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.     

Nonlinear propagation effects in antiresonant high-index inclusion photonic crystal fibers

We experimentally and numerically investigate femtosecond-pulse propagation in a microstructured optical fiber consisting of a silica core surrounded by airholes that are filled with a high-index fluid. This fiber combines the resonant properties of hollow-core bandgap fibers and the high nonlinearity of index-guiding waveguides. A range of nonlinear optical effects can be observed, including soliton propagation, dispersive wave generation, and a Raman self-frequency shift. Tuning the center wavelength of the laser and varying the refractive index of the fluid lead to different propagation effects, mediated by the strongly wavelength-dependent group-velocity dispersion in these photonic bandgap confining structures.     

四方阵列聚苯乙烯/聚甲基丙烯酸甲酯微结构光纤的制造与光学特性

用聚苯乙烯光纤填充625孔聚甲基丙烯酸甲酯微结构光纤预制棒中的空气孔制备了新型微结构光纤预制棒.拉伸后得到了四方阵列聚苯乙烯/聚甲基丙烯酸甲酯微结构聚合物光纤.该光纤的纵方向可以作为传递图像介质,而纵截面上折射率的周期性结构可以作为透射光栅使用,该光栅产生的moiré条纹可以用于测量小角度移动.     

Polycarbonate hollow-core microstructured optical fiber

A hollow-core microstructured polymer optical fiber is fabricated from polycarbonate material and guidance by inhibited coupling in a two-layer structure is demonstrated in two strong transmission bands with minimum losses of 9.0 dB/m at 800 nm and 3.1 dB/m at 1550 nm. The latter corresponds to a loss well below the polycarbonate material loss at this wavelength, and to our knowledge it is the lowest loss hollow-core polymer fiber reported to date. The short-term operational temperature limit of the fiber is shown to be 135 degrees C, significantly higher than that of conventional polymer optical fibers made of other polymers.     

A Bragg-like chirped clad all-solid microstructured optical fiber with ultra-wide bandwidth for short pulse delivery and pulse reshaping

Chirped cladding is proposed as a novel tailoring tool to simultaneously attain wider transmission window and reduced temporal dispersion in an all-solid Bragg-like microstructured optical fiber as compared to its perfectly periodic cladding counterpart. This design route for photonic bandgap microstructured fibers could be exploited as an additional degree of freedom for bandgap engineering. A suitably chirped clad fiber could be gainfully exploited to deliver femto-second pulse with ultra wide bandwidth. Further, generation of self-similar parabolic profile pulse is demonstrated by simulating propagation of an input Gaussian pulse through a 2 m long sample of such a linearly tapered Bragg like fiber.     

Transmission of terahertz radiation using a microstructured polymer optical fiber

A hollow-core microstructured polymer optical fiber was analyzed in the terahertz (THz) region. Spectral analysis of time domain data shows propagation of THz waves in both the hollow-core and the microstructured cladding with a time delay of approximately 20 ps. The frequency range and shift of the transmission bands between different sized waveguides suggested photonic bandgap or resonant guidance. Finite-difference time domain calculations agree relatively well to the experimental transmission results. Propagation losses were estimated to be as low as 0.9 dB/cm.     

Depolarization of light in microstructured fibers filled with liquid crystals

In the paper we analyze microstructured optical fibers filled with typical nematic liquid crystals, i.e., 5CB and 6CHBT under influence of external electric field or temperature. We use the modified Mueller matrix method with an additional depolarization matrix to calculate degree of polarization changes of the light propagating in the liquid-crystal infiltrated microstructured optical fibers. Preliminary experimental results of light depolarization measurements during propagation in these microstructured fibers are also presented.     

Extruded high-NA microstructured polymer optical fibre

We report on use of billet ram extrusion for the first time to fabricate microstructured polymer optical fiber preforms. The shape and relative size of the air holes in the preform are well preserved during fiber drawing. Extrusion conditions have been optimized to prevent issues such as die swell and thermal degradation of the polymer material.     

Design of solid core photonic bandgap fibers for visible supercontinuum generation

We present a numerical study of two dimensional solid core photonic bandgap fiber design criteria for their particular application to blue/visible supercontinuum generation. By exploiting their strong frequency-dependent dispersion when compared to index guiding micro-structured fibers, we highlight the design of solid core photonic bandgap fibers to fulfill group index matching conditions between the first ejected optical soliton and the trapped dispersive wave generated in the visible wavelength range. We study how these matching conditions depend on the opto-geometrical parameters of the micro-structured cladding, and we use frequency-domain numerical simulations to determine the expected supercontinuum spectral characteristics for selected cases. We investigate design criteria to generate short wavelengths by pumping in such photonic bandgap fibers in different pulse duration regimes and we identify a novel class of short wavelength (blue/visible) supercontinuum generation in the 3rd bandgap of a typical structure by pumping into the 2nd bandgap through a high attenuation spectral region.     

