A multi-wavelength fiber laser supporting simultaneous output in multiple transverse modes

Abstract

The present invention discloses a multi-wavelength fiber laser supporting simultaneous output of multiple transverse modes, which relates to the technical field of optical fiber communication. It includes a beam input module, a three-layer ring cavity, and a beam output module connected in sequence. Different few-mode long-period fiber gratings in the three-layer ring cavity are used to obtain LP 01 , LP 11 , LP 21 modes. The reflection of each mode is realized by different few-mode Bragg fiber gratings, and the simultaneous lasing of each mode is achieved under the same wavelength output state. The few-mode Bragg fiber grating is used as a discrete filter, and the polarization controller is adjusted to realize the switching output between single-wavelength, dual-wavelength, and triple-wavelength lasing. The three wavelengths respectively correspond to LP 01 mode, LP 01 and LP 11 hybrid mode, LP 11 mode. While outputting multiple wavelengths, the laser of the present invention realizes the simultaneous output of different transverse modes and can be applied to a mode-division multiplexing - wavelength-division multiplexing optical fiber communication system to expand the transmission capacity.

Description

Technical Field

[0001] The present invention relates to the technical field of optical fiber communication, and more specifically, to a multi-wavelength fiber laser that supports simultaneous output of multiple transverse modes. Background Art

[0002] In order to meet the huge demand for bandwidth expansion in optical access networks, fiber optic communication systems based on multiplexing of multiple physical dimensions have emerged. Since traditional wavelength division multiplexing fiber optic communication systems face the problem of limited bandwidth in the optical fiber communication band, the physical dimension of mode is added to form a mode division multiplexing - wavelength division multiplexing fiber optic communication system. Laser sources that can generate different transverse modes and wavelengths can be applied therein. The key to realizing an all-fiber high-order mode laser is an all-fiber mode conversion device that can selectively excite specific high-order modes. Several mode conversion technologies proposed currently include core misalignment splicing, Bragg fiber gratings, long-period fiber gratings, and fiber mode selection couplers. All-fiber high-order mode lasers based on these mode conversion devices can be divided into two categories. The first category: uses a single-mode gain medium, with the fundamental mode oscillating in the resonant cavity, and high-order modes are excited through a mode conversion device. The second category: uses a few-mode gain medium, with high-order modes oscillating in the resonant cavity, and high-order modes are excited through a mode conversion device. However, the design and manufacture of few-mode rare-earth doped fibers for realizing selective amplification of high-order modes are challenging, so there are significant difficulties in the popularization and application of lasers using few-mode gain media.

[0003] Currently, high-order mode fiber lasers generally output lasers of different transverse modes in a switching manner. The switching output can be achieved by controlling an optical switch, a mode selection coupler, a spatial light modulator, etc. However, there is less research on fiber lasers that can simultaneously output different transverse modes. For multi-wavelength fiber lasers, the key to forming multi-wavelength lasing is a filter. Filters are generally divided into two categories. One category is a comb filter represented by a Mach-Zehnder interferometer, a Sagnac interferometer, etc., which can achieve wavelength tuning. However, due to the overall change characteristics of such filters, their wavelength switching ability is relatively weak. The other category is a discrete filter represented by a Bragg fiber grating. The number of fiber gratings used determines the number of lasing wavelengths, and its wavelength switching ability is strong. However, the use of multiple fiber gratings will increase the insertion loss and complexity of the system.

[0004] Therefore, how to achieve simultaneous output of lasers with different modes and wavelengths at low cost is an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0005] In view of this, the present invention provides a multi-wavelength fiber laser that supports simultaneous output of multiple transverse modes. The present invention uses different few-mode long-period fiber gratings in a three-layer ring cavity to obtain LP01 , LP 11 , LP 21 mode, realizing LP through different few-mode Bragg fiber gratings 01 , LP 11 , LP 21 mode reflection, realizing LP under the same wavelength output state 01 , LP 11 , LP 21 mode simultaneous lasing, using a single few-mode Bragg fiber grating as a discrete filter, and realizing the switching output between single-wavelength, dual-wavelength, and triple-wavelength lasing by adjusting the polarization controller, and the three wavelengths respectively correspond to LP 01 mode, LP 01 and LP 11 hybrid mode, LP 11 mode. While the laser of the present invention outputs multiple wavelengths, it realizes the simultaneous output of different transverse modes, and it can be applied to a mode-division multiplexing - wavelength-division multiplexing optical fiber communication system to realize the expansion of transmission capacity.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A multi-wavelength fiber laser supporting the simultaneous output of multiple transverse modes, including a beam input module, a three-layer ring cavity, and a beam output module connected in sequence;

