Nonlinear performances of dual-pump amplifiers in silicon waveguides

The performances of a dual-pump parametric and Raman amplification process and the wavelength conversion in silicon waveguides are investigated. By setting the Raman contribution fraction f to be 0.043 in our analytical model, the amplification gain of the probe signal can be obtained to be over 10 dB. The pump transfer noise (PTN), the quantum noise (QN), and the total noise figure (TNF) are discussed, and the TNF has a constant value of about 4 dB in the gain bandwidth. An idler signal generated during the parametric amplification (PA) process can be used to realize the wavelength conversion in wavelength division multiplexing (WDM) systems. In addition, the pump signal parameters, the generated free carrier lifetime and effective mode area (EMA) of the waveguide are analysed for the optimization of signal gain and noise characteristics.     

Hybrid chirped-pulse amplification

Conversion efficiency in optical parametric chirped-pulse amplification is limited by spatiotemporal characteristics of the pump pulse. We have demonstrated a novel hybrid chirped-pulse amplification scheme that uses a single pump pulse and combines optical parametric amplification and laser amplification to achieve high gain, high conversion efficiency, and high prepulse contrast without utilization of electro-optic modulators. We achieved an overall conversion efficiency of 37% from the hybrid amplification system at a center wavelength of 820nm. Generation of multiterawatt pulses is possible by use of this simple method and commercial Q -switched pump lasers.     

Quasi-phase-matched generation of tunable blue light in a quasi-periodic structure

We present what is to our knowledge a new approach to generating tunable blue light by cascaded nonlinear frequency conversion in a single LiTaO3 crystal. Simultaneous quasi-phase matching of an optical parametric generation process and a sum-frequency mixing process is achieved by means of structuring the crystal with a quasi-periodic optical superlattice. The spectral (wavelength tuning and bandwidth) and power characteristics of the blue-light generation are studied with a fixed-wavelength 532-nm picosecond laser and a wavelength-tunable nanosecond optical parametric oscillator (OPO) as the pump sources. By tuning the OPO wavelength, we could tune the blue output over approximately 20 nm. Temperature tuning of the blue output at a fixed pump wavelength of 532 nm was limited to approximately 1.5 nm. A maximum blue power of 15 microW was generated at a pump power of 0.5 mW, corresponding to an efficiency of 3%.     

New scheme of a petawatt laser based on nondegenerate parametric amplification of chirped pulses in DKDP crystals

The ultra-broadband phase matching was experimentally observed in a DKDP crystal upon parametric amplification of signal radiation with a wavelength of 911 nm in a pump field with a wavelength of 527 nm. The original scheme was used to excite the first parametric amplification stage by chirped pulses of idler radiation with a wavelength of 1250 nm. The saturated gain of a three-stage parametric amplifier was equal to 10⁸.     

Noise-figure limit of fiber-optical parametric amplifiers and wavelength converters: experimental investigation

Recent theoretical work predicts that the quantum-limited noise figure of a x(3)-based fiber-optical parametric amplifier operating as a phase-insensitive in-line amplifier or as a wavelength converter exceeds the standard 3-dB limit at high gain. The degradation of the noise figure is caused by the excess noise added by the unavoidable Raman gain and loss occurring at the signal and the converted wavelengths. We present detailed experimental evidence in support of this theory through measurements of the gain and noise-figure spectra for phase-insensitive parametric amplification and wavelength conversion in a continuous-wave amplifier made from 4.4 km of dispersion-shifted fiber. The theory is also extended to include the effect of distributed linear loss on the noise figure of such a long-length parametric amplifier and wavelength converter.     

双泵浦光子晶体光纤参量放大研究

利用光子晶体光纤在不同零色散波长附近具有不同色散的特性,研究了在零色散波长为780 nm和1550 nm附近的双泵浦光子晶体光纤参量放大过程.在780 nm附近,讨论了零色散波长变化对双泵浦光子晶体光纤参量放大的影响.数值模拟结果表明:当零色散波长发生微小的变化时,信号增益谱带宽会发生很大的变化.当两泵浦光之间的波长差值减小时,零色散波长的变化对参量放大的影响在很大程度上可以得到抑制,但是增益带宽会有一定的减小.依据这一原理,在1550 nm附近设计光子晶体光纤中的色散平坦光纤参量放大,在5 m长的光子晶体光纤中,当峰值功率为10 W时,得到了增益为65 dB,带宽达到420 nm且极为平坦的增益谱.     

Fibre Optical Parametric Amplification in Defect Bragg Fibres with Zero Dispersion Slow Light Effect

Nonlinearity enhancement by slow light effect and strong light confinement in defect Bragg fibres is demonstrated and anMysed in applications of fibre optical parametric amplifiers. Broadband low group velocity and zero dispersion as well as the strong light confinement by band gap enhances the nonlinear coefficient up to more than one order than the conventional high nonlinear fibres. Moreover, the zero dispersion wavelength of coupled core mode can be designed arbitrarily, under which the phase-matching bandwidth of the nonlinear process can be extended.     

