A ring random fiber laser

Abstract

The application relates to a ring random optical fiber laser, belonging to the technical field of optical fiber lasers, which is composed of a pumping laser light source, a pumping wavelength division multiplexer, a fiber Bragg grating, a fiber coupler, a double-clad ytterbium-doped optical fiber, an adjustable optical fiber delay line, an adjustable splitting-ratio optical fiber coupler and an optical isolator to form a ring cavity, wherein the high-reflection fiber Bragg grating and the random Rayleigh scattering in the double-clad ytterbium-doped optical fiber are used to form the cavity feedback; the ytterbium ion gain and the stimulated Raman scattering are used to realize the mixed gain amplification; the adjustable optical fiber delay line and the adjustable splitting-ratio optical fiber coupler can be used to realize the output of stable single-frequency continuous laser and chaotic laser; and the application has the advantages of simple structure, low cost, lower lasing threshold and higher conversion efficiency.

Description

Technical Field

[0001] This invention belongs to the field of fiber laser technology, and more specifically, relates to a ring random fiber laser. Background Technology

[0002] In recent years, random fiber lasers, as a new branch in the field of fiber lasers, have attracted considerable interest from researchers due to their unique characteristics. Compared with conventional fiber lasers, random fiber lasers are based on random lasing and possess novel feedback characteristics, utilizing multiple random Rayleigh scattering in a disordered medium to achieve lasing. The most common cavity structure for random fiber lasers is a semi-open cavity structure, with one end using a fiber Bragg grating to provide point feedback and the other end using the inherent Rayleigh random scattering within the fiber to provide distributed feedback. The cavity gain is provided by the doped ion active fiber and stimulated Raman gain (or stimulated Brillouin gain). However, due to the semi-open cavity structure, the gain generated by random Rayleigh scattering feedback is relatively weak. Therefore, random fiber lasers based on active ion and stimulated Raman scattering gain have a high lasing threshold and low conversion efficiency.

[0003] The emergence of ring random fiber lasers can improve the conversion efficiency of random fiber lasers and reduce the lasing threshold to some extent.

[0004] The output states of ring fiber lasers generally include single-frequency continuous output (referring to the laser output state where both power and wavelength (or frequency) remain constant), periodic, period-doubling, and chaotic states. Regardless of the output state, when using a laser, we always hope that the output laser can be stable in the state we need, rather than experiencing unstable fluctuations. However, although ring random fiber lasers have overcome the shortcomings of high lasing threshold and low conversion efficiency of semi-open cavity random fiber lasers to some extent, they can still exhibit intermittent chaotic phenomena and mode-hopping behavior during operation, resulting in unstable output states.

[0005] In addition, in existing technologies, the pump light, active ion gain, and stimulated Raman gain in ring random fiber laser systems cannot be fully utilized, and the intracavity feedback mechanism is mainly provided by random Rayleigh scattering, whose feedback effect is not obvious in the laser generation process. Therefore, the reduction of the lasing threshold in existing ring random fiber lasers needs further improvement, and there is also a lot of room for improvement in their conversion efficiency. Summary of the Invention

[0006] To address the problems of existing technologies, the present invention aims to provide a ring cavity random fiber laser with more stable output, lower lasing threshold, higher conversion efficiency, and simple structure that is easy to implement.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a ring random fiber laser, comprising a pump laser source, a pump wavelength division multiplexer, a fiber Bragg grating, and a fiber coupler, a double-clad ytterbium-doped fiber, an adjustable fiber delay line, an adjustable split-ratio fiber coupler, and an optical isolator connected in sequence to form a ring cavity. The laser output from the pump laser source passes sequentially through the pump wavelength division multiplexer, the fiber Bragg grating, and the fiber coupler into the double-clad ytterbium-doped fiber, generating stimulated amplification of random fiber laser. Then, the laser signal passes sequentially through the adjustable fiber delay line and the adjustable split-ratio fiber coupler. The adjustable split-ratio fiber coupler outputs a portion of the laser, while the other portion passes through the optical isolator and enters the fiber coupler to return to the ring cavity for circulation.

[0008] Furthermore, the length of the double-clad ytterbium-doped fiber is 100 to 400 meters, the core diameter is 10 to 25 μm, and the inner cladding diameter is 130 to 300 μm.

[0009] Furthermore, for the single-frequency continuous output state, the splitting ratio of the adjustable splitting ratio fiber coupler is 0~5%; for the chaotic laser output state, the splitting ratio of the adjustable splitting ratio fiber coupler is 20~50%.

[0010] As a recommended implementation, a single fiber Bragg grating with a reflectivity of over 95% is used.

[0011] Furthermore, the pump laser source wavelength is 1018nm, and the applicable optical wavelengths for the pump wavelength division multiplexer are 1018 / 1075nm.

