CN109307586B - Calibration method of optical fiber preform measuring device - Google Patents
Calibration method of optical fiber preform measuring device Download PDFInfo
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- CN109307586B CN109307586B CN201811299892.4A CN201811299892A CN109307586B CN 109307586 B CN109307586 B CN 109307586B CN 201811299892 A CN201811299892 A CN 201811299892A CN 109307586 B CN109307586 B CN 109307586B
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- G01—MEASURING; TESTING
- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
- G01M11/30—Testing of optical devices, constituted by fibre optics or optical waveguides
- G01M11/37—Testing of optical devices, constituted by fibre optics or optical waveguides in which light is projected perpendicularly to the axis of the fibre or waveguide for monitoring a section thereof
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Abstract
The invention relates to a calibration method of an optical fiber preform measuring device, which comprises the steps of relatively positioning a scanning laser light source and a photoelectric position detector at a parallel interval distance, starting the scanning laser light source and the photoelectric position detector, relatively moving the scanning laser light source and the photoelectric position detector along the parallel interval direction, scanning a laser beam from one side boundary of the photoelectric position detector to the detection surface of the photoelectric position detector along a horizontal plane, respectively recording the total length of relative displacement and position sensing signals of the photoelectric position detector, calculating the response linearity of the photoelectric position detector by comparing the relative displacement with the position sensing signals, and finally obtaining an accurate displacement response linearity or position response coordinate curve. The invention solves the problem that the system testing precision is influenced by the change of the response linearity of the photoelectric position detector, and simultaneously increases the measuring length of the photoelectric position detector.
Description
Technical Field
The invention relates to a calibration method of an optical fiber preform measuring device, and belongs to the technical field of optical fiber photoelectric measurement.
Background
Optical fibers are the main carrier of modern data communication, and the optical fiber preparation industry tends to prepare optical fiber preforms with larger diameters from the viewpoint of cost and production efficiency. The measurement of geometric parameters such as the refractive index profile, the inner diameter, the outer diameter and the like of the optical fiber preform is an important quality control link. Currently, such measurements are based on optical-based contactless measurements, in which photoelectric position detectors (photoelectric position sensors) are used. The working principle of the photoelectric position detector is to output the position coordinates of the incident laser beam on the detector in a digital quantity or analog quantity mode. The laser scans the cross section of the prefabricated rod, and records the laser spot position after transmission, and the refractive index and the radius of the scanned position of the optical fiber prefabricated rod can be calculated through Snell's law.
The measurement process has a high requirement on the output response linearity of the light sensing surface on the photoelectric position detector, and due to the semiconductor process, when external factors such as incident light intensity, ambient light intensity, bias voltage on the photoelectric position detector and the like change, the response linearity of the photoelectric position detector is degraded, so that the detection result of the system has errors. In addition, in the sensing edge area of the detector (1/4-1/6 on both sides of the effective length of the detector), due to the influence of aberration of an optical system and circuit noise, the position error and output linearity deterioration of the detector are more obvious, so that the detection precision of the preform is influenced.
On the other hand, as the diameter of the preform increases, the scanning stroke of the laser and the displacement length of the spot to be covered by the photoelectric position detector also increase correspondingly, and the size of the photoelectric position detector for sensing also needs to be increased correspondingly. Due to semiconductor process, the large-sized photoelectric position sensing element is generally expensive, which greatly increases the cost of the measuring device of the large-sized optical fiber preform. Therefore, the measurement length of the photoelectric position detector is increased, the sensing edge area of the detector is fully utilized, and the cost of the measurement device can be effectively reduced.
Disclosure of Invention
The technical problem to be solved by the present invention is to provide a calibration method for an optical fiber preform measurement apparatus, aiming at overcoming the defects existing in the prior art, so as to solve the problem that the measurement accuracy of the system is affected due to the change of the response linearity of the photoelectric position detector, and simultaneously increase the measurement length of the photoelectric position detector.
The technical scheme adopted by the invention for solving the problems is as follows:
the scanning laser light source and the photoelectric position detector are relatively positioned in parallel at a certain distance, wherein the laser beam emitted by the scanning laser light source is vertical to the parallel spacing surface, the detection surface of the photoelectric position detector is parallel to the parallel spacing surface, the scanning laser light source and the photoelectric position detector are started, the scanning laser light source and the photoelectric position detector relatively move along the parallel spacing direction, so that the laser beam scans the detection surface of the photoelectric position detector along the horizontal plane from one side boundary or the adjacent boundary of the photoelectric position detector, the scanning is finished until the other side boundary or the adjacent boundary of the detection surface of the photoelectric position detector, the total length of the relative displacement and the position sensing signal of the photoelectric position detector are respectively recorded, the response linearity of the photoelectric position detector is calculated by comparing the relative displacement with the position sensing signal, and then the response linearity of the photoelectric position detector is calibrated, finally, an accurate displacement response linearity or position response coordinate curve is obtained.
