CN108540216B - High-precision chaotic optical time domain reflectometer - Google Patents

High-precision chaotic optical time domain reflectometer Download PDF

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CN108540216B
CN108540216B CN201810366563.0A CN201810366563A CN108540216B CN 108540216 B CN108540216 B CN 108540216B CN 201810366563 A CN201810366563 A CN 201810366563A CN 108540216 B CN108540216 B CN 108540216B
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王安帮
赵彤
王龙生
胡志宏
郭圆圆
贾志伟
王云才
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Taiyuan University of Technology
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/07—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems
    • H04B10/071—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems using a reflected signal, e.g. using optical time domain reflectometers [OTDR]
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/25—Arrangements specific to fibre transmission
    • H04B10/2589—Bidirectional transmission
    • H04B10/25891—Transmission components
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/40—Transceivers
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
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Abstract

The invention discloses a low-cost high-precision chaotic optical time domain reflectometer, which is characterized in that chaotic optical signals transmitted by a chaotic light transmitting device are divided into detection light I and reference light II through an optical fiber coupler I; the detection light I is emitted into an optical fiber circuit to be detected through the optical circulator, the detection light reflected back from the optical fiber circuit to be detected is received by the photoelectric detector I, and each sampling data is quantized into n binary bits through n-bit ADC I quantization. The reference light II is received by the photoelectric detector II, converted into an electric signal by an optical signal and quantized into n-bit binary bits by the n-bit ADC II. In the effective bit information processing system, two paths of quantized signals are simultaneously extracted by low N (N is less than N) bit effective bits, converted into decimal signals and input into a cross-correlation device for cross-correlation operation, and the result is output to a display device. The invention overcomes the problem of bandwidth limitation of a chaotic light source and a PD in the current COTDR through effective bit information processing, improves the resolution ratio of the COTDR and reduces the cost of the COTDR.

