Frequency conversion optical fiber

Abstract

The present invention discloses a frequency conversion optical fiber, which includes a head fiber section, a frequency conversion fiber section, and a pigtail fiber section. The up-conversion power and conversion efficiency of the optical fiber laser containing the frequency conversion optical fiber continue to increase with the increase of the fundamental frequency optical power. The frequency conversion optical fiber and the laser containing the frequency conversion optical fiber of the present invention have very stable output laser modes. Under different output powers, M x 2 、M y 2 The frequency conversion optical fiber and the laser containing the frequency conversion optical fiber described in the present invention have a strong linear effect. With the increase of pump power, the average output power of the power amplifier stage increases linearly.

Description

Technical Field

[0001] The invention belongs to the technical field of optical fibers, and in particular relates to a frequency conversion optical fiber. Background Art

[0002] Laser is another major invention of mankind since the 20th century, following atomic energy, computers, and semiconductors. In 1958, AL Schawlow and CH Townes jointly discussed the concept of microwave amplifiers and pointed out the method of generating lasers. Then in 1960, TH Maiman and others invented the world's first (ruby) laser. Lasers have achieved extraordinary development speed since their advent. They have not only rejuvenated the ancient optical science and optical technology, but also led to the continuous emergence of a series of emerging industries related to laser technology. The development and application of lasers and laser technology have greatly promoted the vigorous development of human productivity and profoundly affected all aspects of people's lives. Compared with traditional solid-state lasers, fiber lasers use rare earth ion-doped optical fibers as gain media. They have many advantages such as low pumping threshold, high coupling efficiency, good beam quality, convenient thermal management, compact structure, and wide tunable range. They have always been favored by scientific researchers and have become a hot spot in the field of laser research. Fiber lasers have been widely used in optical communications, industrial processing, medical care, national defense and military, scientific research and other application fields, showing a great trend of replacing the traditional solid and gas lasers currently used.

[0003] Nonlinear frequency conversion technology is an important research direction of lasers, which makes the wavelength generated by lasers increase exponentially. Among them, frequency doubling technology plays an irreplaceable role in the development of short-wavelength lasers. In particular, high-power continuous wave (CW) green lasers have a wide range of application values ​​in material processing, titanium sapphire laser pump sources, optical parametric oscillation (OPO), holographic imaging, biomedicine, atomic cooling and capture. In the absence of a gain medium that can directly lasing in the green light band, second harmonic generation (SHG) green lasers based on 1.0μm band lasers are a very attractive approach. As early as 1998, Guskov et al. used continuous fiber laser and periodically poled lithium niobate (PPLN) crystal to obtain a green light output of 440mW; in 2009, Samanta et al. used high-power continuous single-frequency fiber laser and MgO-doped lithium tantalate (LT) crystal to obtain a 532nm single-frequency green light output of 9.64W; in 2014, Stappel et al. used a double-stage structure of MgO-doped lithium tantalate (LT) crystal and also used a 1091nm high-power continuous single-frequency fiber laser to obtain a 545.5nm single-frequency green light output of 12.8W. Among them, based on narrow-linewidth single-frequency fiber laser and periodically poled nonlinear crystal, quasi-phase matching is used to obtain continuous green laser output, which effectively combines the advantages of near-infrared fiber laser (fundamental frequency light) and single-stage second harmonic device, and not only has a compact and practical structure, but also has many advantages of the inherent narrow linewidth and good beam quality of fundamental frequency fiber laser.

