CN108512594B - A Subsequent Processing Method for Improving the Resolution of Chaos Optical Time Domain Reflectometer - Google Patents

Abstract

The invention discloses a subsequent processing method for improving the resolution of a chaotic optical time domain reflectometer. Probe light I and reference light II; Probe light I is emitted into the optical fiber line to be tested through the optical circulator, and the photodetector I is used to receive the probe light reflected back from the optical fiber line to be tested, and quantized by n-bit ADC I. Data is quantized into n-bit binary bits. The reference light II is received by the photodetector II, converted from an optical signal to an electrical signal, and then quantized into n-bit binary bits by an n-bit ADC II. In the significant bit information processing system, the two channels of quantized signals are simultaneously extracted as low N (N<n) significant bits, converted into decimal and input to the cross-correlation device for cross-correlation operation, and the result is output to the display device. The present invention overcomes the problem of limited bandwidth of chaotic light source and PD in the current COTDR, so as to improve the resolution of the COTDR.

Description

A Subsequent Processing Method for Improving the Resolution of Chaos Optical Time Domain Reflectometer

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 technique

Optical Time Domain Reflectometer (OTDR) is a measurement instrument based on backscattered or reflected signals. This instrument can easily perform non-destructive measurements on optical fibers and can continuously display the relative position of the entire optical fiber line It has become the most widely used measuring instrument in the entire industry of optical fiber research, production, laying and maintenance, and occupies an important position in the optical fiber industry.

The traditional OTDR uses a pulsed laser as the light source, and the pulsed laser emits optical pulses to the fiber link under test. The relationship between loss and distance is obtained by measuring the power and flight time of the returned light. For the traditional OTDR that uses a pulsed laser as the light source, the existing problems are that the resolution is low, the resolution is limited by the width of the optical pulse, and the peak power of the OTDR transmitter is limited by the laser. The improvement of the dynamic range is mainly achieved by increasing Optical pulse energy is realized, increasing the dynamic range will reduce the resolution of the OTDR, and increasing the resolution will reduce the dynamic range, which is the contradiction that the traditional pulsed OTDR cannot solve.

In order to solve the contradiction of the traditional pulsed OTDR, the researchers proposed the correlation method OTDR, which uses the optical pulse modulated by the pseudo-random code, and uses the correlation technology for signal processing, which can better solve the contradiction that the resolution and the dynamic range cannot be improved at the same time. , which can greatly improve the dynamic range and resolution of optical time domain reflection (EP0269448, JP9026376). However, due to the limitation of the spectral bandwidth of the pseudo-random code signal, the improvement of its resolution is very limited, and the advantages of the correlation method OTDR measurement are not fully exerted, and this OTDR device requires an expensive pseudo-random code generation device and complex encoding and decoding. encoder.

Subsequently, Chaos Optical Time Domain Reflectometer (COTDR for short) was proposed. Its basic structure and principle are similar to the correlation method OTDR. The patent number is CN200810054534, and the name of the invention is Chaos Optical Time Domain Reflectometer and its measurement method. The patent has made a detailed description of it, and the main change is: use the chaotic optical signal to replace the optical pulse modulated by the pseudo-random code in the correlation method OTDR as the detection signal. The chaotic laser signal is a real random signal, which has a higher bandwidth than the pseudo-random code signal, which can greatly improve the resolution and dynamic range of OTDR (IEEE Photonics Technology Letters, 2008, 20(19): 1636-1638, CN101226100B). However, at present, the chaotic light source in COTDR is mainly composed of semiconductor laser and external cavity feedback device. Its structure is simple, but the generated chaotic light relaxation oscillation is obvious, which limits its bandwidth. In order to further increase the bandwidth of chaotic light sources, more complex structures must be adopted, such as light injection method to generate chaos (Optics Letters, 2009, 34(8): 1144-1146), optical fiber oscillation ring to generate chaos (Applied Physics Letters, 2013 , 102 (3): 031112), which will result in a complex structure and an increase in cost. At the same time, considering the cost of the photodetector (PD) in COTDR, the bandwidth of the COTDR detector in commercial use is much smaller than that of the chaotic light source, resulting in a low utilization rate of the bandwidth of the chaotic light source. Limited by the cost of PD, the highest resolution of COTDR reported so far is 2cm@1GHz PD. (JLT30(21):3420, 2012).

