The application claims priority to Chinese patent application No. 202010888238.8, filed on Aug. 28, 2020, the entire contents of which are incorporated herein by reference.
The present invention relates to the technical field of optical sensing, and more particularly, to a distributed pulsed light amplifier based on optical fiber parameter amplification, and an amplification and performance characterization method.
Optical fibers have the characteristics of on-site passive performance, anti-electromagnetic interference, corrosion resistance, strong adaptability to harsh environments, low signal transmission loss, high security in the transmission process, the capability of integrating tens of thousands of sensing units in one optical fiber, and the like, and are especially suitable for long-term uninterrupted monitoring of super-large, long-line structures or facilities, such as high-speed railways, oil and gas pipelines, urban pipeline networks, etc.; and key fields with high requirements for information security and harsh environments, such as defense, military, aerospace and power industry.
In distributed optical fiber sensing, it is not only necessary to measure environmental physical quantities such as temperature, strain and vibration, but also to perform signal positioning. Among them, the most widely used technology is an optical time-domain reflectometry (OTDR) technology which uses pulsed light as the input, and obtains a position of a sensing point by inversion calculation by using a time at which a back-transmitted sensing signal returns to an input terminal, thereby achieving positioning of the sensing signal. Since the sensing signal is generated by input pulsed light, when the optical fiber loss and environmental noise cause pulse power attenuation and extinction ratio reduction after long-distance transmission, a signal-to-noise ratio of the sensing signal will be degraded, resulting in a decrease in the sensing accuracy. Originating from the optical fiber itself, the signal-to-noise ratio of the sensing signal can be increased by enhancing the scattering efficiency. However, enhanced scattering will inevitably lead to an increase in optical fiber transmission loss, limiting an optical fiber transmission distance. The signal-to-noise ratio of the sensing signal can also be increased by using an optical fiber grating to enhance the signal reflectivity. However, such methods also cause signal crosstalk and limit the transmission distance. Another method is used to increase a signal-to-noise ratio by increasing an extinction ratio of input pulses, which mainly depends on an optical modulator or a multi-level optical modulator with a higher extinction ratio. This method has the main defects of complex system and high energy consumption, and cannot fundamentally solve the problems of power attenuation and extinction ratio reduction caused by optical fiber transmission. A third method is to carry out distributed amplification, which realizes the amplification of a sensing pulse by using the amplification produced by a nonlinear scattering effect of an optical fiber, including stimulated Brillouin scattering and stimulated Raman scattering. This method has a notable signal amplification effect, not only amplifies the pulse itself, but also amplifies an area where there should be no light in a non-pulse duration interval, but actually weak light leakage appears, resulting in a decrease in a pulse extinction ratio, which eventually leads to the signal-to-noise reduction of a sensing signal. It can be seen that none of the existing methods can achieve the effect of performing distributed amplification on the pulse power and the extinction ratio at the same time.
Objects of the present invention are to provide a distributed pulsed light amplifier based on optical fiber parameter amplification, and an amplification and performance characterization method. According to the present invention, high-power pulsed light is used as pump light to generate an optical fiber parameter amplification effect near a zero-dispersion wavelength of an optical fiber, thereby amplifying a power of another sensing pulsed light. Meanwhile, due to the fact that effective optical fiber parameter amplification cannot be achieved through low-power light leakage outside a duration interval of the pump pulsed light, leaked light from the sensing pulsed light cannot be amplified, and thus the effect of amplifying a pulse extinction ratio can be achieved at the same time.
