Optical circulator and optical monitoring method

Abstract

We provide a light circulator that allows for easy detection of damage. [Solution] The device includes a first port P1 into which light is incident, a second port P2 from which light incident from the first port P1 is emitted, a third port P3 from which light incident from the second port P2 is emitted, a first polarizer 5 and a second polarizer 6 located on the first port P1 side, a third polarizer 7 located on the second port P2 side and positioned together with the first polarizer 5 to sandwich the second polarizer 6, a Faraday rotator 8 located between the first polarizer 5 and the second polarizer 6, and a half-wave plate 9 located between the second polarizer 6 and the third polarizer 7, and includes a light emission unit 3 into which a portion of the light incident from the first port P1, passing through the first polarizer 5, the Faraday rotator 8, the second polarizer 6 and the half-wave plate 9, and incident on the third polarizer 7 is reflected and emitted as reflected light.

Description

[Technical Field]

[0001] The present invention relates to an optical circulator and an optical monitoring method. [Background technology]

[0002] An optical circulator is a magneto-optical element that directs light entering from one port to another port, while blocking light from returning to the port from which it entered. Optical circulators are used in optical communication systems, laser processing systems, and other applications.

[0003] Patent Document 1 below discloses an example of an optical circulator having four ports. In this optical circulator, light incident from the first port (port 1) is emitted from the fourth port (port 4). Light incident from the second port (port 2) is emitted from the third port (port 3). Light incident from the third port (port 3) is emitted from the first port (port 1). Light incident from the fourth port (port 4) is emitted from the second port (port 2). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2002-031780 [Overview of the project] [Problems that the invention aims to solve]

[0005] In recent years, laser processing has required even higher laser light intensity. However, increasing the laser light intensity can cause damage to elements such as the Faraday rotor and polarizer in the optical circulator. When these elements are damaged, the laser light can no longer pass through the damaged elements, causing the laser system to malfunction.

[0006] Therefore, when an element of the optical circulator is damaged, the element must be replaced immediately. However, since the Faraday rotator in the optical circulator is housed within a magnet, it is difficult to visually confirm that it is damaged. Similarly, since the polarizer is fixed to a holder, it is difficult to visually confirm that it is damaged.

[0007] Thus, conventionally, even when a failure occurs in a laser system, there has been a problem that it is difficult to confirm which part is damaged.

[0008] An object of the present invention is to provide an optical circulator and an optical monitoring method capable of easily detecting damage to an element when the element of the optical circulator is damaged.

Means for Solving the Problems

[0009] The optical circulator according to Aspect 1 of the present invention includes a first port into which light is incident, a second port that faces the first port and from which the light incident from the first port exits, and is arranged so as not to be located on a straight line connecting the first port and the second port. A third port from which the light incident from the second port exits, a first polarizer arranged on the first port side, a second polarizer, and a third polarizer arranged on the second port side and sandwiching the second polarizer together with the first polarizer. A Faraday rotator arranged between the first polarizer and the second polarizer, and a half-wave plate arranged between the second polarizer and the third polarizer. The half-wave plate and the third polarizer are arranged such that a part of the light incident from the first port, passing through the first polarizer, the Faraday rotator, the second polarizer, and the half-wave plate, and incident on the third polarizer is reflected to become reflected light. The optical circulator further includes an optical output unit capable of extracting the reflected light.

[0010] In the optical circulator of embodiment 2, in embodiment 1, when the relative installation angle Δθ is defined as the difference obtained by subtracting the sum of the angle between the optical transmission axis of the second polarizer and the horizontal plane and the rotation angle of the half-wave plate from the angle between the optical transmission axis of the third polarizer and the horizontal plane, it is preferable that Δθ is between +1° and +8°.

[0011] In the optical circulator of embodiment 3, it is preferable that the rotation angle of the half-wave plate is -51° or more and -39° or less, as in embodiment 2.

[0012] In the optical circulator of embodiment 4, it is preferable that the rotation angle of the Faraday rotor is +45° in any one embodiment from embodiment 1 to embodiment 3.

[0013] In the optical circulator of embodiment 5, it is preferable that the light emitting section is directly or indirectly connected to the photodiode in any one embodiment from embodiment 1 to embodiment 4.

[0014] In the optical circulator of embodiment 6, in any one embodiment from embodiment 1 to embodiment 5, it is preferable that the Faraday rotor comprises a magnet having a through hole and a Faraday element made of a paramagnetic material that transmits light and is disposed within the through hole of the magnet.

[0015] In the optical circulator of embodiment 7, it is preferable that the paramagnetic material is a glass material in embodiment 6.

[0016] In the optical circulator of embodiment 8, it is preferable that the glass material contains, in embodiment 7, Tb2O3 20% to 80%, B2O3 + P2O5 20% to 70%, and SiO20% to 45% in molar percentages on an oxide basis.

[0017] The optical monitoring method according to aspect 9 of the present invention comprises a first port into which light is incident, a second port facing the first port and from which light incident from the first port exits, a third port positioned so as not to be located on a straight line connecting the first port and the second port and from which light incident from the second port exits, a first polarizer positioned on the first port side, a second polarizer, a third polarizer positioned on the second port side and positioned together with the first polarizer to sandwich the second polarizer, a Faraday rotator positioned between the first polarizer and the second polarizer, and a Faraday rotator positioned between the second polarizer and the third polarizer. An optical monitoring method for monitoring the intensity of transmitted light of an optical circulator having a half-wave plate, wherein the half-wave plate and the third polarizer are arranged such that light incident on the optical circulator enters from the first port, passes through the first polarizer, the Faraday rotor, the second polarizer, and the half-wave plate, and a portion of the light incident on the third polarizer is reflected to become reflected light, and the optical circulator further has an optical emission section from which the reflected light can be extracted, and the method is characterized by comprising the step of monitoring the intensity of transmitted light of the optical circulator by measuring the intensity of the reflected light extracted from the optical emission section.

[0018] In the optical monitoring method of embodiment 10, in embodiment 9, it is preferable that the intensity of the light incident on the optical circulator is 300 mW or more and 150 W or less. [Effects of the Invention]

[0019] According to the present invention, it is possible to provide an optical circulator and an optical monitoring method that can easily detect damage to an element of the optical circulator when that element is damaged. [Brief explanation of the drawing]

[0020] [Figure 1] Figure 1 is a schematic diagram showing a light circulator according to the first embodiment of the present invention. [Figure 2] Figure 2 is a schematic diagram illustrating the optical path when light is incident from the first port in an optical circulator according to the first embodiment of the present invention. [Figure 3] Figure 3 is a schematic diagram illustrating the optical path when light is incident from the second port in the optical circulator according to the first embodiment of the present invention. [Figure 4] Figure 4 is a schematic diagram illustrating the optical path when light is incident from the third port in the optical circulator according to the first embodiment of the present invention. [Figure 5] Figure 5 is a schematic diagram of a comparative example optical circulator. [Figure 6] Figure 6 is a schematic diagram illustrating the optical path when light is incident from the first port in the example optical circulator. [Figure 7] Figure 7 is a schematic diagram illustrating the optical path when light is incident from the second port in the example optical circulator. [Figure 8] Figure 8 is a schematic diagram illustrating the optical path when light is incident from the third port in the example optical circulator. [Figure 9] Figure 9 is a schematic cross-sectional view along the direction of light passage, showing a Faraday rotor in a first embodiment of the present invention. [Figure 10] Figure 10 is a schematic diagram showing a light circulator according to a second embodiment of the present invention. [Modes for carrying out the invention]

[0021] Preferred embodiments of the present invention will be described below. However, the following embodiments are merely illustrative, and the present invention is not limited to these embodiments. In addition, in each drawing, components having substantially the same function may be referred to by the same reference numerals.

