CN103727969B - Based on delay pulse Raman amplifiction distributed sensing system - Google Patents

Abstract

The invention discloses a kind of based on delay pulse Raman amplifiction distributed sensing system, including narrow linewidth light source, raman pump light source, the first modulation module being connected with narrow linewidth light source and the second modulation module being connected with raman pump light source, described first modulation module passes sequentially through EDFA Erbium-Doped Fiber Amplifier, circulator is connected with wavelength division multiplexer, described second modulation module is directly connected with wavelength division multiplexer, described wavelength division multiplexer connects sensor fibre, connected by signal generator between described first modulation module and the second modulation module, described circulator passes through wave filter and detector, data acquisition module, computer is sequentially connected with.The present invention realizes the longer effective distance sensing of detection light by having the impulse modulation pumping Raman amplification of certain time-delay amount.

Description

Distributed Sensing System Based on Delayed Pulse Raman Amplification

technical field

The invention relates to the technical field of optical fiber sensing, in particular to a distributed sensing system based on time-delayed pulse Raman amplification.

Background technique

With the development of society, people's dependence on information is becoming more and more serious, and the demand for information transmission is rapidly expanding. The capacity of existing optical fiber systems has been greatly increased, and the simple transmission distance of non-electric regenerative relay has been increased. hot spot. In this context, Raman amplifiers have attracted extensive attention due to their inherent low-noise and wide-bandwidth characteristics.

The so-called Raman amplification is to transfer a part of the incident light power to the Stokes wave with a lower frequency than it. If a weak signal wave and a strong pump light wave are transmitted in the optical fiber at the same time, and the weak signal wavelength is placed in the pump Within the Raman gain bandwidth of light, the signal light can be amplified.

Isotropic pumped distributed Raman amplification has been widely used in the distance extension of time-domain reflectance distributed sensing systems, but its characteristic is that the amplification effect is most significant near the pump end, resulting in the amplified detection light being very large. The linear effect accumulates rapidly near the pump end, thereby deteriorating the quality of the detection optical signal, and further affecting the extension of the sensing distance.

Types of distributed sensing systems include: Phase Sensitive Optical Time Domain Reflectometer (Ф-OTDR), Polarization Sensitive Optical Time Domain Reflectometer (POTDR) and Brillouin Optical Time Domain Reflectometer (BOTDR), etc. The distributed sensing system has many advantages such as anti-electromagnetic interference, high sensitivity, and long measurement distance. It has irreplaceable advantages in anti-invasion of long-distance perimeters such as oil pipelines, airports, and national borders. In order to extend the sensing distance and improve the sensitivity, the existing distributed sensing system generally adopts the method of increasing the Raman pump power, but simply increasing the Raman pump power may easily cause abnormalities such as self-phase modulation and modulation instability. The generation of linear effect reduces the signal-to-noise ratio and limits the sensing distance.

Contents of the invention

The object of the present invention is to solve the above-mentioned problems and provide a distributed sensing system that achieves a longer effective sensing distance of detection light through pulse modulation pump Raman amplification with a certain delay.

The technical scheme that the present invention adopts is as follows:

The invention provides a distributed sensing system based on time-delayed pulse Raman amplification, which includes a narrow linewidth light source, a Raman pump light source, a first modulation module connected to the narrow linewidth light source and a Raman pump light source connected The second modulation module, the first modulation module is connected to the wavelength division multiplexer through the erbium-doped fiber amplifier and the circulator in turn, the second modulation module is directly connected to the wavelength division multiplexer, and the wavelength division multiplexer The sensing optical fiber is connected, the first modulation module and the second modulation module are connected through a signal generator, and the circulator is sequentially connected with a detector, a data acquisition module and a computer through a filter.

The above scheme is further optimized, the circulator has port one, port two and port three, the port one is connected to the erbium-doped fiber amplifier, the port two is connected to the wavelength division multiplexer, and the port three is connected to the filter device connection.

As a further preference for the above solution, the signal generator generates a signal to simultaneously trigger the first modulation module and the second modulation module to generate two optical pulse modulation signals with the same frequency, and the pump light output by the Raman pumping light source passes through the second A modulation module generates a pump pulse with a certain amount of time delay and then enters the wavelength division multiplexer. The detection light output by the narrow linewidth light source is generated by the second modulation module and amplified by an erbium-doped optical fiber amplifier. The detection pulse enters the wavelength division multiplexer through the circulator, and the wavelength division multiplexer couples the pump pulse and the detection pulse into the sensing fiber for propagation. When it propagates to a specific position of the sensing fiber, the pump pulse starts Coincident with the detection pulse, starting from this specific position, the detection pulse will be continuously amplified by the pump pulse, and the detection pulse will continuously undergo Rayleigh scattering in the opposite direction of the propagation direction during the propagation process, and the scattered light will enter the filter through port three of the circulator The influence of noise is filtered by the filter, and the scattered light after filtering the noise enters the detector for photoelectric conversion, and the data of photoelectric conversion is collected by the data acquisition module and sent to the computer for analysis and processing to obtain the characteristics of the scattered light.

