Bending dual-core photonic crystal fiber coupler

In this paper, we systematically study a designed structure of a bending dual-core photonic crystal fiber (PCF). We propose the controllable wavelength-selective coupling PCF. This coupler allows highly accurate control of the filtering wavelength. The different wavelengths can be selected by controlling the bending radius of the fiber. Coupling characteristics of novel bending wavelength-selective coupling PCF are evaluated by using a vector finite element method and their application to a multiplexer demultiplexer (MUX–DEMUX) based on the novel coupler is investigated. When the fiber length is 4168 μm, the bending radius of PCF couplers for 1.48/1.55 μm, 1.3/1.55 μm, 0.98/1.55 μm, and 0.85/1.55 μm is calculated, respectively, and the beam propagation analysis is performed. Different from the traditional wavelength-selective coupling PCF, the dual-core PCF is bent and it can realize the separation of multiple wavelengths.     

光子晶体光纤耦合器中的标量调制不稳定性

从光纤耦合器的耦合模方程出发,用偶奇超模对其进行重写,讨论了当输入条件使奇偶超模其中之一被单独激发时,在光子晶体光纤耦合器中的调制不稳定性.结果表明：光子晶体光纤耦合器中在正常和反常色散区均存在调制不稳定性,并且调制不稳定性与三阶色散项无关、与四阶色散项有关,给出了增益谱在不同色散区随输入功率的变化关系;当满足一定条件时,在光子晶体光纤耦合器中传播的准连续波可以分解成脉冲序列,由此可以分离和提取超短脉冲. 关键词： 光子晶体光纤耦合器 偶次超模 奇次超模 标量调制不稳定性     

Polarization-controlled dispersive wave redirection in dual-core photonic crystal fiber

The complex study of the polarization-controlled supercontinuum generation in a dual-core square lattice photonic crystal fiber made of multicomponent glass was accomplished. The fiber was excited by 100-fs pulses at a 1250-nm wavelength in the anomalous dispersion region and the registered spectra exhibited soliton fission and Raman-induced self-frequency shift processes. The study also involved a detailed analysis of the infrared-to-visible light conversion exhibiting a dispersive wave origin. The special dual-core properties were investigated by separate spectral analysis of each of the two cores and the near-field profile registration. The emphasis was on the visible part of the spectrum where the input energy and polarization direction dependences were studied. The increase in the input energy allowed for the tuning of the wavelength of the visible spectral features, a further rotation of the polarization direction had an effect on the spectral dependence of the light distribution between the cores. The dual-core fiber exhibited a significant coupling performance and the spectral dependence of the visible light distribution is in good agreement with the simulated coupling length spectral characteristics. Single-core excitation in the linear regime revealed the possibility of coupling 50% of the energy to the other core and the same polarization-controlled redirection possibilities as that at the nonlinear experiments. Dual-core excitation of the fiber enhances the light redirection effect with the application potential for the polarization-controlled directional coupler accompanied by nonlinear frequency conversion.     

Wavelength-selective coupling of dual-core photonic crystal fiber and its application

We investigate the coupling characteristics of photonic crystal fiber composed of two cores with different index profiles. The index curves of the fundamental modes of the two cores can cross at a desired wavelength by choosing appropriate index profiles of the cores. As a result, wavelength-selective coupling is achieved. The designed coupler can be applied as an oDtical fiber bandstop filter with 26-nm bandwidth.     

Enhanced sensitivity of hemoglobin sensor using dual-core photonic crystal fiber

A Hemoglobin (Hb) biosensor based on dual-core photonic crystal fiber is proposed and analyzed. In this paper, the effective refractive index dependency on the Hb concentration within a blood sample is utilized in obtaining the transmission spectrum variation. The results are calculated using full vectorial finite element method. Through this study, the effect of the structure geometrical parameters on the sensor performance is optimized to maximize the sensor sensitivity. The numerical results show a sensitivity of 8.013 nm/g/dL for the X-polarized mode at 3.7 cm fiber length and 7.68 nm/g/dL for the Y-polarized mode at 3.2 cm fiber length of the proposed sensor.     

