Abstract:The generation of periodic triangular waveform with variable symmetrical coefficient based on a dual-parallel Mach-Zehnder modulator (DP-MZM) is demonstrated in this work. By properly setting the modulation index and bias points of DP-MZM, desired symmetric/asymmetric triangular waveforms can be generated. Then applying the generated triangular waveform into an amplitude modulator (AM), a single-period signal can be extracted to explore the optical wavelength conversion induced by the self-phase modulation (SPM) effect in a high nonlinear fiber (HNLF). Wavelength shifts of triangular waveforms with different coefficients (10%, 20%, 30%, 40% and 50%) are calculated. In addition, the influence of key parameters of HNLF on the wavelength conversion is analyzed in detail.

Abstract:The nonlinear pulse dynamics have been studied in a thulium/holmium co-doped passively mode-locked fiber laser based on nonlinear optical loop mirror (NOLM). By enhancing the nonlinear effect of the cavity and without changing the polarization state of the cavity, four types of operation states that switch between each other, including the basic mode-locking pulse, the two solitons pulse, the bright-dark pulse, and the harmonic mode-locking pulse, can be obtained. Compared with the laser of single mode-locking state, passively mode-locked fiber lasers (PMLFLs) with switchable operation states can be used in a wide range of applications, such as optical communication, material processing and optical fiber sensing technology.

Abstract:A biosensor based on single-fiber optical tweezers is proposed, which can detect the motion trajectory of cells based on the stable capture and transmission of silica microspheres as well as biological yeast cells by using a tapered optical fiber as a sensing element. The interference cavity is formed by using the fiber tip and the target particle, the detected interference signal is demodulated using Hilbert transform, and the displacement curve of the particle is plotted to realize the particle motion trajectory tracking. This method provides potential technical support for process monitoring of targeted drug delivery in biomedicine.

Abstract:Aminiaturized near infrared single photon detector is demonstrated by integrating a thermoelectric cooler (TEC), a thermistor, and a planar type InGaAs/InP separate absorption, charge and multiplication structure single photon avalanche diode into a butterfly case. The performance of the device at different temperatures is tested. It can achieve 20.3% single photon detection efficiency and 1.38 kHz dark count rate when the chip is cooled to 223 K. The test results show that even when the chip temperature is kept constant, the dark count rate of the device still increases with the increase of ambient temperature, which is consistent with the carrier generation mechanism of semiconductor materials. The mechanism is researched and it is found that thermal radiation of the high temperature case is the main source of dark count. The deep research on the mechanism is beneficial to developing higher performance devices in the future.

Abstract:We have studied the lattice vibrations, optical and mechanical characteristics of the zinc-blende aluminum phosphide (AlP) compound. Investigations have been done into the effect of temperature on refractive index, optical dielectric constant, static dielectric constant, longitudinal and transversal sound velocities, reflectivity, susceptibility, phonon frequencies, micro-hardness, ionicity, and transverse effective charge. AlP is a wide-indirect band gap semiconductor and has a wide range of uses in high-performance optoelectronic devices, such as the manufacturing of infrared photo-detectors and light-emitting diodes. It's important to know the physical properties of semiconductor materials, like the AlP compound, to develop new technologies and devices. The calculations were carried out using the empirical pseudo-potential method (EPM). Comparative analysis with the existing experiment and other theoretical calculations reveals a satisfactory level of agreement.

Abstract:In this paper, a new training sequence structure is proposed, which estimates the in-phase/quadrature (IQ) imbalance factor and channel information in coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems with phase noise caused by laser linewidth. The given training sequence structure consists of four symbols. The first two training symbols have two subsets:a non-zero subset and a zero set mirror position subset. The non-zero subset is used to estimate the channel information, the mirror position subset is used to estimate the IQ imbalance factor, and the last two symbols are also used to estimate the IQ imbalance factor at the transmitter. This method can realize independent compensation for IQ imbalance and channel distortion, and improve the system performance when the data rate is 10 Gbit/s higher than the traditional method.

