Optical pumping fiber laser

Abstract

The invention relates to the technical field of lasers, in particular to an optical pumping fiber laser which comprises a greenhouse cavity with a transmission pumping light incident wall. The substrate is arranged in the greenhouse cavity and is parallel to the incident wall; the photon conversion layer is located on the surface, facing the incident wall, of the substrate, the photon conversion layer comprises a base layer and a plurality of light condensation units, the light condensation units are arranged on the surface of the substrate, and the base layer seals the light condensation units; the optical fiber comprises a main body part and two end parts, the main body part is spirally wound on the surface, away from the incident wall, of the substrate in a single-layer form, and the end parts are provided with resonant cavity mirrors; wherein the light gathering units are arranged above the main body part along the extension direction of the main body part, the pump light is transmitted into the greenhouse cavity from the incident wall, the base layer converts the pump light into fluorescent photons, the fluorescent photons are reflected in the greenhouse cavity, and the fluorescent photons are gathered to the side surface of the optical fiber through the light gathering units so as to pump optical fiber light. The invention is at least beneficial to improving the absorption efficiency of the optical pumping fiber laser on the pumping light.

Description

Technical Field

[0001] The invention belongs to the technical field of lasers, and in particular relates to an optically pumped optical fiber laser. Background Art

[0002] The depletion of traditional fossil energy and the worsening of global environmental problems have created new opportunities and challenges for the development and utilization of sustainable and renewable energy. As an inexhaustible renewable energy, solar energy has been widely used through light conversion technology and has formed a diversified industry. Solar Pumped Lasers (SPL) is an important research direction of light conversion technology, which can directly convert broadband solar radiation into collimated, coherent, monochromatic laser beams.

[0003] Compared with the indirect pumping method of photovoltaic power generation to power semiconductor laser LD (Laser Diode), solar-pumped lasers simplify the energy conversion process and have great potential to improve the utilization rate of solar energy. Therefore, solar-pumped lasers have more application prospects in free-space optical communications, space laser energy transmission, renewable energy circulation, space debris removal, material processing and other fields.

[0004] Since solid lasers have high thermal conductivity and good mechanical properties, and solid lasers can achieve relatively miniaturized resonant cavity structures, solar pumped solid lasers (SPSL) are currently the mainstream research direction of solar pumped lasers. Fiber lasers are a special form of solid lasers. Since optical fibers have a higher specific surface area, they can provide a better thermal management mode, effectively avoiding the difficult-to-eliminate thermal effect problems caused by non-uniform pump light distribution and small heat dissipation area of ​​solid laser rods. The bending flexibility of optical fibers makes them compact and adaptable to a variety of application scenarios in small workspaces, for example, they are easy to integrate into communication equipment and network infrastructure.

[0005] The gain of the fiber laser can be provided by rare earth ions doped in the fiber core, and a resonant cavity can be formed by setting volume mirrors at both ends of the fiber or recording a Bragg grating in the fiber core. The semiconductor laser LD can output a collimated beam with good directionality, which can be directly coupled into the fiber with the help of a simple lens group. Figure 1 (a) shows the principle diagram of semiconductor laser LD pumping the fiber from the fiber end. Figure 1 (b) shows the schematic diagram of the principle of semiconductor laser LD pumping the fiber from the fiber side.

[0006] Solar radiation beams are approximately parallel light with low power density, and have radiation characteristics covering the entire spectrum from ultraviolet band to infrared band. The technical difficulty of solar pumped fiber lasers (SPFL, Solar Pumped Fiber Lasers) is how to increase the spectral matching degree between the pumping solar light coupled into the optical fiber and the solar radiation absorbed by the optical fiber. Since the size of micron-level optical fiber is much lower than that of laser rod, the technical difficulty of solar pumped fiber lasers is significantly increased.

[0007] like Figure 2 As shown in the figure, referring to the end-pumping structure of the sunlight-pumped solid-state laser SPSL, the sunlight is concentrated by the off-axis parabolic mirror OAPM, and the 7.5m long double-clad Nd-doped fluoride fiber is end-pumped. An output laser with a wavelength of 1053nm and a single-side maximum energy of 0.57mW can be obtained, but its slope efficiency is 3.3% and the total conversion efficiency is 0.88%.

