JP2001021841A - Optical isolator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical isolator having a small outer diameter and using a Faraday rotator having a high saturation magnetic field. SOLUTION: The optical isolator is produced by disposing a cylindrical permanent magnet 4a outside of a Faraday rotator 1a, and disposing an end holder 6a consisting of a soft magnetic material in the opposite side of the Faraday rotator 1a to the cylindrical permanent magnet 4a. By disposing the Faraday rotator 1a outside of the cylindrical magnet, the optical isolator obtained has a small outer diameter. Since the soft magnetic material is used for the end holder in the analyzer side, the Faraday rotator used in the obtained optical isolator has high Hs.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical component used in an optical communication system or an optical measuring instrument, in which light emitted from a light source is reflected by an end face of an optical element in the optical system and returns to the light source. The present invention relates to an optical isolator used for preventing the occurrence of an optical signal.

[0002]

2. Description of the Related Art When light emitted from a light source is transmitted using an optical system, light reflected from an end face of an optical element in the optical system returns to the light source.

For example, in optical communication, light emitted from a laser of a light source is converged by a coupling lens and collected on an end face of an optical fiber. At this time, most of the light enters the optical fiber and propagates through it, but some light is
The light is reflected by the end face of the optical fiber and returns to the laser of the light source.

[0004] The light returned to the laser generally has a different phase and a different deflection direction from the light in the laser, so that it becomes noise of the laser light, and the oscillation of the laser is disturbed.

In order to prevent such noise, an optical isolator for blocking return light is used. Further, the optical isolator is required to have high blocking characteristics (isolation) of return light and low transmission loss (insertion loss) of incident light.

FIG. 2 shows a typical structure of a conventional optical isolator. In FIG. 2, a Faraday rotator 1 is disposed as an optical element, a deflector 2b and an analyzer 3b are arranged on both sides thereof, and a cylinder for magnetizing the Faraday rotator 1b in one direction is provided around the Faraday rotator 1b. Type permanent magnet 8b
(Hereinafter, referred to as a cylindrical magnet).

The optical element and the cylindrical magnet are respectively connected to a metal outer peripheral holder 9b and an end holder 10b.
To the metal holder 9 by soldering or the like.
b, 10b are laser welded after mutual positioning.

[0008]

In recent years, optical devices used for optical communication have been miniaturized, like other electronic devices, and there has been a similar demand for optical isolators. .

As can be seen from FIG. 2, it can be said that the size of the optical isolator is determined by the outer diameter of the cylindrical magnet 8b. The inner diameter of the cylindrical magnet 8b is larger than that of the Faraday rotator 1b disposed inside the cylindrical magnet 8b, and the outer diameter is large enough to obtain a magnetic field required to magnetize the Faraday rotator 1b in one direction.

Therefore, in the structure of the conventional optical isolator, the outer diameter cannot be made smaller than the outer diameter of the cylindrical magnet 8b. In addition, in practice, since the outer peripheral holder 9b made of metal is required outside the cylindrical magnet 8b, there is a problem that the outer diameter is further increased.

Therefore, according to the present invention, the outer diameter is reduced,
Another object of the present invention is to provide a miniaturized optical isolator by using a Faraday rotator having a high saturation magnetic field.

[0012]

That is, the present invention provides an optical isolator in which a magnetic field generated from a permanent magnet is applied to a Faraday rotator, wherein the permanent magnet is disposed in front of the Faraday rotator.

[0013] Further, there is provided an optical isolator in which an end holder made of a soft magnetic material is disposed on the opposite side of the permanent magnet with respect to the Faraday rotator.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

First, when the arrangement of the Faraday rotator 1b located at the inner diameter portion of the conventional (see FIG. 2) cylindrical magnet 8b was examined, as shown in FIG.
By disposing a outside the cylindrical magnet 4a, the outer diameter of the cylindrical magnet 4a can be reduced to the size of the Faraday rotator 1a.

