JP5222769B2 - Wedge-type birefringent polarizer for optical isolator, method for manufacturing optical isolator, and optical isolator - Google Patents

Description

  The present invention relates to a wedge-type birefringence polarizer and an optical isolator for an optical isolator, and more specifically, a pair of wedge-type birefringence polarizers used for a polarization-independent optical isolator and the wedge-type birefringence. The present invention relates to an optical isolator manufacturing method using an optical polarizer and an optical isolator.

  For example, in an optical amplifier constituting a repeater of a wavelength division multiplexing optical communication system, a polarization-independent optical isolator is used as a component for transmitting an optical signal output in only one direction.

  As shown in FIG. 5, this polarization-independent optical isolator includes a light incident collimator lens 2A, a first collimator lens 2A between an input optical fiber 1A for introducing incident light and an output optical fiber 1B for extracting outgoing light. 1 wedge-type birefringence polarizer 3A, 45-degree Faraday rotator 4, second wedge-type birefringence polarizer 3B, and output collimator lens 2B are sequentially arranged, and each component is a casing. 6 (see Patent Documents 1 and 2, for example).

  The first wedge-type birefringence polarizer 3A, the 45-degree Faraday rotator 4, and the second wedge-type birefringence polarizer 3B form an isolator unit 5. In the example shown in the figure, the unit 5 has a single-stage configuration, but in order to improve isolation (input / output separation performance), the unit 5 has a multi-stage configuration in which a plurality of stages (two stages) are stacked in series. There is also.

  As shown in FIG. 6, the wedge-type birefringence polarizers 3A and 3B used in this optical isolator each have a vertical surface a and a tapered surface b with respect to the optical path Lz direction. The two polarizers 3A and 3B are aligned (paired) with the same optical characteristics, and the vertical surfaces a and a are orthogonal to the optical path Lz direction, and the vertical surfaces a and a and The taper surfaces b and b are installed in a state where they are positioned so as to be parallel to each other. This is to keep the insertion loss, particularly the transmission loss in the forward direction, low.

Shoko 61-58811 JP-B 61-58809

  Optical isolators are required to ensure high isolation and to keep insertion loss as low as possible. For this purpose, it is necessary to incorporate each component, in particular, the wedge-type birefringence polarizers 3A and 3B with high accuracy.

  In the past, assembly was performed based on the outer shape of the wedge-shaped birefringent polarizer. However, as the device size is reduced, it has become difficult to obtain the required assembly accuracy. In addition, there is a method of capturing optical components that are optically invalid (light leaking in directions other than the transmission direction) with a camera, and using this camera as a clue to adjust positioning during assembly. There was a limit.

  Furthermore, in order to reduce insertion loss, it is necessary that the characteristics of the wedge-type birefringent polarizers 3A and 3B, in particular, the taper angles are well aligned, that is, so-called pairing accuracy is good. As a method for ensuring the pairing accuracy, conventionally, products manufactured in the same production lot have been combined. This is based on the expectation that those manufactured under the same production conditions will have the same characteristics, but this alone provides the pairing accuracy required for wedge-type birefringent polarizers for optical isolators. It was made clear by the present inventors that it cannot be ensured.

  As shown in FIG. 7, the wedge-shaped birefringence polarizers 3A and 3B are cut from a prefabricated long optical material (birefringence material), but even if they are cut from the same material, It has been found that there are subtle variations in optical characteristics, and this is a major impediment to hindering insertion loss reduction of optical isolators.

  The present invention solves the above problems, and its object is to provide a wedge-type birefringent polarizer that is particularly effective for reducing the insertion loss of a polarization-independent optical isolator easily and with good reproducibility. Another object of the present invention is to provide an optical isolator manufacturing method using the wedge-shaped birefringence polarizer, and an optical isolator with small insertion loss and variation.

