Low threshold tunable soliton source

An actively mode-locked erbium-fiber laser with continuous wavelength tuning over the range 1528-1565 nm has been demonstrated. A gain-saturated InGaAsP NTW semiconductor optical amplifier (SOA) is used as the active mode locking element, functioning as an amplitude modulator which provides gain and has <1 dB polarization dependence. The fiber laser is diode pumped at 1480 nm with a threshold of 6 mW, and provides pulses of 25 ps (FWHM) with a transform product of 0.4 and >12 dBm peak power     

GaAs/AlxGa1-xAs superlattice waveguideabsorption modulators with very low drive voltage

The first GaAs/Al_xGa_1-xAs superlattice waveguide absorption modulators operating at ~860 nm that utilize the Wannier-Stark effect are reported. The n=-1 Stark ladder peak, which is the transition from the valence band well to the nearest neighbor conduction band well, is used. This peak shifts rapidly with applied electric field, resulting in drive voltages lower than can be achieved using the quantum-confined Stark effect for quantum-well waveguides of similar structure. For a 1000-μm-long waveguide at 867 nm, the authors obtain an extinction ratio of ~20 dB and a 4-dB attenuation with a drive voltage of 2 V     

In-line optical-fibre filter for wavelength multiplexing

An optical-fibre wavelength-selective directional coupler has been fabricated using evanescent-wave coupling between fibres of dissimilar core radii and refractive-index profiles. This device has a nonperiodic filter response with a bandpass of 90 nm FWHM centred around 1.22 ?m, and has a peak coupling efficiency of 60% with an excess loss of 0.2 dB.     

Rapid long-period grating formation in hydrogen-loaded fibre with157 nm F2-laser radiation

Long-period gratings were fabricated in hydrogen-loaded telecommunication fibre using 157 nm F₂-laser radiation. A >20 dB attenuation peak at 1590 nm was induced with only 5.0 J/cm² accumulated fluence, a value >250-fold smaller in comparison with fluence requirements for 248 nm KrF-laser irradiation     

Low-insertion-loss, tunable wavelength multiplexer on lithium niobate

Integrated-optical dual-channel multi/demultiplexers with a wavelength periodic transmission characteristic are fabricated on X-cut LiNbO3. The devices are designed for the wavelength range ? = 1300-1600nm. Channel separations as low as 30nm, far-end crosstalk attenuation up to 40dB and an insertion loss of fibre-coupled devices below 3dB are achieved. The transmission characteristic can be tuned electro-optically at a rate of 2.5 nm/V.     

掺硅InGaN和掺硅GaN的光学性质的研究

采用光致发光方法研究了采用金属有机化学气相沉积(MOCVD)在蓝宝石衬底上生长的掺硅InGaN和掺硅CaN材料的光学性质。在室温下．InGaN材料带边峰位置为437．0nm，半高宽为14．3nm；GaN材料带边峰位置为363．4nm．半高宽为9．5nm。进行变温测量发现．随温度的升高．两种材料的发光强度降低，半高宽增大；GaN材料的带边峰值能量位置出现红移现象．与Varshini公式符合较好；InGaN材料的带边峰值能量位置则出现红移-蓝移-红移现象．这与InGaN材料的局域态、热效应以及由于电子-空穴对的形成而造成的无序程度增加有关．对大于140K的峰值能量位置的红移用Varshini公式拟合．符合较好。     

泡生法生长Ho3+,Yb3+双掺KGd(WO4)2晶体及其光谱性能

钨酸钆钾(KGd(WO4)2,简称KGW)是一种新型的激光基质材料。以Yb3 作为Ho3 的敏化剂,采用泡生法生长出了单斜晶系的Ho∶Yb∶KGW晶体。通过X射线衍射仪(XRD)分析确认所生长的晶体为-βHo∶Yb∶KGW。热重与差热分析(TG-DTA)测试结果表明,晶体的熔点为1072.31℃,相变温度为1043.09℃。测试了晶体的吸收光谱,对吸收峰值归属进行了确认,计算了相应的光谱参数。Yb3 在981 nm处吸收峰较强,半峰全宽(FWHM)为14 nm。从荧光光谱可以看出,在1022 nm附近,Yb3 发射主峰的半峰全宽达16 nm,对应的是Yb3 的2F5/2和2F7/2的能级之间的跃迁;Ho3 在1985 nm处的荧光发射峰半峰全宽为45 nm左右,发射截面积为1.79×10-20cm2。     

