JPH0416083B2 - - Google Patents

Description

[Detailed description of the invention] (a) Technical field to which the invention pertains The present invention relates to an optical fiber excitation method and device for measuring the transmission characteristics of an optical fiber,
More specifically, the present invention relates to a method and apparatus for making measurement signal light enter an optical fiber so as to be aligned with the center of the core of the optical fiber.

(b) Prior art and its problems When measuring the transmission characteristics of an optical fiber, for example, the loss value, normally a measurement signal is focused on the input end 3 of the optical fiber 5 to be measured by a lens 2, as shown in FIG. Light 1 is guided to enter the core of optical fiber 5. If the center of the light beam of the focused measurement signal light 1 does not match the core center of the optical fiber 5, a sufficient amount of light will not enter the core of the optical fiber, so the S/N ratio of the measurement signal (signal When the optical fiber under test is a multimode fiber, many higher-order mode leakage modes are excited, causing problems such as the inability to accurately measure the transmission characteristics of the optical fiber. . Therefore, in order to align the center of the focused measurement signal light with the core center of the optical fiber to be measured, the input end 3 of the fiber to be measured 5 is fixed to the fine movement table 4, and the position of the input end of the optical fiber is moved and adjusted. It is possible. A photodetector 7 is arranged at the output end 6 of the optical fiber 5 to be measured in order to measure the amount of light emitted from the input end at the output end, and the output of the photoelectric conversion is read by a display 8. I can do it.

However, in the above-mentioned conventional configuration, when trying to maximum excite the optical fiber to be measured, the following problems occurred.

Measurement information at the output end of the optical fiber under test,
In other words, it is necessary to adjust the position of the fine movement stage 4 so as to obtain the maximum excitation based on the value displayed on the display 8 on the output end side. However, if the optical fiber to be measured is long (for example, several hundred meters), It becomes necessary to provide a signal transmission cable for feeding back the displayed value to the incident end side.

As shown in FIG. 4, when the measurement signal light 11 at the input end face of the optical fiber to be measured does not coincide with the core part 10 of the optical fiber and hits the cladding part 9, etc., the measurement signal light 11 is The fiber is not energized at all, so the display on the display 8 is zero. In this case, it is unclear in which direction the fine movement stage 4 should be moved to guide the measurement signal light to the core of the optical fiber. To prevent this kind of situation, the fine movement table 4 is usually provided with a V-groove for positioning the optical fiber, but even so, for example, in a single mode optical fiber with a core diameter of about 5 to 10 μm, the core center may be aligned with the clad center. If the values do not match and are biased, this measure is insufficient.

When the optical fiber to be measured has a plurality of cores as shown in FIG. It is unclear whether is excited by the first core 14 or the second core 15. Specific examples include image fibers in which a large number of pixel fibers are fused and integrated, tape fibers in which fibers are aligned in a line and integrated, and cases in which the transmission characteristics of individual fibers included in a fiber array are measured. It will be done.

(c) Purpose of the Invention The present invention has been made in view of the above-mentioned conventional circumstances, and it is an object of the present invention to provide an optical fiber excitation method and apparatus that can achieve the following matters.

It is not necessary to provide a signal transmission cable for feeding back measurement information on the output end side of the optical fiber to be measured to the input end side.

Even if the measurement signal light does not coincide with the core but hits the cladding at the incident end face of the optical fiber to be measured, the direction in which the fine movement table should be moved can be recognized.

When the optical fiber to be measured has a plurality of cores, it is possible to recognize in which core the measurement signal light is excited.

(d) Structure of the Invention For this purpose, the present invention provides an input end face of an optical fiber fixed to a fine movement table whose position of the input end is adjustable for receiving a focused measurement signal light in order to measure the transmission characteristics of the optical fiber. In the method and apparatus for exciting an optical fiber, the light source is arranged at the output end face of the optical fiber, and the light from the illumination light source passes through the optical fiber core. The core image of the optical fiber emitted from the input end face of the optical fiber and the reflected image of the measurement signal light at the input end face of the optical fiber are received by an imaging section, and the relative positional relationship between the core image and the reflected image is determined. is visually displayed on a monitor, and the position of the fine movement table is adjusted so that the core image and the reflected image overlap with each other, thereby making the measurement signal light coincident with the center of the core of the optical fiber. Features.

