Abstract:A lutetium oxide (Lu2O3) film was proposed and demonstrated for Q-switching operation at 1.55 µm region. It was obtained by solving Lu2O3 powder into isopropyl alcohol and mixing the solution into polyvinyl alcohol (PVA) solution to form a composite precursor solution via stirring, sonicating, and centrifuging processes. The thin film was formed through a drop and dry process and a small piece of this film was integrated into erbium-doped fiber laser (EDFL) cavity to modulate the cavity loss via Q-switching mechanism for pulse generation. The Q-switched laser operated at 1 565 nm with the repetition rate of 75.26 kHz as the pump power was raised to the maximum value of 145.83 mW. The maximum pulse energy of 41.85 nJ was recorded at 145.83 mW pump power. The mode-locked pulse operated at 968.5 kHz with a pulse width of 510 ns was also realized in an extended EDFL cavity. The simple and cost-effective laser should have various applications including material processing, sensing and biomedical areas.

Abstract:We proposed a compact and tunable multimode interferometer (MMI) based on an asymmetric wavy fiber (AMWF), which has axial offset, off-center taper waist, and micro-length. The fabrication process only contains non-axis pulling processes of single-mode fiber on two close positions. Theoretical qualitative analyses and experiments verify the tunable multimode propagation of the AMWF. Experimental results show a nonlinear wavelength response with increasing axis displacement from 0 to 120 μm. In the range of 0—10 μm, the sensitivity reaches the highest value of −1.33 nm/μm. Owing to its cost-effective, high-compact and tunable multimode propagation properties, the AMWF provides a promising platform for micro-nano photonic devices and optical sensing applications.

Abstract:A compact Fano resonant temperature sensor composed of a micro-ring resonator (MRR) coupled double-T-shaped waveguide is developed. The coupling gap and coefficient of the device are optimized by the finite difference time domain (FDTD) method. The maximum slope ratio (SR) of the MRR-coupled single-T-shaped waveguide is −2.13 dB/nm. The SR of the double-T-shaped waveguide is −49.69 dB/nm which is 23 times that of the single-T-shaped waveguide. The simulation results show that the temperature sensitivity of optical intensity decreases with increasing temperature in the range from 303.6 K to 343.8 K. The wavelength-temperature sensitivity of the double-T-shaped waveguide microring is 76.5 pm/K. After introducing the double-T-shaped waveguide structure, the device's performance is greatly improved, and the double-T-shaped waveguide has a good application prospect as a temperature sensor.

Abstract:In this study, the conversion efficiency (CE), open-circuit voltage (VOC) and short-circuit current density (JSC) of wurtzite InxGa1-xN/ZnSnN2 core/shell quantum dot (QD) solar cells are studied by using the detailed balance model. The effects of strain and external electric field have been considered. The results show that with the increase of the core size, the VOC increases, while the JSC and CE decrease. With the increase of shell size or In content, the VOC decreases, while the JSC and CE increase. In addition, our calculations show that the band gap of QD increases due to strain, which leads to an increase of the VOC, but decreases of the CE and JSC. By contrast, the situation is opposite under the effect of external electric field.

Abstract:Fresnel biprism has been applied to the design of plasmonic meta-lenses recently. In order to promote these applications and understand the physics behind them, in this paper we investigate the focusing effect of Fresnel biprism from the perspective of information optics and geometrical optics. The expression for optical field intensity describing the focusing effect of Fresnel biprism is derived according to the relationship between the impulse response function and the optical field. Then the formula of the focal length is achieved. Furthermore, the Fresnel biprism focusing experiment is performed. Specially, the optical field intensity distribution is measured and the corresponding intensity along the axis is obtained. The results show that the focusing effect depends on the base angle, refractive index and base length of the biprism. There exists axial resonance effect in the axial intensity. The experimental results are in accordance with the theoretical results. These results could be valuable to the applications of Fresnel biprism in designing large depth of focus plasmonic meta-lenses.

Abstract:We systematically investigate the influence of growth interruption time on the properties of InAs/GaSb type-II superlattices (T2SLs) epitaxial materials grown by molecular beam epitaxy (MBE). X-ray diffraction (XRD) and atomic force microscope (AFM) are used to characterize the material quality and morphology. The full width at half maximum (FWHM) of the XRD 0th satellite peaks ranges from 32' to 41', and the root mean square (RMS) roughness on a 5 μm×5 μm scan area is 0.2 nm. Photoluminescence (PL) test is used to reveal the influence of the growth interruption time on the optical property. Grazing incidence X-ray reflectivity (GIXRR) measurements are performed to analyze the roughness of the interface. The interface roughness (0.24 nm) is optimal when the interruption time is 0.5 s. The crystal quality of T2SLs can be optimized with appropriate interruption time by MBE, which is a guide for the material epitaxy of high performance T2SL infrared detector.

