JPH03264914A - Optical isolator - Google Patents

Abstract

PURPOSE:To align the optical axes of incident light and exit light by forming a polarizer, Faraday rotator and analyzer into specific constitution, thereby preventing the reflection of the reflected light rays of the respective end faces of the polarizer, the Faraday rotator and the analyzer in the direction of the incident light. CONSTITUTION:The polarizer 1, the Faraday rotator 3 and the analyzer 5 are inclined by a prescribed angle with the optical axis of the incident light 10 and, therefore, the reflected light rays reflected by the end faces of the polarizer 1, the Faraday rotator 3 and the analyzer 5 do not align any longer to the optical axis of the incident light 10. These reflected light rays are, therefore, surely removed from the optical axis of the incident light 10. The isolator is so constituted that optical axis misalignments deltap, deltaf, deltaa attain deltap + deltaf = deltaa 0. The optical axes of the incident light 10 on the optical isolator and the light 11 emitted from the optical isolator are aligned in this way.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is directed to an optical eye 7 used in optical communication, optical measurement, etc.
It concerns the rater.

[Conventional technology]

Conventionally, when a semiconductor laser is used as a light source for optical communication, etc., an optical isolator is attached to prevent the return light of the laser light emitted from the semiconductor laser from entering the semiconductor laser again.

This optical isolator has a structure in which a Faraday rotator is disposed between a polarizer and an analyzer.

However, in this type of conventional optical isolator, the laser light that is incident approximately perpendicularly to the end faces of the polarizer, Faraday rotator, and analyzer that make up the optical isolator is reflected by the end faces and returns to the laser light source as light. There was a problem in that the incident light caused resonance and interference.

FIG. 9 is a diagram showing a conventional optical isolator that solves this problem.

As shown in the figure, this optical isolator includes a polarizer 81, a Faraday rotator 82, and an analyzer 83 arranged in this order, and a ring-shaped magnet 84 attached to the outer periphery of the Faraday rotator 82. ing. Laser light is made to enter the end face of the polarizer 81 obliquely from above.

With this configuration, the reflected light reflected by each end face of the polarizer 81, the Faraday rotator 82, and the analyzer 83 is reflected in a direction different from the direction of the original incident light. There is no resonance interference with the incident light.

[Problem to be solved by the invention]

However, with this optical isolator, the optical axis of the incident light and the optical axis of the output light are misaligned, so when installing this optical isolator inside a device, there is a problem in that it is difficult to align the optical axes. Ta.

In order to solve this problem, as shown in FIG. 10, the polarizer 91 and analyzer 93 are tilted in opposite directions by the same angle θ with respect to the optical axis of the incident light. Some had a structure that made the optical axes of the incident light and the output light coincide.

However, this optical isolator has the problem that the Faraday rotator 92 must be arranged perpendicular to the optical axis, and the light reflected by both end surfaces of the Faraday rotator 9 returns to the direction of the incident light. Ta.

The present invention has been made in view of the above points, and the reflected light reflected by each end face of the polarizer, Faraday rotator, and analyzer of the optical isolator is not reflected in the direction of the original incident light, and An object of the present invention is to provide an optical isolator that can align the optical axes of light incident on the optical isolator and light emitted from the optical isolator.

[Means to solve the problem]

In order to solve the above-mentioned problems, the present invention provides an arrangement in which the end faces of the polarizer 1, the Faraday rotator 3, and the analyzer 5 (excluding the analyzer 5 in some cases) are separated from a plane perpendicular to the optical axis of the incident light 10. each tilted at a predetermined angle within the same plane including the optical axis,
Optical axis deviations Sp, 8f, of the light entering and exiting the polarizer 1, Faraday rotator 3, and analyzer 5, respectively;
lea is δp+8f+δag.

It was configured so that

Further, in the present invention, the polarizer 1, the Faraday rotator 3, the analyzer 5, and the magnet 7 are housed in the case 12, and at least one of the polarizer 1 and the analyzer 5 is housed in the holder 13. The optical isolator was constructed by holding the holder 13 rotatably in the case 12 without changing the angle of incidence of light onto the end face of the polarizer 1 or the analyzer 5.

Further, in the present invention, the polarizer 1, the Faraday rotator 3, and the analyzer 5 are housed in a case 12, and the entire case 12 is made of a magnet.

[Effect]

As mentioned above, polarizer 1. Faraday rotator 3° analyzer 5
Since it is tilted at a predetermined angle with respect to the optical axis of the incident light 10, the reflected light reflected at the end faces of the polarizer, Faraday rotator, and analyzer no longer coincides with the optical axis of the incident light. Therefore, these reflected lights are reliably removed from the optical axis of the incident light.

