JP2018095486A - Bismuth-substituted type rare earth iron garnet crystal film, production method thereof, and optical isolator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a bismuth-substituted type rare earth iron garnet crystal film having industrially high yield, and having a loss reduced to 0.35 dB, while reducing a light absorption amount in 1 μm band.SOLUTION: There is provided a bismuth-substituted type rare earth iron garnet crystal film expressed by following chemical formula (1):NdGdBiFeO...(1) (in the chemical formula (1). x1 satisfied 0.65≤x1≤0.84, and y1 satisfies 1.00≤y1≤1.15).SELECTED DRAWING: Figure 7

Description

  The present invention relates to a bismuth-substituted rare earth iron garnet crystal film, a manufacturing method thereof, and an optical isolator.

  Semiconductor lasers used for optical communications and solid-state lasers used for laser processing, etc., generate laser oscillation when the light reflected from the optical surface or processing surface outside the laser resonator returns to the laser element. It becomes unstable. If the oscillation becomes unstable, signal noise may occur in the case of optical communication, and the laser element may be destroyed in the case of a processing laser. For this reason, an optical isolator is used to block such reflected return light from returning to the laser element.

  As for Faraday rotators used in optical isolators, terbium gallium garnet crystals (hereinafter referred to as TGG) and terbium aluminum garnet crystals have recently been used as fiber lasers that have attracted attention as an alternative to conventional YAG lasers. (Hereinafter referred to as TAG) has been used.

  However, TGG and TAG have a small Faraday rotation coefficient per unit length, and it is necessary to increase the optical path length in order to obtain a 45 ° polarization rotation angle in order to function as an optical isolator. did not become. Moreover, in order to obtain high optical isolation, it is necessary to apply a uniform and large magnetic field to the crystal, so a strong and large magnet was used. For this reason, the size of the optical isolator is large. In addition, since the optical path length is long, the laser beam shape may be distorted in the crystal, and an optical system for correcting the distortion may be required. Furthermore, since TGG is expensive, a small and inexpensive Faraday rotator has been desired.

  On the other hand, by using a bismuth-substituted rare earth iron garnet crystal film (hereinafter referred to as RIG) exclusively used in the field of optical communications for this type of optical isolator, the size can be greatly reduced. is there. However, when the wavelength of light used in RIG is shortened to near 1.1 μm used for processing lasers, light absorption by iron ions contained in RIG increases, and the temperature rises due to this light absorption, resulting in performance deterioration. It has been known.

Therefore, as shown in Patent Document 1, the present researchers have used non-magnetic garnet [(GdCa) ₃ (GaMgZr) ₅ O ₁₂ ], which is applied for RIG growth for optical communication applications, and a lattice constant of 1.2497 nm, By applying non-magnetic garnet [Gd ₃ (ScGa) ₅ O ₁₂ ] (hereinafter referred to as GSGG) having a larger lattice constant of 1.2564 nm and growing the RIG, light absorption of iron ions contained in the RIG is achieved. RIG has been proposed which is shifted to the short wavelength side to reduce the amount of light absorption in the 1 μm band while reducing the insertion loss from 0.36 dB to 0.56 dB in an industrially high yield.

JP 2012-116672 A

Takashi Katsura, Toshimori Sekine, Kenzo Kitayama, Tadashi Sugihara, Noboru Kimizuka, Thermodynamic properties of Fe-lathanoid-O compounds at high temperatures, Journal of Solid State Chemistry, 15 January 1978, volume 23, issues 1-2, pages 43-57 .

  However, in recent years, it has been considered that RIG is used for an optical isolator of a laser device for processing in a further short wavelength region or a high-power processing laser device of 10 W class or higher. For this reason, in the market, a very low-loss RIG with an insertion loss of 0.35 dB or less is required, and a technique that can provide a low-loss RIG in an industrially high yield is desired.

  By the way, there are several methods that can further reduce the light absorption in the RIG, and one of them is a method of increasing the lattice constant of the RIG as described above. The lattice constant of RIG is almost the same as the lattice constant of the single crystal substrate used when manufacturing the RIG due to its manufacturing method. Therefore, in order to increase the lattice constant of RIG, it is necessary to use a single crystal substrate having a larger lattice constant.

In Patent Document 1, a GSGG single crystal substrate having a lattice constant of 1.2564 nm is applied and grown. For this reason, if it is applied to the growth of RIG using a nonmagnetic garnet having a lattice constant larger than 1.2564 nm of GSGG single crystal, light absorption can be further reduced. A single crystal substrate having a lattice constant larger than 1.2564 nm of GSGG includes a non-magnetic garnet Sm ₃ (ScGa) ₅ O ₁₂ (hereinafter referred to as SSGG) single crystal substrate having a lattice constant of 1.264 nm. However, when RIG is produced using SSGG, the Bi content in the RIG crystal increases due to the size of the lattice constant. When the Bi content in the RIG crystal increases, the deviation of the lattice constant from the SSGG single crystal substrate having a lattice constant of 1.264 nm increases, so that the crystal easily breaks, and thus it is not possible to produce RIG with high yield. It was. Therefore, in order to moderately suppress the Bi addition amount, it is necessary to select a rare earth having a large ionic radius. Specifically, La is a candidate, but Non-Patent Document 1 reports that in a melt containing a large amount of La, the perovskite phase is stable and it is difficult to precipitate a garnet phase. On the other hand, if the Bi addition amount is small, the RIG film thickness required to obtain the 45 ° Faraday rotation angle required as an optical isolator increases, and as a result, the reduction of the light absorption amount in the RIG cannot be achieved. . Further, as a method for further reducing light absorption in RIG, it is considered preferable to use a single crystal substrate having a lattice constant larger than 1.2564 nm of GSGG single crystal and smaller than 1.264 nm of SSGG single crystal, At present, such a single crystal substrate has not been sold in the market, so it has been difficult to obtain.

  Therefore, the present invention has been made in view of the above situation, and while reducing the amount of light absorption in the 1 μm band, industrially high yield, and RIG that has reduced loss to 0.35 dB or less, and a method for manufacturing the same, The present invention also provides an optical isolator using the RIG.

  In order to solve the above-described problems, the present inventors have conducted extensive research. As a result, by controlling the lattice constant of RIG, the type of rare earth constituting the RIG, and the amount of addition thereof, light having a wavelength of 1 μm band can be obtained. In contrast, the present inventors have found that a low-loss RIG of 0.35 dB or less can be grown with a high yield. The present invention has been completed based on such technical findings.

That is, according to the first aspect of the present invention, a bismuth-substituted rare earth iron garnet crystal film represented by the following chemical formula (1).
Nd _3-x1-y1 Gd _x1 Bi _y1 Fe ₅ O ₁₂ (1)
(In the chemical formula (1), x1 is 0.65 ≦ x1 ≦ 0.84, and y1 is 1.00 ≦ y1 ≦ 1.15.)

  According to a second aspect of the present invention, there is provided an optical isolator according to the first aspect, wherein a bismuth-substituted rare earth iron garnet crystal film is used for a Faraday rotator.

Further, according to the third aspect of the present invention, a bismuth-substituted rare earth iron garnet crystal film represented by the following formula (1) is grown on a nonmagnetic garnet single crystal substrate by a liquid phase epitaxial growth method. A method of manufacturing a type rare earth iron garnet crystal film is provided.
Nd _3-x1-y1 Gd _x1 Bi _y1 Fe ₅ O ₁₂ (1)
(In the chemical formula (1), x1 is 0.65 ≦ x1 ≦ 0.84, and y1 is 1.00 ≦ y1 ≦ 1.15.)

According to the fourth aspect of the present invention, in the third aspect, the nonmagnetic garnet single crystal substrate is provided with a method for producing a bismuth-substituted rare earth iron garnet crystal film represented by the following formula (2): Is done.
Gd ₃ Sc _x2 Ga _5-x2 O ₁₂ (2)
(In the chemical formula (2), x2 is 2.065 ≦ x2 ≦ 2.117.)

  According to the fifth aspect of the present invention, in the third or fourth aspect, the nonmagnetic garnet single crystal substrate has a lattice constant of 1.25800 nm or more and 1.25850 nm or less. A method of manufacturing a garnet crystal film is provided.

  According to the sixth aspect of the present invention, in any one of the third to fifth aspects, the nonmagnetic garnet single crystal substrate has a bismuth-substituted rare earth iron garnet crystal film having a lattice constant of 1.25830 nm. A manufacturing method is provided.

