Broadband non-collinear double QPM optical parametric amplification in mid-infrared wave

The properties of optical parametric amplification (OPA) based on non-collinear double quasi-phase matching (NDQPM) with single periodically poled KTP (PPKTP) have been investigated theoretically. The NDQPM includes two different non-linear processes: one is optical parametric generation (OPG) and the other is difference frequency generation (DFG). The investigation of our numerical simulation focuses on the gain bandwidth of dependence upon non-collinear angle, grating period and crystal temperature. At a certain non-collinear angle and grating period with fixed temperature, there exists a broadest gain bandwidths of output mid-infrared pulse at 526 nm pump wavelength and certain signal wavelength in PPKTP. These are an optimal values of non-collinear angles and grating period. By accurately tuning the non-collinear angle or temperature near the optimal non-collinear angle, broadband mid-infrared tuning is obtained and an optimal operation of NDQPM can be realized. In this paper, the solutions of the coupled equations of the cascaded processes were discussed, and the spatial-temporal frequency (STF) band of the output idler pulse is analyzed by taking angular dispersion of amplified pulse beam into account. The idler pulse with a certain angular dispersion can improve the OPA bandwidth significantly. So, optical parametric chirped-pulse amplification can be realized in this configuration. For a broadband NDQPM both the acceptance angles and the acceptance temperature are smaller and the gain bandwidth is sensitive to non-collinear angles and temperature, it is important to control the precision of the non-collinear angles and the temperature in experiment.     

Spatial-temporal frequency band of optical parametric amplifier

The spatial-temporal frequency band of optical parametric amplifier for collinear as well as for noncollinear phase-matching is analyzed taking into account angular dispersion of amplified pulsed beam. The simple formulae are derived which make possible determination of the largest frequency bands of parametric amplifiers in noncollinear geometry. It has been demonstrated that a shape of the spatial-temporal frequency band of optical parametric amplifier essentially depends on pump and signal wavelengths, and certain angular dispersion as well as proper beamwidth of signal pulse enable amplification of ultrashort pulses with duration of a few femtoseconds.     

Numerical study on pulse contrast enhancement in a short-pulse-pumped optical parametric amplifier

We investigate pulse cleaning behaviors in short-pulse-pumped optical parametric amplifiers (OPA). We theoretically study the contrast enhancement of amplified signal pulse and generated idler pulse, and reveal their dependence on the parametric gain in both the regimes of small signal and saturated amplifications. The signal contrast enhancement is nearly equal to the parametric gain, while the idler contrast is approximately equal to the product of the contrasts of the pump and signal pulses in a low gain OPA and increases with the gain. The effects of group-velocity mismatch and group-velocity dispersion on the contrast enhancement are also investigated. The results presented in this paper are of value for pulse cleaning.     

光纤中基于交叉相位调制的超短光脉冲串的产生

提出一种在单模光纤正常色散区由连续波产生超短光脉冲串的新方法，即让连续波和一个波长位于光纤正常色散区的调制脉冲串在光纤中同时传输，交叉相位调制效应和群速度色散效应的相互作用能使连续波演化成一串超短光脉冲，其脉冲宽度比调制脉冲串中的脉宽要小得多，本文还通过计算机模拟，对这一方法进行了全面的考察和分析。结果表明，该方法不仅实用，而且可取得较好的效果。     

光纤中基于互相位调制效应的超短光脉冲对的产生

提出一种在单模光纤正常色散区由连续波产生超短光脉冲对的新方法.即让连续波和一个波长位于光纤负色散区的高阶孤子在光纤中同时传输,互相位调制效应和群速度色散效应的互相作用能使连续波演化成超短光脉冲对.本文还通过计算机模拟,对该方法进行了全面的考察和分析.结果表明,此方法实用且效果较好.     