This eliminates the need to provide a signal transmission cable to feed back measurement information from the output end of the optical fiber under test to the input end, and the measurement signal light is transmitted to the core at the input end of the optical fiber under test. It is possible to recognize the direction in which the fine movement table should be moved even if the optical fiber does not match the cladding, and if the optical fiber to be measured has multiple cores, which core is excited by the measurement signal light? A method and apparatus for excitation of an optical fiber are provided that can recognize whether the fiber is present or not.

(E) Embodiments of the Invention An example of the configuration of an optical fiber excitation device according to the present invention is shown in FIG. In FIG. 1, the optical fiber 5 to be measured
An illumination light source 17 is arranged for illuminating the output end 6 of. This illumination light source 17 is removable as described later. It is desirable that the illumination light uniformly hits the entire surface of the output end face 6 of the optical fiber.
Since the light entering the cladding portion of the optical fiber 5 from the light source 17 leaks to the outside while propagating within the optical fiber, only the core portion is observed brightly at the input end 3 of the optical fiber. The core image of the optical fiber input end 3 passes through the lens 2, is reflected by the half mirror 16, passes through the imaging lens 18, is received by the image pickup tube 20, and is displayed as an image 22 on the monitor 21. Separately, a reflected image of the measurement signal light 1 at the input end face of the optical fiber to be measured is also received by the image pickup tube 20 via the lens 2, the half mirror 16, and the imaging lens 18, and is shown as an image 23 on the monitor 21. It will be displayed as follows. In normal cases, the reflectance at the input end face of the optical fiber is about 3 to 4%. In this way, the core image and the reflected image can be observed simultaneously on the screen of the monitor 21, and the relative positional relationship between the two can be recognized. Therefore, while observing the monitor 21, by moving the fine movement stage 4 so that the core image 22 on the input end face 3 and the reflected image 23 of the measurement signal light on the input end face 3 concentrically overlap on the monitor 21, the measurement signal The center of the beam of light 1 coincides with the center of the core of the optical fiber 5, and maximum excitation is achieved. In FIG. 1, a photodetector is not shown on the output end 6 side of the optical fiber 5, but when measuring the transmission characteristics of the optical fiber, the core image 22 coincided with the reflected image 23 of the measurement signal light. Thereafter, the illumination light source 17 may be removed, and the arrangement may be returned to the state in which the photodetector 7 and its photoelectric conversion output display 8 are arranged as shown in FIG.

Note that the boundaries of the core image and the reflected image of the measurement signal light at the incident end face of the optical fiber are not necessarily clearly shown as shown schematically in Figures 4 and 5, and Figure 5 shows the respective intensity distributions. The boundaries of the image often become unclear, as shown by curves 25 and 24. Therefore, in order to align the center of the measurement signal light with the core center and obtain maximum excitation, it is conceivable to use electrical means instead of visual observation. In that case, the spread function f(x, y, z) of the measurement signal light at the input end face of the optical fiber to be measured is
The product f(x, y) of the core light intensity distribution function g(x, y)
By moving the fine movement table 4 so that y, z)·g(x, y) becomes maximum, the maximum excitation can be obtained accurately. Here, the spread function of the measurement signal light at the input end face of the optical fiber to be measured is a function of the position z of the input end of the optical fiber in the optical axis direction. Specifically, the spectrum of the illumination light source is selected so as not to match that of the measurement signal light, and the core image and the reflected image of the measurement signal light at the incident end face of the optical fiber to be measured are captured using a color filter or the like using the imaging tube 20. It is conceivable to separate the two by 1 and then electrically stack them again after photoelectric conversion. When the above-mentioned electrical processing is included in this device, automatic excitation of the optical fiber becomes possible by moving the fine movement table using a servo motor or the like. Maximum excitation is performed continuously on each core of an image fiber, fiber array, etc. in which multiple cores are integrated, and by extracting position information at the time of maximum excitation, each core at the end face of the optical fiber can be determined. It also becomes possible to quantitatively evaluate the arrangement state of the cores.

