JPH0360087B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical fiber axis alignment device that performs highly accurate core detection and core alignment.

In order to reduce the loss when connecting optical fibers with small core diameters, such as single mode optical fibers, it is necessary to reduce the misalignment (axis misalignment) between the core centers of the two optical fibers to be connected. It is necessary to minimize this, and this is called axis alignment or axis alignment.

A conventional method for aligning the core axis of an optical fiber is shown in FIG. One side of the optical fiber to be connected 1 is placed on a support stand 3
The other optical fiber 2 is fixed to a support base 4 connected to a moving device 5 that can be moved slightly in each of the x, y, and z directions as shown in the figure, and the light from the light source 6 is directed to the optical fiber 1. The supporting table 4 is moved by the moving device 5 to align the axis of the core so that the power of the light that is incident, transmitted through the optical fibers 1 and 2, and reaches the light receiver 7 is maximized. However, with this method, the location where the light enters, the location where the light is connected, and the location where the optical power is monitored are generally different, so devices that communicate with each other are required, and workers need to be stationed at each location. If the location, monitoring location, and connection location are remote, it is very inconvenient for work.

On the other hand, as a method for easily aligning the axes only at the connection location, it has been considered to visually observe the core in the fiber and align the fibers to be connected so that there is no misalignment of the axes. FIG. 2 shows an example of such a method. Light sources 11 and 12 are placed on extensions of the x and y axes perpendicular to the axes of the optical fibers 1 and 2,
For the y-axis direction, mirror 1 is passed through the optical fiber.
3, and the optical fiber images are reflected directly through the optical fibers in the x-axis direction through the microscope 14.
When the image is enlarged, the image shown in FIG. 3 is obtained, and a slightly dark core image 20 is observed near the center of the optical fiber. Therefore, the deviation of the core images of both fibers to be connected is detected visually, and the optical fiber support base 4 is manually moved by the moving device 5, or the image signal obtained by the imaging device 15 attached to the microscope 14 is transmitted to the television. 16, and detect the position of the core from this signal by the image processing device 17.
By driving the moving device 5 so as to eliminate the amount of axis deviation determined as a result, the axes of the opposing optical fibers can be aligned.

When observing the core using this method, since the optical fiber is a cylinder, the size of the core is generally larger than the actual size due to the lens effect, and the observed position may also be different from the actual position. will be different. As shown in Fig. 4, when the axis of the core is separated by d from the center of the fiber in a plane orthogonal to the observation direction, when the core is correctly focused on the imaging plane (Fig. In a), the center of the core has a refractive index nd of the fiber with respect to the center of the fiber.
= D It will be observed at a distance of ₀ .
However, when the focus of the microscope is placed at a different position (FIG. 4b), the observed eccentricity D of the core becomes different from D ₀ . FIG. 5 shows the change in D when the focal point position is moved. A change in the focal position of several tens of μm causes a large change in the observation position of the core.

Furthermore, a similar phenomenon occurs when the light source 11 is connected to the line connecting the microscope 14 and the optical fiber 1, as shown in FIG.
It also occurs when the FIG. 7 shows the relationship between the optical axis deviation in FIG. 6 and the observed core position. As expected, an optical axis deviation of several hundred μm causes a large change in the observation position.

In this way, when a shift in the focus position of the microscope or a shift in the optical axis of the light source occurs, the observed core position is greatly affected, and it is extremely difficult to estimate the true core position, which can be caused by an error in alignment. I know what will happen.

On the other hand, in normal alignment of optical fibers, as shown in Figure 8a, a positional shift occurs in the set of optical fibers, and the optical fiber that should originally be at position 21 is placed at position 22 (indicated by the shaded area). Or, as shown in FIG. 8b, especially when observing an image through the mirror 13, if a deviation of Δθ occurs in the angle of the mirror, the virtual image position due to the mirror of the optical fiber or light source will be shifted from the original position 23, 24. 25,2
6, and in any case, a shift in the focal point position and a shift in the optical axis are unavoidable.