[0004] Prior art, such as the Chinese invention patent with publication number CN108199253A, discloses a highly efficient frequency doubling device and method, including a housing and an optical component located in the housing, the housing is provided with an incident light inlet and an outgoing light outlet, the optical component includes a beam collimation device, a beam reduction lens group and a plurality of frequency doubling devices placed in sequence in the direction of light propagation; the frequency doubling device is temperature-controlled by a water-passing heat sink or a temperature-controlled furnace, a beam splitter is provided between two adjacent frequency doubling devices, the beam splitter divides the frequency doubling light mixed with fundamental light generated by the previous frequency doubling device into fundamental light and frequency doubling light, the fundamental light enters the next frequency doubling device, all the frequency doubling lights are combined by a polarization combining method or a fiber fusion method and then output from one outgoing light outlet, or all the frequency doubling lights are output from multiple outgoing light outlets without combining. However, the invention has the problem that thermally induced birefringence will cause depolarization in the frequency doubling of high-power solid-state lasers. Furthermore, it leads to problems such as low energy utilization and damage to the frequency doubling crystal. Summary of the invention

[0005] In order to solve the above problems existing in the prior art, the present invention provides a frequency conversion optical fiber with high conversion efficiency, long service life and good heat resistance.

[0006] The technical solution adopted by the present invention is:

[0007] A frequency conversion optical fiber includes a head fiber section, a frequency conversion section and a tail fiber section along the length direction of the optical fiber, or includes a head fiber section and a frequency conversion section along the length direction of the optical fiber. The frequency conversion section converts the transmission laser frequency into a high-frequency laser, or converts a long-wave laser into a short-wave laser.

[0008] Preferably, the frequency conversion optical fiber includes a head fiber segment, a frequency conversion segment and a pigtail fiber segment along the length direction of the optical fiber, the tail end of the head fiber segment is connected to the head end of the frequency conversion segment by thermal welding, the tail end of the frequency conversion segment is connected to the head end of the pigtail fiber segment by thermal welding, and the tail end of the pigtail fiber segment emits a frequency-converting laser.

[0009] Preferably, the frequency conversion optical fiber includes a head fiber segment and a frequency conversion segment along the length direction of the optical fiber, the tail end of the head fiber segment is connected to the head end of the frequency conversion segment by thermal fusion, and the tail end of the frequency conversion segment emits a frequency conversion laser.

[0010] Preferably, the structure of the head fiber segment includes a head fiber segment core and a head fiber segment cladding; the material of the head fiber segment core is one or more of quartz glass, borate glass, germanate glass, silicate glass, phosphate glass, fluoride glass, and oxyhalide glass; the material of the head fiber segment cladding is one or more of quartz glass, borate glass, germanate glass, silicate glass, phosphate glass, fluoride glass, and oxyhalide glass.

[0011] Preferably, the structure of the frequency conversion segment optical fiber includes a frequency conversion segment fiber core and a cladding; the fiber core of the frequency conversion segment optical fiber is a single crystal fiber with a frequency conversion effect;

[0012] The cladding of the frequency conversion section optical fiber is a glass material or a crystal material whose refractive index is slightly lower than that of the single crystal fiber.

[0013] Preferably, the single crystal fiber is one or more of barium metaborate (β-BaB2O4), lithium triborate (LiB3O5), ammonium dihydrogen phosphate (ADP), potassium dihydrogen phosphate (KDP), potassium dideuterium phosphate (DKDP), cesium dideuterium arsenate (DCDA), cesium dihydrogen arsenate (CDA), lithium niobate (LN), sodium barium niobate, potassium niobate, α-type lithium iodate, gallium arsenide, indium arsenide, zinc sulfide, cadmium telluride, tellurium, and selenium;

[0014] The cladding is one or more of single crystal material, quartz glass, borate glass, germanate glass, silicate glass, phosphate glass, fluoride glass, and oxyhalide glass;

[0015] The cross section of the core of the frequency conversion segment optical fiber is circular, elliptical, or polygonal; the cross section of the cladding of the frequency conversion segment optical fiber is a circular ring, an elliptical ring, or a polygonal ring;

[0016] The cross-sectional area of ​​the core of the frequency conversion segment optical fiber is greater than or equal to 4 square microns.

[0017] Preferably, the structure of the pigtail segment includes a pigtail segment core and a pigtail segment cladding; the material of the pigtail segment core is one or more of quartz glass, borate glass, germanate glass, silicate glass, phosphate glass, fluoride glass, and oxyhalide glass; the material of the pigtail segment cladding is one or more of quartz glass, borate glass, germanate glass, silicate glass, phosphate glass, fluoride glass, and oxyhalide glass.

