JPH06222311A - Bismuth-substituted rare earth-iron-garnet single crystal film, optical isolator and magneto-optical switch - Google Patents

Abstract

PURPOSE:To provide the optical isolator and magneto-optical switch are small in size, simple in construction and low in cost, are easily produced and are indispensable for optical fiber communication and the bismuth substitution type rare earth-iron-garnet single crystal film used therein. CONSTITUTION:The bismuth-substd. rare earth-iron-garnet single crystal film used for a Faraday rotor has the chemical compsn. expressed by GdxRyBi5-x-yFe5-z(AlGa)zO2 (where R is at least one kind among La, Co, Pr, Nd, Sm, Eu, Tb, Dy, Er, Tm, Yb, Lu and Y and (x), (y), (z)are respectively numbers of 1.0<=x<=2.5, 0<=y<=1.9, 0.5<=z<=2.0). This single crystal film maintains the coefft. of Faraday rotation at the time of magnetically saturating the single crystal film even if an external magnetic field is removed after the single crystal film magnetically satd. by impressing the external magnetic field thereto in the perpendicular direction to the single crystal film.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bismuth-substituted rare earth iron garnet single crystal film, an optical isolator using the same as a Faraday rotator, and a magneto-optical switch.

[0002]

2. Description of the Related Art In optical fiber communication, yttrium iron garnet single crystal or bismuth (Bi) substituted iron garnet single crystal is used for the purpose of removing reflection noise to a light source or for optical switching in a communication repeater. Previously used optical isolators and magneto-optical switches are used. These single crystals have a characteristic called a Faraday rotation effect in which the plane of polarization of polarized light that has passed through the single crystal rotates when polarized light is incident in the direction of the magnetic field or in the opposite direction with an external magnetic field applied. This Faraday rotation effect is non-reciprocal, unlike simple optical rotation, and is therefore used in optical isolators and magneto-optical switches.

3 and 4 are diagrams showing the principles of an optical isolator and a magneto-optical switch, respectively. In the optical isolator shown in FIG. 3, two polarizers 7 and 9 having polarization plane selection directions 8 and 10 shifted from each other by 45 ° and a Faraday rotator 5 having a Faraday rotation angle of 45 ° located between them. , And a magnet (not shown) for applying a magnetic field to the Faraday rotator as shown by an arrow 11, which is usually a cylindrical permanent magnet that covers the periphery of the Faraday rotator,
It is composed by. Reference numeral 6 is light that is polarized.

The principle of the magneto-optical switch shown in FIG. 4 is also similar to that of an optical isolator. That is, the magneto-optical switch includes a polarizer 14 having a polarization selection direction 15, a Faraday rotator 12, a polarization beam splitter 16 instead of the exit side polarizer 9, and an electromagnet (not shown) for applying an external magnetic field 17. By electrically reversing the direction of the direct current flowing through this electromagnet and reversing the direction 17 of the magnetic field, the direction of Faraday rotation is reversed and the direction of transmitted light 1
8 is switching.

As the electromagnet for the magneto-optical switch, in addition to the one in which a direct current has to be constantly applied by using a coil, the one in which a coil 24 is wound around a semi-hard magnetic material 23 as shown in FIG. is there. The method of FIG. 5 has an advantage of low power consumption because the optical switching operation is performed only by applying a DC pulse current, and is being put to practical use. In FIG. 5, 21 is a polarizer, 19 is a Faraday rotator, 22 is a polarization beam splitter, 20 is incident light, and 25 is switched output light.

In such an optical isolator and a magneto-optical switch, there is one in which an optical system such as a polarizer is complicated so that the incident light can operate even if it is unpolarized. Is similar to that shown in FIGS.

[0007]

In general, yttrium iron garnet single crystals and bismuth-substituted rare earth iron garnet single crystals show a constant Faraday rotation angle under a magnetic field above the saturation magnetic field, but have a value below the saturation magnetic field. It is common knowledge that the Faraday rotation angle is almost proportional to the external magnetic field under a magnetic field, and that the Faraday rotation effect disappears when the external magnetic field is removed.

