Abstract:Silver nanoparticles (NPs) of 5–15 nm are synthesized with the reduction of silver nitrate (AgNO₃) by formaldehyde (HCHO) and using polyethylenemine (PEI) as a stabilizer. Transmission electron microscopy (TEM) analysis shows the size of the Ag NPs increases with the increase of HCHO contents. The absorption and emission peaks of the original colloids are red shifted with increasing the size of Ag NPs. The absorption and emission peaks are at 344 nm, 349 nm, 357 nm, 362 nm, 364 nm and 444 nm, 458 nm, 519 nm, 534 nm, 550 nm, respectively. The fluorescence intensities of the silver colloids increase with increasing the NPs size (or the contents of HCHO). With the diluted fold increasing, the fluorescence intensity of the diluted silver colloids increases firstly then decreases. Compared with that of the original silver colloids, the emission peaks are blue shifted. For the diluted silver colloids, when the fluorescence intensity is maximum, the emission peaks are all near 444 nm. The 16-fold diluted silver colloid gets to the maximum emission intensity when the mole ratio of AgNO₃ and HCHO is 1:6.

Abstract:A strain-introduced Mach-Zehnder interferometer (MZI) interleaver on lithium niobate (LiNbO₃) is proposed. The structure of the strain-introduced waveguide is designed in detail, and is produced by depositing a SiO₂ film on the annealed proton-exchanged LiNbO₃ waveguide. Considering the sensitivities of the edge strain to the deposition temperature and the thickness of the SiO₂ film, an optimum design of 50 GHz interleaver on this structure is given through analyzing the effective index changes for E _pq ^x mode by finite difference method (FDM). The length of the bending waveguide in this interleaver is just two thirds of that in the conventional interleaver due to the high refractive index difference.

Abstract:A novel element for collimating LED light is designed based on non-imaging optics. It is composed of a refraction lens and a reflector. The upper surface of the lens is freeform and calculated by geometrical optics and iterative process. The lens makes the rays in the range of 0°–45° from the optical axis collimated. The rays in the range of 45°–90° from the optical axis are collimated by the reflector. The inner surface of the reflector is parabolic with its focus located in the LED chip. The designed element is applicable to LED source of any emitting type. For a certain application, the simulation results of the designed element in Tracepro show that it has a very compact structure and good collimating performance. Just investigating the loss in the lens surfaces, this element has high light output efficiency of nearly 99%. Most lighting area radii are no more than 20 mm when the illuminated plane is 5 m away from the LED source.

Abstract:In this paper, a 20 nm palladium-silver (Pd/Ag) ultrathin optical film is used for hydrogen gas sensing. The mole ratio of the two metals is controlled at Pd:Ag=3:1. In the direct current (DC) sputtering machine, the optical thin film is evaporated on the optical glass. Compared with pure palladium, the Pd/Ag alloy can increase the life and the stability of the sensing film. Optimum sputtering parameters for Pd/Ag alloy are presented in this paper, and the effects of different experimental conditions for hydrogen sensor are investigated, including the temperature effect, humidity effect and cross sensitivity of hydrogen sensor for different gases. The experiment results indicate that the hydrogen sensor based on Pd/Ag optical thin film exhibits good sensing characteristics. The existing of CO and water in hydrogen increases the response time and decreases the response amplitude of optical fiber bundle hydrogen sensor. The experiment results show that the increasing temperature can eliminate the effect and shorten hydrogen sensor response time effectively.

Abstract:Transistor laser (TL) model based on InGaP/GaAs/InGaAs/GaAs is analyzed and presented. It is realized that quantum well (QW) with width of 10 nm may be formed for low base threshold current density J _th. The emission wavelength is found to be 1.05 μm, and the indium (In) composition is 0.25 for optimal QW width. It is identified that J _th decreases with the movement of QW towards the base-emitter (B-E) interface. Small signal optical response is calculated, and the effect of QW position is studied. The bandwidth is enhanced due to the movement of the QW towards the emitter base junction.

Abstract:In order to improve the transmission performance of the conventional Mach-Zehnder interferometer (MZI), a novel interleaver combining an “8” form ring resonator with a planar 3×3 single fiber coupler is proposed. Based on the phase modulation provided by the ring resonator, a flat filtering response is obtained by optimizing the coupling angle of resonator. The output expression is derived and numerical simulation is performed. The simulation indicates that the 0.5 dB passband and 25 dB stopband of the proposed interleaver are simultaneously improved remarkably, which are much wider than those of the single-stage MZI and the two-stage MZI interleavers, and the filtering performance of the proposed interleaver, which achieves a nearly square spectrum response, is also much better. Compared with the interleaver based on an asymmetrical MZI with a resonator in one arm, there is no difference between the intensities of two coherent beams in the condition of considering the influence of the propagation loss. Theoretical analysis shows that the influence of the propagation loss on extinction ratio can be effectively reduced.

