Terbium-containing ferromagnetic garnet-type transparent ceramic and magneto-optical device using the same

Abstract

To provide a terbium-containing ferromagnetic garnet-type transparent ceramic capable of being used for each output grade and to provide a magneto-optical device using the same.SOLUTION: A transparent ceramic of the present invention comprises: a sintered compact containing a composite oxide represented by formula (1) (Tb1-x-yYxScy)3(Al1-zScz)5O12, wherein (0.05≤x≤0.45, 0<y<0.1, 0.5<1-x-y<0.95, 0.001<z<0.15, 0<y+z<0.2); and 0.1% or less of SiO2. The transparent ceramics is in a rod shape having an outer diameter R mm of 3.5 mm or more and a length of 14 mm or more, wherein: both end faces are precision-ground and AR-coated for a wavelength N nm; an optical effective diameter r mm is 0.9×R; when a laser beam having an incident beam diameter D and a wavelength N is incident into the optical effective diameter, an average insertion loss is 0.043 dB or less; there are no foreign particles larger than 30 μm within the optical effective diameter; and the total number of foreign particles 10 μm or larger is no more than 4.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a terbium-containing paramagnetic garnet-type transparent ceramic and a magneto-optical device using the same, and more particularly to a terbium-containing paramagnetic garnet-type transparent ceramic suitable for constituting a magneto-optical device such as an optical isolator, and a magneto-optical device using the same. [Background technology]

[0002] In recent years, as it has become possible to achieve higher output, the use of laser processing machines using fiber lasers has become increasingly widespread. However, when external light enters the laser light source built into the laser processing machine, the resonance state becomes unstable, causing the oscillation state to become disturbed. In particular, when the oscillated light is reflected by the optical system along the way and returns to the light source, the oscillation state is greatly disturbed. To prevent this, an optical isolator is usually installed in front of the light source.

[0003] An optical isolator consists of a Faraday rotator, a polarizer arranged on the light input side of the Faraday rotator, and an analyzer arranged on the light output side of the Faraday rotator. The Faraday rotator is used by applying a magnetic field parallel to the light's direction of travel. In this case, the polarization line of the light only rotates in a fixed direction whether it moves forward or backward through the Faraday rotator. Furthermore, the Faraday rotator is adjusted to a length that rotates the polarization line of the light exactly 45 degrees. Here, if the polarization planes of the polarizer and analyzer are shifted 45 degrees from the direction of rotation of the forward light, the polarization of the forward light will be transmitted because it coincides with the polarizer position and the analyzer position. On the other hand, the polarization of the backward light will rotate 45 degrees in the opposite direction to the deviation angle of the polarization plane of the polarizer, which is shifted 45 degrees from the analyzer position. As a result, the polarization plane of the returning light at the polarizer position is shifted by 45 degrees - (-45 degrees) = 90 degrees relative to the polarization plane of the polarizer, and it cannot pass through the polarizer. In this way, it functions as an optical isolator, allowing forward light to pass and exit while blocking backward returning light.

[0004] In recent years, the material used for the Faraday rotator that constitutes the optical isolator has been (Tb 1-x-y Y x Sc y ) 3 (Al 1-z Sc z ) 5 O 12 Terbium-containing paramagnetic garnet-type transparent ceramics having the following composition are becoming more and more popular. For example, the composition and transparency of these ceramics are described in detail in JP 2019-199386 A (Patent Document 1) and WO 2022 / 054596 A (Patent Document 2).

[0005] The manufacturing method is described in detail in JP 2019-104674 A (Patent Document 3), JP 2019-207340 A (Patent Document 4), JP 2019-199078 A (Patent Document 5), JP 2019-199079 A (Patent Document 6), WO 2022 / 054593 A (Patent Document 7), WO 2022 / 054515 A (Patent Document 8), JP 2023-064774 A (Patent Document 9), JP 2023-082887 A (Patent Document 10), JP 2023-128125 A (Patent Document 11), etc.

[0006] Further details regarding quality etc. are provided in Patent Document 7, International Publication No. 2022 / 054595 (Patent Document 12), International Publication No. 2022 / 085107 (Patent Document 13), International Publication No. 2022 / 054592 (Patent Document 14), International Publication No. 2022 / 054594 (Patent Document 15), and JP 2023-128117 A (Patent Document 16). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2019-199386 A [Patent Document 2] International Publication No. 2022 / 054596 [Patent Document 3] JP 2019-104674 A [Patent Document 4] JP 2019-207340 A [Patent Document 5] JP 2019-199078 A [Patent Document 6] JP 2019-199079 A [Patent Document 7] International Publication No. 2022 / 054593 [Patent Document 8] International Publication No. 2022 / 054515 [Patent Document 9] JP 2023-064774 A [Patent Document 10] JP 2023-082887 A [Patent Document 11] JP 2023-128125 A [Patent Document 12] International Publication No. 2022 / 054595 [Patent Document 13] International Publication No. 2022 / 085107 [Patent Document 14] International Publication No. 2022 / 054592 [Patent Document 15] International Publication No. 2022 / 054594 [Patent Document 16] JP 2023-128117 A Summary of the Invention [Problem to be solved by the invention]

[0008] In actual industrial applications of the above-mentioned terbium-containing paramagnetic garnet-type transparent ceramics, the optical quality standards of the Faraday rotators used vary depending on, for example, the output power grade of the laser processing machine. In low-output applications, some contrast source within the optical effective diameter is acceptable, while in high-output applications, the size of the contrast source is naturally subject to strict control. However, there have been no documents that have mentioned the optical quality of Faraday rotators that correspond to such output power grades.

[0009] Incidentally, Patent Document 7 merely illustrates the effect of enabling application to a high-power laser of more than 100 W by specifying the size and number of contrast sources present within the optical effective diameter, but does not suggest at all that the size and number of contrast sources can be varied depending on the output power grade of the laser processing machine.

[0010] The present invention has been made in view of the above circumstances, and has an object to provide terbium-containing paramagnetic garnet-type transparent ceramics that can be used for each output grade, and magneto-optical devices using the same, by processing terbium-containing paramagnetic garnet-type transparent ceramics into a rod shape and subjecting them to AR coating, and then specifying the size and number of contrast sources and the beam insertion loss in a stepwise manner. [Means for solving the problem]

[0011] In order to achieve the above object, in one aspect, the present invention provides a composite oxide represented by the following formula (1) and SiO 2 A terbium-containing paramagnetic garnet-type transparent ceramic comprising a sintered body containing more than 0 mass % and 0.1 mass % or less of (T 1-x-y Y x Sc y ) 3 (Al 1-z Sc z ) 5 O 12 (1) (In the formula, 0.05≦x≦0.45, 0 <y<0.1、0.5<1-x-y<0.95、0.001<z<0.15、0<y+z<0.2である。) The terbium-containing paramagnetic garnet-type transparent ceramics are When the incident beam diameter Dmm is 1.6mm or less, the outer diameter Rmm is 2.2×Dmm or more and 3.5mm or more, It is processed into a rod shape with a length of 14 mm or more, and both end faces are precision polished. Both end faces are treated with AR coating with a wavelength of N nm. When the optical effective diameter rmm used optically is defined by the following formula (2), the average insertion loss when a laser beam having an incident beam diameter Dmm and a wavelength Nnm is incident on this optical effective diameter rmm is 0.043 dB or less, r = 0.9 × R (2) There are no foreign matter, heterogeneous phases, or voids exceeding 30 μm within the optical effective diameter rmm, and the total number of foreign matter, heterogeneous phases, and voids of 10 μm to 30 μm in size within the optical effective diameter rmm is a maximum of 4.

