A bandwidth tunable and mode switchable multi-wavelength random fiber laser

Abstract

The application discloses a bandwidth-tunable and mode-switchable multi-wavelength random fiber laser, which is a bandwidth-tunable and mode-switchable multi-wavelength random fiber laser based on a mixed gain of an erbium-doped optical fiber, stimulated Raman scattering and stimulated Brillouin scattering. The output power of a pump light source is adjusted to make stimulated Raman scattering amplify Rayleigh scattering, and the multi-wavelength random distribution feedback is enhanced, so that flat wide-spectrum multi-wavelength random laser output is obtained. The output wavelength and output power of a tunable narrow-line-width laser source are adjusted to realize dynamic filtering of the wide-spectrum multi-wavelength random laser. The application has the characteristics of simple structure, high reliability, low cost, low threshold power, stable output and full fiber, and also has the unique characteristics of gain type diversity, flat spectrum, large tunable range of spectrum bandwidth, switchable laser output mode and the like, and is expected to be used as a new type of fiber laser light source to play an important role in the fields of optical communication, optical sensing and optical imaging and the like.

Description

Technical Field

[0001] This invention belongs to the field of fiber laser technology, specifically relating to a multi-wavelength random fiber laser with tunable bandwidth and switchable mode. Background Technology

[0002] Fiber random lasers, as a novel type of fiber laser, are characterized by their open or reflectionless cavities, with feedback mechanisms relying on random scattering distributed along the fiber cavity. Compared to traditional lasers, which have emission longitudinal modes dependent on the resonant cavity length, random fiber lasers possess an infinite cavity distributed along the fiber. By exciting a large number of random laser modes, emission lines as broad as the optical gain spectrum can be achieved. Since the demonstration of random distributed feedback based on Rayleigh scattering in 2010, fiber lasers utilizing Rayleigh scattering from long fibers as random distributed feedback have been proposed successively.

[0003] Among them, multi-wavelength random fiber lasers based on Rayleigh scattering, as one of the important research directions and applications of fiber random lasers, have attracted great attention in recent years due to their significant application potential in wavelength division multiplexing communication, high-resolution spectroscopy, and fiber optic sensing. Since 2010, solutions for multi-wavelength random fiber lasers based on random distributed feedback and different filter structures have been proposed one after another. For example, Pinto et al. achieved multi-wavelength random laser output by using a combination of fiber ring structure and photonic crystal fiber as filter elements placed in a random distributed feedback fiber laser cavity. Schemes that use fiber Bragg gratings in series as wavelength selectors or utilize an all-fiber Lyot filter structure to achieve multi-wavelength random laser output have also been proposed and verified. In addition, multi-wavelength random fiber lasers based on the interaction of Raman scattering, stimulated Brillouin scattering, and Rayleigh scattering have attracted widespread attention due to their special multi-wavelength spectral characteristics. However, existing fiber lasers have always struggled to achieve wider wavelength tunable ranges, wider spectral bandwidths, and higher output power, and also cannot simultaneously utilize Raman scattering or Brillouin scattering to amplify Rayleigh scattering over a wide range, thus failing to enhance random distributed feedback.

[0004] Based on the needs of on-site production and research, there is an urgent need for a fiber laser that can achieve a wider wavelength tunable range, a wider spectral bandwidth, and higher output power. Summary of the Invention

[0005] Based on the technical problems existing in the prior art, the present invention provides a multi-wavelength random fiber laser with tunable bandwidth and switchable mode. The present invention utilizes the effective technical means of practical broadband fiber lasers to solve the technical problems of pursuing a wider wavelength tunable range, a wider spectral bandwidth, tunable wavelength spacing, and switchable laser output mode in multi-wavelength fiber lasers.

[0006] To address the aforementioned technical problems, this invention provides a bandwidth-tunable and mode-switchable multi-wavelength random fiber laser. This laser is based on a hybrid gain of erbium-doped fiber, stimulated Raman scattering, and stimulated Brillouin scattering. By adjusting the output power of the pump source, stimulated Raman scattering amplifies Rayleigh scattering, enhancing the multi-wavelength random distribution feedback and thus obtaining a flat, broadband multi-wavelength random laser output. Furthermore, by adjusting the output wavelength and output power of the tunable narrow-linewidth laser source, dynamic filtering of the broadband multi-wavelength random laser is achieved.

