CN108512594B - Subsequent processing method for improving resolution of chaotic optical time domain reflectometer - Google Patents
Subsequent processing method for improving resolution of chaotic optical time domain reflectometer Download PDFInfo
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Abstract
The invention discloses a subsequent processing method for improving the resolution of a chaotic light time domain reflectometer, which is based on the principle of the chaotic light time domain reflectometer, wherein chaotic light signals emitted by a chaotic light emitting 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 problems of the chaos light source and PD bandwidth limitation in the current COTDR, and improves the resolution of the COTDR.
Description
Technical Field
The invention relates to the technical field of optical fiber line measurement, in particular to a subsequent processing method for improving the resolution of a 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-. 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. In order to further increase the bandwidth of the chaotic light source, more complex structures, such as optical injection method (Optics Letters, 2009, 34 (8): 1144) and optical fiber oscillation ring (Applied Physics Letters, 2013, 102 (3): 031112), must be adopted, which results in complex 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 subsequent processing method for improving the resolution of a chaotic optical time domain reflectometer, aiming at solving the problem 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 probe light I through the subsequent processing system (i.e. the valid bit information processing system) are respectively as follows:f′(t) Andg′(t)=k*f′(t-τ 0) (ii) a Then its cross correlation function
. 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 intensity and round trip time of the reflected detection light can be obtained by the cross-correlation instrument or the computer for processingτ 0Therefore, fault location and transmission characteristic detection of the optical fiber circuit are achieved.
The invention is realized by the following technical scheme: a subsequent processing method for improving the resolution of a chaotic optical time domain reflectometer comprises the following steps:
(1) 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;
(2) 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 an optical signal is converted into an electric signal;
(3) the reference light II is received by the photoelectric detector II, and an optical signal is converted into an electric signal;
(4) the photoelectric detector I inputs an electric signal obtained by converting a signal reflected by the detection light I into the n-bit ADC I for quantization; the photoelectric detector II inputs the electric signal converted by the reference light II into an n-bit ADC II for quantization, and each sampling point is quantized into n binary bits;
(5) in a valid bit information processing system, extracting the N least significant bits of two paths of signals quantized into N binary bits, and discarding other most significant bits, wherein N is less than N;
(6) converting the extracted valid bit result into a decimal system;
(7) inputting the decimal result into a cross-correlation processing device for cross-correlation operation;
(8) the calculated result is 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: after the retro-reflected detection signal and the reference signal (i.e. the detection light I and the reference light II) are converted into electric signals, N-bit binary quantization is carried out, low N (N is less than N) bits are extracted and converted into decimal, and the decimal result is input into a cross-correlation processing device for cross-correlation operation. It can be found from the frequency spectrum that the bandwidth of the two signals is larger than that of the chaotic light source, and the bandwidth increases with the decrease of N, mainly because the nonlinear frequency mixing (IEEE Transactions On Circuits and Systems I: regulated Papers, 2014,61(3): 888-. With the benefit of the bandwidth enhancement effect, the COTDR based on the effective bit information processing can overcome the limitations of the chaotic source and the PD bandwidth, 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 effective bit information processing system can be formed by hardware equipment or can be realized by 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 is composed of an N-bit extractor and a decimal converter. The COTDR can be realized by software in commercial use, so that the cost of the COTDR is greatly reduced.
The subsequent processing method for improving the resolution of the chaotic light time domain reflectometer provided by the invention has the following advantages and positive effects: compared with the original COTDR processing method, the method provided by the invention overcomes the limitation of a chaotic light source and PD bandwidth, the resolution ratio is obviously improved, the resolution ratio can reach 1.2mm @1GHz under the existing COTDR device, and the dynamic range is kept unchanged.
Drawings
FIG. 1 is a schematic structural diagram of a chaotic optical time domain reflectometer according to the present invention.
Fig. 2 is a signal flow diagram of a valid bit information processing system according to 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, a decimal converter 15 and a sampling point 16.
Detailed Description
The present invention is further illustrated by the following specific examples.
A subsequent processing method for improving the resolution of a chaotic optical time domain reflectometer comprises the following steps:
(1) 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;
(2) the detection light I is transmitted to an optical fiber circuit 6 to be detected through an optical circulator 5, and is received by a photoelectric detector I9, wherein the detection light I is reflected back from the optical fiber circuit 6 to be detected, and is converted into an electric signal through an optical signal;
(3) the reference light II is received by a photoelectric detector II 7, and an optical signal is converted into an electric signal;
(4) the photoelectric detector I9 inputs the electric signal converted by the signal reflected by the detection light I into the n-bit ADC I10 for quantization; the photoelectric detector II 7 inputs the electric signal converted by the reference light II to an n-bit ADC II 8 for quantization, and each sampling point is quantized into n binary bits;
(5) in the effective bit information processing system 11, extracting the N least significant bits of two paths of signals quantized into N binary bits, and discarding other most significant bits, wherein N is less than N;
(6) converting the extracted valid bit result into a decimal system;
(7) inputting the decimal result into a cross-correlation processing device 12 for cross-correlation operation;
(8) the calculated result is output to the display device 13.
The chaotic optical time domain reflectometer in the embodiment 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 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, an optical fiber with an end surface coated with a reflecting film, or 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 a hardware device 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, and as shown in FIG. 2, the electric signal is quantized through an n-bit ADC I10, and each sampling point 16 is quantized into n binary bits; the reference light II directly irradiates the photoelectric detector II 7, and is quantized by the n-bit ADC II 8, and each sampling point 16 is also quantized into n binary bits; meanwhile, two paths of quantized signals are input into an effective bit information processing system 11 (namely an N bit extractor 14 and a decimal converter 15) to be subjected to low-N (N < N) bit effective bit extraction and converted into decimal (for example, in fig. 2, N =8 is subjected to low-N bit extraction, and N =6 is extracted from low 6 bits in a frame, and high-bit extraction is abandoned), and then the two paths of signals are subjected to cross-correlation operation in a digital correlator, so that the relation between the loss and the distance of an optical fiber line is obtained, a measurement result is displayed through a display device 13, 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, where 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 (1)
1. A subsequent processing method for improving the resolution of a chaotic optical time domain reflectometer comprises the following steps:
(1) 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);
(2) the detection light I is transmitted into an optical fiber circuit to be detected (6) through an optical circulator (5), and the detection light I reflected back from the optical fiber circuit to be detected (6) is received by a photoelectric detector I (9) and converted into an electric signal through an optical signal;
(3) the reference light II is received by a photoelectric detector II (7), and an optical signal is converted into an electric signal;
the method is characterized in that:
(4) the photoelectric detector I (9) inputs an electric signal obtained by converting a signal reflected by the detection light I into the n-bit ADC I (10) for quantization; the photoelectric detector II (7) inputs the electric signal converted by the reference light II to an n-bit ADC II (8) for quantization, and each sampling point is quantized into n binary bits;
(5) in a valid bit information processing system (11), N-bit least significant bits are extracted from two paths of signals quantized into N binary bits, and other most significant bits are discarded, wherein N is less than N;
(6) converting the extracted valid bit result into a decimal system;
(7) inputting the decimal result into a cross-correlation processing device (12) for cross-correlation operation;
(8) the calculated result is output to a display device (13).
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