JP2003315735A - Optical isolator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a single-stage optical isolator which is suitably used for an LD module with a polarization holding fiber. <P>SOLUTION: The optical isolator has a 1st end outer circumference holder 1, a 1st polarizer 4, a 1st garnet crystal 5 applied with a magnetic field by a 1st magnet 3, a 2nd polarizer 6, an end holder 2, a 2nd end outer circumference holder 7, and a 2nd garnet crystal 9 applied with a magnetic field by a 2nd magnet 8 in order along an optical axis and is characterized in that the application directions of the magnetic fields of the 1st magnet 3 and 2nd magnet 8 are opposite to each other. Further, the application directions of the magnetic fields of the 1st magnet 3 and 2nd magnet 8 may be the same. <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 mainly used as an optical passive component in an optical communication system.

[0002]

2. Description of the Related Art An example of a conventional single-stage optical isolator is shown in FIG.
And shown in FIG. First, a description will be given with reference to FIG. This optical isolator includes an outer peripheral holder 33, a first polarizer 3
6, a garnet crystal 37, a magnet 35, a second polarizer 38, and an end holder 34.

The first polarizer 36, the garnet crystal 37, the magnet 35 and the second polarizer 38 are fixed to the holder by a low melting point metal solder, a low melting point glass solder or an organic adhesive to form a one-stage optical isolator semi-finished product. . Next, the end peripheral holder 33 and the end holder 34 are joined by YAG welding to complete the one-stage optical isolator shown in FIG.

FIG. 8 is a sectional view in which polarization directions on the incident side and the outgoing side are added to a completed diagram of the one-stage type optical isolator. It should be noted that all the cross-sectional views in this specification are accurately drawn by the cut edges. The first polarizer 36 and the second polarizer 38 perform the function of transmitting only light in a fixed polarization direction, and the garnet crystal 37, which is a bismuth-substituted rare earth iron garnet crystal, is given a saturation magnetic field,
The plane of polarization of light propagating through the garnet crystal is polished to a thickness of 45 ° about the optical axis.

For light propagating in the forward direction, that is, in the direction of the arrow indicated by the optical axis direction 39 in the forward direction, the propagating light passes through the first polarizer 36 and is then magnetized in a fixed direction with the garnet crystal 37. The Faraday rotator including the magnet 35 rotates the plane of polarization by 45 ° about the optical axis. After that, the light has a polarization direction of 45 with the first polarizer 36.
The polarization direction 41 on the exit side is different from the polarization direction 40 on the entrance side by 45 degrees because the second polarizer 38 arranged so as to be different from each other is transmitted. The polarization directions 40 and 41 shown in FIG. 8 are drawn as seen from the direction perpendicular to the optical axis.

On the other hand, in the reverse direction, of the polarization components of the incident light, the polarization component that has passed through the second polarizer 38 has a Faraday rotator composed of a garnet crystal 37 and a magnet 35 with the optical axis as the rotation axis. , Rotate the plane of polarization by 45 ° in the same direction as in the forward direction. Here, since the polarization direction of the light transmitted through the garnet crystal 37 is different from the polarization direction of the first polarizer 36 by 90 °, the polarization incident from the opposite direction is blocked by the first polarizer 36, and the one-stage type Functions as an optical isolator.

[0007]

When the conventional one-stage optical isolator is used as an optical module, there are the following problems.

For example, in an LD (laser diode) module used as a signal source for an optical fiber communication system, as shown in FIG. 5 or 6, the incident side and the outgoing side have the same polarization direction. A 1.5-stage type optical isolator 27 of a type and a 1.5-stage type optical isolator 31 of a type in which the polarization directions of the incident side and the emission side differ by 90 ° are used. Here, the optical isolator called a 1.5-stage type is an optical isolator including three polarizers and two Faraday rotators arranged between them.

FIG. 5 is a perspective view showing the configuration of an LD module with a polarization maintaining fiber using a polarization plane 0 ° rotation type optical isolator, and FIG. 6 uses a polarization plane 90 ° rotation type optical isolator. It is a perspective view which shows the structure of the LD module with the polarization maintaining fiber. 25 is LD
Chip, 26 is the forward optical axis direction, 28 is the incident side polarization direction, 29 and 32 are the exit side polarization directions, and 30
Indicates a polarization maintaining fiber.

