JP3375286B2 - Optical circulator - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical circulator for separating light passing through a transmission line or an optical switch for switching an optical path in the fields of optical communication and optical measurement. In the fiber collimator composed of the ferrule and the collimator lens, the first birefringent element, the 45 degree Faraday rotator, and the 1
The present invention relates to an optical circulator or optical switch that is downsized (shortening the overall length and diameter) by incorporating a non-reciprocal portion composed of a / 2 wavelength plate and a second birefringent element.

[0002]

2. Description of the Related Art An optical circulator emits light from a port to a specific port, such as emitting light from a port to a port and light from a port to a port. An optical device having a separating function. The optical switch emits incident light from a port to either the port or the port,
Alternatively, it is an optical device having an optical path switching function of emitting incident light from either the port or the port to the port. Usually, an optical circulator uses a 45 degree Faraday rotator configured to apply a fixed magnetic field by a permanent magnet to a Faraday element, and realizes non-reciprocity of light rays by rotating a plane of polarization by 45 degrees, and an optical switch is By using a Faraday rotator whose applied magnetic field changes by an electromagnet, the optical path is switched by controlling so that the polarization plane of outgoing light is switched by 90 degrees.
In any case, it can be considered that the configurations of the basic parts are almost the same. Therefore, the optical circulator will be mainly described below as an example.

Conventionally, optical circulators having various configurations have been developed. As an example, three birefringent elements are arranged in a row with a gap, and a pair of a Faraday element and a half-wave plate is inserted between these birefringent elements, and an entrance / exit section is provided at each end. There is a configuration provided (Japanese Patent Laid-Open No.
No. 61001). A fixed magnetic field is applied to the Faraday element by a permanent magnet to form a 45-degree Faraday rotator whose polarization plane rotates by 45 degrees. This makes it possible to construct an optical circulator that couples the light emitted from one port to the opposite port, the light emitted from the port to the opposite port, and the light emitted from the port to the opposite port if necessary. it can. Here, each port is composed of a combination of a fiber and a lens.

By the way, most of the optical circulators currently in practical use are of the 3-port type. The reason is that in a general bidirectional transmission system or reflected light measurement system, if there are three ports: a port for connecting a light emitting element, a port for connecting a transmission fiber or a sample to be measured, and a port for connecting a light receiving element. This is because it is often sufficient.

[0005]

As described above, in the conventional optical circulator having a plurality of ports, each port has one port.
The lens was combined with each of the fibers of the book. That is, collimate coupling is achieved by combining individual lenses for each fiber. Therefore, the distance between the fibers needs to be a distance commensurate with the lens diameter, and it is inevitable that each optical element on the optical circulator body side must be large, and the optical circulator can be downsized, thinned, and inexpensive. Was a big obstacle for me.

Further, in the conventional structure in which the optical circulator main body is arranged between the facing collimator lenses, in order to increase the isolation, the birefringent element to be used is made thicker (longer in the optical axis direction) and separated. It was necessary to increase the distance. This is because the beam size is expanded although the light is collimated by the lens. This is also an obstacle to downsizing and cost reduction of the optical circulator.

An object of the present invention is to provide an optical circulator or optical switch which can reduce both the length and diameter of the entire apparatus, and can realize cost reduction by downsizing the optical element used and reducing the number of parts. .

[0008]

According to the present invention, a nonreciprocal portion in which a 45 ° Faraday rotator and a ½ wavelength plate are inserted between two birefringent elements is inserted between a ferrule and a collimator lens. Then, the whole is arranged in a line, and two sets of the array units are combined so that the collimator lenses face each other. The ferrules of both array units may both be two-core ferrules having two fibers, or one array unit may have two ferrules.
A combination of a two-core ferrule having one fiber and a single-core ferrule in which the ferrule of the other array unit has one fiber may be used. As described above, the feature of the present invention is that the nonreciprocal portion is inserted into the fiber collimator including the ferrule and the collimator lens.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention includes an optical switch as well as an optical circulator. That is, in the same configuration as the three-port type optical circulator, both Faraday rotators have a configuration in which the direction of the magnetic field applied to the Faraday element is changed by an electromagnet to switch the Faraday rotation angle between 45 degrees and -45 degrees. is there. 1 × 2 type in which the light emitted from the fiber of the single-core ferrule is coupled to one of the fibers of the two-core ferrule, or the light emitted from any fiber of the two-core ferrule is coupled to the fiber of the single-core ferrule 2 × A type 1 optical switch can be constructed.