[0008] The beam input module is used to divide the beam into three paths, including a first beam, a second beam, and a third beam, and input them into the three-layer ring cavity respectively;

[0009] The three-layer ring cavity includes a first resonator A, a second resonator B, and a third resonator C, which are respectively used to receive the first beam, the second beam, and the third beam, and perform wavelength switching, mode switching, and lasing on the received beams;

[0010] The beam output module is used to output beams with different wavelengths and different modes.

[0011] Optionally, the beam input module includes a pump source, a wavelength division multiplexer, a single-mode erbium-doped fiber, and a first single-mode coupler connected in sequence.

[0012] Optionally, the first resonator A includes a first polarization controller, a first few-mode long-period fiber grating, a first few-mode fiber circulator, and a first few-mode fiber coupler connected in sequence, and further includes a first few-mode Bragg fiber grating connected to the first few-mode fiber circulator. The first polarization controller is connected to the beam input module, and the first few-mode fiber coupler is connected to the beam output module.

[0013] Optionally, the second resonant cavity B includes a second polarization controller, a second few-mode long-period fiber grating, a second few-mode fiber circulator, and a second few-mode fiber coupler connected in sequence, and further includes a second few-mode Bragg fiber grating connected to the second few-mode fiber circulator. The second polarization controller is connected to the beam input module, and the second few-mode fiber coupler is connected to the beam output module.

[0014] Optionally, the third resonant cavity C includes a third polarization controller, a third few-mode long-period fiber grating, a fourth few-mode long-period fiber grating, a third few-mode fiber circulator, and a third few-mode fiber coupler connected in sequence, and further includes a third few-mode Bragg fiber grating connected to the third few-mode fiber circulator. The third polarization controller is connected to the beam input module, and the third few-mode fiber coupler is connected to the beam output module.

[0015] Optionally, the beam output module includes a second single-mode coupler.

[0016] Optionally, the periods of the first few-mode long-period fiber grating, the second few-mode long-period fiber grating, the third few-mode long-period fiber grating, and the fourth few-mode long-period fiber grating are 1100 μm, 1088 μm, 1092 μm, and 891 μm, respectively.

[0017] Optionally, the periods of the first few-mode Bragg fiber grating, the second few-mode Bragg fiber grating, and the third few-mode Bragg fiber grating are 1069 μm, 1070 μm, and 1072 μm, respectively.

[0018] Optionally, the splitting ratios of the first single-mode coupler and the second single-mode coupler are both 1:1:1.

[0019] Optionally, the splitting ratios of the first few-mode fiber coupler, the second few-mode fiber coupler, and the third few-mode fiber coupler are all 1:1.

[0020] The working principle of the above laser of the present invention is as follows:

[0021] In the first resonant cavity A, the LP 01 and LP 11 modes are simultaneously obtained by using the first few-mode long-period fiber grating, and lasing is formed by reflecting the LP 01 mode through the first few-mode Bragg fiber grating. In the second resonant cavity B, the LP 01 and LP 11 modes are simultaneously obtained by using the second few-mode long-period fiber grating, and the LP 01 and LP 11mode, the polarization state of the second resonant cavity B is adjusted by using a second polarization controller to achieve switching output between single-wavelength, dual-wavelength, and triple-wavelength lasing, and the three wavelengths respectively correspond to LP 01 mode, LP 01 and LP 11 hybrid mode, LP 11 mode. In the third resonant cavity C, LP 01 , LP 11 , LP 21 mode are simultaneously obtained by using a third few-mode long-period fiber grating and a fourth few-mode long-period fiber grating, and lasing is formed by reflecting the LP 21 mode through a third few-mode Bragg fiber grating. Among them, LP represents the linearly polarized polarization mode. When represented by LP mn , it represents the nth root of the mth-order Bessel function, and a set of m and n values corresponds to one mode.

