Optical circulator and optical monitoring method

Abstract

Provided is an optical circulator in which, when a polarizer in the optical circulator is broken, the breakage of the polarizer can be easily detected.　This optical circulator 1 is characterized by comprising: a first port P1 on which light is made incident; a second port P2 which faces the first port P1 and from which light made incident from the first port P1 is emitted; a third port P3 which is arranged so as not to be positioned on a straight line connecting the first port P1 and the second port P2 and from which light made incident from the second port P2 is emitted; a first polarizer 5 arranged on the first port P1 side; a second polarizer 6; a third polarizer 7 which is arranged on the second port P2 side, and is arranged so as to sandwich the second polarizer 6 together with the first polarizer 5; and a Faraday rotator 8 arranged between the second polarizer 6 and the third polarizer 7, the first polarizer 5 and the second polarizer 6 being arranged so that a part of light incident from the first port P1, passing through the first polarizer 5, and made incident on the second polarizer 6 is reflected and becomes reflected light, and the optical circulator 1 further comprising an optical output part 3 capable of extracting the reflected light.

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. In particular, the polarizer, which makes up the optical circulator, is a relatively fragile element, so it is desirable to understand the extent of its damage. However, polarizers are often located inside the housing of the optical circulator, making it difficult to immediately visually confirm if they are damaged. Thus, conventionally, even if a laser system malfunctions, it is difficult to confirm whether damage has occurred to the polarizer.

[0007] The object of the present invention is to provide an optical circulator and an optical monitoring method that can easily detect damage to a polarizer when the polarizer in the optical circulator is damaged.

[0008] A light circulator according to embodiment 1 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 is incident, 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 is incident, 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, and a Faraday rotator positioned between the second polarizer and the third polarizer, wherein the first polarizer and the second polarizer are positioned such that a portion of the light incident from the first port, passing through the first polarizer and incident on the second polarizer is reflected to become reflected light, and the light circulator further comprises a light emission section from which the reflected light can be extracted.

[0009] In the optical circulator of embodiment 2, in embodiment 1, when the angle at which the light transmission axis of the first polarizer is inclined with respect to the light transmission axis of the second polarizer is defined as the installation angle of the first polarizer, it is preferable that the installation angle is +1° or more and +8° or less.

[0010] In the optical circulator of embodiment 3, it is preferable that the rotation angle of the Faraday rotor is +45° in embodiment 1 or embodiment 2.

[0011] In the optical circulator of embodiment 4, 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 3.

[0012] In the optical circulator of embodiment 5, in any one embodiment from embodiment 1 to embodiment 4, 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.

[0013] In the optical circulator of embodiment 6, it is preferable that the paramagnetic material is a glass material in embodiment 5.

[0014] In the optical circulator of embodiment 7, in embodiment 6, 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%.

[0015] The optical monitoring method according to aspect 8 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 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, and a third polarizer 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 Faraday rotor, wherein the optical circulator is arranged such that a portion of the light incident on the first polarizer, passing through the first polarizer and onto the second 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.

[0016] In the optical monitoring method of embodiment 9, it is preferable that the intensity of the light incident on the optical circulator in embodiment 8 is 300 mW or more and 150 W or less.

[0017] According to the present invention, it is possible to provide an optical circulator and an optical monitoring method that can easily detect damage to a polarizer when the polarizer in the optical circulator is damaged.

[0018] 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 showing an optical circulator according to a modified example of the first embodiment. Figure 7 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 8 is a schematic diagram showing an optical circulator according to the second embodiment of the present invention.

[0019] 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.

[0020] (Optical Circulator) (First Embodiment) Figure 1 is a schematic diagram showing an optical circulator according to the first embodiment of the present invention.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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. Specifically, the third port P3 and the light emitting unit 3 face each other. The straight line connecting the first port P1 and the second port P2 intersects with the straight line connecting the third port P3 and the light emitting unit 3. More specifically, in this embodiment, the straight line connecting the first port P1 and the second port P2 and the straight line connecting the third port P3 and the light emitting unit 3 are perpendicular to each other.