Further, the present invention also provides a reflection type optical circulator. A non-reciprocal part in which a 45 degree Faraday rotator and a half-wave plate are inserted between two birefringent elements,
It is inserted between the three-core ferrule and the collimator lens, and the whole is arrayed in a line, and the polarization plane is reciprocated with another collimator lens facing the collimator lens of the array unit.
Polarization rotator that rotates 0 degrees (eg, quarter-wave plate)
And a reflector are arranged. Here, the three-core ferrule is a ferrule in which three fibers are arranged in parallel. The light from the fiber passes through the nonreciprocal portion twice in the process of reciprocating by the reflector, thereby operating as a two-stage optical circulator. This configuration has the advantages that the total length of the device can be further shortened, the number of parts is small, and the number of assembling steps can be reduced.

[0011]

1 is a block diagram showing an embodiment of an optical circulator according to the present invention, which is an example of a 3-port type. In the present invention, the non-reciprocal portion 10 in which the 45-degree Faraday rotator 16 and the 1/2 wavelength plate 18 are inserted between the two birefringent elements 12 and 14 is used. The non-reciprocal portion 10 is inserted between the two-core ferrule 20 and the collimator lens 22 which form the fiber collimator, and the whole is arranged in a line. On the other hand,
The non-reciprocal portion 10 having the same structure is inserted between the single-core ferrule 24 and the collimator lens 26, and the whole is arranged in a line. Then, these array units are combined so that the collimator lenses 22 and 26 face each other.

Here, the birefringent element 1 of each non-reciprocal portion 10
Reference numerals 2 and 14 are made of rutile, and both end surfaces are parallel to each other, and their optical axes are set at an angle of 45 degrees with the optical axis. The optical axes of the first birefringent element 12 and the second birefringent element 14 are in a vertical relationship when viewed in the optical axis direction (within the paper surface of FIG. 2 described later). The first birefringent element 12 has a polarization splitting / combining function, and the second birefringent element 1
4 has an optical path shift function. The optical axis of the half-wave plate 18 is set to a direction of ± 22.5 degrees from the horizontal axis when viewed in the optical axis direction (in the plane of FIG. 2 described later). The Faraday rotator 16 is configured to apply an external magnetic field to the Faraday element with a permanent magnet, and is set so that the plane of polarization is 45 degrees counterclockwise when viewed from the port on the left side of the drawing. To simplify the drawing, only the Faraday element is shown as the Faraday rotator, and the illustration of the permanent magnets attached to it is omitted. Further, although the optical elements are brought into close contact with each other here, they may be arranged slightly apart from each other.

The two-core ferrule 20 has two fibers 21
This is a ferrule that is housed in close proximity to a book. The collimator lens 22 has a function of converting the light emitted from each fiber 21 of the two-core ferrule 20 into a parallel beam and, conversely, a function of coupling the parallel beam with a corresponding fiber. The single-core ferrule 24 is a ferrule that accommodates one fiber 21. The collimator lens 26 is
It serves to convert the light emitted from the fiber 21 of the single-core ferrule 24 into a parallel beam and, conversely, to couple the parallel beam into the fiber.

Next, FIG. 2 shows a concrete state of the plane of polarization and the direction of the optical axis, and the operation of the optical circulator will be described with reference thereto. In addition, each rectangular portion in the drawings represents the emission surface of each optical element.

