JPH103059A - Polarization-independent optical isolator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To give inverse magnetic fields to a Faraday element without sticking two cylindrical permanent magnets which are magnetized inversely to each other by constituting the combination of directions of Faraday rotations of the Faraday element by a piece of radially oriented permanent magnet. SOLUTION: This polarization-independent isolator has a permanent magnet M which has a sufficient magnetic field to give necessary saturated magnetic field to Faraday elements F1 and F2 and is radially oriented so that it has a N-pole in the inner side of the cylinder part of the permanent magnet M as its pole direction is shown by arrows, and it has a S-pole in the outer side. And the magnet is constituted so as to give inverse magnetic fields to the Faraday elements F1 and F2 respectively. Since the polarization-independent type optical isolator constituted by using this radially oriented permanent magnet M has a sufficient function of an optical isolator and eliminates the need for sticking individual permanent magnets to each other to obtain inverse directions of magnetization, the yield is improved when the optical isolator is produced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention prevents light waves emitted from a laser as a light source from returning to a light source due to various causes in optical communication, transmission of a broadcast wave using light, and measurement using light. The present invention relates to an optical isolator that is used for filtering.

[0002]

2. Description of the Related Art Conventionally, such an optical isolator is composed of a Faraday element, a birefringent element, and a permanent magnet for applying a magnetic field to the Faraday element. When it is necessary to apply rotation, an optical isolator is formed by bonding cylindrical permanent magnets magnetized in the axial direction in the opposite direction.

[0003]

Conventionally, when applying a magnetic field in opposite directions to a plurality of Faraday elements, an optical isolator is constructed by attaching cylindrical permanent magnets in opposite directions and arranging them outside the Faraday element. However, when two cylindrical magnets are adhered to each other, the same poles are brought close to each other, so that a repulsive force acts to cause inconveniences such as breakage of the magnets and troublesome construction.

Therefore, in the present invention, in order to apply a magnetic field in the opposite direction to the Faraday element, it is not necessary to use two permanent magnets, which are magnetized in opposite directions, and use a permanent magnet. Provide an isolator.

[0005]

SUMMARY OF THE INVENTION The present invention comprises a plurality of Faraday elements, a plurality of birefringent elements, and a magnetic field applying mechanism for magnetizing the Faraday element, so as to suppress polarization mode dispersion. In the polarization-independent optical isolator, there is provided a polarization-independent optical isolator characterized in that a combination of directions of Faraday rotation of the Faraday element is constituted by one radially oriented permanent magnet as the magnetic field applying mechanism. .

Further, the present invention provides a first birefringent element, a first birefringent element, a second birefringent element, a third birefringent element, and a third birefringent element which are arranged in the light transmission direction in order. And a fourth birefringent element, wherein the polarization separation directions of the first and second birefringent elements are inclined at about 135 ° with each other in a plane perpendicular to the transmitted light, and the first and second birefringent elements are The ratio of the polarization separation distances of the elements is 2 ^1/2 -1: 1, and the polarization separation directions of the second and third birefringent elements are inclined by about 90 ° with each other in a plane perpendicular to the transmitted light; The ratio of the polarization separation distance between the second and third birefringent elements is 1: 2 ^1/2 −1, and the polarization separation direction of the third and fourth birefringent elements is in a plane perpendicular to the transmitted light. At about 135 ° from each other, the third and fourth
Wherein the ratio of the polarization separation distance of the birefringent element is 2 ^1/2 -1: 1 and the rotation angle of the polarization direction of the transmitted light by the first and second Faraday elements is about 45 °, and 1 The present invention provides an optical isolator characterized in that the radially oriented permanent magnets cause the first Faraday element and the second Faraday element to have the directions of Faraday rotation of transmitted light opposite to each other.

