 1, wherein the opposite surface side of the substrate surface is in contact with air. 3. The antireflection film according to claim 1, wherein the reflectance is 0.1% or less in a wavelength band of λ ± 70 nm centered on the wavelength λ of the transmitted light. Antireflection film. 4. The antireflection film according to claim 3, wherein the wavelength λ is 1310 nm ≦ λ ≦ 1750 nm. 5. An optical component using a garnet single crystal, wherein the antireflection film according to any one of claims 1 to 4 is formed on a light incident surface and a light emitting surface of the garnet single crystal. An optical component characterized in that 6. The optical component according to claim 5, wherein said garnet single _{crystal, Bi a A 3-a Fe} 5-x M x O 12 ( wherein, A represents, Y, Lu,
Yb, Er, Ho, Dy, Tb, Gd, Eu, Sm, N
d, Pr, Ce, La, Pb, one or more elements of Ca, M is Ga, Al, Sc, In, Si, Ge, T
i, Au, Ir are one or more kinds of elements, and a and x are
1.0 ≦ a ≦ 2.4 and 0 <x ≦ 1.5 are satisfied. ) An optical component characterized by being represented by. 7. The optical component of claim 5, wherein said garnet single _{crystal, Bi a A b B 3-} ab Fe 5-x M x O 12 ( wherein, A is, E
One or more elements of r, Dy, Tb, Sm, Nd, Pr, B is Y, Lu, Yb, Ho, Gd, Ce, La,
One or more elements of Pb and Ca, M is Ga, Al, S
One or more elements of c, In, Si, Ge, Ti, Au, and Ir, and a, b, and x are 1.0 ≦ a ≦ 2.4, 0 ≦.
It satisfies a ≦ 0.1 and 0 <x ≦ 1.5. ) An optical component characterized by being represented by. 8. The optical component according to claim 5, wherein the light reflectance is 0.1% or less in the entire region where the wavelength λ of light is 1460 nm ≦ λ ≦ 1530 nm. Optical components characterized by. 9. The optical component according to claim 5, wherein the light reflectance is 0.1% or less in the entire wavelength region λ of 1530 nm ≦ λ ≦ 1565 nm. Optical components characterized by. 10. The optical component according to claim 5, wherein the light reflectance is 0.1% or less in the entire region where the wavelength λ of light is 1565 nm ≦ λ ≦ 1625 nm. Optical components characterized by. 11. The optical component according to any one of claims 5 to 10, wherein the garnet single crystal is used as a Faraday rotator. 12. An anti-reflection film according to claim 1, wherein the anti-reflection film is an optical isolator having a Faraday rotator formed on a light incident / exiting surface. An optical isolator characterized by being a film. 13. An anti-reflection coating according to claim 1, wherein the anti-reflection coating is a light attenuator having a Faraday rotator formed on a light incidence / emission surface. An optical attenuator characterized by being a film.