[0012] Furthermore, the reflection center wavelength of the fiber Bragg grating is 1075 nm.

[0013] As another recommended implementation, two fiber Bragg gratings are provided, and a wavelength division multiplexer is set at the output end of the ring cavity.

[0014] Furthermore, the reflectivity of fiber Bragg gratings is over 95%.

[0015] Furthermore, the pump laser source wavelength is 976nm, and the applicable wavelengths of the pump wavelength division multiplexer are 976 / 1090 / 1150nm.

[0016] Furthermore, the center wavelengths of the reflections from the two fiber Bragg gratings correspond to 1090nm and 1150nm, respectively, and the wavelength division multiplexer is used for the output of 1090nm and 1150nm lasers.

[0017] Beneficial effects:

[0018] According to the present invention, a double-clad ytterbium-doped fiber is used as the gain medium in the ring cavity, which can realize the mixed gain of active ion and stimulated Raman scattering, simplifying the laser system structure without reducing the gain effect. A high-reflectivity fiber Bragg grating is used at the input end of the ring cavity, thereby forming a beneficial feedback with the random distributed Rayleigh scattering in the cavity. This allows the laser to form a back-and-forth loop between the Rayleigh scattering region and the fiber Bragg grating, which not only improves the utilization rate of the pump source, but also improves the utilization rate of ytterbium ion gain and stimulated Raman gain, as well as the beneficial effect of random Rayleigh feedback in the entire laser generation process, thereby reducing the lasing threshold and improving the conversion efficiency.

[0019] This invention employs an adjustable fiber delay line, allowing for fine-tuning of the optical path of the laser within the ring cavity. This avoids instability phenomena such as mode hopping, ensuring stable longitudinal mode output within the cavity and increasing the stability of the ring cavity random fiber laser's output state. An adjustable split-ratio fiber coupler is also used. By adjusting the split-ratio, stable single-frequency continuous output of the ring random fiber laser system can be achieved, or stable chaotic output can be achieved according to actual needs. Furthermore, the introduction of the adjustable split-ratio fiber coupler realizes the ring cavity structure, introducing self-injection feedback into the entire system. Based on fiber Bragg gratings and Rayleigh random feedback, this further improves the total feedback within the cavity, thereby further reducing the lasing threshold.

[0020] Optical isolators ensure that the portion of laser light fed back into the ring cavity is transmitted in one direction, preventing laser light from the other direction from interfering with the adjustable split-ratio fiber coupler. This allows for precise control of the proportion of laser light fed back into the cavity, increasing the stability of the entire system.

[0021] A high-reflectivity fiber Bragg grating is placed at the initial end of the ring cavity to enhance the random Rayleigh feedback generated in the double-clad ytterbium-doped fiber. This allows the back-scattered Rayleigh laser generated within the double-clad ytterbium-doped fiber to be almost completely reflected back into the ring cavity, then propagated forward into the double-clad ytterbium-doped fiber, where it undergoes stimulated emission amplification again. This cycle repeats, ensuring that the ytterbium ion gain and stimulated Raman gain are fully and repeatedly utilized, and the pump light is also fully utilized, thereby reducing the system's lasing threshold and improving conversion efficiency. Simultaneously, the fiber Bragg grating effectively filters laser wavelengths near its reflection center wavelength, narrowing the laser linewidth. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of a ring random fiber laser according to Embodiment 1 of the present invention.

[0023] Figure 2 This is a schematic diagram of the structure of a ring random fiber laser embodiment 2 of the present invention.

[0024] Figure reference numerals: 1. Pumped laser source, 2. Pumped wavelength division multiplexer, 3. Fiber Bragg grating one, 4. Fiber coupler, 5. Double-clad ytterbium-doped fiber, 6. Adjustable fiber delay line, 7. Adjustable splitting ratio fiber coupler, 8. Optical isolator, 9. Fiber Bragg grating two, 10. Fiber Bragg grating three, 11. Wavelength division multiplexer. Detailed Implementation

[0025] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0026] The present invention discloses a ring random fiber laser, comprising a pump laser source 1, a pump wavelength division multiplexer 2, a fiber Bragg grating, a fiber coupler 4, a double-clad ytterbium-doped fiber 5, an adjustable fiber delay line 6, an adjustable split-ratio fiber coupler 7, and an optical isolator 8; wherein the fiber coupler 4, the double-clad ytterbium-doped fiber 5, the adjustable fiber delay line 6, the adjustable split-ratio fiber coupler 7, and the optical isolator 8 are sequentially connected to form a ring cavity, the initial end of the ring cavity is connected to the pump laser source 1 and the fiber Bragg grating, and the output end of the ring cavity is located at the output end of the adjustable split-ratio fiber coupler 7.

