JPH0627646B2 - Optical fiber base material shape measuring device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a high-speed and high-precision optical fiber preform shape measuring apparatus.

(Prior Art) FIG. 1 is a conceptual diagram of a conventional device of this type, in which 1 is a laser beam sending (scanning) unit, 2 is a laser beam, 3 is a light receiving unit (system), and 4 is a receiving unit. It is a measured object.

To operate this, the laser beam scanning unit 1 scans the laser beam 2 with respect to the DUT 4 in the direction of the arrow in FIG. 1, and the output of the “shadow” is detected by the light receiving system 3. The measured value is displayed on the display unit 5 after a simple calculation. In the case of an opaque object, the light output detected by the light receiving system 3 has a shape as schematically shown in FIG. 2, and the time to decay of the light intensity in the figure is measured to measure the object 4 to be measured. The outer diameter is required.

(Problems to be Solved by the Invention) In the conventional apparatus, as shown in FIG. 1, there is a space between the laser beam sending portion 1 and the light receiving portion 3, and the DUT 4 is placed in this space.
Since it was arranged to measure the outer diameter of the linear object or the outer diameter of the transparent glass tube, the wall thickness, etc. % Or less) There is a drawback that the internal dimensions of a transparent object having a difference in refractive index cannot be measured.

(Object of the Invention) An object of the present invention is to arrange the optical fiber preform to be measured in a container filled with a highly precise adjusted refractive index adjusting oil, and to measure only the outer diameter and non-circularity of the optical fiber preform. It is another object of the present invention to provide an optical fiber preform shape measuring device capable of simultaneously measuring the core diameter, the core non-circularity, and the core eccentricity.

(Means for Solving Problems) In order to achieve the above object, the present invention scans a laser light beam in a direction perpendicular to a central axis of an object to be measured whose outer diameter is measured, and the laser light beam is scanned by the object to be measured. In an outer diameter measuring device for measuring the outer diameter of the object to be measured with high accuracy by electrically measuring the time of interruption, in a plane perpendicular to the light beam, between the light emitting part and the light receiving part of the light beam. A container having two transparent front and rear window members is arranged in the container, the center axis of the optical fiber preform to be measured is rotatably arranged in the container in a direction perpendicular to the light flux, and the container is filled with the light. The refractive index n of the refractive index adjusting oil is Or the laser beam is scanned in the direction perpendicular to the central axis of the object to be measured whose outer diameter is to be measured, and the time when the laser beam is interrupted by the object to be measured is electrically measured. In the outer diameter measuring device for measuring the outer diameter of the object to be measured with high accuracy by measuring the distance, the front and rear two sheets are provided in the plane perpendicular to the light beam, in the middle of the light beam sending portion and the light receiving portion. A container having a transparent window material is arranged, the center axis of the optical fiber preform to be measured is rotatably arranged in the container in a direction perpendicular to the luminous flux, and the refractive index adjusting oil filled in the container Refractive index n is The optical fiber preform is characterized by having a mechanism capable of rotating the optical fiber preform at an arbitrary angle with respect to the central axis thereof and moving the optical fiber preform at an arbitrary length in the axial direction.

(Function) Not only the outer diameter and non-circularity of the optical fiber base material, but also the core diameter, without being affected by the difference in refractive index in the optical fiber base material,
The core non-circularity and core eccentricity can be measured at the same time.

(Embodiment) FIG. 3 is a conceptual diagram of an embodiment of the present invention, in which 6 is an optical system of a non-contact laser shape measuring unit, which sends a laser beam (scanning unit) 6a and a light receiving unit (system) 6b. And are connected together. 7 is a quartz optical fiber base material to be measured, 8 is a pair of chucks for holding the optical fiber base material 7, 9 is a glass container containing the refractive index adjusting oil, and 10 is a plane perpendicular to the laser beam 11. A certain transparent window material made of quartz, 12 is a chuck 8
An oil seal bearing for keeping airtightness inside the glass container 9 and the rotating shaft 13 connected with the reference numeral 14, a refractive index adjusting oil filled in the glass container 9, and a function 15 for rotating the rotating shaft 13 at a constant angle. Pulse motor, 15 '
Is a bearing of the rotary shaft 13, 16 is a pulse motor for moving the optical system 6 in the axial direction of the optical fiber preform 7 at a constant interval, and 17 is a rotary shaft with a screw for transmitting the driving force of the pulse motor 16. The optical system 6 is screwed onto a part of the system 6, and the rotation of the rotary shaft 17 causes the optical system 6 to move forward and backward with respect to the axial direction of the optical fiber 7. 18 is a bearing of the rotating shaft 17, 19 is an electric signal processing unit for processing the signal measured by the optical system 6, 20 is a minicomputer for controlling the entire apparatus and arithmetically processing the processed electric signal, and 21 is a calculation result. It is an XY plotter for display.

