Structural analysis of photonic crystal fibers by side scattering of laser light

A side-scattering technique for investigating the inner microstructure of photonic crystal fibers (PCFs) is reported. Multiple scattering is reduced by filling the hollow PCF channels with index-matching fluid. The scattered signal is measured for fixed angles of incidence and detection while the fiber is rotated. A pattern of peaks, unique to each PCF, whether solid or hollow core, correlates closely with the symmetry planes of the PCF structure. As an example of the technique, the twist profile of a structural rocking filter is directly measured.     

Theoretical simulation of a novel birefringent photonic crystal fiber with surface plasmon resonance around 1300 nm

In this paper, a novel birefringent photonic crystal fiber(PCF) with the silver-coated and liquid-filled air-holes along the vertical plane is designed. Simulation results show that the thickness of silver layer, the sizes of holes, and the refractive index of liquid strongly strengthen the gaps between two polarized directions. The surface plasmon resonance peak along y axis can be up to 675.8 d B/cm at 1.33 μm. The proposed PCF has important application in polarization devices, such as filters and beam splitters.     

Polarization characteristics of chiral photonic crystal fibers with an elliptical hollow core

The theoretical study of dielectric-chiral photonic crystal fiber(PCF)with an elliptical hollow core is presented.The band structure of chiral photonic crystal(PhC)is calculated by using a modified plane-wave expansion(PWE)method.By examining the out-of-plane photonic bandgaps(PBGs)of chiral PhC,a kind of chiral PCF with a hollow core is designed and their eigenstates are calculated.The distributions of mode field and polarization state are demonstrated,and how the structural asymmetry of the core together with the chirality in the background affects the modal polarization is discussed.The dependences of birefringence on chirality for different ellipticities of core are investigated.     

Waveguide arrays in selectively infiltrated photonic crystal fibres

The periodic array of air holes in the cladding of a photonic crystal fibre (PCF) provides a convenient scaffold for the introduction of an infiltrating liquid. In this paper we demonstrate a novel platform of one-dimensional tuneable nonlinear photonic lattices produced by selectively infiltrating a row of holes in a PCF. Such structures have been realised by blocking individual holes on one end of a PCF, leaving the desired infiltration pattern unblocked. Unblocked holes are then infiltrated by immersing the unblocked end of the fibre in a reservoir of the infiltrating liquid, allowing for the realisation of a wide variety of periodic structures. Such structures are studied for traditional linear and nonlinear effects in periodic systems.     

Numerical Study on the Waveguiding Properties of Photonic Crystal Fibers

The photonic band structure, mode field distribution, and leakage loss of different photonic crystal fibers are studied by the full vectorial plane wave expansion method and an extended beam propagation method. A comparison on the waveguiding mechanism is conducted among solid-core triangular-lattice PCF, air-core honeycomb PCF, and solid-core honeycomb PCF. For the latter two structures, which conduct light by the photonic bandgap effect, the advantages of down-doped solid-core honeycomb structure are demonstrated for its Gaussian-like mode field distribution and low leakage loss. A combined study on the leakage loss and band structure of solid-core honeycomb PCF has revealed the distinctive properties of photonic bandgap effect.     

Study of non-linear properties of hollow core photonic crystal fiber

A highly non-linear hollow core photonic crystal fiber (PCF) having three ring-hexagonal structure is designed. The full vector finite element method with perfectly matched layer is used to investigate the non-linear properties of hollow core PCF effectively. The effective area of modal pattern is also studied for the same newly designed structure. It is found that when effective area is very small the non-linearity is very high.     

Methodology of splicing large air filling factor suspended core photonic crystal fibres

We report the methodology of effective low-loss fusion splicing a photonic crystal fibre (PCF) to itself as well as to a standard single mode fibre (SMF). Distinctly from other papers in this area, we report on the results for splicing suspended core (SC) PCF having tiny core and non-Gaussian shape of guided beam. We show that studied splices exhibit transmission losses strongly dispersive and non-reciprocal in view of light propagation direction. Achieved splicing losses, defined as larger decrease in transmitted optical power comparing both propagation directions, are equal to 2.71 ±0.25 dB, 1.55 ±0.25 dB at 1550 nm for fibre SC PCF spliced to itself and to SMF, respectively.     