Further, the present invention provides a first birefringent element, a first birefringent element, a second birefringent element, a third birefringent element, and a third birefringent element which are sequentially arranged in the light transmission direction. And a fourth birefringent element, wherein the polarization separation directions of the first and second birefringent elements are inclined at about 135 ° with each other in a plane perpendicular to the transmitted light, and the first and second birefringent elements are The ratio of the polarization separation distances of the elements is 1: 2 ^1/2 -1, and the polarization separation directions of the second and third birefringent elements are inclined by about 90 ° with each other in a plane perpendicular to the transmitted light; The ratio of the polarization separation distance between the second and third birefringent elements is 2 ^1/2 -1: 1, and the polarization separation direction of the third and fourth birefringent elements is in a plane perpendicular to the transmitted light. At about 135 ° from each other, the third and fourth
Wherein the ratio of the polarization separation distance of the birefringent element is 1: 2 ^1/2 -1 and the rotation angle of the polarization direction of the transmitted light by the first and second Faraday elements is about 45 °, and 1 The present invention provides an optical isolator characterized in that the radially oriented permanent magnets cause the first Faraday element and the second Faraday element to have the directions of Faraday rotation of transmitted light opposite to each other.

Further, the present invention provides a first birefringent element, a first birefringent element, a second birefringent element, a second birefringent element, and a third birefringent element which are sequentially arranged in a light transmitting direction. , A third Faraday element and a fourth birefringent element, wherein the polarization separation directions of the first and second birefringent elements are inclined by about 135 ° with each other in a plane perpendicular to the transmitted light. The ratio of the polarization separation distance of the second birefringent element to that of the second birefringent element is 2 ^1/2 :
1, the polarization separation directions of the second and third birefringent elements are inclined at about 45 ° with each other in a plane perpendicular to the transmitted light, and the polarization separation distance of the second and third birefringent elements is 1: 2 ratio
^1/2 , wherein the polarization separation directions of the third and fourth birefringent elements are inclined at about 135 ° with each other in a plane perpendicular to the transmitted light, and the polarization separation direction of the third and fourth birefringent elements is The distance ratio is 2 ^1/2 : 1 and the rotation angle of the polarization direction of the transmitted light by the first, second, and third Faraday elements is about 45.
が, and the rotation angle of the polarization direction of the transmitted light by the first, second, and third Faraday elements is about 45 °, and the first Faraday element is formed by one radially oriented permanent magnet. The direction of Faraday rotation of transmitted light is opposite to that of the second Faraday element, and the direction of Faraday rotation of transmitted light is the same in the second Faraday element and the third Faraday element. An optical isolator characterized in that:

Further, the present invention provides a first birefringent element, a first birefringent element, a second birefringent element, a second birefringent element, and a third birefringent element which are sequentially arranged in a light transmission direction. , A third Faraday element and a fourth birefringent element, wherein the polarization separation directions of the first and second birefringent elements are inclined by about 135 ° with each other in a plane perpendicular to the transmitted light. And the ratio of the polarization separation distance of the second birefringent element to 1: 2
^1/2 , the polarization separation directions of the second and third birefringent elements are inclined by about 45 ° with each other in a plane perpendicular to the transmitted light,
When the ratio of the polarization separation distance between the second and third birefringent elements is 2
^1/2 : 1 and the polarization separation directions of the third and fourth birefringent elements are inclined at about 135 ° with each other in a plane perpendicular to the transmitted light. The ratio of the polarization separation distance is 1: ^21/2 , and the rotation angle of the polarization direction of the transmitted light by the first, second, and third Faraday elements is about 45.
が, and the rotation angle of the polarization direction of the transmitted light by the first, second, and third Faraday elements is about 45 °, and the first Faraday element is formed by one radially oriented permanent magnet. The direction of Faraday rotation of transmitted light is the same as that of the second Faraday element, and the direction of Faraday rotation of transmitted light is opposite to that of the second Faraday element and the third Faraday element. An optical isolator characterized in that:

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In implementing the means for solving the conventional problems, the present invention combines a plurality of Faraday elements, a plurality of birefringent elements and a radially oriented permanent magnet as specifically shown in the embodiments. The present invention provides a polarization-independent optical isolator that can improve the production yield and shorten the working time by designing the optical path lengths of two orthogonal polarization components of light separated in the optical isolator to be the same. is there. Hereinafter, specific examples will be described.

(Embodiment 1) In this embodiment, a polarization-independent optical isolator having two Faraday elements and four birefringent elements will be described. FIG. 1 is a perspective view showing an embodiment of the present invention.

