CN110470251B - Optical fiber length measuring method based on photoelectric oscillator - Google Patents
Optical fiber length measuring method based on photoelectric oscillator Download PDFInfo
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- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
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Abstract
The invention discloses an optical fiber length measuring method based on a photoelectric oscillator, wherein direct current light emitted by a laser is modulated by an intensity modulator, when the optical fiber to be measured is not accessed, the modulated light passes through a photoelectric detector to convert an optical signal into an electric signal, and the electric signal is amplified and filtered to feed back a filtered microwave signal to the intensity modulator to form a photoelectric oscillation loop; the microwave source outputs a microwave signal with the central frequency close to that of an OEO output signal, the mixer can output a microwave signal with the MHz magnitude, so that the frequency is accurately read by the frequency meter, the fundamental frequency is roughly calculated, the accurate fundamental frequency can be obtained through a series of calculations, and then the OEO cavity length at the moment is calculated by utilizing the relationship between the OEO cavity length and the fundamental frequency; when the optical fiber to be measured is accessed, the process is repeated, the cavity length of the OEO can be calculated, and the difference between the cavity lengths is the length of the optical fiber to be measured. When the optical fiber is in km magnitude, the method is influenced by temperature, the measurement precision is in cm magnitude, and the system has simple structure and is easy to operate.
Description
Technical Field
The invention relates to an optical fiber length measuring method based on a photoelectric oscillator.
Background
Optical fibers are the best medium for modern communications and information transmission due to their wide frequency band, low conduction loss, light weight, high interference immunity, high operational reliability, and the ability to transmit information over long distances. With the rapid development of optical fiber communication technology, in some high-precision optical devices, the requirement on the precision of the optical fiber length is very high, and once relative time delay is generated between optical fibers, an output signal is distorted or weakened due to the optical fiber time delay. In addition, in engineering and testing processes, it is necessary to measure the length of the optical fiber, and the precise measurement of the length of the optical fiber is very important for the development, production and maintenance of the optical fiber, so that the precise measurement of the length of the optical fiber is very important in optical fiber communication and optical fiber sensing systems.
Currently, the methods for measuring the length of the optical fiber mainly include: optical Time Domain Reflectometry (OTDR), Optical Frequency Domain Reflectometry (OFDR), all-fiber interferometry, mode-locking, femtosecond pulse, modulation phase shift, laser phase method, and the like.
The OTDR method measures the length of an optical fiber based on the rayleigh scattering principle, and the scattering signal of the optical fiber itself is weak, so the method has high requirements on a light source and a detector, resulting in high cost; in addition, the method has a measurement blind area, and the measurement can not be carried out under the condition that the optical fiber is short, and the measurement precision is m-order. The OFDR method is based on the coherent detection principle to measure the length of an optical fiber, the dynamic range of measurement is large, the measurement precision is mm magnitude, but in order to ensure coherence, the requirement on a light source is high, and due to the temperature, the problem of nonlinearity of light source frequency sweep can be caused.
In recent years, research on the measurement of the length of an optical fiber has been greatly developed. In 2002, gabor et al have implemented the measurement of optical fiber length by using an all-fiber interference system, and have completely solved the problem of the blind zone of the OTDR method. The method has the advantages that the measurement result is slightly different from the measurement result of the OTDR method, the measurement range is small, and the measurement precision is influenced by the interference fringe counting and the length of the reference optical fiber.
In 2007, moustache et al proposed a fiber length measuring method based on the passive mode-locking principle, namely a mode-locking method, which measures the fiber length by using the relationship that the stable pulse period of a mode-locked laser is in direct proportion to the cavity length. The method has the advantages of large measurement range and good stability, but the cost is high, and the length of the optical fiber cannot be measured when the length of the optical fiber is less than 500 m. In 2013, based on a two-color double-frequency space distance measurement method, by Giyundon et al, an all-fiber coupling femtosecond fiber length measurement method is designed by adopting a fiber femtosecond laser. The measuring range of the method can reach 50km, and the measuring precision is cm magnitude.
