Optical isolator and optical monitoring method

Abstract

The invention provides an optical isolator capable of easily detecting damage of elements when the elements of the optical isolator are damaged. The optical isolator (1) is provided with a first polarizer (2) provided on the light incident side, a second polarizer (3) provided on the light exit side, and a Faraday rotator (4) provided between the first polarizer (2) and the second polarizer (3), and when the angle at which the light transmission axis of the second polarizer (3) is inclined with respect to the light transmission axis of the first polarizer (2) is set as the setting angle of the second polarizer (3), the Faraday rotator (4) is set as the setting angle of the second polarizer (3). The installation angle of the second polarizer (3) is different from the rotation angle of the Faraday rotator (4).

Description

Technical Field

[0001] The invention relates to an optical isolator and a light monitoring method for monitoring the intensity of transmitted light of the optical isolator. Background Art

[0002] An optical isolator is a magneto-optical element that transmits light in only one direction and blocks reflected light. An optical isolator is used in laser oscillators used in optical communication systems, laser processing systems, and the like. As such an optical isolator, the following patent document 1 discloses an optical isolator including: a Faraday rotator; a first polarizer disposed at one end of the Faraday rotator in the optical axis direction; and a second polarizer disposed at the other end of the Faraday rotator in the optical axis direction.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2003-322826 Summary of the invention

[0006] Problems to be solved by the invention

[0007] In recent years, laser processing has been continuously increasing its output. However, when the output of the laser is increased, there are cases where components such as the Faraday rotator and polarizer in the optical isolator are damaged. When these components are damaged, there is a problem that the laser cannot be transmitted and the laser system does not work.

[0008] Therefore, when an optical isolator element is damaged, it is necessary to replace the element immediately. However, since the Faraday rotator in the optical isolator is housed in the magnet, it is difficult to visually check whether it is damaged. In addition, since the polarizer is fixed to the holding member, it is also difficult to visually check whether it is damaged.

[0009] Thus, the prior art has a problem that even if a failure occurs in the laser system, it is difficult to identify where the damage has occurred.

[0010] An object of the present invention is to provide an optical isolator and an optical monitoring method that can easily detect damage to an optical isolator element when the optical isolator element is damaged.

[0011] Methods for solving problems

[0012] Various aspects of an optical isolator and an optical monitoring method for solving the above-mentioned technical problems will be described.

[0013] The optical isolator of method 1 is characterized in that it includes: a first polarizer arranged on the light incident side; a second polarizer arranged on the light emitting side; and a Faraday rotator arranged between the first polarizer and the second polarizer, and when the angle at which the light transmission axis of the second polarizer is inclined relative to the light transmission axis of the first polarizer is defined as the setting angle of the second polarizer, the setting angle of the second polarizer is different from the rotation angle of the Faraday rotator.

[0014] In the optical isolator of aspect 2, preferably in aspect 1, the sum of the installation angle of the second polarizer and the rotation angle of the Faraday rotator is within the range of 90°±2°.

[0015] In the optical isolator of mode 3, preferably in mode 1 or mode 2, when the installation angle of the second polarizer is 45°+A° and the rotation angle of the Faraday rotator is 45°-A°, A is greater than or equal to 0.5 and less than or equal to 10.

[0016] The optical isolator of aspect 4 is preferably any one of aspects 1 to 3, further comprising a light emitting section capable of extracting a part of the light incident on the second polarizer.

[0017] In the optical isolator of aspect 5, preferably in aspect 4, a tap port or a photodiode is directly or indirectly connected to the light emitting portion.

[0018] In the optical isolator of aspect 6, preferably in any one of aspects 1 to 5, the Faraday rotator includes a Faraday element disposed in a cylindrical magnet, and the Faraday element is formed of a paramagnetic material that transmits light.

[0019] In the optical isolator of aspect 7, preferably in aspect 6, the Faraday element formed of the paramagnetic material is a glass material.

[0020] In the optical isolator of mode 8, preferably in mode 7, the glass material contains, in mol %, 20% to 80% TB2O3, 20% to 70% B2O3+P2O5, and 0% to 45% SiO2.

[0021] The optical monitoring method of mode 9 monitors the intensity of light transmitted through an optical isolator, wherein the optical isolator includes: a first polarizer arranged on a light incident side, a second polarizer arranged on a light emitting side, and a Faraday rotator arranged between the first polarizer and the second polarizer. The optical monitoring method is characterized in that it includes: a step of taking out a part of the light incident on the second polarizer by reflecting a part of the light incident on the second polarizer using the second polarizer; and a step of monitoring the intensity of light transmitted through the optical isolator by measuring the intensity of the part of the light taken out.

[0022] In the optical monitoring method of aspect 10, preferably in aspect 9, the intensity of the laser light transmitted through the optical isolator is 300 mW or more and 150 W or less.

[0023] Effects of the Invention

[0024] According to the present invention, it is possible to provide an optical isolator and an optical monitoring method that can easily detect damage to an element when the element of the optical isolator is damaged. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a schematic diagram for explaining the optical path when light travels in the forward direction in the optical isolator according to one embodiment of the present invention.

