High repetition rate fiber laser based on active multi-core fiber

Abstract

The application discloses a high-repetition-frequency fiber laser based on an active multi-core optical fiber, which comprises a pump source, a wavelength division multiplexer, an optical circulator, an optical combiner, an optical isolator, a dichroic mirror and an ultra-short resonant cavity based on the active multi-core optical fiber, wherein the ultra-short resonant cavity based on the active multi-core optical fiber comprises a semiconductor saturable absorber mirror, a first coreless optical fiber, a second coreless optical fiber, an active multi-core optical fiber, a ferrule and a dielectric film. The application adopts the active multi-core optical fiber as a gain medium, and provides tens of times of the gain of a common active optical fiber under the same cavity length, so that a high-energy pulse output of the order of 10 nJ can be obtained under a GHz repetition frequency; the application has a stable supermode selection effect, has a simple structure, and has an output mode field far field distribution which is approximately a Gaussian distribution.

Description

Technical Field

[0001] This invention belongs to the field of laser technology, specifically a high repetition rate fiber laser based on an active multi-core fiber. Background Technology

[0002] High repetition rate (HRPR) fiber lasers are passively mode-locked lasers. By using highly doped fiber as the gain medium, the cavity length of the laser resonator can be shortened to the centimeter level, thereby enabling the repetition frequency of the mode-locked pulses to reach the GHz level. The key lies in the fabrication of the ultrashort resonator with a length in the centimeter range. HRPR fiber lasers have important applications in many fields, including high-speed analog-to-digital conversion, high-capacity optical communication networks, and high-resolution spectrometer calibration.

[0003] In existing technologies, a common method for implementing high repetition rate (PRR) fiber lasers is to use single-core fiber with a high rare-earth ion doping concentration as the gain medium. Repetition rates can reach the GHz level, while output pulse energies are typically in the 0.1 nJ range. Currently reported PPR fiber lasers using silica fiber as the gain medium have achieved a maximum repetition rate of 5 GHz, but their output power is relatively low. To obtain even higher repetition rates and greater pulse energies, current PPR fiber lasers generally use multi-component glass fibers with higher doping concentrations as the gain medium, such as phosphate and silicate fibers. These fibers can achieve even higher rare-earth ion doping concentrations, thus reaching repetition rates of around 10 GHz. However, the pulse energy still falls below the nJ level, requiring a subsequent amplification system to meet practical needs. Furthermore, the performance of multi-component glass fibers degrades after prolonged exposure to air, making it difficult for PPR fiber lasers using this approach to operate efficiently for extended periods.

[0004] The existing technology has the following main problems:

[0005] 1. Currently, high repetition rate fiber lasers generally use ordinary single-core gain fiber, which has relatively low output power. They need to be followed by a corresponding optical amplification device before they can be used in practice. However, the amplification process inevitably introduces noise, which leads to a decrease in the stability of the high repetition rate laser.

[0006] 2. Current high repetition rate fiber lasers use single-core fiber as the gain medium, which limits the adjustment dimension. To improve laser performance, the only way is to increase the doping concentration of the gain fiber, which is difficult to operate and has limited effect.

[0007] 3. The multi-component glass fibers used in current high repetition rate fiber lasers have relatively low melting points and hardness, making end-face processing difficult and also inconvenient for splicing with other silica fibers. Summary of the Invention

[0008] To overcome the shortcomings of existing technologies, the purpose of this invention is to provide a high repetition rate fiber laser based on an active multi-core fiber. The laser utilizes an active multi-core fiber and two coreless fiber segments to form an ultrashort resonant cavity. Compared with existing technologies, while maintaining a cavity length in the centimeter range, the cavity gain can be increased by 10-100 times, enabling mode-locked pulse output with a repetition frequency of GHz and pulse energy in the range of 1-10 nJ.

