Ring-Beam Pumped Fiber Laser

Abstract

The present invention relates to the field of laser technology, and in particular to a ring-light pumped fiber laser, comprising: a main body, the outer side of the main body is a ring side, the ring side has a ring groove extending along the circumference of the ring side; a ring-shaped off-axis parabolic mirror arranged outside the ring side, the side of the ring-shaped off-axis parabolic mirror facing the ring side has a reflecting surface; a ring-shaped window layer, the ring-shaped window layer is arranged in the ring groove, and the ring-shaped window layer and the inner wall of the ring groove form a ring-shaped greenhouse cavity; an optical fiber, a ring substrate and a ring-shaped sensitizing layer are arranged in the ring-shaped greenhouse cavity and arranged in sequence along the bottom surface of the ring groove pointing to the ring window layer, the optical fiber is coiled along the circumference of the ring substrate, and is located on the surface of the ring substrate facing the bottom surface of the ring groove. The present invention is at least conducive to improving the absorption efficiency of the optical fiber to the pump light.

Description

Technical Field

[0001] The invention belongs to the technical field of lasers, and in particular relates to a ring light 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 focused light spot is much larger than the size of the micron-scale optical fiber end face, resulting in low conversion efficiency of the end-pumping.

[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 ring light pumped fiber laser, which is at least beneficial to improving the absorption efficiency of the optical fiber to the pump light.

[0011] To achieve the above object, the technical solution created by the present invention is implemented as follows:

[0012] The invention provides a ring-light pumped fiber laser, comprising: a main body, the outer side surface of the main body is a ring side surface, the ring side surface has a ring groove extending in the circumferential direction of the ring side surface; a ring-shaped off-axis parabolic mirror arranged on the outer side of the ring side surface, the side of the ring-shaped off-axis parabolic mirror facing the ring side surface has a reflecting surface; a ring-shaped window layer, the ring-shaped window layer is arranged in the ring groove, and the ring-shaped window layer and the inner wall of the ring groove form a ring-shaped greenhouse cavity; an optical fiber, a ring-shaped substrate and a ring-shaped sensitizing layer are arranged in the ring-shaped greenhouse cavity and arranged in sequence along the bottom surface of the ring groove pointing to the ring window layer, the optical fiber is coiled along the circumferential direction of the ring substrate, and is located on the surface of the ring substrate facing the bottom surface of the ring groove; wherein the reflecting surface receives pump light and converges the pump light into the ring groove, the pump light is injected into the ring-shaped greenhouse cavity from the ring window layer, the ring-shaped sensitizing layer converts the pump light into fluorescent photons, and the fluorescent photons optically pump the optical fiber from the side of the optical fiber.

[0013] Furthermore, the pump light is sunlight, the annular window layer transmits sunlight in the wavelength band of 380nm~550nm into the annular greenhouse cavity, and the wavelength of the fluorescent photons is in the range of 570nm~650nm.

[0014] Furthermore, there is a gap between the annular window layer and the annular sensitizing layer.

[0015] Furthermore, the annular groove is a trapezoidal annular groove, and a dimension of the annular groove in an axial direction of the annular groove is a first dimension, and the first dimension gradually increases in a direction away from the main body.

[0016] Furthermore, the distance from the edge of the annular groove away from the bottom surface of the annular groove to the bottom surface of the annular groove is greater than the distance from the annular window layer to the bottom surface of the annular groove.

[0017] Furthermore, the annular window layer includes a dichroic mirror, and / or the inner wall of the annular groove is an inner wall made of aluminum with high reflectivity or an inner wall made of silver with high reflectivity.

[0018] Furthermore, it also includes: an annular reflective layer, which is arranged on the bottom surface of the annular groove.

[0019] Further, the annular reflective layer includes a high reflective mirror.

[0020] Furthermore, the surface reflectivity of the inner wall of the annular groove and the surface reflectivity of the surface of the annular reflective layer facing the annular greenhouse cavity are both greater than 99%.

[0021] Further, the annular substrate includes a quartz plate.

