JPS62200319A - Optical fiber circuit device - Google Patents

Abstract

PURPOSE:To reduce the influence of internally reflected beams due to optical parts by arranging optical parts in a beam waist forming area so as to have their end faces inclined at an angle to a plane orthogonal to the optical path of optical system of coupled lenses. CONSTITUTION:The optical signal incident from the first optical fiber 11 is sent to the second fiber 12, and the optical signal incident from the fiber 12 is sent to the third fiber 13. A Farady rotator 22 in the beam waist forming area is provided at an angle alpha to the optical path, and thereby, end faces 24 and 25 of the rotator 22 are inclined in the horizontal direction at the angle alphato the plane orthogonal to the optical path of a lens coupled optical system 14. Consequently, the beams reflected on end faces 24 and 25 of the rotator 22 are deviated form the optical path of the optical system 14 and cannot be coupled optically on end faces of fibers 11 and 12. Thus, the influence of internal reflected beams due to optical parts in the beam waist area is reduced considerably.

Description

Detailed Description of the Invention [Summary] The present invention provides an optical fiber circuit device such as an optical circulator, an optical switch, an optical isolator, etc., in which a magneto-optical element is installed in a beam waist region formed by a lens-coupled optical system. By arranging optical components such as the above at an angle to the optical path, optical coupling of internally reflected light by the optical components is prevented, and the harmful effects of internal reflections in optical fiber circuit devices are greatly reduced. be.

[Industrial application field]

The present invention relates to improvements in optical fiber circuit devices, and more particularly, to a lens-coupled optical system for forming a beam waist in the middle of an optical path between fibers, and an optical component disposed in the beam waist forming region. The present invention relates to a structure for preventing optical coupling of internally reflected light in an optical fiber circuit device such as an optical circulator, an optical isolator, an optical switch, etc.

[Conventional technology]

In recent years, there has been a trend toward long-distance transmission and high-speed modulation in optical communication systems, and with this trend, reducing internal reflection in the optical fiber circuit devices used has become an important issue.

Generally, optical fiber circuit devices such as optical circulators, optical isolators, and optical switches include a lens-coupled optical system for forming a beam waist in the middle of the optical path between fibers, and a Faraday optical system disposed in the beam waist forming region. It is equipped with magneto-optical components such as a rotor. In such beam waist type optical fiber circuit devices, internal reflection also occurs at the end surfaces of optical components such as prisms and polarizing plates that are located away from the beam waist; Since the beam is diffused, the effect of internal reflection is small. However, when the beam reflected by the end face of the optical component disposed in the beam waist forming region is guided along the optical path of the lens-coupled optical system, this internally reflected light is optically coupled. Severely affects performance.

In conventional beam waist type optical fiber circuit devices, the end face for input and/or output of the optical component provided in the beam waist forming area was perpendicular to the optical path. The reflected beam optically couples on the optical path of the lens-coupled optical system, which is a major cause of degrading the performance of optical fiber circuit devices.

Conventionally, internal reflection was reduced by forming an anti-reflection film such as a dielectric multilayer film on the surface of an optical component, but the anti-reflection film had a reflectance of 0.5% (reflection of 23 dB).
The extent was the limit.

[Means for solving problems]

FIG. 1 is a diagram showing the basic structure of an optical fiber circuit device according to the present invention. Referring to the figure, the optical fiber circuit device according to the present invention includes a lens-coupled optical system 3 for forming a beam waist in the middle of the optical path between the fibers 1 and 2, and a lens-coupled optical system 3 disposed in the beam waist forming area. The optical component 4 has two mutually parallel end surfaces 5 and 6 for light input and/or exit, and the optical component 4 has two end surfaces 5 and 6 that are lens-coupled. It is characterized in that it is arranged at an angle α with respect to a plane perpendicular to the optical path of the shaped optical system 3.