Compact eye-safe laser sources based on OPOs with KTP or PPKTP crystals

We report on compact eye-safe nanosecond laser sources emitting in the 1.5 μm wavelength range based on non-critically phase-matched parametric interaction in optical parametric oscillators (OPOs) with KTP and periodically poled KTP (PPKTP) crystals, pumped by the fundamental frequency of Nd:YAG lasers. As much as 250 μJ signal pulse energy at 1.5 μm wavelength, 6.5 ns FWHM pulse-width, has been obtained in a PPKTP-OPO, extracavity pumped by a Nd:YAG microlaser oscillator–amplifier at 650 μJ pump pulse energy, 8 ns pulse-width. A single signal pulse of 2.7-mJ output energy at 1.57 μm wavelength, less than 5 ns pulse-width, was generated in a KTP-OPO, intracavity pumped by a passively Q-switched Nd:YAG laser.     

光纤中超短光脉冲特性的计算机模拟

本文从理论上分析了具有自相位调制的光脉冲在色散介质中的传播特性,从而解释了超短光脉冲的压缩机理;并用严谨的数学步骤,将各种文献中形式各异的非线性薛定谔方程归结为统一的形式,避免了因符号定义不同而易于引起的混淆。针对该方程的特点.找到了合适的数值求解法,利用微机获得了在不同色散的介质中,光脉冲振幅、频谱、相位、啁啾等沿光纤方向变化的定量关系曲线。结果表明:在正色散介质中,脉宽及带宽均展宽,而在负色散介质中,脉冲沿传播方向越来越窄,表现为孤子效应。最后结合光栅对,给出了用光纤、光栅对获得1.06μm超短光脉冲时系统各部分的最佳参量。     

Performance analysis of dual-pump optical parametric amplifiers in silicon waveguide

Nondegenerate Four Wave Mixing (FWM) process in a silicon waveguide is influenced by two photon absorption (TPA), TPA induced free carrier absorption (FCA) besides self-phase modulation (SPM), cross-phase modulation (XPM), SRS, GVD and linear scattering losses. Influences of pump parameters of the dual-pump parametric amplifier (OPA) in the silicon waveguide on gain spectrum and noise figure are numerically investigated. Compared with single-pump configuration, dual-pump silicon OPA indicates a flat gain and noise figure. Then impact of waveguide dispersion on bandwidth and ripples for dual-pump silicon optical parametric amplifiers is discussed. Optimal pump configurations are evaluated. The results show that polarization independent net gain of silicon OPA can be achieved by using circular and orthogonally polarized pump.     

利用自制的单频激光器获得近通讯波段正交振幅压缩态光场

利用自制的1.34 μm和0.67 μm双波长输出单频激光器作为泵浦源,泵浦基于PPKTP晶体的光学参量放大器,通过边带锁频技术将光学参量放大腔腔长锁定在激光频率上,将泵浦光和信号光相对相位锁定在π相位,经参量缩小过程获得低于散粒噪声极限约3 dB的正交振幅压缩光.压缩光位于光纤通信窗口——1.3 μm波段.     

Phase modulation conversion and conservation in optical parametric amplifier of femtosecond laser pulses

The influence of the pump pulse, group-velocity mismatch, dispersion and self-phase modulation & cross phase modulation on the phase transfer in the OPA process were analyzed. The results show that very sharp phase modulation can be maintained in mid infrared range by optical parametric amplifier. The period and depth of the periodic modulation can also be maintained due to small group-velocity mismatching in the calculated wavelength range.     

All-optical control of the carrier-envelope phase with multi-stage optical parametric amplifiers verified with spectral interference

Intense ultrashort laser pulses with stabilized carrier-envelope phase (CEP) are generated at 800 nm by using multi-stage collinear and non-collinear optical parametric amplifiers (OPAs). The first-stage collinear OPA is directly pumped by the fundamental-wave pulses and tuned to generate idler pulses at 1600 nm, which are further amplified by a second-stage collinear OPA, and then frequency-doubled to generate CEP-stabilized pulses at 800 nm. A non-collinear OPA is used to amplify the CEP-stabilized pulses at 800 nm. The combination of different OPAs can generate and amplify CEP-stabilized pulses at 800 nm without any detrimental influence from the fundamental-wave pulses. The CEP stabilization is verified with a simple and robust spectral interference setup. The stable interference pattern is measured for every single pulse and compared with the unstable pattern from pulses of random CEP. PACS 42.65.Re; 42.65.Yj; 42.25.Kb     

