A fiber loop ring-down sensing device and method based on random distribution characteristic soliton beams

Abstract

The application discloses a kind of based on random distribution characteristic soliton beam fiber ring ring-down sensing device and method, by passive mode-locking fiber laser and fiber ring-down ring two parts composition;Passive mode-locking fiber laser uses 980nm laser diode as pump source, 1m of high doping concentration doped erbium fiber as gain medium, using nonlinear effect generates with random distribution characteristic soliton beam, soliton beam enters fiber ring-down ring by optical coupler.This application has beneficial effects as follows: (1) in passive mode-locking fiber laser, by adjusting polarization state in cavity and pump current, it generates soliton beam with strong randomness and high stability, the autocorrelation function of soliton beam in a cycle has delta characteristic.(2) soliton beam is used as the light source part of fiber ring-down ring, the possibility of soliton beam sensing in fiber ring-down system is verified, and a new method is provided for fiber ring-down ring sensing.

Description

Technical Field

[0001] This invention relates to the fields of fiber lasers and fiber optic sensing, and specifically to a fiber optic ring decay sensing device based on a soliton bundle with random distribution characteristics. Background Technology

[0002] Fiber optic sensing technology uses light waves as the carrier and optical fibers as the medium to sense and transmit external measured signals. Compared with traditional sensors, fiber optic sensors have advantages such as high sensitivity, large dynamic range, resistance to electromagnetic interference, tolerance to extreme environments, and ease of long-distance measurement. In recent years, a new fiber optic sensing technology—fiber ring decay technology—has emerged. Compared with traditional wavelength- or intensity-based demodulation techniques, fiber ring decay technology achieves sensing by demodulating the decay time of pulses in the fiber optic loop. This method can reduce costs and improve measurement resolution. Most current fiber ring decay technologies use pulsed lasers as the light source and the decay time of the pulse intensity as the measured quantity. When designing this pulse-light-based fiber ring decay loop system, the fiber ring length needs to be considered to avoid crosstalk between pulse signals. A long fiber ring increases losses within the loop, negatively impacting measurement resolution and the shape of the pulse signal. Compared with existing fiber ring decay technology (FLRD), chaotic correlation fiber ring decay technology (CCFLRD) achieves sensing by detecting the decay time of the autocorrelation coefficient of chaotic laser light. The small full width at half maximum (FWHM) of the autocorrelation function allows for very short fiber loop lengths, thus significantly improving detection sensitivity. However, the peak intensity of chaotic lasers is much lower than that of pulses, necessitating an amplifier to amplify the chaotic signal. For chaotic correlation fiber loop decay sensing, we desire a light source with high peak intensity and random time-series distribution. For CCFLRD sensing, noise-like pulses in multi-pulse states are a promising approach as a light source, but autocorrelation detection of noise-like pulses requires an autocorrelator, which is costly and complex. Therefore, multi-pulse lasers with delta-like autocorrelation characteristics represent a novel option for CCFLRD sensing. Summary of the Invention

[0003] This invention addresses the shortcomings of existing technologies by providing a fiber optic ring decay sensing device and method based on a soliton bundle with random distribution characteristics. It realizes a soliton bundle with strong randomness and high stability in a passively mode-locked fiber laser. The autocorrelation function of the soliton bundle has delta-like characteristics over one period. The soliton bundle is input into the fiber optic ring as part of the light source, and the decay time of the autocorrelation coefficient of the soliton bundle over one period is obtained through the FLRD system, proving the possibility of sensing the soliton bundle in the FLRD system.

