A mid-infrared all-fiber laser based on heterogeneous fusion interface feedback

Abstract

The present invention relates to a mid-infrared all-fiber laser based on heterogeneous fusion interface feedback, comprising a pump source, a quartz fiber, a heterogeneous fiber fusion point, a mid-infrared active fiber, a pump stripper, and low-feedback components. The laser light output by the pump source is input into the mid-infrared active fiber through the quartz fiber and the heterogeneous fiber fusion point, and the active fiber absorbs the pump light to generate laser gain. The mid-infrared active fiber is connected to the low-feedback component via the pump stripper, and the pump stripper is used to separate or strip unabsorbed pump light. The heterogeneous fiber fusion point is the fusion point of the quartz fiber and the mid-infrared active fiber. By controlling the cutting angle of the fiber end face before fusion and the net propulsion amount during fusion, the reflection characteristics of the heterogeneous fiber fusion point are changed, so that the interface reflection when the laser is incident on the fusion point is enhanced, thereby achieving effective resonant cavity feedback.

Description

Technical Field

[0001] The present invention relates to the field of lasers, and in particular to a high-efficiency mid-infrared all-fiber laser based on heterogeneous fusion interface feedback. Background Art

[0002] Fiber lasers in the mid-infrared band >2.5μm have advantages such as excellent heat dissipation, good beam quality, and strong environmental adaptability, and can be applied in fields such as material processing, biomedicine, and infrared countermeasures. Mid-infrared fiber lasers use active optical fibers doped with rare earth elements as gain media. The matrix material of the active optical fiber is usually a soft glass material with low phonon energy and a wide light transmission window, such as fluoride and sulfide. Although fluoride fiber lasers and sulfide fiber lasers were reported as early as the last century, most lasers use coated optical lenses as cavity mirrors and the pump light is coupled into the active optical fiber via a spatial optical path, which has failed to realize a fully fiber-optic laser system.

[0003] In the past decade, with breakthroughs in the preparation technology of fluoride fiber Bragg gratings, a few institutions such as Laval University in France and Kyoto University in Japan have successively reported mid-infrared all-fiber fiber lasers using fluoride fiber Bragg gratings as resonant cavity mirrors. Based on a pair of high-reflectivity (>99%) and low-reflectivity (8% to 30%) soft glass fiber Bragg gratings with matching central wavelengths, they have achieved mid-infrared 3μm band laser output of several watts or even tens of watts, and have a more compact system structure compared to spatial optical path coupling systems. However, there are still certain limitations in using soft glass fibers such as fluoride to write fiber Bragg gratings as the cavity mirrors of laser resonators: first, the central wavelength and reflectivity of fluoride fiber Bragg gratings will change with the increase of operating temperature (see [Optics Letters 43(18), 4542-4545(2018)]), which affects the long-term stability of the laser. In addition, due to the low softening temperature of soft glass fiber itself (<400℃), such fiber Bragg gratings are prone to thermal damage. Second, the processing of such fiber Bragg gratings is difficult and has high technical barriers, and requires reliance on expensive femtosecond laser micromachining platforms (see [Optics Letters 47(14), 3435-3438(2022)]). The high price of soft glass fiber itself also increases the development cost of fiber Bragg gratings. In addition, when a pair of fiber Bragg gratings are used to provide feedback for the laser resonator, strict matching of the grating center wavelengths is required, which further increases the technical threshold of mid-infrared all-fiber lasers.

