JP2003337304A - On-ferrule mounted type optical isolator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an on-ferrule mounted type optical isolator which is miniaturized as a whole and has a reduced diameter by tightly and easily fixing each optical element without employing laminate constitution. <P>SOLUTION: The on-ferrule mounted type optical isolator is composed of a combination of: an optical isolator body 24 which has a polarizer 14 and an analyzer 16 arranged before and behind a Faraday element 12 and also has permanent magnets 20 and 22 arranged outside them; and a holder 30 which holds the optical isolator body. The optical isolator body is structured by arranging the two permanent magnets in a long and narrow flat plate shape opposite each other at an interval and sandwiching the optical element between them, and the holder is structure by forming a recessed groove 36 on one side of a cylindrical part 34 having a center through hole 32. The optical isolator body can be inserted into and fixed in the recessed groove with the external surfaces of the permanent magnets exposed and mounted on a ferrule 40 on the opposite side of the holder from the recessed groove. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical isolator, and more specifically, it has a structure in which an optical isolator main body is inserted and fixed in a concave groove of a holder, and the holder can be directly attached to an end face of a ferrule. The present invention relates to an optical isolator.

[0002]

2. Description of the Related Art As is well known, an optical isolator is a nonreciprocal optical device that allows the passage of light in one direction but blocks the passage of light in the opposite direction. For example, optical communication using a semiconductor laser as a light source. It is used in a system to prevent the laser light from returning to the light source side by reflection.
In this type of optical isolator, a polarizer, a Faraday element and an analyzer are arranged in that order in the optical axis direction, and a permanent magnet for applying a magnetic field in the optical axis direction to the Faraday element is provided outside the Faraday element. Is common. The Faraday element changes the plane of polarization of incident light to 4 by the magnetic field of a permanent magnet.
It is rotated by 5 degrees, and the polarizer and the analyzer are set so that their optical axes (polarization transmission axes) are different by 45 degrees.

In recent years, in order to further reduce the distance between the input / output devices and to reduce the size, there has been proposed a structure in which an optical isolator is directly attached to the ferrule end surface of the optical fiber. The optical isolator to be mounted has a structure in which a polarizer, a Faraday element and an analyzer are inserted and fixed in a cylindrical permanent magnet, or a polarizer, a Faraday element and an analyzer are pre-laminated with an adhesive and inserted into the permanent magnet. There is a configuration to do. In any case, the polarizer and the analyzer have the same specifications, and the one is rotated about the optical axis with respect to the other so that the optical axes are adjusted to be different by 45 degrees.

[0004]

A structure in which a polarizer, a Faraday element and an analyzer (collectively referred to as an optical element) are inserted into a cylindrical permanent magnet while maintaining an optically necessary effective area is a ferrule. It is difficult to reduce the size to accommodate the outer diameter. This is because the smaller the size, the more difficult the work of fixing the optical element becomes, and the smaller the adhesive area of the optical element becomes, the weaker the adhesive strength becomes. The structure in which the polarizer, the Faraday element, and the analyzer are previously laminated with an adhesive agent is relatively easy to assemble, but the adhesive agent intervenes in the optical path, which causes damage when high-power light passes through. Problems (such as fears) are likely to occur, and applications (usage conditions) are restricted. In any case, man-hours / parts for adjusting the direction of the optical axis are required, resulting in high cost.

An object of the present invention is to provide a ferrule mounting type optical isolator which can firmly and easily fix each optical element without adopting a laminated structure, and can make the entire size and diameter small. Another object of the present invention is to
(EN) Provided is a ferrule-mounted optical isolator which can be assembled without adjusting the relationship between the optical axes of a polarizer and an analyzer. Still another object of the present invention is to provide a ferrule-mounted optical isolator having a structure capable of firmly fixing the optical isolator to the ferrule end.

[0006]

According to the present invention, a polarizer and an analyzer are arranged in front of and behind a Faraday element, and an optical isolator main body in which a permanent magnet is arranged outside them, and a holder for holding the optical isolator main body. It is a ferrule-mounted optical isolator consisting of a combination of. Here, the optical isolator main body has a structure in which two permanent magnets in the form of elongated flat plates face each other with a gap, and a polarizer, a Faraday element, and an analyzer are positioned between the permanent magnets. It has a structure in which a concave groove is formed on one side of a tubular part having a through hole,
The optical isolator main body is inserted and fixed in the groove with the outer side surface of the permanent magnet exposed, and the end face of the holder opposite to the groove can be attached to the ferrule.

The holder has a cylindrical shape, and a tapered surface or a rounded surface is formed on the outer surface of the permanent magnet so as to match the outer peripheral shape of the holder when the optical isolator body is inserted into the concave groove. The outer diameter of the holder is preferably approximately the same as the outer diameter of the ferrule.

The polarizer and the analyzer are both processed into a strip shape (rectangular flat plate shape) so that their optical axes are different from each other by 45 degrees, and they are fixed to the permanent magnet on their long side surfaces. By so that the isolator characteristic is expressed without adjustment.

