JPH01270021A - Optical isolator - Google Patents

Abstract

PURPOSE:To eliminate the deviation between the optical axes of incident light to the optical isolator and projection light from the optical isolator by slanting the light incidence surfaces of a polarizer and an analyzer in the mutually opposite directions by the same angle from the optical axis of the incident light. CONSTITUTION:The incident light 11a perpendicular to the light incidence/ projection surface of a case frame 6 passes through the polarizer 3 which slants by an angle theta and is made incident as linear polarized light 11c on a Faraday rotator 2 at right angles. Then the light is rotated by 45 deg. through the Faraday rotator 2 to become linear polarized light 11d, which enters the analyzer 4. The polarizer 3 and analyzer 4 are as thick as each other and the analyzer 4 is slanted by the angle theta in the opposite direction from the polarizer 3, so the optical axis of the projection light 11b passed through the analyzer 4 is aligned with the optical axis of the incident light 11a. The tilt angle theta is so set that reflected light from the optical isolator does not return to the light source. Consequently, the deviation between the optical axes between the incident light 11a and projection light 11b is eliminated and the positioning adjustment of the optical isolator is facilitated.

Description

[Detailed Description of the Invention] [Industrial Field of Application] This invention is applicable to optical fibers and lens connectors used in optical communication using semiconductor lasers as light sources and writable video discs. This invention relates to an optical isolator for preventing reflected light.

[Conventional technology]

Conventionally, an optical isolator is a magneto-optic crystal with a thickness such that a Faraday rotation angle of 45 degrees can be obtained between a polarizer and an analyzer whose polarization directions are arranged at an angle of 45 degrees to each other and a predetermined interval is maintained between the polarizer and analyzer. A Faraday rotator consisting of

The basic configuration is that permanent magnets are arranged around the Faraday rotor for applying an external saturation magnetic field to the Faraday rotor.

The principle of this optical isolator will be explained based on FIG.

First, the polarization plane of light incident on the optical isolator in the forward direction will be explained based on FIG. 5(a).

Light 7a that has entered the optical isolator in the forward direction (direction of arrow A) enters the polarizer 3 of the optical isolator. Of the light 7a incident on the polarizer 3, linearly polarized light 7b passes through the polarizer 3. Next, the linearly polarized light 7b that has passed through the polarizer 3 is rotated by 45 degrees in the direction of arrow a by the direction of the magnetic field (direction of arrow 9) of a permanent magnet (not shown) in Faraday rotator 2, and undergoes Faraday rotation. The light passes through the light beam 2 and becomes linearly polarized light 7C. Furthermore, the linearly polarized light 7C rotated by 45 degrees passes through the polarizer 3 and the analyzer 4 disposed at 45 degrees, and the linearly polarized light 7C is rotated by 45 degrees.
d.

This linearly polarized light 7d will be emitted from the optical isolator.

Next, the polarization plane of light incident on the optical isolator from the opposite direction will be explained based on FIG. 5(b).

Light 8a entering the optical isolator from the opposite direction (direction of arrow B) passes through the analyzer 4 of the optical isolator and becomes only linearly polarized light 8b. Then, the linearly polarized light 8b is rotated by 45 degrees in the direction of the arrow a by the Faraday rotator 2, similarly to the case where the light is incident on the optical isolator in the forward direction. This is because of the non-reciprocity of Faraday rotation, the direction of Faraday rotation is determined only by the direction of the magnetic field (direction of arrow 9) from the permanent magnet (Il; 2I not shown), regardless of the incident direction of the light. This is for the purpose of

This linearly polarized light 8c rotated by 45 degrees is perpendicular to the polarizer 3, and thus cannot pass through the polarizer 3.

This optical isolator thus prevents light from entering from the opposite direction of the optical isolator.

Next, an example of a conventional optical isolator of this type will be explained based on FIG. 3.

This conventional optical isolator is shown in Figure 3.
2. Place the polarizer 3 and analyzer 4 on the case frame 6.
It is maintained at a predetermined distance. A Faraday rotator 2 is disposed between the polarizer 3 and the analyzer 4. Further, a permanent magnet 1 for applying an external saturation magnetic field is arranged around the Faraday rotor 2.

This optical isolator includes a polarizer 3. The light input and output surfaces of the Faraday rotator 2 and the analyzer 4 are all parallel to the light input and output surface of the case frame 6. Therefore, the surface reflected light 10c of the polarizer 3.

10d, surface reflected light 10e of Faraday rotator 2;

In order to prevent the surface reflected light Log 10f and the analyzer 4 from returning to the light source (not shown) consisting of a semiconductor laser, the optical axis of the incident light 10a from the light source is set to the light input/output surface of the case frame 6. It is tilted at an appropriate angle rather than perpendicular to the surface.

Note that 10b shown in FIG. 3 represents the light emitted from the optical isolator.

