Highly efficient four-wave mixing induced by quantum constructive interference in rubidium vapour

We demonstrate efficient four-wave mixing with an intensity conversion efficiency of nearly 100% in theory without considering the Doppler-broadening effect in a four-level double-Λ system of hot ⁸⁷Rb gas. The corresponding experimental value of about 73% was reported in our earlier work under the same conditions. This dramatic efficiency is critically dependent on the constructive interference between two four-wave mixing processes relevant to the internally generated four-wave mixing signal.     

Efficient frequency conversion induced by quantum constructive interference

We demonstrate in experiment an efficient cw four-wave mixing scheme with maximal intensity conversion efficiency up to 73% in a double-Λ system of hot rubidium atoms. Relevant theoretical analysis shows that this high conversion efficiency benefits greatly from the constructive interference between two four-wave mixing channels, characterized by two different space-dependent phases.     

色散位移光纤中零色散波长纵向分布对四波混频转换效率的影响

研究了色散位移光纤零色散区域附近的四波混频特性 ,讨论了当零色散波长彼此不同的多段光纤连接起来后对四波混频效率的影响。理论计算结果表明 ,在信号光和抽运光波长间隔较小的区域 ,各光纤对四波混频过程都有贡献 ,且互相调制 ,并出现增益现象 ,有着很复杂的效率图。     

Etalon effect in wave-mixing experiments with photorefractive crystals

We present investigations of the etalon effect in sillenite photorefractive crystals with a pulsed frequency-doubled Nd:YAG laser and show its influence on two- and four-wave mixing. In four-wave mixing the etalon effect allows changes of the diffraction efficiency by more than 80%. Results are supported by theoretical considerations. Received: 15 April 1998/Revised version: 19 June 1998     

有机染料溶液中简并的四波混频和位相复共轭研究

本文研究了近共振增强的四能级系统有机染料溶液中简并的四波混频后向波和前向波的位相复共轭特性。用有效长度为5毫米、浓度为2.5×10^-5克分子的叶绿素A甲醇溶液作介质,当调QNd:YAG倍频抽运光能量为8毫焦耳时,非线性反射率为22％。研究了若丹明6G酒精溶液双光子共振增强的简并的四波混频作用。测量了非线性反射率与介质浓度及抽运波和物波强度的关系曲线。理论分析了四波混频前向波的位相复共轭特性,实验证实了理论的预言。另外,把四重简并的四波混频推广到二重简并。用9740有机染料二氯乙烷饱和吸收溶液作介质,实现了1.06微米到5320埃的象转换。介质长度为5毫米,抽运光能量为5毫焦耳时,转换效率达25％。理论分析表明,用对红外近共振吸收而对可见辐射是透明的介质可实现高效率红外象转换。 关键词：     

SRS generation under phase matching conditions for four-wave interactions of SRS components in birefringent Raman-active crystals

The possibilities of efficient four-wave SRS generation in the schemes of cavity and cavity-amplifier SRS converters with the implementation of phase matching conditions for four-wave mixing of different SRS radiation components at an appropriate orientation of birefringent SRS crystals have been considered based on a numerical simulation. The threshold characteristics and achievable energetic parameters of the SRS generation of different frequency radiation components have been analyzed under the conditions of implementation of phase matching for four-wave mixing. Conditions have been found for a low-threshold SRS-four-wave mixing generation of an anti-Stokes wave with a conversion efficiency of up to 40%, as well as of the first, second, and third Stokes SRS components with conversion efficiencies of up to 90, 80, and 30%, respectively.     

