Wavelength-spacing-switchable brillouin-raman random fiber laser based on pump light regulation

Abstract

This invention provides a wavelength-interval-switching Brillouin-Raman random fiber laser based on pump light modulation, comprising a tunable laser and a first optical coupler. The tunable laser outputs pump light to the first optical coupler. The laser also includes an erbium-doped fiber amplifier, a first optical circulator, a second optical circulator, a first single-mode fiber, a first optical isolator, and a Brillouin-Raman random cavity. The first optical coupler is connected to port a of the first optical circulator, port b of the first optical circulator is connected to port h of the second optical coupler, and port c of the first optical circulator is connected to a first output terminal. By controlling the output power of the erbium-doped fiber amplifier, the switching between multi-wavelength lasers with a single Brillouin frequency shift interval and multi-wavelength lasers with a double Brillouin frequency shift interval is achieved. This invention, by controlling the output power of the erbium-doped fiber amplifier and regulating the power distribution of the pump light, can achieve wide-bandwidth wavelength-interval-switching random laser output.

Description

Technical Field

[0001] This invention relates to a wavelength-spacing switchable Brillouin-Raman random fiber laser based on pump light modulation, belonging to the field of fiber laser technology. Background Technology

[0002] Since their introduction in 2010, random fiber lasers have made significant progress in various fields such as optical communication, fiber optic sensing, optical measurement, and random bit generation, demonstrating broad application prospects. These lasers achieve randomized feedback through Rayleigh scattering induced by the inherent inhomogeneity of the fiber's refractive index, offering advantages such as simple and efficient structure, stable power output, and flexible design. Notably, due to the low threshold and narrow linewidth of stimulated Brillouin scattering, Brillouin random fiber lasers can be cascaded with multiple wavelengths of random lasers. Over the past few decades, various types of Brillouin random fiber lasers have been developed, including broadband, wavelength-tunable, and narrow-linewidth models, to meet specific application requirements.

[0003] Stimulated Raman scattering (SBS) offers broadband and flat gain for stimulated Brillouin scattering, thus attracting extensive research. Brillouin-Raman fiber lasers output multi-wavelength lasers, exhibiting advantages such as high flatness, broadband, and good stability. In Brillouin-Raman random fiber lasers, various nonlinear effects, including Rayleigh scattering, stimulated Raman scattering, and stimulated Brillouin scattering, are combined to generate broadband multi-wavelength Brillouin frequency combs. However, the fixed wavelength spacing of most Brillouin-Raman fiber lasers (0.168 nm or 0.08 nm) limits their application in fields such as optical communication. Several schemes for achieving wavelength spacing switching have been reported to date.

[0004] In one study, Hu et al. realized a 2μm multi-wavelength laser based on a hybrid gain scheme. This laser had switchable frequency spacing, corresponding to single and double Brillouin shifts, respectively. At a bandwidth of 20dB, they obtained seven laser channels with a frequency spacing of 0.1nm (7.62GHz) and eleven laser channels with a frequency spacing of 0.2nm (15.24GHz). Mamdoohi et al. proposed a multi-wavelength Brillouin-Raman fiber laser with tunable optical coupling ratio. A 10GHz multi-wavelength laser was achieved using a 5:5 coupler, while a 20GHz multi-wavelength laser was achieved using a 99:1 coupler. In 2020, Huang et al. proposed a random fiber laser with flexibly switchable wavelength spacing. Wavelength spacing switching was achieved by controlling the gain provided by two erbium-doped fibers (EDFs) and controlling the power of three 980nm semiconductor lasers. In the same year, Wang et al. proposed a tunable, switchable multi-wavelength erbium Brillouin random fiber laser. This laser employs a semi-open cavity structure and incorporates a section of highly nonlinear fiber (HNLF). By adjusting the polarization controller, the wavelength spacing can be switched between single Brillouin frequency shift and double Brillouin frequency shift (BFS). Recently, Wang et al. proposed a switchable broadband multi-wavelength Brillouin-erbium fiber laser. Furthermore, by simply adjusting the feedback power of the Stokes wave, the wavelength spacing of the inversely generated Brillouin-Stokes lines can be switched between double and single Brillouin frequency shifts without requiring additional system configuration.

[0005] However, the schemes used in the above papers all utilize ring cavities and semi-openings to achieve spacing switching, which is expected to broaden the bandwidth of the laser.

[0006] The above-mentioned problems should be considered and solved in the design of Brillouin-Raman random fiber lasers with switchable wavelength spacing based on pump light modulation. Summary of the Invention

[0007] The purpose of this invention is to provide a Brillouin-Raman random fiber laser with switchable wavelength spacing based on pump light modulation, which solves the problem that the bandwidth of lasers in the prior art needs to be increased.

[0008] The technical solution of this invention is:

[0009] A wavelength-spacing switchable Brillouin-Raman random fiber laser based on pump light modulation includes a tunable laser and a first optical coupler. The tunable laser outputs pump light to the first optical coupler. The laser also includes an erbium-doped fiber amplifier, a first optical circulator, a second optical circulator, a first single-mode fiber, a first optical isolator, and a Brillouin-Raman random cavity. The first optical coupler is connected to port a of the first optical circulator; port b of the first optical circulator is connected to port h of the second optical coupler; port c of the first optical circulator is connected to a first output terminal; the first optical coupler is also connected to port d of the second optical circulator via the erbium-doped fiber amplifier; port e of the second optical circulator is connected to port g of the second optical coupler; port f of the second optical circulator is connected to a second output terminal; port i of the second optical coupler is connected to the first optical isolator via the first single-mode fiber; and port j of the second optical coupler is connected to the Brillouin-Raman random cavity. By controlling the output power of the erbium-doped fiber amplifier, switching between multi-wavelength lasers with a single Brillouin frequency shift interval and multi-wavelength lasers with a double Brillouin frequency shift interval can be achieved.

