Experimental demonstration of nonlinearity and dispersion compensation in an embedded link by optical phase conjugation

We report in this letter, the experimental demonstration of simultaneous dispersion and nonlinearity compensation in an embedded link characterized by strongly asymmetrical power profiles. This result is obtained by using a highly efficient optical phase conjugator based on a periodically poled lithium-niobate waveguide, combined with two small dispersion-compensating elements properly inserted in the link.     

Dispersion compensation by optical phase conjugation in silicon waveguide

The use of a silicon-waveguide-based optical phase conjugator at the mid-span of a fibre link for dispersion compensation is experimentally demonstrated, enabling transmission of optical data at up to 40 Gbit/s over 320 km of standard fibre with clear open eye diagrams at the receiver. In addition, the feasibility of dispersion compensation for multiple DWDM channels simultaneously is demostrated. A signal conversion efficiency of -10 dB is obtained with a pump intensity of 37.5 MW/cm² in the waveguide.     

WDM transmissions exploiting optical phase conjugation

Due to the frequency shift occurring in the process of optical phase conjugation (opc) generation, the application of opc in multiple-channel transmission is limited severely by the third-order dispersion. In this paper, taking into account the influence of the frequency shift and the compensation of nonlinear effects, we present an effective method to optimize the dispersion map for broad-band transmissions using optical phase conjugation. The numerical simulation results show that high efficiency wavelength-division-multiplexing (wdm) transmissions can be achieved by using the combination of opc with an optimized dispersion map.     

利用相位共轭实现单根光纤直接传输图象

利用相位共轭介质——光折变晶体掺铁铌酸锂(Fe:LiNbO_3)产生的简并四波混频的波前反转性质,补偿了多模光纤由于模色散引起传输图象的畸变,实现单根多模光纤直接传输图象;研究了相位共轭对传输图象光场偏振态的影响。     

One-parameter adoptive cancellation for satellite microwave links

For dual linearly polarised microwave links (especially to satellites), in situations where differential phase shift is the dominant cause of crosspolarisation, it is proposed to perform adaptive cancellation of crosspolarisation by means of a simplified network having only one variable parameter. A possible construction of the device is suggested and its performance in various situations assessed.     

波导中非弹性散射产生的光学相位共轭

本文研究了在装有CS2的波导管中后向非弹性散射的相位共轭特性和在全息红宝石激光器中应用的可能性。在实验中激光器的放大级产生的光束畸变由共轭波反向再次通过该放大棒，得到了较好的补偿。     

相位共轭实现光学逻辑运算

本文从麦克斯韦电磁场理论出发,给出了用四波混频相位共轭波和泵浦光波及入射物波偏振态之间的关系来实现光学逻辑运算的途径。     

Design theory of long-distance optical transmission systems usingmidway optical phase conjugation

This paper describes the basic system principle, the residual waveform distortion, the optimal design method, the ultimate transmission capacity, and its future improvement of the long-distance optical fiber transmission system using midway optical phase conjugation. We show that the periodic power variation in an optical amplifier chain and the dispersion value fluctuation from span to span along the system cause imperfect compensation for waveform distortion in the midway optical phase conjugation system. The optimal design method for suppressing the residual waveform distortion is proposed and confirmed by using computer simulations     

Characteristics of optical phase conjugation of picosecond pulsesin semiconductor optical amplifiers

Nondegenerate four-wave mixing (FWM) of picosecond optical pulses in semiconductor optical amplifiers is investigated theoretically, taking into account various carrier processes, probe depletion, and cross-gain modulation effects. Analytical solutions for greatly simplified coupled-wave mixing equations are obtained from which conditions where probe depletion and cross-gain modulation effects cannot be neglected are found. On the other hand, the frequency detuning dependence of optimum input pump pulse energy and shaping of output conjugate pulses are observed from numerical simulations. In particular, calculations show that the frequency symmetry of conjugate and probe pulses with respect to the pump pulse does not hold for optical pulse FWM. Two-photon absorption and ultrafast nonlinear refraction effects are shown to decrease the FWM conversion efficiency     

Nonlinear noise amplification in optical transmission systems with optical phase conjugation

Taking into account the influence of group-velocity dispersion (GVD) and the nonlinear Kerr effect, the nonlinear amplification of the amplified spontaneous emission (ASE) noise in fiber transmission systems using optical phase conjugation (OPC) is studied. Under a path-averaged power approximation for long-haul transmission systems, an equivalent system is developed to evaluate ASE noise amplification and accumulation in OPC systems. Combining the theoretical analysis and numerical simulations, the noise suppression effect in OPC systems is demonstrated and discussed. By using the numerical calculation method, the power variation along the system is involved in the evaluation of noise amplification. It is shown that the power variation through the system results in an imperfect compensation of the modulation instability (MI) effect, which furthermore causes the degradation of the noise suppression performance in OPC systems with anomalous dispersion.     

Study of optical phase conjugation in bulk traveling wave semiconductor optical amplifier

Optical phase conjugation (OPC) in a bulk SOA has been optimized both under static and dynamic conditions. Conjugation with gain has been obtained. Dynamic optimization leads to a compromise between conversion efficiency and signal-to-background (S/B) ratio, providing that the modulated signal is kept a minimum of 5 dB weaker than the pump to avoid detrimental saturation effects. Transparent 10-Gb/s phase conjugation with extinction ratio around 20 dB at moderate power levels is reported.     

Compensation for the self-steepening effects in optical fiber communication system using midway optical phase conjugation

Effects of self-steepening (SS) of chirped Gaussian pulses on optical fiber communication system using midway optical phase conjugation (OPC) are analyzed. Dynamic evolution of the ultrashort pulses is simulated numerically. It is found that OPC cannot compensate for pulse waveform distortion due to SS.The initial chirp of pulses and dispersion can counteract SS and improve the compensation performance for the distortion.     