  The bismuth-substituted rare earth iron garnet crystal film (RIG) according to the present invention is manufactured at a high yield with an insertion loss of 0.35 dB or less as compared with the conventional RIG described in Patent Document 1 and the like. be able to. Further, by applying the RIG of the present invention with an insertion loss of 0.35 dB or less, the amount of heat generated in the RIG itself can be reduced. Therefore, when the RIG of the present invention is applied to an optical isolator for a processing laser, it is higher. Since the temperature rise can be significantly suppressed with respect to the power laser beam, it has the effect of suppressing the deterioration of characteristics. Moreover, the manufacturing method of RIG which concerns on this invention can manufacture good quality RIG with a high yield. In addition, since the optical isolator according to the present invention includes the RIG described above, it is possible to significantly suppress a temperature rise with respect to a higher-power laser beam, and to suppress deterioration of characteristics.

It is a graph which shows the chemical formula amount of Sc and the lattice constant of the GSGG single crystal which concerns on embodiment. It is a graph which shows the chemical formula amount of Sc and the lattice constant of the GSGG single crystal which concerns on embodiment. It is a flowchart which shows an example of the manufacturing method of the GSGG single crystal which concerns on embodiment. It is a conceptual diagram which shows an example of the GSGG single crystal which concerns on embodiment. It is a figure which shows schematic structure of the manufacturing apparatus used for the manufacturing method of the GSGG single crystal which concerns on embodiment. It is a flowchart which shows an example of the manufacturing method of the GSGG single crystal substrate which concerns on embodiment. It is a Nd-Gd-Bi ternary composition diagram in RIG. It is a graph which shows the relationship between Bi chemical formula amount and insertion loss in RIG. It is a flowchart which shows an example of the manufacturing method of RIG which concerns on embodiment.

  The present invention will be described below with reference to the drawings. However, the present invention is not limited to this. Further, in the drawings, in order to describe the embodiment, the scale is appropriately changed and expressed by partially enlarging or emphasizing the description. In each of the following drawings, directions in the drawing will be described using an XYZ coordinate system. In this XYZ coordinate system, the vertical direction is the Z direction, and the horizontal direction is the X direction and the Y direction. For each of the X direction, the Y direction, and the Z direction, the side of the arrow is appropriately referred to as a + side (eg, + X side), and the opposite side is referred to as a − side (eg, −X side).

  First, as described above, as a method for further reducing the light absorption in RIG, there is a method for increasing the lattice constant of RIG as compared with the conventional method. In this case, the single crystal substrate used therefor also needs to have a large lattice constant. However, it is considered preferable to use a single crystal substrate having a lattice constant larger than 1.2564 nm of GSGG single crystal and smaller than 1.264 nm of SSGG single crystal. Currently, such a single crystal substrate is in the market. Since it is not sold, it is difficult to obtain.

(1) Investigation of lattice constant and Sc content of GSGG Therefore, in order to solve the problems of the substrate, the present inventors first performed the following technical analysis. First, the relationship between the composition of GSGG single crystal (chemical formula: Gd ₃ Sc _x Ga ₅ -xO ₁₂ , 0 <x <5) and the lattice constant was investigated. GSGG single crystals having various compositions were produced by the Czochralski (CZ) method, and the lattice constants of the produced GSGG single crystals were evaluated. Subsequently, the Sc content in the GSGG single crystal was investigated, and the influence on the lattice constant was examined. It is also conceivable to add a fourth element in addition to the elements Gd _, Sc _and Ga. For example, Lu (lutetium), Nd (neodymium), Eu (europium) and the like. However, by adding these elements, the segregation of these substances differs, so that the control of the lattice constant becomes more difficult as the number of constituent elements increases, and a single crystal and a single crystal substrate having a stable lattice constant cannot be obtained. For example, when Eu is added, since Eu has a valence of 2 (2+), vacancies are easily formed and the crystallinity deteriorates. In addition, since the ion radius is close to Gd, the effect of increasing the lattice constant is small. Gd, Sc and Ga are trivalent (3+) and are easy to stabilize. Therefore, for the purpose of developing a single crystal and a single crystal substrate that can be easily manufactured and have a stable lattice constant, the above three elements of Gd _, Sc _{, and} Ga were studied.

  Table 1 and FIG. 1 show that after processing the manufactured GSGG single crystal into a GSGG substrate, the lattice constant was measured using an X-ray diffractometer (manufactured by Xpert PRO PANalytical), and then the substrate on which the lattice constant was measured was determined by EPMA. The chemical formula amount of Sc is obtained by analysis, and the results are summarized.

なお、表１に示したサンプル１〜６は、後に説明する参考例１２〜参考例１７である。 Investigation of lattice constant and Sc formula weight

Samples 1 to 6 shown in Table 1 are Reference Example 12 to Reference Example 17 described later.

  As shown in Table 1 and FIG. 1, the present inventor has found that the lattice constant is made larger than 1.2564 nm by changing the ratio of the elements constituting the GSGG single crystal from the conventional one. In addition, it can be seen from this result that the lattice constant increases in the GSGG single crystal as the amount of Sc chemical formula increases. Specifically, it was found that at least when the Sc chemical formula amount is 2.00 to 2.15, the lattice constant varies from 1.2573 to 1.25877 depending on the Sc chemical formula amount. From the above results, the present inventors have found that the lattice constant can be made larger than 1.2564 nm and can be easily controlled by controlling the ratio of the elements constituting the GSGG single crystal. The GSGG single crystal and the GSGG single crystal substrate of the present embodiment have been completed based on these technical findings. Thereby, it is possible to secure a GSGG single crystal substrate that can be used for manufacturing RIG having a lattice constant larger than 1.2564 nm and smaller than 1.264 nm.

(2) GSGG single crystal The GSGG single crystal which concerns on this embodiment is demonstrated. The GSGG single crystal C according to this embodiment is represented by the following chemical formula (2).
Gd ₃ Sc _x2 Ga _5-x2 O ₁₂ (2)
(In the chemical formula (2), x2 is 2.00 ≦ x2 ≦ 2.15.)
Here, “GSGG single crystal is represented by chemical formula (2)” means that GSGG single crystal C substantially has the composition of chemical formula (2). That is, the GSGG single crystal C may contain trace amounts of elements other than Gd, Sc, Ga, and O as inevitable impurities, dopants, and the like without departing from the spirit of the present invention. In addition, the chemical formula amount of Sc (the value of x2 in the chemical formula (2)) in the chemical formula (2) is a chemical formula amount measured using EPMA (Electron Probe Micro Analyzer).

Since the lattice constant of the GSGG single crystal C has a positive correlation with x2 in the chemical formula (2) as shown in FIG. 1, it can be easily controlled by controlling x2. The above x2 can be controlled by the composition of the raw material. FIG. 2 is a graph showing the relationship between the chemical formula amount of Sc and the lattice constant. The GSGG single crystal C can easily control the lattice constant within a predetermined range by controlling x2. In the GSGG single crystal C, for example, when the lattice constant is “a” (nm), the relationship between the x2 and the lattice constant a of the crystal preferably satisfies the following formula (1).
0.010314x2 + 1.2236446 ≦ a ≦ 0.010314x2 + 1.2368846 (1)
When x2 and the lattice constant a are in the relationship of the above mathematical formula (1), the GSGG single crystal C can be improved in quality. In addition, the data of each point shown in FIG. 2 are data of Reference Examples 1 to 17 described later. In this specification, “lattice constant” is a value measured by an X-ray diffractometer.

  In the GSGG single crystal C, when x2 is 2.00 ≦ x2 ≦ 2.15, the lattice constant can be easily controlled in the range of 1.25737 nm to 1.25877 nm. When the lattice constant of the GSGG single crystal C is in this range, the GSGG single crystal C can be improved in quality, and suitable for the production of a bismuth-substituted rare earth iron garnet crystal film (RIG) having a lattice constant in the range including this range. Can be used.

  Further, in the GSGG single crystal C, when x2 is 2.065 ≦ x2 ≦ 2.117, the lattice constant can be easily controlled in the range of 1.25800 nm to 1.25850. When the lattice constant of the GSGG single crystal C is in this range, it can be suitably used for the production of the RIG of the present embodiment described later. Among them, when the lattice constant is 1.25830 nm, the present embodiment is more preferably used. It can be suitably used for the production of RIG. The RIG of this embodiment will be described later.

  Note that the size and shape of the GSGG single crystal C are not limited, and are arbitrary. An example of the size and shape of the GSGG single crystal C will be described in a manufacturing method of the GSGG single crystal C described below.

  As described above, since the GSGG single crystal C according to the present embodiment has a lattice constant larger than 1.2564 nm, it can be suitably used for manufacturing an RIG having a lattice constant larger than 1.2564 nm. In addition, the GSGG single crystal C according to the present embodiment has a simple composition because there are three types of metal elements, and further controls the lattice constant by controlling one variable (x2) in the chemical formula. Therefore, a single crystal having a desired lattice constant can be easily manufactured.