In addition, as mentioned above, the optical axis deviations Sp, εf, Sa are δp + δ
Since the configuration is such that f1δago, the optical axes of the light incident on the optical isolator and the light emitted from the optical isolator coincide. Therefore, optical axis adjustment when installing this optical isolator into equipment becomes easy.

Further, as described above, at least one of the polarizer and the analyzer is fixed in a holder, and the holder is placed in the case without changing the incident angle of light to the end face of the polarizer or analyzer. Since it is held rotatably, the plane of polarization can be easily adjusted by rotating the holder to obtain the best isolation.

〔Example〕

Hereinafter, one embodiment of the present invention will be described in detail based on the drawings.

FIG. 1 is a diagram showing one embodiment of an optical isolator according to the present invention.

As shown in the figure, this optical isolator is constructed by arranging a polarizer 1, a Faraday rotator 3, and an analyzer 5 in series in this order, and providing a ring-shaped magnet 7 around the outer periphery of the Faraday rotator 3. has been done.

Here, the polarizer 1, the Faraday rotator 3, and the analyzer 5 are each set at an angle from a plane perpendicular to the optical axis of the incident light so that the reflected light reflected at both end faces does not coincide with the optical axis of the incident light. It is tilted by θp, θf, and θa. Note that the directions in which they are tilted are all within the same plane that includes the optical axis of the incident light, and the tilt angles are not 0@.

When the polarizer, Faraday rotator, and analyzer are tilted as shown in FIG.
When passing through the Faraday rotator 3, the optical axis is shifted downward by δp, then when passing through the Faraday rotator 3, the optical axis is shifted upward by δf, and when passing through the analyzer 5, the optical axis is shifted downward by δp. Shift upward by &a.

In the present invention, the total optical axis deviation is S
The angles θp and θa are set so that p+δf+δa=O.
, θf should be determined, but the method will be explained next.

Figure 2 shows how to determine the optical axis deviation δ between the incident light 17 and the output light 19 when an optical element 15 such as a polarizer is arranged so that its end face is inclined at an angle θ with respect to a plane perpendicular to the incident light. This is a diagram.

As shown in the figure, if the refractive index of air is n, the refractive index of optical element 15 is n', and the thickness of optical element 15 is 2, then the optical axis of output light 19 is shifted from the optical axis of incident light 17. δ is given by.

Therefore, the optical axis deviations of the polarizer 1, Faraday rotator 3, and analyzer 5 are determined by this equation, and the angles θp and θf are adjusted so that the total optical axis deviation becomes 8p + Sf + δa = 0. , θa.

Incidentally, the polarizer 1, Faraday rotator 3, and analyzer 5 that constitute this optical isolator are normally housed and fixed in a case, but the polarization planes of the polarizer 1 and analyzer 5 are set at a predetermined angle around the optical axis. (Usually 45) It is necessary to shift it.

FIG. 3 is a diagram showing an optical isolator equipped with a rotation mechanism for changing the relative angle between the polarization plane of the polarizer 1 and the polarization plane of the analyzer 5 around the optical axis.

As shown in the figure, a polarizer 1, a Faraday rotator 3, an analyzer 5, and a magnet 7 are housed in a case 12. The analyzer 5 and the magnet 7 are fixed within the case 12, and the Faraday rotator 3 is fixed within the magnet 7. - The old photon 1 is fixed in a holder 13, which is attached to the case 12.

FIG. 4 is a cross-sectional view of the holder 13 taken along line A--A shown in FIG. 3.

As shown in the figure, the outer peripheral side surface of the holder 13 has a cylindrical shape.

When this holder 13 is inserted into the case 12 shown in FIG. 3, it becomes rotatable about the central axis perpendicular to the end surface of the polarizer 1. Therefore, even if the polarizer 1 is rotated,
The angle of inclination of the end face of the polarizer 1 with respect to the incident light 10 remains unchanged.

Therefore, after installing each component constituting the optical isolator in the case 12, the holder 13 is rotated and adjusted so that the polarization plane of the polarizer 1 and the polarization plane of the analyzer 5 are shifted by a predetermined angle around the optical axis. If the holder 13 is fixed in this state,
The adjustment work can be easily completed.

Note that this holder 13 may be attached to the analyzer 5 instead of being attached to the polarizer 1.

FIG. 5 is a diagram showing still another embodiment of the present invention.

In this embodiment, the magnet 7 shown in FIG. 3 is omitted,
The entire case 12 is made of magnets.

With this configuration, the number of parts can be reduced.

