Abstract:The thermal lens problem of optical system caused by high temperature environment is a common problem. Athermal design of lenses based on optical calculation software is an effective passive compensation method. But it is difficult to determine its accuracy and measure it experimentally. We describe an athermal design technology and propose a simulated scheme to verify the accuracy of this design. Three materials with negative dn/dT have been selected to compensate for the thermal lenses produced by a fused silica lens. The results show that the compensation effect of N-PSK53A is the best.

Abstract:This work discusses the design methods of 120 GHz on-chip dual-mode and three-mode dielectric resonator antennas (DRAs) based on a standard CMOS technology. The bandwidths of the DRAs are expanded by merging adjacent modes with similar radiation patterns. The impedance bandwidth of 18.6% with the peak gain of 6 dBi is achieved for the proposed on-chip dual-mode DRA. In addition, the impedance bandwidth of 20.1% with the peak gain of 6.9 dBi is achieved for the proposed three-mode DRA. To the best of authors’ knowledge, the on-chip multi-mode DRAs are first proposed. The impedance bandwidth of the proposed three-mode on-chip DRA is wider than the other on-chip DRAs using planar feeding with on-chip ground. The proposed antennas are promising for terahertz applications due to the merits of wide band, high gain and high radiation efficiency.

Abstract:An in-line Mach-Zehnder interferometer (MZI) for simultaneous measurement of temperature and refractive index (RI) is proposed and demonstrated. The sensor is composed of cleaved taper, single-mode fiber (SMF) and spherical structure. Using precision device to measure the position of waist, the cleaved taper structure is obtained by cutting the taper structure. The sensitivities of the temperature are 0.052 nm/ oC and 0.037 nm/ oC in the temperature range of 25—70 oC, respectively. The RI sensitivities are −56.59 nm/RIU and −43.53 nm/RIU in the RI range of 1.335—1.38, respectively. This sensor has many advantages such as compact structure and good stability.

Abstract:2 μm/3 μm laser has been extensively applied to the fields of medical treatment, communication and detection. In this paper, the genetic algorithm is innovatively used to solve the fiber power transmission equation, which improves the accuracy of simulation results. According to the simulation results, a dual-wavelength Er3+:ZBLAN fiber laser based on composite Fabry-Perot (F-P) cavity was designed and constructed. A stable continuous dual-wavelength output was obtained with a pump power of 50 W. The center wavelengths were 2.79 μm and 1.59 μm, respectively, the maximum output powers were 8.19 W and 2.8 W, respectively, the slope efficiencies were 17.7% and 7.17%, respectively, and the stability of the wavelengths in 2 h were 4.6% and 3.1%, respectively.

Abstract:Exploiting a specially designed Fabry-Perot filter as output coupler, a continuous 1 052 nm and 1 061 nm dual-wavelength laser is realized. The threshold, slope efficiency and maximum power of the 1 052 nm and 1 061 nm dual-wavelength laser are 2.55 W, 17.5% and 571 mW, respectively. The competition and coexistent relationships between 1 052 nm, 1 061 nm and 1 064 nm are analyzed. Involved non-degenerate Stark energy level structures are used to classify dual-wavelength lasers. According to this method, dual-wavelength lasers can be classified as different upper and lower non-degenerate Stark energy levels, the same upper but different lower Stark energy levels, different upper but the same lower Stark energy levels. Representative Nd:YAG dual-wavelength lasers are classified according to this criterion. It is found that the realization of front two type lasers is easy and that of third type lasers is challenging. This method can be used as a level of difficulty reference for the realization of dual-wavelength lasers.

Abstract:A novel microfiber nested ring with knot resonator (MNRKR) is proposed and demonstrated. A mathematical model to describe the principle of the tunable feature of MNRKR is illustrated. The improvement of the output spectra is achieved by changing the transmission coefficient and the length of the feedback waveguide. We theoretically and experimentally demonstrate that the free spectral range (FSR) can be doubled by constructive interference without reducing the circumference of microring. Thus, this all-fiber optical device has the potential for achieving a large measuring range of the optical sensor.

