Multiplexed phase-conjugate holographic data storage with a buffer hologram

We describe and demonstrate a volume holographic storage system in which a phase-conjugate object beam is reconstructed by the same reference beam that was used for recording. An intermediate hologram is used as a temporary buffer, recorded with its own reference beam and the data-bearing object beam. Reading this buffer hologram with the phase conjugate of its reference beam reconstructs the phase conjugate of the object beam, which can then be recorded into the desired volume hologram for long-term storage. This method combines the immunity to lens aberrations provided by phase-conjugate readout with the simplicity of using the same multiplexed reference beam for both recording and readout. Only a single pair of phase-conjugate reference beams is required. Experimental results are shown with a single LiNbO(3):Fe crystal used as both buffer and storage holograms and a self-pumped phase-conjugate mirror in BaTiO(3) that provides the pair of phase-conjugate reference beams.     

MULTIGRATING NONDEGENERATE OSCILLATION AND PHASE SHIFT IN THE LINEAR SPPCM

The nondegenerate four-wave mixing in a linear self-pumped phase-conjugate mirror with arbitrary-chosen complex coupling constants has been studied by numerical methods. The frequency detuning and the phase-conjugate reflectivity versus cavity path length detuning for different complex coupling constants are discussed in detail. It is found that multigrating operation in some cases can enlarge the interval of cavity path length detuning to be compensated for by frequency detuning and improve the phase-conjugate beam generation. The phase relation between the output phase-conjugate beam and the input beam is calculated and the result is in agreement with the experimental results.     

Mutually Pumped Phase Conjugation of Three Incoherent Beams with a Novel Photorefractive Crystal

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Enhanced performance of a mutually pumped phase-conjugation setup using two photorefractive crystals

A mutually pumped phase-conjugator (MPPC) consisting of two photorefractive crystals is investigated experimentally at a wavelength of about 807 nm. In addition to a Rh:BaTiO₃ crystal, which is used in a modified bridge configuration for phase-conjugation, a Co:BaTiO₃ crystal is used to amplify the phase-conjugate beam by wave-mixing. The phase-conjugate power is at least doubled compared to that using only one crystal, and the beam quality of the phase-conjugate beam is distinctly improved. Moreover, the temporal stability of the phase-conjugate output using two crystals is much higher than that using only one crystal. Received: 7 December 2000 / Revised version: 12 January 2001 / Published online: 27 April 2001     

Temporal Behavior of Phase Conjugate Wave in Self-Pumped Phase Conjugator with Internal Total Reflection

Several temporal behaviors of the phase-conjugate output of a self-pumped phase conjugator with internal total reflection in BaTiO₃ crystal have been investigated as a function of the beam entrance position and incident angle on the crystal. Different sets of these conditions cause different behavior of phase conjugate wave which are unstable or pulsed output as well as temporally stable output. Classification of these temporal behaviors in phase conjugate wave by incident condition are shown.     

SBS相位共轭补偿现象的实验研究与图示化分析

通过实验观察了受激布里渊散射相位共轭波前补偿现象,分析了单横模激光、波前弱畸变及强畸变激光受激布里渊散射现象的差异.由于工作介质中强烈的热畸变所引起的波前破碎效应,高功率固体激光器的输出光束一般都不是理想的高斯型单横模,而是具有弱畸变或强畸变波前结构的光束,其包含多个子光束.只有总能量足够大的激光束被聚焦到布里渊介质中时,其包含的所有子光束才能各自按单横模受激布里渊散射规律产生后向散射光,再合并而实现完全的相位共轭波前反转,否则就只能实现部分相位共轭波前反转,即部分相位共轭补偿.     

Ce:KNSBN光折变类光纤简并四波混频特性研究

研究了Ce:KNSBN光折变类光纤在泵浦光和信号光夹角分别为小角度和大角度两种情况下简并四波混频的基本特性.当夹角较大时,在光折变类光纤内部形成了两个四波混频作用区域,获得了比小角度情况提高4倍的大相位共轭反射率.给出了Ce:KNSBN光折变类光纤中,在入射夹角分别为小角度和大角度两种情况下,相位共轭光反射率分别随信号光光强、两束泵浦光光强比变化的实验结果,并用理论公式进行了拟合,理论分析和实验结果相符.还研究了Ce:KNSBN光折变类光纤四波混频光栅模式和相位共轭光时间响应特性.光折变类光纤的相位共轭响应时间较快,可为秒量级.     

