阅读说明：本技术 基于强度调制啁啾脉冲压缩的分布式光纤拉曼温度传感器 (Distributed optical fiber Raman temperature sensor based on intensity modulation chirp pulse compression ) 是由 何祖源 樊昕昱 周铂承 于 2020-06-05 设计创作，主要内容包括：一种基于强度调制啁啾脉冲压缩的分布式光纤拉曼温度传感器,包括依次相连的强度调制啁啾脉冲信号发生模块、传感光纤、光电探测模块和温度信号解析模块,其中：强度调制啁啾脉冲信号发生模块生成四部分强度调制啁啾脉冲信号并输出至传感光纤,经自发拉曼散射并在传感光纤的各个位置均产生背向传输的反斯托克斯光和斯托克斯光,籍由光电探测模块得到对应电信号,温度信号解析模块根据电信号进行模数转换及线性变换得到四部分拉曼散射光强数据,再经匹配滤波和解调计算得到光纤沿线的温度数据。本发明采用了强度调制啁啾脉冲压缩技术显著降低系统成本,实现较低成本高性能RDTS系统,并为高空间分辨率RDTS系统的实现奠定基础。(The utility model provides a distributed optical fiber Raman temperature sensor based on intensity modulation chirp pulse compression, includes that intensity modulation chirp pulse signal that links to each other in proper order takes place module, sensing optical fiber, photoelectric detection module and temperature signal and analyzes the module, wherein: the intensity modulation chirp pulse signal generation module generates four parts of intensity modulation chirp pulse signals and outputs the four parts of intensity modulation chirp pulse signals to the sensing optical fiber, anti-Stokes light and Stokes light which are transmitted in a back direction are generated at each position of the sensing optical fiber through spontaneous Raman scattering, a corresponding electric signal is obtained through the photoelectric detection module, the temperature signal analysis module carries out analog-to-digital conversion and linear conversion according to the electric signal to obtain four parts of Raman scattering light intensity data, and the temperature data along the optical fiber is obtained through matched filtering and demodulation calculation. The invention adopts the strength modulation chirp pulse compression technology to obviously reduce the system cost, realizes the RDTS system with lower cost and high performance, and lays a foundation for the realization of the RDTS system with high spatial resolution.)

1. A distributed fiber Raman temperature sensor based on an intensity modulation chirped pulse compression technology is characterized by comprising: intensity modulation chirp pulse signal generation module, sensing optical fiber, photoelectric detection module and the analytic module of temperature signal that link to each other in proper order, wherein: the intensity modulation chirp pulse signal generation module generates four parts of intensity modulation chirp pulse signals and outputs the four parts of intensity modulation chirp pulse signals to the sensing optical fiber, anti-Stokes light and Stokes light which are transmitted in a back direction are generated at each position of the sensing optical fiber through spontaneous Raman scattering, a corresponding electric signal is obtained through the photoelectric detection module, the temperature signal analysis module carries out analog-to-digital conversion and linear conversion according to the electric signal to obtain light intensity data of the four parts of Raman scattering, and then the temperature data along the optical fiber is obtained through matched filtering and demodulation calculation;

the four parts of intensity modulated chirped pulse signals are respectively as follows:

wherein: tau is_pFor pulse width, rect is a rectangular window function, f₀For sweep center frequency, k is sweep rate.

2. The distributed fiber raman temperature sensor according to claim 1, wherein said temperature signal analyzing module comprises: analog-to-digital conversion unit, matched filter unit and demodulation unit, wherein: the analog-to-digital conversion unit is connected with the output end of the photoelectric detection module and transmits Raman scattered light waveform information, the matched filtering unit is connected with the output end of the analog-to-digital conversion unit and outputs a response signal after matched filtering, and the demodulation unit is connected with the output end of the matched filtering unit and outputs temperature information.