[0004] This invention proposes a high-efficiency, all-fiber mid-infrared laser based on heterogeneous fusion interface feedback. By rationally configuring cavity feedback and active fiber parameters, this design eliminates the need for soft glass fiber Bragg gratings (FBGs) such as fluoride, tellurite, or chalcogenide glass, thereby achieving an all-fiber mid-infrared laser system. Literature and patent searches have revealed no related patents or literature reports to date. Summary of the Invention

[0005] The present invention provides a high-efficiency mid-infrared all-fiber laser based on heterogeneous fusion interface feedback. In a mid-infrared fiber laser system with high gain characteristics, the present invention constructs a laser resonant cavity based on the tiny feedback introduced by the fusion interface of different glass-based optical fibers, thereby realizing an all-fiber laser and reducing the process difficulty of system implementation. The present invention is implemented using the following technical solutions:

[0006] A mid-infrared all-fiber laser based on heterogeneous fusion interface feedback includes a pump source, a quartz fiber, a heterogeneous fiber fusion point, a mid-infrared active fiber, a pump stripper, and low feedback components, wherein:

[0007] The laser output from the pump source is input into the mid-infrared active fiber through the fusion point of the quartz fiber and the heterogeneous fiber. The active fiber absorbs the pump light to generate laser gain.

[0008] The mid-infrared active fiber is connected to the low-feedback component through a pump stripper, which is used to separate or strip the unabsorbed pump light;

[0009] The mid-infrared active fiber provides laser gain, so that mid-infrared laser oscillation is generated in the low-feedback resonant cavity composed of the heterogeneous fiber fusion point and the low-feedback components, and is output through the low-feedback components;

[0010] The heterogeneous fiber fusion point is the fusion point of the quartz fiber and the mid-infrared active fiber. By controlling the cutting angle of the fiber end face before fusion and the net propulsion amount during fusion, the reflection characteristics of the heterogeneous fiber fusion point are changed, so that the interface reflection when the laser is incident on the fusion point is enhanced, thereby achieving effective resonant cavity feedback;

[0011] The low-feedback component can achieve a lower laser reflectivity than that of the heterogeneous optical fiber fusion point, thereby ensuring that the main power of the generated laser is output by the low-feedback component.

[0012] Furthermore, the low-feedback component is either an optical fiber end cap, a beveled optical fiber end face, or an anti-reflection-coated optical fiber end face.

[0013] Furthermore, the mid-infrared active optical fiber is a fluoride optical fiber doped with various luminescent ions or an optical fiber with other glass matrices, and has high gain characteristics in the mid-infrared band.

[0014] Furthermore, the doping concentration of the fluoride optical fiber doped with various luminescent ions is greater than 1 mol.%, and the laser upper level lifetime is greater than 1 ms.

[0015] Furthermore, the luminescent ions include but are not limited to a combination of one or more of erbium, thulium, holmium, dysprosium, praseodymium, and terbium.

[0016] Furthermore, a filter device is inserted into the laser resonant cavity to achieve wavelength locking of the laser.

[0017] Furthermore, a modulation device is inserted into the laser resonant cavity to realize the pulsed operation of the laser.

[0018] Furthermore, the heterogeneous fiber fusion point is a special fusion point of quartz fiber and erbium-doped fluoride fiber achieved by using asymmetric fiber fusion technology, and the cutting angle of the quartz fiber and the erbium-doped fluoride fiber is controlled to <1° and the net advancement amount is set to 30-40μm.

[0019] Furthermore, the heterogeneous fiber fusion point is a special fusion point of quartz fiber and erbium-doped fluoride fiber achieved by using asymmetric fiber fusion technology. The cutting angle of erbium-doped fluoride fiber and quartz fiber is controlled at <0.3°, and the net advance amount is set to 32μm.

[0020] Furthermore, the output power of the low-feedback component end is two orders of magnitude higher than the leakage power P1 of the heterogeneous optical fiber fusion point end.

[0021] Compared with the prior art, the high-efficiency mid-infrared all-fiber laser based on heterogeneous fusion interface feedback described in the present invention has the following advantages:

[0022] 1) Compared with existing non-all-fiber mid-infrared fiber lasers, the mid-infrared all-fiber laser of the present invention has a more compact system structure and better environmental adaptability;

[0023] 2) The mid-infrared all-fiber laser described in the present invention can utilize special fusion points of heterogeneous optical fibers and low-feedback components as cavity mirrors. Compared with the currently immature mid-infrared all-fiber laser based on soft glass fiber Bragg gratings, it does not suffer from fiber Bragg grating damage or reflectivity changes under high-power operation.

