Super-large mode field spoke core fiber laser suitable for laser micro-propulsion

Abstract

The invention relates to an ultra-large mode field spoke core fiber laser suitable for laser micro propulsion, which adopts a main oscillation power amplification structure and comprises a seed source, a first amplification stage, a second amplification stage and a main amplification stage, the seed source is a directly modulated semiconductor laser, outputs pulse laser with tunable pulse width and repetition frequency, and the laser of the seed source enters the main amplification light path in a free space coupling mode after being subjected to primary and secondary pre-amplification. The main amplification stage amplifies the average power of laser to hectowatt magnitude by adopting an ultra-large mode field spoke core optical fiber with a bilateral pumping design, and dynamic adjustment of specific impulse and thrust of the micro-thruster is realized by changing the power, pulse width and frequency of the laser. The laser micro-thruster is clear in design principle, the achievable effect of the laser micro-thruster breaks through the limitation of the specific impulse and thrust dynamic range of a common laser micro-thruster, and the multi-task scene application capacity of the laser micro-thruster is remarkably improved.

Description

Technical Field

[0001] The invention relates to a light source system for laser micro-propulsion, in particular to an ultra-large mode field spoke core optical fiber laser suitable for laser micro-propulsion. Background Art

[0002] With the development of mechanical microelectronics technology, satellite miniaturization has become a new trend in the development of contemporary satellites. In order to complete specific tasks and maintain the stability of the orbital formation of distributed satellite systems, it is necessary to perform precise attitude and orbit control operations on microsatellites. The Phipps team in the United States first proposed the idea of ​​using laser micro-propulsion for microsatellites. Laser micro-propulsion technology works by using the interaction mechanism between laser and matter. It uses laser as the energy source. After being focused by optical elements, the laser is focused on the target surface of the ablated material to form a tiny material jet, realize impulse coupling, and generate thrust.

[0003] Laser propulsion technology has the characteristics of small thrust, wide range and controllability, small minimum impulse, and high specific impulse. Therefore, the propulsion technology using laser as energy source has become an effective way to deal with the launch of micro-satellites and the flexible operation of satellites in orbit. In order to make the thruster have the advantage of adjustable performance parameters, the laser parameters of the laser (such as pulse width, power, frequency) are required to be easy to adjust, integrating the advantages of millisecond pulse width and nanosecond pulse width, and can work in both high specific impulse mode and high impulse coupling coefficient mode, so that a lower mass thruster can be used to achieve a wider performance, and the specific impulse and impulse coupling coefficient can be adjusted in real time according to mission requirements. At present, diode lasers are used in msμLPT (millisecond pulse width laser plasma microthruster) and laser-supported combustion microthrusters due to their advantages of small size, light weight, and high electro-optical conversion efficiency, but their power-to-mass ratio and beam quality need to be improved. For the microchip lasers used in nsμLPT (nanosecond pulse width laser plasma microthruster) and LEHT laser-electrostatic field coupled thruster, their electro-optical conversion efficiency is low; while the YAG solid lasers used in laser-supported pulse plasma thrusters and laser-magnetic field coupled thrusters are large in size and heavy in mass, and cannot meet the requirements of satellite-borne. Therefore, it is necessary to carry out research on high-brightness pulse width and repetition rate tunable laser light source technology to meet the needs of new laser plasma microthrusters. Summary of the invention

[0004] The technical problem solved by the present invention is to provide an ultra-large mode field spoke core fiber laser suitable for laser micro-propulsion, which solves the problems of low efficiency, large size and heavy mass of traditional laser propulsion light sources and meets the demand of new laser plasma micro-propulsion for pulsed laser sources.

[0005] The technical solution of the present invention is as follows: An ultra-large mode field spoke core fiber laser applicable to laser micro-thrust includes a seed light source, a first amplification stage, a second amplification stage, and a main amplification stage; the seed light source outputs a pulsed laser signal with adjustable pulse width and repetition frequency according to current modulation; the pulsed laser signal emitted by the seed light source is pre-amplified and filtered by the first amplification stage and the second amplification stage; the main amplification stage amplifies the pulsed laser after pre-amplification and filtering to the order of several hundred watts again and finally outputs it.

[0006] Both the first amplification stage and the second amplification stage adopt all-fiber structure amplification stages.

[0007] The main amplification stage includes a first dichroic mirror, a first focusing lens, a first collimating lens, a forward pump source, an ultra-large mode field spoke core fiber, a second dichroic mirror, a second focusing lens, a second collimating lens, and a backward pump source;

[0008] The laser output from the second amplification stage is coupled and focused into the spoke core fiber through the first dichroic mirror and the first focusing lens. The forward pump light emitted by the forward pump source is collimated by the first collimating lens, reflected by the first dichroic mirror, and focused by the first focusing lens and then enters the spoke core fiber; the backward pump light emitted by the backward pump source is collimated by the second collimating lens, reflected by the second dichroic mirror, and focused by the second focusing lens and then enters the spoke core fiber; the spoke core fiber realizes the power amplification of the pulsed laser to the order of several hundred watts and finally outputs it.