[For production]

According to the above means according to the present invention, a beam entering the optical fiber circuit device from, for example, one fiber 1 is reflected by the end face 5 of the optical component 4 in the beam waist region, and the reflected light is indicated by a dotted line in the figure. Since the reflected light deviates from the optical path of the lens-coupled optical system 3, the reflected light cannot enter the fiber 1 due to optical coupling. Therefore, the influence of internally reflected light by the optical component 4 in the beam waste) 99 range can be greatly reduced.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 2 shows a first embodiment in which the present invention is applied to an optical circulator for single mode fiber. Referring to the figure, the optical circulator has a first port connected to the first fiber 11, a second port connected to the second fiber 12, and a third fiber 13.
and a third port connected to. The optical circulator is equipped with a lens-coupled optical system 14, which includes condenser lenses 15, 16, 17 respectively disposed on the boat, and two prism units 18, 19 as polarization separation elements. It is equipped with A total reflection multilayer film 20 and a polarization separation multilayer film 21 are provided inside the prism units 18 and 19, respectively. In this lens combination type optical system 14, two prism units 1 are used.
The beam waist is formed in the middle of 8.19.

In the beam waist forming area between the two prism units 18 and 19, there is a magneto-optical component made of YIG, etc.
A 5° Farade single rotator 22 is disposed, and the magneto-optical component 22 and the prism unit 1 on the second fiber 12 side
A half-wave plate 23 as a fixed optical rotator for performing optical rotation by 45 degrees is provided between the optical axis and the optical axis 9.

The Faraday rotator 22 has mutually parallel end faces 24, 25 for the input and/or output of light. Furthermore, the Faraday rotator 22 is formed so that its cross section along the optical path of the lens-coupled optical system 14 is rectangular.

The configuration described above is a well-known configuration of a conventional optical circulator. In the optical circulator having such a configuration, the optical signal incident from the first fiber 11 through the lens 15 is converted by the prism unit 18 into two polarized light components whose polarization planes are orthogonal, that is, a dot (symbol a) in the figure.
The light is separated into a vertically polarized component shown by and a horizontally polarized component shown by an arrow (symbol b) in the figure. That is, within the prism unit 18, the horizontally polarized light component passes through the polarization separation multilayer film 21 and exits from the prism unit 18, but the vertically polarized light component is reflected by the polarization separation multilayer film 21 within the prism unit 18, and then The light is reflected by the multilayer film 20 for total reflection and exits from the prism unit 18 . Both polarized light components emitted from the prism unit 18 pass through a 45° Farade rotator 22 and a half-wave plate 23, respectively. At this time, a magnetic field H is applied to the Faraday rotator 22 by the electromagnet 26 in the right direction in the figure.
In other words, since the light is added in the same direction as the traveling direction of the light, the plane of polarization of both polarized light components is changed by the Faraday rotator 22 to 45°.
After that, it is rotated by 45 degrees in the opposite direction by the half-wave plate 23, so the angles of the planes of polarization of both polarized components that have passed through the Faraday rotator 22 and the half-wave plate 23 are the same as before. Both polarized light components are combined by the prism unit 19 and sent to the second fiber 12.

On the other hand, the optical signal entering from the second fiber 12 through the lens 16 is separated into two polarized components by the prism unit 19, and then passes through the half-wave plate 23 and the Faraday rotator 22. The plane of polarization of the component is rotated by 45 degrees by the half-wave plate 23 and then further rotated by 45" in the same direction by the Faraday rotator 22. Therefore, after passing through the half-wave plate 23 and the Faraday rotator 22, The plane of polarization of both polarized light components is 9
The beams are rotated by 0°, combined by the prism unit 18, and sent to the third fiber 13.

That is, an optical signal incident from the first fiber 11 is sent to the second fiber 12, and an optical signal incident from the second fiber 12 is sent to the third fiber 13.

By the way, internal reflection of the incident light from the first fiber 11 and the second fiber 12 occurs at the end surfaces 24 and 25 of the Faraday rotator 22 located in the beam waist forming region. If it is perpendicular to the optical path of the lens-coupled optical system 14, the light reflected from the end face 24, 25 of the Faraday rotator 22 is optically coupled along the optical path, and the first fiber 11 and the second fiber 12 It will be reversely incident on the inside.