FIG. 1 illustrates the arrangement of each element of this embodiment. In FIG. 1, the direction indicated by reference sign A ₁ is the light transmission direction of the optical isolator (hereinafter, referred to as “forward direction”), and the direction indicated by reference sign A ₂ is the light transmission blocking direction of the optical isolator (hereinafter, “reverse direction”). Direction). The symbols B ₁ ,
B ₂ , B ₃ and B ₄ are birefringent elements made of a rutile single crystal. Symbols F ₁ and F ₂ are Faraday elements made of terbium, bismuth, and iron garnet single crystals. In each of the birefringent elements B _{1 to} B ₄ , the optical axis and the surface of the element form an angle of about 48 °, the thickness of the birefringent elements B ₁ and B ₃ is 1 mm, and The thickness of the birefringent elements B ₂ and B ₄ is 0.41 mm.

FIG. 2 is a schematic sectional view showing a state in which a cylindrical radially oriented permanent magnet which is a feature of the present invention is used as a magnetic field applying mechanism of the optical isolator. The radially-oriented permanent magnet M has a magnetic field sufficient to give a saturation magnetic field required for the Faraday element, and the direction of the magnetic pole of the magnet is as shown in FIG.
As shown by the arrow in FIG. 2, the magnet is radially oriented so as to have an N pole inside the permanent magnet cylindrical portion and an S pole outside, and have opposite directions to the Faraday elements F ₁ and F ₂ , respectively. It is configured to apply a magnetic field.

FIG. 3 shows, by arrows, the polarization separation directions and distances of the birefringent elements B ₁ , B ₂ , B ₃ , and B ₄ . FIG. 3 (a)
Is the case of the forward direction of the transmitted light, the birefringent element B _1, in the direction of 12 o'clock of the watch hour hand, the distance is 100 [mu] m,
In the birefringent element B ₂ , the distance is 41 μm in the direction of the hour hand of the watch at 4:30, and in the birefringent element B ₃ , the distance is 100 μm in the direction of the hour hand of the watch at 1:30, the birefringence element B _4, in the direction of 9 o'clock of the watch hour hand distance is 41 .mu.m.

FIG. 3B shows the case of transmitted light in the reverse direction.
The polarization separation distance is the same as the forward direction, and the separation distance is opposite.

The Faraday elements F ₁ and F ₂ are radially oriented outside the Faraday elements F ₁ and F ₂ so that the polarization direction of the light having a wavelength of 1.55 μm is rotated by 45 °. Is saturated by a permanent magnet. Its direction of rotation, as viewed from the forward side, in a direction indicated by an arrow in FIG. 3, the Faraday element F ₁ is a direction rotated counterclockwise, take direction of rotating clockwise in Faraday element F _2.

FIG. 4 shows the optical isolator of this embodiment in which the side cross section is broken down into individual elements, and the positions through which light passes are numbered.

With respect to the birefringent element B ₁ , the position on the forward incident side is set to 1, the position between the birefringent element B ₁ and the Faraday element F ₁ is set to 2, and the position between the Faraday element F ₁ and the birefringent element B ₂ is set. Is 3, the position between the birefringent element B ₂ and the birefringent element B ₄ is 4, and the birefringent element B ₃ and the Faraday element F ₂
Is 5, the position between the Faraday element F ₂ and the birefringent element B ₄ is 6, and the position on the forward emission side with respect to the birefringent element B ₄ is 7.

FIG. 5 shows the state of polarization separation of light transmitted in the forward and reverse directions. FIG. 5A shows the polarization state of light transmitted in the forward direction as viewed from the forward direction at each of the positions 1 to 7 described with reference to FIG. First, at the position 1, light incident from one point in the forward direction is unpolarized light and is represented as a polarized component orthogonal to the two directions. In the position 2, the birefringent element B ₁
As a result, the polarization component in the vertical direction (the extraordinary light component of the rutile crystal) moves 100 μm in the vertical direction, and the polarization component in the horizontal direction (the ordinary light component of the rutile crystal) remains at the original position. In third position, the Faraday element F _1, polarized light component is rotated either 45 ° in a counterclockwise direction. At the position 4, only the polarized light component inclined 45 ° counterclockwise from the vertical direction by the birefringent element B ₂ is at 4: 3 of the hour hand of the clock.
Move 41 μm in the direction of 0 minutes. At the position of 5, only the polarized light component inclined 45 ° counterclockwise from the horizontal direction by the birefringent element B ₃ is shifted by 10 in the direction of the hour hand at 1:30.
Move by 0 μm. The position of 6, the Faraday element F _2, rotating one of the polarization components is also 45 ° clockwise. At the position 7, only the polarization component in the horizontal direction is 41 μm in the direction of 9 o'clock of the hour hand of the clock by the birefringent element B ₄
It moves and coincides with the light of the other orthogonal polarization component.
As a result, light transmitted in the forward direction passes through the optical isolator without being separated into polarized light components.