[0026] Figure 2 This is a schematic diagram for explaining the optical path when light travels in the reverse direction in the optical isolator according to one embodiment of the present invention.

[0027] Figure 3 This is a schematic cross-sectional view showing a Faraday rotator constituting an optical isolator according to one embodiment of the present invention.

[0028] Figure 4 This is a diagram showing an example of the structure of the first magnet.

[0029] Figure 5 This is a diagram showing an example of the structure of the second magnet.

[0030] Figure 6 This is a diagram showing an example of the structure of the third magnet.

[0031] Figure 7 This is a schematic diagram for explaining an example of a light emitting section.

[0032] Figure 8 It is a schematic diagram for explaining another example of the light emitting section.

[0033] Fig. 9 (a) is a schematic cross-sectional view of an optical isolator according to an embodiment of the present invention along the optical axis direction. Fig. 9 (b) Yes Fig. 9 (a) is a schematic diagram of the cross section shown.

[0034] Fig.10 This is a schematic cross-sectional view showing an optical isolator according to an embodiment of the present invention, taken in a direction perpendicular to the optical axis direction.

[0035] Fig.11 It is a perspective view of an optical isolator according to a modified example of the present invention.

[0036] Fig.12 It is a schematic diagram for explaining the light emitting portion of the comparative example. DETAILED DESCRIPTION

[0037] Hereinafter, preferred embodiments will be described. However, the following embodiments are merely illustrative, and the present invention is not limited to the following embodiments. In addition, in each of the drawings, components having substantially the same function are sometimes given the same reference numerals for reference.

[0038] [Optical isolator]

[0039] Figure 1 Schematic diagram for explaining the optical path of light in the forward direction in an optical isolator according to one embodiment of the present invention. Figure 2 This is a schematic diagram for explaining the optical path when light travels in the reverse direction in the optical isolator according to one embodiment of the present invention.

[0040] like Figure 1 and Figure 2 As shown, the optical isolator 1 includes a first polarizer 2, a second polarizer 3 and a Faraday rotator 4. The first polarizer 2 is arranged on the light incident side. The second polarizer 3 is arranged on the light exiting side. In addition, the Faraday rotator 4 is arranged between the first polarizer 2 and the second polarizer 3.

[0041] In this embodiment, when the angle at which the light transmission axis of the second polarizer 3 is tilted relative to the light transmission axis of the first polarizer 2 is defined as the installation angle of the second polarizer 3 , the installation angle of the second polarizer 3 is different from the rotation angle of the Faraday rotator 4 .

[0042] Hereinafter, an example of optical design in which the installation angle of the first polarizer 2 is set to 0°, the installation angle of the second polarizer 3 is set to 47°, and the rotation angle of the Faraday rotator 4 is set to 43° will be described.

[0043] like Figure 1 As shown, the light I0 incident on the optical isolator 1 passes through the first polarizer 2, becomes linearly polarized light, and enters the Faraday rotator 4. The light incident on the Faraday rotator 4 is rotated by 43° by the Faraday rotator 4 and enters the second polarizer 3. The light I0 incident on the second polarizer 3 passes through the second polarizer 3 with a polarization plane of 47°. At this time, the setting angle of the second polarizer 3 is different from the angle after rotation by the Faraday rotator 4, and the difference θ is 4°. Therefore, a part of the light incident on the second polarizer 3 does not travel straight in the second polarizer 3, and can be taken out as reflected light I2. By measuring the intensity of the reflected light I2 taken out, the intensity of the transmitted light of the optical isolator 1 can be monitored.

[0044] In addition, if Figure 2As shown, the reflected return light B of the light I1 after passing through the second polarizer 3 passes through the second polarizer 3 with a polarization plane of 47°. The reflected return light B after passing through the second polarizer 3 is further rotated by 43° by the Faraday rotator 4, and becomes an orthogonal polarization plane that is 90° with respect to the light transmission axis of the first polarizer 2. Therefore, the reflected return light B cannot travel straight through the first polarizer 2. Thus, it is possible to function as an optical isolator 1.

[0045] Thus, according to the optical isolator 1 of this embodiment, since the intensity of transmitted light can be always monitored, when the element of the optical isolator 1 is damaged and the intensity of transmitted light decreases, the damage of the element can be easily detected. In particular, since the reflected light I2 can be always taken out at a constant light amount, unlike the reflected return light B, it can be suitably used for monitoring the intensity of transmitted light.

[0046] In this embodiment, as in the above-mentioned example of optical design, the sum of the installation angle of the second polarizer 3 and the rotation angle of the Faraday rotator 4 is preferably 90°±2°, more preferably 90°±1°, and particularly preferably 90°. In this case, the reflected return light B can be more reliably cut off in the first polarizer 2.