[0012] It is preferable that the average insertion loss is 0.035 dB or less, and the total number of foreign objects, foreign phases, and voids having a size of 10 μm to 30 μm within a circular region having a radius of the incident beam diameter D mm from the center of the optical surface is a maximum of 1.

[0013] It is more preferable that the average insertion loss is 0.030 dB or less, the total number of foreign bodies, foreign phases, and voids having a size of 10 μm to 30 μm within the optical effective diameter rmm is a maximum of 3, and that there are no foreign bodies, foreign phases, or voids having a size exceeding 10 μm within a circular region having a radius of the incident beam diameter Dmm from the center of the optical surface.

[0014] The terbium-containing paramagnetic garnet-type transparent ceramics are The diameter of the incident beam is doubled by the expander, D 2倍 The laser beam is expanded to 1 mm, and the incident beam diameter D 2倍 If mm is 1.6 mm or more, the outer diameter R'mm is 2.2 x D 2倍 mm or more and 5 mm or more, It is processed into a rod shape with a length of 14 mm or more, and both end faces are precision polished. Both end faces are treated with AR coating with a wavelength of N nm. When the optical effective diameter r'mm used optically is defined by the following formula (3), the beam diameter D 2倍 The average insertion loss when a laser beam with a wavelength of N nm is incident on the r'=0.9×R' (3) The total number of foreign objects, heterogeneous phases, and voids of 10 μm to 30 μm in size within the optical effective diameter r mm is a maximum of 2, and the number is within 2 × D from the center of the optical surface. 2倍 Within a circular area with a radius of 1 mm, there is no foreign matter or foreign phase larger than 10 μm, and the number of voids of 10 μm to 30 μm is a maximum of two, and the area is D 2倍 It is preferable that there are no foreign objects, foreign phases, or voids larger than 10 μm within a circular area with a radius of mm.

[0015] Another aspect of the present invention is a magneto-optical device that is constructed using the above-mentioned terbium-containing paramagnetic garnet-type transparent ceramics.

[0016] The magneto-optical device of the present invention may be an optical isolator that includes the above-mentioned terbium-containing paramagnetic garnet-type transparent ceramic as a Faraday rotator and has polarizing materials in front of and behind the optical axis of the Faraday rotator and can be used in the wavelength range of 0.9 μm or more and 1.1 μm or less. Effect of the Invention

[0017] In this way, the average insertion loss is specified, and the effective diameter r mm or the center of the optical surface is D mm, D 2倍 mm or 2×D 2倍 By specifying that no foreign matter, foreign phase, or void of a specified size is present within a circular area with a radius of mm, it is possible to accurately provide terbium-containing paramagnetic garnet-type transparent ceramics that can be used for each output grade and magneto-optical devices using the same, and it is also possible to provide magneto-optical devices such as optical isolators that are suitable for application to laser devices of various output grades. [Brief description of the drawings]

[0018] [Figure 1] 1 is a schematic cross-sectional view showing an example of the configuration of an optical isolator using the terbium-containing paramagnetic garnet-type transparent ceramic according to the present invention as a Faraday rotator. [Diagram 2]1 is a metallurgical microscope image showing an example of a foreign substance in an embodiment, and showing an example of contrast of class E. [Diagram 3] 1 is a metallurgical microscope image showing an example of a contrast example of class E, which is an example of a heterogeneous phase in an embodiment. [Figure 4] 1 is a metallurgical microscope image showing another example of a heterogeneous phase in an embodiment, which is an example of contrast of class E. [Diagram 5] 1 is a metallurgical microscope image showing an example of a void in an embodiment, and a contrast example of class E. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] [1. Terbium-containing paramagnetic garnet-type transparent ceramics] First, an embodiment of the terbium-containing paramagnetic garnet-type transparent ceramic according to the present invention will be described. The terbium-containing paramagnetic garnet-type transparent ceramic according to the present embodiment includes a sintered body of a composite oxide containing terbium, yttrium, scandium, and aluminum and represented by the following formula (1). (T 1-x-y Y x Sc y ) 3 (Al 1-z Sc z ) 5 O 12 (1) (In the formula, 0.05≦x≦0.45, 0 <y<0.1、0.5<1-x-y<0.95、0.001<z<0.15、0<y+z<0.2である。)

[0020] Terbium-containing paramagnetic garnet-type transparent ceramics further contain SiO as a sintering aid. 2 It is preferable that the content of SiO is more than 0 mass% and 0.1 mass% or less. 2 When the content is within this range, the transparency of the resulting paramagnetic garnet-type ceramic sintered body is improved to a practical level and is stable, which is preferable.

[0021] In this embodiment, it is essential that the main components of the six-coordinate sites and the four-coordinate sites in the garnet structure are aluminum (Al). If the main components of these sites can be composed of aluminum, the bondability of the crystal is improved, and as a result, the average value of dn / dt at 30 °C ± 10 °C at a wavelength of 1064 nm can be reduced. The ratio of the six-coordinate sites and the four-coordinate sites occupied by this aluminum is 1 - z (0.001 < z < 0.15).

[0022] In this embodiment, terbium (Tb) and yttrium (Y) are selected as the main components of the eight-coordinate sites, and the concentration of terbium is in the range of 1 - x - y (0.5 < 1 - x - y < 0.95), and the concentration of yttrium is in the range of x (0.05 ≤ x ≤ 0.45).

[0023] In this embodiment, the concentration of scandium (Sc) is added in the range of 0.001 < z < 0.15. In the above formula (1), the range of y is 0 < y < 0.1, and 0.001 < y < 0.03 is preferable. By adding scandium in this way, it becomes possible to stably manufacture a highly transparent sintered body.

[0024] The terbium-containing paramagnetic garnet-type transparent ceramics of this embodiment contain, as the main components, the components of the composition represented by the above formula (1). Here, "containing as the main components" means containing 90% by mass or more of the complex oxide represented by the above formula (1). The content of the complex oxide represented by the above formula (1) is preferably 99% by mass or more, more preferably 99.9% by mass or more, and still more preferably 99.99% by mass or more.

