JP2782085B2 - Alignment method of dual core optical fiber - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for aligning a dual-core optical fiber.

[Prior Art] As shown in FIG. 4, a dual-core optical fiber 10 includes two cores 12 and 14 and a clad 16.

The dual-core optical fiber is composed of the two core parts 12,1
Since light propagates through 4, the fiber 10 must be rotated to make the axes of the two cores 12 and 14 coincide with each other, as shown in FIG.

Conventionally, as shown in FIG.
18 and the optical power sensor 20 are prepared, and the fiber 10 is rotated so that the light receiving level of the optical power sensor 20 is maximized.
The axes were aligned.

[Problems to be Solved by the Invention] However, the above method requires a measuring device such as a light source and an optical power sensor, and also aligns the light source so that the light from the light source enters the two cores of the fiber. Had to be done, and so on.

[Means for Solving the Problems] The present invention relates to the relationship between the luminance distribution of an optical fiber image obtained on an image sensor (such as a TV camera) by light transmitted through an optical fiber and the direction of light transmitted through the optical fiber. It is based on a new perception of that the characteristic feature is that in the brightness distribution of the fiber image, the line with the highest brightness appearing in the fiber image appears at the same position for the connected left and right fibers.

Hereinafter, the principle (the relationship between the luminance distribution of the optical fiber image and the direction of light passing through the optical fiber) will be described first, and then the actual axis alignment method will be described.

[Principle] An optical fiber image obtained on an image sensor by light transmitted through the optical fiber was simulated by a computer.

(1) FIG. 1a shows the result when the angle between the imaginary line 15 passing through the centers of the two cores and the incident parallel ray 4 is 90 degrees.

The outer diameter of the optical fiber 10 is 125 μm, and the diameter of the cores 12 and 14 is 4
μm, the refractive index of the cladding 16 was 1.45, and the refractive indices of the cores 12 and 14 were 1.46.

The parallel ray 24 incident from the left is refracted at the boundary with the optical fiber 10. The light is refracted again at the boundary with the cores 12,14. The refraction angle was calculated according to Fresnel's law.

FIG. 1b shows the light intensity distribution on the focus plane 26 of the image sensor shown in FIG. 1a. As can be seen from the figure, two bright lines (points with high light intensity) are characteristic.

That is, noticeable bright lines 30 and 32 due to the condensing action of the cores 12 and 14 are seen in the fiber image.

These bright lines 30, 31 have the same luminance and appear near both sides of the clad image.

(2) Next, FIG. 2a shows a simulation result when the direction of the incident light 24 coincides with the imaginary line passing through the centers of the two cores by rotating the optical fiber 10 by 90 degrees.

FIG. 2B shows the light intensity distribution on the focus plane of the image sensor.

In this case, the two noticeably bright lines 30, 32 overlap to form a single bright line 34.

(3) That is, the interval between the bright lines changes when the fiber is rotated, and is maximum in FIG. 1a and minimum in FIG. 2a.

Therefore, by rotating the optical fiber 10 to be connected, the brightness distribution of each of them becomes the maximum between two bright lines, as shown in FIG. 1b, or both as shown in FIG. 2b. By minimizing the distance between the two bright lines, accurate core alignment can be achieved.

[Actual Axis Alignment Method] [1] Configuration FIG. 3 shows an outline of an example.

 10A and 10B are optical fibers to be connected.

 35 is a light source and 36 is a lens for making parallel rays.

38 is an objective lens and 40 is an image sensor (for example, TV
Camera) and 42 are control devices including a CPU and the like.

 44 is a TV monitor, and 46A and 46B are optical fiber images.

The brightness distribution above the cursor on the TV monitor 44 is shown on the display 48 at 50A and 50B.

[2] Alignment One optical fiber, for example, 10A is rotated so that its luminance distribution 50A becomes, for example, as shown in FIG. 1b. That is, the interval between the bright lines 30, 32 having the same luminance is set to be maximum.

Then, the same applies to the other optical fiber 10B.

Then, the two cores of both fibers 10A and 10B coincide.

The brightness distribution of both fibers 10A and B6 may be as shown in FIG. 2b.

[Effects of the Invention] The transmitted light of the dual-core optical fiber is captured by an image sensor, and the luminance distribution of the fiber image captured by the image sensor is obtained. In the luminance distribution, the line of the highest luminance appearing in the fiber image is: Since the left and right fibers to be connected are made to appear at the same position, (1) a measuring device such as a light source or an optical power sensor is not required.

(2) Axis alignment with two cores in the light source is not required.

[Brief description of the drawings]

FIGS. 1a to 3 relate to the present invention. FIG. 1a is a computer simulation diagram of ray tracing when the angle between a line passing through the center of the core and an incident light beam is 90 degrees. FIG. 1b is a TV camera. FIG. 2a is a simulation diagram of ray tracing by a computer when the angle between a line passing through the center of the core and the incident light beam is 0 degree, and FIG. 2b is a light intensity distribution diagram at the focus surface of the TV camera. FIG. 3 is a schematic explanatory view of a centering device, FIG. 4 is a general explanatory view of a dual-core optical fiber, FIG. 5 is a general explanatory view of a dual-core optical fiber alignment, FIG. FIG. 4 is an explanatory diagram of a conventional centering method. 10: Dual-core optical fiber 12, 14: Core 16: Cladding 18: Light source 20: Optical power sensor 22: Connecting device 24: Parallel light beam 26: Focus plane 30, 32, 34: Remarkable bright line 35: Light source 38: Objective Lens 40: Image sensor 42: Control device 44: TV monitor 46A, B: Optical fiber image 48: Display 50: Luminance distribution

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Mikio Yoshinuma 1440 Mutsuzaki, Sakura City, Chiba Prefecture Inside the Sakura Plant of Fujikura Electric Cable Co., Ltd. (58) Field surveyed (Int.Cl. ⁶ , DB name) G02B 6/24

Claims (1)

(57) [Claims] 1. A cladding and a cladding having a higher refractive index than the cladding.
A method of aligning a dual-core optical fiber comprising two cores, wherein the transmitted light of light emitted from the side of the dual-core optical fiber is captured by an image sensor, and the brightness distribution of the fiber image captured by the image sensor is determined. An alignment method for a dual-core optical fiber, characterized in that in the luminance distribution, axes are aligned such that the position of the line of the highest luminance appearing in the fiber image coincides with the left and right fibers to be connected.