JPH05289025A - Optical isolator - Google Patents

Abstract

PURPOSE:To provide the optical isolator which can assure an always stable isolation value in a practicable environmental temp. change range regardless of the influence of a change in environmental temp. on a Faraday rotating angle. CONSTITUTION:The dependency of the residual magnetic flux density of the neodymium-iron-boron magnet which is a permanent magnet for magnetic field impression of the conventional optical isolator and is expressed by chemical formula Nd2Fe14B on the environmental temp. changes as shown in Fig. when the neodymium (Nd) is partly substd. with disprosium (Dy). The optical isolator is constituted by using the neodymium-dysprsium-iron-boron magnet expressed by chemical formula (Nd1-yDyy)2Fe14B (where 0.1<=Y<=0.5) as the permanent magnet for magnetic field impression in accordance with the substitution and using the cadmium-manganese-tellurium single crystal expressed by chemical formula Cd1-xMnxTe (where 0.1<=X<=0.5) as the Faraday element.

Description

Detailed Description of the Invention

[0001]

The present invention relates to the chemical formula Cd _1-X Mn _X T
The present invention relates to an optical isolator that uses a cadmium-manganese-tellurium single crystal represented by e (where 0.1≤X≤0.5) as a Faraday rotator and uses a permanent magnet for applying a magnetic field.

[0002]

2. Description of the Related Art Conventionally, a semiconductor laser or a gas laser is often used as a light source of an optical device (system) for optical communication, optical measurement, magneto-optical recording, etc. due to its coherence. When part of the light emitted from these lasers is returned to the lasers themselves, wavelength fluctuations and noise are generated. Therefore, an optical isolator using a Faraday element that produces a Faraday rotation (non-reciprocal optical rotation in a magnetic field) angle, that is, 45 degrees, has been put into practical use in order to block this return light.

Different materials are used for the Faraday element depending on the wavelength of the light source. For example, wavelengths 1.2 to 1.
At 6 [μm], a magnetic garnet (garnet containing iron in the component) single crystal with a large Faraday rotation ability is used, and at shorter wavelengths, lead glass or terbium-gallium-garnet single crystal is used. ..
Of these, magnetic garnet has a large Faraday rotation capability, and when it is used as a Faraday element, the element thickness is several hundred μm.
Since it is thin, it can be used for small isolator. However, since magnetic garnet absorbs light at a wavelength of 1 μm or less, it cannot be used for light having a wavelength of 1 μm or less.

On the other hand, with respect to light having a wavelength of 1 μm or less, for example, 0.633 μm which is an oscillation wavelength of a helium-neon laser or 0.65 to 0.85 [μm] which is an oscillation wavelength of a semiconductor laser called a visible light semiconductor laser. Used lead glass or terbium gallium garnet single crystal that does not absorb light at that wavelength, but these materials do not have a large Faraday rotation capability and their element length is a few c.
Therefore, it is difficult to contribute to miniaturization of the visible light isolator.

Therefore, as described in the summary of academic lectures 30aB-7 at the 15th Japan Society for Applied Magnetics held in 1991, such a problem was solved (that is, there is no light absorption even at a wavelength of 1 μm or less, Moreover, a small visible light isolator with a large Faraday rotation capability has been proposed. This compact visible light isolator has the chemical formula Cd _1-X Mn _X T
The cadmium-manganese-tellurium single crystal represented by e is used for the Faraday element, and the neodymium-iron-boron magnet having a large residual magnetic flux density represented by the chemical formula Nd ₂ Fe ₁₄ B is used for the magnetic field applying magnet.

