Optical fiber and optical fiber laser

Abstract

The invention provides an optical fiber and an optical fiber laser, and belongs to the technical field of laser. The optical fiber comprises a fiber core, a wrapping layer and a plurality of layers of dielectric rods. The cladding layer wraps the fiber core, the multiple layers of dielectric rods are all located in the cladding layer and in the plane where the cross section of the optical fiber is located, the fiber core is located in an area defined by the multiple dielectric rods of each layer of dielectric rods, and the multiple layers of dielectric rods are sequentially arranged in the radial direction of the optical fiber; a plurality of defect cores are arranged between the innermost layer dielectric rod and the outer boundary of the cladding, and the radius of the innermost layer dielectric rod is larger than that of the other layers of dielectric rods. According to the invention, the filtering effect of the optical fiber can be improved.

Description

Technical Field

[0001] The present disclosure relates to the field of laser technology, and in particular to an optical fiber and an optical fiber laser. Background Art

[0002] Optical fiber, for example, all-solid photonic bandgap fiber (AS-PBGF), because of its forbidden band (also called bandgap), can capture light of a specific wavelength in the fiber core for transmission, while causing high loss to light of other wavelengths and preventing them from being transmitted, and can be used as a filter in the filtering field. The forbidden band is also a wavelength band, specifically the wavelength band where the above-mentioned specific wavelength band is located.

[0003] However, the bandgap edge of the current all-solid photonic bandgap fiber is usually relatively flat. For example, at the bandgap edge, the loss incurred by light outside the bandgap during transmission is only a few tenths of a dB / m different from the loss incurred by light inside the bandgap during transmission, resulting in poor filtering effect of the all-solid photonic bandgap fiber. Summary of the invention

[0004] The present disclosure provides an optical fiber and an optical fiber laser, which can solve the problem of poor filtering effect of all-solid photonic bandgap optical fiber in the related art. The technical solution is as follows:

[0005] In one aspect, an optical fiber is provided, the optical fiber comprising a core, a cladding, and a multilayer dielectric rod;

[0006] The cladding is coated outside the core, the multi-layer dielectric rods are all located in the cladding, and in the plane where the cross section of the optical fiber is located, the core is located in the area surrounded by multiple dielectric rods in each layer of dielectric rods, and the multi-layer dielectric rods are arranged in sequence along the radial direction of the optical fiber;

[0007] There are a plurality of defect cores between the innermost dielectric rod and the outer boundary of the cladding, and the radius of the innermost dielectric rod is greater than the radius of the dielectric rods in other layers.

[0008] In the solution disclosed in the present invention, the radius of the innermost dielectric rod is relatively large, which can better wrap the fiber core therein, so that the light beam in a specific band can be better bound in the fiber core, thereby reducing the transmission loss of the light beam in the fiber core.

[0009] In the solution disclosed in the present invention, the radius of the dielectric rod located in the innermost layer is greater than the radius of the dielectric rods located in other layers, and the radius of the dielectric rod and the distance between two adjacent dielectric rods are adjusted through simulation software, which can improve the filtering effect of the optical fiber and make the optical fiber have good filtering effect.

[0010] The optical fiber has a good mode filtering effect because it can couple the high-order mode in the core to the defective core in the cladding for transmission. Therefore, even if the optical fiber introduces a beam of a high-order mode transmission mode because the mode field of the laser is increased by increasing the core, the beam of the high-order mode transmission mode can be coupled to the cladding for transmission and gradually attenuated, making the transmission mode in the core mainly the fundamental mode. Therefore, the optical fiber can take into account both the large mode field and single-mode output of the laser.

[0011] This optical fiber is applied to 976nm fiber lasers. Because it can filter out the 1030nm pump light, most of the light source provided by the pump source is used to pump the 976nm light, thereby improving the conversion efficiency of the fiber laser and outputting relatively pure high-power 976nm laser.

[0012] This fiber is applied to fiber lasers. Although its core is doped with Yb 3+ Although the refractive index increases, the mode filtering effect can still be achieved, thereby relaxing the restriction on the refractive index of the fiber core.

[0013] In a possible implementation, the radius R1 of the innermost dielectric rod is in the range of 3.64 um≤R1≤3.9 um.

[0014] The solution shown in the present disclosure continuously adjusts the radius of the innermost dielectric rod through simulation software, and finds that when the radius of the innermost dielectric rod is between 3.64um and 3.9um, the transmission loss generated at 976nm is relatively low, while the transmission loss generated at 1030nm is relatively large. The transmission losses of the two differ by tens or even hundreds of dB / m. The greater the transmission losses of the two, the better the filtering effect of the optical fiber. It can be seen that when the radius of the innermost dielectric rod is between 3.64um and 3.9um, the optical fiber can have a good filtering effect.

[0015] In a possible implementation manner, the radius R2 of the other layer of dielectric rods has a value range of 3.52 um≤R2≤3.60 um.

[0016] The other layers of dielectric rods are any layer of dielectric rods except the innermost layer of dielectric rods, and the other layers of dielectric rods are all equal.

[0017] The solution shown in the present disclosure continuously adjusts the radius of other layers of dielectric rods through simulation software, and finds that when the radius of other layers of dielectric rods is between 3.52um and 3.60um, the transmission loss generated at 976nm is relatively low, while the transmission loss generated at 1030nm is relatively large. The transmission losses of the two differ by tens or even hundreds of dB / m. The greater the transmission losses of the two, the better the filtering effect of the optical fiber. It can be seen that when the radius of other layers of dielectric rods is between 3.52um and 3.60um, the optical fiber can have a good filtering effect.

[0018] In a possible implementation manner, in the other layers of dielectric rods, a distance A between two adjacent dielectric rods that do not pass through the defective core is in the range of 9um≤A≤12um.

[0019] The solution shown in the present disclosure continuously adjusts the above-mentioned spacing A through simulation software, and finds that when the spacing A is between 9um and 12um, the transmission loss generated at 976nm is relatively low, while the transmission loss generated at 1030nm is relatively large. The transmission losses of the two differ by tens or even hundreds of dB / m. The greater the transmission losses of the two, the better the filtering effect of the optical fiber. It can be seen that when the spacing A is between 9um and 12um, the optical fiber can have a good filtering effect.

