A laser semiconductor-pumped optical fiber and all-fiber laser system

Abstract

The application discloses a kind of laser semiconductor pumped optical fiber, by directly filling semiconductor light-emitting part such as PN type semiconductor in very thin optical fiber, can be under external electric field excitation and the modulation of glass structure refractive index distribution to limit the transmission path and direction of light, make pumping light directly in optical fiber and directional transmission along core.This new type of pumping source generation mode indirectly increases the overall volume of semiconductor light-emitting part and heat dissipation area, improves heat dissipation efficiency, while reducing the use of mirror system in existing semiconductor laser, which directly limits the emission of light through the change of glass refractive index, realizes the output of semiconductor laser in optical fiber, reduces optical shaping and coupling, reduces optical loss and structure volume, realizes the lightweight of semiconductor laser;It is connected with subsequent laser system, wavelength conversion and laser output can be realized, realize the all-fiber of optical fiber laser system, the weight and volume of optical fiber laser system are reduced to the greatest extent.

Description

Technical Field

[0001] This invention relates to the field of fiber laser equipment technology, and more specifically, to a laser semiconductor pump fiber and an all-fiber laser system. Background Technology

[0002] With the rapid development of fiber optic technology, the output power, beam quality, size, and weight of fiber lasers have been rapidly improved, and they have been widely used in areas such as people's lives and national defense security.

[0003] However, existing fiber laser systems generate laser light by coupling a semiconductor pump source into the resonant cavity. The higher the power of the laser system, the higher the power of the semiconductor pump source is required, and the larger the size and weight of the semiconductor pump source becomes, which also increases the heat dissipation pressure. This also increases the overall size and weight of the fiber laser system used in conjunction with the semiconductor pump source. Summary of the Invention

[0004] In response to at least one defect or improvement requirement in the prior art mentioned in the background section, the present invention provides a laser semiconductor pump fiber and an all-fiber laser system to achieve miniaturization, weight reduction and improved heat dissipation efficiency of the semiconductor pump source and the fiber laser system used in conjunction with it.

[0005] To achieve the above objectives, in a first aspect, the present invention provides a laser semiconductor pump fiber, comprising: a fiber core and a semiconductor light-emitting portion and a cladding layer sequentially covering the fiber core;

[0006] The semiconductor light-emitting part can generate laser light of a preset wavelength under the action of an external electric field;

[0007] The fiber core is used to conduct laser light of the preset wavelength;

[0008] The refractive index of the cladding is lower than that of the fiber core, thereby limiting the propagation of the laser of the preset wavelength within the fiber core.

[0009] Furthermore, the semiconductor light-emitting part includes a PN-type semiconductor; the PN-type semiconductor is capable of generating laser light of a preset wavelength under the action of an external electric field.

[0010] Furthermore, the semiconductor light-emitting part also includes a polymer confinement layer covering the PN-type semiconductor; the polymer confinement layer is a polymer material used to maintain the cross-sectional shape of the PN-type semiconductor constant during the optical fiber drawing process.

[0011] Furthermore, the fiber core is the core of a multimode optical fiber.

[0012] Furthermore, the two ends of the fiber core covered by the PN-type semiconductor are respectively provided with a total reflection fiber core segment and a partial reflection fiber core segment;

[0013] The laser of the preset wavelength can be directionally transmitted from the total reflection fiber core segment to the partial reflection fiber core segment within the fiber core.

[0014] Furthermore, the total reflection fiber core segment has a reflectivity of ≥99.5% for the laser of the preset wavelength, and the partial reflection fiber core segment has a reflectivity of ≤10% for the laser of the preset wavelength.

[0015] Furthermore, the refractive index distribution inside the fiber core can be altered by femtosecond laser writing or irradiation with a hydrogen-loaded ultraviolet mask to achieve total and / or partial reflection of the laser of the preset wavelength.

