Optical circulator and optical monitoring method

Abstract

Provided is an optical circulator that makes it possible to easily detect damage to an element of the optical circulator.　This optical circulator 1 is characterized by comprising a first port P1 through which light enters, a second port P2 that is opposite the first port P1 and emits light that has entered through the first port P1, a third port P3 that is provided so as not to be on a straight line that connects the first port P1 and the second port P2 and emits light that has entered through the second port P2, a first polarizer 5 that is provided on the first port P1 side, a second polarizer 6, a third polarizer 7 that is provided on the second port P2 side and sandwiches the second polarizer 6 with the first polarizer 5, a Faraday rotator 8 that is provided between the first polarizer 5 and the second polarizer 6, a 1 / 2 wavelength plate 9 that is provided between the second polarizer 6 and the third polarizer 7, and a light-emitting part 3, the third polarizer 7 and the 1 / 2 wavelength plate 9 being provided such that a portion of light that has entered through the first port P1 and has passed through the first polarizer 5, the Faraday rotator 8, the second polarizer 6, and the 1 / 2 wavelength plate 9 to enter the third polarizer 7 is reflected to become reflected light that can be extracted by the light-emitting part 3.

Description

Optical circulator and optical monitoring method

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

[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, described 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).

[0004] Japanese Patent Publication No. 2002-031780

[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, if an element of the optical circulator is damaged, it must be replaced immediately. However, since the Faraday rotor in the optical circulator is housed within a magnet, it is difficult to visually confirm if it is damaged. Similarly, since the polarizer is fixed in a holder, it is also difficult to visually confirm if it is damaged.

[0007] Thus, conventionally, even when a laser system malfunctions, it is difficult to determine which part is damaged.

[0008] The object of the present invention is 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.

[0009] A light circulator according to embodiment 1 of the present invention includes 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, and a third polarizer positioned on the second port side and positioned together with the first polarizer to sandwich the second polarizer. The device further comprises a light emission section that includes a photon, 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 half-wave plate and the third polarizer are arranged such that a portion of the light incident on the third polarizer, passing through the first polarizer, the Faraday rotator, the second polarizer, and the half-wave plate, is reflected to become reflected light, and the reflected light can be extracted.

[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, in embodiment 7, the glass material is Tb in mol% on an oxide basis. ２ O ３ 20% to 80%, B ２ O ３ +P ２ O ５ 20% to 70%, and SiO ２ It is preferable that it contains 0% to 45%.

[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 arranged 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 located on the first port side, a second polarizer, a third polarizer located on the second port side and positioned together with the first polarizer to sandwich the second polarizer, a Faraday rotator located between the first polarizer and the second polarizer, and a Faraday rotator located 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, it is preferable that the intensity of the light incident on the optical circulator in embodiment 9 is 300 mW or more and 150 W or less.

[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.

[0020] Figure 1 is a schematic diagram showing an optical circulator according to the first embodiment of the present invention. 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 of the present invention. 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 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 is a schematic diagram of an optical circulator in a comparative example. Figure 6 is a schematic diagram illustrating the optical path when light is incident from the first port in the optical circulator in a reference example. Figure 7 is a schematic diagram illustrating the optical path when light is incident from the second port in the optical circulator in a reference example. Figure 8 is a schematic diagram illustrating the optical path when light is incident from the third port in the optical circulator in a reference example. Figure 9 is a schematic cross-sectional view along the direction of light passage showing a Faraday rotor in the first embodiment of the present invention. Figure 10 is a schematic diagram showing a light circulator according to a second embodiment of the present 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] (Optical Circulator) (First Embodiment) Figure 1 is a schematic diagram showing an optical 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 that acts 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 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 line branches off towards the third port P3 is located closer to the first port P1 than the position where the line branches off towards the light emitting unit 3.

[0029] The optical circulator 1 comprises a plurality of elements: a first polarizer 5, a second polarizer 6, a third polarizer 7, a Faraday rotator 8, and a half-wave plate 9. 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 direction in which the light transmission axis extends in the 3 o'clock direction 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, when the direction in which the optical transmission axis of the polarizer extends is different by +180° or -180°, it can be said that they are equivalent except for the direction of reflection inside. In other words, when the direction in which the optical transmission axis of the polarizer extends is different by +180° or -180°, they are equivalent with respect to the behavior of light passing through the polarizer without changing the traveling direction. In the following, when it is described that light "passes through the polarizer", unless otherwise specified, it refers to light passing through the polarizer without changing the traveling direction.

