Device and method for coexistence of bright solitons and dark solitons based on mode division multiplexing resonant cavity

Abstract

The invention discloses a bright and dark soliton coexistence device and method based on a mode division multiplexing resonant cavity, and relates to the technical field of lasers. The bright and dark soliton coexistence device based on the mode division multiplexing resonant cavity comprises an erbium-doped optical fiber amplifier, a first optical coupler, an acousto-optic frequency shifter, a second optical coupler, a third optical coupler, a first mode selection coupler, a second mode selection coupler and an optical fiber annular resonant cavity, wherein the optical fiber annular resonant cavity is a non-uniform dispersion few-mode optical fiber. By implementing the bright and dark soliton coexistence device and method based on the mode division multiplexing resonant cavity, stable coexistence of bright and dark solitons can be realized.

Description

Technical Field

[0001] The present invention relates to the field of laser technology, and more specifically to a device and method for coexistence of bright and dark solitons based on a mode division multiplexing resonant cavity. Background Art

[0002] Kerr time cavity solitons are spatially localized dissipative structures formed by the dual balance of nonlinearity and dispersion, gain and loss of pulsed light in the resonant cavity. In the frequency domain, they appear as comb-like spectra composed of frequency components with uniform intervals and coherent stable phase relationships, also known as optical frequency combs. Optical frequency combs are generally generated by the following methods: mode-locked lasers, optical microresonators, electro-optical modulation, etc. Optical frequency combs have various applications in spectroscopy, atomic clocks, precision ranging, and lidar. In general, the research on the generation of optical frequency combs focuses on adjusting the second-order dispersion parameters, namely, group velocity dispersion (GVD), which is generated in the anomalous GVD region. In particular, in contrast to bright solitons, dark solitons can appear in the normal GVD region and play a vital role in the generation of frequency combs in normal dispersive cavities. As a stable information carrier, dark solitons play a potential role in optical communications and optical signal processing. In recent years, the coexistence of nonlinear states in Kerr resonant cavities has attracted extensive research interest. In 2019, the coexistence of different nonlinear states associated with different polarization modes was experimentally observed for the first time in a monochromatically driven passive Kerr resonator. Subsequently, the influence of higher-order dispersion on the coexistence of solitons generated in whispering gallery mode microresonators was discovered.

[0003] However, in the above work, the types of coexistence states of all nonlinear states are limited. How to multiplex the nonlinear states belonging to the inhomogeneous dispersion region through different modes and ultimately achieve the coexistence of bright and dark solitons remains a challenge. Summary of the invention

[0004] The object of the present invention is to provide a device and method for the coexistence of bright and dark solitons based on a mode division multiplexing resonant cavity, which can achieve stable coexistence of bright and dark solitons.

[0005] In view of the defects of the current method for generating optical frequency combs pointed out in the background technology, the present invention provides a device for the coexistence of bright and dark solitons based on a mode division multiplexing resonant cavity, the device comprising an erbium-doped fiber amplifier, a first optical coupler, an acousto-optic frequency shifter, a second optical coupler, a third optical coupler, a first mode selective coupler, a second mode selective coupler and a fiber ring resonant cavity; the first mode selective coupler and the second mode selective coupler are used for mode conversion and multiplexing; the first optical coupler is used to divide the light field, and the second optical coupler and the second optical coupler are used for periodic pumping and output; the acousto-optic frequency shifter is used to control the pumping frequency to ensure flexible adjustment of the detuning difference between the two modes and control the light field intensity; the fiber ring resonant cavity is an inhomogeneous dispersion few-mode fiber; the output end of the erbium-doped fiber amplifier is connected to the The input end of the first optical coupler is connected; the first output end of the first optical coupler is connected to the input end of the acousto-optic frequency shifter, and the second output end of the first optical coupler is connected to the first input end of the third optical coupler; the output end of the acousto-optic frequency shifter is connected to the first input end of the second optical coupler; the second input end of the second optical coupler is connected to the first port of the second mode selective coupler, and the first output end of the second optical coupler is connected to the first port of the first mode selective coupler; the second input end of the third optical coupler is connected to the second port of the second mode selective coupler, and the first output end of the third optical coupler is connected to the second port of the first mode selective coupler; the third port of the first mode selective coupler, the inhomogeneous dispersion few-mode fiber and the third port of the second mode selective coupler are connected in sequence.