[0024] 3) The components or structures used to provide cavity feedback in the present invention are low-cost and easy to implement, which effectively reduces the technical threshold and system cost of mid-infrared all-fiber lasers. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of the structure of a high-efficiency mid-infrared all-fiber laser based on heterogeneous fusion interface feedback.

[0026] Figure 2 This is the output power of a 2.8μm erbium-doped all-fiber laser based on heterogeneous fusion interface feedback at different pump powers.

[0027] Figure 3 This is the output spectrum of a 2.8μm erbium-doped all-fiber laser based on heterogeneous fusion interface feedback.

[0028] In the accompanying drawings, the components represented by the reference numerals are as follows:

[0029] 1: Pump source; 2: Quartz optical fiber;

[0030] 3: Heterogeneous fiber fusion point; 4: Mid-infrared active fiber;

[0031] 5: Pump stripper; 6: Low feedback components DETAILED DESCRIPTION

[0032] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0033] Example 1

[0034] Example 1 is a high-efficiency mid-infrared erbium-doped all-fiber laser based on heterogeneous fusion interface feedback. It uses a special fusion point of quartz fiber and erbium-doped fluoride fiber to provide cavity feedback, and the fiber end cap is used as a low-feedback component to achieve high-efficiency mid-infrared laser output. Figure 1 , including: a pump source (1), a quartz optical fiber (2), a heterogeneous optical fiber fusion point (3), a mid-infrared active optical fiber (4), a pump stripper (5), and a low-feedback component (6).

[0035] Among them, the heterogeneous fiber fusion point (3) is a special fusion point of quartz fiber and erbium-doped fluoride fiber realized by using asymmetric fiber fusion technology. Due to the large difference in material properties between fluoride fiber and quartz fiber, by controlling the cutting angle of the fiber end face before fusion and the net propulsion amount during fusion, the reflection characteristics of the heterogeneous fiber fusion point (3) can be changed, so that the interface reflection when the laser is incident on the fusion point is enhanced, and effective resonant cavity feedback is achieved. In this embodiment, the cutting angle of erbium-doped fluoride fiber and quartz fiber is controlled at <0.3°, and the net propulsion amount is set to 32μm. The special fusion point achieved has a 10 -2 The pump source (1) is a multimode semiconductor laser with a pump light wavelength of 976nm and a maximum output power of 60W; the quartz fiber (2) is a multimode quartz fiber with a core / cladding diameter of 105 / 125μm, which is used to transmit the pump light; the mid-infrared active fiber (4) is an erbium-doped fluoride fiber, which is used to provide laser gain. It has a double-cladding structure with a length of 7m, a core / inner cladding diameter of 15 / 250μm, a core / inner cladding numerical aperture of 0.14 / 0.46, an erbium ion doping concentration of 7mol.%, and a laser upper energy level ( 4 I 11 / 2) lifetime of 7.9ms and a pump absorption coefficient of 3dB / m; the pump stripper (5) is a cladding power stripper, which is prepared by stripping 5cm of the fiber coating at the rear end of the erbium-doped fluoride fiber (4) and re-coating it with high-refractive-index silver glue; the low-feedback component (6) is a fluoride fiber end cap, which is prepared using a Vytran GPX3400 fusion splicer and a Vytran LDC400A cutting knife. The end cap has an outer diameter of 260μm and a length of 700μm. The end of the end cap is beveled to reduce the resonant cavity feedback introduced by the low-feedback component (6).

