JPH04163421A - Light isolator - Google Patents

Abstract

PURPOSE:To obtain a small-sized light isolator which prevents reflect noise with good extinction performance and less insertion loss by constituting at least either of a polarizer or an analyzer from a glass deflecting plate, and inclining the light incidence angle of the polarizer or the analyzer by a prescribed angle. CONSTITUTION:A polarizer 11, a Faraday rotor 12 which is disposed in a magnetic field in a light traveling direction, and an analyzer 13 are disposed between a light source and an optical system, and at least either of the polarizer or the analyzer is constituted from a glass deflecting plate, and light incidence angle to the polarizer or the analyzer is inclined at 1-30 degree. In this constitution, because a light isolator element is inclined, a surface reflect element which occurs in the respective optical element surfaces deflects from an optical axis and does not return to the light source, so that noise of the light source can be reduced. Besides, because the glass deflecting plate, which is a polarizer or an analyzer, has a short optical path, its profile does not become very large, even if it is disposed with inclination, its contour being processed easily while being inclined.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to an optical isolator that utilizes the magneto-optic effect to prevent light from a light source from being reflected at an end face of an optical system and returning to the light source.

[Conventional technology]

Optical isolators are used in optical communications, optical measurement, etc. For example, in optical communications, the light emitted from a laser light source is projected onto the fiber end face via a lens, and most of it enters the fiber as transmitted light, but it is reflected on the surface of the lens and the fiber end face and reaches the laser light source. It returns and is reflected again on the surface of the end face, resulting in noise. Optical isolators are used to eliminate such noise. The optical isolator consists of a polarizer 1, a Faraday rotator 3, and an analyzer 2 arranged in this order, as shown in FIG. The polarizer 1 has a polarization direction in the direction of the arrow y. The Faraday rotator 3 is placed in the magnetic field S−N,
The polarization plane of the transmitted light is rotated by 45° clockwise when viewed from the incident side (counterclockwise when viewed from the output side in the figure). The polarization direction of the analyzer 2 is rotated by 45 degrees with respect to the polarizer 1 in the direction of arrow -y-IZ. For light O from the light source, only the polarized light having the polarization plane in the force direction of the arrow Oy passes through the polarizer 1, and the polarization plane is rotated by 45 degrees by the Faraday rotator 3 to match the polarization direction y-2 of the analyzer 2. Therefore, it passes through the analyzer 2. The transmitted light O (polarization plane 0y-
Most of the light (Z) enters the next optical system, for example, an optical fiber (not shown), but some of it is surface-reflected at the end face of the optical fiber. The reflected light R (polarization plane Ry - I Z ) passes through the analyzer 2 in the opposite direction to the above, and the polarization plane is rotated by 45° counterclockwise by the Faraday rotator 3 . Therefore, the reflected light is not transmitted because the plane of polarization Rz is perpendicular to the polarizer 1. Therefore, it is possible to prevent the reflected light R from becoming noise. In such optical isolators, the polarizer or analyzer is required to have sufficiently high extinction performance, i.e., to extinguish light with a plane of polarization perpendicular to the direction of polarization. It is required that there is little loss in transmittance of light having , that is, insertion loss is sufficiently low. On the other hand, if the optical end face of the optical isolator is placed perpendicular to the optical axis from the light source as shown in Figure 8, the incident light will be reflected on the surfaces of the polarizer, Faraday rotator, and analyzer and return to the light source, causing noise. It becomes. In order to prevent this noise, it is effective to place the optical end face at an angle with respect to the optical axis from the light source to remove the surface reflected light from the optical path. For example, Japanese Patent Application Laid-Open No. 64-20522 discloses an optical isolator in which a polarizer, a Faraday rotator, and an analyzer are individually tilted to prevent light reflected from the surfaces of the polarizer, Faraday rotator, and analyzer from returning to the light source. Disclosed.