[0020] In a possible implementation manner, the diameter D of the fiber core is in the range of 20um≤D≤25um.

[0021] In the solution shown in the present disclosure, regarding the diameter of the fiber core, generally, the larger the diameter of the fiber core, the larger the mode field radius under the fundamental mode, and the larger the output spot radius. A large mode field can be achieved by increasing the radius of the fiber core, but increasing the radius of the fiber core will introduce higher-order modes, so it is difficult for traditional all-solid photonic bandgap fibers to achieve both large mode field and single-mode output.

[0022] The optical fiber of this solution can couple the high-order modes in the core to the defective core in the cladding for transmission, so the radius of the core can be appropriately made larger. Therefore, the optical fiber of this solution can take into account both large mode field and single-mode output.

[0023] The solution shown in the present disclosure is continuously optimized and verified through simulation software, and it is found that when the core diameter D of the optical fiber is between 20um and 25um, the transmission mode of its output laser is mainly the fundamental mode.

[0024] In a possible implementation manner, the number of layers of the dielectric rods is greater than or equal to three.

[0025] In the solution shown in the present disclosure, the number of layers of dielectric rods can be greater than or equal to three. For the convenience of introduction, three layers can be used as an example. This embodiment does not limit the number of layers of dielectric rods.

[0026] In a possible implementation, within the plane where the cross section of the optical fiber is located, the outermost dielectric rods form a hexagonal shape.

[0027] In the solution shown in the present disclosure, the shape formed by the dielectric rods of each layer can be a hexagon. For example, the number of dielectric rods is three, the number of dielectric rods in the outermost layer is eighteen, and in the plane where the cross section of the optical fiber is located, the eighteen dielectric rods form a hexagon, and each side of the hexagon includes four dielectric rods.

[0028] In a possible implementation, the number of the innermost dielectric rods is six, and within the plane where the cross section of the optical fiber is located, the innermost dielectric rods form a hexagonal shape.

[0029] In the solution shown in the present disclosure, the shape formed by the dielectric rods of each layer can be a hexagon. For example, the number of dielectric rods is three, the number of dielectric rods in the innermost layer can be six, and in the plane where the cross section of the optical fiber is located, the six dielectric rods form a hexagon, and each side of the hexagon includes two dielectric rods.

[0030] In a possible implementation, the number of the innermost dielectric rods is three, and within the plane where the cross section of the optical fiber is located, the innermost dielectric rods form a triangular shape.

[0031] The scheme shown in the present disclosure can still achieve the effect of mode filtering by changing the number of innermost dielectric rods. After simulation verification, in the scheme with three innermost dielectric rods, at 976nm, the transmission loss generated by fundamental mode transmission is lower than the transmission loss generated by the lowest loss high-order mode transmission, so the optical fiber still has a good mode filtering effect.

[0032] Among them, the high-order mode transmission mode of the laser includes many different high-order modes. The lowest loss high-order mode is the high-order mode with the lowest loss generated during transmission. If the transmission loss of the lowest loss high-order mode is relatively large, then the transmission loss of other high-order modes will be even greater.

[0033] In the solution shown in the present disclosure, according to the fundamental mode transmission mode, the transmission loss generated at 976nm is lower than the transmission loss generated at 1000nm, so the optical fiber still has a good filtering effect.

[0034] In a possible implementation, the number of the innermost dielectric rods is four, and within the plane where the cross section of the optical fiber is located, the innermost dielectric rods form a quadrilateral shape.

[0035] The scheme shown in the present disclosure can still achieve the effect of mode filtering by changing the number of innermost dielectric rods. After simulation verification, in the scheme with four innermost dielectric rods, at 976nm, the transmission loss generated by fundamental mode transmission is lower than the transmission loss generated by the lowest loss high-order mode transmission, so the optical fiber still has a good mode filtering effect. According to the fundamental mode transmission mode, the transmission loss generated at 976nm is lower than the transmission loss generated at 1000nm, so the optical fiber still has a good filtering effect.

[0036] On the other hand, a fiber laser is provided, the fiber laser comprising a pump source, a resonant cavity and the above-mentioned optical fiber;

[0037] The pump source is used to provide a light source;

[0038] The optical fiber is a gain medium, which is used to amplify light after absorbing the energy provided by the pump source;

[0039] The resonant cavity is an optical path located between the pump source and the optical fiber, and is used for oscillating and outputting laser light.

[0040] The fiber laser may be a 976 nm fiber laser.

[0041] The pump source may be a semiconductor laser, which is mainly used to complete the conversion of electrical energy into light energy to provide a light source.

[0042] Among them, the resonant cavity is the optical path located between the pump source and the optical fiber, which is used to oscillate the output laser and plays the role of "storing" and "purifying" the laser.

[0043] In the solution disclosed in the present invention, the optical fiber of the fiber laser, as described above, has a radius of the dielectric rod located in the innermost layer that is greater than the radius of the dielectric rods located in other layers, and the radius of the dielectric rod and the distance between two adjacent dielectric rods are adjusted through simulation software, so that the filtering effect of the optical fiber can be improved, so that the optical fiber has a good filtering effect.

[0044] The optical fiber has a good mode filtering effect because it can couple the high-order mode in the core to the defective core in the cladding for transmission. Therefore, even if the optical fiber introduces a beam of a high-order mode transmission mode because the mode field of the laser is increased by increasing the core, the beam of the high-order mode transmission mode can be coupled to the cladding for transmission and gradually attenuated, making the transmission mode in the core mainly the fundamental mode. Therefore, the optical fiber can take into account both the large mode field and single-mode output of the laser.

[0045] This optical fiber is applied to 976nm fiber lasers. Because it can filter out the 1030nm pump light, most of the light source provided by the pump source is used to pump the 976nm light, thereby improving the conversion efficiency of the fiber laser and outputting relatively pure high-power 976nm laser.