[0036] The multimode pump light generated by the pump source (1) is input into the cladding of the mid-infrared active fiber (4) through the quartz fiber (2) and the heterogeneous fiber fusion point (3). The remaining pump light that is not absorbed is filtered out by the pump stripper (5). The mid-infrared active fiber (4) can absorb the 976nm multimode pump light and generate high laser gain in the mid-infrared 2.8μm band. Under the action of the heterogeneous fiber fusion point (3) and the low-feedback component (6), efficient oscillation of the mid-infrared 2.8μm band laser can be achieved. The laser is output by the low-feedback component (6) with low reflectivity.

[0037] The principle of high-efficiency laser output of this system is as follows: the heterogeneous fiber fusion point (3) in this example, that is, the fusion point of the quartz fiber and the mid-infrared active fiber, can provide 10 -2 The laser reflectivity R1 of the order of magnitude can be fine-tuned by changing the fusion parameters of the optical fiber fusion point; the low feedback component (6), that is, the fluoride optical fiber end cap with an end face bevel, can achieve 10 -6 The cavity reflectivity R2 of the magnitude of the feedback introduced by the beveled fiber end face can be referred to the literature [OpticsExpress 20 (2012) 14542-14546]). Since the end cap length and the bevel angle will affect the laser power reflected back into the core of the mid-infrared active fiber, the reflectivity R2 can be changed by changing the end cap length and the fiber bevel angle. Since R1>>R2, the formula (Refer to [Journal of Applied Physics 36(1965)2487-2490]) It can be seen that the output power P2 at the low-feedback component (6) is two orders of magnitude higher than the leakage power P1 at the heterogeneous fiber fusion point (3). Combined with the selected mid-infrared active fiber with high gain characteristics, low-threshold and high-efficiency generation of mid-infrared laser can be achieved, and it can be effectively output through the low-feedback component (6).

[0038] The mid-infrared laser output power of the mid-infrared all-fiber laser in this embodiment is experimentally measured at different pump powers. The results are as follows: Figure 2As shown. When the power of the pump source (1) is about 0.9W, the laser reaches the threshold, and the output laser power is 10mW at this time; increasing the power of the pump source (1), the laser output power increases approximately linearly, and the slope efficiency of the output power compared to the incident pump power is about 20%. As the output power increases, the slope efficiency decreases slightly; when the power of the pump source (1) is 60W, the mid-infrared laser output power reaches 10.3W. The output spectrum of the laser is shown as follows Figure 3 As shown, the central wavelength is 2801.17nm.

[0039] The advantages of the embodiments of the present invention are: significantly reducing the requirements for the reflective performance of optical fiber devices, utilizing the special fusion point of quartz fiber and fluoride fiber to achieve the resonant cavity feedback required by the laser, and reducing the difficulty and cost of implementing a mid-infrared all-fiber laser; the slope efficiency of the laser in this embodiment is close to the common slope efficiency (15-22%) of the current 2.8μm band erbium-doped all-fiber laser based on fiber Bragg gratings. Therefore, the all-fiber laser in the present invention is not only simple and feasible, but also has the characteristic of "high efficiency".

[0040] Furthermore, when processing the heterogeneous fiber fusion point (3), if the cutting angle of the quartz fiber and the erbium-doped fluoride fiber is controlled to be 0.3-1° and the net propulsion amount is set to 30-40 μm, similar results to the above embodiment can be achieved, and the slope efficiency of the all-fiber laser output power compared to the incident pump power is 15-20%.

[0041] Example 2

[0042] Example 2 provides a holmium-praseodymium co-doped all-fiber laser based on heterogeneous fusion interface feedback. This laser uses a special fusion point between a quartz fiber and a holmium-praseodymium co-doped fluorotellurate fiber to provide cavity feedback, and the fiber end face coated with a mid-infrared 2.9-3μm band anti-reflection coating serves as a low-feedback component. The laser structure is shown in Figure 1 , including: a pump source (1), a quartz optical fiber (2), a heterogeneous optical fiber fusion point (3), a mid-infrared active optical fiber (4), a pump stripper (5), and a low-feedback component (6).