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

[0038] Hereinafter, the optical path when light is incident from the first port P1 will be described. As shown in FIG. 2, light I which is linearly polarized light with the angle of the polarization plane being 0° is incident from the first port P1. ０ The direction in which the optical transmission axis of the first polarizer 5 extends is 0°. Here, the polarization plane of the light I incident from the first port P1 ０ and the optical transmission axis of the first polarizer 5 are parallel. Therefore, the light I ０ passes through the first polarizer 5 without changing the traveling direction. Note that non-linearly polarized light incident from the first port P1 may be made linearly polarized light with the angle of the polarization plane being 0° by passing it through the first polarizer 5.

[0039] In this specification, the angle of the polarization plane of the light passing through the polarizer is described as being in the direction parallel to the optical transmission axis of the polarizer. Therefore, the polarization plane of the light I ０ passing through the first polarizer 5 is 0°.

[0040] As shown in FIG. 2, the light I ０ passing through the first polarizer 5 is incident on the Faraday rotator 8. The light I incident on the Faraday rotator 8０ The polarization plane rotates by +45° due to the Faraday effect. As a result, light I that has passed through the Faraday rotator 8 ０ The angle of the polarization plane is +45°.

[0041] Light I passing through Faraday rotor 8 ０ The light I 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°. ０ The polarization plane of the first polarizer and the light transmission axis of the second polarizer 6 are parallel. Therefore, light I ０ The light passes through the second polarizer 6 without changing its direction of travel. ０ The polarization plane angle is +45°. Light I that has passed through the second polarizer 6 ０ The light I incident on the half-wave plate 9. ０ The polarization plane rotates by -41°. As a result, light I that has passed through the half-wave plate 9 ０ The angle of the polarization plane is +45° - 41° = +4°.

[0042] Light I that passed through the half-wave plate 9 ０ The light I 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 light I that has passed through the half-wave plate 9 ０ The polarization plane of the first polarizer and the light transmission axis of the third polarizer 7 are not parallel. Therefore, the third polarizer 7 is polarized to light I ０ Of these, the component parallel to the light transmission axis of the third polarizer 7 is transmitted, and the component not parallel to the light transmission axis of the third polarizer 7 is reflected. In other words, light I ０ This is light I passing through the third polarizer 7 without changing its direction of travel. １ Then, reflected light I is reflected inside the third polarizer 7, changes its direction of propagation, and exits the third polarizer 7. ２ It branches into two. Light I １ It is emitted from the second port P2. Reflected light I ２ The light is emitted from the light-emitting unit 3.

[0043] Here, light I is incident on the third polarizer 7. ０We examine the angle Δα at which the polarization plane of the third polarizer 7 is tilted with respect to the light transmission axis. Light I incident on the third polarizer 7 ０ The polarization plane angle of the first polarizer 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 described above, when the direction in which the light transmission axis of a polarizer extends differs by +180° or -180°, they can be said to be 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, light I ０ Of these, approximately 99% is parallel to the polarization plane of the third polarizer 7, and approximately 1% is perpendicular to the polarization plane of the third polarizer 7. Therefore, light I ０ Of this, approximately 99% is emitted from the second port P2, and approximately 1% is emitted as reflected light from the light emission unit 3.

[0045] In this embodiment, light I incident on the third polarizer 7 ０ A portion of the reflected light I ２ The reflected light I can be extracted from the light emission unit 3. ２ By measuring the intensity, 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 is 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, when an element of the optical circulator 1 is damaged and the intensity of the transmitted light decreases, the damage to the element can be easily detected.

[0046] Reflected light I ２ The intensity is, for example, reflected light I ２ This can be measured by having a photodiode receive the reflected light I. Specifically, the photodiode receives the reflected light I. ２The signal can be converted into an electrical signal, and the intensity of the electrical signal can be measured.

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

[0048] In the above explanation, Optical I ０ The relationship between the polarization plane of the first polarizer and the light transmission axis of the third polarizer 7 was compared. Next, 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 was examined. 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 installation angle.

[0049] Δθ = (a + φ) - b

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

[0051] The above-mentioned Δθ is the light I that passed through the half-wave plate 9. ０ It can be said that this is 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 I. ０ The polarization plane of the third polarizer 7 and the light transmission axis of the third polarizer 7 are parallel. Therefore, light I ０ The light passes straight through the third polarizer 7, and the reflected light I ２This does not occur. 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 I incident on the third polarizer 7 ０ Light I １ It can be suitably emitted as reflected light I ２ It can be extracted as follows. 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. Because Δθ is within the above range, the light I incident on the third polarizer 7 ０ Light I １ It can be suitably emitted as reflected light I ２ It can be extracted as follows.