[0046] This fiber is applied to fiber lasers. Although its core is doped with Yb 3+ Although the refractive index increases, the mode filtering effect can still be achieved, thereby relaxing the restriction on the refractive index of the fiber core. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 is a schematic diagram of the structure of an optical fiber provided by the present disclosure;

[0048] Figure 2 is a schematic cross-sectional view of a fully solid photonic bandgap optical fiber provided by the present disclosure;

[0049] Figure 3 is a schematic diagram showing that the refractive index of a dielectric rod provided by the present disclosure varies with the radius of the dielectric rod;

[0050] Figure 4 is a schematic cross-sectional view of a defect-type all-solid photonic bandgap optical fiber provided by the present disclosure;

[0051] Figure 5 is a schematic cross-sectional view of a defect-type all-solid photonic bandgap optical fiber provided by the present disclosure;

[0052] Figure 6 is a schematic cross-sectional view of a defect-type all-solid photonic bandgap optical fiber provided by the present disclosure;

[0053] Figure 7 It is a schematic diagram of the relationship between the transmission loss and the wavelength when the radius of the innermost dielectric rod is in three sizes and the light is transmitted in the fundamental mode provided by the present invention;

[0054] Figure 8 yes Figure 7 The partial enlarged schematic diagram in the dotted frame;

[0055] Fig. 9 It is a schematic diagram of the relationship between the transmission loss and the wavelength when the radius of the other dielectric rod is in three sizes and the light is transmitted in the fundamental mode provided by the present invention;

[0056] Fig.10 yes Fig. 9 The partial enlarged schematic diagram in the dotted frame;

[0057] Fig.11It is a schematic diagram of the relationship between the transmission loss and the wavelength under three sizes of a spacing A provided by the present disclosure, with the fundamental mode as the transmission mode;

[0058] Fig.12 yes Fig.11 The partial enlarged schematic diagram in the dotted frame;

[0059] Fig.13 It is a schematic diagram of the relationship between transmission loss and wavelength in a fundamental mode transmission mode and a minimum loss high-order mode transmission mode provided by the present disclosure;

[0060] Fig.14 It is a schematic diagram of the relationship between transmission loss and wavelength in a fundamental mode transmission mode and a lowest-loss high-order mode transmission mode in a solution with three innermost dielectric rods provided by the present disclosure;

[0061] Fig.15 It is a schematic diagram of the relationship between transmission loss and wavelength in a fundamental mode transmission mode and a lowest-loss high-order mode transmission mode in a solution with four innermost dielectric rods provided by the present disclosure;

[0062] Fig.16 It is a schematic diagram of the relationship between the difference between the core refractive index and the equivalent refractive index of the cladding of an ytterbium-doped fiber core provided by the present disclosure, and the transmission loss varies with the wavelength under three values;

[0063] Fig.17 It is a schematic diagram of the relationship between the absorption and emission cross sections in an ytterbium-doped optical fiber provided by the present invention, respectively, varying with wavelength.

[0064] Legend

[0065] 1. Fiber core; 2. Cladding; 3. Coating layer; 4. Dielectric rod; 5. Defective core. DETAILED DESCRIPTION

[0066] Although the description of the present disclosure will be introduced in conjunction with some embodiments, this does not mean that the features of this application are limited to the implementation mode. On the contrary, the purpose of introducing the application in conjunction with the implementation mode is to cover other options or modifications that may be extended based on the claims of the present disclosure. In order to provide an in-depth understanding of the present disclosure, the following description will include many specific details. The present disclosure can also be implemented without using these details. In addition, in order to avoid confusion or blurring the focus of the present disclosure, some specific details will be omitted in the description. It should be noted that the embodiments in the present disclosure and the features in the embodiments can be combined with each other without conflict.

[0067] In the embodiments of the present disclosure, the terms "first", "second", "third", and "fourth" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, a feature defined as "first", "second", "third", and "fourth" may explicitly or implicitly include one or more of the features.

[0068] In the embodiments of the present disclosure, "and / or" is only a description of the association relationship of the associated objects, indicating that there may be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0069] In the description of the embodiments of the present disclosure, it should be noted that, unless otherwise clearly specified and limited, the terms "installation" and "connection" should be understood in a broad sense. For example, "connection" can be a detachable connection or a non-detachable connection; it can be a direct connection or an indirect connection through an intermediate medium. The directional terms mentioned in the embodiments of the present disclosure, such as "upper", "lower", "left", "right", "inside", "outside", etc., are only reference directions of the accompanying drawings. Therefore, the directional terms used are for better and clearer explanation and understanding of the embodiments of the present disclosure, 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 embodiments of the present disclosure. "Multiple" means at least two.

[0070] References to "one embodiment" or "some embodiments" etc. described in this specification mean that a particular feature, structure or characteristic described in conjunction with the embodiment is included in one or more embodiments of the present disclosure. Thus, the phrases "in one embodiment", "in some embodiments", "in some other embodiments", "in some other embodiments", etc. appearing in different places in this specification do not necessarily all refer to the same embodiment, but mean "one or more but not all embodiments", unless otherwise specifically emphasized in other ways. The terms "including", "comprising", "having" and their variations all mean "including but not limited to", unless otherwise specifically emphasized in other ways.

[0071] This embodiment relates to an optical fiber, which has a specific filter mode and filtering function. According to the functional classification of optical fibers, the optical fiber can be a single-mode filtering optical fiber. For example, the optical fiber can filter out the high-order modes (HOM) light beam from the fiber core, so that only the fundamental mode (FM) light beam is left in the fiber core, realizing the filter mode function, and then realizing the single-mode output of the optical fiber. The optical fiber can also reduce the transmission loss of the light beam in a specific band, and increase the transmission loss of the light beam outside the specific band, so that the optical fiber outputs a relatively pure light beam in frequency, realizing the filtering function.