3. The temperature detection method of the distributed fiber Raman temperature sensor based on the intensity modulation chirped pulse compression according to claim 1 or 2, characterized by comprising the following implementation steps:

step one, building a distributed optical fiber Raman temperature sensor system based on an intensity modulation chirp pulse compression technology;

secondly, starting a system, wherein laser emitted by a laser is modulated into a chirp pulse signal with four parts of intensity modulation through an intensity modulator controlled by an array waveguide grating; the optical signal is amplified by the erbium-doped fiber amplifier and then is transmitted to the sensing fiber by the wavelength division multiplexer; spontaneous Raman scattering occurs when the optical signal propagates in the sensing optical fiber, so that anti-Stokes light and Stokes light which are transmitted back are generated at each position of the sensing optical fiber; the four chirp optical pulse signals are:

wherein: tau is_pFor pulse width, rect is a rectangular window function, f₀The frequency sweep center frequency is defined as k, and the frequency sweep rate is defined as k;

thirdly, when the external temperature changes to act on the sensing optical fiber, the avalanche photodetector acquires respective Raman scattering Stokes light and anti-Stokes light of the four pulses and performs analog-to-digital conversion and linear conversion through the data acquisition card;

and step four, the signal processing module performs matched filtering and demodulation calculation according to the four parts of Raman scattering light intensity data obtained in the step three to obtain temperature data along the optical fiber.

4. The method of claim 3, wherein the linear transformation is: wherein: y is_k(t), k is 1,2,3,4, which are the reflection signals of the first to fourth partial optical signals, respectively, and the equivalent incident optical signal i (t) is represented by the four segments of incident optical signals, specifically:

5. the method as claimed in claim 3, wherein the matched filtering is performed by: the electric signal obtained by converting the Raman scattering optical signal through the photoelectric detector is correlated with the local matched filter, so as to obtain the actual reflectionLight intensityWherein: i is^*(-t) is a matched filter, which is a specific value of the modulation signal i (t).

6. The method of claim 3, wherein the demodulation calculation is:

Technical Field

The invention relates to a technology in the field of optical fiber sensing, in particular to a distributed optical fiber Raman temperature sensor based on intensity modulation chirp pulse compression.

Background

Raman Distributed Temperature Sensors (RDTS) are capable of obtaining a variety of measurement information across the sensing fiber. The positioning principle of RDTS systems is based on Optical Time Domain Reflectometry (OTDR), where optical pulses are sent to an optical fiber, and the backscattered light is detected and analyzed. In RDTS, the backscattered light consists of anti-stokes, stokes and rayleigh scattered light. The intensity of the anti-stokes light is temperature dependent, while the amplitude of the stokes light is hardly affected by temperature. Therefore, by obtaining the ratio of anti-stokes light to stokes light, temperature information along the fiber can be obtained and the effects of local losses and laser power variations on system stability can be eliminated.

In RDTS systems, both the anti-Stokes light and the Stokes light are very weak. Therefore, in order to increase the sensing distance, a high power laser or an erbium-doped fiber amplifier (erbium-doped fiber amplifier) is generally used to enhance the optical power launched into the fiber. Increasing the pulse width can increase the optical power launched into the fiber, but the system spatial resolution can be degraded as a result. On the other hand, the maximum optical power that can be injected into an optical fiber is limited by certain nonlinear effects such as Stimulated Raman Scattering (SRS). A new pulse compression modulation format is urgently needed at the present stage, the problem that the spatial resolution and the temperature resolution are mutually restricted in the RDTS system can be better solved, and a foundation is laid for realizing the high-spatial-resolution RDTS system; and the influence of the transient effect of the erbium-doped fiber amplifier in the Simplex coding technology on the system can be avoided, and the cost of the system is reduced.

Disclosure of Invention

The invention provides a distributed fiber Raman temperature sensor based on intensity modulation chirp pulse compression, which aims at the problems that the spatial resolution and the temperature resolution of the existing RDTS system are mutually restricted and the existing system based on Simplex coding is influenced by the transient effect of an erbium-doped fiber amplifier to cause the complex structure of the system.