[0009] The first dichroic mirror, the first focusing lens, the first collimating lens, the ultra-large mode field spoke core fiber, the second dichroic mirror, the second focusing lens, and the second collimating lens are on the same optical axis.

[0010] The first focusing lens, the first collimating lens, the second focusing lens, and the second collimating lens are plano-convex lenses or biconvex lenses.

[0011] The first dichroic mirror and the second dichroic mirror are coated with films to achieve high transmission of signal light and high reflection of pump light.

[0012] The center of the ultra-large mode field spoke core fiber is a circular core region, and a plurality of completely identical spoke cores are evenly distributed around the circular core, and N petal-shaped inner claddings with the same radius and radian; a groove ring and an outer cladding are distributed from the inside to the outside of the spoke core.

[0013] The refractive index of the circular core of the ultra-large mode field spoke core fiber is n1, the refractive index of the spoke core is n2, the refractive index of the groove ring is n3, and the refractive indices of the petal-shaped inner cladding and the outer cladding are n4; where n4 < n3 < n2 < n1, the refractive index differences are Δn1 = n1 - n4, Δn2 = n2 - n4, Δn3 = n3 - n4, and the refractive index difference Δn1 = 10 -3 ,1.10×10 -3<Δn2<1.15×10 -3 , 9.0×10 -4 <Δn3<9.6×10 -4 .

[0014] The circular fiber core, spoke core and groove ring are all made of ytterbium-doped YAG materials, and the petal-shaped inner cladding and outer cladding are all made of ytterbium-free YAG materials.

[0015] The cross-sectional structure of the optical fiber does not change along the axial direction of the optical fiber.

[0016] Compared with the prior art, the advantages of the present invention are as follows: the fiber laser has the advantages of good beam quality, easy integration, convenient heat dissipation, high reliability, etc., and can achieve a larger single pulse energy, and the overall power consumption is controllable, which is suitable for small space platform propulsion systems with certain thrust requirements. The main amplifier stage uses ultra-large mode field spoke core fiber as the gain medium, which reduces the generation of nonlinear effects such as stimulated Raman scattering, self-phase modulation, and stimulated Brillouin scattering during the amplification process, and improves the stability and reliability of the light source system. Under the conditions of nanosecond to millisecond pulse width, it has the ability to achieve high-energy laser output, providing a power density of 10 for the laser propulsion system. 6 -10 13 W / cm 2 The comprehensive light source meets the requirements of two working modes: low specific impulse and high thrust and high specific impulse and low thrust. In addition, this power density condition breaks through the limitation of the focal area required for subsequent laser ablation, which can greatly reduce the requirements of the optical focusing system. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a schematic diagram of the ultra-large mode field spoke core fiber laser suitable for laser micro-propulsion of the present invention;

[0018] Figure 2 A schematic diagram of a cross section of a super large mode field spoke core optical fiber in the present invention;

[0019] Figure 3 The equivalent refractive index distribution diagram of the optical fiber structural parameters in the present invention along the radial direction from the center of the optical fiber;

[0020] Figure 4 This is the fundamental mode field distribution diagram of the optical fiber structural parameters at a wavelength of 1.064 μm in the present invention. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0022] In one embodiment, the present invention provides an ultra-large mode field spoke-core fiber laser suitable for laser micro-propulsion, such as Figure 1 As shown, it includes: a seed light source 1, a first amplifying stage 2, a second amplifying stage 3, and a main amplifying stage 4; wherein the main amplifying stage 4 includes: a first dichroic mirror 5, a first focusing lens 6, a first collimating lens 7, a forward pump source 8, an ultra-large mode field spoke core optical fiber 9, a second dichroic mirror 10, a second focusing lens 11, a second collimating lens 12, and a backward pump source 13;

[0023] In this embodiment, the seed light source 1 is a semiconductor laser with a wavelength of 1064nm, an average output power of 20mW, a pulse width adjustment range of 10ns-1ms and a repetition frequency adjustment range of 10-100Hz, and the output pulse laser is transmitted to the first amplifier stage 2 via a single-mode optical fiber; the first amplifier stage 2 and the second amplifier stage 3 are all-fiber structures, and the seed laser is pre-amplified and filtered; the gain of the first amplifier stage 2 is greater than 20dB, and the seed source power is amplified to 2W; the gain of the second amplifier stage 3 is greater than 8dB, and the laser power is further amplified to 15W; the main amplifier stage 4 uses an ultra-large mode field spoke core optical fiber 9 to amplify the average power of the secondary amplified pulse laser to 100W;

