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We present a new scheme to produce a tunable converge elliptical optical vortex (EOV) with a phase-only element: elliptical helical lens (EHL), which is studied theoretically and experimentally. As a result, the properties of converge EOVs can be controlled by adjusting the parameters of EHL. The topological charges of the EOVs can be directly read from the received intensity pattern. Because EHL is a hologram programmed in space light modulator (SLM), converge EOVs can be controlled just by reprogramming the SLM instead of replacing actual instruments. This work has potential applications in particle manipulation, as well as generation of OAM-entangled photons.

In this paper, a method to suppress the higher-order modes in the negative curvature anti-resonance hollow core fibers (NC-AR-HCFs) by utilizing multiple resonant coupling is proposed. With this method, a hollow core fiber is designed. Based on multiple resonant coupling, the loss of LP11 mode even reaches more than 105 dB/km orders of magnitude over a wide wavelength band, and the loss ratio of LP11 mode to LP01 mode of the proposed fiber remains above 105 orders of magnitude in the range of 1200 ∼ 1550 nm, which shows excellent single-mode operation. The effect of multiple resonant coupling and the effective suppression of further-higher-order modes (LP21 mode and LP02 mode) are analyzed in detail. Moreover, we demonstrate that the extra loss caused by the node effect is reduced by changing the thickness of the outer tube that decreases the fractional optical power of the outer tube wall. And the restrictive relation between the higher-order modes suppression and the reduction of bend loss is discussed. The analysis guides the design of NC-AR-HCFs with effectively suppressing higher-order modes.

We propose a hollow-core photonic bandgap fiber (HC-PBGF) with background composed of two materials to support orbital angular momentum (OAM) modes. Numerical models are set up to figure out the effective indexes and confinement losses over 1.3-2.0 μm. Simulation results show that this fiber can support more than 48 OAM modes, of which the effective indexes satisfy the condition for effective index separation (

A micro-notched Bragg fiber is proposed as a simplified method to achieve omnidirectional emission. The output beam can retain Gauss-like distribution when the size of the notch is appropriate. Simulation results show that the width and the depth of the notch significantly affect the features of the radial beam, such as the divergence angle and output energy. According to the result that the initial phase can directly control the phase of the output beam, the notched Bragg fiber is suggested as being suitable for simplifying a Cassegrain optical antenna system, and making up for the energy loss (about 25%) caused by the central obstruction of the secondary mirror.

In this paper, an asymmetric large-mode-area photonic crystal fiber (LMA-PCF) with low bending loss at a smaller bending radius is designed. The finite-element method with a perfectly matched layer boundary is used to analyze the performance of the PCF. To achieve LMA-PCF with low bending loss, the air holes with double lattice constants and different sizes at the core are designed. Numerical results show that this structure can achieve low bending loss and LMA with a smaller bending radius at the wavelength of 1.55 μm. The effective mode area of the fundamental mode is larger than 1000 μm2 when the bending radius is ≥10 cm. The bending loss of the fundamental mode is just 0.0113 dB/m, and the difference between the fundamental and high-order modes of the bending loss is larger than 103 when the bending radius is 10 cm. Simulation results show this novel PCF can achieve LMA and have effective single-mode operation when the bending orientation angle ranges in ±110°. This novel photonic crystal has potential application in high-power fiber lasers.

In this work, a novel design of a high birefringence photonic crystal fiber (HB-PCF) with multimode and low confinement loss is proposed. To achieve high birefringence, the core is designed as an elliptical region, which is enclosed by twelve small holes. Based on this design, replacing the two circular holes at the top and bottom of the core region with two elliptical holes can further improve the birefringence. At the wavelength of 1.55 μm, the birefringence of the fundamental mode (LP01) and the second-order mode (LP11) are 1.70×10−2 and 1.85×10−2, respectively. Meanwhile, the confinement losses maintain on orders of 1×10−5 dB/km (LP01) and 1×10−1 dB/km (LP11). After the effective refractive indices of two types of the proposed HB-PCF are calculated by the finite element method, the birefringence, confinement loss, bending loss, dispersion, and nonlinear coefficient are studied. These results reveal that the HB-PCF might be applied for polarization-maintaining and nonlinear optics.