To further optimize the above solution, the delay of the pump pulse depends on the relative walk-off degree of the probe light and the pump light and the specific parameters of the sensing system, and is controlled by the control program or delay line of the signal generator.

To further optimize the above scheme, in order to ensure that the probe light is sufficiently distributed Raman amplification, the pulse width of the pump pulse should be significantly larger than that of the probe light, that is, in order to ensure that the pump pulse can continue to interact with the probe pulse after it meets the probe pulse. The detection pulse coincides until the end of the sensing fiber, so it is necessary to use two modulation modules to modulate the detection light and pump light respectively to generate detection pulse and pump pulse with different pulse widths.

In summary, owing to adopting above-mentioned technical scheme, the beneficial effect of the present invention is:

1. The present invention adopts the pulse-pumped Raman amplification with a certain amount of delay to replace the traditional continuous light-pumped Raman amplification, and performs pulse modulation on the probe light and the pump light respectively, and generates a certain delay between the two The amount of time; the detection pulse amplified by the erbium-doped fiber amplifier is strong enough in the front section of the sensing fiber and does not need to be amplified. With the extension of the sensing distance, the detection pulse intensity decreases. The stimulated Raman scattering between the pulse and the detection pulse ensures that the detection pulse has a strong enough signal on the longer sensing fiber, and at the same time slows down the broadening of the detection pulse spectrum and ensures the coherence of the detection light. The impact of small nonlinear effects.

2. According to the relevant data, simulate the power distribution of the probe light along the optical fiber. When the Raman pump and probe light start to act at 0km and 10km respectively, set the corresponding peak power of the probe light to 337mW and 500mW respectively. , and the powers injected into the pumps are 1110mW and 600mW respectively. It is calculated that the nonlinear phase shift of the system is significantly smaller than that of continuous light Raman amplification, that is, the nonlinear cumulative effect caused by the system is small, which is conducive to reducing the broadening of the detection light pulse spectrum and ensuring the coherence of the detection light, thereby prolonging the It improves the sensing distance of detecting light and has important practical value.

Description of drawings

The invention will be illustrated by way of example with reference to the accompanying drawings, in which:

Fig. 1 is the structure schematic diagram based on the time-delayed pulse Raman amplification distributed sensing system of the present invention;

Fig. 2 is a schematic diagram of the interaction between the pump pulse and the detection pulse with a delay amount in an embodiment of the present invention;

Fig. 3 is a power distribution diagram of probe light when pump light is injected at different positions in an embodiment of the present invention.

In Figure 1: 1 is the narrow linewidth light source; 2 is the Raman pump light source; 3 is the first modulation module; 4 is the erbium-doped fiber amplifier

Amplifier; 5 is a signal generator; 6 is a second modulation module; 7 is a wavelength division multiplexer; 8 is a sensing fiber; 9 is a circulator; 10

11 is a detector; 12 is a data acquisition module; 13 is a computer.

detailed description

The present invention will be described in detail below in conjunction with the accompanying drawings.

As shown in Figure 1, it is a schematic structural diagram of a distributed sensing system based on time-delayed pulse Raman amplification according to the present invention,

The system includes a narrow linewidth light source 1, a Raman pump light source 2, a first modulation module 3 connected to the narrow linewidth light source 1 and a second modulation module 6 connected to the Raman pump light source 2, the first modulation The module 3 is connected to the wavelength division multiplexer 7 through the erbium-doped fiber amplifier 4 and the circulator 9 in turn, and the second modulation module 6 is directly connected to the wavelength division multiplexer 7, and the wavelength division multiplexer 7 is connected to the sensor An optical fiber 8, the first modulation module 3 and the second modulation module 6 are connected through a signal generator 5, and the circulator 9 is connected with a detector 11, a data acquisition module 12, and a computer 13 in sequence through a filter 10.

The circulator 9 has port one, port two and port three, the port one is connected to the erbium-doped fiber amplifier 4 , the port two is connected to the wavelength division multiplexer 7 , and the port three is connected to the filter 10 .

The signal generator 5 generates a signal and simultaneously triggers the first modulation module 3 and the second modulation module 6 to generate two optical pulse modulation signals with the same frequency, and the pump light output by the Raman pump light source 2 passes through the first modulation module 3 After generating a pump pulse with a certain amount of delay, it enters the wavelength division multiplexer 7, and the detection light output by the narrow linewidth light source 1 passes through the second modulation module 6 to generate a detection pulse and is amplified by the erbium-doped fiber amplifier 4, The amplified detection pulse enters the wavelength division multiplexer 7 through the circulator 9, and the wavelength division multiplexer 7 couples the pump pulse and the detection pulse into the sensing fiber 8 for propagation, and propagates to a specific part of the sensing fiber 8. position, the pump pulse begins to coincide with the detection pulse. From this specific position, the detection pulse will continue to be amplified by the pump pulse, and the detection pulse will continuously undergo Rayleigh scattering in the opposite direction of propagation during the propagation process, and the scattered light will pass through Port 3 of the circulator 9 enters the filter 10 to filter out the influence of noise, and the scattered light after filtering the noise enters the detector 11 for photoelectric conversion, and the photoelectric conversion data is collected by the data acquisition module 12 and sent to the computer 13 for analysis Processing derives the properties of the scattered light.

