A device and method for measuring optical fiber length

Abstract

The present invention relates to the field of optical fiber length measurement technology, and in particular to a device and method for measuring optical fiber length, comprising a front-end interference main optical path combination unit, a light source, a first photoelectric conversion device, a second photoelectric conversion device, a synchronous acquisition unit, a signal processing unit, and a terminal modulation unit, wherein the front-end interference main optical path combination unit comprises a first optical splitter, a second optical splitter, an optical attenuator, a piezoelectric ceramic signal generator, and an optical path delay coil; the terminal modulation unit comprises a terminal blind zone elimination optical fiber, a carrier signal phase modulator, and a reflection device connected in sequence. The present invention achieves the purpose of removing the influence of noise through the technology of phase carrier, uses a phase modulator to load a constant pulse as a disturbance source at the front end of the optical path, thereby obtaining two disturbance signals related thereto, and obtains the length information of the measured optical fiber through the time delay between the two disturbance signals.

Description

Technical Field

[0001] The present invention relates to the technical field of optical fiber length measurement, in particular to a device and method for measuring optical fiber length. Background Art

[0002] With the rapid development of optical fiber technology, improving the accuracy of optical fiber length measurement has become an important issue in the field of optical fiber applications. For example, in optical interferometers, multiple optical fibers of equal length are often required. If the accuracy is not enough, the signal will be distorted or weakened. Another example is the optically controlled phased array antenna used in radar systems, which requires the length error of the delay optical fiber to be in the order of millimeters.

[0003] At present, the commonly used fiber length measurement methods in engineering include: optical time domain reflectometry (OTDR), optical frequency domain reflectometry (OFDR), low coherence optical reflectometry (OLCR), etc. Among them, optical time domain reflectometry can measure the length of tens of kilometers, but the resolution is low, only 0.1km; low coherence optical reflectometry can obtain the measurement accuracy of mm, but the measurement length is limited and the coherence condition of the light source is harsh; the measurement accuracy and measurement length of optical frequency domain reflectometry are between the first two, but the coherence and stability requirements of the light source are higher. Summary of the invention

[0004] In view of the problems of the prior art, the present invention provides a device and method for measuring the length of an optical fiber. The purpose of removing the influence of noise is achieved through the phase carrier technology. A phase modulator is used to load a constant pulse as a disturbance source at the front end of the optical path, thereby obtaining two disturbance signals related thereto, and the length information of the measured optical fiber is obtained through the time delay (flight time) between the two disturbance signals.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] The present invention provides a device for measuring the length of an optical fiber, comprising a front-end interference main optical path combination unit, a light source, a first photoelectric conversion device, a second photoelectric conversion device, a synchronous acquisition unit, a signal processing unit and a terminal modulation unit, wherein the front-end interference main optical path combination unit comprises a first optical splitter, a second optical splitter, an optical attenuator, a piezoelectric ceramic signal generator and an optical path delay coil; the terminal modulation unit comprises a terminal blind spot elimination optical fiber, a carrier signal phase modulator and a reflection device connected in sequence; the first photoelectric conversion device and the second photoelectric conversion device are respectively connected to the synchronous acquisition unit, the synchronous acquisition unit is connected to the signal processing unit, the light source, the first photoelectric conversion device and the second photoelectric conversion device are respectively connected to the first optical splitter, the first optical splitter is connected to the second optical splitter, and the optical path delay coil is connected therebetween; the second optical splitter is connected to the optical attenuator, the optical attenuator is connected to the piezoelectric ceramic signal generator, and the piezoelectric ceramic signal generator is connected to the terminal blind spot elimination optical fiber of the terminal modulation unit through the optical fiber to be measured.

[0007] The piezoelectric ceramic signal generator applies a test signal fm1, and the phase modulator applies a modulation frequency fm2.

[0008] The first optical splitter is a 3×3 optical splitter.

[0009] The second optical splitter is a 2×2 optical splitter.

[0010] Wherein, the carrier signal phase modulator is a lithium niobate modulator.

[0011] Wherein, the reflecting device is a Faraday rotating mirror.

