KR100211792B1 - Optical isolator - Google Patents

Abstract

The present invention relates to an optical isolator that passes light in the forward direction and blocks the light in the reverse direction regardless of the polarization direction.

In particular, the present invention provides an optical isolator having a structure in which time spreading occurs with a minimum optical component.

According to the configuration of the present invention, two optical fibers 11 and 17, two lenses 12 and 16, and a Faraday rotator 14 having a function of rotating the polarization direction of light irreversibly 45 degrees and the light travel in the forward direction The optical axis direction of the second birefringent element 65 is present at a 45 degree rotational position in the direction opposite to the rotational direction of the faradarotater with respect to the optical axis direction of the first birefringent element 63 so that time spreading does not occur. The inclination direction of the two birefringent elements so that the two rays (rays 32 and 33) are parallel ) Is an optical isolator composed of the first birefringent element 13 and the second birefringent element 15 constituted in opposite directions.

Description

Optical isolator

1 is a diagram showing the configuration of the present invention, a schematic diagram when the light in the forward direction.

2 is a diagram showing a configuration of the present invention, a schematic diagram when light travels in the reverse direction.

3 is a view showing the operation of the present invention to show that the two light beams (rays 32, 33) are parallel and there is no time spread when light travels in the forward direction.

4 is a view showing the operation of the present invention when the light emitted in the reverse direction ( 5, 5 ') angle of incidence with forward direction (Fig. 3) Drawing to show the difference from 1).

5 is a view showing the operation of the present invention to show that there is no time spread when the light passing position is different (rays 51 and 52).

6 is a view for showing in detail the configuration of the birefringent elements (63, 65) and the Faraday rotator (64) of the configuration of the present invention.

7 is a view for showing a light ray when the light proceeds in the forward direction in the conventional invention.

8 is a view for showing light rays when the light proceeds in the reverse direction of the conventional invention.

9 is an embodiment of the present invention.

* Explanation of symbols for main parts of the drawings

11 incident light fiber 12 main surface of the lens

13: birefringent element 14: faraday rotator

15 birefringent element 16 main surface of the lens

17: output light fiber 21: optical fiber

22: principal surface of the lens 23: birefringent element

24: Faraday rotator 25: birefringent element

26: principal surface of the lens 27: optical fiber

33: birefringent element 34: Faraday rotator

35 birefringent element 43 birefringent element

44: Faraday rotator 45: birefringent element

53: birefringent element 54: Faraday rotator

55: birefringent element 63: birefringent element

64: Faraday rotator 65: birefringent element

C-axis: Optical axis of birefringent element (OPTIC AXIS)

73: birefringent element 74: Faraday rotator

75: birefringent element 83: birefringent element

84: Faraday rotator 85: birefringent element

91: optical fiber 92: lens

93 birefringent element 94 Faraday rotator

95 birefringent element 96 lens

97: optical fiber 98: ferrule

99: ferrule 100: lens fixing portion

101: lens fixing portion 102: the body

The present invention relates to an optical isolator which allows light to pass in the forward direction and blocks the light in the reverse direction regardless of the polarization direction. In particular, the present invention relates to a structure that is composed of two birefringent elements and one Faraday data, but does not cause time dispersion.

Regardless of the polarization direction, the optical isolator that performs the isolation function mostly uses birefringent material, which passes through the birefringent material and separates it into normal and extraordinary rays, and the speed difference between these two rays is different. This causes time dispersion.

Looking at the prior art, U.S. Patent 4,548,478 consists of two inclined birefringent elements and one Faraday rotator (FIGS. 7 and 8) and the first birefringent element 73 in the forward direction (FIG. 7). The light propagated in the normal ray at the light beam proceeds to the normal light even when passing through the second birefringent element 75 (ray 72), and proceeds to the extraordinry ray at the first birefringent element 73. The light also proceeds to the abnormal light in the second birefringent element 75, and the shape and the optical axis direction (C axis) of the birefringent elements 73 and 75 are arranged so that the incident angle of the light rays 71 and the angles (the exit angles) of the light rays 72 and 73 are the same. It was.

That is, the optical axis direction (C axis) of the second birefringent element 75 with respect to the first birefringent element 73 is disposed at a 45-degree rotational position in the same direction as the rotational direction of the faraero data, and the two birefringent elements 73 and 75 When the two inclination directions are added together, the inclination direction of the device in the same direction becomes parallel quadrilateral ( ) Was placed.

8 is a schematic diagram when light travels in the reverse direction of the conventional invention.

However, in the conventional invention, time propagation occurs due to the speed difference between the two light beams (speed difference between normal light beam and abnormal light beam) when the light beam 72 and the light beam 73 pass through the birefringent elements 73 and 75 in the forward direction (FIG. 7).