[0006]

In the case of the compact visible light isolator described above, the isolation value changes as shown in FIG. 2 when the Faraday rotation angle deviates from 45 degrees. In addition, the chemical formula Cd _1-X Mn _X Te (provided that 0.1 ≦ X
≦ 0.5), the Verdet constant (Faraday rotation ability in unit length and unit magnetic field strength) in the band of wavelength 0.63 to 0.85 [μm] of the cadmium-manganese-tellurium single crystal is The temperature changes as shown in FIG. (In Cd _1-X Mn _X Te, 0.1 ≦
In the range of X ≦ 0.5 and wavelength of 0.63 to 0.85 [μm], the magnitude of the Verde constant changes depending on the composition and the wavelength, but the environmental temperature dependence of the Verde constant depends on the composition and the wavelength. It is constant. Further, the residual magnetic flux density of the neodymium / iron / boron magnet represented by the chemical formula Nd ₂ Fe ₁₄ B changes as shown in FIG. 4 depending on the ambient temperature.

As is apparent from FIGS. 2 to 4, small visible light using a cadmium-manganese-tellurium single crystal and a neodymium-iron-boron magnet as a Faraday element and a permanent magnet for applying a magnetic field, respectively. In the isolator,
For example, even if the reference environment temperature is set to 20 ° C. and the Faraday rotation angle is set to 45 degrees, the Faraday rotation angle greatly changes due to the change in the environment temperature. Therefore, the small visible light isolator described above has a problem that the isolation can be guaranteed only up to about 29 dB in the practical temperature range of −20 to 80 ° C.

Therefore, a technical object of the present invention is to provide an optical isolator capable of always ensuring a stable isolation value regardless of the influence of the Faraday rotation angle by the environmental temperature.

[0009]

According to the present invention, a cadmium-manganese-tellurium single crystal represented by the chemical formula Cd _{1 -X} Mn _X Te (where 0.1≤X≤0.5) is used as a Faraday rotator. In the optical isolator using a permanent magnet for applying a magnetic field, the chemical formula (N
d _1-Y Dy _Y ) ₂ Fe ₁₄ B (provided that 0.1 ≦ Y ≦ 0.
An optical isolator characterized by using the neodymium / dysprodium / iron / boron magnet shown in 5) is obtained.

[0010]

The optical isolator of the present invention has a chemical formula of Nd ₂ Fe.
_The chemical formula (Nd _1-Y Dy _Y ) ₂ Fe ₁₄ B (where 0.1 ≦
The neodymium / dysprosium / iron / boron magnet represented by Y ≦ 0.5) is provided as a permanent magnet for applying a magnetic field.

[0011]

The optical isolator of the present invention will be described in detail below with reference to the accompanying drawings.

First, the outline of the optical isolator of the present invention will be briefly described. In the present invention, a conventional magnet for applying a magnetic field to an optical isolator, which is a neodymium / iron / boron magnet neodymium (N) represented by the chemical formula Nd ₂ Fe ₁₄ B, is used.
When a part of d) is replaced with dysprosium (Dy),
Paying attention to the fact that the environmental temperature dependence of the residual magnetic flux density changes as shown in FIG. 1, such a chemical formula (Nd _{1 -Y} Dy
_The optical isolator is provided with a neodymium / dysprosium / iron / boron magnet represented by _Y ) ₂ Fe ₁₄ B (provided that 0.1 ≦ Y ≦ 0.5) as a permanent magnet for applying a magnetic field.

Also in the case of the optical isolator of the present invention, the chemical formula Cd _1-X Mn _X Te (where 0.1≤X≤0.5)
A cadmium-manganese-tellurium single crystal represented by is provided as a Faraday element. Since such an optical isolator uses a neodymium / dysprodium / iron / boron magnet as a permanent magnet for applying a magnetic field, for example, after setting the Faraday rotation angle to be 45 degrees at a reference environmental temperature of 20 ° C., Even if the environmental temperature changes, the isolation value is always stable regardless of the influence of the environmental temperature on the Faraday rotation angle.

The following are some examples and comparative examples,
The optical isolator of the present invention will be specifically described. The optical isolators according to the examples and the comparative examples are shown in Table 1.
The measurement result of the isolation value in the practical temperature range of −20 to 80 ° C. described below is referred to.