In order to fulfill said objects, the present invention designs a distributed pulsed light amplifier based on optical fiber parameter amplification, comprising a pump pulsed light source, a sensing pulsed light source, a synchronization device, a two-in-one optical coupler, an optical circulator, a parameter amplification optical fiber, a first optical filter, a photoelectric detector and a signal acquisition device, wherein outputs of the pump pulsed light source and the sensing pulsed light source are combined through the two-in-one optical coupler and then enter a first communication terminal of the optical circulator, and are output by a second communication terminal of the optical circulator and then enter the parameter amplification optical fiber; the synchronization device is used to ensure that pump pulsed light output by the pump pulsed light source and sensing pulsed light output by the sensing pulsed light source are synchronized in pulse time; the signal acquisition device is used for acquiring a pulse synchronization trigger signal for the synchronization device; a Rayleigh scattering effect in the parameter amplification optical fiber causes the pump pulsed light and the sensing pulsed light to generate scattered light in a direction opposite to a pulse transmission direction; the scattered light in the direction opposite to the pulse transmission direction is input by the second communication terminal of the optical circulator and then output by a third communication terminal of the optical circulator, and only retains a sensing pulse scattered light signal after passing through the first optical filter; the photoelectric detector is used for performing photoelectric conversion on the sensing pulse scattered light signal; the signal acquisition device is used to acquire an electric signal for the sensing pulse scattered light according to the pulse synchronization trigger signal, and obtain a signal power and a signal-to-noise ratio that vary with the length of the parameter amplification optical fiber according to the electric signal for the sensing pulse scattered light; and by adjusting a pump pulse power and a wavelength of the pump pulsed light source and a sensing pulse power and a wavelength of the sensing pulsed light source, the signal power and the signal-to-noise ratio that vary with the length of the parameter amplification optical fiber can both reach corresponding preset values of the signal power and the signal-to-noise ratio.
The present invention has the following beneficial effects:
The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.
A distributed pulsed light amplifier based on optical fiber parameter amplification as designed by the present invention, as shown in
In the above technical solution, the signal acquisition device 9 is used to calculate the signal power that varies with the length of the parameter amplification optical fiber 6 according to a time-domain variation of the electric signal for the sensing pulse scattered light and in combination with a light velocity in the parameter amplification optical fiber 6, and then calculate the signal-to-noise ratio that varies with the length of the parameter amplification optical fiber 6 in combination with a system (i.e., the amplifier in the present invention) background noise.
In the above technical solution, as shown in
In the above technical solution, the first electrical pulse source 1.3 is used to receive a synchronization control signal sent by the synchronization device 3.
In the above technical solution, as shown in
In the above technical solution, the second electrical pulse source 2.3 is used to receive a synchronization control signal sent by the synchronization device 3.
In the parameter amplification optical fiber 6, the pump pulsed light transmits energy to the sensing pulsed light through the optical fiber parameter amplification process, so as to realize distributed light amplification of the sensing pulsed light. To ensure the effectiveness of optical fiber parameter amplification, a zero-dispersion wavelength of the optical fiber should be close to and slightly smaller than the center wavelength of the pump pulsed light (usually 1 to 5 nm smaller than the pump wavelength). In order to achieve a large effective amplification distance, the transmission loss of the optical fiber subjected to parameter amplification should be as small as possible, which is preferably not higher than the transmission loss of the existing communication optical fiber.
At the same time as the parameter amplification process occurs, the Rayleigh scattering effect in the parameter amplification optical fiber 6 causes the pump pulsed light and the sensing pulsed light to generate back-transmitted scattered light, wherein a sensing pulse back-scattered light signal is a distributed optical fiber sensing signal subjected to distributed light amplification.
The first optical filter 7 is used to obtain the distributed optical fiber sensing signal subjected to distributed light amplification, which has a center wavelength of λS, and a passband range that should ensure that a sensing pulsed light scattering signal is retained, and a pump pulsed light scattering signal is completely filtered out.
The principle of using optical fiber parameter amplification to realize distributed light amplification of a sensing signal, and the specific process of characterization of distributed light amplification performance are as follows.