[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. As a result, the light I incident on the third polarizer 7 ０ Preferably, light I １ It can be emitted as such, and a portion of it is reflected light I ２ It can be extracted as follows.

[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, from the second port P2, linearly polarized light I with a polarization plane angle of 0° ３ Here, light I is incident. ３The polarization plane of the third polarizer 7 and the light transmission axis of the third polarizer 7 are parallel. Therefore, light I ３ The light passes through the third polarizer 7 without changing its direction of travel. ３ The angle of the polarization plane is 0°.

[0055] Light I that passed through the third polarizer 7 ３ The light I incident on the half-wave plate 9. ３ The polarization plane rotates by +41°. As a result, light I that has passed through the half-wave plate 9 ３ The angle of the polarization plane is +41°. This is because the direction in which the half-wave plate 9 rotates the polarization plane of light depends on the direction in which the light passes through the half-wave plate 9.

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

[0057] Light I that passed through the second polarizer 6 ３ The light I incident on the Faraday rotor 8. ３ The plane of polarization rotates by +45° due to the Faraday effect. As a result, light I ３ The angle of the polarization plane is +90°. Note that the direction in which the Faraday rotator 8 rotates the polarization plane of light does not depend on the direction in which the light passes through the Faraday rotator 8.

[0058] Light I passing through Faraday rotor 8 ３ The light I then enters the first polarizer 5. ３ The polarization plane and the light transmission axis of the first polarizer 5 are perpendicular. Therefore, light I ３ It is reflected by the first polarizer 5 and emitted from the third port P3. That is, light I ３ The light is not emitted from the first polarizer 5 to the first port P1 side, 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, from the third port P3, linearly polarized light I with a polarization plane angle of +90° ４ Here, light I is incident. ４ The polarization plane and the light transmission axis of the first polarizer 5 are perpendicular. Therefore, light I ４ The light I reflected by the first polarizer 5 is emitted towards the Faraday rotor 8. ４ The angle of the polarization plane is +90°.

[0060] Light I reflected by the first polarizer 5 ４ The light I incident on the Faraday rotor 8. ４ The plane of polarization rotates by +45° due to the Faraday effect. As a result, light I ４ The angle of the polarization plane is +135°.

[0061] Light I passing through Faraday rotor 8 ４ The light I then enters the second polarizer 6. ４ The polarization plane of the first polarizer and the light transmission axis of the second polarizer 6 are perpendicular. Therefore, light I ４ It is reflected by the second polarizer 6 and emitted towards the housing 2. At this time, light I ４ The light I is absorbed upon impact with the housing 2 shown in Figure 1 and is therefore not emitted from the optical circulator 1. ４ It is not emitted to 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, a method using a fiber coupler 103, as shown in the comparative example optical circulator 101 in Figure 5, can also be considered. 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] FIG. 6 is a schematic diagram for explaining an optical path when light is incident from the first port in the optical circulator of the reference example. FIG. 7 is a schematic diagram for explaining an optical path when light is incident from the second port in the optical circulator of the reference example. FIG. 8 is a schematic diagram for explaining an optical path when light is incident from the third port in the optical circulator of the reference example.

[0067] As shown in FIG. 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. Note that the reference example also differs from the first embodiment in the rotation angle of the Faraday rotator 118, the rotation angle of the half-wave plate 119, and the direction in which the optical transmission axis of the second polarizer 6 extends. More specifically, in the optical circulator of the reference example, the Faraday rotator 118 and the half-wave plate 119 are positioned between the first polarizer 5 and the second polarizer 6. The half-wave plate 119 is positioned between the first polarizer 5 and the Faraday rotator 118. The rotation angle of the Faraday rotator 118 is +43°. The rotation angle of the half-wave plate 119 is -47°. The direction in which the optical transmission axis of the second polarizer 6 extends is +180° or -180°.

[0068] In the reference example, there is no problem in the optical paths shown in FIGS. 6 and 7, but a problem occurs in the optical path shown in FIG. 8. This will be shown in detail below.