[0022] Compared with the prior art, the invention can achieve the following beneficial effects:

[0023] In the ring-shaped light pumped fiber laser proposed by the invention, a ring-shaped off-axis parabolic mirror is used to converge sunlight to form a ring-shaped convergent light spot with a higher power density on the surface of the ring-shaped window layer. The size of the ring-shaped convergent light spot can match the ring-shaped window layer. When the ring-shaped groove is a trapezoidal ring-shaped groove, the inner wall of the ring-shaped groove is a tapered side wall. Due to the reflection of the tapered side wall, the ring-shaped groove has a focusing function. When the ring-shaped convergent light spot falls on the inner wall of the ring-shaped groove that is not covered by the ring-shaped window layer, the ring-shaped groove can reflect the ring-shaped convergent light spot onto the ring-shaped window layer to provide a certain error compensation. The tapered side wall of the ring-shaped groove has a more excellent fluorescent photon confinement effect, which significantly improves the fluorescent photon density near the optical fiber. In addition, the ring-shaped light pumped fiber laser can be set on a solar tracking device to track the incident direction of sunlight in real time, which is conducive to further improving the light conversion efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] 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:

[0025] Figure 1 It is a schematic diagram of the structure of the end-pumped fiber and the side-pumped fiber of the semiconductor laser LD;

[0026] Figure 2 This is a schematic diagram of the structure of a sunlight end-pumped fiber laser;

[0027] Figure 3 The schematic diagram of the structure of the LSC structured sunlight transversely pumped fiber laser;

[0028] Figure 4 Schematic diagram of the transmission path of photons in the cylindrical greenhouse cavity;

[0029] Figure 5 A cross-sectional view of the ring light pumped fiber laser according to an embodiment of the present invention along the plane where the axis is located;

[0030] Figure 6 This is a schematic diagram of the photon transmission process in the annular greenhouse cavity according to an embodiment of the present invention;

[0031] Figure 7 A schematic diagram of a partial structure of a ring light pumped fiber laser according to an embodiment of the present invention;

[0032] Figure 8 This is a simulation analysis diagram of a main body and an annular off-axis parabolic mirror according to an embodiment of the present invention;

[0033] Fig. 9 is the absorption / emission intensity curve of the ring light pumped fiber laser according to the embodiment of the present invention;

[0034] Fig.10 Nd 3+ Schematic diagram of the energy levels of laser transitions;

[0035] Fig.11 Schematic diagram of the spectrum of sunlight.

[0036] Explanation of the reference numerals: 10, main body; 11, annular groove; 20, annular off-axis parabolic mirror; 21, reflecting surface; 15, annular window layer; 110, bottom surface; 12, optical fiber; 13, annular substrate; 14, annular sensitizing layer; 30, sunlight; 16, annular reflecting layer. DETAILED DESCRIPTION

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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 laser to the generated fluorescent photons absorbed by the optical fiber (a) to (f) is analyzed. The probability p of penetrating into the chamber and being absorbed by the sensitizer is calculated respectively. ab (i.e., the probability of process (a)), fluorescence conversion efficiency η FL(i.e., the efficiency of the process (b)) and the probability p of a randomly emitted fluorescent photon 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 walls, that is, process (e), and will be repeatedly reflected multiple times in the cavity. If the reabsorption of fluorescent photons by the sensitizer is considered, that is, process (f), the probability p of a photon being reabsorbed once must also be calculated. RAi .

[0042] 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 liquid LSC structure simplifies the solar concentrating system and solar 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.

[0043] The "natural light intensity" involved in the present invention refers to: the illumination intensity under the standard solar irradiance value AM1.5G.

[0044] In summary, in order to improve the lateral pumping technology and increase the absorption and utilization rate of sunlight, the present invention provides a ring-shaped light-pumped fiber laser, which uses a ring-shaped off-axis parabolic mirror to concentrate sunlight, pump the optical fiber in the ring-shaped greenhouse cavity, and optically pumps the side of the optical fiber in the ring-shaped groove, thereby improving the problem of poor restraint of fluorescent photons in the traditional LSC structure, improving the utilization rate of sunlight, and improving the absorption efficiency of fluorescent photons by optical fibers.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments.

