Abstract:Passively Q-switched thulium doped fiber laser (TDFL) has been successfully demonstrated using gold nanoparticles (GNPs), which were embedded into polyvinyl alcohol as saturable absorber (SA). The stable self-starting Q-switched laser was generated to operate at 1 891 nm when a tiny piece of the prepared film was slot in between two fiber ferrules and incorporated into the laser cavity. The repetition rate can be adjusted from 48.54 kHz to 49.64 kHz while the pulse width decreased from 3.52 μs to 2.38 μs with the increase of 1 550 nm pump power from 840 mW to 930 mW. The corresponding pump power output power linearly increased from 3.62 mW to 6.3 mW with a slope efficiency of 2.53%. The maximum peak power and pulse energy were recorded at about 39 mW and 0.12 µJ, respectively at pump power of 930 mW. The Q-switching operation was caused by the surface plasmon resonance absorption of GNPs.

Abstract:This work demonstrates the atomic vacancy effects on the phonon properties of armchair silicene nanoribbon in a step by step process for the first time. The phonon localization effect figures out the fact that vacancies cause to high-energy phonons become localized, whereas low-energy phonons can easily transmit. The vacancy reduces high-energy phonon transmission severely compared to low-energy phonon. It is also found from phonon density of states that high-frequency phonons soften towards the low-frequency region. The simulated phonon bandstructure verifies that most of the phonon branches transform to a nondegenerate state from a degenerate state and shifted toward a lower frequency regime due to the presence of vacancies. The overall consequences of atomic vacancies on the phonon thermal conductance disclose the reality that only a few atomic vacancies result in a vital reduction of phonon thermal conductance. In addition, the entropy of the disordered system is investigated.

Abstract:By designing the ordered structure on the key physical dimensions, metamaterial can obtain extraordinary physical properties. The method gives transparent conductive absorbing metamaterial with broadband and high absorptivity. In this paper, a kind of absorbing metamaterial with indium tin oxide (ITO) glass substrate is designed. The design method of double-sided etched an open loop and linear metamaterial periodic structures is adopted. The thickness of the absorbing metamaterial is 2.5 mm. The research shows that the working bandwidth is between 8.9 GHz and 17.4 GHz, the absorption rate is 90%, and the transmittance of visible light is 85% on average. The absorbing metamaterial has wide application value to solve the problem of visualization and absorption characteristics.

Abstract:Tantalum pentoxide (Ta2O5) and ultraviolet reflective (UVR) multilayer films were deposited on quartz glass substrates by an electron beam evaporation system equipped with a hall ion source, respectively. The optical properties of Ta2O5 film and the UVR film under the vacuum ultraviolet irradiation were investigated. It is found that the mean transmittance of the Ta2O5 thin film decreased in the 300—500 nm region. The refractive index and extinction coefficient of the single layer increased during the range of 300—1 000 nm, with the variation rate of refractive index less than 1%, which is mainly due to the larger surface roughness and variation of the chemical state of Ta atoms on the surface caused by the irradiation. The mean reflectance of UVR film decreased from 96.5% to 95.4% during the range of 290—450 nm, indicating that the Ta2O5 and UVR films have excellent vacuum ultraviolet irradiation resistant properties.

Abstract:A photoelectric autocollimator with high accuracy and extended measurement range based on the quadrangular pyramid is proposed, and the corresponding algorithms are also deduced. A new image processing algorithm has been proposed to improve the accuracy, and the corresponding errors are also estimated, the error does not exceed half a pixel when the distance between the marks more than two radii. The experimental results have verified that the measurement range of the proposed two-dimensional (2D) quadrangular pyramid photoelectric autocollimator can be increased times than that of the flat mirror photoelectric autocollimator from 10′ to 15′. The accuracy is better than 1″ when the deflection is less than 15′.

Abstract:The carrier recombination was one of the factors limiting the further improvement of the Cu2ZnSnS4 (CZTS) thin film solar cells. In this paper, a proper bandgap structure was designed to solve this problem. The effects of the different bandgap structure on the CZTS thin film solar cells were studied by the solar cell performance simulation software wxAMPS. A graded bandgap structure was designed and optimized. The bandgap with a front bandgap gradient and a flat bandgap gradient had a favorable effect on the CZTS thin film solar cells. Finally, the fill factor (FF) and conversion efficiency (η) of the CZTS thin film solar cell were increased from 36.41% to 42.73% and from 6.85% to 10.03%, respectively. In addition, the effect of donor and acceptor defect densities in CZTS absorber layer near the CdS/CZTS interface on the device performance was studied, η of the CZTS thin film solar cell was increased from 5.99% to 7.55% when the acceptor defect concentration was 1012—1013 cm-3. Moreover, the thicknesses of the CZTS absorber layer were optimized. The FF and η of the CZTS thin film solar cell were increased to 63.41% and 15.04%, respectively.

