Dynamic origin of stripe domains

We investigate stripe domain formation in nanometer sized Co bars. The magnetic equilibrium states and the magnetic spin wave frequencies are obtained from micromagnetic-like simulations. We find that the lowest frequency standing-wave mode has the same spatial structure as the stripe domains at remanence and it goes soft at the field where the stripe domains emerge. We show, therefore, that the final domain structure at remanence, which is not the configuration with lowest energy, is predicted from a high-field analysis of the frequencies of the standing spin waves.     

光纤环形谐振腔的频率锁定及其特性

基于可调分束比的光纤分束器,制作了光纤环形谐振腔并通过调节分束比实现了对光纤环形谐振腔的欠耦合、临界耦合和过耦合的状态控制.实验测量了腔最小反射率与腔损耗之间的关系,获得光纤环形谐振腔的腔内衰减率为κ_0=2π×(1.60±0.03) MHz ,品质因子为Q=(1.10±0.02)×10.8.在此基础上,结合了压电陶瓷拉伸光纤以控制腔长和Pound-Drever-Hall锁频两大技术优势,克服了之前温度反馈控制等方法的反馈带宽窄、噪声大和稳定性差等问题,实现了对光纤环形谐振腔共振频率的快速、灵敏的控制和锁定.结果表明,锁频过程中相位调制功率与相位调制引起腔反射光的强度调制之间的关系为线性关系,进而通过降低相位调制信号的功率以减小相位调制对腔反射光强度调制的影响.当调制功率设定最低为–9 dBm时,光纤环形谐振腔仍能被稳定锁定.该光纤环形谐振腔为其与原子、金刚石色心等发光粒子相互作用的腔量子电动力学实验研究奠定了坚实的基础.     

New speckle control technique using high-speed electro-optic modulators with resonant electrode and polarization-reversed structures

We propose a new technique for reducing speckle noise in laser displays utilizing a high-speed optical phase modulator for expanding the laser beam spectrum. By adopting standing-wave resonant electrodes and polarization-reversed structures to LiTaO₃ electro-optic modulators, high-efficiency phase modulation with a large modulation index at high microwave frequency ranges is obtainable for different color laser beams at the same time. This enables us to expand laser spectra to over 100 GHz and reduce speckle noise. The device design, fabrication, and experimental demonstration for speckle control are reported.     

A distributed frequency modulation continuous wave fiber stress sensor based on a birefringent sagnac ring configuration

A new distributed stress sensor, based on a birefringent fiber Sagnac ring configuration and frequency modulation continuous wave technology, has been investigated. The two forward-coupled mode beams in the Sagnac ring, induced by an applied stress at any given point along the fiber length, produce a beat frequency which can be analysed to determine, simultaneously, the magnitude and position of the stress. The system has a reasonable spatial resolution of 1 m in a dynamic sensing range of 50 m.     

Frequency-modulation-mode-locked optical parametric oscillator

We demonstrate a novel technique for the generation of mode-locked pulses from a continuous-wave (cw) optical parametric oscillator (OPO). The technique is based on the deployment of a phase modulator in combination with an antiresonant ring interferometer internal to a cw OPO, simultaneously providing spectral broadening and phase-to-amplitude feedback modulation. The scheme is implemented in a doubly-resonant cw OPO based on MgO:sPPLT, configured in a standing-wave cavity and pumped at 532 nm. With the phase modulator activated and the cavity length synchronized, a stable train of 800 ps pulses is generated at a repetition rate of 160 MHz. Using single-pass second harmonic generation (SHG) of the OPO output, we observe a four times enhancement in SHG compared with cw operation, confirming the real achievement of energy concentration as a result of mode-locked operation.     