The invention is realized by the following technical scheme:

the invention relates to a distributed optical fiber Raman temperature sensor based on an intensity modulation chirped pulse compression technology, which comprises an intensity modulation chirped pulse signal generation module, a sensing optical fiber, a photoelectric detection module and a temperature signal analysis module which are sequentially connected, wherein: the intensity modulation chirp pulse signal generation module generates four parts of intensity modulation chirp pulse signals and outputs the four parts of intensity modulation chirp pulse signals to the sensing optical fiber, anti-Stokes light and Stokes light which are transmitted in a back direction are generated at each position of the sensing optical fiber through spontaneous Raman scattering, a corresponding electric signal is obtained through the photoelectric detection module, the temperature signal analysis module carries out analog-to-digital conversion and linear conversion according to the electric signal to obtain four parts of Raman scattering light intensity data, and the temperature data along the optical fiber is obtained through matched filtering and demodulation calculation.

The four parts of intensity modulated chirped pulse signals are respectively as follows:

wherein: tau is_pFor pulse width, rect is a rectangular window function, f₀For sweep center frequency, k is sweep rate.

The temperature signal analysis module comprises: analog-to-digital conversion unit, matched filter unit and demodulation unit, wherein: the analog-to-digital conversion unit is connected with the output end of the photoelectric detection module and transmits Raman scattered light waveform information, the matched filtering unit is connected with the output end of the analog-to-digital conversion unit and outputs a response signal after matched filtering, and the demodulation unit is connected with the output end of the matched filtering unit and outputs temperature information.

Technical effects

The invention integrally solves the problems that the mutual restriction of the spatial resolution and the temperature resolution in the RDTS system causes the inherent contradiction between the spatial resolution and the temperature resolution in the system and the performance is limited, and the problems that the Simplex coding-based system is influenced by the transient effect of the erbium-doped fiber amplifier, the system structure is complex and the cost is high.

Compared with the prior art, the method has good performance in the aspects of spatial resolution and temperature resolution, and can meet the industrial requirements of most RDTS systems; only one modulator and one laser are used, so that the system is simple in structure, low in cost and high in measuring speed; firstly, an intensity modulation chirped pulse compression technology is adopted in the RDTS system in the light intensity domain, and the RDTS system has the potential of realizing a high spatial resolution ratio.

Drawings

FIG. 1 is a schematic structural view of the present invention;

FIGS. 2a and 2b are schematic diagrams illustrating effects of the embodiment;

in the figure: 1 laser, 2 polarization controller, 3 array waveguide grating, 4 wavelength division multiplexer, 5 avalanche photodetector, 6 data acquisition card, 7 signal processing module, 8 erbium doped fiber amplifier, 9 intensity modulator, 10 sensing fiber.

Detailed Description

As shown in fig. 1, the present embodiment relates to a temperature sensing system, including: the system comprises an intensity modulator 9, an erbium-doped fiber amplifier 8, a wavelength division multiplexer 4, an avalanche photodetector 5, a data acquisition card 6, a signal processing module 7 and an arbitrary signal generator 3 which are sequentially connected to form a loop, wherein: the laser 1 outputs laser with the wavelength of 1550nm to the polarization controller 2, the polarization controller 2 outputs 1550nm signal light to an optical signal input end of the intensity modulator 9, meanwhile, any signal generator 3 outputs an electrical signal with intensity chirp modulation to a modulation signal receiving end of the intensity modulator 9, the intensity modulator 9 modulates the received 1550nm signal light according to the modulation signal output by any signal generator 3 to obtain four parts of chirp pulse signals with intensity modulation, and the four parts of chirp pulse signals are output to the erbium-doped optical fiber amplifier 8 for amplification and input to the wavelength division multiplexer 4; the wavelength division multiplexer 4 outputs the amplified four-part intensity chirp modulation optical signals to the sensing optical fiber 10, the optical signals are subjected to spontaneous Raman scattering on the sensing optical fiber 10 and generate backward-transmitted anti-Stokes light and Stokes light at each position of the sensing optical fiber and then output to the avalanche photodetector 5, the avalanche photodetector 5 conducts analog-to-digital conversion on optical signal sensing output electric signals to the data acquisition card 6 to obtain four-part Raman scattering light intensity data, and the signal processing module 7 obtains temperature data along the optical fiber through matched filtering and demodulation calculation.