[0012] Among them, the first optical splitter is provided with port 1a, port 1b, port 1c, port 1d and port 1e, and the second optical splitter is provided with port 2a, port 2b and port 2c. The light source is connected to port 1a, the first photoelectric conversion device is connected to port 1b, the second photoelectric conversion device is connected to port 1c, the port 1e is connected to port 2c, the port 1d is connected to port 2a through an optical path delay coil, the port 2b is connected to an optical attenuator, and the optical attenuator is connected to the piezoelectric ceramic signal generator.

[0013] The present invention also provides a method for measuring the length of an optical fiber, which outputs a signal from a light source, generates an interference signal by using a front-end interference main optical path combination unit through a phase carrier technology, passes through the optical fiber to be measured and a terminal modulation unit, and then is converted into an electrical signal by a first photoelectric conversion device and a second photoelectric conversion device, and the length information is demodulated by a signal processing unit;

[0014] The front-end interference main optical path combination unit generates an interference signal. The signal output from the port 1b and the port 1c of the first optical splitter is an interference signal, which is formed by the following optical path:

[0015] Path I: 7-1a-1d-5-2b-2a-3-4-6-12-13-14-13-12-6-4-3-2a-2c-1e-1b / 1c; Path II: 7-1a-1e-2c-2a-3-4-6-12-13-14-13-12-6-4-3-2a-2b-5-1d-1b / 1c.

[0016] Beneficial effects of the present invention:

[0017] When the present invention is working, a signal is output from a light source, and an interference signal is generated by a front-end interference main optical path combination unit through phase carrier technology. After passing through the optical fiber to be measured and the terminal modulation unit, the interference signal is converted into an electrical signal by a first photoelectric conversion device and a second photoelectric conversion device, and the length information is demodulated by a signal processing unit. The present invention achieves the purpose of removing the influence of noise through the phase carrier technology, and uses a phase modulator to load a constant pulse as a disturbance source at the front end of the optical path, thereby obtaining two disturbance signals related thereto, and the length information of the optical fiber to be measured is obtained through the time delay (flight time) between the two disturbance signals, which can improve the signal-to-noise ratio of the length measurement. The synchronous acquisition unit used in the present invention is a high-speed synchronous acquisition system, which can improve the measurement accuracy. The introduction of an optical attenuator in the invention can realize automatic matching of different measurement lengths, and can adapt to the length measurement of optical fibers of different lengths. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The figure is a schematic diagram of the structure of a device for measuring the length of an optical fiber according to the present invention.

[0019] Figure 2 A schematic diagram of the delay relationship between two disturbance signals demodulated by the present invention.

[0020] exist Figure 1 to Figure 2 The reference numerals include:

[0021] 1. First optical splitter; 2. First optical splitter; 3. Optical attenuator; 4. Piezoelectric ceramic signal generator; 5. Optical fiber delay coil; 6. Optical fiber to be tested; 7. Light source; 8. First photoelectric conversion device; 9. Second photoelectric conversion device; 10. Synchronous acquisition unit; 11. Signal processing unit; 12. Terminal blind zone elimination optical fiber; 13. Phase modulator; 14. Faraday reflector; 15. Front-end interference main optical path combination unit; 16. Terminal modulation unit. DETAILED DESCRIPTION

[0022] In order to facilitate the understanding of those skilled in the art, the present invention is further described below in conjunction with the embodiments and drawings, and the contents mentioned in the embodiments are not intended to limit the present invention. The present invention is described in detail below in conjunction with the drawings.