[0008] For the end-pumping mode, the convergent light spot is much larger than the size of the micron-scale optical fiber end face, resulting in a low conversion efficiency of the end-pumping. In addition, end-pumping usually requires a sunlight collection system with a high concentration ratio, and needs to be used in combination with a solar tracking device with a high-precision posture adjustment function. It is necessary to ensure that the convergent light spot is irradiated on the active medium of the optical fiber end face in real time, which has more complex posture adjustment requirements.

[0009] Therefore, there is an urgent need to provide a sunlight-pumped fiber laser with high conversion efficiency and simple structure. Summary of the invention

[0010] In view of this, the present invention aims to provide a light-pumped fiber laser, which is at least beneficial to improving the absorption efficiency of the light-pumped fiber laser to the pump light.

[0011] To achieve the above object, the technical solution created by the present invention is implemented as follows: The invention provides an optically pumped fiber laser, comprising: a greenhouse cavity, the greenhouse cavity having an incident wall for transmitting pump light; a substrate arranged in the greenhouse cavity, and the substrate is parallel to the incident wall; a photon conversion layer, the photon conversion layer is located on the surface of the substrate facing the incident wall, and the photon conversion layer comprises a base layer and a plurality of light-gathering units, the plurality of light-gathering units are arranged on the surface of the substrate, and the base layer seals the plurality of light-gathering units; an optical fiber, the optical fiber comprises a main body located in the greenhouse cavity and two ends extending out of the greenhouse cavity, the main body is spirally wound in a single-layer form on the surface of the substrate away from the incident wall, and the two ends are provided with resonant cavity mirrors; wherein the light-gathering units are arranged above the main body along the extension direction of the main body, the pump light is transmitted from the incident wall into the greenhouse cavity, the base layer converts the pump light into fluorescent photons, the fluorescent photons are reflected in the greenhouse cavity, and the fluorescent photons are gathered to the side of the optical fiber through the light-gathering unit, so as to optically pump the optical fiber.

[0012] Furthermore, the pump light is sunlight, and the incident wall transmits sunlight in the wavelength band of 380nm to 550nm into the greenhouse cavity.

[0013] Furthermore, there is a gap between the photon conversion layer and the incident wall.

[0014] Furthermore, the top reflective portion, the bottom reflective portion and the side wall portion enclose a greenhouse cavity, the top reflective portion and the bottom reflective portion are arranged relatively parallel, the top reflective portion and the bottom reflective portion are connected through the side wall portion, and the top reflective portion serves as an incident wall.

[0015] Furthermore, the top reflective portion and the bottom reflective portion are circular, the side wall portion is annular, and the greenhouse cavity is cylindrical.

[0016] Furthermore, the top reflective portion includes a dichroic mirror; the bottom reflective portion includes a high reflective mirror; and the side wall portion includes a polytetrafluoroethylene ring.

[0017] Furthermore, the surface reflectivity of the high reflector and the side wall facing the greenhouse cavity is greater than 99%.

[0018] Further, the base layer includes a sensitizer.

[0019] Furthermore, the focusing unit includes a micro-ball lens.

[0020] Furthermore, the substrate includes a quartz plate.