Standing-wave nonlinear optics in an integrated semiconductor microcavity

We present a concept of standing-wave optical frequency conversion in dispersive microcavities theoretically and experimentally, allowing efficient ultracompact nonlinear photonics. We developed a time-dependent model, incorporating the dispersion into the structure of the spatial cavity modes, where the conversion efficiency is enhanced by the optimization of a nonlinear cavity mode overlap. We designed and fabricated integrated double-resonance semiconductor microcavities for standing-wave second-harmonic generation. The measured efficiency exhibits a significant maximum near the cavity resonance owing to the intracavity power enhancement and the dispersion-induced wavelength detuning effect on the mode overlap, in good agreement with our theoretical predictions.     

Multiwavelength erbium-doped fiber ring laser using a LiNbO<Subscript>3</Subscript> multifunction chip for fiber gyroscope

We present a novel configuration of multiwavelength erbium-doped fiber ring laser (MW-EDFL) using a LiNbO₃ multifunction chip for fiber gyros at room temperature. The polarizer incorporating a piece of high-birefringence fiber in the input port of the Y-type chip forms the Lyot periodic filter at intervals of 0.5 nm wavelength. One of two modulators inserted in the ring cavity has been used as frequency shifter by applying a sawtoothed signal, while the output port of the other is used as the output port of the laser. Simultaneous multiwavelength lasing is experimentally demonstrated by applying a sawtoothed signal with the order of 10 kHz to the phase modulator to prevent single-wavelength oscillation. The MW-EDFL output is linearly polarization light that meets the requirement of external modulation for wavelength-division-multiplexing applications.     

A high-power single-mode cw dye ring laser

Due to spatial hole burning, standing-wave dye lasers require a large amount of selectivity inside the cavity for single-mode operation. The output power of these lasers is limited by losses caused by the frequency selecting elements. In a travelling-wave laser, on the other hand, spatial hole burning does not exist, thereby eliminating the need for high selectivity. A travelling-wave cw dye laser was realized by unidirectional operation of a ring laser, yielding single mode output powers of 1.2 W at 595 nm and of 55 mW in the UV-region with intracavity frequency doubling.     

Resonance asymmetry phenomenon in waveguide-type optical ring resonator gyro

The intensity output of a silica waveguide ring resonator (WRR) was found to show an asymmetric resonance characteristic. To further analyze and better design the resonator micro optic gyro (RMOG) with a waveguide-type ring resonator, in-depth research of the characteristics of the resonance asymmetry is fully developed for the first time, to the best of our knowledge. Four possible sources of the resonance asymmetry are analyzed and their respective contributions are compared. These four error sources are differential normal mode losses in the coupler, the backscattering induced noises, the polarization fluctuations and the optical Kerr effect. The differential normal mode loss is suspected to be the major contributor to the observed resonance asymmetry in the fabricated silica WRR. Asymmetric resonance curve produces a large output bias error in the RMOG based on the phase modulation technique, which is related to the modulation frequency differences between the CW and CCW lightwaves. Theoretical analysis shows that replacing the reflector WRR with a transmitter one is helpful to eliminate the effect of the different normal mode losses in the coupler on the resonance asymmetry.     

On possibility of using the lowest odd harmonics of the phase modulation frequency in the output signal of the fiber-optic ring interferometer for detection of the sagnac effect

The possibility of using the lowest harmonics of the phase modulation frequency in the output signal of the fiber-optic ring interferometer (FRI) for detection of the FRI rotation angular velocity is considered. It is shown that the use of the third harmonic of the phase modulation frequency is optimal, since, in this case, the effect of insignificant admixture of the second harmonic of the phase modulation frequency on the FRI baseline shift can be completely eliminated. When processing the signal using the first or the fifth harmonic of the phase modulation frequency, it is possible to compensate for the FRI baseline shift because of its weak dependence on the phase modulation amplitude. Upon processing of the FRI output signal using higher odd harmonics of the phase modulation frequency, the signal-to-noise ratio noticeably decreases.     