[0022] As can be seen from the above technical solutions, the present invention discloses a multi-wavelength fiber laser that supports simultaneous output of multiple transverse modes. Compared with the prior art, it has the following beneficial effects:

[0023] At present, high-order mode fiber lasers generally output lasers of different transverse modes in a switching manner, but they cannot achieve simultaneous output of lasers of different transverse modes. The present invention reflects LP 01 , LP 11 , LP 21 modes through different few-mode Bragg fiber gratings to achieve simultaneous lasing of LP 01 , LP 11 , LP 21 modes in the same wavelength output state. For a multi-wavelength fiber laser, in the case of using a discrete filter represented by a few-mode Bragg fiber grating, the number of few-mode Bragg fiber gratings used determines the number of lasing wavelengths, and its wavelength switching ability is strong, but the use of multiple few-mode Bragg fiber gratings will increase the insertion loss and complexity of the system. The present invention uses a single few-mode Bragg fiber grating as a discrete filter, and realizes switching output between single-wavelength, dual-wavelength, and triple-wavelength lasing by adjusting the polarization controller, and the three wavelengths respectively correspond to LP 01 mode, LP 01 and LP 11 hybrid mode, LP 11 mode. The laser of the present invention realizes simultaneous output of different transverse modes in the same wavelength output state while outputting multiple wavelengths and different wavelengths corresponding to different modes, and can be applied to a mode division multiplexing-wavelength division multiplexing fiber communication system to achieve an expansion of the transmission capacity. Description of the Drawings

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained according to the provided drawings.

[0025] Figure 1 Schematic diagram of the device structure of the multi-wavelength fiber laser supporting simultaneous output of multiple transverse modes proposed by the present invention;

[0026] Fig. 2(a) is the transmission spectrum of the first few-mode long-period fiber grating;

[0027] Fig. 2(b) is the transmission spectrum of the second few-mode long-period fiber grating;

[0028] Fig. 2(c) is the transmission spectrum of the third few-mode long-period fiber grating;

[0029] Fig. 2(d) is the transmission spectrum of the fourth few-mode long-period fiber grating;

[0030] Figure 3 Schematic diagram of the experimental system for measuring the mode excitation of few-mode long-period fiber gratings;

[0031] Figure 4 Schematic diagram of the experimental system for measuring the mode reflection of few-mode Bragg fiber gratings;

[0032] Fig. 5(a) is the reflection spectrum of the first few-mode Bragg fiber grating under the condition of the third mode-selective photon lantern exciting LP 01 and LP 11 modes;

[0033] Fig. 5(b) is the reflection spectrum of the second few-mode Bragg fiber grating under the condition of the third mode-selective photon lantern exciting LP 01 and LP 11 modes;

[0034] Fig. 5(c) is the reflection spectrum of the third few-mode Bragg fiber grating under the condition of the third mode-selective photon lantern exciting LP 01 、LP 11 、LP 21 modes;

[0035] Figure 6 is the single-wavelength lasing situation of the LP 01 mode of the first resonant cavity A;

[0036] Fig. 7(a) is the single-wavelength lasing situation of the LP 01 mode of the second resonant cavity B;

[0037] Figure 7(b) shows the single-wavelength lasing of the hybrid mode of LP 01 and LP 11 in the second resonator B;

[0038] Figure 7(c) shows the single-wavelength lasing of the LP 11 mode in the second resonator B;

[0039] Figure 7(d) shows the dual-wavelength lasing of the LP 01 mode and the hybrid mode of LP 01 and LP 11 in the second resonator B;

[0040] Figure 7(e) shows the dual-wavelength lasing of the LP 01 mode and the LP 11 mode in the second resonator B;

[0041] Figure 7(f) shows the dual-wavelength lasing of the hybrid mode of LP 01 and LP 11 and the LP 11 mode in the second resonator B;

[0042] Figure 7(g) shows the triple-wavelength lasing of the LP 01 mode, LP 01 and the hybrid mode of LP 11 and LP 11 mode in the second resonator B;

[0043] Figure 8 shows the single-wavelength lasing of the LP 21 mode in the third resonator C;