[0004] The present invention adopts the following technical solution:

[0005] A fiber optic ring-down sensing device based on randomly distributed soliton bundles consists of a passively mode-locked fiber laser and a fiber optic ring-down ring. The passively mode-locked fiber laser uses a 980nm laser diode as the pump source and a 1m high-doped erbium-doped fiber as the gain medium. It generates a soliton bundle with random distribution characteristics by utilizing nonlinear effects. The soliton bundle enters the fiber optic ring-down ring through an optical coupler. The fiber optic ring-down ring consists of two couplers and a section of single-mode fiber. The output end of the fiber optic ring is connected to a photodetector to convert the optical signal into an electrical signal. The data acquired on the oscilloscope is then processed using a data processing platform.

[0006] The fiber ring decay sensing device based on randomly distributed soliton beams comprises a passively mode-locked fiber laser consisting of a 980nm laser diode pump source (LD), a wavelength division multiplexer (WDM), an erbium-doped fiber (EDF), a polarization controller (PC), a polarization correlation isolator (ISO), and a highly nonlinear fiber (HNLF) forming a ring cavity structure. It employs a nonlinear polarization rotation mode-locking method, with each component connected via a single-mode fiber (SMF). A 980nm laser diode (LD) is used as the pump source, and the pump light is coupled to the ring laser via a 980 / 1550nm wavelength division multiplexer (WDM). In the optical device, the soliton beam signal light then sequentially enters the first polarization controller (PC), polarization-dependent isolator (PD-ISO), and second polarization controller (PC) of the erbium-doped fiber (EDF). Finally, the soliton beam signal light is output from the 10% output port of the 90:10 optical coupler (OC). The erbium-doped fiber (EDF) with a forward pump length of 1m serves as the gain medium. The two polarization controllers (PC) and one polarization-dependent isolator (PD-ISO) constitute a nonlinear polarization rotation mode-locking, with the polarization-dependent isolator located between the two polarization controllers (PC).

[0007] The fiber optic ring-down sensing device based on randomly distributed soliton bundles comprises two couplers and a section of single-mode fiber, with both couplers having a coupling ratio of 95:5. A soliton bundle with random characteristics generated in a passively mode-locked fiber laser enters the ring-down loop through the 5% port of the first coupler OC1. With each loop, the intensity of the soliton bundle attenuates due to losses within the loop. A photodetector is connected to the 5% port of the second coupler OC2 and converts the detected optical signal into an electrical signal.

[0008] The fiber ring decay sensing device based on randomly distributed soliton bundles uses a 10m high nonlinear fiber HNLF to enhance the nonlinear effects in the cavity.

[0009] The fiber ring-down sensing device based on randomly distributed soliton bundles exhibits dispersions of approximately -20 ps for both the EDF and single-mode fiber (SMF) at 1550 nm. 2 / km and -23ps2 / km.

[0010] The fiber optic ring-down sensing device based on randomly distributed soliton bundles has a total ring cavity length of 21.5 m and an intracavity laser dispersion of -0.158 ps. 2 .

[0011] The fiber optic ring decay sensing device based on randomly distributed soliton bundles, under a pump current of 200mA or more, changes the polarization state within the cavity by adjusting the polarization controller knob, so that the phases between each longitudinal mode are the same, and mode locking is achieved by observing the oscilloscope, thus obtaining the soliton bundle.

[0012] A sensing method for any of the aforementioned fiber ring fading sensing devices utilizes nonlinear effects to generate soliton bundles with random distribution characteristics, and the soliton bundles enter the fiber ring fading loop through an optical coupler.

[0013] The beneficial effects of this invention are: (1) By adjusting the intracavity polarization state and pump current in a passively mode-locked fiber laser, a soliton beam with strong randomness and high stability is generated, and the autocorrelation function of the soliton beam within one period has delta-like characteristics. (2) By using the soliton beam as the light source part of the fiber ring decay ring, the possibility of sensing the soliton beam in the fiber ring decay system is verified, providing a new method for sensing the fiber ring decay ring. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the passive mode-locked fiber laser that generates randomly distributed soliton beams, as used in this invention.

[0015] Figure 2 (a) is a timing diagram of a mode-locked fiber laser under different pump currents.