[0047] In addition, in the present embodiment, when the installation angle of the second polarizer 3 is 45°+A° and the rotation angle of the Faraday rotator 4 is 45°-A°, A is preferably 0.5 or more, more preferably 1 or more, further preferably 2 or more, preferably 10 or less, more preferably 7 or less, further preferably 5 or less. When A is equal to or greater than the above lower limit, the intensity of the transmitted light of the optical isolator 1 can be more reliably monitored. When A is equal to or less than the above upper limit, the amount of light transmitted through the second polarizer 3 can be increased.

[0048] Hereinafter, each component constituting the optical isolator will be described.

[0049] (Faraday rotator)

[0050] Figure 3 : is a schematic cross-sectional view showing a Faraday rotator constituting an optical isolator according to one embodiment of the present invention. Figure 3 The N and S characters in represent magnetic poles. The same is true in other drawings described later.

[0051] Figure 3 The Faraday rotator 4 shown includes: a magnetic circuit 11 provided with a through hole 12 for light to pass through; and a Faraday element 24 disposed in the through hole 12. The Faraday element 24 is formed of a paramagnetic material that transmits light.

[0052] The magnetic circuit 11 has: a first magnet 21, a second magnet 22, and a third magnet 23, each of which has a through hole. The magnetic circuit 11 is formed by coaxially arranging the first magnet 21, the second magnet 22, and the third magnet 23 in sequence in the front-back direction. The so-called coaxial arrangement means that the magnets are arranged in a manner that overlaps near the center when viewed from the optical axis direction X. In this embodiment, the through hole 12 of the magnetic circuit 11 is formed by connecting the through holes of the first magnet 21, the second magnet 22, and the third magnet 23.

[0053] The Faraday element 24 can be arranged in the through hole 12 of the magnetic circuit 11. Thus, the Faraday rotator 4 can be formed. In addition, the cross-sectional shape of the Faraday element 24 and the cross-sectional shape of the through hole 12 of the magnetic circuit 11 do not necessarily have to be consistent, but from the viewpoint of applying a uniform magnetic field, it is preferable to make the cross-sectional shape of the Faraday element 24 consistent with the cross-sectional shape of the through hole 12 of the magnetic circuit 11.

[0054] The cross-sectional area of ​​the through hole 12 of the magnetic circuit 11 is preferably 100 mm 2 If the cross-sectional area of ​​the through hole 12 is too large, sufficient magnetic flux density cannot be obtained, and if it is too small, it is difficult to arrange the Faraday element 24 in the through hole 12. The cross-sectional area of ​​the through hole 12 is preferably 3 mm 2 ~80mm 2 , more preferably 4 mm 2 ~70mm 2 , more preferably 5mm 2 ~60mm 2 , especially preferably 7mm 2 ~50mm 2 .

[0055] The cross-sectional shape of the through hole 12 of the magnetic circuit 11 is not particularly limited and may be rectangular or circular. The cross-sectional shape of the through hole 12 of the magnetic circuit 11 is preferably rectangular from the viewpoint of easy assembly and preferably circular from the viewpoint of providing a uniform magnetic field.

[0056] Figure 4 It is a diagram showing an example of the structure of the first magnet (a diagram when viewed from the optical axis direction X). Figure 4 The first magnet 21 shown is composed of four magnet pieces, and has a rectangular (square) cross-sectional shape as a whole. The first magnet 21 may also have a circular cross-sectional shape as a whole. In addition, the number of magnet pieces constituting the first magnet 21 is not limited to the above-mentioned manner. For example, the first magnet 21 may also be composed of six or eight magnet pieces. By combining a plurality of magnet pieces to form the first magnet 21, the magnetic field can be preferably increased. However, the first magnet 21 may also be composed of a single magnet.

[0057] Figure 5 It is a diagram showing an example of the structure of the second magnet (a diagram when viewed from the optical axis direction X). Figure 5 The second magnet 22 shown is composed of a single magnet. The second magnet 22 has a rectangular (square) cross-sectional shape. The second magnet 22 may also have a circular cross-sectional shape. In addition, the second magnet 22 may also be composed of a combination of two or more magnet pieces.

[0058] Figure 6 It is a diagram showing an example of the structure of the third magnet (a diagram when viewed from the optical axis direction X). Figure 6 The third magnet 23 shown is composed of four magnet pieces in the same manner as the first magnet 21, and has a rectangular (square) cross-sectional shape as a whole. The third magnet 23 may also have a circular cross-sectional shape as a whole. By combining a plurality of magnet pieces to form the third magnet 23, the magnetic field can be effectively increased. In addition, the third magnet 23 may also be composed of six or eight magnet pieces, or may be composed of a single magnet.

[0059] In the present embodiment, light is incident from the side of the first magnet 21. In addition, in the magnetic circuit 11, the first magnet 21 and the third magnet 23 are magnetized in the direction Y perpendicular to the optical axis direction X, and the magnetization directions are opposite to each other. Specifically, the first magnet 21 is magnetized in the direction Y perpendicular to the optical axis direction X and in a manner that the through hole 12 side is the N pole. The third magnet 23 is magnetized in the direction Y perpendicular to the optical axis direction X and in a manner that the through hole 12 side is the S pole. The second magnet 22 is magnetized in a direction parallel to the optical axis direction X and in a manner that the first magnet 21 side is the N pole. In addition, in this specification, the direction in which light passes through the through hole 12 of the magnetic circuit 11 is set as the optical axis direction X.