Regenerative mode locking via superposition of higher-order cavity modes in composite cavity fiber lasers

We demonstrate a new method of optical pulse generation in regeneratively mode-locked fiber ring lasers (RML-FRLs). The method is based on generating dominant longitudinal modes in the fiber ring cavity by means of a composite cavity structure and their intermode beating at the photodetector incorporated in the regenerative feedback loop. The beat signal is then used as a modulation signal to generate optical pulses in a regenerative mode-locking scheme, thereby eliminating the requirement for a high-Q rf bandpass filter in a conventional RML-FRL. Optical pulses with a repetition frequency of 3.6 GHz have been generated successfully with a supermode noise suppression of more than 48 dB and a low phase noise of -85 dBc/Hz at 10 kHz offset from the carrier frequency.     

Generation of 10-GHz ultra-short pulses with low time jitter in an actively mode-locked fiber laser

We have experimentally achieved the 8.3-ps ultra-short pulse at 10 GHz repetition rate with the time jitter as low as 590 fs in an actively mode-locked fiber ring laser. The ring-cavity laser is mode-locked by a semiconductor optical amplifier based on cross-gain modulation. The external CW source is modulated with radio frequency signal by an amplitude modulator as the external optical pulses and, then, injected into the fiber ring cavity to achieve active mode locking. Further investigating the laser output characteristics, it indicates that the linewidth of employed CW source affects properties of the generated ultra-short pulse, such as phase noise and time jitter. Ultra-short pulse at high repetition rate with low time jitter can be generated by the optimization of CW laser source.     

Two-dimensional atom localization via quantum interference in a coherently driven inverted-Y system

A scheme for two-dimensional (2D) subwavelength atom localization is proposed, in which the atom is in an inverted-Y configuration and driven by two orthogonal standing-wave lasers. Due to the spatial dependence of atom-field interaction, the quantities of system, including the frequency of spontaneously emitted photon, the population in the excited state, and the probe absorption, carry information about the position of atom in standing-wave fields. We exploit this fact to 2D atom localization, and obtain a high precision and resolution in the position probability distribution.     

光纤移频分布式布里渊光纤传感技术

提出了一种利用布里渊光纤环形腔移频技术实现分布式光纤布里渊传感的方法.该方法基于布里渊光时域分析法原理,将一束单纵模运转激光器输出的激光分为两束|一束光入射布里渊光纤环形腔中产生窄线宽的受激布里渊散射光作为斯托克斯光,另一束光经过低频相位调制后作为泵浦光|斯托克斯光和泵浦光分别相向入射进入传感光纤,通过测量布里渊谱得到光纤温度或应变.利用该方法可将十几GHz的微波频率转化为兆赫信号频率进行探测处理,仅需一台激光器,因此系统结构简单、成本低,还可减小激光器频率波动对测量准确度的影响.实验验证了该方法的可行性.     

High Repetition Rate Optical Pulse Generation Using a Rational Harmonic Mode Locking Technique in a Fiber Ring Laser

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Mammalian spontaneous otoacoustic emissions are amplitude-stabilized cochlear standing waves

Mammalian spontaneous otoacoustic emissions (SOAEs) have been suggested to arise by three different mechanisms. The local-oscillator model, dating back to the work of Thomas Gold, supposes that SOAEs arise through the local, autonomous oscillation of some cellular constituent of the organ of Corti (e.g., the "active process" underlying the cochlear amplifier). Two other models, by contrast, both suppose that SOAEs are a global collective phenomenon--cochlear standing waves created by multiple internal reflection--but differ on the nature of the proposed power source: Whereas the "passive" standing-wave model supposes that SOAEs are biological noise, passively amplified by cochlear standing-wave resonances acting as narrow-band nonlinear filters, the "active" standing-wave model supposes that standing-wave amplitudes are actively maintained by coherent wave amplification within the cochlea. Quantitative tests of key predictions that distinguish the local-oscillator and global standing-wave models are presented and shown to support the global standing-wave model. In addition to predicting the existence of multiple emissions with a characteristic minimum frequency spacing, the global standing-wave model accurately predicts the mean value of this spacing, its standard deviation, and its power-law dependence on SOAE frequency. Furthermore, the global standing-wave model accounts for the magnitude, sign, and frequency dependence of changes in SOAE frequency that result from modulations in middle-ear stiffness. Although some of these SOAE characteristics may be replicable through artful ad hoc adjustment of local-oscillator models, they all arise quite naturally in the standing-wave framework. Finally, the statistics of SOAE time waveforms demonstrate that SOAEs are coherent, amplitude-stabilized signals, as predicted by the active standing-wave model. Taken together, the results imply that SOAEs are amplitude-stabilized standing waves produced by the cochlea acting as a biological, hydromechanical analog of a laser oscillator. Contrary to recent claims, spontaneous emission of sound from the ear does not require the autonomous mechanical oscillation of its cellular constituents.     