[0016] Furthermore, a metal wire is embedded in the polymer confinement layer, which can introduce an external electric field into the PN-type semiconductor and generate laser light of the preset wavelength through electric field excitation.

[0017] Furthermore, both the fiber core and the cladding are made of glass matrix material.

[0018] To achieve the above objectives, in a second aspect, the present invention provides an all-fiber laser system comprising the laser semiconductor pump fiber described in any of the preceding claims, capable of wavelength conversion and / or laser output via the pump light of the laser semiconductor pump fiber.

[0019] In summary, compared with the prior art, the above-described technical solutions conceived by this invention can achieve the following beneficial effects:

[0020] (1) This invention directly fills a semiconductor light-emitting part, such as a PN-type semiconductor, into an extremely thin optical fiber. Under the excitation of an external electric field and the modulation of the refractive index distribution of the glass structure, the transmission path and direction of light can be restricted, so that semiconductor pump light can be directly generated within the optical fiber structure and directionally transmitted in the fiber core. This novel pump source generation method indirectly increases the overall volume and heat dissipation area of ​​the semiconductor light-emitting part, improves heat dissipation efficiency, and reduces the use of lens systems in existing semiconductor lasers. It directly restricts light emission through the change of glass refractive index, realizes the output of semiconductor laser in optical fiber, reduces optical shaping and coupling, reduces optical loss and structural volume, and realizes the lightweighting and miniaturization of semiconductor laser.

[0021] (2) The laser semiconductor pump fiber of the present invention can be used in conjunction with the subsequent laser system to realize wavelength conversion and laser output, thereby realizing the full fiberization of the fiber laser system and minimizing the weight and volume of the fiber laser system. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 A set of side views and cross-sectional views of a novel laser semiconductor pump fiber provided for embodiments of the present invention;

[0024] exist Figure 1 In the diagram, 1 represents the inner cladding (the inner cladding of the optical fiber, which can be simply referred to as the cladding), 2 represents the PN type semiconductor, 3 represents the polymer confinement layer, 4 represents the fiber core, 5 represents the total reflection fiber core segment, and 6 represents the partial reflection fiber core segment.

[0025] Figure 2 This is a schematic diagram of the structure of an all-fiber laser system based on a novel pump fiber of laser semiconductor, provided as an embodiment of the present invention. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0027] The terms "comprising" or "having," and any variations thereof, in the specification, claims, or drawings of this application are intended to cover a non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the steps or units listed, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to such processes, methods, products, or apparatus.

[0028] Existing fiber laser systems generate laser light by coupling a semiconductor pump source into the resonant cavity. The higher the laser power, the higher the power of the required semiconductor pump source, resulting in a larger and heavier pump source, increased heat dissipation pressure, and further increased overall size and weight of the fiber laser. Therefore, the miniaturization and weight reduction of fiber lasers can be addressed by focusing on the miniaturization and weight reduction of the semiconductor pump source and its heat dissipation efficiency.

[0029] This invention discloses a novel pump fiber and all-fiber laser system based on LD (laser semiconductor or laser diode). This novel pump fiber changes the traditional generation and output methods of semiconductor pump light, compressing the semiconductor pump source from the chip to the fiber scale. That is, by directly filling the middle of the fiber used for LD pump transmission with a semiconductor light-emitting part such as a PN-type semiconductor, semiconductor pump light can be generated through the fiber structure, thereby reducing the heat dissipation pressure of semiconductor lasers. This provides more possibilities for semiconductor laser pump generation and semiconductor laser applications, and also provides a new way to achieve the lightweighting and miniaturization of fiber lasers.

