CN102819062A - Air hole square array fiber core annular doping four-core photonic crystal fiber - Google Patents

Abstract

The invention relates to an air hole square array fiber core annular doping four-core photonic crystal fiber, which comprises a fiber cladding and fiber cores, wherein the fiber cladding is formed by distributing a plurality of layers of air hole square arrays; the fiber core is formed by four groups of units lack of air holes; and the four fiber cores are symmetrically distributed at diagonal lines of four quadrants. Each fiber cores comprises an inner core and a doping annular area, wherein the inner core and the fiber cladding are made of quartz materials, and the doping annular area wrapped outside the inner core is made of quartz doped with an oxide capable of increasing a refractive index, so that the refractive index of the doping annular area is a little higher than that of the fiber core. With the adoption of the fiber core annular doping four-core structure, the mode area can be efficiently increased, and the nonlinear effect can be reduced. The fiber core annular doping can form a flat mode field, thereby efficiently reducing the thermal damage effects of the fiber. The fiber cladding is formed by distributing the plurality of layers of air hole square arrays, so that the ultralow limit loss can be realized, and the energy loss can be greatly reduced in the transmitting process.

Description

Translated fromChinese

一种空气孔正方形排列纤芯环状掺杂四芯光子晶体光纤A ring-doped four-core photonic crystal fiber with air holes arranged in a square core

技术领域technical field

本发明涉及一种空气孔正方形排列纤芯环状掺杂四芯光子晶体光纤，尤其涉及同时具有平顶模场、大模式面积和超低限制损耗的光子晶体光纤，属于光纤技术领域。The invention relates to a circularly doped four-core photonic crystal fiber with a square array of air holes, in particular to a photonic crystal fiber with a flat-top mode field, a large mode area and ultra-low confinement loss, and belongs to the field of optical fiber technology.

背景技术Background technique

高功率光纤激光器由于在效率、散热和光束质量等方面的优势，在工业加工、医疗和国防等领域具有广泛的应用前景。然而，拉曼散射、布里渊散射以及四波混频等非线性效应限制了高效率光纤激光器输出功率的进一步提高。非线性效应与光强之间有很大关系，通过提高光纤的模式面积可以有效的降低光强，进而对非线性效应产生抑制作用。光子晶体光纤（PCF），又被称为微结构光纤或多孔光纤，其结构设计灵活可调，这使得它具有许多传统光纤不具备的特性，如高双折射、超低限制损耗、色散可调等等。此种光纤的发明为实现大模式面积提供了一种非常有效的办法。Due to its advantages in efficiency, heat dissipation and beam quality, high-power fiber lasers have broad application prospects in the fields of industrial processing, medical treatment and national defense. However, nonlinear effects such as Raman scattering, Brillouin scattering, and four-wave mixing limit the further improvement of the output power of high-efficiency fiber lasers. There is a great relationship between the nonlinear effect and the light intensity. By increasing the mode area of the fiber, the light intensity can be effectively reduced, thereby inhibiting the nonlinear effect. Photonic crystal fiber (PCF), also known as microstructure fiber or holey fiber, has flexible and adjustable structural design, which makes it have many characteristics that traditional fibers do not have, such as high birefringence, ultra-low confinement loss, and adjustable dispersion etc. The invention of this kind of optical fiber provides a very efficient way to achieve large mode area.