According to the scheme, the scanning area of the detection surface of the photoelectric position detector is a straight line, the middle point of the straight line is a position zero point, one side of the middle point is positive displacement, and the other side of the middle point is negative displacement.
According to the scheme, the comparison process comprises the following steps: recording output signals of a scanning laser light source and a photoelectric position detector when the scanning laser light source and the photoelectric position detector relatively move along the parallel interval direction; recording the distance of the relative movement; and comparing the output signal with the distance of the relative movement.
According to the scheme, the parallel moving device is arranged on the side of the scanning laser light source or the photoelectric position detector and is connected with the scanning laser light source or the photoelectric position detector.
According to the scheme, the parallel moving device is a screw rod sliding seat device, and the screw rod is driven by a motor.
According to the scheme, the photoelectric position detector is a one-dimensional or two-dimensional photoelectric position detector for outputting analog or digital signals.
According to the scheme, the distance between the scanning laser light source and the photoelectric position detector is 60-220 mm.
The invention has the beneficial effects that: 1. by calibrating the response linearity of the photoelectric position detector, the degradation of the response linearity of the photoelectric position detector due to external factors can be overcome, and the position measurement precision of the photoelectric position detector is improved, so that the measurement precision of the optical fiber preform measuring device is improved. 2. The linearity of the sensing areas on the two sides of the photoelectric position detector far away from the central position is measured and calibrated, so that the usable working length of the photoelectric position detector is increased, the sensing edge area of the detector is fully utilized, the photoelectric position detector with a smaller size can be used for completing the detection function of the optical fiber perform rod with a larger size, and the cost of the measuring device is effectively reduced.
Drawings
FIG. 1 is a view showing a state of use of the apparatus for measuring an optical fiber preform according to the present invention.
FIG. 2 is a schematic diagram of the calibration process of the present invention.
FIG. 3 is a schematic view of a side of a photoelectric position detector mounted on a parallel-moving apparatus according to an embodiment of the present invention.
FIG. 4 is a schematic view of the scanning area of a photoelectric position detector according to an embodiment of the present invention.
FIG. 5 is a graph of the coordinates of the displacement response linearity of the photoelectric position detector before calibration.
FIG. 6 is a graph of the coordinates of the linearity of the displacement response of a calibrated photodetector of the present invention.
Detailed Description
The present invention will be further described with reference to the following examples and the accompanying drawings.
The specific working process of calibrating the measuring device comprises the following steps:
firstly, a scanning laser light source 1 and a photoelectric position detector 6 are positioned in parallel at intervals, wherein a laser beam emitted by the scanning laser light source is perpendicular to a parallel spacing surface, a detection surface of the photoelectric position detector is parallel to the parallel spacing surface, a parallel moving device 5 is arranged on the side of the photoelectric position detector, the parallel moving device is a screw rod sliding seat device and comprises a fixed seat 51 and a screw rod sliding seat 52, a screw rod is driven by a motor, the screw rod sliding seat is connected with the photoelectric position detector 6, and the photoelectric position detector can be relatively moved along the parallel spacing direction by driving the screw rod; starting a scanning laser light source and a photoelectric position detector, wherein the scanning laser light source emits a stable laser beam to irradiate a detection surface of the photoelectric position detector, and the wavelength of the laser beam is 632 nm; the parallel moving device drives the screw slide seat to drive the photoelectric position detector to move horizontally through a motor, and the motor can be a stepping motor or a servo motor, so that the scanning laser light source and the photoelectric position detector move relatively along the parallel interval direction, namely, the incident light of the scanning laser light source generates relative displacement on the photoelectric position detector; the laser beam scans the detection surface of the photoelectric position detector from one side boundary of the photoelectric position detector along the horizontal plane, and the scanning is finished until the other side boundary of the detection surface of the photoelectric position detector, and the formed scanning track is as shown in fig. 4. The photoelectric position detector converts the light spot position signal into a digital or analog signal, and records the electric signal (which can be a voltage or current signal) output of the photoelectric position detector as S. The relative displacement of the photo position detector is recorded as d. Due to the defects of the photoelectric position detector, the output of the photoelectric position detector and the displacement change relation of a scanning point in the boundary area of the detector do not keep a linear relation any more. And comparing the relative displacement with the position sensing signal to calculate the response linearity of the photoelectric position detector, calibrating the response linearity of the photoelectric position detector, and finally obtaining an accurate displacement response linearity or position response coordinate curve.
