Based on the transfer matrix method, a detailed theoretical and numerical study on double-phase-shifted fiber Bragg grating (FBG) is investigated. Temporal responses of the double-phase-shifted FBG to optical pulse are analyzed and the influence of the two phase-shifts’ position on the reflected output pulse is evaluated. Results demonstrate that very different temporal pulse waveforms can be achieved by adjusting the length ratio (α=L₂/L₁). Specifically, a transform- limited Gaussian input optical pulse can be shaped into flat-top square pulse (α=1.81) or two identical optical pulse sequences (α=1.93).

The crown-like zinc oxide (ZnO) samples, which are composed of a hexagonal cap and a tower-like shaft, are prepared by vapor transport method. The hexagonal cap, working as a whispering gallery mode (WGM) resonant cavity, demonstrates density-dependent ultraviolet (UV) lasing emission with a broadened and squared photoluminescence (PL) profile under UV excitation at 355 nm. Theoretical analyses based on Fermi golden rule show that the broadened spectrum profile results from the special optical mode density characteristics in a WGM micro-cavity, which is in agreement with the observed results.

Er³⁺/Ce³⁺co-doped tellurite-based glasses with composition of TeO₂-ZnO-Na₂O are prepared by high- temperature melt-quenching technique. Effects of Ce₂O₃content on the 1.53 μm band fluorescence spectra and fluorescence lifetime of Er³⁺are measured and investigated. It is found that the tellurite glass containing Ce₂O₃with molar concentration of 0.25% exhibits an increment of 13% in 1.53 μm fluorescence intensity and an increment of 15% in the ⁴I_13/2 level lifetime. The results indicate that the prepared tellurite-based glass with a suitable Er³⁺/Ce³⁺codoping concentration is an excellent gain medium applied for broadband Er³⁺-doped fiber amplifier (EDFA) pumped with a 980 nm laser diode.

A white emitting phosphor of YAl₃(BO₃)₄:Ce³⁺, Dy³⁺is synthesized by a solid state reaction, and its luminescent properties are investigated. Its phase formation is carried out with X-ray powder diffraction analysis, and there is no crystalline phase other than YAl₃(BO₃)₄. YAl₃(BO₃)₄:Ce³⁺can produce 422 nm blue emission under 367 nm excitation. The emission spectrum of YAl₃(BO₃)₄:Dy³⁺shows several emission peaks under 350 nm excitation, and the peaks locate at 485 nm, 575 nm and 668 nm, respectively. Emission intensities of Ce³⁺and Dy³⁺in YAl₃(BO₃)₄are influenced by their concentrations, and the concentration quenching effect is observed. Energy transfer from Ce³⁺to Dy³⁺in YAl₃(BO₃)₄is validated and proved to be a resonant type via a quadrupole-quadrupole interaction, and the emission color can be tuned from blue to white by tuning the ratio of Ce³⁺/Dy³⁺. Moreover, the critical distance (Rc) of Ce³⁺to Dy³⁺in YAl₃(BO₃)₄is calculated to be 1.904 nm.

Recently, some kinds of structures have been found to show the property of extraordinary optical transmission (EOT). In this paper, we present a novel composite structure based on array of annular apertures (AAA) with compound lattice. The lattice includes two kinds of annular apertures with the same outer radius and different inner radii. The transmission spectrum of this compound periodic AAA can be achieved by adding up the spectra of two corresponding simple periodic AAAs, and the transmission shows EOT property. The transmission peaks of this kind of structure can be adjusted to desire wavelengths by changing the inner radius of aperture or the index of the dielectric material in the aperture. This structure can be used as a filter with dual pass bands when the difference between inner radii or indices of dielectric inside is large enough for two kinds of apertures.

In this paper, we present an innovative method of double balanced differential configuration, in which two adjacent single photon avalanche diodes (SPADs) from the same wafer are configured as the first balanced structure, and the output signal from the first balanced stage is subtracted by the attenuated gate driving signal as the second balanced stage. The compact device is cooled down to 236 K to be characterized. At a gate repetition rate of 400 MHz and a 1 550 nm laser repetition rate of 10 MHz, the maximum photon detection efficiency of 13.5% can be achieved. The dark count rate is about 10^-4ns^-1at photon detection efficiency of 10%. The afterpulsing probability decreases with time exponentially. It is shown that this configuration is effective to discriminate the ultra-weak avalanche signal in high speed gating rates.