In such an LD module, the polarization direction 40 on the incident side shown in FIG. 8 is 45 ° with the polarization direction 41 on the emission side.
When using a different conventional single-stage optical isolator, the polarization direction of the polarization-maintaining fiber 30 must be adjusted in accordance with the polarization direction 41 on the exit side of the single-stage optical isolator, and the polarization direction of the LD module must be adjusted. There is a problem that it takes time to attach the optical isolator.

To explain further, in the LD module using the 1.5-stage optical isolator, the direction of the fast axis or slow axis of the polarization maintaining fiber 30 is LD
It may be parallel or perpendicular to the substrate surface of the chip. On the other hand, when the conventional single-stage optical isolator is used, the direction of the fast axis or the slow axis of the polarization maintaining fiber must be a direction forming an angle of 45 ° with the substrate surface of the LD chip.

This also hinders the common mounting structure of the single-stage type and the 1.5-stage type optical isolators in the production of the LD module.

Therefore, an object of the present invention is to provide a one-stage type optical isolator which can be suitably used for an LD module with a polarization maintaining fiber.

[0014]

A means for solving the problems will be described with reference to FIGS. 1 and 2. Polarization direction 11 on the incident side and polarization direction 12 on the exit side
The polarization plane 0 ° rotation type single-stage type optical isolator having the same is the first end outer peripheral holder 1, the first polarizer 4, the first garnet crystal 5, the first magnet 3, the second polarizer 6, and the end holder. 2, a second end outer circumference holder 7, a second magnet 8 and a second garnet crystal 9.

Further, in magnetizing a semi-finished one-stage optical isolator consisting of the second end outer peripheral holder 7, the second magnet 8 and the second garnet crystal 9, the end holder 2 and the second end outer peripheral holder 7 are illustrated. When the first magnet and the second magnet are magnetized so that the magnetizing directions are opposite to each other after joining by YAG welding as shown in 2, the second Faraday composed of the second magnet 8 and the second garnet crystal 9 is magnetized. Since the polarization plane of the light passing through the rotator rotates in the direction opposite to the rotation direction in the first Faraday rotator, the exit-side polarization direction 12 is the same as the entrance-side polarization direction 11.

On the other hand, as shown in FIGS. 3 and 4, the polarization plane 90 ° rotation type single-stage optical isolator has a first end outer peripheral holder 13, a first polarizer 16, a first garnet crystal 17, and a first magnet. 15, second polarizer 18, end holder 14, second end outer circumference holder 19, second magnet 20
And a second garnet crystal 21.

As in the case of the polarization plane 0 ° rotation type single-stage optical isolator, the semi-finished product of the single-stage optical isolator comprising the second end outer peripheral holder 19, the second magnet 20 and the second garnet crystal 21 is magnetized as shown in FIG. After the end holder 14 and the second end outer peripheral holder 19 are joined by YAG welding as described above, if the first magnet and the second magnet are magnetized in the same direction, the second Faraday rotation is performed. Since the polarization direction of the propagating light passing through the child rotates in the same direction as the rotation direction in the first Faraday rotator, the exit-side polarization direction 24 is 90 ° with respect to the entrance-side polarization direction 23.
different.

In summary, in the optical isolator of the present invention, a magnetic field is sequentially applied in the optical axis direction by the first end outer peripheral holder 1, the first polarizer 4, and the first magnet 3 which are the components. A first garnet crystal 5, a second polarizer 6, an end holder 2, a second end outer circumference holder 7, and a second garnet crystal 9 to which a magnetic field is applied by a second magnet 8 are arranged. And the application directions of the magnetic fields of the second magnet 8 are opposite to each other.

Further, the optical isolator of the present invention comprises a first garnet to which a magnetic field is applied in order along the optical axis by the first end peripheral holder 1, the first polarizer 4 and the first magnet 3 which are constituent parts. Crystal 5, second polarizer 6, end holder 2,
The second end outer peripheral holder 7 and the second garnet crystal 9 to which a magnetic field is applied by the second magnet 8 are arranged, and the magnetic field application directions of the first magnet 3 and the second magnet 8 are the same direction. Is composed of.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. This is a mode in which the present invention is applied to a single-stage optical isolator used in an LD module in which the polarization direction on the output side is the same as or different from the polarization direction on the input side by 90 °.

(Embodiment 1) Embodiment 1 corresponding to claim 1 will be described. FIG. 2 is a sectional view showing a polarization plane of 0 ° rotation type single-stage type optical isolator according to the first embodiment with the polarization planes of the incident side and the emission side added.

