Polarization properties of rectangular lattice photonic crystal fiber

In this paper, polarization properties and propagation characteristics of rectangular lattice photonic crystal fibers with elliptical air-holes are investigated by using the full-vector finite element method with anisotropic perfectly matched layers. Numerical results show that the birefringence of the fiber is induced by asymmetries of the cladding. Moreover, by adjusting its structure parameters, such as the hole pitch Λ, and the air-hole elliptical rate η, we find the optimized design parameters of the fiber with high birefringence (the order of 10⁻²) and limited polarization mode dispersion, operating in a single mode region at an appropriate wavelength range.     

Design of a compact polarization splitter based on the dual-elliptical-core photonic crystal fiber

We propose a compact polarization splitter based on dual-elliptical-core photonic crystal fiber. Two elliptical cores are introduced to increase the difference of effective index between x-polarized and y-polarized mode and three elliptical modulation air holes are used to control the power transfer between the two cores. By optimizing the structure parameters, the length of the polarization splitter is distinctly shortened. Numerical results demonstrate that the compact splitter has the length of 775 μm and up to 50 dB extinction ratio at the central wavelength of 1.55 μm. The corresponding bandwidth of 32 nm could be achieved from the wavelength of 1.534–1.566 μm with the extinction ratio over 20 dB     

Supercontinuum generation in ultra-flat near zero dispersion PCF with selective liquid infiltration

We present a new design study of ultra-flat near zero dispersion PCF with selectively liquid infiltration with all uniform air-holes in the cladding. The dependence of the individual parameters upon dispersion has been presented in detail. The study establishes that varying Λ influences the total dispersion, whereas d has the desired effect of modifying the dispersion slope, and varying n_L modifies both. With the above study we could achieve near zero ultra-flat dispersion as small as 0 ± 0.41 ps/nm/km for broad wavelength range of 452 nm. The optimized near zero ultra-flat dispersion PCF has been targeted for smooth and flat broadband spectrum supercontinuum generation (SCG) for near Infrared (IR) applications. Broadband SC generations corresponding to three different designs of ultra-flat dispersion fiber have been carried out by using picoseconds pulse laser around the first zero dispersion wavelengths (ZDW). The numerical results show that FWHM of around 400 nm with less than a meter long fiber can be achieved with these fibers that cover most of the communication wavelength bands. The proposed design study will be applicable for applications in the field of tomography, Dense Wavelength Division Multiplexing (DWDM) system, spectroscopy, etc.     

Modified design of photonic crystal fibers with flattened dispersion

We present a modified method to design photonic crystal fibers with flattened dispersion characteristics. By replacing the circular air-holes of the first central ring with elliptic air-holes, we observe a more flattened dispersion curve. Plane-wave expansion (PWE) method is used to analyze the dispersion property in a high-index core PCF. The simulation results are presented, and ultra-low and ultra-flattened dispersion curves over wide wavelength range are demonstrated.     

Design of hybrid photonic crystal fiber: Polarization and dispersion properties

A highly birefringent dispersion compensating hybrid photonic crystal fiber is presented. This fiber successfully compensates the chromatic dispersion of standard single mode fiber over E- to L-communication bands. Simulation results reveal that it is possible to obtain a large negative dispersion coefficient of about −1054.4 ps/(nm km) and a relative dispersion slope of 0.0036 nm⁻¹ at the 1550 nm wavelength. The proposed fiber simultaneously provides a high birefringence of order 3.45 × 10⁻² at the 1550 nm. Moreover, it is confirmed that the designed fiber successfully operates as a single mode in the entire band of interest. For practical conditions, the sensitivity of the fibers dispersion properties to a ±2% variation around the optimum values is carefully studied and the nonlinearity of the proposed fiber is also reported and discussed. Such fibers are essential for high speed transmission system as a dispersion compensator, sensing applications, fiber loop mirrors as well as maintaining single polarization, and many nonlinear applications such as four-wave mixing, etc.     