Silica-air photonic crystal fiber design that permits waveguiding by a true photonic bandgap effect

A theoretical investigation of a novel type of optical fiber is presented. The operation of the fiber relies entirely on wave guidance through the photonic bandgap effect and not on total internal reflection, thereby distinguishing that fiber from all other known fibers, including recently studied photonic crystal fibers. The novel fiber has a central low-index core region and a cladding consisting of a silica background material with air holes situated within a honeycomb lattice structure. We show the existence of photonic bandgaps for the silica-air cladding structure and demonstrate how light can be guided at the central low-index core region for a well-defined frequency that falls inside the photonic bandgap region of the cladding structure.     

Highly polarization-dependent periodic coupling in mechanically induced long period grating over air-silica fibers

A very flexible and versatile tunable mechanical grating platform is introduced, with which highly polarization-dependent mode coupling is observed for three types of air-silica microstructured fibers: hollow core fiber, hexagonal-boundary holey fiber (HHF), and circular-boundary holey fiber. The resonances of gratings showed highly polarization-dependent broadband coupling compared with conventional single-mode fibers due to their unique beat-length dispersions between the core and the cladding modes, which could find applications in wideband polarization-dependent loss compensation. We further present significance of the spatial symmetry of HHF in distinct mode coupling for different rotation angles around the fiber axis.     

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.     

Microstructured polymer fiber laser

A microstructured polymer optical fiber doped with Rhodamine 6G dye was fabricated and demonstrated as an optical amplifier and a fiber laser. As an amplifier, the fiber achieved a gain in excess of 30 dB. As a pulsed fiber laser, the fiber exhibited a threshold of 20 microJ, a slope efficiency of 18%, and a lifetime as high as 130,000 shots at 10 Hz. The maximum output energy was 16 microJ. The advantages that such fibers offer lie in the simplicity and flexibility of their fabrication and in their potential for use as compact, tunable solid-state sources.     

Numerical analysis of hollow core photonic band gap fibers with modified honeycomb lattice

An accurate analysis of the air-guiding in hollow core photonic bandgap fibers with a modified honeycomb air-hole lattice has been carried out. The influence of the hollow core dimension, as well as of the cladding geometric parameters on the confinement loss, the nonlinear coefficient and the single-mode behaviour of the fibers has been investigated through a full-vector modal solver based on the finite element method. Simulation results have shown that confinement loss lower than 0.1 dB/km, a nonlinear parameter lower than 0.01 (W · km)^?1 and an effectively single-mode behaviour over a wavelength range of about 150 nm can be achieved with eight air-hole ring modified honeycomb fibers.     

圆形双芯微结构色散补偿光纤的色散特性分析

提出了一种圆形双芯微结构光纤,用频域有限差分法(FDFD),并对其色散特性进行了分析,并与前人提出的六边形双芯微结构色散补偿光纤进行了比较。结果表明:当圆形双芯微结构色散补偿光纤的高折射率区半径保持不变时,改变沿水平直径方向相邻空气洞中心点间的距离和空气洞的直径,能够控制有效模折射率的转折点,并在该处产生较大的负色散。由于圆形双芯微结构色散补偿光纤比六边形双芯微结构色散补偿光纤的有效模折射率对参数变化较为敏感,故前者更易于精确地控制转折点,达到色散补偿的目的。     

倏逝波型光纤气体传感器研究进展

介绍了倏逝波的概念和反映倏逝波光纤气体传感特性的穿透深度参数Z_m。讨论了D形、锥形、纤芯裸露形、纤芯失配型和微结构光纤等不同倏逝波型气体传感的原理和特点,评述了其最新研究进展,对比分析了各传感器的优缺点。对倏逝波型光纤气体传感器的发展趋势进行了展望。     

Microstructured fibers with highly nonlinear materials

We investigated the effect of modification of silica with high concentrations of germanium up to 36 mol% as well as with highly polarizable dopants (e.g., barium and lanthanum) on optical behavior of microstructured fibers. The goal was to investigate the influence of doping on several properties like fiber attenuation, supercontinuum generation and birefringence in microstructured optical fibers (MOF).     

Small-core single-mode microstructured polymer optical fiber with large external diameter

A preform sleeving technique is demonstrated that allows the fabrication of single-mode polymer microstructured fiber with the smallest core and hole dimensions yet reported to our knowledge. For a fixed triangular hole pattern a range of fibers is produced by adjustment to the operating conditions of the draw tower. Numerical modeling is carried out for one of the fibers produced with a 570-microm external diameter, a core diameter of 2.23 microm, an average hole diameter of 0.53 microm, and an average hole spacing of 1.38 microm. This fiber was shown to be endlessly single mode.     

Twisted clad microstructured optical fibers: revisited

The paper discusses confinements corresponding to low-order sustained hybrid modes in twisted clad microstructured optical fiber with twists in the form of conducting sheath helix structure introduced at the core–clad interface and inclined at certain angles. Dispersion relations for such fiber structures are deduced under strict electromagnetic boundary conditions. Varying the angle of pitch (of the introduced conducting sheath helix), investigations in respect of the dependence of power confinements due to the existing low-order hybrid modes have been carried out. The obtained results indicate the usefulness of such microstructured fibers for attenuation or amplification of power in the guide.