[0030] Multimode optical fibers generally consist of three parts from the outer layer to the inner layer: a coating layer (the coating material can be ultraviolet optical adhesive), an inner cladding layer, and a core. By distributing different refractive indices, the numerical aperture can be controlled, enabling light transmission within the multimode fiber. Because the core of a multimode fiber is relatively large, typically greater than 100 micrometers, structural filling can be easily achieved. Therefore, preferably, a portion of the multimode fiber core is replaced with a PN-type semiconductor. Total reflection and partial reflection regions are created at both ends of the PN-type semiconductor using femtosecond lasers or other methods, altering the internal waveguide structure of the fiber. Then, by applying an external electric field, the photon energy of the PN-type semiconductor can be excited and emitted, and directionally transmitted, directly transmitting light into the glass core of the multimode fiber. Under the constraint of the inner cladding and coating layer, light transmission within the core and inner cladding is achieved. By fusion splicing the novel LD pump fiber with an existing fiber laser system, or by drawing the PN-type semiconductor fiber into a combiner, pump light is coupled into the resonant cavity. Then, through a cladding filter and end caps, wavelength conversion and laser output can be achieved.

[0031] like Figure 1 As shown, in one embodiment, a laser semiconductor pump fiber mainly includes a fiber core 4 and a semiconductor light-emitting part and an inner cladding layer 1 that sequentially cover the fiber core 4.

[0032] The inner cladding 1 and the fiber core 4 form the light transmission structure. Both are glass matrix materials. According to the optical fiber numerical aperture design, by adding different non-metallic elements, the refractive index of the fiber core 4 is made to be greater than that of the inner cladding 1, so as to limit the propagation of the laser of the preset wavelength inside the fiber core. The cross-sectional shape of both can be circular and concentric.

[0033] The preferred semiconductor light-emitting part is a PN-type semiconductor 2. N-type semiconductors, also known as electron-type semiconductors, are impurity semiconductors where the concentration of free electrons is much greater than the concentration of holes. Doping and defects can both increase the electron concentration in the conduction band. For germanium and silicon semiconductor materials, doping with group V elements allows impurity atoms to substitute for germanium or silicon atoms in the crystal lattice, providing an extra electron beyond covalent bonding, thus increasing the electron concentration in the conduction band. P-type semiconductors generally refer to hole-type semiconductors, where positively charged holes are the primary conductors. P-type semiconductors are formed by doping pure silicon crystals with trivalent elements (such as boron) that replace silicon atoms in the lattice. In P-type semiconductors, holes are the majority carriers, and free electrons are the minority carriers; conduction is mainly through holes. Because the amount of positive charge is equal to the amount of negative charge in a P-type semiconductor, it is electrically neutral. Holes are mainly provided by impurity atoms, while free electrons are formed by thermal excitation. Combining them together forms a PN junction. Electrons from the N-type semiconductor at the boundary will naturally migrate to the P-type region to fill the holes, leaving behind atoms that have lost electrons and become positively charged. Correspondingly, the atoms at the P-type boundary gain electrons and become negatively charged, thus forming a space charge region at the boundary. A diode is composed of a PN junction, that is, a combination of P-type and N-type semiconductors. Therefore, the characteristics of the PN junction result in the unidirectional conductivity of the diode.

[0034] The PN-type semiconductor 2 is a light-emitting element. It is filled into the LD pump fiber as a whole during the fiber preform stage, and its cross-sectional shape can be circular or rectangular.

[0035] Preferably, the semiconductor light-emitting part further includes a polymer confinement layer 3 covering the PN-type semiconductor 2. During the fiber drawing process, the polymer confinement layer 3 utilizes its own viscosity coefficient at a suitable temperature to ensure that the overall cross-sectional shape of the PN-type semiconductor 2 remains unchanged and reaches the hundred-micrometer level in overall scale. The polymer confinement layer 3 completely covers the outer layer of the PN-type semiconductor 2, and the two have the same cross-sectional shape and are tightly fitted. The PN-type semiconductor 2 and the polymer confinement layer 3 together constitute the semiconductor light-emitting part. If their cross-sectional shapes are circular, they are adapted to the cross-sectional shape and size of the fiber core 4; if they are rectangular, they are internally tangent to the circular fiber core 4.