[0007] The aforementioned bandwidth-tunable and mode-switchable multi-wavelength random fiber laser further enables switching between broadband multi-wavelength random laser output modes and stimulated Brillouin scattering multi-wavelength random laser output modes. The bandwidth-tunable and mode-switchable multi-wavelength random fiber laser employs a semi-open cavity structure design, utilizing back-scattering Rayleigh scattering from a long single-mode fiber to provide randomized feedback, and utilizing active fiber, stimulated Raman scattering, and stimulated Brillouin scattering to provide laser gain. Preferably, dynamic filtering is achieved by adjusting the output power and wavelength of the tunable narrow-linewidth laser source to tune the spectral bandwidth.

[0008] Furthermore, the bandwidth-tunable and mode-switchable multi-wavelength random fiber laser includes a tunable narrow-linewidth laser source, a first optical circulator, a second optical circulator, a first single-mode fiber, a second single-mode fiber, a pump source, a wavelength division multiplexer, an active fiber, an optical isolator, and fiber connectors. The bandwidth-tunable and mode-switchable multi-wavelength random fiber laser adopts a semi-open cavity junction design. It utilizes stimulated Brillouin scattering generated by the active fiber and the first single-mode fiber, and stimulated Raman scattering of the second single-mode fiber to provide laser gain. It utilizes backscattering of the second single-mode fiber to achieve random distribution feedback. The fiber ring mirror composed of the first and second optical circulators and the backscattering of the second single-mode fiber form a random resonant cavity.

[0009] Furthermore, by adjusting the output power of the pump source, a flat, broadband, multi-wavelength random laser output can be obtained.

[0010] Furthermore, dynamic filtering of broadband multi-wavelength random lasers can be achieved by adjusting the output wavelength and output power of a tunable narrow-linewidth laser source, with its spectral bandwidth being tunable over a wide range.

[0011] Preferably, a tunable narrow-linewidth laser source is used to generate stimulated Brillouin scattering pump light, and a first optical circulator and a second optical circulator are used to form an optical fiber ring mirror; a first single-mode fiber and a second single-mode fiber are used to generate Raman scattering, stimulated Brillouin scattering, and Rayleigh scattering; a pump source is used to provide pump light to the active optical fiber; and a wavelength division multiplexer is used to introduce the pump light and connect the gain fiber to the optical circulator.

[0012] More preferably, the active optical fiber is used to generate laser gain and randomized feedback, the optical isolator is used to prevent unnecessary laser feedback from the output end back into the laser cavity, which would affect the stability of the laser, and the fiber optic connector serves as both the laser output port and the probe output port. Furthermore, the pump light of the pump source can have a selectable wavelength of 1480 nm, 980 nm, or 1080 nm.

[0013] Compared with the prior art, the advantages of the present invention, a multi-wavelength random fiber laser with tunable bandwidth and switchable mode, are:

[0014] 1. The fiber laser of the present invention has a simple structure, is easy to control, has low cost, low lasing threshold, high stability, and is all fiber optic;

[0015] 2. The present invention provides a multi-wavelength random fiber laser with tunable bandwidth and switchable mode. It adopts a semi-open cavity structure design, utilizes backscattering of long single-mode fiber to provide random distribution feedback, and utilizes active fiber, stimulated Raman scattering and stimulated Brillouin scattering to provide laser gain. The gain mechanism is diverse, which makes the laser output have special multi-wavelength spectral characteristics and realizes the diversity of laser gain types.

[0016] 3. This invention utilizes tunable bandwidth and switchable mode. By adjusting the output wavelength and power of the tunable narrow linewidth laser source, dynamic filtering of broadband multi-wavelength random lasers can be achieved. The spectral bandwidth is tunable over a large range, resulting in a large tunable range of spectral bandwidth.

