Abstract:A diode-pumped passively Q-switched Nd:YAG/KLu(WO₄)₂ (KLW) Raman laser is presented for the first time. As high as 1.89 W average output power is obtained at the pump power of 15.7 W with the pulse repetition frequency (PRF) of 27.2

Abstract:An all-solid-state Pr:KY₃F₁₀ (Pr:KYF) laser pumped by blue laser (471 nm) has been demonstrated. With the incident pump power of 2.6 W, the maximum output power at 610 nm is 213 mW. Moreover, the intracavity second-harmonic generation (SHG) is also achieved with the maximum ultraviolet (UV) power at 305 nm of 11 mW by using a β-BaB₂O₄ (BBO) nonlinear crystal.

Abstract:A new method is presented to tune Bragg wavelength slightly by using hydrofluoric acid to etch fiber cladding. The spectral characteristics before and after etching and the change properties of Bragg wavelength are studied. Cladding modes are reduced during the etching process. High-order cladding modes are converted into radiation modes, and energy of cladding modes is coupled to the outside. As the cladding radius decreases, the Bragg wavelength shifts to longer direction. Experimental results show that this method can tune Bragg wavelength slightly, and the tunable range is 0.002 −0.120 nm.

Abstract:We investigate the pump-depleted model of a dual-pump fiber optical parametric amplifier (FOPA) with Raman effect. As bandwidth increases, the gain profile of the distorted FOPA would be impacted seriously. Under the widebands, especially when the pump separation is large, zero dispersion wavelength (ZDW) fluctuation is another factor which can not be neglected. Numerical simulations with these comprehensive factors are mainly analyzed to obtain their influence on gain characteristics. Saturated gain spectrum is also discussed in detail.

Abstract:In this paper, bulk heterojunction solar cells with poly-(3-hexylthiophene) (P3HT): [6,6]-phenyl-C61-butyric-acid-methylester (PCBM) as an active layer and modified poly (3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) as a buffer layer are fabricated. The buffer layer is modified by adding 1% to 5% dimethyl sulfoxide (DMSO) into PEDOT: PSS solution before spin-coating. The conductivity of modified PEDOT:PSS and the performance of solar cells with modified PEDOT:PSS are measured. The highest conductivity of modified PEDOT:PSS with 4% DMSO can achieve 89.693 S/cm. The performance of organic solar cell with PEDOT:PSS modified by 4% DMSO is the best. The 4% DMSO-modified-PEDOT:PSS cell has a power conversion efficiency of 3.34%, V _oc of 5.7 V, J _sc of 14.56 mA/cm² and filling factor (FF) of 40.34%.

Abstract:In this paper, we propose a method to realize microwave photonic filter (MPF) with complex coefficient, whose central frequency f ₀ and 3 dB bandwidth are tunable. The complex coefficient is realized by multi-wavelength optical source and stimulated Brillouin scattering (SBS). The central frequency of the filter is tuned by adjusting the phase shift caused by SBS without changing its frequency response. The frequency selectivity of filter can be improved through increasing the bandwidth of broadband optical source (BOS) or decreasing wavelength separation to increase the taps of MPF. The mainlobeto-sidelobe suppression ratio (MSSR) of the filter is affected by the weight of each tap. When the length of fiber is 0.5544 m in birefringence fiber loop mirror (FLM), the MSSR is improved by 18.55 dB compared with that without the weight controlling.

Abstract:A plastic surface-relief grating as a wavelength division multiplexer is designed and fabricated with the conventional mould pressing technique using the transmission-type fused quartz phase grating as mask pattern and polycarbonate as basal material. The experiment results show that in an optimizing process, the plastic surface-relief grating has the highest firstorder diffraction efficiency under adequate groove depth and incident angle, and can be used as the best optical path for wavelength division multiplexing (WDM). We also establish the experiment setup for testing the WDM performance of the plastic surface-relief grating based wavelength division multiplexer. The results show that the proposed wavelength division multiplexer has the high-stability temperature characteristics, the low insertion loss of less than 5 dB, the large isolation of greater than 20 dB, the low polarization-dependent loss (PDL) of less than 0.4 dB and the relatively steep pass-band characteristics. It is a WDM device with good performance, which can be applied in short distance communication.