[0021] Compared with the prior art, the invention can achieve the following beneficial effects: the optically pumped fiber laser provided by the embodiment of the invention can reach the threshold of laser pumping without the need for a solar concentrating system, thus simplifying the solar tracking device and the solar concentrating system. Not only is the structure simple, but also factors such as angular tracking errors that may be introduced by the solar tracking device and the solar concentrating system are avoided. Compared with the solar concentrating system that can only utilize direct sunlight parallel to the optical axis, the system provided by the embodiment of the invention can simultaneously receive direct light and diffuse light, thereby increasing the utilization rate of solar radiation. In addition, the concentrating unit converges fluorescent photons, directs more energetic fluorescent photons to the side of the optical fiber, thereby improving the absorption efficiency of the optical fiber for fluorescent photons. The utilization rate of the pump light transmitted into the greenhouse cavity is improved by using the fluorescent photon conversion function of the base layer in the greenhouse cavity, the reflection constraint restriction of the greenhouse cavity on the fluorescent photons, and the winding arrangement of the optical fiber in the greenhouse cavity. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The drawings constituting part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments and descriptions of the present invention are used to explain the present invention and do not constitute an improper limitation on the present invention. In the drawings: Figure 1It is a schematic diagram of the structure of the end-pumped fiber and the side-pumped fiber of the semiconductor laser LD; Figure 2 This is a schematic diagram of the structure of a sunlight end-pumped fiber laser; Figure 3 The schematic diagram of the structure of the LSC structured sunlight transversely pumped fiber laser; Figure 4 Schematic diagram of the photon transmission process in the cylindrical greenhouse cavity; Figure 5 A schematic diagram of the structure of an optically pumped fiber laser according to an embodiment of the present invention; Figure 6 A schematic diagram of a transmission process of photons in an optically pumped fiber laser according to an embodiment of the present invention; Figure 7 It is a schematic structural diagram of another optically pumped fiber laser according to an embodiment of the present invention; Figure 8 is an absorption / emission intensity curve inside the optically pumped fiber laser according to an embodiment of the present invention; Fig. 9 A schematic diagram of the positional relationship between a focusing unit and an optical fiber in an optically pumped optical fiber laser according to an embodiment of the present invention; Fig.10 It is a schematic diagram of the amplified structure of a focusing unit and a part of optical fiber in the optically pumped optical fiber laser according to an embodiment of the present invention; Fig.11 Nd 3+ Schematic diagram of the energy levels of laser transitions; Fig.12 Schematic diagram of the spectrum of sunlight.

[0023] Explanation of the reference numerals: 10, top reflection part; 11, bottom reflection part; 12, side wall part; 13, base layer; 14, substrate; 15, focusing unit; 16, main body; 20, fluorescent photon; 161, fiber core; 162, inner cladding. DETAILED DESCRIPTION

[0024] After analysis, it was found that compared with the end-face pumping mode, the transverse pumping mode of the solar-pumped fiber laser SPFL has a better conversion efficiency for solar light. Transverse pumping means pumping the side of the optical fiber.

[0025] For solar transversely pumped fiber lasers, the relevant technology proposes the LSC (Luminescent Solar Concentrator, referring to fluorescent / luminescent solar collector) structure. The solar-pumped fiber laser SPFL with LSC structure can receive the sun's diffuse light, reducing the interference of solar tracking accuracy, cloudy and overcast weather and other factors.

[0026] refer to Figure 3 The LSC structure adopts the cascade energy transfer principle of the fluorescence effect of the sensitizer. The sunlight transversely pumped fiber laser based on the LSC structure consists of an active fiber, a sensitizer, and a greenhouse cavity. Before the active fiber is placed in the greenhouse cavity, the resin coating of the fiber needs to be removed by a wet etching method to avoid absorption loss of the pump light by the resin coating. Except for the two ends of the fiber used to form the optical resonant cavity, the active fiber is coiled on the annular side wall of the greenhouse cavity. The sensitizer seals the coiled active fiber. The sensitizer absorbs the visible light part of the sunlight and converts it into fluorescent photons close to the absorption band of rare earth ions. Rare earth ions are the ions doped with the optical fiber. The greenhouse cavity consists of a pair of reflectors and annular side walls. The pair of reflectors includes a bottom reflector and a top reflector. The purpose of the greenhouse cavity is to prevent potentially absorbable fluorescent photons from escaping the greenhouse cavity. The bottom reflector and the annular side wall have extremely high reflectivity for the solar radiation transmitted into the greenhouse cavity and the fluorescent photons converted by the sensitizer. The top reflector can be designed as a short-wave dichroic mirror (DM) with a cut-off wavelength. Usually, the cut-off wavelength is smaller than the wavelength of the fluorescent photons. The top reflector is used to transmit the sunlight beam in the visible light band and reflect the fluorescent photons emitted by the sensitizer.

[0027] The working principle of the greenhouse cavity is similar to that of the pump cavity in a solid-state laser, which is used to combine the confinement mechanism of the photon trap and the cascade energy transfer of the sensitizer to increase the fluorescence photon density in the greenhouse cavity.

