JPS62144041A - Measurement of optical fiber structure - Google Patents

Abstract

PURPOSE:To measure the structure of an optical fiber, by making light transmitting through a liquid filled between an optical fiber to be measured and a transparent tube with the refractive index slightly higher than those of a clad of the optical fiber being measured and the transparent tube to observe it through a transparent plate. CONSTITUTION:An optical fiber 1 to be measured has a tip face 6 which is cut at a right angle to the axis thereof. The tip part 8 thereof is cleared of a cover layer 7 over a fixed length. A transparent plate 3 is arranged vertical to a transparent tube 2 ahead of the front end of the transparent tube 2 with the inner dia. larger than the outer dia. of a clad layer of the fiber 1 and the tip part 8 is inserted into the transparent tube 2. A liquid 4 with the refractive index slightly higher those of the clad of the fiber 1 and the transparent tube 2 is filled between inside the transparent tube 2, between the transparent tube 2 and the transparent plate 3 so that it infiltrates into the tip part 8. Light is projected into the liquid 4 from another optical fiber 5 or light is made to propagate from the fiber 1 itself to observe a end face 6 through the transparent plate 3. In this manner, the outer dia. of the fiber 1 or core shape and the light intensity distribution in the propagation mode can be measured.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Technical field to which the invention pertains The present invention relates to a method for measuring the structure of an optical fiber, and more specifically includes measuring the outer diameter and core shape of an optical fiber, as well as the light intensity distribution of the propagation mode. A method for measuring the structure of optical fibers.

(b) Prior art and its problems Conventionally, the method for measuring the structure of optical fibers regarding the items mentioned above involves cutting the optical fiber to be measured at right angles to the axial direction, enlarging the end face with a lens, and using a television camera. The method used was to observe the In this case, the shape of the core or the light intensity distribution of the propagation mode is measured by the light transmitted through the optical fiber, and the outer diameter of the optical fiber is measured by the light reflected at the end face of the optical fiber. FIG. 2 is a schematic diagram showing a conventional method for measuring the structure of an optical fiber.

In FIG. 2, one end of the optical fiber 11 to be measured is cut so as to form a plane perpendicular to the axial direction and fixed to the fine movement stage 12, and the other end is used for excitation using a V-groove connector 14. Connect to optical fiber 13. Excitation optical fiber 16
Light from a core measurement light source 15 such as a halogen lamp is incident through a lens. An objective lens 16 and a television camera 17 are arranged to observe the end face of the fixed optical fiber 11 fixed to the fine movement stage 12.

Furthermore, in order to shine light onto the end face of the optical fiber to be measured in order to measure the outer diameter of the optical fiber, a half mirror 18 is placed between the objective lens 16 and the television camera 17, and at the same time, the light source 19 for measuring the outer diameter is illuminated. . . . is placed at a position where it is reflected by the mirror 18 and reaches the end of the optical fiber 11 to be measured. With the above configuration, the fine movement stage 12 is adjusted to focus the television camera 17 on the end face of the optical fiber to be measured 11, and the light sources 15 and 5 for core measurement of the optical fiber to be measured are adjusted.
By switching between the light source 19 and the light source 19 for measuring the outer diameter, it is possible to measure the core diameter, the light intensity distribution of the propagation mode, the outer diameter, etc. of the optical fiber to be measured. Further, based on the above measurements, the core center position, its eccentricity, the center position of the light intensity distribution of the propagation mode, its eccentricity, etc. can be determined. Furthermore, it is also possible to AD convert an image taken by a television camera and input it into a computer to automatically calculate the core diameter, outer diameter, core eccentricity, etc.

Here, in the above measurement, it is important that the end face of the optical fiber to be measured is a plane that is almost completely perpendicular to the axial direction. That is, if the end face to be measured is irregular, the television camera will not be able to focus on the end face to be measured, and both transmitted light and reflected light will be affected by the irregularity of the end face, making accurate measurement impossible. Furthermore, regarding the measurement of transmitted light, the large difference in refractive index between the optical fiber core and air has a synergistic effect on accurate measurement with the irregularity of the end face. However, it is difficult to cut the optical fiber to be measured so as to obtain a plane completely perpendicular to the axial direction, which poses a problem in measurement.