[0036] Preferably, the two ends of the fiber core 4 encapsulated by the PN-type semiconductor 2 are respectively provided with a total internal reflection fiber core segment 5 and a partial internal reflection fiber core segment 6. The matrix material of the total internal reflection fiber core segment 5 and the partial internal reflection fiber core segment 6 is glass, which is composed of the partial fiber cores 4 located at both ends of the PN-type semiconductor 2. The refractive index distribution inside the fiber core 4 is changed by femtosecond laser writing or hydrogen-loaded ultraviolet mask irradiation to achieve total internal reflection and / or partial reflection of laser light of a preset wavelength. The linear length of the total internal reflection fiber core segment 5 and the partial internal reflection fiber core segment 6 does not exceed 20 cm. The reflectivity of the total internal reflection fiber core segment 5 for laser light of the preset wavelength is ≥99.5%, and the reflectivity of the partial internal reflection fiber core segment 6 for laser light of the preset wavelength is ≤10%. Laser light of the preset wavelength can be directionally propagated from the total internal reflection fiber core segment 5 to the partial internal reflection fiber core segment 6 within the fiber core 4.

[0037] The new type of pump fiber LD requires an external electric field to output light. Therefore, an external electric field can be introduced into the PN semiconductor 2 by embedding metal wires in the polymer confinement layer 3 to achieve electric field excitation.

[0038] This embodiment first prepares an LD pump fiber preform, designs the LD pump fiber according to the required pump power, determines the size and shape of the PN semiconductor, and then draws the fiber using a drawing tower to prepare a LD pump fiber that meets the requirements. Then, the refractive index of the radial waveguide layer of the LD pump fiber is changed by femtosecond laser writing or hydrogen-loaded ultraviolet mask irradiation to form an internal waveguide structure, achieving total and partial reflection of specific wavelengths. The processed LD pump fiber is then used to prepare a beam combiner according to the fiber laser system design, or directly coupled and injected with a fiber high-reflection grating to achieve pump light coupling. Finally, it is fused with a gain fiber, a low-reflection grating, a cladding optical filter, and a fiber end cap to form an all-fiber laser system based on LD pump fiber pumping.

[0039] In a more specific embodiment, the following can be used: Figure 1 The novel LD pump fiber shown achieves, for example, Figure 2 The 1080nm all-fiber laser system shown.

[0040] The LD pump fiber is designed with fiber dimensions of 200 / 400μm, a numerical aperture of 0.22, and a drawn fiber length of 500cm. The PN semiconductor region has a length of 200cm, and a 150cm transmission fiber is formed before and after the PN semiconductor region by fiber core 4. The PN semiconductor 2 generates pump light at a wavelength of 915nm. After the fiber is drawn, femtosecond lasers are used to directly etch radially before and after the PN semiconductor region, changing the refractive index and altering the internal waveguide structure to create a total reflection region and a partial reflection region for the 915nm wavelength, with a length of approximately 15cm. A 1.5m length is reserved in the output direction of the LD pump fiber for fiber cleaving, splicing, etc.

[0041] The partially reflective region of the processed LD pump fiber is fused with a fiber grating. The fiber grating has a center wavelength of 1080 nm, a reflectivity >99.5%, and a size of 20 / 400 μm. Then, YDF-doped fiber, a low-reflection grating paired with the high-reflection grating, a cladding optical filter, and a QBH are fused sequentially.

