All-fiber structure spontaneous radiation light source based on special welding

Abstract

The invention provides an all-fiber structure spontaneous radiation light source based on special welding, which comprises a pumping source, a special welding point, an active fiber, a pumping filter and a low feedback device, and is characterized in that pump light output by the pumping source is input into the active fiber through the special welding point; the active optical fiber absorbs the pump light to generate broadband spontaneous radiation light, the broadband spontaneous radiation light is spread and accumulated in the axial direction of the optical fiber and is output by the low-feedback device, the low-feedback device and the special fusion welding point are used for regulating and controlling feedback of the two ends of the active optical fiber, it is avoided that the active optical fiber spontaneously generates laser lasing under the action of the pump light, and the broadband spontaneous radiation light source of an all-optical-fiber structure is achieved; the active optical fiber is a rare earth ion doped optical fiber, and the softening temperature of the active optical fiber is lower than that of the pumping source tail fiber; the special fusion welding point is a fusion welding point where the pumping source tail fiber is wrapped in the active optical fiber, the end face cutting angle of the pumping source tail fiber participating in fusion welding is controlled to be larger than or equal to 10 degrees, and the end face cutting angle of the active optical fiber is controlled to be smaller than 0.5 degree.

Description

Technical Field

[0001] This invention relates to the field of lasers, and more particularly to a spontaneous emission light source based on a special fusion splicing all-fiber structure. Background Technology

[0002] Fiber optic broadband spontaneous emission sources, due to their large spectral bandwidth, low temporal coherence, and excellent beam quality, are widely used in biomedical imaging, fiber optic gyroscopes, distributed fiber optic sensing, and spectral measurement. Compared with narrow-linewidth lasers, spontaneous emission sources can effectively suppress coherent noise and speckle effects, improving the signal-to-noise ratio and stability of measurement systems. Compared with traditional halogen lamps, xenon lamps, and other thermal light sources, they offer advantages such as superior beam quality, smaller size, and natural compatibility with fiber optic systems. Therefore, they have become an important development direction for next-generation high-performance broadband light sources.

[0003] In existing technologies, common spontaneous emission (SEV) sources often use rare-earth-doped optical fibers as the gain medium, pumped by semiconductor lasers, to obtain amplified spontaneous emission output under conditions of no resonant cavity or weak feedback. Currently, most common SEV sources adopt a hybrid structure of "fiber + free space + device packaging": the pump laser is collimated and focused before being coupled into the active fiber, and the output is then shaped by devices such as free space filtering, polarization control, or optical isolators before being connected to the back-end application system. This type of structure has a complex optical path, high alignment requirements, and is easily affected by environmental factors such as temperature and vibration, limiting its application scenarios. "All-fiber" SEV sources have significant advantages in terms of power and spectral stability; however, existing all-fiber sources still generally require multiple fiber devices such as couplers and pump signal combiners (e.g., CN 109103736 B, CN106654830 B, CN 108418087 B), which introduces additional system losses and makes the optical feedback problem more complex, making it more difficult to suppress self-excited oscillations and limiting the power increase of SEV sources. Furthermore, realizing a spontaneous emission light source with an all-fiber structure is more challenging in the mid-infrared >2.5 μm band where the readiness of fiber optic device technology is poor. Even with a spatial coupling structure that has poor stability, the maximum spontaneous emission light power generated by the seed source in the mid-infrared is only about 260 mW (see [Journal of Lightwave Technology 43(17), 6001-6005 (2022)]). How to suppress the feedback at both ends of the active fiber is the key to improving the spontaneous emission light power generated by the active fiber.

[0004] This invention utilizes a special welding technique for optical fibers to reduce optical feedback at the input of an active fiber pump, achieving a spontaneous emission light source with an all-fiber structure without the need for complex fiber optic devices. The structure is compact and conducive to high power output. A literature and patent novelty search has yielded no related patents or literature reports to date. Summary of the Invention

[0005] This invention provides a spontaneous emission light source with an all-fiber structure based on special fusion splices. By utilizing special fusion splices that provide low optical feedback to increase the lasing threshold of the active fiber, a spontaneous emission light source with an all-fiber structure capable of supporting high power output is achieved. The system structure is simple and compact. This invention is implemented using the following technical solution: A spontaneous emission light source based on a special fusion splice structure in an all-fiber structure includes: a pump source, a special fusion splice, an active fiber, a pump filter, and a low-feedback device. Pump light output from the pump source is input into the active fiber through the special fusion splice. The active fiber absorbs the pump light, generating broadband spontaneous emission light that propagates and accumulates along the fiber axis, and is output by the low-feedback device. The low-feedback device and the special fusion splice regulate the feedback at both ends of the active fiber, preventing spontaneous laser emission from the active fiber under the action of the pump light, thus realizing a broadband spontaneous emission light source in an all-fiber structure. The active fiber is a rare-earth ion-doped fiber with a softening temperature lower than that of the pump source pigtail. The special fusion splice is a splice where the pump source pigtail is encased within the active fiber. The end-face cutting angle of the pump source pigtail participating in the splicing is controlled at ≥10°, and the end-face cutting angle of the active fiber is controlled at less than 0.5°.