[0022] (Light circulator) (First embodiment) Figure 1 is a schematic diagram showing a light circulator according to the first embodiment of the present invention.

[0023] The optical circulator 1 has multiple ports through which light is incident or emitted. Specifically, the multiple ports of the optical circulator 1 are a first port P1, a second port P2, and a third port P3. Light incident from the first port P1 is emitted from the second port P2. Light incident from the second port P2 is emitted from the third port P3. In this embodiment, light incident from the third port P3 is not emitted from the optical circulator 1.

[0024] In addition, the optical circulator 1 has an optical emission section 3 as a tap port. In this embodiment, a portion of the light incident from the first port P1 can be extracted from the optical emission section 3. The intensity of this light can be monitored. The light incident on the optical circulator 1 is, for example, laser light.

[0025] The specific configuration of the optical circulator 1 will be described below. As shown in Figure 1, the optical circulator 1 has a housing 2. Multiple elements are arranged inside the housing 2. Multiple fiber collimators are connected to the housing 2. Each of these fiber collimators is the first port P1, the second port P2, the third port P3, and the optical emission section 3 as a tap port in this embodiment. Note that each port in this invention may also be an opening provided in the housing 2.

[0026] For example, an aluminum alloy can be used as the material for the housing 2. However, the material for the housing 2 is not particularly limited.

[0027] Each fiber collimator is connected to an optical fiber 4. Light enters the optical circulator 1 from the outside via the optical fiber 4. Light is emitted from the optical circulator 1 to the outside via the optical fiber 4.

[0028] The first port P1 and the second port P2 face each other. On the other hand, the third port P3 and the light emitting unit 3 are positioned so as not to lie on the straight line connecting the first port P1 and the second port P2. In other words, the third port P3 and the light emitting unit 3 are positioned at locations branching off from the straight line connecting the first port P1 and the second port P2. The positions where the straight line branches off towards the third port P3 and towards the light emitting unit 3 are different from each other. Specifically, the position where the straight line branches off towards the third port P3 is located closer to the first port P1 than the position where the straight line branches off towards the light emitting unit 3.

[0029] The optical circulator 1 comprises a first polarizer 5, a second polarizer 6, a third polarizer 7, a Faraday rotator 8, and a half-wave plate 9 as multiple elements. The first polarizer 5 is positioned on the side of the first port P1 and the side of the third port P3. On the other hand, the third polarizer 7 is positioned on the side of the second port P2 and the side of the light emission section 3. The second polarizer 6 is positioned between the first polarizer 5 and the third polarizer 7. The Faraday rotator 8 is positioned between the first polarizer 5 and the second polarizer 6. The half-wave plate 9 is positioned between the second polarizer 6 and the third polarizer 7.

[0030] The first polarizer 5, the second polarizer 6, and the third polarizer 7 are specifically polarizing beam splitters. Each of the first polarizer 5, the second polarizer 6, and the third polarizer 7 has a light transmission axis. The first polarizer 5 splits the light according to the relationship between the direction of the light transmission axis and the polarization plane of the light. More specifically, light incident on the first polarizer 5 is split according to the above relationship into light that passes through without changing its direction of propagation and light that is reflected inside the first polarizer 5, changes its direction of propagation, and is emitted. The same applies to the second polarizer 6 and the third polarizer 7.

[0031] The features of this embodiment are as follows: 1) A second polarizer 6 is positioned between the first polarizer 5 and the third polarizer 7, a Faraday rotator 8 is positioned between the first polarizer 5 and the second polarizer 6, and a half-wave plate 9 is positioned between the second polarizer 6 and the third polarizer 7. 2) The half-wave plate 9 and the third polarizer 7 are positioned such that a portion of the light incident on the third polarizer 7 is reflected to become reflected light. 3) There is a light emission unit 3 that can extract the reflected light reflected by the third polarizer 7. With these features, the intensity of the reflected light that enters from the first port P1, passes through each element, and is extracted from the light emission unit 3 can be monitored. This makes it easy to detect when an element of the optical circulator 1 is damaged. The details will be explained below.

[0032] Figure 2 is a schematic diagram illustrating the optical path when light is incident from the first port in the optical circulator according to the first embodiment.

[0033] In this specification, the direction in which the light transmission axis of a polarizer extends is defined as follows. In the following, the horizontal plane and clockwise direction are used as reference terms to indicate direction. Here, the plane extending parallel to the left and right directions in Figure 2, etc., is defined as the horizontal plane. In Figure 2, etc., the upward direction is the 12 o'clock direction, the rightward direction is the 3 o'clock direction, the downward direction is the 6 o'clock direction, and the leftward direction is the 9 o'clock direction.

[0034] When the first polarizer 5 is positioned such that the direction in which the light transmission axis of the first polarizer 5 extends is parallel to the horizontal plane, the light transmission axis extends in the 3 o'clock and 9 o'clock directions. In this case, when viewed from the first port P1 side to the second port P2 side, the 3 o'clock direction of the direction in which the light transmission axis extends is defined as 0°. Furthermore, the counterclockwise rotation direction is defined as the positive direction, and the clockwise rotation direction is defined as the negative direction. Note that +180° and -180° mean the same angle, so in the following explanation, only one of them may be mentioned. In this specification, both the angle at which the polarization plane of light rotates due to the Faraday rotator 8 and the angle at which it rotates due to the half-wave plate 9 are referred to as the rotation angle.

[0035] In this invention, the direction in which the light transmission axis of a polarizer acting as a polarizing beam splitter extends is assumed to be between -180° and +180°. For a polarizer with a light transmission axis extending at 0° and a polarizer with a light transmission axis extending at +180°, the angle of the polarization plane of light is the same when light parallel to the light transmission axis is passed through without changing the direction of light propagation. On the other hand, for a polarizer with a light transmission axis extending at 0° and a polarizer with a light transmission axis extending at +180°, the direction in which the light is emitted differs by 180° when reflecting light perpendicular to the light transmission axis and changing its direction of propagation before emission. The same applies to a polarizer with a light transmission axis extending at 0° and a polarizer with a light transmission axis extending at -180°.

[0036] Therefore, if the direction in which the light transmission axis of a polarizer extends differs by +180° or -180°, it can be said that they are equivalent except for the direction of internal reflection. In other words, if the direction in which the light transmission axis of a polarizer extends differs by +180° or -180°, the behavior of light passing through the polarizer without changing its direction of propagation is equivalent. In the following, when it is stated that light "passes through a polarizer," unless otherwise specified, it means that the light passes through the polarizer without changing its direction of propagation.

[0037] In this embodiment, the direction in which the light transmission axis of the first polarizer 5 extends is 0°. The direction in which the light transmission axis of the second polarizer 6 extends is +45°. The direction in which the light transmission axis of the third polarizer 7 extends is +180° or -180°, and the case of +180° will be described in the following explanation. The direction in which the light transmission axis of a polarizer extends can be adjusted, for example, by tilting a polarizer that was set up so that the direction in which the light transmission axis extends is 0° to a predetermined angle.

[0038] The following describes the optical path when light is incident from the first port P1. As shown in Figure 2, linearly polarized light I0 with a polarization plane angle of 0° is incident from the first port P1. The direction in which the light transmission axis of the first polarizer 5 extends is 0°. Here, the polarization plane of the light I0 incident from the first port P1 and the light transmission axis of the first polarizer 5 are parallel. Therefore, the light I0 passes through the first polarizer 5 without changing its direction of propagation. Alternatively, light that is not linearly polarized and incident from the first port P1 may be made linearly polarized with a polarization plane angle of 0° by passing it through the first polarizer 5.