[0042] Under the influence of an external electric field, the novel LD pump fiber can be excited to emit a 915nm wavelength laser. The directional transmission of the 915nm wavelength laser is achieved through the total internal reflection region and the partial internal reflection region in the novel LD pump fiber. At the same time, when the 915nm wavelength pump light enters the fiber core 4, the numerical aperture of the light is restricted by the combined action of the fiber core 4 and the inner cladding 1, causing the pump light to undergo total internal reflection in the fiber core 4 and propagate along the fiber core extension direction. Inevitably, some pump light will leak into the inner cladding 1. Under the action of the inner cladding 1 and the coating layer, the transmission of light can be further restricted, so that the pump light always propagates in the fiber. After passing through a high-reflectivity grating, the laser enters the YDF-doped fiber. Through energy level conversion, wavelength conversion and 1080nm laser output are achieved. When the laser passes through a low-reflectivity grating, the remaining 915nm and 1080nm light achieve specific wavelength reflection and transmission under wavelength selection. After passing through the cladding optical filter, the remaining 915nm wavelength laser is diffused under the condition of total internal reflection failure, while the generated 1080nm laser transmission in the fiber core is unaffected. After passing through the QBH end cap, the stable output of the 1080nm laser is achieved.

[0043] Because of the adoption of the new LD pump fiber, the entire structure is fully fiberized. All the fibers can be placed on the fiber cold plate. By using the grooving method, according to the design of power, beam quality and nonlinear effect suppression, fiber grooves are made on the surface of the fiber cold plate to place the fiber parts, while ensuring that each splice point is within a straight fiber groove for 10cm before and after.

[0044] It should also be noted that the partially reflective region of the processed LD pump fiber can be fused with the fiber grating. Alternatively, the LD pump fiber can be fabricated using a fiber combiner, by tapering the transmission portion of the LD pump fiber near the partially reflective region before fusion splicing it with the fiber grating to achieve superposition coupling of pump power and increase the power of the pump light.

[0045] The foregoing description is merely an exemplary embodiment of this disclosure and should not be construed as limiting the scope of this disclosure. Any equivalent changes and modifications made in accordance with the teachings of this disclosure shall still fall within the scope of this disclosure. Other embodiments of this disclosure will be readily apparent to those skilled in the art upon consideration of the specification and practice of the disclosure herein. This invention is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not described herein. The specification and embodiments are to be considered exemplary only, and the scope and spirit of this disclosure are defined by the claims.

[0046] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0047] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A laser semiconductor pump fiber, characterized in that, include: The fiber core and the semiconductor light-emitting part and cladding layer that sequentially cover the fiber core; The semiconductor light-emitting part includes a PN-type semiconductor, which can generate laser light of a preset wavelength under the action of an external electric field; The semiconductor light-emitting part further includes a polymer confinement layer covering the PN semiconductor; the polymer confinement layer is a polymer material used to keep the cross-sectional shape of the PN semiconductor constant during the fiber drawing process; metal wires are embedded in the polymer confinement layer, which can introduce an external electric field into the PN semiconductor and generate laser light of the preset wavelength through electric field excitation. The two ends of the fiber core covered by the PN-type semiconductor are respectively provided with a total reflection fiber core segment and a partial reflection fiber core segment; the laser of the preset wavelength can be directionally transmitted from the total reflection fiber core segment to the partial reflection fiber core segment within the fiber core; The fiber core is used to conduct laser light of the preset wavelength; The refractive index of the cladding is less than that of the fiber core.

2. The laser semiconductor pump fiber as described in claim 1, characterized in that, The fiber core is the core of a multimode optical fiber.

3. The laser semiconductor pump fiber as described in claim 1, characterized in that, The total reflection fiber core segment has a reflectivity of ≥99.5% for the laser of the preset wavelength, and the partial reflection fiber core segment has a reflectivity of ≤10% for the laser of the preset wavelength.

4. The laser semiconductor pump fiber as described in claim 1, characterized in that, The refractive index distribution inside the fiber core is altered by femtosecond laser writing or irradiation with a hydrogen-loaded ultraviolet mask to achieve total and / or partial reflection of laser light of the preset wavelength.

5. The laser semiconductor pump fiber as described in any one of claims 1-4, characterized in that, Both the fiber core and the cladding are made of glass matrix material.

6. An all-fiber laser system, characterized in that, It includes the laser semiconductor pump fiber as described in any one of claims 1-5, which enables wavelength conversion and / or laser output through the pump light of the laser semiconductor pump fiber.

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