JPH07104227A - Optical fiber type non-reciprocity device - Google Patents

Abstract

PURPOSE:To reduce light reflection and loss while connecting to another optical system with a simple constitution by removing a portion of an optical fiber for transmission and putting a magneto-optical material into that portion. CONSTITUTION:A portion of a clad 3 of a qualtz single mode optical fiber is removed and a magneto-optical material 4 is put into that portion. Even though a core 2 is an isotropic material, a non-reciprocity phase shift is made by making the core 2 and the material 4 closer to a transmission light beam and actuating. Since a non-reciprocity characteristic is yielded even though the core 2 is isotropic material, no need is required for the fiber 1 itself or the material of the core 2 to be the material 4, a non-reciprocity characteristic is added at an arbitrary position by machining the arbitrary isotropic fiber 1. Thus, an optical isolator, an optical circulator and a modulator are very easily and inexpensively constituted employing this technique.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical isolator, an optical circulator, and an optical isolator used in the fields of optical communication and optical measurement.
The present invention relates to a non-reciprocal device applied to an optical switch or the like, and particularly to an optical fiber type non-reciprocal device which is entirely configured in a fiber type.

[0002]

2. Description of the Related Art Optical isolators and optical circulators have been manufactured by utilizing the nonreciprocal action due to the magneto-optical effect. A waveguide formed of magnetic garnet or the like and a waveguide layer having a magneto-optical effect is called a magneto-optical waveguide.
Of the magneto-optical effects, the one that utilizes non-reciprocal action may be called a non-reciprocal waveguide. The non-reciprocal waveguide is used for a waveguide type isolator, a modulator, etc., and performs non-reciprocal phase shift and non-reciprocal polarization plane rotation (Faraday rotation).
The conventional non-reciprocal waveguide is a rib type (FIG. 4A) in which the waveguide layer 5 is formed on the substrate 6, and the cladding 3.
A rectangular type such as an embedded type (FIG. 4B) in which the waveguide layer 5 is embedded is the mainstream. This is formed by a liquid phase epitaxial (LPE) method, a sputtering method, or the like. Further, a Faraday rotating fiber in which a magneto-optical material is molded into a fiber type for a fiber sensor, or a fiber type Faraday rotator having a configuration in which a magneto-optical material 4 (Faraday rotator) is sandwiched between optical fibers 1 as a fiber type device (FIG. 5) Etc. are also proposed.

The non-reciprocal action of the magneto-optical waveguide will be briefly described with reference to FIG. In the waveguide mode of light in such a three-dimensional waveguide, the main component of the electromagnetic field is Ex
And the E ^x mode, which is a Hy, and the main component of the electromagnetic field Ey H
It is roughly divided into E ^y modes that are x. These modes have become hybrid mode, E ^x mode for simplicity the TE mode at the Ey = 0, E ^y mode H
Each can be approximated to the TM mode by setting y = 0. Note that E (Ex, Ey, Ez) is the electric field vector, H
Let (Hx, Hy, Hz) be the magnetic field vector. Waveguide layer 5
In the conventional non-reciprocal waveguide formed of a magneto-optical material, non-reciprocal phase shift occurs in the TM mode by applying a magnetic field in the X direction of the waveguide. This is a phenomenon in which the propagation constants of light propagating in the + Z direction and light propagating in the −Z direction are different, and the propagation constant of the TM mode when no magnetic field is applied is β
If TM, the propagation constant when a magnetic field is applied is βTM ± Δβ (the double sign ± corresponds to the Z direction). This Δβ is the amount of non-reciprocal phase shift and is called the non-reciprocal phase amount. These are described in detail in the literature such as "Shingakuron VOL. J71-C pp702-708 Inuzuka, Okamura, Yamamoto 1988". Further, by applying a magnetic field in the Z direction, the propagated light undergoes Faraday rotation. This is non-reciprocal rotation of the plane of polarization (TE-TM mode conversion), and both the light propagating in the + Z direction and the light propagating in the −Z direction propagate in the same direction and at the same angle about the magnetic field direction. It rotates in the opposite direction based on the direction.

[0004]

However, as shown in FIG. 4 (A),
The rectangular non-reciprocal waveguide as shown in (B) is manufactured by using a thin film manufacturing technique such as sputtering, but it is very time-consuming and expensive. Further, in reality, the waveguide alone cannot be used as a device, and must be used by connecting it to an optical fiber or LD, so that a coupling optical system such as a lens is required. Coupling loss always occurs at the light input / output section, the number of parts such as lenses increases, and the time and effort for adjustment increase.

Although there is a fiber-shaped magneto-optical material, it was originally designed for a sensor or the like and was not devised to solve the problem of connecting rectangular waveguides.
It is difficult and expensive to form a magneto-optical material such as garnet into a fiber. In addition, although it is relatively easy to connect other fibers with a connector or the like, there is a problem that reflection occurs at the connection point because the refractive index of quartz, which is a material of a normal fiber, is greatly different from that of the magneto-optical material.