[0027] The optical circulator 1 comprises a plurality of elements: a first polarizer 5, a second polarizer 6, a third polarizer 7, and a Faraday rotator 8. The first polarizer 5 is positioned on the first port P1 side. On the other hand, the third polarizer 7 is positioned on the second port P2 side. The second polarizer 6 is positioned between the first polarizer 5 and the third polarizer 7. The Faraday rotator 8 is positioned between the second polarizer 6 and the third polarizer 7.

[0028] 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.

[0029] The features of this embodiment are as follows: 1) A second polarizer 6 is positioned between a first polarizer 5 and a third polarizer 7, and a Faraday rotator 8 is positioned between the second polarizer 6 and the third polarizer 7. 2) The first polarizer 5 and the second polarizer 6 are positioned such that a portion of the light incident on the second polarizer 6 is reflected to become reflected light. 3) There is a light emission unit 3 that can extract the reflected light reflected by the second polarizer 6.

[0030] These features allow monitoring of the intensity of the reflected light that enters from the first port P1, passes through the first polarizer 5 and the second polarizer 6, and is extracted from the light emission unit 3. This makes it easy to detect damage to either the first polarizer 5 or the second polarizer 6 in the light circulator 1. The details of this will be explained below.

[0031] 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.

[0032] 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.

[0033] When the second polarizer 6 is positioned such that the direction in which the light transmission axis of the second polarizer 6 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, the angle in which the polarization plane of light is rotated by the Faraday rotator 8 is referred to as the rotation angle.

[0034] 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°.

[0035] 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.

[0036] In the present embodiment, the direction in which the optical transmission axis of the first polarizer 5 extends is +4°. The direction in which the optical transmission axis of the second polarizer 6 extends is 0°. The direction in which the optical transmission axis of the third polarizer 7 extends is +45°. Note that the direction in which the optical transmission axis of the polarizer extends can be adjusted, for example, by tilting a polarizer installed so that the direction in which the optical transmission axis extends is 0° to a predetermined angle.

[0037] Hereinafter, the optical path when light is incident from the first port P1 will be described. As shown in FIG. 2, light I ０’ which is linearly polarized light with a polarization plane angle of 0° is incident from the first port P1. The direction in which the optical transmission axis of the first polarizer 5 extends is +4°. Here, the polarization plane of the light I ０’ incident from the first port P1 and the optical transmission axis of the first polarizer 5 are not parallel. Therefore, the first polarizer 5 transmits the component parallel to the optical transmission axis of the first polarizer 5 among the light I ０’ and reflects the component not parallel to the optical transmission axis of the first polarizer 5. In other words, the light I ０’ branches into the light I ０ that passes through the first polarizer 5 without changing the traveling direction and the reflected light that is reflected inside the first polarizer 5 and changes the traveling direction and exits from the first polarizer 5.

[0038] FIG. 2 does not show the reflected light that is reflected inside the first polarizer 5 and changes the traveling direction and exits from the first polarizer 5. However, the reflected light hits the housing 2 shown in FIG. 1 and does not exit from the optical circulator 1.

[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, in Figure 2, light I that has passed through the first polarizer 5 without changing its direction of propagation is shown. ０ The plane of polarization is +4°.

[0040] In the example shown in Figure 2, linearly polarized light with a polarization plane angle of 0° is incident from the first port P1. Alternatively, non-linearly polarized light incident from the first port P1 may be passed through the first polarizer 5 to obtain linearly polarized light with a polarization plane angle of +4°. Alternatively, linearly polarized light with a polarization plane angle of +4° may be incident from the first port P1.

