JPH0424684B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for producing magneto-optic garnets used as optical isolator materials. [Prior Art] In general, information is recorded on and read out from optical disks and magneto-optical disks using a semiconductor laser as a light source, but some of the light emitted from the semiconductor laser as a light source is Returning to a semiconductor laser causes inconveniences such as mode hopping noise, so an optical isolator is required to block this returning light. As shown in Fig. 1, the optical isolator is composed of a Faraday rotator 1 that rotates the plane of polarization of light oscillated by a light source by 45 degrees, an analyzer 2 and a polarizer 3 placed between it. . Here, polarizer 2,
The optical axes of the analyzers 3 are tilted at 45 degrees with respect to each other. That is, after the polarized light emitted from the semiconductor laser 4 passes through the polarizer 2, the plane of polarization is rotated by 45 degrees by the Faraday rotator 1, and passes through the analyzer 3 (hereinafter, this light is referred to as forward light 5). . On the other hand, light in the opposite direction, such as light 5 in the forward direction that has passed through an optical isolator and returned after being reflected by an optical disk etc., has its polarization plane rotated by 45 degrees again by the Faraday rotator 1. The plane of polarization is tilted 90 degrees with respect to the optical axis of polarizer 2. Therefore, it cannot pass through this polarizer 2. Based on the above principle, the optical isolator blocks the return light 6. In this optical isolator, it is desired that the loss of light in the forward direction be as small as possible, and for this purpose, the thickness of the Faraday rotator is made thin. Or/and it is necessary to reduce the optical absorption coefficient α of the magnetic garnet crystal serving as the Faraday rotator. One way to make the Faraday rotator thinner, that is, to increase the amount of Faraday rotation per unit length (hereinafter referred to as the Faraday rotation coefficient), is to use a material in which the rare earth elements located at the dodecahedral sites of magnetic garnet are replaced with a large amount of Bi ( It is effective to use Bi-substituted magnetic garnet (hereinafter referred to as Bi-substituted magnetic garnet). In optical communication systems that use light with a wavelength of 1.3 to 1.55 μm, thick films of (GdBi) ₃ (FeAlGa) ₅ O ₁₂ (Bi-substituted iron, aluminum, and gallium garnet) crystals grown by the LDE method, which can be produced in large quantities, are used. , the optical absorption in this wavelength range is quite small (absorption coefficient,
α<2cm ^-1 ), it has already been put into practical use as an optical isolator material. It has been proposed to use this magnetic garnet thick film as an optical isolator material in a wavelength range of 0.78 to 0.83 .mu.m, usually referred to as the 0.8 .mu.m band, used in optical disks and magneto-optical disks. [Problem to be solved by the invention] However, in the wavelength range of 0.78 to 0.83 μm,
Magnetic garnets have unavoidable light absorption due to the presence of trivalent iron (Fe ³⁺ ), and because these light absorptions overlap, they exhibit considerably large light absorption. In order to realize an optical isolator with low insertion loss in this wavelength range, it is necessary to reduce optical absorption in a magnetic garnet film with a large amount of Bi substituted. The inclusion of impurities from materials and flux is unavoidable, and no insertion loss per 45 degrees has been reported to be less than 1.5 dB. On the other hand, in recent years, in the ion beam sputtering method that does not use a crucible or flux, garnets whose 12 sides are occupied by Bi, that is,
The synthesis of bismuth iron garnet (Bi ₃ Fe ₅ O ₁₂ ) has been reported, and the figure of merit (Faraday rotation angle per 1 dB of insertion loss) at a wavelength of 0.8 μm is 55
(deg/dB) is obtained. In other words, the insertion loss per Faraday rotation angle of 45 degrees is 0.8 dB.
However, when depositing garnet by sputtering, there is a drawback that the film thickness cannot be precisely controlled. For example, when trying to obtain a film thickness (18 μm) that causes a Faraday rotation of 45 degrees at a wavelength of 0.78 μm,
The actual film thickness that can be obtained varies within a range of 18 ± 4 μm. That is, there was a problem in that the Faraday rotation angle varied within a range of 45±10 degrees. To solve this problem, it is possible to deposit a film thicker than 18 μm in advance and polish it to 18 μm, but bismuth iron garnet is extremely brittle, and cracks may occur during polishing or minute scratches may occur on the surface. It is often impractical. The technical problem of the present invention is to control the Faraday rotation of the entire crystal to 45 degrees by depositing a garnet film with a Faraday rotation of less than 45 degrees by ion beam sputtering, and then growing a thin film using the LPE method.
The present invention provides a method for producing magneto-optic garnets used as optical isolator materials in the 0.8 μm band. [Means for Solving the Problems] According to the present invention, a Faraday rotation of 45
A method for producing a magneto-optic garnet is obtained, which is characterized in that a garnet film of less than a few degrees is provided at a time, and a thin film is grown on the garnet film by the LPE method. Furthermore, the nonmagnetic garnet substrate to which the present invention can be applied is not limited to samarium scandium gallium garnet or gadolinium scandium gallium garnet, but also nonmagnetic garnet substrates typified by gadolinium gallium garnet (GGG). It covers everything. Furthermore, the composition of the ion beam sputtered thin film that can be applied to the present invention is not limited to Bi ₃ Fe ₅ O ₁₂ .
Bi ₃ Fe _5-x M _x O ₁₂ (x=0~2 M is Ga or/
and Al). Further, the LPE membrane to which the present invention can be applied is Pr _1.5
It is not limited to Bi _1.5 Fe ₄ Ca ₁ O ₁₂ but covers all Bi-substituted magnetic garnets. [Example] An example of the present invention will be described. A Faraday rotation angle of 36 degrees (film thickness
When bismuth iron garnet (Bi ₃ Fe ₅ O ₁₂ ) was deposited to give a thickness of 14.4 μm), the Faraday rotation varied within a range of 36±9 degrees due to variations in the film thickness. On these sputtered films, a Pr _1.5 Bi _1.5 Fe ₄ Ga ₁ O ₁₂ thin film (film thickness 0 to 6 μm) with a Faraday rotation angle of 0 to 9 degrees was grown using the LPE method so that all Faraday rotation angles were 45 degrees. did. The surfaces of these samples after LPE growth were all mirror surfaces, and could be used as Faraday rotators for optical isolators. Further, the optical insertion loss of the sample was 0.8 to 1.0 dB, as shown in Table 1. In Table 1,
For comparison, we also show the minimum insertion loss value reported for a Bi-substituted magnetic garnet thick film grown by the LPE method. In other words, the insertion loss when the thin film was grown by LPE after being deposited by ion beam sputtering was smaller than that of the magnetic garnet film grown by LPE alone. The wavelength range to which the present invention can be applied is 0.78 μm.
The wavelength range is not limited to 0.78 to 0.83 μm, which is usually referred to as the 0.8 μm band.

〔Effect of the invention〕

As explained above, according to the method for producing a magneto-optic garnet of the present invention, a 0.8 μm band optical isolator material with good surface condition and low insertion loss can be produced with good reproducibility.

[Brief explanation of drawings]

FIG. 1 is a diagram used to explain the principle of an optical isolator. In the figure, 1 is a Faraday rotator, 2 is a polarizer, and 3
is an analyzer, 4 is a semiconductor laser, 5 is forward light,
6 is the return light.

Claims (1)

[Claims] 1. A garnet film with a Faraday rotation of several degrees less than 45 degrees is provided on a nonmagnetic garnet substrate by ion beam sputtering, and
A method for manufacturing magneto-optical garnets characterized by growing a thin film using the LPE method.