In 2013, leaf university et al proposed a method for measuring fiber length using a phase modulated optical link. The method is suitable for accurate length measurement of medium and short optical fibers, and the measurement accuracy is mm magnitude; if longer fibers are to be measured, the requirements for the reference fiber and the light source are higher and the cost is higher. In 2016, Zhuxingbang et al utilized the high-speed modulation signal synchronization technology and the high-frequency signal phase difference measurement technology of integrated vector network analyzer to design and develop a single-mode optical fiber length measuring device, the precision can reach the order of mum when measuring the short optical fiber, and the precision can reach the order of m when measuring the long optical fiber, but the device is greatly influenced by temperature, and the measuring accuracy can be influenced.
In 2017, xu Zi Yan et al propose a laser phase method to measure the length of an optical fiber, and measure the length of the optical fiber by using the proportional relationship between the phase shift of the light wave modulated by intensity generated in the transmission process of the measured optical fiber and the length of the measured optical fiber.
Disclosure of Invention
Aiming at the prior art, the invention provides an optical fiber length measuring method based on a photoelectric oscillator, which solves the problems of limitation of the existing optical fiber length measuring technology by a measuring range, poor stability and the like. The invention is not limited by the measuring range, more importantly, the length of the measured optical fiber can be calculated by the relational expression of the OEO cavity length and the frequency interval, and the invention has the advantages of low cost and high stability.
In order to solve the above technical problem, the present invention provides an optical fiber length measuring method based on a photoelectric oscillator, which includes the following optical devices and electronic devices: a laser, an intensity modulator, a photoelectric detector, an electric amplifier, a band-pass filter, a mixer, a microwave source and a frequency meter; the direct current light emitted by the laser is modulated by the intensity modulator and then enters the photoelectric detector, an optical signal is converted into an electric signal, the electric signal is amplified by the electric amplifier and then passes through the band-pass filter, and the filtered microwave signal is fed back to the intensity modulator to be used as a modulation signal, so that a photoelectric oscillation circuit is formed;
the fiber length measurement was performed as follows:
step one, adjusting the bias voltage of the intensity modulator to enable the photoelectric oscillation circuit to start oscillation successfully and output a stable microwave signal, wherein the center frequency of the microwave signal is fhm；
Step two, the center frequency output by the microwave source is fms＝fhm+/-100 MHz microwave signal and microwave signal f output by the photoelectric oscillation circuithmWhen the frequency meter is connected to the mixer, the frequency meter measures the center frequency f of the microwave signal after mixinglm；
Step three, repeating the step two n times to obtain the central frequency f of the microwave signal after n times of frequency mixinglm1、flm2、flm3、……、flmnAccording to the formula fhm＝fms+flmDetermining the center frequency f of the microwave signal output from the photoelectric oscillation circuit corresponding to each measurementhm1、fhm2、fhm3、……、fhmn；
Step four, the mode interval | f of the microwave signal of the photoelectric oscillation circuithm2–fhm1|、|fhm4–fhm3|、……、|fhmn–fhmn-1The greatest common divisor of | is the rough value f of the fundamental frequency of the photoelectric oscillation circuitb *(ii) a Further obtaining the oscillation mode number of the photoelectric oscillation circuit
Wherein the content of the first and second substances,
rounding up and rounding up; fundamental frequency of the electric oscillation circuit
Step five, calculating the cavity length L of the photoelectric oscillation circuit as c/nfbWherein n is the refractive index of the optical fiber at the moment temperature, and c is the speed of light; the following two cases are included:
1) under the condition of not connecting the optical fiber to be measured, the cavity length of the photoelectric oscillation circuit is recorded as L1(ii) a And connecting the optical fiber to be detected between the intensity modulator and the photoelectric detector, and returning to the step two.