单偏振单模聚合物光子晶体光纤设计

 设计了一种聚甲基丙烯酸甲酯(PMMA)基的单偏振单模(SPSM)微结构聚合物光纤(MPOF)。利用全矢量有限元法和光束传播法相结合分析了这种光纤的偏振特性和约束损耗。通过优化光纤结构参数,发现在0.51 μm～0.62 μm的可见光波长范围,由于基模两个正交偏振模的截止波长不同,这种微结构聚合物光纤只能传输基模中的一个偏振模,从而实现单偏振单模运转。该11圈圆空气孔六角排列光纤结构的传导偏振模在0.57 μm波长处约束损耗仅为1.13 dB/m,这种低损耗的单偏振单模微结构聚合物光纤可有效消除传统保偏光纤固有的偏振串扰和偏振模色散。     

Ultra-wideband single-polarization single-mode, high nonlinearity photonic crystal fiber

We report a novel design of photonic crystal fiber (PCF) with a rectangular array of four closely-spaced, highly elliptical air holes in the core region and a circular-air-hole cladding. The proposed PCF is able to support ultra-wideband single-polarization single-mode (SPSM) transmission from the visible band to the near infrared band. With the aid of the inner cladding formed by the central air holes, one polarization of the fundamental mode can be cut off at very short wavelengths and ultra-wideband SPSM propagation can be achieved. The inner cladding also suppresses the higher order modes and allows large air filling fraction in the outer cladding while the proposed fiber remains SPSM, which significantly reduces the mode effective area and the confinement loss. Our simulation results indicate that the proposed PCF has a 1540 nm SMSP range with <0.25 dB/km confinement loss and an effective area of 2.2 μm². Moreover, the group velocity dispersion (GVD) of the proposed PCF can also be tuned to be flat and near zero at the near infrared band (∼800 nm) by optimizing the outer cladding structure, potentially enabling many nonlinear applications.     

全玻璃实心保偏光子晶体光纤的研制

设计并采用棒管法结合毛细管堆积技术制备了一种全玻璃材料的实心保偏光子晶体光纤,光纤端面测试结果表明,这种结构设计有效克服了传统光子晶体光纤制造过程中空气孔易于塌陷的困难,光纤微结构保持良好.采用剪断法测得在1550nm波长下光纤的传输损耗为6.84dB/m.测试了输出光的偏振度,结果表明该光纤具有较好的保偏特性,说明采用此方法研制具有高保偏性能且制作工艺简单的光子晶体光纤是可行的.     

Polarization and dispersion properties of elliptical hole golden spiral photonic crystal fiber

An elliptical air-hole golden spiral photonic crystal fiber (EGS-PCF) is analyzed with the full-vectorial finite element method. The air-holes in the EGS-PCF are arranged in a spiral pattern governed by the Golden Ratio, where the design has been inspired by the optimal arrangement of seeds found in nature. The EGS-PCF exhibits extremely high birefringence (～0.022 at operating wavelength 1550 nm) which is particularly useful for generating a polarization stable supercontinuum (SC). The fiber can also be designed to have a Zero Dispersion Wavelength (ZDW) at a suitable wavelength for only one polarization and large negative dispersion for the other, leading to a single-polarization SC. In addition, the fiber dispersion can be designed to obtain ZDWs at 800 nm and 1064 nm simultaneously, which can facilitate broadband supercontinuum generation (SCG) through multi-wavelength pumping.     

Design and analysis of novel octagonal photonic crystal fiber with F-doped elliptical hole core

A design of octagonal photonic crystal fiber (OPCF) with F-doped elliptical hole core is proposed. The proposed design is simulated through an full vector finite element method (FVFEM) and anisotropic perfectly matched layers (APML). Numerical results show that the designed OPCF has the ultra-flattened dispersion of 0 ± 0.4 ps/(nm km) from 1.34 μm to 1.72 μm (380 nm band) which covers S, C and L communication bands, a low confinement loss of less than 10⁻⁷ dB/m in the same wavelength range, and the corresponding birefringence and nonlinear coefficient are about 2.12 × 10⁻² and 50.67 W⁻¹ km⁻¹ at 1.55 μm, respectively. The proposed OPCF may have great potential applications in super-continuum (SC) generation, dispersion compensation, polarization maintaining and so on.     

