JPS592016A - Optical isolator - Google Patents

Abstract

PURPOSE:To obtain an optical isolator of small-sized constitution in which the dependency of the loss in a reverse direction on wavelength is decreased by using an optical rotator of which the dependency on wavelength varies with the combination of two sheets of specific phase difference plates with respect to a Faraday rotor. CONSTITUTION:The light in a forward direction through an optical fiber 1 and a lens 2 is separated to an ordinary ray and an extraordinary ray by a tapered polarizing and synthesizing element 3, and both rays are polarized to the polarized light rotating by 45 from the optical axis of the element 3 by means of an optical rotator 4 of which the dependency on wavelength offsets the dependency on wavelength of a 45 deg. Farady rotor 5 and the rotor 5. The extraordinary ray is made parallel with the ordinary ray by a polarizing and synthesizing element 6 similar to he element 3, and both rays are made incident to an optical fiber 8 through a lens 7. On the other hand, the light in a reverse direction passes through the rotor 5, whereafter the deviation in the angle of Faraday rotation owing to the dependency on wavelength of the rotor 5 is corrected by the rotator 4 and both ordinary ray and extraordinary ray are refracted by the element 3 so that the light in the reverse direction is not made incident to the fiber 1. The optical isolator of the small-sized constitution which uses the optical rotator and decreases the dependency of the loss in the reverse direction on the wavelength is thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical Field of the Invention The present invention relates to an optical isolator, and particularly relates to an optical isolator that reduces wavelength dependence and is improved.

Prior Art and Problems The present inventor has previously proposed an optical isolator for use in a tapered birefringent material plate tube polarization separation/synthesis element that transmits 100 - 2 σ in the forward direction, and furthermore, An optical isolator was proposed in which an optical rotator formed by a '/2 elongated plate is disposed close to the 460 Falade single rotator disposed between the above-mentioned polarization separation/synthesis elements to transmit light in the forward direction. However, these isolators have a wavelength shift of about 2% or more.

This caused deterioration of the original isolator's isolator, in which light from the opposite direction was transmitted through without being removed.

(3) Object of the Invention In view of the above drawbacks, the object of the present invention 9) is to provide an original isolator in which the wavelength dependence of reverse loss is reduced.

Another object of the invention is to provide an optical isolator that allows the use of small optical polarizers.

(4) Structure of the Invention The object of the present invention is to provide a first structure comprising a tapered birefringent material plate.
A second polarization combining element P consisting of a Kutsu polarization separation element, an optical rotator % 45077 Rade rotator, and a tapered birefringent material plate (included in the order 7J, the optical isolator has two optical polarizers Q). It is an optical rotator that combines a retardation plate, and the wavelength dependence of the optical rotation angle of the optical rotation photon is 45°.
Same as the wavelength dependence of Faraday rotator, and the 45°
7 Alade one rotator Q] This can be achieved by an optical isolator characterized in that it acts so as to cancel the wavelength dependence.

(5) Example of Invention C/J Figures 1 and 2 are schematic diagrams showing the original isolator 2 according to the present invention. Particularly, Figure 1 shows the state of transmission of light in the forward direction, and Figure 2 shows the state of transmission of light in the forward direction. It shows the transmission state of light GjJ in the opposite direction.

As shown in FIG. 1, a tapered first birefringent material (polarization splitting element) 3. is provided on the left side of the 45° Faraday rotator 5.
An optical rotator 4 which is a combination of two retardation plates unique to the present invention is disposed, and a tapered second birefringent material (polarization combining element) 6 is disposed on the right side. Tapered first σ
] When light is incident on the polarization separation element in the forward direction (from left to right in Figure 1), the refractive index differs depending on the polarization, so it is separated from the ordinary light and extraordinary light and refracted in a different direction, and is incident on the optical rotator 4 and transmitted. The light is further incident on the 45° Faraday rotator 5. The optical axis of the tapered second polarization combining element 6 is rotated by 45 degrees in the light beam direction V with respect to the optical axis of the tapered first polarization separating element 3. The ordinary light and the extraordinary light that have passed through the stand H and the Satoru 6 are emitted parallel to each other, and both are focused onto the optical fiber 8 by the lens 7. On the other hand, the light beam in the opposite direction (from right to left in Figure 2) enters the tapered polarization separation element 6, and after 17C, it separates into ordinary light and extraordinary light and is refracted in different directions at 45° Faraday rotator 5. The plane of polarization is rotated by 450 and the light is emitted.

The ordinary light 5 whose polarization plane has been rotated by 45° is incident on the optical rotator 4 . In this case, if the incident wavelength λ is Δλ wavelength Q], the wavelength dependence of the Faraday rotator θ, Δθ
, but this Δθ is input.

is used with an optical rotator 4 having a set of 60 μm λ equal to , and acting in the opposite direction to the Faraday rotator. The deviation of the Faraday rotation angle caused by the change in the wavelength in the Faraday rotator is compensated for. Therefore, the extraordinary light emitted from the optical rotator 4 is the polarization synthesis optical The polarized light is rotated by 90 degrees with respect to the axis and undergoes anomalous refraction.

On the other hand, the ordinary light with a polarization plane of 6 (shown by a wavy line) is similarly
The polarizing table H and the element 3 receive the Zino [reflection] as extraordinary light. For this reason, when the light is focused into the fiber by the lens 2, the backward light does not enter the fiber 1.

The optical rotator 4 is made of a combination of two phase plates in order to be small, and is made of a birefringent material plate such as quartz, and may have a thickness of 30 to 100 .mu.m and a diameter of 3 to 5 .mu.m. As an example, there is a combination of a 1/2 wavelength plate and a J/4 wavelength plate, and after linearly polarized light is rotated by the e'/2 wavelength plate, the main axis of the 1/4 wavelength plate is set as the polarization direction. It is possible to convert the elliptical polarization caused by Δλ into a change in the angle of optical rotation.

(6) Effects of the invention As is clear from the above explanation, the wavelength dependence of reverse loss can be achieved by using an optical rotator that combines two retardation plates that have the same wavelength dependence as that of a 450 Faraday rotator. Thus, it is possible to obtain an optical isolator with reduced thermal resistance and miniaturization.

[Brief explanation of the drawing]

Figure w41 and Figure 2 are schematic diagrams for explaining the present invention. J, 8...Fiber% 2.7...Lens, 3.6...Tapered polarization splitting element, 4
... Self... Rotator, 5...45° Faraday rotator. Patent applicant Fujitsu Ltd. Patent agent Akira Aoki Patent attorney Kazuyuki Nishidate 1) Yukio Patent attorney Akira Yamaguchi

Claims (1)

[Claims] A first +7J polarization polarizer J1 optical rotator made of a tapered birefringent material plate, a 45° Faraday rotator, and a second polarization rotator made of a tapered birefringent material plate. In the original isolator including in this order; the optical rotator is an optical rotator made by combining two retardation plates, and the optical rotation angle of the optical rotator has a wavelength dependence of 45°; the wavelength of the Faraday rotator; Same as dependence. An optical isolator characterized in that the optical isolator is operated to cancel the wavelength dependence of the 45° Faraday rotator.