Shu-Guang Li

Tunable Fiber Polarization Filter by Filling Different Index Liquids and Gold Wire Into Photonic Crystal Fiber

A tunable fiber polarization filter by filling different index liquids into the central hole of photonic crystal fiber (PCF) is proposed and demonstrated. The dispersion characteristics and loss spectra of the polarization filter are evaluated by finite element method (FEM). The gold wires are selectively filled into the cladding air holes of the PCF. When the phase matching condition is satisfied, the liquid-core mode couples to surface plasmon polaritons (SPP) mode intensely. The resonance wavelength varies with the change of the structural parameters and liquids. By adjusting the refractive index of the liquid, we realize the polarization filter at the wavelength of 1.31, 1.49, and 1.55 μm, respectively, under the optimized structural parameters. This is the first time to propose the narrowband polarization filter at the communication wavelength of 1.31 μm to our best knowledge based on the coupling between liquid-core mode and SPP mode, and the full width half maximum (FWHM) is only 16 nm. The loss of X-polarized mode is 44336 dB/m at λ = 1.31 μm, and the corresponding loss of V-polarization mode is 224 dB/m. By comparison, we find the birefringence in our structure is further better than that in conventional structure. High birefringence is helpful to separate the resonance wavelength positions of the two orthogonal polarized modes. The result also reveals that resonance loss becomes small with increasing the distance between liquid core and gold wire.

Design of a polarized filtering photonic-crystal fiber with gold-coated air holes.

A novel design of a gold-coated photonic-crystal fiber (PCF) is studied by using the finite element method. The cross-section structure of the PCF is composed of a square lattice of air holes in which two air holes are gold coated, and the air-hole layout is modified. The resonance strength and the impact of structural parameters of the PCF on the polarization filter characteristics are studied. Numerical results show that the resonance strength and wavelengths are different in two polarized directions. The resonance strengths that we obtain can reach a value of 720xa0dB/cm at the wavelength of 1.31xa0μm. When the fiber length is 400xa0μm, the crosstalk can reach a value of 247.2xa0dB at the wavelength of 1.31xa0μm, which can be applied in many polarization filter devices. And when the length of fiber is longer than 200xa0μm, the crosstalk is better than 20xa0dB with wavelength ranges from 1.2 to 2xa0μm. Meanwhile, we can realize the filtering effect with a very short fiber.

High stability supercontinuum generation in lead silicate SF57 photonic crystal fibers

We report supercontinuum (SC) generation in a lead silicate SF57 photonic crystal fiber by using a 1550 nm pump source. The effective nonlinear coefficient of the SF57 fiber is simulated to be 111.5 W−1km−1 at 1550 nm. The fiber also shows ultraflat dispersion from 1700 nm to 2100 nm. Our results reveal that with an increase of the average power of the incident pulse from 10 mW to 90 mW, the SC of the SF57 photonic crystal fiber is generated from 1300 nm to 1900 nm with high stability and without significant change in spectral broadening.

Filtering Characteristics and Applications of Photonic Crystal Fibers Being Selectively Infiltrated With One Aluminum Rod

The filtering characteristics and applications of photonic crystal fibers being selectively infiltrated with one aluminum rod were investigated based on the finite-element method. The aluminum rod being selectively infiltrated into one cladding air hole acted as a defect core and generated surface plasmon polaritons on its surface. As the phase matching condition was satisfied, the light transferring in fiber core coupled to the surface of the aluminum rod and the confinement losses of core modes experienced an abrupt increase. The filtering characteristics could be modified by adjusting the fiber structure parameters, such as diameters of air holes and the aluminum rod. Two applications of the photonic crystal fibers being selectively infiltrated with one aluminum rod were studied. First, a polarization filter with ultrabroad bandwidth was designed based on the cascaded resonances between fiber core modes and surface plasmon polariton modes. The bandwidth of the polarization filter was as broad as 600 nm covering wavelengths from 1.4 to 2.0 μm. Second, an intensity-type refractive index sensor was designed based on the filtering characteristics. The output power ratio and sensitivity increased as the refractive index of analyte increases and reached to 3.91 dB and 128 dB/RIU in x-polarized direction at the analyte refractive index of 1.37, respectively.