FIG. 2A shows a state in which light is transmitted from port to port. The light emitted from the port
It is separated into ordinary light and extraordinary light by the first birefringent element 12 of the first array unit, and passes through the Faraday rotator 16 and the half-wave plate 18. At that time, the polarization plane of the ordinary light rotates by 90 degrees, but the extraordinary light does not rotate as a result because the polarization plane returns to the original state. Since the second birefringent element 14 becomes an ordinary light, the light goes straight without any optical path shift. The collimator lens 22 forms a parallel beam, which passes through the next collimator lens 26. At that time, it is converted into a position point-symmetric with respect to the center of the lens. In the second array unit, since the second birefringent element 14 is also an ordinary light, it goes straight, and passes through the half-wave plate 18 and the Faraday rotator 16, and the polarization plane of one does not rotate, On the other hand, the plane of polarization rotates 90 degrees. In the next first birefringent element 12, the ordinary ray and the extraordinary ray are combined into a single ray, which is coupled to the port. By this operation, the first birefringent element 12 of the first array unit and the first birefringent element 1 of the second array unit
In 2, the relationship between ordinary and extraordinary light is reversed,
The optical path lengths of both are equal and polarization dispersion does not occur.

FIG. 2B shows a state in which light is transmitted from port to port. The light emitted from the port
It is separated into ordinary light and extraordinary light by the first birefringent element 12 of the second array unit, and passes through the Faraday rotator 16 and the half-wave plate 18. At that time, the polarization plane of the extraordinary light rotates by 90 degrees, but the polarization plane of the ordinary light does not rotate as a result because the polarization plane returns to the original state. Since it becomes extraordinary light for the second birefringent element 14, the light path shifts. Collimator lens 2
It becomes a parallel beam at 6 and passes through the next collimator lens 22. At that time, the light is converted into a point-symmetrical position with respect to the center of the lens, but since the light is incident at a symmetrical position with respect to the center of the lens, the positions of the light emitted from the two lenses are only changed as a result. does not change. In the first array unit, the extraordinary light that has been extraordinary to the second birefringent element 14 undergoes an optical path shift, passes through the half-wave plate 18 and the Faraday rotator 16, and one has a polarization plane. It does not rotate, and the polarization plane of the other rotates 90 degrees. Next first birefringent element 12
Then, the ordinary ray and the extraordinary ray are combined into one ray, which is coupled to the port. Even in this operation, since the relationship between the ordinary ray and the extraordinary ray is reversed in the first birefringent element 12 of the first array unit and the first birefringent element 12 of the second array unit, the optical paths of both are reversed. The lengths are equal and polarization dispersion does not occur.

The thickness (length in the optical axis direction) of the rutile which is the first birefringent element 12 in both array units is the same for both, and should be about 30 times (300 μm) the mode field diameter of the fiber. Good. Further, the thickness (length in the optical axis direction) of the rutile which is the second birefringent element 14 of both array units is 5 of the fiber interval in the two-core ferrule.
It should be doubled. As a collimator lens,
For example, a gradient index rod lens or the like can be used. Collimator lenses 22 and 26 and ferrules 20 and 2
The distance from 4 (the focal length of the lens) is about 2 mm, so that it is possible to insert the non-reciprocal portion 10 between them. Although the light from the two-core ferrule 20 has a spread, it is emitted in parallel to each other and has a beam diameter of about 5 μm when entering the non-reciprocal portion 10. Therefore, the area of each optical element forming the non-reciprocal portion 10 is large. Is extremely small. Lens 2
The light collimated through 2 has a beam diameter of 50 μm
It will be about. In this way, the two sets of array units are joined together in the expanded state, and a slight dimensional deviation in the optical axis direction between the two array units is allowed, so that the alignment is extremely easy.