[0018] Preferably, the refractive index of the core of the head fiber segment minus the refractive index of the cladding of the head fiber segment is greater than or equal to 10 -7 The refractive index of the frequency conversion section core minus the refractive index of the frequency conversion section cladding is greater than or equal to 10 -7 The refractive index of the core of the pigtail segment minus the refractive index of the pigtail segment cladding is greater than or equal to 10 -7 .

[0019] Preferably, the material of the cladding of the head fiber segment is the same as the cladding material of the frequency conversion segment, or the refractive index difference between the two is less than or equal to 10 -6 ;

[0020] The material of the pigtail section cladding is the same as the cladding material of the frequency conversion section or the refractive index difference between the two is less than or equal to 10 -6 .

[0021] The present invention also relates to a laser containing a frequency conversion optical fiber, the structure of which includes a pump light source, a focusing lens, a half-wave plate, a polarization beam splitter, the frequency conversion optical fiber, a coated dichroic mirror and a focusing lens which are connected in sequence and arranged coaxially.

[0022] The beneficial effects of the present invention are:

[0023] (1) The present invention provides a frequency conversion optical fiber, which includes a head fiber segment, a frequency conversion segment optical fiber, and a pigtail fiber segment. For an optical fiber laser containing the frequency conversion optical fiber, the SH power and conversion efficiency continue to increase with the increase of the fundamental frequency light power, without an obvious downward trend, and the conversion efficiency is extremely high.

[0024] (2) The frequency conversion fiber of the present invention has a very stable output laser mode and has a single transverse mode TEM001 output; at different output powers, M x 2 、M y2 The frequency conversion fiber and the laser containing the frequency conversion fiber of the present invention have a strong linear effect. With the increase of pump power, the average output power of the power amplifier stage increases linearly, and the light-to-light conversion efficiency is about 39.6%.

[0025] (3) The frequency conversion optical fiber described in the present invention is plug-and-play and can be well matched to laser components. It is simple and convenient, and the cost of assembly and disassembly is extremely low. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] 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.

[0027] Figure 1 This is a schematic structural diagram of a frequency conversion fiber laser of the present invention;

[0028] Figure 2 Schematic diagram of the structure of the frequency conversion fiber connected to the external laser. DETAILED DESCRIPTION

[0029] To make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described in detail below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other implementation methods obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention.

[0030] Example 1

[0031] This embodiment provides a frequency conversion fiber laser, the structure of which is as follows Figure 1 As shown, the structure includes a pump light source, a focusing lens, a half-wave plate, a polarization beam splitter, a frequency conversion optical fiber, a coated dichroic mirror and a focusing lens which are connected in sequence and arranged coaxially.

[0032] The structure of the frequency conversion optical fiber is as follows Figure 2 As shown, it includes a head fiber segment, a frequency conversion segment optical fiber, and a pigtail segment; the structure of the head fiber segment includes a head fiber segment core and a head fiber segment cladding; the material of the head fiber segment core is quartz glass; the material of the head fiber segment cladding is borate glass.

[0033] The structure of the frequency conversion segment optical fiber includes a frequency conversion segment core and a cladding; the core of the frequency conversion segment optical fiber is a single crystal fiber with a frequency conversion effect, the cross-sectional shape of the single crystal fiber is a circle, and the cross-sectional shape of the cladding is a ring; as an optional implementation, the core of the frequency conversion segment optical fiber is one of barium metaborate (β-BaB2O4), lithium triborate (LiB3O5), and ammonium dihydrogen phosphate (ADP) with a frequency conversion effect, and the refractive index of the core of the frequency conversion segment optical fiber minus the refractive index of the cladding is greater than or equal to 10 -7 The cladding of the frequency conversion section optical fiber is quartz glass with a refractive index slightly lower than that of the single crystal fiber. The cross-sectional area of ​​the core of the frequency conversion section optical fiber is greater than or equal to 4 square microns. Preferably, in this embodiment, the core of the frequency conversion section optical fiber is barium borate (β-BaB2O4), and the refractive index of the core of the frequency conversion section optical fiber minus the refractive index of the cladding is greater than 10 -7 The cross-sectional area of ​​the core of the frequency conversion segment optical fiber is greater than 4 square microns.