Ultra-broadband polarization splitter based on graphene layer-filled dual-core photonic crystal fiber

An ultra-broadband polarization splitter based on graphene layer-filled dual-core photonic crystal fiber(GDC-PCF)that can work in a wavelength range from 1120 nm to 1730 nm is proposed in this paper. Through optimizing fiber configuration, the polarization splitter has an extinction ratio of-56.3 dB at 1.55 μm with a fiber length of 4.8 mm.Compared with the photonic crystal fiber reported splitters, to our knowledge, the GDC-PCF splitter with the extinction ratio below-20 dB has a super wide bandwidth of 610 nm. Due to the excellent splitting characteristics, the GDC-PCF will be used in coherent optical communication systems in a wavelength range from infrared to mid-infraed.     

Terahertz polarization splitter based on an asymmetric dual-core photonic crystal fiber

By employing the liquid crystal refractive index changes induced by applied electric field, a novel terahertz polarization splitter with tunable the operating frequency and bandwidths has been proposed and theoretically analyzed. It possesses an extinction ratio as high as the polarization splitters based on the two-dimensional photonic crystal waveguides. These distinguished features ensure its important applications in the integrated optical systems.     

All-optical switching and multifrequency generation in a dual-core photonic crystal fiber

We demonstrate all-optical switching at 1550 nm between two weakly coupled cores in a photonic crystal fiber for intensities up to 0.5 TW/cm2. Spectrum analysis at higher intensities reveals that the output was dominated by continuum generation primarily towards shorter wavelengths.     

新型超宽带双芯光子晶体光纤偏振分束器的研究

提出了一种新型超宽带双芯光子晶体光纤偏振分束器. 应用全矢量有限元法,系统地研究了光纤结构参数对偏振分束器带宽和偏振分束器长度的影响. 分析结果表明：增加掺氟区折射率,既能提高分束器带宽,也能减少分束器长度;增大光纤中空气孔的孔距及孔径与孔距比,可以增加分束器的带宽,但同时也会导致分束器的长度增大,使得器件尺寸增大. 因此,在设计中需兼顾分束器的带宽和长度来选取光纤的结构参数. 通过结构参数的优化,设计出一种短长度、高消光比和超宽带的偏振分束器,其长度为7.362 mm,消光比高于20 dB的带宽为600 nm. 关键词： 光子晶体光纤 偏振分束器 超宽带 全矢量有限元法     

Design of a polarization splitter for an ultra-broadband dual-core photonic crystal fiber

A novel ultra-broadband polarization splitter based on a dual-core photonic crystal fiber (DC-PCF) is designed. The full-vector finite element method and coupled-mode theory are employed to investigate the characteristics of the polarization splitter. According to the numerical results, a graphene-filled layer not only broadens the working bandwidth but also reduces the size of the polarization splitter. Furthermore, the fluorine-doped region and the germanium-doped region can broaden the bandwidth. Also, the 4.78 mm long polarization splitter can achieve an extinction ratio of -98.6 dB at a wavelength of 1550 nm. When extinction ratio is less than -20 dB, the range of the wavelength is 1027 nm-1723 nm with a bandwidth of 696 nm. Overall, the polarization splitter can be applied to all-optical network communication systems in the infrared and near-infrared wavelength range.     

A compact and low-loss polarization splitter based on dual-core photonic crystal fiber

The characteristics of a novel dual-core photonic crystal fiber are investigated. In the center of photonic crystal fiber, an energy transmission channel is introduced. The optimized photonic crystal fiber can be used for polarization splitter, which has a short length and low loss.     

Higher-order mode investigations by intermodal interference in a dual-core photonic crystal fiber

This article presents an investigation of the linear optical properties of a dual-core photonic crystal fiber with a square lattice made of a multicomponent glass in a second communication window. An experimental method based on intermodal interference was used to determine the effective refractive indices of higher-order modes, with knowledge of the fundamental mode dispersion. The effective refractive indices were also determined by an FDTD-based simulation and the obtained values provided a good agreement in comparison to the experimental results. The obtained results help to clarify the nonlinear spectral transformation processes observed in the same fiber at propagation in the higher-order modes.     