1*2 polarisation-independent acousto-optic filter tunable over 1.30-1.56 mu m

A polarisation-independent, electronically tunable, acousto-optic filter made with commercially available components is demonstrated. It has a bandwidth (FWHM) of 4 nm, two complementary outputs, a fibre-to-fibre insertion loss of 6-8 dB, and is continuously tunable over 1.30-1.56 mu m. It is suitable for use in multiaccess WDM networks requiring approximately=microsecond-tuning time.<>     

MOEMS variable optical attenuator with improved dynamic characteristics based on robust design

The design and preliminary data of a novel microoptoelectromechanical systems variable optical attenuator (VOA) driven by a pair of V-beam electrothermal actuators is described. This VOA deploys a face-to-face arranged pair of 45/spl deg/ tilted mirrors in front of two coaxially aligned lensed fibers to form retro-reflection planar light path for attenuation. The initial insertion loss is 0.7 dB at 1550 nm and the maximum dynamic range of attenuation is 50 dB, respectively. The polarization-dependent loss is measured as 0.15 dB at 20-dB attenuation. The dynamic attenuation deviation is less than /spl plusmn/0.36 dB at 20-dB attenuation with respect to 20-G shock of periodical mechanical vibration at 1 K Hz, in which it complies with requirements of the Telcordia GR1221 regulations.     

Pulsed dye amplification and frequency doubling of singlelongitudinal mode semiconductor lasers

A single-longitudinal-mode CW AlGaAs semiconductor laser (786 nm) has been pulse-amplified in a Nd:YAG-pumped dye system by 80 dB, yielding 4-ns (FWHM) infrared pulses having energies of 1.2 mJ. These amplified pulses have then been frequency-doubled in a KDP crystal to yield 110 μJ of tunable ultraviolet radiation at 393 nm. The amplified diode laser linewidth at 786 nm is measured to be 118 MHz     

Fibre-optic spectral filters consisting of concatenated dual-core fibres

Fibre-optic spectral filters using concatenated dual-core fibres are reported. Both a spectral bandpass filter with 17 nm FWHM (full width at half-maximum) and a band-elimination filter with -60.8 dB extinction ratio have been realised.     

Novel microstrip bandstop filter

A microstrip bandstop filter is described that overcomes the problems of radiation and surface-wave generation at high frequencies (40 GHz). An attenuation greater than 17 dB has been measured over at least a 10% bandwidth. The peak attenuation in the band can exceed 30 dB.     

一种具有平顶陡边响应的新型谐振腔增强型(RCE)光电探测器的理论分析及模拟

提出了一种适用于波分复用系统的具有平顶陡边响应的新型谐振腔增强型 (RCE)光电探测器结构 ,模拟得到了量子效率从峰值下降 0 5dB的线宽 1 8nm ,10dB的线宽 5 6nm ,2 0dB的线宽 10 4nm ,量子效率峰值99 7%,几乎没有凹陷的响应曲线。     

适于InGaAsP光放大器偏振不灵敏的增益介质

研制了适于InGaAsP光放大器偏振不灵敏的增益介质 ,采用有源区内交替的张应变和压应变排列的混合应变量子阱结构 ,器件做成带有倾角的扇形。实验中发现该结构既抑制了激射又改善了器件的偏振灵敏性 ,实现了偏振灵敏度小于 0 5dB ,10 0mA偏置时可达 0 1dB。在较大的电流范围内 ,峰的半高全宽 (FWHM)为 4 0nm。     

AlN-SiC微波衰减陶瓷在X波段的选频衰减性能

以氮化铝、碳化硅为原料,氧化钇为烧结助剂,在1900℃、氮气气氛中,采用热压烧结工艺制备了AlN-SiC复相微波衰减材料。借助网络分析仪,研究了该材料在8~12GHz的微波衰减性能。结果表明,当SiC质量分数从0增加到9%时,该材料的谐振损耗峰所对应的频率从10.86GHz降低到10.11GHz,所对应的峰值从3.2dB降低到0.7dB,而该材料的有效衰减带增大;在900~1000℃、氢气(纯度≥99.99%)气氛中保温30~50min后,该材料的谐振频率维持在10.65~10.62GHz,谐振峰峰值略微减小;这表明在氢气气氛中的热处理对该材料的微波衰减性能影响较小。     