In order to operate this, first, the silica single mode optical fiber preform 7 is fixed by the chuck 8 and the inside of the glass container 9 is filled with silicon oil having a refractive index of 1.4570 (refractive index adjusting oil 14). . Then, the optical system 6 is operated and H
The parallel light flux 11 of the e-Ne laser is scanned in a direction perpendicular to the central axis of the optical fiber preform 7, and the light reception signal at that time is
It is sent to the electric signal processing unit 19. FIG. 4 schematically shows an example of measurement of a received light signal. Points A and A ′ at which the signal intensity is remarkably reduced are the boundaries between the cladding portion of the optical fiber preform 7 and the refractive index adjusting oil 14, Similarly, points B and B'are
It corresponds to the boundary between the clad portion and the core portion of the optical fiber preform 7. Where the times t ₁ and t between these pulsed signals are
The core diameter and outer diameter of the optical fiber preform 7 can be determined by electrically measuring ₂ . Further, the laser beam can be scanned at a speed of several msec or less per scanning by using an appropriate deflector, so that high-speed measurement and signal averaging processing can be easily performed. The fourth
The fact that an optical signal as shown in the figure can be obtained will be described later in detail.

Next, these data are averaged several tens to several thousand times in the electric signal processor 19, and then stored in the storage device incorporated in the minicomputer 20. Then, a pulse signal is sent from the minicomputer 20 to the pulse motor 15 to rotate the rotary shaft 13 by 5 °, and the same measurement as above is performed.

At this time, the respective points A, A ', B and B'in FIG. 4 are also recorded as their relative time positions as data. These data can be used to determine the non-circularity of the core diameter and the outer diameter when the core is eccentric in FIG.

Hereafter, the same measurement as above is performed for all rotation angles (360 ° direction).
Is performed (72 measurement points), and those data are recorded in the min computer 20.

Then, from the minicomputer 20, the pulse motor 16
Pulse to the optical system 6 to rotate the rotary shaft 17
Is moved in the axial direction of the optical fiber preform 7 by 10 mm, and the same measurement as above (72 measurement points) is performed. Hereinafter, if the above measurement is carried out while repeatedly moving the optical system 6 at intervals of 10 mm and the result is displayed on the plotter 21, the outer diameter in the axial direction of the optical fiber preform 7, the outer diameter non-circularity, the core diameter, The longitudinal dependence of the non-circularity of the core and the eccentricity of the core is required with high accuracy. Moreover, the measurement interval can be arbitrarily selected within a required range.

The non-circularity of the outer diameter and the core diameter, and the eccentricity of the core diameter are given by the following equations in the case of a single mode fiber preform.

Non-circularity of outer diameter = (maximum outer diameter-minimum outer diameter) / (standard outer diameter)
× 100 (%) Non-circularity of core diameter = (maximum core diameter−minimum core diameter) / (standard core diameter) × 100 (%) Eccentricity of core = (distance between center of base material and center of core) /
(Standard outer diameter) × 100 (%) Here, the center of the base material and the center of the core are easily determined by applying the least squares method to the measured values in the 360 ° direction (measurement points 72 points). It

FIG. 5 shows an example of the above-mentioned measurement, and the length is about 40.
cm is the longitudinal dependence of the eccentricity of the core of the single mode optical fiber preform. From this measurement, it was confirmed that the eccentricity of the optical fiber preform used in the measurement was within 0.52%.

In this embodiment, the case where the optical fiber preform is held horizontally has been described, but it is possible to use a vertical type because of the device structure.

The condition of the refractive index of the refractive index adjusting oil and the principle of obtaining the signal shown in FIG. 4 will be described below. FIG. 6 is an explanatory diagram related to the operation of the present measuring apparatus, showing a cross section of the optical system 6 in FIG. 3, in which 22 is a condenser lens and 23
Is an optical detector.

In FIG. 6, P-P ', Q-Q', RR ', S-
S ′ and T−T ′ represent He—Ne laser light beams scanned in the x direction, and the relationship between the position of the light beam in the x direction and the received optical signal is as follows when n <n _1. is there. Here, FIG. 6 shows a case where the window member 10 is made of quartz having a refractive index n ₁ , and by doing so, unnecessary reflection with the refractive index adjusting oil 14 can be reduced. The deviation of the refractive index of the window material from n ₁ does not have an essential effect on the measurement.

That is, He-N incident on the window material 10 in the vertical direction
When the e-laser light flux comes into contact with the cladding and core of the optical fiber preform 7, it is refracted or reflected due to the magnitude relationship of the refractive indices between the mediums at the contact points, and is deviated from the condensing system 22 so that it is almost received by the photodetector 23. Disappear. The conditions of refraction or reflection are as follows.

(1) Refraction and reflection on the outer periphery of the cladding of the optical fiber preform 7 (a) Refraction occurs when n <n ₁ .

(b) Reflects when n> n ₁ .

(2) Refraction on the outer periphery of the core of the optical fiber preform 7 (a) Since n ₁ <n ₀ is always satisfied, refraction occurs.

Except for the above-mentioned contact points, since the difference in the refractive index between the angular media is small, the light beam travels substantially straight, is condensed by the condensing system 22, and is received by the photodetector 23.