[0050] refer to Figure 5 and Figure 7The present invention provides a ring-type optical pumped fiber laser, comprising: a main body 10, wherein the outer side surface of the main body 10 is a ring-type side surface, and the ring-type side surface has a ring-type groove 11 extending along the circumferential direction of the ring-type side surface; a ring-type off-axis parabolic mirror 20 arranged on the outer side of the ring-type side surface, and the side of the ring-type off-axis parabolic mirror 20 facing the ring-type side surface has a reflecting surface 21; a ring-type window layer 15, wherein the ring-type window layer 15 is arranged in the ring-type groove 11, and the ring-type window layer 15 and the inner wall of the ring-type groove 11 form a ring-type greenhouse cavity; a ring-type greenhouse cavity is arranged in the ring-type greenhouse cavity, and the ring-type window layer 15 and the inner wall of the ring-type groove 11 form a ring-type greenhouse cavity; a ring-type window layer 15 ... The bottom surface 110 of the annular groove 11 points to the direction of the annular window layer 15, and the optical fiber 12, the annular substrate 13 and the annular sensitizing layer 14 are arranged in sequence. The optical fiber 12 is coiled along the circumference of the annular substrate 13 and is located on the surface of the annular substrate 13 facing the bottom surface 110 of the annular groove 11; wherein the reflecting surface 21 receives the pumping light and converges the pumping light into the annular groove 11, the pumping light is emitted from the annular window layer 15 into the annular greenhouse cavity, and the annular sensitizing layer 14 converts the pumping light into fluorescent photons, and the fluorescent photons optically pump the optical fiber 12 from the side of the optical fiber 12.

[0051] Furthermore, the pump light is sunlight 30 .

[0052] It should be noted that the annular side surface, annular groove 11, annular off-axis parabolic mirror 20, annular window layer 15, annular greenhouse cavity, annular sensitizing layer 14 and annular substrate 13 involved in the embodiment of the present invention are all annular structures. The advantage of such a setting is that it can increase the area for receiving pump light, which is beneficial to improve the conversion efficiency of sunlight 30.

[0053] In some embodiments of the present invention, the main body 10 may be annular, as long as the annular groove 11 can be provided on the outer side wall of the main body 10 .

[0054] In addition, before the optical fiber 12 is placed in the annular greenhouse cavity, a wet etching method is required to remove the resin coating of the optical fiber 12 to avoid absorption loss of the pump light caused by the resin coating.

[0055] The annular greenhouse cavity is used to prevent potentially absorbable fluorescent photons from escaping the greenhouse cavity. The annular sensitizing layer 14 can be used to absorb a portion of the pump light with a higher intensity and convert it into fluorescent photons close to the absorption band of the doped ions in the optical fiber 12. The inner wall of the annular greenhouse cavity has extremely high reflectivity for both the pump light transmitted into the annular greenhouse cavity and the fluorescent photons converted by the annular sensitizing layer 14. The annular window layer 15 is used to transmit the pump light and reflect the fluorescent photons emitted by the annular sensitizing layer 14.

[0056] The annular off-axis parabolic mirror 20 is used to converge direct sunlight 30 to achieve a higher pump light power density on the annular window layer 15, thereby increasing the reception utilization rate of the annular sensitizing layer 14 for the energy of the sunlight 30. Different from the sunlight end-pumped fiber laser, the technical solution provided by the embodiment of the present invention uses the annular sensitizing layer 14 to absorb sunlight 30 as an intermediate medium, adopts the cascade energy transmission principle, and pumps the side of the optical fiber 12, which is conducive to improving the absorption utilization rate of the optical fiber 12 for the pump light, and the structural parameters of the annular off-axis parabolic mirror 20 are not affected by the end face structure of the optical fiber 12.

[0057] The annular groove 11 can be used as a secondary concentrator for an annular light-pumped fiber laser. The specific principle of the secondary concentrator is as follows: in some examples, the annular light-pumped fiber laser is disposed on a solar tracking device, which may introduce an angular tracking error, which is intuitively manifested as the annular convergent light spot converged by the annular off-axis parabolic mirror 20 deviating from the position of the annular window layer 15, causing part of the incident sunlight 30 to directly hit the inner wall of the annular groove 11. Based on the mirror reflection effect of the inner wall of the annular groove 11, the deviated annular convergent light spot will be re-reflected to the surface of the annular window layer 15.