[0039] In this specification, the angle of the polarization plane of light that has passed through a polarizer is described as being parallel to the light transmission axis of the polarizer. Therefore, the polarization plane of light I0 that has passed through the first polarizer 5 is 0°.

[0040] As shown in Figure 2, light I0 that has passed through the first polarizer 5 is incident on the Faraday rotator 8. The plane of polarization of light I0 incident on the Faraday rotator 8 is rotated by +45° due to the Faraday effect. As a result, the angle of the plane of polarization of light I0 that has passed through the Faraday rotator 8 is +45°.

[0041] Light I0 that has passed through the Faraday rotator 8 is incident on the second polarizer 6. The direction in which the light transmission axis of the second polarizer 6 extends is +45°. Here, the plane of polarization of light I0 that has passed through the Faraday rotator 8 and the light transmission axis of the second polarizer 6 are parallel. Therefore, light I0 passes through the second polarizer 6 without changing its direction of propagation. The angle of the plane of polarization of light I0 that has passed through the second polarizer 6 is +45°. Light I0 that has passed through the second polarizer 6 is incident on the half-wave plate 9. The plane of polarization of light I0 that has been incident on the half-wave plate 9 rotates by -41°. As a result, the angle of the plane of polarization of light I0 that has passed through the half-wave plate 9 is +45°-41°=+4°.

[0042] Light I0 that has passed through the half-wave plate 9 is incident on the third polarizer 7. The direction in which the light transmission axis of the third polarizer 7 extends is +180°. Here, the polarization plane of light I0 that has passed through the half-wave plate 9 and the light transmission axis of the third polarizer 7 are not parallel. Therefore, the third polarizer 7 transmits the component of light I0 that is parallel to the light transmission axis of the third polarizer 7, and reflects the component that is not parallel to the light transmission axis of the third polarizer 7. In other words, light I0 is split into light I1 that passes through the third polarizer 7 without changing its direction of propagation, and reflected light I2 that is reflected inside the third polarizer 7, changes its direction of propagation, and is emitted from the third polarizer 7. Light I1 is emitted from the second port P2. Reflected light I2 is emitted from the light emission section 3.

[0043] Here, we consider the angle Δα at which the polarization plane of light I0 incident on the third polarizer 7 is inclined with respect to the light transmission axis of the third polarizer 7. The polarization plane angle of light I0 incident on the third polarizer 7 is +4°. The direction in which the light transmission axis of the third polarizer 7 extends is +180°. In this case, Δα = +4° - (+180°) = -176°. As mentioned above, when the direction in which the light transmission axis of a polarizer extends differs by +180° or -180°, it can be said that they are equivalent except for the direction of internal reflection. Therefore, a polarizer with a light transmission axis extending in the direction of +180° and a polarizer with a light transmission axis extending in the direction of 0° can be said to be equivalent in terms of the behavior of light passing through the polarizer. Thus, Δα = +4° - (+180°) = -176° is equivalent to Δα = +4° - 0° = +4° in terms of the behavior of light passing through the polarizer.

[0044] When Δα = +4°, specifically, about 99% of the light I0 has a component parallel to the polarization plane of the third polarizer 7, and about 1% has a component perpendicular to the polarization plane of the third polarizer 7. Therefore, about 99% of the light I0 is emitted from the second port P2, and about 1% is emitted as reflected light from the light emission unit 3.

[0045] In this embodiment, a portion of the light I0 incident on the third polarizer 7 can be extracted as reflected light I2 from the light emission unit 3. By measuring the intensity of the extracted reflected light I2, the intensity of the transmitted light from the optical circulator 1 can be constantly monitored. In this specification, the transmitted light from the optical circulator 1 refers to the light that has passed through each element of the optical circulator 1. By monitoring the intensity of the transmitted light from the optical circulator 1, damage to an element of the optical circulator 1 can be easily detected when the intensity of the transmitted light decreases due to damage to an element.

[0046] The intensity of reflected light I2 can be measured, for example, by having a photodiode receive the reflected light I2. Specifically, the photodiode converts the reflected light I2 into an electrical signal, and the intensity of the electrical signal is measured.

[0047] In this embodiment, the light emission unit 3 is connected to a photodiode (not shown). More specifically, the light emission unit 3 is indirectly connected to the photodiode via the optical fiber 4 shown in Figure 1. Therefore, reflected light I2 is emitted from the light emission unit 3 to the photodiode via the optical fiber 4. For example, if the light emission unit 3 is an opening provided in the housing 2, the photodiode may be directly connected to the light emission unit 3.

[0048] The above explanation compared the relationship between the polarization plane of light I0 and the light transmission axis of the third polarizer 7. Next, we will examine the relationship between the light transmission axis of the second polarizer 6, the rotation angle of the half-wave plate 9, and the light transmission axis of the third polarizer 7. Let a be the angle of the light transmission axis in the second polarizer 6, φ be the rotation angle of the half-wave plate 9, and b be the angle of the light transmission axis in the third polarizer 7. The angle of the light transmission axis in a polarizer refers to the angle between the light transmission axis and the horizontal plane. The difference Δθ, obtained by subtracting the sum of angle a and rotation angle φ from angle b, is expressed by the following formula. In the following explanation, Δθ may be referred to as the relative mounting angle.

[0049] Δθ = (a + φ) - b

[0050] In this embodiment, Δθ = {+45° + (-41°)} - (+180°) = -176°.

[0051] The aforementioned Δθ can be said to be equivalent to the angle Δα at which the light transmission axis of the third polarizer 7 is tilted with respect to the polarization plane of light I0 that has passed through the half-wave plate 9. If Δθ is 0°, then the polarization plane of light I0 incident on the third polarizer 7 and the light transmission axis of the third polarizer 7 are parallel. Therefore, light I0 passes straight through the third polarizer 7, and no reflected light I2 is produced. In contrast, in this embodiment, Δθ is not 0°. Specifically, in this embodiment, θ = -176°. And, similar to the angle Δα, Δθ = -176° can be said to be equivalent to Δθ = +4° in terms of the behavior of light passing through the polarizer. As a result, the light I0 incident on the third polarizer 7 can be suitably emitted as light I1, and a portion can be extracted as reflected light I2. However, Δθ is not limited to the above.

[0052] It is preferable that Δθ is +1° or greater, and more preferably +1.5° or greater. This can also be rephrased as it is preferable that Δθ is -179° or greater, and more preferably -178.5° or greater. On the other hand, it is preferable that Δθ is +8° or less, and more preferably +6° or less. This can also be rephrased as it is preferable that Δθ is -172° or less, and more preferably -174° or less. By having Δθ within the above range, the light I0 incident on the third polarizer 7 can be suitably emitted as light I1, and a portion can be extracted as reflected light I2.

[0053] The rotation angle φ of the half-wave plate 9 is preferably -53° or greater, and more preferably -51° or greater. On the other hand, the rotation angle φ of the half-wave plate 9 is preferably -37° or less, and more preferably -39° or less. This allows the light I0 incident on the third polarizer 7 to be preferably emitted as light I1, and a portion to be extracted as reflected light I2.