[0060] In addition, light may be incident from the side of the third magnet 23. In this case, the first magnet 21 may be magnetized so that the through hole 12 side is the S pole, the third magnet 23 may be magnetized so that the through hole 12 side is the N pole, and the second magnet 22 may be magnetized so that the first magnet 21 side is the S pole.

[0061] The first magnet 21, the second magnet 22 and the third magnet 23 are made of permanent magnets. As the permanent magnets, rare earth magnets are particularly preferred, and magnets mainly composed of samarium-cobalt (Sm-Co) and magnets mainly composed of neodymium-iron-boron (Nd-Fe-B) are preferred.

[0062] The length L1 of the first magnet 21 is, for example, preferably 5 mm or more, more preferably 8 mm or more, particularly preferably 10 mm or more, preferably 30 mm or less, more preferably 25 mm or less, and particularly preferably 20 mm or less. The length L2 of the second magnet 22 is, for example, preferably 3 mm or more, more preferably 5 mm or more, further preferably 8 mm or more, particularly preferably 10 mm or more, preferably 30 mm or less, more preferably 25 mm or less, further preferably 20 mm or less, and particularly preferably 15 mm or less. In addition, the length L3 of the third magnet 23 is, for example, preferably 5 mm or more, more preferably 8 mm or more, particularly preferably 10 mm or more, preferably 30 mm or less, more preferably 25 mm or less, and particularly preferably 20 mm or less. In addition, the length L1 of the first magnet 21, the length L2 of the second magnet 22, and the length L3 of the third magnet 23 are all lengths along the optical axis direction X.

[0063] The magnetic circuit 11 is not limited to the structure including the first magnet 21, the second magnet 22, and the third magnet 23 each having a through hole. For example, the magnetic circuit 11 may be composed of a single magnet having a through hole.

[0064] A paramagnetic material can be used as the Faraday element 24. As the paramagnetic material, a glass material is preferably used. The Faraday element 24 formed of a glass material has a small change in the Verdet's constant and a small decrease in the extinction ratio caused by defects, etc., as in a single crystal material, and is also less affected by stress from an adhesive, so that a stable Verdet constant and a high extinction ratio can be maintained.

[0065] The glass material used for the Faraday element 24 preferably contains at least one rare earth element selected from Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, and Tm. In particular, it is preferred to contain Tb. In addition, Tb is present in trivalent and tetravalent states in the glass material, but in this specification, all of them are expressed as values ​​converted to TB2O3.

[0066] In the glass material used for the Faraday element 24, the ratio of Tb3+ to the total Tb is preferably 55% or more, more preferably 60% or more, further preferably 80% or more, and particularly preferably 90% or more. If the ratio of Tb3+ to the total Tb is too small, the light transmittance at a wavelength of 300nm to 1100nm is likely to decrease.

[0067] As the glass material used for the Faraday element 24, for example, a glass material containing, in terms of mol%, 20% to 80% of TB2O3, 20% to 70% of B2O3+P2O5, and 0% to 45% of SiO2 can be used.

[0068] The content of TB2O3 is preferably 20% to 80% in mole %, more preferably 30% to 80%, further preferably 40% to 80%, and particularly preferably 51% to 80%. When the content of TB2O3 is within the above range, a good Faraday effect can be obtained more effectively.

[0069] B2O3+P2O5 (the sum of the contents of B2O3 and P2O5) is preferably 20% to 70% in mole %, more preferably 25% to 60%, further preferably 30% to 55%, and particularly preferably 30% to 45%. By making the sum of the contents of B2O3 and P2O5 within the above range, it is particularly easy to expand the vitrification range. In addition, the preferred contents of B2O3 and P2O5 are as follows.

[0070] The content of B2O3 is preferably 0% to 70% in mole %, more preferably 0% to 60%, further preferably 0% to 55%, and particularly preferably 1% to 45%. When the content of B2O3 is within the above range, the Faraday effect can be obtained and the glass transition range can be further expanded.

[0071] The content of P2O5 is preferably 0% to 70% in mole %, more preferably 0% to 60%, further preferably 0% to 55%, and particularly preferably 1% to 45%. When the content of P2O5 is within the above range, the Faraday effect can be obtained and the glass transition range can be further expanded.

[0072] The content of SiO2 is preferably 0% to 45% in mole %, more preferably 0% to 40%, further preferably 0% to 35%, and particularly preferably 1% to 30%. When the content of SiO2 is within the above range, the Faraday effect can be obtained and the vitrification range can be further expanded.