FIG. 1 is a sectional view of a semi-finished product of a one-stage optical isolator of a polarization plane 0 ° rotation. The first end outer peripheral holder 1, the first polarizer 4, the first garnet crystal 5, the first magnet 3, the first magnet 3 Polarization plane 0 ° rotation type single-stage optical isolator semi-finished product (upper half of FIG. 1) consisting of two polarizers 6 and end holder 2, second end outer circumference holder 7, second magnet 8
And the second garnet crystal 9 with polarization plane 0 ° rotation type single-stage optical isolator semi-finished product (lower half of Fig. 1)
By AG welding, a polarization plane 0 ° rotation type single-stage optical isolator is completed.

Here, the first polarizer 4 has the same direction as the polarization direction 11 on the incident side, and the second polarizer 6 has the same direction as the polarization direction after being rotated by the first Faraday rotator in the forward direction. It is arranged to have.

The forward operation is as follows. That is, it has a polarization direction 11 on the incident side and an optical axis direction 10 in the forward direction.
After passing through the first polarizer 4, the incident light propagating in the direction of is rotated about the optical axis in the first Faraday rotator including the first garnet crystal 5 and the first magnet 3 magnetized in a certain direction. And the plane of polarization is rotated by 45 °.

Next, the light passing through the first Faraday rotator is magnetized so as to pass through the second polarizer 6 and, after assembly, in the direction opposite to that of the first magnet 3. In the second Faraday rotator composed of the second magnet 8 and the second garnet crystal 9, the plane of polarization is set to 4 in the direction opposite to that in the first Faraday rotator with the optical axis as the center of rotation.
It rotates by 5 ° and propagates as outgoing light having a polarization direction 12 on the outgoing side. As a result, the polarization direction 12 on the output side is the same as the polarization direction 11 on the input side.

On the other hand, the reverse operation is as follows.
That is, the incident light propagating in the direction opposite to the optical axis direction 10 in the forward direction has a polarization plane of 45 ° in the same rotation direction as in the forward direction in the second Faraday rotator with the optical axis as the rotation center.
Rotate. After passing through the second Faraday rotator,
The light transmitted through the second polarizer 6 has its plane of polarization rotated by 45 ° in the first Faraday rotator in the direction opposite to that in the second Faraday rotator, and thus is blocked by the first polarizer 4.
In this way, the single-stage optical isolator functions.

(Second Embodiment) A second embodiment corresponding to claim 2 will be described below. FIG. 4 is a sectional view showing a completed view of a polarization plane 90 ° rotation type single-stage optical isolator according to the second embodiment, with polarization directions on the incident side and the emission side added.

FIG. 3 is a sectional view of a semi-finished product of a single-stage optical isolator of the polarization plane 90 ° rotation. The first end outer peripheral holder 13, the first polarizer 16, the first garnet crystal 17, the first magnet 15, Second polarizer 18 and end holder 1
Polarization plane 90 ° rotation type single-stage optical isolator semi-finished product (upper half of FIG. 3) consisting of 4 and second end outer circumference holder 19,
Polarization plane 90 ° rotation type single-stage optical isolator consisting of the second magnet 20 and the second garnet crystal 21 is completed by YAG welding the semi-finished product of polarization plane 90 ° rotation type single-stage optical isolator (lower half of FIG. 3). To do.

Here, the first polarizer 16 has the same direction as the polarization direction 23 on the incident side, and the second polarizer 18 has the same direction as the polarization direction after being rotated by the first Faraday rotator in the forward direction. It is arranged to have.

The operation in the forward direction is as follows.
That is, the incident light having the polarization direction 23 on the incident side and propagating in the forward optical axis direction 22 is transmitted through the first polarizer 16, and then is polarized in the first garnet crystal 17 and a certain direction. The plane of polarization is rotated by 45 ° about the optical axis in the first Faraday rotator composed of one magnet 15.

Next, the polarized wave that has passed through the first Faraday rotator passes through the second polarizer 18 and then the first magnet 1
In the second Faraday rotator composed of the second magnet 20 and the second garnet crystal 21, which are magnetized so that the magnetization direction is the same as that of the magnetized direction of the first Faraday rotator, the first Faraday rotator is centered on the optical axis. The plane of polarization is rotated by 45 ° and emitted in the same direction as in the rotor. as a result,
The polarization direction 24 on the output side is 90 degrees from the polarization direction 23 on the input side.
° Different.