The solution provided by the present invention is as follows.
(1) An input collimator lens, a first wedge-type birefringence polarizer, a 45-degree Faraday rotator, a second optical fiber between an input-side optical fiber that introduces incident light and an output-side optical fiber that derives outgoing light The wedge-type birefringence polarizer and the light-emitting collimator lens are the wedge-type birefringence polarizer used in the polarization-independent optical isolator incorporated in the casing in a state where each is positioned. And
One of the front and back surfaces of the rectangular plate is a vertical surface, the other is a tapered surface inclined with respect to the vertical surface, and the cross-sectional shape when the inclination is viewed from the side is a trapezoid,
As well as the tapered surface and the vertical plane and incident and exit surfaces of the light, at least one side surface differs from the entering-emitting surface is mirror-finished optical plane,
A wedge-type birefringent polarizer for an optical isolator.

(2) A wedge-type birefringence polarizer for an optical isolator characterized in that the optical plane is formed on a wedge-shaped bottom side surface having a trapezoidal cross section in the means (1).
(3) A method for manufacturing a polarization-independent optical isolator using the wedge-type birefringent polarizer for optical isolators according to means (1) or (2), wherein the optical plane is used as an optical position reference. A pair of wedge-shaped birefringent polarizers paired on the basis of optical measurements, and when these wedge-shaped birefringent polarizers are assembled in the casing, the optical plane is used as a position reference, respectively. An optical isolator manufacturing method comprising positioning.
(4) An optical isolator using the wedge-type birefringent polarizer for optical isolators according to means (1) or (2).

  The insertion loss of the optical isolator can be effectively reduced with good reproducibility.

It is a perspective view which shows the Example of the wedge type birefringent polarizer which concerns on this invention. It is the schematic which illustrates the optical measuring method at the time of performing pairing and positioning of the wedge type | mold birefringence polarizer which concerns on this invention. It is the schematic which shows the optical isolator of the 1 step | paragraph structure using the wedge type | mold birefringence polarizer which concerns on this invention. It is the schematic which shows the optical isolator of the 2 step | paragraph structure using the wedge type | mold birefringence polarizer which concerns on this invention. It is the schematic which shows the structural concept of a polarization independent type optical isolator. It is a perspective view of a wedge type birefringence polarizer used for an optical isolator. It is a perspective view which shows an example of the manufacturing method of a wedge type | mold birefringence polarizer.

  FIG. 1 shows wedge-type birefringence polarizers 3A and 3B for an optical isolator according to the present invention. Each of the wedge-shaped birefringence polarizers 3A and 3B shown in the figure has a rectangular plate shape, and has a vertical surface a and a tapered surface b with respect to the optical path Lz direction. In addition, a wedge-shaped bottom side surface d having a trapezoidal cross section is formed on a mirror-finished optical plane 31. The top side surface c facing the bottom side surface d does not necessarily need to be an optical plane, but it is of course preferable that this surface c is also an optical plane.

  The two polarizers 3A and 3B are paired so that their characteristics, in particular, the taper angles are aligned with high precision, and this pairing is performed based on optical measurement performed with the optical plane 31 as an optical position reference.

  The optical measurement is performed using an autocollimator, as FIG. 2 schematically illustrates. The autocollimator can measure a characteristic difference such as a taper angle difference with high accuracy by comparing the positions of the emitted light and reflected light of the laser collimated lights L1 to L3. At this time, the optical plane 31 is used as the position reference. Those having the best matching optically measured characteristics with respect to the optical plane 31 are selected and used. That is, it is paired.

  FIG. 3 shows an embodiment of a polarization-independent optical isolator configured using wedge-type birefringence polarizers 3A and 3B according to the present invention. The optical isolator of this embodiment includes an incident collimator lens 2A and a first wedge-type birefringence polarization between an input side optical fiber 1A for introducing incident light and an output side optical fiber 1B for extracting outgoing light. The optical element 3A, the 45-degree Faraday rotator 4, the second wedge-type birefringence polarizer 3B, and the light-emitting collimator lens 2B are sequentially arranged.