Growth and characterization of GaN thin films on SiC SOI substrates

SiC semiconductor-on-insulator (SOI) structures have been investigated as substrates for the growth of GaN films. The SiC SOI was obtained through the conversion of Si SOI wafers by reaction with propane and H₂. (111) SiC SOI have been produced by this carbonization process at temperatures ranging from 1200 to 1300°C. X-ray diffraction (XRD) and infrared spectroscopy (FTIR) are used to chart the conversion of the Si layer to SiC. Under our conditions, growth time of 3 min at 1250°C is sufficient to completely convert a 1000? layer. XRD of the SiC SOI reveals a single SiC peak at 2θ = 35.7° corresponding to the (111) reflection, with a corrected full width at half-maximum (FWHM) of ~590±90 arc-sec. Infrared spectroscopy of SiC SOI structures obtained under optimum carboniza-tion conditions exhibited a sharp absorption peak produced by the Si-C bond at 795 cm⁻¹, with FWHM of ∼ 20–25 cm⁻¹. Metalorganic CVD growth of GaN on the (111) SiC SOI was carried out with trimethylgallium and NH₃. The growth of a thin (≤200?), low temperature (500°C) GaN buffer layer was followed by the growth of a thick (∼2 μm) layer at 1050°C. Optimum surface morphology was obtained for zero buffer layer. XRD indicates highly oriented hexagonal GaN, with FWHM of the (0002) peak of ~360±90 arc-sec. Under high power excitation, the 300°K photoluminescence (PL) spectrum of GaN films exhibits a strong near band-edge peak (at λ_p~371 nm, with FWHM = 100–150 meV) and very weak yellow emission. Under low power excitation, the 370 nm PL emission from the GaN/SiC SOI structure increases rapidly with SiC carbonization temperature, while the yellow band (∼550–620 nm) correspondingly decreases.     

34GHzTE01模基波回旋速调管高频系统设计与实验

利用场匹配理论,建立了具有突变结构谐振腔的级联散射矩阵。通过数值计算,研究了具有突变结构谐振腔中各模式的反射相移随漂移段半径变化、工作模式的反射相移随腔体半径的变化、腔体中各模式的传播常数随腔体半径的变化、谐振腔的腔体长度和半径的关系,并完成了Ka波段TE01模回旋速调管的输入腔、群聚腔、输出腔的设计。同时给出了一支Ka波段TE01模四腔基波回旋速调管高频系统和整管的优化设计方案。PIC模拟表明：在中心频率34GHz,注电压70kV,注电流11A的情况下,获得了输出功率390kW,饱和增益42.9dB,电子效率50.6%,3dB输出带宽360MHz的结果。 通过样管的热测实验显示在34GHz,注电压70kV,注电流11A,获得了301kW的稳定输出脉冲峰值功率,41.8dB的增益,39.1%的效率,285MHz的3dB输出带宽。     

适用于光纤放大器的Er3 -Yb3 共掺双包层光纤

研制出一种适用于光纤放大器的Er^3＋-Yb^3＋共掺双包层光纤（EYDCF），它在980nm和1530nm的吸收分别达到16．8dB／m和20．6dB／m，980nm吸收带半高宽达到200nm。在波长为980nm、泵浦功率为2w的条件下，可以得到28．8dBm（760mW）的输出，相比掺Er^3＋光纤（EDF），EYDCF的增益高，所需光纤长度短，所以非线性效应的发生得到抑制。     

Characteristics of Er-doped Al2O3 thin filmsdeposited by reactive co-sputtering

Er-doped Al₂O₃ thin films have been deposited by reactive co-sputtering onto thermally oxidized Si-wafers. The deposition process has been optimized with respect to the requirements originating from the application of these multilayer structures as integrated optical amplifiers for the third telecom window, i.e., the wavelength range 1.52-1.55 μm. The films obtained at a substrate temperature of only 400°C are amorphous and show a homogenous structure, without columns or grains. For slabguides, background losses smaller than 0.25 dB/cm have been obtained, even without any annealing. A relatively broad luminescence band, having an FWHM of ~55 nm around the 1.533-μm wavelength, has been measured. From gain versus pumping power curves, an upconversion coefficient lower then 20·10^-25 m³/s has been derived, being half of the values reported up to now in the literature. Simulations based on experimentally determined material parameters and assuming a channel attenuation of 0.5 dB/cm indicate, for 0.24 at.% Er channel devices with an optimal channel length of 7.7 cm, an amplification of 8 dB at 1.533 μm for a pump wavelength of 1.48 μm, and a pump power of only 8.7 mW