Simultaneous achievement of highly birefringent and nonlinear photonic crystal fibers with an elliptical tellurite core

Design of Single-Mode Single-Polarization Large-Mode-Area Multicore Fibers

In laser science and industry, considerable effort is directed toward designing fibers for fiber laser and fiber amplifier applications, each of which offers a particular advantage over the others. Evanescently coupled multicore fibers, however, have been studied less extensively due to the relatively small mode area in the single-mode regime. Here, by proposing a new structure with stress-applying parts in a 37-core fiber and optimizing this structure through a comprehensive framework, we present 21 solutions characterized by large-mode-area and high beam quality in the single-mode, single-polarization regime. Different fiber designs are optimal for different output parameters. In one design, the mode area can significantly increase to above 880 μm2, which is comparable with that of photonic-crystal fibers. Moreover, besides the single-mode operation, the beam quality factor (M2 factor) of the fundamental mode is considered an output parameter in the bent state and is improved up to 1.05 in another design. A comprehensive tolerance analysis is then performed to assess the performance of the designs under deviations from normal conditions. Moreover, in spite of the shifts in the loss of modes, the proposed high beam quality LMA fibers maintain single-polarization, single-mode operation across a wide range of core pitches, bending orientation angles, and bending radius deviations. Our results highlight the potential of multicore fibers for the efficient operation of fiber lasers and amplifiers.

Numerical investigation of high birefringence and nonlinearity tellurite glass photonic crystal fiber with microstructured core

In this paper, a novel photonic crystal fiber (PCF) based on tellurite glass with high birefringence and high nonlinearity is designed. Six small air holes arranged nearly rectangularly are added in the fiber core to form the near-elliptic core. By using the finite-element method with the help of COMSOL Multiphysics software, we investigate and simulate the birefringence, effective mode area, nonlinear coefficient, and the dispersion characteristics. Simulation results show that by optimizing the structure parameters of the core, at the wavelength of 1.55 µm, the birefringence is up to ${5.05} \times {{1}}{{{0}}^{- 2}}$; the nonlinear coefficient can reach a maximum of ${{1896}}\;{{\rm{W}}^{- 1}}\;{\rm{k}}{{\rm{m}}^{- 1}}$; moreover, the zero dispersion points can be obtained around the wavelength 1.55 µm. The proposed structure is easy to fabricate. The advantage of the proposed PCF has potential applications in polarization control, communication systems, and supercontinuum generation.

Dual-demodulation large-scope high-sensitivity refractive index sensor based on twin-core PCF

In this paper, a refractive index (RI) sensor based on the twin-core photonic crystal fiber (TC-PCF) is presented. Introducing the rectangular array in the core area makes the PCF possible to obtain high birefringence and low confinement loss over the wavelength range from 0.6 µm to 1.7 µm. Therefore, the core region can enhance the interaction between the core mode and the filling material. We studied theoretically the evolution characteristics of the birefringence and operating wavelength corresponding to the strongest polarization point under the condition of filling the rectangular array with RI matching fluid range from 1.33 to 1.41. Simulation results reveal that the proposed TC-PCF has opposite evolutions of change rates between the B and wavelength, and the maximum RI sensing sensitivities of 1.809×10^-2 B/RIU and 8 700 nm/RIU at low and high RI infill are obtained respectively, which means that the TC-PCF features of dual-parameter demodulation for the RI sensing can maintain a high refractive index sensing sensitivity within a large scope of RI ranging from 1.33 to 1.41. Compared with the results of single-parameter demodulation, it is an optimized method to improve the sensitivity of low refractive index sensors, which has great application potency in the field of biochemical sensing and detection.

Elliptical-spiral elliptical-hole photonic crystal fiber with high birefringence, large nonlinearity, and two zero dispersion

This paper presents a soft-glass (SF-57) elliptical-spiral photonic crystal fiber with elliptical air holes for achieving high birefringence, large nonlinearity, and tailoring two zero-dispersion wavelengths (ZDWs) in the near-infrared region. A full-vector finite-element method with perfectly matched boundary layer is used to characterize the properties of the photonic crystal fiber for different ellipticity ratios. The designed fiber has a birefringence 4 times higher than the circular-spiral structure. There are two ZDWs at around 1.2 µm and 2.8 µm which can be finely tuned depending on the ellipticity ratios along with a large nonlinearity. Due to the superior guiding properties, the proposed structure can be used for polarization control and broadband supercontinuum generation.

Polarization-maintaining fiber composed of an elliptical ring core and two circular air holes

In this paper, a new polarization-maintaining fiber (PMF) composed of an elliptical ring core and two circular air holes is exploited. The PMF could support 10 guided modes with refractive index differences $\Delta {n_{{\rm eff}}}$Δn_eff of all the adjacent modes larger than ${{10}^{ - 4}}$10^-4. Moreover, the optimum parameters of the PMF covering the entire $C + L$C+L band are obtained. Last, the chromatic dispersion $D$D of the designed elliptical ring core fiber, the confinement loss $\alpha $α, and the power fraction $\chi $χ of the two-air core are calculated. The calculation results show that $D$D, $\alpha $α, and $\chi $χ are compatible with traditional step-index fiber, and the designed elliptical ring core fiber is suitable for mode-division multiplexing and optical fiber sensors.

Simultaneous achievement of an ultrashort length and a high extinction ratio polarization splitter based on the dual-core photonic crystal fiber with Ge20Sb15Se65 glass

A polarization splitter based on dual-core photonic crystal fiber with ${{\rm Ge}_{20}}{{\rm Sb}_{15}}{{\rm Se}_{65}}$ glass is proposed to realize ultrashort length and high extinction ratio simultaneously at the common wavelength of 1.55 µm. The characteristics of the polarization splitter have been investigated by the finite element method. By tailoring the structure parameters on the performance of the splitter, the optimized parameters are obtained to analyze the birefringence, the coupling length, the normalized power transfer, and the extinction ratio. A comparison with other designs demonstrates the advantages of our polarization splitter, which can find potential applications in optical communication systems, optical fiber sensing, etc.