Next, positions 1 to 7 of light transmitted in the opposite direction
5 (b) shows the polarization state as viewed from the forward direction in FIG.
First, at the position 7, light incident from one point in the opposite direction is unpolarized light and is represented as a polarized component orthogonal to the two directions. At the position 6, only the polarization component in the horizontal direction is 41 μm in the 3 o'clock direction of the hour hand of the timepiece by the birefringent element B ₄ .
I'm moving. In position 5, the Faraday element F _2, any polarization Mitsunari fraction is also rotated 45 ° clockwise. At the position 4, only the polarized light component inclined 45 ° clockwise from the vertical direction is moved by 100 μm in the direction of 7:30 of the hour hand of the clock by the birefringent element B ₃ . At the position 3, only the polarized light component inclined 45 ° clockwise from the horizontal direction due to the birefringent element B ₂ is at 10:03 of the hour hand of the clock.
Move 41 μm in the direction of 0 minutes. The second position, the Faraday element F _1, any polarization component is rotated 45 ° counterclockwise. In position 1, the birefringent element B
_{Due to 1} , only the vertical component moves by 100 μm in the direction of the 6 o'clock of the hour hand of the clock.

As a result, the light transmitted in the opposite direction is separated into a polarized light component when passing through the optical isolator, and is separated as shown in FIG.
It does not return to the 1 position.

(Embodiment 2) Next, a second embodiment will be described with reference to FIG.
This will be described with reference to FIGS. FIG. 11 is an explanatory diagram of the arrangement of birefringent elements and Faraday elements in an optical isolator according to the second embodiment of the present invention. FIG.
FIG. 8 is an explanatory diagram of a state in which a radially oriented permanent magnet is used as a constituent element of an optical isolator according to a second embodiment of the present invention. Arrows from N to S represent lines of magnetic force. FIG.
FIG. 9 is an explanatory diagram of polarization separation and polarization rotation of a birefringent element and a Faraday element in an optical isolator according to a second example of the present invention. FIG. 14 is an explanatory diagram of position numbering for explaining the functions of the birefringent element and the Faraday element constituting the optical isolator according to the second embodiment of the present invention. FIG. 15 is an explanatory diagram of the polarization separation and the polarization rotation of the forward and backward transmitted light at the respective number positions described in FIG. In the present embodiment, FIGS.
As can be seen from FIG. 5, with respect to the first embodiment shown in FIGS. 1 to 5, the order of each element and the direction of the magnetic field applied to the Faraday element are arranged in reverse to the forward direction of the transmitted light. It was done. As described in detail in the description of the first embodiment,
Also in the present embodiment, the light transmitted in the opposite direction is separated into a polarized light component when passing through the optical isolator, and FIG.
It does not return to the 1 position.

(Embodiment 3) In a third embodiment of the present invention, a polarization-independent optical isolator having three Faraday elements and four birefringent elements will be described.

FIG. 6 is a perspective view for explaining the arrangement of each element of this embodiment. 6, the direction indicated by the arrow labeled A ₁ is an optical isolator light transmission direction (hereinafter, referred to as forward), and the direction indicated by reference numeral A ₂ are the optical isolator light transmission blocking direction (hereinafter , The opposite direction)
It is. Symbols B ₁ , B ₂ , B ₃ and B ₄ are birefringent elements made of rutile single crystal. Symbols F ₁ , F ₂ , and F ₃ are Faraday elements made of terbium, bismuth, and iron garnet single crystals.

In each of the birefringent elements B _{1 to} B ₄ , the optical axis and the surface of the element make an angle of about 48 °, and the thickness of the birefringent elements B ₁ and B ₃ is 1 .41 mm, and the thickness of the birefringent elements B ₂ and B ₄ is 1.0 mm.