[0009] To achieve the above objectives, the technical solution of the present invention is as follows:

[0010] A high-repetition-rate fiber laser based on an active multi-core fiber is characterized by comprising a pumping device, an active multi-core fiber ultrashort resonator, and a laser output device. The pumping device includes a pump source and a pump light input module. The pump source is connected to the active multi-core fiber ultrashort resonator via the pump light input module, coupling the pump light into the active multi-core fiber ultrashort resonator. The laser output device couples the mode-locked laser pulse generated by the active multi-core fiber ultrashort resonator out of the cavity. The device includes a semiconductor saturable absorber mirror, a first coreless optical fiber, an active multi-core optical fiber, a ferrule, a second coreless optical fiber, and a dielectric film. One end of the first coreless optical fiber is connected to one end of the active multi-core optical fiber, and one end of the second coreless optical fiber is connected to the other end of the active multi-core optical fiber. The diameters of the first and second coreless optical fibers match the diameter of the active multi-core optical fiber and are encapsulated within the ferrule. The semiconductor saturable absorber mirror is disposed on one end face of the ferrule, and the dielectric film is disposed on the other end face of the ferrule.

[0011] The active multi-core optical fiber is a rare-earth ion-doped glass optical fiber, and the doped rare-earth ions may include one or more of erbium, ytterbium, thulium, holmium, neodymium, praseodymium, and bismuth.

[0012] The active multi-core optical fiber has 3-100 cores.

[0013] The first and second coreless optical fibers are made of a single glass medium, and the fiber length is 1-50mm.

[0014] The pumping device includes a pump source and a pump light input module, wherein the pump light input module is a lens group, an optical fiber combiner, or a wavelength division multiplexer.

[0015] The pump source is a multi-mode pump source, with one or more pumps, and the pumping method is core pumping or cladding pumping.

[0016] The laser output device is a dichroic mirror, or a circulator, isolator, or wavelength division multiplexer, isolator.

[0017] The auxiliary device includes a sleeve and a fixing insert.

[0018] The pump light emitted by the pump source is coupled into the ultrashort resonant cavity through a first lens and a second lens; or two or more pump sources are connected to the pump end pigtail of an optical fiber combiner, and the pigtail of the combiner is connected to the end of the ultrashort resonant cavity with the dielectric film; or the pump source pigtail is connected to the pump end pigtail of a wavelength division multiplexer, and the common end of the wavelength division multiplexer is connected to the end of the ultrashort resonant cavity with the dielectric film.

[0019] The dichroic mirror is positioned between two lenses, allowing pump transmission and reflecting the laser output; or the circulator's port 2 is connected to the end of the ultrashort resonant cavity with a dielectric film via a fixed sleeve, the isolator's input fiber is connected to the circulator's port 3, and the isolator's output end outputs the laser; or the wavelength division multiplexer's pass end is connected to the isolator's input end, and the isolator's output end outputs the laser.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] 1. The high repetition rate fiber laser provided by the present invention uses active multi-core fiber as the gain medium. Under the same cavity length, the gain provided is tens of times that of ordinary active fiber. Therefore, high energy pulse output in the order of 1 to 10 nJ can be obtained at a repetition frequency of GHz.

[0022] 2. Since the effective mode field area of ​​active multi-core fiber is 1-2 orders of magnitude larger than that of ordinary single-core fiber, and each fiber core is discretely distributed, the nonlinear and thermal effects inside the gain fiber are alleviated, which is conducive to the long-term stable operation of high repetition rate fiber lasers at high output power.

[0023] 3. Since no subsequent optical amplification device is required, the high repetition rate fiber laser provided by this invention has a simple structure, is easy to maintain, and has a relatively simple manufacturing process, which is conducive to mass production.

[0024] 4. The active multi-core fiber ultrashort resonator is encapsulated in a ferrule with an outer diameter of 2.5 cm and a length in the centimeter range. The semiconductor saturable absorber mirror and the dielectric film are respectively set at both ends of the ferrule. The entire ultrashort resonator has a compact structure, stable performance, and is easy to cooperate with other laser systems.

[0025] 5. Since the ultrashort resonator provided by this invention incorporates two segments of coreless optical fiber as a supermode selection device, it has a stable in-phase supermode selection function, resulting in an output mode field far-field distribution that is approximately Gaussian.

[0026] 6. Three pump sources and related devices are provided to facilitate the construction of high repetition rate fiber lasers based on multi-core optical fibers according to different pump sources. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the active multi-core fiber ultrashort resonator structure of the present invention.

[0028] Figure 2 This is a schematic diagram of the structure of Embodiment 1 of the high repetition rate fiber laser based on multi-core fiber of the present invention.

[0029] Figure 3 This is a schematic diagram of the structure of Embodiment 2 of the high repetition rate fiber laser based on multi-core fiber of the present invention.

[0030] Figure 4 This is a schematic diagram of the structure of embodiment 3 of the high repetition rate fiber laser based on multi-core fiber of the present invention.