[0072] Based on the mode filtering function of the optical fiber, the optical fiber can be used as a filter in the filtering field. For example, the optical fiber can also be used as a gain medium in a fiber laser (FL) to filter out the unnecessary bands from the required bands, thereby gaining the required bands, thereby increasing the conversion power and outputting a high-power, high-quality beam.

[0073] For example, the optical fiber can be used as a gain fiber for a 976nm fiber laser. Through the mode filtering effect of the optical fiber, the 976nm fiber laser can output high-power, high-quality 976nm laser light.

[0074] The optical fiber is used as a gain fiber of a 976nm fiber laser, and the specific wavelength band mentioned above is a wavelength band near 976nm.

[0075] Although all-solid photonic bandgap fibers are currently used to achieve mode filtering effects, the edge change of the bandgap of traditional all-solid photonic bandgap fibers is relatively gentle. For example, the transmission loss at 1000nm is only a few tenths of dB / m greater than the transmission loss at 976nm, resulting in poor filtering effects of traditional all-solid photonic bandgap fibers.

[0076] If the traditional all-solid photonic bandgap fiber is applied to the 976nm fiber laser, then due to the poor filtering effect of the light at 1030nm, the fiber laser will not only gain the 976nm light, but also the 1030nm light, resulting in low light-to-light conversion efficiency. Moreover, an additional filter needs to be arranged to filter the 1030nm after gain in order to output the 976nm laser.

[0077] The optical fiber shown in this scheme has a relatively narrow bandgap, and the transmission loss varies greatly at the edge of the bandgap. The transmission loss corresponding to the wavelength within the bandgap is much lower than the transmission loss corresponding to the wavelength outside the bandgap, thereby improving the filtering effect of the optical fiber.

[0078] This type of fiber is applied to 976nm fiber lasers. Because it has a better filtering effect on light at 1030nm, the fiber laser has less energy to gain 1030nm, and most of the energy is used to gain 976nm, so the light-to-light conversion efficiency can be improved. Moreover, since the fiber has filtered the light outside the bandgap relatively cleanly, there is no need to arrange additional filters to filter the light beam outside the bandgap.

[0079] The structural features of this optical fiber for achieving mode filtering will be introduced below.

[0080] like Figure 1 The figure is a schematic diagram of the structure of an optical fiber, which includes a core 1, a cladding 2 and a coating 3 arranged from the inside to the outside, wherein the core 1 and the cladding 2 are both made of quartz, and the coating 3 is made of plastic.

[0081] The filtering of the optical fiber can be achieved through the photonic bandgap effect, that is, the light of a specific wavelength band is captured in the fiber core 1 for transmission, while the light of other wavelengths is highly lost and cannot be transmitted.

[0082] In order to make the optical fiber have the photonic bandgap effect, the light guiding method of the optical fiber is photonic bandgap light guiding. According to the classification of light guiding methods, this optical fiber is called all-solid photonic bandgap fiber. All-solid photonic bandgap fiber means that regularly arranged high-refractive index dielectric rods are introduced into the cladding 2. At this time, the core destroys the periodic defects of the cladding structure, thereby realizing the photonic bandgap effect, so that light of a certain wavelength is captured in the core, while other wavelengths experience high loss and cannot be transmitted.

[0083] Among them, the all-solid photonic bandgap fiber has a bandgap, which is also called a forbidden band. The specific band mentioned above is also the bandgap of the all-solid photonic bandgap fiber.

[0084] In order to make the optical fiber into a fully solid photonic bandgap fiber, then, Figure 2 As shown, the optical fiber further includes a plurality of dielectric rods 4, each layer of dielectric rods includes a plurality of dielectric rods 4, and the plurality of dielectric rods 4 are regularly arranged in sequence from the inside to the outside along the radial direction to form a periodic structure. Figure 2 FIG. 1 is a schematic diagram of a cross section of an optical fiber. In the plane where the cross section of the optical fiber is located, the fiber core 1 is located in the area surrounded by multiple dielectric rods 4 in each layer of dielectric rods. For example, Figure 2 As shown, the fiber core 1 is located in the area surrounded by the innermost layer of dielectric rods, and in the two adjacent layers of dielectric rods, the inner layer of dielectric rods close to the fiber core 1 is located in the area surrounded by the outer layer of dielectric rods away from the fiber core 1, so that the fiber core 1 is located in the area surrounded by any layer of dielectric rods.

[0085] According to the arrangement rule of the multi-layer dielectric rods 4, a dielectric rod should be arranged at the position of the core 1, but it is occupied by the core 1. Therefore, the core 1 destroys the periodic defect of the cladding structure, so that the light of a specific band that cannot be transmitted from the periodic structure is captured and transmitted in the core 1. That is, the light falling within the band gap of the all-solid photonic bandgap optical fiber cannot be transmitted in the periodic structure formed by the multi-layer dielectric rods, but is captured and transmitted in the core 1.

[0086] In one example, regarding the material of the dielectric rod, the dielectric rod is a high refractive index dielectric rod. The reason for choosing a high refractive index dielectric rod is that the refractive index of the cladding 2 is close to the refractive index of the core 1. Adding a high refractive index dielectric rod to the cladding 2 can make the equivalent refractive index of the cladding 2 and the dielectric rod greater than the refractive index of the core 1, so that a light beam of a specific wavelength band can be confined in the core for transmission, thereby realizing the photonic bandgap effect.

[0087] In one example, the high refractive index dielectric rod may be a germanium-doped quartz rod, the refractive index at the outer boundary of which is close to the refractive index of quartz, and the refractive index at the middle position is higher than the refractive index of quartz, but the overall refractive index of the dielectric rod is higher than the refractive index of quartz. The relationship between the refractive index of the dielectric rod and its radius can be referred to Figure 3 As shown, Figure 3 The position where the radius is 0 is the center of the dielectric rod.

[0088] In an example, the number of layers of the dielectric rods may be greater than or equal to three. For ease of introduction, three layers may be used as an example. This embodiment does not limit the number of layers of the dielectric rods.