[0073] In addition, paramagnetic materials other than glass materials can be used in the Faraday element 24. For example, paramagnetic single crystals and ceramics can be used in the Faraday element 24. For example, Tb3Ga5O 12 、Tb3Al5O 12 、Tb3Sc2Al3O 12 、Y3Al5O 12 , TB2Hf2O7, LiTbF4, NaTbF4, CeF3 and other single crystals. In addition, Tb-Ga type oxide ceramics, Tb-Al type oxide ceramics, Tb-Sc-Al type oxide ceramics, Y-Al type oxide ceramics, Tb-Hf type oxide ceramics, Tb type fluoride ceramics, Ce type fluoride ceramics can be used in the Faraday element 24.

[0074] The cross-sectional shape of the Faraday element 24 is not particularly limited, but is preferably circular in order to obtain a uniform Faraday effect. The diameter of the Faraday element 24 can be, for example, 1 mm or more and 10 mm or less. In addition, especially when a high-output laser is used, the diameter of the Faraday element 24 can also be 5 mm or more, 10 mm or more, more than 10 mm, 15 mm or more, and especially 20 mm or more.

[0075] The length of the Faraday element 24 is preferably 1 mm or more, more preferably 3 mm or more, further preferably 5 mm or more, preferably 20 mm or less, more preferably 15 mm or less, further preferably 12 mm or less. When the length of the Faraday element 24 is within the above range, the rotation angle of the Faraday rotator 4 can be more reliably adjusted to a desired range. In addition, especially when a high-output laser is used, the length of the Faraday element 24 may be 10 mm or more, 20 mm or more, more than 20 mm, 30 mm or more, and particularly 40 mm or more.

[0076] The Faraday rotator 4 is preferably used for a wavelength of 350 nm to 1300 nm, more preferably for a wavelength of 450 nm to 1200 nm, further preferably for a wavelength of 500 nm to 1200 nm, particularly preferably for a wavelength of 800 nm to 1100 nm, and most preferably for a wavelength in the range of 900 nm to 1100 nm.

[0077] (1st polarizer and 2nd polarizer)

[0078] like Figure 3 As shown, the first polarizer 2 can be arranged at one end of the magnetic circuit 11 in the optical axis direction X. In addition, the second polarizer 3 can be arranged at the other end of the magnetic circuit 11 in the optical axis direction X. As the first polarizer 2 and the second polarizer 3, for example, a polarization beam splitter can be used. As the polarization beam splitter, for example, a polarization beam splitter formed by joining two triangular prisms via a polarization separation film can be used. As the material of the prism, for example, glass can be used.

[0079] (Light exit part)

[0080] The optical isolator of the present invention may also include a light emitting portion. The light emitting portion is an opening portion provided in the housing of the optical isolator. By using the opening portion, the light branched in the housing can be removed. The shape of the opening portion is not particularly limited as long as it is a shape that can remove the light reflected by the second polarizer 3.

[0081] Figure 7 This is a schematic diagram for explaining an example of a light emitting section.

[0082] exist Figure 7In the optical isolator 1A shown, the above-mentioned first polarizer 2, second polarizer 3 and Faraday rotator 4 are arranged in a housing 30. An end 30a on one side of the housing 30 is an end provided on the light incident side. Therefore, in the housing 30, the first polarizer 2 is arranged on the end 30a side. In addition, an end 30b on the other side of the housing 30 is an end provided on the light emitting side. Therefore, in the housing 30, the second polarizer 3 is arranged on the end 30b side. In addition, in the housing 30, a Faraday rotator 4 is arranged between the first polarizer 2 and the second polarizer 3 in the optical axis direction X. In addition, in the housing 30, a light emitting portion 31 for extracting the light branched in the housing 30 is provided. In addition, an optical fiber 32 is connected to the ends 30a and 30b of the housing 30 and the light emitting portion 31.

[0083] As described above, a part of the incident light can be taken out as reflected light by using the second polarizer 3. The reflected light can be emitted from the light emitting portion 31 by using the optical isolator 1A. Furthermore, by aligning and connecting the light emitted from the light emitting portion 31 to the TAP port and taking it out, the intensity of the transmitted light of the optical isolator 1A can be monitored.

[0084] In addition, as a method for monitoring the intensity of light transmitted through the optical isolator, the following method can also be considered: Fig.12 As shown in the comparative example optical isolator 101, a fiber coupler 103 is connected to the optical fiber 102 on the output side to monitor the branched light. However, the fiber coupler has a problem that the laser resistance is insufficient when the laser output is greatly reduced.

[0085] In contrast, Figure 7 In the optical isolator 1A shown, a fiber coupler is not used, and part of the light is reflected by the second polarizer 3, so that the light can be easily taken out as reflected light, and thus the laser resistance is excellent. Therefore, the optical isolator 1A can increase the output of the laser.

[0086] Figure 8 It is a schematic diagram for explaining another example of the light emitting section.

[0087] exist Figure 8 In the optical isolator 1B shown in FIG. 1 , the photodiode 33 is directly connected to the light emitting portion 31. In this embodiment, the light emitting portion 31 is provided at the opening of the housing 30. Figure 7 The optical isolator 1A is the same as that of FIG. 1. In addition, the opening is preferably covered with a transparent member such as glass.

