新型光学聚合物——Topas环烯烃共聚物微结构光纤的设计及特性分析

以新型光学聚合物Topas 环烯烃共聚物（折射率为1.53）为基质,设计了四种微结构聚合物光纤.应用有限元方法对各种光纤在波长0.5—2.0 μm范围内的基模有效折射率、模场面积和数值孔径进行了计算.研究了结构参数对模场分布、单模特性和色散特性的影响.得出了具有极大/小模场面积、无限单模传输和平坦近零色散的光纤结构参数.与石英、聚甲基丙烯酸甲酯基质的微结构光纤相比,该光纤具有更大的数值孔径和较宽的平坦近零色散范围.为光纤的制备提供了理论指导. 关键词： 微结构聚合物光纤 有限元方法 传输特性 Topas 环烯烃共聚物     

Miniature microstructured fiber coil with high magneto-optical sensitivity

Magneto-optic Faraday Effect in a miniature coil wound from a microstructured spun-type optical fiber is investigated theoretically and experimentally for the first time. It is shown that such a microstructured fiber allows one to efficiently accumulate the Faraday phase shift in a magnetic field even when the fiber is wound into a coil of very small diameter. For example, a fiber coil of diameter 5 mm with 100 turns has a magneto-optic sensitivity of about 70% of its “ideal” value and agrees well with theoretical data.     

Analysis of high birefringence photonic crystal fiber with octagonal and squarely lattice

Aiming at the requirement of high birefringence, a new kind of photonic crystal fiber (PCF) with octagonal and squarely lattice is proposed. In this structure, squarely lattices are added in the inner layer to obtain high birefringence. Birefringence and dispersion as a function of wavelength and size of PCF are analyzed by using Finite Element Method (FEM). Simulation results show that this kind of PCF exhibits high birefringence with a magnitude of 10^?3, and one zero dispersion point is obtained simultaneously. In addition, the characteristics of PCF can be tuned by changing the size of fiber.     

Structural and wavelength dependence of mode power distribution for a broadband dispersion compensating microstructured fiber

Approximate empirical analysis of mode power distribution (MPD) carried by the fundamental mode is newly investigated based on a broadband dispersion compensating microstructured fiber (MF). The fraction of modal power in the core region, η, is defined with the help of extending the applicability of well-established classical optical fiber theories to MFs. In doing so, the influences of structural parameters and wavelength on MPD characteristics of the fundamental mode are systematically analyzed in detail based on simple physically consistent concepts of conventional fibers. As a result, it is shown that for the optimum MF design in Ref. [11] as a multimode fiber, when the number of guiding modes increases, the mode power ratio of the fundamental mode constantly increases from 69.4%; in addition, we find that as wavelength increases within 1.2-1.6 μm, mode power confinement ability of the fundamental mode is lessened for single-mode propagation, whereas for multimode propagation it becomes enhanced.     

Maintaining single polarization and dispersion compensation with modified rectangular microstructure optical fiber

In this paper, we propose and numerically demonstrate a highly birefringent microstructure optical fiber which shows negative dispersion coefficient of about −288 to −550 ps/(nm km) covering S to L wavelength bands and −425 ps/(nm km) at the excitation wavelength 1550 nm. This proposed design successfully compensate the dispersion covering S to L communication bands ranging from 1460 to 1625 nm along with relative dispersion slope (RDS) perfectly matched to that of single mode fiber of about 0.0036 nm⁻¹. Apart from dispersion compensation, the designed MOF offers high birefringence of 2.94 × 10⁻² at 1550 nm and better compensation ratio with design simplicity due to circular air-holes in the fiber cladding.     

填充ENZ材料的太赫兹高双折射及近零平坦色散微结构光纤北大核心CSCD

为了实现太赫兹波的保偏波导传输,设计了一种含有纤芯缺陷孔和椭圆形包层空气孔的高双折射微结构光纤。通过在包层空气孔中选择性地填充太赫兹近零介电常量(epsilon-nearzero,ENZ)材料,引入了几何结构和材料分布的双重不对称性,破坏了2个偏振基模的简并以获得高双折射特性。应用有限元方法研究了光纤的双折射、损耗和色散等传输特性随结构参数的变化规律。在0.5 THz~2 THz的宽频段范围内获得了大于0.01的高双折射。x和y偏振基模的损耗在0.8 THz附近具有最小值,分别为0.903 dB·cm^(-1)和0.851 dB·cm^(-1)。纤芯缺陷孔可以有效调节色散特性,y偏振基模在1 THz~1.8 THz范围内具有(0±0.054)ps·THz^(-1)·cm^(-1)近零平坦色散特性。光纤的传输特性对ENZ材料的折射率变化不敏感。研究结论为研制太赫兹保偏光纤提供了理论参考。     

Cellulose acetate polymer film modified microstructured polymer optical fiber towards a nitrite optical probe

A novel microstructured polymer optical fiber (MPOF) probe for nitrites (NO₂⁻) detection was made by forming rhodamine 6G (Rh 6G)-doped cellulose acetate (CA) on the side wall of array holes in a MPOF. It was found that the MPOF probe only have a response to nitrites in a certain concentration of sulfuric acid solution. The calibration graph of fluorescence intensity versus nitrites concentration was linear in the range of 2.0 × 10^− 4 g/ml-5.0 × 10^− 3 g/ml. The method possesses ease of chemical modification, low cost design, and potential for direct integration with existing instrumentation, and has been applied to the determination of nitrites in real samples with satisfactory results.     