The center through hole of the holder has a shape in which the capillary portion of the ferrule is just fitted, and in the fitted state, the end face of the holder and the end face of the ferrule are abutted and fixed by welding or adhesion.

[0010]

1 is a perspective view showing an embodiment of a ferrule-mounted optical isolator according to the present invention, in which A is a disassembled state and B is a state after assembly. Further, FIG. 2 is an explanatory view thereof, in which A shows a partially broken side surface and B shows a front surface. The ferrule-mounted optical isolator 10 includes an optical isolator main body 24 in which a polarizer 14 and an analyzer 16 are arranged in front of and behind the Faraday element 12, and a pair of permanent magnets 20 and 22 are arranged outside them, and the optical isolator main body 24. Holder 3 for holding
It consists of a combination with 0.

In the optical isolator main body 24, two permanent magnets 20 and 22 in the form of elongated flat plates are arranged to face each other with a space therebetween, and between the polarizer 14, the Faraday element 12,
The analyzer 16 is assembled so as to be sandwiched. Polarizer 1
4 and the analyzer 16 are made of, for example, a rutile crystal,
Both of them are processed into the same strip shape (rectangular flat plate shape) so that their optical axes differ from each other by 45 degrees. For example, the optical axis of the polarizer 14 is set in the direction parallel to the long side (or the vertical direction), while the optical axis of the analyzer 16 is set in the direction of 45 degrees with respect to the long side. The Faraday element 12 is made of a magnetic garnet single crystal (for example, Bi-substituted rare earth iron garnet single crystal), and is processed into a strip shape (rectangular flat plate shape) having the same shape as the polarizer 14 and the analyzer 16. The thickness is set so that the incident light of the used wavelength rotates its polarization plane by 45 degrees.

The permanent magnets 20, 22 are, for example, SmCo rare earth sintered magnets, and are magnetized in the longitudinal direction. The width dimension of the permanent magnets 20 and 22 in the form of elongated flat plates is set to be slightly larger than the dimension of the long side of an optical element such as a polarizer. Since the permanent magnets 20 and 22 are basically flat plates, they can be easily processed and the manufacturing cost is low. The Faraday element 12 is surface-bonded to one of the permanent magnets 20 on the side surface on the long side, and the polarizer 14 and the analyzer 16 are attached to the other permanent magnet 22 on the side surface on the long side by a predetermined distance (Faraday). It is surface-bonded at a distance larger than the thickness of the element 12. As described above, since the optical elements are surface-bonded on the side surface on the long side, the bonding area is increased and the fixing strength is increased. The facing surfaces of the permanent magnets 20 and 22 (the surfaces to which the optical elements are bonded) are previously polished with a grindstone. Further, as shown in FIG. 1, it is preferable that chamfering 26 be applied to the ridges in the longitudinal direction of the surfaces of the permanent magnets 20 and 22 to which the optical elements are bonded. Then, the chamfer 26 can be used to place the adhesive on a part of the side surface of the optical element on the short side, so that the adhesive strength between the permanent magnet and the optical element can be further increased.

The optical isolator main body 24 is constructed by combining the permanent magnet 22 to which the polarizer 14 and the analyzer 16 are bonded and the permanent magnet 20 to which the Faraday element 12 is bonded so as to face each other. In this way, by arranging the polarizer 14 and the analyzer 16 whose optical axes are set in a predetermined direction in advance on the same plane of the same permanent magnet 22, there is no adjustment of the optical axis at the time of assembly. Then, the desired isolator characteristic is developed. Further, since each optical element is individually fixed to the permanent magnet, an air layer is provided between the optical elements and there is no adhesive layer, so that problems such as damage to high-power light do not occur.

The holder 30 has a structure in which a concave groove 36 is formed on one side of a cylindrical portion 34 having a central through hole 32 in a direction orthogonal to the central axis. In other words, it has a cylindrical portion 34 having the central through hole 32, and a pair of holding pieces 38 integrally protruding from one side in the central axis direction,
The groove 36 is formed by the pair of holding pieces 38. Therefore, the outer peripheral surface of the sandwiching piece 38 is flush with the outer peripheral surface of the cylindrical portion 34. The optical isolator main body 24 is inserted into the groove 36 and fixed by adhesion.

One permanent magnet 20 to which the Faraday element 12 is adhered and the other permanent magnet 22 to which the polarizer 14 and the analyzer 16 are adhered are placed in the holder 30 with the optical element adhering surfaces facing each other and parallel to each other. Built in the groove 36,
The permanent magnets 20 and 22 are bonded and fixed on the entire side surfaces (three surfaces) in contact with each other. Since the contact area is large, sufficient fixing strength can be secured. As the work, it is preferable to perform one work by fitting one permanent magnet into the groove 36 and adhering it, and then fitting the other permanent magnet into the groove 36 and adhering it separately. This is because the polarizer / analyzer and the Faraday element are held by separate permanent magnets on only one side, respectively, and thermal stress due to temperature fluctuations is relaxed.

