Ground-state cooling based on a three-cavity optomechanical system in the unresolved-sideband regime

In the unresolved sideband regime,we propose a scheme for cooling mechanical resonator close to its ground state in a three-cavity optomechanical system,where the auxiliary cavities are indirectly connected with the mechanical resonator through standard optomechanical subsystem.The standard optomechanical subsystem is driven by a strong pump laser field.With the help of the auxiliary cavities,the heating process is suppressed and the cooling process of the mechanical resonator is enhanced.More importantly,the average phonon number is much less than 1 in a larger range.This means that the mechanical resonator can be cooled down to its ground state.All these interesting features will significantly promote the physical realization of quantum effects in multi-cavity optomechanical systems.

SIDEBANDS OF X-RAY DIFFRACTION IN AGE-HARDENED Cu-Ti ALLOY

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Effective sideband cooling in an ytterbium optical lattice clock

Sideband cooling is a key technique for improving the performance of optical atomic clocks by preparing cold atoms and single ions into the ground vibrational state.In this work,we demonstrate detailed experimental research on pulsed Raman sideband cooling in a 171 Yb optical lattice clock.A sequence comprised of interleaved 578 nm cooling pulses resonant on the 1st-order red sideband and 1388 nm repumping pulses is carried out to transfer atoms into the motional ground state.We successfully decrease the axial temperature of atoms in the lattice from 6.5μK to less than 0.8μK in the trap depth of 24μK,corresponding to an average axial motional quantum number<nz><0.03.Rabi oscillation spectroscopy is measured to evaluate the effect of sideband cooling on inhomogeneous excitation.The maximum excitation fraction is increased from 0.8 to 0.86,indicating an enhancement in the quantum coherence of the ensemble.Our work will contribute to improving the instability and uncertainty of Yb lattice clocks.

Investigation on Mesh and Sideband Vibrations of Helical Planetary Ring Gear Using Structure, Excitation and Deformation Symmetries

Time?variant excitations in planetary gear trains can cause excessive noise and vibration and even damage the system on a permanent basis. This paper focuses on the elastic vibrations of a helical planetary ring gear subjected to mesh and planet?pass excitations. Motivated by the structure, excitation and deformation symmetries, this paper proposes dual?frequency superposition and modulation methods to capture the mesh and sideband vibrations. The transi?tion between ring gear tooth and planet is introduced to address the excitations and vibrations. The phasing e ect of ring gear tooth and planet on various deformations is formulated. The inherent connections between the two types of vibrations are identified. The vibrations share identical exciting rules and the wavenumber and modulating signal order both equal the linear combination of tooth and planet counts. The results cover in?plane bending and extensional, out?of?plane bending and torsional deformations. Main findings are verified by numerical calculation and comparisons with the open literature. The analytical expressions can be used to determine whether the sideband is caused by component fault or only by elastic vibration. The methods can be extended to other power?transmission systems because little restriction is imposed during the analysis.

Tunable second-order sideband effects in hybrid optomechanical cavity assisted with a Bose-Einstein condensate

We theoretically investigated a second-order optomechanical-induced transparency(OMIT) process of a hybrid optomechanical system(COMS), which a Bose-Einstein condensate(BEC) in the presence of atom-atom interaction trapped inside a cavity with a moving end mirror. The advantage of this hybrid COMS over a bare COMS is that the frequency of the second mode is controlled by the s-wave scattering interaction. Based on the traditional linearization approximation, we derive analytical solutions for the output transmission intensity of the probe field and the dimensionless amplitude of the second-order sideband(SS). The numerical results show that the transmission intensity of the probe field and the dimensionless amplitude of the SS can be controlled by the s-wave scattering frequency. Furthermore, the control field intensities,the effective detuning, the effective coupling strength of the cavity field with the Bogoliubov mode are used to control the transmission intensity of the probe field and the dimensionless amplitude of the SS.