[0025] The terbium-containing paramagnetic garnet-type transparent ceramics of this embodiment are processed so as to have a length of 14 mm or more and are used as a target magneto-optical material. By setting the length to 14 mm or more, although it depends on the configuration and size of the magnet to be externally mounted, it is preferable because it is possible to rotate the incident light in the wavelength band of 0.9 μm or more and 1.1 μm or less by 45 degrees with a correct magnetic circuit design.

[0026] The outer diameter R mm of the terbium-containing paramagnetic garnet-type transparent ceramic of this embodiment is set to 2.2×D mm or more and 3.5 mm or more when the incident beam diameter D mm is 1.6 mm or less.

[0027] The terbium-containing paramagnetic garnet-type transparent ceramic of this embodiment is processed into a rod shape having a length of 14 mm or more, and is used as the target magneto-optical material. By making the length 14 mm or more, it is possible to rotate incident light in the wavelength band of 0.9 μm to 1.1 μm by 45 degrees by a correct magnetic circuit design, although this depends on the configuration and size of the external magnet, which is preferable. In addition, both end faces of the terbium-containing paramagnetic garnet-type transparent ceramic of this embodiment are precision-polished as optical surfaces.

[0028] In the terbium-containing paramagnetic garnet-type transparent ceramic of this embodiment, when the optically utilized effective optical diameter rmm is defined by the following formula (2), the average insertion loss when a laser beam having an incident beam diameter Dmm and a wavelength Nnm is incident within this optically effective diameter rmm is 0.043dB or less. r = 0.9 × R (2)

[0029] The terbium-containing paramagnetic garnet-type transparent ceramic of this embodiment has no foreign matter, heterogeneous phase, or void exceeding 30 μm within the optical effective diameter rmm, and the total number of foreign matter, heterogeneous phase, and voids of 10 μm to 30 μm size within the optical effective diameter rmm is a maximum of 4. By specifying the average insertion loss and the foreign matter, heterogeneous phase, and voids in this manner, it is possible to provide a terbium-containing paramagnetic garnet-type transparent ceramic for a grade with an output of up to 40 W (up to a practical output of 30 W considering a safety factor).

[0030] Also, the average insertion loss is preferably 0.035 dB or less, and the total number of foreign bodies, heterogeneous phases, and voids of 10 μm to 30 μm in size within a circular region having a radius of the incident beam diameter D mm from the center of the optical surface is preferably a maximum of 1. This makes it possible to provide a terbium-containing paramagnetic garnet-type transparent ceramic for a grade with an output of up to 80 W (up to a practical output of 65 W considering a safety factor).

[0031] Furthermore, it is more preferable that the average insertion loss is 0.030 dB or less, the total number of foreign bodies, heterogeneous phases, and voids of 10 μm to 30 μm in size within the optical effective diameter rmm is a maximum of 3, and it is more preferable that there are no foreign bodies, heterogeneous phases, or voids exceeding 10 μm in size within a circular region having a radius of the incident beam diameter Dmm from the center of the optical surface. This makes it possible to provide terbium-containing paramagnetic garnet-type transparent ceramics for grades with laser output up to 120 W (up to 100 W for practical use considering a safety factor).

[0032] Furthermore, the total number of foreign objects, heterogeneous phases, and voids of 10 μm to 30 μm size within the optical effective diameter r mm is a maximum of 2, and the maximum number of foreign objects, heterogeneous phases, and voids of 2 × D from the center of the optical surface is a maximum of 2. 2倍 Within a circular area with a radius of 1 mm, there is no foreign matter or foreign phase larger than 10 μm, and the number of voids with a size of 10 μm to 30 μm is a maximum of two, and the area is D 2倍 It is even more preferable that there is no foreign matter, heterogeneous phase, or void larger than 10 μm within a circular region having a radius of 1 mm. This makes it possible to provide a terbium-containing paramagnetic garnet-type transparent ceramic for a grade with a laser output of up to 240 W (up to a practical output of 200 W considering a safety factor).

[0033] [2. Manufacturing method of terbium-containing paramagnetic garnet-type transparent ceramics] Next, an embodiment of a method for producing a terbium-containing paramagnetic garnet-type transparent ceramic according to the present invention will be described. The production method of this embodiment includes the steps of mixing oxides of terbium, yttrium, aluminum, and scandium to prepare a mixed raw material, forming the mixed raw material to obtain a molded body, degreasing the molded body to obtain a degreased body, sintering the degreased body to obtain a sintered body, densifying the sintered body by hot isostatic pressing (HIP), annealing the densified sintered body, and precision polishing the annealed sintered body. If the HIP treatment is performed as is, the paramagnetic garnet-type transparent ceramic is reduced and some oxygen deficiency occurs. Therefore, it is preferable to recover the oxygen deficiency by performing a slight oxidation HIP treatment or an annealing treatment in an oxidizing atmosphere after the HIP treatment. This makes it possible to obtain a transparent garnet-type oxide ceramic without oxygen defect absorption. Each step will be described below.

[0034] [2-1. Preparation process of mixed raw materials] The raw materials used in the present invention are oxide powders of terbium, yttrium, scandium, and aluminum, and the purity of the raw materials is preferably 99.9% by mass or more, and more preferably 99.99% by mass or more.

[0035] These elements are weighed in predetermined amounts and then silicon oxide (SiO 2 ) in an amount of more than 0 mass % and not more than 0.1 mass %, and is appropriately treated using a wet ball mill, a bead mill, or a jet mill.

[0036] In the garnet-type oxide powder raw material used in the present invention, various organic additives may be added for the purpose of improving the quality stability and yield in the subsequent ceramic manufacturing process. In the present invention, these are not particularly limited. That is, various dispersants, binders, lubricants, plasticizers, etc. can be suitably used. However, it is preferable to select high-purity types of these organic additives that do not contain unnecessary metal ions. In addition, the order of addition of each organic additive must be appropriately designed so as not to hinder the management of the properties (particle size distribution, etc.) of the raw material to be manufactured.

[0037] [2-2. Molding process] In the manufacturing method of the present embodiment, a normal press molding process can be suitably used. That is, a very common uniaxial pressing process in which a mold is filled and pressurized from a certain direction, a cold isostatic pressing (CIP) process in which a mold is sealed and stored in a deformable waterproof container and pressurized with hydrostatic pressure, and a warm isostatic pressing (WIP) process can be suitably used. The applied pressure can be appropriately adjusted while checking the relative density of the resulting molded body, and is not particularly limited. For example, the manufacturing cost can be reduced by controlling the pressure within a pressure range of about 300 MPa or less that can be handled by a commercially available CIP device or WIP device. Alternatively, a hot press process, a discharge plasma sintering process, a microwave heating process, and the like in which not only the molding process but also sintering is performed at once during molding can be suitably used. Furthermore, a molded body can be produced by a casting molding method instead of a press molding method. A molding method such as pressurized casting molding, centrifugal casting molding, and extrusion molding can also be adopted by optimizing the combination of the shape and size of the oxide powder as the starting material and various organic additives.