[0006] Furthermore, the above-mentioned inhomogeneous dispersion few-mode optical fiber includes a cladding, and a first stress rod, a core, and a second stress rod wrapped inside the cladding; the first stress rod, the core, and the second stress rod are arranged in a straight line with equal intervals in sequence; and the cross-sections of the cladding, the first stress rod, the core, and the second stress rod are all circular.

[0007] Furthermore, the diameter of the cladding is 125 μm, the radius of the core is 4 μm, the radii of the first stress rod and the second stress rod are both r2=20 μm, and the distance between the center of the first stress rod and the center of the core is 32.5 μm.

[0008] Furthermore, the first stress rod and the second stress rod are made of boron-doped silicon dioxide, and the core is made of germanium-doped silicon dioxide.

[0009] Furthermore, the doping concentration of the above-mentioned boron-doped silicon dioxide is 30%.

[0010] Furthermore, the doping component of the above germanium-doped silicon dioxide is GeO2.

[0011] Furthermore, the doping concentration of the germanium-doped silicon dioxide is 6%.

[0012] Furthermore, the length of the above-mentioned inhomogeneous dispersion few-mode optical fiber is 85 meters.

[0013] Furthermore, the coupling ratio of the first optical coupler is 50 / 50; the coupling ratios of the second optical coupler and the second optical coupler are both 95 / 5.

[0014] The present invention also provides a method for applying to the above-mentioned device for coexistence of bright and dark solitons based on a mode division multiplexing resonant cavity, comprising the following steps: S1: connecting a laser to an erbium-doped fiber amplifier, the laser being used to generate continuous wave laser; S2: starting the laser, the second output end of the second optical coupler outputs a first mode laser signal, and the second output end of the third optical coupler outputs a second mode laser signal.

[0015] The device and method for coexistence of bright and dark solitons based on a mode division multiplexing resonant cavity provided by the present invention have the following beneficial effects: The resonant cavity of the present invention adopts a 85m long heterogeneous dispersion few-mode optical fiber, and the heterogeneous dispersion few-mode resonant cavity needs to use two modes, the fundamental mode and the high-order mode. Not only that, it is also necessary to obtain that the dispersion signs of the fundamental mode and the high-order mode are opposite, so the traditional single-mode optical fiber cannot meet the requirements; in order to conduct dynamic research in the mode multiplexing resonant cavity, the present invention designs a non-uniform dispersion few-mode optical fiber that meets the conditions, and dopes stress rods to increase the number of modes, which can simultaneously support the LP01 mode with anomalous dispersion and the LP11 mode with normal dispersion; by changing the detuning difference between the two modes, various coexisting nonlinear states can be excited in the two modes, which may be applied in the fields of optical communication and laser radar; the second-order dispersion values ​​of the fundamental mode and the high-order mode are very close, the sizes of the modes are similar, and there is a certain symmetry, and the second-order dispersion sizes of the two modes are both 10 -27 , the influence of higher-order dispersion will become stronger, therefore, the present invention also takes third-order dispersion into consideration; the light field of the present invention is transmitted throughout the whole process, and unlike the homogeneous dispersion few-mode fiber resonator, no mode exchange is performed, and finally it is still output in the fundamental mode, and this cycle is repeated, and the changes in the light field of each circle can be observed in an oscilloscope. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which: Figure 1 The cross-sectional structure and electric field intensity distribution diagram of the non-uniform dispersion few-mode optical fiber provided by the present invention; Figure 2 It is a parameter diagram of the inhomogeneous dispersion few-mode optical fiber provided by the present invention; Figure 3 It is a schematic diagram of the composition of a device for coexistence of bright and dark solitons based on a mode division multiplexing resonant cavity provided by the present invention; Figure 4 It is a schematic diagram of the resonance peak and coexistence simulation results of the first nonlinear state provided by the present invention; Figure 5 is a schematic diagram of the resonance peak and coexistence simulation results of the second nonlinear state provided by the present invention; Figure 6 It is a schematic diagram of the resonance peak and coexistence simulation results of the third nonlinear state provided by the present invention; Figure 7 It is a schematic diagram of the resonance peak and coexistence simulation results of the fourth nonlinear state provided by the present invention. DETAILED DESCRIPTION

[0017] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, specific embodiments of the present invention are now described in detail with reference to the accompanying drawings.

