JPH06148569A - Optical isolator - Google Patents

Abstract

PURPOSE:To provide an optical isolator of polarized wave independent type which is constituted small and from a min. number of components and which is easy to assemble. CONSTITUTION:A dispersed light emitted by an optical fiber F1 is transmitted by a complex refraction plate 11, and thereby true refracting directions of different polarization components orthogonally intersecting are changed, and polarizing direction of each polarization component is changed approx. 45deg. by a magnetic-optical element 12. The dispersed light of each polarization component, advances while converged by a lens 13 of finite system, and on this route, the polarizing direction if further 45deg. changed by an anisotropic crystal plate 14, and the beam is passed through the same route by another complex refraction plate 15 to be fed to another optical fiber F2. The reflected light by the end face of this optical fiber F2 passes through the crystal plate 14 and magnetic-optical element 12 and returns, whereby the polarizing direction of each polarization component is changed, and each polarization component transmitted by the first named complex refraction plate 11 is converted at the convegence points falpha and fbeta, and it is possible to prevent from returning to the optical fiber F1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical isolator arranged between a light emitting portion and a light incident portion, and more particularly to a polarization independent optical isolator which can be miniaturized as a whole and is easy to assemble. .

[0002]

2. Description of the Related Art In an optical communication device, for example, when laser light emitted from one optical fiber is incident on the other optical fiber, reflected light from the end face of the optical fiber on the incident side returns to the optical fiber on the emitting side. An optical isolator is used to prevent this. As the most basic of this optical isolator, when light with a predetermined polarization direction is incident,
There is a so-called polarization dependent type in which the reflected light is a polarization component that cannot return to the optical fiber on the output side. In this polarization-dependent optical isolator, since the polarization direction of the light incident on the optical isolator is determined, it is impossible to use light having different polarization components orthogonal to each other. Therefore, there is a polarization-independent optical isolator 1 as shown in FIG. 3 that is suitable for use of light that is not linearly polarized light.

FIG. 3 shows a case where the optical isolator 1 is arranged between the optical fiber F1 on the output side and the optical fiber F2 on the input side. The in-line type optical isolator 1 includes a collimator lens 2, a birefringent plate 3 and a 1/1 from an output side optical fiber F1 to an incident side optical fiber F2.
The two-wave plate 4, the polarization-dependent optical isolator 5, the half-wave plate 6, the birefringent plate 7, and the condenser lens 8 are arranged in this order. In the polarization-dependent optical isolator 5,
An anisotropic crystal plate and a magneto-optical element are incorporated.

In this in-line type optical isolator 1, divergent light from the optical fiber F1 on the output side is converted into a parallel light flux by the collimator lens 2 and by the birefringent plate 3.
Different polarization components are separated into La and Lb paths, one path of which is a half-wave plate 4, a polarization-dependent optical isolator 5,
It passes through the half-wave plate 6, and the other path passes only the optical isolator 5. Then, both polarized components return to the same path through the birefringent plate 7 and enter the optical fiber F2 on the incident side by the condenser lens 8. Half-wave plates 4 and 6 on one path
Since the optical fiber F2 on the incident side is provided by
The reflected return light from the end face of the optical fiber is focused on a portion other than the end face of the optical fiber F1 on the emission side, and this return light can be prevented from entering the optical fiber F1 on the emission side.

[0005]

However, the conventional in-line type optical isolator 1 as shown in FIG. 3 has the problems listed below. (1) The collimating lens 2 is provided on the incident side and the condenser lens 8 is provided on the emitting side so that the parallel light flux passes through the optical isolator 1. Therefore, at the stage of assembling the optical isolator 1, it is necessary to align the optical axes of the collimator lens 2 and the condenser lens 8 and the optical axes of the collimator lens 2 and the condenser lens 8 and the polarization-dependent optical isolator 5. Assembly work of the optical isolator 1 is very difficult. Furthermore, when the optical isolator 1 is mounted between the optical fibers F1 and F2, the optical fiber F
It is necessary to align the optical axes of 1 and the collimator lens 2 and the optical axis of the condenser lens 8 and the optical fiber F2, which requires assembly work accuracy.