[0038] In order to produce the 4 mm diameter garnet-type transparent oxide ceramic material of the present invention near-net, it is possible to use, for example, a uniaxial press molding tool with an inner diameter of 7 mm. Note that, since the length direction varies depending on the material and size of the magnet surrounding the material, it is advisable to prepare a molding tool that is somewhat longer.

[0039] [2-3. Degreasing process] In the manufacturing method of this embodiment, a normal degreasing process can be suitably used. That is, a temperature-raising degreasing process using a heating furnace can be performed. In addition, the type of atmospheric gas used at this time is not particularly limited, and air, oxygen, hydrogen, etc. can be suitably used. The degreasing temperature is preferably in a range not higher than a temperature at which the organic components of the organic additives added can be sufficiently decomposed and removed, and not higher than 1000°C.

[0040] [2-4. Sintering process] In the manufacturing method of this embodiment, a general sintering process can be suitably used. That is, a heat sintering process such as a resistance heating method or an induction heating method can be suitably used. In addition, the atmosphere at this time is preferably a reduced pressure environment (vacuum). Furthermore, the degree of vacuum is preferably 1×10 -3 If the degree of vacuum is controlled within this range, even in the case of a large sintered body having a diameter of 8 mm or more, it is preferable because the oxygen gas desorbed from the degreased body can be sufficiently discharged to the center of the body.

[0041] The sintering temperature in the sintering step is preferably 1400 to 1780° C., particularly preferably 1500 to 1750° C. If the sintering temperature is in this range, densification is promoted while suppressing heterogeneous phase precipitation, which is preferable.

[0042] A sintering holding time of several hours in the sintering process is sufficient, but it is preferable to control the relative density of the sintered body within the range of 93.8% to 97.2%. Control of the sintered density can be performed by conducting several preliminary experiments.

[0043] [2-5. Hot isostatic pressing (HIP) processing process] In the manufacturing method of this embodiment, after the sintering process, a hot isostatic pressing (HIP) process is performed to densify the sintered body until the relative sintered density is 99.9% or more. If the relative sintered density in the sintering process is properly managed, that is, if the HIP process can be performed in a state where the sintered grain size is not excessively large, the HIP stress is transmitted widely and uniformly from the outer periphery to the center of the sintered body, the closed pores are crushed, and the sintered body is firmly densified. In other words, a substantially ideal sintered body is obtained that has no stress unevenness, no unintended void unevenness, and few remaining small bubbles.

[0044] The type of pressurized gas medium used here is an inert gas such as argon or nitrogen, or Ar-O 2 can be suitably used. The pressure applied by the pressurized gas medium is preferably 50 to 300 MPa, more preferably 100 to 300 MPa. If the pressure is less than 50 MPa, the transparency improvement effect may not be obtained, and if the pressure exceeds 300 MPa, further improvement in transparency cannot be obtained even if the pressure is increased, and the load on the device becomes too heavy, which may damage the device. The applied pressure is preferably 196 MPa or less, which is easy to handle with a commercially available HIP device.

[0045] The treatment temperature (predetermined holding temperature) is set in the range of 1100 to 1780°C, preferably 1200 to 1730°C. If the heat treatment temperature exceeds 1780°C, the risk of oxygen vacancies increases, which is not preferable. If the heat treatment temperature is less than 1100°C, the effect of improving the transparency of the sintered body is hardly obtained. There is no particular restriction on the holding time of the heat treatment temperature, but holding for too long a period of time is not preferable because the risk of oxygen vacancies increases. Typically, it is preferably set in the range of 1 to 3 hours.

[0046] The heater material, heat insulating material, and treatment vessel for the HIP treatment are not particularly limited, but graphite, molybdenum (Mo), tungsten (W), and platinum (Pt) are preferably used, and yttrium oxide and gadolinium oxide are also preferably used for the treatment vessel. In particular, when the treatment temperature is 1500°C or less, platinum (Pt) can be used for the heater material, heat insulating material, and treatment vessel, and Ar-O can be used as the pressurized gas medium. 2 This is preferable because it can prevent the occurrence of oxygen vacancies during HIP treatment. When the treatment temperature exceeds 1500°C, graphite is preferable as the heater material and heat insulating material, but in this case, it is preferable to select graphite, molybdenum (Mo), or tungsten (W) as the treatment container, and further select either yttrium oxide or gadolinium oxide as a double container inside, and fill the container with an oxygen release material, because this can minimize the amount of oxygen vacancies during HIP treatment.

[0047] [2-6. Re-sintering process] In the manufacturing method of this embodiment, after the HIP treatment, re-sintering may be performed for 8 hours or more at a temperature higher than the HIP treatment temperature. However, it is not preferable to set the upper limit temperature to 1780°C or higher because it increases the risk of oxygen deficiency. The re-sintering time should be longer for a sintered body with a higher laser output grade.

[0048] [2-7. Annealing process] In the manufacturing method of the present embodiment, after the resintering process is completed, it is preferable to perform an oxidation annealing process (oxygen deficiency recovery process) in an oxygen atmosphere or in the air at a temperature equal to or lower than the HIP processing temperature, typically 1000 to 1500°C, in order to recover oxygen deficiencies in the obtained transparent ceramic sintered body. The retention time at this time is preferably longer as the laser output grade used becomes higher. For example, it is preferable that the retention time is 5 hours or more for grades with a laser output of up to 40 W (up to 30 W for practical use with a safety factor), 20 hours or more for grades with a laser output of up to 80 W (up to 65 W for practical use with a safety factor), and 40 hours or more for grades with a laser output of up to 120 W (up to 100 W for practical use with a safety factor).

[0049] [2-8. Precision polishing process] In the manufacturing method of this embodiment, it is preferable to precisely polish or optically polish both end faces on the optically utilized axis of the paramagnetic garnet-type transparent ceramics that has undergone the above-mentioned series of manufacturing steps. In this case, the optical surface precision is preferably λ / 2 or less for grades with laser output up to 40 W (up to 30 W for practical use with a safety factor) when the measurement wavelength is λ=633 nm, and is particularly preferably λ / 8 or less for grades with laser output up to 80 W (up to 65 W for practical use with a safety factor) and up to 120 W (up to 100 W for practical use with a safety factor).

[0050] Furthermore, with regard to the optical surface roughness at this time, it is preferable that the average roughness of the precision-polished surface be arithmetic mean height Sa≦0.70 nm and root mean square height Sq≦0.89 nm, since this is compatible with all laser output grades.

[0051] Then, by applying an AR coating (anti-reflective film) that matches the laser wavelength of the laser processing machine, it is possible to provide terbium-containing paramagnetic garnet-type transparent ceramics that are compatible with all laser output grades.