Characterize and optimize the four-wave mixing in dual-interferometer coupled silicon microrings

By designing and fabricating a series of dual-interferometer coupled silicon microrings, the coupling condition of the pump, signal, and idler beams can be engineered independently and then we carried out both the continuous-wave and pulse pumped four-wave mixing experiments to verify the dependence of conversion efficiency on the coupling conditions of the four interacting beams, respectively. Under the continuous-wave pump, the four-wave mixing efficiency gets maximized when both the pump and signal/idler beams are closely operated at the critical coupling point, while for the pulse pump case, the efficiency can be enhanced greatly when the pump and converted idler beams are all overcoupled. These experiment results agree well with our theoretical calculations. Our design provides a platform for explicitly characterizing the four-wave mixing under different pumping conditions, and offers a method to optimize the four-wave mixing, which will facilitate the development of on-chip all-optical signal processing with a higher efficiency or reduced pump power.     

Evolution of first-order sidebands from multiple FWM processes in HiBi optical fibers

The generation of two idler waves inside a high birefringent (HiBi) optical fiber through three four-wave mixing (FWM) processes is studied theoretically. The coupled-equations for the field amplitudes are derived and analytically solved, in the co-polarized and orthogonal polarization schemes. The obtained solutions take into account the delayed Raman response of the medium. The polarization sensitivity of the generation of the idler waves is analyzed. Results show that the stimulated Raman scattering does not change the efficiency of the idler wave generation in the co-polarized scheme, whereas in the orthogonal polarization scheme that nonlinear process decreases the efficiency of the four-wave mixing processes. Results also show that this set of multiple four-wave mixing processes is physically quite different from the typical single or dual pump four-wave mixing configurations. Findings show that the power transfer from the pumps to the idler fields can lead to a monotonous growth, or a periodic evolution of the sidebands along the fiber. Results show that the process efficiency varies greatly with the angle between the two pump polarizations.     

电磁诱导透明窗口中温度、功率及偏振特性对四波混频信号的影响

电磁诱导透明(EIT)效应改变了介质的吸收特性,导致了线性极化率的抑制和非线性极化率的提高,从而可以实现高效率四波混频的产生.实现了基于EIT的高效四波混频,且研究了样品温度、入射光功率和入射光偏振状态对四波混频信号的影响特性.研究发现,温度对样品铷的两个同位素87Rb和85Rb的影响有所差别,它们分别存在一个最佳工作...     

Four-wave mixing in Raman fibre amplifiers in the 3rd telecommunications window

The efficiency of four-wave mixing (FWM) between two wavelength channels in Raman amplifiers operating around 1550 nm has been investigated. Measurements of FWM in Raman amplifiers utilizing different gain fibre types demonstrated that choice of gain fibre and pump power can seriously impact channel cross talk via four-wave mixing.     

Pump-depleting four-wave mixing in supercontinuum-generating microstructure fibers

Four-wave mixing processes are shown to provide a high efficiency of non-linear optical frequency conversion and spectral transformation of ultrashort pulses in supercontinuum-generating microstructure fibers. Pump-depleting conversion of 800-nm radiation to the spectral range around 500 nm is achieved by phase-matching the parametric four-wave mixing process for 80-fs Ti:sapphire-laser pulses. The ways to use microstructure fibers for generating frequency-tunable radiation through four-wave mixing with the maximum efficiency of pump-field frequency conversion are discussed. PACS 42.65.Wi; 42.81.Qb     

Zn∶Fe∶LiNbO_3晶体二波耦合和相位共轭效应的研究

采用二波耦合和四波混频实验,研究了Zn:Fe:LN(Fe:0.03wt.%,Zn:5.0mol)晶体的光折变二波耦合衍射效率和长时间照射下透射光强随时间的动态变化行为,以及其相位共轭效应,分别测试了其二波耦合衍射效率和其相位共轭反射率,结果表明该晶体的衍射率可达到56%,且其衍射效率随着其信号光的减小先增大后减小,相位共轭反射率随信号光的增大呈减小的趋势,最高共轭反射率可达到650%。     

Quantum entanglement of Fock states with perfectly efficient ultraslow single-probe photon four-wave mixing

We propose a method to achieve quantum entanglement of two Fock states with perfectly efficient, ultraslow propagation enhanced four-wave mixing. A cold atomic medium is illuminated with a two-mode cw control laser to produce coherent mixtures of excited states. An ultraslowly propagating, single-photon quantum probe field completes the four-wave mixing with 100% photon flux conversion efficiency, creating a depth dependent entanglement of two Fock states. We show that at a suitable propagation distance, a maximum entangled state is created with a single-photon wave-packet state that has 50% probability of being in each of two product-type Fock states.     