[0015]

[Table 1]

(Example 1) In Example 1, Cd _0.9 Mn
A cadmium-manganese-tellurium single crystal having a composition of _0.1 Te was used as a Faraday element and was used as a permanent magnet for applying a magnetic field (N
Using a neodymium-dysprodium-iron-boron magnet having a composition of d _0.9 Dy _0.1 ) ₂ Fe ₁₄ B, four types for wavelengths of 0.633, 0.67, 0.78 and 0.85 [μm] are prepared. An optical isolator was assembled. Each optical isolator has a Mn concentration x of 0.1 and a Dy concentration y of 0.1.
Is. Here, since the Verdet constant differs depending on the wavelength, the thickness of each Faraday element was changed, and the Faraday rotation angle was set to just 45 degrees at a temperature of 20 ° C.

-20 to 8 of these four types of optical isolators
As shown in Table 1, the isolation values in the temperature range of 0 [° C.] were at least 41 dB or more. This value of 41 dB was in good agreement with the value expected from the temperature dependence of the Verdet constant of the Faraday element and the residual magnetic flux density of the permanent magnet.

(Example 2) In Example 2, Cd _0.9 Mn
A cadmium-manganese-tellurium single crystal having a composition of _0.1 Te was used as a Faraday element and was used as a permanent magnet for applying a magnetic field (N
d _0.7 Dy _0.3 ) ₂ Fe ₁₄ B having a composition of neodymium-dysprodium-iron-boron magnet was used for four types of wavelengths of 0.633, 0.67, 0.78 and 0.85 [μm], respectively. An optical isolator was assembled. Each optical isolator has a Mn concentration x of 0.1 and a Dy concentration y of 0.3.
Is. Since the Verdet constant also varies depending on the wavelength, the thickness of each Faraday element was changed so that the Faraday rotation angle was set to just 45 degrees at a temperature of 20 ° C.

-20 to 8 of these four types of optical isolators
As shown in Table 1, the isolation values in the temperature range of 0 [° C.] were at least 43 dB or more. or,
This value of 43 dB was in good agreement with the value expected from the temperature dependence of the Verdet constant of the Faraday element and the residual magnetic flux density of the permanent magnet.

Example 3 In Example 3, Cd _0.9 Mn
A cadmium-manganese-tellurium single crystal having a composition of _0.1 Te was used as a Faraday element and was used as a permanent magnet for applying a magnetic field (N
Using a neodymium-dysprodium-iron-boron magnet having a composition of d _0.5 Dy _0.5 ) ₂ Fe ₁₄ B, four types for wavelengths of 0.633, 0.67, 0.78, 0.85 [μm] are prepared. An optical isolator was assembled. Each optical isolator has a Mn concentration x of 0.1 and a Dy concentration y of 0.5.
Is. Since the Verdet constant also varies depending on the wavelength, the thickness of each Faraday element was changed so that the Faraday rotation angle was set to just 45 degrees at a temperature of 20 ° C.

-20 to 8 of these four types of optical isolators
As shown in Table 1, the isolation values in the temperature range of 0 [° C] were at least 40 dB or more. or,
This value of 40 dB was also in good agreement with the value expected from the temperature dependence of the Verdet constant of the Faraday element and the residual magnetic flux density of the permanent magnet.

Comparative Example 1 In Comparative Example 1, Cd _0.9 Mn
A cadmium-manganese-tellurium single crystal with a composition of _0.1 Te is used as a Faraday element, and Nd is used as a permanent magnet for applying a magnetic field.
_Using a neodymium / iron / boron magnet having a composition of ₂ Fe ₁₄ B, wavelengths of 0.633, 0.67, 0.78,
Four types of optical isolators for 0.85 [μm] were assembled. In each optical isolator, the Mn concentration x is 0.1,
The Dy concentration y is 0. Since the Verdet constant also varies depending on the wavelength, the thickness of each Faraday element was changed so that the Faraday rotation angle was set to just 45 degrees at a temperature of 20 ° C.