[0010] Furthermore, the Brillouin Raman random cavity includes a first wavelength division multiplexer, a hybrid gain fiber, a second wavelength division multiplexer, a second optical isolator, a third optical isolator, a first Raman pump laser, a fourth optical isolator, and a second Raman pump laser. Port j of the second optical coupler is connected to the second wavelength division multiplexer through the first wavelength division multiplexer and the hybrid gain fiber. The second wavelength division multiplexer is connected to the second optical isolator and then to the first Raman pump laser through the third optical isolator. The first wavelength division multiplexer is also connected to the second Raman pump laser through the fourth optical isolator.

[0011] Furthermore, the hybrid gain fiber includes a second single-mode fiber and a dispersion compensation fiber, and the first wavelength division multiplexer is connected to the second wavelength division multiplexer in sequence through the second single-mode fiber and the dispersion compensation fiber.

[0012] Furthermore, when the first single-mode fiber is 20kM, the center wavelength of the tunable laser is 1530nm-1550nm, and the output power of the erbium-doped fiber amplifier is controlled within [76.8mW-119mW]. The fiber laser outputs multi-wavelength laser with a single Brillouin frequency shift interval.

[0013] Furthermore, when the first single-mode fiber is 20kM, the center wavelength of the tunable laser is 1516nm-1550nm. When the output power of the erbium-doped fiber amplifier is controlled to be [0mW-76.8mW) or greater than or equal to 366.5mW, the fiber laser outputs a multi-wavelength laser with double Brillouin frequency shift interval.

[0014] Furthermore, the pump light is split into the pump light of the first-order stimulated Brillouin scattering branch and the pump light of the Brillouin pump branch by the first optical coupler.

[0015] Furthermore, this fiber laser outputs multi-wavelength laser light at one Brillouin frequency shift interval, specifically,

[0016] S11. The pump light of the first-order stimulated Brillouin scattering branch is amplified by the erbium-doped fiber amplifier, passes through port d to port e of the second optical circulator, and then enters port g of the second optical coupler.

[0017] S12. Port h of the second optical coupler outputs 50% power pump light to the first optical circulator, and port i of the second optical coupler outputs the remaining 50% power pump light into the first single-mode fiber, exciting first-order stimulated Brillouin scattering light propagating to the right; the newly generated Stokes light, together with the pump light, enters the hybrid gain fiber of the Brillouin Raman random cavity on the right side through the second optical coupler.

[0018] S13. The second-order Stokes beam propagating to the left is generated under the gain of the Raman pump beam, while the third-order Stokes beam propagating to the right is excited when the threshold condition is reached. Under strong Raman pumping conditions, i.e., when both the first and second Raman pump lasers are at maximum power output, the cascaded Stokes beam will also be excited. The even-order Stokes beam is output from the first output terminal through port c of the first optical circulator, while the odd-order Stokes beam is output from the second optical isolator.

[0019] S14. The odd-order Stokes light excited by the Brillouin pump branch and the even-order Stokes light excited by the first-order stimulated Brillouin scattering branch are superimposed and output from the first output terminal through port c of the first optical circulator, forming a multi-wavelength laser with a single Brillouin frequency shift interval. Similarly, the even-order Stokes light generated by the Brillouin pump branch and the odd-order Stokes light generated by the first-order stimulated Brillouin scattering branch are superimposed and output from the second optical isolator. A multi-wavelength laser with a single Brillouin frequency shift interval is observed at the first output terminal and the second optical isolator, respectively.

[0020] Furthermore, this fiber laser outputs multi-wavelength laser light with twice the Brillouin frequency shift interval, specifically,

[0021] S21. The pump light of the Brillouin pump branch passes through port a to port b of the first optical circulator and then enters port h of the second optical coupler. Among them, the pump light of the Brillouin pump branch with 50% power is output from port f of the second optical circulator, and the pump light of the remaining 50% power of the Brillouin pump branch enters the bidirectional Raman-pumped hybrid gain fiber of the Brillouin Raman random cavity.

[0022] S22. When the threshold of stimulated Brillouin scattering is reached, the Brillouin Raman random cavity generates a first-order backward-propagating Stokes beam. The first-order backward-propagating Stokes beam passes through the hybrid gain fiber of the Brillouin Raman random cavity again to generate a forward-propagating second-order Stokes beam.

[0023] S23. Subsequently, the cascaded Stokes beams are excited in this mode in the hybrid gain fiber until the higher-order threshold condition is no longer met. Thus, the odd-order Stokes beams enter port b of the first optical circulator through the second optical coupler and are output from the first output terminal through port c of the first optical circulator; the even-order Stokes beams are output from the second optical isolator on the right.