FIG. 7 is a cross-sectional view schematically showing a state in which a cylindrical radially oriented permanent magnet which is a feature of the present invention is used as a magnetic field applying mechanism of the optical isolator. The radially-oriented permanent magnet M has a magnetic field sufficient to give a necessary saturation magnetic field to the Faraday element, and the direction of the magnetic pole of the magnet is N-pole inside the permanent magnet cylinder as shown by the arrow in FIG. The Faraday element F ₁ is a magnet oriented radially so as to have an S pole on the outside, and is configured to apply an opposite magnetic field to a set of Faraday elements F ₁ , F ₂ , and F ₃ .

FIG. 8 shows the birefringent elements B ₁ , B ₂ , B ₃ ,
The polarization separating direction and distance of the B ₄ is shown in FIG optical transmission direction and a plane perpendicular. FIG. 8A shows the case of transmitted light in the forward direction. In the birefringent element B ₁ , the polarization separation distance is 141 μm in the direction of 4:30 of the short hand of the timepiece, and in the birefringent element B ₂ . , In the direction of 9 o'clock of the hour hand, the distance is 100μ
m, and in the birefringent element B ₃ , 7:30
In the direction of the minute, the distance is 141 μm and the birefringent element B ₄
Then, in the direction of 3 o'clock of the hour hand of the watch, the distance is 100 μm. FIG. 8B shows the case of transmitted light in the reverse direction, where the polarization separation distance is the same as the forward direction and the separation direction is opposite.

The Faraday elements F ₁ , F ₂ and F ₃ are arranged around the Faraday elements F ₁ , F ₂ and F ₃ such that the polarization direction of the light having a wavelength of 1.55 μm is rotated by 45 °. Saturated magnetization by the permanent magnet.
Its direction of rotation, viewed from the forward direction, a direction indicated by an arrow in FIG. 2, the Faraday element F ₁ takes a direction of rotating counterclockwise direction, the clockwise Faraday element F _2, F _3.

FIG. 9 is a diagram in which the side cross section of the optical isolator is disassembled into respective elements, and respective positions through which light passes are numbered. Respect birefringent element B _1, 1 to the position of the forward incident side, the birefringent element B ₁ and position 2 between the Faraday element F _1, the Faraday element F ₁ and position 3 between the birefringent element B _2, birefringent element B ₂ and position 4 between the Faraday element F _2, position 5 between the Faraday element F ₂ and the birefringent element B _3, a position between the birefringent element B ₃ and the Faraday element F ₃ 6 The position between the Faraday element F ₃ and the birefringent element B ₄ is 7
And then, and shows the position of the forward emission side as 8 with respect to the birefringent element B _4.

FIG. 10 shows the state of polarization separation of light transmitted in the forward and reverse directions. FIG. 10A shows a polarization state of light transmitted in the forward direction at each of the positions 1 to 8 described in FIG. 9 as viewed from the forward direction. First, at the position 1, light incident from one point in the forward direction is unpolarized light and is represented as a polarized light component orthogonal to two directions inclined 45 ° clockwise and counterclockwise from the horizontal direction. At position 2, the polarized light component (the extraordinary light component of the rutile crystal) in the direction inclined 45 ° clockwise from the horizontal direction moves 141 μm in the direction of 4:30 due to the birefringent element B ₁ , Polarized light component inclined 45 ° clockwise (ordinary light component of rutile crystal)
Remains in its original position. At the position 3, the polarization components are all rotated counterclockwise by the Faraday element F ₁ .
It rotates 5 °. At the position 4, only the horizontal polarization component moves 100 μm in the 9 o'clock direction of the hour hand of the timepiece by the birefringent element B ₂ . In the position of No. 5, the Faraday element F
_{Due to 2} , both polarization components are rotated clockwise by 45 °. At position 6, the birefringent element B ₃
Only the component inclined 45 ° counterclockwise from the horizontal direction moves 141 μm in the direction of the short hand at 7:30. The position of 7, the Faraday element F _3, is rotated either of the polarization components is also 45 ° clockwise. At the position 8, only the horizontal polarization component moves 100 μm in the direction of the 3 o'clock of the hour hand of the timepiece by the birefringent element B ₄ , and coincides with the light of the other orthogonal polarization component. As a result, light transmitted in the forward direction passes through the element of the optical isolator without being separated into polarized light components.