[0044] where A is the first resonator, B is the second resonator, C is the third resonator, 1 is the pump source, 2 is the wavelength division multiplexer, 3 is the single-mode erbium-doped fiber, 4 is the first single-mode coupler, 5 is the first polarization controller, 6 is the first few-mode long-period fiber grating, 7 is the first few-mode fiber circulator, 8 is the first few-mode Bragg fiber grating, 9 is the first few-mode fiber coupler, 10 is the second polarization controller, 11 is the second few-mode long-period fiber grating, 12 is the second few-mode fiber circulator, 13 is the second few-mode Bragg fiber grating, 14 is the second few-mode fiber coupler, 15 is the third polarization controller, 16 is the third few-mode long-period fiber grating, 17 is the fourth few-mode long-period fiber grating, 18 is the third few-mode fiber circulator, 19 is the third few-mode Bragg fiber grating, 20 is the third few-mode fiber coupler, 21 is the second single-mode coupler, 22 is the spectral analyzer, 23 is the charge-coupled device, 24 is the laser, 25 is the single-mode fiber circulator, 26 is the first mode-selective photon lantern, 27 is the second mode-selective photon lantern, 28 is the power meter, 29 is the broad-spectrum light source, and 30 is the third mode-selective photon lantern. Detailed implementation mode

[0045] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

[0046] An embodiment of the present invention discloses a multi-wavelength fiber laser supporting simultaneous output of multiple transverse modes. Refer to Figure 1 , which includes a beam input module, a three-layer ring cavity, and a beam output module connected in sequence;

[0047] The beam input module is used to divide the beam into three paths, including a first beam, a second beam, and a third beam, and input them into the three-layer ring cavity respectively;

[0048] The three-layer ring cavity includes a first resonant cavity A, a second resonant cavity B, and a third resonant cavity C, which are respectively used to receive the first beam, the second beam, and the third beam, and perform wavelength switching, mode switching, and lasing on the received beams;

[0049] The beam output module is used to output beams with different wavelengths and different modes.

[0050] Optionally, the beam input module includes a pump source 1, a wavelength division multiplexer 2, a single-mode erbium-doped fiber 3, and a first single-mode coupler 4 connected in sequence.

[0051] The beam output module includes a second single-mode coupler 21.

[0052] In a specific embodiment, the model of the pump source 1 is selected as a 980nm pump source, and the wavelength division multiplexer 2 is selected as a 980 / 1550 wavelength division multiplexer. The pump light output by the 980nm pump source 1 enters the single-mode erbium-doped fiber 3 through the 980 / 1550 wavelength division multiplexer 2, and then the beam is divided into three paths by the first single-mode coupler 4.

[0053] Specifically, the first beam enters the 1 port of the first polarization controller 5, the first few-mode long-period fiber grating 6, the 1 port of the first few-mode fiber circulator 7, the 2 port of the first few-mode fiber circulator 7, the first few-mode Bragg fiber grating 8, the 3 port of the first few-mode fiber circulator 7, the first few-mode fiber coupler 9, and the 1 port of the second single-mode coupler 21 in sequence from the 1 port of the first single-mode coupler 4, thereby forming the first resonant cavity A.

[0054] The second light beam enters successively from port 2 of the first single-mode coupler 4 into the second polarization controller 10, the second few-mode long-period fiber grating 11, port 1 of the second few-mode fiber circulator 12, port 2 of the second few-mode fiber circulator 12, the second few-mode Bragg fiber grating 13, port 3 of the second few-mode fiber circulator 12, the second few-mode fiber coupler 14, and port 2 of the second single-mode coupler 21, thereby forming the second resonant cavity B.

[0055] The third light beam enters successively from port 3 of the first single-mode coupler 4 into the third polarization controller 15, the third few-mode long-period fiber grating 16, the fourth few-mode long-period fiber grating 17, port 1 of the third few-mode fiber circulator 18, port 2 of the third few-mode fiber circulator 18, the third few-mode Bragg fiber grating 19, port 3 of the third few-mode fiber circulator 18, the third few-mode fiber coupler 20, and port 3 of the second single-mode coupler 21, thereby forming the third resonant cavity C.

[0056] In the specific implementation process, the periods of the first few-mode long-period fiber grating 6, the second few-mode long-period fiber grating 11, the third few-mode long-period fiber grating 16, and the fourth few-mode long-period fiber grating 17 are 1100 μm, 1088 μm, 1092 μm, and 891 μm respectively.