[0018] Figure 3 The schematic diagram of the device for coexistence of bright and dark solitons based on the mode division multiplexing resonant cavity of this embodiment is shown. In this embodiment, the device for coexistence of bright and dark solitons based on the mode division multiplexing resonant cavity includes an erbium-doped fiber amplifier, a first optical coupler, an acousto-optic frequency shifter, a second optical coupler, a third optical coupler, a first mode selective coupler, a second mode selective coupler and a fiber ring resonator; the first mode selective coupler and the second mode selective coupler are used for mode conversion and multiplexing; the first optical coupler is used to split the light field, and the second optical coupler and the second optical coupler are used for periodic pumping and output; the acousto-optic frequency shifter is used to control the pumping frequency to ensure flexible adjustment of the detuning difference between the two modes and control the light field intensity; the fiber ring resonator is an inhomogeneous dispersion few-mode fiber; the output end of the erbium-doped fiber amplifier is connected to the input end of the first optical coupler; the third optical coupler ... third optical coupler is used to control the pumping frequency to ensure flexible adjustment of the detuning difference between the two modes and control the light field intensity; the third optical coupler is used to control the pumping frequency to ensure The first output end of an optical coupler is connected to the input end of an acousto-optic frequency shifter, and the second output end of the first optical coupler is connected to the first input end of a third optical coupler; the output end of the acousto-optic frequency shifter is connected to the first input end of a second optical coupler; the second input end of the second optical coupler is connected to the first port of a second mode selective coupler, and the first output end of the second optical coupler is connected to the first port of the first mode selective coupler; the second input end of the third optical coupler is connected to the second port of the second mode selective coupler, and the first output end of the third optical coupler is connected to the second port of the first mode selective coupler; the third port of the first mode selective coupler, the inhomogeneous dispersion few-mode fiber, and the third port of the second mode selective coupler are connected in sequence.

[0019] Specifically, the above-mentioned inhomogeneous dispersion few-mode optical fiber includes a cladding, and a first stress rod, a core and a second stress rod wrapped inside the cladding; the first stress rod, the core and the second stress rod are arranged in a straight line with equal intervals; the cross-sections of the cladding, the first stress rod, the core and the second stress rod are all circular.

[0020] Specifically, the diameter of the cladding is 125 μm, the radius of the core is 4 μm, the radii of the first stress rod and the second stress rod are both r2=20 μm, and the distance between the center of the first stress rod and the center of the core is 32.5 μm.

[0021] Specifically, the first stress rod and the second stress rod are made of boron-doped silicon dioxide, and the core is made of germanium-doped silicon dioxide.

[0022] Specifically, the doping concentration of the boron-doped silicon dioxide is 30%.

[0023] Specifically, the doping component of the germanium-doped silicon dioxide is GeO2.

[0024] Specifically, the doping concentration of the germanium-doped silicon dioxide is 6%.

[0025] Specifically, the length of the above-mentioned inhomogeneous dispersion few-mode optical fiber is 85 meters.

[0026] Specifically, the coupling ratio of the first optical coupler is 50 / 50; the coupling ratios of the second optical coupler and the second optical coupler are both 95 / 5.

[0027] This embodiment provides a method for applying to the above-mentioned bright and dark soliton coexistence device based on mode division multiplexing resonant cavity, comprising the following steps: S1: connecting a laser to an erbium-doped fiber amplifier, the laser being used to generate continuous wave laser; S2: starting the laser, the second output end of the second optical coupler outputting a first mode laser signal, and the second output end of the third optical coupler outputting a second mode laser signal; Specifically, the wavelength of the continuous wave laser is 1550nm; Optionally, the first mode laser signal and the second mode laser signal are observed using an oscilloscope.

