Noiseless amplification and signal-to-noise ratio in single-sideband transmission

We study the properties of optical single-sideband (SSB) modulation with respect to signal-to-noise ratio and limits to spectral efficiency. We show that SSB signals undergo truly noiseless amplification, which can be understood in view of Heisenberg's uncertainty principle. Yet, contrary to previously published results, this phenomenon offers no advantages in terms of the signal-to-noise ratio of the amplified signal. We show that, when an intensity receiver is used, single-sideband modulation can improve spectral efficiency in the limit of a high optical signal-to-noise ratio and in the presence of a strong carrier signal.     

Noiseless amplification of images in a confocal cavity

We study the noiseless amplification of an optical image by means of a confocal cavity containing a parametric medium. We demonstrate, in the ideal situation, the possibility of preserving the signal-to-noise ratio while amplifying uniformly the entire image. Some specific effects, which may degrade the performances of the scheme, are taken into account. Received 23 March 2000     

高功率可调谐双频激光全光纤放大实验研究

基于全光纤以及主控振荡功率放大器,设计并搭建了一套扫频范围为125~165 MHz的拍频信号的放大系统。并设计了一套基于1064 nm的Nd:YAG单块非平面环形腔激光器作为单频种子源。通过声光移频的方式将1064 nm单频激光分成中心频差为150 MHz的两束激光进行拍频。双频激光初始功率为50 mW,通过放大系统将双频功率放大到10 W。通过实验及分析得出两束频差为150 MHz的激光功率比率在放大之后保持不变,且经过放大的激光信号中,拍频信号所占的功率成分可以通过调节双频功率比以及单臂分量的偏正态来获得最大输出。同时对拍频信号的信噪比及线宽进行了实验分析。     

Coherent signal amplification in rhodopsin media

A quantum optics model that explains the sensitivity of the dark-adapted rhodopsin to a single photon is presented. We describe the absorption of photons by rhodopsin molecules using the three-level A-type model for its retinal chromofore, with 3 states being the all-trans, 11-cis and the photoexcited S ₁ state. The abinitio calculations have been performed to estimate the parameters of the model. The text was submitted by the authors in English.     

Robust amplification in adaptive signal transduction networks

Amplification of small changes in input signals is an essential feature of many biological signal transduction systems. An important problem is how sensitivity amplification can be reconciled with wide dynamic range of response. Here a general molecular mechanism is proposed, in which both high amplification and wide dynamic range of a sensory system is obtained, and this without fine-tuning of biochemical parameters. The amplification mechanism is based on inhibition of the enzymatic activity of the sensory complex. As an example, we show how this ‘inhibition-driven amplification’ mechanism might function in the bacterial chemotaxis network, where it could explain several intriguing experimental observations connected with the existence of high gain, wide dynamic range and robust adaptation.     

Intensity-dependent parametric amplification for traveling-wave signal processing

We propose and demonstrate a nonlinear parametric amplification system that relies on sequential use of a nonlinear phase shift (Kerr-like effect) and on phase-sensitive parametric amplification. We demonstrate amplification that is 50% better than with a bare phase-sensitive amplifier as well as two additional effects: inversion of weak optical modulation and suppression of classical noise.     

Optimal signal amplification in weighted scale-free networks

It has been revealed that un-weighted scale-free (SF) networks have an effect of amplifying weak signals [Acebro?n et al., Phys. Rev. Lett. 99, 128701 (2007)]. Such a property has potential applications in neural networks and artificial signaling devices. However, many real and artificial networks, including the neural networks, are weighted ones with adaptive and plastic couplings. For this reason, here we study how the weak signal can be amplified in weighted SF networks by introducing a parameter to self-tune the coupling weights. We find that the adaptive weights can significantly extend the range of coupling strength for signal amplification, in contrast to the relatively narrow range in un-weighted SF networks. As a consequence, the effect of finite network size occurred in un-weighted SF networks can be overcome. Finally, a theory is provided to confirm the numerical results.     

Acoustical power amplification and damping by temperature gradients

Ceperley proposed a concept of a traveling wave heat engine ["A pistonless Stirling engine-The traveling wave heat engine," J. Acoust. Soc. Am. 66, 1508-1513 (1979).] that provided a starting point of thermoacoustics today. This paper verifies experimentally his idea through observation of amplification and strong damping of a plane acoustic traveling wave as it passes through axial temperature gradients. The acoustic power gain is shown to obey a universal curve specified by a dimensionless parameter ωτα; ω is the angular frequency and τα is the relaxation time for the gas to thermally equilibrate with channel walls. As an application of his idea, a three-stage acoustic power amplifier is developed, which attains the gain up to 10 with a moderate temperature ratio of 2.3.     

Analytical model of signal amplification in silicon waveguides

In this paper, an analytical model to investigate the parametric amplification (PA) and the PA + stimulated Raman scattering (SRS) in silicon waveguides is put forward. When two pump signals are employed, the PA bandwidth of the probe signal is so large that the Raman contribution has to be considered. When Raman contribution fraction f is set to be 0, only the PA occurs to amplify the probe signal, and when f is set to be 0.043, the PA and the SRS amplify the probe signal at the same time. The signal amplifications of both single and dual pump schemes are investigated by using this model. With this model, three main affecting factors, i.e., zero dispersion wavelength (ZDWL), third-order dispersion (TOD), and fourth-order dispersion (FOD), are discussed in detail.     