(2) There are a large number of components inside the optical isolator 1, and the anisotropic crystal plate and the magneto-optical element are also provided inside the polarization dependent optical isolator 5 provided therein. Therefore, the total number of parts is large and the cost is high.

(3) Laser light from the optical fiber is collimated lens 2, birefringent plate 3, 1/2 wavelength plate 4, polarization dependent optical isolator 5, 1/2 wavelength plate 6, birefringent plate 7. , And the condenser lens 8, the entire optical path length becomes very long. Further, since the parallel light flux passing through the path of Lb shown in FIG. 3 must not be applied to the half-wave plates 4 and 6, the dimension in the effective radial direction (vertical direction in FIG. 3) must be long. The width or thickness of the optical isolator 1 becomes very large.

SUMMARY OF THE INVENTION The present invention is to solve the above-mentioned conventional problems, and to provide a polarization-independent optical isolator which can be constructed in a small size with a minimum number of parts and which can be easily assembled and adjusted. Has an aim.

[0009]

According to the present invention, in an optical isolator arranged between a light emitting portion and a light incident portion, the refractive index of orthogonal polarization components is increased in order from the light emitting portion to the light incident portion. Different birefringent plates, a magneto-optical element that makes the incident light and the outgoing light different in polarization direction by approximately 45 degrees, a finite lens that focuses the light from the emitting portion and makes it enter the incident portion, and the polarization direction is almost the same. It is characterized in that a crystal plate having an optical property or anisotropy that changes by 45 degrees and a birefringent plate are arranged.

[0010]

In the above means, the divergent light emitted from the emitting portion such as the optical fiber is transmitted through the birefringent plate, whereby the refraction directions of the optical axes of different polarization components orthogonal to each other are changed, and further, the magneto-optical elements are used to change the refraction directions. The polarization direction of the polarization component is almost 4
Can be changed 5 times. The divergent light of each polarization component travels after being focused by a finite lens, and in this path the polarization direction is further changed by approximately 45 degrees by the crystallizing or anisotropic crystal plate, and the same path as the birefringent plate. Then, it is incident on an incident part such as an optical fiber. The reflected light from this incident portion returns to the original path, but at this time, the polarization direction of each polarization component is changed by further passing through the magneto-optical element through the light-polarizing or anisotropic crystal plate, and Both polarization components that have passed through the refraction plate are focused on a portion other than the emitting portion, and reflected return light can be prevented from entering the emitting portion.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. 1A and 1B show the structure of an optical isolator as one embodiment of the present invention. FIG. 1A shows an emission path from an emission side optical fiber, and FIG. 3 shows a path of reflected return light from the end face of the optical fiber on the side. FIG. 2 is an explanatory diagram showing polarization directions of polarization components at respective positions on the optical path of the optical isolator. Figure 1 (A)
In (B), the optical isolator 10 of the present invention is provided between the optical fiber F1 on the output side and the optical fiber F2 on the input side. The internal structure of the optical isolator 10 is such that the optical fiber F1 on the output side to the optical fiber F2 on the input side.
Toward the birefringent plate 11, the magneto-optical element 12, the finite lens 13, and the crystal plate 1 having the optical property or anisotropy.
4 and the birefringent plate 15 are arranged in this order.

The birefringent plates 11 and 15 change the refractive index of ordinary light and extraordinary light with respect to the birefringent material.
For example, it is composed of calcite crystals. The magneto-optical element 12 has a function of rotating the polarization direction in the same direction by approximately 45 degrees with respect to light in any direction due to the Faraday effect when a magnetic field is applied from the outside. In addition, the crystallizing or anisotropic crystal plate 14 changes the polarization direction by 45 degrees clockwise on the exit side with respect to the light incident from the left side in FIG. 1, and changes the polarization direction with respect to the light entering from the right side. It has the function of returning 45 degrees.