Distributed fiber-optic vibration sensor using a ring Mach-Zehnder interferometer

A novel distributed fiber-optic vibration sensing system is proposed and demonstrated. By employing a ring Mach-Zehnder interferometer (MZI) structure as the sensing section, both position and frequency can be determined by combining two phase signals from the ring configuration. A spatial resolution better than 38 m is successfully verified in a 1.01 km prototype system of single vibration. Moreover, the feasibility of separately locating multiple vibrations is also theoretically simulated and experimentally investigated.     

两腔级联纠缠增强的理论分析

高纠缠度的纠缠源是实现高保真度量子信息传输与处理的保障,因为受到光学元器件自身性能不完美的限制,通过有效的操控手段来提高光场的纠缠度是十分必要的.连续变量Einstein-Podolsky-Rosen纠缠态光场可以利用工作在阈值以下的非简并光学参量放大器来获得.将两个非简并光学参量放大器级联,可以利用第二个光学腔来操控第一个光学腔输出的纠缠态光场,在一定条件下实现光场的纠缠增强.本文通过理论分析设计出两种光学腔级联的实验系统,其中,纠缠产生装置采用具有三共振结构的半整块驻波腔,输出到目前为止世界上单腔获得两组份纠缠态光场纠缠度的最高值,操控光学腔采用驻波腔或四镜环形腔的结构.详细对比分析了不同结构的操控腔对纠缠增强效果的影响,得出利用不同腔形作为操控腔的最佳实验方案.同时分析了级联腔输出光场的纠缠度随不同物理参量的变化关系,得出进一步优化的最佳实验系统参量,为实验获得更高纠缠度的纠缠态光场提供了依据.     

High-frequency modulation of the spatial field structure in a ruby laser

A laser is considered in which the nonuniformity in the deexcitation of the level populations by the standing-wave field is eliminated by a longitudinal variation of the field structure. The field is varied by two phase modulators on different sides of the active element. The phase shifts of the modulators are equal in value but opposite in sign, so that there is no detuning of the resonator and no amplitude modulation. It is shown theoretically that for a modulation amplitude _m = 1.202 the deexcitation nonuniformity is completely eliminated and only one longitudinal mode is generated. Under these conditions the linewidth of the spectrum was reduced by a factor of not less than 10.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, Vol. 12, No. 1, pp. 81–86, January, 1969.In conclusion we wish to thank R. D. Zaitsev for manufacturing the modulating crystals, and V. S. Mel'chenko for providing the interferometer.     

双束流负载效应

分析研究了双束流储存环上的束流负载效应.束团纵向尾场的作用分别为:能量损失、同步频移和耦合束不稳定性,这里只研究前两个方面.以来团连续分布的束团串情形和均匀分布情形为例,给出了同步相移、频移与高次模参数及高频腔分布的关系.研究结果有助于优化高频腔的工作模式(通过调节调谐杆的位置来改变高次模的频率)和环上束团的分布,以减小束流负载效应.当高频腔关于对撞点对称分布时,正负电子的束流负载效应相同,可以用补偿单束流负载效应的方法来补偿正负电子束团的相位.