Abstract:A filter-less frequency doubling generator with tunable phase shift based on dual-polarization modulation is proposed and analyzed. The setup is composed with a continuous-wave laser, a dual-polarization Mach-Zehnder modulator and a linear polarizer followed by a photodetector. The modulator is used to generate frequency doubling modulation signals on orthogonal polarization axis. By tuning the polarization state before the polarizer, the initial phase of the generated microwave signal can be tuned manually. At the meantime, the signal amplitude will remain constant. It is found the generated signal's frequency is twice of the driven frequency. The electrical phase shift can be tuned within full range ((0°—360°). Without using any optical filter or wavelength-dependent component, this scheme is featured with good frequency tunability and multi-wavelength operation.

Abstract:A structure of optical arbitrary waveform generation (OAWG) based on an array of tunable apodized waveguide Bragg gratings (WBGs) is proposed. The WBGs array on lithium niobate (LN) consists of several apodized gratings, waveguides and electrodes deposited on both sides of gratings and waveguides. The properties of OAWG are analyzed using transfer matrix method. Due to the electro-optic effect of LN, the amplitude and phase of incident light source are controlled via adjusting the voltages on electrodes. Consequently, the optical pulses with different waveforms are obtained and the amplitude is linearly tuned. In addition, voltages compensating amplitude and phase distortion are demonstrated.

Abstract:A compact directional backlight module of time-multiplexed auto-stereoscopic display based on side-glowing polymer optical fiber (SGPOF) is proposed. The optical system is mainly composed of SGPOF array and cylindrical lens array. Spatial crosstalk is reduced by inserting a grating film as multi-slit diaphragm between the SGPOF array and the cylindrical lens array. A theoretical model is constructed based on the imaging optics principle of the off-axis ray. In the experiments, the cylindrical lens array concentrates a small number of views on three different view zones, the display can provide high luminance. The measurement results show that the luminance uniformity of the backlight module is up to 89.6%, and in the viewing zone the crosstalk is lower than 10%. The backlight module is compacted that the thickness being only 7 mm. The full-resolution and low-crosstalk 3D images are realized by using SGPOF backlight.

Abstract:This paper describes a new approach to regulate the photoelectric properties of two-dimensional SiC materials. The first-principles pseudo-potential plane wave method is used to calculate the geometric structure, electronic structure and optical properties of two-dimensional (2D) SiC co-doped by the adjacent elements of C-Si (such as B and N). The results show that:after B-N co-doping, the supercell lattices of 2D SiC are observed obviously deformation near the doped atoms. Meanwhile, the band structures of 2D SiC co-doped by B-N become rich. As the impurity level enters the forbidden band, the band gap decreases, and the distribution of density of states near the Fermi level changes accordingly. The calculation of optical properties shows that the ability to absorb electromagnetic waves of 2D SiC has been enhanced obviously in the low energy range after B-N co-doping. The reason is originated from the transition of the 2p state of B and N. At the same time, the static dielectric constant increases and the peak of reflectivity decreases. The above results indicate that the optoelectronic properties of 2D SiC can be modulated by co-doping B-N.

Abstract:With the development of visible light communication (VLC) and widespread applications of smart terminals with complementary-metal-oxide-semiconductor (CMOS) image sensor, researchers pay more and more attention in VLC systems with CMOS-based receiver. The blooming effect and light noise make the threshold decision in image processing difficult, which deteriorates the system performance a lot. In this paper, an efficient demodulation scheme is proposed to improve the performance of image processing. In the proposed demodulation scheme, a region of interest (ROI) based column matrix selection scheme is employed to avoid blooming effect, and an adaptive contrast enhancement (ACE) algorithm is designed to increase the contrast of bright and dark stripes. Experimental results show that the proposed scheme especially fits for high fluctuation data pattern. The demodulation with a data rate of 5.76 kbit/s can successfully achieve 7% forward error correction (FEC) limit even when the illuminance is very low.

Abstract:Optical orthogonal frequency division multiplexing (O-OFDM) has been widely adopted as a high-speed data transmission technique in visible light communication systems. This technique usually suffers from high peak-to-average-power ratio (PAPR). In this paper, a new PAPR reduction technique is proposed for O-OFDM signals. At the transmitter, a matrix transformation with the Gaussian elements is applied to the time-domain O-OFDM signal and at the receiver, the inverse matrix is used to recover the original signal. We show that the Gaussian orthogonal matrices can reconstruct the original signals without degrading the bit error rate (BER) performance. Gram-Schmidt technique is used to orthogonalize the Gaussian matrices. Computer simulations are conducted for 16-QAM baseband modulated symbols and about 3 dB PAPR reduction gain is achieved by the proposed approach compared with conventional O-OFDM.