[0058] refer to Figure 6 , analyze the transmission process of sunlight entering the annular groove and being converted into fluorescent photons and absorbed by the optical fiber (a)~(h). The sunlight concentrated by the annular off-axis parabolic mirror is directly incident on the incident window (annular window layer), or reflected by the side wall of the annular groove to the outer surface of the annular window layer. The sunlight is transmitted into the annular greenhouse cavity through the annular window layer, enters the annular sensitizing layer (i.e. (a)), is absorbed by the sensitizer, and partially converted into fluorescent photons (i.e. (b)). The probability that the annular sensitizing layer receives the incident sunlight photons is p ab (i.e., the probability of process (a)), the fluorescence conversion efficiency converted to fluorescent photons is η FL (i.e., the efficiency of process (b)). Since the fluorescent photons are randomly emitted in three-dimensional space in the annular sensitizing layer, the possible transmission paths are mainly divided into the following two types: the first is to directly enter the optical fiber surface through the annular substrate (i.e., (c)); the second is to use the high reflection constraint effect of the annular window layer and the side wall of the annular groove on the emission spectrum of the fluorescent photons, and the fluorescent photons are reflected multiple times (i.e., process (d)) until they enter the side of the optical fiber at the bottom of the annular substrate 3. For the fluorescent photons incident on the side wall of the annular groove, some of the fluorescent photons may be absorbed by the side wall or generate Fresnel reflection loss (i.e., process (e)), and the energy transmission loss of this part should be removed during calculation.

[0059] After analysis, it is found that, unlike the traditional planar cylindrical cavity, the tapered sidewall of the annular groove is equivalent to the secondary concentrator in the study of solar-pumped solid-state lasers, which is used to guide the fluorescent photons reflected from the sidewall to the optical fiber at the bottom of the annular groove. The above two transmission paths ((c) and (d)) together form the density of fluorescent photons incident on the optical fiber surface, where the probability of the optical fiber absorbing fluorescent photons (i.e. process (f)) is p AF If the reabsorption of fluorescence photons by the sensitizer is considered (i.e. process (g)), the probability p of a single reabsorption of a fluorescence photon must also be calculated. RAi .

[0060] Since the optical fiber cannot absorb all the incident fluorescent photons, some fluorescent photons will escape from the side of the optical fiber toward the bottom of the annular groove. These fluorescent photons are reflected back into the optical fiber by the side wall and the annular reflection layer (i.e., process (h)), which helps to improve the optical fiber's absorption efficiency of fluorescent photons.

[0061] The structural model of the ring-light pumped fiber laser was established using the three-dimensional design software UG (Unigraphics NX), and the TracePro simulation software was imported for non-sequential ray tracing analysis. The ring-shaped off-axis parabolic mirror 20 can avoid the dispersion effect on incident light of different wavelengths, such as Figure 8 As shown, if the incident window of the annular groove 11 for receiving the annular focused light spot is larger than the size of the annular focused light spot, theoretically the annular groove 11 can receive 100% of the sunlight 30 focused by the annular off-axis parabolic mirror 20. Figure 8 In the simulation analysis, the working surface (i.e., the reflecting surface 21) of the annular off-axis parabolic mirror 20 can be set as a total reflection mirror surface, and the outer surface of the annular window layer 15 of the annular groove 11 can be set as an energy receiving surface for simulating the incident window.

[0062] In some embodiments provided by the present invention, the annular window layer 15 transmits sunlight 30 in the wavelength band of 380nm~550nm into the annular greenhouse cavity, and the wavelength of the fluorescent photons is in the range of 570nm~650nm. In some examples, the peak wavelength of the fluorescent photons is at 590nm.

[0063] The reason for this setting is: Fig.11, 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 light 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 annular greenhouse cavity prevents the bands that cannot be absorbed by the annular sensitizing layer 14 from entering the annular greenhouse cavity, which is beneficial to avoiding the accumulation of waste heat in the annular greenhouse cavity, and thus avoiding negative effects such as thermal effects.