已有研究证明，对光子晶体光纤的石英纤芯进行掺杂，掺杂ZrO₂、TiO₂、Al₂O₃、GeO₂、P₂O₅等材料可以使石英玻璃的折射率增加（高掺杂），掺杂B₂O₃、F等原料可以使石英玻璃的折射率降低（低掺杂），掺杂后的光纤能够获得更大的模式面积，但是目前这种掺杂技术仅仅局限于单芯光纤，限制了模式面积的进一步提高。如果采用多芯光纤，虽然与单芯光纤相比可以获得更大的模场面积，但从其每个纤芯来看，输出光束均为传统的高斯光束，当泵浦光功率较大时，很容易损伤光纤端面。Studies have proved that doping the silica core of photonic crystal fiber, doping ZrO₂ , TiO₂ , Al₂ O₃ , GeO₂ , P₂ O₅ and other materials can increase the refractive index of silica glass (highly doped doping), doping B₂ O₃ , F and other raw materials can reduce the refractive index of silica glass (low doping), and the doped optical fiber can obtain a larger mode area, but at present this doping technology is limited to Single-core fiber limits the further improvement of the mode area. If a multi-core fiber is used, although a larger mode field area can be obtained compared with a single-core fiber, from the perspective of each fiber core, the output beam is a traditional Gaussian beam. When the pump light power is large, It is easy to damage the fiber end face.

发明内容Contents of the invention

本发明目的在于提供一种同时具有大模场面积、低限制损耗和平顶模式的一种空气孔正方形排列纤芯环状掺杂四芯光子晶体光纤。The purpose of the present invention is to provide a circularly doped four-core photonic crystal optical fiber with square air holes arranged in a core with large mode field area, low confinement loss and flat-top mode.

本发明主要是采用四芯光子晶体光纤并对纤芯进行掺杂，同时又设计合理的包层空气孔结构参数。The invention mainly adopts four-core photonic crystal fiber and dopes the fiber core, and at the same time designs reasonable air hole structure parameters of the cladding layer.

本发明的光子晶体光纤的主要结构是由四个纤芯和光纤包层组成的。其中，光纤包层内设有均匀的多层正方形阵列分布的空气孔，空气孔直径d=4μm，两孔间距Λ=10μm。由四组缺失3′3个空气孔的单元构成纤芯，四个纤芯对称地分布在空气孔方阵即四个象限的对角线上。其中，每个纤芯由纯石英内芯和折射率高的掺杂环形区域组成，其中石英内芯的半径ra在6~10μm范围。而包在内芯外面的高掺杂环形区域是在石英内掺杂了增加折射率的氧化物—二氧化锗，并且掺杂的摩尔百分数为4.11%~4.38%，使折射率（在1.4502~1.4506范围内）略高于石英内芯的折射率（1.45）。该高掺杂环形区域的外环半径rb=18μm，于是高掺杂环形区域圆环厚度为其外环半径rb与内环半径ra的差，即rb-ra，控制在8~12μm范围内。The main structure of the photonic crystal fiber of the present invention is composed of four fiber cores and fiber cladding. Among them, the optical fiber cladding is provided with air holes distributed in a uniform multi-layer square array, the diameter of the air holes is d=4μm, and the distance between two holes is Λ=10μm. The fiber core is composed of four groups of units missing 3'3 air holes, and the four fiber cores are symmetrically distributed on the diagonals of the air hole square array, that is, the four quadrants. Wherein, each fiber core is composed of a pure silica inner core and a doped annular region with a high refractive index, wherein the radius ra of the quartz inner core is in the range of 6-10 μm. The highly doped annular region wrapped outside the inner core is doped with germanium dioxide, an oxide that increases the refractive index, in the quartz, and the molar percentage of doping is 4.11%~4.38%, so that the refractive index (between 1.4502~ 1.4506 range) slightly higher than the refractive index of the quartz core (1.45). The outer ring radius rb of the highly doped ring region is 18 μm, so the ring thickness of the highly doped ring region is the difference between the outer ring radius rb and the inner ring radius ra, namely rb-ra, which is controlled within the range of 8-12 μm.

本发明与现有技术相比具有如下优点：Compared with the prior art, the present invention has the following advantages:

1、与单芯光纤相比四芯光子晶体光纤能够有效增大模式面积，能够承受更强的泵浦光，从而有效降低非线性效应的影响，大大提高光纤传输激光功率的阈值。1. Compared with single-core optical fiber, four-core photonic crystal fiber can effectively increase the mode area and withstand stronger pump light, thereby effectively reducing the influence of nonlinear effects and greatly increasing the threshold value of laser power transmitted by the fiber.