Although the above embodiment is a 3-port type in which a two-core ferrule is used for one array unit and a single-core ferrule is used for the other array unit, the present invention uses a two-core ferrule for both array units. It can also be applied to the optical circulator used. Two fibers of one two-core ferrule serve as ports and ports, and two fibers of the other two-core ferrule serve as ports and ports. The operation principle as an optical circulator is basically the same as that shown in FIG. 2, in which the light emitted from the port is coupled to the port, the light emitted from the port is coupled to the port,
Light emitted from the port is coupled to the port. However, the light emitted from the port does not return to the port.

The present invention can be applied to an optical switch as well as the above optical circulator. The basic configuration in that case may be the same as in FIG. However, the two Faraday rotators apply an external magnetic field to the Faraday element by an electromagnet, and control the direction of the external magnetic field (direction of drive current to the electromagnet) to change the Faraday rotation angle to 45 degrees and -45 degrees. Be able to switch every time. Then, one ferrule is set on the exit side and the other ferrule is set on the entrance side. Thereby, in response to the switching operation by the electromagnet, for example, a 2 × 1 type (2
It is possible to realize an input × 1 output type optical switch or a 1 × 2 type (1 input × 2 output type) optical switch that couples light emitted from a port to either a port or a port.

FIG. 3 is a constitutional view showing still another embodiment of the optical circulator according to the present invention, which is a reflection type example.
The non-reciprocal portion 10 in which the 45-degree Faraday rotator 16 and the half-wave plate 18 are inserted between the two birefringent elements 12 and 14.
Are inserted between the three-core ferrule 30 and the collimator lens 32, and the whole is arranged in a line. 3-core ferrule 30
Is a configuration in which three fibers 31 are arranged in parallel and housed.
Since the configuration of the non-reciprocal portion 10 may be the same as that of the example shown in FIG. 1, the corresponding members are designated by the same reference numerals, and the description thereof will be omitted.

This optical circulator utilizes reflection,
It is designed on the assumption that light travels back and forth. Therefore, the reflecting portion 34 is provided so as to face the collimator lens 32 of this array unit. The reflector 34 includes another collimator lens 36 facing the collimator lens 32 of the array unit, a quarter-wave plate 38, and a mirror (reflector) 4
0 and they are installed in line with the array unit. Here, the quarter-wave plate 38 of the reflecting section 34 is set such that its optical axis is set at a direction of 45 degrees from the horizontal axis when viewed in the optical axis direction (within the paper surface in FIGS. 4 and 5), and the plane of polarization is set. It performs the function of rotating 90 degrees back and forth. Therefore, a 45 degree Faraday rotator can be used instead of this quarter wave plate.

The operation of this reflection type optical circulator will be described with reference to FIGS. These figures also show the specific state of the polarization plane and the direction of the optical axis, and each rectangular portion in the drawings represents the emission surface of each optical element.

FIG. 4 shows how light is transmitted from the outer port back to the central port. The light from the port is separated into ordinary light and extraordinary light by the first birefringent element 12, and the Faraday rotator 16 and the half-wave plate 1 are separated.
Pass 8. At that time, the plane of polarization of the extraordinary light rotates by 90 degrees, but that of ordinary light does not rotate as a result because the plane of polarization returns to the original state. Since it becomes extraordinary light for the second birefringent element 14, the light travels with an optical path shift. The lens 32 forms a parallel beam, which is then focused by the next lens 36. At that time, the light is converted into a point-symmetrical position with respect to the center of the lens, but since the light is incident at a symmetrical position with respect to the center of the lens, the positions of the light emitted from the two lenses are only changed as a result. does not change. Then, the quarter-wave plate 38 converts the linearly polarized wave into a circularly polarized wave and focuses it on the mirror 40. The return light reflected by the mirror 40 is converted into a linearly polarized wave again by the quarter-wave plate 38. After all, in the quarter-wave plate 32, the plane of polarization is rotated by 90 degrees while the light reciprocates. The lens 36 forms a parallel beam, and the next lens 32 focuses and advances. At that time, the light is converted into a point-symmetrical position with respect to the center of the lens, but since the light is incident at a symmetrical position with respect to the center of the lens, the positions of the light emitted from the two lenses are only changed as a result. does not change. The light becomes ordinary light for the second birefringent element 14. Each light beam has a half-wave plate 18
In the Faraday rotator 16, one of the polarization planes rotates by 90 degrees, but the other does not rotate. Then, the ordinary light and the extraordinary light are combined into a single light beam by the first birefringent element 12,
Emit to the central port. In this way, the light emitted from the port is coupled to the port and does not return to the port.
Does not bind to port.