[0024] Furthermore, by controlling the output power of the erbium-doped fiber amplifier, the first output terminal and the second optical isolator achieve bidirectional separated Stokes light output, specifically as follows:

[0025] When the erbium-doped fiber amplifier is turned off, the fiber laser separates and outputs odd-order and even-order Stokes light, wherein the odd-order Stokes light is obtained from the first output end, and the even-order Stokes light is obtained from the second optical isolator;

[0026] When the output power of the erbium-doped fiber amplifier exceeds 366.5mW, even-order Stokes light is obtained at the first output terminal, and odd-order Stokes light is obtained at the second optical isolator.

[0027] The beneficial effects of this invention are: this wavelength-interleaved Brillouin-Raman random fiber laser based on pump light modulation, by controlling the output power of the erbium-doped fiber amplifier and thus regulating the power distribution of the pump light, can achieve large-bandwidth wavelength-interleaved random laser output. This invention enables a large-bandwidth, wavelength-interleaved, and more convenient multi-wavelength random fiber laser, possessing great potential in the fields of wavelength division multiplexing and optical communication. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the structure of a wavelength-switched Brillouin-Raman random fiber laser based on pump light modulation according to an embodiment of the present invention.

[0029] Figure 2 The following is a schematic diagram of the spectrum of the output double Brillouin frequency shift interval in the embodiment, wherein (a) is a schematic diagram of the spectrum of the first output terminal Out1 outputting a bandwidth of approximately 60nm with a bandwidth of 1516nm-1576nm with a double Brillouin frequency shift interval in the embodiment, and (b) is a magnified schematic diagram of the spectrum of the output 1516nm-1519nm in the embodiment.

[0030] Figure 3This is a schematic diagram of the spectrum of a multi-wavelength laser with a single Brillouin frequency shift interval and a multi-wavelength laser with a double Brillouin frequency shift interval, wherein (a) is a schematic diagram of the spectrum of the tunable laser and the first single-mode fiber in the embodiment; (b) is a schematic diagram of the spectrum of the first output terminal 10Out1 when the first-order stimulated Brillouin scattering branch and the Brillouin pump branch are turned on individually in the embodiment; (c) is a schematic diagram of the spectrum of the first output terminal Out1 with a single Brillouin frequency shift interval when the first-order SBS and BP branches are turned on simultaneously in the embodiment; and (d) is a schematic diagram of the spectrum of the first output terminal Out1 and the second optical isolator ISO2 with a double Brillouin frequency shift interval when the Brillouin pump branch is turned on individually in the embodiment.

[0031] Figure 4 These are schematic diagrams of the output spectrum of a single Brillouin frequency shift interval in the embodiment. Among them, (a) is a schematic diagram of the spectrum of a single Brillouin frequency shift interval with a bandwidth of about 44nm from 1530nm to 1574nm output by the first output terminal Out1 in the embodiment, and (b) is a schematic diagram of the spectrum of 1530nm-1532nm measured by the first output terminal Out1 when the BP light wavelength is 1530nm.

[0032] Figure 5 This is a schematic diagram illustrating wavelength interval switching achieved by adjusting the power of the erbium-doped fiber amplifier in the embodiment.

[0033] Figure 6 This is a schematic diagram of the power of the erbium-doped fiber amplifier required for single-wavelength interval tuning in the embodiment;

[0034] Figure 7 This is a schematic diagram of the spectrum of the first output terminal Out1 when the BP wavelength is tuned from 1550nm to 1525nm in the embodiment.

[0035] Figure 8 This is a schematic diagram of the spectrum of double-wavelength spaced multi-wavelength laser measured at the first output terminal Out1 in the embodiment, with the BP light wavelength tuned from 1550nm to 1516nm.

[0036] Figure 9 This is a schematic diagram illustrating the effect of tuning the BP optical power from 7.6dBm to 12.6dBm on the bandwidth of random multi-wavelength lasers in the embodiment.

[0037] Figure 10 This is a schematic diagram illustrating the effect of tuning the Raman pump power from 823.8mW to 1702mW on the bandwidth of a random multi-wavelength laser in the embodiment.

[0038] Wherein: 1-tunable laser, 2-first optical coupler, 3-erbium-doped fiber amplifier, 4-first optical circulator, 5-second optical circulator, 6-first single-mode fiber, 7-first optical isolator, 8-Brillouin Raman random cavity, 9-second optical coupler, 10-first output terminal, 11-second output terminal;

[0039] 81-First wavelength division multiplexer, 82-Second single-mode fiber, 83-Dispersion compensation fiber, 84-Second wavelength division multiplexer, 85-Second optical isolator, 86-Third optical isolator, 87-First Raman pump laser, 88-Fourth optical isolator, 89-Second Raman pump laser. Detailed Implementation

[0040] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0041] Example

[0042] A wavelength-spacing switchable Brillouin-Raman random fiber laser based on pump light modulation, such as Figure 1 The system includes a tunable laser 1 and a first optical coupler 2. The tunable laser 1 outputs pump light to the first optical coupler 2. It also includes an erbium-doped fiber amplifier 3, a first optical circulator 4, a second optical circulator 5, a first single-mode fiber 6, a first optical isolator 7, and a Brillouin Raman random cavity 8. The first optical coupler 2 is connected to port a of the first optical circulator 4. Port b of the first optical circulator 4 is connected to port h of the second optical coupler 9. Port c of the first optical circulator 4 is connected to a first output terminal 10. The first optical coupler 2 also... Erbium-doped fiber amplifier 3 is connected to port d of second optical circulator 5, port e of second optical circulator 5 is connected to port g of second optical coupler 9, port f of second optical circulator 5 is connected to second output terminal 11, port i of second optical coupler 9 is connected to first optical isolator 7 through first single-mode fiber 6, and port j of second optical coupler 9 is connected to Brillouin Raman random cavity 8; the output power of erbium-doped fiber amplifier 3 is controlled to achieve switching between multi-wavelength laser with one Brillouin frequency shift interval and multi-wavelength laser with two Brillouin frequency shift interval.