Therefore, when the yttrium iron garnet single crystal film or the bismuth-substituted rare earth iron garnet single crystal film is used in the above optical isolator or magneto-optical switch, a magnet for applying an external magnetic field is indispensable. As a result, miniaturization and cost reduction were hindered.
In particular, in a magneto-optical switch, a coil wound around a semi-hard magnetic material has a complicated structure, becomes large in size, and becomes considerably expensive as shown in FIG.

Therefore, the technical problem of the present invention is to provide an optical isolator and a magneto-optical switch, which are indispensable for optical fiber communication, which are simple in structure, small in size, and easily manufactured at low cost, and a bismuth-substituted rare earth iron garnet used for the same. It is to provide a crystalline film.

[0010]

In order to solve these problems, the present inventor has found that the yttrium iron garnet single crystal or the bismuth-substituted rare earth iron garnet single crystal used in the Faraday rotator is faradaic even if the external magnetic field disappears. The present invention has been completed by finding out that the present invention has the ability to hold the rotation angle.

According to the present invention, in the bismuth-substituted rare earth iron garnet single crystal film grown by the LPE method, the single crystal film has a chemical composition of Gd _{x Ry} Bi _3-xy.
Fe _{5- z} (AlGa) _z O ₁₂ (where R is La, Ce,
Pr, Nd, Sm, Eu, Tb, Dy, Er, Tm, Y
at least one of b, Lu, and Y, x, y,
z is 1.0 ≦ x ≦ 2.5, 0 ≦ y ≦ 1.9,
It is a number of 0.5 ≦ z ≦ 2.0. ), The Faraday rotation effect at the time of magnetic saturation is maintained even if the external magnetic field is removed after applying the external magnetic field in the direction crossing the single crystal film surface to cause magnetic saturation. A bismuth-substituted rare earth iron garnet single crystal film is obtained.

Further, according to the present invention, there is obtained a Faraday rotator characterized by comprising the bismuth-substituted rare earth iron garnet single crystal film.

Further, according to the present invention, there is provided an optical isolator which is used in a state in which an external magnetic field is applied to the Faraday rotator to cause magnetic saturation and the external magnetic field is removed.

Further, according to the present invention, there is provided a magneto-optical switch which is characterized in that an external magnetic field is applied to the Faraday rotator to cause magnetic saturation, and the Faraday rotator is used with the external magnetic field removed.

Further, according to the present invention, the Faraday rotator and an electromagnet for applying an external magnetic field to the Faraday rotator are provided, and a DC pulse current is applied to the electromagnet at any time to perform a light switching operation. A magneto-optical switch is obtained which is characterized by carrying out.

[0016]

When the bismuth-substituted rare earth iron garnet single crystal film of the present invention is used as a Faraday rotator, a Faraday rotation angle can be given to incident light without applying an external magnetic field.

[0017]

EXAMPLES Examples of the present invention will be described below.

Example 1 Gadolinium oxide (Gd ₂ O)
₃ ), iron oxide (Fe ₂ O ₃ ), aluminum oxide (Al
₂ O ₃ ), gallium oxide (Ga ₂ O ₃ ), bismuth oxide (Bi ₂ O ₃ ), lead oxide (PbO), boron oxide (B ₂
O ₃ ), respectively 1,7,1,1,25,50,15 mol
% Of non-magnetic calcium / magnesium / zirconium-substituted gadolinium / gallium / garnet (chemical formula (GdCa) ₃ (GaMgZr) ₅ O) with a total weight of 5 kg dissolved and mixed in a platinum crucible.
_A bismuth-substituted gadolinium / iron / aluminum / gallium / garnet (chemical formula: Gd _1.8 Bi _1.2 Fe _4.0 Al _0.5 Ga on the single crystal substrate ₁₂ shown by the LPE method.
_A single crystal film (denoted by _0.5 O ₁₂ ) was grown. While applying a magnetic field to the single crystal film in the direction perpendicular to the film surface, light with wavelengths of 1.31 μm and 1.55 μm was made incident in the same direction, and the change in the Faraday rotation coefficient was measured while changing the intensity of the applied magnetic field. . The results are shown in FIGS. 1 and 2.

As shown in the figure, in this single crystal film, once an external magnetic field having a magnitude equal to or higher than the saturation magnetic field was applied, the Faraday rotation coefficient remained substantially unchanged even if the external magnetic field was removed.

