Tunable highly birefringent solid-core photonic liquid crystal fibers

Experimental results of temperature-, electric field-, and hydrostatic-pressure-induced effects in solid-core highly birefringent photonic liquid crystal fibers are presented. Selective infiltration of the photonic crystal fibers with liquid crystals was found to induce birefringence axes switching resulting in a variety of tunable photonic liquid crystal fibers-based devices.     

Loss-reduced highly birefringent selectively liquid-filled photonic crystal fibers

We have theoretically investigated the birefringence and loss properties of the selectively liquid-filled photonic crystal fibers with the liquid asymmetrically infiltrated into one-line air holes along x-axis. A high birefringence value B = 1.74 × 10⁻³ can be achieved at λ = 1.55 μm. By varying the index of the infiltrating liquid, the birefringence values are shown to be well tuned. In addition, the confinement losses can be efficiently reduced by diminishing the number of liquid holes, which is quite useful for optical devices.     

Light propagation in highly birefringent photonic liquid crystal fibers

Photonic liquid crystal fibers have already been demonstrated as a promising perspective for creation of new classes of dynamically tunable optical fiber devices. By combining different geometries of photonic crystal fibers with a variety of different liquid crystals it is possible to obtain a new generation of fibers with dynamically tunable properties, e.g., transmission spectra, attenuation or dispersion. In this paper, tunable birefringence in a commercially available highly birefringent Blazephotonics PM-1550-01 photonic crystal fiber selectively filled with a low birefringence liquid crystal has been experimentally demonstrated. Theses experimental results have been compared with simulations based on the multipole method.     

Highly birefringent photonic crystal fibers

We report a strongly anisotropic photonic crystal fiber. Twofold rotational symmetry was introduced into a single-mode fiber structure by creation of a regular array of airholes of two sizes disposed about a pure-silica core. Based on spectral measurements of the polarization mode beating, we estimate that the fiber has a beat length of approximately 0.4 mm at a wavelength of 1540 nm, in good agreement with the results of modeling.     

Design of defect-core in highly birefringent photonic crystal fibers with anisotropic claddings

The influence of defect-core on the birefringence and confinement losses of rectangular-lattice photonic crystal fibers are investigated numerically by applying the multipole method. Numerical results illustrate that the birefringence in such fibers is determined not only by the arrangement of air holes in the cladding but also the shape of the core. It is found that asymmetry of the core represented by its rectangular shape implies a higher effective index of the mode that is parallel with the longer side of the rectangle, whereas the anisotropic rectangular-lattice cladding gives rise to just the opposite effect and thus the resulting birefringence can be controlled by a proper combinations of both mechanisms. In particular, effect of the asymmetry of the core on the birefringence is dominant for shorter wavelength. Increased birefringence and reduced confinement loss can be achieved, if we form the core by the omission of several air holes in a row to reduce its negative effect on the birefringence. On the other hand, when asymmetry is increased in the other direction, a negative birefringence at shorter wavelength can be achieved. This occurs due to the fact that asymmetry of the core at higher frequencies overcomes the effect of the asymmetric cladding. As a result, its possible to achieve zero birefringence in anisotropic cladding photonic crystal fiber with an asymmetric core.     

在双Lamder模型中实现可调控光子带隙

研究驻波场相干驱动下四能级双Lamder模型的电磁感应光子带隙.当耦合场是远共振或共振时,来自于两邻近能级间的自发辐射相干效应(SGC)有助于实现一个或两个光子带隙.当自发辐射相干效应不存在时,探测场被原子系统强烈吸收,因此导致光子带隙严重形变甚至无法形成.数值结果表明,光子带隙结构是由SGC效应导致探测场和耦合场之间的相干增强Kerr非线性调制而产生,并改变驻波场的耦合方式,使系统实现单光子带隙转变为双光子带隙的动态调控.     