[0028] Solar light transversely pumped fiber lasers all use a technical method combined with the fluorescence effect of sensitizers. For planar liquid LSC structures, Figure 4 The plane cylinder shown is used as the basic configuration. Based on the Monte Carlo photon tracing method, the transmission process from the incident sunlight on the laser to the generated fluorescent photons being absorbed by the optical fiber is analyzed (a) to (f). The probability p of the sunlight transmitted into the chamber being absorbed by the sensitizer is calculated respectively. ab (i.e., the probability of process (a)), fluorescence conversion efficiency η FL (i.e., the probability of process (b)) and the probability p of a fluorescent photon emitted randomly in three-dimensional space reaching the side wall PR (i.e., the probability of process (c)). Near the annular inner wall of the chamber, only a portion of the fluorescent photons will be absorbed by the active optical fiber (i.e., process (d)). The probability of process (d) is defined as p AF , the remaining fluorescent photons will be reflected or absorbed by the side wall, which is process (e), and will be repeatedly reflected multiple times in the cavity, which is process (c). If the reabsorption of fluorescent photons by the sensitizer is considered, which is process (f), the probability p of a photon being reabsorbed once must also be calculated. RAi .

[0029] It can be seen that in the planarized liquid LSC structure, the fiber core volume only occupies a small part of the internal space of the greenhouse cavity, and the fiber is located on the side wall of the greenhouse cavity, and the transmission path of the fluorescent photons is not optimized. Through calculation, the data shows that less than 0.05% of the solar radiation photons are absorbed by the doped ions Nd in the optical fiber. Although the planarized LSC structure simplifies the solar concentration system and real-time tracking device, and can achieve laser output at a minimum of 24% of the natural light intensity, it requires at least hundreds of meters of active optical fiber to compensate for the problem of weak pump light intensity, and therefore has a high material cost.

[0030] The "under 24% of natural light intensity" involved in the embodiments of the present invention refers to: under the irradiation of 24% of the standard solar irradiance value AM1.5G.

[0031] In summary, in order to improve the lateral pumping technology and improve the absorption efficiency of optical fiber to fluorescent photons, the embodiment of the present invention provides an optically pumped fiber laser with a simple structure and high light conversion efficiency. On the basis of the solid-state LSC structure, a focusing array composed of multiple focusing units is introduced, and the optical fiber is wound and arranged in a spiral manner in the same plane. The focusing units are arranged along the spiral on the upper surface of the substrate, and the focusing units are sealed in the base layer. The base layer is used to generate fluorescent photons based on pump light. The converging lens directionally converges the fluorescent photons to the side surface of the optical fiber, thereby improving the absorption efficiency of the optical fiber to the fluorescent photons. When the absorption utilization rate of the pump light is high, it is possible to avoid setting a longer optical fiber, which is beneficial to reducing material costs.

[0032] In order to make the purpose, technical solution and advantages of the invention more clear, the invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described here are only used to explain the invention and do not constitute a limitation of the invention.

[0033] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0034] In the description of the invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the invention, unless otherwise specified, the meaning of "multiple" is two or more.

[0035] In the description of the invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installation", "connection" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the invention can be understood according to specific circumstances.

[0036] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments.

[0037] refer to Figures 5 to 7 , Fig. 9 and Fig.10 The invention provides an optically pumped fiber laser, comprising: a greenhouse cavity, the greenhouse cavity having an incident wall for transmitting pump light; a substrate 14 arranged in the greenhouse cavity, and the substrate 14 is parallel to the incident wall; a photon conversion layer, the photon conversion layer is located on the surface of the substrate 14 facing the incident wall, and the photon conversion layer includes a base layer 13 and a plurality of light-gathering units 15, the plurality of light-gathering units 15 are arranged on the surface of the substrate 14, and the base layer 13 seals the plurality of light-gathering units 15; an optical fiber, the optical fiber includes a main body 16 located in the greenhouse cavity and two ends extending out of the greenhouse cavity, the main body 16 is spirally wound in a single-layer form on the surface of the substrate 14 away from the incident wall, and both ends have a resonant cavity mirror; wherein the light-gathering unit 15 is arranged above the main body 16 along the extension direction of the main body 16, the pump light is transmitted into the greenhouse cavity from the incident wall, the base layer 13 converts the pump light into fluorescent photons, the fluorescent photons are reflected in the greenhouse cavity, and the fluorescent photons 20 are converged to the side of the optical fiber through the light-gathering unit 15, so as to optically pump the optical fiber.