[0024] The main amplifier stage 4 of this embodiment includes: a first dichroic mirror 5, a first focusing lens 6, a first collimating lens 7, a forward pump source 8, an ultra-large mode field spoke core fiber 9, a second dichroic mirror 10, a second focusing lens 11, a second collimating lens 12, and a backward pump source 13; the first dichroic mirror 5, the first focusing lens 6, the first collimating lens 7, the ultra-large mode field spoke core fiber 9, the second dichroic mirror 10, the second focusing lens 11, and the second collimating lens 12 are on the same optical axis; the collimated secondary amplified laser is focused by the first dichroic mirror 5 and the first focusing lens 6 to enter the spoke core fiber, the forward pump light enters the spoke core fiber 9 after being collimated and focused by the first collimating lens 7, the first dichroic mirror 5, and the first focusing lens 6, and the forward pump light enters the spoke core fiber 9 after being collimated and focused by the second collimating lens 12, the second dichroic mirror 10, and the second focusing lens 11; the spoke core fiber 9 realizes power amplification of hundreds of watts of pulsed laser and finally outputs it.

[0025] In this embodiment, the first focusing lens 6, the first collimating lens 7, the second focusing lens 11 and the second collimating lens 12 are one of plano-convex mirrors and bi-convex mirrors; the first dichroic mirror 5 and the second dichroic mirror 10 have high transmission for 1064nm signal light and high reflection for 976nm pump light, and are placed at an angle of 45°;

[0026] The cross-sectional structure of the ultra-large mode field spoke core optical fiber 9 of this embodiment is as follows: Figure 2As shown in the figure, it includes: a circular core region 14, eight identical spoke cores 15 evenly distributed around the circular core, eight petal-shaped inner claddings 16 with the same radius and radian, a groove ring 17 distributed from the inside to the outside around the periphery of the spoke cores, and an outer cladding 18. The refractive index of the circular core 14 is n1, the refractive index of the spoke core 15 is n2, the refractive index of the groove ring 17 is n3, and the refractive indices of the petal-shaped inner cladding 16 and the outer cladding 18 are n4; n4 < n3 < n2 < n1; the refractive index differences are Δn1 = n1 - n4, Δn2 = n2 - n4, Δn3 = n3 - n4. The radius r1 of the circular core 14 is 28 - 32 μm, the width t of the spoke core 15 is 17 - 21 μm, the thickness t1 of the groove ring 17 is 12 - 16 μm, r2 = 110 μm, r3 = 150 μm. The refractive index difference Δn1 = 10 -3 , 1.10×10 -3 < Δn2 < 1.15×10 -3 , 9.0×10 -4 < Δn3 < 9.6×10 -4 ; The circular core 14, the spoke core 15, and the groove ring 17 are made of doped YAG material, and the petal-shaped inner cladding 16 and the outer cladding 18 are made of undoped YAG material. The cross-sectional structure of the spoke core optical fiber does not change along the optical waveguide axis.

[0027] Figure 3 shows the distribution diagram of the equivalent refractive index along the radial direction from the center of the optical fiber when the structural parameters of the ultra-large mode field spoke core optical fiber 9 of the present invention are r1 = 30 μm, r2 = 110 μm, r3 = 150 μm, t = 21 μm, t1 = 15 μm, Δn1 = 10 -3 , Δn2 = 1.12×10 -3 , Δn3 = 9.2×10 -4 .

[0028] Figure 4 shows the fundamental mode field distribution diagram at a wavelength of 1.064 μm when the structural parameters of the ultra-large mode field spoke core optical fiber 9 of the present invention are r1 = 30 μm, r2 = 110 μm, r3 = 150 μm, t = 21 μm, t1 = 15 μm, Δn1 = 10 -3 , Δn2 = 1.12×10 -3 , Δn3 = 9.2×10 -4 . It can be obtained that the mode field of the fundamental mode呈星状分布在圆形纤芯和辐条芯区域。进一步计算得到超大单模模场面积为9171.5μm 2 , breaking through the limitation of the effective mode field area of general petal-shaped optical fibers, and further effectively solving nonlinear problems such as stimulated Raman scattering and stimulated Brillouin scattering, providing a relatively stable and reliable laser light source for the laser micropropulsion system.

[0029] The design principle of the invention is clear. By adjusting the parameters such as power, pulse width, frequency, etc., the micro propulsion system can be provided with an average power of more than 100W and a power density of 10 6 -10 13 W / cm 2 The light source can achieve the effect that meets the requirements of two working modes: low specific impulse and high thrust and high specific impulse and low thrust, and greatly reduces the requirements for subsequent focusing optical systems.