2、多层气孔正方形排列形成包层使得限制损耗很低，超低的限制损耗减少了传输过程中的能量损失，可以传输高功率。2. The multi-layer air holes are arranged in squares to form a cladding, which makes the confinement loss very low. The ultra-low confinement loss reduces the energy loss in the transmission process and can transmit high power.

3、由于对四个纤芯的环形区域进行了增大折射率的高掺杂，使得纤芯中环形区域的折射率高于内芯折射率，因此从此种光纤中输出的光束不再呈高斯状，而是平顶状分布，即输出光束为能量均匀分布的平顶模场，具有较低的峰值功率，大大提高了光纤的热损伤阈值，同时这种掺杂也可以使光纤获得更大的模式面积。3. Since the annular regions of the four cores are highly doped to increase the refractive index, the refractive index of the annular regions in the core is higher than that of the inner core, so the output beam from this fiber is no longer Gaussian shape, but a flat-top distribution, that is, the output beam is a flat-top mode field with uniform energy distribution, and has a lower peak power, which greatly improves the thermal damage threshold of the fiber. At the same time, this doping can also make the fiber obtain a larger the model area.

4、由纯石英内芯和高掺杂环形区域组成的纤芯使得这种光纤的有效模式面积随波长的增大而减小，而传统光纤或者光子晶体光纤的有效模式面积随波长的增大而增大。这也是本发明的一个独特之处。4. The core composed of pure silica core and highly doped ring region makes the effective mode area of this fiber decrease with the increase of wavelength, while the effective mode area of traditional optical fiber or photonic crystal fiber increases with wavelength And increase. This is also a unique feature of the present invention.

附图说明Description of drawings

图1         是本发明实施例1的光子晶体光纤横截面图。Fig. 1 is a cross-sectional view of a photonic crystal fiber according toEmbodiment 1 of the present invention.

图2         是本发明实施例1的光子晶体光纤模场分布图。Fig. 2 is a distribution diagram of the mode field of the photonic crystal fiber inEmbodiment 1 of the present invention.

图3         是本发明实施例1光子晶体光纤的有效模式面积和限制损耗随波长变化关系图。Fig. 3 is a graph showing the relationship between the effective mode area and the confinement loss of the photonic crystal fiber inEmbodiment 1 of the present invention as a function of wavelength.

图4         是本发明实施例2光子晶体光纤的有效模式面积和限制损耗随波长变化关系图。Fig. 4 is a graph showing the relationship between the effective mode area and confinement loss of the photonic crystal fiber according toEmbodiment 2 of the present invention as a function of wavelength.

图5         是本发明实施例3光子晶体光纤的有效模式面积和限制损耗随波长变化关系图。Fig. 5 is a graph showing the relationship between the effective mode area and confinement loss of the photonic crystal fiber according to Embodiment 3 of the present invention as a function of wavelength.

图6         是本发明实施例4光子晶体光纤的有效模式面积和限制损耗随波长变化关系图。Fig. 6 is a graph showing the relationship between the effective mode area and confinement loss of the photonic crystal fiber according to Embodiment 4 of the present invention as a function of wavelength.