[0064] Furthermore, there is a gap between the annular window layer 15 and the annular sensitizing layer 14 to meet the constraint conditions of total reflection transmission. Specifically, if a liquid sensitizer is used as the annular sensitizing layer, the liquid sensitizer forms a close optical contact with the inner surface of the annular window layer, that is, there is no air or other impurities between the medium interfaces. Since the refractive index of the liquid sensitizer solution and the annular window layer is similar, it is difficult for the fluorescent photons to achieve total reflection at the interface in the annular greenhouse cavity, and the lossy reflection of the fluorescent photons on the inner surface of the annular window layer will produce a high transmission loss. In the embodiment of the present invention, the annular sensitizing layer is a solid sensitizer layer, so that an air gap can be formed between the annular sensitizing layer and the annular window layer. Due to the significant difference in refractive index between the annular sensitizing layer and the air, the total reflection transmission of the fluorescent photons in the annular greenhouse cavity can be achieved within the range of the total reflection critical angle. In summary, compared with the liquid sensitizer, the solid annular sensitizing 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.

[0065] For further reference, Figure 5 The annular groove 11 is a trapezoidal annular groove, and the dimension of the trapezoidal annular groove in the axial direction A-A1 of the annular groove 11 is a first dimension. In the direction radially away from the main body 10, the first dimension gradually increases.

[0066] For further reference, Figure 7 The distance from the edge of the annular groove 11 away from the bottom surface 110 of the annular groove 11 to the bottom surface 110 of the annular groove 11 is greater than the distance from the annular window layer 15 to the bottom surface 110 of the annular groove 11 .

[0067] Furthermore, the annular window layer 15 includes a dichroic mirror. In some examples, the dichroic mirror can be a short-wave 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. The reason for this setting is that the dichroic mirror can transmit light beams in the visible light range of sunlight, that is, transmit light beams less than the cut-off wavelength, and reflect fluorescent photons greater than the cut-off wavelength.

[0068] In some embodiments provided by the present invention, the inner wall of the annular groove 11 is an inner wall made of aluminum with high reflectivity or an inner wall made of silver with high reflectivity. In some examples, the material of the main body 10 is aluminum, and the inner wall of the annular groove 11 is ground and polished to make the inner wall of the annular groove 11 an inner wall made of aluminum with high reflectivity; in other examples, the material of the main body 10 is aluminum, and a silver film with high reflectivity is plated on the inner wall of the annular groove to make the inner wall of the annular groove 11 a silver inner wall with high reflectivity.

[0069] Furthermore, the annular light pumped fiber laser further includes: an annular reflective layer 16, which is disposed on the bottom surface 110 of the annular groove 11. After the annular sensitizing layer 14 absorbs the sunlight 30, it will emit fluorescent photons in random directions in the three-dimensional space. Under the reflection of the side wall of the annular groove 11 and the constraint of the annular window layer 15, most of the fluorescent photons will be transmitted to the side of the optical fiber 12 through the annular substrate 13. Since the optical fiber 12 cannot absorb all the incident fluorescent photons, some fluorescent photons will escape from the optical fiber 12 toward one side of the bottom of the annular groove 11. These fluorescent photons are reflected again into the optical fiber 12 by the side wall and the annular reflective layer 16, which is conducive to improving the absorption efficiency of the optical fiber 12 for fluorescent photons.

[0070] Furthermore, the annular reflective layer 16 includes a high reflective mirror.

[0071] Furthermore, the surface reflectivity of the inner wall of the annular groove 11 and the surface reflectivity of the surface of the annular reflective layer 16 facing the annular greenhouse cavity are both greater than 99%. This is conducive to further improving the limiting ability of the annular groove 11 on pump light and fluorescent photons.

[0072] Furthermore, the annular substrate 13 includes a quartz plate. The quartz plate has good temperature resistance and light transmission properties, and can prevent parasitic absorption from affecting the fluorescence photon density in the greenhouse cavity.

[0073] In some embodiments of the present invention, the annular sensitizing layer 14 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 in fiber 12 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.

[0074] In some embodiments of the present invention, both ends of the optical fiber 12 extend out of the annular greenhouse cavity, and the length of the optical fiber 12 extending out of the annular greenhouse cavity is in the range of 1m to 2m, and both ends of the optical fiber 12 are used to set the resonant cavity mirrors.