[0006] Furthermore, the pump source is a semiconductor laser or fiber laser with fiber-coupled output.

[0007] Furthermore, the rare earth ions are one or more combinations of erbium, ytterbium, neodymium, thulium, holmium, and dysprosium.

[0008] Furthermore, the active optical fiber is a double-clad erbium-doped fluoride optical fiber.

[0009] Furthermore, the glass matrix of the active optical fiber is quartz glass, fluoride glass, silicate glass, phosphate glass, tellurite glass, or germanate glass.

[0010] Furthermore, the low-feedback device is a beveled fiber end face, an anti-reflection fiber end cap, or a fiber isolator.

[0011] Furthermore, near the output end of the active optical fiber, the outer cladding of the optical fiber is stripped and coated with an adhesive whose refractive index is higher than that of the inner cladding of the optical fiber, thus forming a pump filter.

[0012] Furthermore, the pump source is a multi-transverse mode semiconductor laser coupled from a quartz fiber with a wavelength of 981 nm; the active fiber is a double-clad erbium-doped fluoride fiber with an erbium ion doping concentration of 7 mol%, used to absorb the 981 nm pump light emitted by the pump source and provide broadband optical gain in the 2.7~2.8 μm band.

[0013] Compared with existing technologies, the all-fiber spontaneous emission light source based on special fusion splicing described in this invention has the following advantages: 1) Reducing the feedback of the active fiber end face through special fusion splices is beneficial to significantly improve the laser lasing threshold, thereby enabling high-power broadband spontaneous emission light output through higher pump power, meeting more application scenarios.

[0014] 2) Compared with spontaneous emission light sources with spatial optical coupling structures, the present invention has a more compact system structure and better environmental adaptability; 3) This invention can realize a spontaneous emission light source with an all-fiber structure without relying on fiber optic devices such as fiber optic couplers, wavelength division multiplexers, and pump signal combiners. It is low in cost and easy to implement. In the mid-infrared band where fiber optic devices are not yet mature, the technical route described in this invention has more obvious advantages. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of a spontaneous emission light source based on a special fusion splicing all-fiber structure.

[0016] Figure 2 This is the output spectrum of a spontaneous emission light source based on a special fusion splicing all-fiber structure.

[0017] Figure 3 The power curves of the spontaneous emission light source are shown for different cutting angles of the fiber optic pigtail end face of the pump source.

[0018] The attached diagram lists the components represented by each number as follows: 1: Pump source; 2: Special welding point; 3: Active optical fiber; 4: Pump filter; 5: Low feedback device; 6: Pump source pigtail end face at special fusion splice. Detailed Implementation

[0019] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention.

[0020] The spontaneous emission light source based on a special fusion splicing all-fiber structure proposed in this invention is described in the laser structure section. Figure 1 It includes: pump source 1, special fusion splice 2, active optical fiber 3, pump filter 4, and low feedback device 5.

[0021] The pump light output from pump source 1 is input into the active optical fiber through special fusion splice 2. The active optical fiber absorbs the pump light, generates broadband spontaneous emission light, and propagates and accumulates along the fiber axis, which is then output by low feedback device 5. The function of low feedback device 5 and special fusion splice 2 is to regulate the feedback at both ends of the active optical fiber, preventing the active optical fiber with high gain characteristics from spontaneously generating laser lasing under the action of pump light, thereby realizing a broadband spontaneous emission light source with an all-fiber structure.

[0022] In this embodiment, pump source 1 is a multi-mode semiconductor laser coupled from a quartz fiber with a wavelength of 981 nm. Its core and cladding diameters are 105 / 125 μm, respectively. The output power of the pump source can be changed by controlling the pump drive current. Active fiber 3 is a double-clad erbium-doped fluoride fiber with an erbium ion doping concentration of 7 mol%, with core and cladding diameters of 15 / 250 μm and a length of 2.3 m. It is used to absorb the 981 nm pump light emitted by pump source 3 and provide broadband optical gain in the 2.7~2.8 μm band. The output end face of the active fiber is beveled with a cutting angle controlled at ≥10°, forming the low feedback device 5 of the system. The outer cladding of the active fiber is stripped near the output end and coated with an adhesive with a refractive index higher than that of the inner cladding, forming the pump filter 4 of the system. This causes the inner cladding of the active fiber to lose the waveguide constraint of total internal reflection, thereby filtering out the unabsorbed pump light in the inner cladding of the active fiber.