[0043] This wave-spaced switchable Brillouin-Raman random fiber laser, based on pump light modulation, achieves wide-bandwidth, wave-spaced switchable random laser output by controlling the output power of the erbium-doped fiber amplifier and thus regulating the power distribution of the pump light. This invention enables a high-bandwidth, wave-spaced switchable, and more convenient multi-wavelength random fiber laser, possessing significant potential in wavelength division multiplexing and optical communication.

[0044] like Figure 1The Brillouin Raman random cavity 8 includes a first wavelength division multiplexer 81, a hybrid gain fiber, a second wavelength division multiplexer 84, a second optical isolator 85, a third optical isolator 86, a first Raman pump laser 87, a fourth optical isolator 88, and a second Raman pump laser 89. Port j of the second optical coupler 9 is connected to the second wavelength division multiplexer 84 through the first wavelength division multiplexer 81 and the hybrid gain fiber. The second wavelength division multiplexer 84 is connected to the second optical isolator 85 and is connected to the first Raman pump laser 87 through the third optical isolator 86. The first wavelength division multiplexer 81 is also connected to the second Raman pump laser 89 through the fourth optical isolator 88.

[0045] The Brillouin Raman random cavity 8 serves as the gain medium for random multi-wavelength lasers and provides Raman gain. Within the Brillouin Raman random cavity 8, two optical isolators, the first and second optical isolators 85, are used to isolate Fresnel reflections. The first Raman pump laser 87 and the second Raman pump laser 89 are two 1455nm Raman pump lasers. The outputs of the two Raman pump lasers are connected to the third and fourth 1455nm optical isolators 86 and 88, respectively, to prevent mutual interference between the Raman pumps.

[0046] The hybrid gain fiber comprises a second single-mode fiber 82 and a dispersion-compensating fiber 83. The first wavelength division multiplexer 81 is connected to the second wavelength division multiplexer 84 via the second single-mode fiber 82 and the dispersion-compensating fiber 83. The Brillouin Raman random cavity 8 uses the hybrid gain fiber as the gain medium, comprising a 10 km length of the second single-mode fiber 82 and a 7.2 km length of the dispersion-compensating fiber 83. The dispersion-compensating fiber 83 has a very high Raman gain coefficient.

[0047] This type of pump-light-tunable wavelength-switched Brillouin-Raman random fiber laser, when the first single-mode fiber 6 is 20kM, has a center wavelength of 1530nm-1550nm for the tunable laser 1 and controls the output power of the erbium-doped fiber amplifier 3 within the range of [76.8mW-119mW]. The fiber laser outputs multi-wavelength laser with a single Brillouin frequency shift interval. When the center wavelength of the tunable laser 1 is 1516nm-1550nm and the output power of the erbium-doped fiber amplifier 3 is controlled within the range of [0mW-76.8mW] or greater than or equal to 366.5mW, the fiber laser outputs multi-wavelength laser with a double Brillouin frequency shift interval.

[0048] like Figure 1 The pump light is split into the pump light of the first-order stimulated Brillouin scattering branch and the pump light of the Brillouin pump branch after passing through the first optical coupler 2.

[0049] This fiber laser outputs multi-wavelength laser light with a single Brillouin frequency shift interval, specifically...

[0050] S11. The pump light of the first-order stimulated Brillouin scattering branch is amplified by the erbium-doped fiber amplifier 3, passes through port d to port e of the second optical circulator 5, and then enters port g with the second optical coupler 9.

[0051] S12. Port h of the second optical coupler 9 outputs 50% power pump light to the first optical circulator 4, and port i of the second optical coupler 9 outputs the remaining 50% power pump light into the first single-mode fiber 6SMF, exciting first-order stimulated Brillouin scattering light propagating to the right; the newly generated Stokes light, together with the pump light, enters the hybrid gain fiber of the Brillouin Raman random cavity 8 on the right side through the second optical coupler 9.

[0052] S13. The second-order Stokes beam propagating to the left is generated under the gain of the Raman pump beam, while the third-order Stokes beam propagating to the right is excited when the threshold condition is reached. Under strong Raman pumping conditions, i.e., both the first Raman pump laser 87 and the second Raman pump laser 89 are in the maximum power output state, the cascaded Stokes beam will also be excited. The even-order Stokes beam is output from the first output terminal 10 through port c of the first optical circulator 4, while the odd-order Stokes beam is output from the second optical isolator 85.

[0053] S14. The odd-order Stokes light excited by the Brillouin pump branch and the even-order Stokes light excited by the first-order stimulated Brillouin scattering branch are superimposed and output from the first output terminal 10 through port c of the first optical circulator 4, forming a multi-wavelength laser with a single Brillouin frequency shift interval. Similarly, the even-order Stokes light generated by the Brillouin pump branch and the odd-order Stokes light generated by the first-order stimulated Brillouin scattering branch are superimposed and output from the second optical isolator 85. A multi-wavelength laser with a single Brillouin frequency shift interval is observed at the first output terminal 10 and the second optical isolator 85, respectively.