[0017] 4. This invention amplifies Rayleigh scattering by adjusting the output power of the pump source, thereby enhancing multi-wavelength random distribution feedback and obtaining flat broadband multi-wavelength random laser output; compared with lasers of the prior art, the spectral flatness of the laser of this invention is improved by 1 to 3 orders of magnitude.

[0018] 5. The laser output mode of the present invention can be switched. By adjusting the output power and wavelength of the tunable narrow linewidth laser source, the spectral bandwidth can be tuned within a large range. At the same time, it realizes the switching between broadband multi-wavelength random laser mode and stimulated Brillouin scattering multi-wavelength random laser mode, which can more flexibly realize field applications in multiple occasions and scenarios. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the structure of the bandwidth-tunable and mode-switchable multi-wavelength random fiber laser of the present invention.

[0020] Figure 2 This is a spectrum of broadband multi-wavelength random laser output from the bandwidth-tunable and mode-switchable multi-wavelength random fiber laser of the present invention.

[0021] Figure 3 This is a spectrum of stimulated Brillouin multiwavelength random laser output from the bandwidth-tunable and mode-switchable multiwavelength random fiber laser of the present invention.

[0022] The reference numerals in the attached figures are as follows: 1. Tunable narrow linewidth laser source; 2. First optical circulator; 4. Second optical circulator; 3. First single-mode fiber; 8. Second single-mode fiber; 5. Pump source; 6. Wavelength division multiplexer; 7. Active fiber; 9. Optical isolator; 10. Fiber optic connector. Detailed Implementation

[0023] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0024] It should be noted that when an element is referred to as being "fixed to" or "set on" another element, it can be directly or indirectly on that other element. When an element is referred to as being "connected to" another element, it can be directly or indirectly connected to that other element. Unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0025] It should be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention.

[0026] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0027] This invention proposes a bandwidth-tunable and mode-switchable multi-wavelength random fiber laser, which is based on erbium-doped fiber, stimulated Raman scattering, and stimulated Brillouin scattering hybrid gain, and possesses both bandwidth tunability and mode-switchability. This invention enhances multi-wavelength random distribution feedback by adjusting the output power of the pump source to amplify Rayleigh scattering through stimulated Raman scattering, thereby obtaining a flat, broadband multi-wavelength random laser output. By adjusting the output wavelength and output power of the tunable narrow-linewidth laser source, dynamic filtering of the broadband multi-wavelength random laser is achieved, with its spectral bandwidth tunable over a wide range. Furthermore, switching between the broadband multi-wavelength random laser output mode and the stimulated Brillouin scattering multi-wavelength random laser output mode can be realized.

[0028] This invention discloses a bandwidth-tunable and mode-switchable multi-wavelength random fiber laser with a semi-open cavity structure. It utilizes backscattering of Rayleigh scattering from a long single-mode fiber to provide randomly distributed feedback, and employs active fiber, stimulated Raman scattering, and stimulated Brillouin scattering to provide laser gain. This diverse gain mechanism results in unique multi-wavelength spectral characteristics in the laser output. The spectral bandwidth is tuned by adjusting the output power and wavelength of the tunable narrow-linewidth laser source.

[0029] Compared to existing technologies, the multi-wavelength random fiber laser of this invention offers a tunable spectral bandwidth over a wide range, while simultaneously enabling switching between a broadband multi-wavelength random laser mode and a stimulated Brillouin scattering (SBS) multi-wavelength random laser mode. This invention cleverly utilizes active fiber gain, stimulated Brillouin scattering, Raman scattering, and Rayleigh scattering to provide laser gain, resulting in diverse and switchable laser gains. Employing a semi-open structure design, the backscattering of Rayleigh scattering in the long single-mode fiber acts as a large number of randomly distributed mirrors, forming an optical resonant cavity with a fiber optic ring mirror composed of a first and second optical circulator. Further amplification through stimulated Raman scattering and Rayleigh scattering yields a broadband multi-wavelength random laser output. Dynamic filtering of the broadband multi-wavelength random laser can be achieved by adjusting the output wavelength and power of the tunable narrow-linewidth laser source, with a tunable spectral bandwidth over a wide range. Furthermore, the broadband multi-wavelength random laser output mode can be switched to a stimulated Brillouin scattering (SBS) multi-wavelength random laser mode, solving technical challenges related to the rich output characteristics, wide spectral bandwidth, tunable bandwidth, and switchable laser modes of fiber lasers.

