JP2794306B2 - Magnetic garnet material and Faraday rotating element - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a magnetic garnet material, a Faraday rotator using the same, and an optical isolator using the Faraday rotator to eliminate reflection noise.

(Prior Art) The use of an optical isolator has been proposed for removing reflected noise in optical communication using a semiconductor laser, optical measurement equipment, and the like. An optical isolator is a device that removes reflected light by inserting a Faraday rotator into the optical path of a semiconductor laser and rotating the plane of polarization of the reflected light by approximately 90 ° with respect to the plane of polarization of the original light. In other words, since the Faraday rotator is a magneto-optical element having a function of rotating the plane of polarization according to the magnitude of the external magnetic field, the thickness of the element and the external magnetic field are adjusted to rotate the plane of polarization of the transmitted light by about 45 °. If it is adjusted to, the plane of polarization will rotate about 90 ° between going and returning. Therefore, it is optimal for removing reflection noise of laser light having a fixed wavelength, and can be easily adjusted so as to be adaptable to laser lights of different wavelengths.

As main Faraday rotators (magneto-optical elements) for optical isolators, YIG-based bulk single crystals and Bi-substituted rare earth iron garnets are known.

The YIG-based Faraday rotator has the advantage of a small change in rotation angle with respect to temperature and light wavelength, but has a small Faraday rotator (about 220 ° / c for a YIG single crystal).
m), the crystal diameter is small (12 mm or less), and the productivity is poor. For this reason, practically, Bi-substituted rare earth iron garnets which have a large Faraday rotation capability, a large crystal diameter (50 mmφ or more), and are thin and good are mainly used. The present invention relates to an improvement of this type of Faraday rotator.

(Problems to be Solved) However, Bi-substituted rare earth iron garnet has a large Faraday rotation ability, but a large change in temperature and wavelength of the rotation angle, and a large deviation in the rotation angle due to the difference in temperature and wavelength. Various proposals have hitherto been made to solve this problem, but no satisfactory Faraday rotator made of a Bi-substituted rare earth iron garnet material has been proposed. As an attempt to reduce the temperature coefficient, there is a method of replacing a part of Bi with Tb, Dy, or the like. As a result, the temperature coefficient of the rotation angle decreased, but the Faraday rotation ability decreased due to the decrease in Bi, and it was necessary to increase the crystal thickness accordingly.

(Problems to be Solved by the Invention) Bi-substituted rare earth iron garnet materials to which Tb or the like is added
Although it is necessary to increase the film thickness as described above, the problem of cracks occurs due to the increase in the film thickness, and the product yield is reduced, and the product yield is reduced overall. That is,
This type of Faraday rotator uses a GGG (Gd ₃ Ga ₅ O ₁₂ or one in which some of these components are replaced with other elements) substrate, but a Bi-substituted rare earth iron garnet to which Tb or the like is added. The difference in thermal expansion coefficient between the material and the substrate is large, for example, 200μ
When growing the crystal to a thickness of 400 m or more, especially 400 μm or more, concentric cracks are slightly different as it goes to the outer circumference, leaving a groove on the outer circumference side after surface polishing, diameter about 50 mm, rotation angle 45 ° The area of the inner part which can be polished to a considerable thickness and then cut out and collected is limited, thereby reducing the overall yield.

As an attempt to solve the cracking problem, there is a method of intentionally cracking the substrate from the beginning to limit irregular cracking in the Bi-substituted rare earth iron garnet crystal film (Japanese Patent Laid-Open No. Sho 62-29).
No. 2694) It is not an essential solution. It has also been proposed to laminate two or more layers of different materials (JP-A-63-69799, JP-A-63-270396, JP-A-63-110417).
No.), and the process becomes complicated, which is not preferable. Other, thick film
Although there are a large number of references mentioning Bi-substituted rare earth iron garnet materials, they have not examined or recognized the problem of cracking (for example, Japanese Patent Application Laid-Open No. 63-159225 ... However, the problem of cracking cannot be avoided from the viewpoint of the composition and the production method), but if the problem of cracking is considered, there must have been a limit to thickening the film.

(Object of the Invention) Accordingly, an object of the present invention is to provide a magnetic garnet material, a Faraday rotator using the same, and an optical isolator that uses the Faraday rotator to eliminate reflection noise, thereby increasing the crack ( The problem is to solve the problem of (crack) and improve the yield of products.

Magnetic garnet material (SUMMARY OF THE INVENTION) The present _{invention, Bi x Nd y Tb z A} 3-xyz Fe 5-w B w O 12 becomes a magnetic garnet material (wherein A having a composition represented by the chemical formula Bi, Nd, And at least one element selected from the group consisting of other rare earth elements and Y and the like which can be substituted for Tb, and B is a group consisting of elements such as Sc, Ga, Al and In which can be substituted for Fe. X, y, z, and w are values satisfying 0.5 ≦ x ≦ 1.0 0.05 ≦ y ≦ 0.5 1.5 ≦ z ≦ 2.45 0 ≦ w ≦ 0.5).

The Faraday rotation element of the present invention is an optical element using the above-mentioned material.

The isolator of the present invention is a device in which this Faraday rotator is incorporated in an optical transmission system.

According to the present invention, cracking does not occur even when a thick film is formed, particularly when a film having a thickness of 700 μm or more is formed, so that the quality is stabilized and the product yield is improved.