[0043] The pump source (1) is a Raman fiber laser capable of generating a single-mode laser with a wavelength of 1150 nm. The core / cladding diameter of the quartz fiber (2) is 10 / 125 μm, and the 1150 nm pump light is transmitted in the core. The mid-infrared active fiber (4) is a holmium-praseodymium co-doped fluorotellurate fiber with a single cladding structure, a length of 0.5 m, a core / cladding diameter of 10 / 250 μm, and a holmium ion doping concentration of 3 mol.% (laser upper energy level). 5I6 lifetime 3.5ms), praseodymium ion doping concentration 0.3mol.%; the heterogeneous fiber fusion point (3) is the fusion point of the quartz fiber (2) and the mid-infrared active fiber (4), and the different glass matrices of the two optical fibers make the heterogeneous fusion interface have reflection characteristics for the transmitted laser; the pump stripper (5) is a 1150nm / 2900nm filter-type wavelength division multiplexer for separating unabsorbed pump light. If this device is omitted, it will not affect the implementation of this embodiment; the low feedback component (6) is a fiber end face coated with a mid-infrared 2.9-3μm band anti-reflection film, which is used to reduce the reflectivity of the fiber end face and isolate the fiber end face from water molecules in the air, thereby protecting the fiber.

[0044] The principle of this embodiment is as follows: the mid-infrared active optical fiber (4) can absorb the 1150nm single-mode laser output by the pump source (1) and generate high laser gain in the mid-infrared 2.9-3μm band; the processing method of the heterogeneous optical fiber fusion point (3) and the laser reflectivity that can be provided are similar to those in Example 1, both of which are much lower than the reflectivity of the high-reflection fiber Bragg grating in the conventional all-fiber laser (>90%); the low-feedback component (6), that is, the optical fiber end face coated with the mid-infrared anti-reflection coating, can introduce <10 -3 The laser reflectivity can be changed by changing the cutting angle of the optical fiber end face or adjusting the film system design; under the above conditions, the system can achieve the effective output of mid-infrared laser in the 2.9-3 μm band from the low feedback component (6).

[0045] In the above-mentioned embodiments 1 and 2, the heterogeneous fiber fusion splice (3) is the fusion splice of the quartz fiber (2) and the mid-infrared active fiber (4), and is characterized in that the reflection characteristics of the heterogeneous fiber fusion splice (3) can be changed by controlling the cutting angle of the fiber end face before fusion and the net propulsion amount during fusion, so that the interface reflection when the laser is incident on the fusion splice is enhanced, thereby achieving effective resonant cavity feedback.

[0046] The low-feedback component (6) can be a component or structure such as an optical fiber end cap of different length and material, a beveled optical fiber end face, an optical fiber end face coated with an anti-reflection film, etc., and is characterized in that the low-feedback component (6) can achieve a lower laser reflectivity than the heterogeneous optical fiber fusion point (3), thereby ensuring that the main power of the generated laser is output by the low-feedback component (6).

[0047] The mid-infrared active optical fiber (4) can be a fluoride optical fiber doped with various luminescent ions or an optical fiber with other glass matrices, and is characterized in that the optical fiber has high gain characteristics in the mid-infrared band, which is reflected in the doping concentration being greater than 1 mol.% and the laser upper energy level lifetime being greater than 1 ms; the optical fiber type can be a single-clad optical fiber, a double-clad optical fiber, an anti-resonant optical fiber, etc.; the luminescent ions include but are not limited to a combination of one or more of erbium, thulium, holmium, dysprosium, praseodymium, and terbium.

[0048] In a specific implementation, a filter device can be inserted into the laser resonant cavity to achieve wavelength locking of the laser.

[0049] In specific implementation, a modulation device can be inserted into the laser resonant cavity to achieve pulsed operation of the laser.