[0030] The working principle of this invention's bandwidth-tunable and mode-switchable multi-wavelength random fiber laser is as follows: Under the action of the pump light from the pump source, the active fiber generates spontaneous emission. During the propagation of spontaneous emission, the microscopic irregularities of the fiber itself cause randomly distributed Rayleigh scattering. After Rayleigh scattering, the vast majority of photons propagating in the fiber escape from the fiber core, with only a very small portion being backscattered and still bound by the fiber; this portion of photons is called backscattered Rayleigh light. Under the gain provided by the pump light from the pump source, the scattered photons are amplified. Backscattered random Rayleigh scattering in the single-mode fiber is equivalent to the action of a large number of randomly distributed mirrors, returning a portion of the spontaneous emission to the laser cavity. This forms a closed feedback loop with the fiber ring mirror composed of the first and second optical circulators, achieving optical amplification, satisfying the conditions for laser formation, and realizing the lasing of a random fiber laser. When the pump power of the pump source reaches a certain threshold, a large amount of random laser output can be achieved within the gain spectrum of the active fiber. Then, by increasing the output power of the pump source, the second single-mode fiber generates stimulated Brillouin scattering and stimulated Raman scattering, providing gain to the laser. Furthermore, stimulated Raman scattering further amplifies Rayleigh scattering, enhancing the random distribution feedback effect, thereby achieving broadband multi-wavelength random laser output. Further, a tunable narrow-linewidth laser source is introduced to provide gain for stimulated Brillouin scattering generated by the first single-mode fiber. The stimulated Brillouin scattering generated by the first single-mode fiber is further amplified by the pump source and the active fiber, while simultaneously promoting stimulated Raman scattering and Rayleigh scattering in the second single-mode fiber, thus generating a broad-spectrum multi-wavelength random laser output. This invention changes the intensity of stimulated Brillouin scattering and Raman scattering by adjusting the output wavelength and power of a tunable narrow-linewidth laser, thereby switching between different laser gain types and changing the laser output mode. This allows the spectral bandwidth to be tunable over a wide range, and the broadband multi-wavelength laser output mode and the stimulated Brillouin multi-wavelength laser output mode can be switched.

[0031] In a preferred embodiment, the bandwidth-tunable and mode-switchable multi-wavelength random fiber laser of the present invention mainly comprises a tunable narrow-linewidth laser source, an optical circulator, a single-mode fiber, a pump source, a wavelength division multiplexer, an active fiber, an optical isolator, and fiber connectors. It adopts a semi-open cavity structure design, utilizing stimulated Raman scattering and stimulated Brillouin scattering from the active fiber and single-mode fiber to provide laser gain, and utilizing backscattering Rayleigh scattering from the long single-mode fiber to provide random distribution feedback. A fiber ring mirror composed of a first optical circulator and a second optical circulator forms a random resonant cavity with the backscattering Rayleigh scattering from the long single-mode fiber. By adjusting the output power of the pump source, a flat broadband multi-wavelength random laser output can be obtained. Furthermore, by adjusting the output wavelength and power of the tunable narrow-linewidth laser source, the intensity of stimulated Brillouin scattering and stimulated Raman scattering can be changed, thereby switching different laser gain types and changing the laser output mode. This allows the spectral bandwidth to be tunable over a large range, and enables switching between broadband multi-wavelength random laser output modes and stimulated Brillouin multi-wavelength laser output modes. Multiwavelength random fiber lasers with tunable bandwidth and switchable modes not only have the characteristics of simple structure, high reliability, low cost, low threshold power, stable output and all-fiber, but also have unique features such as diverse gain types, flat spectrum, large tunable spectral bandwidth and switchable laser output modes. They are expected to play an important role as a new type of fiber laser source in optical communication, optical sensing and optical imaging.