SUMMARY OF THE INVENTION

In order to solve the problem of chaotic light source and PD bandwidth limitation in COTDR, the present invention significantly improves the resolution of COTDR and at the same time greatly reduces the cost of COTDR, and provides a subsequent processing method for improving the resolution of chaotic optical time domain reflectometer.

。当τ=τ ₀时，互相关函数存在峰值，互相关函数的峰值与返射光强度有关（US8502964B2）。基于此原理，通过互相关仪或计算机进行处理就可以获得探测光返射的强度与往返时间τ ₀，从而实现光纤线路的故障定位与传输特性的检测。The invention improves the patent with the patent number of CN200810054534 in the background technology. In the invention, an n-bit ADC is used to replace the original A/D converter, and an effective bit information processing system is added to the original COTDR. The measurement principle is to The chaotic light is divided into probe light I and reference light II. Let the functional relationship satisfied by the reference light be f(t), and the functional relationship g ( t )=k* f satisfied by the probe light I after being retroreflected by the optical fiber line to be tested ( t -τ ₀ ). The functional relationship that the reference light II and the retroreflected probe light I satisfy by the subsequent processing system (that is, the effective bit information processing system) are: f′ ( t ) and g′ ( t )=k* f′ ( t - τ ₀ ); then its cross-correlation function

. When τ = τ ₀ , the cross-correlation function has a peak value, and the peak value of the cross-correlation function is related to the intensity of the reflected light (US8502964B2). Based on this principle, the intensity and round-trip time τ ₀ of the detection light can be obtained by processing with a cross-correlator or a computer, so as to realize the fault location of the optical fiber line and the detection of the transmission characteristics.

The present invention is achieved through the following technical solutions: a subsequent processing method for improving the resolution of a chaotic optical time domain reflectometer, comprising the following steps:

(1) The chaotic light signal emitted by the chaotic light emitting device is divided into probe light I and reference light II through the fiber coupler;

(2) The probe light I is transmitted to the optical fiber line to be tested through the optical circulator, and the photodetector I is used to receive the probe light I retroreflected from the optical fiber line to be tested, and convert the optical signal into an electrical signal;

(3) The reference light II is received by the photodetector II, and the optical signal is converted into an electrical signal;

(4) The photodetector I inputs the converted electrical signal from the signal reflected by the detection light I into the n-bit ADC I for quantization; the photodetector II inputs the electrical signal converted from the reference light II to the n-bit ADC II for quantization, Each sampling point is quantized into n binary bits;

(5) In the significant bit information processing system, extract the least significant bits of N bits for the signals that are both quantized into n binary bits, and discard the other most significant bits, where N<n;

(6) Convert the extracted significant bit result to decimal;

(7) Input the decimal result into the cross-correlation processing device for cross-correlation operation;

(8) The calculated result is output to the display device.

The basic principle of improving COTDR resolution through effective bit information processing mentioned in the present invention: after the retroreflected detection signal and reference signal (ie, detection light I and reference light II) are converted into electrical signals, n-bit binary quantization is performed. , extract the low N (N<n) bits and convert them into decimal, and input the decimal result into the cross-correlation processing device for cross-correlation operation. Through its spectrum, it can be found that the bandwidth of the two signals will be larger than the bandwidth of the chaotic light source, and the bandwidth will increase with the decrease of N. This is mainly because nonlinear mixing will occur in the process of extracting the least significant bit (IEEE Transactions On Circuits and Systems I: Regular Papers, 2014, 61(3):888-901). Benefiting from this bandwidth enhancement effect, COTDR based on this effective bit information processing can overcome the limitation of chaotic source and PD bandwidth, significantly improve the resolution of COTDR, and greatly reduce the cost of COTDR. However, it should be noted that the maximum bandwidth that can be achieved with this bandwidth-enhancing effect is limited by the sampling rate of the ADC (Nyquist's law).