Description

High-precision chaotic optical time domain reflectometer
Technical Field
The invention relates to the technical field of optical fiber line measurement, in particular to a high-precision chaotic optical time domain reflectometer which can realize high-precision detection of optical fiber faults.
Background
An Optical Time Domain Reflectometer (OTDR) is a measuring instrument based on back scattering or reflection signals, which can conveniently perform nondestructive measurement on an Optical fiber and continuously display the relative position and fault point position of the whole Optical fiber line, becomes the most widely applied measuring instrument in the whole industry of Optical fiber research, production, laying and maintenance, and plays an important role in the Optical fiber industry.
In the conventional OTDR, a pulse laser is used as a light source, the pulse laser emits light pulses to an optical fiber link to be measured, and the relationship between loss and distance is obtained by measuring the power and the flight time of return light. For a conventional OTDR using a pulse laser as a light source, there are problems that the resolution is low, the resolution is limited by the width of an optical pulse, and the peak power of an OTDR transmitter is limited by the laser, and the improvement of the dynamic range is mainly achieved by improving the energy of the optical pulse, and the improvement of the dynamic range reduces the resolution of the OTDR, and the improvement of the resolution reduces the dynamic range, which is a contradiction that cannot be solved by the conventional pulsed OTDR.
In order to solve the contradiction of the conventional pulse OTDR, researchers have proposed a correlation method OTDR, which uses pseudo-random code modulated optical pulses and performs signal processing by using correlation techniques, so that the contradiction that the resolution and the dynamic range cannot be simultaneously improved can be better solved, and the dynamic range and resolution of optical time domain reflection can be greatly improved (EP 0269448, JP 9026376). However, because of the limited spectrum bandwidth of the pseudo-random code signal, the resolution is improved only to a limited extent, and the advantages of the correlation OTDR measurement are not fully exerted, and such an OTDR device requires an expensive pseudo-random code generator and a complex encoder and decoder.
Subsequently, a Chaos Optical Time Domain Reflectometer (COTDR) is proposed, the basic structure and principle of which are similar to those of OTDR of related method, the patent number is CN200810054534, and a patent named Chaos Optical Time Domain Reflectometer and a measurement method thereof describes the Chaos Optical Time Domain Reflectometer in detail, and the main changes are as follows: and (3) replacing optical pulse modulated by pseudo random code in the related OTDR with the chaotic optical signal as a detection signal. The chaotic laser signal is a true random signal, has a higher bandwidth than a pseudo random code signal, and can greatly improve the resolution and dynamic range of OTDR (IEEE Photonics Technology Letters, 2008, 20(19): 1636-1638, CN 101226100B). However, the conventional COTDR chaotic light source mainly comprises a semiconductor laser and an external cavity feedback device, and has a simple structure, but the generated chaotic light has obvious relaxation oscillation, so that the bandwidth of the chaotic light source is limited. To further increase the bandwidth of the chaotic light source, more complicated structures, such as optical injection method (Optics Letters, 2009, 34 (8): 1144-1146) and optical fiber oscillation ring (Applied Physics Letters, 2013, 102 (3): 031112), are required, which results in complicated structure and increased cost. Meanwhile, the cost of a Photoelectric Detector (PD) in the COTDR is considered, the bandwidth of the commercial COTDR detector is far smaller than that of the chaotic light source, and the utilization rate of the bandwidth of the chaotic light source is low. The highest resolution reported for COTDR is currently 2cm @1GHz PD, subject to PD cost. (JLT 30 (21): 3420, 2012).
Disclosure of Invention
The invention provides a high-precision chaotic optical time domain reflectometer, which aims to solve the problems of bandwidth limitation of a chaotic light source and a PD (photo diode) in a COTDR (coherent-tunable.
The invention improves the patent with the patent number of CN200810054534 in the background technology, in the invention, the original A/D converter is replaced by an n-bit ADC, and an effective bit information processing system is added in the original COTDR, the measurement principle is that the chaotic light is divided into a detection light I and a reference light II, the functional relation formula satisfied by the reference light is set as f (t), and the functional relation formula satisfied by the detection light I after being retroreflected by an optical fiber line to be measuredg(t)=k*f(t-τ0). The functional relations satisfied by the reference light II and the retroreflected detection light I through the effective bit information processing system are respectively as follows:f′(t) Andg′(t)=k*f′(t-τ 0) (ii) a Then its cross correlation function
Figure 88964DEST_PATH_IMAGE001
. When in useτ=τ 0There is a peak in the cross-correlation function, the peak of the cross-correlation function being related to the intensity of the reflected light (US 8502964B 2). Based on the principle, the reflected detection light can be obtained by processing through a cross-correlation instrument or a computerIntensity and round trip time ofτ 0Therefore, fault location and transmission characteristic detection of the optical fiber circuit are achieved.
The invention is realized by the following technical scheme: a high-precision chaotic optical time domain reflectometer comprises a chaotic light emitting device, an optical fiber coupler, a photoelectric detector, a cross-correlation processing device and a display device, and also comprises two n-bit ADCs and an effective bit information processing system; a chaotic light signal emitted by the chaotic light emitting device is divided into a detection light I and a reference light II through an optical fiber coupler; the detection light I is transmitted to an optical fiber circuit to be detected through an optical circulator, the detection light I reflected back from the optical fiber circuit to be detected is received by a photoelectric detector I, and each sampling point is quantized into n binary bits and input into an effective bit information processing system through n-bit ADC I quantization; the reference light II is received by the photoelectric detector II, an optical signal is converted into an electric signal, the electric signal is quantized by the n-bit ADC II, and each sampling point is quantized into n binary bits and input into the effective bit information processing system; the two paths of quantized signals are simultaneously processed in the effective bit information processing system, then input into a cross-correlation processing device to perform cross-correlation operation, and finally output to a display device.
The basic principle of the invention for improving the resolution of the COTDR by the effective bit information processing is as follows: the retroreflected detection signal and reference signal (i.e., the detection light I and the reference light II) are binary quantized by N bits, and the low N (N < N) bits are extracted and converted into decimal. Through the frequency spectrum, the bandwidth of two paths of signals is larger than that of a chaotic light source, and the bandwidth is increased along with the reduction of N, mainly because nonlinear frequency mixing (IEEE Transactions On Circuits and Systems I: regulated Papers, 2014,61(3): 888-901) occurs in the process of extracting the least significant bit. With the benefit of the bandwidth enhancement effect, the COTDR based on the effective bit information processing can overcome the limitation of the bandwidth of a chaotic source and a PD (photodetector), remarkably improve the resolution of the COTDR, and greatly reduce the cost of the COTDR. However, it should be noted that: the maximum bandwidth that this bandwidth enhancement effect can achieve is limited by the sampling rate of the ADC (nyquist's law).
The detection light I is amplified by the optical amplifier and then emitted into an optical fiber circuit to be detected by the optical circulator.