-20 to 8 of these four types of optical isolators
The isolation values in the temperature range of 0 [° C.] were 29 dB or more at the minimum as shown in Table 1, which was inferior to the cases of Examples 1, 2 and 3 described above. Also, this 2
The value of 9 dB was also in good agreement with the value expected from the temperature dependence of the Verdet constant of the Faraday element and the residual magnetic flux density of the permanent magnet.

Example 4 In Example 4, Cd _0.7 Mn was used.
A cadmium-manganese-tellurium single crystal with a composition of _0.3 Te is used as a Faraday element and is used as a permanent magnet for applying a magnetic field (N
Using a neodymium-dysprodium-iron-boron magnet having a composition of d _0.9 Dy _0.1 ) ₂ Fe ₁₄ B, four types for wavelengths of 0.633, 0.67, 0.78 and 0.85 [μm] are prepared. An optical isolator was assembled. In each optical isolator, the Mn concentration x is 0.3 and the Dy concentration y is 0.1.
Is. Since the Verdet constant also varies depending on the wavelength, the thickness of each Faraday element was changed so that the Faraday rotation angle was set to just 45 degrees at a temperature of 20 ° C.

-20 to 8 of these four types of optical isolators
As shown in Table 1, the isolation values in the temperature range of 0 [° C.] were at least 41 dB or more. or,
The value of 41 dB was also in good agreement with the value expected from the temperature dependence of the Verdet constant of the Faraday element and the residual magnetic flux density of the permanent magnet.

Example 5 In Example 5, Cd _0.7 Mn
A cadmium-manganese-tellurium single crystal with a composition of _0.3 Te is used as a Faraday element and is used as a permanent magnet for applying a magnetic field (N
d _0.7 Dy _0.3 ) ₂ Fe ₁₄ B having a composition of neodymium-dysprodium-iron-boron magnet was used for four types of wavelengths of 0.633, 0.67, 0.78 and 0.85 [μm], respectively. An optical isolator was assembled. In each optical isolator, the Mn concentration x is 0.3 and the Dy concentration y is 0.3.
Is. Since the Verdet constant also varies depending on the wavelength, the thickness of each Faraday element was changed so that the Faraday rotation angle was set to just 45 degrees at a temperature of 20 ° C.

-20 to 8 of these four types of optical isolators
As shown in Table 1, the isolation values in the temperature range of 0 [° C.] were at least 43 dB or more. Also, this value of 43 dB was in good agreement with the value expected from the temperature dependence of the Verdet constant of the Faraday element and the residual magnetic flux density of the permanent magnet.

(Example 6) In Example 6, Cd _0.7 Mn
A cadmium-manganese-tellurium single crystal with a composition of _0.3 Te is used as a Faraday element and is used as a permanent magnet for applying a magnetic field (N
Using a neodymium-dysprodium-iron-boron magnet having a composition of d _0.5 Dy _0.5 ) ₂ Fe ₁₄ B, four types for wavelengths of 0.633, 0.67, 0.78, 0.85 [μm] are prepared. An optical isolator was assembled. In each optical isolator, the Mn concentration x is 0.3 and the Dy concentration y is 0.5.
Is. Since the Verdet constant also varies depending on the wavelength, the thickness of each Faraday element was changed so that the Faraday rotation angle was set to just 45 degrees at a temperature of 20 ° C.

-20 to 8 of these four types of optical isolators
As shown in Table 1, the isolation values in the temperature range of 0 [° C.] were at least 40 dB or more. Also, this value of 40 dB was in good agreement with the value expected from the temperature dependence of the Verdet constant of the Faraday element and the residual magnetic flux density of the permanent magnet.

