Nonlinear dual-core photonic crystal fiber couplers

We study nonlinear modes of dual-core photonic crystal fiber couplers made of a material with the focusing Kerr nonlinearity. We find numerically the profiles of symmetric, antisymmetric, and asymmetric nonlinear modes and analyze all-optical switching generated by the instability of the symmetric mode. We also describe elliptic spatial solitons controlled by the waveguide boundaries.     

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.     

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.     

High sensitivity plasmonic temperature sensor based on a side-polished photonic crystal fiber

A high sensitivity plasmonic temperature sensor based on a side-polished photonic crystal fiber is proposed in this work.In order to achieve high sensitivity and high stability,the gold layer is coated on the side-polished photonic crystal fiber to support surface plasmon resonance.The mixture of ethanol and chloroform is used as the thermosensitive liquid.The performances of the proposed temperature sensor were investigated by the finite element method(FEM).Simulation results indicate that the sensitivity of the temperature sensor is as high as 7.82 nm/℃.It has good linearity(R;=0.99803),the resolution of 1.1×10;℃,and the amplitude sensitivity of 0.1008℃;.In addition,the sizes of the small air hole and polishing depth have little influence on the sensitivity.Therefore,the proposed sensor shows a high structure tolerance.The excellent performance and high structure tolerance of the sensor make it an appropriate choice for temperature measurement.     

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     

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.     

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.     

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 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.     

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.     

High sensitivity dual core photonic crystal fiber sensor for simultaneous detection of two samples

The optical control ability of photonic crystal fiber (PCF) is a distinctive property suitable for improving sensing and plasma performance. This article proposes a dual-core D-channel PCF sensor that can detect two samples simultaneously, which effectively solves the problems of coating difficulty and low wavelength sensitivity. The PCF has four layers of air holes, which dramatically reduces the optical fiber loss and is more conducive to the application of sensors in actual production. In addition, by introducing dual cores on the upper and lower sides of the central air hole, reducing the spacing between the core and the gold nanolayer, a stronger evanescent field can be generated in the cladding air hole. The optical fiber sensor can detect the refractive index of two samples simultaneously with a maximum sensitivity of 21300 nm/RIU. To the best of our knowledge, the sensitivity achieved in this work is the highest sensitivity with the dual sample synchronous detection sensors. The detection range of the refraction index is 1.35-1.41, and the resolution of the sensor is 4.695×10^-6. Overall, the sensor will be suitable for medical detection, organic chemical sensing, analyte detection, and other fields.     

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.     

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.     

Highly sensitive octagonal photonic crystal fiber based sensor

In this study, a number of propagation characteristics of hexagonal and octagonal photonic crystal fiber (H-PCF and O-PCF) structures, where both core and cladding are microstructured have been investigated by employing the full vectorial finite element method (FEM). The confinement loss, the effective refractive index and the relative sensitivity coefficient behaviors of the O-PCF and the standard H-PCF are numerically investigated and compared. It is found that under the same design parameters O-PCF structure has significantly lower losses and higher relative sensitivity coefficient compared with H-PCF structure.