Design of single polarization single mode dispersion compensating photonic crystal fiber

In this paper, we present a photonic crystal fiber based on hexagonal structure for improved negative dispersion as well as high birefringence in the telecom wavelength bands. It is demonstrated that it is possible to obtain negative dispersion coefficient of −712 ps/(nm km) and relative dispersion slope (RDS) perfectly match to that of single mode fiber (SMF) of about 0.0036 nm⁻¹ at the operating wavelength 1550 nm. The proposed fiber exhibits high birefringence of the order 2.11 × 10⁻² with nonlinear coefficient about 57.57 W⁻¹ km⁻¹ at 1550 nm. Moreover, it is confirmed that the designed fiber successfully operates as a single mode in the entire band of interest.     

Design of a highly nonlinear twin bow-tie polymer photonic quasi-crystal fiber with high birefringence

A twin bow-tie polymer-based photonic quasi-crystal fiber with high birefringence, high nonlinearity and low dispersion as well as maintaining single mode operation is presented in the wavelength range 1.8–2.2 μm. Through optimizing fiber structure parameter using a full-vector finite-element method combined with perfectly matched layers boundary condition, the birefringence is as high as 2.43 × 10⁻³, the nonlinearity is as high as 118 W⁻¹ km⁻¹, and the dispersion is only 25 ps/nm/km at 2 μm with the holes pitch of 3.3 μm. From the point of fabrication, the influences of deviation of each air hole diameter are discussed to verify the robustness of the photonic quasi-crystal fiber designed.     

Oxygen gas optrode based on microstructured polymer optical fiber segment

In this article, we first propose a novel type of oxygen gas optrode by forming fluorophore doped sensing film in the array microholes with the characteristics of microstructured optical fiber (MOF) segment. Comparing with the conventional O₂ detecting method, this slender shaped optrode shows potential in trace amount of O₂ sensing and online O₂ monitoring. Organical silicate gel or plastified cellulose acetate are chosen as sensing films and tris (4,7-diphenyl-1,10-phenathroline) ruthenium(II) dichloride ([Ru(dpp)₃]Cl₂) or meso-tetraphenylporphyin (TPP) as quenching fluorophores. From the experimental results, we find [Ru(dpp)₃]²⁺-Gel-MOF optrode has favorable sensing characteristics, and the Stern-Volmer plots are linear in the full concentration range of O₂ (0-100% v/v). The ratio of I₀/I₁₀₀, where I₀ and I₁₀₀ respectively represents the fluorescence intensities of the optrode exposed to 100% N₂ and 100% O₂, as a sensitivity of the optrode is 10.8. Simultaneously, the optrode can make a quick response within 50 ms.     

A polymer photonic crystal fiber with high and flattened birefringence

A novel high birefringence polymer photonic crystal fiber (PCF) is proposed in this work. This PCF is composed of a polymer core and a cladding with elliptical air holes and squeezed triangular lattice. The high birefringence is introduced on the combined effect of elliptical air holes and the squeezed lattice. Our numerical results based on the supercell lattice method indicate that the birefringence can reach as high as 0.0018 at 650 nm wavelength with a properly designed cladding structure. We also analyze the dependence of the birefringence on structure parameters. And we design a PCF that has high and flattened birefringence.     

Coupling coefficient of two-core microstructured optical fiber

In this paper, coupled-mode theory is applied to a two-core microstructured optical fiber for the first time to calculate the coupling coefficients for different fiber structures by employing a simple effective index model approach. The dependence of the mode coupling properties upon the geometrical parameters of the two-core structures (air-hole arrangement, hole size, and pitch size) and wavelength are evaluated systematically. The effective index coupled-mode theory is compared with the finite-element method based super-mode theory in details and the results show good agreement. The coupling characteristics are proven to be insensitive to the longitudinal strain by considering the photoelastic effects.     

孔助光纤(Hole-assisted lightguide fiber)色散和双折射特性的研究

通过改变包层中空气孔的参数,孔助光纤（hole-assisted lightguide fiber）具有比传统光纤更容易调节的色散和双折射特性.采用有限差分法研究了包层空气孔数目、大小和位置等参数对孔助光纤色散和双折射特性的影响.数值计算结果表明：增加空气孔的数目和尺寸以及减小空气孔到纤芯的距离都能够使得零色散向短波长方向移动,减小空气孔与纤芯的距离有助于获得更大的双折射.     