Four-Wave Mixing in Microwires to All-Optical Signal Processing in Mode-Division Multiplexing Systems

Abstract

Mode-division multiplexing requires all-optical signal processing techniques that are able to deal with a new coding dimension, the spatial mode. In this context, optical microwires emerge as a potential highly non-linear and multi-modal waveguide envisioning the development of all-optical signal processing devices to mode-division multiplexing systems based on the four-wave mixing process. The inter- and intramodal phase-matching conditions for the four-wave mixing process are mapped as a function of the microwire diameter and the wavelength of signals. Moreover, the efficiency of four-wave mixing considering a strong guiding regime is investigated in the multi-modal regime.     

Frequency converters based on FWM in traveling-wave optical amplifiers: Theoretical aspects

We summarize the results of a theoretical model, developed to investigate the performance of a frequency converter based on four-wave mixing in a bulk traveling wave amplifier. The theory predicts very high values of conversion efficiency and signal-to-background ratio in the bandwidth of the converted signal. These results, whose experimental confirmation is reported elsewhere, increase the potential of using four-wave mixing in semiconductor amplifiers in actual optical systems.     

Resonant photorefractive effect in InGaAs/GaAs multiple quantum wells

Semi-insulating InGaAs/GaAs multiple quantum wells are fabricated by metal-organic vapor-phase epitaxy and proton implantation. Two-wave mixing gain and four-wave mixing diffraction efficiency are measured at wavelengths of 0.91-0.94microm in the Franz-Keldysh geometry. We observe a large photorefractive effect caused by the excitonic electro-optic effect. The maximum diffraction efficiency reaches ~1.5x10(-4) .     

Two-photon resonant parametric generation in alkali metal vapours

Two-photon resonant four-wave mixing has been studied both theoretically and experimentally. Tunable infrared radiation between 2 and 20 μm has been generated in potassium and caesium vapours. The mixing efficiency is found to be severely limited by competition with Raman scattering.     

Generation of a sub-20-fs single optical pulse by four-wave Raman mixing using two Raman cells filled with molecular hydrogen

To attempt to expand the spectral domain for pulse shortening, we generated several emission lines by stimulated Raman scattering and subsequent four-wave Raman mixing. The efficiency of generation of the Raman emission was improved by passing the beam through two Raman cells that were connected in series. The group-velocity dispersion induced by a Raman cell window and hydrogen was compensated for by means of a pair of chirped mirrors for pulse compression. By a phase lock of the emission lines in the process of four-wave Raman mixing, the pulse width was reduced from 114 to 17 fs in the second Raman cell.     

在等离子体中的二重简并四波混频

本文分析了在均匀等离子体中的二重简并四波混频(一种实时红外象转换过程)。通过典型例子说明红外象转换效率为1所需的泵功率是现实的。 关键词：     

光纤四波混频多波长时钟信号整形

将两路时钟信号作为泵浦光,与连续探测光一同耦合进高非线性光纤中,四波混频产生的两路闲频光作为整形后的时钟信号,并通过控制两路时钟信号之间的相对时间延迟来减小光纤四波混频干扰。研究了整形前时钟信号占空比的变化与整形后时钟质量的关系以及最佳占空比下输入时钟信号和输出时钟信号的相对幅度抖动的关系,发现在占空比由小到大变化的过程中,整形后时钟信号的质量总体上先变好后变坏;在最佳占空比0.14下,两路时钟信号的相对幅度抖动由原来的13.934 9%和13.958 6%下降到2.03%和2.12%,表明了该方案的可行性。