In the present invention, the effective bit information processing system can be composed of hardware equipment or realized by computer software, and its main function is to extract the low N (N<n) effective bits from the result of n-bit ADC quantization, and then convert it into decimal system, input into the cross-correlation device. The hardware device consists of an N-bit decimator and a decimal converter. It can be realized by software in commercial use, which greatly reduces the cost of COTDR.

A subsequent processing method for improving the resolution of a chaotic optical time domain reflectometer provided by the present invention has the following advantages and positive effects: Compared with the original COTDR processing method, the method provided by the present invention overcomes the chaotic light source and PD Due to the limitation of bandwidth, the resolution is significantly improved. Under the existing COTDR device, the resolution can reach 1.2mm@1GHz, and the dynamic range remains unchanged.

Description of drawings

FIG. 1 is a schematic structural diagram of a chaotic optical time domain reflectometer in the present invention.

FIG. 2 is a schematic diagram of the signal flow of the significant bit information processing system in the present invention.

FIG. 3 is a comparison diagram of cross-correlation diagrams of different significant bit information processing.

In the figure: 1-chaotic light emitting device, 2-miniature fiber ring, 3-fiber coupler, 4-optical amplifier, 5-optical circulator, 6-fiber line to be tested, 7-photodetector II, 8-n Bit ADC II, 9-photodetector I, 10-n-bit ADC I, 11-effective bit information processing system, 12-cross-correlation processing device, 13-display device, 14-N-bit decimator, 15-decimal converter, 16 - Sampling points.

Detailed ways

The present invention will be further described below in conjunction with specific embodiments.

A subsequent processing method for improving the resolution of a chaotic optical time domain reflectometer, comprising the following steps:

(1) The chaotic light signal emitted by the chaotic light emitting device 1 is divided into the probe light I and the reference light II through the fiber coupler 3;

(2) The detection light I is transmitted to the optical fiber line 6 to be tested through the optical circulator 5, and the detection light I retroreflected from the optical fiber line 6 to be tested is received by the photodetector I9, and the optical signal is converted into an electrical signal;

(3) The reference light II is received by the photodetector II7, and the optical signal is converted into an electrical signal;

(4) The photodetector I9 inputs the converted electrical signal of the signal reflected by the detection light I into the n-bit ADC I10 for quantization; the photodetector II7 inputs the converted electrical signal of the reference light II into the n-bit ADC II8 for quantization, Each sampling point is quantized into n binary bits;

(5) In the significant bit information processing system 11, extract the least significant bits of N bits for the two signals quantized into n binary bits, and discard the other most significant bits, where N<n;

(6) Convert the extracted significant bit result to decimal;

(7) Inputting the decimal result into the 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 this embodiment includes a chaotic optical transmitter 1 , an optical fiber coupler 3 , a photodetector, a cross-correlation processing device 12 , a display device 13 , two n-bit ADCs, and an effective-bit information processing system 11 ; The chaotic light signal emitted by the chaotic light transmitting device 1 is divided into probe light I and reference light II through the optical fiber coupler 3; The probe light I reflected back in the optical fiber line 6 to be tested is quantized by the n-bit ADC I10, and each sampling point is quantized into n binary bits and input into the effective bit information processing system 11; the reference light II is received by the photodetector II7, and the The optical signal is converted into an electrical signal, and then quantized by n-bit ADCII8. Similarly, each sampling point is also quantized into n binary bits and input into the effective bit information processing system 11; the two quantized signals are simultaneously processed in the effective bit information processing system 11. After processing, it is input to the cross-correlation processing device 12 for cross-correlation operation, and the final result is output to the display device 13 . The chaotic light emitting device 1 is a chaotic semiconductor laser, specifically an optical feedback chaotic semiconductor laser, which is composed of a semiconductor laser, a fiber coupler and a feedback device, wherein the feedback device is a digital reflectometer or an optical fiber coated with a reflective film on the end face or a grating It is formed with a tunable optical attenuator; the detection light I is amplified by the optical amplifier 4 and then transmitted to the optical fiber line 6 to be measured through the optical circulator 5; the optical circulator 5 is a fiber coupler or a beam splitter, in this embodiment A beam splitter is used; the cross-correlation processing device 12 is a digital correlator or a computer, and a digital correlator is used in this embodiment. In this embodiment, a micro optical fiber ring 2 is added after the chaotic light transmitting device 1 to increase the energy of the chaotic light in the low frequency part, and the frequency 1/T of the micro optical fiber ring 2 is greater than the PD bandwidth; the effective bit information processing in this embodiment The system 11 is a hardware device composed of an N-bit decimator 14 and a decimal converter 15 .

