Chunyong Yang

Engineering ultra-flattened-dispersion photonic crystal fibers with uniform holes by rotations of inner rings

We present a novel method for engineering ultra-flattened-dispersion photonic crystal fibers with uniform air holes by rotations of inner air-hole rings around the fiber core. By choosing suitable rotation angles of each inner ring, theoretical results show that normal, anomalous, and nearly zero ultra-flattened-dispersion fibers in wide spectra ranges of interest can be obtained alternatively. Moreover, in our dispersion sensitive analysis, these types of fibers are robust to variations from optimal design parameters. The method is suitable for the accurate adjustment of fiber dispersion within a small range, which would be valuable for the fabrication of ultra-flattened-dispersion fibers and also have potential applications in wide-band high-speed optical communication systems.

Slow Light in Square-Lattice Chalcogenide Photonic Crystal Holey Fibers

Slow light in square-lattice chalcogenide photonic-crystal (PC) holey fibers with uniform longitude geometry are proposed and theoretically investigated. By using the planewave-expansion method, a largest normalized complete 2-D photonic bandgap (CPBG) width of about 7.4% is found in an optimized connected-rod square-lattice chalcogenide PC, and the CPBG remains open with a refractive-index contrast as low as 2.48:1. We then consider the PCs as cladding layers to form holey fibers, and group indices up to several hundreds are predicted.

Single hole twin eccentric core fiber sensor based on anti-resonant effect combined with inline Mach-Zehnder interferometer

A novel fiber curvature sensor without temperature cross interference based on a single hole twin eccentric core fiber has been proposed. Anti-resonant mechanism combined with inline Mach-Zehnder interference (MZI) structure are applied to the measurands detection. The spectrum is composed of a comb spectrum caused by the inline MZI and several dominant resonant wavelengths induced by anti-resonant effect. The curvature sensitivity of -1.54dB/m-1 can be achieved by intensity demodulation of the selected dip of Gaussian fitting. Similarly, the temperature sensitivity of 70.71pm/°C and 34.17pm/°C are respectively achieved by tracking coherent decrease point obtained by the FFT band pass filter method and Gaussian fit dip. Consequently, a relatively higher resolution of temperature measurement can be realized by the two methods mentioned above. The proposed sensor has a great potential for structural health monitoring, such as buildings, towers, bridges, and many other infrastructures due to its compact structure, easy fabrication and without cross impacts.

Compact high extinction ratio asymmetric polarization beam splitter of periodic rods waveguide

A compact high extinction ratio polarization beam splitter based on an asymmetric directional coupler was proposed and theoretically investigated. The asymmetric directional coupler consists of a silicon wire waveguide and a 1D periodic silicon rods waveguide, which results in an ultracompact polarization splitting length. By using the plane wave expansion method, a minimum coupling length of 3.43 μm was obtained, and the length was then confirmed by finite-difference time-domain simulation. Moreover, for 1550 nm wavelength, high extinction ratios of about 28 and 18 dB were also observed for TE and TM polarizations, respectively. The ultrahigh extinction ratio for TE polarization is mainly arising from the appearance of TM bandgap in the periodic rods waveguide. In addition, for both polarizations, the extinction ratios are all above 10 dB covering a 180 nm bandwidth, and it was also demonstrated that the device has a high transmission for TM polarization.

Ultrathin graphene diaphragm-based extrinsic Fabry-Perot interferometer for ultra-wideband fiber optic acoustic sensing

An ultra-wideband fiber optic acoustic sensor based on graphene diaphragm with a thickness of 10nm has been proposed and experimentally demonstrated. The two reflectors of the extrinsic Fabry-Perot interferometer is consist of fiber endface and graphene diaphragm, and the cavity is like a horn-shape. The radius of the effective area of the ultrathin graphene diaphragm is 1mm. Attributed to the strong van der Waals force between the diaphragm and the ceramic ferrule, the sensor head can be applied not only in the air but also underwater. Experimental results illustrate that ultra-wideband frequency response is from 5Hz to 0.8MHz, covering the range from infrasound to ultrasound. The noise-limited minimum detectable pressure level of 0.77Pa/Hz1/2@5Hz and 33.97μPa/Hz1/2@10kHz can be achieved, and the applied sound pressure is 114dB and 65.8dB, respectively. The fiber optic acoustic sensor may have a great potential in seismic wave monitoring, photoacoustic spectroscopy and photoacoustic imaging application due to its compact structure, simple manufacturing, and low cost.