[0028] In some embodiments, the above-mentioned device for coexistence of bright and dark solitons based on a mode division multiplexing resonant cavity can also be implemented in the following manner.

[0029] In this embodiment, a non-uniform dispersion few-mode fiber is designed, which can simultaneously support the LP01 mode with anomalous dispersion and the LP11 mode with normal dispersion; by changing the detuning difference between the two fiber modes, various coexisting nonlinear states can be excited in the two modes, and the few-mode fiber may be used in the fields of optical communication and laser radar; Specifically, the design of heterogeneous dispersed few mode fiber (HDFMF) is as follows: Figure 1 As shown; the stress rods are composed of boron-doped silicon dioxide with a doping concentration of 30%, while the core is composed of germanium-doped (i.e., GeO2) silicon dioxide with a doping concentration of 6%; Figure 1(a) shows the cross-sectional details of the few-mode fiber: d1=32.5μm, r1=4μm, r2=20μm, D=125μm; Figure 1 (b) and (c) show the electric field intensity distribution of LP01 and LP11, respectively; like Figure 2 The figure shows the parameter diagram of inhomogeneous dispersion few-mode fiber. Figure 2 (a) and (e) show the refractive index of LP01 and LP11; Figure 2 (b) and (f) show the first-order dispersion of LP01 and LP11; Figure 2 (c) and (g) show the second-order dispersion of LP01 and LP11; Figure 2 (d) and (h) show the third-order dispersion of LP01 and LP11; specifically, Figure 2 (a), (b), (c), and (d) show the fiber parameters of LP01. Figure 2 Figures (e), (f), (g), and (h) show the fiber parameters of LP11. The effective refractive index difference between the two modes at 1550nm is greater than 10. -4 , indicating that the crosstalk between modes can be ignored; Figure 2 As shown in (c) and (g) in Figure 2, the GVD of the LP01 and LP11 modes are β 21 = -2.49 × 10 -4 ps 2 / m and β 22 =2.13×10 -4 ps 2 / m; Since GVD is small enough and close to zero, the third-order dispersion needs to be considered; Figure 2 As shown in (d) and (h) in Figure 1, the third-order dispersion of the LP01 and LP11 modes is β 31 =6.88×10 -7 ps 3 / m and β 32 =2.2×10 -7 ps 3 / m; The device based on the coexistence of bright and dark solitons in the mode-division multiplexing resonant cavity, that is, the scheme of mode-division multiplexing fiber resonator, is as follows Figure 3As shown; in this embodiment, an 85-meter-long fiber ring resonator constructed of inhomogeneous dispersion few-mode fiber is used; the fiber ring resonator also includes two mode selection couplers (MSC1, MSC2) for mode conversion and multiplexing, and two optical couplers (OC2, OC3) with a coupler ratio of 95 / 5 are used for periodic pumping and output; an acoustooptic frequency shifter (AOFS) is used to control the pump frequency to ensure flexible adjustment of the detuning difference between the two modes and to control the light field intensity; in an erbium doped fiber amplifier (Erbium doped fiber After the amplifier, EDFA, a 50 / 50 optical coupler (OC1) is used to split the optical field; after passing through MSC1, one of the input light branches is converted from LP01 mode to LP11 mode, and the other remains in LP01 mode; after circulating in the HDFMF, MSC2 converts the LP11 mode to LP01 mode and keeps the LP01 mode unchanged; during each round trip in the cavity, an oscilloscope (OSC1, OSC2) monitors the two output waveforms.