FIG. 5 shows how light is transmitted back from the central port to the outer port. In this case, too, the situation is similar to the case where light is transmitted from the port to the port. The light from the port is separated into ordinary light and extraordinary light by the first birefringent element 12, and the Faraday rotator 16
And the half-wave plate 18. At that time, the plane of polarization of the extraordinary light rotates by 90 degrees, but that of ordinary light does not rotate as a result because the plane of polarization returns to the original state. Since it becomes extraordinary light for the second birefringent element 14, the light travels with an optical path shift. The lens 32 forms a parallel beam, which is then focused by the next lens 36. At that time, it is converted into an emission position that is point-symmetric with respect to the center of the lens. The quarter-wave plate 38 converts the linearly polarized wave into a circularly polarized wave and focuses it on the mirror 40. The return light reflected by the mirror 40 is again converted into a linearly polarized wave by the quarter-wave plate 38. After all, in the quarter-wave plate 38, the plane of polarization rotates 90 degrees while the light reciprocates. The lens 36 forms a parallel beam, and the next lens 32 focuses and advances. Also in that case, the light is converted into an emission position that is point-symmetric with respect to the center of the lens. The light becomes ordinary light for the second birefringent element 14.
The polarization planes of the respective light beams are rotated by 90 degrees on the half wave plate 18 and the Faraday rotator 16, but the other is not rotated. Then, the ordinary light and the extraordinary light are combined by the first birefringent element 12 to form one light beam, which is emitted to the outer port. In this way, the light emitted from the port is coupled to the port, does not return to the port, and does not couple to the port.

Even if light is emitted from the port, it can be returned by following the optical path of passing through the optical circulator body and the like, being reflected by the mirror, and passing through the optical circulator body and the like again. No port exists. Therefore, it does not couple to ports and.

FIG. 6 is a block diagram showing another embodiment of the present invention. The birefringent element near the three-core ferrule in FIG. 3 is divided into two equal parts, and a ½ wavelength plate 46 is inserted between the birefringent element pieces 42 and 44. The portion indicated by reference numeral 48 is the portion that was the birefringent element 12 in FIG. Since other configurations may be the same as those in FIG. 3, corresponding optical elements are designated by the same reference numerals, and description thereof will be omitted. Birefringent element piece 42, 1 /
The combination of the two-wave plate 46 and the birefringent element piece 44
It functions as a single birefringent element, whereby the optical paths of the forward path and the return path are equalized, and polarization dispersion does not occur. That is, the polarization is switched between the two birefringent element pieces by the half-wave plate 46, and the optical path length difference is made zero.

The state is shown in FIG. In the first birefringent element piece 42, it is separated into ordinary light o and extraordinary light e, and
The plane of polarization is rotated by 90 degrees by the two-wave plate 46. Second divided
In the birefringent element piece (4), the relationship between the extraordinary ray e and the ordinary ray o is inverted and further separated. Two birefringent element pieces 42,
When the thickness of 44 (length in the direction of the optical axis) is set to be the same (just half the thickness of the birefringent element 12 shown in FIG. 3) and the optical axis is rotated 180 degrees about the optical axis, separation occurs. The optical path lengths of the forward and backward paths of the light beam are the same, and a reflection-type optical circulator without polarization dispersion (dispersion compensation method) can be configured. Although the number of parts is increased, the divided birefringent element pieces 42 and 44 may be half the size of the birefringent element 12 shown in FIG. The length dimension does not increase so much and the cost does not increase significantly.

