High-power near single-mode continuous optical fiber green laser

Abstract

The invention provides a high-power near single-mode continuous optical fiber green laser, and belongs to the technical field of optical fiber green lasers. The FOL seed source is used for generating and outputting linear polarization seed light; the amplifier unit is connected with an output end light path of the FOL seed source and is used for performing power amplification on the input seed light to obtain fundamental frequency light; and the frequency multiplication unit is connected with an output end light path of the amplifier unit and is used for carrying out frequency multiplication processing on the fundamental frequency light to obtain required green laser output. The FOL seed source directly injects pump light into a first active optical fiber by adopting a grating pair and side pumping coupling mode, a first pump source, the first active optical fiber and the grating pair form a resonant cavity structure, and stable seed light can be output; the frequency doubling part adopts a polarization beam combination mode, and the frequency doubling efficiency and the green laser power are improved through secondary frequency doubling.

Description

Technical Field

[0001] The invention relates to the technical field of optical fiber green light lasers, and in particular to a high-power near single-mode continuous optical fiber green light laser. Background Art

[0002] The working band of the laser prepared by the green laser light source is around 532nm. The absorption rate of metal materials to green light in this band is much greater than that of near-infrared lasers. The processing efficiency of green lasers on metals is significantly higher than that of near-infrared lasers. In addition, the backlight reflection during green laser welding is small, the welding spatter is small, and the damage to the laser is small. Therefore, it is particularly suitable for welding operations of various copper materials in the field of new energy vehicles.

[0003] At present, the main schemes for continuous green lasers include diode-pumped solid-state laser frequency-doubled green light, semiconductor green laser, disk continuous green light and fiber continuous green light frequency-doubled. Due to the complex structural design, gain medium thermal effect, poor stability, and beam quality degradation, diode-pumped solid-state laser frequency-doubled green light and semiconductor green laser have great difficulties in outputting high power such as kilowatt-level green light and high brightness such as near-single mode; disk continuous green light has a huge challenge in beam quality despite the breakthrough of kilowatt-level power due to the complex gain medium and resonant cavity design of the laser system; fiber laser technology has efficient thermal management, good beam quality, and high photoelectric conversion efficiency, so it has technical potential in generating high-power and high-brightness green lasers.

[0004] Therefore, it is very necessary to provide a high-power near-single-mode continuous fiber green laser to achieve high-power, high-brightness green laser output and improve the current situation of complex structure and poor stability of existing high-power green lasers. Summary of the invention

[0005] In view of this, the present invention proposes a high-power near-single-mode continuous fiber green light laser that injects pump light into the resonant cavity through side pumping, stably outputs seed light with high beam quality, and achieves power enhancement through power amplification, frequency doubling and polarization combining.

[0006] The present invention provides a high-power near single-mode continuous fiber green laser, comprising a FOL seed source, an amplifier unit and a frequency doubling unit arranged in sequence, wherein:

[0007] A FOL seed source, used for generating and outputting linearly polarized seed light;

[0008] An amplifier unit is connected to the output end of the FOL seed source and is used to amplify the power of the input seed light to obtain the fundamental frequency light;

[0009] The frequency doubling unit is connected to the output optical path of the amplifier unit and is used to perform frequency doubling processing on the fundamental frequency light to obtain the required green laser output.

[0010] On the basis of the above technical solution, preferably, the FOL seed source includes a narrowband high-reflection grating, a first pump source, a first active optical fiber, a narrowband low-reflection grating, a polarization-maintaining isolator and a polarization-maintaining optical fiber mode field adapter with a cladding power stripping function; the first end of the first active optical fiber is optically connected to one end of the narrowband high-reflection grating, the other end of the narrowband high-reflection grating is cut at an angle of 8° and fixed by glue, the second end of the first active optical fiber is optically connected to one end of the narrowband low-reflection grating, the other end of the narrowband low-reflection grating is optically connected to the input end of the polarization-maintaining isolator, the output end of the first pump source is optically connected to the pump input end of the side of the first active optical fiber, A narrowband high-reflection grating, a first pump source, a first active optical fiber and a narrowband low-reflection grating constitute a grating pair resonant cavity, which is used to convert the pump light input by the first pump source into a laser with a random polarization state; the output end of the polarization-maintaining isolator is optically connected to the input end of the polarization-maintaining optical fiber mode field adapter with a cladding power stripping function, and the polarization-maintaining isolator converts the laser with a random polarization state into a linearly polarized seed light output; the polarization-maintaining optical fiber mode field adapter with a cladding power stripping function performs mode stripping on the input linearly polarized seed light, filters out the cladding light caused by numerical aperture NA mismatch and optical fiber fusion, and performs mode field adaptation for the subsequent access amplifier unit.

[0011] Preferably, the polarization-maintaining optical fiber mode field adapter with cladding power stripping function is produced by etching a certain length at both ends of the fusion point of the mode field adapter MFA to make a cladding light stripping device CPS, and integrating the cladding light stripping device CPS with the mode field adapter MFA into an integrated structure.