[0030] It should be noted that the coupled mean field Lugiato-Lefever equation (LLE) of the mode multiplexing cavity is expressed as equations (1) and (2): (1) (2) Where t R is the round trip time, α1 and α2 are the cavity losses, δ1 and δ2 are the cavity frequency detuning, γ 11 and γ 22 is self-phase modulation, γ 12 is the cross-phase modulation (XPM) coefficient, β 21 and β 22 is the second-order dispersion coefficient, β 31 and β 32 is the third-order dispersion coefficient; Δβ1 is the group delay, θ is the power coupling coefficient between the pump field and the resonator; k(z) = ±1, and the change of sign indicates mode exchange; the parameters used for simulation are shown in Table 1; Table 1 Corresponding physical parameters Table 1 Corresponding physical parameters

[0031] The effect of cross-phase modulation was added to study the coexistence of the two modes, and all possible nonlinear states of the two modes were obtained. Finally, the four typical nonlinear states of LP01 were excited by precisely controlling the detuning difference, and the Turing mode, chaotic state, breathing state and stable bright soliton of LP01 were obtained to coexist with the stable dark soliton of LP11 respectively. Some phenomena different from the usual nonlinear states were obtained in the anomalous dispersion region. It should be noted that as the detuning difference increases, stable bright solitons and dark solitons can coexist and are stable when a sufficiently appropriate detuning difference is considered, which provides a useful way to simultaneously generate stable bright and dark solitons in the mode division multiplexing resonant cavity and also provides potential for the generation of bright and dark solitons; various nonlinear states coexist such as Figure 4-7 As shown; Figure 4 The resonant peaks and coexistence of nonlinear states, i.e., Turing modes and dark solitons, are calculated; Figure 4 (a) in the figure shows that when selecting Δ δ =0.46rad, the intracavity power corresponds to the CW steady-state solution of equations (1) and (2), Figure 4 (b) shows the time domain diagram of the Turing mode of LP01. Figure 4 (c) shows the time domain diagram of the stable dark soliton state of the LP11 mode. Figure 4 (d) in the figure shows the time domain variation of the coexistence state. Figure 4 (e) shows the light field evolution of Turing modes, dark solitons and coexistence states under selected detuning, i.e., Figure 4 The vertical line of the blue dashed line in (a); Figure 5 The resonance peaks and coexistence of nonlinear states, i.e., chaotic states and dark solitons, are calculated; Figure 5 (a) in Figure 2 shows that the intracavity power corresponds to the CW steady-state solution of equations (1) and (2), Figure 5 (b) shows the time domain diagram of the chaotic state of LP01 mode. Figure 5 (c) shows the time domain profile of the LP11 mode stable dark soliton; Figure 5 (d) in the figure shows the time domain variation of the coexistence state; Figure 5 The light field evolution of the two modes (e), (f), and (g) under the selected detuning amount, that is, Figure 5 The vertical line of the blue dashed points in (a); Figure 6 The resonant peaks and coexistence of nonlinear states, i.e., breathing states and dark solitons, are calculated; Figure 6 (a) in the figure shows that when selecting Δ δ =-0.43rad, the intracavity power corresponds to the CW steady-state solution of equations (1) and (2), Figure 6 (b) shows the time domain diagram of the breathing state of LP01. Figure 6 (c) shows the time domain image of the stable dark soliton state of LP11; Figure 6 (d) in the figure shows the time domain variation of the coexistence state; Figure 6 (e) shows the light field evolution of the breathing state, dark soliton and coexistence state under the selected detuning, i.e., Figure 6 The vertical line of the blue dashed line in (a); Figure 7 The resonance peaks and coexistence of nonlinear states, i.e., bright and dark solitons, are calculated; Figure 7 (a) in the figure shows that when selecting Δ δ =-0.59rad detuning difference, the intracavity power corresponds to the CW steady-state solution of equations (1) and (2), Figure 7 (b) shows the time domain diagram of the bright soliton state of LP01. Figure 7 (c) shows the time domain image of the stable dark soliton state of LP11; Figure 7 (d) in the figure shows the time domain variation of the coexistence state; Figure 7 (e) shows the light field evolution of bright solitons, dark solitons and coexistence states under selected detuning, i.e., Figure 7 The vertical line to the blue dashed line in (a).

[0032] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation modes, which are merely illustrative rather than restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the present invention and the claims, all of which are within the protection of the present invention.