2) At the access standbyIn the case of the optical fiber, the cavity length of the photoelectric oscillation circuit is recorded as L2(ii) a Finally obtaining the length L of the optical fiber to be measuredFiber＝L2-L1。
Compared with the prior art, the invention has the beneficial effects that:
because the invention utilizes the principle of the photoelectric oscillator, the microwave signal with stable output can be generated, the signal quality is greatly improved, the requirements on the light source and the optical device are greatly reduced, and the invention is easy to control and adjust, simple in structure, lower in cost and higher in stability; secondly, the frequency is measured by a mixer, a microwave source, a frequency meter and an OEO cavity length and fundamental frequency relation fbc/(nL), the length of the optical fiber to be measured can be calculated regardless of the length of the optical fiber, and the measuring range is not limited.
Drawings
FIG. 1 is a schematic diagram of an optical fiber length measuring method based on a photoelectric oscillator according to the present invention.
In the figure: the method comprises the following steps of 1-laser, 2-intensity modulator, 3-optical fiber to be tested, 4-photoelectric detector, 5-electric amplifier, 6-band-pass filter, 7-frequency mixer, 8-microwave source and 9-frequency meter.
Detailed Description
The invention will be further described with reference to the following figures and specific examples, which are not intended to limit the invention in any way.
The design idea of the invention is that because the photoelectric oscillation circuit (OEO) can output stable microwave signals, the low-frequency microwave signals output by the frequency mixer can be accurately read by the frequency meter, so that the fundamental frequency f can be roughly obtainedb *(ii) a Through a series of calculations, the precise fundamental frequency f can be obtainedbThen, the cavity length of the OEO can be calculated by utilizing the relation between the cavity length of the OEO and the fundamental frequency, and the cavity length L of the OEO corresponding to the optical fiber not to be tested and the optical fiber to be tested is measured1And L2Obtaining the difference between the two cavity lengths, Δ L ═ L2-L1And then the length of the optical fiber to be measured can be calculated according to the refractive index n of the optical fiber at the moment.
As shown in fig. 1, the method for measuring the length of an optical fiber based on an optoelectronic oscillator according to the present invention includes the following optical devices and electronic devices: a laser 1, an intensity modulator 2, a photodetector 4, an electrical amplifier 5, a band-pass filter 6, a mixer 7, a microwave source 8 and a frequency meter 9.
The direct current light emitted by the laser 1 is modulated by the intensity modulator 2, enters the photoelectric detector 4 when not connected to the optical fiber to be detected, converts an optical signal into an electric signal, amplifies the electric signal by the electric amplifier 5, filters the electric signal by the band-pass filter 6, and feeds back the filtered microwave signal to the intensity modulator 2 as a modulation signal, thereby forming a photoelectric oscillation circuit.
The method comprises the steps that an optical fiber 3 to be measured is connected between an intensity modulator 2 and an electric detector 4, direct current light emitted by a laser 1 is modulated through the intensity modulator 2, when the optical fiber to be measured is connected, the modulated light passes through a section of the optical fiber 3 to be measured and then enters the photoelectric detector 4, an optical signal is converted into an electric signal, the electric signal is amplified through an electric amplifier 5, filtering is carried out through a band-pass filter 6, and the filtered microwave signal is fed back to the intensity modulator 2 to serve as a modulation signal, so that a photoelectric oscillation loop is formed.