[0057] In the specific implementation process, the periods of the first few-mode Bragg fiber grating 8, the second few-mode Bragg fiber grating 13, and the third few-mode Bragg fiber grating 19 are 1069 μm, 1070 μm, and 1072 μm respectively.

[0058] In the specific implementation process, the splitting ratios of the first single-mode coupler 4 and the second single-mode coupler 21 are both 1:1:1.

[0059] In the specific implementation process, the splitting ratios of the first few-mode fiber coupler 9, the second few-mode fiber coupler 14, and the third few-mode fiber coupler 20 are both 1:1.

[0060] Furthermore, the wavelength lasing and spot distribution are measured at port 2 of the first few-mode fiber coupler 9, the second few-mode fiber coupler 14, and the third few-mode fiber coupler 20 respectively by using a spectral analyzer 22 and a charge-coupled device 23.

[0061] Next, experimental verification is carried out on the mode excitation effect of the few-mode long-period fiber grating and the mode reflection effect of the few-mode Bragg fiber grating:

[0062] I. Mode excitation measurement experiment of the few-mode long-period fiber grating

[0063] The few-mode long-period fiber grating realizes the function of mode conversion in the resonant cavity. A chirped long-period grating is written on the few-mode fiber, and LP is obtained in the core of the few-mode fiber by using it.01 、LP 11 、LP 21 mode. The transmission spectra of different few-mode long-period fiber gratings are shown in Fig. 2(a), Fig. 2(b), and Fig. 2(c). The experimental system for mode excitation measurement is as Figure 3 shown. The system consists of a laser 24, a single-mode fiber circulator 25, a first mode-selective photon lantern 26, a first few-mode long-period fiber grating 6, a second few-mode long-period fiber grating 11, a third few-mode long-period fiber grating 16, a fourth few-mode long-period fiber grating 17, a second mode-selective photon lantern 27, and a power meter 28. The LP 01 mode is excited by the first mode-selective photon lantern 26. When it enters the first few-mode long-period fiber grating 6 or the second few-mode long-period fiber grating 11, the LP 01 and LP 11 modes can be obtained simultaneously. When it enters the third few-mode long-period fiber grating 16 and the fourth few-mode long-period fiber grating 17, the LP 01 and LP 11 modes are obtained simultaneously by the third few-mode long-period fiber grating 16, and the LP 11 and LP 21 modes are obtained simultaneously by the fourth few-mode long-period fiber grating 17. Thus, the LP 01 、LP 11 、LP 21 modes are obtained simultaneously. The mode separation is achieved by the second mode-selective photon lantern 27, and the power of the LP 01 、LP 11 、LP 21 mode output ports of the second mode-selective photon lantern 27 is measured by the power meter 28. The mode losses of the first mode-selective photon lantern 26 and the second mode-selective photon lantern 27, and the mode power ratios of the first few-mode long-period fiber grating 6, the second few-mode long-period fiber grating 11, and the third few-mode long-period fiber grating 16 and the fourth few-mode long-period fiber grating 17 are shown in Table 1 and Table 2. As can be seen from Table 2, the power ratios of obtaining the LP 01 and LP 11 modes simultaneously through the first few-mode long-period fiber grating 6 or the second few-mode long-period fiber grating 11 are close. The LP 01 、LP 11 、LP 21 modes are obtained simultaneously by using the third few-mode long-period fiber grating 16 and the fourth few-mode long-period fiber grating 17. The power ratios of the LP 01 and LP 11 modes are relatively small, and the power ratio of the LP 21 mode is relatively large.