Abstract:High-performance phosphorescent white organic light-emitting devices (PhWOLEDs) with color stability and low efficiency decay are demonstrated by inserting wide band-gap materials between emitting layers. The two devices with N,N′-dicarbazolyl-3,5-benzene (mCP) and p-bis(triphenylsilyl)benzene (UGH2) as the interlayer exhibit both slight Commission Internationale del’Eclairage (CIE) coordinates variations of (± 0.010, ± 0.005) and (± 0.013, ± 0.006) in a wide voltage range, and low decay in current efficiency which shifts from the peak value 35.4 cd·A⁻¹ and 27.4 cd·A⁻¹ to 28.8 cd·A⁻¹ and 23.5 cd·A⁻¹ at 40000 cd·m⁻², respectively. The improvements are attributed to the charge carriers balance and the elimination of energy transfer loss by confining the carrier accumulation at the exciton formation interface through the interlayer.

Abstract:The rare earth Ce³⁺ ion doped SiO₂-B₂O₃-BaO-Gd₂O₃ system is synthesized by high-temperature melting method. The density, transmission, excitation spectra and scintillating properties of the glasses are investigated. The results indicate that all the samples have good physical and scintillating properties. The emission peak wavelength of all samples is 390 nm under X-ray radiation. Gd³⁺ ions have a negative impact on scintillating properties when its concentration reaches a certain level. Gd³⁺ ions sensitize the luminescence of Ce³⁺ ions, and the ideal concentration is 15 mol% for Gd³⁺ ions. Also the decay characteristics of Ce³⁺ and Gd³⁺ ions are investigated. These samples have potential practical applications in high energy physics.

Abstract:In order to characterize the metallic-oxide grayscale films fabricated by laser direct writing (LDW) in indium film, a new method with micro-Raman spectroscopy and atomic force microscope (AFM) is proposed. Raman spectra exhibit the characteristic band of In₂O₃ centered at 490 cm⁻¹, in which the intensities increase with the decreasing optical density of the In-In₂O₃ grayscale films. The mapping information of Raman spectra shows that the signal intensities of the film in the same grayscale area are uniform. Combining with the information of In-In₂O₃ grayscale film from AFM, the quantitative relationship between the concentration of In₂O₃ and the Raman signal intensity is shown. Compared with the conventional methods, the resolution of micro-Raman scattering method is appropriate, and the scanning speed is proper to analyze the structure of metallic-oxide grayscale films.

Abstract:A time interleaved differential phase shift keying (DPSK) remodulation technique is proposed to mitigate the effect of Rayleigh backscattering (RBS)-induced noise in a single fiber colorless wavelength-division-multiplexing passive optical network (WDM-PON). In order to achieve a cost effective optical network unit (ONU) solution without dedicated laser sources for upstream signals to provide optimum symmetric capacity in a colorless WDM-PON, remodulation becomes the core attraction. Also as the performance of colorless WDM-PON systems suffers from the transmission impairments due to RBS, it is mitigated by using this remodulation scheme. Simulation results show that downstream and upstream signals achieve the error-free performance at 10 Gbit/s with negligible penalty, and enhance the tolerance to RBS-induced noise over a 25 km single-mode fiber.

Abstract:Based on the optimization and improvement for the construction method of systematically constructed Gallager (SCG) (4, k) code, a novel SCG low density parity check (SCG-LDPC)(3969, 3720) code to be suitable for optical transmission systems is constructed. The novel SCG-LDPC (6561,6240) code with code rate of 95.1% is constructed by increasing the length of SCG-LDPC (3969,3720) code, and in a way, the code rate of LDPC codes can better meet the high requirements of optical transmission systems. And then the novel concatenated code is constructed by concatenating SCG-LDPC(6561,6240) code and BCH(127,120) code with code rate of 94.5%. The simulation results and analyses show that the net coding gain (NCG) of BCH(127,120)+SCG-LDPC(6561,6240) concatenated code is respectively 2.28 dB and 0.48 dB more than those of the classic RS(255,239) code and SCG-LDPC(6561,6240) code at the bit error rate (BER) of 10⁻⁷.

Abstract:A highly birefringent index-guiding photonic crystal fiber (PCF) with flattened dispersion and low confinement loss is proposed by introducing two small air holes with the same diameter in the core area. The fundamental mode field, birefringence, confinement loss, effective mode area and dispersion characteristic of the fibers are studied by the full-vector finite element method (FEM). Simulation results show that a high birefringence with the order of 10⁻³ and a low confinement loss of 0.001 dB/km are obtained at 1550 nm. Furthermore, flattened chromatic dispersion from 1450 nm to 1590 nm is obtained.