Further, in order to arrange the polarization directions of the polarizer 3 and the analyzer 4 at 45 degrees with respect to each other, the case frame 6 is provided with a groove at the location where the analyzer 4 is installed, as shown in FIG. The analyzer 4 is placed in this groove.

[Problem to be solved by the invention]

A conventional optical isolator has a polarizer of the optical isolator.
In order to prevent the respective surface reflected lights 10c to 10h from the Faraday rotator 2 and the transverse photon 4 from returning to the light source consisting of a semiconductor laser, the light input/output surface of the case frame 6 is set perpendicular to the optical axis of the incident light 10a. It needs to be tilted at a more appropriate angle. Therefore, as shown in FIG. 3, there is a problem in that the output light 10b from the optical isolator is deviated from the optical axis of the incident light 10a by δ. As a result, there is a problem in that it is difficult to adjust the position of the optical isolator.

Furthermore, due to factors such as the deviation of the Faraday rotation angle of the Faraday rotor 2 from the 45 degree Faraday rotation angle and the manufacturing accuracy of the case frame 6, the analyzer 4 is tilted from the groove of the case frame 6, as shown in FIG. In this case, the isolation ratio may be the best in some cases, and there is a problem in that it is difficult to align the analyzer 4.

Also, as shown in Figure 4, when manufacturing the optical isolator,
There are cases where the analyzer 4 is fixed at an angle of θ with respect to the V-groove, and the optical axis of the analyzer 4 is shifted by Δ compared to the case where the analyzer 4 is accurately fixed to the V-groove, and the output light 10b There is a problem that the effective beam diameter becomes small.

Therefore, an object of the present invention is to provide an optical isolake that can eliminate misalignment of the optical axes of incident light and outgoing light.

Another object of the present invention is to provide an optical isolator that allows easy alignment of an analyzer and prevents the effective beam diameter from becoming small.

[Means to solve the problem]

The optical isolator of the first invention is characterized in that the light incident surfaces of the polarizer and the analyzer are tilted in opposite directions by the same angle with respect to the optical axis of the incident light.

In the optical isolator of the second invention, either one of the polarizer and the analyzer is further fixed to a holder having a cylindrical outer surface with the optical axis passing through the inside thereof as the central axis, and the central axis and the central axis are fixed to the case frame. It is characterized by the provision of a coaxial cylindrical concave holder holding portion.

[For production]

According to the configuration of the first invention, since the light incident surfaces of the polarizer and the analyzer are arranged at the same angle with respect to the optical axis of the incident light and are inclined in opposite directions, the optical isolator There is no misalignment of the optical axis between the incident light on the optical isolator and the output light from the optical isolator.

According to the configuration of the second invention, either the polarizer or the analyzer is further fixed to a holder having a cylindrical outer surface whose central axis is the optical axis passing through the inside thereof, and the central axis of the case frame is connected to the holder. Since the polarizer and analyzer are placed on the coaxial cylindrical concave holder holding part, the polarizer and analyzer can be rotated relative to each other around the optical axis, making relative positioning of the polarizer and analyzer easy and effective. This can prevent the beam diameter from becoming smaller.

(Embodiment) An optical isolator according to an embodiment of the present invention will be described based on FIGS. 1 and 2.

As shown in FIG. 1, this optical isolator consists of a polarizer 3
The light incident surfaces of the analyzer 4 are tilted in opposite directions by the same angle θ with respect to the optical axis of the incident light 11a.

The polarizer 3 and analyzer 4 are held by a case frame 6 at a predetermined distance.

Furthermore, a Faraday rotator 2 made of a magneto-optic crystal is disposed between the polarizer 3 and the analyzer 4.

A case frame 6 around the Faraday rotor 2 is provided with a permanent magnet 1 for applying an external saturation magnetic field to the Faraday rotor 2.

Further, the analyzer 4 is fixed to a holder 5 having a cylindrical outer surface centered on the optical axis 11e passing through the inside thereof, and a cylindrical concave holder holding part 5' coaxial with the central axis of the holder 5 is attached to the case frame 6. The configuration is as follows.

This holder holding portion 5' is formed to have the same radius as the radius of the outer peripheral surface of the holder 5.

Incidentally, the inclination angle θ of the polarizer 3 and the analyzer 4 with respect to the optical axis of the incident light 11a is such that when the incident light enters the light input/output surface of the case frame 6 perpendicularly, It is set so that the surface reflected light from the Faraday rotator 2 and the analyzer 4 does not return to the light source (not shown), and the optical axes of the incident light 11a and the output light 11b do not deviate.

Furthermore, the light input/output surfaces of each of the Faraday rotator 2 and the case frame 6 are perpendicular to the optical axis of the incident light 11a.

The operation of this optical isolator will be explained below.