[0088] With the optical isolator 1B, the intensity of light transmitted through the optical isolator 1B can be monitored by directly taking in the reflected light emitted from the light emitting portion 31 .

[0089] In the optical isolator 1B, part of the light reflected by the second polarizer 3 can be easily taken out as reflected light, so the laser resistance is excellent. Therefore, the optical isolator 1B can also increase the output of the laser. In addition, in the optical isolator 1B, since a tap port is not used, there is also an advantage that no coupling loss occurs at the tap port.

[0090] As the light emitting unit 31, in addition to emitting the reflected light from the optical isolator 1B to the outside of the housing 30 as described above, there is also a method of converting the reflected light into an electric signal and transmitting the electric signal to the outside of the housing 30. For example, there is also a method of converting the reflected light into an electric signal by providing a photodiode or the like in the housing 30, and transmitting the converted electric signal to the outside of the housing 30.

[0091] Fig. 9 (a) is a schematic cross-sectional view of an optical isolator according to an embodiment of the present invention, taken along the optical axis direction. Fig. 9 (b) Yes Fig. 9 (a) is a schematic diagram of the cross section shown. Fig. 9 In the optical isolator 1C shown in (a) and (b), Figure 1 An example of a specific structure of the optical isolator 1 is shown.

[0092] The optical isolator 1C includes a first polarizer 2, a second polarizer 3, a Faraday rotator 4, and a housing 6. The first polarizer 2 is disposed on the light incident side in the optical axis direction X. The second polarizer 3 is disposed on the light exiting side in the optical axis direction X. The Faraday rotator 4 is disposed between the first polarizer 2 and the second polarizer 3.

[0093] The Faraday rotator 4 includes a magnet 7 and a Faraday element 8. In the present embodiment, the magnet 7 has a square cylindrical shape. In addition, the magnet 7 has a through hole 7a through which light passes. In addition, the direction in which light passes through the through hole 7a of the magnet 7 is defined as the optical axis direction X. In addition, the Faraday element 8 is formed of a paramagnetic material that transmits light.

[0094] The magnet 7 has a first end face 7b, a second end face 7c, and a side face 7d. The first end face 7b and the second end face 7c are opposite to each other in the optical axis direction X. The first end face 7b is an end face on one side of the optical axis direction X of the magnet 7. The second end face 7c is an end face on the other side of the optical axis direction X of the magnet 7. The side face 7d is connected to the first end face 7b and the second end face 7c. In addition, a through hole 7a is formed in both the first end face 7b and the second end face 7c.

[0095] like Fig.10As shown, the cross-sectional shape of the through hole 7a of the magnet 7 along the direction orthogonal to the optical axis direction X is a square. The cross-sectional shape of the through hole 7a is not limited to a substantially rectangular shape including the square as described above, but may also be a substantially circular shape including a circular shape. In addition, the shape of the magnet 7 is not limited to a square tube shape, and may be a cylindrical shape, for example.

[0096] A pipe member 9 is provided in the through hole 7a of the magnet 7. In the present embodiment, the pipe member 9 is a metal pipe. The pipe member 9 has a cylindrical shape. In addition, the pipe member 9 has a through hole 9a through which light passes. The cross-sectional shape of the through hole 9a of the pipe member 9 along the direction orthogonal to the optical axis direction X is circular. In the present embodiment, SUS304 is used as the material of the pipe member 9. However, the shape and material of the pipe member 9 are not particularly limited.

[0097] The Faraday element 8 is disposed in the through hole 9a of the pipe member 9. However, the pipe member 9 is not necessarily required. In this case, the Faraday element 8 may be disposed in the through hole 7a of the magnet 7.

[0098] The first polarizer 2 is provided on the first end face 7b side of the magnet 7. The second polarizer 3 is provided on the second end face 7c side of the magnet 7. The first polarizer 2 and the second polarizer 3 are provided in the optical axis direction X with the Faraday element 8 interposed therebetween and facing each other.

[0099] In the optical isolator 1C, the first polarizer 2, the second polarizer 3, and the Faraday rotator 4 are provided in a housing 6. As a material of the housing 6, for example, an aluminum alloy can be used. However, the material of the housing 6 is not particularly limited.

[0100] In the optical isolator 1C, light is incident on the first polarizer 2 via the first optical fiber collimator 10a. The light becomes linearly polarized light through the first polarizer 2 and is incident on the Faraday element 8. Moreover, the polarization plane of the light after passing through the Faraday element 8 is rotated. The light emitted from the Faraday element 8 is incident on the second polarizer 3. The light after passing through the second polarizer 3 is guided from the optical isolator 1C to the optical fiber via the second optical fiber collimator 10b.

[0101] In the optical isolator 1C as well, when the angle at which the light transmission axis of the second polarizer 3 is tilted relative to the light transmission axis of the first polarizer 2 is defined as the setting angle of the second polarizer 3, the setting angle of the second polarizer 3 is different from the rotation angle of the Faraday rotator 4. Therefore, a part of the light incident on the second polarizer 3 does not travel straight in the second polarizer 3 and can be taken out as reflected light I2. By measuring the intensity of the reflected light I2 taken out, the intensity of the transmitted light of the optical isolator 1C can be monitored.