The system is based on an OEO principle, and the OEO can output stable microwave signals with frequency intervals after the process is carried out for a plurality of times. The microwave source 8 outputs a microwave signal with a center frequency close to that of the microwave signal output by the OEO, and the mixer 7 can output a microwave signal with a lower frequency, so that the output frequency can be accurately calculated by the frequency meter 9, and the fundamental frequency f can be roughly calculated by the frequency meterb *Using the relation f between the OEO cavity length and the front of the fundamental frequencybThrough a series of calculations, the exact fundamental frequency f can be obtainedbThen, the cavity length of the OEO can be finally calculated, and the cavity lengths L of the OEO corresponding to the optical fiber not to be tested and the optical fiber to be tested are measured1And L2Obtaining the difference between the two cavity lengths, Δ L ═ L2-L1And then the length of the optical fiber to be measured can be calculated according to the refractive index n of the optical fiber at the moment. The method comprises the following specific steps:
step one, adjusting the bias voltage of the intensity modulator 2 to enable the photoelectric oscillation circuit to be capable ofThe oscillation can be successfully started, and a stable microwave signal is output, wherein the center frequency of the microwave signal is fhm；
Step two, the center frequency f output by the microwave source 8msAnd the central frequency f of the microwave signal output by the OEO ring cavityhmClose frequencies, i.e. fms＝fhm+/-100 MHz, and then the microwave signal output by the microwave source 8 and the microwave signal f output by the photoelectric oscillation circuithmConnected to the mixer 7, the mixer can output microwave signals with MHz level, and the frequency meter 9 measures the center frequency f of the mixed microwave signalslmNamely, the frequency is accurately read by the frequency meter, and when the frequency is lower than 100MHz, the measurement accuracy of the frequency meter can easily reach 0.01 Hz.
Step three, repeating the step two n times to obtain the central frequency f of the microwave signal after n times of frequency mixinglm1、flm2、flm3、……、flmnAccording to the formula fhm＝fms+flmDetermining the center frequency f of the microwave signal output from the photoelectric oscillation circuit corresponding to each measurementhm1、fhm2、fhm3、……、fhmn；
Step four, the mode interval | f of the microwave signal of the photoelectric oscillation circuithm2–fhm1|、|fhm4–fhm3|、……、|fhmn–fhmn-1The greatest common divisor of | is the rough value f of the fundamental frequency of the photoelectric oscillation circuitb *Fundamental frequency fb *Obtaining the oscillation mode number of the photoelectric oscillation circuit for the frequency interval of the adjacent oscillation starting modes
Wherein the content of the first and second substances,
rounding up and rounding up; according to the obtained high-order oscillation frequency fhm1And the number of oscillation modes Nhm1To deduce the precise fundamental frequency of the electric oscillating circuit
Step five, solving the cavity length L of the photoelectric oscillation circuit as c/nf according to the OEO cavity length and the mode-hopping interval relationbWherein n is the refractive index of the optical fiber at the moment temperature, and c is the speed of light; the following two cases are included:
1) under the condition of not connecting the optical fiber 3 to be measured, the cavity length of the photoelectric oscillation circuit is recorded as L1(ii) a And connecting the optical fiber 3 to be tested between the intensity modulator 2 and the photoelectric detector 4, and returning to the step two.
2) Under the condition of connecting the optical fiber 3 to be tested, the cavity length of the photoelectric oscillation circuit is recorded as L2(ii) a Performing difference operation on the two to obtain the length L of the optical fiber to be measuredFiber＝L2-L1。
The measuring method of the invention can calculate the length of the optical fiber to be measured, the optical fiber is influenced by temperature when in km magnitude, the measuring precision is in cm magnitude, and the system has simple structure, lower cost and easy operation.
While the present invention has been described with reference to the accompanying drawings, the present invention is not limited to the above-described embodiments, which are illustrative only and not restrictive, and various modifications which do not depart from the spirit of the present invention and which are intended to be covered by the claims of the present invention may be made by those skilled in the art.