On the other hand, the operation in the opposite direction is as follows. That is, the incident light propagating in the direction opposite to the optical axis direction 22 in the forward direction rotates the polarization plane by 45 ° in the second Faraday rotator in the same rotation direction as in the forward direction about the optical axis as the rotation center.

Next, after passing through the second Faraday rotator, the polarization component passing through the second polarizer 18 has a polarization plane in the first Faraday rotator in the same rotation direction as in the second Faraday rotator. Since it rotates by 45 °, the first polarizer 16
Shut off by. In this way, the single-stage optical isolator functions.

By the way, since the one-stage type optical isolator of the present invention has a simpler structure than that of the 1.5-stage type optical isolator by the fact that the number of polarizers is smaller by one, it is low in cost depending on the required characteristics of isolation. An optical isolator can be provided.

[0035]

EFFECTS OF THE INVENTION According to the present invention, (1) For an LD module with a polarization maintaining fiber, which is desired to emit linearly polarized waves in the same or 90 ° different polarization directions on the incident side and the emitting side in the optical isolator section, When using a 1.5-stage optical isolator and a single-stage optical isolator of polarization plane 0 ° rotation type or polarization plane 90 ° rotation type Can be shared.

(2) Compared with the case of using the conventional single-stage optical isolator in which the polarization directions of the incident side and the exit side are different by 45 °, it is not necessary to adjust the angle of the polarization direction, so that the mounting is not necessary. You can save time.

That is, according to the present invention, it is possible to provide a one-stage type optical isolator that can be suitably used in the production of an LD module with a polarization maintaining fiber.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a semi-finished optical isolator of a polarization plane 0 ° rotation type.

FIG. 2 is a cross-sectional view showing a completed view of a polarization plane 0 ° rotation type single-stage optical isolator, with polarization directions of an incident side and an outgoing side added.

FIG. 3 is a cross-sectional view of a semi-finished product of a single-stage optical isolator that rotates a polarization plane by 90 °.

FIG. 4 is a cross-sectional view showing polarization directions of an incident side and an output side in a completed diagram of a polarization plane 90 ° rotation type single-stage optical isolator.

FIG. 5 is a perspective view showing a configuration of an LD module with a polarization maintaining fiber using an optical isolator of a polarization plane 0 ° rotation type.

FIG. 6 is a perspective view showing a configuration of an LD module with a polarization maintaining fiber using an optical isolator of a polarization plane 90 ° rotation type.

FIG. 7 is a cross-sectional view of a conventional one-stage type optical isolator semi-finished product.

FIG. 8 is a cross-sectional view showing the completed single-stage optical isolator of the related art with polarization directions on the incident side and the emission side added.

[Explanation of symbols]

1,13 First end outer peripheral holder 2,14,34 End holder 3,15 First magnet 4,16,36 First polarizer 5,17 First garnet crystal 6,18,38 Second polarizer 7, 19 2nd end outer periphery holder 8, 20 2nd magnet 9, 21 2nd garnet crystal 10, 22, 26, 39 Forward optical axis direction 11, 23, 28, 40 Incident side polarization direction 12, 24, 29, 32, 41 Polarization direction on output side 25 LD chip 27 Polarization plane 0 ° rotation type 1.5-stage optical isolator 31 Polarization plane 90 ° rotation type 1.5-stage optical isolator 30 Polarization maintaining fiber 33 End Peripheral holder 35 Magnet 37 Garnet crystal

Claims (2)

[Claims] 1. A first garnet crystal, a second polarizer, an end holder, and a second end to which a magnetic field is applied by a first end outer peripheral holder, a first polarizer, and a first magnet in order in the optical axis direction. An optical isolator, in which an outer peripheral holder and a second garnet crystal to which a magnetic field is applied by a second magnet are arranged, and the magnetic fields of the first magnet and the second magnet are applied in opposite directions. 2. A first garnet crystal, a second polarizer, an end holder, and a second end to which a magnetic field is applied by a first end outer peripheral holder, a first polarizer, and a first magnet in order in the optical axis direction. An optical isolator, in which an outer peripheral holder and a second garnet crystal to which a magnetic field is applied by a second magnet are arranged, and the magnetic fields of the first magnet and the second magnet are applied in the same direction.