[0102] In addition, in the optical isolator 1C, if Fig. 9 As shown in (a) and (b), a light emitting portion 5 as an opening is provided in a part of the wall of the housing 6. In the optical isolator 1C, the reflected light I2 branched in the housing 6 can be taken out by the light emitting portion 5, and the intensity of the taken out reflected light I2 can be measured.

[0103] The shape of the light emitting portion 5 is not particularly limited as long as the reflected light I2 can pass therethrough, and may be, for example, a substantially circular shape, a substantially rectangular shape, or a long hole.

[0104] The size of the light emitting portion 5 is not particularly limited, and can be, for example, 1 mm to 8 mm. The light emitting portion 5 can be sealed by a transparent member that allows the reflected light I2 to pass through, or an anti-reflection film can be formed on the transparent member to make the reflected light I2 pass through more easily.

[0105] In the above-mentioned embodiment, the light emitting portion 5 is described as being provided in the opening of the housing 6, but the present invention is not limited to this method. For example, a method in which a photodiode is provided in the housing 6, an optical signal is converted into an electrical signal in the housing 6, and the electrical signal is taken out from the housing 6 also falls within the scope of the light emitting portion 5.

[0106] Fig.11 1 is a perspective view of an optical isolator of a modified example of the present invention. This modified example differs from the optical isolator 1C in that the first optical fiber collimator 10a and the second optical fiber collimator 10b are not provided. Except for the above aspects, the optical isolator 1D of this modified example has the same structure as the optical isolator 1C. The optical isolator 1D can be used as a free-space optical isolator. In the optical isolator 1D of this modified example, part of the light incident on the second polarizer 3 is reflected by the second polarizer 3 and taken out as reflected light I2, and the intensity of the taken out reflected light I2 is measured, thereby enabling the intensity of the transmitted light of the optical isolator 1D to be monitored.

[0107] [Optical monitoring method]

[0108] The optical monitoring method of the present invention is a method for monitoring the intensity of light transmitted through an optical isolator. More specifically, in an optical isolator 1 including a first polarizer 2, a second polarizer 3, and a Faraday rotator 4 as in the above-mentioned embodiment, a part of light incident on the second polarizer 3 is reflected by the second polarizer 3 to extract a part of the light, and the intensity of the extracted light is measured, thereby monitoring the intensity of light transmitted through the optical isolator 1.

[0109] Since the light monitoring method can always monitor the intensity of light transmitted through the optical isolator 1, when the element of the optical isolator 1 is damaged and the intensity of light transmitted is reduced, the damage of the element can be easily detected. In addition, since the intensity of light transmitted through the optical isolator 1 can be monitored without using an optical fiber coupler with low laser resistance, the output of the laser can be increased.

[0110] The intensity of the laser light transmitted through the optical isolator 1 is preferably 300 mW or more, more preferably 500 mW or more, more preferably 1 W or more, more preferably 5 W or more, and particularly preferably 10 W or more. The optical monitoring method of the present invention can cope with the high output of the laser light because the optical isolator 1 is not easily damaged even when the intensity of the laser light is increased. In addition, the upper limit of the intensity of the laser light is, for example, 150 W or less, preferably 50 W or less.

[0111] However, the intensity of the laser light transmitted through the optical isolator 1 is not limited to the above-mentioned form. For example, a high-power laser light of 1 kW or more, particularly 10 kW or more, may be used for the purpose of laser processing, laser analysis, laser nuclear fusion, etc.

[0112] In addition, the ratio of the light reflected and taken out by the second polarizer 3 is preferably 0.1% or more, more preferably 0.3% or more, preferably 10% or less, and more preferably 4% or less, relative to the entire light incident on the second polarizer 3. When the ratio of the light reflected and taken out by the second polarizer 3 is greater than the above lower limit, the intensity of the light transmitted through the optical isolator 1 can be more reliably monitored. In addition, when the ratio of the light reflected and taken out by the second polarizer 3 is less than the above upper limit, the amount of light transmitted through the second polarizer 3 can be increased. In addition, the ratio of the light reflected and taken out by the second polarizer 3 can be adjusted by the rotation angle of the Faraday rotator 4 and the setting angle of the second polarizer 3.

[0113] (Example)

[0114] Hereinafter, the present invention will be described in more detail based on specific examples. The present invention is not limited to the following examples at all, and can be implemented with appropriate changes within the scope of the gist thereof.

[0115] (Example 1)

[0116] In Example 1, so that Figure 1 and Figure 2 The optical isolator was manufactured in the manner of the optical design shown. A cylindrical Faraday element with a diameter of 3 mm and a length of 10 mm was used in the Faraday rotator. In addition, the outer diameter of the magnet was 20 mm, the length of the magnet in the optical axis direction was 30 mm, and the diameter of the through hole was 3.2 mm.