具体实施方式Detailed ways

实施例1Example 1

在图1所示的本发明实施例1的光子晶体光纤横截面图中，该光纤主要是由纤芯和光纤包层组成的。其中，光纤包层1内有13′13-3′3′4=133个均匀的正方形阵列的空气孔2，空气孔直径d=4μm，两孔间距Λ=10μm。四组缺失3′3个空气孔的单元构成纤芯，四个纤芯对称地分布在四个象限的对角线上。每个纤芯包括有内芯3和掺杂的环形区域4，其中内芯为石英材质，其半径ra=6μm，而包在内芯外面的高掺杂环形区域为石英基掺杂了摩尔百分比为4.25%的二氧化锗，使其折射率为1.4504，略高于石英内芯的折射率1.45。上述高掺杂环形区域的厚度为其外环半径rb(为18μm)与内环半径ra的差，rb-ra=18-6=12μm。In the cross-sectional view of the photonic crystal fiber inEmbodiment 1 of the present invention shown in FIG. 1 , the fiber is mainly composed of a core and a cladding. Wherein, there are 13'13-3'3'4=133air holes 2 in a uniform square array in theoptical fiber cladding 1, the diameter of the air holes is d=4 μm, and the distance between two holes Λ=10 μm. Four groups of units lacking 3'3 air holes constitute the core, and the four cores are symmetrically distributed on the diagonals of the four quadrants. Each fiber core includes an inner core 3 and a doped annular region 4, wherein the inner core is made of quartz with a radius of ra=6μm, and the highly doped annular region wrapped outside the inner core is quartz-based doped with a molar percentage It is 4.25% germanium dioxide, which makes its refractive index 1.4504, which is slightly higher than the refractive index of 1.45 of the quartz inner core. The thickness of the highly doped annular region is the difference between the outer radius rb (18 μm) and the inner radius ra, rb-ra=18-6=12 μm.

在图2所示的本发明实施例1的光纤在1.55 μm处的模场分布图中，从图中可以看出，各个纤芯输出的激光能量相同，并且在纤芯区域均匀分布，形成平顶模场。In the mode field distribution diagram of the optical fiber in Example 1 of the present invention shown in Figure 2 at 1.55 μm, it can be seen from the figure that the laser energy output by each fiber core is the same, and is uniformly distributed in the fiber core area, forming a flat Top mold field.

在图3所示的本发明实施例1光纤的有效模式面积和限制损耗随波长的变化关系图中，该光纤的有效模式面积在2900 μm²以上，属于大模式面积光纤，并且随着波长的增大其有效模式面积减小，在光通信的低损耗传输窗口λ=1.55 μm处，其有效模式面积为3107 μm²。在整个计算波长范围内，该光纤的限制损耗都极低。在传输窗口λ=1.55 μm处，它的限制损耗为9.71′10^-6 dB/km。In Fig. 3, which shows the relationship between the effective mode area and confinement loss of the optical fiber of Example 1 of the present invention as a function of wavelength, the effective mode area of the optical fiber is above 2900^μm2 , which belongs to a large mode area fiber, and increases with the wavelength Increasing its effective mode area decreases, and its effective mode area is 3107 μm² at the low-loss transmission window of optical communication λ=1.55 μm. The confining loss of this fiber is extremely low over the entire calculated wavelength range. At the transmission window λ=1.55 μm, its limiting loss is 9.71′10^-6 dB/km.

实施例2Example 2

本发明实施例2与实施例1基本相同，不同之处在于掺杂二氧化锗的摩尔百分比减小到4.11%（对应折射率1.4502），其有效模式面积和限制损耗随波长的变化关系如图4所示。从图中可以看出，该光纤与实施例1光纤相比，获得了较小的有效模式面积和更高的限制损耗。在λ=1.55 μm处，其有效模式面积为2934μm²，限制损耗为1.42′10^-4 dB/km。Example 2 of the present invention is basically the same as Example 1, except that the molar percentage of doped germanium dioxide is reduced to 4.11% (corresponding to a refractive index of 1.4502), and the relationship between the effective mode area and confinement loss with wavelength is shown in the figure 4. It can be seen from the figure that, compared with the fiber in Example 1, the optical fiber has a smaller effective mode area and higher confinement loss. At λ=1.55 μm, its effective mode area is 2934μm² , and the limiting loss is 1.42′10^-4 dB/km.