Since the permanent magnets 20 and 22 in the form of elongated flat plates are inserted into the groove 36, the angle around the optical axis is uniquely determined. When the permanent magnets 20 and 22 are inserted into the concave groove 36, the permanent magnets 20 and 22 are made to match the outer peripheral shape of the holder 34.
Tapering (or radiusing) is performed in advance on the outer corners of the. The taper surface is designated by reference numeral 28. Thereby, the permanent magnets 20 and 22 do not excessively protrude from the outer peripheral surface of the holder 30, and the outer diameter of the optical isolator can be reduced. Further, by making the permanent magnets 20 and 22 exposed, further miniaturization can be realized. Each optical element is protected by the sandwiching portion 38 of the holder 30 and the permanent magnets 20 and 22. Also, the permanent magnet 2
Since the permanent magnets 20 and 22 are fixed so that the permanent magnets 20 and 22 are sandwiched by the sandwiching portion 38 of the holder 30, mechanical strength against vibrations and impacts from various directions is improved.

The holder 30 can be mounted on the ferrule 40 on the side opposite to the groove 36. 2A
As shown in, the center through hole 32 of the holder 30 has a shape in which the capillary portion 42 of the ferrule 40 is just fitted,
The end face of the holder and the end face of the ferrule are abutted and fixed in the fitted state. If both the holder and ferrule are made of stainless steel, both should be in multiple locations around the entire circumference (eg, 8 locations)
Then, it is fixed by YAG welding 44.

Each of the optical elements (polarizer 14, Faraday element 12, analyzer 16) has permanent magnets 20, 2 which are slightly tilted from a state perpendicular to the optical axis in order to prevent end face reflection.
Attach to 2. Since the optical element adhering surface of the permanent magnets 20 and 22 is a flat surface and the optical element has a strip shape, the adhering in an inclined state is easy. In addition, the capillary section 4
The tip surface of 2 is also polished so as to be slightly inclined (for example, 8 degrees) from the state perpendicular to the optical axis. By making such an inclination, reflected return light is prevented.

[0019]

According to the present invention, in the optical isolator main body, two elongated flat plate-shaped permanent magnets are arranged facing each other with a space therebetween, and the polarizer, the Faraday element, and the analyzer are sandwiched between them. With such a structure, the optical element can be firmly and easily fixed. Further, since it is not necessary to laminate the optical elements with each other, there is no fear of damage such as damage to high power light. Further, the holder has a structure in which a concave groove is formed on one side of a cylindrical portion having a central through hole, and the optical isolator main body is inserted and fixed in the concave groove, so that the permanent magnet is exposed and the outer periphery of the permanent magnet is exposed. By making taper processing and rounded shapes, it is possible to further reduce the size and diameter.

When the polarizer and the analyzer are processed into strips so that their polarization axes are different from each other by 45 degrees and fixed to the permanent magnet at their long sides, the isolator characteristic is expressed without adjustment, and the adjustment work is performed. The man-hours and parts required for this are no longer needed, and it can be manufactured at low cost. In addition, the center through hole of the holder is shaped to fit the capillary part of the ferrule, and if the holder end face and the ferrule end face are abutted and fixed in such a fitted state, they will be joined to the ferrule end of the optical isolator. The strength is further improved.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of a ferrule-mounted optical isolator according to the present invention.

FIG. 2 is an explanatory diagram of a ferrule-mounted optical isolator according to the present invention.

[Explanation of symbols]

10 Ferrule-mounted optical isolator 12 Faraday element 14 Polarizer 16 Analyzer 20,22 Permanent magnet 24 Optical isolator body 30 holder 32 Central through hole 34 Cylindrical part 36 groove 40 ferrule

Claims (4)

[Claims] 1. An optical isolator comprising a combination of an optical isolator main body in which a polarizer and an analyzer are arranged before and after the Faraday element, and a permanent magnet is arranged outside them, and a holder for holding the optical isolator main body. , The optical isolator main body has a structure in which two permanent magnets in the form of elongated flat plates face each other with a gap, and a polarizer, a Faraday element, and an analyzer are located between the permanent magnets. It has a structure in which a concave groove is formed on one side of a cylindrical portion having a hole, and the optical isolator main body is inserted and fixed in the concave groove with the outer surface of the permanent magnet exposed, and the opposite side of the concave groove of the holder. A ferrule-mounted optical isolator characterized in that it can be attached to a ferrule at the end face of the ferrule. 2. The holder has a cylindrical shape, and a tapered surface or a rounded surface is formed on the outer surface of the permanent magnet so as to match the outer peripheral shape of the holder when the optical isolator body is inserted into the groove. The ferrule-mounted optical isolator according to 1. 3. The polarizer and the analyzer are processed into strips so that their optical axes are different from each other by 45 degrees, and are fixed to the permanent magnets on the sides of their long sides, whereby no adjustment is required. The ferrule-mounted optical isolator according to claim 1 or 2, wherein the isolator characteristic is exhibited. 4. The center through hole of the holder has a shape in which the capillary portion of the ferrule is fitted, and the end face of the holder and the end face of the ferrule are abutted and fixed in the fitted state. The ferrule-mounted optical isolator described.