Abstract:We investigate the spectra of the gain and pump-to-signal relative intensity noise (RIN) transfer in silicon optical parametric amplifier (SOPA) with Raman effect, and draw a conclusion that Raman effect makes the spectra narrower from 260 nm to 180 nm. A maximum gain also appears at 1622 nm. Moreover, the effects of the related parameters in SOPA on the gain and the pump-to-signal RIN transfer characteristics are also discussed. The high gain (16 dB) and low pump-to-signal RIN transfer (7 dB) can be obtained by using the appropriate parameters of pump and silicon waveguide.

Abstract:In view of dispersion compensating in multiple wavebands at the same time, this paper proposes a novel multi-waveband dispersion compensating fiber (DCF) based on hybrid photonic crystal fiber (PCF). The proposed fiber can compensate multiple wavebands at the same time. The mechanism of the multi-waveband dispersion compensation is analyzed, and the different material-filled structure is discussed numerically. The simulation results show that the multi-waveband DCF can compensate multiple wavelengths at the same time. By a reasonable design, this fiber can replace the multi-dispersion compensating system composed by cascaded multiple devices, and minimize the loads of the system in an efficient way.

Abstract:High peak-to-average power ratio (PAPR) is the main disadvantage in orthogonal frequency-division multiplexing (OFDM) communication systems, which also exists in OFDM-radio over fiber (RoF) systems. In this paper, we firstly analyze the impact of high PAPR on a 40 GHz OFDM-RoF system, and then describe the theory of Nyquist pulse shaping technology for reducing PAPR. To suppress PAPR further, an improved Nyquist pulse shaping technology is proposed, in which the distribution of original-data amplitude is changed by properly selecting the time-limited waveforms of the different subcarriers. We firstly apply the improved Nyquist pulse shaping technology to an OFDM-RoF system. The simulation results show that PAPR is effectively reduced by more than 2 dB with the bit error rate (BER) declining by about 0.125%.

Abstract:In this paper, the dependence of birefringence on the orientation of elliptical holes in triangular-lattice elliptical-hole photonic crystal fibers (PCFs) is investigated numerically. A resonant enhancement of birefringence between the anisotropic lattice arrangement and oriented elliptical holes is observed, and the birefringence varies periodically with the ellipticalhole orientation. When the major axes of adjacent elliptical holes are parallel, the birefringence approaches the maximum. Based on the numeric analysis, a novel highly birefringent PCF is proposed, and the maximum modal birefringence of 0.086 is achieved.

Abstract:A simple experiment for laser diffraction of capillary waves on liquid film surface (LFS) is realized. Steady and visible diffraction patterns are obtained. The dispersion relation of capillary waves on LFS is verified by laser diffraction. In particular, both the relation between the wave number and the film thickness at a fixed angular frequency and the relation between the angular frequency and the wave number at a fixed film thickness are investigated. The theoretical and experimental results are in good agreement.

Abstract:We study the dynamics of quantum discord of a two-qubit system coupled to a common structured reservoir at zero temperature. The conditions to maximize reservoir-induced quantum discord for the two-qubit system wiht an initially factorized state are derived. In particular, when the two qubits are placed in a lossy cavity, high values of quantum discord can be obtained in the dispersive regime, even in the bad-cavity limit. Finally, we show that under certain conditions, the quantum discord dynamics exhibits quantum beats.

Abstract:We report a two-layer model to describe the thermal response of continuous-wave (CW) terahertz (THz) irradiated skin. Based on the Pennes bio-heat conduction equation, the finite element method (FEM) is utilized to calculate the temperature distribution. The THz wave with a Gaussian beam profile is used to simulate the photo-thermal mechanism. The simulation results show the dynamic process of temperature increasing with irradiation time and possible thermal damage. The factors which can affect temperature distribution, such as beam radius, incident power and THz frequency, are investigated. With a beam radius of 0.5 mm, the highest temperature increase is 3.7 K/mW.

Abstract:A model of sub-wavelength metallic grating without host media is proposed. Under the excitation of TE polarized light, the extraordinary transmission is also found, and their transmission energy distributions corresponding to different structural parameters of this model are calculated systematically by using finite difference time domain (FDTD) method. The influence of slit width, grating thickness and grating period on the location of transmission peak is obtained. By studying these relations, it is found that Fabry-Perot-like (FPL) effect of the slit is the main physical reason of this extraordinary transmission. Varying the slit width can cause the change of reflection phase transition at both ends, and then the characteristics of FPL resonance of slit cavity are affected. The surface mode of metallic gratings has less effect on the location of transmission peak.