[0069] As shown in FIG. 6, light I which is linearly polarized light with an angle of the polarization plane of 0° is incident from the first port P1. １００ The angle of the polarization plane of the light I that has passed through the first polarizer 5 is 0°. １００

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

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

[0072] 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 light I １００ incident on the second polarizer 6 is inclined with respect to the optical transmission axis of the second polarizer 6. The angle of the polarization plane of light I １００ incident on the second polarizer 6 is -4°. The direction in which the optical transmission axis of the second polarizer 6 extends is -180°. At this time, Δβ = -4° - (-180°) = +176°. However, similar to Δα above, 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, for light I １００ about 99% is the component parallel to the polarization plane of the second polarizer 6, and about 1% is the component orthogonal to the polarization plane of the second polarizer 6. Therefore, １００ about 99% of light I 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 the polarization plane of 0° is incident from the second port P2. Light I １０３ incident from the second port P2 passes through the second polarizer 6. The angle of the polarization plane of light I １０３ at this time is 0°.

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

[0076] Light I that has passed through the Faraday rotator 118 １０３The 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 I 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 emitted 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 and the light transmission axis of the first polarizer 5 are perpendicular. Therefore, light I １０４ The light I reflected by the first polarizer 5 is emitted towards the half-wave plate 119. ４ The angle of the polarization plane 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 119 １０４ 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 the 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, even when Δγ differs by +180° or -180°, the behavior of light passing through the polarizer is equivalent. 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 traffic comes from the second port P2 via optical I １０５ It leaks as such, and approximately 99% of it is reflected light I from the light emission unit 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 modification of the first embodiment.

[0084] In the modified example, as in the first embodiment, the light I incident on the third polarizer 7...０ Light I １ It can be suitably emitted as reflected light I ２ It can be extracted as such. Furthermore, the intensity of the light extracted from the light emission unit 3 can be monitored, making it easy to detect damage to the element.

[0085] (Modified Version) In this modified version, 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 is +180° or -180° different from that in Figure 4. In this modified version, 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 perpendicular 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 arranged 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 includes multiple magnets, or when a magnet includes 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 shape of the through-hole 16a in the magnet constituting the magnetic circuit 16, 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 shape of the through-hole 16a as 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 as 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 reliably adjusted to 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 small, 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] The glass material used in the Faraday element 17 is Tb in mol% on an oxide basis. ２ O ３ 20% to 80%, B ２ O ３ +P ２ O ５ 20% to 70%, and SiO ２ Glass materials containing 0% to 45% 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 a range is written as "~", 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] Tb in the glass material used in the Faraday element 17 ２ O ３ The content of is preferably more than 20% in mole percent 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. ２ O３ By increasing the content of [substance], it becomes easier to obtain a good Faraday effect. On the other hand, the Tb of the glass material used in the Faraday element 17 ２ O ３ The content may be, for example, 80% or less. Note that Tb exists in a trivalent or tetravalent state in glass, but in this specification, all of these are referred to as Tb. ２ O ３ It is expressed as a converted value.

[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 300 nm to 1100 nm 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] SiO ２ This component forms the glass skeleton and broadens the vitrification range. The vitrification range is the range of compositions in which glass can be obtained. SiO ２ Since it does not contribute to improving the Verde constant, SiO ２ If the content is too high, it becomes difficult to obtain a sufficient Faraday effect. Therefore, SiO ２ The content of 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] B ２ O ３ This component forms a glass skeleton and broadens the vitrification range. However, B２ O ３ Since this does not contribute to improving Verde constant, B ２ O ３ If the content is too high, it becomes difficult to obtain a sufficient Faraday effect. Therefore, B ２ O ３ The content of 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] P ２ O ５ It forms a glass skeleton and is a component that broadens the vitrification range. However, P ２ O ５ Since this does not contribute to improving the Verde constant, P ２ O ５ If the content is too high, it becomes difficult to obtain a sufficient Faraday effect. Therefore, P ２ O ５ The content of 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] B ２ O ３ +P ２ O ５ (B ２ O ３ and P ２ O ５ The sum of the contents of each is preferably 20% to 70%, more preferably 25% to 60%, even more preferably 30% to 55%, and particularly preferably 30% to 45%. ２ O ３ and P ２ O ５ The sum of the content of these elements being within the above range makes it particularly easy to broaden the vitrification range.

[0109] Al ２ O ３Al is a component that increases glass-forming ability. Glass-forming ability is an indicator of how easily glass can be formed. The higher the glass-forming ability of a material, the easier it is for glass to form. ２ O ３ Since it does not contribute to improving the Verde constant, Al ２ O ３ If the content is too high, it becomes difficult to obtain a sufficient Faraday effect. Therefore, Al ２ O ３ The content of is preferably 0% to 50%, and particularly preferably 0% to 30%.

[0110] La ２ O ３ , Gd ２ O ３ , Y ２ O ３ It is a component that stabilizes vitrification. However, La ２ O ３ , Gd ２ O ３ or Y ２ O ３ If the content is too high, vitrification will actually be suppressed. Therefore, La ２ O ３ , Gd ２ O ３ , Y ２ O ３ The content of each is preferably 10% or less, and particularly preferably 5% or less.