[0038] Before the optical fiber is placed in the greenhouse cavity, a wet etching method is used to remove the resin coating of the optical fiber to avoid absorption loss of the pump light by the resin coating. The base layer 13 can be used to absorb a portion of the pump light with a higher intensity and convert it into fluorescent photons 20 close to the absorption band of the doped ions in the optical fiber. The greenhouse cavity is used to prevent potentially absorbable fluorescent photons 20 from escaping the greenhouse cavity.

[0039] The inner wall of the greenhouse cavity has extremely high reflectivity for the pump light transmitted into the greenhouse cavity and the fluorescent photons 20 converted by the base layer 13. The incident wall is used to transmit the pump light and reflect the fluorescent photons 20 emitted by the sensitizer. The greenhouse cavity has a limiting effect or a reflective constraint effect on the generated fluorescent photons.

[0040] Furthermore, the pump light is sunlight, and the incident wall transmits sunlight in the 380nm~550nm band into the greenhouse cavity. The reason for this setting is that, Fig.12 , where yellow, orange and red represent the visible light band, short-wave infrared band and long-wave infrared band respectively. The solar spectrum has a higher radiation intensity in the visible light band. Therefore, the energy of sunlight is mainly concentrated in the visible light band. Therefore, choosing to transmit sunlight in the 380nm~550nm band is beneficial to absorbing and utilizing the higher intensity beams in the sunlight. In addition, limiting the ultraviolet light below 380nm and the long-wave visible light and infrared light above 550nm from entering the greenhouse cavity prevents the bands that cannot be absorbed by the base layer 13 from entering the greenhouse cavity, which is beneficial to avoiding the accumulation of waste heat in the greenhouse cavity, and thus avoiding negative effects such as thermal effects.

[0041] The incident wall has a reflective effect on the fluorescent photons with a reflection center wavelength near 580nm, which can prevent the fluorescent photons from overflowing the greenhouse cavity.

[0042] In some embodiments of the present invention, the wavelength of the fluorescent photons is in the range of 570 nm to 650 nm. In some examples, the peak wavelength of the fluorescent photons is at 590 nm.

[0043] Furthermore, there is a gap between the photon conversion layer and the incident wall to meet the constraint conditions of total reflection transmission. Specifically, if a liquid sensitizer is used as the photon conversion layer, the liquid sensitizer forms a close optical contact with the inner surface of the incident wall, that is, there is no air or other impurities between the medium interfaces. Since the refractive index of the liquid sensitizer solution and the incident wall is similar, it is difficult for the fluorescent photons to achieve total reflection at the interface in the greenhouse cavity, and the lossy reflection of the fluorescent photons on the inner surface of the incident wall will produce a high transmission loss. In the embodiment of the present invention, the photon conversion layer is a solid sensitizer layer, so that an air gap can be formed between the photon conversion layer and the incident wall. Due to the significant difference in refractive index between the photon conversion layer and the air, the total reflection transmission of the fluorescent photons in the greenhouse cavity can be achieved within the total reflection critical angle range. In summary, compared with the liquid sensitizer, the solid photon conversion layer can achieve the limitation of the total reflection cone angle within a certain range of incident angles, thereby improving the constraint ability of fluorescent photons.

[0044] For further reference, Figure 5 and Figure 7 The top reflecting part 10, the bottom reflecting part 11 and the side wall part 12 form a greenhouse cavity. The top reflecting part 10 and the bottom reflecting part 11 are arranged relatively parallel. The top reflecting part 10 and the bottom reflecting part 11 are connected by the side wall part 12, and the top reflecting part 10 serves as the incident wall.

[0045] Furthermore, the top reflective portion 10 and the bottom reflective portion 11 are circular, the side wall portion 12 is annular, and the greenhouse cavity is cylindrical.

[0046] Furthermore, the top reflection portion 10 includes a dichroic mirror. In some examples, the dichroic mirror can be a short-wave pass dichroic mirror. It should be noted that the cut-off wavelength of the dichroic mirror is required to be slightly lower than the wavelength of the fluorescent photons 20. The reason for this setting is that the dichroic mirror can transmit the light beam in the visible light range of the sunlight, that is, transmit the light beam less than the cut-off wavelength, and reflect the fluorescent photons 20.