[0031] In the diagram: 1-Semiconductor saturable absorber mirror, 2-First coreless fiber, 3-Active multi-core fiber, 4-Framing, 5-Second coreless fiber, 6-Dielectric film, 7-Lens, 8-Dichroic mirror, 9-Pump source, 10-Sleeve, 11-Fixed ferrule, 12-Circulator, 13-Isolator, 14-Bundle combiner, 15-Wavelength division multiplexer. Detailed Implementation

[0032] To illustrate the technical content, structural features, objectives, and effects of this invention in detail, the technical solution of this invention will be further described in detail below with reference to specific embodiments and accompanying drawings, but this should not be construed as limiting the scope of protection of this invention.

[0033] Example 1, such as Figure 2 As shown,

[0034] This embodiment is based on a high-repetition-rate fiber laser using an active multi-core fiber, comprising a pumping device, an active multi-core fiber ultrashort resonator, and a laser output device. The pumping device includes a pump source 9 and a pump light input module. The pump source 9 is connected to the active multi-core fiber ultrashort resonator via the pump light input module, coupling the pump light into the active multi-core fiber ultrashort resonator. The laser output device couples the mode-locked laser pulse generated by the active multi-core fiber ultrashort resonator out of the cavity. The active multi-core fiber ultrashort resonator includes semiconductor saturable... The system comprises an absorption mirror 1, a first coreless optical fiber 2, an active multi-core optical fiber 3, a ferrule 4, a second coreless optical fiber 5, and a dielectric film 6. One end of the first coreless optical fiber 2 is connected to one end of the active multi-core optical fiber 3, and one end of the second coreless optical fiber 5 is connected to the other end of the active multi-core optical fiber 3. The diameters of the first coreless optical fiber 2 and the second coreless optical fiber 5 match the diameter of the active multi-core optical fiber 3 and are encapsulated within the ferrule 4. The semiconductor saturable absorber mirror 1 is disposed on one end face of the ferrule 4, and the dielectric film 6 is disposed on the other end face of the ferrule 4. The first coreless optical fiber 2 and the second coreless optical fiber 5 are made of a single glass dielectric, and the optical fiber length is 1-50 mm.

[0035] like Figure 1 As shown, the active multi-core fiber ultrashort resonant cavity includes: a semiconductor saturable absorber mirror 1, a first coreless fiber 2, an active multi-core fiber 3, a ferrule 4, a second coreless fiber 5, and a dielectric film 6.

[0036] The semiconductor saturable absorber mirror 1 is disposed on one end face of the first coreless optical fiber 2, the other end of the first optical fiber 2 is fused to the active multi-core optical fiber 3, the other end of the active multi-core optical fiber 3 is fused to one end of the second coreless optical fiber 5, the above optical fiber portions are fixed in the fiber core 4 with optical adhesive, and a dielectric film 6 is disposed on the other end face of the ferrule 4.

[0037] In practical applications, the ultrashort resonant cavity is a Fabry-Perot cavity structure. The entire resonant cavity system is encapsulated in the ferrule 4. The overall length of the resonant cavity system is 1-10 cm, which can achieve mode-locked pulse output with a repetition frequency of 1-10 GHz. Due to the addition of active multi-core fiber 3, the mode-locked pulse energy can reach 1-10 nJ, and the output mode field is approximately Gaussian distributed.

[0038] The semiconductor saturable absorber mirror 1 is fixed on one end face of the ferrule 4. It has a center wavelength of 1030 nm, an area of ​​1×1 mm, a thickness of 450 μm, a modulation depth of 10%, an unsaturated loss of 7%, and a saturated flux of 40 μJ / cm². 2 The relaxation time is 1 ps, and the damage threshold is 3 mJ / cm². 2 .

[0039] The dielectric film 6 is a two-color dielectric film, which is deposited on one end face of the ferrule 4 by plasma sputtering. It has high transmittance (>80%) for pump light and high reflectance (>80%) for signal light.

[0040] The two ends of the active multi-core fiber 3 are respectively fused to the first coreless fiber 2 and the second coreless fiber 5, and fixed in the ferrule 4 with optical adhesive. Specifically, it is a seven-core ytterbium-doped fiber with a cladding diameter of 900 μm.