[0052] [3. Magneto-optical devices] Further, an embodiment of the magneto-optical device according to the present invention will be described. The magneto-optical device of this embodiment is constructed using the above-mentioned terbium-containing paramagnetic garnet-type transparent ceramic. Specifically, it is preferable to apply a magnetic field parallel to the optical axis of the above-mentioned terbium-containing paramagnetic garnet-type transparent ceramic, and then set a polarizer and an analyzer so that their optical axes are shifted by 45 degrees from each other to construct and use the magneto-optical device. In particular, the above-mentioned terbium-containing paramagnetic garnet-type transparent ceramic is suitably used as a magneto-optical device, particularly as a Faraday rotator of an optical isolator with a wavelength of 0.9 to 1.1 μm.

[0053] FIG. 1 is a cross-sectional view showing an example of an optical isolator, which is a magneto-optical device including a Faraday rotator made of the paramagnetic garnet-type transparent ceramics according to the present embodiment as an optical element. As shown in FIG. 1, the optical isolator 100 includes a Faraday rotator 110 made of the above-mentioned paramagnetic garnet-type transparent ceramics, a polarizer 120 made of a polarizing material, and an analyzer 130 inside the housing 150. These are arranged in the order of the polarizer 120, the Faraday rotator 110, and the analyzer 130 along the optical axis 112 of the Faraday rotator. The polarized light vibration plane of the polarizer 120 and the polarized light vibration plane of the analyzer 130 are arranged so that the relative angle is 45°. In addition, the optical isolator 100 includes a magnet 140 for applying a magnetic field to the Faraday rotator 110 on at least one of the side surfaces of the Faraday rotator 110 inside the housing 150.

[0054] Such an optical isolator 100 can be suitably used in an industrial fiber laser device (not shown). The optical isolator can prevent the reflected light of the laser light emitted from the laser light source from returning to the light source, causing the oscillation to become unstable. EXAMPLES

[0055] EXAMPLES The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0056] [Examples 1 to 17, Comparative Examples 1 to 15] Terbium oxide powder, yttrium oxide powder, and scandium oxide powder manufactured by Shin-Etsu Chemical Co., Ltd., and aluminum oxide powder manufactured by Taimei Chemical Co., Ltd. were obtained. In addition, liquid tetraethyl orthosilicate (TEOS) manufactured by Kishida Chemical Co., Ltd. was obtained. The purity of the powder raw materials was 99.95% by mass or more, and the purity of the liquid raw materials was 99.999% by mass or more. Using the above raw materials, the mixing ratio was adjusted to produce composite oxide raw materials with the two types of final compositions shown in Table 1.

[0057] The mixing ratio was adjusted by weighing and mixing the powders of each oxide such that the mole numbers of terbium, yttrium, aluminum, and scandium were in the mole ratios of each composition in Table 1. Next, TEOS was added, and the amount of SiO 2 The ingredients were weighed out so as to obtain the mass percentages shown in Table 1 and added to each ingredient.

[0058] [Table 1]

[0059] Then, while taking care to prevent each material from being mixed with the other, they were dispersed and mixed in ethanol using an alumina ball mill. The processing time was 20 hours. After that, a spray drying process was performed to produce granular raw materials with an average particle size of 20 μm. For each of the two types of oxide raw materials obtained, 100 pieces of each were produced using a uniaxial press molding tool with an inner diameter of 7 mm. The amount of raw material filled was adjusted so that the length of each of the green bodies was 30 mm. Then, all of the green bodies were subjected to isostatic pressing at a pressure of 198 MPa to obtain CIP green bodies. All of the obtained green bodies were degreased in a muffle furnace at 800 °C for 3 hours to obtain degreased green bodies.

[0060] All of the degreased green bodies were then sintered in a vacuum sintering furnace at a sintering temperature of 1500 to 1570° C. for 3 hours to obtain sintered bodies with a sintered density of 93.8% to 97.2%.

[0061] The obtained sintered bodies were placed in a carbon heater HIP furnace and HIP-treated in Ar at 200 MPa, 1600°C, and 3 hours. The relative density of each of the obtained sintered bodies was 99.9% or more. In addition, their appearance was bluish gray (oxygen deficiency absorption).

[0062] Thereafter, all of the HIP-treated sintered bodies were heat-treated in a vacuum sintering furnace at a sintering temperature of 1730°C for 15 hours in an attempt to eliminate residual bubbles throughout the entire area, including the center of the sintered body.

[0063] Next, each of the obtained ceramic sintered bodies was annealed in an atmospheric heating furnace at 1450° C. for 30 hours to sufficiently recover the oxygen vacancies.

[0064] After that, each of the obtained ceramic sintered bodies was subjected to centerless peripheral grinding to adjust the outer diameter to 4 mm. It is generally known that the outer diameter of a sintered body varies in finished size due to variations in the degree of shrinkage. Therefore, in order to mount it in optical equipment such as a fiber laser processing machine, it is preferable that the outer diameter is machined to a uniform value with high precision.

[0065] After that, they were cut and precision-polished to a length of 17 mm each. The optical end faces of the samples were finished to have an optical surface precision of λ / 8 (when the measurement wavelength λ=633 nm) or less, and the average roughness of the precision-polished surface was arithmetic mean height Sa≦0.70 nm and root-mean-square height Sq≦0.89 nm.

[0066] Next, both end faces of all the samples of composition 1 were coated with an AR coating (anti-reflection film) with a wavelength of 1030 nm, and both end faces of all the samples of composition 2 were coated with an AR coating with a wavelength of 1064 nm to prepare a series of evaluation samples.

[0067] The positions and numbers of contrast sources such as foreign matter, heterogeneous phases, and voids were measured and counted by the following method for 100 samples of each type obtained as described above, for a total of 200 samples.

[0068] [How to observe contrast sources] Using a Zeiss metallurgical microscope in transmission mode and a 1.25x objective lens, each sample was evaluated for the presence of foreign matter, foreign phases, or voids greater than 30 μm in size, and if any were present, the samples were classified as Class E (Comparative Examples 8, 9, and 15).

[0069] Next, using 5x and 10x objective lenses, each sample was evaluated for the presence of foreign matter, heterogeneous phases, and voids with sizes exceeding 10 μm and not exceeding 30 μm. If any were present, their positions (whether they were within a circular region with a radius of the incident beam diameter Dmm from the center of the optical surface or outside of it) and the number of particles were all counted. After that, all samples with the number of particles being 5 or more were classified into Class D (Comparative Examples 4-7, 13, and 14), those with the number of particles being 4 or less and 2 or more within the circular region of radius Dmm were classified into Class C (Examples 7-9, 15-17, Comparative Examples 3 and 12), those with the number of particles being 4 or less and 1 or less within the circular region of radius Dmm were classified into Class B (Examples 4-6, 12-14, Comparative Examples 2 and 11), and those with the number of particles being 3 or less and not (0) within the circular region of radius Dmm were classified into Class A (Examples 1-3, 9-11, Comparative Examples 1 and 10).