The specific operation of this embodiment is as follows: after the chaotic laser signal generated by the chaotic semiconductor laser passes through the miniature optical fiber ring 2 to increase the energy of the low-frequency part of the chaotic light source, it is divided into two paths through the fiber coupler 3: the detection light I and the reference light II; the detection light I passes through the The optical amplifier 4 is transmitted to the optical fiber line 6 to be tested through the optical circulator 5, and the echo signal scattered or reflected in the line is converted into an electrical signal by the photodetector I9, as shown in Figure 2, quantized by the n-bit ADC I10, each time The sampling points 16 are quantized into n binary bits; the reference light II is directly irradiated to the photodetector II7, and then quantized by the n-bit ADC II8, and each sampling point 16 is also quantized into n binary bits; The signal is input to the significant bit information processing system 11 (ie, the N-bit decimator 14 and the decimal converter 15), and the lower N (N<n) significant bits are extracted and converted into decimal (for example, in FIG. 2, n=8, Extract the low N bits, N=6, which is the extraction of the lower 6 bits in the frame, and discard the extraction of the upper two bits), and then perform the cross-correlation operation on the two signals in the digital correlator to obtain the optical fiber line loss and distance. relationship, display the measurement results through the display device 13, and realize high-precision fault location and detection of optical fiber transmission characteristics. Figure 3 is a comparison diagram of the cross-correlation graphs for extracting different significant bits of information under the same conditions. The lower 8-bit processing is wider than the FWHM (full width at half maximum) of the lower 7-bit processing, which proves that the lower 7-bit extraction processing is higher than the lower 8-bit extraction processing. resolution is significantly higher.

In practical applications, n-bit ADC I10 and n-bit ADC II8 can be determined according to actual needs and costs; similarly, when extracting low-N (N<n) significant bits in an effective-bit information processing system, the size of N is also based on actual needs. , signal quality, so that high-precision resolution measurements can be achieved in different situations.

The scope of protection of the present invention is not limited to the above specific embodiments, and for those skilled in the art, the present invention may have various modifications and changes, any modifications, improvements and equivalents made within the concept and principle of the present invention All replacements should be included within the protection scope of the present invention.

Claims (1)

1. a subsequent processing method for improving the resolution of a chaotic optical time domain reflectometer, comprising the steps: (1) The chaotic light signal emitted by the chaotic light emitting device (1) is divided into the probe light I and the reference light II through the fiber coupler (3); (2) The probe light I is transmitted to the optical fiber line (6) to be tested through the optical circulator (5), and the probe light I retroreflected from the optical fiber line (6) to be tested is received by the photodetector I (9), Convert from optical signal to electrical signal; (3) The reference light II is received by the photodetector II (7), and the optical signal is converted into an electrical signal; It is characterized by: (4) The photodetector I (9) inputs the converted electrical signal from the signal reflected back by the detection light I into the n-bit ADC I (10) for quantization; the photodetector II (7) converts the electrical signal converted from the reference light II to The signal is input to the n-bit ADC II (8) for quantization, and each sampling point is quantized into n binary bits; (5) In the significant bit information processing system (11), extract the least significant bits of N bits for the two signals quantized into n binary bits, and discard the other most significant bits, where N<n; (6) Convert the extracted significant bit result to decimal; (7) Inputting the decimal result into the cross-correlation processing device (12) for cross-correlation operation; (8) The calculated result is output to the display device (13).

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