[0054] This fiber laser outputs multi-wavelength laser light with twice the Brillouin frequency shift interval, specifically...

[0055] S21. The pump light of the Brillouin pump branch passes through port a to port b of the first optical circulator 4 and then enters port h of the second optical coupler 9. Among them, the pump light of the Brillouin pump branch with 50% power is output from port f of the second optical circulator 5, and the pump light of the remaining 50% power of the Brillouin pump branch enters the bidirectional Raman-pumped hybrid gain fiber of the Brillouin Raman random cavity 8.

[0056] S22. When the threshold of stimulated Brillouin scattering is reached, the Brillouin Raman random cavity 8 generates a first-order backward-propagating Stokes beam. The first-order backward-propagating Stokes beam passes through the hybrid gain fiber of the Brillouin Raman random cavity 8 again to generate a forward-propagating second-order Stokes beam.

[0057] S23. Subsequently, the cascaded Stokes beams are excited in this mode in the hybrid gain fiber until the higher-order threshold condition is no longer met. Thus, the odd-order Stokes beams enter port b of the first optical circulator 4 through the second optical coupler 9 and are output from the first output terminal 10 through port c of the first optical circulator 4; the even-order Stokes beams are output from the second optical isolator 85 on the right.

[0058] This type of pump-light-tunable wavelength-spacing Brillouin-Raman random fiber laser achieves bidirectional separated Stokes light output by controlling the output power of the erbium-doped fiber amplifier 3 and the first output terminal 10 and the second optical isolator 85. Specifically...

[0059] When the erbium-doped fiber amplifier 3 is turned off, the fiber laser separates and outputs odd-order and even-order Stokes light, wherein the odd-order Stokes light is obtained from the first output terminal 10, and the even-order Stokes light is obtained from the second optical isolator 85.

[0060] When the output power of the erbium-doped fiber amplifier 3 exceeds 366.5mW, the first output terminal 10 obtains even-order Stokes light, and the second optical isolator 85 obtains odd-order Stokes light.

[0061] This wave-spacing-switching Brillouin-Raman random fiber laser, based on pump light modulation, can easily switch between single and double Brillouin frequency shift intervals by adjusting the pump light power. Simultaneously, this fiber laser can output both odd-order and even-order Stokes light.

[0062] This wavelength-spacing switchable Brillouin-Raman random fiber laser, based on pump light modulation, comprises a tunable laser 1 on the left and a hybrid gain fiber on the right. The tunable laser 1 uses a Brillouin pump laser (AQ2200-136) with a wavelength tuning range of 970 nm to 1680 nm. The hybrid gain fiber consists of 7.2 km of dispersion-compensating fiber 83DCF and 10 km of single-mode fiber SMF2. Gain is provided by two Raman pump lasers (OS8147-850-1455, center wavelength 1545 nm). The Brillouin pump laser and the hybrid gain fiber are interconnected via a second optical coupler 9 with four ports. To the left of the second coupler is a 20 km long first single-mode fiber 6, serving as the gain medium for the stimulated Brillouin scattering light in the first-order stimulated Brillouin scattering branch. An erbium-doped fiber amplifier 3 is used to control the pump light power of the first-order stimulated Brillouin scattering branch. Isolators were installed at both ends of the laser to reduce interference from Fresnel reflections.

[0063] This pump-light-tunable wavelength-switched Brillouin-Raman random fiber laser achieves switchable Brillouin wavelength spacing simply by controlling the output power of the erbium-doped fiber amplifier 3. This fiber laser is the first fully open-cavity, wavelength-switched random fiber laser.

[0064] This wave-spaced switchable Brillouin-Raman random fiber laser, based on pump light modulation, achieves switching between single and double Brillouin frequency shift intervals by controlling the power of the pump light and the first-order stimulated Brillouin scattering light. When the output power of the erbium-doped fiber amplifier 3 is 0mW, the laser outputs a multi-wavelength random laser with a bandwidth of approximately 60nm and a double Brillouin frequency shift interval; when the output power of the erbium-doped fiber amplifier 3 is 119mW, it outputs a multi-wavelength random laser with a bandwidth of 44nm and a single Brillouin frequency shift interval. Furthermore, this fiber laser features a fully open-cavity structure, and the interval switching is simple and efficient, making commercialization possible.

[0065] This wave-spaced switchable Brillouin-Raman random fiber laser, based on pump light modulation, employs a fully open-cavity structure and can achieve multi-wavelength output with single-wavelength Brillouin pumping and double Brillouin frequency shift wavelength spacing, while also enabling switching between the two. By simultaneously injecting pump light and its first-order stimulated Brillouin scattering light into the Brillouin-Raman random cavity 8, the laser output exhibits a single-wavelength Brillouin frequency shift wavelength spacing. The wavelength spacing switching effect can be achieved by controlling the intensity of the first-order stimulated Brillouin scattering light. Experimental results show that the multi-wavelength laser can be switched between double Brillouin frequency shift multi-wavelength emission with a bandwidth of approximately 60 nm and single Brillouin frequency shift multi-wavelength emission spanning 1530 nm to 1574 nm. This fiber laser meets a wide range of application requirements and has great potential in wavelength division multiplexing and optical communication.