Claims

1. A device for coexistence of bright and dark solitons based on a mode division multiplexing resonant cavity, characterized in that: The device comprises an erbium-doped fiber amplifier, a first optical coupler, an acousto-optic frequency shifter, a second optical coupler, a third optical coupler, a first mode selective coupler, a second mode selective coupler and a fiber ring resonator; the first mode selective coupler and the second mode selective coupler are used for mode conversion and multiplexing; the first optical coupler is used to split the light field, and the second optical coupler and the second optical coupler are used for periodic pumping and output; the acousto-optic frequency shifter is used to control the pumping frequency to ensure flexible adjustment of the detuning difference between the two modes and control the light field intensity; the fiber ring resonator is an inhomogeneous dispersion few-mode fiber; the output end of the erbium-doped fiber amplifier is connected to the input end of the first optical coupler; the first output end of the first optical coupler is connected to the input end of the acousto-optic frequency shifter, and the second output end of the first optical coupler is connected to the first input end of the third optical coupler; the output end of the acousto-optic frequency shifter is connected to the first input end of the second optical coupler; the second input end of the second optical coupler is connected to the first port of the second mode selective coupler, and the first output end of the second optical coupler is connected to the first port of the first mode selective coupler; The second input end of the third optical coupler is connected to the second port of the second mode selective coupler, and the first output end of the third optical coupler is connected to the second port of the first mode selective coupler; the third port of the first mode selective coupler, the inhomogeneous dispersion few-mode fiber and the third port of the second mode selective coupler are connected in sequence.

2. The device for coexistence of bright and dark solitons based on a mode division multiplexing resonant cavity according to claim 1, characterized in that: The inhomogeneous dispersion few-mode optical fiber includes a cladding, and a first stress rod, a core, and a second stress rod wrapped inside the cladding; the first stress rod, the core, and the second stress rod are arranged in a straight line with equal spacing; the cross-sections of the cladding, the first stress rod, the core, and the second stress rod are all circular.

3. The device for coexistence of bright and dark solitons based on a mode division multiplexing resonant cavity according to claim 2, characterized in that: The diameter of the cladding is 125 μm, the radius of the core is 4 μm, the radii of the first stress rod and the second stress rod are both 20 μm, and the distance between the center of the first stress rod and the center of the core is 32.5 μm.

4. The device for coexistence of bright and dark solitons based on a mode division multiplexing resonant cavity according to claim 2, characterized in that: The first stress rod and the second stress rod are boron-doped silicon dioxide, and the core is germanium-doped silicon dioxide.

5. The device for coexistence of bright and dark solitons based on a mode division multiplexing resonant cavity according to claim 2, characterized in that: The doping concentration of the boron-doped silicon dioxide is 30%.

6. The device for coexistence of bright and dark solitons based on a mode division multiplexing resonant cavity according to claim 2, characterized in that: The doping component of the germanium-doped silicon dioxide is GeO2.

7. The device for coexistence of bright and dark solitons based on a mode division multiplexing resonant cavity according to claim 2, characterized in that: The doping concentration of the germanium-doped silicon dioxide is 6%.

8. The device for coexistence of bright and dark solitons based on a mode division multiplexing resonant cavity according to claim 1, characterized in that: The length of the inhomogeneous dispersion few-mode optical fiber is 85 meters.

9. The device for coexistence of bright and dark solitons based on a mode division multiplexing resonant cavity according to claim 1, characterized in that: The coupling ratio of the first optical coupler is 50 / 50; the coupling ratios of the second optical coupler and the second optical coupler are both 95 / 5.

10. A method for applying to the device for coexistence of bright and dark solitons based on a mode division multiplexing resonant cavity as claimed in any one of claims 1 to 9, the method comprising the following steps: S1: connecting a laser to the erbium-doped fiber amplifier, wherein the laser is used to generate continuous wave laser; S2: Start the laser, the second output end of the second optical coupler outputs a first mode laser signal, and the second output end of the third optical coupler outputs a second mode laser signal.

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