JP2789124B2 - Optical isolator - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical isolator that removes return light generated by reflection and scattering of light emitted from a light source.

[Conventional technology]

Conventional optical isolators are installed immediately before a light emitting source such as a laser diode, and receive and transmit outgoing light emitted from the laser diode or the like, and return generated by reflection, scattering, etc. of the transmitted outgoing light. Has a function of removing light.

FIG. 4 shows a conventional optical isolator of this type.

As shown in the figure, this optical isolator has a plate-like Faraday rotator 82 disposed between a cubic or cylindrical polarizer 81 and an analyzer 83, and the polarizer 81 and the Faraday rotator 82 The analyzer 83 is configured to be housed in a cylindrical magnet 84.

Here, the Faraday rotator 82 is usually formed of a Bi-substituted garnet plate, and is configured to rotate the plane of polarization of incident light by 45 °.

The polarizer 81 and the analyzer 83 are each configured by a polarization beam splitter.

The magnet 84 applies a predetermined magnetic field so that the Faraday rotator 82 has a necessary rotation angle.

In the parallel light incident from the left side of the figure, only light having a predetermined polarization plane is transmitted by the polarizer 81, and the polarization plane is rotated by 45 ° by the Faraday rotator 82, and passes through the analyzer 83 in this state. Then, the light enters the desired optical component.

On the other hand, from the right side of the optical isolator, return light generated by reflection, scattering, or the like enters.

Then, of the return light, 45 with respect to the polarization plane of the polarizer 81.
The light having the rotated polarization plane is transmitted through the analyzer 83, and the polarization plane is further rotated by 45 ° by the Faraday rotator.

Eventually, only light having a polarization plane rotated by 90 ° with respect to the polarization plane of the polarizer 81 is incident on the polarizer 81, but this light cannot pass through the polarizer 81 and is almost reflected there. Therefore, the returning light is surely removed.

[Problems to be solved by the invention]

By the way, since the conventional optical isolator has a structure in which parallel light incident on the optical isolator is passed as it is as parallel light, in order to enlarge the opening, the opening diameter shown in FIG. With polarizer
It is necessary to increase the diameters of 81, Faraday rotator 82 and analyzer 83 accordingly.

However, the garnet constituting the Faraday rotator 82 is still expensive, and a large garnet has a problem that the price is high.

Further, in the above-mentioned conventional optical isolator, the outer diameter of the magnet 84 is usually required to be 3 to 5 times the opening diameter. Therefore, when the opening diameter is increased, the outer diameter of the magnet becomes 3 to 5 times larger. There is also a problem that the outer diameter of the entire optical isolator becomes considerably large.

The present invention has been made in view of the above points, and it is an object of the present invention to provide an optical isolator in which the difference between the outer diameter and the opening diameter of the optical isolator is small and the size of the Faraday rotator to be used can be reduced.

[Means for solving the problem]

In order to solve the above-mentioned problem, the present invention, as shown in FIG. 1, arranges a polarizer 1, a Faraday rotator 3, and an analyzer 5 in series in this order with respect to incident light. In an optical isolator provided with magnets 7 for applying a magnetic field to the Faraday rotator 3 on the outer periphery, infinite conjugate type lenses 9 and 11 are disposed on both sides of the Faraday rotator 3 and are parallel to one of the lenses 9 or 11. If light enters, the other lens
The Faraday rotator 3 was arranged at a focal position between the two lenses 9 and 11 so that parallel light was emitted from 11 or 9.

Further, the polarizer 1 and the analyzer 5 are formed on both surfaces of the Faraday rotator 3 or formed in the two lenses 9 and 11, respectively.

[Action]

By configuring the optical isolator as described above, the parallel light incident on one spherical lens 9 is focused on the installation position of the Faraday rotator 3 after passing through the polarizer 1,
Further, the light passes through the analyzer 5 and is emitted from the spherical lens 11 as parallel light.

Therefore, the spot size of the light incident on the Faraday rotator can be reduced, and the size of the Faraday rotator to be used can be reduced.

Also, the incoming and outgoing light can be made substantially equal to the effective diameter of the lens.
Therefore, the difference between the outer diameter of the optical isolator and the diameter of the opening becomes small.

〔Example〕

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

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

As shown in the figure, this optical isolator has a polarizer 1, a Faraday rotator 3, and an analyzer 5 arranged in series in this order with respect to the incident light, and magnets 7 provided on the outer periphery thereof, and further, on both sides thereof. Ball lenses 9 and 11 are disposed in the case 13 and these components are housed in a case 13.

 Hereinafter, each component will be described.

The Faraday rotator 3 is formed in a plate shape, and has a thickness that rotates the polarization plane of light incident on the Faraday rotator 3 by 45 °.

The polarizer 1 is configured by making the laminated polarizer thin, and is attached to the left side of the Faraday rotator 3.

The analyzer 5 is also formed by reducing the thickness of the laminated analyzer, and is attached to the right side of the Faraday rotator 3. The analyzer 5 is fixed at a position shifted from the polarization plane of the polarizer 1 by 45 ° around the optical axis.

The magnet 7 is formed in a cylindrical shape, and the polarizer 1, the Faraday rotator 3, and the analyzer 5 are fixed to the inner peripheral surface thereof. The magnet 7 applies a magnetic field to the Faraday rotator 3 in the optical axis direction.

The spherical lens 9 is arranged on the left side of the polarizer 1, and the spherical lens 11 is arranged on the right side of the analyzer 5.