For the reasons described above, it was explained that a pulsed optical output as shown in FIG. 4 can be obtained. Here, this pulse has a certain width because the spot size of the incident light beam is finite and its intensity distribution is almost Gaussian, and the light receiving surface of the photodetector has a certain size. This is because they have it. In the measurement example of FIG. 4, the spot size is 0.3 mmφ (1 / e ² ), and the closed light receiver has a width of 0.5.
mm, and the focusing distance of the condenser lens in front of the light receiver is 11
It was 0 mm. Measurement errors due to such pulse broadening can be easily reduced to sufficient accuracy by calibrating with reference samples.

Next, the error caused by the refraction of the light beam on the cladding surface is obtained as follows. In FIG. 6, the following equation is obtained by Snell's law.

On the other hand, when the light flux S contacts at the 0'point, the distance d in FIG. 6 is given by d = bsin θ ₁ (2).

Also, with the triangle S "00 ', Since ∠0 ′S ″ 0 = θ ₂ , the following equation is obtained.

bsin θ ₂ = a (3) From the expressions (1) to (3), the measured value d corresponding to the core radius when the light flux S contacts the core is Given in.

Therefore, the measurement error ΔE of the core diameter 2a is given by the following equation.

Generally, the optical fiber preform has a non-circularity and an eccentricity of 1 to 2%.
In order to determine this with high accuracy, at least 0.1% or less of the measurement accuracy of the base material shape is required, so the condition of the following equation is required.

In addition, in order to measure the shape of the clad,
It is necessary to obtain the signals A and A ', and the condition is given by the following equation.

n ₁ ≠ n (7) Regarding the measurement of the clad diameter, there is no factor of refraction before the light flux comes into contact with the clad, and therefore there is no error factor due to the above refractive index adjusting oil.

(Effect of the Invention) As described above, according to the first invention, by rotating the optical fiber preform while scanning the laser beam,
The shape of the optical fiber preform can be accurately measured without being affected by the difference in refractive index. According to the second aspect of the invention, the outer diameter of the optical fiber preform, the noncircularity of the outer diameter, the core diameter, the noncircularity of the core diameter, and the eccentricity of the core are continuously non-destructively and highly accurately in the longitudinal direction. Since it can be measured, it has an advantage that it is extremely effective for quality control of the optical fiber preform.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of a conventional device of this type, FIG. 2 is a graph showing a measurement example thereof, FIG. 3 is a conceptual diagram of the entire device showing an embodiment of the present invention, and FIG. FIG. 5 is an explanatory diagram of a measurement example of a received light signal, and FIG. 5 is a graph showing a measurement example of the longitudinal eccentricity dependence of the core eccentricity of the optical fiber preform by the device of the present invention,
FIG. 6 is an explanatory view of the operating principle of the device of the present invention and calculation of measurement error, and FIG. 7 is a flowchart of measurement by the device of the present invention. 6 ... Optical system of laser shape measuring unit, 7 ... Optical fiber base material, 8 ... Chuck, 9 ... Glass container, 10 ... Window material, 11 ... Laser beam, 12 ... Oil seal bearing,
13 ... Rotary shaft, 14 ... Refractive index adjusting oil, 15 ...
… Pulse motor for rotating sample, 16 …… Pulse motor for moving optical system, 17 …… Rotating shaft with screw, 18 ……
Bearings, 19 ... Electric signal processing unit, 20 ... Minicomputer, 21 ... XY plotter, 22 ... Condensing lens,
23 ... Optical detector.

Claims (2)

[Claims] 1. An object to be measured by scanning a laser beam in a direction perpendicular to a central axis of the object to be measured whose outer diameter is measured, and electrically measuring a time when the laser beam is blocked by the object to be measured. In an outer diameter measuring device for highly accurately measuring the outer diameter of a container, a container having two front and rear transparent window members in a plane perpendicular to the light beam is arranged between the light beam sending part and the light receiving part. , The central axis of the optical fiber preform to be measured is rotatably arranged in the container in a direction perpendicular to the light flux, and the refractive index n of the refractive index adjusting oil filled in the container is A shape measuring apparatus for an optical fiber preform characterized by satisfying the following relationship. 2. An object to be measured by scanning a laser beam in a direction perpendicular to a central axis of the object to be measured whose outer diameter is measured, and electrically measuring a time when the laser beam is blocked by the object to be measured. In an outer diameter measuring device for highly accurately measuring the outer diameter of a container, a container having two front and rear transparent window members in a plane perpendicular to the light beam is arranged between the light beam sending part and the light receiving part. , The central axis of the optical fiber preform to be measured is rotatably arranged in the container in a direction perpendicular to the light flux, and the refractive index n of the refractive index adjusting oil filled in the container is The shape of the optical fiber preform characterized by satisfying the following relationship and having a mechanism capable of rotating the optical fiber preform at an arbitrary angle with respect to its central axis and moving the optical fiber at an arbitrary length in the axial direction. measuring device.