[0023] Special fusion splice 2, formed by welding a pump source pigtail and an active fiber 3, is crucial for generating high-power spontaneous emission light. In this invention, the end-face cutting angle of the two fibers involved in the splicing is the core factor determining the quality of this special fusion splice. By controlling the end-face cutting angle of the pump source pigtail before splicing, the optical feedback introduced by the splice can be effectively reduced, thereby avoiding laser lasing and supporting the generation of high-power spontaneous emission light. Since the softening temperature of the pump source pigtail (quartz fiber) is much higher than that of the active fiber (fluoride fiber), a net advance of approximately 30 μm is required to insert the quartz fiber into the molten fluoride fiber, so that the fluoride fiber tightly wraps around the embedded quartz fiber, resulting in a strong fiber fusion splice. This type of splice introduces significant optical feedback, leading to laser lasing output at a lower pump gain, which is detrimental to generating broadband spontaneous emission light. To address this issue, in this embodiment, during the processing of the special fusion splice 2, the cutting angle of the pump source pigtail end face 6 participating in the fusion is controlled to ≥10°, and the cutting angle of the active fiber end face is controlled to below 0.5°. This is because a silica fiber end face with a certain tilt angle will cause the fluoride fiber face connected to it after fusion annealing to also form a corresponding tilt. This tilted fusion interface can effectively reduce the optical feedback introduced by the fusion splice. Furthermore, a welding strategy is adopted where the low softening temperature fiber is fused and then tightly wrapped around the high softening temperature fiber, giving the fusion splice both low feedback and high strength characteristics.

[0024] In this embodiment, when the pump current is 2.7 A and the pump power is 22 W, the active optical fiber can generate approximately 0.7 W of spontaneous emission light output, with the spectrum as shown below. Figure 2 As shown, the spectrum covers 2730–2830 nm, with a 3 dB bandwidth of 28 nm. This pump power still does not reach the laser lasing threshold. By further increasing the pump power and enhancing system scattering, it is expected that higher power spontaneous emission light output can be achieved. Compared to the conventional spatial optical coupling mid-infrared spontaneous emission light source approach, this embodiment achieves higher output power and has a more reliable all-fiber structure, which is beneficial for practical applications.

[0025] To illustrate the effect of special fusion splice 2, the end face cutting angle of the pump source pigtail was controlled at 0°, 7°, and 10°, respectively. The change in spontaneous emission light output power with pump drive current was compared. Figure 3 As shown, when the end-face cutting angle of the pump source pigtail is small, the spontaneous emission output power is higher under the same pump drive current, indicating that the fusion splice provides greater feedback and improves the extraction efficiency of the forward signal to the active fiber gain. However, the fusion splice with a small end-face cutting angle also lowers the lasing threshold of the system. The laser lasing problem at 2784 nm prevents the spontaneous emission output power from exceeding 150 mW. Using a fusion splice with a larger end-face cutting angle can solve this problem, but at the cost of some conversion efficiency, a higher spontaneous emission output power is achieved. As mentioned earlier, a pump current of 2.7 A still does not allow the system to reach the laser lasing threshold.

[0026] To illustrate the impact of the low-feedback device 5, the following comparative experiments were conducted. When the end face cutting angle of the pump source pigtail was 0°, and the output end of the active fiber did not use the low-feedback device (oblique cut), but instead used a 0° flat cut to provide approximately 4% feedback, the device could not achieve spontaneous emission light output when the pump current was greater than 0.7 A and the active fiber directly emitted light. When the end face cutting angle of the pump source pigtail was 10°, and the output end of the active fiber used a 0° flat cut, spontaneous emission light output could only be achieved when the pump current was less than 1 A. However, due to the high feedback provided at the output end, the backward signal amplification process dominated, and the maximum output forward spontaneous emission light power was only 23 mW. The above results demonstrate the beneficial effects of the present invention in achieving a high-power spontaneous emission light source using the special fusion splice 2 and the low-feedback device 5.