Comparative Example 2 In Comparative Example 2, Cd _0.7 Mn
A cadmium-manganese-tellurium single crystal with a composition of _0.3 Te was used as a Faraday element, and Nd was used as a permanent magnet for applying a magnetic field.
_Using a neodymium / iron / boron magnet having a composition of ₂ Fe ₁₄ B, wavelengths of 0.633, 0.67, 0.78,
Four types of optical isolators for 0.85 [μm] were assembled. In each optical isolator, the Mn concentration x is 0.3,
The Dy concentration y is 0. Again, since the Verdet constant varies depending on the wavelength, the thickness of each Faraday element is changed so that the Faraday rotation angle is exactly 4 at a temperature of 20 ° C.
It was set to be 5 degrees.

-20 to 8 of these four types of optical isolators
The isolation values in the temperature range of 0 [° C.] were 29 dB or more at the minimum as shown in Table 1, which was inferior to those of Examples 4, 5 and 6 described above. This value of 29 dB was also in good agreement with the value expected from the temperature dependence of the Verdet constant of the Faraday element and the residual magnetic flux density of the permanent magnet.

Example 7 In Example 7, Cd _0.5 Mn
A cadmium-manganese-tellurium single crystal having a composition of _0.5 Te is used as a Faraday element and is used as a permanent magnet for applying a magnetic field (N
Using a neodymium-dysprodium-iron-boron magnet having a composition of d _0.9 Dy _0.1 ) ₂ Fe ₁₄ B, four types for wavelengths of 0.633, 0.67, 0.78 and 0.85 [μm] are prepared. An optical isolator was assembled. Each optical isolator has a Mn concentration x of 0.5 and a Dy concentration y of 0.1.
Is. Since the Verdet constant also varies depending on the wavelength, the thickness of each Faraday element was changed so that the Faraday rotation angle was set to just 45 degrees at a temperature of 20 ° C.

-20 to 8 of these four types of optical isolators
As shown in Table 1, the isolation values in the temperature range of 0 [° C.] were at least 41 dB or more. Also, this value of 41 dB was in good agreement with the value expected from the temperature dependence of the Verdet constant of the Faraday element and the residual magnetic flux density of the permanent magnet.

Example 8 In Example 8, Cd _0.5 Mn was used.
A cadmium-manganese-tellurium single crystal having a composition of _0.5 Te is used as a Faraday element and is used as a permanent magnet for applying a magnetic field (N
d _0.7 Dy _0.3 ) ₂ Fe ₁₄ B having a composition of neodymium-dysprodium-iron-boron magnet was used for four types of wavelengths of 0.633, 0.67, 0.78 and 0.85 [μm], respectively. An optical isolator was assembled. In each optical isolator, the Mn concentration x is 0.5 and the Dy concentration y is 0.3.
Is. Since the Verdet constant also varies depending on the wavelength, the thickness of each Faraday element was changed so that the Faraday rotation angle was set to just 45 degrees at a temperature of 20 ° C.

-20 to 8 of these four types of optical isolators
As shown in Table 1, the isolation values in the temperature range of 0 [° C.] were at least 43 dB or more. Also, this value of 43 dB was in good agreement with the value expected from the temperature dependence of the Verdet constant of the Faraday element and the residual magnetic flux density of the permanent magnet.

(Example 9) In Example 9, Cd _0.5 Mn
A cadmium-manganese-tellurium single crystal having a composition of _0.5 Te is used as a Faraday element and is used as a permanent magnet for applying a magnetic field (N
Using a neodymium-dysprodium-iron-boron magnet having a composition of d _0.5 Dy _0.5 ) ₂ Fe ₁₄ B, four types for wavelengths of 0.633, 0.67, 0.78, 0.85 [μm] are prepared. An optical isolator was assembled. For each optical isolator, the Mn concentration x is 0.5 and the Dy concentration y is 0.5.
Is. Since the Verdet constant also varies depending on the wavelength, the thickness of each Faraday element was changed so that the Faraday rotation angle was set to just 45 degrees at a temperature of 20 ° C.