[0032] The following is in conjunction with the appendix Figure 1-3This paper specifically describes the bandwidth-tunable and mode-switchable multi-wavelength random fiber laser of the present invention. The bandwidth-tunable and mode-switchable multi-wavelength random fiber laser of the present invention offers diverse and switchable laser gain types. The laser utilizes active fiber, stimulated Raman scattering (SRS), and stimulated Brillouin scattering (SBS) to provide laser gain, exhibiting diverse gain mechanisms. By changing the output power of the pump source 5, the output power of the tunable narrow-linewidth laser source 1, and the wavelength, the laser gain mechanism can be switched to provide laser gain only from the active fiber, from active fiber and stimulated Brillouin scattering, from active fiber and stimulated Raman scattering, or from all three (active fiber, stimulated Raman scattering, and stimulated Brillouin scattering) jointly providing laser gain. The laser of the present invention utilizes the first optical circulator 2 and the second optical circulator 4 to form a fiber optic ring mirror, simultaneously introducing stimulated Brillouin pump light and functioning as an optical mirror. The laser output end of the pump source 5 is sequentially connected to a wavelength division multiplexer 6, an active optical fiber 7, a second single-mode optical fiber 8, and an optical isolator, forming a semi-open resonant cavity structure together with the fiber ring mirror composed of the first optical circulator 2 and the second optical circulator 4. Preferably, the active optical fiber 7 includes one of the gain fibers such as erbium-doped fiber, ytterbium-doped fiber, erbium-ytterbium co-doped fiber, or thulium-doped fiber. Further, the tunable narrow-linewidth laser source 1 includes a laser whose output wavelength is located within the gain spectrum of the active optical fiber 7, serving as the pump light for stimulated Brillouin scattering. In a preferred embodiment, the first single-mode fiber 3 and the second single-mode fiber 8 include various types of single-mode fibers with lengths ranging from 1km to 50km, used to generate sufficient backscattering Rayleigh scattering, stimulated Brillouin scattering, and stimulated Raman scattering.

[0033] like Figure 1 As shown, a bandwidth-tunable and mode-switchable multi-wavelength random fiber laser includes:

[0034] A tunable narrow-linewidth laser source 1 is used to generate stimulated Brillouin scattering pump light;

[0035] The first optical circulator 2 and the second optical circulator 4 are used to form an optical fiber ring mirror;

[0036] The first single-mode fiber 3 and the second single-mode fiber 8 are used to generate Raman scattering, stimulated Brillouin scattering and Rayleigh scattering.

[0037] Pump light source 5 is used to provide pump light to the active optical fiber;

[0038] Wavelength division multiplexer 6 is used to introduce pump light and connect the gain fiber to the optical circulator;

[0039] Active fiber 7 is used to generate laser gain;

[0040] Optical isolator 9 is used to prevent unnecessary laser feedback from the output end back into the laser cavity, which would affect the stability of the laser.

[0041] Fiber optic connector 10 serves as both a laser output port and a detection output port.

[0042] As a first optimization of the present invention, the pump light of the pump source can be selected with a wavelength of 1480nm, 980nm or 1080nm.

[0043] As a second optimization of the present invention, the active optical fiber may be selected from one of the gain fibers such as erbium-doped fiber, ytterbium-doped fiber, erbium-ytterbium co-doped fiber, or thulium-doped fiber.

