Abstract:A high-performance zinc oxide (ZnO)/polyvinylpyrrolidone (PVP) humidity sensor was prepared by simple coprecipitation method with PVP as surfactant. The coprecipitation method has low reaction temperature, little energy consumption and simple preparation, which is suitable for large-scale production. The PVP makes sample’s surface with more hydroxyl and oxygen vacancies than pure ZnO, which can absorb more water molecules and promote the decomposition of water molecules into H3O+ to form effective ion conduction. When the molar ratio of PVP to ZnO is 1:1, the ZnO/PVP humidity sensor has low hysteresis (~4.2%), short response/recovery time (9/10 s), excellent stability and high sensitivity with more than 4 orders of magnitude in relative humidity (RH) range from 11% to 95%. Moreover, the ZnO/PVP humidity sensor can distinguish different respiratory states of human body, which has a potential in monitoring and prevention of respiratory diseases.

Abstract:A respiratory monitoring system was proposed based on optical fiber. The sensor consists of photonic crystal fiber (PCF) spliced with multimode fiber (MMF) to fabricate Michelson interferometer. The sensor is inserted into an oxygen mask tube and then put on the nose and mouth to monitor the respiratory rate (RR) for different cases. The results showed that when breathing increased, the intensity of light decreased. The intensity of light in the sleeping case of breathing was more intense than that when the intensity of working sport was measured. The working sport case was a higher transmittance than that of sleeping. The sensitivity of the sensor was also measured to be 231.9 pm/RH.

Abstract:Enhancing the spectral quality of the signal without varying the extinction ratio is a challenge for millimeter (MM) wave generation. Here, we propose a novel extinction ratio tolerant frequency 8-tupling technique using two Mach-Zehnder modulators (MZMs) with optimal splitting ratio in parallel configuration. Although the proposed technique is not affected by extinction ratio, a high quality MM wave is still obtained with complete unwanted sideband suppression. Two non-ideal MZMs with π/2 and π phase shifter realize MZM with optimal splitting ratio, which acts as a high extinction ratio modulator. The 80 GHz MM wave with 62 dB optical sideband suppression ratio (OSSR) and 54 dB radio frequency sideband suppression ratio (RSSR) is generated from 10 GHz local oscillator signal at 2.403 6 modulation index (MI). Performance of the present work has been evaluated using various MIs, phase drifts and extinction ratios. Sideband suppression ratio (SSR) greater than 10 dB is reported in a wide MI ranging from 2.36 to 2.47. Further, both the SSRs are tolerant towards MZM extinction ratio. The work is ideal for wavelength division multiplexing (WDM) applications due to its filterless characteristics.

Abstract:We have numerically presented an actively mode-locked fiber laser with tunable repetition rate based on phase modulator. By finely optimizing intra-cavity parameters, the ultrashort pulses with tunable repetitive frequency at giga hertz level can be easily generated due to the balance between dispersion and nonlinearity in the fiber laser cavity. When the pulse frequency is changed from 1.0 GHz to 4.2 GHz, the spectral width increases from ~15.65 nm to ~27.25 nm. In addition, the corresponding pulse duration decreases from ~81.59 ps to ~31.57 ps. Moreover, these output pulses with giga hertz repetitive rates and the picosecond widths can be further compressed by using the reasonable dispersion medium. For the pulse regime with repetition frequency at giga hertz level, the obtained smallest pulse duration is about ~62 fs based on chirp pulse compression. We hope that these simulation results can promote further research and application in the ultrashort pulse lasers with high repetition rate.

Abstract:In this paper, Cd1-xZnxS thin films were prepared by chemical bath deposition (CBD), and the effects of different zinc doping content on the morphological structure and optical properties of Cd1-xZnxS buffer layers are systematically discussed. The experimental results show that in the deposition process of different substrates, the crystal structure of the film is all hexagonal, and when the concentration of zinc sulfate (ZnSO4) precursor is varied from 0 to 0.025 M, the films are uniform and dense. With the increase of zinc content, the X-ray diffraction (XRD) peak of the films shifted behind that of CdS film (002). It showed 70% to 90% transmittance in the visible region and the optical band gap increased gradually. The band gap value of the films obtained ranged from 2.43 eV to 3.01 eV. It shows the potential feasibility of its application to photovoltaic devices.

