Apparatus and method for bright-dark soliton coexistence based on mode division multiplexing resonator

Abstract

The application discloses a device and method for coexistence of bright-dark solitons based on a mode division multiplexing resonant cavity, and relates to the technical field of lasers.The device for coexistence of bright-dark solitons based on the mode division multiplexing resonant cavity 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 selection coupler, a second mode selection coupler and a fiber ring resonant cavity, and the fiber ring resonant cavity is a non-uniform dispersion few-mode fiber.The device and method for coexistence of bright-dark solitons based on the mode division multiplexing resonant cavity can realize stable coexistence of bright-dark solitons.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of laser, more particularly, to a device and method for coexistence of bright and dark solitons based on mode division multiplexing resonator. BACKGROUND

[0002] Kerr cavity solitons are spatially localized dissipative structures formed by the nonlinear and dispersive, gain and loss balance of pulsed light in a resonator, which in the frequency domain is represented by a comb spectrum of uniformly spaced frequency components with coherent stable phase relationship, also known as optical frequency comb. Optical frequency comb is generally generated by several methods: mode-locked laser, optical microresonator, electro-optic modulation, etc. Optical frequency comb has various applications in spectroscopy, atomic clock, precise ranging and laser radar. Generally speaking, the research on the generation of optical frequency comb focuses on adjusting the second-order dispersion parameter, i.e. group velocity dispersion (GVD), which is generated in the abnormal GVD region. In particular, unlike bright solitons, dark solitons can appear in the normal GVD region and play a crucial role in the generation of frequency combs in normal dispersion cavities. As a stable information carrier, dark solitons play a potential role in optical communication and optical signal processing. In recent years, the coexistence of nonlinear states in Kerr resonators has attracted widespread research interest. In 2019, the coexistence of different nonlinear states related to different polarization modes was first observed in a single-color driven passive Kerr resonator. Subsequently, it was found that high-order dispersion has an effect on the soliton coexistence generated by the whispering gallery mode microresonator.

[0003] However, in the above work, the types of coexistence states of all nonlinear states are limited. How to multiplex nonlinear states belonging to the non-uniform dispersion region through different modes and ultimately realize the coexistence of bright and dark solitons is still a challenge. SUMMARY

[0004] The present application aims to provide a device and method for coexistence of bright and dark solitons based on mode division multiplexing resonator, which can realize stable coexistence of bright and dark solitons.

[0005] In view of the defects of the current optical frequency comb generation method pointed out in the background art, the present application provides a device for coexistence of bright and dark solitons based on mode division multiplexing resonant cavity, which 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 selection coupler, a second mode selection coupler and a fiber ring resonant cavity; the first mode selection coupler and the second mode selection coupler are used for mode conversion and multiplexing; the first optical coupler is used for splitting the optical 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 for controlling the pumping frequency and ensuring flexible adjustment of the detuning difference between the two modes, and controlling the intensity of the optical field; the fiber ring resonant cavity is a non-uniformly dispersed few-mode fiber; the output end of the erbium-doped fiber amplifier is connected with the input end of the first optical coupler; the first output end of the first optical coupler is connected with the input end of the acousto-optic frequency shifter, and the second output end of the first optical coupler is connected with the first input end of the third optical coupler; the output end of the acousto-optic frequency shifter is connected with the first input end of the second optical coupler; the second input end of the second optical coupler is connected with the first port of the second mode selection coupler, and the first output end of the second optical coupler is connected with the first port of the first mode selection coupler; the second input end of the third optical coupler is connected with the second port of the second mode selection coupler, and the first output end of the third optical coupler is connected with the second port of the first mode selection coupler; the third port of the first mode selection coupler, the non-uniformly dispersed few-mode fiber and the third port of the second mode selection coupler are connected in sequence.

[0006] Further, the above-mentioned non-uniformly dispersed few-mode fiber comprises 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 straight lines at equal intervals in sequence; the cross sections of the cladding, the first stress rod, the core and the second stress rod are all circular.

[0007] Further, the diameter of the above-mentioned 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] Further, the above-mentioned first stress rod and the second stress rod are boron-doped silica, and the core is germanium-doped silica.

[0009] Further, the doping concentration of the above-mentioned boron-doped silica is 30%.

[0010] Further, the doping component of the above-mentioned germanium-doped silica is GeO2.

[0011] Further, the doping concentration of the above-mentioned germanium-doped silica is 6%.