[0012] Preferably, the amplifier unit comprises two second pump sources, a first polarization-maintaining pump combiner, a second polarization-maintaining active optical fiber, a second polarization-maintaining pump combiner, two third pump sources, a polarization-maintaining cladding light stripper and a collimator; the input ends of the first polarization-maintaining pump combiner are respectively optically connected to the output ends of the polarization-maintaining optical fiber mode field adapter with a cladding power stripping function, the outputs of the two second pump sources are merged into the first polarization-maintaining pump combiner, the output end of the first polarization-maintaining pump combiner is optically connected to one end of the second polarization-maintaining active optical fiber, and the second polarization-maintaining active optical fiber is optically connected to the output end of the polarization-maintaining optical fiber mode field adapter with a cladding power stripping function. The other end of the optical fiber is optically connected to one end of the second polarization-maintaining pump combiner, the outputs of the two third pump sources are merged into the second polarization-maintaining pump combiner, the other end of the second polarization-maintaining pump combiner is optically connected to the input end of the polarization-maintaining cladding light stripper, the output end of the polarization-maintaining cladding light stripper is optically connected to the input end of the collimator, and the output end of the collimator is optically connected to the input end of the frequency doubling unit; the amplifier unit amplifies the input seed light and outputs the fundamental frequency light with amplified power, and the collimator expands and collimates the spot size of the fundamental frequency light.

[0013] Further preferably, the first polarization-maintaining pump combiner and the second polarization-maintaining pump combiner are combined by using any one of forward pumping, reverse pumping or bidirectional pumping.

[0014] Further preferably, the first polarization-maintaining pump combiner and the second polarization-maintaining pump combiner adopt any one of (2+1)×1, (4+1)×1, (6+1)×1, (8+1)×1, and (12+1)×1.

[0015] Further preferably, the frequency doubling unit includes at least one frequency doubling processing component, a dichroic mirror, at least one baseband processing component and a polarization beam combiner; at least one frequency doubling processing component receives the baseband light output by the collimator, performs a first frequency doubling conversion on the baseband light, and then outputs it to the dichroic mirror; the dichroic mirror separates the first green laser light after frequency doubling and the residual baseband light; the residual baseband light is sent to at least one baseband processing component for a second frequency doubling conversion to obtain a second green laser light; the first green laser light and the second green laser light are combined at the polarization beam combiner to obtain the required green laser light.

[0016] More preferably, the at least one frequency doubling processing component comprises a first total reflection mirror, a second total reflection mirror, a first half-wave plate, a first focusing lens and a first LBO frequency doubling crystal which are arranged in sequence, the incident end of the first total reflection mirror is optically connected to the output end of the collimator, the exit end of the first total reflection mirror is optically connected to the incident end of the second total reflection mirror, the exit end of the second total reflection mirror is optically connected to the incident end of the first half-wave plate, the first total reflection mirror and the second total reflection mirror are arranged in a mirror image, the exit end of the first half-wave plate is optically connected to the incident end of the first focusing lens, the exit end of the first focusing lens is optically connected to the incident end of the collimator, and the exit end of the first total reflection mirror is optically connected to the incident end of the second total reflection mirror. The transmitting end is optically connected to the input end of the first LBO frequency doubling crystal, and the output end of the first LBO frequency doubling crystal is optically connected to the input end of the dichroic mirror; the first half-wave plate is used to change the linear polarization direction of the input power-amplified fundamental frequency light, the first focusing lens focuses the fundamental frequency light on the first LBO frequency doubling crystal, and the rotation angle of the first half-wave plate, the position of the first focusing lens and the temperature of the first LBO frequency doubling crystal are adjusted to improve the efficiency of the first frequency doubling to obtain the first green laser; the first green laser enters the polarization beam combiner after being reflected at the incident side of the dichroic mirror.

[0017] Still further preferably, at least one baseband processing component includes a second focusing lens, a second LBO frequency doubling crystal, a third total reflection mirror, a fourth total reflection mirror and a second half-wave plate which are arranged in sequence; the input end of the second focusing lens is optically connected to the transmission output end of the dichroic mirror, the output end of the second focusing lens is optically connected to the input end of the second LBO frequency doubling crystal, the output end of the second LBO frequency doubling crystal is optically connected to the incident end of the third total reflection mirror, the output end of the third total reflection mirror is optically connected to the incident end of the fourth total reflection mirror, and the output end of the fourth total reflection mirror is optically connected to the incident end of the third total reflection mirror. The incident end optical path of the second half-wave plate is connected, the third total reflection mirror and the fourth total reflection mirror are arranged in mirror image, and the output end of the second half-wave plate is connected to the polarization beam combiner optical path; the second focusing lens focuses the residual fundamental frequency light on the second LBO frequency doubling crystal, and the second LBO frequency doubling crystal performs a second frequency doubling conversion on the residual fundamental frequency light to obtain a second green laser. After the output optical path is adjusted by the third total reflection mirror and the fourth total reflection mirror, the second half-wave plate is used to change the polarization reversal of the second green laser so that the first green laser and the second green laser are combined at the polarization beam combiner.