Abstract:We proposed an ultra-high sensitivity triple-core fiber refractive index (RI) sensor with a modified Vernier effect for marine RI measurement and demonstrated it by numerical simulation. This sensor composes a pair of parallelized spatial mode Mach-Zehnder interferometers (MZIs), both of which are involved in sensing, but possess different interfering modes. By designing an MZI RI fiber optic sensor based on Vernier effect in air, it is demonstrated that in the low RI such as air environment, only the modes involved in sensing interference are affected by the environment to generate Vernier effect. In the high RI marine environment, both sensing interferometer and reference interferometer need to be affected by the ambient RI to generate Vernier effect. The simulation results indicate that the proposed novel sensing structure can amplify its sensitivity from −15 428 nm/RIU to −24 857 nm/RIU in the marine environment.

Abstract:A tri-color quad-beam digital shearography is proposed to achieve the measurement of absolute three-dimensional (3D) displacement gradients. Four laser beams with three different center wavelengths are symmetrically irradiated to the object surface from the upper and lower left and right directions. Four phase maps are then extracted from the two interferograms obtained from two shots. Based on these four phase maps, the absolute 3D displacement gradients are determined. This means of absolute 3D displacement gradient measurement effectively improves the measurement capability of digital shearography and expands its application range.

Abstract:The terahertz (THz) absorptions of maleic hydrazide polymorphs (MH2 and MH3) have been measured utilizing terahertz time-domain spectroscopy (THz-TDS). MH2 and MH3 have displayed totally different THz absorption features compared to their basically identical infrared spectral peaks. Experimental THz spectrum of MH2 showed six distinct absorption features while MH3 demonstrated five characteristic absorption peaks in the range of 10—160 cm-1. Spectral interpretation has been carried out in the framework of density functional theory (DFT) using periodic unit cell models. The simulation yields a good quality with respect to the measured features. Further analysis into the mode of vibration showed that the low-frequency THz spectral features (<112 cm-1) are contributed by intermolecular interactions mediated by in-plane/out-of-plane collective vibrations. The varied intermolecular interactions and crystal habits are the primarily reason for the THz spectral differences of MH2 and MH3.

Abstract:To address the problems of insufficient dimensionality of electroencephalogram (EEG) feature extraction, the tendency to ignore the importance of different sequential data segments, and the poor generalization ability of the model in EEG based emotion recognition, the model of convolutional neural network and bi-directional long short-term memory and self-attention (CNN+BiLSTM+self-attention) is proposed. This model uses convolutional neural network (CNN) to extract more distinctive features from both spatial and temporal dimensions. The bi-directional long short-term memory (BiLSTM) is used to further preserve the long-term dependencies between the temporal phases of sequential data. The self-attention mechanism can change the weights of different channels to extract and highlight important information and address the often-ignored importance of different channels and samples when extracting EEG features. The subject-dependent experiment and subject-independent experiment are performed on the database for emotion analysis using physiological signals (DEAP) and collected datasets to verify the recognition performance. The experimental results show that the model proposed in this paper has excellent recognition performance and generalization ability.

Abstract:To address the problems of insufficient dimensionality of electroencephalogram (EEG) feature extraction, the tendency to ignore the importance of different sequential data segments, and the poor generalization ability of the model in EEG based emotion recognition, the model of convolutional neural network and bi-directional long short-term memory and self-attention (CNN+BiLSTM+self-attention) is proposed. This model uses convolutional neural network (CNN) to extract more distinctive features from both spatial and temporal dimensions. The bi-directional long short-term memory (BiLSTM) is used to further preserve the long-term dependencies between the temporal phases of sequential data. The self-attention mechanism can change the weights of different channels to extract and highlight important information and address the often-ignored importance of different channels and samples when extracting EEG features. The subject-dependent experiment and subject-independent experiment are performed on the database for emotion analysis using physiological signals (DEAP) and collected datasets to verify the recognition performance. The experimental results show that the model proposed in this paper has excellent recognition performance and generalization ability.