[0066] Figure 2 (a) is a schematic diagram of the spectrum of the first output terminal 10Out1 in the embodiment, with a bandwidth of approximately 60 nm and a bandwidth of 1516 nm-1576 nm, double the Brillouin frequency shift interval. Figure 2 As can be seen in (a), compared with the existing fiber lasers with an output bandwidth of 37.8nm-39.72nm, the fiber laser of the embodiment has the effect of increasing the output bandwidth due to the nonlinear effect of bidirectional Raman pumping and hybrid gain fiber, thus achieving increased bandwidth. Figure 2 (b) is a magnified schematic diagram of the 1516nm-1519nm spectrum output in the embodiment. Figure 2 As can be seen in (b), odd-order Stokes light with a wavelength spacing of 0.168 nm is output from Out1 on the left.

[0067] Figure 3This is a schematic diagram of the spectrum of a multi-wavelength laser with a single Brillouin frequency shift interval and a multi-wavelength laser with a double Brillouin frequency shift interval, as implemented in an embodiment. Figure 3 (a) is a schematic diagram of the spectrum of the first-order stimulated Brillouin scattering light generated by the tunable laser 1 and the first single-mode fiber 6 in the embodiment. Figure 3 (b) is a schematic diagram of the spectrum of the first output terminal 10Out1 when the first-order stimulated Brillouin scattering branch and the Brillouin pump branch are turned on individually in the embodiment, where up is the spectrum of the first output terminal 10Out1 when the first-order stimulated Brillouin scattering branch is turned on alone, and Down is the spectrum of the first output terminal 10Out1 when the Brillouin pump branch is turned on alone. Figure 3 (c) is a schematic diagram of the spectrum of the first output terminal 10Out1 with a single Brillouin frequency shift interval when the first-order SBS and BP branches are simultaneously turned on in the embodiment. Figure 3 (d) is a schematic diagram of the spectrum of the double Brillouin frequency shift interval between the first output terminal 10Out1 and the second optical isolator 85ISO2 when the Brillouin pump branch is turned on alone in the embodiment. In order to obtain multi-wavelength laser with a single BFS interval, the erbium-doped fiber amplifier 3EDFA is turned on to amplify BP, thereby generating a first-order Brillouin Stokes beam BS1, which is injected into the cavity together with the unamplified BP. Figure 3 In (a), the solid line represents the spectrum of tunable laser 1 with a center wavelength of 1550.6 nm and a power of 10 mW, and the dashed line represents the spectrum of the first-order Brillouin-Stokes light BS1 generated in a 20 km SMF. Both were measured without Raman pumping at the second output terminal Out2. The first-order stimulated Brillouin scattered light propagating to the right enters the hybrid gain fiber, generating another set of double-BFS wavelength-spaced Brillouin combs as a new BP. To clearly understand the formation process of multi-wavelength lasers with single Brillouin frequency shift intervals, the Brillouin pump branch and the first-order SBS branch are first turned on separately. When the Brillouin pump branch works alone, the odd-order SBS spectrum observed at the first output terminal Out1 is as follows: Figure 3 The solid line in (b) is shown. Figure 3 The dashed line in (b) represents the even-order SBS spectrum (relative to BP1) because only the first-order stimulated Brillouin scattering branch is active when the EDFA output power is set to 76.8 mW. Therefore, when both branches are activated simultaneously, the Brillouin pump branch produces odd-order Stokes light at the first output terminal Out1, while the first-order stimulated Brillouin scattering branch produces even-order Stokes light at the first output terminal Out1. Figure 3 (c) is the spectrum of a single Brillouin shift interval. Figure 3 (d) is the spectrum of double Brillouin shift interval.

[0068] Figure 4 This is a schematic diagram of the spectrum of the output single Brillouin frequency shift interval in the embodiment. Figure 4 (a) is a schematic diagram of the spectrum of the first output terminal 10Out1 in the embodiment, with a bandwidth of 1530nm-1574nm and a single Brillouin frequency shift interval of approximately 44nm. The BP power is 10mW and the EDFA output power is 119mW. Figure 4 (b) is a schematic diagram of the spectrum of 1530nm-1532nm measured at the first output terminal 10Out1 when the wavelength of the pump light, i.e., the BP light, is 1530nm. It can be clearly seen that there is a single BFS with a wavelength spacing of 0.08nm.

[0069] Figure 5 This is a schematic diagram illustrating wavelength interval switching achieved by adjusting the power of the erbium-doped fiber amplifier 3 in the embodiment. Figure 6 This is a schematic diagram of the power required for single-wavelength interval tuning of the erbium-doped fiber amplifier 3 in the embodiment. The characteristic of the Brillouin pump operation switching Brillouin wavelength interval proposed in this embodiment is optical control, i.e., control of the EDFA output power. Figure 5 The dynamic change of EDFA power with wavelength spacing switching is shown when the BP wavelength is 1550.6 nm. It can be seen that when the EDFA is off, the output spectrum is an odd-order SBS comb structure with a double BFS spacing of 0.168 nm. When the EDFA output power increases to 76.8 mW, the wavelength spacing changes to a single BFS spacing of 0.08 nm. With further increases in EDFA output power, since the next-order stimulated Brillouin scattering branch is superior to the Brillouin pump branch (BP branch) at high EDFA power, the spectrum again changes to an even-order SBS comb structure with a double BFS spacing of 0.168 nm. It is worth noting that the EDFA power required for the Brillouin multi-wavelength laser to switch from a double BFS spacing to a single BFS spacing is related to the BP wavelength, such as... Figure 6 As shown, when the BP wavelength is tuned from 1550nm to 1530nm, the required power increases from 76.8mW to 119mW. There are two reasons for this: firstly, the gain of the EDFA is uneven, and secondly, the required BP power is higher at shorter wavelengths. Furthermore, the required EDFA power for generating a first-order SBS using a 20km first single-mode fiber 6SMF is also related to the length of the first single-mode fiber 6SMF used. Using a longer SMF can reduce the threshold power.