In the above solution, the pulse width of the generated periodic pump pulse mainly depends on the length of the sensing fiber 8 .

The delay of the pump pulse depends on the relative walk-off degree of the probe light and the pump light and the specific parameters of the sensing system, and is controlled by the control program or delay line of the signal generator 5 .

The amplification of the probe pulse is closely related to the amount of delay of the pump pulse.

Due to the group velocity dispersion in the sensing fiber 8 and the frequency difference between the pump light and the probe light, there is a gap in the propagation speed between the pump pulse and the probe pulse, so the pump can be tuned by setting the delay The position where the pulse and the probe pulse coincide in the sensing fiber 8 .

In order to ensure sufficient distributed Raman amplification of the probe light, the pulse width of the pump pulse should be significantly larger than that of the probe light, that is, to ensure that the pump pulse can continuously coincide with the probe pulse after meeting the probe pulse until the sensing fiber At the end, it is necessary to use two modulation modules to modulate the probe light and the pump light respectively to generate probe pulses and pump pulses with different pulse widths.

Example

In order to illustrate the nonlinear effect caused by increasing the pump power more specifically, take a 50km G.652 optical fiber as an example. Because pulses of different wavelengths are transmitted at different speeds in the fiber, the 1550nm probe light and the 1455nm pump light have a group velocity mismatch. This characteristic leads to the walk-off phenomenon. The dispersion parameter is: Therefore, for the faster pump pulse to interact with the slower probe pulse, it is necessary to ensure that there is a certain delay in the pump pulse. Taking the time delay of 10ns as an example, the pump pulse will undergo stimulated Raman scattering with the detection pulse at 10km, thereby amplifying the detection optical signal. Fig. 2 is a schematic diagram of the interaction between the pump pulse and the probe pulse with a delay amount.

In order to further illustrate that the distributed sensing system based on delayed pulse Raman amplification helps to reduce the nonlinear effect, the coincidence of the pump pulse and the detection pulse is delayed to 10km, and the coincidence of the pump pulse and detection pulse at 0km Compared with the effect of pulse generation (that is, the pump light is continuous light), the relevant data is simulated by computer, and the power distribution diagram of the 1550nm probe light is obtained, as shown in Figure 3. At this time, when the Raman pump and probe light start to interact at 0km and 10km, the corresponding peak powers of the probe light are 337mW and 500mW respectively, and the powers injected into the pump are 1110mW and 600mW respectively.

According to the calculation formula of nonlinear phase shift:

It is calculated that: the nonlinear phase shift of Raman amplification starting from 0km is ${\mathrm{\φ}}_0=2W^{-1}/km\×\underset{0}{\overset{Z}{\∫}}p\left(L\right)dL=46.020;$ The nonlinear phase shift of Raman amplification starting at 10km is

It can be seen that the nonlinear phase shift caused by the injection of the pump pulse with a delay of 10 ns is obviously smaller than that of the continuous injection of the pump light.

The nonlinear phase shift caused by continuous light, that is, the influence of spectrum broadening caused by nonlinear effects is small, which is conducive to the realization of longer distance optical fiber sensing.

The present invention is not limited to the foregoing specific embodiments. The present invention may extend to any new feature or any new combination disclosed in this specification, as well as any new method or process step or any new combination disclosed.

Claims (1)

1. one kind based on delay pulse Raman amplifiction distributed sensing system, it is characterised in that: include narrow linewidth light source (1), draw The first modulation module (3) that graceful pump light source (2) is connected with narrow linewidth light source (1) and be connected with raman pump light source (2) Two modulation modules (6), described first modulation module (3) passes sequentially through EDFA Erbium-Doped Fiber Amplifier (4), circulator (9) with wavelength-division again Connecting with device (7), described second modulation module (6) is directly connected with wavelength division multiplexer (7), and described wavelength division multiplexer (7) connects Sensor fibre (8), is connected by signal generator (5) between described first modulation module (3) and the second modulation module (6), institute State circulator (9) to be sequentially connected with detector (11), data acquisition module (12), computer (13) by wave filter (10)；Institute Stating circulator (9) and have port one, port two and port three, described port one is connected with EDFA Erbium-Doped Fiber Amplifier (4), described end Mouth two is connected with wavelength division multiplexer (7), and described port three is connected with wave filter (10).