[0117] As the first polarizer 2, a polarization beam splitter (PBS) was used, and it was set in a way that the amount of transmitted light was the largest when the polarization angle was 0°. The Faraday rotator 4 was set in the magnetic circuit, and the length was adjusted so that the rotation angle of the Faraday rotator 4 was 43°. As the second polarizer 3, a polarization beam splitter (PBS) was used, and it was set in a way that the setting angle of the second polarizer 3 was 47°. The optical isolator 1 manufactured in this way was irradiated with a laser with a wavelength of 1030nm, and a part of the light was reflected by the second polarizer 3, and it was taken out as monitoring light, and the light intensity was measured. Among them, in Example 1, the proportion of light emitted through the second polarizer 3 (the transmittance of the emitted light) was 99%. In addition, the proportion of light reflected and taken out by the second polarizer 3 (the monitoring light extraction rate) was 1%.

[0118] (Examples 2 to 5)

[0119] The optical isolator was manufactured in the same manner as in Example 1, and the intensity of transmitted light of the optical isolator was monitored, except that the installation angle of the first polarizer 2, the installation angle of the second polarizer 3, and the rotation angle of the Faraday rotator 4 were changed as shown in the following Table 1. The output light transmittance and the monitored light extraction rate of the optical isolator manufactured in Examples 2 to 5 are shown in the following Table 1.

[0120] [Table 1]

[0121]

[0122]

[0123] As shown in Table 1, it can be confirmed that the monitoring light extraction rate of the optical isolators manufactured in Examples 1 to 5 is 1% to 10%, and sufficient transmitted light intensity can be monitored within this range. In addition, it was confirmed that in the optical isolators manufactured in Examples 1 to 5, the reflected return light cannot pass through the first polarizer and is cut off, and functions as an optical isolator.

[0124] Description of Reference Numerals

[0125] 1, 1A, 1B, 1C, 1D...Optical isolator

[0126] 2…1st polarizer

[0127] 3…Second polarizer

[0128] 4…Faraday rotator

[0129] 5. 31…Light exit part

[0130] 6, 30… Shell

[0131] 7…Magnet

[0132] 7a, 9a, 12...through holes

[0133] 7b…1st end face

[0134] 7c…2nd end face

[0135] 7d…side

[0136] 8, 24…Faraday element

[0137] 9…Tube parts

[0138] 10a…1st fiber collimator

[0139] 10b…Second fiber collimator

[0140] 11…Magnetic circuit

[0141] 21…1st magnet

[0142] 22…Second magnet

[0143] 23…The third magnet

[0144] 30a, 30b…end

[0145] 32…Fiber Optic

[0146] 33…Photodiode.

Claims

1. An optical isolator, characterized in that: include: A first polarizer disposed on the light incident side; A second polarizer disposed on the light exit side; and a Faraday rotator disposed between the first polarizer and the second polarizer, When the angle at which the light transmission axis of the second polarizer is inclined with respect to the light transmission axis of the first polarizer is defined as the installation angle of the second polarizer, the installation angle of the second polarizer is different from the rotation angle of the Faraday rotator.

2. The optical isolator according to claim 1, wherein: The sum of the setting angle of the second polarizer and the rotation angle of the Faraday rotator is within the range of 90°±2°.

3. The optical isolator according to claim 1, wherein: When the installation angle of the second polarizer is 45°+A° and the rotation angle of the Faraday rotator is 45°-A°, A is greater than or equal to 0.5 and less than or equal to 10.

4. The optical isolator according to any one of claims 1 to 3, characterized in that: The device further includes a light emitting portion capable of extracting a portion of the light incident on the second polarizer.

5. The optical isolator according to claim 4, characterized in that: The light emitting portion is directly or indirectly connected to a tap port or a photodiode.

6. The optical isolator according to any one of claims 1 to 3, characterized in that: The Faraday rotator includes a Faraday element disposed in a cylindrical magnet, and the Faraday element is formed of a paramagnetic material through which light can pass.

7. The optical isolator according to claim 6, characterized in that: The Faraday element formed of the paramagnetic material is a glass material.

8. The optical isolator according to claim 7, characterized in that: The glass material contains, by mole percent, 20% to 80% of TB2O3, 20% to 70% of B2O3+P2O5, and 0% to 45% of SiO2.

9. A light monitoring method for monitoring the intensity of light transmitted through an optical isolator, the optical isolator comprising: A first polarizer is arranged on the light incident side, a second polarizer is arranged on the light exit side, and a Faraday rotator is arranged between the first polarizer and the second polarizer, and the light monitoring method is characterized by comprising: a step of taking out a part of the light by reflecting a part of the light incident on the second polarizer by the second polarizer; and The step of monitoring the intensity of light transmitted through the optical isolator by measuring the intensity of a portion of the extracted light.

10. The optical monitoring method according to claim 9, characterized in that: The intensity of the laser light transmitted through the optical isolator is 300 mW or more and 150 W or less.

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