[0023] A device for measuring the length of an optical fiber, such as Figure 1 As shown, it includes a front-end interference main optical path combination unit, a light source, a first photoelectric conversion device, a second photoelectric conversion device, a synchronous acquisition unit, a signal processing unit and a terminal modulation unit, wherein the front-end interference main optical path combination unit includes a first optical splitter, a second optical splitter, an optical attenuator, a piezoelectric ceramic signal generator and an optical path delay coil; the terminal modulation unit includes a terminal blind spot elimination optical fiber, a carrier signal phase modulator and a reflection device connected in sequence; the first photoelectric conversion device and the second photoelectric conversion device are respectively connected to the synchronous acquisition unit, the synchronous acquisition unit is connected to the signal processing unit, the light source, the first photoelectric conversion device and the second photoelectric conversion device are respectively connected to the first optical splitter, the first optical splitter is connected to the second optical splitter, and the optical path delay coil is connected therebetween; the second optical splitter is connected to the optical attenuator, the optical attenuator is connected to the piezoelectric ceramic signal generator, and the piezoelectric ceramic signal generator is connected to the terminal blind spot elimination optical fiber of the terminal modulation unit through the optical fiber to be tested. Specifically, when the present invention is working, a signal is output from a light source, and an interference signal is generated by a front-end interference main optical path combination unit through phase carrier technology. After passing through the optical fiber to be measured and the terminal modulation unit, the interference signal is converted into an electrical signal by a first photoelectric conversion device and a second photoelectric conversion device, and the length information is demodulated by a signal processing unit; the present invention achieves the purpose of removing the influence of noise through the phase carrier technology, and uses a phase modulator to load a constant pulse as a disturbance source at the front end of the optical path, thereby obtaining two disturbance signals related thereto, and obtaining the length information of the optical fiber to be measured through the time delay (flight time) between the two disturbance signals, which can improve the signal-to-noise ratio of the length measurement. The synchronous acquisition unit used in the present invention is a high-speed synchronous acquisition system, which can improve the measurement accuracy. The introduction of an optical attenuator in the invention can realize automatic matching of different measurement lengths, and can adapt to the length measurement of optical fibers of different lengths.

[0024] Wherein, the first photoelectric conversion device and the second photoelectric conversion device are PINFET photoelectric conversion devices.

[0025] Wherein, the piezoelectric ceramic signal generator applies a test signal fm1, and the phase modulator applies a modulation frequency fm2. Wherein, the first optical splitter is a 3×3 optical splitter. Wherein, the second optical splitter is a 2×2 optical splitter. Wherein, the carrier signal phase modulator is a lithium niobate modulator. Wherein, the reflecting device is a Faraday rotation mirror. Wherein, the first optical splitter is provided with port 1a, port 1b, port 1c, port 1d and port 1e, the second optical splitter is provided with port 2a, port 2b and port 2c, the light source is connected to port 1a, the first photoelectric conversion device is connected to port 1b, the second photoelectric conversion device is connected to port 1c, the port 1e is connected to port 2c, the port 1d is connected to port 2a through an optical path delay coil, the port 2b is connected to an optical attenuator, and the optical attenuator is connected to the piezoelectric ceramic signal generator.

[0026] The present invention also provides a method for measuring the length of an optical fiber, which outputs a signal from a light source, generates an interference signal by using a front-end interference main optical path combination unit through a phase carrier technology, passes through the optical fiber to be measured and a terminal modulation unit, and then is converted into an electrical signal by a first photoelectric conversion device and a second photoelectric conversion device, and the length information is demodulated by a signal processing unit;

[0027] The front-end interference main optical path combination unit generates an interference signal. The signal output from the port 1b and the port 1c of the first optical splitter is an interference signal, which is formed by the following optical path:

[0028] Path I: 7-1a-1d-5-2b-2a-3-4-6-12-13-14-13-12-6-4-3-2a-2c-1e-1b / 1c; Path II: 7-1a-1e-2c-2a-3-4-6-12-13-14-13-12-6-4-3-2a-2b-5-1d-1b / 1c.

[0029] The optical paths of path I and path II are the same, only the order in which the light passes through is different, so the interference condition is automatically met and interference is formed.

[0030] The original signal measured by the optical fiber length measuring device provided by the present invention can be regarded as the superposition of the interference signal and a series of noises generated by Rayleigh scattering:

[0031]

[0032] In the formula and is the interference coefficient of the system, and φ 0 and is the initial phase, Δφ(t) and It is the phase change caused by external interference. Since the noise generated by the interference is superimposed on the signal, it is difficult to filter out useful phase information from the signal. Therefore, a phase modulator is connected to extract useful signals using phase carrier technology. A high-frequency sinusoidal signal f is loaded at the end modulation unit. m2 After that, the received signal will change to:

[0033]

[0034] Where f m2 is the frequency of the external high-frequency sinusoidal signal, expressed as P B replace And by performing Bessel expansion on the formula, we can get the following formula: P=P B +A cos(φ 0 +Δφ(t))[J 0 (φ c )+2J 2 (φ c )cos(4πf m2 t)+...]+Asin(φ 0 + Δφ(t))[2J 1 (φ c )cos(2πf m2 t)+2J 3 (φ c )cos(6πf m2 t)...]