Further, even in the structure in which the magneto-optical material 4 is sandwiched between the optical fibers 1 as shown in FIG. 5, reflection occurs at the boundary between the optical fiber 1 and the magneto-optical material 4, and since there is no lens, the coupling efficiency is further deteriorated. It was

In order to solve the above problems, an object of the present invention is to provide a non-reciprocal waveguide using the magneto-optical effect,
An object of the present invention is to provide an optical fiber type nonreciprocal device which has a simple structure and has less reflection and loss of light in connection with other optical systems.

[0008]

In order to solve the above-mentioned problems, the present invention provides a method for directly adding non-reciprocal characteristics to an ordinary optical fiber for transmission. Specifically, by removing a part of the cladding of the optical fiber for transmission and loading the part with a magneto-optical material,
It causes non-reciprocity in a fiber that is isotropic in nature.

[0009]

In the past, in order to produce the magneto-optical effect, the waveguiding layer in which light is mainly present and the core itself are formed of a magneto-optical material. Here, there are causes of difficulty in formation, a difference in refractive index, and a problem of bonding. However, even if the light is confined, the electromagnetic field of the propagating light leaks to the outside of the waveguide layer. As a result of the examination as to whether or not it is possible to generate the magneto-optical effect in the core of the optical fiber which was originally isotropic by applying the magneto-optical material to the electromagnetic field leaching to the outside, It was also found that the magnitude of the magneto-optical effect was at a practical level.

[0010]

FIG. 1 shows an embodiment of the present invention. A part of the cladding 3 of the quartz single mode optical fiber 1 is removed, and the magneto-optical material 4 is loaded on the part. Here, a Ce-substituted YIG single crystal is loaded.

FIG. 2 is a schematic view of the structure of FIG. 1 for analysis and shows a cross section perpendicular to the light propagation direction. The core 2 of the optical fiber 1 is originally circular, but approximates a square. The magnetic field is applied in the X direction. FIG. 3 shows the non-reciprocal phase shift amount calculated by the finite element method by changing the distance H between the core 2 and the magneto-optical material 4 in the structure of FIG. The magneto-optical material 4 has a thickness d = 0.4 μm and a core diameter of 6
μm, the optical fiber 1 is made of quartz, and the core 2 has a refractive index of 1.504, the cladding 3 has a refractive index of 1.5, and C.
The e-substituted YIG has a refractive index of 2.23 and a magneto-optical constant γ of 7.7 × 10 ⁻³ . Non-reciprocal phase shift amount is H
Change from 0 μm to 3 μm, about 16.5r
It shows ad / cm. Looking at the above-mentioned documents for reference, the non-reciprocal phase shift of the rectangular non-reciprocal waveguide is a value of about 1.0 to 2.2 rad / cm, and the same or more non-reciprocal phase shift amount occurs. It can be seen that a practical device can be formed. Thus, even if the core 2 is an isotropic substance, it is possible to cause a non-reciprocal phase shift by bringing the core 2 and the magneto-optical material 4 close to each other and acting on the propagating light.

Therefore, even if the core is an isotropic substance, more non-reciprocity occurs. Therefore, the optical fiber itself or the material of the core does not need to be a magneto-optical material, and an arbitrary isotropic fiber can be used. By processing the, non-reciprocity can be added to any place. This makes it possible to construct an optical isolator, an optical circulator, a modulator, etc. very easily and inexpensively.

[0013]

[Effect] The present invention has a simple structure and does not need any optical alignment because it has no lens. In addition, the number of parts is small and the size is small. In addition, when the same fiber as the transmission fiber is used to connect to another optical fiber, there is no difference in the refractive index at the connection point, reflection is small, and coupling efficiency is improved. Further, non-reciprocity can be generated at any place of the optical fiber. As described above, since the nonreciprocal characteristic can be directly added to any transmission fiber, it has high applicability and great utility value.

[Brief description of drawings]

FIG. 1 is a perspective view of an optical fiber type nonreciprocal device showing an embodiment of the present invention.

FIG. 2 is a schematic sectional view of the present invention.

FIG. 3 is a graph showing a non-reciprocal phase shift amount in the present invention.

FIG. 4 is a diagram showing a conventional example of a non-reciprocal waveguide.

FIG. 5 is a view showing a conventional example of a fiber type Faraday rotator.

[Explanation of symbols]

1: optical fiber, 2: core, 3: clad, 4: magneto-optical material, 5: waveguiding layer, 6: substrate

Claims (1)

[Claims] 1. A non-reciprocal optical fiber type non-reciprocal type, characterized in that a magneto-optical effect is produced in a core of an optical fiber by removing a part of a clad of the optical fiber and loading a magneto-optical material in the removed portion. device.