(c) Purpose of the invention The present invention has been made in view of the above-mentioned conventional circumstances, and includes:
Accurately measures the core shape, propagation mode light intensity distribution, outer diameter, etc. of an optical fiber without being affected by the irregularity of the end face of the optical fiber under test or the difference in refractive index between the optical fiber core and air. Our goal is to provide a way to do so.

(D) Structure of the Invention The present invention provides a transparent tube having an inner diameter larger than the outer diameter of the cladding of the optical fiber to be measured, and a thin transparent plate is placed near the tip of the transparent tube perpendicularly to the transparent tube, and the coating layer is removed inside the transparent tube. The distal end portion of the optical fiber to be measured is inserted and fixed to a position where it is almost in contact with the transparent plate, and the cladding of the optical fiber to be measured and the refraction of the transparent tube are formed at least within the transparent tube and between the transparent tube and the transparent plate. The transparent tube is filled with a liquid having a refractive index slightly higher than the optical fiber to be measured, and light is incident into the transparent tube from the rear end side and propagated into the liquid along the transparent tube. To measure the diameter (observe the end face of the optical fiber to be measured through the transparent plate, and change the incidence of light into the transparent tube to enter the light from the rear end of the optical fiber to be measured and enter the core of the optical fiber to be measured. The method is characterized in that the end face of the optical fiber to be measured is observed through the transparent plate in order to propagate light and determine the core shape and light intensity distribution of the propagation mode of the optical fiber to be measured.

(e) Effect of the invention According to the above configuration, the optical fiber to be measured has a refractive index slightly higher than the refractive index of the cladding of the optical fiber to be measured and the transparent tube filled between the optical fiber to be measured and the transparent tube arranged around it. The outer diameter of an optical fiber can be measured through a transparent plate by propagating light through a liquid, and the light transmitted through the optical fiber to be measured and emitted from its tip is transmitted through the liquid surrounding the tip of the fiber to be measured. By observing the optical fiber through a transparent plate after propagation, the core shape of the optical fiber, the light intensity distribution of the propagation mode, etc. can be measured.

(F) Embodiments of the Invention Preferred embodiments of the invention will now be described with reference to the accompanying drawings. As shown in FIG.
The coating layer 7 is removed over a certain length of the twisted tip portion 8. However, the tip end face 6 does not form an accurate plane perpendicular to the axis due to the difficulty of cutting peculiar to optical fibers, and has an irregular state. An optical fiber to be measured 1 with a thin transparent plate filter arranged perpendicularly to the transparent tube 2 in front of the front end of a transparent tube 2 having an inner diameter larger than the outer diameter of the cladding layer of the optical fiber to be measured, and a coating layer removed inside the transparent tube 2. Insert the tip part 8 of the
The optical fiber 1 to be measured is fixed so that it abuts against the transparent plate filter, or is located near it at a certain degree. Here, the cladding of the optical fiber 1 to be measured and It is filled with a liquid 4 having a refractive index slightly higher than that of the transparent tube 2. Note that, as mentioned above, the tip end surface 6 of the optical fiber 1 to be measured is not a precise plane perpendicular to the axis, so it is impossible for it to come into close contact with the transparent plate 3. The liquid 4 will fill even the slightest gap. In this state, the structure of the optical fiber 1 to be measured is measured.

First, the method for measuring the outer diameter of the optical fiber to be measured will be explained. Another optical fiber 5 is guided to the inner diameter part of the rear end of the transparent tube 2, and the 6C light in the liquid 4 in the transparent tube 2 is emitted. The light emitted from the optical fiber 5 passes through the liquid 4 to the optical fiber 1 to be measured.
Because it has a higher refractive index than the cladding and transparent tube 2,
It propagates through repeated total reflections at the interface between the liquid 4 and the cladding of the tip portion 8 of the optical fiber to be measured and between the liquid 4 and the transparent tube 2. Therefore, the end face 6 of the optical fiber to be measured
When observed through the transparent plate 3, the end face 6 of the optical fiber to be measured is dark, and the liquid 4 around it becomes bright due to the propagated light. Therefore, the outer diameter of the tip 8 of the optical fiber to be measured is Accurate measurements can be made without being affected by the cutting condition of the end face 6 of the.