[0018] More preferably, the first focusing lens and the second focusing lens are any one of f50, f60, f100, f120, f150, f200 or f250; the length of the first LBO frequency doubling crystal and the second LBO frequency doubling crystal is 25 mm, 40 mm or 60 mm.

[0019] The high-power near single-mode continuous fiber green laser provided by the present invention has the following beneficial effects compared with the prior art:

[0020] The present invention uses a resonant cavity structure composed of a first active optical fiber and a grating pair to laterally inject pump light into a first pump source, and then converts the pump light into linearly polarized seed light through a polarization-maintaining isolator. The seed light has high beam quality and is power-amplified after being processed by an amplification unit to obtain fundamental frequency light with good stability and high power. The fundamental frequency light is polarized and combined to improve the frequency doubling efficiency of green light, effectively utilize the residual fundamental frequency light, improve the utilization rate of the fundamental frequency light, and increase the output power of green light. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0022] Figure 1 This is a schematic diagram of the structure of a high-power near single-mode continuous fiber green laser of the present invention;

[0023] Figure 2 A schematic diagram of a 3dB bandwidth spectrum of a 1064nm signal light outputted by a seed source of a high-power near single-mode continuous fiber green laser of the present invention;

[0024] Figure 3 A schematic diagram of a 10dB bandwidth spectrum of a 1064nm fundamental frequency light output by an amplifier unit of a high-power near single-mode continuous fiber green laser of the present invention;

[0025] Figure 4 A schematic diagram of a 20 dB bandwidth spectrum of a 1064 nm fundamental frequency light output by an amplifier unit of a high-power near single-mode continuous fiber green laser of the present invention;

[0026] Figure 5 It is a schematic diagram of the structure of the pump fiber and the active fiber in the side pump coupling mode of the present invention.

[0027] Reference numerals: 100, FOL seed source; 200, amplifier unit; 300, frequency multiplication unit;

[0028] 1. Narrowband high-reflection grating; 2. First pump source; 3. First active optical fiber; 4. Narrowband low-reflection grating; 5. Polarization-maintaining isolator; 6. Polarization-maintaining optical fiber mode field adapter with cladding power stripping function; 7. Second pump source; 8. First polarization-maintaining pump combiner; 9. Second polarization-maintaining active optical fiber; 10. Second polarization-maintaining pump combiner; 11. Third pump source; 12. Polarization-maintaining cladding light stripper; 13. Collimator; 14. First total reflection mirror; 15. Second total reflection mirror; 16. First half-wave plate; 17. First focusing lens; 18. First LBO frequency doubling crystal; 19. Dichroic mirror; 20. Second focusing lens; 21. Second LBO frequency doubling crystal; 22. Third total reflection mirror; 23. Fourth total reflection mirror; 24. Second half-wave plate; 25. Polarization combiner. DETAILED DESCRIPTION

[0029] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] Existing diode-pumped solid-state laser frequency-doubled green light and semiconductor green light lasers have great difficulties in outputting high power such as kilowatt-level green light and high brightness such as near single-mode due to complex structural design, gain medium thermal effect, poor stability, and beam quality degradation. Figure 1As shown, the present invention provides a high-power near single-mode continuous fiber green laser, comprising a FOL seed source 100, an amplifier unit 200 and a frequency doubling unit 300 arranged in sequence, wherein:

[0031] The FOL seed source 100 is used to generate and output linearly polarized seed light;

[0032] The amplifier unit 200 is optically connected to the output end of the FOL seed source 100 and is used to amplify the power of the input seed light to obtain the fundamental frequency light;

[0033] The frequency doubling unit 300 is optically connected to the output end of the amplifier unit 200 and is used to perform frequency doubling on the fundamental frequency light to obtain the required green laser output.

[0034] like Figure 1 As shown, the FOL seed source 100 includes a narrowband high-reflection grating 1, a first pump source 2, a first active optical fiber 3, a narrowband low-reflection grating 4, a polarization-maintaining isolator 5 and a polarization-maintaining optical fiber mode field adapter 6 with a cladding power stripping function. The first end of the first active optical fiber 3 is optically connected to one end of the narrowband high-reflection grating 1, the other end of the narrowband high-reflection grating 1 is cut at an angle of 8° and then fixed with glue, the second end of the first active optical fiber 3 is optically connected to one end of the narrowband low-reflection grating 4, the other end of the narrowband low-reflection grating 4 is optically connected to the input end of the polarization-maintaining isolator 5, the output end of the first pump source 2 is optically connected to the pump input end on the side of the first active optical fiber 3, and the narrowband high The reflective grating 1, the first pump source 2, the first active optical fiber 3 and the narrowband low-reflective grating 4 constitute a grating pair resonant cavity, which is used to convert the pump light input by the first pump source 2 into a laser with a randomly polarized state; the output end of the polarization-maintaining isolator 5 is optically connected to the input end of the polarization-maintaining optical fiber mode field adapter 6 with a cladding power stripping function, and the polarization-maintaining isolator 5 converts the laser with a randomly polarized state into a linearly polarized seed light output; the polarization-maintaining optical fiber mode field adapter 6 with a cladding power stripping function performs mode stripping on the input linearly polarized seed light, filters out the cladding light caused by numerical aperture NA mismatch and optical fiber fusion, and performs mode field adaptation for the subsequent access amplifier unit 200.