在双Lamder模型中实现可调控光子带隙

研究驻波场相干驱动下四能级双Lamder模型的电磁感应光子带隙。当耦合场是远共振或共振时,来自于两邻近能级间的自发辐射相干效应(SGC)有助于实现一个或两个光子带隙。当自发辐射相干效应不存在时,探测场被原子系统强烈吸收,因此导致光子带隙严重形变甚至无法形成。数值结果表明,光子带隙结构是由SGC效应导致探测场和耦合场之间的相干增强Kerr非线性调制而产生,并改变驻波场的耦合方式,使系统实现单光子带隙转变为双光子带隙的动态调控。     

Analysis of air-guiding photonic bandgap fibers

We present what is to our knowledge the first theoretical analysis of air-guiding photonic bandgap fibers. The fibers are characterized by a large hollow core and a microstructured cladding exhibiting photonic bandgap effects. Using an efficient, full-vectorial numerical method, we explain the operational principle of the fibers and obtain detailed information about the properties of the air-guided modes. This information includes accurate determination of the modes' spectral extent, cutoff properties, and mode-field distributions.     

Soliton formation in hollow-core photonic bandgap fibers

The formation of solitons upon compression of linearly chirped pulses in hollow-core photonic bandgap fibers is investigated numerically. The dependence of soliton duration on the chirp and power of the input pulse and on the dispersion slope of the fiber is investigated, and the validity of an approximate scaling relation is tested. It is concluded that compression of input pulses of several ps duration and sub-MW peak power can lead to a formation of solitons with ∼100 fs duration and multi-megawatt peak powers. The dispersion slope of realistic hollow-core fibers appears to be the main obstacle for forming still shorter solitons.     

Progress in solid core photonic bandgap fibers

We investigate both experimentally and numerically confinement and bend losses in solid-core photonic bandgap fibers. We proposed two designs, based on the addition of air regions in the cladding, allowing these losses to be reduced significantly while keeping the optical properties of bandgap fibers. We also present and discuss numerical results on the impact of transversal defects on the fiber confinement loss in the case of a realistic low loss fiber.     

Directional coupling in twin-core photonic bandgap fibers

The frequency dependence of the coupling length in a twin-core photonic bandgap fiber is investigated numerically. In contrast to the case of index-guiding fibers, the coupling length exhibits a maximum if the cores are sufficiently well separated. The fiber design proposed is of interest for fabricating broadband tunable couplers.     

Modal properties of solid-core photonic bandgap fibers

The modal behavior of a 500-μm² mode area photonic bandgap fiber was theoretically and experimentally investigated. First, a full-vector finite element algorithm was used to predict the modal properties. Then, a low-coherence reflectometry technique was employed to measure the chromatic dispersion and evaluate the number of guided modes. A short length of fiber was found to guide only two LP modes with different attenuation coefficients. The measured chromatic dispersion of the fundamental mode was found in close agreement with theoretical value. The large positive dispersion is theoretically explained by the positive waveguide dispersion induced by weak a spectral variation of radial electric field distribution in Bragg fibers.     

Measurements of sensitivity to hydrostatic pressure and temperature in highly birefringent photonic crystal fibers

We report on experimental studies of polarimetric sensitivity to hydrostatic pressure and temperature in two highly birefringent index guided photonic crystal fibers, in which birefringence is induced by one row of the cladding holes with diameters smaller than the other cladding holes. The sensitivity measurements were carried out in the spectral range from 0.6 μm to 1.6 μm. Our results show that absolute value of the polarimetric sensitivity to hydrostatic pressure can reach 23 rad/MPa × m, which is almost one order of magnitude higher than in conventional fibers with elliptical core. Simultaneously, polarimetric sensitivity to temperature is at least two orders of magnitude lower than in conventional highly birefringent fibers. Moreover, we proved experimentally that one of the investigated fibers is completely insensitive to temperature at certain wavelength.     