Raman sideband cooling of rubidium atoms in optical lattice

We develop a simple and practical scheme to apply sideband cooling to a cloud of rubidium atoms. A sample containing 4 × 10^(70) ^(87)Rb is trapped in a far red detuned optical lattice. Through optimizing the relevant parameters, i.e., laser detuning, magnetic field, polarization, and duration time, a temperature around 1.5 μK and phase space density close to 1/500 are achieved. Compared with polarization gradient cooling, the temperature decreases by around one order of magnitude. This technique could be used in high precision measurement such as atomic clocks and atom interferometer. It could also serve as a precooling means before evaporation cooling in a dipole trap, and may be a promising method of achieving quantum degeneracy with purely optical means.

Sideband manipulation of population inversion in a three-level Λ atomic system

Sideband manipulation of population inversion in a three-level Λ atomic configuration is investigated theoretically.Compared with the case of a nearly monochromatic field,a population inversion between an excited state and a ground state has been found in a wide sideband intensity range by increasing the difference in frequency between three components.Furthermore,the population inversion can be controlled by the sum of the relative phases of the sideband components of the trichromatic pump field with respective to the phase of the central component.Changing the sum phase from 0 to π,the population inversion between the excited state and the ground state can increase within nearly half of the sideband intensity range.At the same time,the sideband intensity range that corresponds to the system exhibiting inversion ρ 00 > ρ 11 also becomes wider evidently.

Demonstration of fully-connected quantum communication network exploiting entangled sideband modes

Quantum communication network scales point-to-point quantum communication protocols to more than two detached parties,which would permit a wide variety of quantum communication applications.Here,we demonstrate a fully-connected quantum communication network,exploiting three pairs of Einstein–Podolsky–Rosen(EPR)entangled sideband modes,with high degree entanglement of 8.0 dB,7.6 dB,and 7.2 dB.Each sideband modes from a squeezed field are spatially separated by demultiplexing operation,then recombining into new group according to network requirement.Each group of sideband modes are distributed to one of the parties via a single physical path,making sure each pair of parties build their own private communication links with high channel capacity better than any classical scheme.

Sideband-free dispersion-managed Yb-doped mode-locked fiber laser with Gires–Tournois interferometer mirrors

High-order dispersion introduced by Gires–Tournois interferometer mirrors usually causes spectral sidebands in the nearzero dispersion region of mode-locked fiber lasers.Here,we demonstrate a sideband-free Yb-doped mode-locked fiber laser with dispersion-compensating Gires–Tournois interferometer mirrors.Both the simulation and the experiment demonstrate that the wavelength and energy of the sidebands can be tuned by changing the transmission coefficient of the output mirror,the pump power,and the ratio of the net cavity dispersion to the net third-order dispersion in the cavity.By optimizing these three parameters,the laser can generate a sideband-free,Gaussian-shaped spectrum with a 13.56-nm bandwidth at-0.0232 ps^(2)net cavity dispersion,which corresponds to a 153-fs pulse duration.

Parametric generation and phase locking of multiple sidebands in the regime of full-back-conversion

Parametric interaction allows both forward and backward energy transfers among the three interacting waves.The back-conversion effect is usually detrimental when unidirectional energy transfer is desired.In this theoretical work,we manifest that the back-conversion effect underpins the direct generation of the picosecond pulse train without the need for a laser resonator.The research scenario is an optical parametric amplification(OPA)that consists of a second-order nonlinear medium,a quasi-continuous pump laser and a sinusoidal amplitude-modulated seed signal.The back-conversion of OPA can transfer the modulation peaks(valleys)of the incident signal into output valleys(peaks),which inherently induces spectral sidebands.The generation of each sideband is naturally accompanied with a phase shift of±π.In the regime of full-back-conversion,the amount and amplitude of the sidebands reach the maximum simultaneously,and their phase constitutes an arithmetic sequence,leading to the production of a picosecond pulse train.The generated picosecond pulse train can have an ultrahigh repetition rate of 40 GHz or higher,which may facilitate ultrafast applications with ultrahigh speed.