[0027] Example 1

[0028] like Figure 1 As shown, a ring random fiber laser includes a pump laser source 1, a pump wavelength division multiplexer 2, a fiber Bragg grating 3, a fiber coupler 4, a double-clad ytterbium-doped fiber 5, an adjustable fiber delay line 6, an adjustable splitting ratio fiber coupler 7, and an optical isolator 8.

[0029] Pump light with a wavelength of 1018 nm provided by pump laser source 1 passes sequentially through pump wavelength division multiplexer 2, fiber Bragg grating 3, and then enters fiber coupler 4, and then enters double-clad ytterbium-doped fiber 5. Under the combined effect of ytterbium ion gain and stimulated Raman gain, amplified laser with a wavelength of 1075 nm is generated. After that, it passes through tunable fiber delay line 6, tunable splitting ratio fiber coupler 7 and optical isolator 8 to form a closed loop.

[0030] The Rayleigh random scattering in the fiber Bragg grating-3 and the double-clad ytterbium-doped fiber 5 together constitutes the feedback in the cavity. There is both forward-propagating laser and reverse-propagating laser between the two, which can ensure that the laser can propagate back and forth in the double-clad ytterbium-doped fiber. This not only improves the utilization rate of the pump source, but also improves the utilization rate of ytterbium ion gain and stimulated Raman gain, thereby reducing the lasing threshold and improving the conversion efficiency.

[0031] Fiber optic coupler 4 combines the pump light, the laser reflected from the fiber Bragg grating-3, and a portion of the laser injected back from the output port, and transmits them within the cavity. The splitting ratio of the fiber optic coupler's coupling arm is no higher than 5%.

[0032] The adjustable fiber delay line 6 serves as a device for fine-tuning the optical path within the ring cavity, effectively stabilizing the longitudinal mode output within the cavity and enabling the laser to oscillate at the selected center wavelength of the system (1075nm in this embodiment).

[0033] By adjusting the adjustable splitting ratio fiber coupler 7, the percentage of laser light fed back into the cavity can be controlled, thereby controlling the output state of the ring fiber laser system. When the splitting ratio of the adjustable splitting ratio fiber coupler 7 is in the range of 0~5%, it corresponds to a stable single-frequency continuous output state; when the splitting ratio of the adjustable splitting ratio fiber coupler 7 is in the range of 20~50%, it corresponds to a chaotic laser output state.

[0034] In this embodiment, the pump wavelength division multiplexer 2 is used to inject pump light with a wavelength of 1018nm into the ring cavity, while preventing residual laser with a center wavelength of 1075nm that is transmitted in reverse within the ring cavity from penetrating into the pump laser source.

[0035] Example 2

[0036] Compared with Embodiment 1, this embodiment differs in that two fiber Bragg gratings are set at the initial end of the ring cavity, namely fiber Bragg grating two 9 and fiber Bragg grating three 10; a wavelength division multiplexer 11 is added at the output end of the ring cavity, specifically as follows: Figure 2 As shown.

[0037] In this embodiment, the pump light with a wavelength of 976nm emitted by the pump laser source 1 passes sequentially through the pump wavelength division multiplexer 2, fiber Bragg grating 2 9, fiber Bragg grating 3 10, and fiber coupler 4 before entering the double-clad ytterbium-doped fiber 5. Under the action of ytterbium ion gain, a laser with a wavelength of 1090nm is generated. Then, under the action of stimulated Raman gain, an amplified laser with a wavelength of 1150nm is generated. After that, it passes through the adjustable fiber delay line 6, the adjustable splitting ratio fiber coupler 7, and the optical isolator 8 to form a closed loop.

[0038] The center wavelengths reflected by fiber Bragg grating 2 (9) and fiber Bragg grating 3 (10) correspond to 1090nm and 1150nm, respectively; the wavelength division multiplexer 11 connected at the output end of the adjustable split ratio fiber coupler 7 is used for the output of 1090nm and 1150nm lasers.

[0039] In this invention, the main body of the ring cavity is a double-clad ytterbium-doped fiber. Under certain pumping conditions, it can provide mixed active ion and stimulated Raman gain, as well as random Rayleigh feedback. Therefore, considering the balance of various system parameters, the optimal fiber length can be easily determined to obtain the best conversion efficiency. The optimal fiber length of the double-clad ytterbium-doped fiber 5 is in the range of 100~400 meters, the core diameter is in the range of 10~25 μm, the inner cladding diameter is in the range of 130~300 μm, and the ytterbium doping concentration is in the range of 0.5×10⁻⁶. 24 ~ 4×10 24 m -3 The higher the ytterbium doping concentration, the shorter the corresponding length of the double-clad ytterbium-doped fiber.

