Photorefractive phase conjugators

The author presents a tutorial review of various kinds of optical phase conjugators using photorefractive materials. These include externally pumped phase conjugators (EPPCs), self-pumped phase conjugators (SPPCs), and mutually pumped phase conjugators (MPPCs). He briefly describes optical phase conjugation and the photorefractive effect. He also describes wave mixing in photorefractive media. The energy transfer in two-wave mixing and the holographic nature of four-wave mixing are discussed     

粗糙介质面对高斯波束的散射

该文研究了当入射场为光波束时粗糙介质面的散射问题。利用波束的平面波谱展开方法及基尔霍夫近似理论导出了散射场和非相干截面计算公式,并对后向非相干截面进行了数值计算,最后对其结果进行了分析讨论。     

Using multiple mutually incoherent fiber lasers to pump a coherentsignal beam in an optical parametric oscillator

We use three-dimensional numerical modeling to show that multiple mutually incoherent lasers can be used to pump a single resonated coherent signal beam in an optical parametric oscillator (OPO). We consider as an example an OPO based on periodically poled lithium niobate pumped noncollinearly by CW Yb-doped fiber lasers. Our modeling, which neglects thermal lensing, is appropriate when the average power is kept low by chopping or pulsing the pump beams at a low duty cycle. We find that a signal beam can be produced with near-diffraction-limited beam quality and power considerably exceeding that of a single pump laser     

多光束照明方式对平滑光强起伏效果的影响研究

基于多光纤耦合输出半导体激光作为照明光源的主动成像系统比较了多束非相干聚焦光束和准直光束平滑光强起伏的效果,分析了两种光束受湍流引起的光束短期扩展和束心抖动的异同,为多光束照明方式提供了参考。采用相位屏近似方法模拟激光大气传输,模拟结果表明对这种主动成像系统采取准直发射方式可以有效平滑光强起伏,而聚焦发射方式则不能实现此目的。     

扩散对非相干耦合屏蔽光伏亮孤子之间相互作用的影响

为了得到扩散效应对非相干耦合屏蔽光伏亮-亮孤子对相互作用的影响的结果,将两束互不相干的光束做为入射波,采用数值方法求解有扩散的波传播方程.结果表明,当两孤子中心间距适当的条件下,非相干屏蔽光伏亮孤子对之间发生相互吸引和缠绕现象;如果两孤子间距过大或过小时,孤子之间没有相互作用.扩散效应使两孤子光束整体向同一方向偏转.     

非相干光对Ce:KNSBN晶体两波耦合的影响研究

理论分析和实验研究了非相干光照射下Ce:KNSBN晶体中的两波耦合,发现非相干光在很大范围内可有效地控制晶体中的两波耦合效应。实验结果和理论分析趋势相一致。     

光纤激光非相干合成效果分析

为了研究光纤激光的非相干合成特性, 建立了圆环状排布的光纤激光阵列光束合成模型, 模拟分析了单元光束束腰半径w₀、波前畸变和光束间距对非相干及相干合成远场光束质量的影响。讨论了多路激光平行性对非相干合成效果的影响, 并进行了相关实验验证。结果表明, 单元光束无波前畸变时, 当光束间距为d₀=2.8w₀时, 非相干与相干合成光束质量相等; 单元光束存在波前畸变时, 光束间距有所减小, 这是因为波前畸变对非相干合成影响更小; 对于非相干合成, 随着多路激光之间不平行度的增大, 非相干合成光束质量逐渐变差, 并且单元光束质量越好, 对多路激光平行性要求越高。该研究可为实际光纤激光合成系统设计分析提供参考。     

双光子非相干耦合亮-暗混合屏蔽光伏孤子族

为了得到双光子非相干耦合亮-暗混合屏蔽光伏孤子族的结果,采用数值模拟方法,对稳态情况下多束互不相干的光束,在有外加电场的双光子光伏光折变晶体中的传播进行了研究。结果表明,具有相同偏振和相同波长的多束互不相干的入射光束,可在晶体中形成双光子非相干耦合亮-暗混合屏蔽光伏孤子族。双光子非相干耦合屏蔽光伏孤子族,可以看成是屏蔽孤子族和光伏孤子族的统一形式。当光伏场可忽略时,屏蔽光伏孤子族就转化为屏蔽孤子族,而当外加电场不存在时,屏蔽光伏孤子族相当于开路和闭路条件下的光伏孤子族。当孤子族中只含有两个光束分量时,孤子族就变为屏蔽光伏孤子对。研究结果可为空间光孤子理论的发展提供理论依据。     

Optimization of DSF- and SOA-based phase conjugators byincorporating noise-suppressing fiber gratings

We compare the performance of dispersion-shifted-fiber (DSF) and semiconductor-optical-amplifier (SOA) based laser phase conjugators for a 10-Gb/s nonreturn-to-zero system with respect to conversion efficiency, noise figure, and distortion. Fiber gratings are used for signal extraction and amplified spontaneous emission (ASE) suppression, allowing closer wavelength spacing and reducing the conjugation noise figure by up to 12 dB. Despite the higher SOA conversion efficiency, both conjugators give similar noise figures with ASE suppression. However, the DSF-based conjugator has the advantage of distortion tolerance at higher input power     

光折变晶体中的相位共轭

近几年来,光折变相位共轭器及其在非线性光学中的应用取得了有意义的进步。本文主要叙述光折变晶体中的四波混频以及各种光学相位共轭器的结构,简单地介绍了相位共轭器在光信息处理中的一些应用。     