The chaotic light emitting device is a chaotic semiconductor laser or a chaotic fiber laser, and the chaotic semiconductor laser is an optical feedback chaotic semiconductor laser, an external light injection chaotic semiconductor laser or a semiconductor laser and an optical fiber oscillation ring; the chaotic fiber laser is a single-ring fiber chaotic laser or a double-ring fiber chaotic laser with intensity modulation. The optical circulator is a fiber coupler or a beam splitter. The cross-correlation processing device is a digital correlator or a computer.
Preferably, a micro optical fiber ring can be added to improve the energy of the low-frequency part chaotic light source, the micro optical fiber ring for improving the low-frequency part chaotic light energy is added behind the chaotic light emitting device, and the frequency 1/T (T is the period of the optical fiber ring) of the micro optical fiber ring is greater than the PD bandwidth.
The effective bit information processing system can be realized by hardware or computer software, and has the main functions of: and extracting low N (N is less than N) bit effective bits of the quantized result of the N-bit ADC, converting the effective bits into decimal numbers, and inputting the decimal numbers into a cross-correlation device. The hardware device consists of an N-bit decimator and a decimal converter. The COTDR can be realized by software in commercial use, so that the cost of the COTDR is greatly reduced.
Compared with the existing optical time domain reflectometer, the high-precision chaotic optical time domain reflectometer provided by the invention has the following advantages and positive effects: the invention has the advantages of wide dynamic range, strong anti-interference capability, large noise tolerance, easy integration and the like; under the same requirements of resolution and dynamic range, the method has lower cost and better meets the commercial standard; compared with the original COTDR, the invention overcomes the limitation of a chaotic light source and PD bandwidth, obviously improves the resolution, can reach 1.2mm @1GHz under the existing COTDR device, and keeps the dynamic range unchanged.
Drawings
Fig. 1 is a schematic structural view of the present invention.
Fig. 2 is a schematic diagram of a hardware implementation structure of the valid bit information processing system of the present invention.
Fig. 3 is a cross-correlation diagram comparing different significance information processing.
In the figure: the device comprises a chaotic light emitting device 1, a micro optical fiber ring 2, an optical fiber coupler 3, an optical amplifier 4, an optical circulator 5, an optical fiber circuit to be tested 6, a photoelectric detector II 7, an ADC II 8-N, a photoelectric detector I9, an ADC I10-N, an effective bit information processing system 11, a cross-correlation processing device 12, a display device 13, an extractor 14-N and a decimal converter 15.
Detailed Description
The present invention is further illustrated by the following specific examples.
A high-precision chaotic optical time domain reflectometer is shown in figure 1 and comprises a chaotic light emitting device 1, an optical fiber coupler 3, a photoelectric detector, a cross-correlation processing device 12, a display device 13, two n-bit ADCs and an effective bit information processing system 11; a chaotic light signal emitted by the chaotic light emitting device 1 is divided into a detection light I and a reference light II through an optical fiber coupler 3; the detection light I is transmitted into an optical fiber circuit 6 to be detected through an optical circulator 5, the detection light I reflected back from the optical fiber circuit 6 to be detected is received through a photoelectric detector I9, quantization is carried out through an n-bit ADC I10, and each sampling point is quantized into n binary bits and input into an effective bit information processing system 11; the reference light II is received by a photoelectric detector II 7, an optical signal is converted into an electric signal, the electric signal is quantized by an n-bit ADC II 8, and each sampling point is quantized into n binary bits and input into an effective bit information processing system 11; the two paths of quantized signals are processed in the effective bit information processing system 11 at the same time, then input into the cross-correlation processing device 12 for cross-correlation operation, and finally output to the display device 13.
The chaotic light emitting device 1 in the embodiment is a chaotic semiconductor laser, in particular to an optical feedback chaotic semiconductor laser, and consists of a semiconductor laser, an optical fiber coupler and a feedback device, wherein the feedback device is a digital reflectometer, or an optical fiber with an end surface coated with a reflecting film, or consists of a grating and a variable optical attenuator; the detection light I is amplified by the optical amplifier 4 and then emitted into the optical fiber circuit 6 to be detected by the optical circulator 5; the optical circulator 5 is a fiber coupler or a beam splitter, and the beam splitter is adopted in the embodiment; the cross-correlation processing device 12 is a digital correlator or a computer, and in this embodiment, a digital correlator is used. In the embodiment, a micro optical fiber ring 2 for improving the low-frequency partial chaotic light energy is added behind the chaotic light emitting device 1, and the frequency 1/T of the micro optical fiber ring 2 is greater than the PD bandwidth; the significant bit information processing system 11 in the present embodiment is realized by hardware, and as shown in fig. 2, the hardware device is constituted by an N-bit decimator 14 and a decimal converter 15.
The embodiment specifically operates as follows: after the chaotic laser signal generated by the chaotic semiconductor laser improves the low-frequency part chaotic light source energy through the micro optical fiber ring 2, the chaotic laser signal is divided into two paths through the optical fiber coupler 3: detecting light I and reference light II; the detection light I is transmitted to an optical fiber line 6 to be detected through an optical amplifier 4 and an optical circulator 5, an echo signal scattered or reflected in the line is converted into an electric signal through a photoelectric detector I9, the electric signal is quantized through an n-bit ADC I10, and each sampling point is quantized into n binary bits; the reference light II directly irradiates to the photoelectric detector II 7, and is quantized by the n-bit ADC II 8, and each sampling point is quantized into n binary bits. The two quantized signals are simultaneously input to the significant bit information processing system 11 (i.e., the N bit extractor 14 and the decimal converter 15) for low N (N < N) bit significant bit extraction and conversion into a decimal system, as shown in fig. 2. And then performing cross-correlation operation on the two paths of signals in a digital correlator so as to obtain the relation between the loss and the distance of the optical fiber line. The display device 13 displays the measurement result, and high-precision fault location and detection of optical fiber transmission characteristics are realized. Fig. 3 is a cross-correlation diagram comparing processes of extracting different significant bits under the same conditions, and the FWHM (full width at half maximum) of the lower 8-bit process is wider than that of the lower 7-bit process, demonstrating that the resolution of the lower 7-bit decimation process is significantly higher than that of the lower 8-bit decimation process.
In practical application, the n-bit ADC I10 and the n-bit ADC II 8 can be determined according to actual needs and cost; similarly, when extracting low N (N < N) significant bits in a significant bit information processing system, the size of N is determined according to actual requirements and signal quality, so that high-precision resolution measurement can be realized under different conditions.
The scope of the invention is not limited to the above embodiments, and various modifications and changes may be made by those skilled in the art, and any modifications, improvements and equivalents within the spirit and principle of the invention should be included in the scope of the invention.