[Problem to be solved by the invention]

When a polarizing beam splitter (PBS) or a prism such as a Rochon prism is used as a polarizer and an analyzer in a conventional optical isolator, the angle of inclination cannot be made very large because the viewing angle is small. Also, when birefringent crystals (e.g. calcite or rutile) are used as polarizers and analyzers, the viewing angle will be wider than that of a polarizing beam splitter;
Since the shape is close to a cube, the optical path length becomes long, and by tilting it, the outer diameter becomes thick, and it is difficult to process the shape by tilting it.The present invention improves these points. The purpose of this invention is to provide an optical isolator with excellent extinction performance and insertion loss.

[Means for Solving the Problems] In order to achieve the above object, the present inventors focused on the fact that a glass polarizing plate can be used as a polarizer or an analyzer, and has a short optical path length. Then, in order to use the glass polarizing plate tilted as a polarizer or analyzer for an optical isolator, the authors investigated the tilt angle dependence of the optical properties of a glass polarizing plate and completed the present invention. That is, in the optical isolator to which the present invention is applied, a polarizer, a Faraday rotator placed in a magnetic field in the direction of propagation of light, and an analyzer are arranged between the light source and the optical system.
At least one of the polarizer and the analyzer is a glass polarizing plate, and a light incident angle with respect to the polarizer or the analyzer is inclined by 1 to 30 degrees. [Operation] By tilting the elements of the optical isolator as described above, the surface reflection components occurring on the surfaces of each optical element are deviated from the optical axis and do not return to the light source, so that noise in the light source can be reduced. Since the glass polarizing plate, which is a polarizer and/or an analyzer, has a short optical path length, even if it is arranged at an inclination, its external size does not become very large, and it is also easy to process the shape by inclining it. If the light incident angle to the polarizer or analyzer is between 1 and 30 degrees, the extinction performance as an optical isolator is sufficiently high and the insertion is possible. It is possible to prevent the surface reflection component from returning to the light source while the loss is sufficiently low.According to the inventor, from the viewpoint of extinction performance and insertion loss, the angle of incidence of light to the glass polarizing plate, which is a polarizer, is preferably 30° or less. This can be understood by referring to Figures 6 and 7 which show the experimental results.In other words, Figure 6 shows a glass polarizing plate with a light incident angle of 0.
The extinction ratio is plotted when the glass polarizing plate is tilted at an angle of incidence of 0 to 90 degrees, and the insertion loss is plotted in FIG. 7 when the glass polarizing plate is tilted at a light incident angle of 0 to 90 degrees. In addition, regardless of whether the polarizing plate is tilted in the direction of the polarization plane or in the direction crossing the polarization plane, both the extinction ratio and the pilot flame loss depend on the angular characteristics between the paths. shows. As shown in Fig. 6, when the inclination angle, that is, the light incidence angle is less than 30°, the extinction ratio is approximately constant;
It can be seen that the extinction ratio decreases when the angle is 0° or more. Furthermore, as shown in Figure 7, when the angle of inclination becomes 30° or more, the insertion loss increases.On the other hand, when the angle of incidence of light on the polarizer is less than 1°, the surface reflection component The degree of deviation from the optical axis is too small and it returns to the light source, so the noise of the light source cannot be reduced.Therefore, the angle of incidence of light on the glass polarizing plate, which is a polarizer, is between 1 and 3.
0° is preferred.