[0054] Figure 3 is a schematic diagram illustrating the optical path when light is incident from the second port in the optical circulator according to the first embodiment. As shown in Figure 3, linearly polarized light I3 with a polarization plane angle of 0° is incident from the second port P2. Here, the polarization plane of light I3 and the light transmission axis of the third polarizer 7 are parallel. Therefore, light I3 passes through the third polarizer 7 without changing its direction of propagation. The polarization plane angle of light I3 after passing through the third polarizer 7 is 0°.

[0055] Light I3 that has passed through the third polarizer 7 is incident on the half-wave plate 9. The plane of polarization of light I3 incident on the half-wave plate 9 is rotated by +41°. As a result, the angle of the plane of polarization of light I3 that has passed through the half-wave plate 9 is +41°. This is because the direction in which the half-wave plate 9 rotates the plane of polarization of the light depends on the direction in which the light passes through the half-wave plate 9.

[0056] Light I3 that has passed through the half-wave plate 9 is incident on the second polarizer 6. Here, the polarization plane of light I3 and the light transmission axis of the second polarizer 6 are not parallel. Therefore, the second polarizer 6 transmits the component of light I3 that is parallel to the light transmission axis of the second polarizer 6, and reflects the component that is not parallel to the light transmission axis of the second polarizer 6. Specifically, when Δθ = +4°, of the light I3 that has passed through the half-wave plate 9, approximately 99% is parallel to the polarization plane of the second polarizer 6, and approximately 1% is perpendicular to the polarization plane of the second polarizer 6. Therefore, of the light I3, approximately 99% is transmitted through the second polarizer 6, and approximately 1% is reflected light. Figure 3 does not show the reflected light reflected inside the second polarizer 6. However, this reflected light hits the housing 2 shown in Figure 1 and is absorbed, so it is not emitted from the light circulator 1.

[0057] Light I3, having passed through the second polarizer 6, enters the Faraday rotator 8. The plane of polarization of light I3 entering the Faraday rotator 8 is rotated by +45° due to the Faraday effect. As a result, the angle of the plane of polarization of light I3 becomes +90°. Note that the direction in which the Faraday rotator 8 rotates the plane of polarization of the light does not depend on the direction in which the light passes through the Faraday rotator 8.

[0058] Light I3 that has passed through the Faraday rotator 8 is incident on the first polarizer 5. Here, the polarization plane of light I3 that has passed through the Faraday rotator 8 and the light transmission axis of the first polarizer 5 are orthogonal. Therefore, light I3 is reflected by the first polarizer 5 and emitted from the third port P3. In other words, light I3 does not exit from the first polarizer 5 toward the first port P1, but is reflected inside the first polarizer 5 and emitted from the third port P3.

[0059] Figure 4 is a schematic diagram illustrating the optical path when light is incident from the third port in the optical circulator according to the first embodiment. As shown in Figure 4, linearly polarized light I4 with a polarization plane angle of +90° is incident from the third port P3. Here, the polarization plane of light I4 and the light transmission axis of the first polarizer 5 are orthogonal. Therefore, light I4 is reflected by the first polarizer 5 and emitted towards the Faraday rotator 8. The polarization plane angle of the light I4 reflected by the first polarizer 5 is +90°.

[0060] The light I4 reflected by the first polarizer 5 enters the Faraday rotator 8. The plane of polarization of the light I4 that enters the Faraday rotator 8 is rotated by +45° due to the Faraday effect. As a result, the angle of the plane of polarization of the light I4 becomes +135°.

[0061] Light I4 that has passed through the Faraday rotor 8 is incident on the second polarizer 6. Here, the polarization plane of light I4 that has passed through the Faraday rotor 8 and the light transmission axis of the second polarizer 6 are orthogonal. Therefore, light I4 is reflected by the second polarizer 6 and emitted towards the housing 2. At this time, light I4 hits the housing 2 shown in Figure 1 and is absorbed, so it is not emitted from the light circulator 1. In other words, light I4 is not emitted towards the second port P2.

[0062] As in this embodiment, it is preferable that the rotation angle of the Faraday rotor 8 is +45°. This allows the optical circulator 1 to perform its function more reliably. Specifically, it is possible to more reliably prevent light incident from the first port P1 from exiting the second port P2, light incident from the second port P2 from exiting the third port P3, and light incident from the third port P3 from exiting the optical circulator 1. However, the rotation angle of the Faraday rotor 8 may be between +43° and +47°.

[0063] Incidentally, as a method for monitoring the intensity of transmitted light from an optical circulator, it is also possible to use a fiber coupler 103, as shown in the comparative example optical circulator 101 in Figure 5. Specifically, in the comparative example, the fiber coupler 103 is connected to the optical fiber 4 connected to the second port P2. The fiber coupler 103 splits the light for monitoring from the light to be emitted to the outside. However, there is a problem in that it is difficult to sufficiently suppress damage to the fiber coupler 103 when the intensity of the laser light used is increased.

[0064] In contrast, in this embodiment shown in Figure 1, a portion of the light can be easily extracted from the light emission unit 3 as reflected light without using a fiber coupler. Therefore, the optical circulator 1 of this embodiment has excellent resistance to laser light. Consequently, when using the optical circulator 1, the intensity of the laser light can be increased.

[0065] In this embodiment, the arrangement of each element as shown in Figures 1 and 2 allows for more reliable performance as a light circulator, and also enables the extraction of a portion of the light as reflected light from the light emission section. This is illustrated by referring to a reference example.

[0066] Figure 6 is a schematic diagram illustrating the optical path when light is incident from the first port in the reference example optical circulator. Figure 7 is a schematic diagram illustrating the optical path when light is incident from the second port in the reference example optical circulator. Figure 8 is a schematic diagram illustrating the optical path when light is incident from the third port in the reference example optical circulator.

[0067] As shown in Figure 6, the reference example differs from the first embodiment in that it does not have a third polarizer and in the position of the half-wave plate 9. Furthermore, the reference example also differs from the first embodiment in the rotation angle of the Faraday rotor 118, the rotation angle of the half-wave plate 119, and the direction in which the light transmission axis of the second polarizer 6 extends. More specifically, in the optical circulator of the reference example, the Faraday rotor 118 and the half-wave plate 119 are located between the first polarizer 5 and the second polarizer 6. The rotation angle of the Faraday rotor 118 is +43°. The rotation angle of the half-wave plate 119 is -47°. The direction in which the light transmission axis of the second polarizer 6 extends is +180° or -180°.

[0068] In the example shown, there are no problems with the optical paths shown in Figures 6 and 7, but problems arise with the optical path shown in Figure 8. The details are explained below.

[0069] As shown in Figure 6, from the first port P1, linearly polarized light I with a polarization plane angle of 0° is emitted. 100 The light is incident on the first polarizer 5. 100 The angle of the polarization plane is 0°.

[0070] Light I that passed through the first polarizer 5 100 The light I incident on the half-wave plate 119. 100 The polarization plane rotates by -47°. As a result, light I that has passed through the half-wave plate 119 100 The plane of polarization is -47°.

[0071] The light that has passed through the half - wavelength plate 119 is incident on the Faraday rotator 118. The light I 100 incident on the Faraday rotator 118 rotates by +43° due to the Faraday effect. As a result, the angle of the polarization plane of the light I 100 becomes - 4°.

[0072] The light I that has passed through the Faraday rotator 118 100 is incident on the second polarizer 6. Here, consider the angle Δβ by which the polarization plane of the light I 100 incident on the second polarizer 6 is inclined with respect to the light transmission axis of the second polarizer 6. The angle of the polarization plane of the light I 100 incident on the second polarizer 6 is - 4°. The direction in which the light transmission axis of the second polarizer 6 extends is - 180°. At this time, Δβ=-4°-(-180°)= + 176°. However, similar to the above - mentioned Δα, even when Δβ differs by + 180° or - 180°, the behavior of light passing through the polarizer is equivalent. Therefore, it can be said that Δβ = + 176° and Δβ=-4° are equivalent as described above.