[0040] In both embodiments, the reflectivity of each fiber Bragg grating is above 95%. The fiber Bragg grating can not only narrow the laser linewidth, but also form an intracavity feedback together with random Rayleigh scattering in the cavity. This improves the utilization rate of the pump source, as well as the utilization rate of ytterbium ion gain and stimulated Raman gain, thereby reducing the lasing threshold and improving the conversion efficiency.

[0041] To mitigate the potential multi-mode competition that could lead to mode hopping, this invention incorporates an adjustable fiber delay line. By adjusting the adjustable fiber delay line 6, the intracavity optical path can be effectively fine-tuned, enabling the system to operate stably near the selected wavelength.

[0042] The adjustable splitting ratio fiber coupler 7 has a splitting ratio range of 0~5% or 20~50%. When the splitting ratio is in the range of 0~5%, it corresponds to a stable single-frequency continuous output state; when the splitting ratio is in the range of 20~50%, it corresponds to a chaotic laser output state. By adjusting the adjustable splitting ratio fiber coupler, the output state can be controlled relatively precisely, which can not only obtain a stable single-frequency continuous output, but also obtain a chaotic laser source for use in secure communication systems.

[0043] Optical isolator 8 ensures that the portion of the laser fed back into the annular cavity is transmitted in one direction.

[0044] The use of a ring cavity allows a portion of the output laser to be injected back into the cavity as positive feedback, which to some extent reduces the lasing threshold of the system.

[0045] In this embodiment, the pump wavelength division multiplexer 2 injects pump light with a wavelength of 976nm into the ring cavity, while preventing residual laser light with center wavelengths of 1090nm and 1150nm that are transmitted in reverse within the ring cavity from penetrating into the pump laser source.

[0046] The above are merely preferred embodiments of the present invention and are not limited to the present invention. Any modifications, equivalent substitutions, and improvements made within the principles and implementation guidelines of the present invention should be included within the protection scope of the present invention.

Claims

1. A ring random fiber laser, characterized in that, The application relates to a random fiber laser device, which comprises a pump laser light source (1), a pump wavelength division multiplexer (2), a fiber Bragg grating, and a fiber coupler (4), a double-clad Yb-doped fiber (5), an adjustable fiber delay line (6), an adjustable fiber coupler (7) with a variable splitting ratio, and an optical isolator (8) connected in sequence to form a ring cavity, wherein the laser output by the pump laser light source (1) enters the double-clad Yb-doped fiber (5) through the pump wavelength division multiplexer (2), the fiber Bragg grating (3) and the fiber coupler (4) in sequence to generate stimulated random fiber laser, and then the laser signal passes through the adjustable fiber delay line (6) and the adjustable fiber coupler (7) with a variable splitting ratio in sequence, the adjustable fiber coupler (7) with a variable splitting ratio outputs part of the laser, and the other part of the laser enters the fiber coupler (4) through the optical isolator (8) to circulate in the ring cavity. The fiber Bragg grating is two. A wavelength division multiplexer (11) is arranged at the output end of the ring cavity. The wavelength of the pump laser light source (1) is 976 nm. The center wavelengths of the two fiber Bragg gratings are 1090 nm and 1150 nm respectively. The main body of the ring cavity is a double-clad Yb-doped fiber (5), which can provide active ion and stimulated Raman mixed gain and random Rayleigh feedback under certain pumping conditions. The use of the ring cavity makes part of the output laser as forward feedback injection into the cavity, thereby reducing the lasing threshold of the system to a certain extent. The use of the ring cavity makes the laser overflowing from the input end of the ring cavity reflected back into the cavity to become forward transmission laser, thereby further reducing the lasing threshold of the system and improving the conversion efficiency to a certain extent. When the splitting ratio of the adjustable fiber coupler (7) with a variable splitting ratio is 0-5%, the single-frequency continuous output state is achieved. When the splitting ratio of the adjustable fiber coupler (7) with a variable splitting ratio is 20-50%, the chaotic laser output state is achieved.

2. A ring random fiber laser according to claim 1, wherein, The length of the double-clad Yb-doped fiber (5) is 100-400 meters, the core diameter is 10-25 mu m, and the inner cladding diameter is 130-300 mu m.

3. The ring random fiber laser according to claim 1, wherein, The reflectivity of the fiber Bragg grating is above 95%.

4. A ring random fiber laser according to claim 3, wherein, The pump wavelength division multiplexer (2) is suitable for wavelength parameters of 976 / 1090 / 1150 nm.

5. The ring random fiber laser according to claim 3, wherein, The wavelength division multiplexer (11) is used for the output of 1090 nm and 1150 nm lasers.

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