周期信号傅里叶分析一种实验观测方法

介绍了用两只动圈扬声器组成谐波装置，用于对周期信号进行傅里叶分析。讨论了谐波共振时振幅的特性。     

数字式光信号检测和再生电路的理论分析及实验研究

对微型计算机控制的数字信号光纤传输系统中的光信号检测和再生电路的结构，工作原理和信号的再生条件进行了理论分析，并提出了相应的实验研究方法，实验结果与理论分析所得结论十分一致。     

Wavelength division demultiplexing by photonic crystal waveguides with asymmetric corrugated surfaces

<正>We propose a new type of wavelength division demultiplexer composed of a photonic crystal waveguide with asymmetric corrugated exit surface.The focus displacement for different symmetric corrugated surfaces is relative to the intensity of the excited surface mode.By systematically investigating the effects of the parameters of the corrugated surface on the focus shift,we demonstrate an on-axis focus by a photonic crystal waveguide with an asymmetric corrugated exit surface at a specific wavelength.The precise equivalences of surface modes at each side of the exit surface are broken.Thus,for the light source with other wavelengths,the emerging beams are off-axis focused at different directions,similar to the function of a wavelength division demultiplexer.     

Stochastic Resonance for a SQUID with Dichotomous Resistance

We investigate the response to the ac current for a superconducting quantum interference device （SQUID） with a dichotomous resistance. It is shown that, for some suitably selected parameters＇ values, stochastic resonance appears for the amplitude of the stationary average voltage of the SQUID versus the correlation time of the dichotomous noise. Our result can provide some useful insights for the investigation of the response of the SQUID （especially for the ones with the nano junctions） to the temporal-periodic signal （including the input ac current, the irradiation microwave, the detected temporal-periodic signal, and the added ac voltage）.     

Continuous Imaging of a Single Neutral Atom in a Variant Magneto-Optical Trap／hyperlinks

We demonstrate continuous imaging of a single 87Rb atom confined in a steep magneto-optical trap with an electron-multiplying charge-coupled device （EMCCD） camera and realize a one-dimensional micro-optical trap array with a Dammann grating. We adopt several methods to reduce the noise in the fluorescence signal we obtain with the EMCCD. Step jumping characteristics of the fluorescence demonstrate capturing and losing of individual atoms.     

Performance comparison of power fading mitigation techniques in multiband OFDM-UWB signals transmission along LR-PONs

The single sideband （SSB） modulation is assessed as a means to mitigate the dispersion-induced power fading on the distribution of ortogonal frequency division multiplexing （OFDM） ultra wideband （UWB） radio signals along long-reach passive optical networks （LR-PONs）. Particularly, two different SSB ar- chitectures, namely, Sieben＇s architecture and four phase modulator （FPM） architecture are optimized to provide maximum sideband suppression. The minimum optical signal-to-noise ratio （OSNR） required to simultaneously distribute all the 14 OFDM-UWB sub-bands along the LR-PON distances ranging between 80 and 100 km is also evaluated through numerical simulation. FPM architecture is preferable over Sieben＇s architecture because the latter SSB architecture generates carriers-carriers beat term at the photodetector output with high power, thereby causing significant degradation in the OFDM-UWB sub-bands with lower central frequencies. The simultaneous distribution of the 14 SSB OFDM-UWB sub-bands in the LR-PON using the FPM architecture shows a minimum OSNR penalty of 3 dB compared with the centralized dis- persion compensation technique.     

Solitons with Periodic Behavior in an SBN：75 Photorefractive Crystat

We study the formation of spatial solitons in an SBN： 75 photorefractive crystal by a 532 nm continuous-wave laser beam. The output beam from the crystal cannot be compressed proportionally to the voltage of the applied electric field. Quasi-steady-state spatial solitons are formed instantaneously at a voltage of 900 V. Interestingly, the quasi- steady-state solitons exhibit a periodic behavior consisting of formation/broken/reformation cycles. If we increase the input intensity of the soliton beam but keep the same signal-to-background intensity ratio, the solitons stay for a longer time in the quasi-steady state and a longer period of soliton formation/broken/reformation cycle is also observed.     

Study of FSK/IM orthogonal modulation system with optical Manchester-coded payload

<正>We study the performance of an orthogonal modulation system with frequency-shift keying(FSK) label and optical Manchester-coded(MC) payload.Simulation result shows that by introducing an optical MC payload,the available extinction ratio(ER) value of a FSK and intensity modulation(IM) orthogonal modulation system can be improved from 5 to 9 dB for system optimization,exhibiting great advantages over the traditional non-return-to-zero(NRZ) payload.Besides,the bit error rate(BER) characteristics of both label and payload show a more remarkable advantage than that of NRZ coding,verifying itself as a perfect candidate for the payload coding method in orthogonal modulation systems.     

Generation of Sub-2 Cycle Optical Pulses with a Differentially Pumped Hollow Fiber

We report the generation of optical pulses with an energy of 0. 55 m^3 and duration of 1.6-cycle （4.4 fs） at repetition rate of 1 kHz using a differentially pumped hollow fiber and chirped mirrors. Compared to the statically gasfilled scheme, the differentially pumping hollow fiber is demonstrated to support more energy output with higher transmission efficiency, and to increase the spectral broadening due to a reduction of ionization defocusing in plasma at the fiber entrance. The differentially pumping technique is proved to be an effective way to obtain optical pulses with mono-cycle and higher energy.