[Examples] Examples of the present invention will be described in detail below. In order to make the optical isolator of the embodiment shown in FIG. (GdBi) 3FesO+i is epitaxially grown to 300 μm and then processed to a diameter of 2 mm.This Faraday rotator 12 has an insertion loss of 0.1 dB, an extinction ratio of 42 dB, and a Faraday rotation angle of 4.
It was 4.7 degrees. The polarizer 11 and analyzer 13 have an extinction ratio of 53 dB, an insertion loss of 0.025 dB, and a diameter of 2 mm.
Make a glass polarizing plate of x 0.2 mmt. Using these polarizer 11, analyzer 13, and Faraday rotator 12, an optical isolator shown in FIG. 1 was prototyped. As shown in the figure, a polarizer 1 is attached to the inner circumference of the cylindrical magnet 10.
1. Faraday rotator 12 and analyzer 13 are sandwiched and fixed in order between rings 14, 15, 16 and 17, respectively. This optical isolator was used in an optical system consisting of a laser light source and a lens (not shown, only the optical axis is indicated by C). Initially, the central axis 0 of the optical isolator was arranged to align with the optical axis C of the optical system. As a result, the extinction ratio was 42 dB and the insertion loss was 0.16 dB. Approximately 0.2% of the light reflected from the end face of the polarizer 11 with respect to the incident light was generated, which returned to the laser light source side and became noise. Next, the central axis O of the optical isolator is θ=1 with respect to the optical axis C.
It was tilted at 0°. As a result, the polarizer 1 of the optical isolator
The end-reflected light from step 1 no longer returns to the light source. The extinction ratio and insertion loss of the optical isolator remained unchanged. The embodiment shown in FIG. 2 is an optical isolator using a 0.2 mm x 0.2 mm rectangular glass polarizing plate as a polarizer 11 and an analyzer 13. The other configurations are similar to the optical isolator shown in FIG. FIG. 3 shows a sectional view of an optical isolator of another embodiment to which the present invention is applied. To make this optical isolator, first prepare the following optical elements. As the Faraday rotator 12, 450B of 5fFeGalsO+a (TbEuBi)
After epitaxial growth, it is tilted at 7 degrees with respect to both planes and processed to have a diameter of 2 mm. This Faraday rotator 1
The characteristics of No. 2 are a Faraday rotation angle of 44.7 degrees, an extinction ratio of 43 dB, and an insertion loss of 0.03 dB. As the polarizer 11 and the analyzer 13, a 0.2+n+nt glass polarizing plate having an extinction ratio of 53 dB and an insertion loss of 0.023 dB is tilted at 7 degrees with respect to both planes and processed to have a shape of 2 m+sφ. Using these polarizer 11, analyzer 13, and Faraday rotator 12, an optical isolator shown in FIG. . A polarizer 1 is installed inside the lens barrels 21 and 22.
1. The Faraday rotator 12 and the analyzer 13 are sandwiched and fixed in order between rings 24, 25, 26 and 27, each having a 7° inclination. At this time, the Faraday rotator 12 is located inside the cylindrical magnet 23. This optical isolator has an outer diameter of 3.2+omφ, a length of 2.2 mm, and an effective beam diameter of 1.6×φ. Further, the extinction ratio of this optical isolator was 42 dB, and the insertion loss was 0.09 dB. This optical isolator was used in an optical system consisting of a laser light source and a lens (not shown, only the optical axis is indicated by C). When this optical isolator was arranged so that the center of the lens barrel coincided with the optical axis C, it was confirmed that the end-face reflected light did not return to the light source. The example shown in FIG. 4 is an optical isolator to which the present invention is not applicable. The polarizer 1 and the analyzer 2 are 2 mm x 2 mm rectangular rutile prisms arranged at an angle inside the lens barrels 21 and 22. Therefore, the effective beam diameter of the optical isolator is 1.
This is reduced to 3 m+aφ, which is about 58% compared to the optical isolator of the embodiment shown in FIG. 3 (using a glass polarizing plate). FIG. 5 shows a sectional view of an optical isolator of another embodiment to which the present invention is applied. This example is a so-called multistage optical isolator. The Faraday rotators 12 and 32 used in this optical isolator are (TbEuBi)s (Fe
After epitaxially growing Gal sO,t to a thickness of 450 um, the outer shape was processed to a size of 2 ml 1 φ at an angle of 7° with respect to both planes. The characteristics of the Faraday rotator 12 are that the Faraday rotation angle is 44.7 degrees and the extinction ratio is 42 dB.
, the insertion loss is 0.021 dB. The characteristics of the Faraday rotator 32 are that the Faraday rotation angle is 44.8 degrees,
The extinction ratio is 44 dB and the insertion loss is 0.020 dB. Polarizer 11 and analyzer 13 and polarizer 31 and analyzer 33
A 0.2 mmt glass polarizing plate with an extinction ratio of 53 dB and an insertion loss of 0.020 dB is tilted at 7 degrees with respect to both planes and 2I! Machining the outer shape to 1Illφ. These polarizer 11, Faraday rotator 12, analyzer 1
3 and polarizer 31, Faraday rotator 32, analyzer 3
An optical isolator shown in FIG. 5 was fabricated as a prototype using No. 3. As shown in the figure, cylindrical magnets 2 are placed inside the lens barrels 21 and 22.
3. Cylindrical magnets 43 are arranged inside the lens barrels 41 and 42, respectively. Inside the lens barrels 21 and 22, a polarizer 11, a Faraday rotator 12, and an analyzer 13 are sandwiched and fixed in order between rings 24, 25, 26 and 27 whose surfaces are inclined at 7 degrees, respectively. At this time, the Faraday rotator 12 is connected to the cylindrical magnet 2.
Located inside 3. Inside the lens barrels 41 and 42, there are rings 44, 45, 46 and 47 with a polarizer 31, a Faraday rotator 32, and an analyzer 33, respectively, with an inclination of 7°.
Pinch and secure in place. At this time, Faraday rotator 32
is located inside the cylindrical magnet 43. The outer diameter of this optical isolator is 3.2+amφ, the length is 4.4mm, and the effective beam diameter is 1.6mφ. Further, the extinction ratio of this optical isolator is 71 dB, and the insertion loss is 0.14 dB. This optical isolator was used in an optical system consisting of a laser light source and a lens (not shown, only the optical axis is indicated by C). When this optical isolator was arranged so that the center of the lens barrel coincided with the optical axis C, it was confirmed that the end-face reflected light did not return to the light source. Effects of the Invention As described above in detail, the optical isolator to which the present invention is applied has excellent extinction performance and insertion loss, can prevent noise due to surface reflection, and is small in size.