Further, in a bismuth-substituted rare earth iron garnet single crystal film of any composition, even if an external magnetic field having a magnitude higher than the saturation magnetic field is once applied and then the external magnetic field is removed, the Faraday rotation coefficient is equal to or higher than the saturation magnetic field. In order to clarify whether or not the value is maintained, the bismuth-substituted rare earth iron garnet single crystal film with extremely wide range of composition was grown by the LPE method, and the relation between the external magnetic field and the Faraday rotation coefficient was investigated. did. As a result, the chemical formula Gd
_x R _y Bi _3-xy Fe _5-z (AlGa) _z O ₁₂ (however,
R is La, Ce, Pr, Nd, Sm, Eu, Tb, D
At least one of y, Er, Tm, Yb, Lu, and Y, and x, y, and z are 1.0 ≦ x ≦ 2.5 and 0 ≦ y.
≦ 1.9 and 0.5 ≦ z ≦ 2.0. In the composition shown in (), we found that once an external magnetic field with a magnitude greater than the saturation magnetic field was applied, the Faraday rotation coefficient maintained a value above the saturation magnetic field even if the external magnetic field was removed.

By the way, in the bismuth-substituted rare earth iron garnet single crystal film grown by the LPE method, platinum mixed in from the crucible and a flux in the melt (a small amount of lead oxide and boron oxide in this embodiment) were mixed. ), Lead and boron (boron) mixed in as impurities are present.

Further, in a bismuth-substituted rare earth iron garnet single crystal film grown by the LPE method, an element such as silicon having a valence other than plus 3 valences when ionized in order to reduce light absorption or the like. , Magnesium, calcium, vanadium, etc. may be mixed in as trace impurities.

Example 2 Bismuth-substituted gadolinium / iron / aluminum / gallium / garnet grown in Example 1 (chemical formula Gd _1.8 Bi _1.2 Fe _4.0 Al
_0.5 Ga _0.5 O ₁₂ ) is applied to a single crystal film in the direction perpendicular to the film surface, and then an external magnetic field with a strength higher than the saturation magnetic field is once applied, and then a light with a wavelength of 1.31 μm and a wavelength of 1.55 μm And polished to a thickness that produces a Faraday rotation of 45 °. In this case, the thickness was 375 μm (for wavelength 1.31 μm) and 563 μm (wavelength 1.55 μm), respectively.

An optical isolator using the bismuth-substituted gadolinium / iron / aluminum / gallium / garnet single crystal film as a Faraday rotator was assembled. That is, the optical isolator shown in FIG. 3 does not require the external magnetic field applying magnet. Since this optical isolator does not require a magnet for applying an external magnetic field,
It was small and easy to assemble.

Example 3 Bismuth-substituted gadolinium / iron / aluminum / gallium / garnet (chemical formula Gd _1.8 Bi _1.2 Fe _4.0 Al) grown in Example 1
_0.5 Ga _0.5 O ₁₂ ) is applied to a single crystal film in the direction perpendicular to the film surface, and then an external magnetic field with a strength higher than the saturation magnetic field is once applied, and then a light with a wavelength of 1.31 μm and a wavelength of 1.55 μm And polished to a thickness that produces a Faraday rotation of 45 °. The thickness of each single crystal film is 375 μm
(For wavelength 1.31μm), 563μm (wavelength 1.55μ
m).

Then, a magneto-optical switch using these bismuth-substituted gadolinium / iron / aluminum / gallium / garnet single crystal films as Faraday rotators was assembled.

That is, a magneto-optical switch of the type shown in FIG. 4 is obtained. At this time, as a magnet for applying an external magnetic field for switching, a coil wound around an iron core was used, and a DC pulse current was applied to the coil to reverse the Faraday rotation and perform optical switching. This magneto-optical switch is smaller and has a much simpler structure than a conventional magneto-optical switch in which a coil 24 is wound around a semi-hard magnetic material 23 as shown in FIG. Was easy.