[0070] For reference, examples of contrast of foreign bodies, heterogeneous phases, and bonds observed in transmission mode with a Zeiss metallurgical microscope are shown in Figures 2 to 5. Note that all of these contrast examples correspond to observation examples of Class E, which exceeds 30 μm.

[0071] Next, the insertion loss was measured at a wavelength of 1030 nm for the composition 1 group and at a wavelength of 1064 nm for the composition 2 group by the following method.

[0072] [Insertion loss measurement method] The insertion loss of the AR-coated optical sample was measured as follows, with reference to JIS C 61300-3-2.

[0073] The optical system was manufactured in-house using NKT Photonics' 1030 nm and 1064 nm wavelength laser light sources, collimator lenses, polarizers, an automatic work stage movable in the XY axes, an analyzer, a power meter manufactured by Gentec, and a Ge photodetector. The beam diameter incident on the measurement sample was set to approximately 1 mmφ by adjusting the NA and distance of the divergent beam emitted from the fiber end face attached to the NKT Photonics laser light source and the collimator lens that receives it.

[0074] Under these conditions, the insertion loss was measured as follows. First, the parallel light emitted through the collimator lens was received by a Ge photodetector without passing through the sample, and the light intensity I 0 Then, the sample was placed and the XY jig automatic work stage was adjusted so that the beam was set at the approximate center of the measurement sample, and the received light intensity I' was measured again. After that, the insertion loss was calculated based on the following formula. Insertion loss (dB) = -10 × log 10 (I' / I 0 ')

[0075] The obtained insertion loss values ​​were classified according to the following criteria: samples with an insertion loss value of 0.030 dB or less were defined as Class 1 (Examples 1, 4, 7, 9, 12, 15, Comparative Example 4), samples with an insertion loss value of more than 0.030 dB and less than or equal to 0.035 dB were defined as Class 2 (Examples 2, 5, 8, 10, 13, 16, Comparative Examples 5, 8, 13), samples with an insertion loss value of more than 0.035 dB and less than or equal to 0.043 dB were defined as Class 3 (Examples 3, 6, 9, 11, 14, 17, Comparative Examples 6, 14, 15), and samples with an insertion loss value of 0.043 dB or more were defined as Class 4 (Comparative Examples 1, 2, 3, 7, 9, 10, 11, 12).

[0076] As a result of the above, grouping was completed for the two compositions, Compositions 1 and 2. The obtained results are summarized in Table 2. As can be seen from Table 2, there were also comparative examples with zero corresponding numbers in this grouping, so these were marked as not applicable.

[0077] [Table 2]

[0078] For each sample classified as above, the beam quality (M 2 ) and the rate of change of the beam diameter were measured and evaluated.

[0079] [Beam quality (M 2 ) Evaluation method] The beam quality was measured using a collimated output variable CW laser beam with a wavelength of 1070 nm and a diameter of 1.1 mm manufactured by IPG Co., Ltd. for both compositions 1 and 2, using a Coherent ModeMaster PC M 2 Beam Propagation Analyzer 2 The values ​​were measured. Specifically, a work holder was set between the light source and the analyzer, and a beam separator capable of attenuating the laser light intensity transmitted through the work holder to 1 / 1000 or less was placed behind it, and the beam whose output was adjusted by the beam separator was introduced into the beam propagation analyzer. At this time, the distance between the reference plane (full bezel) of the beam propagation analyzer and the sample holder was 1.9 m, and the distance between the reference plane and the collimator was 2.1 m.

[0080] The measurement procedure is as follows: First, the M of the original beam with output intensities of 10W, 20W, 40W, 80W, and 120W is measured. 2 Measure the value and call this value m p Next, each sample with a length of 17 mm was placed in the optical path, and the M of the transmitted light at each output intensity of 10 W, 20 W, 40 W, 80 W, and 120 W was measured. 2 Measure the value, n p The beam quality in this invention is n p / m p The beam quality was evaluated by p / m p If the value is less than 1.04, it is judged as passing, and if it is 1.05 or more, it is judged as failing. Then, the maximum laser output intensity within the passing range of the same group was defined as the passing maximum output of that group.

[0081] [Method for evaluating beam diameter change rate] The rate of change in beam diameter was measured using an optical system with the same configuration as the beam quality evaluation measurement system described above. That is, a collimated output variable CW laser light with a wavelength of 1070 nm and a diameter of 1.1 mm manufactured by IPG Co., Ltd. was used, and a Coherent ModeMaster PC M 2 The light was received by a beam propagation analyzer, and the beam diameter at the reference plane (full bezel) was measured using the beam profile evaluation mode of the analyzer.

[0082] The measurement procedure is as follows: First, the beam diameter of each original beam with output intensity of 10W, 20W, 40W, 80W, and 120W is measured, and the value at that time is expressed as r 0p Next, each sample with a length of 17 mm was placed in the optical path, and the beam diameter of the transmitted light was measured at each output intensity of 10 W, 20 W, 40 W, 80 W, and 120 W. p The beam diameter change rate in the present invention is |(1-r p / r0 p )|×100 was calculated, and a value of 10% or less was judged as a pass, and a value of more than 10% was judged as a fail. The maximum laser output intensity within the pass range for the same group was then defined as the maximum pass output for that group. The pass / fail results for each class measured in the above manner are summarized in Table 3.

[0083] [Table 3]

[0084] The results in Table 3 were further evaluated for quality as follows. That is, in order to mount the terbium-containing paramagnetic garnet-type transparent ceramics of the present invention on an actual laser processing machine and operate normally, when a laser beam is incident on the ceramics, the beam quality (M 2 ) and beam diameter change rate are both within the standard (beam quality n p / m p is 1.04 or less, and the beam diameter change rate |(1-r p / r0p )|×100 must be 10% or less), so the lower of the evaluation results in Table 3 was defined as the maximum laser output value for that class.

[0085] The results were summarized as follows: terbium-containing paramagnetic garnet-type transparent ceramics with a contrast group of class A and an insertion loss group of class 1 are applicable to a maximum laser output of 120W, terbium-containing paramagnetic garnet-type transparent ceramics with a contrast group of class B and an insertion loss group of class 2 are applicable to a maximum laser output of 80W, terbium-containing paramagnetic garnet-type transparent ceramics with a contrast group of class C and an insertion loss group of class 3 are applicable to a maximum laser output of 40W, terbium-containing paramagnetic garnet-type transparent ceramics with a contrast group of class D and an insertion loss group of class 4 are only applicable to a maximum laser output of 20W, and terbium-containing paramagnetic garnet-type transparent ceramics with a contrast group of class E are only applicable to a maximum laser output of 10W.

