I型准相位匹配周期性极化铌酸锂倍频蓝光输出

在周期为 14 .5 μm的周期性极化铌酸锂中 ,利用d3 1,得到了一阶I型EωYEωY-E2ωZ (oo-e)准相位匹配蓝光二次谐波。在 15 0℃下 ,由 114 μJ抽运光 ,得到了 5 2 μJ ,0 .4 73μm倍频蓝光 ,对应于平均最大转换效率 4 5 .6 %。制备了一阶和三阶周期分别为 4 .5 μm和 13.5 μm的周期性极化铌酸锂。在EωZEωZ-E2ωZ (ee -e)准相位匹配 0 .4 73μm蓝光倍频中 ,15 0℃下 ,分别得到了 4 1.3%和 19%的倍频转换效率。oo -e准相位匹配比传统的ee -e准相位匹配有较大的光栅周期 ,尤其在短波长区域倍频输出应用中 ,降低了周期性结构制作的困难 ,其较大的容许带宽在实验中提高了频率转换效率。实验结果表明了在周期性极化铌酸锂中准相位匹配倍频的偏振相关性。     

Ⅰ型准相位匹配周期性极化铌酸锂倍频蓝光输出

在周期为14．5μm的周期性极化铌酸锂中,利用d31得到了一阶Ⅰ型EY^ωEY^ω-Ez^2ω(oo-e)准相位匹配蓝光二次谐波。在150C下,由114μJ抽运光,得到了52μJ,0．473μm倍频蓝光,对应于平均最大转换效率45．6%。制备了一阶和三阶周期分别为4．5μm和13．5μm的周期性极化铌酸锂。在EY^ωEY^ω-Ez^2ω(ee-e)准相位匹配0．473μm蓝光倍频中。150C下,分别得到了41．3%和19%的倍频转换效率。oo-e准相位匹配比传统的ee-e准相位匹配有较大的光栅周期,尤其在短波长区域倍频输出应用中,降低了周期性结构制作的困难,其较大的容许带宽在实验中提高了频率转换效率。实验结果表明了在周期性极化铌酸锂中准相位匹配倍频的偏振相关性。     

宽带准连续光纤激光在周期极化铌酸锂中倍频特性的研究

双包层光纤激光器和非线性光学材料(如周期性极化的铌酸锂晶体,PPLN)相结合,开辟了实用性非线性光学器件的一个新领域。研究了准相位匹配周期性极化反转铌酸锂晶体对宽带准连续光纤激光倍频的温度特性和频谱特性。在理论上,从准相位匹配相位失配关系出发,推导了晶体温度与抽运源中心波长的关系以及温度响应带宽,并和已报道实验结果进行了比较,二者符合得很好。此外,还推导了倍频周期极化铌酸锂晶体对抽运基频光源的响应谱线带宽。在实验上,采用长度20mm,极化周期6．5μm,厚度0．5mm的周期极化铌酸锂晶体光纤激光器准连续宽带输出进行了倍频,获得了在不同控制温度下的倍频光光谱,并对此进行了详细分析。     

PPLT倍频宽线宽掺镱双包层光纤放大激光

分别通过理论和实验研究了周期性极化的钽酸锂（PPLT）倍频宽线宽准连续掺镱双包层光纤放大激光.PPLT样品长为40 mm,极化周期为7.67 μm.基频光的中心波长为1064 nm,线宽约为6 nm.从基频光的光谱特性出发,利用超晶格倍频理论,解释了实验中获得的倍频温度与二次谐波功率之间的关系.在基频光的功率为2.2 W时,获得的宽线宽光纤激光倍频效率为1.8%.     

准相位匹配扇形光栅铌酸锂光波导倍频绿光输出

采用外加电场极化方式对具有扇形光栅的 0 .5mm厚Z切铌酸锂晶体进行极化反转 ,制成了退火质子交换光波导。极化反转周期为 5 .8μm～ 6 .2 μm ,采用Nd∶YAG激光器输出的 1.0 6 4 μm连续激光为基频光波 ,实现了0 .5 32 μm倍频绿光输出 ,相互作用长度为 4mm ,耦入波导的基频光波功率为 10mW ,获得了 2 0 μW的绿色倍频光输出 ,归一化转换效率为 12 5 % (W·cm2 )。     

低电场周期极化化学比掺镁铌酸锂绿光倍频器

对气相平衡扩散输运工艺制备的化学比掺镁铌酸锂晶体进行周期极化,实验中发现化学比掺镁铌酸锂晶体的矫顽场为12kV/mm,只有常用的同成分铌酸锂晶体的矫顽场的1/20,用低电场就可以制备出结构均匀周期为62～64μm的周期性极化结构.在室温下对此周期极化结构进行二次谐波倍频实验,其归一化倍频转换效率为48%/W。     

准相位匹配周期极化高掺镁铌酸锂532 nm倍频准连续输出研究

对周期性极化高掺镁铌酸锂倍频过程进行了准相位匹配倍频理论研究。在室温下通过外加电场极化法,用较低的极化开关电场～5．5kV／mm,在厚为1mm、长为10mm、宽为10mm的掺镁铌酸锂基片上成功地制备了周期为5．8～7．3pm(间隔0．3pm)的一阶准相位匹配倍频周期性极化光学微结构。将温度控制在70℃左右,以波长为1．060μm的Nd：YAG激光为基频光源,对所研制的光学微结构样品进行倍频通光实验验证。当入射基频光为920mW时,可以获得约15mW的532nm准连续倍频蓝光输出．其归一化转换效率高达1．77％／W。     