The lens 13 is a finite system lens located at the center of the optical isolator 10, and the focal lengths in both directions coincide with the end faces of the respective optical fibers F1 and F2. Each optical component forming the optical isolator 10 is housed and assembled in a case. The optical fibers F1 and F2 are connected to the optical isolator 10 by a connector method or the like.

Next, the optical function of the optical isolator 10 will be described. 2 (a) to 2 (o) are shown in FIG.
(A) on routes L1, L2, L3, L4 shown in (A) and (B)
The polarization directions of the polarization components at the respective positions (a) to (o) are shown. In FIG. 1A, the X-Y coordinates are taken with the X-axis being the direction orthogonal to the paper surface and the Y-axis being the vertical direction in the drawing, and the XY coordinates are shown in FIG. 2A. Divergent light whose optical axis coincides with the path L1 is emitted from the optical fiber F1 on the exit side. This divergent light is linearly polarized light such as laser light, and the optical axis is X-
It is located in the Y coordinate plane. The polarization component in the X-axis direction at the position (a) emitted from the optical fiber F1 is β1, and the polarization component in the Y-axis direction is α1.

When this diverging light enters the birefringent plate 11, the polarization component α1 which is the ordinary light and the polarization component β1 which is the extraordinary light with respect to the birefringence plate 11 have different refractive indexes, so that they pass through the birefringence plate 11. Then, the optical axis of the polarization component α1 is the path L1
And the optical axis of the polarization component β1 coincides with the path L2. The polarization directions of the polarization components α1 and β1 at the positions (b) and (c) on the paths L1 and L2 when transmitted through the birefringent plate 11 are shown in FIG.
Shown in (b) and (c). When the respective polarization components pass through the magneto-optical element 12 to which a magnetic field is applied, the polarization directions of the polarization components α1 and β1 are both rotated substantially 45 degrees clockwise in FIG. 2 due to the Faraday effect (FIG. 2 (d )
(See (e)). The divergent light flux of each polarization component is focused by the finite lens 13 toward the optical fiber F2.

When the respective polarized light components α1 and β1 which become the focused light flux pass through the crystal plate 14 having the light irradiating property or the anisotropy, FIG.
As shown in (f) and (g), the polarization direction is further rotated clockwise by 45 degrees in FIG. Next birefringent plate 1
For 5, the polarization component β1 becomes ordinary light and the polarization component α1 becomes extraordinary light. Due to birefringence, the optical axes of both polarization components α1 and β1 coincide with each other and are incident on the end face of the optical fiber F2.

The path of the return light of the light reflected by the end face of the optical fiber F2 on the incident side is shown in FIG. 1 (B). The reflected return light from the end face of the optical fiber F2 is shown in FIG. 2 (i). As shown, the polarization components α2 and β2 are included. Of the reflected return light, the polarization component β2 becomes ordinary light for the birefringent plate 15, and the polarization component α2 becomes extraordinary light. Due to the birefringence effect of the birefringence plate 15, the polarization component α of the reflected return light which is divergent light.
The optical axis of 2 coincides with the path L3, and the optical axis of the polarization component β2 coincides with the path L4 (see FIGS. 2 (j) and 2 (k)). Crystal plate 1 in which the polarization components α2 and β2 of the return light are optically or anisotropic
After passing through 4, the polarization direction is returned to the angle of 45 degrees as shown in FIGS.

The divergent return light of each of the polarization components α2 and β2 whose optical axes coincide with the paths L3 and L4 are focused by the lens 13 toward the optical fiber F1. When the focused return light passes through the magneto-optical element 12 to which a magnetic field is applied, the polarization directions of the polarization components α2 and β2 are changed by 45 degrees in the clockwise direction in FIG. The polarization directions of the respective polarization components α2 and β2 of the reflected return light transmitted through the magneto-optical element 12 are shown in FIG.
(N) and (o) are shown.