Next, positions 1 to 8 of light transmitted in the reverse direction
FIG. 10B shows the polarization state viewed from the forward direction in FIG. First, at the position 8, light incident from one point in the opposite direction is unpolarized light and is represented as a polarized component orthogonal to the two directions. The position of 7, the birefringent element B _4, only the polarized component tilted in the horizontal direction is 100μm moves in 9 o'clock direction of the timepiece hour hand. At the position 6, all the polarization components are clockwise 45 ° by the Faraday element F ₃ .
It is spinning. In position 5, the birefringent element B _3, are 141μm moved in the direction of 1:30 only watch hour hand polarization component inclined 45 ° from the horizontal direction in the counterclockwise direction. The position of the 4, the Faraday element F _2, rotating one of the polarization components is also 45 ° clockwise. In third position, the birefringent element B _2, only the polarized component tilted in the horizontal direction is 100μm moved in the direction of o'clock hour hand 3 of the watch. The second position, the Faraday element F _1, any polarization component is rotated 45 ° counterclockwise.
At the position 1, only the component inclined 45 ° clockwise from the horizontal direction by the birefringent element B ₁ is at 10:03 of the hour hand of the clock.
It has moved 141 μm in the direction of 0 minutes. As a result, when the light transmitted in the opposite direction passes through the element of the optical isolator, it is separated into a polarized light component and does not return to the position 1 in FIG.

(Embodiment 4) Next, a fourth embodiment will be described with reference to FIG.
This will be described with reference to FIG. FIG. 16 is an explanatory diagram of an arrangement of birefringent elements and Faraday elements in an optical isolator according to another embodiment of the present invention. FIG. 17 is an explanatory diagram of a state in which a radially oriented permanent magnet is used as a constituent element of an optical isolator according to another embodiment of the present invention. Arrows from N to S represent lines of magnetic force. FIG. 18 is an explanatory diagram of polarization separation and polarization rotation of a birefringent element and a Faraday element in an optical isolator according to another embodiment of the present invention. FIG. 19 is an explanatory diagram of position numbering for explaining respective functions of a birefringent element and a Faraday element constituting an optical isolator according to another embodiment of the present invention. FIG. 20 is an explanatory diagram of the polarization separation and the polarization rotation of the forward and backward transmitted light at each number position described in FIG. This embodiment is different from the third embodiment shown in FIGS. 6 to 10 in that the order of the elements and the direction of the magnetic field applied to the Faraday element are different from those of the third embodiment shown in FIGS. They are arranged in reverse with respect to the forward direction. As described in detail in the description of the third embodiment, also in this embodiment, the light transmitted in the opposite direction is separated into a polarized light component when passing through the optical isolator, and is separated into 1 in FIG.
Never return to the position.

In the above-described embodiment, four examples of the configuration of the plurality of Faraday elements and the plurality of birefringence elements have been described. However, the configuration of the polarization-independent optical isolator is not limited to four. Of course, the use of the radially oriented magnet as described in the present embodiment as a magnetic field application mechanism for realizing a combination of Faraday elements magnetized in opposite directions is of course also effective.

[0034]

As described above, a polarization-independent optical isolator constituted by using a radially oriented magnet is:
It has a sufficient optical isolator function, and it is not necessary to bond individual permanent magnets in opposite magnetization directions as in the past, so the yield in manufacturing the optical isolator is higher than in the past. And assembly time can be shortened.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an arrangement of a birefringent element and a Faraday element in an optical isolator according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a state in which a radially oriented permanent magnet is used as a constituent element of the optical isolator according to the embodiment of the present invention. Arrows from N to S represent lines of magnetic force.

FIG. 3 is an explanatory diagram of polarization separation and polarization rotation of a birefringent element and a Faraday element in the optical isolator according to the embodiment of the present invention.

FIG. 4 is an explanatory diagram of position numbering for explaining respective functions of a birefringent element and a Faraday element constituting the optical isolator according to the embodiment of the present invention.