实施例3Example 3

本发明实施例3与实施例1基本相同，不同之处在于掺杂二氧化锗的摩尔百分比增加到4.38%（对应折射率1.4506），其有效模式面积和限制损耗随波长的变化关系如图5所示。从图中可以看出，该光纤与第一实施例光纤相比获得了更大的有效模式面积和更低的限制损耗。在λ=1.55 μm处，其有效模式面积为3244μm²，限制损耗为1.32′10^-6 dB/km。Example 3 of the present invention is basically the same as Example 1, except that the molar percentage of doped germanium dioxide is increased to 4.38% (corresponding to a refractive index of 1.4506), and the relationship between the effective mode area and confinement loss as a function of wavelength is shown in Figure 5 shown. It can be seen from the figure that the optical fiber has a larger effective mode area and lower confinement loss than the optical fiber of the first embodiment. At λ=1.55 μm, its effective mode area is 3244μm² , and the limiting loss is 1.32′10^-6 dB/km.

实施例4Example 4

本发明实施例4与实施例1基本相同，不同之处在于内纤芯半径r_a增加到10μm，则掺杂圆环部分的厚度r_b-r_a=18-10=8μm，其有效模式面积和限制损耗随波长的变化关系如图6所示。从图中可以看出，该光纤与实施例1光纤相比，获得了更大的有效模式面积，但是限制损耗也有所增加。在λ=1.55 μm处，其有效模式面积为3395μm²，限制损耗为1.02′10^-4 dB/km。Embodiment 4 of the present invention is basically the same asEmbodiment 1, except that the inner core radius r_a is increased to 10 μm, then the thickness of the doped ring part r_b -r_a =18-10=8 μm, and its effective mode area The relationship between the limit loss and the wavelength is shown in Figure 6. It can be seen from the figure that, compared with the fiber in Example 1, the optical fiber has a larger effective mode area, but the confinement loss has also increased. At λ=1.55 μm, its effective mode area is 3395μm² , and the limiting loss is 1.02′10^-4 dB/km.

Claims (2)

Translated fromChinese

1.一种空气孔正方形排列纤芯环状掺杂四芯光子晶体光纤，它是由纤芯和光纤包层组成的，其特征在于：光纤包层内设有均匀的多层正方形阵列分布空气孔，空气孔直径d=4μm，两孔间距Λ=10μm，由四组缺失3′3个空气孔的单元构成纤芯，四个纤芯对称地分布在四个象限的对角线上，每个纤芯由纯石英内芯和折射率高的掺杂环形区域组成，其中石英内芯的半径r_a在6~10μm，高掺杂的环形区域的外半径r_b=18μm，掺杂区域圆环的厚度即r_b-r_a控制在8~12μm内。1. A square arrangement of air holes in the core annularly doped four-core photonic crystal fiber, which is composed of a core and an optical fiber cladding, is characterized in that: the optical fiber cladding is provided with a uniform multi-layer square array distribution of air Holes, the air hole diameter d=4μm, the distance between two holes Λ=10μm, the core is composed of four groups of units missing 3′3 air holes, and the four cores are symmetrically distributed on the diagonals of the four quadrants, each A fiber core is composed of a pure silica core and a doped annular region with a high refractive index, wherein the radius r_a of the quartz inner core is 6-10 μm, the outer radius r_b of the highly doped annular region is 18 μm, and the doped region is circular The thickness of the ring, that is, r_b -r_a, is controlled within 8~12 μm.2.根据权利要求1所述的一种空气孔正方形排列纤芯环状掺杂四芯光子晶体光纤，其特征在于：包在内芯外面的高掺杂环状区域是由石英内掺杂二氧化锗形成，掺杂的摩尔百分数控制在4.11%~4.38%，相应的使其折射率控制在1.4502~1.4506的范围内，略高于石英内芯的折射率1.45。2. A kind of air hole square arrangement core annular doped four-core photonic crystal fiber according to claim 1, characterized in that: the highly doped annular region wrapped outside the inner core is made of quartz doped with two Germanium oxide is formed, and the molar percentage of doping is controlled at 4.11%~4.38%, and the corresponding refractive index is controlled within the range of 1.4502~1.4506, which is slightly higher than the refractive index of the quartz core at 1.45.

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