宽带光参量放大过程中的转换效率提升

建立了宽带光参量放大数值模拟平台,并基于此对宽带光参量放大系统的能量转换效率提升进行优化设计,根据模拟计算结果可以对实验中能够达到的最优化能量转换效率进行预判。建立了验证实验平台并进行了实验,研究并攻克了实验中遇到的参量荧光抑制、信号光,泵浦光空间精确匹配、脉宽精确匹配、时间波形整形等关键技术难点。在抑制参量荧光的同时实现了宽带光参量放大过程能量转换效率的提升,在单级宽带光参量放大过程中获得了30%的能量转换效率。     

基于双抽运参量放大中的信号波和闲频波特性

根据信号波和闲频波所满足的耦合非线性薛定谔方程,导出了双抽运参量放大增益系数g、信号波的放大因子和闲频波转换效率,并在输入总抽运功率不变的情况下,仅改变双抽运功率P1,P2的比值s,对参量放大增益系数g、信号波的放大因子和闲频波转换效率理论研究和数值模拟;数值模拟结果表明：相位匹配条件下,通过改变双抽运功率的比值 ,可获得适当的放大的信号波和一定转换效率的闲频波。     

基于双抽运参量放大中的信号波和闲频波特性

根据信号波和闲频波所满足的耦合非线性薛定谔方程,导出了双抽运参量放大增益系数g、信号波的放大因子和闲频波转换效率,并在输入总抽运功率不变的情况下,仅改变双抽运功率P1,P2的比值s,对参量放大增益系数g、信号波的放大因子和闲频波转换效率理论研究和数值模拟;数值模拟结果表明：相位匹配条件下,通过改变双抽运功率的比值 ,可获得适当的放大的信号波和一定转换效率的闲频波。     

Optical parametric amplification of a supercontinuum in a gas

Amplification of supercontinuum light via four-wave optical parametric amplification in a gas-filled hollow fiber is investigated. By pumping with a femtosecond pulse in the near-infrared, amplification was observed in the wavelength range 500–700 nm, with an amplification gain up to 100. The amplification bandwidth obtained here supports sub-10-fs pulse durations. The wavelength and gas-pressure dependence of the amplification gain in this regime significantly differ from those predicted from only the linear phase mismatch. The nonlinear phase mismatch, arising from nonlinear phase modulations induced by a pump pulse, dominates the features observed for the amplification, i.e., a low phase-matching pressure and an amplification gain depending on wavelength. To investigate the effect of phase modulations on the parametric amplification, numerical analysis and simulations are used to reproduce the measured wavelength dependence of the amplification gain.     

A tunable fiber parametric oscillator for the 2 μm wavelength range employing an intra-cavity thulium doped fiber active filter

We report an efficient fiber parametric oscillator operating in the wavelengths range of 1.97 μm to 2.14 μm. The oscillator is based on narrow band parametric amplification and employs a thulium doped fiber placed at the loops end as an intra-cavity active filter. The filter eliminates any signal generated by stimulated Raman scattering which inherently accompanies the parametric process. Short wavelength parametric oscillations and the pump signal are also absorbed. Only the long wavelength parametric oscillations can build up in the resonantly pumped system which emits 4 ns pulses at ~ 1 MHz with a maximum peak pulse power of 20 W.     

啁啾匹配和同步抖动对光参量啁啾脉冲放大的影响

 通过研究光参量啁啾脉冲放大过程转换效率随泵浦光啁啾参数的变化,以及信号光和泵浦光波长的对应关系,确立了信号光和泵浦光同步时实现线性啁啾匹配的方法。以磷酸二氢钾作为非线性晶体,研究了信号光和泵浦光之间的线性啁啾匹配和时间同步抖动对光参量啁啾脉冲放大后信号光脉冲波形和转换效率的影响。结果表明：在时间同步的情况下,线性啁啾匹配时的信号光脉冲波形很对称,转换效率也较高;在同步抖动程度一定的情况下,不同泵浦光啁啾参数时,信号光的增益及放大后的脉冲波形差异较大;在线性啁啾匹配程度一定时,信号光和泵浦光时间同步抖动越严重,放大信号光的脉冲波形变化越大,信号光增益越小,且转换效率也越低。     

级联参量振荡产生太赫兹辐射的理论研究

针对光学参量振荡产生太赫兹波转换效率低的缺点, 提出了级联参量振荡产生太赫兹波的新机理以提高转换效率. 以周期极化铌酸锂晶体为例, 对级联参量振荡产生太赫兹波的原理和过程进行了理论研究. 分析了抽运光波长、周期极化铌酸锂晶体极化周期和工作温度对产生一阶、二阶闲频光频率的影响. 推导了三波共线相互作用条件下太赫兹波的增益特性和吸收特性. 计算结果表明, 通过级联参量振荡可以有效提高太赫兹波的转换效率, 并可以得到宽调谐的太赫兹波输出. 基于分析结果, 设计了周期极化铌酸锂晶体级联参量振荡产生高效率、宽调谐、窄线宽、连续太赫兹波的实验. 关键词： 太赫兹波 太赫兹波参量振荡 级联参量振荡     