微结构聚合物光纤中高双折射可调效应研究

通过在纤芯附近引入两个直径较大的空气孔诱导纤芯局部双折射,在包层减小x方向的孔间隔诱导包层双折射,设计实现了一种高双折射随波长可调效应的微结构光纤.采用全矢量平面波方法,以聚合物甲基丙烯酸甲酯为基材,对其偏振特性和基模模场进行了研究.结果发现,该光纤基模双折射在光通信波段呈现两个最大值,且最大双折射大小和位置随光纤结构和波长的变化可以进行调节.通过调节光纤结构参数,模拟得到了该光纤具有高双折射和零偏振模色散的最佳设计参数. 关键词： 导波与光纤光学 双折射可调 聚合物 全矢量平面波法     

Sol-gel matrix modified microstructured optical fibre towards a fluoride sensitive optical probe

In this article, we report an optical fluoride probe based on microstructured polymer optical fibers (MPOFs) which is modified with morin-Al complex doped silica gel film. This probe is fabricated by sol-gel fluxion coating process. Sol solution doped with morin-Al is directly inhaled into array holes of MPOF and then forms morin-Al-gel matrix film in them. The sensing probe shows different fluorescence intensity to different fluoride ion concentrations in the aqueous solution. The range of response is 5-50 mmol/L, under the condition of pH 4.6.     

Optimization of microstructured fibers with germanium-doped core for broad normal dispersion range

We have numerically studied different designs of technologically feasible microstructured fibers with a germanium-doped core in order to obtain normal dispersion reaching possibly far in the mid infrared. Hexagonal, Kagome and the combination of both geometries were numerically examined with respect to different constructional parameters like pitch distance, filling factor of air holes, number of layers surrounding the core, and level of germanium doping in the core. Our analysis showed that the broadest range of normal dispersion reaching 2.81?μm, while keeping an effective mode area smaller than 30?μm², was achieved for a hexagonal lattice and a 40?mol% GeO₂ doped core. The proposed fibers designs can be used in generation of a normal dispersion supercontinuum reaching the mid-IR region.     

热可调液晶填充微结构聚合物光纤设计及特性分析

通过在微结构聚合物光纤(mPOF)的包层空气孔中填充液晶材料获得了高度热可调的带隙型mPOF. 带隙随温度的增加发生显著的蓝移, 带隙上边界的温度灵敏度可达-5.5 nm/℃. 采用全矢量有限元方法对模场特性以及基模有效模场面积的分析结果表明, 该填充液晶的mPOF在带隙的中心波长附近具有大的有效模场面积, 和相同结构未填充液晶的mPOF连接时具有较高的功率耦合效率. 研究结论为mPOF在温度传感领域的应用及各种可调光纤器件的制备提供了理论参考.     

Design and analysis of a photonic crystal fiber with four-hole unit

A novel photonic crystal fiber (PCF) based on a four-hole unit is proposed in order to meet the requirements of high birefringence, negative dispersion and confinement loss in fiber-optic communication. The proposed design has been simulated based on the full vector finite element method (FVFEM) and anisotropic perfectly matched layers (APML). Analysis results show that the proposed PCF can achieve a high birefringence to the order of 10⁻² at the wavelength of 1.55 μm, a large negative dispersion over a wide wavelength range and confinement losses lower than 10⁻⁹ dB/m simultaneously, which has important applications in polarization-maintaining (PM) fibers, single-polarization single-mode (SPSM) fibers, dispersion compensation fibers and so on.     

低损耗高双折射太赫兹Topas光子带隙光纤

以太赫兹低损耗聚合物材料Topas环烯烃共聚物为基材,设计了一种带隙型光子晶体光纤.光纤由三角形排列的圆角正六边形空气孔构成包层,缺失四个近邻空气孔构成近菱形的二重对称空气芯.采用有限元法分析了该光纤在太赫兹波段的传输特性.结果表明:在1.5THz附近约0.3THz的宽频范围内存在光子带隙,光纤可以基于光子带隙效应将太赫兹波束缚在空气芯中传输.在1.4~1.6THz范围内具有10-3数量级的高双折射;x偏振基模和y偏振基模的损耗都小于0.1cm-1,分别在1.53THz和1.5THz处达到最小值0.029 1cm-1和0.028 7cm-1.所设计的太赫兹Topas光子带隙光纤具备结构简单、易制备、直径小而易弯曲的特点.     

A novel ultrahigh birefringent hole-assistant microstructured optical fiber with low confinement loss

A novel hole-assistant microstructured optical fiber with a rectangle-like core and four elliptical holes as cladding is proposed. By employing a full-vector finite element method, the modal birefringence and confinement loss are numerically investigated, and the results show that in such a structure, an ultrahigh modal birefringence of 2.91×10⁻² and a low confinement loss (<1 dB/km) can be simultaneously obtained at excited wavelength of 1.55 μm. It is significant that such a microstructured optical fiber is easily fabricated with its simple structure and exhibits improved performance.