[0070] Figure 7 This is a schematic diagram of the spectrum of the first output terminal 10Out1 with the BP wavelength tuned from 1550nm to 1525nm in the embodiment, showing a single wavelength interval. (Example) Figure 7 The Brillouin pump wavelength of the fiber laser is tunable, ranging from 1525nm to 1550nm.

[0071] Figure 8This is a schematic diagram of the spectrum measured at the first output terminal Out1 in the embodiment, showing the wavelength of double-wavelength-spaced BP light tuned from 1550nm to 1516nm. Figure 8 As can be seen, the embodiment does not have strict requirements on the center wavelength of the pump light within the range of 1516nm-1550nm, which allows for easy system setup.

[0072] Figure 9 This is a schematic diagram illustrating the effect of tuning the BP optical power from 7.6dBm to 12.6dBm on the bandwidth of random multi-wavelength lasers in the embodiment. Figure 10 This is a schematic diagram illustrating the effect of tuning the Raman pump power from 823.8mW to 1702mW on the bandwidth of a random multi-wavelength laser in this embodiment. Figure 9 and Figure 10 As can be seen, the embodiment has low power requirements for Raman pump light, which makes it easier to build the system.

[0073] This type of pump-light-tunable wavelength-spacing Brillouin-Raman random fiber laser features a fully open-cavity Brillouin-Raman random cavity 8, capable of outputting bidirectional random laser light. Random feedback is provided through Rayleigh scattering at both ends. The first-order stimulated Brillouin scattering branch is adjusted using an erbium-doped fiber amplifier 3. Figure 1 The dashed line and the power ratio of the Brillouin pump branch enable switching between single and double Brillouin frequency shift intervals. Experiments verified that when the power of the erbium-doped fiber amplifier 3 is set to 0mW, only the Brillouin pump branch (BP) light enters the Brillouin Raman random cavity 8 through the first optical circulator 4Cir 1. This generates a cascade effect of stimulated Brillouin scattering in the hybrid gain fiber of the Brillouin Raman random cavity 8, producing a laser output with a bandwidth of approximately 60nm (1516nm-1576nm) and a spacing of 0.168nm under the pumping of two Raman pump lasers. When both the first-order SBS and BP branches are activated simultaneously, and the power of the erbium-doped fiber amplifier 3 is set to 119mW, a laser output with a bandwidth of approximately 44nm (1530nm-1574nm) and a spacing of 0.08nm can be obtained.

[0074] This wave-spaced switchable Brillouin-Raman random fiber laser, based on pump light modulation, achieves an output bandwidth of up to 60 nm for double-wavelength-spaced lasers and 44 nm for single-wavelength-spaced lasers. Two bidirectional Raman lasers provide broadband, flat gain for the random multi-wavelength laser. By adjusting different Raman pump powers, multi-wavelength laser outputs with varying bandwidths are achieved. This fiber laser has four output terminals, expanding its applicability.

[0075] The above description is merely an embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A wavelength-spacing switchable Brillouin-Raman random fiber laser based on pump light modulation, comprising a tunable laser and a first optical coupler, wherein the tunable laser outputs pump light to the first optical coupler, characterized in that: It also includes an erbium-doped fiber amplifier, a first optical circulator, a second optical circulator, a first single-mode fiber, a first optical isolator, and a Brillouin-Raman random cavity. The first optical coupler is connected to port a of the first optical circulator, port b of the first optical circulator is connected to port h of the second optical coupler, port c of the first optical circulator is connected to the first output terminal, the first optical coupler is also connected to port d of the second optical circulator through the erbium-doped fiber amplifier, port e of the second optical circulator is connected to port g of the second optical coupler, port f of the second optical circulator is connected to the second output terminal, port i of the second optical coupler is connected to the first optical isolator through the first single-mode fiber, and port j of the second optical coupler is connected to the Brillouin-Raman random cavity; the output power of the erbium-doped fiber amplifier is controlled to achieve switching between multi-wavelength lasers with a single Brillouin frequency shift interval and multi-wavelength lasers with a double Brillouin frequency shift interval; The Brillouin Raman random cavity includes a first wavelength division multiplexer, a hybrid gain fiber, a second wavelength division multiplexer, a second optical isolator, a third optical isolator, a first Raman pump laser, a fourth optical isolator, and a second Raman pump laser. Port j of the second optical coupler is connected to the second wavelength division multiplexer through the first wavelength division multiplexer and the hybrid gain fiber. The second wavelength division multiplexer is connected to the second optical isolator and then to the first Raman pump laser through the third optical isolator. The first wavelength division multiplexer is also connected to the second Raman pump laser through the fourth optical isolator. The hybrid gain fiber includes a second single-mode fiber and a dispersion compensation fiber. The first wavelength division multiplexer is connected to the second wavelength division multiplexer in sequence through the second single-mode fiber and the dispersion compensation fiber.