Suppression of Gordon-haus effect and interaction of dark soliton by optical phase conjugation

The optical phase conjugation is put forward for the first time to suppress the Gordon-Haus effect caused by amplifier spontaneous emission noise, and soliton interaction in the dark soliton transmission system. The simulation results show : If the conjugator is sited at proper situation, it can suppress the Gordon-Haus effect or the dark soliton interaction effectively.     

Digital adaptive phase noise reduction in coherent optical links

Coherent optical links enable high-density constellations and, consequently, a higher throughput. However, the phase noise associated with the transmitter and the receiver lasers is a challenging issue in coherent lightwave systems. The authors present an approach that relies on using digital signal processing techniques to compensate for the laser phase-noise effects. The proposed approach exploits the digital processing power to address the problems arising from optical imperfections. The authors present an adaptive filtering scheme that reduces the effect of the laser phase noise and, consequently, relaxes the laser linewidth requirement. The proposed approach shows how the signal processing techniques can be exploited to compensate for the optical impairments by utilizing the continuing scale down in size and power in very large scale integration (VLSI) technology.     

含相位物体的光学非线性测量技术研究进展

光学非线性的研究离不开对材料光学非线性系数的测量,快捷可靠的测量技术一直是非线性光学研究领域的热点之一。4f相位相干成像技术因其独特的优势受到了人们的重视,其中相位物体的应用引起了广泛的关注。简述了4f相位相干成像技术的基本原理及特点,然后重点介绍了含相位物体的非线性测量技术的研究进展。综述了反射4f探测技术、含相位物体透过率的测量方法、相位物体Z扫描技术、基于相位物体的时间分辨泵浦探测技术和4f泵浦探测技术,并比较了这些方法的特点和应用。     

两种相位共轭技术对光纤中超短光脉冲传输失真的补偿比较

通过理论分析和数值计算,比较了时域相位共轭技术和频域相位共轭技术对光纤中由于色散和非线性引起的超短光脉冲传输失真的补偿效果。结果表明,在仅考虑群速度色散和自相位调制效应时,时域相位共轭技术与频域相位共轭技术的补偿效果一致;当需要考虑三阶色散时,频域相位共轭技术的补偿效果优于时域相位共轭技术;当需要考虑脉冲内拉曼散射时,时域相位共轭技术的补偿效果优于频域相位共轭技术;当上述四种效应同时考虑时,频域相位共轭技术的补偿效果略优于时域相位共轭技术。同时还对上述两种补偿技术的应用进行了讨论。     

Techniques for high-speed implementation of nonlinear cancellation

The authors present techniques for breaking the bottleneck caused by delays in the feedback loop, which can severely limit the maximum data rate of a detector, operating with nonlinear cancellation (NLC). The authors first show how to simplify the loop to avoid high-speed switching of analog signals by using multiple decision elements, each with a different threshold level. The authors then show how to use lookahead computation to increase the delay permissible in the feedback loop. The authors describe nonlinear cancellation, and outline some of the problems of implementing NLC at high data rates. Techniques for overcoming these problems are developed and are illustrated with the example of a simple one-tap NLC. The authors describe how to generalize the techniques to more complex NLCs and present some more examples     

Polarization-preserving phase conjugation and temporal reversal ofan arbitrarily-polarized pulsed optical signal by means oftime-and-space-domain holography

Polarization-preserving phase conjugation of an arbitrarily-polarized multiple-pulse optical signal by using a modified scheme of time-and-space-domain holography is predicted theoretically and demonstrated experimentally. The experimental results obtained by utilizing octaethylporphin-doped polystyrene at 1.8 K as a spectrally-selective recording material indicate that in full accordance with the theory, the reconstructed phase-conjugated replicas of the multiple-pulse optical signal appear temporally reversed and have conjugated wavefronts while the original temporal and spatial dependence of the polarization state is restored. Thus, complete phase conjugation of an optical signal is demonstrated     

Non-frequency-shifted phase conjugation by Brillouin-enhanced four-wave mixing

We present a theoretical treatment of four-wave mixing (FWM) in a Brillouin-active medium for the case in which the pump waves differ in frequency by approximately twice the Brillouin frequency shift of the medium and in which the probe-wave frequency is approximately the arithmetic mean of the frequencies of the two pump waves. Under these conditions, the conjugate wave produced by the FWM process has the desirable property of being at the same frequency as the probe. We derive the coupled amplitude equations describing this interaction. We solve these equations analytically in the limit of negligible pump depletion and find that large phase conjugate reflectivities are readily achievable. The coupled amplitude equations are solved numerically for the general case, and it is found that large power transfer from the pumps to the output wave is possible. The output wave is shown to be a nearly perfect phase conjugate of the probe wave, even far into the regime where pump depletion effects are important. Our formalism predicts the existence of a parametric instability in the propagation of the pump waves, but good performance is predicted before the onset of this instability.     

Optical phase conjugation and nonlinear optical bandpass filtercharacteristics in CdSSe microcrystallite-doped glass

Experimental measurements of the backward CW four-wave mixing response in semiconductor-doped glass in a regime important to applications are described. In particular, it is shown that lowering the operating temperature to 125 K yields a χ³≈2×10 ^-4 ESU. Aberration correction through optical phase conjugation is demonstrated with a phase conjugate reflectivity of 0.3% along with a wide-angle field-of-view response. In addition, the nearly-degenerate four-wave mixing response of importance to tunable bandpass optical filters is reported