When the pump pulsed light and the sensing pulsed light in the above system enter a high nonlinear optical fiber at the same time, and the pump pulsed light and the sensing pulsed light are synchronized in time, the optical fiber parameter amplification occurs, the energy of the pump pulsed light is transferred to the sensing pulsed light to amplify the sensing pulsed light, and at the same time, idler-frequency pulse light having a wavelength of λI is generated, with a center wavelength is λI=2λP−λS. Under the premise that the power of the sensing pulsed light is relatively low, and thus a high-order four-wave mixing product can be ignored, the variations in power and relative phase difference of the pump pulsed light, the sensing pulsed light and the idler-frequency pulsed light as a function of the optical fiber length Z are given by the following set of coupled wave equations:
in which Pp, PS and PI are the powers of the pump pulsed light, the sensing pulsed light and the idler-frequency pulsed light; y is a non-linear coefficient of the optical fiber; θ is a relative phase difference; z represents the length of the parameter amplification optical fiber and is given by:
θ(z)=Δβz+2ϕP(z)−ϕS(z)−ϕI(z) (5)
in which, Δβ a chromatic-dispersion-induced linear phase mismatch, which is given by:
in which, β3 and β4 are third-order and fourth-order derivatives of a propagation constant β(ω) at a zero-dispersion circular frequency ω0, respectively. Since the effect of higher-order chromatic dispersion can be ignored, only the effects of β3 and β4 on the linear phase mismatch are considered here. ϕP (Z), ϕS(Z) and ϕI(Z) are phases of the pump pulsed light, the sensing pulsed light and the idler-frequency pulsed light respectively, which are given by their respective initial phases together with the nonlinear phase shift produced by the transmission process; θ(z) represents the variation in relative phase difference (the relative phase relationship among the pump light, the sensing light and the idler-frequency light) with a transmission distance of light in the parameter amplification optical fiber; and ωP and ωS are circular frequencies of the pump pulsed light and the sensing pulsed light respectively.
When the amplifier works under a condition of phase matching, i.e., θ(z)≈π/2, the third term on the right side of the equal sign in Equation (4) can be ignored. At this time, then:
wherein the second term is a phase adaptation term caused by the nonlinear phase shift in the transmission process. In a shorter optical fiber, the optical fiber parameter amplifier works in a pumped non-depleted mode (Pp »PS), then Equation (6) can be simplified as:
wherein κ is a phase mismatch parameter, and the variations of the powers of the sensing pulsed light and the idler-frequency pulsed light with the length of the optical fiber are given by Equations (9) and (10):
in which, PS(z) represents the variation of the power of the sensing pulsed light with the length of the optical fiber; Ps(0) represents the power of the input sensing pulsed light; PI(z) represents the variation of the power of the idler-frequency pulsed light with the length of the optical fiber; sinh is a hyperbolic sine function; and a parameter gain coefficient g is given by:
in which, L is an effective length of the optical fiber subjected to the parameter amplification. In the case of considering that the optical fiber has no transmission loss, L=z. In the case that the optical fiber has transmission loss, then:
in which α is a linear attenuation coefficient of the optical fiber.
When the non-depletion assumption of the pump pulsed light is set up, the power of the sensing pulsed light can be calculated according to Formula (10) and the input optical power PS(0) of the sensing pulsed light. When the non-depletion assumption of the pump pulsed light cannot be set up due to the transmission loss and the transfer of the power to the sensing pulsed light and the idler-frequency pulsed light, the power of the sensing pulsed light needs to be calculated by solving Equations sets (1) to (4). These calculation methods can provide a basis for adjusting the center wavelength and power of the pump light in the following steps.
A pulsed light amplification method based on the amplifier includes the following steps:
An amplifier performance characterization method using the above-mentioned pulsed light amplification method includes the following steps:
The content that has not been described in detail in this specification belongs to the prior art known to those skilled in the art.
Number | Date | Country | Kind |
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2020108882388 | Aug 2020 | CN | national |
Number | Date | Country | |
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Parent | PCT/CN2021/120470 | Sep 2021 | US |
Child | 17583285 | US |