[0035] The first pump source 2 and the first active optical fiber 3 adopt a side pump coupling mode, and the pump light is directly injected into the first active optical fiber 3. The grating pair resonant cavity structure is combined with a polarization-maintaining isolator 5, which is conducive to outputting a stable seed light with high beam quality. The FOL seed source 100 has a simple structure and good stability. In this embodiment, the narrowband high-reflection grating 1 has a 3dB bandwidth of 0.3nm, a 1064nm reflectivity greater than 99.5%, and can withstand a signal light power of 20W; the first pump source 2 is a 30W 976 pump source; the first active optical fiber 3 is a 10 / 125 active optical fiber, with an absorption coefficient of 4.8dB / m@976, a length of 3.5m, parameter 10 represents the core diameter, parameter 125 represents the cladding diameter, and the numerical aperture NA is 0.08; the narrowband low-reflection grating 4 has a 3dB bandwidth of 0.05nm, a 1064nm reflectivity less than 10%, and can withstand a signal light power of 20W; the narrowband high-reflection grating 1, the first pump source 2, the first active optical fiber 3, and the narrowband low-reflection grating 4 together constitute the seed source part. The polarization-maintaining isolator 5 is a 20W polarization-maintaining isolator, which converts the 1064nm seed light of the random polarization state into a 1064nm linearly polarized laser.

[0036] like Figure 5 As shown, the side pump coupling method uses the melt taper technology, first taper the pump fiber to a certain extent, then place the pump fiber close to the signal fiber and melt it at high temperature, while maintaining a certain amount of stretching, to form a special waveguide structure, and couple the pump fiber into the signal fiber. The side pump coupling method in this scheme draws on the manufacturing process of the beam combiner, directly replaces the passive signal fiber in the beam combiner structure with the first active fiber, and couples the pump fiber of the first pump source into the first active fiber by melt taper, so only the resonant cavity structure of narrowband high-reflection grating-first active fiber-narrowband low-reflection grating remains. This resonant cavity structure does not require the use of a beam combiner device, reduces the number of fiber fusion points, and the injection point of the pump light is directly located in the resonant cavity, which can reduce the pressure on the grating, making the structure and performance of the resonant cavity more stable and reliable.

[0037] Polarization-maintaining fiber mode field adapter 6 with cladding power stripping function The polarization-maintaining fiber mode field adapter 6 with cladding power stripping function is to make a cladding light stripping device CPS by etching a certain length at both ends of the fusion point of the mode field adapter MFA, and integrate the cladding light stripping device CPS with the mode field adapter MFA into an integrated structure, perform mode stripping on the input linear polarized seed light, and perform mode field adaptation for the subsequent access amplifier unit. In this embodiment, the input fiber of the polarization-maintaining fiber mode field adapter 6 with cladding power stripping function is 10 / 125, and the output fiber is 20 / 400. The mode stripping is performed at the taper fusion point to filter out the cladding light caused by the mismatch of the numerical aperture NA and the fiber fusion. Considering that if there is too much cladding light, the temperature of this section of the optical fiber will rise significantly, so as to avoid depolarization and reduce the extinction ratio, the structure is designed to be water-cooled.

[0038] In high-power fiber lasers and fiber amplifiers, the pump light and the signal light undergo energy exchange in the doped fiber, the pump is weakened, and the signal is enhanced. The pump energy cannot be completely absorbed, and some will remain and be transmitted in the cladding of the double-clad fiber. This part of energy is often unnecessary and may cause damage to subsequent devices. When the mode field adapter MFA connects two optical fibers with different mode field diameters MFD and numerical apertures NA, the fundamental mode signal can obtain the maximum pass rate at the fusion point; we can integrate the two functional devices, the mode field adapter MFA and the cladding power stripper CPS, to reduce fusion loss and product size space.

[0039] like Figure 2 As shown, Figure 2 The 3dB bandwidth spectrum calculated by THRESE method at a seed light power of 18W is shown, with a bandwidth of 0.0674nm. The experimentally measured polarization extinction ratio of the seed light is greater than 15dB. Figure 2-Figure 4 Medium c is the center frequency, △λ is the bandwidth. Each scale on the horizontal axis represents 0.5nm, dBm / D represents the power axis scale; RES shows the wavelength resolution of 0.02nm; SENS shows the measurement sensitivity, and this embodiment selects the sensitivity of the spectrometer at HIGH3; AVG means the average number is 1; SPAN means the number of sampling points is 5001.