光折变晶体中非相干光前向耦合及其对噪音栅擦除的研究

对光折变晶体 Ce:KNSBN中两束 e偏振简并非相干光的前向耦合进行了理论分析和实验研究 ,并通过非相干光耦合作用在实验上获得了亮环和暗环的衍射图样 ,从而获得了一种利用非相干光擦除来克服光折变晶体中扇形效应的简便方法。     

Theoretical noise performance of coherence-multiplexedinterferometric sensors

If a number of fiber-optic interferometric sensors are arranged so that their outputs are returned to the user via a common optical bus, then some method of distinguishing the returns from different sensors must be used to recover individual signals. One such method involves using light with a short coherence length, so that returns from different sensors will be mutually incoherent. The interferometric signal associated with each sensor can then be recovered via appropriate optical processing. The author considers sensors multiplexed using this technique and calculates their noise performance. It is found that for systems with only a few sensors, the minimum detectable phase is limited by the noise associated with incoherent interference; this can be minimized by using light with as short a coherence length as is practical. The maximum number of sensors that can be multiplexed is limited by optical power loss. A ladder topology is tentatively found to give the best performance     

Analysis of Gaussian beam propagation and diffraction by inhomogeneous wave tracking

Inhomogeneous waves behave locally like A(r) exp[ikS(r)], where A and S are spatially dependent complex amplitude and phase functions, and k is the (large) free-space wavenumber. A previously developed asymptotic theory for high-frequency propagation and scattering of such waves is here applied to the propagation and scattering of paraxial Gaussian beams. Attention is given to Gaussian beams in free space, to beams in a lens-like medium with parabolic variation of the refractive index, and to beam reflection by a cylindrical obstacle. In the latter instance, the obstacle size may be comparable to the incident beamwidth, thereby introducing substantial distortion into the reflected beam. The results obtained from the asymptotic theory are verified by comparison with rigorously derived solutions, thereby confirming the validity of the theory, which can also be applied to more general medium and obstacle configurations.     

非相干LED白光产生无衍射光的光源设计

非相干光源产生无衍射光束的实验中,入射光束的均匀性对产生无衍射光束的质量有很大影响。文中以非相干光源白光LED为例,通过对LED自身发光特性的分析,对光线传播过程进行数学建模,用非成像光学光通量守恒原理,对均匀照明设计方法进行理论推导,得到了一种基于非成像光学产生均匀光束的透镜设计方法。用三维建模软件进行建模并用光学仿真软件进行光线追迹,确定用该方法设计的透镜能满足实验对入射光束均匀度的要求,并初步实验获得较高质量的零阶无衍射Bessel光,验证了该设计方法的合理性。     

非相干光对光折变相位共轭镜的非负效应

本文以BaTiO3:Ce自汞浦相位共轭镜为例,理论上和实验上对非相干光作用在光折变相位共轭镜的四波混频区产生的非负效应进行探讨和验证。     

Laser wave propagation through the atmosphere

Communications with coherent light through the atmosphere bring out new system limitations besides the ones imposed by attenuation and scattering normally associated with incoherent waves. This is so because the laser directivity and coherence responsible for increased channel capacity are easily destroyed or at least degraded by the presence of random thermal turbulences. Simple expressions describing the effects of atmospheric turbulence on laser beam propagation are obtained. Corresponding calculations yield the order of magnitude of such random phenomena as beam scanning, phase variation, beam cross-section change, amplitude and frequency modulation. In particular, the polarization fluctuation is predicted quantitatively in terms of the atmosphere mean square refractive index and its turbulence correlation length.     

Beam fanning and double phase conjugation in a fiber-likephotorefractive sample

Unexpectedly fast response (35 ms) of beam fanning has been measured in a fiber-like photorefractive sample of Bi₁₂TiO ₂₀ (BTO) crystal. Nonlinear interaction between different directions of fanned beams is responsible for unusual angular distribution of the fanning emerged from the fiber that can be used for double phase-conjugate mirror (DPCM) recording with higher efficiency in a wider range of the pump's incidence than in a bulk sample. The DPCM with conversion efficiency up to 8% has been recorded in the BTO fiber at λ=632.8 nm for a 2×3 mW input light power. Practically, it means that no adjustment is needed to achieve an effective interaction of mutually incoherent beams, except introducing the pump beam into the fiber     

复杂像散高斯光束的并合光束特性

利用Wigner分布函数 ,对复杂像散高斯光束的并合问题进行了详细研究 ,得到了相干和非相干并合光束的光强分布和M2 因子的解析表达式。解析结果和数值计算均表明 ,并合光束的特性与子光束数目、相对间距和几何排布等因素有关。以光束传输因子 (M2 )作为标准时 ,相干并合光束质量优于非相干并合 ;以桶中功率 (PIB)作为标准时 ,相干并合光束质量并不总优于非相干并合。     

自泵浦位相共轭器中自增强现象与光致宏观电场

研究了自泵浦位相共轭器利用间歇入射光在无光照期间的新奇的自增强现象。发现采用间歇入射光可以显著缩短掺铈与掺锰钾钠铌酸锶钡单晶自泵浦江相共轭器的响应时间。通过实测晶体的光伏与热释电电场，利用电荷输运的基本模型．对实验现象给出了定性解释，且给出了进一步的实验验证。据此，分析了自泵浦位相共轭器的保真度下降的原因。