Generation of broadly tunable picosecond mid-infrared laser and sensitive detection of a mid-infrared signal by parametric frequency up-conversion in MgO:LiNbO₃ optical parametric amplifiers

Picosecond optical parametric generation and amplification in the near-infrared region within 1.361-1.656 μm and the mid-infrared region within 2.976-4.875 μm is constructed on the basis of bulk MgO:LiNbO 3 crystals pumped at 1.064 μm.The maximum pulse energy reaches 1.3 mJ at 1.464 μm and 0.47 mJ at 3.894 μm,corresponding to a pumpto-idler photon conversion efficiency of 25%.By seeding the hard-to-measure mid-infrared radiation as the idler in the optical parametric amplification and measuring the amplified and frequency up-converted signal in the near-infrared or even visible region,one can measure very week mid-infrared radiation with ordinary detectors,which are insensitive to mid-infrared radiation,with a very high gain.A maximum gain factor of about 7 × 10 7 is achieved at the mid-infrared wavelength of 3.374 μm and the corresponding energy detection limit is as low as about 390 aJ per pulse.     

Fiber parametric oscillator for the 2 μm wavelength range based on narrowband optical parametric amplification

We describe a widely tunable synchronously pumped coherent source based on the process of narrowband parametric amplification in a dispersion-shifted fiber. Using an experimental fiber with a zero-dispersion wavelength of 1590 nm and pump wavelengths of 1530 to 1570 nm yields oscillations at 1970 to 2140 nm-the longest reported wavelength for a fiber parametric oscillator. The long-wavelength oscillations are accompanied by simultaneous short-wavelength oscillations at 1200 to 1290 nm. The parametric gain is coupled to stimulated Raman scattering. For parametric oscillations close to the Raman gain peak, the two gain processes must be discriminated from each other. We devised two configurations that achieve this discrimination: one is based on the exploitation of the difference in group delay between the wavelengths where Raman and parametric gain peak, and the other uses intracavity polarization tuning.     

Quantum properties of optical images in coupled nondegenerate parametric processes

Quantum properties of parametric amplification and frequency conversion of an optical image in coupled parametric interactions are analyzed for the case of a remote object. The coupled-wave interaction consists of a traditional process of parametric amplification in the high-frequency pump field accompanied by the frequency mixing of generated and pump waves. The photon number density and signal-to-noise ratio at the interacting frequencies are studied in the image plane at the output of the nonlinear frequency converter in the fixed pump field approximation. The degree of entanglement of optical images at frequencies above and below the pump frequency is investigated.     

光学参变啁啾脉冲放大相位失配啁啾脉冲频谱整形新方法

相位匹配是实现高效光学参变啁啾脉冲放大(OPCPA)能量转换的关键之一,通过对几种常用非线性晶体的光学参变啁啾脉冲放大过程进行数值模拟研究,结果表明一定程度的相位失配不但能增加光学参变啁啾脉冲放大增益带宽,而且会使啁啾脉冲光谱强度分布中间凹陷。提出利用光学参变啁啾脉冲放大相位失配放大作为啁啾脉冲频谱整形的新方法,通过理论分析和模拟计算,找到了光学参变啁啾脉冲放大相位失配啁啾脉冲频谱整形效果的控制量;并对几种常用非线性晶体在简并、近简并、非简并等条件下的光学参变啁啾脉冲放大相位失配放大特性进行了比较。     

BBO，LBO，KDP晶体光参量啁啾脉冲放大特性的比较研究

 对BBO，LBO，KDP晶体I类非共线匹配下的光参量啁啾脉冲放大的相位匹配、参量范围、增益特性等进行了理论分析，重点对BBO和LBO的光参量啁啾脉冲放大特性进行了比较。结果表明对于以光参量啁啾脉冲放大系统代替800nm中心波长的Ti:sappire再生放大系统，用BBO晶体可获得更宽的增益带宽，而对1 053nm中心波长的种子光用LBO晶体更好。     

Efficiency-enhanced picosecond mid-infrared optical parametric downconversion based on a cascaded optical superlattice

We demonstrate an efficiency-enhanced picosecond(ps) mid-infrared radiation via optical parametric downconversion. Based on a ceiscaded periodically poled MgO-doped stoichiometric lithium tantalate crystal(MgO:sPPLT), a tandem optical parametric oscillation-optical parametric amplification(OPO-OPA) process is achieved. Compared with a single OPO process, the conversion efficiency obtains an enhancement of 71%.