[0040] Likewise Figure 1 As shown, the amplifier unit 200 includes two second pump sources 7, a first polarization-maintaining pump combiner 8, a second polarization-maintaining active optical fiber 9, a second polarization-maintaining pump combiner 10, two third pump sources 11, a polarization-maintaining cladding light stripper 12 and a collimator 13; the input ends of the first polarization-maintaining pump combiner 8 are respectively optically connected to the output ends of the polarization-maintaining optical fiber mode field adapter 6 with a cladding power stripping function, the outputs of the two second pump sources 7 are merged into the first polarization-maintaining pump combiner 8, the output end of the first polarization-maintaining pump combiner 8 is optically connected to one end of the second polarization-maintaining active optical fiber 9, and the output end of the second polarization-maintaining active optical fiber 9 is optically connected to the output end of the polarization-maintaining optical fiber mode field adapter 6 with a cladding power stripping function. The other end is optically connected to one end of the second polarization-maintaining pump combiner 10, the outputs of the two third pump sources 11 are merged into the second polarization-maintaining pump combiner 10, the other end of the second polarization-maintaining pump combiner 10 is optically connected to the input end of the polarization-maintaining cladding light stripper 12, the output end of the polarization-maintaining cladding light stripper 12 is optically connected to the input end of the collimator 13, and the output end of the collimator 13 is optically connected to the input end of the frequency doubling unit 300; the amplifier unit 200 amplifies the input seed light and outputs the fundamental frequency light with amplified power, and the collimator 13 expands and collimates the spot size of the fundamental frequency light.

[0041] The two second pump sources 7 are both 600W 976 pump sources, and the pump pigtail is 220 / 242; the first polarization-maintaining pump combiner 8 uses a (6+1)×1 polarization-maintaining pump combiner, the pump pigtail is 220 / 242, the input signal fiber is 20 / 400, and the output signal fiber is 20 / 400; the second polarization-maintaining active fiber 9 is a 20 / 400 polarization-maintaining active fiber with an absorption coefficient of 1.5dB / m@976, a length of 13m, and a numerical aperture NA of 0.06; the second polarization-maintaining pump combiner 10 uses a (6+1)×1 polarization-maintaining pump combiner, the pump pigtail is 220 / 242, the input signal fiber is 20 / 400, and the output signal fiber is 20 / 400; the two third pump sources 11 are both 600W976 pump sources, and the pump pigtail is 220 / 242; the two second pump sources 7, the first polarization-maintaining pump combiner 8, the second polarization-maintaining active fiber 9, the second polarization-maintaining pump combiner 10, and the two third pump sources 11 are mainly used to amplify the seed light power. The polarization-maintaining cladding light stripper 12 is a 20 / 400 polarization-maintaining CPS, with the same structural design and water cooling, and outputs high-power and high-brightness linearly polarized 1064nm fundamental frequency light; the collimator 13 expands and collimates the spot size of the output fundamental frequency light to 2-6mm.

[0042] like Figure 1 As shown in the figure, the combination of the first polarization-maintaining pump beam combiner 8 and the second polarization-maintaining pump beam combiner 10 is bidirectional pumping. This is only an example. In actual use, it is possible to use only the first polarization-maintaining pump beam combiner 8 for full forward pumping, or only the second polarization-maintaining pump beam combiner 10 for full reverse pumping.

[0043] The first polarization-maintaining pump combiner 8 and the second polarization-maintaining pump combiner 10 can be matched with a pump source with appropriate pump power and adopt any one of (2+1)×1, (4+1)×1, (6+1)×1, (8+1)×1, and (12+1)×1. Here, the parameters 2, 4, 6, 8, 12, etc. before the plus sign in the brackets represent the number of pump pigtails input to the combiner, and the parameter 1 after the plus sign in the brackets represents the number of signal pigtails input to the combiner; the parameter 1 after the multiplication sign represents that the pump signal and the signal transmitted by the optical fiber are transmitted in the same optical fiber.

[0044] Figure 3 The figure shows the 10dB bandwidth spectrum calculated by the THRESE method when the 1064nm signal optical power is 1000W, and the bandwidth is 0.1687nm; Figure 4 The figure shows the 20dB bandwidth spectrum calculated by the THRESE method when the 1064nm signal optical power is 1000W, and the bandwidth is 0.2540nm.

[0045] like Figure 1As shown, the frequency doubling unit 300 includes at least one frequency doubling processing component, a dichroic mirror 19, at least one baseband processing component and a polarization beam combiner 25; at least one frequency doubling processing component receives the baseband light output by the collimator 13, performs a first frequency doubling conversion on the baseband light, and then outputs it to the dichroic mirror 19; the dichroic mirror 19 separates the first green laser light after frequency doubling and the residual baseband light; the residual baseband light is sent to at least one baseband processing component for a second frequency doubling conversion to obtain a second green laser light; the first green laser light and the second green laser light are combined at the polarization beam combiner 25 to obtain the required green laser light.