[0041] Light I that passed through the first polarizer 5 ０ The light I that passed through the first polarizer 5 is incident on the second polarizer 6. ０ The polarization plane of is +4°. The direction in which the light transmission axis of the second polarizer 6 extends is 0°. Here, light I that has passed through the first polarizer 5 ０ 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 is polarized to light I ０ 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. In other words, light I ０ This is light I passing through the second polarizer 6 without changing its direction of travel. １ Then, reflected light I is reflected inside the second polarizer 6, changes its direction of propagation, and exits the second polarizer 6. ２ It branches into two. Light I passes through the second polarizer 6 without changing its direction of travel. １ The angle of the polarization plane is 0°. Light I １ The reflected light I is incident on the Faraday rotor 8. ２ The light is emitted from the light-emitting unit 3.

[0042] Light I incident on the Faraday rotor 8 １ The polarization plane rotates by +45° due to the Faraday effect. As a result, light I that has passed through the Faraday rotator 8 １ The angle of the polarization plane is +45°.

[0043] Light I passing through Faraday rotor 8１ 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 +45°. Here, light I １ The polarization plane of the third polarizer 7 and the light transmission axis of the third polarizer 7 are parallel. Therefore, light I １ The light I passes through the third polarizer 7 without changing its direction of travel and is emitted from the second port P2. １ The angle of the polarization plane is +45°.

[0044] In this embodiment, light I incident on the second polarizer 6 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 of the transmitted light, 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 the first polarizer 5 and the second polarizer 6 of the optical circulator 1. By monitoring the intensity of the transmitted light from the optical circulator 1, damage to the first polarizer 5 or the second polarizer 6 of the optical circulator 1 can be easily detected when the first polarizer 5 or the second polarizer 6 of the optical circulator 1 is damaged and the intensity of the transmitted light decreases.

[0045] 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. ２ The signal can be converted into an electrical signal, and the intensity of the electrical signal can be measured.

[0046] 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.

[0047] Incidentally, as mentioned above, the angle of the polarization plane of light that has passed through the polarizer is parallel to the light transmission axis of the polarizer. Therefore, the light I incident on the second polarizer 6 ０ The angle at which the polarization plane of the first polarizer is inclined with respect to the light transmission axis of the second polarizer 6 is the same as the angle at which the light transmission axis of the first polarizer 5 is inclined with respect to the light transmission axis of the second polarizer 6. Here, let the angle at which the light transmission axis of the first polarizer 5 is inclined with respect to the light transmission axis of the second polarizer 6 be the installation angle α of the first polarizer 5. The direction in which the light transmission axis of the first polarizer 5 extends is +4°, and the direction in which the light transmission axis of the second polarizer 6 extends is 0°. Therefore, the installation angle α of the first polarizer 5 is +4° - 0° = +4°.

[0048] If the installation angle α is 0°, then the light I incident on the second polarizer 6 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 straight through the second polarizer 6, and the reflected light I ２ This does not occur. In contrast, in this embodiment, the installation angle α is not 0°. Specifically, in this embodiment, the installation angle α is +4°. As a result, the light I incident on the second polarizer 6 ０ Light I １ It can be suitably emitted as reflected light I ２ It can be extracted as follows.

[0049] More specifically, Optical I ０ 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 ０ Of this, approximately 99% passes through the second polarizer 6, and approximately 1% is emitted from the light emission unit 3 as reflected light. However, the installation angle α is not limited to the above.

[0050] The mounting angle α of the first polarizer 5 is preferably +1° or more, and more preferably +1.5° or more. On the other hand, the mounting angle α of the first polarizer 5 is preferably +8° or less, and more preferably +6° or less. As will be described later, this is equivalent in terms of the behavior of light passing through the polarizer to the case where the mounting angle α is -179° or more, or -178.5° or more, and -172° or less, or -174° or less. When the mounting angle α is within the above range, the light I incident on the second polarizer 6 ０ Light I １ It can be suitably emitted as reflected light I ２ It can be extracted as follows.

[0051] 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 +45° ３ Here, light I is incident. ３ The 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 +45°.

[0052] Light I that passed through the third polarizer 7 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°.