In order to compensate for this, European Patent EP 0 533 398 A1 has devised to install an additional time spread compensation plate. However, as the number of parts increases, more effort is required for parts processing and assembly, and the more light passes, the lower the light efficiency.

It is an object of the present invention to provide an optical isolator in which there is no time spread with the smallest possible component.

The configuration of the present invention for achieving this is described with reference to FIG. 1, FIG. 2, and FIG.

1 is a view showing the configuration of the present invention schematically showing the progress of light in the forward direction.

The configuration of the present invention is an incident light fiber (part 11) for transmitting information, a lens (part 12) for making the light spread in the optical fiber 11 (part 12) and a birefringent element that functions to separate light into normal and abnormal light (Part 13) and the Faraday rotator (Part 14), which performs the function of rotating the polarization direction by 45 degrees, and the two types of light (beams 13, 15 and 14, 16) advance in parallel in correspondence with part 13 A lens (part 16) is used to focus light parallel to the birefringent element (part 15) in which the optical axis direction of the material is arranged so that time spreading does not occur.

FIG. 2 is a schematic view showing that the light is blocked when traveling in the reverse direction in the present invention, and when the light travels in the reverse direction from the exiting light fiber 27, the incident light fiber 21 is not focused.

6 is a view for showing in detail how the birefringent element and the Faraday rotator is configured in the present invention.

In particular, when the light proceeds in the forward direction, the two light rays (rays 32 and 33) are parallel, and in each ray, the normal ray (O-RAY) and the abnormal ray (E-RAY) are generated at the intersection, so that the time spread (DISPERSION) In the reverse direction, two beams (rays 42 and 43) are not parallel to each other so that the isolation function can be performed. ) And the optical axis direction (C axis) will be described in detail.

In FIG. 6, the first birefringent element 63 has one side It is also inclined and the optical axis direction (c-axis) exists in the plane which the yz-axis makes.

Faraday Rotator 64 rotates the polarization direction irreversibly 45 degrees with the x-axis as the rotation axis (45 degrees clockwise in this figure).

The second birefringent element 65 has one side It is also inclined and arranged in the opposite direction with the element 63 so as to have a trapezoidal shape when the two inclination directions are combined.

The optical axis direction (c axis) of the second birefringent element 65 exists on the yz axis plane, and the direction in which the Faraday Rotator 64 rotates the polarization direction of light with respect to the optical axis direction of the first birefringent element 63 (in this figure, about the x axis). The optical axis direction is present at a position rotated 45 degrees in a direction opposite to the clockwise direction).

That is, in the forward direction, light that is normal light in the birefringent element 63 becomes abnormal light in the birefringent element 65, and light in which the abnormal light in the birefringent element 63 becomes normal light in the birefringent element 65 is disposed.

3, 4, and 5, the operation of the present invention, that is, the isolation function and the time spread which is a feature of the present invention, will be described.

The angle of inclination of the birefringent elements 33 and 35 in this structure ) And the angle between the rays (31, 32, 33, etc.) and the X axis ( ) Is small enough.

In FIG. 3, two light rays 32 and 33 are parallel and no dispersion occurs when light flows in the forward direction.

When the light beam 31 enters the birefringent element 33, it is divided into the normal ray (o) and the abnormal ray (e). If the refractive index is no and ne, the angle between the two ray rays and the x axis after passing through the birefringence element 33

Expressed as an expression (in this structure And Because we make it small enough = , sin = Assume and calculate it).

When this light passes through the Faraday rotator 34, the angle of the element 34 is parallel, so 2, 2 'does not change.

When the birefringent element 35 passes, the normal and abnormal rays are changed, and the angle formed with the x-axis when passing the birefringent element 35 is changed. 3, 3 '

Becomes

In the formulas (1), (3) and (2), (4)

Becomes

In other words, the two rays (rays 32 and 33) are parallel in the equations (5) and (6), so that a lens can be used to focus at a point. In addition, since the normal light beam and the abnormal light beam change when passing the first birefringent element 33 and the second birefringent element 35, there is no time spread between the light ray 32 and the light ray 33.

4 is to show that the light is blocked in the reverse direction in the present invention.

In Fig. 4, 43 and 45 represent birefringent elements and 45 represents Faraday rotator.

x-axis When the light 41 of 3 is incident to the birefringent element 45 in the reverse direction, the light is separated into normal rays and abnormal rays.

Becomes

The angle of light does not change when this light passes the Faradayrotator, a parallel plane plate.

When light passes through the birefringent element 43, the normal ray of light passes through the birefringent element 43 due to the irreversible polarization of the faraday data. Abnormal light is generated even when the device 43 passes.