[0044] Furthermore, a multi-wavelength random fiber laser with tunable bandwidth and switchable mode includes a tunable narrow-linewidth laser source 1, a first optical circulator 2, a second optical circulator 4, a first single-mode fiber 3, a second single-mode fiber 8, a pump source 5, a wavelength division multiplexer 6, an active fiber 7, an optical isolator 9, and an optical fiber connector 10. The tunable narrow-linewidth laser source 1 is a tunable narrow-linewidth laser with a wavelength tuning range of 1525nm-1565nm, an output power range of 5mW-32mW, and a linewidth of less than 100kHz. The first optical circulator 2 and the second optical circulator 4 each have ports 1, 2, and 3, where port 1 is the input port and port 2 is a bidirectional port. The three ports are output ports; the first single-mode fiber 3 and the second single-mode fiber 8 are both ordinary commercial single-mode fibers with a core diameter of 9μm, of which the first single-mode fiber 3 is about 10km long and the second single-mode fiber 8 is about 20km long; the pump light source 5 is a semiconductor laser with a working wavelength of 980nm and a maximum output power of about 600mW; the wavelength division multiplexer 6 is a three-port wavelength division multiplexer with a 980nm end, a 980 / 1550nm end and a 1550nm end; the active fiber 7 is an erbium-doped gain fiber with a length of about 10m; the optical isolator 9 is an SMF-28e fiber with a fiber length of 1 meter; the fiber connector 10 is an FC type fiber connector.

[0045] The specific connection method for a bandwidth-tunable and mode-switchable multi-wavelength random fiber laser is as follows:

[0046] The input port of the first optical circulator 2 is connected to the output port of the tunable narrow-linewidth laser source 1. The bidirectional port of the first optical circulator 2 is connected to the first single-mode fiber 3. The output port of the first optical circulator 2 is connected to the input port of the second optical circulator 4. The bidirectional port of the second optical circulator 4 is connected to the transmission port of the wavelength division multiplexer 6, preferably a 1550 nm port, which allows conventional 1550 nm signals to pass through and can be used with optical devices such as 100 Mbps, 1 Gbps, and 10 Gbps optical modules. The output port of the second optical circulator 4 is connected to the first single-mode fiber 3. The pump source 5 is sequentially connected to the wavelength division multiplexer 6, the active fiber 7, the second single-mode fiber 8, and the optical isolator 9. The output port of the optical isolator 9 is the output port of a bandwidth-tunable and mode-switchable multi-wavelength random fiber laser. The first optical circulator 2, the second optical circulator 4, and the second single-mode fiber 8 constitute a fiber optic ring mirror. In this system, pump source 5 serves as the pump source for stimulated Raman scattering of active fiber 7 and second single-mode fiber 8. Backward Rayleigh scattering from the second single-mode fiber 8 provides randomized optical feedback for laser generation. First single-mode fiber 3 is used to generate stimulated Brillouin scattering. Tunable narrow-linewidth laser source 1 serves as the pump source for stimulated Brillouin scattering. The stimulated Brillouin scattering from active fiber 7, first single-mode fiber 3, and stimulated Raman scattering from second single-mode fiber 8 collectively provide laser gain.

[0047] The fiber type of the output end of the tunable narrow linewidth laser source 1, the input and output ends of the first optical circulator 2 and the second optical circulator 4, the output end of the pump source 5, the input and output ends of the wavelength division multiplexer 6, and the input and output ends of the optical isolator 9 are all ordinary single-mode optical fibers.

[0048] The connections between the output of pump source 5 and the 980nm port of wavelength division multiplexer 6, between the 980nm / 1550nm ends of the wavelength division multiplexer and the erbium-doped fiber, and between the erbium-doped fiber and the single-mode fiber are all fixedly spliced ​​using a fiber optic fusion splicer. Other connections are made using FC / APC type fiber optic connectors.

[0049] like Figure 2 As shown, when the fixed pump source output power is 600mW, the tunable narrow-linewidth laser source power is 8mW, and the wavelength of the tunable narrow-linewidth laser source is 1545nm, the laser output mode is a broadband multi-wavelength random laser with a spectral bandwidth of approximately 35nm, and the spectral flatness is good. During the experiment, by adjusting the output power and wavelength of the tunable narrow-linewidth laser source, the tunable range of the spectral bandwidth was obtained from 3nm to 35nm.

[0050] like Figure 3The image shows the output spectrum of a laser when the wavelength of a fixed tunable narrow-linewidth laser source is 1565.0 nm, the power is 20 mW, and the output power of the pump source is 600 mW. From... Figure 3 As can be seen from this, the laser output mode at this time is stimulated Brillouin multi-wavelength random laser.