Claims (7)

1. The utility model provides a chaos optical time domain reflectometer of high accuracy, includes chaos light emitting device (1), fiber coupler (3), photoelectric detector, cross-correlation processing apparatus (12) and display device (13), its characterized in that: the system also comprises two n-bit ADCs and an effective bit information processing system (11); a chaotic light signal emitted by the chaotic light emitting device (1) is divided into a detection light I and a reference light II through an optical fiber coupler (3); the detection light I is transmitted into an optical fiber circuit to be detected (6) through an optical circulator (5), the photoelectric detector I (9) receives the detection light I reflected back from the optical fiber circuit to be detected (6), the detection light I is quantized through an n-bit ADC I (10), and each sampling point is quantized into n binary bits and input into an effective bit information processing system (11); the reference light II is received by a photoelectric detector II (7), an optical signal is converted into an electric signal, then the electric signal is quantized by an n-bit ADC II (8), and each sampling point is quantized into n binary bits and input into an effective bit information processing system (11); the two paths of quantized signals are simultaneously processed in an effective bit information processing system (11), then input into a cross-correlation processing device (12) for cross-correlation operation, and finally output to a display device (13), wherein the effective bit information processing system (11) is composed of an N bit extractor (14) and a decimal converter (15).
2. The high-precision chaotic optical time domain reflectometer according to claim 1, characterized in that: the detection light I is amplified by the optical amplifier (4) and then emitted into the optical fiber circuit (6) to be detected by the optical circulator (5).
3. The high-precision chaotic optical time domain reflectometer according to claim 1, characterized in that: the chaotic light emitting device (1) is a chaotic semiconductor laser or a chaotic fiber laser, and the chaotic semiconductor laser is an optical feedback chaotic semiconductor laser, an external light injection chaotic semiconductor laser or a semiconductor laser and an optical fiber oscillation ring; the chaotic fiber laser is a single-ring fiber chaotic laser or a double-ring fiber chaotic laser with intensity modulation.
4. The high-precision chaotic optical time domain reflectometer according to claim 1, characterized in that: the optical circulator (5) is a fiber coupler or a beam splitter.
5. The high-precision chaotic optical time domain reflectometer according to claim 1, characterized in that: the cross-correlation processing device (12) is a digital correlator or a computer.
6. The high-precision chaotic optical time domain reflectometer according to claim 1, characterized in that: a micro optical fiber ring (2) for improving the low-frequency partial chaotic light energy is added behind the chaotic light emitting device (1), the frequency 1/T of the micro optical fiber ring (2) is greater than the PD bandwidth, and T is the optical fiber ring period.
7. The high-precision chaotic optical time domain reflectometer according to claim 1, characterized in that: the effective bit information processing system (11) is realized through software, low N-bit effective bit extraction is carried out on the quantized result of the N-bit ADC, then the low N-bit effective bit extraction is converted into a decimal system, and the decimal system is input into the cross-correlation processing device (12), wherein N is less than N.
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CN109802721B (en) * 2019-01-18 2022-02-01 太原理工大学 OTDR device and measuring method based on physical random code correlation detection
CN110740030B (en) * 2019-09-23 2022-07-05 太原理工大学 Integrated chaotic signal generator with double-microring waveguide structure

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