JPS60130934A - Optical isolator - Google Patents

Abstract

PURPOSE:To decrease the deterioration in isolation due to an incomplete Farady rotor by using two optical isolators in series in the optical isolators comprising a birefringence taper plate and a 45 deg. Farady rotor. CONSTITUTION:The 1st stage optical isolator is constituted by providing the 1st 45 deg. Farady rotor 4A between the 1st birefringence taper plate 3A and the 2nd birefringence taper plate 3B. On the other hand, the 2nd stage optical isolator is constituted by providing the 2nd 45 deg. Farady rotor 4B between the 3rd birefringence taper plate 3C and the 4th birefringence taper plate 3D. They are arranged in series to form 2-stage constitution and the tilt direction of the 1st and 2nd biregringence taper plates and the 3rd and 4th birefringence taper plates is shifted by 90 deg. mutually. Since the optical isolators are used twice in this way, the deterioration of isolation due to the incomplete Farady rotor or the like is decreased.

Description

[Detailed description of the invention] (m+ Technical field of invention The present invention relates to the configuration of an optical isolator.

(Yama) Technology background: Semiconductor lasers are used as light sources in optical communication networks.
Noise occurs in the optical signal when it is irradiated with reflected light or the like in the middle of the circuit network that has been transmitted in the opposite direction by the optical fiber. Therefore, an optical isolator is inserted in front of the semiconductor laser to prevent the light transmitted in the opposite direction from irradiating the semiconductor laser and to stabilize the operation of the semiconductor laser, and the light beam in the forward direction forms a circuit network. Inject into optical fiber□
However, the light rays in the opposite direction are diverted out of the optical fiber. ' □(C1 Prior art and problems Figure 1 shows an example of the configuration of a conventional optical isolator consisting of a birefringent tapered plate and a 45 degree Faraday rotator. Figure 2 shows the operation of the optical isolator. <al is a diagram showing the operation with respect to the forward direction light ray, and the figure 2 (color) is the diagram showing the operation with respect to the reverse direction light ray. In the figure, iA', IB are optical fibers, 2A, 2B are lenses, and 3A.

3B is a birefringent tapered plate, and 4 is a 45 degree Faraday rotator.

The operation of the optical isolator shown in FIG. 1 is as shown in FIG. 2(a), in which a forward light beam entering the birefringent tapered plate 3^ from the optical fiber 1A via the lens 2A is directed to the birefringent tapered plate 3A. The light beam is separated into two beams while passing through the 45-degree Faraday rotator 4 and the birefringent tapered plate 3B, but the two separated beams are parallel and condensed by the lens 2B and enter the optical fiber 1B. Further, as shown in the second figure, the light beam in the opposite direction that enters the birefringent tapered plate 3B from the optical fiber 1B via the lens 2B is transmitted to the birefringent tapered plate 3B.
B. While passing through the 45-degree Faraday rotator 4 and the birefringent tapered plate 3A, the light beam is separated into two directions, and the light beam passes through the lens 2.
Even if the light passes through the optical fiber 1A, the light is not focused and does not enter the optical fiber 1A.

However, since the optical fiber 1A is located between the two separated beams, the component that was not completely rotated by the Faraday rotator actually travels straight toward the optical fiber 1A, reducing the light incident on the optical fiber 1A to zero. Therefore, such optical isolators could not sufficiently remove noise generated in optical signals.

(d) Purpose of the Invention An object of the present invention is to provide an optical isolator with high isolation by sufficiently removing light rays in the opposite direction that are incident on an optical fiber.

(a) Structure and object of the invention is to provide a unit comprising a first 45 degree Faraday rotator disposed between a first birefringent tapered plate and a second birefringent tapered plate, and a third birefringent tapered plate. units in which a second 45-degree Faraday rotator is arranged between the first and second birefringent tapered plates and the fourth birefringent tapered plate are arranged in series, and This is achieved by shifting the inclination direction of the birefringent tapered plate by 90 degrees.