强脉冲信号在光纤参变放大器中的放大特性研究

考虑到抽运损耗、走离、色散和非线性等效应,用分步傅里叶方法求解耦合的非线性薛定谔方程组,就强脉冲信号在连续光抽运光纤参变放大器中的放大情况进行了理论研究。研究结果表明,强脉冲信号除经历振幅放大,脉冲时域展宽等过程外,还会发生令人感兴趣的脉冲分裂现象,即一个脉冲信号分裂为两个子脉冲。而且即使在连续光抽运的情况下,走离效应对强脉冲信号的放大也产生了显著影响,即促使两个子脉冲振幅不等以及脉冲漂移。最后,强脉冲信号独特的放大特性用光纤参变放大器的饱和增益特性做了很好的解释,并指出脉冲分裂现象在信号抽样、脉冲压缩、光时分复用系统中有潜在用途。     

Transmission of 20 Gb/s PAM-4 signal over 20 km optical fiber using a directly modulated tunable DBR laser

We report 20 Gb/s transmission of four-level pulse amplitude modulation(PAM) signal using a directly modulated tunable distributed Bragg reflector(DBR) laser. Transmission distance over 20 km was achieved without using optical amplifiers and optical dispersion compensation modules. A wavelength tuning range of 11.5 nm and a 3 dB bandwidth greater than 10 GHz over the entire wavelength tuning range were obtained.     

Ultrashort Gaussian pulse-width expansion and shape deformation induced by group velocity dispersion

Pulse-width expansion and pulse-shape deformation of an ultrashort Gaussian pulse induced by both low and high order group velocity dispersion were theoretically analyzed in terms of energy conservation and coupled equations for three wave radiations. As an example, the optical parametric interaction processes in a negative uniaxial crystal of CsLiB₆O₁₀ with 50 fs of ultrashort Gaussian pulse were simulated. The results indicate that the degree of the pulse expansion induced by low and high order group velocity dispersion is determined by both the wavelength of the incident wave and the crystal length. A pulse could be expanded to 1.41 times its initial value as a crystal length equals the dispersion length and further heavily expanded with decreasing wave-length and increasing crystal length. The pulse expansion induced by high order group velocity dispersion using an incident wavelength of 213 nm is 1.6 times that when using 532 nm in a 50 fs pulse width without chirp modulation, and the symmetry deformation and the frequency pushing phenomena of the ultrashort pulse shape are also found. The text was submitted by the authors in English.     

对应于铯原子D1线连续可调谐正交压缩态光场的制备

铯原子D₁线的非经典光由于其波长接近于量子点的独特优势,在固态量子信息网络的发展中有着重要的应用前景.在之前的工作中,利用两镜连续简并光学参量振荡器中的参量下转换过程,制备出2.8 d B正交压缩真空态光场.然而,所产生光场的压缩度较低,对于对压缩光具有实用意义的可调谐性能也未做进一步探究.理论分析表明,光学参量振荡器后腔镜对信号光透射率的增加及内腔损耗的减小可以提高压缩度.因此,本文在该研究基础上,通过使用高光洁度腔镜及优化腔镜镀膜参数等方式对光学参量振荡器进行改良,降低了光学参量腔阈值,获得压缩度为3.3 d B的单模正交压缩真空光.当光学参量腔运转为参量反放大状态时,在系统稳定运行的情况下,制备的明亮压缩态光场能够连续调谐80 MHz,为其在量子信息网络中的应用奠定了良好的基础.     