By the way, when the Faraday rotator 3 is installed as in each of the above embodiments, as shown in FIG. There may be cases where the numbers do not match.

In such a case, use the method below to adjust the rotation angle (
(usually 45°).

That is, if the Faraday rotation angle is θF, then θ'
f=sin-' (sin θf/nf) C A constant specific to two substances M: Magnetization magnitude (normally saturation magnetization is used).

Therefore, for example, if you want the rotation angle of the plane of polarization rotated by the Faraday rotator 3 to be 45 degrees, insert θF-45@ into this equation to find if, and set the Faraday rotator 3 so that the thickness is equal to the thickness if. All you have to do is adjust the thickness.

Note that in the embodiment shown in FIG.
, θf, and θa are specifically determined as an example: 11a-1p-3wn , l, f -0,36mn
Conditions of na = np -1,5, nf -2,3 (θ
a-θf), the results are as shown in FIGS. 7 and 8.

As can be seen from both figures, according to the present invention, the total of each optical axis deviation was almost O, and there was almost no optical axis deviation.

In each of the above embodiments, the polarizer 1, Faraday rotator 3, and analyzer 5 are all tilted at a predetermined angle with respect to the optical axis of the incident light 10, but the polarization plane of the light rotated by the Faraday rotator 3 When the angle is 45°, the end face of the analyzer 5 may be arranged perpendicular to the optical axis. Because polarizer 1
．． The returned light that passes through the Faraday rotator 3 and is reflected by both end faces of the analyzer 5 passes through the Faraday rotator 3 twice, so it enters the polarizer 1 with its plane of polarization rotated by 90 degrees. This is because the light cannot pass through the polarizer 1.

〔Effect of the invention〕

As described above in detail, the optical isolator according to the present invention has the following excellent effects.

(1) Reflected light generated at the end faces of the polarizer, Faraday rotator, and analyzer can be reliably removed from the optical axis of the incident light.

(Since the optical axes of the incident light and the emitted light can match, it becomes easy to adjust the optical axis when installing this optical isolator inside a device.

■Storing the polarizer, Faraday rotator, analyzer, and magnet in a case, fixing at least one of the polarizer and analyzer in a holder, and attaching the holder to the polarizer or analyzer. If the optical isolator is rotatably held in the case without changing the angle of incidence of the light onto the end face, it becomes easy to adjust the plane of polarization around the optical axis when manufacturing the optical isolator.

(4) If the polarizer, Faraday rotator, and analyzer are housed in a case made of magnets, the number of parts can be reduced and costs can be reduced.

[Brief explanation of drawings]

FIG. 1 is a diagram showing one embodiment of the optical isolator according to the present invention, FIG. 2 is a diagram for determining the optical axis deviation δ between the incident light 17 and the output light 19 in the optical element 15, and FIG. Diagram 4 showing an embodiment in which a case is attached to an isolator.
The figure is a cross-sectional view showing the holder 13 taken along the line A-A shown in FIG. 3, FIG. 5 is a view showing still another embodiment of the present invention, and FIG. Figures 7 and 8 are diagrams showing the state of optical axis deviation when specific numerical values are applied to the example shown in Figure 1, and Figures 9 and 10 are diagrams showing the state in which the light is transmitted. FIG. 1 is a diagram showing a conventional optical isolator. In the figure, 1... polarizer, 3... Faraday rotator, 5
... Analyzer, 7... Magnet, 10... Incident light, 11
... Outgoing light, 12... Case, 13... Holder.

Claims (3)

[Claims] (1) In an optical isolator in which a polarizer, a Faraday rotator, and an analyzer are arranged in series in this order with respect to the incident light, and a magnet is provided on the outer periphery of the Faraday rotator to apply a magnetic field to the Faraday rotator. , at least the end faces of the polarizer and the Faraday rotator are each tilted at a predetermined angle from a plane perpendicular to the optical axis of the incident light within the same plane that includes the optical axis, the polarizer, the Faraday rotator, and the analyzer An optical isolator characterized in that the optical axis deviations δp, δf, and δa between the incident light and the emitted light are as follows: δp+δf+δa≒0. (2) The polarizer, Faraday rotator, analyzer, and magnet are housed in a case, and at least one of the polarizer and analyzer is fixed in a holder, and the holder is used to store the polarizer or the analyzer. The optical isolator according to claim 1, wherein the optical isolator is rotatably held in the case without changing the angle of incidence of light onto the end face of the analyzer. (3) The optical isolator according to claim 1 or 2, wherein the polarizer, Faraday rotator, and analyzer are housed in a case, and the entire case is made of a magnet.