Abstract:There is an increasing need for high performance oscillators as the faster transmission networks demand for high frequency signals. Opto-electronic oscillators (OEO) enable us to make better oscillators in terms of size, weight and power. In this paper, photonic integration is proposed for realizing the OEO with micro ring resonator (MRR) and radio-frequency (RF) amplifiers of monolithic microwave integrated circuit (MMIC), which can be used for generating 110 GHz sine wave. The OEO architecture is proposed and block diagram developed considering Silicon based MRR and three-stage RF amplifier based on GaN high-electron-mobility transistor (HEMT). A simulation model is developed according to the Klein model of MRR and is validated against the calculated performance parameters. MRR dimensions are calculated as with silicon on insulator (SOI) technology and a radius 5.27 μm for the device is derived. Free spectral range (FSR) of 48.52 nm and filter rejection ratio of 16.79 dB are obtained for this device. The proposed RF amplifier is modelled with GaN parameters derived from high frequency pinch-off model and with power amplifier considerations. The gain for this amplifier is obtained as 10.6 dB. The OEO design is developed in this project in such a way that the system can be manufactured with the existing methods.

Abstract:A novel fluid sensing system based on side-polished optical fiber (SPOF) is proposed, which realizes the fluid replaceability and effective refractive index (RI) sensing characteristics. Numerical investigations demonstrate that the photonic bandgap effect can be obtained if the RI of liquid is higher than that of substrate material in the wavelength range studied. The relationship between bandgap edge wavelength and RI is studied theoretically. The SPOF with a depth of 57 μm is used in the experiment to realize the construction of the fluid channel. After filling three different liquids, the result shows that the wavelength of the bandgap edge has a red shift with RI increased, which is nearly linear in the RI range of 1.56—1.6 with a sensitivity about 5 543.64 nm/RIU. The proposed sensing system can be flexibly applied to the field of fluid characteristic sensing such as biochemical solution characteristic detections.

Abstract:The amplifying dynamics of the pulse burst in Yb3+-doped fiber amplifier (YDFA) with high-power pulse pump is numerically analyzed by a finite-difference time-domain (FDTD) method. The numerical simulations show that the amplitude uniformity of the amplified pulse burst can be modified by adjusting the parameters of pump, such as relative delay and power. Though optimizing the pump parameters, we can reduce the gain difference between the pulses in a burst and improve the efficiency of coherent pulse stacking based on Gires-Tournois interferometers (GTIs). These results can be applied to the design of high energy ultra-short pulse amplifiers based on burst-mode amplification and coherent pulse stacking technology.

Abstract:In this paper, we propose and numerically investigate a novel circular lattice photonic crystal fiber (CL-PCF) using controllable GeO2 doped silica, suitable for modes carrying quantized orbital angular momentum (OAM). Large effective index separations between 25 supported vector modes (≥10-4) are confirmed over large bandwidth (C+L bands) leading to 48 OAM modes bearing information. The simulations show that the modes in the proposed CL-PCF have good features including low and flat dispersion (within 51.82 ps/km/nm), low confinement loss (lower than 0.002 dB/m), high effective mode area (88.5 μm2) and low nonlinearity (1.22 W-1.km-1). These promising results show that the proposed CL-PCF could be an arguably candidate in fiber-based OAM multiplexing or other applications using OAM states.

Abstract:Event-based cameras generate sparse event streams and capture high-speed motion information, however, as the time resolution increases, the spatial resolution will decrease sharply. Although the generative adversarial network has achieved remarkable results in traditional image restoration, directly using it for event inpainting will obscure the fast response characteristics of the event camera, and the sparsity of the event stream is not fully utilized. To tackle the challenges, an event-inpainting network is proposed. The number and structure of the network are redesigned to adapt to the sparsity of events, and the dimensionality of the convolution is increased to retain more spatiotemporal information. To ensure the time consistency of the inpainting image, an event sequence discriminator is added. The tests on the DHP19 and MVSEC datasets were performed. Compared with the state-of-the-art traditional image inpainting method, the method in this paper reduces the number of parameters by 93.5% and increases the inference speed by 6 times without reducing the quality of the restored image too much. In addition, the human pose estimation experiment also revealed that this model can fill in human motion information in high frame rate scenes.