2. The wavelength-spacing switchable Brillouin-Raman random fiber laser based on pump light modulation as described in claim 1, characterized in that: When the first single-mode fiber is 20kM, the center wavelength of the tunable laser is 1530nm-1550nm, and the output power of the erbium-doped fiber amplifier is controlled within [76.8mW-119mW]. The fiber laser outputs multi-wavelength laser with a single Brillouin frequency shift interval.

3. The wavelength-spacing switchable Brillouin-Raman random fiber laser based on pump light modulation as described in claim 1, characterized in that: When the first single-mode fiber is 20kM, the center wavelength of the tunable laser is 1516nm-1550nm. When the output power of the erbium-doped fiber amplifier is controlled to be [0mW-76.8mW) or greater than or equal to 366.5mW, the fiber laser outputs a multi-wavelength laser with double Brillouin frequency shift interval.

4. The wavelength-spacing switchable Brillouin-Raman random fiber laser based on pump light modulation as described in claim 1, characterized in that: The pump light is split into the pump light of the first-order stimulated Brillouin scattering branch and the pump light of the Brillouin pump branch after passing through the first optical coupler.

5. The wavelength-spacing switchable Brillouin-Raman random fiber laser based on pump light modulation as described in claim 4, characterized in that: This fiber laser outputs multi-wavelength laser light with a single Brillouin frequency shift interval, specifically... S11. The pump light of the first-order stimulated Brillouin scattering branch is amplified by the erbium-doped fiber amplifier, passes through port d to port e of the second optical circulator, and then enters port g of the second optical coupler. S12. Port h of the second optical coupler outputs 50% power pump light to the first optical circulator, and port i of the second optical coupler outputs the remaining 50% power pump light into the first single-mode fiber, exciting first-order stimulated Brillouin scattering light propagating to the right; the newly generated first-order stimulated Brillouin scattering light, together with the pump light, enters the hybrid gain fiber of the Brillouin Raman random cavity on the right side through the second optical coupler. S13. The second-order Stokes beam propagating to the left is generated under the gain of the bidirectional Raman pump beam, while the third-order Stokes beam propagating to the right is excited when the threshold condition is reached. Under strong Raman pumping conditions, i.e., when both the first and second Raman pump lasers are at maximum power output, the cascaded Stokes beam will also be excited. The even-order Stokes beam is output from the first output terminal through port c of the first optical circulator, while the odd-order Stokes beam is output from the second optical isolator. S14. The odd-order Stokes light excited by the Brillouin pump branch and the even-order Stokes light excited by the first-order stimulated Brillouin scattering branch are superimposed and output from the first output terminal through port c of the first optical circulator, forming a multi-wavelength laser with a single Brillouin frequency shift interval. Similarly, the even-order Stokes light generated by the Brillouin pump branch and the odd-order Stokes light generated by the first-order stimulated Brillouin scattering branch are superimposed and output from the second optical isolator. A multi-wavelength laser with a single Brillouin frequency shift interval is observed at the first output terminal and the second optical isolator, respectively.

6. The wavelength-spacing switchable Brillouin-Raman random fiber laser based on pump light modulation as described in claim 4, characterized in that: This fiber laser outputs multi-wavelength laser light with twice the Brillouin frequency shift interval, specifically... S21. The pump light of the Brillouin pump branch passes through port a to port b of the first optical circulator and then enters port h of the second optical coupler. Among them, the pump light of the Brillouin pump branch with 50% power is output from port f of the second optical circulator, and the pump light of the remaining 50% power of the Brillouin pump branch enters the bidirectional Raman-pumped hybrid gain fiber of the Brillouin Raman random cavity. S22. When the threshold of stimulated Brillouin scattering is reached, the Brillouin Raman random cavity generates a first-order backward-propagating Stokes beam. The first-order backward-propagating Stokes beam passes through the hybrid gain fiber of the Brillouin Raman random cavity again to generate a forward-propagating second-order Stokes beam. S23. Subsequently, the cascaded Stokes beams are excited in this mode in the hybrid gain fiber until the higher-order threshold condition is no longer met. Thus, the odd-order Stokes beams enter port b of the first optical circulator through the second optical coupler and are output from the first output terminal through port c of the first optical circulator; the even-order Stokes beams are output from the second optical isolator on the right.

7. The wavelength-spacing switchable Brillouin-Raman random fiber laser based on pump light modulation as described in claim 1, characterized in that: By controlling the output power of the erbium-doped fiber amplifier, the first output terminal and the second optical isolator achieve bidirectional separated Stokes light output. Specifically... When the erbium-doped fiber amplifier is turned off, the fiber laser separates and outputs odd-order and even-order Stokes light, wherein the odd-order Stokes light is obtained from the first output end, and the even-order Stokes light is obtained from the second optical isolator; When the output power of the erbium-doped fiber amplifier exceeds 366.5mW, even-order Stokes light is obtained at the first output terminal, and odd-order Stokes light is obtained at the second optical isolator.

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