[0035] Except for the first two terms, all the formulas contain cos(nπf c t)(n=1,2,3...) this term, and the second term Acos(φ 0 +Δφ(t))J 0 (φ c ), by adjusting the amplitude of the appropriate external high-frequency signal, J 0 (φ c ) is 0. This achieves the division of P B All signals except P are moved to the high frequency section, and P B Still at low frequency. At this time, adding a high-pass filter at the signal receiving end can filter out the noise signal caused by Rayleigh scattering. Furthermore, the corresponding phase change information Δφ(t) can be obtained through the traditional phase demodulation method. In addition to this solution, there are many other signal demodulation technologies that are relatively mature. The signal demodulation process can be implemented by hardware or software.

[0036] The device uses a piezoelectric ceramic signal generator with a loading frequency of f in the front-end interference main optical path combination unit. m1The pulse signal δ(t) of the device as a whole will cause the pulse signal to affect both the forward signal and the reflected signal at the same time. The reflected signal is received first, and its phase information can be expressed as Δφ(δ(t)). The forward signal has to pass through the entire test fiber and the end modulation unit, and after being reflected by the reflector at the end, it passes through the entire test fiber and is received by the signal receiving end. Its phase information can be expressed as Δφ(δ(t+τ)). τ is the time delay between the reflected signal and the forward signal. According to the principle of the time delay, the relationship between the time delay and the fiber length can be calculated:

[0037]

[0038] Where d is the length of the fiber, n is the average refractive index of the fiber, and c is the speed of light in a vacuum. Considering the fiber length of the system itself, the delay of the system itself should be subtracted during the measurement. Specifically, the time interval τ when the entire system is connected to the fiber under test is first measured. total , then remove the fiber under test and measure the time interval τ of the system alone insert By subtracting the two, we can obtain the time interval τ of the signal passing through the optical fiber under test. F :τ F =τ total -τ insert ;

[0039] The optical fiber length measurement system provided by the present invention can achieve a relatively high measurement accuracy (0.1 meter) over a medium to long distance (one hundred and twenty kilometers) by removing noise through a phase demodulation technology.

[0040] The specific embodiments are:

[0041] In this embodiment, the light source used is a superluminescent diode (SLD), the optical fiber used for the delay coil 5 is a G652 single-mode optical fiber, the test optical fiber used is a 60km long single-mode optical fiber, the jumper is an FC / PC single-mode optical fiber jumper, the end blind zone elimination optical fiber is a 20km long single-mode optical fiber, and the photodetectors 8 and 9 are PINFET photodetectors of model **. A pulse signal with a frequency of 100Hz, a pulse width of 5μs, and an amplitude of 10Vpp is applied to the piezoelectric ceramic (PZT) signal generator 4. A sinusoidal signal with a frequency of 1MHz is applied to the phase modulator 13. When the pulse is applied to the entire optical fiber system, a high-speed synchronous acquisition system with a sampling rate of 500MHz is used to collect the signal, and then the signal input by the photodetectors 8 and 9 is demodulated by the signal processing system 11, and the phase is restored to obtain the following. Figure 2The delay relationship between the two disturbance signals is shown in Figure 1. The measured delay between the two disturbance signals is 783.32μs, which is converted into a total system fiber length of 79973.242m. After deducting the blind zone elimination fiber length of 19960.012m, the test fiber length is 60013.230m.

[0042] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention is disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with the profession can make some changes or modifications to equivalent embodiments of equivalent changes by using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent changes and modifications made to the above embodiments according to the technology of the present invention are within the scope of the technical solution of the present invention without departing from the content of the technical solution of the present invention.