[0075] In some embodiments of the present invention, the two ends of the optical fiber 12 are respectively a high reflection end and an output end. The resonant cavity mirror at the high reflection end is set as a beam splitter, which not only realizes high reflection of the laser wavelength beam, but also reflects the fluorescent band to improve the absorption efficiency of the optical fiber to the fluorescent photons. The beam splitter completely transmits the remaining bands to avoid interference with the laser oscillation in the resonant cavity and negative interference such as heat deposition inside the optical fiber. 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 12 jointly realize the oscillation amplification of the laser wavelength.

[0076] In some embodiments of the present invention, the lasing wavelength is in the range of 1000nm to 1100nm.

[0077] In some embodiments of the present invention, the optical fiber 12 is an active optical fiber, specifically a neodymium-doped SiO2 active optical fiber, and the optical fiber 12 and the annular sensitizing layer 14 are respectively attached to the surfaces of the two opposite sides of the annular substrate 13. The optical fiber adhesive for attaching the optical fiber 12 is a UV-curable 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 12.

[0078] It should be noted that the optical fiber 12 needs to be wet-etched to remove the resin coating layer outside the optical fiber 12. For example, a mixture of H2SO4, H2O2 and H2O at 70°C can be used to remove the resin coating layer.

[0079] In some embodiments of the present invention, the optical fiber 12 may be a fluoride optical fiber, a neodymium-doped SiO2 optical fiber, or a Nd-doped 3+ Fluoride optical fiber, the transverse pumping system reported in domestic and foreign experiments at present, all use neodymium-doped SiO2 optical fiber, while the Nd-doped 3+ The fluoride optical fiber of Nd doped3+ When using a fluoride optical fiber, the annular substrate 13 and the optical fiber adhesive need to be replaced with a material having a refractive index matching that of the glass of the fluoride optical fiber.

[0080] In addition, it is known that the short-wave bidirectional color characteristics of the dichroic mirror serving as the annular window layer 15 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 annular greenhouse cavity. Fig. 9 The transmittance curve and normalized absorption / edge emission intensity (with the highest intensity as the normalized benchmark) of the ring light-pumped fiber laser are shown. The blue curve represents the transmittance of the ring light-pumped fiber laser. Specifically, when the light is incident vertically, part of the light will directly pass through the light-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 light-pumped fiber laser and is transmitted. The red curve represents the absorption rate of pump light of different wavelengths absorbed by the annular sensitizing layer. The red and blue lines are symmetric about 0.5 normalized unit arb.unit, which is attributed to the absorption characteristics of the sensitizer in the annular sensitizing layer 13. The yellow curve represents the fluorescence emission intensity near the optical fiber at the bottom of the annular groove, indicating the wavelength and intensity of the fluorescent photons formed at the bottom of the annular groove of the annular greenhouse cavity during multiple reflections and reabsorption of light. The black dotted line represents the absorption coefficient of the optical fiber, indicating the proportion of fluorescent photons in the greenhouse cavity absorbed by the optical fiber during transmission, specifically showing the absorption of the optical fiber at different wavelengths, according to Fig. 9 and Fig.10 It can be seen that the fluorescence photon emission peak near the wavelength of 590nm represented by the yellow curve is consistent with the Nd 3+ exist 2 G 7 / 2 + 4 G 5 / 2 The absorption peaks of the energy levels overlap highly, so Nd 3+ Can effectively absorb fluorescent photons.

[0081] In some embodiments of the present invention, the annular light-pumped fiber laser further includes a solar tracking device, on which the main body 10 and the annular off-axis parabolic mirror 20 are both arranged, and the solar tracking device is used to track the sun's position, so that the annular off-axis parabolic mirror 20 can receive high-intensity direct sunlight 30. The combination of the high-concentration-ratio annular off-axis parabolic mirror 20 and the annular greenhouse cavity can achieve higher laser gain.

[0082] Some of the terms mentioned above are explained as follows:

[0083] 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 pump cavity of the solar light transversely 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.

[0084] 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.

[0085] A Shortpass Dichroic Mirror is an optical component with specific spectral selectivity for reflecting or transmitting light.

[0086] 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.