[0016] Figure 2 (b) is the spectrum of the mode-locked fiber laser under different pump currents.

[0017] Figure 2 (c) represents the pulse width variation of the mode-locked fiber laser under different pump currents.

[0018] Figure 2 (d) is the spectrum of the mode-locked fiber laser at a pump current of 360mA.

[0019] Figure 2 (e) is a timing diagram of a mode-locked fiber laser with a pump current of 360mA.

[0020] Figure 2 (f) is the autocorrelation curve of the mode-locked fiber laser at a pump current of 360mA.

[0021] Figure 2 (g) is the autocorrelation plot of a single periodic soliton beam of a mode-locked fiber laser with a pump current of 360mA, obtained by autocorrelation function calculation.

[0022] Figure 3 This is a schematic diagram of the soliton time-fiber oscillation loop sensing system used in this invention.

[0023] Figure 4 (a) is a diagram of the autocorrelation peak fading curve in soliton bundle fiber optic fading loop sensing.

[0024] Figure 4 (b) is the autocorrelation peak fading curve of the soliton bundle fiber fading loop sensing that generates additional loss.

[0025] In the diagram, LD: semiconductor laser, WDM: wavelength division multiplexer, EDF: erbium-doped fiber, SMF: single-mode fiber, OC: optical coupler, PC: polarization controller, ISO: optical isolator, PD: photodetector, OSC: oscilloscope, OSA: spectrometer, AC: autocorrelation analyzer. Detailed Implementation

[0026] The present invention will be described in detail below with reference to specific embodiments.

[0027] A fiber ring ring decay sensing device based on a randomly distributed soliton bundle of a passively mode-locked fiber laser consists of a passively mode-locked fiber laser and a fiber ring decay ring. (Reference) Figure 1The diagram shows the structure of the soliton-beam fiber laser, which is the light source part of the present invention. The passively mode-locked fiber laser consists of a ring cavity structure composed of a 980nm laser diode pump source (LD), a wavelength division multiplexer (WDM), an erbium-doped fiber (EDF), a polarization controller (PC), a polarization correlation isolator (ISO), and a highly nonlinear fiber (HNLF). It adopts a nonlinear polarization rotation mode-locking method, and the components are connected by a single-mode fiber (SMF). A 980nm laser diode (LD) was used as the pump source. The pump light was coupled into a ring laser through a 980 / 1550nm wavelength division multiplexer (WDM), and then sequentially entered the first polarization controller (PC), polarization-dependent isolator (PD-ISO), and second polarization controller (PC) of an erbium-doped fiber (EDF). Finally, the soliton beam signal light was output from the 10% output port of a 90:10 optical coupler (OC). A 1m long, highly doped erbium-doped fiber (EDF) was used as the gain medium. The two polarization controllers (PCs) and the PD-ISO constituted a nonlinear polarization rotation mode-locking mechanism, with the PD-ISO located between the two PCs. The intracavity PD-ISO ensured unidirectional operation of the pulse, and the two PCs were used to adjust the polarization state within the cavity. During the experiment, with a pump current of over 200mA, the polarization state within the cavity was changed by adjusting the polarization controller knobs to make the phases of each longitudinal mode the same. Mode-locking was achieved by observing the oscilloscope, thus obtaining the soliton beam.

[0028] A 10m high-nonlinear fiber (HNLF) was used to enhance the nonlinear effects in the cavity. At 1550nm, the dispersion of the EDF and single-mode fiber (SMF) was approximately -20ps. 2 / km and -23ps 2 / km.

[0029] The total length of the annular cavity is 21.5m, and the intracavity laser dispersion is approximately -0.158ps. 2 The spectrum was monitored using a spectrometer with a resolution of 0.02 nm. The output pulse sequence was detected by a 12.5 GHz photodetector (PD) and then observed using a 2.5 GHz bandwidth oscilloscope (OSC). The fine structure of the pulses was observed using an autocorrelator (AC).