Abstract:The laser dazzling effect has always been a crucial issue for the scientific community. Nevertheless, the experiments to study the laser dazzling effect may cost a lot. Therefore, the technology of simulation is promising for this field. Additionally, the effectiveness of the laser dazzling needs to be evaluated by a no reference cost functions. A general model of CCD is proposed in this paper. Additionally, two cost functions are proposed to evaluate the image. The simulation result based on the model shows feasibility of the cost functions. Afterwards an experiment is carried out to testify these cost functions. Different factors include the intensity of the irradiance, the beam radius and the dazzling location of the laser are taken into consideration. The experimental result shows the cost functions have monotonous relationship with the degree of the laser dazzling. This result indicates that the cost functions can be used in the field to measure the degree of the laser dazzling.

Abstract: Convolutional neural networks (CNNs) based methods for automatic discriminant of prohibited items in X-ray images attract attention increasingly. However, it is difficult to train a reliable CNN model using the available X-ray security image databases, since they are not enough in sample quantity and diversity. Recently, generative adversarial network (GAN) has been widely used in image generation and regarded as a power model for data augmentation. In this paper, we propose a data augmentation method for X-ray prohibited item images based on GAN. First, the network structure and loss function of the self-attention generative adversarial network (SAGAN) are improved to generate the realistic X-ray prohibited item images. Then, the images generated by our model are evaluated using GAN-train and GAN-test. Experimental results of GAN-train and GAN-test are 99.91% and 98.82% respectively. It implies that our model can enlarge the X-ray prohibited item image database effectively.

Abstract:The compressive sensing technology has a great potential in high-dimensional vision processing. The existing video reconstruction methods utilize the multihypothesis prediction to derive the residual sparse model from key frames. However, these methods cannot fully utilize the temporal correlation among multiple frames. Therefore, this paper proposes the video compressive sensing reconstruction via long-short-term double-pattern prediction, which consists of four main phases:the first phase reconstructs each frame independently; the second phase adaptively updates multiple reference frames; the third phase selects the hypothesis matching patches from current reference frames; the fourth phase obtains the reconstruction results by using the patches to build the residual sparse model. The experimental results demonstrate that as compared with the state-of-the-art methods, the proposed methods can obtain better prediction accuracy and reconstruction quality for video compressive sensing.

Abstract:In this study, time resolved (TR) Monte Carlo (MC) simulation program code was run to generate photon fluencies with increasing time steps. TR MC simulation was performed for ten time series from 4 ps to 52 ps. Generated photon fluencies were transferred to the image analysis programming platform. Imaging device geometry was created for test purpose in image reconstruction programming platform environment. Forward model weight matrix functions were calculated during each time period for 38 sources, and 38 detectors according to the back-reflected imaging geometry. A homogenous phantom, which simulated tissue, was chosen. Depending on the homogeneous tissue optical properties, such as tissue absorption coefficient μa, and tissue scattering coefficient μs, photons emitted from the laser source positions; migrated differently inside the imaging tissue. Photons migrate inside the tissue by some multiplication factor of ps depending on the tissue type for each 100-micrometer vertical distance. Superficial photons come photodetector point fast, depend on the source-detector neighborhood distances and tissue optical properties, respectively. Time resolved diffuse optic tomography (TRDOT) imaging systems are an emerging biomedical optic imaging modality due to progressive electronic technologies are helping to build the systems faster and cheap. As such, emerging microelectronic technology is giving important access to design and implement compact laser sources and photodetector units. Vertical cavity surface emitting light (VCSEL) as laser source and single photon avalanche diode (SPAD) arrays as photodetector units are becoming in common use as important hardware tools for designers and researchers in this field. TR diffuse photon analysis should be done routinely for better understanding of TRDOT devices. Hence, MC simulation driven TR photon fluence analysis was done for such a purpose in this study.