Siwen Zheng

Nanoscale dielectric-graphene-dielectric tunable infrared waveguide with ultrahigh refractive indices

We propose in this paper a dielectric-graphene-dielectric tunable infrared waveguide based on multilayer metamaterials with ultrahigh refractive indices. The waveguide modes with different orders are systematically analyzed with numerical simulations based on both multilayer structures and effective medium approach. The waveguide shows hyperbolic dispersion properties from mid-infrared to far-infrared wavelength, which means the modes with ultrahigh mode indices could be supported in the waveguide. Furthermore, the optical properties of the waveguide modes could be tuned by the biased voltages on graphene layers. The waveguide may have various promising applications in the quantum cascade lasers and bio-sensing.

Mode-coupling analysis and trench design for large-mode-area low-cross-talk multicore fiber

The complete analytical solutions of the mode-coupling dynamics for seven-core multicore fibers (MCFs) with identical cores is proposed. All the coupling coefficients C(mn) of adjacent cores and nonadjacent cores as a function of the structural parameters are investigated. It is shown that the coupling coefficients can decrease by adjusting the structural parameters. In addition, the trench-assisted structure could be used for suppressing cross talk in MCF, and the effective area A(eff) can be enlarged without degrading the crosstalk properties. Simulations suggest that low cross talk and/or large A(eff) could be achieved by adjusting the trench parameters. Large mode area could be obtained by utilizing small trench (small trench width c, small refractive index difference Δ(trench)) in the trench-assisted MCF (TA-MCF), whereas low cross talk could be achieved by utilizing larger trench (large trench width c, large Δ(trench)) in the TA-MCF.

Analysis and characterization of Er–Yb codoped-depressed inner cladding fiber

A 125 μm-diameter erbium-ytterbium-codoped single-mode fiber is reported. The utilization of depressed inner cladding guarantees the improvement of trade-off between the effective area and bending sensitivity compared to step-index profiles. Changes of cutoff wavelength, effective area, and macrobend loss under the influence of various structural parameters, and the balancing selection of core radius and subsidence layer width are investigated systematically. For the laboratory-made depressed inner cladding fiber, a macrobend loss of 0.06 dB/loop for a bending radius as tight as 10 mm was achieved, while maintaining an effective area of 164.22 μm² with intact single-mode properties at 1550 nm. The maximum small signal gain was achieved at 40.9 dB, and the gain fluctuation was less than 1 dB at the C-band. The fiber is suitable for high-power, small, portable, and handy optical fiber devices.

Analytic solution of cut-off wavelength of bend-insensitive fibers based on frustrated total reflection

An analytic method for solving the cut-off wavelength of single groove-assisted bend-insensitive fiber (BIF) was proposed. Combined with the concepts of frustrated total reflection and numerical aperture, the cut-off wavelength formula for the BIF was deduced. Experimental results showed that, compared to the traditional analytic and numeric methods, this method had higher accuracy in the calculation of cut-off wavelength for BIFs that had a large proportion of depressed inner-cladding layer, which significantly expanded the range of accurately predicting the cut-off wavelength.