[0012] Further, the length of the above-mentioned non-uniformly dispersed few-mode fiber is 85 meters.

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

[0014] The application further provides a method applied to the device for coexistence of bright and dark solitons 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.

[0015] The device and method for coexistence of bright and dark solitons based on mode division multiplexing resonant cavity provided by the application have the following beneficial effects:

[0016] The resonant cavity of the application adopts a 85m-long heterogeneous dispersion few-mode optical fiber, and the heterogeneous dispersion few-mode resonant cavity needs to use two modes of a fundamental mode and a high-order mode, and not only this, but also needs to obtain opposite signs of dispersion of the two modes, therefore, the traditional single-mode optical fiber cannot meet the requirements; in order to study the dynamics in the mode multiplexing resonant cavity, the application designs a non-uniform dispersion few-mode optical fiber meeting the conditions, dopes a stress rod to increase the mode number, and can simultaneously support an LP01 mode with abnormal dispersion and an LP11 mode with normal dispersion; by changing the detuning difference of the two modes, various coexisting nonlinear states can be excited in the two modes, and the application is possible in the fields of optical communication and laser radar; the values of the second-order dispersion of the two modes of the fundamental mode and the high-order mode are very close, the sizes of the modes are similar, have a certain symmetry, and the sizes of the second-order dispersion of the two modes are both 10 -27 , the influence of the high-order dispersion will become strong, therefore, the application also considers the third-order dispersion; the optical field of the application is transmitted through the whole transmission, and is different from the homogeneous dispersion few-mode optical fiber resonant cavity in that the mode is not exchanged, and finally is outputted by still taking the fundamental mode, and in this way, the light field changes of each cycle can be observed in an oscilloscope. BRIEF DESCRIPTION OF DRAWINGS

[0017] The application will be further described below in combination with the drawings and examples, and the drawings are as follows:

[0018] Figure 1 is a cross-sectional structure and an electric field intensity distribution diagram of the non-uniform dispersion few-mode optical fiber provided by the application;

[0019] Figure 2 is a parameter diagram of the non-uniform dispersion few-mode optical fiber provided by the application;

[0020] Figure 3 is a device composition schematic diagram of the coexistence of bright and dark solitons based on mode division multiplexing resonant cavity provided by the application;

[0021] Figure 4 is the first nonlinear state resonance peak and coexistence simulation result schematic diagram provided by the present application;

[0022] Figure 5 is the second nonlinear state resonance peak and coexistence simulation result schematic diagram provided by the present application;

[0023] Figure 6 is the third nonlinear state resonance peak and coexistence simulation result schematic diagram provided by the present application;

[0024] Figure 7 is the fourth nonlinear state resonance peak and coexistence simulation result schematic diagram provided by the present application. DETAILED DESCRIPTION

[0025] In order to have a clearer understanding of the technical features, objectives and effects of the present application, the specific embodiments of the present application will be described in detail with reference to the drawings.

[0026] Figure 3 The present embodiment shows a schematic diagram of the device for bright-dark soliton coexistence based on mode division multiplexing resonant cavity. In the present embodiment, the device for bright-dark soliton coexistence based on mode division multiplexing resonant cavity 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 selection coupler, a second mode selection coupler and a fiber ring resonant cavity; the first mode selection coupler and the second mode selection coupler are used for mode conversion and multiplexing; the first optical coupler is used for splitting the optical 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 for controlling the pumping frequency and ensuring flexible adjustment of the detuning difference between the two modes and controlling the optical field intensity; the fiber ring resonant cavity is a non-uniform dispersion few-mode fiber; the output end of the erbium-doped fiber amplifier is connected with the input end of the first optical coupler; the first output end of the first optical coupler is connected with the input end of the acousto-optic frequency shifter, and the second output end of the first optical coupler is connected with the first input end of the third optical coupler; the output end of the acousto-optic frequency shifter is connected with the first input end of the second optical coupler; the second input end of the second optical coupler is connected with the first port of the second mode selection coupler, and the first output end of the second optical coupler is connected with the first port of the first mode selection coupler; the second input end of the third optical coupler is connected with the second port of the second mode selection coupler, and the first output end of the third optical coupler is connected with the second port of the first mode selection coupler; the third port of the first mode selection coupler, the non-uniform dispersion few-mode fiber and the third port of the second mode selection coupler are connected in sequence.

[0027] Specifically, the non-uniform dispersion few-mode fiber comprises 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 at equal intervals in sequence; the cross sections of the cladding, the first stress rod, the core and the second stress rod are all circular.