(3) Manufacturing method of GSGG single crystal Next, the manufacturing method of the GSGG single crystal which concerns on embodiment is demonstrated. 3A and 3B are flowcharts illustrating an example of a method for manufacturing a GSGG single crystal according to the embodiment. FIG. 4 is a conceptual diagram illustrating an example of a GSGG single crystal according to the embodiment. FIG. 5 is a diagram illustrating a schematic configuration of a manufacturing apparatus used in the method for manufacturing a GSGG single crystal according to the embodiment. In addition, the manufacturing method of the GSGG single crystal demonstrated below is an example, Comprising: The manufacturing method of a GSGG single crystal is not limited. Further, when describing the flowchart of FIG. 3, FIGS. 1, 2, 4, and 5 are referred to as appropriate.

The manufacturing method of the GSGG single crystal according to the embodiment includes a raw material melt 9 (see FIG. 3A) in which a raw material containing Gd, Sc and Ga is melted by the Czochralski method (rotary pulling method) in step S1. GSGG single crystal C represented by the following chemical formula (2) is manufactured by bringing the seed crystal SC into contact with and rotating the seed crystal SC (see FIG. 5).
Gd ₃ Sc _x2 Ga _5-x2 O ₁₂ (2)
(In the formula (2), x2 is 2.00 ≦ x2 ≦ 2.15.

  In step S1, the GSGG single crystal C is grown as a single crystal including a shoulder portion SH and a straight body portion SB as shown in FIG. Step S1 is performed by a known apparatus capable of performing the Czochralski method.

  First, an example of an apparatus capable of performing the Czochralski method will be described with reference to FIG. In addition, the apparatus demonstrated below is an example, Comprising: The apparatus used for the manufacturing method of the GSGG single crystal which concerns on this embodiment is not limited. This production apparatus includes a growth furnace 1 for producing a GSGG single crystal C by a known Czochralski method. The structure of the growth furnace 1 will be briefly described. The growth furnace 1 includes a cylindrical chamber 2, a high-frequency coil 10 installed inside the chamber 2, and a heat insulating material 3 arranged inside the high-frequency coil 10. And an iridium crucible 8 or the like. In addition, although the dimension of the said growth furnace 1 depends on the magnitude | size of the GSGG single crystal C to manufacture, it is a diameter of about 0.6 m and height about 1 m as an example.

  Further, the growth furnace 1 is provided with two openings (not shown), and an inert gas, preferably argon gas, is supplied and discharged through these openings, so that a chamber 2 for crystal growth is provided. The inside is filled with an inert gas. In the growth furnace 1, a thermometer (thermocouple, not shown) for measuring temperature is installed below the bottom of the crucible 8. The measurement result of this thermometer is output to the control part CONT.

  The high-frequency coil 10 is made of a copper tube, and the electric power supplied is controlled through the control unit CONT so that the crucible 8 is heated at a high frequency and the temperature is adjusted. A plurality of heat insulating materials 3 are disposed inside the high-frequency coil 10 (on the lifting shaft 4 side), and a hot zone 5 is formed by an atmosphere surrounded by the plurality of heat insulating materials 3.

  The temperature gradient of the hot zone 5 can be varied over a wide range depending on the shape and configuration (material) of the heat insulating material 3, and the shape and configuration of the heat insulating material 3 is designed according to the type of single crystal to be grown, and the appropriate hot A temperature gradient of zone 5 is formed. Further, the temperature gradient of the hot zone 5 can be finely adjusted by adjusting the relative position of the high-frequency coil 10 to the crucible 8. In addition, the said heat insulating material 3 is comprised with the refractory material of high melting | fusing point.

  The crucible 8 is formed in a cup shape, and the bottom thereof is disposed on the heat insulating material 3 and held by the heat insulating material 3. Further, on the upper side of the crucible 8, a pulling shaft 4 for holding the seed crystal SC and the grown GSGG single crystal C and pulling it while rotating is installed. The pulling shaft 4 can be moved in the vertical direction by a drive unit (not shown) and can be rotated around the axis. This drive unit is connected to the control unit CONT, and the rotation speed and the pulling speed of the pulling shaft 4 are controlled.

  The crucible 8 is filled with the raw material, the crucible 8 is placed in the chamber 2 of the growth furnace 1 and heated by the high frequency coil 10 to melt the raw material, and then the seed crystal SC is brought into contact with the raw material melt 9. The raw material melt 9 is sequentially crystallized on the lower side of the seed crystal SC by gradually lowering the temperature and simultaneously raising the temperature while rotating the pulling shaft 4. Then, it is possible to grow a GSGG single crystal C having a desired diameter and full length by adjusting the input power to the high-frequency coil 10, the rotational speed of the pulling shaft 4, and the pulling speed according to conventional growth conditions.

  Returning to the description of FIG. 3, step S1 of FIG. 3A will be described in detail. Step S1 in FIG. 3A is performed by, for example, steps S2 to S8 shown in FIG. In addition, the following description is an example and does not limit step S1.

First, in step S2 of FIG. 3B, a raw material containing Gd, Sc, and Ga is adjusted. For example, gadolinium oxide (Gd ₂ O ₃ ) powder, scandium oxide (Sc ₂ O ₃ ) powder, gallium oxide (Ga ₂ O ₃ ) powder, or the like is applied to the raw material of the GSGG single crystal. The mixing ratio of these raw materials is appropriately determined depending on the composition of the GSGG single crystal C to be grown. The mixing ratio of each raw material is set so that the composition of the GSGG single crystal C to be grown becomes the above-described chemical formula (2). The mixing ratio of each raw material is determined based on the incorporation rate of each element into the crystal, the growth conditions, and the like, and can be set by a known method in this field or a preliminary experiment. In addition, said raw material is an example and you may use another raw material.

  In addition, in the adjustment of the raw material in Step S2, when the lattice constant of the GSGG single crystal C to be grown is within a predetermined range, in Step S3, the number of Sc atoms and the number of Ga atoms are adjusted with respect to the number of Gd atoms in the raw material. Thus, the lattice constant is controlled within a predetermined range. As described above, since GSGG single crystal C has a positive correlation between x2 and the lattice constant, the number of Sc atoms and the number of Ga atoms with respect to the number of Gd atoms in the raw material are adjusted to obtain the lattice constant. Control within a predetermined range is possible. For the number of Sc atoms and the number of Ga atoms relative to the number of Gd atoms in the raw material, for example, x2 indicating the chemical formula amount of Sc corresponding to the target lattice constant a is obtained based on the above formula (1). The number of Sc atoms and the number of Ga atoms are adjusted with respect to the number of Gd atoms in the raw material so that the amount of the chemical formula of Sc of the GSGG single crystal C to be grown becomes x2. In this embodiment, when x2 in the chemical formula (2) is in the range of 2.00 ≦ x2 ≦ 2.15, the lattice constant of the GSGG single crystal C to be manufactured is a predetermined range of 1.25737 nm to 1.25877 nm. can do.

  Subsequently, in step S4 of FIG. 3B, the raw material adjusted in step S2 is filled into the crucible 8.

  Subsequently, in step S5 of FIG. 3B, the raw material is melted. For example, as shown in FIG. 5, the crucible 8 filled with the raw material is placed in the chamber 2 and heated by the high frequency coil 10 to melt the raw material. The temperature at which the raw material is melted is appropriately set according to conditions such as the melting temperature of the raw material and the temperature at which the GSGG single crystal C is grown.

  Subsequently, in step S6 of FIG. 3B, the shoulder portion SH (see FIG. 4) is grown. For example, as shown in FIG. 5, the shoulder SH is grown by bringing the seed crystal SC into contact with the raw material melt 9 and gradually lifting the pulling shaft 4, thereby simultaneously lowering the temperature. The raw material melt 9 is sequentially crystallized on the lower side of the substrate. The crystal orientation in the growth direction of the GSGG single crystal C to be grown is not particularly limited. However, since the GSGG single crystal substrate S (see FIG. 4) having the crystal orientation (111) is widely used, (111) It is preferable that In the growth of the shoulder SH, temperature adjustment (eg, adjustment of the temperature gradient of the hot zone 5) by adjusting the input power to the high-frequency coil 10 according to the growth conditions, adjustment of the pulling speed and rotation speed of the pulling shaft 4 Etc., the shoulder SH having a desired diameter can be grown. The temperature adjustment, the pulling speed and the rotating speed of the pulling shaft 4 can be set by a known method in this field or a preliminary experiment, respectively. The size of the shoulder portion SH is not limited. For example, the length (the length from the lower end of the seed crystal SC in FIG. 4 to the interface inversion position) is set to about 60 mm, and the diameter is set to about 60 mm.