[0064] Table 1 Mode Losses of Mode-Selective Photon Lanterns

[0065]

[0066] Table 2 Ratio of the power of each mode to the total power of the few-mode long-period fiber grating

[0067]

[0068] II. Mode reflection measurement experiment of few-mode Bragg fiber grating

[0069] The role of the few-mode Bragg fiber grating in realizing mode reflection in the resonator. A Bragg grating is written on the few-mode fiber by the femtosecond laser point-by-point writing method, so that it reflects LP 01 , LP 11 , LP 21 modes in the core of the few-mode fiber. Since the reflection wavelength of the few-mode Bragg fiber grating corresponds to the transverse mode, in the few-mode Bragg fiber grating with a specific period, the higher the mode order, the shorter the corresponding wavelength. In addition to the self-coupling of the modes, there is also the mutual coupling of two modes, and the mutual coupling reflection wavelength is between the corresponding wavelengths of the self-coupling of the two modes. The measurement experiment of the reflection spectrum of the few-mode Bragg fiber grating is as shown in Figure 4 . The system consists of a broadband light source 29, a first single-mode coupler 4, a third mode-selective photon lantern 30, a first few-mode fiber circulator 7, a first few-mode Bragg fiber grating 8, a second few-mode Bragg fiber grating 13, a third few-mode Bragg fiber grating 19, and a spectrum analyzer 22. The LP 01 , LP 11 , LP 21 modes are excited by the third mode-selective photon lantern 30, and the reflection spectrum of the few-mode Bragg fiber grating is measured by the first spectrum analyzer 22 at port 3 of the first few-mode fiber circulator 7. The reflection spectra of the first few-mode Bragg fiber grating 8, the second few-mode Bragg fiber grating 13, and the third few-mode Bragg fiber grating 19 are shown in Fig. 5(a), Fig. 5(b), and Fig. 5(c). Fig. 5(a) and Fig. 5(b) are the reflection spectra of the first few-mode Bragg fiber grating 8 and the second few-mode Bragg fiber grating 13 under the condition that the third mode-selective photon lantern 30 excites the LP 01 and LP 11 modes. Fig. 5(c) is the reflection spectrum of the third few-mode Bragg fiber grating 19 under the condition that the third mode-selective photon lantern 30 excites the LP 01 , LP 11 , LP 21 modes.

[0070] In the first resonant cavity A, since the peak difference between the 1st reflection peak and other reflection peaks in the reflection spectrum of the first few-mode Bragg fiber grating 8 in Fig. 5(a) is greater than 7 dB, only lasing is formed near the peak of the 1st reflection peak in the first resonant cavity A, corresponding to the LP 01 mode, as Figure 6 shown. In the second resonant cavity B, since the peaks of the 2nd, 3rd, and 4th reflection peaks in the reflection spectrum of the second few-mode Bragg fiber grating 13 in Fig. 5(b) are close, lasing is formed near the peaks of the 2nd, 3rd, and 4th reflection peaks in the second resonant cavity B, corresponding to the LP 01 mode, LP 01 and LP 11 hybrid mode, LP 11 mode respectively, and by adjusting the polarization controller, switching output between single-wavelength, dual-wavelength, and triple-wavelength lasing can be achieved, that is, the permutations and combinations of the three wavelengths, as shown in Fig. 7. In the third resonant cavity C, since the peak difference between the 4th reflection peak and other reflection peaks in the reflection spectrum of the third few-mode Bragg fiber grating 19 in Fig. 5(c) is greater than 3 dB, and at the same time, since the LP 01 mode, LP 11 mode, and LP 21 mode are simultaneously obtained through the third few-mode long-period fiber grating 16 and the fourth few-mode long-period fiber grating 17 in Table 2, where the power ratios of the LP 01 mode and the LP 11 mode are relatively small, and the power ratio of the LP 21 mode is relatively large, therefore, only lasing is formed near the peak of the 4th reflection peak in the third resonant cavity C, corresponding to the LP 21 mode, as Figure 8 shown. From Figure 6 , Fig. 7(c), Figure 8 it can be seen that the lasing wavelengths formed near the peaks of the 1st reflection peak of the first few-mode Bragg fiber grating 8, the 4th reflection peak of the second few-mode Bragg fiber grating 13, and the 5th reflection peak of the third few-mode Bragg fiber grating 19 are the same, and correspond to the LP 01 mode, LP 11 mode, and LP 21 mode respectively, thus realizing the simultaneous lasing of different transverse modes in the same wavelength output state. From Fig. 7, it can be seen that lasing is formed near the peaks of the 2nd, 3rd, and 4th reflection peaks of the second few-mode Bragg fiber grating 13. By adjusting Figure 1 the second polarization controller 10 in the second resonant cavity B, switching output between single-wavelength, dual-wavelength, and triple-wavelength lasing is achieved, and the three wavelengths correspond to the LP 01 mode, LP 01 and LP 11 hybrid mode, LP 11 mode respectively. From Figure 6 , Fig. 7(g), Figure 8It can be seen that the multi-wavelength fiber laser proposed by the present invention, which supports simultaneous output of multiple transverse modes, outputs multiple wavelengths, and different wavelengths correspond to different modes. At the same time, it realizes the simultaneous lasing of different transverse modes in the output state of the same wavelength. It can further improve the mode power ratio of the few-mode long-period fiber grating and reduce the peak difference between the reflection peaks of the few-mode Bragg fiber grating, so that in each layer of the resonant cavity, by adjusting the polarization controller, the lasing of multiple wavelengths can be realized, and different wavelengths correspond to different transverse modes.