[0073] When Δβ=-4°, specifically, among the light I 100 , the component parallel to the polarization plane of the second polarizer 6 is about 99%, and the component orthogonal to the polarization plane of the second polarizer 6 is about 1%. Therefore, about 99% of the light I 100 is emitted from the second port P2, and about 1% is emitted from the light emission part 3 as reflected light.

[0074] As shown in FIG. 7, light I 103 which is linearly polarized light with an angle of 0° of the polarization plane is incident from the second port P2. The light I 103 incident from the second port P2 passes through the second polarizer 6. The angle of the polarization plane of the light I 103 at this time is 0°.

[0075] The light I that has passed through the second polarizer 6 103 is incident on the Faraday rotator 118. The light I 103The plane of polarization rotates by +43° due to the Faraday effect. As a result, light I 103 The angle of the polarization plane is +43°.

[0076] Light I passing through Faraday rotor 118 103 The light I incident on the half-wave plate 119. 103 The polarization plane rotates by +47°. As a result, light I that has passed through the half-wave plate 119 103 The plane of polarization is +90°.

[0077] Light I that passed through the half-wave plate 119 103 The light I that has passed through the half-wave plate 119 is incident on the first polarizer 5. 103 The polarization plane is perpendicular to the light transmission axis of the first polarizer 5. Therefore, light I 103 The light is not emitted from the first polarizer 5 to the first port P1 side. 103 The light I that has passed through the first polarizer 5 is reflected inside the first polarizer 5 and exits from the third port P3. 103 The angle of the polarization plane is +90°.

[0078] As shown in Figure 8, from the third port P3, linearly polarized light I with a polarization plane angle of +90° is emitted. 104 Here, light I is incident. 104 The polarization plane of the first polarizer 5 and the light transmission axis are perpendicular. Therefore, light I 104 The light is reflected by the first polarizer 5 and emitted towards the half-wave plate 119. The polarization plane angle of the light I4 reflected by the first polarizer 5 is +90°.

[0079] Light I that has passed through the first polarizer 5 as described above 104 The light I incident on the half-wave plate 119. 104 The polarization plane rotates by -47°. As a result, light I that has passed through the half-wave plate 119 104 The plane of polarization is +43°.

[0080] Light I that passed through the half-wave plate 119104 The light I incident on the Faraday rotor 118. 104 The plane of polarization rotates by +43° due to the Faraday effect. As a result, light I 104 The angle of the polarization plane is +86°.

[0081] Light I passing through Faraday rotor 118 104 It is incident on the second polarizer 6. Here, I 100 Similarly, light I incident on the second polarizer 6 104 We examine the angle Δγ at which the polarization plane of the second polarizer 6 is tilted with respect to the light transmission axis. Light I incident on the second polarizer 6 104 The polarization plane angle of the first polarizer is +86°. The direction in which the light transmission axis of the second polarizer 6 extends is +180°. In this case, Δγ = +86° - (+180°) = -94°. However, Δγ is equivalent in terms of the behavior of light passing through the polarizer even when it differs by +180° or -180°. Therefore, Δγ = -94° is equivalent to Δγ = +86°.

[0082] The second polarizer 6 is light I 104 Of these, the component parallel to the polarization plane of the second polarizer 6 is transmitted, and the component not parallel to the polarization plane of the second polarizer 6 is reflected. When Δγ = -94°, specifically, the light I incident on the second polarizer 6 104 Of these, approximately 1% is a component parallel to the polarization plane of the second polarizer 6, and approximately 99% is a component perpendicular to the polarization plane of the second polarizer 6. Therefore, light I 104 Of this, approximately 1% is emitted from the second port P2, and approximately 99% is emitted from the light emission unit 3 as reflected light. Therefore, the light I incident from the third port P3 104 Approximately 1% of the connections are from the second port P2 to optical I 105 It leaks as such, and approximately 99% of it is reflected light I from the light emission part 3. 106 Therefore, in the reference example, unlike the first embodiment, the light I incident from the third port P3 of the optical circulator is emitted as follows. 104 It is emitted from another port.

[0083] Incidentally, for example, the direction in which the light transmission axis of the third polarizer 7 extends may be the same as in the case shown in Figure 2, while the direction in which the light transmission axis of the second polarizer 6 extends may differ by +180° or -180° from the case shown in Figure 2. This will be shown below as a modified example of the first embodiment.

[0084] In the modified configuration, as in the first embodiment, the light I0 incident on the third polarizer 7 can be suitably emitted as light I1, and a portion can be extracted as reflected light I2. Furthermore, the intensity of the light extracted from the light emission unit 3 can be monitored, and damage to the element can be easily detected.

[0085] (modified version) In this modified example, the direction in which the light transmission axis of the third polarizer 7 extends is the same as in Figure 4, while the direction in which the light transmission axis of the second polarizer 6 extends differs by +180° or -180° from the case shown in Figure 4. In this modified example, the angle at which the light transmission axis of the second polarizer 6 is inclined with respect to the light transmission axis of the first polarizer 5 is +45°.

[0086] In this modified example, when linearly polarized light I with a polarization plane angle of +90° is incident from the third port P3, the polarization plane of light I that has passed through the Faraday rotator 8 is +135°. The direction in which the light transmission axis of the second polarizer 6 extends is -135°. Therefore, the polarization plane of light I that has passed through the Faraday rotator 8 and is incident on the second polarizer 6 is orthogonal to the light transmission axis of the second polarizer 6. As a result, light I is reflected by the second polarizer 6 and emitted towards the housing 2. In this modified example, the reflection direction differs by +180° or -180° compared to the case shown in Figure 4. However, in both the case shown in Figure 4 and this modified example, light I is emitted towards the housing 2 and not emitted from the light circulator. Therefore, it functions as a light circulator, similar to the first embodiment.

[0087] The details of each element constituting the optical circulator of the present invention will be described below.

[0088] (Faraday rotor) Figure 9 is a schematic cross-sectional view along the direction of light passage, showing a Faraday rotor in the first embodiment.

[0089] The Faraday rotor 8 has a magnetic circuit 16 with through-holes 16a through which light passes, and a Faraday element 17 placed inside the through-holes 16a. When light passes through the Faraday element 17, the plane of polarization of the light rotates due to the Faraday effect.

[0090] The magnetic circuit 16 consists of one magnet. The magnet constituting the magnetic circuit 16 may include multiple magnetic pieces. In this case, the magnet only needs to be composed of multiple magnetic pieces combined together. Alternatively, the magnetic circuit 16 may have multiple magnets, each with a through-hole. In this case, for example, the multiple magnets may be aligned in the direction through which light passes, and the through-holes of the multiple magnets may constitute a single through-hole. At least one of the multiple magnets may include multiple magnetic pieces.

[0091] The magnets constituting the magnetic circuit 16 are cylindrical in shape. That is, the outer shape of the magnets, as viewed from the direction through which light passes, is circular. In this case, it is easy to apply a uniform magnetic field to the Faraday element 17. However, the outer shape of the magnets, as viewed from the direction through which light passes, may be, for example, a square. In this case, when the magnetic circuit 16 contains multiple magnets, or when a magnet contains multiple magnetic pieces, the assembly of the magnets is easier. Alternatively, the outer shape of the magnets, as viewed from the direction through which light passes, may be a polygon other than a square.