  Subsequently, when the crystal diameter of the shoulder portion SH becomes a desired size, an interface inversion operation is performed in step S7 of FIG. In order to suppress the occurrence of distortion associated with facet growth by the interface inversion operation, the interface shape is made flat from a convex shape. Specifically, the interface is flattened by stopping the pulling of the crystal and increasing the rotation of the crystal.

  Subsequently, after the interface inversion is finished, in step S8 in FIG. 3B, the pulling up of the seed crystal SC (see FIG. 4) is resumed to grow the straight body portion SB (see FIG. 4). In the growth of the straight body portion SB, the temperature adjustment (eg, adjustment of the temperature gradient of the hot zone 5) by adjusting the input power to the high frequency coil 10 according to the growth conditions, the lifting speed of the lifting shaft 4 and the rotational speed By performing adjustment or the like, the straight body portion SB having a desired diameter can be grown. The temperature adjustment, the pulling speed and the rotating speed of the pulling shaft 4 can be set by a known method in this field or a preliminary experiment, respectively. In the final stage of growing the straight body portion SB, for example, the bottom end portion SBa of the straight body portion SB is grown so as to have a conical shape (see FIG. 4). This is in order to suppress the occurrence of dislocations generated by separating and cooling the straight body portion SB from the raw material melt 9. Although the magnitude | size of the straight body part SB is not limited, For example, length is set to about 70 mm-150 mm, and the diameter is set to about 60 mm. Through the above steps, a GSGG single crystal C having a desired diameter and length is manufactured. The method for producing a GSGG single crystal according to the present embodiment can efficiently produce a high-quality GSGG single crystal C.

  The grown GSGG single crystal C is taken out from the growth furnace 1 and subjected to an annealing process for removing thermal strain, and then processed into a GSGG single crystal substrate S having a thickness conforming to the standard.

(4) GSGG Single Crystal Substrate Next, the GSGG single crystal substrate according to the present embodiment will be described. The GSGG substrate S according to the present embodiment is a substrate using the above-described GSGG single crystal C. For example, as shown in FIG. 4, the GSGG substrate S is obtained by dividing (slicing) a GSGG single crystal C and performing surface treatment (surface processing). The thickness of the treated GSGG single crystal substrate S is not limited and is arbitrary. For example, the thickness of the GSGG single crystal substrate S is about 600 μm. The surface treatment applied to the GSGG single crystal substrate S is not limited and is arbitrary. For example, the surface of the GSGG single crystal substrate S may be subjected to an etching process such as chemical etching or physical etching and / or a process such as a mirror surface process (mirror surface processing). The GSGG single crystal substrate S has the same or substantially the same composition as the GSGG single crystal C described above, and has the same lattice constant as that of the GSGG single crystal C described above. Therefore, for example, the GSGG single crystal substrate S has a lattice constant of 1.25737 nm or more and 1.25877 nm or less, and can be suitably used for manufacturing an RIG having a lattice constant including at least this range.

(5) Manufacturing method of GSGG single crystal substrate Next, the manufacturing method of the GSGG single crystal substrate which concerns on embodiment is demonstrated. FIG. 6 is a flowchart showing an example of a method for manufacturing a GSGG single crystal substrate according to the embodiment. In addition, the manufacturing method of the GSGG single crystal substrate S demonstrated below is an example, Comprising: The manufacturing method of the GSGG single crystal substrate S is not limited.

  In the manufacturing method of the GSGG single crystal substrate S according to the present embodiment, first, in Step S9 of FIG. 6, the GSGG single crystal substrate S is manufactured from the GSGG single crystal C manufactured by the GSGG single crystal manufacturing method according to the above-described embodiment. It is a manufacturing method. Step S9 is implemented by step S10-step S12, for example.

  First, in step S10, the GSGG single crystal C is divided (sliced) with a predetermined thickness. For example, in step S10, the effective portion EP of the GSGG single crystal C is divided by a predetermined thickness. The effective part EP used in step S10 is cut off from the straight body part SB by a cutting device having an inner peripheral blade or the like, and the outer shape is adjusted by a cylindrical grinder. Further, the effective portion EP is preferably one in which the crystal orientation is faced to (111). The division of the effective portion EP of the GSGG single crystal C is performed by a cutting device such as a wire saw, for example. Although this thickness is not specifically limited, For example, it is about 600 micrometers.

  Subsequently, in step S11 of FIG. 6, the divided GSGG single crystal substrate S is etched. In the etching process, for example, the entire surface of the substrate surface and side surfaces are etched in order to prevent chipping of the substrate end face and scratches on the surface. The etching process is performed, for example, by chemical etching using acid or the like, or physical etching using silica or the like. Whether or not step S11 is performed is arbitrary.

  Subsequently, mirror surface processing is performed in step S12 of FIG. In the mirror surface processing, for example, polishing processing by mechanical polishing using colloidal silica or the like is performed, and the substrate surface is mirror-finished. Through the above steps, the GSGG single crystal substrate S is completed. The manufacturing method of the GSGG single crystal substrate S according to the present embodiment can efficiently manufacture a high-quality GSGG single crystal substrate S. In addition, the method of the mirror surface processing of the GSGG single crystal substrate S is not limited to the said method, but is arbitrary. For example, the mirror finishing may be performed by chemical physical polishing.

(6) RIG
The RIG (not shown) of this embodiment will be described. The RIG of this embodiment is represented by the following chemical formula (1).
Nd _3-x1-y1 Gd _x1 Bi _y1 Fe ₅ O ₁₂ (1)
(In the chemical formula (1), x1 is 0.65 ≦ x1 ≦ 0.84, and y1 is 1.00 ≦ y1 ≦ 1.15.)
In FIG. 7, the Nd-Gd-Bi ternary composition diagram in RIG of this embodiment is shown.

(7) Selection of rare earths The kind of rare earth elements constituting the RIG needs to be Nd and Gd.

  When a crystal is grown on a substrate by a liquid phase epitaxial growth method, the lattice constants of the substrate and the crystal film must be matched. In the GSGG single crystal substrate S having a lattice constant of 1.25737 to 1.25877 nm as described above, since the lattice constant is larger than that of the conventional one, there are a plurality of rare earth elements that can be selected from this large lattice constant.

  However, if Bi having a large ion radius is not included in the RIG, the Faraday rotation performance of the RIG is lowered, the thickness of the RIG necessary for the Faraday rotation angle to be 45 ° increases, and the insertion loss due to light absorption increases. End up. Therefore, it is not preferable to select an element having a large ion radius (for example, La or the like) because it is difficult to contain Bi in RIG.

RIG is generally represented by the following chemical formula (3).
R _3-x3-y3 Gd _x3 Bi _y3 Fe ₅ O ₁₂ (3)
(In chemical formula (3), R is a rare earth element other than Gd.)
Here, as the amount of Bi increases, the thermal expansion coefficient of RIG increases as the amount of Bi increases, so the difference in lattice constant from the substrate increases, RIG cracks during growth, dislocations occur in RIG, etc. There is a problem that productivity is lowered and performance is deteriorated. From past experience, it has been found that when the Bi amount (y3) exceeds 1.3, it is difficult to cultivate a high-quality RIG, and an RIG with a Bi amount exceeding 1.3 is obtained. It is also not preferable to use a rare earth element having a small ion radius (for example, Tm, Yb, Lu, etc.).

  On the other hand, among rare earths with large ionic radii, those with a small segregation coefficient, such as Ce and Pr, are likely to cause lattice mismatch with non-magnetic substrates, and grow high-quality RIGs with high productivity. This is not preferable because it becomes difficult.

  For this reason and the past research results, Nd and Gd were selected as the types of constituent rare earth elements in RIG as described above. Therefore, when Nd and Gd were selected as the rare earth elements constituting RIG, it was confirmed that good insertion loss and high yield were obtained.

(8) Evaluation of insertion loss and non-defective product rate By the way, the temperature rise of the Faraday rotator to which RIG is applied is caused by light absorption near 1 μm by iron ions, and the absorption coefficient increases with the temperature rise. Will result in a temperature rise. For this reason, when the RIG is applied to a 10 W-class processing laser, the insertion loss is required to be 0.35 dB or less.

Table 3 of the examples shows that RIGs having various compositions represented by the above chemical formula (1) are grown by liquid phase epitaxial growth method, the amount of each chemical formula is determined by EPMA quantitative analysis, and then each grown RIG is dicing saw. Then, the thickness of the RIG was adjusted by polishing so that the Faraday rotation angle was 45 ° with respect to light having a wavelength of 1.06 μm, and antireflection films for light having a wavelength of 1.06 μm were formed on both sides. Thereafter, YVO ₄ laser light having a wavelength of 1.06 μm is incident to measure insertion loss, and the results are summarized.