[0028] Specifically, the diameter of the cladding is 125 μm, the radius of the core is 4 μm, the radius of the first stress rod and the second stress rod is r2=20 μm, and the distance between the center of the first stress rod and the center of the core is 32.5 μm.

[0029] Specifically, the first stress rod and the second stress rod are boron-doped silica, and the core is germanium-doped silica.

[0030] Specifically, the doping concentration of the boron-doped silica is 30%.

[0031] Specifically, the doping component of the germanium-doped silica is GeO2.

[0032] Specifically, the doping concentration of the germanium-doped silica is 6%.

[0033] Specifically, the length of the non-uniform dispersion few-mode fiber is 85 meters.

[0034] Specifically, the coupling ratio of the first optical coupler is 50 / 50; and the coupling ratios of the second optical coupler and the third optical coupler are both 95 / 5.

[0035] The embodiment provides a method applied to the device for coexistence of bright and dark solitons based on a mode division multiplexing resonant cavity.

[0036] Specifically, the wavelength of the continuous wave laser is 1550 nm.

[0037] Optionally, the first mode laser signal and the second mode laser signal are observed by using an oscilloscope.

[0038] In some embodiments, the device for coexistence of bright and dark solitons based on a mode division multiplexing resonant cavity can also be implemented in the following manner.

[0039] In the embodiment, a non-uniform dispersion few-mode fiber is designed, which can support an LP01 mode with abnormal dispersion and an LP11 mode with normal dispersion at the same time; by changing the difference in mode mismatch of the two optical fibers, various coexisting nonlinear states can be excited in the two modes, and the few-mode fiber can be applied in the fields of optical communication and laser radar.

[0040] In particular, the design of the heterogeneous dispersed few mode fiber (HDFMF) is shown in Figure 1 ; the stress rod is composed of boron-doped silica with a doping concentration of 30%, while the core is composed of germanium-doped (i.e., GeO2) silica with a doping concentration of 6%; Figure 1 (a) gives the cross-sectional details of the few mode fiber: d1=32.5 μm, r1=4 μm, r2=20 μm, D=125 μm; Figure 1 (b) and (c) show the electric field intensity distribution of LP01 and LP11, respectively;

[0041] As shown in Figure 2 , the parameter map of the heterogeneous dispersed few mode fiber, Figure 2 (a), (e) show the refractive index of LP01 and LP11; Figure 2 (b), (f) show the first order dispersion of LP01 and LP11; Figure 2 (c), (g) show the second order dispersion of LP01 and LP11; Figure 2 (d), (h) show the third order dispersion of LP01 and LP11; in particular, Figure 2 (a), (b), (c), (d) show the fiber parameters of LP01, respectively, Figure 2 (e), (f), (g), (h) show the fiber parameters of LP11, respectively; the effective refractive index difference between the two modes at 1550 nm is higher than 10 -4 , indicating that the crosstalk between the modes can be ignored; as shown in Figure 2 (c) and (g), the GVD of LP01 and LP11 modes are β 21 =-2.49×10 -4 ps 2 / m and β 22 =2.13×10 -4 ps 2 / m, respectively; since the GVD is small enough and has already approached zero, the third order dispersion needs to be considered; as shown in Figure 3 (d) and (h), the third order dispersion of LP01 and LP11 modes are β 31 =6.88×10 -7 ps 3 / m and β 32 =2.2×10 -7 ps 3 / m, respectively;

[0042] An apparatus for the coexistence of bright and dark solitons based on mode division multiplexing resonator, i.e. a scheme of mode division multiplexing fiber resonator as shown in Figure 4-7 In this embodiment, a 85-meter long fiber ring resonator constructed by a non-uniformly dispersive few-mode fiber is used; the fiber ring resonator further comprises two mode selection couplers (MSC1, MSC2) for mode conversion and multiplexing, two optical couplers (OC2, OC3) with a coupling ratio of 95 / 5 for periodic pumping and output; an acousto-optic frequency shifter (AOFS) is used for controlling the pumping frequency, ensuring flexible adjustment of the detuning difference between the two modes, for controlling the light field intensity; after an erbium doped fiber amplifier (EDFA), a 50 / 50 optical coupler (OC1) is used to split the light 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, oscilloscopes (OSC1, OSC2) monitor the two output waveforms.