Abstract:A distributed architecture of optical line terminal (OLT) equipment is proposed for response to national bandwidth acceleration requirements and for future smooth evolution to 50G passive optical network (PON). This architecture moves the forwarding function of the control board to each service board to improve the switching capacity and performance of the system. The traditional control boards of centralized architecture OLT equipment have exchange and traffic processing function, and every service board is only controlled by the control board. In the distributed architecture of OLT equipment, control boards still maintain exchange function, whereas service boards have traffic processing functions. This method separates the exchange and traffic processing functions, which improves reliability. This paper also presents optical access network equipment combined with telemetry technology that provides reliable guarantee for intelligent analysis and data mining. Compared with the traditional push mode of network management, the data collected by network management combined with telemetry technology and artificial intelligence (AI) analysis can be used for network planning, assurance of the bandwidth and accurate operation.

Abstract:When optical fiber is deployed in practical engineering, bending and stretching of fiber optics is inevitable, which will affect optical communication. The fiber losses of different bending radii are simulated by COMSOL software. In order to verify the accuracy of simulation results, an experiment was designed to measure the losses of single-mode fiber under different bending radii and tension forces. The results show that the sensitive bending diameter of fiber loss is between 5 mm and 10 mm. The tensile effect has little influence on the fiber loss, but when the tensile force is greater than 160 N, the fiber breaks. This study provides an important reference for fiber layout in practical engineering.

Abstract:Due to the error of digital sampling, there is a deviation between the zero optical path difference (ZOPD) detection position of the interference signal in the infrared gas analyzer and the actual position. To solve this problem, a high-precision detection method of the ZOPD position based on wavelet transform is proposed. Firstly, the wavelet envelope curve of the interference signal is obtained by the wavelet transform, which can obtain the phase information and amplitude information of the maximum modulation position, and then the optimal ZOPD position is calculated by using the amplitude and phase information. The experimental results show that the error of the wavelet transform method is 19.617 nm, and the relative error is reduced by 93.11% compared with the peak method.

Abstract:A broadband tunable instantaneous frequency measurement (IFM) system is designed based on the stimulated Brillouin scattering effect of the highly nonlinear fiber in which the carrier suppressed single sideband modulated signal of the Brillouin frequency shift acts as pump light. The amplitude comparison function (ACF) is constructed by the power radio of the two paths in the system. The frequency measurement range and measurement accuracy can be tuned by changing the frequency difference of the two phase modulation signals. The tunable frequency measurement ranges of 2—5 GHz, 2—10 GHz, 2—15 GHz, 2—20 GHz, and 2—24 GHz are realized, and the corresponding measurement accuracies are 3.64 dB/GHz, 2.17 dB/GHz, 1.87 dB/GHz, 1.22 dB/GHz, and 0.77 dB/GHz, respectively.

Abstract:To balance the speed and accuracy in semantic segmentation of the urban street images for autonomous driving, we proposed an improved U-Net network. Firstly, to improve the model representation capability, our improved U-Net network structure was designed as three parts, shallow layer, intermediate layer and deep layer. Different attention mechanisms were used according to their feature extraction characteristics. Specifically, a spatial attention module was used in the shallow network, a dual attention module was used in the intermediate layer network and a channel attention module was used in the deep network. At the same time, the traditional convolution was replaced by depthwise separable convolution in above three parts, which can largely reduce the number of network parameters, and improve the network operation speed greatly. The experimental results on three datasets show that our improved U-Net semantic segmentation model for street images can get better results in both segmentation accuracy and speed. The average mean intersection over union (MIoU) is 68.8%, which is increased by 9.2% and the computation speed is about 38 ms/frame. We can process 27 frames images for segmentation per second, which meets the real-time process and accuracy requirements for semantic segmentation of urban street images.

Abstract:Because chaotic systems are unpredictable, ergodic and sensitive to initial values and parameters, they are often used in the field of encryption. To avoid the bad randomness of the random key generated by the low dimensional chaotic map system, a 5-dimensional multi-wing hyperchaotic system is adopted in this paper. The key stream generated by the chaotic system is related to the plaintext image. So it can effectively resist the attacks of selecting plaintext. The plaintext graph is decomposed into binary form by bit plane decomposition technique, and then these bit planes are divided into high and low groups. The designed control matrix is used to identify the specific scrambling mode, and each bit is permuted within and between groups. Finally, bit diffusion is used to change the pixel value of each pixel. Theoretical analysis and numerical simulation show that the algorithm has good encryption performance for image encryption.