Correlation between the birefringence and the structural parameter in photonic crystal fiber

In order to simply design a highly birefringent photonic crystal fiber (HB-PCF), we numerically simulated the correlation between the birefringence and the structural parameter of photonic crystal fiber with square-lattice or triangle-lattice air-holes by using multipole method. It is shown that the phase birefringence B(λ) and the group birefringence G(λ) can be modulated by the structure parameter of normalized wavelength λ/Λ and the relative air-hole size d/Λ. Numerical results show very high phase and group birefringence of the order of 10⁻². The group birefringence becomes negative in the region where phase birefringence increases with an increase in normalized wavelength that does not appear in traditional highly birefringent fibers.     

Design of a highly nonlinear twin bow-tie polymer photonic quasi-crystal fiber with high birefringence

A twin bow-tie polymer-based photonic quasi-crystal fiber with high birefringence, high nonlinearity and low dispersion as well as maintaining single mode operation is presented in the wavelength range 1.8–2.2 μm. Through optimizing fiber structure parameter using a full-vector finite-element method combined with perfectly matched layers boundary condition, the birefringence is as high as 2.43 × 10⁻³, the nonlinearity is as high as 118 W⁻¹ km⁻¹, and the dispersion is only 25 ps/nm/km at 2 μm with the holes pitch of 3.3 μm. From the point of fabrication, the influences of deviation of each air hole diameter are discussed to verify the robustness of the photonic quasi-crystal fiber designed.     

Analysis of a highly birefringent photonic crystal fiber with ellipse–rhombus air core

A novel highly birefringent photonic crystal fiber with small effective mode area is proposed. Four elliptical air-holes are designed in the internal layer of the fiber to cause the anisotropy, and the fiber has the property of highly birefringence and small effective mode area. The influences of elliptical air-holes on effective index, birefringence, effective mode area and nonlinear coefficient are analyzed by using full-vector finite element method (FEM). Simulation results show the birefringence can achieve the magnitude of 10⁻³ under the condition of d > 2.3 μm and a > 1.4 μm, which d and a are the distance and semimajor axis of elliptical air holes. By adjusting the parameters d and a, different effective mode area and nonlinear coefficient can be obtained, which demonstrates the flexibility of the proposed photonic crystal fiber.     

Highly birefringent photonic crystal fibers with flattened dispersion and low effective mode area

A highly birefringent index-guiding photonic crystal fibers with flattened dispersion and low effective area is proposed by introducing elliptical air holes in the cladding and small holes both in the core area and in the cladding. With the plane wave expansion (PWE) method, the birefringent, dispersion and effective area of the fundamental modes in such photonic crystal fibers are analyzed in detail. The simulation result shows that high birefringence with a magnitude of the order of 10⁻³, flattened chromatic dispersion from 1100 nm to 1800 nm and low effective area (which mean high nonlinearity) are obtained. Furthermore, the influences on the birefringence and dispersion by geometrical parameters have also been discussed and a modest number of design parameters are given.     

New nonlinear and dispersion flattened photonic crystal fiber with low confinement loss

A new nonlinear dispersion flattened photonic crystal fiber with low confinement loss is proposed. This fiber has threefold symmetry core. The doped region in the core and the big air-holes in the 1st ring can make high nonlinearity in the PCF. And the small air-holes in the 1st ring and the radial increasing diameters air-holes rings in cladding can be used to achieve the dispersion properties of the PCF. We can achieve the optimized optical properties by carefully selecting the PCFs structure parameters. A PCF with flattened dispersion is obtained. The dispersion is less than 0.8 ps/(nm km) and is larger than −0.7 ps/(nm km) from 1.515 μm to 1.622 μm. The nonlinear coefficient is about 12.6456 W⁻¹ km⁻¹, the fundamental mode area is about 10.2579 μm². The confinement loss is 0.30641 dB/km. This work may be useful for effective design and fabrication of dispersion flattened photonic crystal fibers with high nonlinearities.     