[0086] In actual operation, it is customary to set a safety factor for the maximum laser output. For example, a sample with a maximum laser output of 120W is usually installed in a laser processing machine with a regular use of 100W, a sample with a maximum laser output of 80W is usually installed in a laser processing machine with a regular use of 65W, a sample with a maximum laser output of 40W is usually installed in a laser processing machine with a regular use of 30W, and a sample with a maximum laser output of only 20W can only be installed in a small laser processing machine with a regular use of 15W or less.

[0087] [Examples 18 and 19, Comparative Examples 16 to 19] A raw material having the composition shown in Table 1 was additionally prepared in the same manner as in Examples 1 to 17 and Comparative Examples 1 to 15. The slurry was then dispersed, mixed, and spray-dried in the same manner as in Examples 1 to 17 and Comparative Examples 1 to 15 to prepare a granular raw material having an average particle size of 20 μm.

[0088] For each of the two oxide raw materials obtained, 30 compacts were produced using a uniaxial press molding tool with an inner diameter of 10 mm. The amount of raw material filled was adjusted so that the length of each compact was 30 mm. All compacts were then subjected to isostatic pressing at a pressure of 198 MPa to obtain CIP compacts. All of the obtained compacts were then degreased in a muffle furnace at 800°C for 3 hours to obtain degreased compacts.

[0089] All of the degreased green bodies were then sintered in a vacuum sintering furnace at a sintering temperature of 1500 to 1570° C. for 3 hours to obtain sintered bodies with a sintered density of 93.8% to 97.2%.

[0090] The obtained sintered bodies were placed in a carbon heater HIP furnace and HIP-treated in Ar at 200 MPa, 1600°C, and 3 hours. The relative density of each of the obtained sintered bodies was 99.9% or more. In addition, their appearance was bluish gray (oxygen deficiency absorption).

[0091] Thereafter, all of the HIP-treated sintered bodies were heat-treated in a vacuum sintering furnace at a sintering temperature of 1730°C for 15 hours in an attempt to eliminate residual bubbles throughout the entire area, including the center of the sintered body.

[0092] Next, each of the obtained ceramic sintered bodies was annealed in an atmospheric heating furnace at 1450° C. for 40 hours to sufficiently recover the oxygen vacancies.

[0093] After that, the outer diameter of each of the obtained ceramic sintered bodies was adjusted to 6.5 mm by centerless peripheral grinding. After that, each was cut and precision polished to an equal length of 16 mm. At this time, both optical end faces of the samples were finished so that the optical surface precision was λ / 8 (when the measurement wavelength λ = 633 nm) or less, and the average roughness of the precision-polished surface was arithmetic mean height Sa ≦ 0.70 nm and root mean square height Sq ≦ 0.89 nm.

[0094] Next, both end faces of all the samples of composition 1 were coated with an AR coating (anti-reflection film) with a wavelength of 1030 nm, and both end faces of all the samples of composition 2 were coated with an AR coating with a wavelength of 1064 nm to prepare a series of evaluation samples.

[0095] For a total of 60 samples (30 samples of each type) obtained in the above manner, the same microscope as in Examples 1 to 17 and Comparative Examples 1 to 15 was used to measure and count the positions and numbers of contrast sources of foreign matter, heterogeneous phases, and voids, except that the inspection criteria were changed to the method described below.

[0096] Using the transmission mode of a Zeiss metallurgical microscope and a 1.25x objective lens, each sample was evaluated for foreign matter, foreign phases, and voids over 30 μm in size. If any were found, the samples were discarded in this example. The reason for discarding the samples was that in this example, a high-power laser of over 120 W was used for the test, and if there was a large scattering source over 30 μm, the scattered light would be emitted outside the sample during the laser irradiation test, and in some cases, the scattered light could heat up the surrounding objects, causing a fire.

[0097] Next, using 5x and 10x objective lenses, each was evaluated for the presence of foreign matter, foreign phases, and voids with sizes exceeding 10μm and less than 30μm. If any were present, their location (D 2倍 mm, or is it within a circular area with a radius of 2 × D 2倍 mm or within a circular area with a radius of 2 x D 2倍 In this embodiment, the number of particles was counted based on whether the particle was outside the circular area having a radius of D mm. 2倍 Only samples with no foreign matter, foreign phases, or voids larger than 10 μm within a circular area of ​​1 mm were selected. The reason for this is to avoid the risk of heat generation and the risk of scattered light entering the tester's eyes due to the strong scattered light generated when a high-power laser of over 120 W is irradiated, as described above. Next, 2倍 Over 2×D mm 2倍In the optical range of 10 mm or less, there are no foreign bodies or phases exceeding 10 μm, and the number of voids of 10 μm to 30 μm is two or less. 2倍 The group in which the total number of foreign bodies, heterogeneous phases, and voids of 10 μm to 30 μm in size within the outer effective diameter exceeding mm is 2 or less is classified as class α (Examples 18 and 19, Comparative Examples 16 and 18), and the group in which the total number of foreign bodies, heterogeneous phases, and voids of 10 μm to 30 μm in size within the outer effective diameter exceeding 2 × D 2倍 In the optical range of 10 mm or less, samples with one or more foreign matter or heterogeneous phases of 10 μm to 30 μm in size, or samples with three or more voids of 10 μm to 30 μm in size, or samples with a diameter of 2 × D 2倍 All samples in which the total number of foreign matter, heterogeneous phases, and voids of 10 μm to 30 μm within the outer effective diameter exceeding 3 mm was categorized as class β (Reference Examples 1 and 2, Comparative Examples 18 and 19).

[0098] As a result, in the composition 1 sample group, there were 7 class α, 11 class β, and 12 discarded. In the composition 2 sample group, there were 14 class α, 13 class β, and 3 discarded.

[0099] Next, the insertion loss was measured at a wavelength of 1030 nm for the composition 1 group, and at a wavelength of 1064 nm for the composition 2 group, in exactly the same manner as in Examples 1-17 and Comparative Examples 1-15.

[0100] The obtained insertion loss values ​​were classified according to the following criteria. That is, samples with an insertion loss value of 0.030 dB or less were classified as Class 1 (Examples 18 and 19, Reference Examples 1 and 2), samples with an insertion loss value of more than 0.030 dB and less than 0.035 dB were classified as Class 2 (Comparative Examples 16 to 19), and samples with an insertion loss value of more than 0.035 dB were discarded. The reason for discarding the samples here is that in this example, a high-power laser of more than 120 W was used for the test, and in the case of samples with an absorption source or scattering source with an insertion loss value of more than 0.035 dB, the sample may abnormally heat up during the laser irradiation test or the scattered light may radiate outside the sample, and in some cases, the scattered light may heat up the surrounding objects, causing a fire.

[0101] As a result, grouping was completed for the two compositions, Compositions 1 and 2, in this example. The results are summarized in Table 4. Note that the insertion loss was not measured for the contrast group that was discarded. Furthermore, the insertion loss group that was discarded was not subjected to further evaluation.