[0053] Light I passing through Faraday rotor 8 ３ The light I then enters the second polarizer 6. ３ The polarization plane of the first polarizer and the light transmission axis of the second polarizer 6 are perpendicular. Therefore, light I ３ It is reflected by the second polarizer 6 and emitted towards the third port P3. That is, light I ３The light I is not emitted from the second polarizer 6 towards the first polarizer 5, but is reflected inside the second polarizer 6 and emitted from the third port P3. ３ The angle of the polarization plane is +90°.

[0054] 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 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 Faraday rotator 8. That is, light I ４ The light I reflected by the second polarizer 6 is not emitted towards the light emission unit 3. ４ The angle of the polarization plane is +90°.

[0055] Light I reflected by the second polarizer 6 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°.

[0056] Light I passing through Faraday rotor 8 ４ It is incident on the third polarizer 7. Here, the light I that has passed through the Faraday rotator 8 ４ The polarization plane of the third polarizer 7 and the light transmission axis of the third polarizer 7 are perpendicular. Therefore, light I ４ It is reflected by the third polarizer 7 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.

[0057] 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°.

[0058] 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, the fiber coupler 103 has a problem in that it is difficult to sufficiently suppress damage when the intensity of the laser light used is high.

[0059] 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.

[0060] Incidentally, for example, the direction in which the light transmission axis of the second polarizer 6 shown in Figure 2 extends may differ from that of the first embodiment by +180° or -180°. This is shown below as a modification of the first embodiment. In this modification as well, similar to the first embodiment, the light I incident on the second polarizer 6 ０ Light I １ It can be suitably emitted as reflected light I ２ This allows the light to be extracted as follows. Furthermore, the intensity of the light extracted from the light emission unit 3 can be monitored, and damage to the first polarizer 5 or the second polarizer 6 can be easily detected.

[0061] (Modified Version) Figure 6 is a schematic diagram showing a modified version of the first embodiment of an optical circulator.

[0062] In this modified example, the direction in which the light transmission axis of the second polarizer 6 extends is +180° or -180°. In this modified example, the direction in which the light transmission axis of the second polarizer 6 extends is +180° or -180° different from that of the first embodiment. Therefore, the arrangement of the light emission section 3 and the third port P3 in this modified example is reversed compared to the first embodiment.

[0063] In this modified example, the installation angle α of the first polarizer 5, which is the angle at which the light transmission axis of the first polarizer 5 is inclined with respect to the light transmission axis of the second polarizer 6, is α = +4° - (+180°) = -176°. However, if the direction in which the light transmission axis of the polarizer extends differs by +180° or -180°, the direction in which the light is emitted when the direction of propagation is changed and emitted differs by 180°, but the behavior of the light passing through the polarizer is equivalent. Therefore, α = +4° - (+180°) = -176° is equivalent to α = +4° - 0° = +4° in terms of the behavior of the light passing through the polarizer. Thus, in this modified example as well, similar to the first embodiment, the light incident on the second polarizer 6 can be suitably emitted from the second port P2, and a portion can be extracted from the light emission unit 3 as reflected light. However, the installation angle α is not limited to the above.

[0064] The mounting angle α of the first polarizer 5 is preferably -179° or greater, and more preferably -178.5° or greater. On the other hand, the mounting angle α of the first polarizer 5 is preferably -172° or less, and more preferably -174° or less. In this case, the mounting angle α is equivalent in terms of the behavior of light passing through the polarizer to cases where it is +1° or greater, or +1.5° or greater, and 8° or less, or 6° or less. By having the mounting angle α of the first polarizer 5 within the above range, the light incident on the second polarizer 6 can be suitably emitted from the second port P2, and a portion can be extracted from the light emission unit 3 as reflected light.

[0065] The details of each element constituting the optical circulator of the present invention will be described below.

[0066] (Faraday rotor) Figure 7 is a schematic cross-sectional view along the direction of light passage, showing a Faraday rotor in the first embodiment.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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 22 mm or less, more preferably 20 mm or less, and even more preferably 17 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.

[0075] The Faraday rotator 8 is preferably used in the wavelength range of 330 nm to 1300 nm, more preferably in the wavelength range of 350 nm to 1200 nm, even more preferably in the wavelength range of 380 nm to 1200 nm, even more preferably in the wavelength range of 390 nm to 1100 nm, and particularly preferably in the wavelength range of 400 nm to 1100 nm.