Abstract:Cu(In,Ga)Se₂ (CIGS) films are deposited on the Na-free glass substrate using three-stage co-evaporation process, and the effects of thickness and growth temperature on the orientation of CIGS film are investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). When the growth of CIGS film does not experience the Cu-rich process, the increase of the growth temperature at the second stage () promotes the (112) orientation of CIGS film, and weakens the (220) orientation. Nevertheless, when the growth of CIGS film experiences Cu-rich process, the increase of significantly promotes the (220) orientation. In addition, with the thickness of CIGS film decreasing, the extent of (In,Ga)₂Se₃ (IGS) precursor orientation does not change except for the intensity of Bragg peak, yet the (220) orientation of following CIGS film is hindered, which suggests that (112) plane preferentially grows at the initial growth of CIGS film.

Abstract:Eu²⁺-activated reddish-orange-emitting Ca₃Si₂O₇ phosphors were synthesized with the addition of NH₄Cl flux. When the phosphors were synthesized in a nominal composition of (Ca_0.99Eu_0.01)₃Si₂O₇ without flux addition, a Ca₃Si₂O₇ phase responsible for reddish-orange emission was identified to coexist with an intermediate phase of a-Ca₂SiO₄ for green emission. With the addition of NH₄Cl flux, a-Ca₂SiO₄ was suppressed while the pure phase Ca₃Si₂O₇ was obtained as the flux content was 3 wt%. Through varying the amount of flux, the emission color of samples can be tuned from green to reddish-orange, corresponding to the phase transformation from a-Ca₂SiO₄ to Ca₃Si₂O₇. Through optimizing the doping concentration of Eu²⁺, the optimized photoluminescence (PL) properties for reddish-orange emission can be achieved, which makes this kind of phosphor prospective in the applications of the phosphor-converted white light emitting diodes (PC-WLEDs).

Abstract:The preparation of aluminum nitrogen (AlN) film without Al texture is of great significance for the manufacture of high-performance surface acoustic wave (SAW) device. We research the process factors which bring Al into AlN film due to radio frequency (RF) magnetron sputtering system, and discuss how the process parameters influence the AlN thin film containing Al. In the research, it is found that the high sputtering power, the low deposition pressures and low partial pressure of Ar can lead to growing Al-texture during AlN thin film preparation, and the experiment also shows that filling the chamber with nitrogen gas can recrystallize a small amount of Al composition into AlN film during the annealing process in the high temperature environment.

Abstract:After the development trend of high-speed long-haul optical communication systems and the theory of the concatenated code are analyzed, the comparative researches on the performances of the two concatenated codes of the inner-outer type and the improved interleaving type are performed in detail. The theoretical analyses and simulation results show that the inner-outer type concatenated code has the greater redundancy, and the improved interleaving type concatenated code is a superior concatenated code with the advantages of the better error correction performance, moderate redundancy and easy implementation. As a result, the improved interleaving type concatenated code can be better used in high-speed long-haul optical communication systems.

Abstract:Novel highly nonlinear photonic crystal fibers (HN-PCFs) with flattened dispersion are proposed by omitting 19 air holes as the fiber core. The simulation results show that the high nonlinearity and the flattened dispersion can be achieved simultaneously by employing only two types of air holes in the cladding. To reduce the confinement loss, the modified designs are presented. The confinement loss is below 0.1 dB/km at 1.55 μm, when seven layers of air-hole rings are introduced to the cladding. After modifying, the dispersion can change from −0.5 ps/(nm·km) to +0.5 ps/(nm·km) in the range from 1.35 μm to 2.06 μm, and the effective mode area is as low as 2.27 μm² at 1.55 μm.

Abstract:A novel method to generate binary frequency shift-keying (BFSK) radio frequency (RF) signals in optical domain is proposed. In the proposed system, an optical short pulse train is converted into super-Gaussian RF pulses with high frequency based on optical pulse shaping by two Mach-Zehnder fiber interferometers (MZIs). And the generated RF signals are coded using a fast electro-optic switch. By properly designing the MZIs, BFSK RF signals with desired code pattern and modulation index can be generated. A theoretical model for describing the system is developed, and the generation of BFSK RF signals in millimeter-wave regime is demonstrated via simulations.