[0028]

As described above, according to the present invention, a non-reciprocal part composed of a birefringent element, a 45 ° Faraday rotator, a ½ wavelength plate and a birefringent element is provided between a fiber collimator composed of a ferrule and a lens. Since two sets of inserted array units are arranged to face each other, it is possible to reduce the diameter of the optical element and to achieve high isolation because of the two-stage type, and at the same time, to assemble multiple ports. Since it can be performed, the number of steps can be reduced.

Further, the present invention is a reflection type optical circulator in which a lens, a polarization rotator and a reflector are arranged at one end of the array unit, so that the forward and backward paths are substantially two-stage type. Isolation can be realized, yet the number of parts can be reduced, and the length dimension of the entire device can be further shortened.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram showing an embodiment of an optical circulator according to the present invention.

FIG. 2 is an explanatory diagram of its operation.

FIG. 3 is an overall configuration diagram showing another embodiment of the optical circulator according to the present invention.

FIG. 4 is a diagram for explaining the operation of the port → port.

FIG. 5 is a diagram for explaining the operation of the port → port.

FIG. 6 is an overall configuration diagram showing still another embodiment of the optical circulator according to the present invention.

FIG. 7 is an operation explanatory diagram of the main part thereof.

[Explanation of symbols] 10 Non-reciprocal part 12,14 Birefringent element 16 45 degree Faraday rotator 18 1/2 wave plate 20 2-core ferrule 21 fiber 22 Collimator lens 24 Single Core Ferrule 26 Collimator lens

─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Tsuguo Tokumasu 5-36-11 Shimbashi, Minato-ku, Tokyo Fuji Electric Chemicals Co., Ltd. (56) Reference JP-A-5-88112 (JP, A) ( 58) Fields investigated (Int.Cl. ⁷ , DB name) G02B 27/28

Claims (6)

(57) [Claims] 1. A non-reciprocal part in which a 45 ° Faraday rotator and a ½ wavelength plate are inserted between two birefringent elements is inserted between a two-core ferrule and a collimator lens to form a whole line. An optical circulator characterized by arranging and arranging two sets of the array units so that the collimator lenses face each other. 2. A non-reciprocal part in which a 45-degree Faraday rotator and a half-wave plate are inserted between two birefringent elements is inserted between a ferrule and a collimator lens, and the whole is arranged in a line. , A two-core ferrule in which two sets of the array units are combined so that the collimator lenses face each other, and the ferrule of one array unit has two fibers,
An optical circulator in which the ferrule of the other array unit is a single-core ferrule having one fiber. 3. A non-reciprocal part in which a 45 ° Faraday rotator and a ½ wavelength plate are inserted between two birefringent elements is inserted between a ferrule and a collimator lens, and the whole is arranged in a line. , A two-core ferrule in which two sets of the array units are combined so that the collimator lenses face each other, and the ferrule of one array unit has two fibers,
The ferrule of the other array unit is a single-core ferrule having one fiber, and the applied magnetic field of the Faraday rotator is varied to switch the Faraday rotation angle between 45 ° and −45 ° 2 × 1 type or 1 × 2. Type optical switch. 4. A non-reciprocal part, in which a 45 ° Faraday rotator and a ½ wavelength plate are inserted between two birefringent elements, is inserted between a three-core ferrule and a collimator lens to form a whole. A light characterized by being arranged by arranging and arranging another collimator lens facing the collimator lens of the array unit, a polarization rotation element for rotating the polarization plane 90 degrees back and forth, and a reflector. Circulator. 5. The optical circulator according to claim 4, wherein the polarization rotator that reciprocally rotates the plane of polarization by 90 degrees is a quarter-wave plate. 6. A birefringent element close to a 3-core ferrule is
The optical circulator according to claim 4 or 5, wherein the birefringent element pieces are equally divided and a half-wave plate is inserted between the birefringent element pieces to eliminate polarization dispersion.