A novel polarization splitter based on dual-core elliptical-holes hybrid photonic crystal fiber

A novel kind of polarization splitter in dual-core elliptical holes hybrid photonic crystal fiber is proposed. Numerical results show that the splitter can reach small coupling length ratio of 0.5, for wavelength from 1.15 μm to 1.9 μm. At wavelength 1.55 μm, the extinction ratio can achieve ?64 dB and the 1.92-mm-long splitter is suggested to achieve extinction ratio better than ?10 dB, a bandwidth of 150 nm. The fiber has small coupling length ratio, small coupling length and high extinction ratio and it is more suitable for fabricating polarization splitter.     

Wavelength-selective coupling of dual-core photonic crystal fiber with a hybrid light-guiding mechanism

A novel class of wavelength-selective coupling photonic crystal fiber (PCF) that operates by a hybrid light-guiding mechanism has been proposed. Different from the traditional PCF coupler operating principle, this fiber coupler shares properties of both the total internal reflection index-guided and the photonic bandgap mechanism. This coupler allows highly accurate control of the filtering wavelength; both bandstop and bandpass filters can be easily implemented. The spectral transmission results demonstrate that the bandpass characteristic of the coupler is very narrow and free of sidelobes. Moreover, the operating wavelength and the coupling length can be continuously tuned by changing the refractive index of the filling material. This research gives a physical insight into the propagation mechanism in the PCF coupler and is crucial for future applications of the proposed device.     

Efficient photonic crystal directional couplers

We demonstrate highly efficient and spectrally flat broadband coupling in photonic crystal directional couplers. The result is obtained by use of a novel design with smaller holes between coparallel photonic crystal waveguides for efficient channel-to-channel coupling. The system studied is based on a planar hexagonal photonic crystal lattice of holes made in silicon-on-insulator material. Results from three-dimensional finite-difference time domain modeling are shown to closely match results measured on fabricated samples.     

太赫兹双芯光子带隙光纤定向耦合器

提出了一种低损耗、宽频段太赫兹双芯光子带隙光纤定向耦合器,光纤的包层由亚波长尺度呈三角晶格排列的空气孔组成, 两个纤芯分别由去掉7个空气孔构成.利用全矢量有限元法对光纤的色散、耦合特性以及损耗特性进行了理论分析. 研究表明,这种耦合器的损耗系数小于0.021 cm^-1,更重要的是可以实现0.14 THz范围内的宽频定向耦合. 这种定向耦合器在太赫兹通信系统中滤波、波分复用、偏振分离和开关等技术中有潜在的应用价值.     

Optical solitons switching in asymmetric dual-core nonlinear fiber couplers

With study on the switching characteristics in a asymmetric dual-core nonlinear fiber coupler, it is found the switch efficiencies when the dispersion values of two fibers have opposite signs are much higher than those when they have same signs. Meanwhile, when the dispersion values of two fibers have same signs, the switch efficiencies become much higher if the dispersion value of one core is decreased. In addition, the switch threshold power becomes lower than the one with the same sign if the nonlinearity coefficient of two fibers is opposite. The result shows that asymmetric coupler has much higher switch efficiencies and lower switch threshold power than symmetric coupler.     

Temperature characteristics of a core-mode interferometer based on a dual-core photonic crystal fiber

A core-mode Fabry–Perot (FP) interferometer is constructed by using a dual-core photonic crystal fiber (DCPCF). The FP cavity is formed by a single piece of DCPCF, which can also serve as a direct sensing probe without any additional components. We theoretically and experimentally studied its temperature responses in the range of 40–480 °C. The temperature sensitivity is 13 pm/°C which matches the theoretical results. Since the temperature sensitivity of the proposed sensor is independent on cavity length, precise control of the length of FP cavity or photonic crystal fiber is not required. The sensor size can be as short as 100–200 μm, and its fabrication only involves splicing and cleaving, which make the sensor production very cost-effective. The proposed FP interferometric sensor based on a DCPCF can find applications in high-temperature measurement especially those that need accurate point measurement with high sensitivity.