[0051] This invention discloses a bandwidth-tunable and mode-switchable multi-wavelength random fiber laser with a semi-open cavity structure design. It utilizes stimulated Raman scattering and stimulated Brillouin scattering from active fiber and single-mode fiber to provide laser gain, and backscattering from long single-mode fiber to provide random distribution feedback. A fiber ring mirror composed of a first optical circulator and a second optical circulator forms a random resonant cavity with the backscattering from the long single-mode fiber. By adjusting the output power of the pump source, a flat, broadband multi-wavelength random laser output can be obtained. Furthermore, by adjusting the output wavelength and power of the tunable narrow-linewidth laser source, the intensity of stimulated Brillouin scattering and stimulated Raman scattering can be changed, thereby switching different laser gain types and altering the laser output mode. This allows for tunability of the spectral bandwidth over a wide range and enables switching between broadband multi-wavelength random laser output modes and stimulated Brillouin multi-wavelength laser output modes. Multiwavelength random fiber lasers with tunable bandwidth and switchable modes not only have the characteristics of simple structure, high reliability, low cost, low threshold power, stable output and all-fiber, but also have unique features such as diverse gain types, flat spectrum, large tunable spectral bandwidth and switchable laser output modes. They are expected to play an important role as a new type of fiber laser source in optical communication, optical sensing and optical imaging.

[0052] The above description is merely a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the working principle and structural composition of the present invention should be included within the protection scope of the present invention.

Claims

1. A bandwidth-tunable and mode-switchable multi-wavelength random fiber laser, characterized in that: The system includes a tunable narrow-linewidth laser source, a first optical circulator, a second optical circulator, a first single-mode fiber, a second single-mode fiber, a pump source, a wavelength division multiplexer, an active fiber, an optical isolator, and fiber connectors. The multi-wavelength random fiber laser with tunable bandwidth and switchable modes adopts a semi-open cavity structure design. Random distribution feedback is achieved by utilizing the backscattering of Rayleigh from the second single-mode fiber. The fiber ring mirror composed of the first and second optical circulators forms a random resonant cavity with the backscattering of Rayleigh from the second single-mode fiber. The first and second single-mode fibers are used to generate Raman scattering, stimulated Brillouin scattering, and Rayleigh scattering. The pump source is used to provide pump light to the active optical fiber; the wavelength division multiplexer is used to introduce the pump light and connect the active optical fiber, the first optical circulator, and the second optical circulator. The output of the pump light source is connected to the pump wavelength port of the wavelength division multiplexer. The common port of the wavelength division multiplexer is connected in sequence to the active optical fiber, the second single-mode optical fiber, and the optical isolator. The output of the optical isolator is connected to the optical fiber connector. Port 1 of the first optical circulator is connected to the output of the tunable narrow linewidth laser source; port 2 of the first optical circulator is connected to the first single-mode fiber; port 3 of the first optical circulator is connected to port 1 of the second optical circulator; and port 2 of the second optical circulator is connected to the transmission port of the wavelength division multiplexer. The third port of the second optical circulator is connected to the first single-mode fiber; the pump source is connected in sequence to the wavelength division multiplexer, the active fiber, the second single-mode fiber, and the optical isolator; the lengths of the first single-mode fiber and the second single-mode fiber range from 1km to 50km. The bandwidth-tunable and mode-switchable multi-wavelength random fiber laser enhances multi-wavelength random distribution feedback by adjusting the output power of the pump source to amplify Rayleigh scattering through stimulated Raman scattering. Dynamic filtering of the broadband multi-wavelength random laser is achieved by adjusting the output wavelength and output power of the tunable narrow-linewidth laser source. The bandwidth-tunable and mode-switchable multi-wavelength random fiber laser enables switching between broadband multi-wavelength random laser output modes and stimulated Brillouin scattering multi-wavelength random laser output modes. Laser gain is provided by active fiber, stimulated Raman scattering, and stimulated Brillouin scattering.

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