[0092] The through-hole 16a in the magnet constituting the magnetic circuit 16 is circular when viewed from the direction through which light passes. In this case, it is easy to apply a uniform magnetic field to the Faraday element 17. However, the shape of the through-hole 16a when viewed from the direction through which light passes may be, for example, a square. In this case, when the magnetic circuit includes multiple magnets, or when a magnet includes multiple magnetic pieces, the assembly of the magnets is easier. Alternatively, the shape of the through-hole 16a when viewed from the direction through which light passes may be a polygon other than a square.

[0093] Permanent magnets are used as the magnets constituting the magnetic circuit 16. Rare earth magnets are preferably used as the permanent magnets, and among them, magnets mainly composed of samarium-cobalt (Sm-Co) or neodymium-iron-boron (Nd-Fe-B) are more preferably used.

[0094] The Faraday element 17 has a cylindrical shape. This makes it easier to obtain a uniform Faraday effect in the Faraday rotor 8. However, the shape of the Faraday rotor 8 is not limited to the above.

[0095] The diameter of the Faraday element 17 can be, for example, 1 mm or more and 10 mm or less. However, when using high-intensity laser light, the diameter of the Faraday element 17 may be 5 mm or more, 10 mm or more, more than 10 mm, 15 mm or more, and especially 20 mm or more.

[0096] The length of the Faraday element 17 is preferably 1 mm or more, more preferably 3 mm or more, and even more preferably 5 mm or more. On the other hand, the length of the Faraday element 17 is preferably 20 mm or less, more preferably 15 mm or less, and even more preferably 12 mm or less. When the length of the Faraday element 17 is within the above range, the rotation angle of the Faraday rotor 8 can be adjusted more reliably within the desired range. However, when using high-intensity laser light, the length of the Faraday element 17 may be 10 mm or more, 20 mm or more, more than 20 mm, 30 mm or more, and especially 40 mm or more.

[0097] The Faraday rotator 8 is preferably used in the wavelength range of 350 nm to 1300 nm, more preferably in the wavelength range of 450 nm to 1200 nm, even more preferably in the wavelength range of 500 nm to 1200 nm, even more preferably in the wavelength range of 800 nm to 1100 nm, and particularly preferably in the wavelength range of 900 nm to 1100 nm.

[0098] For example, a paramagnetic material that transmits light can be used for the Faraday element 17. It is preferable to use a paramagnetic glass material as the material for the Faraday element 17. When a glass material is used for the Faraday element 17, the influence of defects in the material is smaller, unlike when a single crystal material is used. Therefore, the Verde constant can be stabilized in the Faraday element 17, and a high extinction ratio can be maintained. In addition, paramagnetic materials other than glass can also be used for the Faraday element 17.

[0099] As the glass material used in the Faraday element 17, a glass material containing Tb2O3 20% to 80%, B2O3 + P2O5 20% to 70%, and SiO20% to 45% in molar percentages on an oxide basis can be used. In this specification, for example, when a + b + c + ... is written, it means the sum of the contents of a, b, and c. In this specification, when "~" is written in a range, the range includes the upper and lower limits.

[0100] The following details the preferred materials used for the glass material.

[0101] It is preferable that the glass material used in the Faraday element 17 contains at least one rare earth element selected from Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, and Tm. It is particularly preferable that the glass material contains Tb.

[0102] The Tb2O3 content in the glass material used for the Faraday element 17 is preferably more than 20% in molar percentages on an oxide basis, more preferably 25% or more, even more preferably 28% or more, even more preferably 29% or more, 30% or more, 31% or more, 32% or more, 34% or more, 36% or more, 38% or more, 40% or more, 41% or more, and particularly preferably 49% or more. Increasing the Tb2O3 content in this way makes it easier to obtain a good Faraday effect. On the other hand, the Tb2O3 content in the glass material used for the Faraday element 17 may be, for example, 80% or less. Note that Tb exists in the glass in trivalent and tetravalent states, but in this specification, all of these are expressed as values ​​converted to Tb2O3.

[0103] In the glass material used in the Faraday element 17, Tb relative to total Tb 3+The proportion of is preferably 55% or more in mole percent, more preferably 60% or more, even more preferably 70% or more, even more preferably 80% or more, even more preferably 90% or more, and particularly preferably 95% or more. Tb relative to total Tb 3+ If the proportion is too low, the light transmittance in the wavelength range of 300nm to 1100nm tends to decrease.

[0104] Furthermore, the Faraday element 17 may contain the following components. In the following descriptions of the component content, unless otherwise specified, "%" means "mol%". In addition, if the component is an oxide, unless otherwise specified, "%" means "mol% in terms of oxide equivalent".

[0105] SiO2 forms the glass skeleton and is a component that broadens the vitrification range. The vitrification range is the range of compositions in which glass can be obtained. Since SiO2 does not contribute to improving the Verde constant, if the SiO2 content is too high, it becomes difficult to obtain a sufficient Faraday effect. Therefore, the SiO2 content is preferably 0% to 50%, more preferably 0% to 45%, even more preferably 0% to 40%, even more preferably 1% to 35%, and particularly preferably 1% to 30%.

[0106] B2O3 forms the glass skeleton and is a component that broadens the vitrification range. However, since B2O3 does not contribute to improving the Verde constant, if the B2O3 content is too high, it becomes difficult to obtain a sufficient Faraday effect. Therefore, the B2O3 content is preferably 0% to 70%, more preferably 0% to 60%, even more preferably 0% to 55%, even more preferably 0% to 50%, even more preferably 1% to 45%, and particularly preferably 1% to 40%.

[0107] P2O5 forms the glass skeleton and is a component that broadens the vitrification range. However, since P2O5 does not contribute to improving the Verde constant, if the P2O5 content is too high, it becomes difficult to obtain a sufficient Faraday effect. Therefore, the P2O5 content is preferably 0% to 70%, more preferably 0% to 60%, even more preferably 0% to 55%, even more preferably 0% to 50%, even more preferably 1% to 45%, and particularly preferably 1% to 40%.

[0108] The sum of the B2O3 and P2O5 content is preferably 20% to 70%, more preferably 25% to 60%, even more preferably 30% to 55%, and particularly preferably 30% to 45%. Having the sum of the B2O3 and P2O5 content within the above range makes it particularly easy to broaden the vitrification range.

[0109] Al2O3 is a component that enhances glass-forming ability. Glass-forming ability is an indicator of how easily glass is formed in a material. The higher the glass-forming ability of a material, the easier it is to form glass. Since Al2O3 does not contribute to improving the Verde constant, if the Al2O3 content is too high, it becomes difficult to obtain a sufficient Faraday effect. Therefore, the Al2O3 content is preferably 0% to 50%, and particularly preferably 0% to 30%.

[0110] La2O3, Gd2O3, and Y2O3 are components that stabilize vitrification. However, if the content of La2O3, Gd2O3, or Y2O3 is too high, vitrification will be suppressed. Therefore, it is preferable that the content of La2O3, Gd2O3, and Y2O3 is 10% or less each, and particularly preferable that it be 5% or less.

[0111] Dy2O3, Eu2O3, and Ce2O3 are components that stabilize vitrification and contribute to improving the Verde constant. However, if the content of Dy2O3, Eu2O3, or Ce2O3 is too high, vitrification will be suppressed. Therefore, it is preferable that the content of Dy2O3, Eu2O3, and Ce2O3 is 15% or less each, and particularly preferable that it is 10% or less. Note that Dy, Eu, and Ce present in the glass exist in trivalent and tetravalent states, but in this specification, all of these are expressed as values ​​converted to Dy2O3, Eu2O3, and Ce2O3, respectively.