Also, when observing a direct fiber image (vertical direction) and a fiber image via a mirror (horizontal direction) at the same time, as shown in Figure 8c, the distances to both images are different, so both must be focused. That is impossible.

As mentioned above, when aligning the core axis by directly observing the core of the optical fiber to be connected, if there is an error in the positional relationship between the optical fiber, the microscope, and the light source, the observation position of the core may change. The drawback was that accurate core axis alignment was not possible.

The present invention was made in view of the above circumstances, and
The purpose of this device is to provide an optical fiber axis alignment device that can accurately align the core axis. A position adjustment device that finely moves the light source and the microscope so that the light source and the microscope are arranged on a straight line taking into account the reflection angle and the focal point of the microscope matches a predetermined position of the optical fiber, and an imaging device that captures the fiber image obtained by the microscope. The device, the slope of the dip from the bright level to the dark level at the upper and lower edges of the fiber, and the two dark level bands near the upper edge of the fiber, which appear in the image signal scanned in the direction perpendicular to the axis of the fiber image obtained by this imaging device. It is characterized by being provided with an image processing device that detects a width ratio, and a control device that controls the position adjustment device so that the degree of inclination is a predetermined constant value and the width ratio of the dark band is 1. That is.

Hereinafter, the present invention will be explained in detail based on embodiments shown in the drawings.

FIG. 9 shows an embodiment of the present invention, and in this figure, the same components as in FIGS. 1 and 2 are given the same reference numerals. The apparatus shown in this figure has a microscope 14 arranged along an X axis perpendicular to the fiber axis, and a Y axis perpendicular to the fiber axis.
A position adjustment device 31 for fine movement in the axial direction and a light source 1
1 and 12 in the Y-axis and X-axis directions, respectively, and the image signal obtained by the imaging device 15 attached to the microscope 14 is adjusted to the focal state by the image processing device 41 as in FIG. The control device 42 extracts information on the optical axis deviation and information on the optical axis deviation, and the control device 42 drives the position adjustment devices 31 to 33 to move the sources 11, 12 and the microscope 14.

A typical example of the signal when the optical fiber image is scanned in a direction perpendicular to the axis is shown in Figure 10, with dark level bands 51 and 5 near the upper and lower edges of the fiber.
2, and there is a slight drop in level at the position corresponding to the core part. If there is a misalignment in the optical axis between the optical fiber and the light source, the dark level bands 51, 5
The width of 2 is different on the top and bottom. Furthermore, if there is an optical axis misalignment between the microscope and the optical fiber, the fiber image will not be centered on the entire screen. Furthermore, for the focal position,
Since the slope of the drop from the bright level to the dark level on both sides of the dark level differs depending on the sharpness of the image, the focal position can be determined by monitoring the slopes 53 and 54.

FIG. 11 shows the ratio of the optical axis deviation Δy and the widths W ₁ and W ₂ of the dark level bands 51 and 52 in FIG. 10.
This shows the relationship between W ₁ /W ₂ , and when Δy is 0, it takes a value of 1, and when it deviates from it, the value of W ₁ /W ₂ becomes larger than 1 or smaller than 1 depending on the direction.

Therefore, the width of the bright level band is detected by the image processing device 41, which inputs the image signal and performs its calculation, and controls the width of the bright level band so that the ratio is 1 and the fiber center is located at the center of the screen. The device 42 may control the light source and each position adjustment device of the microscope. If W ₁ /W ₂ is 1±0.05, the optical axis deviation can be suppressed to within ±50 μm.

Fig. 12 shows the relationship between the defocus Δf ₀ and the slope (differential coefficient) from the bright level to the dark level. When focused on the center of the fiber, Δf ₀ =
If it is set to 0, when the focus shifts toward the front side of the fiber (Δf ₀ >0), the slope becomes steeper and the differential coefficient increases, and when the focus shifts toward the back side of the fiber (Δf ₀ <0), the slope becomes gentler. The microscope is reduced. Therefore, if the differential coefficient is set to, for example, about 0.065±0.01, the focal position shift can be suppressed to at least ±15 μm. In this way, if the control device controls the position adjustment device of the microscope so that the differential coefficient becomes a constant value,
The focal point position will always be kept constant.

