JPH0949988A - Optical isolator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical isolator which has an improved impact resistance and high reliability and is used for a visible wavelength region by forming metallized films on both surfaces of the optical surface of a Faraday rotor to be joined and solder joining this rotator to a holder via a polarizer and analyzer from both sides on the incident side and exit side of a laser beam. SOLUTION: The metallized films are formed on both surfaces of the optical surface of the Faraday rotator 2 having an antireflection film formed. At this time, the metallized films are formed as three-layered films composed of Cr as a ground surface film, Ni as an intermediate film and Au as a joint film. Further, the similar antireflection films and metallized films are also formed on both surfaces of the optical surfaces of the polar cores used as the polarizer 1 and the analyzer 3. A magnet 5, the polarizer side end holder 4, the polarizer 1 (polar core) 1 and the Faraday rotor 2 are soldered with a solder 7 in an electric furnace of a reducing atmosphere. Further, the analyzer 3 (polar core) and the analyzer side end holder 6 are similarly soldered in the electric furnace of the reducing atmosphere.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical isolator utilizing the Faraday effect used in optical communication, optical measurement, etc., and more particularly to the structure of an optical isolator used in the visible wavelength range.

[0002]

2. Description of the Related Art In recent years, an optical communication system using a semiconductor laser as a light source and an optical application device using a semiconductor laser have been widely used, and their applications and scales have been expanded.

In order to improve the accuracy and stability of these optical communication systems and optical application equipment, optical isolators are used for the purpose of removing the return light to the semiconductor laser, and the low noise and wide band of the fiber amplifier, It is indispensable to take advantage of features such as high output.

This optical isolator comprises a polarizer, an analyzer,
It consists of an optical element consisting of a Faraday rotator, a permanent magnet for generating a magnetic field, and a holder for fixing and protecting them.

Presently, as a Faraday rotator material for optical isolators for optical communication in the 1.3 μm band and the 1.5 μm band,
Bismuth-substituted garnet thick film has been put to practical use. However, 0.98 μm used in fiber amplifiers
At a short wavelength such as the band, 1.047 μm band, there is a strong absorption edge based on Fe ions, and there is a problem that the crystal transmission loss becomes large, so that it has not been put to practical use.

To solve this problem, CdMnTe or Cd
Studies are being conducted to put a so-called visible light isolator for a short wavelength of 1 μm band or shorter into practical use by using a semiconductor made of a single crystal of MnHgTe as a Faraday rotator.

Further, conventionally, an organic adhesive has been used as a method for fixing and adhering each optical element and a holder.
The adhesive strength is poor over a long period of time, and gas is released from the adhesive.This gas forms an organic film on the crystal surface due to laser light and increases insertion loss, so long-term reliability is improved. Cannot be secured.

Therefore, an optical isolator, such as a repeater for optical communication, which is required to have a high degree of reliability for a long time, is formed by a metal fusion method instead of the conventional fixing method using an organic adhesive. Optical isolator is used.

Further, in the optical isolator for the fiber amplifier, compared with the optical isolator for the optical communication repeater,
Since light with a power of 00 times or more passes therethrough, it is desired to put a visible light isolator formed by a metal fusion method into practical use.

FIG. 4 is a sectional view of a metal fusion type optical isolator used for optical communication in the 1.3 μm band and the 1.5 μm band. The optical element composed of the polarizer 1 ′ and the Faraday rotator 2 ′ and the polarizer side end holder 4 are simultaneously soldered with the solder material 7
The analyzer 3'and the magnet 5 are fixed to the analyzer side end holder 6 by soldering.

The end holder 4 on the side of the polarizer and the end holder 6 on the side of the analyzer are joined by laser welding through an external holder 12 to form a one-stage optical isolator.
At this time, the metallized film 11 for fixing the solder of each optical element
Is formed in a portion where light does not pass, as shown in FIG.

[0012]

However, when a CdMnTe single crystal and a CdMnHgTe single crystal were used for the Faraday rotator of the visible light isolator and soldering was performed by the conventional method, the performance deteriorated due to a slight impact. .

That is, as in the conventional method using the conventional bismuth-substituted garnet, CdMnTe single crystal and CdM
A metallized film is formed on the optical surface of the nHgTe single crystal, and A
Solder joint with the holder by u-Sn solder, 30c
When dropped from m, CdMnTe single crystal and CdM
Since the nHgTe single crystal peels off from the holder,
It was not practical.

Therefore, a technical object of the present invention is to provide an optical isolator used in the visible wavelength range of high reliability, which has a significantly improved impact resistance.

[0015]

DISCLOSURE OF THE INVENTION The present invention provides a metal fusion type optical isolator comprising a polarizer, an analyzer, an optical element having a Faraday rotator made of a semiconductor, a permanent magnet for generating a magnetic field and a holder. , A metallized film is formed on the two optical surfaces of the Faraday rotator that is joined to the polarizer and the analyzer, and soldered to the end holder via the polarizer and the analyzer from both the laser light incident side and the laser light incident side. It is an optical isolator characterized by the above.

(Operation) As a result of intensive studies on the above-mentioned problems, CdMnT used as a visible light isolator
For e and CdMnHgTe single crystals, the soldering did not have sufficient adhesive strength because the metallized film had no problem and the single crystal itself was brittle. I found out that it was because I was destroyed.