Biomimetic spiral grating for stable and highly efficient absorption in crystalline silicon thin-film solar cells

In the original manuscript, the maximum short-circuit current in Fig. 2 and the description of angular stability for polarization in Fig. 6 are found incorrect owing to negligence. The incorrect maximum integrated absorption also led to errors appeared in Fig. 3 and Fig. 4(d), in which the mistake value was used to plot. In this erratum, all of those mistakes have been corrected. Moreover, both higher Fourier expansion order and the resolution of frequency are adopted in the recalculation to make sure the updated results to be reliable. The updated data presented still support the main conclusions drawn in the previous manuscript.

Turbulence heterodyne coherent mitigation of orbital angular momentum multiplexing in a free space optical link by auxiliary light

A novel scheme is proposed to mitigate the atmospheric turbulence effect in free space optical (FSO) communication employing orbital angular momentum (OAM) multiplexing. In this scheme, the Gaussian beam is used as an auxiliary light with a common-path to obtain the distortion information caused by atmospheric turbulence. After turbulence, the heterodyne coherent detection technology is demonstrated to realize the turbulence mitigation. With the same turbulence distortion, the OAM beams and the Gaussian beam are respectively utilized as the signal light and the local oscillation light. Then the turbulence distortion is counteracted to a large extent. Meanwhile, a phase matching method is proposed to select the specific OAM mode. The discrimination between the neighboring OAM modes is obviously improved by detecting the output photocurrent. Moreover, two methods of beam size adjustment have been analyzed to achieve better performance for turbulence mitigation. Numerical results show that the system bit error rate (BER) can reach 10-5 under strong turbulence in simulation situation.

Preparation, structure and optical properties of transparent conducting gallium-doped zinc oxide thin films

Abstract Highly conductive gallium-doped zinc oxide (GZO) transparent thin films were deposited on glass substrates by RF magnetron sputtering. The deposited films were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), four-point probe and UV-Vis spectrophotometer, respectively. The effect of growth temperature on the structure and optoelectrical properties of the films was investigated. The results demonstrate that high quality GZO films oriented with their crystallographic c-axis perpendicular to the substrates are obtained. The structure and optoelectrical properties of the films are highly dependent on the growth temperature. It is found that with increasing growth temperature, the average visible transmittance of the deposited films is enhanced and the residual stress in the thin films is obviously relaxed. The GZO films deposited at the growth temperature of 400°C, which have the largest grain size (74.3 nm), the lowest electrical resistivity (1.31×10-3 Ω·cm) and the maximum figure of merit (1.46×1O-2Ω-1), exhibit the best optoelectrical properties. Furthermore, the optical properties of the deposited films were determined by the optical characterization methods and the optical energy-gaps were evaluated by extrapolation method. A blue shift of the optical energy gap is observed with an increase in the growth temperature.

Absorption Enhancement in Thin-Film Amorphous Silicon Solar Cells by Symmetric Sub-Structure Binary Gratings

Absorption enhancement in thin-film amorphous silicon solar cells with symmetric sub-structure binary gratings is investigated by rigorous coupled wave analysis, and up to 1.77 times absorption is obtained in a preliminary optimized structure.

Effect of Argon Gas Pressure on Optical Properties of Zinc Oxide Thin Films Deposited by RF Magnetron Sputtering Technique

Zinc oxide (ZnO) thin films were deposited by radio frequency (RF) magnetron sputtering technique on glass substrates in pure argon gas. The optical transmission stectra of the films were measured by ultraviolet-visible spectrophotometer. The effects of argon gas pressure on optical properties of the deposited films were investigated. The optical band-gap of the films was evaluated in terms of the Taucs law. The results show that the argon gas pressure has slightly affected the optical band-gap of the deposited films. Furthermore, the refractive index and extinction coefficient of the films were determined by means of the optical characterization methods. Meanwhile, the dispersion behavior of the refractive index was studied by the single-oscillator model of Wemple and DiDomenico, and the physical parameters of the average oscillator strength, average oscillator wavelength, oscillator energy, the refractive index dispersion parameter and the dispersion energy were obtained.