Considering the influence of more random atmospheric turbulence, worse pointing errors and highly dynamic link on the transmission performance of mobile multiple-input multiple-output (MIMO) free space optics (FSO) communication systems, this paper establishes a channel model for the mobile platform. Based on the combination of Alamouti space-time code and time hopping ultra-wide band (TH-UWB) communications, a novel repetition space-time coding (RSTC) method for mobile 2×2 free-space optical communications with pulse position modulation (PPM) is developed. In particular, two decoding methods of equal gain combining (EGC) maximum likelihood detection (MLD) and correlation matrix detection (CMD) are derived. When a quasi-static fading and weak turbulence channel model are considered, simulation results show that whether the channel state information (CSI) is known or not, the coding system demonstrates more significant performance of the symbol error rate (SER) than the uncoding. In other words, transmitting diversity can be achieved while conveying the information only through the time delays of the modulated signals transmitted from different antennas. CMD has almost the same effect of signal combining with maximal ratio combining (MRC). However, when the channel correlation increases, SER performance of the coding 2×2 system degrades significantly.

With the rapid development of optical elements with large capacity and high speed, the network architecture is of great importance in determing the performance of wavelength division multiplexing passive optical network (WDM-PON). This paper proposes a switching structure based on the tunable wavelength converter (TWC) and the arrayed- waveguide grating (AWG) for WDM-PON, in order to provide the function of opitcal virtual private network (OVPN). Using the tunable wavelength converter technology, this switch structure is designed and works between the optical line terminal (OLT) and optical network units (ONUs) in the WDM-PON system. Moreover, the wavelength assignment of upstream/downstream can be realized and direct communication between ONUs is also allowed by privite wavelength channel. Simulation results show that the proposed TWC and AWG based switching structure is able to achieve OVPN function and to gain better performances in terms of bite error rate (BER) and time delay.

A direct detection optical orthogonal frequency division multiplexing (DDO-OFDM) system using turbo codes is built, and the transmission performance comparison between coded system and uncoded system is analyzed. Three decoding algorithms, which are Log-maximum a posteriori (MAP), Max-Log-MAP and threshold Max-Log-MAP, are used in the turbo coded system. By comparing three decoding algorithms, the system using Max-Log-MAP algorithm has the best bit error rate (BER) performance. At the transmission distance of 240 km, the uncoded system with transmission rate of 30 Gbit/s can get the BER performance at the degree of 8.93×10^-3with optical signal to noise ratio (OSNR) of 24 dB, while the turbo coded system with transmission rate of 50 Gbit/s can achieve it within OSNR of 20 dB.

A microwave photonic link (MPL) with high spurious-free dynamic range (SFDR) is proposed and analyzed. The optical carrier is divided equally into two paths. The path 1 is modulated by radio frequency (RF) signals in a Mach-Zehnder modulator (MZM), and the phase of path 2 is controlled before the combination with path 1. By properly adjusting the phase difference of the two paths with the optical phase shifter, the third-order intermodulation distortion (IMD3) can be significantly suppressed. A proof-of-concept simulation is carried out. The results show that a reduction of 40 dB in the IMD3 and an improvement of 21.1 dB in the SFDR are achieved as compared with the conventional MZM-based MPL. The proposed MPL shows the advantages of simple structure, low cost and high efficiency.

The scintillation indices (SIs) of Gaussian beams and vortex beams propagating in turbulent atmosphere are investigated experimentally. It is shown that with the increase of propagation distance, the SI of Gaussian beam around optical axis increases gradually, but the SI of vortex beam with topological charge of 4 increases, achieves the maximum value at a fixed distance, and then decreases as the continued increase of propagation distance. The SI of vortex beam can be smaller than that of Gaussian beam under certain conditions.

In order to realize the online measurement of lamp dimension, the bulb image dimension measurement based on vision (BIDMV) is proposed. The image of lamp is obtained by camera. After image processing, such as Otsu algorithm, median filter, ellipse fitting and envelope rectangle fitting, the dimension of lamp can be calculated. Based on this method, a non-contact real-time measurement system of the lamp’s dimension is developed. The precision of the proposed method is 0.07 mm, and it can satisfy the tolerance of the National Standard GB15766.1-2008. The experiment results show that the proposed method has a faster measuring speed and a higher precision compared with other measurement methods.

Considering the air-water interface and ocean water’s optical attenuation, the performance of quantum key distribution (QKD) based on air-water channel is studied. The effects of photons’ various incident angles to air-water interface on quantum bit error rate (QBER) and the maximum secure transmission distance are analyzed. Taking the optical attenuation of ocean water into account, the performance bounds of QKD in different types of ocean water are discussed. The simulation results show that the maximum secure transmission distance of QKD gradually reduces as the incident angle from air to ocean water increases. In the clearest ocean water with the lowest attenuation, the maximum secure transmission distance of photons far exceeds the the working depth of underwater vehicles. In intermediate and murky ocean waters with higher attenuation, the secure transmission distance shortens, but the underwater vehicle can deploy other accessorial methods for QKD with perfect security. So the implementation of OKD between the satellite and the underwater vehicle is feasible.