[0047] Furthermore, the bottom reflective portion 11 includes a high reflective mirror, and the side wall portion 12 includes a polytetrafluoroethylene ring, the rough surface of which has the ability to diffusely restrict the fluorescent photons 20. The bottom reflective portion 11 and the side wall portion 12 have extremely high reflectivity for the fluorescent photons 20 and the light beam transmitted into the greenhouse cavity.

[0048] Furthermore, the surface reflectivity of the high reflector and the side wall portion 12 facing the greenhouse cavity is greater than 99%, which is conducive to further improving the conversion efficiency.

[0049] Furthermore, the base layer 13 includes a sensitizer.

[0050] In some embodiments of the present invention, the base layer 13 may be a solid sensitizer film layer. In some examples, the solid sensitizer film layer may include a sensitizer and a polymer. The sensitizer may be composed of a combination of Y083 (Lumogen Yellow 083) dye and O240 (Lumaogen Orange 240) dye. The polymer may be a fluorinated polyurethane. The function of the polymer is equivalent to a refractive index matching liquid, which is used to prevent reflection or scattering losses at the interface. The O240 dye and the Y083 dye are dissolved in chloroform and mixed with the fluorinated polyurethane main body to obtain a solid sensitizer film layer. The emission peak of the O240 dye is at 590 nm. For doping ions such as Nd 3+ The emission peak of O240 dye is similar to that of Nd 3+ exist( 2 G 7 / 2 + 4 G 5 / 2 ) are close to each other, that is, O240 dye can be used to convert pump light into a level close to Nd 3+ The purpose of adding Y083 dye is to enhance the absorption of blue light by the sensitizer and expand the absorption range of pump light.

[0051] Furthermore, the focusing unit 15 includes a micro-ball lens. A plurality of micro-ball lenses constitute a micro-ball lens array, which is sealed in a solid sensitizer film layer, and the micro-ball lenses in the micro-ball lens array are arranged along the spiral line of the optical fiber winding, for directionally focusing the fluorescent photons 20 on the side surface of the optical fiber.

[0052] Furthermore, the substrate 14 includes a quartz plate. The quartz plate has good temperature resistance and light transmission properties, and can prevent parasitic absorption from affecting the density of the fluorescent photons 20 in the greenhouse cavity.

[0053] In some embodiments of the present invention, reference Figure 5 , the quartz plate is a circular quartz substrate 14; in other embodiments of the present invention, reference Figure 7 , the quartz substrate 14 can also be circular. It should be noted that, Figure 5 The greenhouse cavity is surrounded by a top reflective portion 10, a bottom reflective portion 11 and two opposite annular side walls 12. Figure 5 The conversion efficiency of the structure shown is higher because the ratio of the volume of the optical fiber to the volume of the greenhouse cavity is larger, which avoids the reflection of fluorescent photons in the part of the greenhouse cavity where the optical fiber is not set, causing loss.

[0054] In some embodiments of the present invention, the two ends of the optical fiber are respectively a high reflection end and an output end, and the resonant cavity mirror at the high reflection end is set as a beam splitter, which not only realizes the high reflection effect on the laser wavelength beam, but also reflects the fluorescent band to improve the absorption efficiency of the optical fiber to the fluorescent photons. The resonant cavity mirror at the output end is an output coupling mirror or a fiber Bragg grating (FBG), and the resonant cavity mirrors at both ends of the optical fiber jointly realize the oscillation amplification of the laser wavelength.

[0055] In some embodiments of the present invention, the length of both ends of the optical fiber extending out of the greenhouse cavity is in the range of 1m to 2m, which is used to set the resonant cavity mirror.

[0056] In some embodiments of the present invention, the lasing wavelength is in the range of 1000nm to 1100nm.

[0057] In some embodiments of the present invention, reference Fig.10 The main body 16 includes a core 161 and an inner cladding 162 .

[0058] In some embodiments of the present invention, the optical fiber is an active optical fiber, specifically, a neodymium-doped SiO 2 The active optical fiber, the optical fiber and the focusing unit 15 are respectively attached to the surfaces of the two opposite sides of the substrate 14. The optical fiber adhesive for attaching the optical fiber is a UV curing adhesive, such as NOA85 (Norland Optical Adhesive), which has a refractive index matching that of the quartz plate material, and can avoid reflection or scattering losses at the interface between the optical fiber adhesive and the optical fiber.