[0112] MgO, CaO, SrO, and BaO are components that stabilize vitrification and increase the chemical durability of the glass material. However, since MgO, CaO, SrO, and BaO do not contribute to improving the Verde constant, if the content of MgO, CaO, SrO, or BaO is too high, it becomes difficult to obtain a sufficient Faraday effect. Therefore, it is preferable that the content of MgO, CaO, SrO, and BaO is 0% to 10%, and particularly preferable that it is 0% to 5%.

[0113] GeO2 is a component that enhances glass-forming ability. However, since GeO2 does not contribute to improving the Verde constant, if the GeO2 content is too high, it becomes difficult to obtain a sufficient Faraday effect. Therefore, the GeO2 content is preferably 0% to 15%, more preferably 0% to 10%, and particularly preferably 0% to 9%.

[0114] Ga2O3 is a component that enhances glass-forming ability and broadens the vitrification range. However, if the Ga2O3 content is too high, the glass material becomes prone to devitrification. In addition, since Ga2O3 does not contribute to improving the Verde constant, if the Ga2O3 content is too high, it becomes difficult to obtain a sufficient Faraday effect. Therefore, a Ga2O3 content of 0% to 6% is preferable, and 0% to 5% is particularly preferable.

[0115] Fluorine is a component that enhances glass-forming ability and broadens the vitrification range. However, if the fluorine content is too high, fluorine may volatilize during the melting of the raw material, causing changes in composition and potentially adversely affecting vitrification. In addition, it tends to increase the striations in the glass material. Therefore, the fluorine content (F2 equivalent) is preferably 0% to 10%, more preferably 0% to 7%, and particularly preferably 0% to 5%.

[0116] Sb2O3 can be added as a reducing agent. However, to avoid discoloration or to consider the environmental impact, it is preferable that the Sb2O3 content be 0.1% or less.

[0117] Furthermore, paramagnetic materials other than glass can also be used for the Faraday element 17. For example, paramagnetic single crystals or ceramics can be used for the Faraday element 17. For example, Tb3Ga5O 12 Tb3Al5O 12 Tb3Sc2Al3O 12 Y3Al5O 12 Single crystals such as Tb2Hf2O7, LiTbF4, NaTbF4, and CeF3 can be used. Alternatively, Tb-Ga oxide ceramics, Tb-Al oxide ceramics, Tb-Sc-Al oxide ceramics, Y-Al oxide ceramics, Tb-Hf oxide ceramics, Tb fluoride ceramics, and Ce fluoride ceramics can be used for the Faraday element 17.

[0118] (Polarizers and half-wave plates) As shown in Figure 1, the first polarizer 5, the second polarizer 6, and the third polarizer 7 are polarizing beam splitters. As a polarizing beam splitter, for example, a polarizing beam splitter can be used in which two triangular prisms are joined together via a polarization separation film. As the material for the triangular prism, for example, glass can be used.

[0119] The half-wave plate 9 is a wave plate that creates a phase difference of half a wavelength in the incident light. When linearly polarized light is incident on the half-wave plate 9, the plane of polarization of the linearly polarized light rotates. The direction in which the half-wave plate 9 rotates the plane of polarization of the light depends on the direction in which the light passes through the half-wave plate 9. As the material for the half-wave plate 9, quartz or an appropriate polymer can be used.

[0120] (Light circulator) (Second embodiment) Figure 10 is a schematic diagram showing an optical circulator according to the second embodiment.

[0121] This embodiment differs from the first embodiment in that the light-emitting section 23 is an opening provided in the housing 2, and the photodiode 25 is directly connected to the light-emitting section 23. The shape of the opening for the light-emitting section 23 can be, for example, approximately circular, oval, or rectangular.

[0122] The housing 2 may be provided with a cover member to close the opening that serves as the light emission section 23. In this case, the cover member may be a light-transmitting material that allows reflected light reflected from inside the third polarizer 7 to pass through. An anti-reflective coating may be provided on the cover member. This makes it easier for reflected light to pass through the laminate of the cover member and the anti-reflective coating.

[0123] In the optical circulator 21, reflected light emitted from the light emission unit 23 is received by the photodiode 25 without passing through the optical fiber 4. The reflected light is converted into an electrical signal by the photodiode 25, and this electrical signal is transmitted to the outside. The photodiode 25 shown in Figure 10 is a device that includes wiring connected to the outside. By measuring the intensity of the above electrical signal externally, the intensity of the transmitted light in the optical circulator 21 can be monitored. This makes it easy to detect when an element of the optical circulator 21 is damaged.

[0124] In this embodiment as well, a portion of the light incident from the first port P1 can be easily extracted from the light output unit 23 without using a fiber coupler. Therefore, the optical circulator 21 has excellent resistance to laser light. Consequently, when using the optical circulator 21, the intensity of the laser light can be increased.

[0125] In addition, in the optical circulator 21, the light emission unit 23 is not a fiber collimator. As a result, there is no coupling loss when the light is emitted from the light emission unit 23. Since the emitted light is received by the photodiode 25 without passing through the optical fiber 4, there is no loss due to the transmission of the emitted light. Therefore, the intensity of the transmitted light in the optical circulator 21 can be easily monitored.

[0126] In the first and second embodiments, the photodiode is located outside the housing, and the reflected light is emitted from the light-emitting section to the outside of the housing. In this invention, the photodiode may be located inside the housing, and the light-emitting section may be the part of the third polarizer that emits reflected light. The emitted light from the light-emitting section may be received by a photodiode located inside the housing. The reflected light may then be converted into an electrical signal by the photodiode, and the converted electrical signal may be transmitted to the outside of the housing.

[0127] (Optical monitoring method) The optical monitoring method of the present invention is a method for monitoring the intensity of transmitted light from an optical circulator. Specifically, the method is a method for monitoring the intensity of transmitted light from an optical circulator according to the present invention, as shown in Figures 1 and 10. As described above, the optical circulator of the present invention has a first port P1, a second port P2, a third port P3, a first polarizer 5, a second polarizer 6, a third polarizer 7, a Faraday rotator 8, and a half-wave plate 9.

[0128] In the above optical circulator, the first port P1 and the second port P2 face each other, and light incident from the first port P1 exits from the second port P2. The third port P3 is positioned so as not to lie on a straight line connecting the first port P1 and the second port P2. Light incident from the second port P2 exits from the third port P3. The first polarizer 5 is positioned on the first port P1 side. The third polarizer 7 is positioned on the second port P2 side and is positioned together with the first polarizer 5 to sandwich the second polarizer 6. The Faraday rotator 8 is positioned between the first polarizer 5 and the second polarizer 6. The half-wave plate 9 is positioned between the second polarizer 6 and the third polarizer 7.

[0129] The half-wave plate 9 and the third polarizer 7 are arranged such that a portion of the light incident on the third polarizer 7, after passing through the first polarizer 5, the Faraday rotator 8, the second polarizer 6, and the half-wave plate 9, is reflected to become reflected light. The above-mentioned optical circulator has an optical emission unit that can extract the reflected light reflected by the third polarizer 7. The optical monitoring method of the present invention is a method of monitoring the intensity of transmitted light that has passed through each element of the above-mentioned optical circulator by measuring the intensity of the reflected light extracted from the optical emission unit.

[0130] This optical monitoring method allows for continuous monitoring of the intensity of light transmitted through the optical circulator. This makes it easy to detect when an element of the optical circulator is damaged and the intensity of transmitted light decreases. Therefore, the intensity of the laser light can be increased.

