JPH0242333A - Optical fiber inspection method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an optical fiber inspection method that can highly accurately inspect the processing accuracy of the end face of a polished optical fiber and quickly determine pass/fail.

[Prior art] Conventionally, in order to judge processing accuracy, an illumination device is provided at one end of the fiber, and as shown in Fig. 5, the line from the outer circumferential line 3 of the core 1-1, which appears bright, to the boundary line 2 obtained by polishing, is measured. Measuring the distance elf and measuring the amount of deviation of the boundary line from the core center (for example, tolerance ± 2 μm) and making a pass/fail judgment takes time, and the core outer circumference line 3 is a problem in the optical fiber manufacturing method. Therefore, there is a problem in that it is difficult to inspect for pass/fail judgments for items that cannot be clearly seen with good contrast.

[Purpose of the invention]

An object of the present invention is to provide an optical fiber inspection method that can inspect the end face of a polished optical fiber with high precision and quickly.

[Summary of the invention]

Utilizing the property that the skew light has a larger fiber acceptance angle than the meridional light, the fiber A feature is that a minute diameter dark part is made available at the center of the core, and the machined shape can be quickly inspected based on whether or not this dark part matches the machined shape boundary line.

[Embodiments of the invention]

Figure 1 shows an outline of the fiber polishing apparatus. As shown in FIG. 2, the fiber 1 consists of a core 1-1, which is a light transmitting part, and a cladding 1-2, which has a smaller refractive index than the core, and the outer periphery of the cladding 1-2 is covered with a covering part 1-3. When processing a fiber with a polishing tool (such as a grindstone) 10, as shown in FIG.
The coating portion 1-3 of the fiber 1 is fixed to the fiber 1, and the coating portion is removed from the fiber tip by a predetermined length Q, as shown in FIG. 2, so that the cladding 1-2 is exposed. The holder 5 is fixed to a cutting table 8 by a clamp 7, the cutting depth of the table 8 is given by a limit switch 9, and the fiber tip 1-2 is polished with a polishing force corresponding to the bending angle at that time.

If the angle φ between the holder and the grindstone is increased, the polishing pressure for the fiber will be increased. Therefore, in rough polishing, the polishing efficiency can be increased by increasing φ, and in final polishing, the angle φ can be decreased and the polishing pressure can be decreased to prevent chipping from occurring on the fiber polished surface. The processed shape of the glass fiber is, for example, as shown in Fig. 3, in which the tip is formed into a roof shape at a predetermined angle β, but the above angle φ and the cutting depth jit (the amount of fiber deflection after the fiber contacts the grinding wheel surface) A predetermined finishing angle β can be obtained by adjusting .

The purpose of forming the fiber tip into a ridge shape at an angle β is to change the light receiving angle α1 to the light receiving angle α when the tip is flat in FIG.

This is to increase the light transmission efficiency by increasing the size. In the processing shown in Figure 3, the ridgeline (boundary line) 2 of the roof must be at the center of the core 1-1 as shown in Figure 5.
For example, when the core diameter is 10 μm, the allowable deviation amount from the center is ±1 to 2 μm or less. Conventionally, the distance erf of the boundary line 2 from the outer circumferential line 3 of the core was measured, which had the problem of taking time to measure.
．． The main component of both claddings 1 and 2 is Sin, and the optical characteristics are similar, so even when light is incident from the other end, the core outer circumferential line 3 does not always appear clearly with good contrast and is blurred. , sufficient measurement accuracy could not be obtained.

In the present invention, a method shown in FIG. 4 is used in order to improve the measurement accuracy and shorten the measurement time variation.

Considering the fiber incident light divided into meridional light and skew light, the maximum acceptance angle θM for the meridional light is n s in e M= q = numerical aperture of the fiber...
・Given as (1). However, n is the external refractive index where the fiber is placed (n=1 in air), no is the refractive index of the core, and n is the refractive index of the cladding. On the other hand, the acceptance angle θ for the skew light is sin θcos y≦−67−
Aperture of π1 fiber... is given by (2). However, r
is the angle formed by the projection AF of the skew light AB onto the fiber cross section and the normal line A from point A, as shown in FIG.

Since cosr≦1 in equation (2), the acceptance angle for the skew light is larger than for the meridional light.

The angle formed by the skew light AB in FIG. 7 and the line AA' parallel to the optical axis is θ. If ZBA○=ω, then from Fig. 7, cosω=sinθQCOS r (3) (This means that the projection of the unit vector AC on AB onto AF is A D, and the projection of A D onto AO If AE is
It is clear that AE is a projection of AC onto AO. ) Now, from equations (1) and (2), cozy=sinθM/S 1 no-(4) or
sLnθc = n 1/ no ・
...Define Y and θC (critical angle) that satisfy (5). For example n.

=1.5. Considering the case of n t = 1.3, (
From formula 5), θC=60”, and from formula (1), OM=4
8° (however, n=1). Now θyo≦θ≦O
If the exit surface is viewed by the observation device 12 as shown in FIG. 4 at an angle of c<am, a dark portion will be formed in the region where ye<7. In equation (3), ω≧ω. Then, ω0 is the critical angle when the skew light is transmitted by total reflection at the interface between the core and the cladding, and when ω≧ω, the light is transmitted, but ω less than ω. Light cannot be transmitted. Therefore (3
) From the equation, when r<r, light does not propagate and the above-mentioned dark area is formed. The diameter of the dark area in Figure 6 is α. , let the diameter of core 1-1 be α. . =0 engineering 5inr...(6
).