The two spherical lenses 9 and 11 are arranged so that when parallel light enters one spherical lens 9, the parallel light is emitted from the other spherical lens 11, and the focal position between the two spherical lenses 9 and 11 is adjusted. The Faraday rotator 3 is disposed at a position.

Next, the state of light incident on the optical isolator will be described.

The parallel light that has entered the spherical lens 9 from the left side of the spherical lens 9 passes through the polarizer 1, then focuses at the installation position of the Faraday rotator 3, passes through the analyzer 5, and enters the spherical lens 11. Then, the light is emitted with substantially the same parallel light as that incident on the spherical lens 9, and is incident on desired optical components.

Here, the state of the polarization plane of light when passing through each optical component will be described.

First, only the light having a predetermined polarization plane passes through the polarizer 1 in the light passing through the spherical lens 9, and then the polarization plane is rotated by 45 ° in the Faraday rotator 3. The light passes under the condition, and is emitted to the outside through the spherical lens 11.

On the other hand, from the right side of the optical isolator, return light generated by reflection, scattering, or the like enters.

Of the returned light, light having a polarization plane rotated by 45 ° with respect to the polarization plane of the polarizer 1 passes through the analyzer 5,
The Faraday rotator 3 further rotates the plane of polarization by 45 °.

After all, only light having a polarization plane rotated by 90 ° with respect to the polarization plane of the polarizer 1 is incident on the polarizer 1, but this light cannot pass through the polarizer 1. This ensures that the return light is removed.

By configuring the optical isolator as described above, the aperture diameter of the optical isolator can be increased without increasing the size of the Faraday rotator 3.

 FIG. 2 is a view showing another embodiment of the present invention.

In this embodiment, the polarizer 1 'and the analyzer 5' are not mounted on the Faraday rotator 3, but are mounted inside the spherical lens 9 'and the spherical lens 11'.

In order to form the spherical lenses 9 'and 11', the spherical lenses are divided into hemispheres, and a dielectric multilayer film is deposited on the divided surfaces to have a polarizing beam splitter function.
Then, the divided hemispherical lenses may be joined.

Even with such a configuration, by installing the Faraday rotator 3 at the focal position between the spherical lenses 9 'and 11', the Faraday rotator 3 can be made smaller than the aperture diameter of the optical isolator.

 FIG. 3 is a view showing still another embodiment of the present invention.

In this embodiment, three cases 13-1, 13
The case 13-1 has a spherical lens 9 fixed thereto, the case 13-2 has a polarizer 1, a Faraday rotator 3, an analyzer 5 and a magnet 7 fixed thereto. The ball lens 11 is fixed to -3.

The case 13-1 and the case 13-3 are respectively attached to both sides of the case 13-2.

With this configuration, the case 13-2 to which the Faraday rotator 3 and the like are attached is the same, and the spherical lens 9 and the case 13-
The diameter of the incoming and outgoing light can be freely changed only by changing the size of 1 or the size of the spherical lens 11 and the case 13-3. Therefore, when this optical isolator is combined with another optical system, the connection becomes easy.

In each of the above embodiments, a spherical lens is used for the coupling lens system. However, the present invention is not limited to this, and other infinite conjugate lenses such as a graded index lens and an aspherical molded lens are used. Is also good.

Further, in the above embodiment, the Faraday rotator 3 is arranged at the focal position of the spherical lenses 9 and 11, but may be slightly shifted as long as the convergent light is within the range of the isolator optical system.

〔The invention's effect〕

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

(1) Since the incoming and outgoing light (all of which are parallel light) can be made substantially equal to the effective diameter of the lens, the aperture diameter with respect to the outer diameter of the optical isolator can be significantly increased as compared with the conventional optical isolator.

(2) Since the position of the Faraday rotator is substantially the focal point between the two lenses, the spot size of the light incident on the Faraday rotator can be reduced. For this reason, the size of the Faraday rotator to be used may be small, and the cost of the optical isolator can be reduced. Although the present invention requires two spherical lenses, these spherical lenses are much cheaper parts than the Faraday rotator.

[Brief description of the drawings]

FIG. 1 is a view showing one embodiment of an optical isolator according to the present invention, FIG. 2 is a view showing another embodiment of the present invention, FIG. 3 is a view showing still another embodiment of the present invention, FIG. FIG. 4 is a diagram showing a conventional optical isolator. In the figure, 1 ... polarizer, 3 ... Faraday rotator, 5 ...
Analyzer, 7 ... magnet, 9, 11, 9 ', 11' ... ball lens,
It is.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Toshimichi Yasuda 2-14-9 Tamagawadai, Setagaya-ku, Tokyo Kyocera Corporation Tokyo Yoga Office (56) References JP-A-62-21119 (JP, A) (58) Field surveyed (Int.Cl. ⁶ , DB name) G02B 27/28

Claims (3)

(57) [Claims] 1. A light having a polarizer, a Faraday rotator, and an analyzer arranged in series in this order with respect to incident light, and a magnet provided on an outer periphery of the Faraday rotator to apply a magnetic field to the Faraday rotator. In the isolator, an infinite conjugate type lens is arranged on both sides of the Faraday rotator, and if parallel light is incident on one lens, it is arranged so that parallel light is emitted from the other lens. An optical isolator characterized by being installed at a substantially focal position between two lenses. 2. The optical isolator according to claim 1, wherein the polarizer and the analyzer are formed on both surfaces of the Faraday rotator. 3. The apparatus according to claim 1, wherein the polarizer and the analyzer are respectively formed in the two lenses.
An optical isolator as described.