  FIG. 8 is a graph showing the relationship between the amount of Bi chemical formula and insertion loss in RIG. As can be seen from Table 3 and FIG. 7, the insertion loss of RIG tends to decrease as the amount of Bi chemical formula increases. When RIG is applied to a 10W class processing laser, the insertion loss is required to be less than 0.35 dB. Therefore, RIG should have at least a Bi chemical formula of 1.0 or more. Is confirmed.

  In addition, as a rule of thumb, the yield rate of non-defective products at the time of production of RIG is determined to be 90% or higher as a high yield. As can be seen from Table 3, the percentage of acceptable products tends to decrease as the amount of Bi chemical formula increases. When the amount of Bi increases, the thermal expansion coefficient of RIG increases as the amount of Bi increases, so the difference in lattice constant from the substrate increases, causing RIG to crack during growth, causing dislocations in RIG, etc. It is thought that the rate is decreasing. From the results shown in Table 3, it is confirmed that the RIG has a good Bi formula amount of 1.15 or less. The Gd chemical formula amount (x1) may be 3-x1-y1> 0 from the chemical formula (1). However, as shown in Table 3, the Gd chemical formula amount (x1) is limited by the chemical formula amount (y1) of Bi. The Gd chemical formula amount (x1) tends to increase as the Bi chemical formula amount (y1) increases. The Gd chemical formula amount (x1) is preferably 0.65 or more and 0.84 or less. When the Gd chemical formula amount (x1) is at least within this range, as shown in Table 3, the Bi chemical formula amount (y1) is set to the above-described favorable range of 1.00 ≦ y1 ≦ 1.15. Therefore, it is possible to manufacture the above-described high-quality RIG.

  Further, from the results shown in Table 3, the RIG of the present embodiment can be satisfactorily manufactured when the lattice constant of the GSGG single crystal substrate S is in the range of 1.25800 nm to 1.25850 nm, and the lattice constant is 1.25830 nm. If it is, it is confirmed that it can be manufactured more favorably. Further, when the lattice constant is less than 1.25800 nm, the insertion loss exceeds 0.35 dB. If it exceeds 1.25850 nm, the Bi stoichiometry must be increased, and the yield rate is reduced. Moreover, x2 in the said Chemical formula (2) which shows Sc chemical formula amount at this time is 2.065 <= x2 <= 2.117. Incidentally, as described above, conventionally, a single crystal substrate having a lattice constant larger than 1.2564 nm of GSGG and smaller than 1.264 nm of SSGG has not been sold in the market, so that it is difficult to manufacture the RIG. However, since the GSGG single crystal substrate S according to the present embodiment has a lattice coefficient larger than that of the conventional GSGG, it can be suitably applied to the manufacture of such RIG.

  From the above results, in the chemical formula (1), x1 indicating the chemical formula amount of Gd is in the range of 0.65 ≦ x1 ≦ 0.84, and y1 indicating the chemical formula amount of Bi is 1.00 ≦ y1 ≦ It is confirmed that the range of 1.15 is desirable.

  The RIG of the present embodiment as described above has a characteristic of an insertion loss of 0.35 dB or less when applied as a Faraday rotator. Thereby, the RIG of this embodiment can be suitably used as a Faraday rotator. Further, the RIG of the present embodiment can be suitably used as an optical isolator that uses the RIG of the present embodiment as a Faraday rotator. For example, when the RIG of the present embodiment is applied to an optical isolator used for a processing laser or the like, the temperature rise can be significantly suppressed even for a higher power laser beam, so that deterioration of characteristics can be suppressed. .

(9) Manufacturing method of RIG Next, the manufacturing method of RIG which concerns on embodiment is demonstrated. FIG. 9 is a flowchart illustrating an example of a manufacturing method of the RIG according to the embodiment. Note that the RIG manufacturing method described below is an example, and does not limit the RIG manufacturing method.

The manufacturing method of RIG which concerns on embodiment manufactures RIG represented by following Chemical formula (1) by liquid layer epitaxial growth in step S20 of FIG. 9 (A).
Nd _3-x1-y1 Gd _x1 Bi _y1 Fe ₅ O ₁₂ (1)
(In the chemical formula (1), x1 is 0.65 ≦ x1 ≦ 0.84, and y1 is 1.00 ≦ y1 ≦ 1.15.)

  Step S20 in FIG. 9A is performed by, for example, steps S21 to S24 shown in FIG. 9B. In addition, the following description is an example and does not limit step S20.

First, in step S21 in FIG. 9B, a raw material containing Nd, Gd, Bi, and Fe is prepared. For example, the raw materials for RIG include neodymium oxide (Nd ₂ O ₃ ) powder, gallium oxide (Ga ₂ O ₃ ) powder, gadolinium oxide (Gd ₂ O ₃ ) powder, bismuth oxide (Bi ₂ O ₃ ) powder, and monoxide. Lead (PbO) powder, iron oxide (Fe ₂ O ₃ ) powder, boron oxide (B ₂ O ₃ ) powder, or the like is applied. The mixing ratio of these raw materials is appropriately determined depending on the composition of the RIG to be grown. The mixing ratio of each raw material is set so that the composition of the RIG composition to be grown becomes the above-described chemical formula (1). The mixing ratio of each raw material is determined based on conditions such as the composition of the RIG to be grown, the incorporation rate of each element into the RIG, the lattice constant of the substrate to be used, the growth temperature, etc. Can be set by a known method or a preliminary experiment. In addition, said raw material is an example and you may use another raw material.

  Next, in step S22 of FIG. 9B, the raw material is melted. In step S22, for example, the raw material powder prepared in step S21 is filled in a platinum crucible and heated by a known apparatus capable of growing crystals by liquid layer epitaxial growth to melt the raw material powder of the platinum crucible. The melted raw material melt is made uniform by stirring.

  Next, in step S23 of FIG. 9B, the raw material melt is brought into a supersaturated state. In step S23, the temperature of the raw material melt is gradually lowered to bring the raw material melt into a supersaturated state. This temperature is set as the RIG growth temperature. The growth temperature of RIG is determined based on conditions such as the composition of RIG to be grown, the lattice constant, the composition of the raw material, and the like, which influence each other. For example, generally, the Bi chemical formula amount (y1) of the RIG to be grown can be reduced as the growth temperature is higher when the RIG is grown from a raw material melt having the same composition. In general, when RIG is grown from a raw material melt having the same composition, the lattice constant tends to increase as the growth temperature increases. The growth temperature of RIG can be set by a preliminary experiment. The growth temperature of RIG is set to about 770 ° C. to 790 ° C., for example.

  Next, in step S24 of FIG. 9B, the RIG is grown by immersing the substrate in the raw material melt. By step S24, the RIG is grown on the substrate. As the substrate used in step S24 of FIG. 9B, for example, the GSGG single crystal substrate S according to the above-described embodiment is used. As the GSGG single crystal substrate S, a substrate manufactured in advance in step S9 (step S10 to step S12) in FIG. 6 can be used. That is, the RIG manufacturing method according to the present embodiment may include the above-described manufacturing method of the GSGG single crystal substrate S. Further, as described above, the GSGG single crystal substrate S preferably has a lattice constant of 1.25800 nm or more and 1.25850 nm or less, and more preferably 1.25830 nm. Further, when the lattice constant of the GSGG single crystal substrate S is less than 1.25800 nm, the insertion loss exceeds 0.35 dB. Further, when the lattice constant of the GSGG single crystal substrate S exceeds 1.25850 nm, the amount of Bi chemical formula must be increased, and the yield rate of RIG to be grown is reduced. For the immersion of the substrate in the raw material melt, for example, only one side is immersed in the raw material melt. The substrate is immersed in the raw material melt and then rotated at a predetermined rotation speed. Although the rotation speed of a board | substrate is not specifically limited, For example, it sets to about 40-100 rpm. The thickness of the RIG to be grown is not particularly limited, but is set to about 600 μm, for example.

  Next, in step S25 of FIG. 9B, the substrate is removed from the RIG grown on the substrate. In step S25, the substrate is removed from the RIG grown on the substrate, for example, by grinding and polishing. The RIG according to the present embodiment is completed through the above steps. The manufacturing method of RIG which concerns on this embodiment can manufacture RIG which concerns on above-described this embodiment with a high yield.

(10) Optical isolator In the optical isolator according to the embodiment, the RIG according to the present embodiment is used as a Faraday rotator. For example, the optical isolator is composed of a Faraday rotator having a magnetic body that applies a magnetic field to the RIG and the RIG according to the present embodiment, which is a Faraday element, a polarizer, and an analyzer, and transmits light in one direction. , Blocking the return light. The RIG according to the present embodiment is less than 0.35 dB in insertion loss as described above, and the amount of heat generated in the RIG itself can be reduced. Therefore, the RIG according to the present embodiment is suitable as an optical isolator used as a Faraday rotator. Can be used.