[Brief explanation of the drawing]

FIG. 1 is a diagram of an optical isolator to which the present invention is applied, FIGS. 2 and 3 are diagrams of another embodiment, FIG. 4 is a sectional view of an optical isolator to which the present invention is not applied, and FIG. A sectional view of another embodiment of the optical isolator to which the invention is applied, FIGS. 6 and 7 are diagrams showing the angular characteristics of the glass polarizing plate, and Section 8 is a perspective view illustrating the operating principle of the optical isolator. 1.11.31...Polarizer 2.13.33...Analyzer 3.12.32...-Faraday rotator 10.23.4
3... Cylindrical magnet 21.22.41.42... Lens barrel 14-17.24-27.44-47... Ring patent applicant Shin-Etsu Chemical Co., Ltd. Figure 5 Figure 8 Figure 3 Figure 2 (b) Loss of talent to Yuzu (dB)

Claims (1)

[Claims] 1. An optical isolator in which a polarizer, a Faraday rotator placed in a magnetic field in the direction of propagation of light, and an analyzer are arranged between a light source and an optical system, wherein the polarizer and the An optical isolator characterized in that at least one of the analyzers is a glass polarizing plate, and a light incident angle to the polarizer or the analyzer is inclined by 1 to 30 degrees. 2. The optical isolator according to claim 1, wherein the combination of a polarizer, a Faraday rotator, and an analyzer is arranged in multiple stages. 3. In the optical isolator according to claim 1 or 2, the light incident surfaces of the polarizer, the Faraday rotator, and the analyzer are arranged parallel to each other, and the light incident angle is 1 to 1 as described above. An optical isolator characterized in that the 30° inclination is maintained by tilting the entire optical isolator. 4. In the optical isolator according to claim 1 or 2, the light incident surface of each optical element of the polarizer, the Faraday rotator, and the analyzer is independently tilted to achieve the above-mentioned light incident angle of 1 to 30. An optical isolator characterized in that an inclination of ° is maintained. 5. The optical isolator according to claim 1, 2, 3, or 4, wherein the Faraday rotator is a magnetic garnet film epitaxially grown on a paramagnetic garnet substrate. Isolator.