As described above, in Examples 2 and 3, the bismuth-substituted gadolinium / iron / aluminum / gallium / garnet (chemical formula Gd _1.8 Bi _1.2) grown in Example 1 was used.
Although an optical isolator and a magneto-optical switch using a Faraday rotator made of a single crystal film (represented by Fe _4.0 Al _0.5 Ga _0.5 O ₁₂ ) are shown, the composition is not limited to this composition, and the composition shown in Example 1, that is, the chemical formula Gd _x R _y Bi _3-xy F
e _5-z (AlGa) _z O ₁₂ (where R is La, Ce, P
r, Nd, Sm, Eu, Tb, Dy, Er, Tm, Y
at least one of b, Lu, and Y, x, y,
z is 1.0 ≦ x ≦ 2.5, 0 ≦ y ≦ 1.9,
It is a number of 0.5 ≦ z ≦ 2.0. It is needless to say that the present invention includes all of the optical isolators and the magneto-optical switches, each of which has a Faraday rotator made of the bismuth-substituted rare earth iron garnet single crystal film shown in FIG.

[0029]

As described above, according to the present invention, the Faraday rotation can be applied without the need for an applied magnetic field, so that the optical isolator and the magneto-optical switch, which are indispensable for optical fiber communication, can be miniaturized. ， With its simple structure, it can be easily manufactured at low cost, so its industrial value is extremely large.

[Brief description of drawings]

FIG. 1 is a wavelength of 1.31 μm of a bismuth-substituted gadolinium / iron / aluminum / gallium / garnet (chemical formula Gd _1.8 Bi _1.2 Fe _4.0 Al _0.5 Ga _0.5 O ₁₂ ) single crystal film according to Example 1 of the present invention. FIG. 3 is a diagram showing a relationship between an external magnetic field and Faraday rotation with respect to the light.

FIG. 2 is a wavelength of 1.55 μm of a bismuth-substituted gadolinium / iron / aluminum / gallium / garnet (chemical formula Gd _1.8 Bi _1.2 Fe _4.0 Al _0.5 Ga _0.5 O ₁₂ ) single crystal film according to Example 1 of the present invention. FIG. 3 is a diagram showing a relationship between an external magnetic field and Faraday rotation with respect to the light.

FIG. 3 is a perspective view showing the principle of an optical isolator.

FIG. 4 is a perspective view showing the principle of a magneto-optical switch.

FIG. 5 is a diagram showing a configuration of a magneto-optical switch using a semi-hard magnetic material for an electromagnet.

[Explanation of symbols]

5,12,19 Faraday rotator 6,13,20 Light 7 Incident side polarizer 8 Polarization plane selection direction of incident side polarizer 7 Exit side polarizer 10 Polarization plane selection direction of exit side polarizer 9 11 External magnetic field Application direction 14,21 Polarizer 15 Polarization plane selection direction of the polarizer 14,22 Polarization beam splitter 17 Reversible external magnetic field direction 18,25 Two lights switched by the direction of external magnetic field 23 Semi-hard magnetic material 24 coils

Claims (5)

[Claims] 1. A bismuth-substituted rare earth iron garnet single crystal film grown by the LPE method, wherein the single crystal film has a chemical composition of Gd _x R _y Bi _3-xy Fe _5-z (AlGa) _z O ₁₂ (however, , R is La, Ce, Pr, Nd, Sm, Eu, Tb,
At least one of Dy, Er, Tm, Yb, Lu, and Y, where x, y, and z are 1.0 ≦ x ≦ 2.
5, 0 ≦ y ≦ 1.9 and 0.5 ≦ z ≦ 2.0. ), The Faraday rotation effect at the time of magnetic saturation is maintained even if the external magnetic field is removed after applying the external magnetic field in the direction crossing the single crystal film surface to cause magnetic saturation. Bismuth-substituted rare earth iron garnet single crystal film. 2. A Faraday rotator comprising the bismuth-substituted rare earth iron garnet single crystal film according to claim 1. 3. An optical isolator, which is used in a state where the external magnetic field is removed by applying an external magnetic field to the Faraday rotator according to claim 2 for magnetic saturation. 4. A magneto-optical switch which is used in a state in which an external magnetic field is applied to the Faraday rotator according to claim 2 to magnetically saturate the external magnetic field. 5. A Faraday rotator according to claim 2, and an electromagnet for applying an external magnetic field to the Faraday rotator, and a DC pulse current is applied to the electromagnet at any time to perform a light switching operation. Is a magneto-optical switch.