(F) Effects of the Invention As described above, according to the present invention, an optical fiber fixed to a fine movement table whose incident end is adjustable for receiving a focused measurement signal light in order to measure the transmission characteristics of the optical fiber. In the excitation method and apparatus for an optical fiber, the light source is arranged on the output end surface of the optical fiber, and the light from the illumination light source illuminates the optical fiber core. An imaging unit receives a core image of the optical fiber passing through and exiting from the input end face of the optical fiber and a reflected image of the measurement signal light at the input end face of the optical fiber, and calculates the relative relationship between the core image and the reflected image. The positional relationship is visually displayed on a monitor, and the position of the fine movement table is adjusted so that the core image and the reflected image overlap with each other, so that the measurement signal light is made to coincide with the center of the core of the optical fiber. It is characterized by

This visually displays the core image of the optical fiber at the input end of the optical fiber and the reflected image of the measurement signal light at the input end face of the optical fiber on the monitor so that the relative positional relationship between the two can be seen. Maximum excitation of the optical fibers can be achieved by adjusting the position of the fine movement table that fixes the input ends of the optical fibers so that they overlap. Therefore, it is not necessary to provide a signal transmission cable for feeding back measurement information from the output end of the optical fiber under test to the input end, and the measurement signal light is transmitted to the input end of the optical fiber under test. It is possible to recognize the direction in which the fine movement table should be moved even when the fiber does not match the core and hits the cladding, and when the optical fiber to be measured has multiple cores, the measurement signal light is excited in any of the cores. A method and apparatus for excitation of an optical fiber are provided that can recognize whether the optical fiber is moving or not.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the configuration of the optical fiber excitation device according to the present invention, FIG. 2 is a diagram showing the light intensity distribution function of the core and the spread function of the measurement signal light at the input end face of the optical fiber, and FIG. 3 is a diagram showing the spread function of the measurement signal light. FIG. 4 is a schematic diagram showing the configuration of a conventional optical fiber excitation device, and FIGS. 4 and 5 are diagrams showing the position function of the input end face of the optical fiber and the measurement signal light, respectively. DESCRIPTION OF SYMBOLS 1...Measurement signal light, 3...Incidence end face of optical fiber, 4...Fine movement table, 5...Optical fiber, 6...
Output end face of optical fiber, 17...Light source for illumination, 2
0...imaging section, 21...monitor.

Claims (1)

[Scope of Claims] 1. In order to measure the transmission characteristics of the optical fiber, the focused measurement signal light is applied to the core of the optical fiber on the input end face of the optical fiber, the input end of which is fixed to a fine movement table whose position is adjustable. In the excitation method of an optical fiber in which the light is incident centrally, an illumination light source is disposed on the output end face of the optical fiber, and the light from the illumination light source passes through the optical fiber core and exits from the input end face of the optical fiber. An imaging section receives a core image of the emitted optical fiber and a reflected image of the measurement signal light at the incident end face of the optical fiber, and visually displays the relative positional relationship between the core image and the reflected image on a monitor. A method for excitation of an optical fiber, characterized in that the measurement signal light is incident on the core center of the optical fiber by adjusting the position of the fine movement table so that the core image and the reflected image overlap with each other. . 2. A device for guiding a measurement signal light for measuring the transmission characteristics of an optical fiber so as to condense it on an input end face of the optical fiber, and a device that guides the measurement signal light to be focused on the input end face of the optical fiber, and An optical fiber excitation device including a position-adjustable fine movement stage for fixing the input end of the optical fiber to align the input end with the core center, an illumination light source removably disposed on the output end of the optical fiber; , a core image of the optical fiber in which light from the illumination light source passes through the core of the optical fiber and exits from the input end face of the optical fiber, and a reflected image of the measurement signal light at the input end face of the optical fiber. 1. An optical fiber excitation device comprising: an imaging section that receives light; and a monitor that visually displays a relative positional relationship between the core image and the reflected image received by the imaging section.