Phase conjugation via unequal amplitude multiple gratings in photorefractives: A simple shooting method for numerical solution

We present a simple shooting method to obtain numerical solutions of the nonlinear coupled-wave equations for degenerate four-wave mixing in photorefractive crystals when four different types of the index gratings of unequal amplitudes are responsible for phase-conjugation. Our analysis includes the effects of pump depletion and absorption in the medium. Intensities of the four beams, both inside and at the output surface, are obtained as a function of four unequal coupling strengths and absorption coefficient. Intensity of the generated phase-conjugate beam is shown as a function of both the small and wide ranges of signal beam intensity. It is found that the multigrating operation with a careful choice of coupling constants and their combinations may improve the phase-conjugate wave generation. Also the presence of absorption reduces the phase-conjugate intensity more significantly when all the gratings are operative than when a single grating is allowed. Numerical results obtained from the computer calculations are presented in graphical form.     

200 W phase-conjugate mirror for CW radiation

We have demonstrated a loop phase-conjugate mirror that has produced up to 200 W phase-conjugate average output power at a 140% reflectivity for a CW input beam at a wavelength of 1.03 μm. A high conjugation fidelity was established by showing that more than 80% of the output beam power was contained within a 1.3-1.7 times diffraction limited beam after double passing a heavily aberrating amplifier chain.     

纠缠压缩真空态的纠缠转移

通过分析光学分束器对压缩真空态光场的作用,发现如果分束器的输入光是两束具有同样振幅和相位的单模压缩真空态光场,则输出光为双模压缩真空态光场;若分束器的输入光是两束具有同样振幅但有π相位差的单模压缩真空态光场,则输出光仍为两束单模压缩真空态光场.对于双模压缩真空态光场,每个模中容纳的光子数可以是基数或偶数.而对于单模压缩真空态光场,每个模中只能包含偶数个光子.根据这些结果,提出了一个纠缠转移的方案.在这个方案中,两个纠缠压缩真空态光场被用作量子信道,通过利用光学分束器作用和光子数探测的方法,并在经典通讯的帮助下,实现了三个通讯伙伴之间的纠缠转移.     

波片光轴偏差对偏振分光光束振幅和相位的影响研究

研究了在线偏振光入射、波片和偏振分束器结合使用时波片光轴偏差对偏振分束器分出的两束光的振幅和相位的影响。给出了在两种放置情况下,任意波片光轴方向偏差对偏振分光光束振幅和相位影响的表达式。详细分析了1/4波片和1/8波片的影响性质,给出了具体的振幅和相位影响关系式。     

Multiple-beams Mutually Pumped Phase Conjugation Generated by a Bridge Phase Conjugator in Photorefractive Ba1-xSrxTi03 Crystal

A new method generating multiple-beams mutually pumped phase conjugation (MMPPC) in a photorefractive Bat- xSrxTiO3 crystal is demonstrated, in which a pumping beam is incident upon a-face of the crystal and two signal beams are introduced into + c face of the crystal with the almost same incident angle and position. The time evolution of the phase conjugations from signal beams and the dependence of phase-conjugate reflectivities on the input-beam intensity ratios are presented. Also, the amplitude coupled-wave equations based on the model of two interaction reigns is derived. The results obtained by numerical calculation of the corresponding coupled-wave equations show qualitative agreement with the experimental results.     

Multiple-beams Mutually Pumped Phase Conjugation Generated by a Bridge Phase Conjugator in Photorefractive Ba1 - xSrxTi03 Crystal

A new method generating multiple-beams mutually pumped phase conjugation (MMPPC) in a photorefractive Bat- xSrxTiO3 crystal is demonstrated, in which a pumping beam is incident upon a-face of the crystal and two signal beams are introduced into + c face of the crystal with the almost same incident angle and position. The time evolution of the phase conjugations from signal beams and the dependence of phase-conjugate reflectivities on the input-beam intensity ratios are presented. Also, the amplitude coupled-wave equations based on the model of two interaction reigns is derived. The results obtained by numerical calculation of the corresponding coupled-wave equations show qualitative agreement with the experimental results.     