[0043] It should be noted that the coupling mean field Lugiato Lefever equation (LLE) of the mode multiplexing cavity is represented by equations (1) and (2):

[0044] (1)

[0045] (2)

[0046] where t R is the round trip time, α1 and α2 are the resonator losses, δ1 and δ2 are the resonant resonator frequency detuning, γ 11 and γ 22 are the self-phase modulations, γ 12 is the cross-phase modulation (XPM) coefficient, β 21 and β 22 are the second-order dispersion coefficients, β 31 and β 32 are the third-order dispersion coefficients; Δβ1 is the group delay, θ is the power coupling coefficient between the pump field and the resonator; k(z) = ±1, the change of the sign represents mode exchange; the parameters used for simulation are shown in Table 1;

[0047] Table 1 Corresponding physical parameters Table 1 Corresponding physical parameters

[0048]

[0049] The influence of cross-phase modulation is added to investigate the coexistence of the two modes and obtain all possible nonlinear states of the coexistence of the two modes; finally, four typical nonlinear states of LP01 are excited by precisely controlling the detuning difference, and the Turing mode, chaotic state, breath state and stable bright soliton of LP01 coexist with the stable dark soliton of LP11 respectively; and some phenomena different from the usual nonlinear states are obtained in the anomalous dispersion region;

[0050] It should be noted that, with the increase of the detuning difference, the stable bright soliton and dark soliton can coexist, and are stable when considering a suitable detuning difference, which provides a useful way for the simultaneous generation of stable bright and dark solitons in mode division multiplexing resonators, and also provides potential for the generation of bright and dark solitons; the coexistence of various nonlinear states is shown in Figure 4 ;

[0051] Figure 4 The resonance peaks and coexistence of nonlinear states, i.e., the Turing mode and dark soliton, are calculated; delta Fig. 6 (a) shows the in-cavity power corresponding to the CW steady-state solution of equations (1) and (2) after choosing the detuning difference Δ Figure 4 = 0.46 rad, Figure 4 Fig. 6 (b) shows the time-domain diagram of the Turing mode of LP01, Figure 4 Fig. 6 (c) shows the time-domain profile of the stable dark soliton state of LP11 mode, Figure 4 Fig. 6 (d) shows the time-domain variation of the coexistence state, Figure 4 Fig. 6 (e) shows the optical field evolution of the Turing mode, dark soliton and coexistence state under the selected detuning, i.e., the vertical line of the blue dotted line in Figure 5 Fig. 6 (a);

[0052] Figure 5 The resonance peaks and coexistence of nonlinear states, i.e., the chaotic state and dark soliton, are calculated; Figure 5 Fig. 7 (a) shows the in-cavity power corresponding to the CW steady-state solution of equations (1) and (2), Figure 5 Fig. 7 (b) shows the time-domain diagram of the chaotic state of LP01 mode, Figure 5 Fig. 7 (c) shows the time-domain profile of the stable dark soliton of LP11 mode; Figure 5 Fig. 7 (d) shows the time-domain variation of the coexistence state; Figure 5 Fig. 7 (e), (f), (g) show the optical field evolution of the two modes under the selected detuning, i.e., Figure 6 Fig. 7 (a) the vertical line of the blue dotted line;

[0053] Figure 6The resonant peaks and coexistence of the nonlinear states, i.e. the breathing state and the dark soliton, are calculated; delta (a) of FIG. 1 shows that, after choosing a detuning difference of Δ Figure 6 =-0.43 rad, the in-cavity power corresponds to the CW steady-state solution of equations (1) and (2), Figure 6 (b) of FIG. 1 shows the time-domain graph of the breathing state of LP01, Figure 6 (c) of FIG. 1 shows the time-domain graph of the stable dark soliton state of LP11; Figure 6 (d) of FIG. 1 shows the time-domain variation of the coexistence state; Figure 6 (e) of FIG. 1 shows the light field evolution of the breathing state, the dark soliton and the coexistence state under the selected detuning, i.e. Figure 7 the vertical line of the blue dotted line in (a) of FIG. 1;

[0054] Figure 7 The resonant peaks and coexistence of the nonlinear states, i.e. the bright soliton and the dark soliton, are calculated; delta (a) of FIG. 2 shows that, after choosing a detuning difference of Δ Figure 7 =-0.59 rad, the in-cavity power corresponds to the CW steady-state solution of equations (1) and (2), Figure 7 (b) of FIG. 2 shows the time-domain graph of the bright soliton state of LP01, Figure 7 (c) of FIG. 2 shows the time-domain graph of the stable dark soliton state of LP11; Figure 7 (d) of FIG. 2 shows the time-domain variation of the coexistence state; Figure 7 (e) of FIG. 2 shows the light field evolution of the bright soliton, the dark soliton and the coexistence state under the selected detuning, i.e. ​ the vertical line of the blue dotted line in (a) of FIG. 2.