[0076] 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.

[0077] 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 ２A glass material containing 0% to 45% can be used. In this specification, for example, when expressed as a + b + c +..., it means the sum of the contents of a, b, and c. In this specification, when the range is expressed as "~", the range includes the upper limit value and the lower limit value.

[0078] In the following, details of preferred materials used for the glass material are shown.

[0079] The glass material used for the Faraday element 17 preferably contains at least one rare earth element selected from Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm. It is particularly preferable that the above glass material contains Tb.

[0080] Tb in the glass material used for the Faraday element 17 ２ O ３ The content of is preferably more than 20 mol% in terms of oxide conversion, more preferably 25% or more, still 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. By increasing the content of Tb in this way, it becomes easier to obtain a good Faraday effect. On the other hand, the content of Tb in the glass material used for the Faraday element 17 ２ O ３ may be, for example, 80% or less. In the glass, Tb exists in a trivalent or tetravalent state, but in this specification, all of these are represented as values converted to Tb ２ O ３ O. ２ O ３ is represented as a converted value.

[0081] In the glass material used for the Faraday element 17, the ratio of Tb to total Tb ３＋ is preferably 55% or more in mol%, more preferably 60% or more, still more preferably 70% or more, even more preferably 80% or more, still more preferably 90% or more, and particularly preferably 95% or more. Tb to total Tb ３＋If the ratio is too small, the light transmittance at wavelengths of 300 nm to 1100 nm tends to decrease.

[0082] Furthermore, the Faraday element 17 can contain the following components. In the description of the content of each of the following components, unless otherwise specified, "%" means "mol%". In addition, when the component is an oxide, unless otherwise specified, "%" means "mol% in terms of oxide".

[0083] SiO ２ forms a glass skeleton and is a component that widens the vitrification range. The vitrification range is the range of compositions from which glass can be obtained. SiO ２ does not contribute to the improvement of the Verdet constant. Therefore, if the content of SiO ２ is too high, it becomes difficult to obtain a sufficient Faraday effect. Thus, the content of SiO ２ is preferably 0% to 50%, more preferably 0% to 45%, still more preferably 0% to 40%, even more preferably 1% to 35%, and particularly preferably 1% to 30%.

[0084] B ２ O ３ forms a glass skeleton and is a component that widens the vitrification range. However, B ２ O ３ does not contribute to the improvement of the Verdet constant. Therefore, if the content of B ２ O ３ is too high, it becomes difficult to obtain a sufficient Faraday effect. Thus, the content of B ２ O ３ is preferably 0% to 70%, more preferably 0% to 60%, still more preferably 0% to 55%, even more preferably 0% to 50%, even more preferably 1% to 45%, and particularly preferably 1% to 40%.

[0085] P ２ O ５ forms a glass skeleton and is a component that widens the vitrification range. However, P ２ O ５ does not contribute to the improvement of the Verdet constant. Therefore, ２ O ５If 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%.

[0086] 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.

[0087] Al ２ O ３ Al 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%.

[0088] 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 O３ 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.

[0089] 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 ３ The 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.

[0090] 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%.

[0091] 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%.

[0092] 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%.

[0093] 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%.

[0094] 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.

[0095] 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.

[0096] (Polarizers) 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.

[0097] (Optical Circulator) (Second Embodiment) Figure 8 is a schematic diagram showing an optical circulator according to the second embodiment.

[0098] 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.

[0099] 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 second polarizer 6 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.

[0100] 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 8 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.

[0101] 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.

[0102] 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.

[0103] 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 second 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.

[0104] (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, 6 and 8. 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, and a Faraday rotator 8.

[0105] 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 the 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 rotor 8 is positioned between the second polarizer 6 and the third polarizer 7.