高功率全光纤啁啾脉冲放大激光系统

采用基于非线性偏振旋转原理的光纤被动锁模激光器作为主振荡器。输出信号脉冲的重复频率为30 MHz,脉冲半高全宽为265 fs。信号脉冲通过全光纤啁啾脉冲激光放大系统展宽至100 ps后,经过1级芯径10 m的光纤预放大器和1级芯径50 m的光纤功率放大器将脉冲平均功率放大至10 W,斜率效率41.5%。输出脉冲经光栅压缩器将脉宽压缩至594 fs。     

高功率全光纤啁啾脉冲放大激光系统

采用基于非线性偏振旋转原理的光纤被动锁模激光器作为主振荡器。输出信号脉冲的重复频率为30MHz,脉冲半高全宽为265fs。信号脉冲通过全光纤啁啾脉冲激光放大系统展宽至100ps后,经过1级芯径10μm的光纤预放大器和1级芯径50μm的光纤功率放大器将脉冲平均功率放大至10W,斜率效率41.5%。输出脉冲经光栅压缩器将脉宽压缩至594fs。     

Noiseless quantum circuits for the Peres separability criterion

In this Letter we give a method for constructing sets of simple circuits that can determine the spectrum of a partially transposed density matrix, without requiring either a tomographically complete positive-operator-valued measurement or the addition of noise to make the spectrum non-negative. These circuits depend only on the dimension of the Hilbert space and are otherwise independent of the state.     

基于混沌理论的微弱信号放大原理与方法研究

本文首先根据混沌理论的基本特征,特别是混沌运动对于初值的敏感依赖性和初值与混沌轨道之间一一对应的理论基础,建立了帐篷映射的非线性放大模型,研究了帐篷映射可实现非线性放大的具体特征以及输入与输出的二进制对应关系;然后分别对正弦信号和带有噪声的正弦信号进行了非线性放大的数值仿真和电路模拟试验,并与线性放大结果进行了对比分析和优缺点讨论,验证了微弱信号非线性放大的优越性.     

Noiseless Linear Amplification with General Local Unitary Operations

Noiseless linear amplification(NLA),first proposed by Ralpha et al,is a nondeterministic amplification process which gives gain to the Fock state |n → g~n|n,with g being the amplification gain.We here give a general framework for improving the NLA scheme with arbitrary general local unitary operations.We derive the improvement in the amplification gain in 0-1 photon subspace.In particular,we study if the local unitary is composed of single mode squeezing and coherent displacement operation.Finally,numerical simulations show that local unitary operation could give a further enhancement in the amplification gain as well as the success probability,making the NLA more feasible in future optic quantum communications.     

抽运功率密度对布里渊放大的影响

利用瞬态包含抽运抽空的SBS理论模型对布里渊放大器进行了数值模拟,给出了能量提取效率、Stokes种子光放大率、Stokes种子光脉宽压缩率和抽运光脉宽压缩率随抽运功率密度的变化规律.并用实验进行了验证,理论与实验符合得较好. 关键词： 布里渊放大器 能量提取效率 抽运功率密度     

High average power ultra-fast fiber chirped pulse amplification system

We report on a high-gain diode-pumped ytterbium-doped fiber-amplifier system delivering pulse energies in the 100-μJ range at high repetition rates (32 kHz) with nearly-diffraction-limited beam quality (M²∼1.7) at a 1060-nm center wavelength. Femtosecond seed-laser pulses are stretched in a commercially available single-mode fiber and compressed after amplification to subpicosecond pulse duration. In a multimode Yb-doped fiber amplifier we have demonstrated average powers of up to 22 W and single-pulse energies of up to 130 μJ. Received: 16 August 2000 / Revised version: 4 September 2000 / Published online: 8 November 2000     

High power pulse amplification of ytterbium-doped double-clad fiber amplifier

By solving a set of time-dependent equations, the characteristics of the ytterbium-doped double-clad fiber amplifier are presented. Besides the steady state in the fiber of the upper-state population, pump power and amplified spontaneous emission without the input signal, the dynamic characteristics of the high power Gaussian pulse amplification like the evolution of pulse waveform distortion, upper-state population distribution and stored energy and pulse energy of the amplifier under the forward and backward pump,are simulated. The relations between the output pulse energy of the amplifier and the different input pulse peak power or pump power are also discussed. The models and results can provide important guide for the design and optimization of the high power pulse amplification.     

Amplified spontaneous emission and power amplification in high-power DF laser systems

Amplified spontaneous emission （ASE） always occurs in high-power DF laser systems with master oscillator-power amplifier （MOPA） configuration. ASE not only reduces the energy extraction efficiency of the laser system, but also negatively influences its heat management. The interaction between the ASE flux and the coherent laser flux, as well as the effect of ASE on cuboid DF amplifiers, is studied using a finite difference method and an iterative arithmetic. In addition, the influence of ASE on coherent laser amplification is discussed in detail.     

Weak laser pulse signal amplification based on a fiber Brillouin amplifier

We propose a high-gain and frequency-selective amplifier for a weak optical signal based on stimulated Brillouin scattering in a single mode fiber. To be able to satisfy the needs of high gain and high signal-to-noise ratio laser pulse amplification, different fiber lengths and core diameters are used to fulfill this experiment. In the experiment, a 430 nW(peak power) pulsed signal is amplified by 70 dB with a signal-to-noise ratio of 14 dB. The small size, high gain, low cost, and low noise of the fiber Brillouin amplifier make it a promising weak signal amplification method for practical applications such as lidar.