[0102] [Table 4]

[0103] For each sample classified as described above, only the incident power setting was changed, and the other settings were the same as in Examples 1 to 17 and Comparative Examples 1 to 15, and the beam quality (M 2 ) and the rate of change in beam diameter were measured and evaluated. In this embodiment, the output intensity of the incident beam was set to three conditions: 120 W, 180 W, and 240 W. The pass / fail results for each class measured in the above manner are summarized in Table 5.

[0104] [Table 5]

[0105] For the results in Table 5, similarly to Examples 1 to 17 and Comparative Examples 1 to 15, the lower acceptable maximum laser output value was defined as the maximum laser output value for that class, and the quality was judged. The results were summarized as follows. First, it was summarized that terbium-containing paramagnetic garnet-type transparent ceramics with a contrast group of class α and an insertion loss group of class 1 are applicable to a maximum laser output of 240 W, terbium-containing paramagnetic garnet-type transparent ceramics with a contrast group of class β and an insertion loss group of class 1 are applicable to a maximum laser output of 180 W, and terbium-containing paramagnetic garnet-type transparent ceramics with an insertion loss group of class 2 are applicable to a maximum laser output of 120 W.

[0106] In this embodiment, the outer diameter of the sample is increased (outer diameter 6.5 mm), and the beam diameter is expanded to 2 mm by an expander. Both of these have a negative effect of increasing manufacturing costs. Therefore, the comparative example group with a maximum applicable laser output of 120 W is not worth this increased cost.

[0107] Next, the terbium-containing paramagnetic garnet-type transparent ceramics with a contrast group of class β and an insertion loss group of class 1 were applicable to a maximum laser output of 180 W. Whether or not the applicable power is worth the increased cost is a decision to be made by the laser processing machine manufacturer who actually designs the laser processing machine, so this patent avoids making a definitive statement as a reference example.

[0108] Finally, the terbium-containing paramagnetic garnet-type transparent ceramics with a contrast group of class α and an insertion loss group of class 1 was applicable to a maximum laser output of 240 W, which was twice the maximum laser output of 120 W in Examples 1 and 9. Therefore, this was judged to be an example that was definitely effective.

[0109] In actual operation, it is customary to provide a safety margin for the maximum laser output value. Therefore, it is considered appropriate to install a sample with a maximum laser output value of 240 W in a laser processing machine with a regular use of 200 W, and a sample with a maximum laser output value of 180 W in a laser processing machine with a regular use of 150 W.

[0110] Although the present invention has been described above using the above-mentioned embodiment, the present invention is not limited to this embodiment, and can be modified within the scope of what a person skilled in the art can imagine, such as other embodiments, additions, modifications, deletions, etc., and any aspect is within the scope of the present invention as long as it achieves the effects of the present invention. [Explanation of symbols]

[0111] 100 Optical isolator 110 Faraday Rotator 120 Polarizer 130 Analyzer 140 Magnet 150 Case

Claims

1. A composite oxide represented by the following formula (1) and SiO as a sintering aid ２ A terbium-containing paramagnetic garnet-type transparent ceramic comprising a sintered body containing more than 0 mass % and 0.1 mass % or less of (Tb １-ｘ-ｙ Y ｘ Sc ｙ ) ３ (Al １－ｚ Sc ｚ ) ５ O １２ (1) (In the formula, 0.05≦x≦0.45, 0<y<0.1, 0.5<1−x−y<0.95, 0.001<z<0.15, and 0<y+z<0.2.) The terbium-containing paramagnetic garnet-type transparent ceramics are When the incident beam diameter D mm is 1.6 mm or less, the outer diameter R mm is 2.2 × D mm or more and 3.5 mm or more; The rod is machined into a length of 14 mm or more, both end faces of which are precision-polished, and both end faces are coated with an AR coating having a wavelength of N nm. When an optically utilized optical effective diameter r mm is defined by the following formula (2), the average insertion loss when a laser beam having an incident beam diameter D mm and a wavelength N nm is incident on this optical effective diameter r mm is 0.043 dB or less, r=0.9×R (2) A terbium-containing paramagnetic garnet-type transparent ceramic having no foreign matter, heterogeneous phase, or void exceeding 30 μm within an optically effective diameter rmm, and the total number of foreign matter, heterogeneous phase, and voids having sizes between 10 μm and 30 μm within an optically effective diameter rmm is a maximum of 4.

2. 2. The terbium-containing paramagnetic garnet-type transparent ceramic according to claim 1, wherein the average insertion loss is 0.035 dB or less, and the total number of foreign bodies, heterogeneous phases, and voids having a size of 10 μm to 30 μm within a circular region having a radius of the incident beam diameter D mm from the center of the optical surface is a maximum of 1.

3. 3. The terbium-containing paramagnetic garnet-type transparent ceramic according to claim 1, wherein the average insertion loss is 0.030 dB or less, the total number of foreign bodies, heterogeneous phases, and voids having a size of 10 μm to 30 μm within the optical effective diameter r mm is a maximum of 3, and there are no foreign bodies, heterogeneous phases, or voids exceeding 10 μm within a circular region having a radius of the incident beam diameter D mm from the center of the optical surface.

4. The terbium-containing paramagnetic garnet-type transparent ceramics are The diameter of the incident beam is doubled by the expander. ２倍 The laser beam is expanded to 1 mm, and the incident beam diameter D ２倍 When the outer diameter R' mm is 1.6 mm or more, the outer diameter R' mm is 2.2 x D ２倍 mm or more and 5 mm or more, The rod is machined into a length of 14 mm or more, both end faces of which are precision-polished, and both end faces are coated with an AR coating having a wavelength of N nm. When the optically effective diameter r' mm used optically is defined by the following formula (3), the beam diameter D ２倍 The average insertion loss when a laser beam having a wavelength of N nm is incident on the fiber at 1000 nm is 0.030 dB or less. r'=0.9×R' (3) The total number of foreign objects, heterogeneous phases, and voids of 10 μm to 30 μm in size within the optical effective diameter r mm is a maximum of 2, and the maximum number of foreign objects, heterogeneous phases, and voids is 2×D from the center of the optical surface. ２倍 Within a circular area with a radius of 10 mm, there is no foreign matter or foreign phase exceeding 10 μm, the number of voids of 10 μm to 30 μm is a maximum of two, and the area is within D ２倍 2. The terbium-containing paramagnetic garnet-type transparent ceramic according to claim 1, which has no foreign matter, foreign phase, or void exceeding 10 μm in size within a circular region having a radius of 1 mm.

5. A magneto-optical material comprising the terbium-containing paramagnetic garnet-type transparent ceramic according to claim 1 or 4.

6. 6. The magneto-optical device according to claim 5, which is an optical isolator having the terbium-containing paramagnetic garnet-type transparent ceramic as a Faraday rotator and having polarizing materials in front of and behind the optical axis of the Faraday rotator and usable in the wavelength range of 0.9 μm or more and 1.1 μm or less.

Images