[0059] It should be noted that the optical fiber needs to be wet-etched to remove the resin coating on the outside of the optical fiber. For example, 70°C H 2 SO 4 , H 2 O 2 and H 2 O mixed etching solution to remove the resin coating layer.

[0060] In addition, it is known that the short-wave bidirectional color characteristics of the dichroic mirror serving as the top reflector 10 determine the wavelength band of the incident solar light. In some embodiments of the present invention, the incident solar light in the wavelength band of 380nm to 550nm is allowed, and the incident ultraviolet light below 380nm and long-wave visible light or infrared light above 550nm is restricted. This helps to avoid the accumulation of waste heat in the greenhouse cavity. Figure 8The transmittance curve and normalized absorption / edge emission intensity (with the highest intensity as the normalized benchmark) of the optically pumped fiber laser are shown. The blue curve represents the transmittance of the optically pumped fiber laser. Specifically, when the light is incident vertically, part of the light will directly pass through the optically pumped fiber laser without being absorbed, thus forming transmitted light. The blue curve shows how the proportion of transmitted light changes at different wavelengths, showing the part of the incident light that is not absorbed by the optically pumped fiber laser and is transmitted. The red curve represents the absorptivity of pump light of different wavelengths absorbed by the base layer. The red and blue lines are symmetric about 0.5 normalized units arb.unit, which is attributed to the absorption characteristics of the sensitizer in the base layer 13. The yellow curve represents the fluorescence emission intensity at the edge of the inner wall of the greenhouse cavity, indicating the wavelength and intensity of the fluorescence photons emitted from the edge of the inner wall of the greenhouse cavity during multiple reflections and reabsorption. The black dotted line refers to the partial absorption spectrum of the neodymium-doped fiber, indicating the absorption intensity for different wavelengths under the normalized unit arb.unit, specifically showing the absorption of the fiber at different wavelengths. According to Figure 8 and Fig.11 It can be seen that the yellow curve is located at the fluorescence photon emission peak near the wavelength of 590nm and the Nd 3+ exist 2 G 7 / 2 + 4 G 5 / 2 The absorption peaks of the energy levels overlap highly, so Nd 3+ Fluorescent photons 20 can be efficiently absorbed.

[0061] In some embodiments of the present invention, a micro-ball lens array is added to the solid sensitizer film layer, and the micro-ball lenses are arranged in an array on the upper surface of the quartz plate along the spiral winding path of the optical fiber. Since the sensitizer in the solid sensitizer film layer emits fluorescent photons 20 in random directions in three-dimensional space after absorbing solar photons, the micro-ball lenses sealed in the solid sensitizer film layer are used to direct and converge the fluorescent photons 20 to radiate on the surface of the optical fiber, which is beneficial to improve the absorption efficiency of the optical fiber for the fluorescent photons 20. Figure 6 Schematic diagram of the photon transmission path after the introduction of the microsphere lens array. The focusing effect of the microsphere lens on fluorescent photons significantly improves the absorption efficiency of the doped elements in the optical fiber for the pump light.

[0062] In some embodiments of the present invention, the optical fiber is Nd-doped 3+ Silica fiber or Nd-doped 3+ Fluoride optical fiber, the transverse pumping system reported in domestic and foreign experiments all uses Nd-doped 3+ Silica fiber, while Nd-doped 3+ Fluoride optical fiber is beneficial to shorten the length of the optical fiber. It should be noted that the use of Nd doped 3+When using a fluoride optical fiber, both the substrate 14 and the optical fiber adhesive need to be replaced with a material that matches the glass refractive index of the fluoride optical fiber.

[0063] Regarding some of the terms mentioned above, explanations are as follows: The fluorescent solar collector LSC is a device used to improve the efficiency of solar energy utilization. In photovoltaic cells, the basic principle is to use fluorescent materials to convert incident sunlight into fluorescent photons with longer wavelengths, and transmit the fluorescence to the photovoltaic cells at the edge of the collector through total internal reflection to achieve photoelectric conversion. For the transverse pumping cavity of the solar-pumped fiber laser, fluorescent materials are also used to convert sunlight into fluorescent photons. The difference is that the position of the optical fiber is relatively flexible. It is usually fixed to the inner annular wall of the chamber to maximize the radius of curvature and reduce the bending loss of the optical fiber.