  Hereinafter, the present invention will be described in more detail by way of examples and comparative examples of the present invention, but the present invention is not limited to these examples.

  Examples of the present invention will be specifically described below with reference to comparative examples. Reference Examples 1 to 17 are reference examples for manufacturing a GSGG single crystal substrate. Each of Reference Examples 1 to 17 has a composition in which the Sc chemical formula amount x2 of the chemical formula (2) satisfies 2.00 ≦ x2 ≦ 2.15 at the composition design stage. The lattice constant is a value measured using an X-ray diffractometer, and the Sc chemical formula amount is a chemical formula amount obtained from EPMA quantitative analysis.

[Reference Example 1]
A predetermined amount of premixed powder of Gd ₂ O ₃ , Sc ₂ O ₃ , and Ga ₂ O ₃ is charged into an iridium crucible having a diameter of 150 mm and a height of 150 mm, and the high-frequency coil 10 is used using the growth furnace 1 shown in FIG. Then, after the raw material melt 9 was obtained, growth of the GSGG single crystal C was attempted under normal growth conditions to obtain a GSGG single crystal C. The obtained GSGG single crystal C was cut into a wafer shape with an inner peripheral blade, and the lattice constant of the GSGG single crystal substrate S finished to a mirror surface using a polishing liquid such as colloidal silica was measured with an X-ray diffractometer to be 1.25800 nm. It was good. Next, when the Sc content was measured by EPMA quantitative analysis and the chemical formula amount was determined, it was as good as 2.068 at.fu.

[Reference Example 2]
A GSGG single crystal C was grown and processed into a substrate to obtain a GSGG single crystal substrate S, as in Reference Example 1, except that different raw materials were used. When the lattice constant of the GSGG single crystal substrate S was measured with an X-ray diffractometer, it was as good as 1.25850 nm. Next, when the content of Sc was measured by EPMA quantitative analysis to determine the chemical formula amount, it was as good as 2.117 at.fu.

[Reference Example 3]
A GSGG single crystal C was grown and processed into a substrate to obtain a GSGG single crystal substrate S, as in Reference Example 1, except that different raw materials were used. When the lattice constant of the GSGG single crystal substrate S was measured with an X-ray diffractometer, it was as good as 1.25825 nm. Next, when the Sc content was measured by EPMA quantitative analysis and the chemical formula amount was determined, it was as good as 2.093 at.fu.

[Reference Example 4]
A GSGG single crystal C was grown and processed into a substrate to obtain a GSGG single crystal substrate S, as in Reference Example 1, except that different raw materials were used. When the lattice constant of the GSGG single crystal substrate S was measured with an X-ray diffractometer, it was as good as 1.25830 nm. Next, when the content of Sc was measured by EPMA quantitative analysis to determine the chemical formula amount, it was as good as 2.098 at.fu.

[Reference Example 5]
A GSGG single crystal C was grown and processed into a substrate to obtain a GSGG single crystal substrate S, as in Reference Example 1, except that different raw materials were used. When the lattice constant of the GSGG single crystal substrate S was measured with an X-ray diffractometer, it was as good as 1.25800 nm. Next, when the content of Sc was measured by EPMA quantitative analysis to determine the chemical formula amount, it was as good as 2.066 at.fu.

[Reference Example 6]
A GSGG single crystal C was grown and processed into a substrate to obtain a GSGG single crystal substrate S, as in Reference Example 1, except that different raw materials were used. When the lattice constant of the GSGG single crystal substrate S was measured with an X-ray diffractometer, it was as good as 1.25850 nm. Next, when the content of Sc was measured by EPMA quantitative analysis and the chemical formula amount was determined, it was as good as 2.115 at.fu.

[Reference Example 7]
A GSGG single crystal C was grown and processed into a substrate to obtain a GSGG single crystal substrate S, as in Reference Example 1, except that different raw materials were used. When the lattice constant of the GSGG single crystal substrate S was measured with an X-ray diffractometer, it was as good as 1.25835 nm. Next, when the Sc content was measured by EPMA quantitative analysis and the chemical formula amount was determined, it was as good as 2.100 at.fu.

[Reference Example 8]
A GSGG single crystal C was grown and processed into a substrate to obtain a GSGG single crystal substrate S, as in Reference Example 1, except that different raw materials were used. When the lattice constant of the GSGG single crystal substrate S was measured with an X-ray diffractometer, it was as good as 1.25797 nm. Next, when the content of Sc was measured by EPMA quantitative analysis to determine the chemical formula amount, it was 2.064 at.fu.

[Reference Example 9]
A GSGG single crystal C was grown and processed into a substrate to obtain a GSGG single crystal substrate S, as in Reference Example 1, except that different raw materials were used. When the lattice constant of the GSGG single crystal substrate S was measured with an X-ray diffractometer, it was as good as 1.25795 nm. Next, when the Sc content was measured by EPMA quantitative analysis and the chemical formula amount was determined, it was 2.061 at.fu.

[Reference Example 10]
A GSGG single crystal C was grown and processed into a substrate to obtain a GSGG single crystal substrate S, as in Reference Example 1, except that different raw materials were used. When the lattice constant of the GSGG single crystal substrate S was measured with an X-ray diffractometer, it was as good as 1.25853 nm. Next, the Sc content was measured by EPMA quantitative analysis, and the chemical formula amount was determined to be 2.118 at.fu.

[Reference Example 11]
A GSGG single crystal C was grown and processed into a substrate to obtain a GSGG single crystal substrate S, as in Reference Example 1, except that different raw materials were used. When the lattice constant of the GSGG single crystal substrate S was measured with an X-ray diffractometer, it was as good as 1.25855 nm. Next, the Sc content was measured by EPMA quantitative analysis, and the chemical formula amount was determined to be 2.119 at.fu.

[Reference Example 12]
A GSGG single crystal C was grown and processed into a substrate to obtain a GSGG single crystal substrate S, as in Reference Example 1, except that different raw materials were used. When the lattice constant of the GSGG single crystal substrate S was measured with an X-ray diffractometer, it was as good as 1.25737 nm. Next, when the content of Sc was measured by EPMA quantitative analysis to determine the chemical formula amount, it was 2.00 at.fu.

[Reference Example 13]
A GSGG single crystal C was grown and processed into a substrate to obtain a GSGG single crystal substrate S, as in Reference Example 1, except that different raw materials were used. When the lattice constant of the GSGG single crystal substrate S was measured with an X-ray diffractometer, it was as good as 1.25741 nm. Next, when the content of Sc was measured by EPMA quantitative analysis to determine the chemical formula amount, it was 2.03 at.fu.

[Reference Example 14]
A GSGG single crystal C was grown and processed into a substrate to obtain a GSGG single crystal substrate S, as in Reference Example 1, except that different raw materials were used. When the lattice constant of the GSGG single crystal substrate S was measured with an X-ray diffractometer, it was as good as 1.25797 nm. Next, the Sc content was measured by EPMA quantitative analysis to determine the chemical formula amount, which was 2.06 at.fu.

[Reference Example 15]
A GSGG single crystal C was grown and processed into a substrate to obtain a GSGG single crystal substrate S, as in Reference Example 1, except that different raw materials were used. When the lattice constant of the GSGG single crystal substrate S was measured with an X-ray diffractometer, it was as good as 1.25814 nm. Next, the Sc content was measured by EPMA quantitative analysis to determine the chemical formula amount, which was 2.09 at.fu.

[Reference Example 16]
A GSGG single crystal C was grown and processed into a substrate to obtain a GSGG single crystal substrate S, as in Reference Example 1, except that different raw materials were used. When the lattice constant of the GSGG single crystal substrate S was measured with an X-ray diffractometer, it was as good as 1.25863 nm. Next, the Sc content was measured by EPMA quantitative analysis, and the chemical formula amount was determined to be 2.12 at.fu.

[Reference Example 17]
A GSGG single crystal C was grown and processed into a substrate to obtain a GSGG single crystal substrate S, as in Reference Example 1, except that different raw materials were used. When the lattice constant of the GSGG single crystal substrate S was measured with an X-ray diffractometer, it was as good as 1.25877 nm. Next, the Sc content was measured by EPMA quantitative analysis, and the chemical formula amount was determined to be 2.15 at.fu.

These results are summarized in Table 2.