Maintaining single polarization and dispersion compensation with modified rectangular microstructure optical fiber

In this paper, we propose and numerically demonstrate a highly birefringent microstructure optical fiber which shows negative dispersion coefficient of about −288 to −550 ps/(nm km) covering S to L wavelength bands and −425 ps/(nm km) at the excitation wavelength 1550 nm. This proposed design successfully compensate the dispersion covering S to L communication bands ranging from 1460 to 1625 nm along with relative dispersion slope (RDS) perfectly matched to that of single mode fiber of about 0.0036 nm⁻¹. Apart from dispersion compensation, the designed MOF offers high birefringence of 2.94 × 10⁻² at 1550 nm and better compensation ratio with design simplicity due to circular air-holes in the fiber cladding.     

Design of double cladding dispersion flattened photonic crystal fiber with deformation insensitive outer cladding air-holes

A design of double cladding dispersion flattened photonic crystal fiber (DF-PCF) is proposed. To employ traditional stack and draw technology, the cladding of the DF-PCF is consisted of triangular periodic air-holes with the same hole to hole pitch. Simulation results show that the small air-holes in the inner cladding are mainly for dispersion management. The large air-holes in the outer cladding are mainly used for light confinement and have little impact on the dispersion tailoring. Thus, the dispersion profile of the double cladding DF-PCFs is insensitive to the deformation of air-holes in the outer cladding. Considering that the larger air-holes are apt to deform in the drawing procedure, the characteristics mentioned above make the realization of DF-PCFs relative easy by employing conventional stack and draw technology and modest air-hole rings (less than 10 rings) in the cladding.     

Design of Topas microstructured fiber with ultra-flattened chromatic dispersion and high birefringence

A microstructured polymer optical fiber (mPOF) with both ultra-flattened near-zero chromatic dispersion and high birefringence based on Topas cyclic olefin copolymer is designed. Three rings of uniform elliptical air holes are arranged in triangular lattice in the cladding and an extra small defected hole is introduced in the fiber core. Guided modes, dispersion, birefringence and mode confinement properties of the designed mPOF are investigated by using the full-vector finite element method. Dispersion values between ± 0.5 ps/km/nm over the wavelength 1.1-1.7 μm and high birefringence of the order of 10⁻³ are obtained for the optimized fiber structure. Low confinement losses and small effective mode area are obtained at the same time. The relatively simple architecture of the proposed Topas mPOF can be fabricated by our extrusion-stretching techniques.     

Design of high duty ratio nonlinear photonic crystal fiber with near-zero flattened dispersion after 1.205 μm

The paper presents a high nonlinear photonic crystal fiber (HN-PCF) with highly duty ratio for time-stretch analog-to-digital conversion (TSADC). The simulation results show that a nonlinear of 42.26 W⁻¹ km⁻¹ and the flattened dispersion of less than 1.0 ps/(nm km) are obtained in more than 495 nm waveband (1205–1700 nm). Owing to its high nonlinear coefficient and flattened dispersion, the high nonlinear PCF is expected to be suitable for supercontinuum (SC) generation. The numerical simulation results demonstrate that the proposed high duty ratio HN-PCF can generate wideband SC.     

Polarization maintaining large nonlinear coefficient photonic crystal fibers using rotational hybrid cladding

In this paper, we present and explore a new hybrid cladding design for improved birefringence and highly nonlinear photonic crystal fibers (PCFs) in a broad range of wavelength bands. The birefringence of the fundamental mode in such a PCF is numerically analyzed using the finite element method (FEM). It is demonstrated that it is possible to design a simple highly nonlinear hybrid PCF (HyPCF) with a nonlinear coefficient of the about 46 W⁻¹ km⁻¹ at a 1.55 μm wavelength. According to simulation, the highest modal birefringence and lowest confinement loss of our proposed structure at the excitation wavelength of λ = 1.55 μm can be achieved at a magnitude of 1.77 × 10⁻² and of the order less than 10² dB/km with only five rings of air-holes in the fiber cladding.