[0030] refer to Figure 2 (a) shows the time series of the soliton beam within one period under different pump currents. It can be seen that the solitons in the soliton beam are randomly distributed within the time interval of one period, and the number of solitons increases with the increase of pump current, which indicates that the randomness of the soliton beam increases.

[0031] refer to Figure 2(b) shows the output spectrum of the soliton beam under different pump currents. Unlike the spectrum of a conventional pulse, the left side of the soliton beam spectrum has a more complex shape, which is the result of coherent superposition between solitons.

[0032] refer to Figure 2 (c) shows the autocorrelation curve of the soliton beam measured by an autocorrelation meter when the pump current increases from 160mA to 360mA. It can be seen that the pulse duration increases with the increase of pump current.

[0033] refer to Figure 2 (d) and (e) are the output spectrum and timing diagram of the soliton beam at a pump current of 360mA, respectively.

[0034] refer to Figure 2 (f) is the autocorrelation curve of the soliton beam at a pump current of 360mA, which shows that the pulse width of the soliton beam is 745fs.

[0035] refer to Figure 2 (g) is the autocorrelation plot of a single period obtained by autocorrelation function calculation of soliton beam when pump current is 360mA. It can be seen that soliton beam has good delta-like characteristics, indicating that soliton beam has strong randomness.

[0036] refer to Figure 3 This is a schematic diagram of the fiber optic ring-down loop structure used in this invention. The fiber optic ring-down loop consists of two couplers and a section of single-mode fiber, with a coupling ratio of 95:5 for both couplers. A soliton beam with random characteristics generated in a passively mode-locked fiber laser enters the ring-down loop through the 5% port of the first coupler OC1. With each loop, the intensity of the soliton beam attenuates due to losses within the loop. A photodetector is connected to the 5% port of the second coupler OC2 and converts the detected optical signal into an electrical signal, which is displayed on a high-speed sampling oscilloscope. The data processing platform performs autocorrelation calculations on the acquired soliton beam signal and then uses Origin software to fit a function to the ring-down curve of the autocorrelation peak obtained after the autocorrelation calculation, thereby obtaining the ring-down time of the soliton beam autocorrelation peak.

[0037] refer to Figure 4 (a) shows the soliton bundle autocorrelation peak decay curve obtained in this device. It can be seen that the soliton bundle autocorrelation peak decays exponentially. The distance between two adjacent autocorrelation peaks in the figure is the time it takes for the soliton bundle to complete one cycle in the decaying loop. According to the formula, the length of the fiber decaying loop is 0.88m.

[0038] refer to Figure 4(b) shows the soliton bundle autocorrelation peak fading curve obtained by bending the sensing unit to increase the loss in the fiber optic ring-down loop in this device. It can be seen that the autocorrelation curve decays rapidly and the number of peaks decreases, indicating that the additional loss introduced in the fiber optic ring-down loop can be detected, proving that it is feasible to apply the soliton bundle to fiber optic ring-down loop sensing.

[0039] The sensing principle of this device

[0040] The pulse strength within the fiber optic loop satisfies:

[0041]

[0042] Where I represents the pulse intensity at time t; L represents the fiber loop length; c represents the speed of light in vacuum; n represents the effective refractive index of the fiber core; and A represents the total loss of the loop, including fiber absorption loss, coupler insertion loss, connection loss, and scattering loss.

[0043] A=α²L+E+β

[0044] Where α2 represents the absorption coefficient per unit length of optical fiber; E represents the insertion loss and connection loss; and β represents the scattering loss.

[0045]

[0046] When I decays to 1 / e of I0, the initial ringing time τ0 of the sensor can be obtained as:

[0047]

[0048] When the sensing unit changes due to external factors, such as pressure or temperature, an additional loss B is introduced into the fiber optic ring-down loop, and the ring-down time changes as follows:

[0049]

[0050] but:

[0051]

[0052] in The working principle of fiber optic ring-down loop sensing is linearly related to the measured loss B of the sensing system.