FIG. 5 is an explanatory diagram of polarization separation and polarization rotation of forward and backward transmitted light at each number position described in FIG. 4;

FIG. 6 is an explanatory diagram of an arrangement of a birefringent element and a Faraday element in an optical isolator according to a third embodiment of the present invention.

FIG. 7 is an explanatory diagram of a state where a radially oriented permanent magnet is used as a constituent element of an optical isolator according to a third embodiment of the present invention. Arrows from N to S represent lines of magnetic force.

FIG. 8 is an explanatory diagram of polarization separation and polarization rotation of a birefringent element and a Faraday element in an optical isolator according to a third embodiment of the present invention.

FIG. 9 is an explanatory diagram of position numbering for explaining respective functions of a birefringent element and a Faraday element constituting the optical isolator according to the third embodiment of the present invention.

FIG. 10 is an explanatory diagram of polarization separation and polarization rotation of forward and backward transmitted light at each number position described in FIG. 9;

FIG. 11 is an explanatory diagram of an arrangement of birefringent elements and Faraday elements in an optical isolator according to a second example of the present invention.

FIG. 12 is an explanatory view of a state where a radially oriented permanent magnet is used as a constituent element of an optical isolator according to a second embodiment of the present invention. Arrows from N to S represent lines of magnetic force.

FIG. 13 is an explanatory diagram of polarization separation and polarization rotation of a birefringent element and a Faraday element in an optical isolator according to a second example of the present invention.

FIG. 14 is an explanatory diagram of position numbering for explaining respective functions of a birefringent element and a Faraday element constituting the optical isolator according to the second embodiment of the present invention.

FIG. 15 is a diagram showing the forward direction at each number position shown in FIG. 14;
FIG. 4 is an explanatory view of polarization separation and polarization rotation of backward transmitted light.

FIG. 16 is an explanatory diagram of an arrangement of a birefringent element and a Faraday element in an optical isolator according to a fourth embodiment of the present invention.

FIG. 17 is an explanatory diagram of a state where a radially oriented permanent magnet is used as a constituent element of an optical isolator according to a fourth embodiment of the present invention. Arrows from N to S represent lines of magnetic force.

FIG. 18 is an explanatory diagram of polarization separation and polarization rotation of a birefringent element and a Faraday element in an optical isolator according to a fourth embodiment of the present invention.

FIG. 19 is an explanatory diagram of position numbering for explaining respective functions of a birefringent element and a Faraday element constituting the optical isolator according to the fourth embodiment of the present invention.

20 is a diagram illustrating the forward direction at each number position described in FIG. 19;
FIG. 4 is an explanatory view of polarization separation and polarization rotation of backward transmitted light.

[Explanation of symbols]

A ₁ , A ₁₁ Light transmission direction A ₂ , A ₂₁ Light transmission element direction B _{1 to} B ₄ , B _{11 to} B ₄₁ Birefringent element F _{1 to} F ₃ , F _{11 to} F ₃₁ Faraday element M Radially oriented permanent magnet N , S Permanent magnet poles

Claims (5)