[0046] Specifically, at least one frequency doubling processing component includes a first total reflection mirror 14, a second total reflection mirror 15, a first half-wave plate 16, a first focusing lens 17 and a first LBO frequency doubling crystal 18 which are arranged in sequence, the incident end of the first total reflection mirror 14 is optically connected to the output end of the collimator 13, the exit end of the first total reflection mirror 14 is optically connected to the incident end of the second total reflection mirror 15, the exit end of the second total reflection mirror 15 is optically connected to the incident end of the first half-wave plate 16, the first total reflection mirror 14 and the second total reflection mirror 15 are arranged in a mirror image, the exit end of the first half-wave plate 16 is optically connected to the incident end of the first focusing lens 17, the exit end of the first focusing lens 17 is optically connected to the incident end of the collimator 13, and the exit end of the first total reflection mirror 14 is optically connected to the incident end of the second total reflection mirror 15. The input end optical path of the first LBO frequency doubling crystal 18 is connected, and the output end of the first LBO frequency doubling crystal 18 is connected to the input end optical path of the dichroic mirror 19; the first half-wave plate 16 is used to change the linear polarization direction of the input power-amplified fundamental frequency light, and the first focusing lens 17 focuses the fundamental frequency light on the first LBO frequency doubling crystal 18. The rotation angle of the first half-wave plate 16, the position of the first focusing lens 17, the temperature of the first LBO crystal and the temperature of the first LBO frequency doubling crystal 18 are adjusted to improve the efficiency of the first frequency doubling and obtain the first green laser; the first green laser enters the polarization beam combiner 25 after reflection at the incident side of the dichroic mirror 19. In this embodiment, the power of the first green laser is above 500W.

[0047] The first total reflection mirror 14 and the second total reflection mirror 15 are both 1064nm total reflection mirrors; the first half-wave plate 16 is a 1064nm half-wave plate, and the polarization direction of the linearly polarized 1064nm fundamental frequency light can be changed by rotating the first half-wave plate 16. The dichroic mirror 19 is coated with a 532nm high reflection film and a 1064nm high transmission film, and is used to separate the 532nm first green laser obtained by the first frequency doubling conversion from the residual linearly polarized 1064nm fundamental frequency light.

[0048] At least one baseband processing component includes a second focusing lens 20, a second LBO frequency doubling crystal 21, a third total reflection mirror 22, a fourth total reflection mirror 23 and a second half-wave plate 24 which are arranged in sequence; the input end of the second focusing lens 20 is optically connected to the transmission output end of the dichroic mirror 19, the output end of the second focusing lens 20 is optically connected to the input end of the second LBO frequency doubling crystal 21, the output end of the second LBO frequency doubling crystal 21 is optically connected to the incident end of the third total reflection mirror 22, the output end of the third total reflection mirror 22 is optically connected to the incident end of the fourth total reflection mirror 23, the output end of the fourth total reflection mirror 23 is optically connected to the second half-wave plate 19, and the output end of the second focusing lens 20 is optically connected to the input end of the second LBO frequency doubling crystal 21. The incident end optical path of the wave plate 24 is connected to the third total reflection mirror 22 and the fourth total reflection mirror 23 in a mirror-like arrangement, and the output end of the second half-wave plate 24 is optically connected to the polarization beam combiner 25; the second focusing lens 20 focuses the residual fundamental frequency light on the second LBO frequency doubling crystal 21, and the second LBO frequency doubling crystal 21 performs a second frequency doubling conversion on the residual fundamental frequency light to obtain a second green laser. After the output optical path is adjusted by the third total reflection mirror 22 and the fourth total reflection mirror 23, the second half-wave plate 24 is used to change the polarization reversal of the second green laser so that the first green laser and the second green laser are combined at the polarization beam combiner 25.

[0049] The residual linearly polarized 1064nm fundamental frequency light is focused by the second focusing lens 20 and enters the second LBO frequency doubling crystal 21, and is frequency-doubled and converted into a 532nm second green laser; the third total reflection mirror 22 and the fourth total reflection mirror 23 are both coated with a 532nm total reflection film; the second half-wave plate 24 is a 532nm half-wave plate, and the linear polarization direction of the 532nm second green laser can be changed by rotating the second half-wave plate 24, so that it can better enter the polarization beam combiner 25. The polarization beam combiner 25 combines the first green laser and the second green laser with different polarization directions into one beam, and obtains a kilowatt-level, high-brightness, nearly single-mode 532nm green laser.