Next, an example of the RIG according to the embodiment manufactured using the GSGG single crystal substrate S according to the embodiment will be specifically described. Examples 1 to 10 are examples in which RIG represented by the following chemical formula (1) is manufactured using the GSGG single crystal substrate S according to the embodiment.
Nd _3-x1-y1 Gd _x1 Bi _y1 Fe ₅ O ₁₂ (1)
(In the chemical formula (1), x1 is 0.65 ≦ x1 ≦ 0.84, and y1 is 1.00 ≦ y1 ≦ 1.15.) In Examples 1 to 6 and Comparative Examples 1 to 4, For all the GSGG single crystal substrates S, the GSGG single crystal substrate S of Reference Example 4 having a diameter of 1 inch and a lattice constant of 1.25830 nm was used. In Example 7, the GSGG single crystal substrate S of Reference Example 1 was used, and in Example 8, the GSGG single crystal substrate S of Reference Example 2 was used.

  Incidentally, the Bi amount and the Gd amount are values of the chemical formula amount obtained from the EPMA quantitative analysis. In addition, the defect rate and non-defective rate are each 11 mm square cut from the RIG, and then 100 mm from the 11 mm square to 100 mm, and then from the 1 mm square, depending on the shape or the number of pits in the surface, It is the result obtained by sorting. As for defective products, those with corner chipping deformation due to cracks generated during RIG, or those with no corner chipping, but having 5 or more pits in a 1 mm square plane by observation with a metal microscope or infrared microscope. Similarly, the non-defective product was selected as having no corners and the number of in-plane pits was 5 or less, and the occurrence rates based on the results were also shown. Table 3 compares the RIG defect rate, non-defective rate, and insertion loss according to the example and the comparative example.

  The acceptance criteria were such that the insertion loss representing the light absorption amount was ≦ 0.35, and the yield rate at that time was 90% or more.

[Example 1]
First, as a raw material, 2.20 g of _{Nd 2 O 3, Gd 2 O} 3 to 2.37 g, 29.27 g of _{Fe 2 O 3, Bi 2 O} 3 to 254.97g, 201.52g of _{PbO, B} 2 O Each 9.67 g of ₃ was weighed, dissolved in a platinum crucible at 1000 ° C., and sufficiently stirred and mixed so that the melt had a uniform composition.

  Next, in order to epitaxially grow RIG, the temperature of the melt was lowered to a growth temperature of 780 ° C. Thereafter, the GSGG substrate was placed so that only one surface was immersed in the melt, and RIG was epitaxially grown while rotating the GSGG substrate. When the obtained RIG was quantitatively analyzed by EPMA, the Bi amount was 1.15 and the Gd amount was 0.78.

When an 11 mm square and further a 1 mm square were cut from the RIG grown under such conditions and observed, 10 defective products and 90 good products were good. Further, after adjusting the thickness of the RIG by polishing so that the Faraday rotation angle is 45 ° with respect to light having a wavelength of 1.06 μm, an antireflection film for light having a wavelength of 1.06 μm is formed on both surfaces, and then the wavelength 1 When .06 μm YVO ₄ laser light was incident and the insertion loss (IL) was measured, the result was very good at 0.31 dB.

[Example 2]
As raw materials, 2.26 g of Nd ₂ O ₃ , 2.31 g of Gd ₂ O ₃ , 29.27 g of Fe ₂ O ₃ , 254.97 g of Bi ₂ O ₃ , 201.52 g of PbO and B ₂ O ₃ were used. RIG was grown in the same manner as in Example 1 except that 9.67 g was weighed and the raw material composition was changed, and the growth temperature was 781 ° C. The obtained RIG had a Bi content of 1.13 and a Gd content of 0.75.

When RIG was observed in the same manner as in Example 1, there were 8 defective products and 92 non-defective products. Further, after adjusting the thickness of the RIG by polishing so that the Faraday rotation angle is 45 ° with respect to light having a wavelength of 1.06 μm, an antireflection film for light having a wavelength of 1.06 μm is formed on both surfaces, and then the wavelength 1 When .06 μm YVO ₄ laser light was incident and the insertion loss (IL) was measured, the result was very good at 0.32 dB.

[Example 3]
As raw materials, Nd ₂ O ₃ 2.48 g, Gd ₂ O ₃ 2.40 g, Fe ₂ O ₃ 29.11 g, Bi ₂ O ₃ 254.88 g, PbO 201.45 g, B ₂ O ₃ RIG was grown in the same manner as in Example 1 except that 9.67 g was weighed and the raw material composition was changed, and the growth temperature was changed to 786 ° C. The obtained RIG had a Bi content of 1.08 and a Gd content of 0.73.

When RIG was observed in the same manner as in Example 1, the number of defective products was 5 and the number of non-defective products was 95, which was extremely good. Further, after adjusting the thickness of the RIG by polishing so that the Faraday rotation angle is 45 ° with respect to light having a wavelength of 1.06 μm, an antireflection film for light having a wavelength of 1.06 μm is formed on both surfaces, and then the wavelength 1 When .06 μm YVO ₄ laser light was incident and the insertion loss (IL) was measured, it was a good result of 0.34 dB.

[Example 4]
As raw materials, Nd ₂ O ₃ 2.40 g, Gd ₂ O ₃ 2.33 g, Fe ₂ O ₃ 29.19 g, Bi ₂ O ₃ 254.93 g, PbO 201.49 g, B ₂ O ₃ RIG was grown in the same manner as in Example 1 except that 9.67 g was weighed and the raw material composition was changed, and the growth temperature was changed to 784 ° C. The obtained RIG had a Bi content of 1.05 and a Gd content of 0.73.

When RIG was observed in the same manner as in Example 1, the number of defective products was 4 and the number of non-defective products was 96, which was extremely good. Further, after adjusting the thickness of the RIG by polishing so that the Faraday rotation angle is 45 ° with respect to light having a wavelength of 1.06 μm, an antireflection film for light having a wavelength of 1.06 μm is formed on both surfaces, and then the wavelength 1 When .06 μm YVO ₄ laser light was incident and the insertion loss (IL) was measured, it was a good result of 0.34 dB.

[Example 5]
As raw materials, Nd ₂ O ₃ 2.36 g, Gd ₂ O ₃ 2.37 g, Fe ₂ O ₃ 29.19 g, Bi ₂ O ₃ 254.93 g, PbO 201.49 g, B ₂ O ₃ RIG was grown in the same manner as in Example 1 except that 9.67 g was weighed and the raw material composition was changed, and the growth temperature was changed to 784 ° C. The obtained RIG had a Bi content of 1.00 and a Gd content of 0.69.

When RIG was observed in the same manner as in Example 1, it was found that 2 defective products and 98 non-defective products were extremely good. Further, after adjusting the thickness of the RIG by polishing so that the Faraday rotation angle is 45 ° with respect to light having a wavelength of 1.06 μm, an antireflection film for light having a wavelength of 1.06 μm is formed on both surfaces, and then the wavelength 1 When .06 μm YVO ₄ laser light was incident and the insertion loss (IL) was measured, it was a good result of 0.35 dB.

[Example 6]
As raw materials, 2.51 g of Nd ₂ O ₃ , 2.57 g of Gd ₂ O ₃ , 29.02 g of Fe ₂ O ₃ , 254.83 g of Bi ₂ O ₃ , 201.41 g of PbO and B ₂ O ₃ RIG was grown in the same manner as in Example 1 except that 9.67 g was weighed and the raw material composition was changed, and the growth temperature was changed to 787 ° C. The obtained RIG had a Bi amount of 1.10 and a Gd amount of 0.74.

When RIG was observed in the same manner as in Example 1, the number of defective products was 4 and the number of non-defective products was 96, which was extremely good. Further, after adjusting the thickness of the RIG by polishing so that the Faraday rotation angle is 45 ° with respect to light having a wavelength of 1.06 μm, an antireflection film for light having a wavelength of 1.06 μm is formed on both surfaces, and then the wavelength 1 When .06 μm YVO ₄ laser light was incident and the insertion loss (IL) was measured, it was a good result of 0.33 dB.

[Example 7]
As raw materials, Nd ₂ O ₃ 2.29 g, Gd ₂ O ₃ 2.34 g, Fe ₂ O ₃ 29.24 g, Bi ₂ O ₃ 254.95 g, PbO 201.51 g, B ₂ O ₃ RIG was grown in the same manner as in Example 1 except that 9.67 g was weighed and the raw material composition was changed, and the growth temperature was changed to 786 ° C. The obtained RIG had a Bi content of 1.15 and a Gd content of 0.84.

When RIG was observed in the same manner as in Example 1, 10 defective products and 90 good products were found to be good. Further, after adjusting the thickness of the RIG by polishing so that the Faraday rotation angle is 45 ° with respect to light having a wavelength of 1.06 μm, an antireflection film for light having a wavelength of 1.06 μm is formed on both surfaces, and then the wavelength 1 When .06 μm YVO ₄ laser light was incident and the insertion loss (IL) was measured, the result was very good at 0.31 dB.

