JP3495066B2 - Optical fiber type non-reciprocal device - Google Patents

Description

Description: 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 more particularly, to an optical fiber type non-reciprocal device having a fiber type as a whole. 2. Description of the Related Art Optical isolators and optical circulators have been manufactured utilizing the non-reciprocal action of the magneto-optical effect. A waveguide formed by magnetic garnet or the like and having a waveguide layer having a magneto-optical effect is particularly called a magneto-optical waveguide.
A non-reciprocal waveguide that uses a non-reciprocal effect among the magneto-optical effects may be used. The non-reciprocal waveguide is used for a waveguide type isolator, a modulator, and the like, and performs non-reciprocal phase shift and rotation of a non-reciprocal polarization plane (Faraday rotation).
Conventional non-reciprocal waveguides include a rib type (FIG. 4A) in which a waveguide layer 5 is formed on a substrate 6 and a clad 3.
A rectangular type such as an embedded type in which a waveguide layer 5 is embedded therein (FIG. 4B) was mainly used. This is formed by a liquid phase epitaxial (LPE) method, a sputtering method, or the like. Further, a Faraday rotation fiber in which a magneto-optical material is molded into a fiber type for a fiber sensor, or a fiber type Faraday rotator in which a magneto-optical material 4 (Faraday rotator) is sandwiched between optical fibers 1 as a fiber type device (FIG. 5). Etc. have also been 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 ^Ey mode which is x. These modes have become hybrid mode, E ^x mode for simplicity the TE mode at the Ey = 0, E ^y mode H
It is possible to approximate each of the TM modes by setting y = 0. E (Ex, Ey, Ez) is an electric field vector, H
Let (Hx, Hy, Hz) be the magnetic field vector. Waveguide layer 5
In a conventional non-reciprocal waveguide formed by using a magneto-optical material, a 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 constant of light propagating in the + Z direction is different from the propagation constant of light propagating in the −Z direction, and the propagation constant of the TM mode when no magnetic field is applied is β
If TM, the propagation constant at the time of applying a magnetic field is βTM ± △ β (the compound ± corresponds to the Z direction). This Δβ is the amount of nonreciprocal phase shift and is called the nonreciprocal phase amount. These are described in detail in literatures such as "Religion Theory Vol. J71-C pp 702-708 Inuzuka, Okamura, Yamamoto 1988". Further, by applying a magnetic field in the Z direction, the propagating light causes Faraday rotation. This is a non-reciprocal rotation of the polarization plane (TE-TM mode conversion). Both the light propagating in the + Z direction and the light propagating in the -Z direction propagate in the same direction and the same angle about the direction of the magnetic field. It rotates in the opposite direction based on the direction. SUMMARY OF THE INVENTION In view of the above problems, the present invention provides a method for removing a part of a cladding of an optical fiber in a longitudinal direction and loading a magneto-optical material on the removed portion to form a core and a magnetic material. By bringing the optical material close to 3 μm or less, the magneto-optical material acts on an electromagnetic field that has permeated outside the core, which is a waveguide layer, to cause a non-reciprocal magneto-optical effect on the core of the optical fiber. It is characterized by the following. [0005] In addition, there is a magneto-optical material formed into a fiber shape, but it was not originally designed for a sensor or the like to solve the problem of connection of a rectangular waveguide.
It is difficult and expensive to mold a magneto-optical material such as garnet into a fiber shape. In addition, although coupling with other fibers is relatively easy using a connector or the like, there is a problem that reflection occurs at a connection point because the refractive index of quartz, which is a material of ordinary fibers, and that of a magneto-optical material are significantly different. Further, even in the structure in which the magneto-optical material 4 is interposed between the optical fiber 1 as shown in FIG. 5, reflection occurs at the boundary between the optical fiber 1 and the magneto-optical material 4, and the coupling efficiency is further deteriorated because there is no lens. Was. An object of the present invention is to provide a non-reciprocal waveguide using the magneto-optical effect to solve the above-mentioned problems.