[0030] The above shows and describes the basic principles, main features and advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. An ultra-large mode field spoke core fiber laser suitable for laser micro-propulsion, characterized in that: The invention comprises a seed light source (1), a first amplifying stage (2), a second amplifying stage (3), and a main amplifying stage (4); the seed light source (1) outputs a pulse laser signal with tunable pulse width and repetition frequency according to current modulation; the first amplifying stage (2) and the second amplifying stage (3) pre-amplify and filter the pulse laser signal emitted by the seed light source (1); the main amplifying stage (4) amplifies the pulse laser signal after pre-amplification and filtering again to the order of hundreds of watts and finally outputs it.

2. The ultra-large mode field spoke core fiber laser suitable for laser micro-propulsion according to claim 2, characterized in that: The first amplifying stage (2) and the second amplifying stage (3) both adopt all-fiber structure amplifying stages.

3. The ultra-large mode field spoke core fiber laser suitable for laser micro-propulsion according to claim 1, characterized in that: The main amplifier stage (4) comprises a first dichroic mirror (5), a first focusing lens (6), a first collimating lens (7), a forward pump source (8), an ultra-large mode field spoke core optical fiber (9), a second dichroic mirror (10), a second focusing lens (11), a second collimating lens (12) and a backward pump source (13); The laser light output from the second amplifier stage (3) is coupled and focused into the spoke core optical fiber (9) through the first dichroic mirror (5) and the first focusing lens (6); the forward pump light emitted by the forward pump source (8) is collimated by the first collimating lens (7), reflected by the first dichroic mirror (5), focused by the first focusing lens (6), and then enters the spoke core optical fiber (9); the backward pump light emitted by the backward pump source (13) is collimated by the second collimating lens (12), reflected by the second dichroic mirror (10), focused by the second focusing lens (11), and then enters the spoke core optical fiber (9); the spoke core optical fiber (9) amplifies the power of the pulse laser light to the order of hundreds of watts and finally outputs the power.

4. The ultra-large mode field spoke core fiber laser suitable for laser micro-propulsion according to claim 3, characterized in that: The first dichroic mirror (5), the first focusing lens (6), the first collimating lens (7), the ultra-large mode field spoke core optical fiber (9), the second dichroic mirror (10), the second focusing lens (11), and the second collimating lens (12) are located on the same optical axis.

5. The ultra-large mode field spoke core fiber laser suitable for laser micro-propulsion according to claim 3, characterized in that: The first focusing lens (6), the first collimating lens (7), the second focusing lens (11) and the second collimating lens (12) are plano-convex lenses or bi-convex lenses.

6. The ultra-large mode field spoke core fiber laser suitable for laser micro-propulsion according to claim 3, characterized in that: The first dichroic mirror (5) and the second dichroic mirror (10) are coated to achieve high transmission of signal light and high reflection of pump light.

7. The ultra-large mode field spoke core fiber laser suitable for laser micro-propulsion according to claim 3, characterized in that: The center of the ultra-large mode field spoke core optical fiber (9) is a circular core region (14), around which a plurality of identical spoke cores (15) and N petal-shaped inner claddings (16) with the same radius and curvature are evenly distributed; and a groove ring (17) and an outer cladding (18) are distributed from the inside to the outside on the periphery of the spoke core (15).

8. The ultra-large mode field spoke core fiber laser suitable for laser micro-propulsion according to claim 7, characterized in that: The refractive index of the circular core (14) of the ultra-large mode field spoke-core fiber is n1, the refractive index of the spoke core (15) is n2, the refractive index of the trench ring (17) is n3, and the refractive indices of the petal-shaped inner cladding (16) and the outer cladding (18) are n4; where n4 < n3 < n2 < n1, the refractive index differences are Δn1 = n1 - n4, Δn2 = n2 - n4, Δn3 = n3 - n4, and the refractive index difference Δn1 = 10 -3 , 1.10×10 -3 < Δn2 < 1.15×10 -3 , 9.0×10 -4 < Δn3 < 9.6×10 -4 .

9. The ultra-large mode field spoke core fiber laser suitable for laser micro-propulsion according to claim 7, characterized in that: The circular fiber core (14), the spoke core (15), and the groove ring (17) are all made of ytterbium-doped YAG materials, and the petal-shaped inner cladding (16) and the outer cladding (18) are all made of ytterbium-free YAG materials.

10. The ultra-large mode field spoke core fiber laser suitable for laser micro-propulsion according to claim 7, characterized in that: The cross-sectional structure of the optical fiber does not change along the axial direction of the optical fiber.

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