Photonic generation of tunable microwave signals by beating a dual-wavelength single longitudinal mode fiber ring laser

A novel method of generating tunable microwave signals in the photonic domain is proposed. Eighteen pairs of stable dual-wavelength single longitudinal mode lasings are achieved by incorporating a fiber Bragg grating based Fabry–Pérot filter and a tunable fiber grating into a fiber ring cavity. The frequency of the generated microwave signal obtained by beating the dual-wavelength laser with a photodetector can be tuned simply through configuring the working wavelength of the laser. A series of microwave frequencies of 9.4885, 9.572, 9.7111, 9.8498, 9.9598 and 10.0712 GHz are generated experimentally. The proposed method is useful in applications such as wireless access networks, sensor networks, radio-over-fiber systems and software-defined radio. PACS 41.20.-q; 42.55.Wd; 41.81.-i     

General analyses of infinite impulse microwave photonic filters with an intensity modulator in an opto–electronic feedback loop

Designs of coherence-free microwave photonic filters with infinite impulse response (IIR) are presented. They are based on an electrical–optical modulator or electrical-absorption modulator with an opto–electronic feedback loop. General theoretical analyses for those configurations are obtained. When an electrical–optical intensity modulator is used for the IIR filter, the stopband of the filter can be switched to passband and vice versa. Measured results match closely with the theoretical expressions and demonstrate more than 30 dB rejection ratio and high frequency selectivity.     

Design of novel DS-OCDMA encoders/decoders using phase sampled long period grating

A novel long period grating structure with phase sampled technique is proposed to act as encoders/decoders in the direct sequence optical code division multiple access (DS-OCDMA) system. The structure with address code of 31 chips is designed and the relation between the sample period, the input pulse width and the refractive index difference is given. The encoded and decoded results are demonstrated to verify the feasibility of utilizing the coupling ratio to the cladding mode. The whole structure is expected to move on the photonic crystal fiber, for it can support the large refractive index difference between the core mode and cladding mode, as well as minimize the wavelength shift caused by the temperature change.     

Novel tunable microwave photonic notch filter using a 3 × 3 coupler based Sagnac loop

We propose a simple and stable structure to realize a tunable negative coefficients microwave photonic notch filter. A 3 × 3 coupler based Sagnac loop interferometer with an asymmetrically placed phase modulator is used to acquire the notches. Our system is simply implemented and with good stability. Theoretical analysis and experimental results are presented and show a good agreement. The structure is proved to be a robust filter with more than 35 dB rejection deep notches.     

Photonic ultrawideband monocycle pulse generation using a single electro-optic modulator

A compact approach to photonic-assisted ultrawideband (UWB) monocycle pulse generation is proposed and experimentally demonstrated based on the wavelength dependence of the half-wave voltage of a Mach-Zehnder modulator (MZM). By employing a single MZM with dual-wavelength injection at around 1310 and 1550 nm, a pair of polarity-reversed monocycle pulses with the full width at half-maximum of about 80 ps and the fractional bandwidth of greater than 160% can be generated. The experiment results agree well with the theoretical prediction. The simple setup and the convenience to control the monocycle pulse polarity are favorable for future applications.     

OnP-Q ordered semigroups

In this paper,P-ordered andQ-ordered semigroups are studied. Some characterizations and properties of such semigroups are obtalned. Also the relationship between maximal (minimum) regular ordered semigroups and unitary regular semigroups is investigated.Research is partiallysupported by CUHK grant No. 220.600.080.     

Novel coordination of dicyanamide, [N(CN)2]-: preferential binding of the amide nitrogen

CoII[N(CN)2]2(H2BiIm)2, 1, and [CoII[N(CN)2](H2BiIm)2]Cl, 2 (H2BiIm = 2,2'-biimidazole) have been structurally, spectroscopically, and magnetically characterized with both containing dicyanamides bound in unprecedented manners; namely, solely via the amide nitrogen for 1, and via an imide N forming 1-D helical chains for 2.     

在非球形引力摄动下金星轨道器运动的分析解 *

给出了行星轨道器在慢自转中心天体 (如金星、水星等 )非球形引力摄动下运动的分析摄动解 ,它适用于 0相似文献   

Special control of the cutoff frequencies in a 2D photonic crystal coupled-cavity waveguide

We show theoretically that the upper and lower cutoff frequencies of the guided band in a 2D photonic crystal coupled-cavity waveguide can be controlled independently or synchronously by changing two configuration parameters of the waveguide simultaneously. The independent control range for the lower and upper cutoff frequencies can be as large as 68.6% and 67.9% of photonic band gap, respectively. The two cutoff frequencies can also be tuned in the same direction over equal distances up to 25.7% of photonic band gap. These results offer an efficient way for designing the various dispersion relations for photonic crystal waveguides.     

Mechanism and thermochemistry of oxidation of HCl and HBr at high temperatures. The heat of formation of HO2

Using currently available thermochemical and kinetic data and estimation methods to analyze the thermochemistry and the kinetic parameters of the elementary reactions involved in the oxidation of HCl and HBr, reaction mechanisms are proposed which account for the previously reported reaction products, the rate law, and the kinetic data. For oxidation of HCl, two competitive pathways, the radical initiation by hydrogen abstraction and the fourcenter reaction pathway, were invoked to account for the observations. In the oxidation of HBr one must invoke a fast surface reaction of the type to account for the reaction.