Soliton-induced supercontinuum generation in liquid-filled photonic crystal fibre

We aim to study the nonlinear optical phenomena with ultra-broadband radiation in photonic crystal fibre (PCF). While PCFs with cores made from different glasses are well studied in previous works, in this paper, it is planned to investigate the dynamics of nonlinear processes of supercontinuum generation (SCG) in liquid-filled PCF (LCPCF) to understand the physical phenomena of femtosecond pulse propagation, particularly, the temporal and spectral changes of the pulse propagating through specific PCFs. Since the CS₂-filled LCPCF has complex nonlinear phenomena, we intend to analyse the role of saturable nonlinear response and slow nonlinear response on SCG in detail. For the physical explanation, soliton fission and modulational instability techniques will be implemented to investigate the impact of slow nonlinear response and saturable nonlinear response respectively, in SCG process.     

高双折射的混合格子太赫兹光子晶体光纤的设计与研究

提出了一种新型高双折射的混合格子太赫兹光子晶体光纤,通过对芯区亚波长尺寸的空气孔进行多种格子组合排列,增加结构的非对称性实现高的模式双折射. 全文仿真建模采用专业的有限元计算软件COMSOL Multiphysics 4.0,结果表明:混合格子太赫兹光子晶体光纤在很宽的频率范围内都具有较高的双折射(达到10^-2)和低的限制损耗,且通过改变光纤的某些参数可以灵活地控制其双折射或限制损耗特性. 相比于同类光通信波段光纤,由于太赫兹波波长较大,能够降低芯区微结构加工的难度,具有可行性. 关键词： 双折射 混合格子 太赫兹光子晶体光纤 限制损耗     

利用Kagome光纤实现多芯光子晶体光纤的输出合束

多芯光纤的输出光束只能在远场和焦点附近实现良好的同相位超模合束,这种超模传输特性大大影响了多芯光纤的应用范围.一种新型中空Kagome光纤为解决这一难题提供了可行的方案,利用中空Kagome光纤可以实现七芯光纤输出模式的整形合束.本文利用中心波长800 nm的钛宝石飞秒激光作为激光源,耦合入七芯非线性光子晶体光纤,得到700 nm至1050 nm的展宽光谱,并实现同相位超模输出.随后,将非线性展宽之后的宽谱七芯光束耦合至Kagome光子晶体光纤中,从Kagome光纤输出光斑呈高斯分布的模式传输,不再演变回七芯模式,耦合效率71%.实验还进一步验证此方法适用于不同结构的多芯光纤,为多芯光纤在高功率激光等领域的应用提供了参考.     

光子晶体光纤模式的简并特性研究

应用光子晶体光纤（PCF）的全矢量模型，根据对称性分析，按照最小波导扇面及相应的边界条件，将PCF中的模式进行了分类，并将PCF中的模式类比阶跃光纤来命名. 分析表明，PCF中的模式或者为非简并的，此时能够反映波导结构对称性；或者为简并对，必须二者组合才反映波导结构的对称性. 当简并对中的两个模式都具有与PCF波导结构相同的对称性时，简并将被击破而形成两个非简并模. 关键词： 光子晶体光纤 模式 简并     

Plasmonically enhanced optical transmission through a metalized nanostructured photonic crystal fiber taper

A subwavelength holey plasmonic structure was proposed by adiabatically tapering a photonic crystal fiber (PCF) and subsequently metalizing the cleaved end facet. By coupling a white light into the PCF side, we experimentally observed an enhanced optical transmission in the spectral domain through the plasmonic structure at the tapered end. We further showed numerically that the proposed device renders a focused directional beam, due to its Fresnel-zone-like configuration and the plasmonic lensing effects.     

空气孔正方形排列的低损耗高双折射光子晶体光纤的数值模拟

提出了一种正方形排列渐增空气孔高双折射光子晶体光纤，并利用多极方法对光纤基模的模场分布、色散、双折射以及损耗特性进行了数值模拟.模拟结果表明利用这种结构可以在包层空气孔层数较少的情况下实现极低的限制损耗，通过调节内层空气孔的分布可以有效地控制光纤的双折射和色散特性.本结果对高双折射光子晶体光纤的制备具有一定的指导意义. 关键词： 光子晶体光纤 双折射 限制损耗 多极方法     

Study of heat transfer characteristics in PCFG fabrication technology using heat method