[0111] Dy ２ O ３ , Eu ２ O ３ Ce ２ O ３ This component stabilizes vitrification and contributes to improving the Verde constant. However, Dy ２ O ３ , Eu ２ O ３ or Ce ２ O ３ If the content is too high, vitrification will actually be suppressed. Therefore, Dy ２ O ３ , Eu ２ O ３ Ce ２ O ３The content of each is preferably 15% or less, and particularly preferably 10% or less. Note that Dy, Eu, and Ce present in the glass exist in trivalent or tetravalent states, but in this specification, all of them are referred to as Dy ２ O ３ , Eu ２ O ３ Ce ２ O ３ It is expressed as a converted value.

[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] GeO ２ It is a component that enhances glass-forming ability. However, GeO ２ Since it does not contribute to improving the Verde constant, GeO ２ If the content is too high, it becomes difficult to obtain a sufficient Faraday effect. Therefore, GeO ２ The content of is preferably 0% to 15%, more preferably 0% to 10%, and particularly preferably 0% to 9%.

[0114] Ga ２ O ３ This component enhances the glass-forming ability and broadens the vitrification range. However, Ga ２ O ３ If the content is too high, the glass material will be more prone to devitrification. In addition, Ga ２ O ３ Since Ga does not contribute to improving the Verde constant, ２ O ３ If the content is too high, it becomes difficult to obtain a sufficient Faraday effect. Therefore, Ga ２ O ３ The content of is preferably 0% to 6%, and particularly preferably 0% to 5%.

[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 negatively affecting vitrification. In addition, it tends to increase the striations in the glass material. Therefore, the fluorine content (F ２ The conversion rate is preferably 0% to 10%, more preferably 0% to 7%, and particularly preferably 0% to 5%.

[0116] Sb as a reducing agent ２ O ３ Sb can be added. However, to avoid discoloration or to consider the environmental impact, ２ O ３ It is preferable that the content is 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, the Faraday element 17 can be made of Tb ３ Ga ５ O １２ , Tb ３ Al ５ O １２ , Tb ３ Sc ２ Al ３ O １２ , Y ３ Al ５ O １２ , Tb ２ HF ２ O ７ LiTbF ４ NaTbF ４ CeF ３ Single crystals such as the above 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 also 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 polarizing beam splitters, 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 prisms, 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] (Optical 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 as 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 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-described 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 300 mW or more, more preferably 500 mW or more, even more preferably 1 W or more, even more preferably 5 W or more, and particularly preferably 10 W or more. On the other hand, the light intensity is preferably, for example, 150 W or less, and more preferably 50 W 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, and the direction in which the light transmission axis of the polarizing beam splitter extended was set to 0°. A Faraday rotor with a rotation angle of +45° was used. A polarizing beam splitter was used as the second polarizer, and the direction in which the light transmission axis of the polarizing beam splitter extended was 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, and the direction in which the light transmission axis of the polarizing beam splitter extended was 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 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) Optical circulators were fabricated in the same manner as in Example 1, except that the rotation angle of the Faraday rotor and the rotation angle of the half-wave plate were changed as shown in Table 1 below, and the intensity of the light emitted from the optical circulators was monitored. In addition, the light transmittance at the second port and the light extraction rate at the light emission section of the optical circulators fabricated in Examples 2-6 were calculated. 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 expressed as 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]

[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 was possible within this range.

[0141] 1…Optical circulator 2…Housing 3…Optical emitter 4…Optical fiber 5-7…First to third polarizers 8…Faraday rotor 9…Half-wave plate 16…Magnetic circuit 16a…Through hole 17…Faraday element 21…Optical circulator 23…Optical emitter 25…Photodiode 101…Optical circulator 103…Fiber coupler 118…Faraday rotor 119…Half-wave plate P1-P3…First to third ports

Claims

1. The device comprises: a first port into which light is incident; a second port opposite to the first port, 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, 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 half-wave plate and the third polarizer are positioned such that a portion of the light incident from the first port, passing through the first polarizer, the Faraday rotator, the second polarizer, and the half-wave plate, is reflected by the third polarizer 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 a molar content of Tb in terms of oxide. 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 An optical monitoring method comprising the steps of: 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, the optical circulator further has an optical emission section from which the reflected light can be extracted, and the intensity of the transmitted light from the optical circulator is monitored by measuring the intensity of the reflected light extracted from the optical emission section.

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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