Abstract:We propose an arrayed waveguide grating (AWG)-based 10 Gbit/s per channel full duplex wavelength division multiplexing passive optical network (WDM-PON). A chirp managed directly modulated laser with return-to-zero (RZ) differential phase shift keying (DPSK) modulation technique is utilized for downlink (DL) direction, and then the downlink signal is re-modulated for the uplink (UL) direction using intensity modulation technique with the data rate of 10 Gbit/s per channel. A successful WDM-PON transmission operation with the data rate of 10 Gbit/s per channel over a distance of 25 km without any optical amplification or dispersion compensation is demonstrated with low power penalty.

Abstract:Based on the genetic algorithm (GA), a new genetic probability decoding (GPD) scheme for forward error correction (FEC) codes in optical transmission systems is proposed. The GPD scheme can further offset the quantification error of the hard decision by making use of the channel interference probability and statistics information to restore the maximal likelihood transmission code word. The theoretical performance analysis and the simulation result show that the proposed GPD scheme has the advantages of lower decoding complexity, faster decoding speed and better decoding correction-error performance. Therefore, the proposed GPD algorithm is a better practical decoding algorithm.

Abstract:The performance of colorless wavelength-division multiplexed passive optical network (WDM-PON) systems suffers from the transmission impairments mainly due to Rayleigh backscattering (RB). In this paper, we propose and demonstrate a single fiber colorless WDM-PON which enhances the tolerance to RB induced noise. The high extinction ratio in both return-to-zero (RZ)-shaped differential phase shift keying (DPSK) downstream (DS) data signal and intensity-remodulated upstream (US) data signal helps to improve the tolerance to RB induced noise. Simulation results show that downstream and upstream signals can achieve error-free performance at 10 Gbit/s with negligible penalty and improve the tolerance to RB induced noise over 25 km standard single-mode fiber.

Abstract:Considering fluctuant dark count rate in practical quantum key distribution (QKD) system, a new decoy-state method with one vacuum state and one weak decoy state is presented based on a heralded single photon source (HSPS). The method assumes that the dark count rate of each pulse is random and independent. The lower bound of the count rate and the upper bound of the error rate of a single photon state are estimated. The method is applied to the decoy-state QKD system with and without the fluctuation of dark count rate. Because the estimation of the upper bound of a single photon state’s error rate is stricter, the method can obtain better performance than the existing methods under the same condition of implementation.

Abstract:A theoretical model of cascaded terahertz (THz) difference-frequency generation is established based on one-dimensional coupled-wave equations. The relationships between sphalerite crystals’ wave vector mismatches and difference-frequency pump waves are analyzed. To produce terahertz wave with the frequency of 1.5 THz, 80-order cascaded difference-frequency is applied. By introducing crystal absorption, we calculate the optimum crystal length and pump frequency under actual circumstances. It is found that Stokes waves dominate the terahertz waves output in cascaded progress, and cascaded difference-frequency can increase the photon conversion efficiency obviously.

Abstract:Tianjin University of Technology and Springer-Verlag Berlin Heidelberg 2012 In this paper, we study the effect of spontaneously generated coherence (SGC) on transient evolution of gain without inversion (GWI) in a Doppler broadened quasi Λ-type four-level atomic system. It is shown that transient evolution of GWI is very sensitive to the variation of SGC strength, and the transient maximum value and steady value of GWI both increase with SGC strength increasing. The transient and steady values of GWI with SGC are much larger than those without SGC. When Doppler broadening is present, the transient maximum value and steady value of GWI first increase and then decrease with Doppler broadening width (D) increasing, and the value of D which corresponds to the maximum transient GWI is different from that corresponding to the maximum steady GWI. The time needed for reaching the steady GWI increases with D increasing. The steady GWI, which is larger than that without Doppler broadening (D = 0), can be obtained by choosing appropriate D and SGC strength.

Abstract:When semiconductor quantum wells (SQWs) interact with lasers, the group velocity of the low-intensity light pulse is studied theoretically. It is shown that by adjusting the parameters, slow light propagation of the probe field can be exhibited in such a system. Meanwhile, the probe absorption-gain spectra can be changed from absorption to zero, i.e., electromagnetically induced transparency (EIT). It is easy to observe the light propagation experimentally, and it leads to potential applications in many fields of solid-state quantum information, for example, optical switching, detection and quantum computing.