[0089] In one example, the shape formed by the dielectric rods of each layer may be a hexagon. Figure 2 As shown in the figure, there are three layers. The number of dielectric rods in the innermost layer can be six. In the plane where the cross section of the optical fiber is located, the six dielectric rods form a hexagon, and each side of the hexagon includes two dielectric rods. The number of dielectric rods in the middle layer can be twelve. In the plane where the cross section of the optical fiber is located, the twelve dielectric rods form a hexagon, and each side of the hexagon includes three dielectric rods. The number of dielectric rods in the outermost layer is eighteen. In the plane where the cross section of the optical fiber is located, the eighteen dielectric rods form a hexagon, and each side of the hexagon includes four dielectric rods.

[0090] In another example, Figure 5 As shown, the number of the innermost dielectric rods may also be three, and within the plane where the cross section of the optical fiber is located, the innermost dielectric rods form a triangular shape.

[0091] In another example, Figure 6As shown, the number of the innermost dielectric rods may also be four, and the innermost dielectric rods form a quadrilateral shape in the plane where the cross section of the optical fiber is located.

[0092] The filter mode of the optical fiber can be realized by defect coupling. For example, a defect core can be introduced in the cladding 2 to promote the coupling of the defect core of the cladding 2 with the high-order mode light beam transmitted in the core 1, so that the high-order mode light beam in the core 1 is coupled to the defect core of the cladding. Then, the high-order mode light beam is transmitted in the cladding. The loss of the high-order mode light beam itself is relatively large. Transmission in the cladding further aggravates its loss. Moreover, even if it cannot be completely lost, when the optical fiber of this embodiment is docked into a single-mode optical fiber, the light beam in the cladding will not enter the single-mode optical fiber, but will be completely filtered out.

[0093] Then, a defect core is introduced into the cladding 2, so that the optical fiber is a defect-type all-solid photonic bandgap optical fiber, such as Figures 4 to 6 As shown, there are a plurality of defective cores 5 between the innermost dielectric rod and the outer boundary of the cladding 2 .

[0094] Among them, defective core 5 is, reference Figure 4 As shown in the figure, in the periodic structure formed by the multilayer dielectric rods, if one of the dielectric rods in a certain layer is removed, a defect will be formed in the area surrounded by the adjacent dielectric rods at the location of the removed dielectric rod. Since the defect can transmit light within the forbidden band, it is called a defect core.

[0095] Therefore, regarding the formation of the defective core 5 in the cladding 2 , some dielectric rods 4 in the cladding 2 may be removed, and the defective core may be formed at the location of the removed dielectric rods 4 .

[0096] In one example, since the innermost dielectric rods 4 are used to cover the fiber core 1 to reduce the transmission loss of the fundamental mode light beam in the fiber core 1, some dielectric rods in other layers except the innermost dielectric rods 4 can be removed in forming the defective core 5.

[0097] For example, Figures 4 to 6 , and refer to Figure 2 As shown, some dielectric rods of the intermediate layer between the outermost layer and the innermost layer may be removed, e.g. Figure 4 As shown, the dielectric rods at two vertices on each side of the hexagon in the middle layer of dielectric rods can be removed, so that the surrounding dielectric rods form a defective core 5 at the position, thus obtaining six defective cores 5. Figure 4As shown, a dielectric rod should be arranged in the area between the sixth dielectric rod f and the third dielectric rod c in the second layer of dielectric rods, but no dielectric rod is arranged, so the area at this position surrounded by the surrounding adjacent dielectric rods forms a defective core, that is, the first dielectric rod a, the second dielectric rod b, the third dielectric rod c, the fourth dielectric rod d, the fifth dielectric rod e and the sixth dielectric rod f form a defective core 5.

[0098] In one example, it is also possible to flexibly select which dielectric rod in the middle layer to remove according to the arrangement of the dielectric rods in the innermost layer. For example, the dielectric rod in the middle layer that is opposite to the dielectric rod in the innermost layer may be removed.

[0099] like Figure 5 As shown, the number of dielectric rods 4 in the innermost layer is three, and each dielectric rod in the innermost layer is opposite to the dielectric rod at the vertex of the middle layer. Then, the dielectric rod at the vertex can be removed to form a defective core.

[0100] like Figure 6 As shown, the number of the innermost dielectric rods 4 is four, and the innermost dielectric rods are opposite to the dielectric rods at the middle position of the side length of the middle layer, so the dielectric rods at that position of the middle layer can be removed to form a defective core. The innermost dielectric rods are opposite to the dielectric rods at the apex of the middle layer, so the dielectric rods at that position of the middle layer can be removed to form a defective core.

[0101] In another example, the defective core 5 can also be formed by removing some dielectric rods in the outermost layer. For example, the cladding 2 includes relatively many layers of dielectric rods, such as six or seven layers of dielectric rods. The number of layers of dielectric rods is relatively large. Then, the defective core 5 can be formed by removing some dielectric rods in the outermost layer.

[0102] The present embodiment does not limit the formation position of the defective core.

[0103] In one example, if Figure 4 As shown, the radius of the innermost dielectric rod is larger than the radius of the other dielectric rods, while the radii of the other dielectric rods are equal. The relatively large radius of the innermost dielectric rod can better wrap the fiber core 1 therein, so that the light beam of a specific wavelength band can be better bound in the fiber core, thereby reducing the transmission loss of the light beam in the fiber core.

[0104] In one example, in order to make the optical fiber have a better filtering effect, the radius of the dielectric rod and the arrangement of the dielectric rod can be adjusted and optimized through simulation software. The arrangement of the dielectric rod mainly refers to the spacing between two adjacent dielectric rods, for example, Figure 4As shown, the spacing may be the spacing A between two adjacent dielectric rods in other layers of dielectric rods whose connecting line does not cross the defective core 5. Once the radius of the dielectric rods in other layers, the radius of the innermost dielectric rod, the spacing A and the diameter of the core are determined, the spacing between two adjacent dielectric rods in the innermost dielectric rod layer is also determined, so the spacing between two adjacent dielectric rods in the innermost dielectric rod layer is not described here.