Abstract:We report a theoretical analysis of the electronic, optical, and mechanical properties of zinc-blende GaP semiconductor material. High-temperature impact on the interesting features has been reported. The temperature dependence of sound velocity and phonon frequencies of GaP has been determined. The pseudopotential technique has been used in our study. The current study can help in our comprehension of how temperature affects the electronic characteristics of GaP material. Our findings show generally a good accordance with the experiment. The prediction properties could be used in optoelectronic applications in the high-temperature range.

Abstract:A decision feedback equalization (DFE) algorithm is proposed by simplifying Volterra structure. The simplification principle and process of the proposed Volterra-based equalization algorithm are presented. With the support of this algorithm, the signal damage for four-level pulse amplitude modulation signal (PAM-4) is compensated, which is caused by device bandwidth limitation and dispersion during transmission in C-band intensity modulation direct detection (IM-DD) fiber system. Experiments have been carried out to demonstrate that PAM-4 signals can transmit over 2 km in standard single-mode fiber (SSMF) based on a 30 GHz Mach-Zehnder modulator (MZM). The bit error rate (BER) can reach the threshold of hard decision-forward error correction (HD-FEC) (BER=3.8×10-3) and its sensitivity is reduced by 2 dBm compared with traditional feedforward equalization (FFE). Meanwhile, the algorithm complexity is greatly reduced by 55%, which provides an effective theoretical support for the commercial application of the algorithm.

Abstract:The selection of appropriate codes for an optical code division multiple access (OCDMA) network, which determines the maximum number of users and bit error rate (BER) supported by the system, is crucial. This study proposed a variable weight zero cross-correlation Latin square (VW-ZLS) code for spectral amplitude coding (SAC)-OCDMA systems, which offers high autocorrelation and zero cross-correlation, while providing differentiated quality of service (QoS) features. Using direct detection (DD) technology, the data rate of the proposed VW-ZLS code reached 4.8 Gbit/s under the condition that BER does not exceed 10-9. This was 0.5 Gbit/s higher than that of zero cross-correlation magic square variable weight optical orthogonal code (ZMS-VWOOC) with the same cross-correlation characteristics. Further, simulation results showed that in SAC-OCDMA system, the VW-ZLS code was better than ZMS-VWOOC and exhibited excellent performance.

Abstract:In order to meet the reflectivity measurement requirements of any incident angle at different points of the large size special high mirror, a rotating cavity ring-down spectroscopy high reflectivity measurement system was built, in which the rotation function of the resonant cavity was set, and the lifting and parallel travelling mechanism of the measured mirror was added. Furthermore, the uncertainty of the measurement results was analyzed and calculated. The results showed that the reflectivity of a high reflective mirror measured by the system was 99.979 5%, the measurement accuracy reached the order of 10-6, and the combined standard uncertainty of reflectivity measurement was 0.002 8%. Collectively, these results provide a detection guarantee for the maintenance of the large size special high mirror, and provide ideas and methods for the uncertainty analysis of measurement results of similar equipment parameters.

Abstract:Aero-optic imaging is a kind of optical effect, which describes the imaging deviation on the imaging plane. In this paper, the effect of the change of Mach number of blunt aircraft on the aero-optic imaging deviation is studied. The imaging deviations of Mach number 0.5—3 are analyzed systematically. The results show that with the increase of Mach number, imaging deviation increases gradually, and the increase rate is gradually slow. Imaging deviation slope decreases gradually with the increase of Mach number, and gradually tends to be zero, suggesting that imaging deviation is not sensitive to the change of the larger Mach number. In other words, the Mach number of smaller changes can lead to larger imaging deviation. As the Mach number of the aircraft increases, the slope of the imaging offset tends to be closer and closer to 0. When the Mach number of the aircraft increases to a certain extent, the change of the imaging offset will not have much influence. Therefore, in order to reduce the impact of flight speed on imaging migration, the aircraft should fly at a higher Mach number.

Abstract:Implicit polynomials (IPs) are considered as a powerful tool for object curve fitting tasks due to their simplicity and fewer parameters. The traditional linear methods, such as 3L, MinVar, and MinMax, often achieve good performances in fitting simple objects, but usually work poorly or even fail to obtain closed curves of complex object contours. To handle the complex fitting issues, taking the advantages of deep neural networks, we designed a neural network model continuity-sparsity constrained network (CSC-Net) with encoder and decoder structure to learn the coefficients of IPs. Further, the continuity constraint is added to ensure the obtained curves are closed, and the sparseness constraint is added to reduce the spurious zero sets of the fitted curves. The experimental results show that better performances have been obtained on both simple and complex object fitting tasks.