Mechanism for Phase Conjugation Reflections of Two Mutually Coherent Beams from Potassium Sodium Strontium Barium Niobate

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Study of the Frog-legs Phase Conjugator in BaTiO_3

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Mutually pumped phase conjugator using a BaTiO3 crystal having two inclined faces

A pentagon-shaped undoped BaTiO₃ crystal was used to construct a high-quality mutually pumped phase conjugator. It yields two very stable phase-conjugate outputs (ǃ.7% fluctuation in intensity) with high reflectivity (the highest ᅝ%) when the two incident beams are of equal intensities. The response time of the conjugator is rather fast (ƻ s) and the tolerance of the acceptance angle is large too (걄°). Fine structures (35 7m) in an image, after passing through a phase aberrator, can be recovered by the conjugate waves yielded by this conjugator.     

Fast response self-pumped phase conjugator based on a +c-face incident configuration in a pentagon-shaped BaTiO3 crystal

We propose a novel geometry for a self-pumped phase conjugator that uses a +c-face incident configuration in a photorefractive pentagon-shaped 0°-cut BaTiO₃ crystal for obtaining fast response in phase conjugation. A steady phase-conjugate output with a fast response time 0.4 s is obtained when the incident beam has a 4 W/cm² intensity. The influences of position and angle on the temporal phase-conjugate response are also investigated. The advantage of this phase conjugator using this novel configuration is improved resolution of a phase-distorted image with a value as high as 128 lp/mm.     

Loss of phase of collapsing beams

We experimentally investigate the phase of an optical field after it has undergone wave collapse. We confirm the theoretical prediction that it acquires a large cumulative nonlinear phase shift that is highly sensitive to small fluctuations of the laser input power. This results in an effective postcollapse "loss of phase," whereby the phase of the transmitted beam shows a significant increase in sensitivity to the input fluctuations of the pulse energy. We also investigate interactions between two beams that each undergoes collapse and observe large fluctuations in the output mode profiles, which are due to the postcollapse loss of their relative phase difference. Such effects should occur in all systems that exhibit wave collapse.     

Narrow bandwidth operation of high-power broad-area diode laser using cascaded phase-conjugate injection locking

A broad-area laser is injection-locked by another broad-area laser that is also injection-locked by a single-mode diode laser. Two double-phase conjugate mirrors of photorefractive BaTaO₃ are used to couple the master laser beams to the first slave laser, and the first slave laser output to the second slave laser. One of the double-phase conjugate mirrors is built up with the beams from two broad-area lasers. Two slave lasers are oscillating in single longitudinal mode at 808.5 nm and the spectral width is the same as that of the master laser. Final single-mode output power from the second slave broad-area laser is 840 mW, which is limited by the power of the injection beam. This work verifies the possibility of the multi-stage cascaded injection locking of high-power diode lasers with phase-conjugate injection. Received: 18 November 1998 / Revised version: 29 January 1999 / Published online: 7 April 1999     

Three Gaussian beam heterodyne interferometer for surface profiling

A novel three Gaussian beam interferometric technique for profiling optical smooth surfaces is presented. The technique is based on the heterodinization of three Gaussian beams, two of them with the same temporal frequency. The first beam is used as a probe beam after being focused and reflected from the surface under test. The second beam is reflected from a reference surface. The third beam is obtained from the first diffraction order of a Bragg cell and thus, it is shifted in its temporal frequency. The three beams are coherently added at the sensitive plane of a photodetector that integrates the overall intensity of the beams. We show analytically that the electrical signal at the output of the photodetector consists of a temporal carrier whose amplitude is a sinusoidal function of the local topography. We include the measurement of the topography of a sample consisting in a blazed-reflecting grating calibrated by means of an atomic force microscope.