[0050] The first focusing lens 17 and the second focusing lens 20 are selected from any one of f50, f60, f100, f120, f150, f200 or f250; the length of the first LBO frequency doubling crystal 18 and the second LBO frequency doubling crystal 21 is 25mm, 40mm or 60mm. As a preferred embodiment, the first focusing lens 17 is selected from f100; the length of the first LBO frequency doubling crystal 18 is 40mm. The second focusing lens 20 is selected from f200, and the length of the second LBO frequency doubling crystal 21 is 40mm.

[0051] Of course, in the above content, the number of at least one frequency doubling processing component and at least one baseband processing component can be more than one, and the polarization beam combining method is not limited to the above-mentioned two green laser beams with different polarization directions, but can also be a corresponding combination of multiple frequency doubling processing components and multiple baseband processing components.

[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 protection scope of the present invention.

Claims

1. A high-power near single-mode continuous fiber green laser, characterized in that: The invention comprises a FOL seed source (100), an amplifier unit (200) and a frequency multiplication unit (300) which are arranged in sequence, wherein: A FOL seed source (100), used to generate and output linearly polarized seed light; An amplifier unit (200) is connected to the output optical path of the FOL seed source (100) and is used to amplify the power of the input seed light to obtain fundamental frequency light; The frequency doubling unit (300) is connected to the output optical path of the amplifier unit (200) and is used to perform frequency doubling processing on the fundamental frequency light to obtain the required green laser output.

2. A high-power near single-mode continuous fiber green laser according to claim 1, characterized in that: The FOL seed source (100) comprises a narrowband high-reflection grating (1), a first pump source (2), a first active optical fiber (3), a narrowband low-reflection grating (4), a polarization-maintaining isolator (5), and a polarization-maintaining optical fiber mode field adapter (6) with a cladding power stripping function; the first end of the first active optical fiber (3) is optically connected to one end of the narrowband high-reflection grating (1); the other end of the narrowband high-reflection grating (1) is cut at an angle of 8° and then fixed by glue; the second end of the first active optical fiber (3) is optically connected to one end of the narrowband low-reflection grating (4); the other end of the narrowband low-reflection grating (4) is optically connected to the input end of the polarization-maintaining isolator (5); the output end of the first pump source (2) is optically connected to the pump input end on the side of the first active optical fiber (3). A narrowband high-reflection grating (1), a first pump source (2), a first active optical fiber (3) and a narrowband low-reflection grating (4) form a grating pair resonant cavity for converting pump light input by the first pump source (2) into laser light in a random polarization state; the output end of a polarization-maintaining isolator (5) is optically connected to the input end of a polarization-maintaining optical fiber mode field adapter (6) with a cladding power stripping function, and the polarization-maintaining optical fiber mode field adapter (6) with a cladding power stripping function converts the laser light in a random polarization state into linearly polarized seed light for output; the polarization-maintaining optical fiber mode field adapter (6) with a cladding power stripping function performs mode stripping on the input linearly polarized seed light, filters out cladding light caused by numerical aperture NA mismatch and optical fiber fusion splicing, and performs mode field adaptation for subsequent access to an amplifier unit (200).

3. A high-power near single-mode continuous fiber green laser according to claim 2, characterized in that: The polarization-maintaining optical fiber mode field adapter (6) with cladding power stripping function is produced by etching a certain length at both ends of the fusion point of the mode field adapter MFA to produce a cladding light stripping device CPS, and integrating the cladding light stripping device CPS with the mode field adapter MFA into an integrated structure.

4. A high-power near single-mode continuous fiber green laser according to claim 2, characterized in that: The amplifier unit (200) comprises two second pump sources (7), a first polarization-maintaining pump combiner (8), a second polarization-maintaining active optical fiber (9), a second polarization-maintaining pump combiner (10), two third pump sources (11), a polarization-maintaining cladding light stripper (12) and a collimator (13); the input end of the first polarization-maintaining pump combiner (8) is optically connected to the output end of a polarization-maintaining optical fiber mode field adapter (6) with a cladding power stripping function, the output ends of the two second pump sources (7) are optically connected to the pump fiber input end of the first polarization-maintaining pump combiner (8), the output end of the first polarization-maintaining pump combiner (8) is optically connected to one end of a second polarization-maintaining active optical fiber (9), and the output end of the second polarization-maintaining active optical fiber (9) is optically connected to the output end of the polarization-maintaining optical fiber mode field adapter (6) with a cladding power stripping function. The other end is optically connected to one end of a second polarization-maintaining pump beam combiner (10); the output ends of the two third pump sources (11) are optically connected to the pump fiber input end of the second polarization-maintaining pump beam combiner (10); the other end of the second polarization-maintaining pump beam combiner (10) is optically connected to the input end of a polarization-maintaining cladding light stripper (12); the output end of the polarization-maintaining cladding light stripper (12) is optically connected to the input end of a collimator (13); the output end of the collimator (13) is optically connected to the input end of a frequency doubling unit (300); the amplifier unit (200) amplifies the input linearly polarized seed light and outputs the fundamental frequency light after power amplification; the collimator (13) expands and collimates the spot size of the fundamental frequency light.