Further, CdMnTe and CdMnHg
Since the Verdet constant of Te single crystal is as small as 1/5 to 1/10 of that of bismuth-substituted garnet, the crystal needs to be elongated in the optical axis direction for use as an optical isolator.

Therefore, in the conventional method of forming the metallized film on the optical surface, a so-called cantilever beam is used, in which a rectangular parallelepiped crystal is supported only on one bottom surface, and the impact is concentrated on the bonding surface, and the crystal is destroyed. Was invited.

From the above, as shown in FIG. 1, metallized films are formed on both sides of the optical surface of the crystal, that is, on both the light incident side and the light emitting side, and indirectly by a polarizer, an analyzer and an internal ring. By solder-joining with the end holder, it becomes a double-supported beam, so that it is possible to prevent the impact from being concentrated on the adhesive surface and to improve the impact resistance.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to embodiments.

As shown in FIG. 3, CdMnHgTe as a Faraday rotator 2 having an antireflection film 13 formed thereon.
The metallized film 11 is formed on both sides of the optical surface (1.3 mm × 1.3 mm) of the single crystal (1.3 mm × 1.3 mm × 2.5 mm).
Was formed.

At this time, the metallized film 11 has Cr of 0.35 μm as a base film and Ni of 0.35 μm as an intermediate film.
m, and Au as a bonding film was formed as a three-layer film of 0.15 μm.

Further, although not shown, a polar core (1.3 mm × 1.3) used as a polarizer and an analyzer.
mm × 0.4mm Corning optical surface (1.3m
The same antireflection film and metallized film were formed on both sides (m × 1.3 mm). After that, the first soldering was performed.

That is, as shown in FIG. 2A, a Ni-plated cylindrical magnet 5 (outer diameter φ4 mm, inner diameter φ1.
6 mm, length 2.7 mm), Au-plated polarizer side end holder 4 (stainless steel), polarizer 1 (polar core) and Faraday rotator 2 in an electric furnace in a reducing atmosphere,
Soldering was performed with the solder material 7. Here, the end holder 4 on the side of the polarizer is previously attached to the outer holder 1 at the laser welding point 9 in advance.
2 (made of stainless steel) and laser welded were used.

Further, similarly, the analyzer 3 (polar core)
The analyzer-side end holder 6 was soldered in an electric furnace in a reducing atmosphere.

Next, the optical axis was adjusted. As shown in FIGS. 2A and 2B, the second solder material 8 was inserted between the Faraday rotator 2 and the analyzer 3 to align the optical axes. That is, the analyzer side end holder 6 is used for the outer holder 1
After being fitted like the lid of 2, the laser light is actually made incident from the side of the polarizer 1 and the side of the analyzer 3 is rotated to fix the laser at the place with the highest isolation. The fixing at this time was performed by welding the analyzer side end holder 6 and the outer holder 12 by laser welding.

Finally, the second soldering was performed. That is,
The optical isolator, in which the outer holder 12 and the analyzer-side end holder 6 are welded, is placed again in an electric furnace in a reducing atmosphere,
By the second solder material 8, the Faraday rotator 2 and the analyzer 3
Was soldered.

A drop test was conducted on the visible light isolator as shown in FIG. 1 manufactured as described above. Table 1 shows the results. In the pass / fail judgment at this time, the change in isolation before and after the fall is within the measurement error range (0.5 dB).
The following).

[0029]

As is apparent from Table 1, according to the present invention,
The impact resistance could be increased significantly. In addition, in the conventional product, when dropped from a height of 30 cm, CdM
The nTe single crystal was peeled from the holder and measurement was impossible.

[0031]

As described above, according to the present invention,
In the visible light metal fusion type optical isolator, a metallized film is formed on both sides of the optical surface of the Faraday rotator to be joined, and a polarizer is provided from both the incident side and the outgoing side of the laser light,
By soldering to the holder via the analyzer, it is possible to provide a highly reliable visible light isolator having high impact resistance.

[Brief description of drawings]

FIG. 1 is a sectional view of an optical isolator according to an embodiment of the present invention.

2 is an explanatory view showing an optical isolator of an embodiment of the present invention, FIG. 2 (a) is an explanatory view showing a state before assembly, FIG.
(B) is sectional drawing which shows the state after an assembly.

FIG. 3 is a perspective view of a Faraday rotator used in the optical isolator according to the exemplary embodiment of the present invention.

FIG. 4 is a sectional view showing the structure of a conventional optical isolator.

FIG. 5 is a perspective view showing a metallized film formed on an optical element used in a conventional optical isolator.

[Explanation of symbols]

 1, 1'polarizer 2, 2'Faraday rotator 3, 3'analyzer 4 (polarizer side) end holder 5 magnet 6 (analyzer side) end holder 7 (first) solder material 8 second Solder material 9 Laser welding point 11 Metallized film 12 External holder 13 Antireflection film

Claims (1)

[Claims] 1. A metal fusion type optical isolator comprising an optical element having a polarizer, an analyzer, and a Faraday rotator made of a semiconductor, a permanent magnet for generating a magnetic field, and a holder, and is joined to the polarizer and the analyzer. Faraday rotator 2
An optical isolator characterized in that a metallized film is formed on the optical surface of the surface and soldered to an end holder through a polarizer and an analyzer from both the laser light incident side and the laser light emitting side.