Claims (1)
1. An optical fiber length measuring method based on a photoelectric oscillator is characterized by comprising the following optical devices and electronic devices: the device comprises a laser (1), an intensity modulator (2), a photoelectric detector (4), an electric amplifier (5), a band-pass filter (6), a mixer (7), a microwave source (8) and a frequency meter (9);
the direct current light emitted by the laser (1) is modulated by the intensity modulator (2), then enters the photoelectric detector (4), is converted into an electric signal, is amplified by the electric amplifier (5), and then passes through the band-pass filter (6), and feeds back the filtered microwave signal to the intensity modulator (2) as a modulation signal, so that a photoelectric oscillation loop is formed;
the fiber length measurement was performed as follows:
step one, adjusting the bias voltage of the intensity modulator (2) to enable the photoelectric oscillation circuit to start oscillation successfully and output a stable microwave signal, wherein the center frequency of the microwave signal is fhm；
Step two, the center frequency output by the microwave source (8) is fms＝fhm+/-100 MHz microwave signal and microwave signal f output by the photoelectric oscillation circuithmIs connected to the mixer (7), and the frequency meter (9) measures the center frequency f of the microwave signal after mixinglm；
Step three, repeating the step two n times to obtain the central frequency f of the microwave signal after n times of frequency mixinglm1、flm2、flm3、……、flmnAccording to the formula fhm＝fms+flmDetermining the center frequency f of the microwave signal output from the photoelectric oscillation circuit corresponding to each measurementhm1、fhm2、fhm3、……、fhmn；
Step four, the mode interval | f of the microwave signal of the photoelectric oscillation circuithm2–fhm1|、|fhm4–fhm3|、……、|fhmn–fhmn-1The greatest common divisor of | is the rough value f of the fundamental frequency of the photoelectric oscillation circuitb *(ii) a Further obtaining the oscillation mode number of the photoelectric oscillation circuit
Wherein the content of the first and second substances,
rounding up and rounding up; fundamental frequency of the electric oscillation circuit
Step five, obtainingThe cavity length L of the photoelectric oscillation circuit is c/nfbWherein n is the refractive index of the optical fiber at the moment temperature, and c is the speed of light; the following two cases are included:
1) under the condition of not connecting the optical fiber (3) to be measured, the cavity length of the photoelectric oscillation circuit is recorded as L1(ii) a Connecting the optical fiber (3) to be tested between the intensity modulator (2) and the photoelectric detector (4), and returning to the second step;
2) under the condition of connecting the optical fiber (3) to be measured, the cavity length of the photoelectric oscillation circuit is recorded as L2(ii) a Finally obtaining the length L of the optical fiber to be measuredFiber＝L2-L1。
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| JPS62159005A (en) * | 1986-01-07 | 1987-07-15 | Hitachi Cable Ltd | Measuring method for length of optical fiber |
| US5926492A (en) * | 1996-09-02 | 1999-07-20 | Nippon Telegraph & Telephone Corporation | Laser pulse oscillator |
| CN102353963A (en) * | 2011-07-15 | 2012-02-15 | 于晋龙 | Distance measuring system for optical domain based dual-loop optoelectronic oscillators |
| CN102494617A (en) * | 2011-12-09 | 2012-06-13 | 华中科技大学 | Single mode fiber length measuring system |
| CN107342816A (en) * | 2017-06-28 | 2017-11-10 | 天津大学 | A kind of signal generator for producing multichannel microwave signal simultaneously based on optical-electronic oscillator |
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- 2019-08-30 CN CN201910819037.XA patent/CN110470251B/en not_active Expired - Fee Related
Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS62159005A (en) * | 1986-01-07 | 1987-07-15 | Hitachi Cable Ltd | Measuring method for length of optical fiber |
| US5926492A (en) * | 1996-09-02 | 1999-07-20 | Nippon Telegraph & Telephone Corporation | Laser pulse oscillator |
| CN102353963A (en) * | 2011-07-15 | 2012-02-15 | 于晋龙 | Distance measuring system for optical domain based dual-loop optoelectronic oscillators |
| CN102494617A (en) * | 2011-12-09 | 2012-06-13 | 华中科技大学 | Single mode fiber length measuring system |
| CN107342816A (en) * | 2017-06-28 | 2017-11-10 | 天津大学 | A kind of signal generator for producing multichannel microwave signal simultaneously based on optical-electronic oscillator |
Non-Patent Citations (2)
| Title |
|---|
| Fiber‐length‐dependence phase noise of injection‐locked optoelectronic oscillator;Jun Hong,Sheng等;《Microwave and Optical Technology Letters》;20131231;全文 * |
| 光纤长度对基于光电振荡器距离测量的影响;张涛等;《中国激光》;20130930;第40卷(第9期);全文 * |
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