Claims

1. A device for measuring the length of an optical fiber, characterized in that: The invention comprises a front-end interference main optical path assembly unit (15), a light source (7), a first photoelectric conversion device (8), a second photoelectric conversion device (9), a synchronous acquisition unit (10), a signal processing unit (11) and a terminal modulation unit (16), wherein the front-end interference main optical path assembly unit (15) comprises a first optical splitter (1), a second optical splitter (2), an optical attenuator (3), a piezoelectric ceramic signal generator (4) and an optical path delay coil (5); the terminal modulation unit (16) comprises a terminal blind zone elimination optical fiber (12), a carrier signal phase modulator (13) and a reflection device (14) connected in sequence; the first photoelectric conversion device (8) and the second photoelectric conversion device The devices (9) are respectively connected to the synchronous acquisition unit (10), the synchronous acquisition unit (10) is connected to the signal processing unit (11), the light source (7), the first photoelectric conversion device (8) and the second photoelectric conversion device (9) are respectively connected to the first optical splitter (1), the first optical splitter (1) is connected to the second optical splitter (2), and the optical path delay coil (5) is connected therebetween; the second optical splitter (2) is connected to the optical attenuator (3), the optical attenuator (3) is connected to the piezoelectric ceramic signal generator (4), and the piezoelectric ceramic signal generator (4) is connected to the terminal blind zone elimination optical fiber (12) of the terminal modulation unit (16) through the optical fiber to be tested (6); The piezoelectric ceramic signal generator (4) applies a test signal fm1, and the phase modulator (13) applies a modulation frequency fm2; The first optical splitter (1) is provided with a port 1a, a port 1b, a port 1c, a port 1d and a port 1e, the second optical splitter (2) is provided with a port 2a, a port 2b and a port 2c, the light source (7) is connected to the port 1a, the first photoelectric conversion device (8) is connected to the port 1b, the second photoelectric conversion device (9) is connected to the port 1c, the port 1e is connected to the port 2c, the port 1d is connected to the port 2a via the optical path delay coil (5), the port 2b is connected to the optical attenuator (3), and the optical attenuator (3) is connected to the piezoelectric ceramic signal generator (4).

2. A device for measuring the length of an optical fiber according to claim 1, characterized in that: The first optical splitter (1) is a 3×3 optical splitter.

3. The device for measuring the length of an optical fiber according to claim 1, characterized in that: The second optical splitter (2) is a 2×2 optical splitter.

4. The device for measuring the length of an optical fiber according to claim 1, characterized in that: The carrier signal phase modulator (13) is a lithium niobate modulator.

5. The device for measuring the length of an optical fiber according to claim 1, characterized in that: The reflecting device (14) is a Faraday rotation mirror.

6. A method for measuring the length of an optical fiber, characterized in that: A signal is output from a light source (7), and an interference signal is generated by a front-end interference main optical path combination unit (15) through a phase carrier technology. After passing through the optical fiber to be tested (6) and the end modulation unit (16), the signal is converted into an electrical signal by a first photoelectric conversion device (8) and a second photoelectric conversion device (9), and the length information is demodulated by a signal processing unit (11); The front-end interference main optical path combination unit (15) generates an interference signal, and the signal output from the ports 1b and 1c of the first optical splitter (1) is an interference signal formed by the following optical path: Path I: light source - port 1a - port 1d - optical fiber delay coil - port 2b - port 2a - optical attenuator - piezoelectric ceramic signal generator - optical fiber to be tested - end blind zone elimination optical fiber - phase modulator - Faraday reflector - phase modulator - end blind zone elimination optical fiber - optical fiber to be tested - piezoelectric ceramic signal generator - optical attenuator - port 2a - port 2c - port 1e - port 1b / 1c; Path II: light source - port 1a - port 1e - port 2c - port 2a - optical attenuator - piezoelectric ceramic signal generator - optical fiber to be tested - end blind spot elimination optical fiber - phase modulator - Faraday reflector - phase modulator - end blind spot elimination optical fiber - optical fiber to be tested - piezoelectric ceramic signal generator - optical attenuator - port 2a - port 2b - optical fiber delay coil - port 1d - port 1b / 1c.

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