The fiber gratings fabrication technology with the heating method in a photonic crystal fiber (PCF) based on structural change is examined. The principle of photonic crystal fiber gratings (PCFGs) is analyzed in theory. The heat transfer theory and finite element method are used to examine the thermal field distribution in the fiber and the influence of the air hole structure in the cladding, and the parameters of the laser beam in the process of grating fabrication are discussed. The results show that gratings can be formed by the periodic collapse of air holes in the cladding of PCFs. Under double-point heating condition, the energy is uniformly distributed in the radial direction and is approximate to Gaussian distribution in the axial direction. With the same size of the luminous spot, as the layers and radius of the air holes increase, the laser power needed to make the air holes collapse decreases. With the same laser power, as the luminous spot radius increases, the needed heating time increases. Moreover, the relationship between the laser power needed and the air filling rate is obtained as the number of layers of the air holes changes from 1 to 7. This kind of PCFG can overcome the long-term thermal instability of conventional gratings in substance and thus has great potential applications in the related field of optical fiber sensors.     

Measured sensitivity of arc-induced long-period grating sensors in photonic crystal fibre

Reported are experimental results from investigations of the sensing properties of long-period gratings (LPGs) recorded in two different geometries of photonic crystal fibre (PCF): a large-mode area PCF and an endlessly single mode PCF. The LPGs have been characterised for their sensitivity to temperature, bending, surrounding index and strain. The LPGs in both fibres have been found to have negligible temperature sensitivity whilst exhibiting useful strain sensitivities. Strong directional bend sensitivity is shown by one PCF whilst the other shows good non-directional bend sensitivity. The fibres exhibit differing sensitivities to surrounding refractive index.     

Experimental characterization of an off-axis scheme for pumping high-power photonic crystal fiber lasers

We experimentally investigate a free-space, off-axis method for pumping high-power photonic crystal fiber (PCF) lasers and amplifiers. The method is based on off-axis injection of the pump beam, exploiting the relatively high numerical aperture of the PCF pump cladding. With this method, we obtain pump coupling efficiency of more than 97 % for incidence angles as high as 30 degrees and show that with more than 60-W pump power the laser efficiency and beam quality do not significantly depend on the incidence angle. Our results indicate that this off-axis pumping method, with its significant advantages over the standard on-axis methods, can be exploited in high-power photonic crystal lasers and amplifiers.     

Novel design of photonic crystal fibres with low confinement losses, nearly zero ultra-flatted chromatic dispersion, negative chromatic dispersion and improved effective mode area

A novel photonic crystal fibre (PCF) with a low confinement loss and nearly zero ultra-flatted chromatic dispersion and negative chromatic dispersion at a wide telecommunication window is presented. Important PCF design parameters, such as the effects of air holes and geometrical parameters on the effective index, confinement losses, chromatic dispersion and effective mode area, have been thoroughly investigated by employing the full vectorial finite element method. Significant reduction of the confinement loss and low chromatic dispersion of the PCF, with three rings of air holes, has been obtained by carefully incorporating additional air holes.     

Modeling a sensitive pressure and temperature sensor using rectangular PCF by 2-D FDTD technique

We propose a sensitive pressure and temperature sensor depends on hollow core rectangular photonic crystal fiber. The proposed modeling is carried out by implementing 2-D finite difference time domain (FDTD) method. The two parameters like pressure and temperature plays a vital role in reservoir engineering to increase the production rates of oil well and our sensor technique is depend on the transmission peak wavelength shift which is caused by temperature/pressure change, and geometrical parameter of the structure of rectangular PCF. Here we have done simulation for various work using 2-D FDTD method application to sensing. We have shown the proposed design which provides the sensitivity with linear dependence of the resonance wavelength over refractive index of PCF holes at a operating wavelength of 1.55 μm.     

Ytterbium doped phosphate glass photonic crystal fiber laser

We demonstrate the 3% mol ytterbium doped phosphate glass air-clad photonic crystal fibre (PCF) laser of 43-cm length in single-mode operation. The fabrication and testing of the laser is introduced. The laser has the diameter of the core of 12 μm created in photonic microstructure and generates at wavelength of 1030 nm. Near 4-W output power and 14.6% slope efficiency against the launched pump power is demonstrated in preliminary characterization. The difference of refractive indices achieved in doped and undoped glass is Δn = 0.0004. We used the doped glass with the negative core-cladding Δn to assure the photonic crystal fibre way of single-mode propagation.