An optical fiber link detection system and method based on digital modulation signal

A digital linear and frequency modulation signal technology, applied in the transmission system, electromagnetic wave transmission system, electrical components, etc., can solve the problems of high cost, conflict between dynamic range and measurement resolution, and achieve the effect of increasing equipment cost

Inactive Publication Date: 2018-12-18

WUHAN POST & TELECOMM RES INST CO LTD

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AI-Extracted Technical Summary

Problems solved by technology

[0006] The technical problem to be solved by the present invention is that the existing optical time domain ref...

Method used

Because each digital chirp light pulse is the same to the detection curve of the same detected optical fiber, therefore, the present invention's solution superimposes the detection results of the chirp signals of different frequency modulation ranges, which is equivalent to multiple detection The results are averaged to further reduce the noise and improve the accuracy of the detection results.

Compared with prior art, the scheme provided by the present invention, the distance resolution of optical fiber detection is determined by the frequency sweep range of chirp signal, and has nothing to do with pulse width, thus can realize by sending a wider pulse Large dynamic ...

Abstract

The invention discloses an optical fiber link detection system and a method based on a digital linear frequency modulation signal. The system comprises a digital modulation signal generator, a circulator and a receiver. The digital modulation signal generator is used for generating a detection signal in the form of a digital modulation optical pulse and injecting the detected optical fiber throughthe circulator. The receiver extracts the detected optical fiber features carried by the detection signal from the backscattered signal. The invention utilizes the characteristic that the linear frequency modulation signal has excellent energy gathering in the fractional Fourier domain, by using digital LFM optical pulse as detection signal, LFM signals with different FM ranges are separated fromnoise in backscattered signals, and the characteristics of detected optical fiber are extracted, which can improve the dynamic range and measurement range resolution of optical fiber link detection simultaneously without increasing the cost.

Application Domain

Electromagnetic transmission

Technology Topic

PhysicsVIT signals +8

Image

Examples

Experimental program(5)

Example Embodiment

[0049] Specific Example 1.

[0050] like figure 1 As shown, the optical fiber link detection system based on a digital chirp signal provided by the specific embodiment 1 of the present invention includes a digital chirp signal generator 10 , a circulator 20 and a receiver 30 .

[0051] The digital chirp signal generator 10 is used to generate a digital chirp signal as a detection signal, and convert it into an optical pulse and inject it into the optical fiber 40 to be detected. In this specific embodiment, the digital chirp signal generator 10 is composed of a pulsed laser 11 and a laser controller 12 . The pulsed laser 11 is used to generate pulsed optical signals, and the laser controller 12 uses the periodic digital linear frequency modulation electrical signal generated by the FPGA to control the pulsed laser 11 to generate corresponding optical pulses through the driver, and is injected into the detected optical fiber 40 by the circulator 20 (transmission fiber).

[0052] On the one hand, the circulator 20 injects light pulses into the detected optical fiber 40 , and on the other hand simultaneously receives the backscattered signal of the detected signal reflected by the detected optical fiber, and inputs it into the receiver 30 .

[0053] After receiving the backscattered signal input by the circulator 20, the receiver 30 digitizes the backscattered signal, and extracts the detected optical fiber characteristics carried by the detection signal, such as the transmission loss of the optical fiber, the attenuation of the connector, and the optical fiber. Fiber characteristics such as length and breakpoints.

[0054] In the present invention, the detection signal is a digital linear frequency modulation signal. In order to realize optical fiber detection, the pulse laser is controlled by the digital linear frequency modulation electrical signal to generate a corresponding optical pulse signal, and the optical pulse signal reflected by the detected optical fiber is transmitted in the receiver through the photoelectric signal. The detector is restored to a digital chirp signal, and the digital chirp signal is analyzed and processed. That is to say, in the solution of the present invention, the optical pulse signal is transmitted in the optical fiber, and the digital chirp signal is processed by the receiver to perform fractional Fourier transformation.

[0055] In this specific embodiment, the laser controller 12 may be implemented by a single-chip microcomputer or an FPGA, such as the FPGA chip Cyclone V of Altera Corporation.

[0056] The period of the digital chirp signal is T, because the period T will be limited by the length of the detected fiber, therefore, the period T should satisfy Where: c is the speed of light in vacuum, L is the length of the detected fiber, n is the average refractive index of the detected fiber.

[0057] The circulator 3 can use an optical circulator in the C+L band, such as the circulator CIR-3-1550-A-025-1-APC produced by Accelerator Technology.

[0058] Compared with the prior art, in the solution provided by the present invention, the distance resolution of optical fiber detection is determined by the sweep frequency range of the chirp signal, and has nothing to do with the pulse width, so a relatively wide pulse can be sent to achieve a large dynamic range. At the same time, the range resolution can be improved by increasing the frequency sweep range, which solves the conflicting problem between the dynamic range and the measurement range resolution of the traditional optical time domain reflectometer.

[0059] In addition, the digital chirp signal can be directly generated by the pulsed laser controlled by the laser controller through the chirp electrical signal, that is, directly generated by the direct modulated laser, without additional optical and electronic equipment, so the equipment cost will not be increased.

[0060] The mathematical expression of the digital chirp electrical signal s(t) is:

[0061] s(t)=Arect(t/T 0 )sign(cos(2π(f 0 t+μt 2 /2))).

[0062] Among them, A is the pulse amplitude of the chirp electrical signal, rect is the rectangular window function, t is the time independent variable of the chirp electrical signal, T 0 is the length of the chirp electrical signal, sign is a discrete function, indicating that the digital signal is obtained by this function, f 0 is the center frequency of the chirp electrical signal, and μ is the FM slope of the chirp electrical signal. like figure 2 Shown is a time domain diagram of a linear frequency modulated electrical signal.

Example Embodiment

[0063] Specific Example 2.

[0064] In the specific embodiment 2 of the present invention, the receiver 30 includes a reflected signal receiving unit 31 and a digital signal processing unit 32 . The reflected signal receiving unit 31 is configured to receive the backscattered signal output from the circulator 20 , convert it into a digital signal, and transmit it to the digital signal processing unit 32 . The digital signal processing unit 32 is configured to receive the digital signal output by the reflected signal receiving unit 31, and extract the fiber characteristics of the detected fiber carried on the chirp signal from the digital signal.

[0065] Further, the digital signal processing unit 32 uses the fractional Fourier transform algorithm to separate the chirp signals of different frequency modulation ranges from noise, respectively extracts the chirp signals of different frequency modulation ranges, and superimposes them to output the curve track of the detection signal. As an output result, the detected fiber characteristics carried by the detection signal are thus obtained.

[0066] In this specific embodiment, the reflected signal receiving unit 31 may be implemented by an avalanche photodiode (APD), such as an avalanche photodiode APD110C produced by Thorlabs. The digital signal processing unit 32 can be implemented by a digital signal processing (DSP) chip, such as a DSP chip TMSC6657 produced by TI.

Example Embodiment

[0067] Specific Example 3.

[0068] like image 3 As shown, the reflected signal receiving unit 31 includes a photodetector 311, an amplifying filter circuit 312, and an analog-to-digital converter 313. The photodetector 311 is used to convert the backscattered signal from the circulator 20 into an analog electrical signal, and the amplifying and filtering circuit 312 is used to amplify the analog electrical signal output by the photodetector 311 to filter out part of the noise, and the analog-to-digital converter 313 is used to convert the analog electrical signal into a digital electrical signal for subsequent digital signal processing. Thus, the conversion of photoelectric signal to digital signal is realized, and a part of noise is filtered out, and the signal quality is improved.

PUM

Description & Claims & Application Information

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