5. A high-power near single-mode continuous fiber green laser according to claim 4, characterized in that: The combination of the first polarization-maintaining pump beam combiner (8) and the second polarization-maintaining pump beam combiner (10) adopts any one of forward pumping, reverse pumping or bidirectional pumping.

6. A high-power near single-mode continuous fiber green laser according to claim 4, characterized in that: The first polarization-maintaining pump beam combiner (8) and the second polarization-maintaining pump beam combiner (10) are any one of (2+1)×1, (4+1)×1, (6+1)×1, (8+1)×1, and (12+1)×1.

7. A high-power near single-mode continuous fiber green laser according to claim 4, characterized in that: The frequency doubling unit (300) comprises at least one frequency doubling processing component, a dichroic mirror (19), at least one baseband processing component and a polarization beam combiner (25); the at least one frequency doubling processing component receives the baseband light output by the collimator (13), performs a first frequency doubling conversion on the baseband light and outputs it to the dichroic mirror (19); the dichroic mirror (19) separates the first green laser light after the frequency doubling and the residual baseband light; the residual baseband light is sent to the at least one baseband processing component for a second frequency doubling conversion to obtain a second green laser light; the first green laser light and the second green laser light are combined at the polarization beam combiner (25) to obtain the required green laser light.

8. A high-power near single-mode continuous fiber green laser according to claim 7, characterized in that: The at least one frequency doubling processing component comprises a first total reflection mirror (14), a second total reflection mirror (15), a first half-wave plate (16), a first focusing lens (17) and a first LBO frequency doubling crystal (18) which are arranged in sequence; the incident end of the first total reflection mirror (14) is optically connected to the output end of the collimator (13); the output end of the first total reflection mirror (14) is optically connected to the incident end of the second total reflection mirror (15); the output end of the second total reflection mirror (15) is optically connected to the incident end of the first half-wave plate (16); the first total reflection mirror (14) and the second total reflection mirror (15) are arranged in mirror image; the output end of the first half-wave plate (16) is optically connected to the incident end of the first focusing lens (17); the first focusing lens (18) is optically connected to the incident end of the collimator (13); The output end of the first LBO frequency doubling crystal (17) is optically connected to the input end of the first LBO frequency doubling crystal (18), and the output end of the first LBO frequency doubling crystal (18) is optically connected to the input end of the dichroic mirror (19); the first half-wave plate (16) is used to change the linear polarization direction of the input power-amplified fundamental frequency light, the first focusing lens (17) focuses the fundamental frequency light on the first LBO frequency doubling crystal (18), and the rotation angle of the first half-wave plate (16), the position of the first focusing lens (17) and the temperature of the first LBO frequency doubling crystal (18) are adjusted to jointly improve the efficiency of the first frequency doubling to obtain a first green laser; the first green laser enters the polarization beam combiner (25) after being reflected at the incident side of the dichroic mirror (19).

9. A high-power near single-mode continuous fiber green laser according to claim 8, characterized in that: At least one baseband processing component comprises a second focusing lens (20), a second LBO frequency doubling crystal (21), a third total reflection mirror (22), a fourth total reflection mirror (23) and a second half-wave plate (24) which are arranged in sequence; the input end of the second focusing lens (20) is optically connected to the transmission output end of the dichroic mirror (19), the output end of the second focusing lens (20) is optically connected to the input end of the second LBO frequency doubling crystal (21), the output end of the second LBO frequency doubling crystal (21) is optically connected to the incident end of the third total reflection mirror (22), the output end of the third total reflection mirror (22) is optically connected to the incident end of the fourth total reflection mirror (23), the output end of the fourth total reflection mirror (23) is optically connected to the incident end of the third total reflection mirror (22), and the output end of the fourth total reflection mirror (23) is optically connected to the output end of the third total reflection mirror (23). The incident ends of the two half-wave plates (24) are optically connected, the third total reflection mirror (22) and the fourth total reflection mirror (23) are arranged in mirror image, and the output end of the second half-wave plate (24) is optically connected to the polarization beam combiner (25); the second focusing lens (20) focuses the residual fundamental frequency light on the second LBO frequency doubling crystal (21), the second LBO frequency doubling crystal (21) performs a second frequency doubling conversion on the residual fundamental frequency light to obtain a second green laser, and after the output optical path is adjusted by the third total reflection mirror (22) and the fourth total reflection mirror (23), the second half-wave plate (24) is used to change the linear polarization direction of the second green laser so that the first green laser and the second green laser are combined at the polarization beam combiner (25).

10. A high-power near single-mode continuous fiber green laser according to claim 9, characterized in that: The first focusing lens (17) and the second focusing lens (20) are selected from any one of f50, f60, f100, f120, f150, f200 or f250; the lengths of the first LBO frequency doubling crystal (18) and the second LBO frequency doubling crystal (21) are any one of 25 mm, 40 mm or 60 mm.

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