[0041] Ferrule 4 is a ceramic ferrule with an inner diameter of 900 μm, which matches the cladding diameter of the active multi-core fiber 3. Its outer diameter is 2.5 mm. Both ends of ferrule 4 need to be vertically polished.

[0042] The pumping device includes a semiconductor pump source 9, a dichroic mirror 8, a first lens 7-1, and a second lens 7-2.

[0043] The semiconductor pump source 9 is a multimode laser with a center wavelength of 976 nm and a maximum pump power of 1 W. The pump light is output through a multimode fiber pigtail with a core diameter of 80 μm, collimated by the second lens 7-2, then passed through the dichroic mirror 8, and finally converged by the first lens 7-1 before being coupled into the ultrashort resonant cavity.

[0044] The laser output device includes a first lens 7-1 and a dichroic mirror 8. The laser output from the ultrashort resonant cavity is reflected by the dichroic mirror 8 and output. The dichroic mirror 8 has high transmittance (>90%) for pump light and high reflectance (>90%) for signal light.

[0045] Example 2

[0046] like Figure 3 As shown, this embodiment includes a pumping device, an active multi-core fiber ultrashort resonant cavity, and a laser output device.

[0047] The difference between this embodiment and embodiment 1 is that the pumping device consists of two semiconductor pump sources 9 and an optical fiber combiner 14; the multi-core optical fiber 3 in the ultrashort resonant cavity is replaced with a 19-core ytterbium-doped optical fiber; the laser output module consists of a multimode optical fiber circulator 12 and an optical isolator 13, and the entire system adopts an all-fiber structure.

[0048] Both pump sources 9 are multimode semiconductor pump sources with a maximum output power of 40 W, a center wavelength of 980 nm, and a fiber optic core diameter of 100 μm.

[0049] The fiber combiner 14 is a 2+1 combiner with a double-clad structure, a core diameter of 100 μm, and an inner cladding diameter of 400 μm.

[0050] The active multi-core optical fiber 3 is a 19-core ytterbium-doped optical fiber with a cladding diameter of 1200 μm.

[0051] The diameters of the first coreless optical fiber 2 and the second coreless optical fiber 5 are 1200 μm, which matches the cladding diameter of the active multi-core optical fiber 3.

[0052] The insert 4 is a ceramic insert with an inner diameter of 1200 μm, and both ends of the insert 4 are vertically polished.

[0053] A semiconductor saturable absorber mirror 1 is fixed on one end face of the ferrule 4. Its center wavelength is 1030 nm, its area is 1×1 mm, its thickness is 450 μm, its modulation depth is 7%, its unsaturated loss is 5%, and its saturated flux is 60 μJ / cm². 2 The relaxation time is 2 ps, and the damage threshold is 5 mJ / cm². 2 .

[0054] The multimode fiber circulator 12 has a center wavelength of 1030 μm and a bandwidth of ±50 nm. The pigtail has a double-clad structure with a core diameter of 100 μm and an inner cladding diameter of 400 μm. The pigtail at port 1 is fused to the pigtail at the output end of the fiber combiner 14. After the coating layer of the pigtail at port 2 is removed, it is inserted into a ceramic ferrule 11 with an inner diameter of 400 μm and fixed with optical adhesive. The end face of the ferrule 11 is vertically polished and then mechanically connected to the ultrashort resonant cavity through the sleeve 10.

[0055] The input pigtail of the fiber optic isolator 13 is fused to the port 3 end of the fiber optic combiner 14, and the laser is output through the fiber optic isolator 13.

[0056] Example 3

[0057] like Figure 4 As shown, this embodiment differs from Embodiment 1 in that: the pumping device consists of a semiconductor pump source 9 and a wavelength division multiplexer 15; the multi-core fiber 3 in the active multi-core fiber ultrashort resonator is replaced with a 7-core neodymium-doped fiber; the laser output module consists of a wavelength division multiplexer 15 and an optical isolator 13, and the entire system adopts an all-fiber structure.

[0058] The semiconductor pump source 9 has a maximum output power of 40 W, a center wavelength of 808 nm, and a fiber optic core diameter of 60 μm. The fiber optic pigtail of the semiconductor pump source 9 is fused to the fiber optic pigtail of the pump end of the wavelength division multiplexer 15.