From equations (4) and (6), the dark area diameter is the observation angle θ (θ, ≦0
≦θC).

Based on the above considerations, the conditions for the formation of a small-diameter dark area are as follows: (1) In addition to meridional light, skew light is required, so generally it is not a parallel light source but a scattered light source (Fig. 4, 1l).
-1) is required.

(2) Since it is necessary to set the IiIII angle θ≧OM, the incident angle θ of the incident light must also be set θ≧02, and generally, as shown in FIG. 4, the convex lens 1
1-2 is required. Furthermore, in order to make the wt observation angle sufficiently large such that θ≧θ□, it is generally sufficient to increase the magnification of the microscope objective lens.

By using the illumination-observation system shown in FIG. 4, the core 1-1 is illuminated as shown in FIG.

Even if the central dark part 4 can be made dark<am and the core peripheral line 3 is not clear, by appropriately adjusting the observation angle θ, it is possible to make the central dark part 4 coincide with the processed ridge-shaped ridge line 2,
Discrepancies can be clearly observed, and processing precision can be determined quickly and easily. (FIG. 13 shows the observation microscope ta) Here, in FIG. 1, the depth of cut is set by the limit switch α in FIG. 1, but there are cases where sufficient positioning accuracy cannot be obtained with the limit switch alone.

As a countermeasure against this, a proximity sensor (capacitance type, eddy current type, air type, optical type, etc.) is installed at the tip of the holder 5 in the figure, facing the grinding wheel 10.
6 can be provided, but the shape may become large and workability may deteriorate.

Therefore, in the present invention, an optical contact detection method between the fiber 1-2 and the grindstone 1o shown in FIGS. 8 and 9 was devised.

As shown in FIG. 8(α), parallel light is irradiated from a distance using an illumination bag @14 and monitored with an observation device 15 such as a magnifying glass. Observed as in the monitor image in b), when the fiber is not in contact with the grindstone, the length of the bright line 16 is the crut protrusion length Q. be equivalent to. On the other hand, in the state shown in Figure 9 when the fiber is in contact with the grindstone, the fiber tip is deflected, and the angle of this deflection is the protrusion length of the rad Ω. Since it is proportional to the square of Ct, the light reflected by the bent portion of the fiber tip deviates greatly from the wt sensor 15, and as a result, the length QL of the bright line 16 obtained in the monitor image of FIG. 9(b) is Ct< Qo becomes. This makes it possible to detect contact between the fiber and the grindstone with high precision, and to accurately determine the amount of cut after contact.

Further, since the illumination/observation system can be placed sufficiently away from the main body of the polishing apparatus, work efficiency is not impaired.

〔Effect of the invention〕

According to the present invention, it is possible to simplify and speed up the inspection method for the accuracy of the finished shape of a fiber, which has a large economical effect.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the main body of the polishing apparatus, FIG. 2 is an explanatory diagram showing the tip of the optical fiber, FIG. 3 is an explanatory diagram showing the processed shape of the tip of the optical fiber, and FIG. , an explanatory diagram showing a fiber illumination-am device of the present invention, FIG. 5 is a diagram showing an observed image of a conventional fiber end face, and FIG. 6 is a diagram showing a fiber end face 1 according to the present invention! FIG. 7, a diagram showing image detection, is an explanatory diagram of skew light. FIGS. 8 and 9 are diagrams for explaining detection of the presence or absence of contact between the optical fiber and the grindstone, and FIG. 8 (α) is a diagram showing the case where the optical fiber and the grindstone are not in contact. 9(b) is a diagram showing the monitor image, FIG. 9(α) is a diagram showing the case where the optical fiber and the grindstone are in contact, and FIG. 9(b) is a diagram showing the monitor image. DESCRIPTION OF SYMBOLS 1...Fiber, 1-1...Core, 1-2...Clad, 1-3...Coating, 2...Roof-shaped boundary line, 3...Core outer peripheral contour line. 4... Small diameter central dark area, 5... Holder, 6... Proximity sensor, 7... Clamp, 8... Cutting table, 9... Limit switch. DESCRIPTION OF SYMBOLS 10... Polishing tool, 11... Illuminating device, 11-1... Light source lamp, 11-2... Condenser lens, 12... Objective lens, 13... Microscope, 14... lighting equipment. 15...Magnifying glass, 16...Emission line. 5th ward Akira Niguchi (Ataku 70 Akira 1ku 8th day Akira de prisoner)

Claims (1)

[Claims] 1. Inject the scattered light at an incident angle sufficiently larger than the maximum acceptance angle corresponding to the fiber numerical aperture in meridional light at the entrance surface of the optical fiber, and at an angle sufficiently larger than the above maximum acceptance angle at the exit surface of the fiber. Observe a minute dark area in the center of the core of the optical fiber, and measure the amount of deviation between the boundary line of the polished optical fiber end face and the minute dark area using the polished end surface of the optical fiber as the output surface (observation surface). An optical fiber inspection method characterized by inspecting fiber processing accuracy.