Surface plasmon resonance-induced tunable polarization filters based on nanoscale gold film-coated photonic crystal fibers

Surface plasmon resonance induced tunable polarization filters based on nanoscale gold film-coated photonic crystal fibers were proposed and analyzed. The characteristics of the polarization filter were calculated by finite element method (FEM). The gold film was selectively coated on the inner wall of one cladding air hole which was located near the fiber core along the y-axis direction. When the phase of core fundamental mode and surface plasmon polaritons (SPPs) mode matches,the two modes couple with each other intensely. Numerical results show that the resonance wavelength and strength vary with fiber structural parameters and the index of the infilling liquid. The fiber parameters were optimized to achieve specific functions. Under the optimal structure, we realized a dual channel filter at the communication wavelength of 1.31 µm and 1.55 µm for y polarization direction and x polarization direction. Then a single channel polarized filter at the communication wavelength of 1.55 µm is also achieved by adjusting the refractive index of the infilling liquid. The proposed polarization filters realized dual channel filtering and single channel filtering simultaneously under the same structure for the first time to the best of our knowledge.

A highly nonlinear and birefringent photonic crystal fiber with zero dispersion at 2 µm eye-safe spectral window

A novel highly nonlinear and birefringent photonic crystal fiber with zero dispersion at 2 m eye-safe spectral window is proposed in this paper. By using the full-vector finite-element method, the key propagation characteristics of the designed PCF are investigated at 2 m eye-safe spectral window. Furthermore, a more effective and accurate method has been used to optimize the two small air holes diameters of and the ratio of at the wavelength of 2 m. When the parameters of and d/ are 0.2 m and 0.91, the birefringence, nonlinearity and confinement loss can reach to an order of , 25.32 , and 0.044 dB/m, respectively. The zero-dispersion coefficient of the designed PCF can be achieved at the wavelength of 2 m.

Broadband single-polarization single-mode photonic crystal fibers with three different background materials

A modified structure of single-polarization single-mode (SPSM) photonic crystal fiber (PCF) with different background materials is presented and analyzed by using the full-vector finite-element method. Simulation results confirmed that the proposed PCF can realize low-loss SPSM on three wavebands with the same structure and different background materials. The wavebands are 1.46-1.60 μm for silica-based fiber, 1.97-2.3 μm for lead silicate glass fiber, and 3.16-3.58 μm for chalcogenide glass fiber. For three PCFs with different background materials, only the slow-axis mode exists and the confinement loss is less than 100 dB/m in the SPSM wavebands.

A Novel Method Based on Digital Image Processing Technique and Finite Element Method for Rapidly Modeling Optical Properties of Actual Microstructured Optical Fibers

The cross-section image of microstructure optical fiber (MOF) is usually characterized by the irregular shape, disordered distribution of the air pores, and multiple sources of noise. The traditional modeling of fiber structure does not work for these MOFs, and it is difficult to obtain the actual cross-section structure. A new method based on the digital image processing technique and finite element method (FEM) is introduced. With this method, the actual cross-section structure of MOFs can be rapidly modeled by gray scale processing, filtering, threshold, and edge detection, which is vital to the simulation of the basic properties of the fiber with FEM precisely. The method is proved to be feasible and reliable in that the dispersion coefficients of an actual fiber simulated are greatly consistent with the experimental results. In addition, the influence of perfect matched layer thinkness, as well as the curve fitting interval selection of the dispersion coefficients on the research results, is explored in the paper, which forms a basis for the correct setting of these parameters. The method has the advantages of strong adaptability, good modeling effect, rapid simulation, and accurate results. Finally, the method applies to all kinds of cross-section modeling of fiber, especially for disordered structure modeling.