[Claims] 1. A polarization independent optical isolator comprising a plurality of Faraday elements, a plurality of birefringent elements, and a magnetic field applying mechanism for magnetizing the Faraday element, and configured to suppress polarization mode dispersion. A polarization-independent optical isolator, wherein a combination of directions of Faraday rotation of the Faraday element is constituted by one radially oriented permanent magnet as the magnetic field applying mechanism. 2. A first birefringent element, a first Faraday element, a second birefringent element, which are sequentially arranged in a light transmission direction.
A third birefringent element, a third Faraday element, and a fourth birefringent element, wherein the polarization separation directions of the first and second birefringent elements are inclined at about 135 ° with each other in a plane perpendicular to the transmitted light. Wherein the ratio of the polarization separation distance between the first and second birefringent elements is 2 ^1/2 -1: 1 and the polarization separation direction of the second and third birefringent elements is perpendicular to the transmitted light. About 9
It is inclined by 0 °, the ratio of the polarization separation distance of the second and third birefringent elements is 1: 2 ^1/2 −1, and the polarization separation direction of the third and fourth birefringent elements is transparent. Are inclined at about 135 ° with each other in a plane perpendicular to the light, the ratio of the polarization separation distance of the third and fourth birefringent elements is 2 ^1/2 −1: 1, and the first and second birefringent elements are The rotation angle of the polarization direction of the transmitted light by the second Faraday element is about 45 °, and the Faraday rotation of the transmitted light is performed between the first Faraday element and the second Faraday element by one radially oriented permanent magnet. An optical isolator characterized in that directions are opposite to each other. 3. A first birefringent element, a first Faraday element, a second birefringent element, which are arranged in order in a light transmission direction.
A third birefringent element, a third Faraday element, and a fourth birefringent element, wherein the polarization separation directions of the first and second birefringent elements are inclined at about 135 ° with each other in a plane perpendicular to the transmitted light. Wherein the ratio of the polarization separation distance between the first and second birefringent elements is 1: 2 ^1/2 -1 and the polarization separation direction of the second and third birefringent elements is perpendicular to the transmitted light. About 9
It is inclined by 0 °, the ratio of the polarization separation distance of the second and third birefringent elements is 2 ^1/2 −1: 1, and the polarization separation direction of the third and fourth birefringent elements is transmitted. Are inclined by about 135 ° with each other in a plane perpendicular to the light, the ratio of the polarization separation distance of the third and fourth birefringent elements is 1: 2 ^1/2 −1, and the first and second birefringent elements are The rotation angle of the polarization direction of the transmitted light by the second Faraday element is about 45 °, and the Faraday rotation of the transmitted light is performed between the first Faraday element and the second Faraday element by one radially oriented permanent magnet. An optical isolator characterized in that directions are opposite to each other. 4. A first birefringent element, a first Faraday element, a second birefringent element, which are sequentially arranged in a light transmission direction.
The first Faraday element, the third birefringent element, the third Faraday element, and the fourth birefringent element;
The polarization separation directions of the first and second birefringent elements are inclined by about 135 ° in a plane perpendicular to the transmitted light, and the ratio of the polarization separation distance of the first and second birefringent elements is 2 ^1/2 : 1, the polarization separation directions of the second and third birefringent elements are inclined at about 45 ° with each other in a plane perpendicular to the transmitted light, and the polarization separation distance of the second and third birefringent elements is the ratio is 1: 2 ^1/2, the third and are inclined approximately 135 degrees from each other in a plane perpendicular to the fourth polarization separating direction transmitted light of the birefringent element, said third and fourth double The ratio of the polarization separation distance of the refraction element is 2 ^1/2 : 1; the rotation angle of the polarization direction of the transmitted light by the first, second, and third Faraday elements is about 45 °; and The rotation angle of the polarization direction of the transmitted light by the first, second, and third Faraday elements is about 45 °, and one radially oriented permanent magnet is used. The directions of the Faraday rotation of the transmitted light are opposite to each other in the first Faraday element and the second Faraday element, and the Faraday rotation of the transmitted light is opposite in the second Faraday element and the third Faraday element. Optical isolators characterized by having the same direction. 5. A first birefringent element, a first Faraday element, a second birefringent element, which are sequentially arranged in a light transmission direction,
The first Faraday element, the third birefringent element, the third Faraday element, and the fourth birefringent element;
The polarization separation directions of the first and second birefringent elements are inclined by about 135 ° in a plane perpendicular to the transmitted light, and the ratio of the polarization separation distance between the first and second birefringent elements is 1: 2 ^{1 / 2} , the polarization separation directions of the second and third birefringent elements are inclined at about 45 ° with each other in a plane perpendicular to the transmitted light, and the polarization separation distance of the second and third birefringent elements is ratio 2 ^1/2: 1, the third and are inclined approximately 135 degrees from each other in a plane perpendicular to the fourth polarization separating direction transmitted light of the birefringent element, said third and fourth double The ratio of the polarization separation distance of the refraction element is 1: 2 ^1/2 , and the rotation angle of the polarization direction of the transmitted light by the first, second, and third Faraday elements is about 45 °, and
The rotation angle of the polarization direction of the transmitted light by the first, second, and third Faraday elements is about 45 °, and the first Faraday element and the second Faraday element are formed by one radially oriented permanent magnet. The direction of Faraday rotation of transmitted light is the same as that of the element, and the directions of Faraday rotation of transmitted light of the second Faraday element and the direction of Faraday rotation of the third Faraday element are opposite to each other. Optical isolator.