[0087] The embodiment of the present invention provides a ring-shaped light-pumped fiber laser that uses a ring-shaped off-axis parabolic mirror to focus direct sunlight, and can form a ring-shaped focusing light spot with a high power density on the surface of the ring-shaped window layer away from the ring-shaped greenhouse cavity, and the ring-shaped focusing light spot can overlap with the size of the surface of the ring-shaped window layer away from the ring-shaped greenhouse cavity. The ring-shaped groove is used as a secondary concentrator. Compared with the existing LSC structure using a cylindrical greenhouse cavity, the trapezoidal ring-shaped groove with a highly reflective film coated on the inner wall provided by the embodiment of the present invention has a stronger ability to confine fluorescent photons, which helps to increase the density of fluorescent photons at the bottom of the ring-shaped groove and improve the absorption efficiency of optical fibers to fluorescent photons.

[0088] In addition, since the solar tracking system may introduce angular tracking errors, causing part of the incident sunlight to be unable to directly hit the surface of the annular window layer away from the annular greenhouse cavity, the side wall of the trapezoidal annular groove can reflect the deviated light to the surface of the annular window layer away from the annular greenhouse cavity, thereby reducing the interference of the tracking error and enabling the annular light-pumped fiber laser equipped with a solar tracking device to have a certain tracking error compensation capability.

[0089] 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.

[0090] 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. A ring light pumped fiber laser, characterized in that: include: A main body, wherein the outer side surface of the main body is an annular side surface, the annular side surface has an annular groove extending along the circumference of the annular side surface, the annular groove is a trapezoidal annular groove, the dimension of the annular groove in the axial direction of the annular groove is a first dimension, and the first dimension gradually increases in a direction away from the main body; an annular off-axis parabolic mirror arranged outside the annular side surface, wherein the annular off-axis parabolic mirror has a reflecting surface on a side facing the annular side surface; An annular window layer, wherein the annular window layer is arranged in the annular groove, and the annular window layer and the inner wall of the annular groove form an annular greenhouse cavity; An optical fiber, an annular substrate and an annular sensitizing layer are arranged in the annular greenhouse cavity and arranged in sequence along the bottom surface of the annular groove pointing to the annular window layer, the optical fiber is coiled along the circumference of the annular substrate and is located on the surface of the annular substrate facing the bottom surface of the annular groove; A solar tracking device, wherein the main body and the annular off-axis parabolic mirror are both arranged on the solar tracking device; The reflecting surface receives the pump light and converges the pump light into the annular groove, the pump light is emitted into the annular greenhouse cavity from the annular window layer, the annular sensitizing layer converts the pump light into fluorescent photons, and the fluorescent photons optically pump the optical fiber from the side of the optical fiber.

2. The ring light pumped fiber laser according to claim 1, characterized in that: The pump light is sunlight, the annular window layer transmits the sunlight in the wavelength band of 380nm to 550nm into the annular greenhouse cavity, and the wavelength of the fluorescent photons is in the range of 570nm to 650nm.

3. The ring light pumped fiber laser according to claim 1, characterized in that: There is a gap between the annular window layer and the annular sensitizing layer.

4. The ring light pumped fiber laser according to claim 1, characterized in that: The distance from the edge of the annular groove away from the bottom surface of the annular groove to the bottom surface of the annular groove is greater than the distance from the annular window layer to the bottom surface of the annular groove.

5. The ring light pumped fiber laser according to claim 1, characterized in that: The annular window layer includes a dichroic mirror, and / or the inner wall of the annular groove is an inner wall made of aluminum with high reflectivity or an inner wall made of silver with high reflectivity.

6. The ring light pumped fiber laser according to claim 1 or 5, characterized in that: Also includes: An annular reflective layer is arranged on the bottom surface of the annular groove.

7. The ring light pumped fiber laser according to claim 6, characterized in that: The annular reflective layer includes a high reflective mirror.

8. The ring light pumped fiber laser according to claim 6, characterized in that: The surface reflectivity of the inner wall of the annular groove and the surface reflectivity of the surface of the annular reflective layer facing the annular greenhouse cavity are both greater than 99%.

9. The ring light pumped fiber laser according to claim 1, characterized in that: The annular substrate includes a quartz plate.

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