However, when the Faraday rotator 1a is disposed outside the cylindrical magnet 4a, the magnetic field applied to the Faraday rotator 1a is weaker than when the Faraday rotator 1a is disposed inside.
Therefore, by arranging a soft magnetic material on the opposite side of the cylindrical magnet 4a across the Faraday rotator 1a, an optical isolator that can apply the same magnetic field to the Faraday rotator 1a as when it is disposed inside is provided. I got it.

[0017]

Embodiments of the present invention will be described below.

(Embodiment 1) FIG. 1 is a sectional view of the structure of an optical isolator according to the present invention, and FIG. 2 is a sectional view of the structure of a conventional optical isolator in comparison with FIG. The optical isolator of the present invention in FIG.
Optical element composed of polarizer 2a, analyzer 3a, cylindrical magnet 4
a, a positioning ring 7a made of SUS304 for fixing the optical element and the cylindrical magnet, an outer peripheral holder 5a, and an end holder 6a made of SUS430 which is a soft magnetic material.

The Faraday rotator 1a is a garnet single crystal, and is composed of (Gd, Bi) ₃ (Fe, Al, Ga) ₅
Is a material represented by O _12. The dimensions are 1.6 x 1.6
X The thickness is 0.5 (unit: mm). In addition, cylindrical magnet 4
a is a commercially available Sm-Co magnet (manufactured by Tokin, LM-24)
FH) was used.

As shown in FIG. 2, the comparative example has a conventional structure in which a Faraday rotator 1b is disposed inside a cylindrical magnet 8b, and a polarizer 2b and an analyzer 3b are made of a SUS304 outer peripheral holder 9b and an end holder. 10b, a positioning ring 7b for fixing the Faraday rotator 1b.

Table 1 shows the results of measuring the forward insertion loss (dB) and isolation (dB) characteristics of the optical isolator according to the present invention and the optical isolator of the comparative example.

[0022]

[Table 1]

As is clear from the comparison between FIG. 1 and FIG. 2 and Table 1, when the invention of the first embodiment is compared with the comparative example, the light having the same optical isolator characteristics and a small outer diameter is obtained. An isolator was obtained.

(Embodiment 2) In an optical isolator having the same structure as that of the invention of Embodiment 1 shown in FIG. 1, a positioning ring 7a, an outer peripheral holder 5a and an end holder 6a are made of SUS430 which is a soft magnetic material. An optical isolator was fabricated. Other components are the same as in the first embodiment.

The Faraday rotation according to the second embodiment of the present invention
The child 1a has a Faraday rotation angle of 45 deg.
(Tb, B) when the magnetic field (saturation magnetic field Hs) is about 700 (Oe)
i) ₃Fe₅O₁₂Is a garnet single crystal represented by
You. The dimensions are 1.6 x 1.6 x thickness 0.5 (unit:
mm).

Table 2 shows forward insertion loss (dB) and isolation (dB) characteristics of the optical isolator.

[0027]

[Table 2]

From Table 2, it can be seen that by using a soft magnetic material for the end holder, the Faraday rotator having a high Hs has sufficient characteristics as compared with the conventional product (comparative example) as in the invention of the first embodiment. Was obtained.

[0029]

As described in the above description, according to the present invention, an optical isolator having a small outer diameter can be obtained by disposing a Faraday rotator outside a cylindrical magnet. . Further, by using a soft magnetic material for the end holder on the analyzer side, an optical isolator using a Faraday rotator having a high Hs can be obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration of an optical isolator of the present invention.

FIG. 2 is a cross-sectional view illustrating a configuration of a conventional (comparative example) optical isolator.

[Explanation of symbols]

 1a, 1b Faraday rotator 2a, 2b Polarizer 3a, 3b Analyzer 4a, 8b Cylindrical permanent magnet (cylindrical magnet) 5a, 9b Peripheral holder 6a, 10b End holder 7a, 7b Positioning ring

Claims (1)

[Claims] 1. An optical isolator in which a magnetic field generated from a permanent magnet is applied to a Faraday rotator, wherein the permanent magnet is disposed in front of the Faraday rotator, and the Faraday rotator is interposed between the permanent magnet and the Faraday rotator. An optical isolator characterized in that an end holder made of a soft magnetic material is arranged on the opposite side.