可调谐准相位匹配高效宽带二次谐波转换

高效宽带二次谐波转换在光通信、信号处理和光谱学等很多领域都有重要的应用.通常高效宽带二次谐波转换的研究都集中在几个波长,为了得到可调谐准相位匹配高效宽带二次谐波转换,理论分析了准相位匹配和群速度匹配条件.在此基础上,分别计算了0型和Ⅰ型准相位匹配情况下,温度对5 mol%掺杂氧化镁周期性极化铌酸锂和周期性极化铌酸锂晶体准相位匹配高效宽带二次谐波转换的影响.对于5 mol%掺杂氧化镁周期性极化铌酸锂晶体,在0型和Ⅰ型准相位匹配情况下,分别得到了调谐宽度15 nm和341 nm的可调谐准相位匹配高效宽带二次谐波转换;对于周期性极化铌酸锂晶体,在0型和Ⅰ型准相位匹配情况下,分别得到了调谐宽度44 nm和98 nm的可调谐准相位匹配高效宽带二次谐波转换.拓展了准相位匹配高效宽带二次谐波转换的波长范围.     

高效率内腔式2 μm简并光学参量振荡器

报道了一种高效率的2 μm光学参量振荡器. 利用1.064 μm声光调Q Nd:YVO₄激光器抽运基于氧化镁掺杂周期性极化铌酸锂的内腔式光学参量振荡器, 在简并状态实现了稳定高效的2 μm激光输出. 当808 nm激光二极管抽运功率为20 W, Q开关工作频率为15 kHz时, 产生了平均功率为3.5 W、脉冲宽度为1.4 ns的2 μm激光, 光-光转换效率为17.5%, 斜效率为25%. 据我们所知, 该转换效率在2 μm波段内腔式光学参量振荡器中是最高的.     

周期极化KTiOPO4晶体连续倍频绿光输出

采用外加电场极化方法，在Z切1mm厚的KTiOPO4晶体中实现了周期性极化反转。晶体的极化反转周期为9．0／μm，相互作用长度为3mm。波长为1．064μm的基频光功率为900mW，晶体中心温度为32℃时，获得0．532μm、22μW的倍频绿光输出，二次谐波转换效率为0．0024％。     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Hybrid Wavelength and Code Division Multiple Access in Optical Networks

A review of schemes for multiple access in fiber optic networks shows that a hybrid of wavelength and code division multiple access (WCDMA) combines the best features of both. In particular, the hybrid scheme retains the large information carrying capacity of wavelength division multiple access (WDMA) and flexibility of code division multiple access (CDMA). In this paper WDMA, optical CDMA (OCDMA), and WCDMA networks are discussed. In OCDMA networks, concept of incoherent and coherent coding including inverse decoding and matched filter is introduced. The delay performance of both WDMA and WCDMA networks, under the simple suboptimum access protocols based on cyclic search, is computed. It has been shown quantitatively that tuning delay significantly affects the delay performance of both WDMA and WCDMA networks. Futhermore, delay performance of WCDMA networks is always better than the WDMA networks for the same tuning delay, load, and number of users.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Measurement of nonlinear coefficient of optical fiber based on small chirped soliton transmission

We measure the waveform and phase curves of short optical pulses before and after transmission over different lengths of fibers by use of the pulse analyzer with the frequency-resolved optical gating (FROG),and numerically simulate pulse evolution under the experimental conditions.The nonlinear coefficient of the fiber is given by comparing the experimental results with the numerical ones.Difference between the experiment and numerical simulation is analyzed.     

Resonance scattering of canonical elastic shells in absorbing fluid medium

Resonance scattering of elastic spherical shell and cylindrical shell while the surrounding fluid medium has absorption is studied. The normal mode solution derived using exact elastic theory and the separation of variables is still applicable. However, the scattering form function has to be modified for the absorbing medium, otherwise the unreasonable result would be obtained. The backscattering form function in the absorbing medium is redefined, and the form function of elastic spherical and cylindrical shell with vacuum or solid matter filled is calculated in various absorption conditions. The results show that the absorption of surrounding fluid leads to notable attenuation of the coincidence resonances in the mid-frequency, but it has a little influence on the low-frequency resonance scattering induced by the filler inside the shell.     

Single-beam self-referenced phase-sensitive surface plasmon resonance sensor with high detection resolution

A versatile and low-cost single-beam self-referenced phase-sensitive surface plasmon resonance(SPR)sensing system with ultra-high resolution performance is presented.The system exhibits a root-mean-square phase fluctuation of ±0.0028.over a period of 45 min.i.e.a resolution of±5.2×10-9 refractive index units.The enhanced performance has been achieved through the incorporation of three design elements:a true single-beam configuration enabling complete self-referencing so that only the phase change associated with SPR gets detected,a differential measurement scheme to eliminate spurious signals not related to the sensor response,and the elimination of retardation drifts by incorporating temperature stabilization in the liquid crystal phase modulato .Our design should bring the detection sensitivity of non-labeling SPR biosensing closer to that achievable by conventional fluorescence-based techniques.     

Influences of SiO2 protective layers and annealing on the laser-induced damage threshold of Ta2O5 films

Ta2O5 films are prepared on BK7 substrates with conventional electron beam evaporation deposition.The effects of SiO2 protective layers and annealing on the laser-induced damage threshold (LIDT) of the films are investigated.The results show that SiO2 protective layers exert little influence on the electric field intensity(EFI)distribution,microstructure and microdefect density but increase the absorption slightly.Annealing iS effective on decreasing the microdefect density and the absorption of the films.Both SiO2 protective layers and annealing are beneficial to the damage resistance of the films and the latter is more effective to improve the LIDT.Moreover,the maximal LIDT of Ta2O5 films is achieved by the combination of SiO2 protective layers and annealing.