[0050] Unless otherwise specified, the models and specifications of the components in the embodiments of the present invention are not limited. Any component that can perform the above functions may be used.

[0051] Those skilled in the art will understand that the accompanying drawings are only a schematic diagram of a preferred embodiment, and the serial numbers of the embodiments of the present invention are only for description and do not represent the advantages or disadvantages of the embodiments.

[0052] 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 in the scope of protection of the present invention.

Claims

1. A mid-infrared all-fiber laser based on heterogeneous fusion interface feedback, comprising a pump source, a quartz fiber, a heterogeneous fiber fusion point, a mid-infrared active fiber, a pump stripper, and low-feedback components, wherein: The laser output from the pump source is input into the mid-infrared active fiber through the fusion point of the quartz fiber and the heterogeneous fiber. The active fiber absorbs the pump light to generate laser gain. The mid-infrared active fiber is connected to the low-feedback component through a pump stripper, which is used to separate or strip the unabsorbed pump light; The mid-infrared active fiber provides laser gain, so that mid-infrared laser oscillation is generated in the low-feedback resonant cavity composed of the heterogeneous fiber fusion point and the low-feedback components, and is output through the low-feedback components; The heterogeneous fiber fusion point is the fusion point of the quartz fiber and the mid-infrared active fiber. By controlling the cutting angle of the fiber end face before fusion and the net propulsion amount during fusion, the reflection characteristics of the heterogeneous fiber fusion point are changed, so that the interface reflection when the laser is incident on the fusion point is enhanced, thereby achieving effective resonant cavity feedback; The low-feedback component can achieve a lower laser reflectivity than that of the heterogeneous optical fiber fusion point, thereby ensuring that the main power of the generated laser is output by the low-feedback component.

2. The mid-infrared all-fiber laser according to claim 1, characterized in that: The low-feedback component is an optical fiber end cap, a beveled optical fiber end face, or an optical fiber end face coated with an anti-reflection film.

3. The mid-infrared all-fiber laser according to claim 1, characterized in that: The mid-infrared active optical fiber is a fluoride optical fiber doped with various luminescent ions or an optical fiber with other glass matrices, and has high gain characteristics in the mid-infrared band.

4. The mid-infrared all-fiber laser according to claim 3, characterized in that: The doping concentration of the fluoride optical fiber doped with various luminescent ions is greater than 1 mol.%, and the laser upper energy level lifetime is greater than 1 ms.

5. The mid-infrared all-fiber laser according to claim 3, characterized in that: The luminescent ions include one or more of erbium, thulium, holmium, dysprosium, praseodymium, and terbium.

6. The mid-infrared all-fiber laser according to claim 1, characterized in that: A filter device is inserted into the laser resonant cavity to achieve wavelength locking of the laser.

7. The mid-infrared all-fiber laser according to claim 1, characterized in that: Inserting a modulation device into the laser resonant cavity enables pulsed operation of the laser.

8. The mid-infrared all-fiber laser according to claim 1, characterized in that: The heterogeneous fiber fusion point is a special fusion point of quartz fiber and erbium-doped fluoride fiber achieved by using asymmetric fiber fusion technology, and the cutting angle of the quartz fiber and the erbium-doped fluoride fiber is controlled to be less than 1°, and the net advancement amount is set to 30-40μm.

9. The mid-infrared all-fiber laser according to claim 1, characterized in that: The heterogeneous fiber fusion point is a special fusion point of quartz fiber and erbium-doped fluoride fiber achieved by using asymmetric fiber fusion technology. The cutting angle of erbium-doped fluoride fiber and quartz fiber is controlled at <0.3°, and the net advance amount is set to 32μm.

10. The mid-infrared all-fiber laser according to claim 1, characterized in that: The output power of the low-feedback component end is two orders of magnitude higher than the leakage power P1 of the heterogeneous optical fiber fusion point end.

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