Next, a method for measuring the core shape, propagation mode, etc. of the optical fiber to be measured will be explained. Instead of the light entering from the optical fiber 5 for measuring the outer diameter of the optical fiber as described above, light is entered from the rear end side of the optical fiber 1 to be measured and the light is propagated to the core of the optical fiber 1 to be measured. . The light propagated through the core is emitted from the distal end surface 6 of the optical fiber 1 to be measured, and then propagates through the liquid 4 having a refractive index slightly higher than the refractive index of the cladding of the optical fiber 1 to be measured. As described above, the liquid 4 has a refractive index slightly higher than the refractive index of the cladding of the optical fiber 1 to be measured. Here, since the refractive index of the core of the optical fiber is slightly larger than the refractive index of the cladding, the refractive index of the core of the optical fiber 1 to be measured and that of the liquid 4 are approximate. Therefore, when the light is emitted from the core of the optical fiber 1 to be measured into the liquid 4, the influence of the irregular state of the tip surface 6 is small, and the propagation state of the light does not change significantly.

Then, the tip surface 6 of the covered optical fiber 1 is observed through the transparent plate 6, and the core shape and center position of the core, as well as the light intensity distribution of the propagation mode and the center position are detected. diameter, core eccentricity,
The propagation mode diameter and the eccentricity of the propagation mode can be measured.

(g) Effects of the Invention As described above, according to the present invention, when measuring the outer diameter of an optical fiber to be measured, light propagating in a liquid filled in a transparent tube surrounding the tip of the optical fiber to be measured is used. Since the measurement is performed, accurate measurement can be performed without being directly influenced by the irregular state of the end face of the optical fiber to be measured. In addition, when measuring the core shape of the optical fiber to be measured, the light intensity distribution of the propagation mode, etc., the light that has propagated through the core of the optical fiber to be measured is emitted from the tip of the optical fiber to be measured. This propagation equation is observed through a transparent plate. Therefore, the propagation state of the light emitted from the core of the optical fiber to be measured hardly changes, and accurate measurement can be performed with almost no influence from the irregularity of the tip surface of the optical fiber to be measured.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the principle of the optical fiber structure measuring method of the present invention, and FIG. 2 is a schematic diagram showing the principle of the conventional optical fiber structure measuring method. 1...Optical fiber to be measured 2...Transparent
Bright tube 6...Transparent plate 4...Liquid Patent applicant Sumitomo Electric Industries, Ltd. Figure 2 Wenhei Sun Renda

Claims (1)

[Claims] A thin transparent plate is arranged perpendicularly to the transparent tube near the tip of a transparent tube having an inner diameter larger than the outer diameter of the cladding of the optical fiber to be measured, and the tip portion of the optical fiber to be measured from which the coating layer has been removed is placed inside the transparent tube. The optical fiber to be measured is inserted and fixed to a position where it is approximately in contact with the transparent plate, and has a refractive index that is at least slightly higher than the refractive index of the cladding of the optical fiber to be measured and the transparent tube within the transparent tube and between the transparent tube and the transparent plate. The transparent tube is filled with a liquid, and light is incident into the transparent tube from the rear end side of the transparent tube to propagate into the liquid along the transparent tube and pass through the transparent plate in order to measure the outer diameter of the optical fiber to be measured. The end face of the optical fiber to be measured is observed, and the light is input from the rear end of the optical fiber to be measured by changing the incidence of light into the transparent tube, and the light is propagated to the core of the optical fiber to be measured. A method for measuring the structure of an optical fiber, comprising observing the end face of the optical fiber to be measured through the transparent plate in order to determine the core shape and the light intensity distribution of the propagation mode.