[0027] In the above embodiments, the pump source 1 is not limited to a multi-mode semiconductor laser coupled from a silica fiber; it can be a semiconductor laser or a fiber laser. The pump source can operate in continuous wave mode or pulsed mode. Its pigtail can be a single-mode fiber or a multimode fiber, and can be a silica fiber or other glass fiber with high softening temperature characteristics.

[0028] The active optical fiber 3 is a rare-earth ion-doped optical fiber, which generates spontaneous emission light through rare-earth ion energy level transitions under the action of pump light; the rare-earth ions include, but are not limited to, one or more combinations of erbium, ytterbium, neodymium, thulium, holmium, and dysprosium; the glass matrix of the active optical fiber includes, but is not limited to, fluoride glass, silicate glass, phosphate glass, tellurate glass, and germanate glass, and its softening temperature should be lower than that of the pump source pigtail.

[0029] The special fusion splice 2 is the fusion splice of the pump source pigtail and the active optical fiber 3. The cutting angle of the end face 6 of the pump source pigtail participating in the welding is controlled to be ≥10°, and the cutting angle of the end face of the active optical fiber is controlled to be below 0.5°. Taking advantage of the fact that the softening temperature of the pump source pigtail is higher than that of the active optical fiber, a welding strategy is adopted in which the low softening temperature optical fiber melts and tightly wraps the high softening temperature optical fiber, so that the fusion splice has the characteristics of low feedback and high strength at the same time.

[0030] The low-feedback device 5 can be a beveled fiber end face, an anti-reflection fiber end cap, or a fiber isolator. Its key feature is its ability to reduce backlight feedback to the fiber core, thus preventing laser lasing in the active fiber. In practical applications, an optical isolator can be connected after the low-feedback device 5 to suppress backlight, or a spectral filter can be connected to select a specific spectral band for output.

[0031] Unless otherwise specified, the model and specifications of the various devices in this embodiment of the invention are not specifically limited, and any device that can perform the above functions is acceptable.

[0032] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A spontaneous emission light source based on a special fusion splicing all-fiber structure, including: The system comprises a pump source, a special fusion splice, an active optical fiber, a pump filter, and a low-feedback device. Pump light from the pump source is input into the active optical fiber through the special fusion splice. The active optical fiber absorbs the pump light, generating broadband spontaneous emission light that propagates and accumulates along the fiber axis. This emission is then output by the low-feedback device. The low-feedback device and the special fusion splice regulate the feedback at both ends of the active optical fiber, preventing spontaneous laser emission under the influence of the pump light and achieving a broadband spontaneous emission light source with an all-fiber structure. The active optical fiber is a rare-earth ion-doped fiber with a softening temperature lower than that of the pump source pigtail. The special fusion splice is a fusion point where the pump source pigtail is encased within the active optical fiber. The end-face cutting angle of the pump source pigtail participating in the splicing is controlled to be ≥10°, and the end-face cutting angle of the active optical fiber is controlled to be below 0.5°.

2. The all-fiber spontaneous emission light source based on special fusion splicing according to claim 1, characterized in that, The pump source is a semiconductor laser or fiber laser with fiber-coupled output.

3. The all-fiber spontaneous emission light source based on special fusion splicing according to claim 1, characterized in that, The rare earth ions are one or more combinations of erbium, ytterbium, neodymium, thulium, holmium, and dysprosium.

4. The all-fiber spontaneous emission light source based on special fusion splicing according to claim 1, characterized in that, The active optical fiber is a double-clad erbium-doped fluoride optical fiber.

5. The all-fiber spontaneous emission light source based on special fusion splicing according to claim 1, characterized in that, The glass matrix of the active optical fiber is quartz glass, fluoride glass, silicate glass, phosphate glass, tellurite glass, or germanate glass.

6. The all-fiber spontaneous emission light source based on special fusion splicing according to claim 1, characterized in that, The low-feedback device is a beveled fiber end face, an anti-reflection fiber end cap, or a fiber isolator.

7. The all-fiber spontaneous emission light source based on special fusion splicing according to claim 1, characterized in that, A pump filter is constructed by stripping the outer cladding of an active optical fiber near its output end and coating it with an adhesive whose refractive index is higher than that of the inner cladding.

8. The all-fiber spontaneous emission light source based on special fusion splicing according to claim 1, characterized in that, The pump source is a multi-transverse mode semiconductor laser coupled from a quartz fiber with a wavelength of 981 nm; the active fiber is a double-clad erbium-doped fluoride fiber with an erbium ion doping concentration of 7 mol%, used to absorb the 981 nm pump light emitted by the pump source and provide broadband optical gain in the 2.7~2.8 μm band.

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