Note that the set value of the differential coefficient need not be set to 0.065, and may be set to a differential coefficient corresponding to a focal state that makes it easy to detect the core from the image signal. However, in this case, as described above, the relationship between the observed core eccentricity D and the actual core eccentricity d is not simply a multiple of the refractive index, as shown in FIG. Therefore, the magnification M according to the focal state at that time
It is necessary to estimate the true position of the core by (D=Md).

Thus, by monitoring the ratio of the width of the dark level band at the edge of the optical fiber of the image signal and the slope from the light level to the dark level, the microscope and light source can easily provide an optimal optical axis and focus condition. The core position can be detected accurately. These operations can be easily automated by using a computer or the like for the processing device 41 and the control device 42.

In addition, the image processing device 41 can also have the functions of the image processing device 17 for core position detection explained in FIG. 2, so it can extract accurate core positions from the processing results and A highly accurate axis alignment device can be realized by determining the amount of axis deviation and controlling the moving device 5 that moves the optical fiber support base 4 so as to eliminate it.

As explained above, according to the optical fiber axis alignment device of the present invention, the inclination of the fiber image image signal detected by the image processing device is made constant, and the width of the two dark level bands is By adjusting the position of the microscope and light source so that the ratio of I can do it.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of an optical fiber axis alignment device using the conventional optical power monitoring method, Fig. 2 is an explanatory diagram of an optical fiber axis alignment device with a core direct observation system, and Fig. 3 is an explanatory diagram of an optical fiber axis alignment device using a conventional optical power monitoring method. A diagram showing an example of the image, Figure 4a,
b is an explanatory diagram of changes in the core observation position due to focal position deviation, Fig. 5 is a diagram showing the verification results, Fig. 6 is an explanatory diagram of optical axis deviation during axis alignment, and Fig. 7 is an illustration of optical axis deviation due to optical axis deviation. Demonstration diagram of changes in core observation position, No. 8
The figure is an explanatory diagram of the case where optical axis shift and focus shift occur.
FIG. 9 is a schematic configuration diagram showing an example of the optical fiber shaft alignment device of the present invention, FIG. 10 is a waveform diagram showing an example of an observed optical fiber image signal, and FIGS. FIG. 3 is an explanatory diagram showing the effects of the invention. 1, 2... Optical fiber, 3, 4... Optical fiber support stand, 5... Moving device, 11, 12... Light source,
13...Mirror, 14...Microscope, 15...Imaging device, 16...TV, 17...Image processing device, 2
0... Core section, 31, 32, 33... Position adjustment device, 41... Image processing device, 42... Control device.

Claims (1)

[Scope of Claims] 1. A microscope placed at a position perpendicular to the axis of the optical fiber near the abutting portion of two linearly abutted optical fibers to be connected, a light source placed on the opposite side across the optical fibers, and The core position of the optical fiber is detected by observing the optical fiber using one or both of the light sources placed in other orthogonal directions of the optical fiber axis with a mirror interposed therebetween, and the light source is used to hold the optical fiber to be connected. In a device that aligns the core axis of an optical fiber by moving a fiber fixing table, the light source, the optical fiber, and the microscope are arranged in a straight line, or the light source, the optical fiber, the mirror, and the microscope are arranged in a straight line taking into account the reflection angle of the mirror. a position adjusting device for finely moving the light source and the microscope so as to align the focal point of the microscope with a predetermined position of the optical fiber; an imaging device for capturing a fiber image obtained by the microscope; The slope of the dip from the bright level to the dark level at the upper and lower edges of the fiber and the width of the two dark level bands near the upper and lower edges of the fiber, which appear in the image signal scanned perpendicularly to the axis of the fiber image obtained by the device. and a control device that controls the position adjusting device so that the degree of inclination is a predetermined constant value and the ratio of the width of the dark band is 1. Optical fiber shaft alignment device.