[0064] Sensitizer refers to the fluorescent material in LSC. Based on the principle of cascade energy transfer, the sensitizer can absorb sunlight and convert it into fluorescent photons. The sensitizer can include liquid sensitizers and solid sensitizers. For example, rhodamine R6G is a liquid sensitizer, and Y083 dye and O240 dye are solid sensitizers.

[0065] A Shortpass Dichroic Mirror is an optical component with specific spectral selectivity for reflecting or transmitting light.

[0066] Monte Carlo photon tracing is a method that uses Monte Carlo simulation technology to study the propagation and scattering behavior of light in a medium. This method is based on random sampling and statistical analysis, and estimates the propagation and scattering characteristics of light by simulating the random motion of a large number of photons. The paths of photons and interaction events (such as scattering and absorption) are generated based on specific probability distributions, and the final result is the statistical average of these photon paths.

[0067] The focusing unit 15 in the embodiment of the present invention is used to focus the fluorescent photons 20 emitted along a random direction inside the base layer 13 on the side of the optical fiber, thereby increasing the density of the fluorescent photons 20 on the surface of the optical fiber and improving the absorption efficiency of the optical fiber for the fluorescent photons 20. The cascade energy transfer principle of the sensitizer and the focusing scheme of the microsphere lens array are combined to significantly increase the density of the fluorescent photons 20 on the side of the optical fiber.

[0068] It should be understood that the various forms of processes shown above can be used to reorder, add or delete steps. For example, the steps described in the disclosure of the present invention can be performed in parallel, sequentially or in different orders, as long as the desired results of the technical solution disclosed in the present invention can be achieved, and this document does not limit this.

[0069] The above specific implementations do not constitute a limitation on the protection scope of the present invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. An optically pumped fiber laser, characterized in that: include: a greenhouse cavity having an incident wall that transmits the pump light; A substrate disposed in the greenhouse cavity, wherein the substrate is parallel to the incident wall; A photon conversion layer, the photon conversion layer is located on the surface of the substrate facing the incident wall, and the photon conversion layer includes a base layer and a plurality of light-gathering units, the plurality of light-gathering units are arranged on the surface of the substrate, and the base layer seals the plurality of light-gathering units; An optical fiber, the optical fiber comprising a main body located in the greenhouse cavity and two ends extending out of the greenhouse cavity, the main body being spirally wound in a single-layer form on a surface of the substrate away from the incident wall, and the two ends having resonant cavity mirrors; The focusing unit is arranged above the main body along the extension direction of the main body, the pump light is transmitted from the incident wall into the greenhouse cavity, the base layer converts the pump light into fluorescent photons, the fluorescent photons are reflected in the greenhouse cavity, and the fluorescent photons are converged to the side of the optical fiber through the focusing unit to optically pump the optical fiber.

2. The optically pumped fiber laser according to claim 1, characterized in that: The pump light is sunlight, and the incident wall transmits the sunlight in the wavelength band of 380nm to 550nm to enter the greenhouse cavity.

3. The optically pumped fiber laser according to claim 1, characterized in that: There is a gap between the photon conversion layer and the incident wall.

4. The optically pumped fiber laser according to claim 1, characterized in that: The greenhouse cavity is surrounded by a top reflective portion, a bottom reflective portion and a side wall portion, the top reflective portion and the bottom reflective portion are relatively parallel and connected to each other through the side wall portion, and the top reflective portion serves as the incident wall.

5. The optically pumped fiber laser according to claim 4, characterized in that: The top reflective portion and the bottom reflective portion are circular, the side wall portion is annular, and the greenhouse cavity is cylindrical.

6. The optically pumped fiber laser according to claim 5, characterized in that: The top reflection part includes a dichroic mirror; the bottom reflection part includes a high reflection mirror; and the side wall part includes a polytetrafluoroethylene ring.

7. The optically pumped fiber laser according to claim 6, characterized in that: The surface reflectivity of the high reflector and the side wall portion facing the greenhouse cavity is greater than 99%.

8. The optically pumped fiber laser according to claim 1, characterized in that: The base layer includes a sensitizer.

9. The optically pumped fiber laser according to claim 1, characterized in that: The light focusing unit includes a micro-ball lens.

10. The optically pumped fiber laser according to claim 1, characterized in that: The substrate includes a quartz plate.

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