[0105] Among them, the filtering effect is achieved by comparing the transmission loss caused by different transmission modes at the same wavelength. The greater the difference in transmission loss between the two, the better the filtering effect.

[0106] For example, at the same wavelength, if the loss caused by the light beam transmitting in the fundamental mode is lower than, or even much lower than, the loss caused by the light beam transmitting in the lowest loss high-order mode, then the optical fiber has a good mode filtering effect.

[0107] Among them, the high-order mode transmission mode of the laser includes many different high-order modes. The lowest loss high-order mode is the high-order mode with the lowest loss generated during transmission. If the transmission loss of the lowest loss high-order mode is relatively large, then the transmission loss of other high-order modes will be even greater.

[0108] The filtering effect is achieved by comparing the transmission losses of light beams of different wavelengths under the same transmission mode. The greater the difference in transmission losses between the two, the better the filtering effect.

[0109] For example, in the fundamental mode, if the transmission loss generated at 976nm is lower than, or even much lower than, the transmission loss generated at 1000nm, it means that the bandgap of the optical fiber is relatively narrow, the edge of the bandgap changes steeply, and it has a good filtering effect.

[0110] This kind of optical fiber with a narrow bandgap and a steep bandgap edge change can be applied to fiber lasers to improve the gain conversion efficiency and the quality of the output beam.

[0111] The bandgap is a wavelength band to which a specific wavelength band is allowed to pass through the core of the all-solid photonic bandgap optical fiber, for example, it may be a wavelength band at 976 nm.

[0112] Then, the following simulation target is to optimize the size and arrangement of the dielectric rods by taking the optical fiber outputting light of 976nm wavelength.

[0113] like Figures 7 to 16 As shown, it is a schematic diagram of simulation results under different conditions.

[0114] like Figure 7As shown in the figure, in the schemes where the radii of the innermost dielectric rod are 3.64um, 3.78um, and 3.9um respectively, the transmission is carried out in the fundamental mode. The relationship between the transmission loss and the wavelength is shown in the figure. Figure 8 Shown Figure 7 The enlarged diagram in the dotted box. Then, Figure 7 It can be seen that the transmission loss of the light beam near 976nm is low, while the transmission loss of the light beam near 1000nm increases sharply. The transmission loss difference between these two wavelengths is large. For example, the difference between the transmission loss of these two wavelengths can be as high as tens or even hundreds of dB / m. It can be seen that when the value range of the innermost dielectric rod radius R1 is 3.64um≤R1≤3.9um, the expected filtering effect can be achieved well.

[0115] In one example, R1 may select a value corresponding to a minimum transmission loss based on simulation results.

[0116] like Fig. 9 As shown in the figure, in the schemes where the radii of the outermost dielectric rods are 3.52um, 3.58um, and 3.60um respectively, the transmission is carried out in the fundamental mode. The relationship between the transmission loss and the wavelength is shown in the figure. Fig.10 Shown Fig. 9 The enlarged diagram in the dotted box. Then, Fig. 9 It can be seen that the transmission loss of the light beam near 976nm is low, while the transmission loss of the light beam near 1000nm increases sharply. The transmission loss difference between these two wavelengths is large. For example, the difference between the transmission loss of these two wavelengths can be as high as tens or even hundreds of dB / m. It can be seen that when the value range of the radius R2 of the outermost dielectric rod is 3.52um≤R2≤3.60um, the expected filtering effect can be achieved well.

[0117] In one example, R2 may select a value corresponding to a minimum transmission loss based on simulation results.

[0118] like Fig.11 As shown, in the other layers of dielectric rods, the spacing A between two adjacent dielectric rods 4 that do not pass through the defective core 5 is 9.5um, 10.5um, and 11.5um respectively. All are transmitted in the fundamental mode transmission mode. The schematic diagram of the relationship between the transmission loss and the wavelength is as follows, Fig.12 Shown Fig.11 The enlarged diagram in the dotted box. Then, Fig.11It can be seen that the transmission loss of the light beam near 976nm is low, while the transmission loss of the light beam near 1000nm increases sharply. The transmission loss difference between these two wavelengths is large. For example, the difference between the transmission loss of these two wavelengths can be as high as tens or even hundreds of dB / m. It can be seen that when the value range of the spacing A is 9.5um≤A≤11.5um, the expected filtering effect can be achieved well.

[0119] In one example, A may select a value corresponding to the minimum transmission loss based on simulation results.

[0120] In summary, when the radius R1 of the innermost dielectric rod is in the range of 3.64um≤R1≤3.9um, the radius R2 of the outermost dielectric rod is in the range of 3.52um≤R2≤3.60um, and the spacing A between two adjacent dielectric rods 4 that do not pass through the defective core 5 in other layers of dielectric rods is in the range of 9.5um≤A≤11.5um, the expected filtering effect can be well achieved.

[0121] It is also possible to verify through simulation software that the optical fiber has a filter mode effect under the above structural characteristics.

[0122] like Fig.13 As shown, the relationship between the transmission loss and the wavelength when the transmission is carried out according to the fundamental mode, and the relationship between the transmission loss and the wavelength when the transmission is carried out according to the lowest loss high-order mode.

[0123] in, Fig.13 In the simulation shown, the radius of the innermost dielectric rod can be a value in the range of 3.64um≤R1≤3.9um, the radius of the outermost dielectric rod can be a value in the range of 3.52um≤R2≤3.60um, the spacing A can be a value in the range of 9.5um≤A≤11.5um, and the diameter of the fiber core 1 can be a certain value.

[0124] like Fig.13 As shown, in the fundamental mode, the transmission loss of the light beam at 976nm is 2.59dB / m, and the transmission loss at 1030nm is as high as 213.09dB / m. The loss ratio between the two is 210dB. It can be seen that the optical fiber has a good filtering effect under the fundamental mode.

[0125] Continue to refer Fig.13 As shown, at 976nm, in the fundamental mode, the transmission loss is 2.59dB / m, and in the lowest loss high-order mode, the transmission loss is 52.59dB / m. The difference between the two is large, which shows that the optical fiber has a good mode filtering effect and can filter the light beam transmitted in the high-order mode.