Therefore, the angle when passing through the birefringent element 43 5 ', 5

Becomes

From (7), (9) and (8), (10)

It becomes

In equations (5) and (11) 5 'and Relationship of 1

In formulas (5) and (12) 5 and If you represent a relationship of 1

Becomes

In other words, when light travels backward in equations (13) and (14), ray 42 is (no-ne) Incident angle in forward direction ( Since it is out of 1), it does not collect in the incident light fiber.

In the schematic diagram of FIG. 2, when light flows in the reverse direction, the light is not collected by the lens 22 on the incident light fiber 21 in the drawing.

5 shows that there are no time spreads after two light beams (rays 51 and 52) having different positions passing through the present invention pass through the optical system of the present invention.

(Rays 51,52 in FIG. 5 correspond to rays 13,15 in FIG. 1).

Two parallel rays, rays 51 and 52, At an angle of 1 Look at the two rays that form 3 and exit.

The point where ray 51 meets the first birefringent element 53 is A, the point where ray 2 passes through the second birefringent element 55 is B, the point where ray 52 meets the first birefringent element 53 is F, and the second birefringent element 55 The point passing through is called G, and the point F is drawn perpendicular to the beam 51 at the point C. The point is C. The point D is drawn perpendicular to the beam 51 at the point D, and the point D is called. Draw a line parallel to the Z-axis at H to meet the point H, and draw a line parallel to the Z-axis at point B at the point B to meet the point I.

Optical path length from point C to point D of light beam 51 and optical path length from point F to point G of light beam 52 (OPTICAL) to demonstrate that light beam 51 and light beam 52 pass through the optical system of the present invention with no time spread. PATH LENGTH) is the same.

The optical path lengths are the same because the sections from point A to point B of ray 51 and from point H to point I of ray 52 are parallel to each other and pass through the same material.

therefore

The optical path length of the CA section in ray 51 is δ1

The optical path length of the BD section is called δ2

The optical path length of the FH section at ray 52 is δ3

When the optical path length of the IG interval is δ4

Comparing the results, we can see the time spread of the light beam 51 and the light beam 52.

If the length from point A to point F in birefringent element 53 is L, the length from point B to point G in birefringent element 55 is also L.

If equations (15) and (16) are expressed in terms of L and angle

Becomes

Of equation (17) Substituting equation (5) into 3

Becomes

That is, in Equations (19) and (20), two optical path lengths become the same so that there is no time spread between the light rays 51 and 52.

As described above, the configuration of the present invention (FIG. 1) rotates two optical fibers 11 and 17 and two lenses 12 and 16 parallel to light and irreversibly rotates the polarization direction of light by 45 degrees. The second birefringent element 15 with respect to the first birefringent element 13 so as to occur when the normal ray (O-RAY) and the abnormal ray (E-RAY) intersects when the Faraday rotator 14 and the light proceed in the forward direction. The optical axis direction (C axis) is present in the rotational position 45 degrees in the direction opposite to the rotational direction of the Faraday data, and under the above conditions, the first birefringent element 13 and the first birefringent element 13 and the Slope of the birefringent element 15 ( Optical isolator configured so that the angle) becomes opposite direction.

9 illustrates an embodiment of the present invention, wherein the optical fibers 91 and 97, the ferrules 98 and 99 supporting the lens, the lens 92 and 96 and the lens fixing portions 100 and 101 fixing the lens and the birefringence are shown in FIG. It is an example comprised of the elements 93 and 95, the Faraday rotator 94, and the body 102 which fixes the whole.

Importantly, it is important that the end faces of the ferrules 98 and 99 have a certain angle with respect to the optical fibers 91 and 97 so that the signal reflected from this face is not noise. In addition, it is important to incline the end face of the lens so that the signal reflected by the end faces of the lenses 92 and 96 is minimized so that light does not reflect back from the interface and return to the incident light fiber.

Claims (1)

The first lens 12 and the second lens having a function of converting the information of the light into a desired form with the first information transmission medium 11 and the second information transmission medium 17 which function to transmit the information of light. (16) and a Faraday rotator 14 which functions to irreversibly rotate the polarization state of light by 45 degrees and two birefringent elements 13, 15 inclined on one side, and normal light when the light proceeds in the forward direction. 45 in the direction opposite to the rotational direction of the faradarotator with respect to the optical axis direction (C axis) of the first birefringent element 13 so that o-rays and e-rays intersect at the two birefringent elements. In the rotational position, the optical axis direction (C axis) of the second birefringent element 15 is present, and when the light proceeds in the forward direction in the above state, the two light beams (rays 32 and 33) are parallel and proceed in the opposite direction. There are two birefringence so that the two rays (rays 42 and 43) are not parallel Inclined directions of the elements 13 and 15 ( ) Is an optical isolator comprising a first birefringent element (13) and a second birefringent element (15) configured to be disposed in the opposite direction.