-20 to 8 of these four types of optical isolators
As shown in Table 1, the isolation values in the temperature range of 0 [° C.] were at least 40 dB or more. Also, this value of 40 dB was in good agreement with the value expected from the temperature dependence of the Verdet constant of the Faraday element and the residual magnetic flux density of the permanent magnet.

Comparative Example 3 In Comparative Example 3, Cd _0.5 Mn was used.
Cadmium-manganese-tellurium single crystal with a composition of _0.5 Te is used as a Faraday element, and Nd is used as a permanent magnet for applying a magnetic field.
₂ Fe ₁₄ B having a composition of neodymium / iron / boron magnet, wavelengths of 0.633, 0.67, 0.78,
Four types of optical isolators for 0.85 [μm] were assembled. For each optical isolator, the Mn concentration x is 0.5,
The Dy concentration y is 0. Again, since the Verdet constant varies depending on the wavelength, the thickness of each Faraday element is changed so that the Faraday rotation angle is exactly 4 at a temperature of 20 ° C.
It was set to be 5 degrees.

-20 to 8 of these four types of optical isolators
As shown in Table 1, the isolation values in the temperature range of 0 [° C.] were all at least 29 dB or more, which was inferior to those of Examples 7, 8 and 9 described above. This value of 29 dB was also in good agreement with the value expected from the temperature dependence of the Verdet constant of the Faraday element and the residual magnetic flux density of the permanent magnet.

Each of the above Examples (1 to 9) and each Comparative Example (1
~ 3), the optical isolator of each comparative example is
While the isolation value is 29 dB or more in the temperature range of 20 to 80 [° C.], the optical isolator of each example has an isolation value of 40 dB or more. It can be seen that stable isolation can be obtained regardless of changes in environmental temperature.

[0041]

As described above, according to the present invention,
A visible light isolator that is hardly affected by a change in environmental temperature due to practical temperature, can always secure stable isolation in the practical temperature change range, and can contribute to miniaturization is realized.

[Brief description of drawings]

FIG. 1 is a permanent magnet for magnetic field application provided in the optical isolator of the present invention, which has a chemical formula (Nd _{1 -Y} Dy _Y ) ₂ Fe _14.
It is a figure which shows the environmental temperature dependence of the residual magnetic flux density in the neodymium-disprodium-iron-boron magnet shown by B (however, 0.1 <= Y <= 0.5).

FIG. 2 is a diagram showing a change in isolation value due to a deviation of a Faraday rotation angle from 45 degrees in a conventional optical isolator.

FIG. 3 shows a Faraday rotator included in the optical isolator of the present invention or a conventional optical isolator, which is a cadmium-manganese-tellurium single crystal represented by the chemical formula Cd _1-X Mn _X Te (where 0.1 ≦ X ≦ 0.5). Crystal wavelength 0.63 to 0.85 [μm]
It is a figure which shows the environmental temperature dependence of the Verde constant in the range of.

FIG. 4 is a diagram showing the environmental temperature dependence of the residual magnetic flux density in a neodymium / iron / boron magnet represented by a chemical formula (Nd ₂ Fe ₁₄ B), which is a permanent magnet for applying a magnetic field included in a conventional optical isolator. ..

Claims (1)

[Claims] 1. The chemical formula Cd _1-X Mn _X Te (provided that 0.
An optical isolator using a cadmium-manganese-tellurium single crystal represented by 1 ≦ X ≦ 0.5) as a Faraday rotator and a permanent magnet for applying a magnetic field,
The permanent magnet has the chemical formula (Nd _1-Y Dy _Y ) ₂ Fe ₁₄ B
(However, 0.1 ≦ Y ≦ 0.5) Neodymium
An optical isolator characterized by using dysprodium / iron / boron magnets.