[0126] The above simulation design is based on the number of innermost dielectric rods 4 being six, forming a hexagon in the plane where the cross section of the optical fiber is located, to wrap the fiber core. In fact, changing the number of innermost dielectric rods 4 can still achieve the effect of mode filtering.

[0127] like Fig.14 As shown, Figure 5 The optical fiber shown shows the relationship between the transmission loss and wavelength under fundamental mode transmission, and the transmission loss and wavelength under the lowest loss high-order mode transmission. Fig.14 It can be seen that at 976nm, the transmission loss generated by fundamental mode transmission is lower than the transmission loss generated by the lowest loss high-order mode transmission, so the optical fiber still has a good filtering effect. According to the fundamental mode transmission method, the transmission loss generated at 976nm is lower than the transmission loss generated at 1000nm, so the optical fiber still has a good filtering effect.

[0128] like Fig.15 As shown, Figure 6 The optical fiber shown shows the relationship between the transmission loss and wavelength under fundamental mode transmission, and the transmission loss and wavelength under the lowest loss high-order mode transmission. Fig.15 It can be seen that at 976nm, the transmission loss generated by fundamental mode transmission is lower than the transmission loss generated by the lowest loss high-order mode transmission, so the optical fiber still has a good filtering effect. According to the fundamental mode transmission method, the transmission loss generated at 976nm is lower than the transmission loss generated at 1000nm, so the optical fiber still has a good filtering effect.

[0129] In one example, regarding the diameter of the fiber core, generally, the larger the diameter of the fiber core, the larger the mode field radius under the fundamental mode, and the larger the output spot radius. Large mode field can be achieved by increasing the radius of the fiber core, but increasing the radius of the fiber core will introduce higher-order modes, so it is difficult for traditional all-solid photonic bandgap fibers to achieve both large mode field and single-mode output.

[0130] The optical fiber of this solution can couple the high-order modes in the core to the defective core in the cladding for transmission, so the radius of the core can be appropriately made larger. Therefore, the optical fiber of this solution can take into account both large mode field and single-mode output.

[0131] In an example, the core diameter D of the optical fiber may be in the range of 20 um≤D≤25 um.

[0132] In one example, since the dielectric rod 4 is arranged along the length of the optical fiber, mode filtering is performed at any position along the length of the optical fiber. Therefore, the optical fiber can achieve distributed filtering instead of filtering only at a certain position.

[0133] As mentioned above, the optical fiber can be used in an optical fiber laser. If the optical fiber is used in an optical fiber laser, rare earth elements need to be doped into the core of the optical fiber so that the optical fiber is called a gain medium, and the transmitted light is amplified. Amplifying the light means increasing the power of the light, so that the optical fiber laser can output high-power laser light.

[0134] For example, Yb can be doped into the core of the optical fiber. 3+ , and becomes ytterbium-doped fiber (ytterbium-doped fiber, YDF).

[0135] Theoretically, as Yb in ytterbium-doped fiber 3+ The increase in concentration will cause the refractive index of the fiber core to be higher than the equivalent refractive index of the cladding and dielectric rod, which will lead to total internal reflection light guidance and affect the photonic bandgap light guidance of the optical fiber. Therefore, in the relevant scheme, Yb is added to the fiber core. 3+ Later, some low-refractive-index substances, such as fluorine and aluminum, will be doped to lower the refractive index of the ytterbium-doped core to ensure that the refractive index of the core is highly close to the equivalent refractive index, such as keeping the refractive index of the two the same to four decimal places.

[0136] However, the optical fiber of this scheme adopts the structural features described above. After simulation verification, even if the refractive index of the core is 0.007 higher than the equivalent refractive index of the cladding and the dielectric rod, it can still achieve single-mode transmission at 976nm and high loss ratio filtering at 1030nm, thereby widening the gap between the core refractive index and the equivalent refractive index.

[0137] The equivalent refractive index of the cladding and the dielectric rod, that is, the dielectric rod is embedded in the cladding, and the cladding and the dielectric rod can be regarded as a whole, and the refractive index of the whole.

[0138] like Fig.16 As shown, when the difference between the core refractive index and the equivalent refractive index is +0.005, +0.007, and +0.01 respectively, all are transmitted according to the fundamental mode, and the resulting transmission loss varies with the wavelength.

[0139] Depend on Fig.16 It can be seen that the difference between the core refractive index and the equivalent refractive index is controlled within 0.007, and the optical fiber has a good filtering effect.

[0140] The optical fiber is used in 976nm fiber lasers, which can enable the fiber lasers to output high-power, high-quality 976nm lasers and improve conversion efficiency.

[0141] like Fig.17As shown in the figure, it is the relationship between the cross-section and wavelength of ytterbium-doped fiber. Ytterbium-doped fiber has emission peaks at both 976nm and 1030nm. Therefore, ytterbium-doped fiber can not only emit 976nm laser, but also absorb 976nm light and emit unnecessary 1030nm light. If the emitted 1030nm is not filtered out, it will continue to gain and produce high-power 1030nm laser, which will reduce the efficiency of the gain 976nm laser.

[0142] According to the above simulation results, the optical fiber of this scheme will produce a large transmission loss for the light beam near 1000nm, and filter out the laser near 1000nm. Therefore, the optical fiber of this scheme, when applied to the 976nm fiber laser, can filter out the emitted 1030nm laser and reduce the gain of 1030nm, so that most of the energy of the pump source of the fiber laser is used to gain 976nm, thereby improving the conversion efficiency.

[0143] Since the optical fiber of this solution can couple the high-order mode into the defective core, the core outputs the fundamental mode laser, and the fundamental mode laser has more concentrated energy and better beam quality, thereby improving the beam quality of the optical fiber.

[0144] It can be seen that the application of this optical fiber in the 976nm fiber laser can produce high-quality, high-power 976nm laser and improve the laser conversion efficiency.