The wavelength of the laser 1 is 1550 nm.

The wavelength division multiplexer 5 has a working wavelength of 1550nm/1450nm/1663 nm.

The number of channels of the avalanche photodetector 5 is 2.

The number of channels of the data acquisition card 6 is 2.

The sensing fiber 10 is a single mode fiber.

The embodiment relates to a temperature detection method based on intensity modulation chirp pulse compression of the system, which comprises the following implementation steps:

step one, building a distributed optical fiber Raman temperature sensor system based on an intensity modulation chirp pulse compression technology;

secondly, starting a system, wherein laser emitted by a laser is modulated into a chirp pulse signal with four parts of intensity modulation through an intensity modulator controlled by an array waveguide grating; the optical signal is amplified by the erbium-doped fiber amplifier and then is transmitted to the sensing fiber by the wavelength division multiplexer; spontaneous Raman scattering occurs when the optical signal propagates in the sensing optical fiber, so that anti-Stokes light and Stokes light which are transmitted back are generated at each position of the sensing optical fiber; the four chirp optical pulse signals are:

wherein: tau is_pFor pulse width, rect is a rectangular window function, f₀For sweep center frequency, k is sweep rate.

Thirdly, when the external temperature changes to act on the sensing optical fiber, the avalanche photodetector acquires respective Raman scattering Stokes light and anti-Stokes light of the four pulses and performs analog-to-digital conversion and linear conversion through the data acquisition card;

the linear transformation is as follows:

wherein: y is_k(t), k is 1,2,3,4, which are the reflection signals of the first to fourth partial optical signals, respectively, and the equivalent incident optical signal i (t) is represented by the four segments of incident optical signals, specifically:

and step four, the signal processing module performs matched filtering and demodulation calculation according to the four parts of Raman scattering light intensity data obtained in the step three to obtain temperature data along the optical fiber.

The matched filtering means that: performing correlation operation on the electrical signal obtained by converting the Raman scattering optical signal by the photoelectric detector and the local matched filter to obtain the actual reflected light intensityWherein: i x (-t) is a matched filter, which is a specific value of the modulated signal I (t).

The demodulation calculation refers to:

wherein: t is the temperature value of the optical fiber to be measured, k is Boltzmann constant, Deltav is the Raman frequency shift of the optical fiber, h is Planck constant, p_as(T) is the anti-Stokes light intensity, p, received during measurement in the optical fiber to be measured_sT is the intensity of Stokes light received in the optical fiber to be measured, p_asT₀For the temperature of the optical fiber to be measured as the reference temperature T₀The received anti-stokes light intensity, p_sT₀For the temperature of the optical fiber to be measured as the reference temperature T₀The received stokes light intensity.

Through concrete implementationThe experiments are as follows: the tail end of the optical fiber is placed in a constant-temperature water tank with the water temperature of 50 ℃ at the room temperature of 20 ℃ for about 100 m; tau is_pThe pulse width is selected to be 3us, the sweep frequency range is selected to be 70MHz, the length of the temperature measuring optical fiber is 24km, the spatial resolution of 1.6m and the temperature resolution of 1.8 ℃ are realized in the measuring distance of 24km, and experimental data graphs are shown in fig. 2a and fig. 2 b.

Compared with the prior art, the device only adopts one intensity modulator to modulate the optical signal, and has the advantage of lower cost compared with other coding-based systems. The system adopts a novel modulation method based on the intensity modulation chirp pulse signal while the cost is low, excellent comprehensive performance is realized, performance indexes such as spatial resolution, temperature resolution and the like are better represented, the spatial resolution of 1.6m and the temperature resolution of 1.8 ℃ are in the leading level in the prior art, and the system has obvious advantages compared with the same type of products.

The foregoing embodiments may be modified in many different ways by those skilled in the art without departing from the spirit and scope of the invention, which is defined by the appended claims and all changes that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.