[0071] The various embodiments in this specification are described in a progressive manner. The key point of each embodiment is the difference from other embodiments. The same or similar parts among the various embodiments can be referred to each other.

[0072] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but will be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A multi-wavelength fiber laser supporting simultaneous output in multiple transverse modes, characterized in that, It includes a beam input module, a three-layer ring cavity, and a beam output module connected in sequence; The beam input module is used to divide the beam into three paths, including a first beam, a second beam, and a third beam, and input them into the three-layer ring cavity respectively; The three-layer ring cavity includes a first resonator A, a second resonator B, and a third resonator C, which are respectively used to receive the first beam, the second beam, and the third beam, and perform wavelength switching, mode switching, and lasing on the received beams; The beam output module is used to output beams with different wavelengths and different modes; The first resonator A includes a first polarization controller (5), a first few-mode long-period fiber grating (6), a first few-mode fiber circulator (7), and a first few-mode fiber coupler (9) connected in sequence, and also includes a first few-mode Bragg fiber grating (8) connected to the first few-mode fiber circulator (7). The first polarization controller (5) is connected to the beam input module, and the first few-mode fiber coupler (9) is connected to the beam output module; The second resonator B includes a second polarization controller (10), a second few-mode long-period fiber grating (11), a second few-mode fiber circulator (12), and a second few-mode fiber coupler (14) connected in sequence, and also includes a second few-mode Bragg fiber grating (13) connected to the second few-mode fiber circulator (12). The second polarization controller (10) is connected to the beam input module, and the second few-mode fiber coupler (14) is connected to the beam output module; The third resonator C includes a third polarization controller (15), a third few-mode long-period fiber grating (16), a fourth few-mode long-period fiber grating (17), a third few-mode fiber circulator (18), and a third few-mode fiber coupler (20) connected in sequence, and also includes a third few-mode Bragg fiber grating (19) connected to the third few-mode fiber circulator (18). The third polarization controller (15) is connected to the beam input module, and the third few-mode fiber coupler (20) is connected to the beam output module; The periods of the first few-mode long-period fiber grating (6), the second few-mode long-period fiber grating (11), the third few-mode long-period fiber grating (16), and the fourth few-mode long-period fiber grating (17) are 1100μm, 1088μm, 1092μm, and 891μm respectively; The periods of the first few-mode long-period fiber grating (6), the second few-mode long-period fiber grating (11), the third few-mode long-period fiber grating (16), and the fourth few-mode long-period fiber grating (17) are 1100μm, 1088μm, 1092μm, and 891μm respectively.

2. The multi-wavelength fiber laser capable of simultaneously outputting multiple transverse modes according to claim 1, wherein, The beam input module includes a pump source (1), a wavelength division multiplexer (2), a single-mode erbium-doped fiber (3), and a first single-mode coupler (4) connected in sequence.

3. The multi-wavelength fiber laser capable of simultaneously outputting multiple transverse modes according to claim 2, wherein The beam output module includes a second single-mode coupler (21).

4. A multi-wavelength fiber laser supporting simultaneous output of multiple transverse modes according to claim 2, characterized in that, The splitting ratios of the first single-mode coupler (4) and the second single-mode coupler (21) are both 1:1:

1.

5. A multi-wavelength fiber laser capable of simultaneously outputting multiple transverse modes according to claim 1, characterized in that, The splitting ratios of the first few-mode fiber coupler (9), the second few-mode fiber coupler (14), and the third few-mode fiber coupler (20) are all 1:1.

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