Taking the data of one measurement as an example, d is plotted as ordinate and S value is plotted as abscissa, as shown in fig. 5. And (3) taking the value d as a reference, extending the approximate straight line 71 in the middle section of the S/d curve to two ends to obtain line segments 74 and 75, calculating the difference between the line segments 74 and 75 and the original curve segments 72 and 73, recording the difference as a correction value to establish a comparison table, and setting each S value in the comparison table as a correction value. The calibration process is completed. The data volume of the comparison table can be increased in an interpolation mode, and the calibration fineness is improved. The data volume of the comparison table can be increased by increasing the d-step subdivision mode, and the calibration fineness is improved.
The mathematical and physical principles are explained as follows:
when the mechanical displacement device drives the screw rod to generate displacement through the motor, the rotation angle and the displacement generated by the rotation of the screw rod satisfy the relational expression: d is P x (n/360).
Wherein n is the rotation angle of the screw rod and can be any integer. And P is a lead of the screw rod and is determined by the process parameters of the screw rod. When the type of the screw rod is fixed and the rotating angle is fixed, the displacement d is determined. Along with the rotation of lead screw, according to photoelectric position detector 6's output characteristic in the overall process, can be divided into three regions with the surface of detector, it is respectively: linear scan region 61, and non-linear scan regions 62 and 63. The formation of 62 and 63 is due to many factors such as material defects, incident light intensity, bias voltage, etc. of the photo position detector itself. According to the characteristic that the photoelectric position detector works in the linear region, the signal output of 6 satisfies the following relative position relation between the linear scanning region 61 and the scanning laser beam and the photoelectric position detector:
S1＝k1*x1+b1
wherein S1 is read out and quantified directly as an electrical signal (voltage or current signal) on the measuring device. X is the position coordinate of the incident laser beam irradiated on the photoelectric position detector, and K and b are the corresponding slope and intercept of linear fitting.
At both ends of the detector 6 non-linearly scanning the areas 62 and 63, the signals S2 and S3 generated by the lead screw push position detector can be written as:
when the expressions of S1, S2, and S3 are different, it indicates that an error occurs in the output linearity of the photoelectric position detector 6, and calibration needs to be performed according to the actual displacement of the screw rod step.
The calibration method is to take the actual stepping displacement of the screw rod as a reference, take uniform step length such as 0.01mm as an interval and calibrate the output value of the photoelectric position detector point by point.
The following is illustrated by a set of actual test data:
the lead screw displacement is taken as a vertical coordinate, the output of the detector is taken as a horizontal coordinate, and the displacement and the output are plotted after normalization, so that the linear corresponding relation between the detector output and the lead screw displacement is not satisfied any more in an area far away from the center of the detector before calibration. After the detector output is calibrated, the area satisfying the linear corresponding relation between the detector output and the displacement is obviously increased. The figure of the attached table one also illustrates this intuitively.
TABLE 1
The method has the advantages that: the linearity of the sensing areas on the two sides of each photoelectric position detector far away from the central position can be measured and calibrated through the displacement of the screw rod, so that the available working length of the photoelectric position detector is enlarged, the photoelectric position detector with smaller size can be used for completing the test function, and the manufacturing cost of the measuring device is saved.
In the measuring process, the scanning laser light source moves on the horizontal rail, scans along the horizontal plane at one side boundary of the optical fiber perform, and returns to the original point after scanning is finished at the other side boundary. In the scanning process, the transmitted and refracted emergent laser beams act on the surface of the photoelectric position detector, and the photoelectric position detector converts the spot position signals into digital or analog signals. By reasonably designing the installation position of the photoelectric position detector on the mechanical displacement device and the total length of mechanical displacement, the response linearity of the photoelectric position detector at the moment can be calculated by comparing the position signal output by the photoelectric position detector and the displacement generated by the mechanical displacement device, so that the photoelectric position detector is calibrated.