Therefore, in this embodiment, the Faraday rotator 22
are installed at an angle α with respect to the optical path, so that the end surfaces 24 and 25 of the Faraday rotator 22 are oriented horizontally (
(parallel to the plane of the paper) by an angle α (for example, approximately 7°). Therefore, the end face 24 of the Faraday rotator 22
, 25 is removed from the optical path of the lens-coupled optical system 14 and is transmitted to the first fiber 11 and the second fine
It becomes impossible to optically couple the end face.

The tilt angle α of the Faraday rotator 22 is preferably 2° or more, thereby reducing internal reflection by 30 dB to 60 dB.
Experiments have shown that this can be improved further. Although the Faraday rotator 22 can be tilted in any direction, since the Faraday rotator 22 is thin in the direction perpendicular to the plane of the paper, it is desirable to tilt it in the horizontal direction.

FIG. 3 shows a second embodiment in which the present invention is applied to an optical switch. In the figure, the same reference numerals are given to the same components as in the first embodiment.

In this embodiment, the Faraday rotator 2 is
By switching the direction of the magnetic field H applied to 2,
The optical signal incident from the first fiber 11 is transferred to the second fiber 1.
It can be selectively sent to the second or third fiber 13. That is, when the direction of the magnetic field H applied to the Faraday rotator 22 is the same as the traveling direction of the polarized component of the optical signal, the two parts separated by the prism unit 18 are
The planes of polarization of the two polarized light components a and b pass through the Faraday rotator 22 and the half-wave plate 23 to become the same as the original angle, are combined by the prism unit 19, and sent to the second fiber 12. On the other hand, when the direction of the magnetic field H applied to the Faraday rotator 22 is opposite to the traveling direction of the polarization component of the optical signal, the plane of polarization of the two polarization components a and b separated by the prism unit 18 is 2
2 and the half-wave plate 23, the light is rotated by 90 degrees, and as a result, it is synthesized in the prism unit 19 as shown by the dotted line in the figure and sent to the third fiber 13.

Also in this second embodiment, the Faraday rotator 22 is disposed horizontally at an angle α with respect to the optical path of the lens-coupled optical system 14, so that the light reflected by the end surface 24 of the Faraday rotator 22 is It is possible to optically couple at the end face of the first fiber 11 and prevent reverse incidence.

Although the illustrated embodiments have been described above, it will be obvious to those skilled in the art that the present invention is equally applicable to optical isolators. Further, as the polarization separation element in an optical circulator, optical switch, optical isolator, etc., any type of element other than the illustrated right-angle prism unit may be used. Furthermore, the present invention can be similarly applied to a device in which an electro-optic component other than a magneto-optic crystal is disposed in the beam waist forming region.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, the light reflected by the end face of the optical component in the beam waist region is removed from the optical path of the lens-coupled optical system, and the internally reflected light by the optical component in the beam waist region is removed. Since it is possible to prevent light from entering the fiber through optical coupling, the influence of internally reflected light from optical components in the beam waist region can be greatly reduced, making it possible to improve the performance of optical fiber circuit devices.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the principle configuration of an optical fiber circuit device according to the present invention. FIG. 2 is a diagram showing a first embodiment in which the present invention is applied to an optical circulator. FIG. 3 is a diagram showing a first embodiment in which the present invention is applied to an optical switch. It is a figure which shows the 2nd Example when applied. In the figure, 1, 2, 11, 12, 13 are optical fibers,
Reference numeral 3.14 indicates a lens combination type optical system, 4 indicates an optical component, and 22 indicates a Faraday rotator as an optical component.

Claims (1)

[Claims] 1. A lens-coupled optical system for forming a beam waist in the middle of the optical path between fibers, and an optical component disposed in the beam waist forming region, the optical component being An optical fiber circuit device having two end faces parallel to each other for the input and/or exit of the optical component, the end face of which is at an angle with respect to a plane perpendicular to the optical path of the lens-coupled optical system. An optical fiber circuit device characterized in that the optical fiber circuit device is arranged in such a manner that the optical fiber circuit device is arranged as shown in FIG.