Amplitude and phase characterization of weak blue ultrashort pulses by downconversion

We present difference-frequency generation cross-correlation frequency-resolved optical gating, a new method of characterizing the amplitude and phase of weak ultrashort pulses in the blue spectral region. The method uses the spectrally resolved downconversion signal of the blue pulse and a fully characterized reference pulse with a lower center frequency. The amplitude and phase of the blue test pulse are retrieved from the corresponding spectrogram and electric field of the reference pulse with an interactive Fourier-transform algorithm.     

Trends in ultrashort and ultrahigh power laser pulses based on optical parametric chirped pulse amplification

Since the proof-of-principle demonstration of optical parametric amplification to efficiently amplify chirped laser pulses in 1992,optical parametric chirped pulse amplification(OPCPA)became the most promising method for the amplification of broadband optical pulses.In the meantime,we are witnessing an exciting progress in the development of powerful and ultrashort pulse laser systems that employ chirped pulse parametric amplifiers.The output power and pulse duration of these systems have ranged from a few gigawatts to hundreds of terawatts with a potential of tens of petawatts power level.Meanwhile,the output pulse duration based on optical parametric amplification has entered the range of fewoptical-cycle field.In this paper,we overview the basic principles,trends in development,and current state of the ultrashort and laser systems based on OPCPA,respectively.     

Theoretical study of gain distortions in dual-pump fiber optical parametric amplifiers

We study analytically and numerically the small signal gain in dual-pump fiber optical parametric amplifiers by including the phase modulation of the pump waves needed for practically increasing the stimulated Brillouin scattering threshold. As for the single-pump case, we show that large signal gain distortions are generated under co-phase modulation, which depend on the rise/fall time of the phase modulation and on the fiber dispersion slope. However, it is clearly confirmed that the counter-phase modulation scheme allows to efficiently suppress these gain distortions over the whole flat gain region. In addition, we demonstrate through realistic numerical simulations that this useful technique overcomes the additional impact of pump-phase modulation to amplitude modulation conversion and zero-dispersion wavelength variations.     

基于互逆光纤色散的微波光子雷达系统设计和实现

提出一种基于互逆光纤色散的微波光子雷达系统设计方案,既可以产生宽带线性调频信号,又可以实现线性调频信号的光域脉冲压缩.在发射端利用互逆色散光纤产生线性调频信号.在接收端,雷达回波信号通过马赫-曾德调制器调制到预啁啾的光信号上,然后经过色散光纤的进一步色散.最终在探测器端可以得到目标回波信号脉冲压缩后的结果.该方案无需脉冲压缩过程中数字化和离线处理,且具有脉冲压缩比的调谐作用.理论、数值仿真和实验证明了该设计方案能有效进行线性调频信号的光域脉冲压缩.实验产生了C波段下时宽1.2ns,带宽3.2GHz的线性调频信号,并通过互逆色散光纤将该信号压缩到了0.09ns,脉冲压缩比达13.3.     

基于光前置放大器的量子密钥分发融合经典通信方案

量子密钥分发融合经典通信方案将连续变量量子密钥分发和经典通信合并到了一起,为将来在现有的光网络上同时进行密钥分发和经典通信提供了一个有效的方法.然而,在量子信号上叠加一个经典信号将会给连续变量量子密钥分发系统引入过噪声从而大大降低系统的性能.本文提出基于光前置放大器的量子密钥分发融合经典通信方案,即在接收端插入光前置放大器来提升系统的性能.首先,在相同比特误码率条件下,光前置放大器对信号的放大能够降低对发送端经典信号调制振幅的要求,从而降低经典信号对量子信号的噪声影响;其次,光前置放大器能够补偿接收端探测器的不完美;再次,对于本地本振光的情形,放大器还能放大弱相位参考脉冲,从而降低参考脉冲散粒噪声带来的相位过噪声.在实际可达到的系统参数下,数值仿真结果表明本文提出的方案相比于原方案在安全密钥率和传输距离上都有很好的提升.这些结果表明本方案为量子密钥分发融合经典通信方案的进一步发展和实际应用提供了一个十分有效而实用的方法.