[0034] The structure of the pigtail segment includes a pigtail segment core and a pigtail segment cladding. As an optional embodiment, the refractive index of the pigtail segment core minus the refractive index of the cladding is greater than or equal to 10. -7 Preferably, in this embodiment, the material of the core of the pigtail segment is germanate glass, and the material of the pigtail segment cladding is 30SiO2-20CdF2-15AlO 1.5 -10YbF3-24PbF2-ErF3 oxyhalide glass, the refractive index of the core of the pigtail segment minus the refractive index of the cladding is greater than 10 -7 The material of the pigtail fiber section cladding is consistent with the cladding material of the frequency conversion section optical fiber. The tail end of the fiber core of the head fiber section and the fiber core of the frequency conversion section optical fiber are thermally fused into a whole.

[0035] The fundamental frequency light output from the pump light source is collimated by a focusing lens (Lens) with a focal length of 10 cm, then passes through a half-wave plate, and then passes through a polarization beam splitter (PBS) to become horizontally polarized light, and then coupled into the frequency conversion optical fiber involved in the present invention. Then, it is fixed in the output direction of the nonlinear crystal through two coated dichroic mirrors (DM) with high reflection (reflectivity>99%) for 1064nm wavelength and high transmission (transmittance>99%) for 532nm wavelength, which are used to effectively separate the fundamental frequency light and SH green light emitted from the nonlinear crystal. Subsequently, the output SH green light is focused by a lens with a focal length of 10 cm and enters a power meter (PM) or other detector to measure its output performance. When the temperature is controlled at about 212.8℃, the relationship curve between SH power and conversion efficiency and fundamental frequency light power is measured. When the fundamental frequency light power is 22.1W, the maximum output power of 532nm green light is 2.9W, and the SH conversion efficiency is about 13.2%.

[0036] Example 2

[0037] This embodiment provides a frequency conversion fiber laser, the structure of which includes a pump light source, a focusing lens, a half-wave plate, a gain medium, a frequency conversion fiber, a coated dichroic mirror and a focusing lens, which are connected in sequence and arranged coaxially.

[0038] The frequency conversion optical fiber includes a head fiber segment, a frequency conversion segment optical fiber, and a pigtail segment; the structure of the head fiber segment includes a head fiber segment core and a head fiber segment cladding; the material of the head fiber segment core is quartz glass; the material of the head fiber segment cladding is borate glass.

[0039] The cross-sectional shape of the single crystal fiber in the frequency conversion segment optical fiber is elliptical, and the cross-sectional shape of the cladding is an elliptical ring; the structure of the frequency conversion segment optical fiber includes a frequency conversion segment core and a cladding; as an optional implementation, the core of the frequency conversion segment optical fiber is one of potassium dihydrogen phosphate (KDP), dideuterium potassium phosphate (DKDP), cesium dideuterium arsenate (DCDA), cesium dihydrogen arsenate (CDA), and lithium niobate (LN) having a frequency conversion effect, and the refractive index of the core of the frequency conversion segment optical fiber minus the refractive index of the cladding is greater than or equal to 10 -7 Preferably, in this embodiment, the core of the frequency conversion section optical fiber is cesium deuterium arsenate (DCDA), and the refractive index of the core of the frequency conversion section optical fiber minus the refractive index of the cladding is greater than 10 -7 ; The cladding of the frequency conversion section optical fiber is quartz glass with a refractive index slightly lower than that of the single crystal fiber.