(Specific Description of the Invention) The present invention relates to a conventionally known Bi-substituted rare earth iron garnet,
It relates to improvements, the basic composition of which is known. That, Bi substituted rare earth iron garnet used as a basic composition in the present invention is represented by _{Bi x Tb z A 3-xyz} Fe 5-w B w O 12. Here, A is zero (JP-A-62-105931) or a small amount of Gd (JP-A-63-35421), La (JP-A-63-15921).
225), Yb (JP-A-62-288199), Pr (JP-A-64-3)
No. 6005) and B is zero or a small amount of Al, G
a, In, Sc, etc. Refer to the respective documents for reasons and amounts of addition of these components. With respect to x, z and w in the present invention, generally conventional selection criteria hold.

The present invention is characterized in that Nd is further added in order to solve the problem of cracks that can occur when forming a thick film. As seen above, it has been proposed to add a rare earth metal element to improve the Faraday rotability, etc., but specific examples of adding Nd are described in conventional literature for any purpose. And there is no suggestion as a means to control or prevent cracking which is the subject of the present invention.

More specifically, the present invention relates to a magnetic garnet material represented by the chemical formula of Bi _x Nd _y Tb _z A _3-xyz Fe _5-w B _w O _12, a Faraday rotating element using the same, and an isolator using the same. (Where A is one or more elements selected from the group consisting of other rare earth elements which can be substituted for Bi, Nd, and Tb and elements such as Y, and B is Sc, Ga, Al, which can be substituted for Fe, In
One or more elements selected from the group consisting of
X, y, z, and w are numerical values satisfying 0.5 ≦ x ≦ 1.0 0.05 ≦ y ≦ 0.5 1.5 ≦ z ≦ 2.450 ≦ w ≦ 0.5).

The reasons for limiting the ranges of x, y, z and w in the above composition are as follows.

If x is too small, the Faraday rotation ability decreases, and if it is too large, the temperature change and wavelength change of the Faraday rotation angle increase. If y is too small, there is no effect on crack prevention, and if y is too large, light absorption loss increases. If z is too small, the temperature stability is lost, and if it is too large, the Faraday rotation ability is reduced.

In the present invention, by setting the composition and the component ratio in the above ranges, a thickness sufficient to compensate for the decrease in the Faraday rotation ability due to the addition of the temperature stabilizer Tb is achieved without causing a cracking problem. I can do it. According to the present invention,
It was found that when a film was formed with a thickness of about 500 μm on a GGG substrate having a diameter of 50 mm with a certain composition, neither crack nor swirl was generated, and therefore, 100% yield could be achieved.

 Hereinafter, examples of the present invention will be described in detail.

Examples 1, 2, 3, 4, 5 and Comparative Examples 1, 2, 3 Ca—Mg—Zr substitution using a PbO—Bi ₂ O ₃ —B ₂ O ₃ flux and having a lattice constant a of 12.496 as a substrate A magnetic garnet film having the composition and thickness shown in the following Tables 1 to 8 was formed on this substrate by a well-known liquid phase epitaxial growth method using a single crystal plate of 50 mm in diameter of GGG. Next, for two types of laser light wavelengths, the Faraday rotation ability (rotation angle of the polarization plane per 1 cm of transmission length), temperature characteristics (fluctuation of the rotation angle of the polarization plane per 1 ° C., ie, temperature coefficient), and wavelength characteristics (per 1 nm) The variation of the rotation angle of the polarization plane, that is, the wavelength coefficient, the cracks (cracks, the depth of the cracks around the sample), and the swirl (the depth of the spiral growth pattern) were measured.
The results are shown in these tables.

(Effects) From the table, it can be seen that cracking and swirl are significantly improved by adding Nd according to the present invention. The addition of Nd lowers the Faraday rotatory power, but can be easily compensated for by increasing the thickness. Since the swirl portion can be easily removed by surface polishing, the Faraday rotator can be cut out at a yield of 100%.

Further, it can be seen that the temperature characteristics and the wavelength characteristics are not inferior to those of the related art.

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G02F 1/09-1/095 G02B 27/28 C30B 28/00-35/00 H01F 1/12-1/375 H01F 10 / 00-10/30 H01F 41/14-41/28 G11B 11/00-13/06 G01R 33/00-33/64 G01R 15/00-17/22 CA (STN) REGISTRY (STN)

Claims (3)

(57) [Claims] 1. A magnetic garnet material having a composition represented by the chemical formula of Bi _x Nd _y Tb _z A _3-xyz Fe _5-w B _w O ₁₂ (where A is Bi, Nd, and other R is at least one element selected from the group consisting of rare earth elements and Y, and B is
At least one element selected from the group consisting of elements such as Sc, Ga, Al, and In which can be substituted for Fe, and x, y, z, and w are 0.5 ≦ x ≦ 1.0 0.05 ≦ y ≦ 0.5 1.5 ≦ z ≦ 2.45 0 ≦ w ≦ 0.5). 2. A Faraday rotator represented by a chemical formula of Bi _x Nd _y Tb _z A _3-xyz Fe _5-w B _w O ₁₂ (where A is Bi, Nd,
And at least one element selected from the group consisting of Y and other rare earth elements that can be substituted for Tb, and B is a kind selected from the group consisting of elements such as Sc, Ga, Al, and In that can be substituted for Fe. The above elements, and x, y, z and w are numerical values satisfying 0.5 ≦ x ≦ 1.0 0.05 ≦ y ≦ 0.5 1.5 ≦ z ≦ 2.450 ≦ w ≦ 0.5). 3. An optical isolator using the Faraday rotator according to claim 2.