[0106] The first polarizer 5 and the second polarizer 6 are arranged such that a portion of the light incident on the second polarizer 6, passing through the first polarizer 5 and entering the second polarizer 6, is reflected to become reflected light. The light circulator has a light emission unit that can extract the reflected light reflected by the second polarizer 6. The light monitoring method of the present invention is a method of monitoring the intensity of transmitted light that has passed through the first polarizer 5 and the second polarizer 6 of the light circulator by measuring the intensity of the reflected light extracted from the light emission unit.

[0107] This light monitoring method allows for continuous monitoring of the intensity of transmitted light from the light circulator. This makes it easy to detect damage to the first polarizer 5 or the second polarizer 6 of the light circulator when the intensity of transmitted light decreases due to damage to either polarizer 5 or 6.

[0108] 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.

[0109] 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.

[0110] The proportion of reflected light extracted by the second polarizer 6 is preferably 0.1% or more, and more preferably 0.3% or more, of the total light incident on the second polarizer 6. On the other hand, the proportion of reflected light extracted by the second polarizer 6 is preferably 10% or less, and more preferably 4% or less, of the total light incident on the second polarizer 6.

[0111] When the proportion of reflected light extracted by the second polarizer 6 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 second polarizer 6 is less than or equal to the upper limit, the amount of light transmitted through the second polarizer 6 can be increased even further. The proportion of light extracted by the second polarizer 6 can be adjusted by the installation angle α of the first polarizer 5.

[0112] <Examples> (Example 1) In Example 1, an optical circulator was fabricated to have the structure shown in Figure 1. Specifically, a polarizing beam splitter was used as the first polarizer, and the direction in which the optical transmission axis of the polarizing beam splitter extended was set to +4°. A polarizing beam splitter was used as the second polarizer, and the direction in which the optical 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 third polarizer, and the direction in which the optical transmission axis of the polarizing beam splitter extended was set to +45°.

[0113] 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 second 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.

[0114] (Examples 2-7) Except for changing the installation angle of the first polarizer and the rotation angle of the Faraday rotor as shown in Table 1 below, optical circulators were fabricated in the same manner as in Example 1, and the intensity of 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 2-7 were calculated. The results are shown in Table 1.

[0115] 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."

[0116]

[0117] As shown in Table 1, the percentage of light emitted from the light output section of the optical circulators fabricated in Examples 1 to 7, i.e., the light extraction rate, was 1 to 3%, and it was confirmed that monitoring was possible within this range.

[0118] 1…Optical circulator 2…Housing 3…Optical emitter 4…Optical fiber 5-7…First to third polarizers 8…Faraday rotor 16…Magnetic circuit 16a…Through hole 17…Faraday element 21…Optical circulator 23…Optical emitter 25…Photodiode 101…Optical circulator 103…Fiber coupler P1-P3…First to third ports

Claims

1. A light 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 is incident; 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 is incident; 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; and a Faraday rotator positioned between the second polarizer and the third polarizer, wherein the first polarizer and the second polarizer are positioned such that a portion of the light incident from the first port, passing through the first polarizer and incident on the second polarizer is reflected to become reflected light, and further comprising a light emission section capable of extracting the reflected light.

2. The optical circulator according to claim 1, wherein when the angle at which the light transmission axis of the first polarizer is inclined with respect to the light transmission axis of the second polarizer is defined as the installation angle of the first polarizer, the installation angle is between +1° and +8°.

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

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

5. 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.

6. The optical circulator according to claim 5, wherein the paramagnetic material is a glass material.

7. 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 optical circulator according to claim 6, containing 0% to 45%.

8. An optical monitoring method for monitoring the intensity of transmitted light of an optical circulator, comprising: a first port into which light is incident; a second port facing the first port and from which light incident from the first port is emitted; 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 is emitted; 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; and a Faraday rotator positioned between the second polarizer and the third polarizer, wherein the first polarizer and the second polarizer are positioned in the optical circulator such that a portion of the light incident from the first port, passing through the first polarizer and incident on the second polarizer is reflected to become reflected light; and the optical circulator further comprises an optical emission 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.

9. The optical monitoring method according to claim 8, 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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