掺K^＋和Ag^＋的LaMnO3的室温庞磁电阻效应

采用固相烧结法制备了名义成分为La1-xKxMnO3(x=0.1-0.4)和La0.8K0.2-yAgyMnO3(y=0-0.2)的多晶样品，发现用K、Ag取代La后，可使菱面体结构的这种钙钛矿型稀土锰氧化物居里温度升高至室温附近，从而使样品的室温磁电阻增大，其中La0.8K0.2MnO3在μ0H=1T磁场下的磁电阻可达13．5％。该值比单纯掺Na和掺Ag的同样成分的稀土锰氧化物的磁电阻要大。通过对磁电阻与磁化强度之间密切关系的讨论，探讨了磁电阻效应的微观机理。     

Ce3+-activated fluoride crystals as prospective activemedia for widely tunable ultraviolet ultrafast lasers with direct 10-nspumping

New possibilities have been investigated for recently developed solid-state tunable ultraviolet (UV) laser materials such as Ce³⁺ ion-activated LuLiF₄ (LLF) and LiCaAlF₆ (LiCAF). With their broad-gain width, demonstrated reliability, and high efficiency, they are attractive for ultrashort pulse generation and amplification. To prove that, we have demonstrated UV picosecond-pulse amplification using Ce:LLF. For such new laser materials, we proposed a passive self-injection seeding scheme for the direct generation of short-pulse trains, which does not require CW operation capability or an external short-pulse seeding laser, Using this simple scheme, a UV sub-nanosecond pulse train is directly and passively generated from Ce:LLF pumped by a standard 10-ns KrF excimer laser, and Ce:LiCAF pumped by the fourth harmonic of a conventional 10-ns Q-switched Nd:YAG laser     

Long-wavelength-band Er3+-doped fiber amplifierincorporating a ring-laser as a seed signal generator

A novel dual-stage architecture for long-wavelength-band (L-band) erbium-doped fiber amplifier, which incorporates a gain-clamped amplifier based on a ring-laser feedback as a seed signal generator in the first stage is described. This technique has elevated the intensity of a short-wavelength amplified spontaneous emission (ASE) by 29%, from 11.3 mW of ASE power to 14.6 mW with a feedback lasing at 1560 nm. This strong laser then improves the L-band gain enormously, as large as 17.1 dB and noise figures are lower than 4.8 dB for the entire signal range in the flat-gain operation. The seeding signal reduces pump-to-ASE losses in the second stage to 38% compared to a conventional amplifier without feedback. Noise figure penalties are negligible due to efficient low-noise characteristics in the first stage. The proposed amplifier provides 25 dB gain for 50 wavelength-division-multiplexed signals at -30 dBm/ch with gain flatness less than 1.1 dB with only 980 nm pumping     

Er3+-doped channel optical waveguide amplifiers for WDMsystems: a comparison of tellurite, alumina and Al/P silicate materials

Er³⁺-doped tellurite and Er³⁺-doped alumina optical waveguide amplifiers are analyzed both as single amplifiers and as elements of 16-channel wavelength-division multiplexing (WDM) systems; their performances are compared with that from Er³⁺-doped Al/P silica waveguide amplifiers. The amplifier model is based on propagation and population-rate equations and includes both uniform and pair-induced up-conversion mechanisms. It is solved numerically by combining finite elements and the Runge-Kutta algorithm. The analysis predicts that Er³⁺-doped tellurite waveguides exhibit improved gain characteristics compared with alumina and Al/P silica waveguides. Using Er³⁺-doped tellurite waveguide amplifiers, it is suggested that 16 WDM channels may be transmitted to a maximum distance of 4250 km. By using in-line notch gain equalizing filters, the maximum transmission distance can be increased to 5250 km     

Widely tunable, near- to mid-infrared femtosecond and picosecondoptical parametric oscillators using periodically poledLiNbO3 and RbTiOAsO4

We describe the operation and characterization of Ti:sapphire laser-pumped femtosecond and picosecond optical parametric oscillators based the new quasi-phase-matched nonlinear materials of periodically poled LiNbO₃ and RbTiOAsO₄ with broad tunability in the near- to mid-infrared. We discuss the merits of the two materials for use in ultrafast optical parametric oscillators (OPOs) and compare and contrast their properties to the birefringent materials. We demonstrate an extended spectral coverage from <1 μm to >5 μm, pump power thresholds as low as 45 mW, average mid-infrared output powers in excess of 100 mW, and pulse durations of 100-200 fs and 1-2 ps at ~80 MHz repetition rate. We also report the efficient operation of Ti:sapphire-pumped femtosecond OPOs in all-solid-state configurations by utilizing diode-laser-based input pump sources     

Ce3+:LiCaAlF6 crystal for high-gain orhigh-peak-power amplification of ultraviolet femtosecond pulses and newpotential ultraviolet gain medium: Ce3+:LiSr0.8Ca0.2AlF6

To develop high-peak-power ultrashort pulse laser systems in the ultraviolet region, a large Ce³⁺:LiCaAlF₆ (Ce:LiCAF) crystal, a tunable ultraviolet laser medium with large saturation fluence and broad gain spectrum width, was grown successfully with a diameter of more than 70 mm. To demonstrate high small signal gain, a four-pass confocal amplifier with 60 dB gain and 54 μJ output energy was constructed. Chirped pulse amplification (CPA) in the ultraviolet region was demonstrated using Ce:LiCAF for higher energy extraction. A modified bow-tie-style four-pass amplifier pumped by 100-mJ 266-nm 10-Hz pulses from a Q-switched Nd:YAG laser had 370-times gain and delivered 6-mJ 290-nm pulses. After dispersion compensation, the output pulses can be compressed down to 115 fs. This is the first ultraviolet, all-solid-state high-peak-power CPA laser system using ultraviolet gain media, and this demonstration shows further scalability of the Ce:LiCAF CPA system. Additionally, a new gain medium, Ce³⁺ :LiSr_0.8Ca_0.2AlF₆, with longer fluorescence lifetime and sufficient gain spectrum width over 18 nm was grown to upgrade this system as a candidate for a final power amplifier gain module     

Integrated optical, wavelength selective, acoustically tunable2×2 switches (add-drop multiplexers) in LiNbO3

Fully packaged, polarization independent, integrated acoustooptic 2×2 switches have been developed which can be also used as add/drop multiplexers. The devices have been fabricated in X-cut Y-propagating LiNbO₃ and can be operated at wavelengths around 1550 nm. They consist of passive polarization splitters and acoustooptic TE-TM converters with weighted coupling. A filter bandwidth of 2.0 nm and a tuning range of 130 nm have been obtained. The fiber-to-fiber insertion loss is <4.6 dB and a residual polarization dependence of 1.3 dB for bar-state and 0.1 dB for cross-state routing has been achieved     

用于多表集抄系统的自适应M-BUS主机电路设计

针对国家电网的电、水、气、热多表集抄,提出了一种自适应的MBUS主机电路,通过调整LDO的反馈电阻来实现对M-BUS总线电平的控制,使用电容来采样、锁存总线电流数值,自动适应外部总线电流的变化,从而完成对从机数据的收发。文中详细阐述了主机电路的收发原理,并结合实际应用的特点,实现了与主控电路的光电隔离。现场应用表明,该电路抗干扰能力强、可靠性高、带负载能力强。