含点蚀的行星齿轮系统动力学特性及损伤评估研究

齿面点蚀是一种典型的行星齿轮系统故障。为识别点蚀状态,本文开展动力学特性研究并提出了一种新型的评估指标。首先,虑及过渡曲线和齿间结构耦合效应,利用改进Weber法建立了精确的含点蚀故障齿轮副啮合刚度模型,并研究了故障程度对啮合刚度的影响规律。然后,综合考虑时变啮合刚度、静态传动误差、齿侧间隙和时变振动传递路径等多种因素构建了行星齿轮系统平移-扭转动力学模型,揭示了点蚀程度对系统动态特性的影响规律,并基于振动信号频谱特点提出了边带能量因子(Sideband Energy Factor,SEF)用于损伤评估。最后,利用实验验证了仿真模型的正确性及所提指标的有效性。

基于GPU的北斗B1宽带复合信号实时发生器设计

为了实现北斗B1C+B1I信号的联合生成,提出一种基于软件无线电和图形处理器(graphics processing unit,GPU)加速的北斗B1宽带复合信号的实时生成方法,该方法针对单边带复数二进制偏移载波(single-sideband complex binary offset carrier,SCBOC)调制方式的信号体制进行设计,系统根据用户配置的接收机运动轨迹和星历文件,生成中频信号并通过射频端发射。为了进一步提升GPU并行运算速度,从优化设备内存结构、设计并行线程架构和统一计算设备架构流(compute unified device architecture stream,CUDA)加速3个方面,设计了基于异步运算的加速采样点数据计算的CUDA优化实现方案。测试结果证明,优化后的算法可以基于SCBOC调制实时生成北斗B1I+B1C信号,基于GTX3060的GPU平台,信号90 M采样率下能实现8颗卫星复合信号的实时生成。

基于IAS信号自适应窄带解调的RV减速器摆线轮故障特征提取

RV(rotary vector)减速器广泛应用于工业机器人,研究其关键零部件的故障检测方法具有重要意义。由于RV减速器结构复杂、摆线轮转速低、故障冲击较弱等问题,造成摆线轮故障特征难以用常规振动分析方法提取。针对上述问题,提出一种基于瞬时角速度信号自适应窄带解调的RV减速器摆线轮故障特征提取方法。首先对编码器角度信号进行采集,然后使用向前差分法获得瞬时角速度信号,在此基础上,使用角域同步平均提取摆线轮周期相关同步分量,消除非同步干扰,并通过构建边带信噪比指标选取故障信息丰富的啮合谐波频带进行带通滤波,最后对滤波后的信号进行窄带解调,实现对RV减速器摆线轮的故障特征提取。试验结果表明,该方法可以有效地提取RV减速器摆线轮故障特征,且自适应实现优化带宽选择。

Tunable optical second-order sideband effects in a parity-time symmetric optomechanical system

We theoretically investigate the optical second-order sideband generation(OSSG)in an optical parity-time(PT)symmetric system,which consists of a passive cavity trapping the atomic ensemble and an active cavity.Compared with the double-passive system,it is found that near the exceptional point(EP),the efficiency of the OSSG increases sharply not only for the blue probepump detuning resonant case but also for the red one.Using experimentally achievable parameters,we study the effect of the atomic ensemble on the efficiency of the OSSG in the PT-symmetric system.The numerical results show that the efficiency of the OSSG is 30%higher than that of the first-order sideband,which is realized easily by simultaneously modulating the atom-cavity coupling strength and detuning.Moreover,the efficiency of the OSSG can also be tuned effectively by the pump power,and the efficiency is robust when the pump power is strong enough.This study may have some guidance for modulating the nonlinear optical properties and controlling light propagation,which may stimulate further applications in optical communications.