[0055] The embodiments of the present application are described above in combination with the drawings, but the present application is not limited to the above specific embodiments, and the above specific embodiments are only illustrative but not restrictive, and those skilled in the art can make many forms under the guidance of the present application without departing from the purpose of the present application and the scope protected by the claims, which are all within the protection of the present application.

Claims

1. A device for the coexistence of bright and dark solitons based on a mode-division multiplexing resonator, characterized in that, The device 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 selection coupler, a second mode selection coupler, and a fiber ring resonator. The first and second mode selection couplers are used for mode switching and multiplexing. The first optical coupler is used to divide the optical field, and the second and third optical couplers are used for periodic pumping and output. The acousto-optic frequency shifter is used to control the pump frequency, ensuring flexible adjustment of the detuning difference between the two modes and controlling the optical field intensity. The fiber ring resonator is a non-uniform dispersion few-mode fiber. The output of the erbium-doped fiber amplifier is connected to the input of the first optical coupler. The first output of the first optical coupler is connected to the input of the acousto-optic frequency shifter, and the second output of the first optical coupler is connected to the first input of the third optical coupler. The output of the acousto-optic frequency shifter is connected to the first input of the second optical coupler. The second input of the second optical coupler is connected to the first port of the second mode selection coupler, and the first output of the second optical coupler is connected to the first port of the first mode selection coupler. The second input terminal of the third optical coupler is connected to the second port of the second mode selection coupler, and the first output terminal of the third optical coupler is connected to the second port of the first mode selection coupler; the third port of the first mode selection coupler, the non-uniform dispersion few-mode fiber, and the third port of the second mode selection coupler are connected in sequence. The non-uniform dispersion few-mode fiber includes a cladding, and a first stress bar, a core, and a second stress bar enclosed within the cladding; the first stress bar, the core, and the second stress bar are arranged in a straight line at equal intervals; the cross-sections of the cladding, the first stress bar, the core, and the second stress bar are all circular; The non-uniform dispersion few-mode fiber 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. By precisely controlling the detuning difference, four typical nonlinear states of LP01 are excited, and the Turing mode, chaotic state, breathing state, and stable bright soliton of LP01 coexist with the stable dark soliton of LP11, respectively. As the detuning difference increases, the stable bright soliton and dark soliton can coexist and are stable when a sufficiently suitable detuning difference is considered.

2. The device for bright and dark solitons coexisting based on a mode-division multiplexing resonator according to claim 1, characterized in that, The diameter of the cladding is 125 μm, the radius of the core is 4 μm, the radius of the first stress bar and the second stress bar are both 20 μm, and the distance between the center of the first stress bar and the center of the core is 32.5 μm.

3. The device for bright and dark solitons coexisting based on a mode-division multiplexing resonator according to claim 1, characterized in that, The first stress bar and the second stress bar are boron-doped silicon dioxide, and the core is germanium-doped silicon dioxide.

4. The device for bright and dark solitons coexisting based on a mode-division multiplexing resonator according to claim 3, characterized in that, The boron-doped silicon dioxide has a doping concentration of 30%.

5. The device for bright and dark solitons coexisting based on a mode-division multiplexing resonator according to claim 3, characterized in that, The germanium-doped silicon dioxide is doped with GeO2.

6. The device for bright and dark solitons coexisting based on a mode-division multiplexing resonator according to claim 3, characterized in that, The germanium-doped silicon dioxide has a doping concentration of 6%.

7. The device for bright and dark solitons coexisting based on a mode-division multiplexing resonator according to claim 1, characterized in that, The length of the non-uniform dispersion few-mode fiber is 85 meters.

8. The device for bright and dark solitons coexisting based on a mode-division multiplexing resonator 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.

9. A method for using a device based on a mode-division multiplexing resonator for bright and dark solitons as described in any one of claims 1-8, the method comprising the following steps: S1: Connect the laser to the erbium-doped fiber amplifier, the laser being used to generate continuous wave laser; S2: Start the laser, the second output terminal of the second optical coupler outputs the first mode laser signal, and the second output terminal of the third optical coupler outputs the second mode laser signal.

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