An object of the present invention is to provide an optical fiber type non-reciprocal device having a simple configuration and having less light reflection and loss in connection with another optical system. SUMMARY OF THE INVENTION The present invention provides a method for directly adding non-reciprocal characteristics to a normal optical fiber for transmission to solve the above-mentioned problems. 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 fibers that are isotropic in nature. Conventionally, in order to generate a magneto-optical effect, a waveguide layer or a core itself in which light mainly exists has been formed of a magneto-optical material. Here, there were difficulties involved in the formation, the refractive index difference, and the problem of the coupling. However, even though the light is confined, the electromagnetic field of the propagating light is seeping out of the waveguide layer. As a result of examining whether or not it is possible to cause a magneto-optical effect on the originally isotropic optical fiber core by applying a magneto-optical material to the electromagnetic field that has oozed out, And the magnitude of the magneto-optical effect was also found to be at a practical level. FIG. 1 shows an embodiment of the present invention. A part of the clad 3 of the quartz single mode optical fiber 1 is removed, and a magneto-optical material 4 is loaded on the part. Here, a Ce-substituted YIG single crystal is loaded. FIG. 2 is a schematic diagram 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 essentially circular, but approximated to a square. A magnetic field is applied in the X direction. FIG. 3 shows the non-reciprocal phase shift calculated by the finite element method while changing the distance H between the core 2 and the magneto-optical material 4 in the structure of FIG. The thickness d of the magneto-optical material 4 is 0.4 μm, and the core diameter is 6
The optical fiber 1 is made of quartz, the refractive index of the core 2 is 1.545, the refractive index of the clad 3 is 1.5, and C
The refractive index of the e-substituted YIG is 2.23, and the magneto-optical constant γ is 7.7 × 10 ⁻³ . Non-reciprocal phase shift is H
About 16.5r from 0 μm to 3 μm
ad / cm. According to the literature mentioned above 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 a non-reciprocal phase shift amount equal to or more than that occurs. It can be seen that a practical device can be formed. As described above, even when the core 2 is an isotropic substance, a non-reciprocal phase shift can be generated by bringing the core 2 and the magneto-optical material 4 closer to each other and acting on the propagating light. Therefore, even if the core is made of an isotropic substance, non-reciprocity occurs. Therefore, the optical fiber itself or the material of the core does not need to be a magneto-optical material. By processing, non-reciprocity can be added to an arbitrary portion. Thus, an optical isolator, an optical circulator, a modulator, and the like can be configured very easily and inexpensively. The present invention has a simple structure and does not require an optical alignment because there is no lens. Further, 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, the reflection is small, and the coupling efficiency is increased. Further, non-reciprocity can be generated at an arbitrary portion of the optical fiber. As described above, since nonreciprocal characteristics can be directly added to an arbitrary transmission fiber, the applicability is high and the utility value is high.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of an optical fiber type non-reciprocal device showing one embodiment of the present invention. FIG. 2 is a schematic cross-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 diagram showing a conventional example of a fiber type Faraday rotator. [Description of Signs] 1: optical fiber, 2: core, 3: clad, 4: magneto-optical material, 5: waveguide layer, 6: substrate

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-198122 (JP, A) JP-A-55-26544 (JP, A) Transactions of the Institute of Electronics, Information and Communication Engineers C, 1988, Vol. J71-C, No. 5, 702-708 (58) Field surveyed (Int. Cl. ⁷ , DB name) G02F 1/09 505 G02B 27/28

Claims (1)

(57) [Claim 1] A part of a cladding of an optical fiber in a longitudinal direction is removed, and a magneto-optical material is loaded on the removed part to remove the cladding.
By bringing the magneto-optical material close to 3 μm or less,
The magnetic light is applied to the electromagnetic field that has leaked out of the core, which is a wave layer.
An optical fiber type non-reciprocal device characterized in that a non-reciprocal magneto-optical effect is generated in a core of an optical fiber by acting a chemical material .