  Each component is incorporated in a state in which it is positioned in the casing 6, but the incorporation of the wedge-shaped birefringence polarizers 3A and 3B, which has the greatest influence on the insertion loss, is performed under optical measurement using an autocollimator. This is performed while positioning the taper angle with high accuracy. This positioning can also be performed with high reproducibility and high accuracy by using the optical plane 31 as a reference.

  The optical isolator shown in FIG. 3 has a single-stage configuration with only one unit 5. However, in the present invention, as shown in FIG. 4, a plurality of (two-stage) isolator units 51 and 52 are stacked in series. This is also effective when a multi-stage configuration is used.

  Although this multi-stage optical isolator can increase the isolation, there is a problem that it is difficult to align the optical axes between the units 51 and 52. However, in the present invention, an optical plane is provided on at least one side surface of the wedge shape. By using the wedge-shaped birefringence polarizers 3A and 3B on which 31 is formed, the optical axis alignment can be performed easily, with good reproducibility, and with high accuracy.

As described above, the wedge-type birefringence polarizers 3A and 3B for optical isolators according to the present invention have the following effects by using at least one side surface of the wedge shape as a mirror-finished optical plane. It is done.
(1) The light component produced by the difference in taper angle between the wedge-type birefringent polarizers 3A and 3B used in pairs can be reduced.
(2) Light components generated due to poor assembly symmetry of the wedge type birefringent polarizers 3A and 3B used in pairs can be reduced.
(3) It is possible to reduce the light component generated when the optical axis angle error of the wedge-shaped birefringence polarizers 3A and 3B used in pairs and the rotation angle of the Faraday rotator 4 are different.
(4) When used in two stages (multistage), it is possible to reduce the light component generated due to a shift in the optical axis between the first and second stages.

  As described above, by reducing the optical components that are ineffective in the optical isolator, it is possible to obtain an optical isolator with low insertion loss and small variation with good reproducibility.

DESCRIPTION OF SYMBOLS 1A, 1B Optical fiber 2A, 2B Collimator lens 3, 3A, 3B Wedge-type birefringence polarizer 31 Mirror-finished optical plane 4 Faraday rotator 5, 51, 52 isolator unit 6 Casing Lz Optical path a Vertical plane b Tapered surface d Wedge-shaped bottom side c Cedge-shaped top side

Claims (4)

Between an input-side optical fiber for introducing incident light and an output-side optical fiber for deriving outgoing light, a collimator lens for incident light, a first wedge-shaped birefringent polarizer, a 45-degree Faraday rotator, and a second wedge-shaped The wedge-type birefringence polarizer used in a polarization-independent optical isolator in which a birefringence polarizer and a collimating lens for light emission are respectively positioned and incorporated in a casing,
One of the front and back surfaces of the rectangular plate is a vertical surface, the other is a tapered surface inclined with respect to the vertical surface, and the cross-sectional shape when the inclination is viewed from the side is a trapezoid,
As well as the tapered surface and the vertical plane and incident and exit surfaces of the light, at least one side surface differs from the entering-emitting surface is mirror-finished optical plane,
A wedge-type birefringent polarizer for an optical isolator.   2. The wedge-type birefringent polarizer for an optical isolator according to claim 1, wherein the optical plane is formed on a side surface of a wedge-shaped base having a trapezoidal cross section. A method of manufacturing a polarization-independent optical isolator using the wedge-type birefringent polarizer for an optical isolator according to claim 1 or 2, wherein the optical plane is based on an optical measurement based on the optical position. A plurality of paired wedge-type birefringent polarizers are used, and when these wedge-type birefringent polarizers are assembled in the casing, positioning is performed with the optical plane as a position reference. A method for manufacturing an optical isolator. Optical isolator characterized by using a wedge-shaped birefringent polarizer for an optical isolator according to claim 1 or 2.

Images