[0059] The wavelength division multiplexer 15 is a multimode wavelength division multiplexer with an operating wavelength of 808 / 920 nm, a fiber core diameter of 60 μm, and a cladding diameter of 250 μm. After the coating layer is removed from the common end pigtail of the wavelength division multiplexer 15, it is inserted into a ceramic ferrule 11 with an inner diameter of 250 μm and fixed with optical adhesive. After the end face of the ceramic ferrule 11 is vertically polished, it is mechanically connected to the ultrashort resonator through the sleeve 10.

[0060] The inner diameter of the sleeve 10 is 2.5 cm, which matches the outer diameter of the insert 4 and the ceramic insert 11.

[0061] The active multi-core optical fiber 3 is a 7-core neodymium-doped optical fiber with a cladding diameter of 900 μm.

[0062] The first coreless optical fiber 2 and the second coreless optical fiber 5 have a diameter of 900 μm and are fused to both ends of the active multi-core optical fiber 3, respectively.

[0063] The semiconductor saturable absorber mirror 1 is fixed on one end face of the ceramic ferrule 4. It has a center wavelength of 920 nm, an area of ​​1 × 1 mm, a thickness of 450 μm, a modulation depth of 5%, an unsaturated loss of 5%, and a saturated flux of 60 μJ / cm². 2 The relaxation time is 1.5 ps, and the damage threshold is 4 mJ / cm². 2 .

[0064] The dielectric film 6 is a dichroic film deposited on one end face of the ceramic ferrule 4, which has high transmittance (>80%) for 808 nm laser and high reflectance (>70%) for 920 nm laser.

[0065] The optical fiber isolator 13 has a center wavelength of 920 nm, the input pigtail is fused to the signal pigtail of the wavelength division multiplexer 15, and the output end outputs a 920 nm high repetition rate mode-locked laser pulse.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit the technical solutions. Those skilled in the art should understand that any modifications or equivalent substitutions to the technical solutions of the present invention without departing from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. A high repetition rate fiber laser based on active multi-core fiber, characterized in that... The system includes a pumping device, an active multi-core fiber ultrashort resonator, and a laser output device. The pumping device includes a pump source (9) and a pump light input module. The pump source (9) is connected to the active multi-core fiber ultrashort resonator via the pump light input module to couple pump light into the active multi-core fiber ultrashort resonator. The laser output device couples the mode-locked laser pulse generated by the active multi-core fiber ultrashort resonator out of the cavity. The active multi-core fiber ultrashort resonator includes a semiconductor saturable absorber mirror (1), a first coreless fiber (2), and an active multi-core fiber (3). The ferrule (4), the second coreless fiber (5), and the dielectric film (6) are provided. One end of the first coreless fiber (2) is connected to one end of the active multi-core fiber (3), and one end of the second coreless fiber (5) is connected to the other end of the active multi-core fiber (3). The diameters of the first coreless fiber (2) and the second coreless fiber (5) are matched with the diameter of the active multi-core fiber (3) and are encapsulated in the ferrule (4). A semiconductor saturable absorber mirror (1) is disposed on one end face of the ferrule (4), and the dielectric film (6) is disposed on the other end face of the ferrule (4).

2. The high repetition rate fiber laser based on active multi-core fiber as described in claim 1, characterized in that, The active multi-core optical fiber (3) is a rare earth ion doped glass optical fiber. The doped rare earth ions may include one or more of erbium, ytterbium, thulium, holmium, neodymium, praseodymium, and bismuth.

3. The high repetition rate fiber laser based on active multi-core fiber as described in claim 1, characterized in that, The active multi-core optical fiber (3) has 3-100 cores.

4. The high repetition rate fiber laser based on active multi-core fiber as described in claim 1, characterized in that, The first coreless optical fiber (2) and the second coreless optical fiber (5) are made of a single glass medium and have a fiber length of 1-50 mm.

5. The high repetition rate fiber laser based on active multi-core fiber as described in claim 1, characterized in that, The pumping device includes a pump source (9) and a pump light input module, wherein the pump light input module is a lens group (7), or an optical fiber combiner (14), or a wavelength division multiplexer (15).

6. The high-repetition-rate fiber laser based on active multi-core fiber as described in claim 1, characterized in that, The pump source (9) is a multi-mode pump source, with one or more pumps, and the pumping method is core pumping or cladding pumping.

7. The high repetition rate fiber laser based on active multi-core fiber as described in claim 1, characterized in that, The laser output device is a dichroic mirror (8), or a circulator (12) and isolator (13), or a wavelength division multiplexer (15) and isolator (13).

Images