基于高折射率断环结构的全固光子带隙光纤的设计

设计了基于断环结构的全固光子带隙光纤,其背景材料为熔石英而断环结构由若干掺杂的高折射率介质柱构成.基于平面波展开法计算得到的态密度图和Bloch模场分布表明,该种光纤中的一个高阶带隙可以得到调节并被极大展宽,带隙调节的基本原理是断环可以同时控制包层介质柱的线偏振模式的角向和径向模式阶数.研究表明,断环中的介质柱数目决定了受影响最小的一组线偏振模式的最高角向阶数,而带隙宽度受介质柱尺寸影响很大.这一宽的高阶带隙可以用来设计带隙中心分别在800和1550 nm、带宽分别为488和944 nm的全固光子带隙光纤 关键词： 全固光子带隙光纤 光子带隙 光纤设计 平面波展开法     

High group birefringence in air-core photonic bandgap fibers

A numerical investigation of group birefringence is carried out on a recently reported highly birefringent hollow-core photonic bandgap fiber by use of an efficient vector finite-element method. The hollow fiber core has an area as large as that of approximately four airholes in the cladding region and assumes a rhombic shape with round corners, and the airholes in the cladding region are hexagonal and provide a high air-filling fraction. Numerical results show very high group birefringence of the order of 10(-2) and phase birefringence of the order of 10(-3).     

Near-infrared Raman spectroscopy using hollow-core photonic bandgap fibers

We report a NIR Raman spectroscopy system incorporating hollow-core photonic bandgap fibers (HC-PBFs) in both the excitation and collection paths. Raman excitation was achieved at NIR laser wavelength of 785 nm. We demonstrate that using HC-PBFs, Raman spectroscopy can be performed without the use of an additional longpass filter on the collection side. A narrow bandpass filter on the excitation side is also not required. These results provide a framework where HC-PBF based Raman probes can be developed and used in space restricted biomedical and sensing applications.     

Doped photonic bandgap fibers for short-wavelength nonlinear devices

Microstructured photonic bandgap fibers with a doped honeycomb cladding structure and the guiding defect defined by the absence of doping are proposed as nonlinear optical fibers for short wavelengths. It is shown that zero-dispersion wavelengths below 500 nm and corresponding effective areas of 1-2 microm2 can be obtained if structures with interhole distances near 600 nm can be fabricated. The cutoff wavelength for guidance of second-order modes can be controlled by variation of the radius and index contrast of the doped regions.     

全固态光子带隙光纤第1带隙内模场分布特性

利用多极法计算了全固态光子带隙光纤第1带隙内不同波长处的基模模场分布,得到2维归一化光强分布特性.由于该光纤具有三角形(C<,6v>)的对称结构,影响了光纤内的模场分布,为此计算了该结构两个具有代表性的方向上的模场分布,分析了带隙内两个不同的结构方向上的模场分布特性.结果表明.在长波长区域,两个方向上的模场半径并不相等,但都随波长的增加而减小,其变化规律与全内反射导光的光纤不同.     

Coupling and decoupling of dual-core photonic bandgap fibers

Coupling characteristics of dual-core photonic bandgap fibers with triangular photonic crystal cladding are investigated by use of a vector plane-wave expansion method and a vector finite-element method. We demonstrate the eigenmodes and the coupling length for two orthogonal polarizations. A decoupling phenomenon is found at a certain wavelength in this fiber configuration. The decoupling effect is attributed to the effect of surface modes on the eigenmodes. The decoupling wavelength decreases as the ratio of core radius to cladding air-hole pitch increases from 1.05 to 1.15.     

Ultrasensitive UV-tunable grating in all-solid photonic bandgap fibers

We study the shift of a long period grating’s resonance wavelength with UV induced refractive index changes in an all-solid photonic bandgap fiber. A long period grating is mechanically imprinted in an all-solid photonic bandgap fiber with Germanium doped silica high-index rods in a lower-index silica background. The index of the high-index rods is modified through UV exposure, and we observe that the long period grating’s resonance shifts with the bandgaps. With a sensitivity of 21,000 nanometers per refractive index unit and a 8.8 nm resonance width changes of refractive index of 3 × 10⁻⁶ are in principle detectable