(f) Examples of the invention The present invention will be explained in detail below with reference to the accompanying drawings.

FIG. 3 is a perspective view showing one embodiment of the present invention, and FIG. 4 is a diagram showing the operation of the optical isolator according to the present invention. FIG. 4) is a diagram showing the operation for light rays in the opposite direction. Note that the first
Objects that are the same as those in the figure are represented by the same symbols.
A, 1B is an optical fiber, 2A.

2B is a lens, 3^ is a first birefringent tapered plate, 3B is a second birefringent tapered plate, 3C is a third birefringent tapered plate, 3
D is the fourth birefringent tapered plate, 4^ is the first 45-degree Faraday rotator, and 4B is the second 45-degree Faraday rotator.

The optical isolator according to the present invention is manufactured by shifting the inclination direction of the birefringent tapered plate of the conventional optical isolator by 90 degrees as shown in FIG. ! ! A first birefringent tapered plate 3A and a second birefringent tapered plate 3B are connected to each other.
A 455 degree Faraday rotator 4A is disposed to constitute a first stage optical isolator, and a second 455 degree double refraction rotator 4A is provided between the third birefringent taper plate 3C and the fourth birefringence taper plate 3D.
A second-stage optical isolator is constructed by disposing B, and a two-stage connected optical isolator is constructed by arranging them in series. Then, the inclination directions of the first and second birefringent tapered plates and the inclination directions of the third and fourth birefringent tapered plates are set to 90 degrees.
It is shifted by 0 degrees.

The forward light beam incident on the optical isolator having such a configuration from the optical fiber 1A via the lens 2A is shown in FIG. 4(a).
As shown in Figure 2, the beam is separated into two beams while passing through the first optical isolator, and each beam is further separated into two beams while passing through the second optical isolator, but the separated quaternary beam are parallel, and the light is focused by the lens 2B and enters the optical fiber 1B.

In addition, as shown in Figure 4, the light beam in the opposite direction entering the birefringent tapered plate 3B from the optical fiber 1B via the lens 2B is divided into two light beams while passing through the second stage optical isolator in reverse. The light beams are separated, and each light beam is separated into two beams while passing through the first stage optical isolator in reverse. According to this configuration, since the light passes through the optical isolator twice, deterioration in isolation due to imperfections in the Faraday rotator is extremely small.

(g) Effects of the Invention As described above, according to the present invention, it is possible to sufficiently remove light rays incident on an optical fiber in the opposite direction, and to provide an optical isolator with high isolation.

[Brief explanation of drawings]

First FI! J is a configuration example of an optical isolator consisting of a conventional birefringent tapered plate and a 45-degree Faraday rotator, and Figure 2 is a diagram showing the operation of the optical isolator. Figure 2) is a diagram showing the operation for rays in the opposite direction, 3rd W! J is a perspective view showing one embodiment of the present invention, and FIG. 4 is a view showing the operation of the optical isolator according to the present invention. is a diagram showing the operation for light rays in the opposite direction. In the figure, 1^ and 1B are optical fibers, 2^ and 2B are lenses, 3^ is the first birefringent taper plate, and 3B is the second birefringent taper plate. 3C is the third birefringent tapered plate, 3D is the fourth birefringent tapered plate, 4A is the first 45 degree Faraday rotator, and 4B is the second 45 degree Faraday rotator. 72) Ne4Z

Claims (1)

[Claims] In an optical isolator comprising a wax refractive Taber plate and a 45 degree Faraday rotator, a unit comprising a first 45 degree Faraday rotator disposed between a first birefringent tapered plate and a second birefringent taper plate; Units each having a second 45 degree Faraday rotator arranged between the third birefringent tapered plate and the fourth birefringent tapered plate are arranged in series, and the inclination direction of the first and second birefringent tapered plates is An optical isolator characterized in that the inclination directions of the third and fourth birefringent tapered plates are shifted by 90 degrees.