This optical isolator has a light i! made of, for example, a semiconductor laser, perpendicular to the light input/output surface of the case frame 6. ! (
(not shown). Then, the incident light 11a perpendicular to the light input/output surface of the case frame 6 passes through the polarizer 3 tilted at an angle θ with respect to the optical axis of the incident light 11a. Next, the linearly polarized light 11c that has passed through the polarizer 3 is perpendicularly incident on the Faraday rotator 2. The linearly polarized light 11c incident on this Faraday rotator 2 is, as in the conventional case,
The light is rotated by 45 degrees in the Faraday rotator 2 depending on the direction of the magnetic field of the permanent magnet 1 (not shown) and the thickness of the Faraday rotator 2, and passes through the Faraday rotator 2 to become linearly polarized light lid. Furthermore, this linearly polarized light lid is incident on the analyzer 4. Here, the thickness of the polarizer 3 and the analyzer 4 are the same, and the analyzer 4 is tilted at an angle θ in a direction opposite to that of the polarizer 3 from perpendicular to the optical axis of the incident light 11a. The optical axis of the emitted light 11b that has passed through the filter 4 becomes the same as the optical axis of the incident light 11a.

Also, the inclination angle θ of the polarizer 3 and the analyzer 4 with respect to the optical axis of the incident light 11a is determined by the polarizer 3. Since the setting is such that the surface reflected light from the Faraday rotator 2 and the analyzer 4 does not return to the light source, there is no reflected light from the optical isolator to the light source.

As a result, it is possible to eliminate the misalignment of the optical axes of the incident light 11a and the output light 11b, and also to eliminate the reflected light from the optical isolator to the light source, so that the light input/output surface of the case frame 6 of the optical isolator is aligned with the light input from the light source. It can be arranged perpendicularly to the light 11a. Therefore, the positioning adjustment of the optical isolator can be easily performed.

Further, the analyzer 4 is fixed to a holder 5 having a cylindrical outer surface whose central axis is the optical axis 11e passing through the inside of the analyzer 4.
is placed on the cylindrical concave holder holding portion 5' coaxial with the central axis of the holder 5 of the case frame 6, so that the analyzer 4 can be
The polarizer 4 can be rotated in the direction of arrow C shown in FIG. 2 with the optical axis lie passing through the inside of the analyzer 4 as the central axis, and the polarizer 3 and the analyzer 4 can be relatively rotated around the optical axis.

As a result, the relative alignment between the polarizer 3 and the analyzer 4 can be easily achieved, and the output light 11b from the optical isolator can be easily aligned.
This can prevent the effective beam diameter from becoming smaller.

In addition, in this embodiment, the analyzer 4 is fixed with the holder 5,
Although the analyzer 4 is designed to rotate around the optical axis lie passing through the inside of the analyzer 4, a holder is provided on the polarizer 3 so that the polarizer 3 can be rotated around the optical axis passing through the inside of the polarizer 3. You can.

〔Effect of the invention〕

In the optical isolator of the first invention, the polarizer and the analyzer are arranged at the same angle with respect to the optical axis of the incident light and are tilted in opposite directions, so that the incident light and the analyzer are arranged in opposite directions. Misalignment of the optical axis with the light emitted from the optical isolator can be eliminated.

The optical isolator of the second invention further includes identifying either the polarizer or the analyzer as a holder having a cylindrical outer surface whose central axis is the optical axis passing through the inside thereof, and which is coaxial with the central axis of the case frame. Since the polarizer and analyzer are placed in the cylindrical concave holder holding part, the polarizer and analyzer can be rotated relative to each other around the optical axis, making it easy to align the polarizer and analyzer relative to each other, and to improve the effective beam. This can prevent the diameter from becoming smaller.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the structure of an optical isolator according to an embodiment of the present invention, FIG. 2 is a side view as seen from the analyzer side of FIG. 1, and FIG. 3 is a cross-sectional view showing the structure of a conventional optical isolator. figure,
FIG. 4 is a sectional view taken along the line ■-IV in FIG. 3, and FIG. 5 is a configuration diagram for explaining the principle of the basic configuration of a conventional optical isolator. 2...Faraday rotator, 3...Polarizer, 4...Analyzer 5...Holder, 5'...Paholder holding part, 6...
・Case frame Figure 1 Figure 2 Figure 3 (a) (b) Figure 5

Claims (2)

[Claims] (1) In an optical isolator in which a polarizer and an analyzer are held at a predetermined interval by a case frame, and a Faraday rotator is disposed between the polarizer and the analyzer, light incident on the polarizer and the analyzer An optical isolator characterized in that its surfaces are tilted in opposite directions by the same angle with respect to the optical axis of incident light. (2) Either one of the polarizer and the analyzer is fixed to a holder having a cylindrical outer surface whose central axis is the optical axis passing through the inside thereof, and the holder with a cylindrical concave surface coaxial with the central axis is held on the case frame. The optical isolator according to claim (1), further comprising a portion.