[0131] The intensity of the light incident on the light circulator is preferably 300mW or more, more preferably 500mW or more, even more preferably 1W or more, even more preferably 5W or more, and particularly preferably 10W or more. On the other hand, the light intensity is preferably, for example, 150W or less, and more preferably 50W or less.

[0132] According to the optical monitoring method of the present invention, the intensity of transmitted light from an optical circulator can be monitored without using a fiber coupler with low resistance to laser light. Therefore, even when the intensity of the laser light is increased, the optical circulator is less likely to be damaged. Accordingly, it can also be used when using a high-power laser oscillator. For example, a high-intensity laser light of 1 kW or more may be used for purposes such as laser processing, laser analysis, or laser nuclear fusion, and an even higher intensity laser light of 10 kW or more may be used.

[0133] The proportion of reflected light extracted by the third polarizer 7 is preferably 0.1% or more, and more preferably 0.3% or more, of the total light incident on the third polarizer 7. On the other hand, the proportion of reflected light extracted by the third polarizer 7 is preferably 10% or less, and more preferably 4% or less, of the total light incident on the third polarizer 7.

[0134] When the proportion of reflected light extracted by the third polarizer 7 is greater than or equal to the lower limit, the intensity of the transmitted light from the light circulator can be monitored more reliably. On the other hand, when the proportion of reflected light extracted by the third polarizer 7 is less than or equal to the upper limit, the amount of light transmitted through the third polarizer 7 can be increased even further. The proportion of light extracted by the third polarizer 7 can be adjusted by the rotation angle of the half-wave plate 9 and the relative installation angle of the third polarizer 7.

[0135] <Examples> (Example 1) In Example 1, an optical circulator was fabricated to have the optical design shown in Figure 1. Specifically, a polarizing beam splitter was used as the first polarizer, with the direction in which the light transmission axis of the polarizing beam splitter extended set to 0°. A Faraday rotor with a rotation angle of +45° was used. A polarizing beam splitter was used as the second polarizer, with the direction in which the light transmission axis of the polarizing beam splitter extended set to +45°. The rotation angle of the half-wave plate was set to -41°. A polarizing beam splitter was used as the third polarizer, with the direction in which the light transmission axis of the polarizing beam splitter extended set to 0°.

[0136] The optical circulator fabricated in this manner was irradiated with laser light of a wavelength of 1030 nm, and a portion of the light was reflected by a third polarizer. The intensity of the light emitted from the optical circulator was then monitored. At this time, the emitted light transmittance, which is the proportion of light emitted from the second port, and the light extraction rate, which is the proportion of light emitted from the light output section, were calculated. The results are shown in Table 1.

[0137] (Examples 2-6) Except for changing the rotation angle of the Faraday rotor and the rotation angle of the half-wave plate as shown in Table 1 below, an optical circulator was fabricated in the same manner as in Example 1, and the intensity of the light emitted from the optical circulator was monitored. In addition, the light transmittance at the second port and the light extraction rate at the light emission section were calculated for the optical circulators fabricated in Examples 2 to 6. The results are shown in Table 1.

[0138] In Table 1, "angle of the light transmission axis in the first polarizer" means "angle of the light transmission axis of the first polarizer and the horizontal plane." "Angle of the light transmission axis in the second polarizer" means "angle of the light transmission axis of the second polarizer and the horizontal plane." "Angle of the light transmission axis in the third polarizer" means "angle of the light transmission axis of the third polarizer and the horizontal plane." As described above, the relative mounting angle Δθ is given by Δθ = (a + φ) - b, where a is the angle of the light transmission axis in the second polarizer, φ is the rotation angle of the half-wave plate, and b is the angle of the light transmission axis in the third polarizer.

[0139] [Table 1]

[0140] As shown in Table 1, the percentage of light emitted from the light output section of the optical circulators fabricated in Examples 1 to 6, i.e., the light extraction rate, was 1 to 2%, and it was confirmed that monitoring is possible within this range. [Explanation of Symbols]

[0141] 1… Light circulator 2…Cabinet 3…Light emission section 4… Fiber optic 5-7...1st to 3rd polarizers 8... Faraday rotor 9…1 / 2 wavelength plate 16…Magnetic circuits 16a...Through hole 17…Faraday 21... Light Circulator 23…Light emission section 25…Photodiode 101... Light Circulator 103…Fiber coupler 118... Faraday rotor 119...1 / 2 wavelength plate P1~P3…Ports 1 to 3

Claims

1. The first port into which light enters, Opposite the first port is a second port from which light incident on the first port is emitted, The third port is positioned so as not to be located on a straight line connecting the first port and the second port, and the light incident from the second port exits through the third port, The first polarizer located on the first port side, The second polarizer, A third polarizer is positioned on the second port side and is positioned together with the first polarizer so as to sandwich the second polarizer, A Faraday rotor positioned between the first polarizer and the second polarizer, A half-wave plate positioned between the second polarizer and the third polarizer, Equipped with, The half-wave plate and the third polarizer are arranged such that light incident on the third polarizer passes through the first polarizer, the Faraday rotator, the second polarizer, and the half-wave plate, and a portion of the light is reflected to become reflected light. A light circulator further comprising a light emitting section capable of extracting the reflected light.

2. The optical circulator according to claim 1, wherein when the relative installation angle Δθ is the difference obtained by subtracting the sum of the angle between the light transmission axis of the second polarizer and the horizontal plane and the rotation angle of the half-wave plate from the angle between the light transmission axis of the third polarizer and the horizontal plane, Δθ is between +1° and +8°.

3. The optical circulator according to claim 2, wherein the rotation angle of the half-wave plate is -51° or more and -39° or less.

4. The optical circulator according to claim 1, wherein the rotation angle of the Faraday rotor is +45°.

5. The optical circulator according to claim 1, wherein the light emitting section is directly or indirectly connected to a photodiode.

6. The optical circulator according to claim 1, wherein the Faraday rotor comprises a magnet having a through hole and a Faraday element disposed within the through hole of the magnet and made of a paramagnetic material through which light passes.

7. The optical circulator according to claim 6, wherein the paramagnetic material is a glass material.

8. The glass material has an oxide equivalent of mol%, Tb ２ O ３ 20% to 80%, B ２ O ３ +P ２ O ５ 20% to 70%, and SiO ２ The light circulator according to claim 7, containing 0% to 45%.

9. An optical monitoring method for monitoring the intensity of transmitted light from an optical circulator, comprising: a first port into which light is incident; a second port opposite to the first port and from which light incident from the first port exits; a third port positioned so as not to lie on a straight line connecting the first port and the second port and from which light incident from the second port exits; a first polarizer positioned on the first port side; a second polarizer; a third polarizer positioned on the second port side and positioned together with the first polarizer to sandwich the second polarizer; a Faraday rotator positioned between the first polarizer and the second polarizer; and a half-wave plate positioned between the second polarizer and the third polarizer, wherein the optical monitoring method monitors the intensity of transmitted light from the optical circulator, In the optical circulator, the half-wave plate and the third polarizer are arranged such that a portion of the light incident on the third polarizer is reflected to become reflected light, after passing through the first polarizer, the Faraday rotor, the second polarizer, and the half-wave plate, which are incident on the third polarizer. The light circulator further includes a light emitting section capable of extracting the reflected light, A light monitoring method comprising the step of monitoring the intensity of transmitted light from a light circulator by measuring the intensity of the reflected light taken out from the light emitting unit.

10. The optical monitoring method according to claim 9, wherein the intensity of the light incident on the optical circulator is 300 mW or more and 150 W or less.

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