A colored 3D surface reconstruction method which effectively fuses the information of both depth and color image using Microsoft Kinect is proposed and demonstrated by experiment. Kinect depth images are processed with the improved joint-bilateral filter based on region segmentation which efficiently combines the depth and color data to improve its quality. The registered depth data are integrated to achieve a surface reconstruction through the colored truncated signed distance fields presented in this paper. Finally, the improved ray casting for rendering full colored surface is implemented to estimate color texture of the reconstruction object. Capturing the depth and color images of a toy car, the improved joint-bilateral filter based on region segmentation is used to improve the quality of depth images and the peak signal-to-noise ratio (PSNR) is approximately 4.57 dB, which is better than 1.16 dB of the joint-bilateral filter. The colored construction results of toy car demonstrate the suitability and ability of the proposed method.

In this paper, the surface-enhanced Raman scattering (SERS) is used as an analytical tool for the detection and identification of pathogenic bacteria of Escherichia coli (E. coli) and Salmonella typhimurium (S. typhimurium). Compared with normal Raman signal, the intensity of SERS signal is greatly enhanced. After processing all SERS data, the obvious differences between the SERS spectra of two species are determined. And applying the chemometric tools of principal component analysis and hierarchical cluster analysis (PCA-HCA), the SERS spectra of two species are distinguished more accurately. The results indicate that SERS analysis can provide a rapid and sensitive method for the detection of pathogenic bacteria.

A novel fiber Bragg grating (FBG) displacement sensor is proposed, which can achieve wide measuring range displacement detection with variable measurement precision due to its mechanical transfer structure of helical bevel gear. A prototype is designed and fabricated. The maximum detection displacement of this prototype is 1.751 m, and the precision grade changes from 0.2% to 6.7%. Through analyzing the experiment data which is obtained in the calibration experiment, the measuring range of this sensor is from 0 m to 1.532 m, and the wavelength shift errors between experiment data and theory calculation are all less than 5%.

To calibrate the tracing performance of the thirty meter telescope (TMT) tertiary mirror, for the special requirement of the TMT, the laser tracker is used to verify the motion. Firstly, the deviation is divided into two parts, namely, the repeatable error and the unrepeatable part. Then, based on the laser tracker, the mearturement and evalutation methods of the rigid body motion for the mirror are established, and the Monte Carol method is used to determine the accuracy of the mothod. Lastly, the mothod is applied to the turn table of a classical telescope and the residual error is about 4 arc second. The work of this paper will guide the next desgin and construction work of the thirty meter telescope tertiary mirror.

In this paper, the positive influence of apodization weighting method on frequency characteristics of surface acoustic wave (SAW) temperature sensor is investigated. Simulation and experiment results show that side lobe suppression abilities of the sensor can be improved by using apodization weighting which is based on Chebyshev window. Meanwhile, we find that the side lobe of the sensor can be further restrained, when the dummy electrodes are removed. Frequency- temperature characteristics of the devices are independent of the inclusion of dummy electrodes. The apodization weighted SAW temperature sensor shows great application potential in occasions with strong electromagnetic interference.

We demonstrate a laser-diode (LD) pumped actively Q-switched laser with Nd:Sc_0.2Y_0.8SiO₅(Nd:SYSO) crystal for the first time. A stable actively Q-switched laser is obtained at dual wavelengths of 1 075.2 nm and 1 078.2 nm. The maximum average output power of 720 mW is obtained at the repetition rate of 15 kHz under the pump power of 8.7 W. The minimum pulse width of 58 ns is obtained at the repetition rate of 5 kHz under the pump power of 8.7 W, corresponding to the peak power of 1.9 kW and the pulse energy of 112 μJ.

We propose a compact dual-band bandpass filter (BPF) based on one-dimensional porous silicon (PS) photonic crystal by electrochemical etching. By inserting three periods of high and low reflective index layers in the center of porous silicon microcavity (PSM), two sharp resonant peaks appear in the high reflectivity stop band on both sides of the resonance wavelength. Through simulation and experiment, the physical mechanisms of the two resonance peaks and the resonance wavelength are also studied. It is found that the resonance wavelength can be tuned only by adjusting the effective optical thickness (EOT) of each PS layer, in which different resonance wavelengths have different widths between the two sharp resonance peaks. Besides, the analysis indicates that oxidization makes the blue shift become larger for high wavelength than that for low wavelength. Such a fabricated BPF based on PS dual-microcavity is easy to be fabricated and low cost, which benefits the application of integrated optical devices.