Since the polarization component β2 shown in FIG. 2 (o) becomes ordinary light with respect to the birefringent plate 11, its optical axis is L.
The light passes through the birefringent plate 11 while matching with 4, and is focused on a point indicated by fβ in FIG. The focus point indicated by fβ is deviated in the Y-axis direction from the end face of the optical fiber F1 on the exit side. Since the polarization component α2 shown in FIG. 2 (n) becomes extraordinary light with respect to the birefringent plate 11, the optical axis of the focused light of this polarization component α2 is from the path L3 as shown in FIG. 2 (B). It is refracted so as to deviate upward in the Y-axis, and the focused light of the polarized component α2 is focused on the focal point indicated by fα. This focus point fα is displaced in the Y-axis direction from the end face of the optical fiber F1 on the exit side.

Thus, the optical isolator 1 having the above structure
When 0 is used as the in-line type, the optical fiber F1
All the polarization components emitted from the optical fiber F2 are incident on the optical fiber F2, and all the polarization components of the reflected return light from the end face of the optical fiber F2 are focused on a part other than the end face of the optical fiber F1 and reflected back into the optical fiber F1. No light is incident. In the above embodiment, the optical isolator 10 is arranged between the optical fiber F1 on the output side and the optical fiber F2 on the input side.
For example, divergent light emitted from a light source such as a semiconductor laser may be incident on the optical fiber F2 via the optical isolator 10, or divergent light from the optical fiber F1 may be received by a light receiving element via the optical isolator 10. Good.

[0021]

The present invention described above has the effects listed below. (1) The optical isolator can be composed of the minimum of five optical components, which is small and low in cost.

(2) As a method of assembling the optical isolator, the optical components from the birefringent plate 11 to the birefringent plate 15 are sequentially assembled one by one, and at this time, the optical axes are aligned one by one to achieve a high level. It can be assembled with high precision, and the assembling work becomes much easier than the one using two lenses shown in FIG.

(3) Since only one lens is used in the optical isolator, for example, the optical fibers of each of the emission part and the incidence part are aligned and joined so that the optical axis is aligned with one lens. Since all that is required is a simple connection work for the entire optical path.

(4) Since the lens is provided almost at the center of the optical isolator, the optical path length from the emitting part to the incident part is adjusted by matching the focal lengths on both sides of this lens to the emitting part and the incident part. Not only can it be made the shortest, the optical isolator can be made short, and the lens design is easy.

(5) As shown in FIGS. 1 (A) and 1 (B), the distance between the optical paths L1 and L2 and L3 and L4 in the Y-axis direction is such that the reflected return light deviates from the emitting portion such as an optical fiber. Since the dimensions are all that is required, the dimensions in the vertical direction in FIG.

[Brief description of drawings]

FIG. 1 is an explanatory diagram for explaining the arrangement of each optical component and the path of light when an optical isolator according to the present invention is arranged between optical fibers, (A) showing a path of emitted light, and (B) showing reflection. The path of the returning light is shown.

2A to 2O are explanatory diagrams showing polarization directions of polarization components at positions (a) to (o) in FIGS. 1A and 1B.

FIG. 3 is an explanatory diagram showing a structure of a conventional in-line type optical isolator.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Optical isolator 11 Birefringent plate 12 Magneto-optical element 13 Finite system lens 14 Optical or anisotropic crystal plate 15 Birefringent plate F1 Output side optical fiber F2 Entrance side optical fiber

Claims (1)

[Claims] 1. An optical isolator arranged between a light emitting portion and a light incident portion, wherein a birefringent plate in which refractive indexes of orthogonal polarization components are different from each other in the order from the light emitting portion to the light incident portion, the incident light. Magneto-optical element that makes the polarization directions of the output light and the output light different by approximately 45 degrees, a finite lens that focuses the light from the output portion and makes it enter the input portion, and the polarization direction is approximately 4
An optical isolator comprising a crystal plate having an optical property or anisotropy that changes by 5 degrees, and a birefringent plate.