The using state of the device for measuring the optical fiber preform is shown in figure 1, and the device comprises a scanning laser light source 1, a light-transmitting container 2, refractive index matching oil 3, an optical fiber preform 4 in a clamping state and a parallel moving device 5 provided with a photoelectric position detector. A photoelectric position detector 6 is mounted on the mechanical displacement device, and the detection surface of the photoelectric position detector faces the incidence direction of the laser. And starting a laser light source to emit a detection laser beam, shaping the detection laser beam by a beam expander and a lens, enabling the detection laser beam to enter the transparent oil tank, penetrating through the oil liquid of the test oil to be emitted from the other side of the transparent oil tank, and enabling the detection laser beam to be incident to the photoelectric position detector. The detector converts the position signal into an electric signal, the electric signal is converted into a digital signal through a circuit and is transmitted to a computer, and the computer analyzes and processes the acquired data to draw a refractive index distribution curve of the measured preform.
Claims (7)
1. A calibration method for an optical fiber preform measuring device is characterized in that
The scanning laser light source and the photoelectric position detector are relatively positioned in parallel at a certain distance, wherein the laser beam emitted by the scanning laser light source is perpendicular to the parallel spacing surface, the detection surface of the photoelectric position detector is parallel to the parallel spacing surface, the scanning laser light source and the photoelectric position detector are started, the scanning laser light source and the photoelectric position detector relatively move along the direction of the parallel spacing surface, so that the laser beam scans the detection surface of the photoelectric position detector along the direction of the parallel spacing surface from one side boundary or the adjacent boundary of the photoelectric position detector, the scanning is finished until the other side boundary or the adjacent boundary of the detection surface of the photoelectric position detector, the total length of the relative displacement and the position sensing signal of the photoelectric position detector are respectively recorded, and the response linearity of the photoelectric position detector is calculated by comparing the relative displacement with the position sensing signal, and then calibrating the response linearity of the photoelectric position detector, and finally obtaining an accurate displacement response linearity or position response coordinate curve.
2. A method of calibrating an optical fiber preform measuring device according to claim 1, wherein the scanning area of the detection surface of the photoelectric position detector is a straight line, the midpoint of the straight line is a position zero point, one side of the midpoint is a positive displacement, and the other side of the midpoint is a negative displacement.
3. A method of calibrating an optical fiber preform measuring device according to claim 1 or 2, wherein said comparing comprises: and recording output signals of the detector when the scanning laser light source and the photoelectric position detector relatively move along the direction parallel to the spacing surface, recording the distance of the relative movement, and comparing the output signals with the distance of the relative movement.
4. A method for calibrating an apparatus for measuring an optical fiber preform according to claim 1 or 2, wherein a parallel moving means is provided on the side of the scanning laser light source or the photoelectric position detector, and the parallel moving means is connected to the scanning laser light source or the photoelectric position detector.
5. A method of calibrating an optical fiber preform measuring device according to claim 4, wherein said parallel moving means is a lead screw slider means, and the lead screw is driven by a motor.
6. A method of calibrating an optical fiber preform measuring device according to claim 1 or 2, wherein said photoelectric position detector is a one-dimensional or two-dimensional photoelectric position detector for analog or digital signal output.
7. A method of calibrating an optical fiber preform measuring device according to claim 1 or 2, wherein the scanning laser light source and the photoelectric position detector are spaced apart in parallel by a distance of 60mm to 220 mm.
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| US5136154A (en) * | 1991-05-10 | 1992-08-04 | Advanced Fuel Research, Inc. | Method and system for photoconductive detector signal correction |
| JPH05107569A (en) * | 1991-10-14 | 1993-04-30 | Nippon Telegr & Teleph Corp <Ntt> | Measuring instrument for tertiary nonlinear optical characteristics |
| US6686585B2 (en) * | 2001-09-19 | 2004-02-03 | Microe Systems Corporation | Position encoder with scale calibration |
| WO2008138848A2 (en) * | 2007-05-11 | 2008-11-20 | Nctengineering Gmbh | Device for and method of determining a position of a movable object |
| US7894079B1 (en) * | 2009-11-09 | 2011-02-22 | Mitutoyo Corporation | Linear displacement sensor using a position sensitive photodetector |
| CN103499976B (en) * | 2013-10-14 | 2015-10-07 | 吴江市博众精工科技有限公司 | A kind of CCD correcting mechanism |
| CN106352801B (en) * | 2016-10-17 | 2018-03-02 | 海伯森技术（深圳）有限公司 | A kind of modification method of laser triangle displacement sensor and its nonlinearity erron |
| CN107764844B (en) * | 2017-09-21 | 2020-04-21 | 重庆真测科技股份有限公司 | Position adjusting system and method for large CT detection equipment |
| CN107504997B (en) * | 2017-10-17 | 2019-10-25 | 中国科学技术大学 | A kind of gamma correction system and method for photodetector |
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