[0053] It should be understood that those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A fiber optic ring-down sensing device based on a soliton bundle with random distribution characteristics, characterized in that, It consists of two parts: a passively mode-locked fiber laser and a fiber ring-down ring. The passively mode-locked fiber laser uses nonlinear effects to generate a soliton beam with random distribution characteristics. The autocorrelation function of the soliton beam over one period has delta-like characteristics, and the solitons in the soliton beam are randomly distributed within the time interval of one period. The soliton beam enters the fiber ring-down ring through an optical coupler. The fiber ring-down ring consists of two couplers and a section of single-mode fiber. The output end of the fiber ring-down ring is connected to a photodetector to convert the optical signal into an electrical signal. The data acquired on the oscilloscope is then processed by a data processing platform. The passively mode-locked fiber laser consists of a ring cavity structure composed of a 980 nm laser diode (LD) pump source, a wavelength division multiplexer (WDM), an erbium-doped fiber (EDF), a polarization controller (PC), a polarization correlation isolator (ISO), and a highly nonlinear fiber (HNLF). It employs a nonlinear polarization rotation mode-locking method, with each component connected via a single-mode fiber (SMF). The 980 nm laser diode (LD) serves as the pump source, with the pump light coupled into the ring laser through the 980 / 1550 nm WDM. The light then sequentially enters the erbium-doped fiber (EDF), the first polarization controller (PC), the polarization correlation isolator (ISO), and the second polarization controller (PC). Finally, the soliton beam signal light is output from the 10% output port of a 90:10 optical coupler (OC). The highly doped erbium-doped fiber (EDF) with a forward pump length of 1 m serves as the gain medium. The two polarization controllers (PC) and one polarization correlation isolator (ISO) constitute the nonlinear polarization rotation mode-locking mechanism, with the polarization correlation isolator located between the two polarization controllers (PC).

2. The fiber optic ring decay sensing device based on a soliton bundle with random distribution characteristics according to claim 1, characterized in that, The fiber ring decay ring consists of two couplers and a section of single-mode fiber, with a coupling ratio of 95:5 for both couplers. The soliton beam with random distribution characteristics generated in the passively mode-locked fiber laser enters the ring decay ring through the 5% port of the first coupler OC1. Each time the ring decays, the intensity of the soliton beam is attenuated due to the loss within the ring. The photodetector is connected to the 5% port of the second coupler OC2 and converts the detected optical signal into an electrical signal.

3. The fiber optic ring decay sensing device based on a soliton bundle with random distribution characteristics according to claim 1, characterized in that, A 10m high nonlinear fiber HNLF is used to enhance the nonlinear effects in the cavity.

4. The fiber optic ring decay sensing device based on a soliton bundle with random distribution characteristics according to claim 1, characterized in that, At 1550 nm, the dispersion of erbium-doped fiber (EDF) and single-mode fiber (SMF) is -20 ps, ​​respectively. 2 / km and -23 ps 2 / km.

5. The fiber optic ring decay sensing device based on a soliton bundle with random distribution characteristics according to claim 1, characterized in that, The total length of the annular cavity is 21.5 m, and the intracavity laser dispersion is -0.158 ps. 2 .

6. The fiber optic ring decay sensing device based on a soliton bundle with random distribution characteristics according to claim 1, characterized in that, With a pump current of 200mA or more, the polarization state inside the cavity is changed by adjusting the polarization controller knob, so that the phases between each longitudinal mode are the same. At the same time, mode locking is achieved by observing the oscilloscope, and a soliton beam is obtained.

7. A sensing method based on the fiber optic ring decay sensing device according to any one of claims 1-6, characterized in that, A soliton bundle with random distribution characteristics is generated by utilizing nonlinear effects. The soliton bundle enters the fiber ring-down loop through an optical coupler.

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