[0040] The structure of the pigtail segment includes a pigtail segment core and a pigtail segment cladding, wherein the material of the pigtail segment core is germanate glass. As an optional embodiment, the material of the pigtail segment cladding is phosphate glass, fluoride glass, or oxyhalide glass, wherein the refractive index of the pigtail core minus the refractive index of the cladding is greater than or equal to 10. -7 Preferably, in this embodiment, the material of the pigtail cladding is 30SiO2-20CdF2-15AlO 1.5 -10YbF3-24PbF2-ErF3 oxyhalide glass, wherein the refractive index of the pigtail core minus the refractive index of the cladding is greater than 10 -7 .

[0041] The material of the pigtail fiber section cladding is consistent with the cladding material of the frequency conversion section optical fiber. The tail end of the fiber core of the head fiber section and the fiber core of the frequency conversion section optical fiber are bonded into a whole by thermal fusion bonding.

[0042] The frequency conversion fiber involved in the patent of this invention was fused to a directly purchased fiber laser for testing. When the temperature was controlled at about 212.8°C, the relationship curve between SH power and conversion efficiency and fundamental frequency optical power was measured. When the fundamental frequency optical power was 25.5W, the maximum output power of 532nm green light was 3.2W, and the SH conversion efficiency was about 15.2%.

[0043] Example 3

[0044] This embodiment provides a frequency conversion optical fiber, which is externally connected to a commercially available optical fiber laser. Figure 2 The frequency conversion optical fiber includes a head fiber segment, a frequency conversion segment optical fiber, and a pigtail segment; the structure of the head fiber segment includes a head fiber segment core and a head fiber segment cladding; the material of the head fiber segment core is quartz glass; the material of the head fiber segment cladding is borate glass.

[0045] The cross-sectional shape of the single crystal fiber in the frequency conversion segment optical fiber is a hexagon, and the cross-sectional shape of the cladding is a hexagonal ring; the structure of the frequency conversion segment optical fiber includes a frequency conversion segment core and a cladding; as an optional implementation, the core of the frequency conversion segment optical fiber is one of cesium dihydrogen arsenate (CDA), lithium niobate (LN), sodium barium niobate, potassium niobate, α-type lithium iodate, gallium arsenide, indium arsenide, zinc sulfide, cadmium telluride, tellurium, and selenium with a frequency conversion effect, and the refractive index of the core of the frequency conversion segment optical fiber minus the refractive index of the cladding is greater than or equal to 10 -7 Preferably, in this embodiment, the core of the frequency conversion section optical fiber is sodium barium niobate, and the refractive index of the core of the frequency conversion section optical fiber minus the refractive index of the cladding is greater than 10 -7 The cladding of the frequency conversion section optical fiber is quartz glass with a refractive index slightly lower than that of the single crystal fiber.

[0046] The structure of the pigtail segment includes the pigtail segment core and the pigtail segment cladding. The pigtail core is made of germanate glass. The pigtail cladding is made of 30SiO2-20CdF2-15AlO 1.5 -10YbF3-24PbF2-ErF3 oxyhalide glass, wherein the refractive index of the pigtail fiber core minus the refractive index of the cladding is greater than 10 -7 The refractive index difference between the cladding material of the pigtail section and the cladding material of the frequency conversion section optical fiber is less than 10 -6 The tail end of the core of the head fiber section and the core of the frequency conversion section optical fiber are bonded together by heat fusion bonding.

[0047] The frequency conversion fiber involved in the patent of this invention was fused to a directly purchased fiber laser for testing. When the temperature was controlled at about 212.8°C, the relationship curve between SH power and conversion efficiency and fundamental frequency optical power was measured. When the fundamental frequency optical power was 22.1W, the maximum output power of 532nm green light was 3.2W, and the SH conversion efficiency was about 16.3%.

[0048] The present invention is not limited to the above-mentioned optimal implementation mode. Anyone can derive other various forms of products under the inspiration of the present invention. However, no matter what changes are made in the shape or structure, all technical solutions that are the same or similar to those of the present application fall within the protection scope of the present invention.