[0145] In the disclosed embodiment, in the optical fiber, the radius of the dielectric rod located in the innermost layer is greater than the radius of the dielectric rods located in other layers, and the radius of the dielectric rod and the distance between two adjacent dielectric rods are adjusted through simulation software, which can improve the filtering effect of the optical fiber and make the optical fiber have good filtering effect.

[0146] The optical fiber has a good mode filtering effect because it can couple the high-order mode in the core to the defective core in the cladding for transmission. Therefore, even if the optical fiber introduces a beam of a high-order mode transmission mode because the mode field of the laser is increased by increasing the core, the beam of the high-order mode transmission mode can be coupled to the cladding for transmission and gradually attenuated, making the transmission mode in the core mainly the fundamental mode. Therefore, the optical fiber can take into account both the large mode field and single-mode output of the laser.

[0147] This optical fiber is applied to 976nm fiber lasers. Because it can filter out the 1030nm pump light, most of the light source provided by the pump source is used to pump the 976nm light, thereby improving the conversion efficiency of the fiber laser and outputting relatively pure high-power 976nm laser.

[0148] This fiber is applied to fiber lasers. Although its core is doped with Yb 3+Although the refractive index increases, the mode filtering effect can still be achieved, thereby relaxing the restriction on the refractive index of the fiber core.

[0149] The disclosed embodiment also provides a fiber laser, which includes a pump source, a resonant cavity and the optical fiber described above, wherein the pump source can be a semiconductor laser, which is mainly used to complete the conversion of electrical energy into light energy to provide a light source. The optical fiber is a gain medium, which is used to amplify the light after absorbing the energy provided by the pump source. The resonant cavity is an optical path located between the pump source and the optical fiber, which is used to oscillate and output laser light, and plays the role of "storing" and "purifying" the laser.

[0150] The fiber laser may be a 976 nm fiber laser.

[0151] As described above, the optical fiber of the fiber laser has a radius of the dielectric rod located in the innermost layer that is greater than the radius of the dielectric rods located in other layers. By adjusting the radius of the dielectric rod and the distance between two adjacent dielectric rods through simulation software, the filtering effect of the optical fiber can be improved, so that the optical fiber has a good filtering effect.

[0152] The optical fiber has a good mode filtering effect because it can couple the high-order mode in the core to the defective core in the cladding for transmission. Therefore, even if the optical fiber introduces a beam of a high-order mode transmission mode because the mode field of the laser is increased by increasing the core, the beam of the high-order mode transmission mode can be coupled to the cladding for transmission and gradually attenuated, making the transmission mode in the core mainly the fundamental mode. Therefore, the optical fiber can take into account both the large mode field and single-mode output of the laser.

[0153] This optical fiber is applied to 976nm fiber lasers. Because it can filter out the 1030nm pump light, most of the light source provided by the pump source is used to pump the 976nm light, thereby improving the conversion efficiency of the fiber laser and outputting relatively pure high-power 976nm laser.

[0154] This fiber is applied to fiber lasers. Although its core is doped with Yb 3+ Although the refractive index increases, the mode filtering effect can still be achieved, thereby relaxing the restriction on the refractive index of the fiber core.

[0155] The above description is only one embodiment of the present disclosure and is not intended to limit the present disclosure. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present disclosure should be included in the protection scope of the present disclosure.

Claims

1. An optical fiber, characterized in that: The optical fiber comprises a core (1), a cladding (2) and a multi-layer dielectric rod (4); The cladding (2) is coated on the outside of the fiber core (1), the multi-layer dielectric rods (4) are all located in the cladding (2), and in the plane where the cross section of the optical fiber is located, the fiber core (1) is located in the area surrounded by multiple dielectric rods (4) in each layer of dielectric rods (4), and the multi-layer dielectric rods (4) are arranged in sequence along the radial direction of the optical fiber; There are a plurality of defect cores (5) between the innermost dielectric rod (4) and the outer boundary of the cladding (2), and the radius of the innermost dielectric rod (4) is greater than the radius of the dielectric rods (4) in other layers.

2. The optical fiber according to claim 1, characterized in that The radius R1 of the innermost dielectric rod (4) has a value range of 3.64um≤R1≤3.9um.

3. The optical fiber according to claim 1 or 2, characterized in that: The radius R2 of the other layer of dielectric rods (4) has a value range of 3.52um≤R2≤3.6um.

4. The optical fiber according to any one of claims 1 to 3, characterized in that: In the other layers of dielectric rods (4), the distance A between two adjacent dielectric rods (4) that do not pass through the defective core (5) is within a range of 9um≤A≤12um.

5. The optical fiber according to any one of claims 1 to 4, characterized in that: The diameter D of the fiber core (1) is in the range of 20um≤D≤25um.

6. The optical fiber according to any one of claims 1 to 5, characterized in that: The number of layers of the dielectric rods (4) is greater than or equal to three.

7. The optical fiber according to any one of claims 1 to 6, characterized in that: In the plane where the cross section of the optical fiber is located, the outermost dielectric rods (4) form a hexagonal shape.

8. The optical fiber according to any one of claims 1 to 7, characterized in that: The number of the innermost dielectric rods (4) is six, and within the plane where the cross section of the optical fiber is located, the innermost dielectric rods (4) form a hexagonal shape.

9. The optical fiber according to any one of claims 1 to 7, characterized in that: The number of the innermost dielectric rods (4) is three, and within the plane where the cross section of the optical fiber is located, the innermost dielectric rods (4) form a triangular shape.

10. The optical fiber according to any one of claims 1 to 7, characterized in that: The number of the innermost dielectric rods (4) is four, and within the plane where the cross section of the optical fiber is located, the innermost dielectric rods (4) form a quadrilateral shape.

11. A fiber laser, characterized in that: The fiber laser comprises a pump source, a resonant cavity and the optical fiber according to any one of claims 1 to 10; The pump source is used to provide a light source; The optical fiber is a gain medium, which is used to amplify light after absorbing the energy provided by the pump source; The resonant cavity is an optical path located between the pump source and the optical fiber, and is used for oscillating and outputting laser light.

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