Multicolored sideband generation based on cascaded four-wave mixing with the assistance of spectral broadening in multiple thin plates

The generation of multicolored sidebands with the spectrum from 377 to 970 nm in a 0.5-mm-thick N-WG280 Schott glass based on a cascaded four-wave mixing(CFWM) process is demonstrated. The experimental setup is compact and economical. A pulse with a broadened spectrum from 670 to 900 nm is generated by utilizing two 0.18-mm-thick fused silica glass plates and is used to provide two input beams for the CFWM process.The new frequency components generated from the self-phase modulation effect in the two thin glass plates contribute to the broadening of the total spectral range of the generated multicolored sidebands.

Highly linear W-band receiver front-end based on higher-order optical sideband processing

A highly linear W-band receiver front-end based on higher-order optical sideband(OSB) processing is proposed and experimentally demonstrated. Two-tone analysis shows that by manipulating higher-order OSBs, the thirdorder intermodulation distortion(IMD3) introduced by optoelectronic components(mainly modulators) in the receiver front-end can be further suppressed, and a 9 dB improvement of the ratio of the fundamental and IMD3 can be attained. In the experiment, the spurious-free dynamic range of the W-band receiver front-end is up to 122.1 d B·Hz^(2∕3), with improvement by 9 dB compared with that of only processing the five OSBs.

Photonic-assisted FSK signal generation based on carrier phase-shifted double sideband modulation

An approach to generate high-speed and wideband frequency shift keying(FSK)signals based on carrier phase-shifted double sideband(CPS-DSB)modulation is proposed and experimentally validated.The core part of the scheme is a pair of cascaded polarization-sensitive LiNbO_(3) Mach–Zehnder modulators and phase modulators,whose polarization directions of the principal axes are mutually orthogonal to each other.A proof-of-concept experiment is carried out,where a 0.5 Gb/s FSK signal with the carrier frequencies of 4 and 8 GHz and a 1 Gb/s FSK signal with the carrier frequencies of 8 and 16 GHz are generated successfully.

Intense,wideband optical waveform generation by self-balanced amplification of fiber electro-optical sideband modulation

We demonstrate a simple method to obtain accurate optical waveforms with a gigahertz-level programmable modulation bandwidth and a watt-level output power for wideband optical control of free atoms and molecules.Arbitrary amplitude and phase modulations are transferred from microwave to light with a low-power fiber electro-optical modulator.The sub-milliwatt optical sideband is co-amplified with the optical carrier in a power-balanced fashion through a tapered semiconductor amplifier(TSA).By automatically keeping TSA near saturation in a quasi-continuous manner,typical noise channels associated with pulsed high-gain amplifications are efficiently suppressed.As an example application,we demonstrate interleaved cooling and trapping of two rubidium isotopes with coherent nanosecond pulses.

30-GHz millimeter-wave carrier generation with single sideband modulation based on stimulated Brillouin scattering

A new technique to generate a millimeter（mm）-wave carrier of 32.57 GHz(fLO=10.85 GHz) with single sideband modulation（SSB） for radio-over-fiber（RoF） systems is experimentally demonstrated by using stimulated Brillouin scattering（SBS）.The SSB is realized by directly amplifying the +3rd sideband of the modulated optical carrier in the process of SBS.The pump wave is provided through a double Brillouin scattering frequency shifting configuration.The use of the same laser source to generate the pump wave ensures the stability of the mm-wave generation system since the relative frequency shift between them can be eliminated.In addition, the mm-wave carrier obtains an RF power gain of 21 dB with the SBS amplification and a 3-dB bandwidth of 10kHz.

Experimental study of balanced optical homodyne and heterodyne detection by controlling sideband modulation

We experimentally study optical homodyne and heterodyne detections with the same setup, which is flexible to manipulate the signal sideband modulation. When the modulation only generates a single signal sideband, the light field measurement by mixing the single sideband at ω0 ±? with a strong local oscillator at the carrier frequency ω0on a beam splitter becomes balanced heterodyne detection. When two signal sidebands at ω0 ±? are generated and the relative phase of the two sidebands is locked, this measurement corresponds to optical balanced homodyne detection. With this setup, we may confirm directly that the signal-to-noise ratio with heterodyne detection is two-fold worse than that with homodyne detection. This work will have important applications in quantum state measurement and quantum information.