[Example 8]
As raw materials, Nd ₂ O ₃ 2.36 g, Gd ₂ O ₃ 2.37 g, Fe ₂ O ₃ 29.19 g, Bi ₂ O ₃ 254.93 g, PbO 201.49 g, B ₂ O ₃ RIG was grown in the same manner as in Example 1 except that 9.67 g was weighed and the raw material composition was changed, and the growth temperature was 782 ° C. The obtained RIG had a Bi content of 1.00 and a Gd content of 0.65.

When RIG was observed in the same manner as in Example 1, the number of defective products was 4 and the number of non-defective products was 96, which was extremely good. Further, after adjusting the thickness of the RIG by polishing so that the Faraday rotation angle is 45 ° with respect to light having a wavelength of 1.06 μm, an antireflection film for light having a wavelength of 1.06 μm is formed on both surfaces, and then the wavelength 1 When .06 μm YVO ₄ laser light was incident and the insertion loss (IL) was measured, it was a good result of 0.34 dB.

[Comparative Example 1]
As raw materials, 2.30 g of Nd ₂ O ₃ , 2.60 g of Gd ₂ O ₃ , 29.11 g of Fe ₂ O ₃ , 254.87 g of Bi ₂ O ₃ , 201.44 g of PbO and B ₂ O ₃ were used. RIG was grown in the same manner as in Example 1 except that 9.67 g was weighed and the raw material composition was changed, and the growth temperature was changed to 784 ° C. The obtained RIG had a Bi content of 1.16 and a Gd content of 0.78.

When RIG was observed in the same manner as in Example 1, 12 defective products and 88 non-defective products were defective. Further, after adjusting the thickness of the RIG by polishing so that the Faraday rotation angle is 45 ° with respect to light having a wavelength of 1.06 μm, an antireflection film for light having a wavelength of 1.06 μm is formed on both surfaces, and then the wavelength 1 When .06 μm YVO ₄ laser light was incident and the insertion loss (IL) was measured, the result was very good at 0.32 dB. However, there were 12 defective products and 88 good products, and the non-defective product rate was 90% or less.

[Comparative Example 2]
As a raw material, 2.36 g of _Nd 2 _{O 3,} 2.37g of _Gd 2 _{O 3, 29.19g} of _Fe 2 _{O 3, 254.93g} of _Bi 2 _{O 3, 201.48g} of _PbO, the B 2 _{O 3} RIG was grown in the same manner as in Example 1 except that 9.67 g was weighed and the raw material composition was changed, and the growth temperature was changed to 783 ° C. The obtained RIG had a Bi content of 0.99 and a Gd content of 0.71.

When RIG was observed in the same manner as in Example 1, one defective product and 99 non-defective products were found to be extremely good. Further, after adjusting the thickness of the RIG by polishing so that the Faraday rotation angle is 45 ° with respect to light having a wavelength of 1.06 μm, an antireflection film for light having a wavelength of 1.06 μm is formed on both surfaces, and then the wavelength 1 When .06 μm YVO ₄ laser light was incident and the insertion loss (IL) was measured, it was as poor as 0.36 dB.

[Comparative Example 3]
As a raw material, 2.31 g of _Nd 2 _{O 3,} 2.44g of _Gd 2 _{O 3, 29.28g} of _Fe 2 _{O 3, 254.61g} of _Bi 2 _{O 3, 201.24g} of _PbO, the B 2 _{O 3} RIG was grown in the same manner as in Example 1 except that 10.12 g each was weighed to change the raw material composition and the growth temperature was 782 ° C. The RIG obtained had a Bi content of 1.17 and a Gd content of 0.78.

When RIG was observed in the same manner as in Example 1, 13 defective products and 87 non-defective products were defective. Further, after adjusting the thickness of the RIG by polishing so that the Faraday rotation angle is 45 ° with respect to light having a wavelength of 1.06 μm, an antireflection film for light having a wavelength of 1.06 μm is formed on both surfaces, and then the wavelength 1 When .06 μm YVO ₄ laser light was incident and the insertion loss (IL) was measured, it was very good at 0.31 dB, but it was 13 defective products, 87 good products, and the non-defective product rate was 90% or less. It was.

[Comparative Example 4]
As raw materials, 2.27 g of Nd ₂ O ₃ , 2.45 g of Gd ₂ O ₃ , 29.11 g of Fe ₂ O ₃ , 255.21 g of Bi ₂ O ₃ , 201.71 g of PbO and B ₂ O ₃ were used. RIG was grown in the same manner as in Example 1 except that 9.25 g was weighed and the raw material composition was changed, and the growth temperature was 783 ° C. The obtained RIG had a Bi content of 0.98 and a Gd content of 0.71.

When RIG was observed in the same manner as in Example 1, one defective product and 99 non-defective products were found to be extremely good. Further, after adjusting the thickness of the RIG by polishing so that the Faraday rotation angle is 45 ° with respect to light having a wavelength of 1.06 μm, an antireflection film for light having a wavelength of 1.06 μm is formed on both surfaces, and then the wavelength 1 When .06 μm YVO ₄ laser light was incident and the insertion loss (IL) was measured, it was as poor as 0.37 dB.

These results are summarized in Table 3.

  As described above, the bismuth-substituted rare earth iron garnet crystal film (RIG) according to the present invention has an insertion loss of 0.35 dB or less compared to the conventional RIG described in Patent Document 1 and the like, and It can be produced with high yield. Further, by applying the RIG of the present invention with an insertion loss of 0.35 dB or less, the amount of heat generated in the RIG itself can be reduced. Therefore, when the RIG of the present invention is applied to an optical isolator for a processing laser, it is higher. Since the temperature rise can be significantly suppressed with respect to the power laser beam, it has the effect of suppressing the deterioration of characteristics. Moreover, the manufacturing method of RIG which concerns on this invention can manufacture good quality RIG with a high yield. In addition, since the optical isolator according to the present invention includes the RIG described above, it is possible to significantly suppress a temperature rise with respect to a higher-power laser beam, and to suppress deterioration of characteristics.

  The technical scope of the present invention is not limited to the aspects described in the above-described embodiments. One or more of the requirements described in the above embodiments and the like may be omitted. In addition, the requirements described in the above-described embodiments and the like can be combined as appropriate. In addition, as long as it is permitted by law, the disclosure of all documents cited in the above-described embodiments and the like is incorporated as a part of the description of the text.

  The RIG according to the present invention has an insertion loss of 0.35 dB or less. Since the RIG according to the present invention can reduce the amount of heat generated due to light absorption at a wavelength of about 1 μm, the industrial applicability used in the Faraday rotator for optical isolators of high-power laser devices for processing can be reduced. Have.

DESCRIPTION OF SYMBOLS 1 ... Growing furnace 2 ... Chamber 3 ... Heat insulating material 4 ... Shaft 5 ... Hot zone 8 ... Crucible 9 ... Raw material melt 10 ... High frequency coil CONT ... Control part C ... GSGG single crystal S ... GSGG single crystal substrate SC ... seed crystal SH ... shoulder part SB ... straight barrel part SBa ... lower end EP ... effective part

Claims (6)

A bismuth-substituted rare earth iron garnet crystal film represented by the following chemical formula (1).
Nd _3-x1-y1 Gd _x1 Bi _y1 Fe ₅ O ₁₂ (1)
(In the chemical formula (1), x1 is 0.65 ≦ x1 ≦ 0.84, and y1 is 1.00 ≦ y1 ≦ 1.15.)   An optical isolator in which the bismuth-substituted rare earth iron garnet crystal film according to claim 1 is used for a Faraday rotator. A method for producing a bismuth-substituted rare earth iron garnet crystal film, wherein a bismuth-substituted rare earth iron garnet crystal film represented by the following formula (1) is grown on a nonmagnetic garnet single crystal substrate by a liquid phase epitaxial growth method.
Nd _3-x1-y1 Gd _x1 Bi _y1 Fe ₅ O ₁₂ (1)
(In the chemical formula (1), x1 is 0.65 ≦ x1 ≦ 0.84, and y1 is 1.00 ≦ y1 ≦ 1.15.) The said nonmagnetic garnet single crystal substrate is a manufacturing method of the bismuth substitution type rare earth iron garnet crystal film of Claim 3 represented by following formula (2).
Gd ₃ Sc _x2 Ga _5-x2 O ₁₂ (2)
(In the chemical formula (2), x2 is 2.065 ≦ x2 ≦ 2.117.)   The method for producing a bismuth-substituted rare earth iron garnet crystal film according to claim 3 or 4, wherein the nonmagnetic garnet single crystal substrate has a lattice constant of 1.25800 nm or more and 1.25850 nm or less. The method for producing a bismuth-substituted rare earth iron garnet crystal film according to any one of claims 3 to 5, wherein the nonmagnetic garnet single crystal substrate has a lattice constant of 1.25830 nm.

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