Claims

1. A frequency conversion optical fiber, characterized in that: The optical fiber includes a head fiber section, a frequency conversion section and a pigtail fiber section along the length direction. The tail end of the head fiber section is connected to the head end of the frequency conversion section by thermal fusion, the tail end of the frequency conversion section is connected to the head end of the pigtail fiber section by thermal fusion, and the tail end of the pigtail fiber section emits frequency conversion laser. The structure of the head fiber segment includes the head fiber segment core and the head fiber segment cladding; the material of the head fiber segment core is quartz glass; the material of the head fiber segment cladding is borate glass; the structure of the frequency conversion segment optical fiber includes the frequency conversion segment core and the cladding; the core of the frequency conversion segment optical fiber is barium borate (β-BaB2O4), the cladding of the frequency conversion segment optical fiber is quartz glass with a refractive index slightly lower than that of the single crystal fiber, and the refractive index of the core of the frequency conversion segment optical fiber minus the refractive index of the cladding is greater than 10 -7 The cross-sectional area of ​​the core of the frequency conversion segment optical fiber is greater than 4 square microns; the cross-sectional area of ​​the core of the frequency conversion segment optical fiber is circular; the cross-sectional area of ​​the cladding of the frequency conversion segment optical fiber is annular; the structure of the pigtail segment includes a pigtail segment core and a pigtail segment cladding, the material of the pigtail segment core is germanate glass, and the material of the pigtail segment cladding is 30SiO2-20CdF2-15AlO 1.5 -10YbF3-24PbF2-ErF3 oxyhalide glass, the refractive index of the core of the pigtail segment minus the refractive index of the cladding is greater than 10 -7 ; The material of the pigtail section cladding is consistent with the cladding material of the frequency conversion section optical fiber; Alternatively, the structure of the head fiber segment includes a head fiber segment core and a head fiber segment cladding; the material of the head fiber segment core is quartz glass; the material of the head fiber segment cladding is borate glass; the structure of the frequency conversion segment optical fiber includes a frequency conversion segment core and a cladding; the core of the frequency conversion segment optical fiber is cesium deuterium arsenate (DCDA), and the refractive index of the frequency conversion segment optical fiber core minus the refractive index of the cladding is greater than 10 -7 The cladding of the frequency conversion segment optical fiber is quartz glass with a refractive index slightly lower than that of the single crystal fiber; the cross-section of the core of the frequency conversion segment optical fiber is circular; the cross-section of the cladding of the frequency conversion segment optical fiber is a ring; the structure of the pigtail segment includes a pigtail segment core and a pigtail segment cladding, the material of the pigtail segment core is germanate glass, and the material of the pigtail segment cladding is 30SiO2-20CdF2-15AlO 1.5 -10YbF3-24PbF2-ErF3 oxyhalide glass, wherein the refractive index of the pigtail core minus the refractive index of the cladding is greater than 10 -7 ; The material of the pigtail section cladding is consistent with the cladding material of the frequency conversion section optical fiber; Alternatively, the structure of the head fiber segment includes a head fiber segment core and a head fiber segment cladding; the material of the head fiber segment core is quartz glass; the material of the head fiber segment cladding is borate glass; the structure of the frequency conversion segment optical fiber includes a frequency conversion segment core and a cladding; the core of the frequency conversion segment optical fiber is sodium barium niobate, and the refractive index of the frequency conversion segment optical fiber core minus the refractive index of the cladding is greater than 10 -7 The cladding of the frequency conversion section optical fiber is quartz glass with a refractive index slightly lower than that of the single crystal fiber; the cross section of the core of the frequency conversion section optical fiber is circular; the cross section of the cladding of the frequency conversion section optical fiber is a ring; the structure of the pigtail section includes a pigtail section core and a pigtail section cladding, the material of the pigtail core is germanate glass; the material of the pigtail cladding is 30SiO2-20CdF2-15AlO 1.5 -10YbF3-24PbF2-ErF3 oxyhalide glass, wherein the refractive index of the pigtail fiber core minus the refractive index of the cladding is greater than 10 -7 , where the refractive index of the pigtail core minus the refractive index of the cladding is greater than 10 -7 ; The material of the cladding of the pigtail section is consistent with the cladding material of the optical fiber in the frequency conversion section.

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