Design theory of high-Q optical ring resonator with asymmetric three-layered dielectrics

An optical ring resonator with asymmetric three-layered dielectrics is shown to have an anomalously highQ-factor compared with the conventional symmetric three-layered ring resonator by several orders of magnitude for suitably chosen parameters. A new leaky mode which can propagate on the asymmetric structure is found having an extremely small attenuation loss near the cut-off frequency of the guided mode, but which does not exist in the symmetric structure. Optimum values of the normalized frequency for a single-mode operation to suppress the undesired leaky modes are discussed. It is also shown that the size of the ring resonator using the asymmetric structure can be reduced considerably from that of the ordinary symmetric resonator.     

Theoretical analysis of feedback high birefringence fiber loop mirror for application in single-frequency fiber lasers

A feedback high birefringence fiber loop mirror with a piece of erbium-doped fiber and a polarization controller is newly proposed. When the erbium-doped fiber is properly pumped to offset the loss of the feedback ring in the loop mirror, narrowband transmission peaks with large effective free spectral range can be achieved by the intrinsic vernier effect between orthogonally polarized lights respectively traveling along the two primary axes of the high birefringence fiber. In addition, the side transmission suppression ratio can reach about 6 dB. These special properties are independent of the polarization state of the input signal, which makes it feasible for the proposed feedback high birefringence fiber loop mirror to be employed as a narrowband filter in single-frequency fiber lasers.     

Control of Q-switched mode locking by active feedback

It is demonstrated that Q-switching dynamics in mode-locked lasers can be controlled by use of an active feedback loop. Analytic design rules for the feedback loop are presented. Suppression of Q-switched mode locking in a diode-pumped, passively mode-locked Nd:YVO(4) laser is shown experimentally and numerically.     

利用振幅调制器进行光电负反馈抑制激光强度噪声

采用振幅调制器作为抑制激光强度噪声的元件，首先对光电负反馈回路进行了简要的理论分析，然后利用该光电负反馈进行抑制激光二极管抽运全固化单频环形Nd:YVO4红外激光器强度噪声的实验。结果表明，在0－1MHz的低频段，强度噪声大幅度降低，最大降低约15dB。     

Longitudinal mode competition in semiconductor lasers under optical feedback: Regime of short-external cavity

This paper introduces a theoretical study of longitudinal mode competition in semiconductor lasers subject to optical feedback. The study is based on a model of time-delay multimode rate equations taking into account both symmetric and asymmetric suppressions of modal gain. The model is numerically solved and applied to the case of a short-external cavity. Mode competition is characterized along the feedback-induced period-doubling route to chaos as well as under chaotic dynamics. Contributions of symmetric and asymmetric gain suppressions to both mode dynamics and modal operation under OFB are clarified. The results show that under chaotic dynamics, mode competition induces multimode hopping giving rise to asymmetric multimode output spectra. In regimes of continuous-wave operation, mode competition supports single-mode oscillation, and the side-mode suppression ratio improves with the increase of feedback. In the regime of strong feedback, the lasing mode moves to either long- or short-wavelength side in a seemingly random fashion, which is strongly related to asymmetric gain suppression.     

BEPCⅡ横向束流反馈系统样机在BEPC上的实验

为了抑制BEPCⅡ产生的耦合束团不稳定性, 提高储存环中的流强, 研制了一套逐束团横向束流反馈系统的样机并在BEPC上做了实验, 得到了理想的结果. 当束团不稳定时, 频谱仪上可以观察到横向边带, 此时将反馈系统闭环工作于阻尼状态时, 横向边带立即消失. 本文介绍了样机系统的组成、各部分的功能和实验结果.     

The Experiments of Transverse Feedback System on the BEPC

In order to cure the transverse coupled-bunch instabilities of BEPCⅡ and improve the beam current of the rings, a prototype of transverse bunch-by-bunch feedback system was studied and made. The experiment of this prototype on the BEPC storage ring shows that this system can work well. The beam instabilities can be successfully suppressed when the feedback loop is closed. This paper describes the prototype of the transverse feedback system and the preliminary test results.     

Nonlinear standing waves in a resonator with feedback control

An experimental study is presented to demonstrate that nonlinear effect on standing waves in a resonator can be reduced by a feedback loop responding to the second harmonic. The resonator was a cylindrical tube sealed at one end and driven by a horn driver unit at another end. The feedback control loop consisted of a pressure sensor, a frequency filter, a phase shifter, and an actuator. The results show that the waveform distortions can be eliminated and large amplitude sinusoidal pressure oscillations are obtained. A simple model is proposed for a qualitative discussion on the control mechanism, which shows that the feedback loop alters the imaginary part of the complex mode frequency so as to suppress (or enhance) the second harmonic.     

热对流环中混沌的控制技术

本文应用谱展开法将描述一维热对流环中流体层流自然对流循环的质量、动量和能量守恒方程化为一组无穷维的常微分方程组;其一阶模态为自封闭的Lorenz方程。应用线性与非线性反馈控制,通过数值模拟发现混饨的线性和非线性反馈控制技术可以明显改变热对流环中流体的运动特征,达到我们所希望的流型,即增强混沌或抑制混沌。     

Analysis of resonance asymmetry phenomenon in resonator integrated optic gyro

Resonator integrated optic gyro(RIOG) is a high-accuracy gyroscope based on the Sagnac effect. The waveguidetype ring resonator is a key rotation sensing element in the RIOG. An asymmetric resonance line shape is found in the optic resonator. These asymmetries will induce offset errors when the phase modulation spectroscopy technique(PMST)is applied to the RIOG. The polarization errors and the difference among normal mode losses are found to be the two main sources of resonance asymmetry in an experiment. These sources are fully investigated and their contributions to the offset errors are compared. The analysis shows that proper modulation frequencies in clockwise(CW) and counterclockwise(CCW) directions can reduce an RIOG bias error. A transmissive resonator is recommended to obtain a better resonance line shape.     

Passive phase locking of an array of four fiber amplifiers by an all-optical feedback loop

We report the passive phase locking of an array of four fiber amplifiers in a unidirectional ring cavity. The feedback loop consists of a single-mode fiber that filters intracavity the far-field pattern of the four emitted beams. The pointing of the laser output can be managed by the intracavity filtering.     

Controlling mode locking in optical ring cavities

Imperfections in the surface of intracavity elements of an optical ring resonator can scatter light from one mode into the counterpropagating mode. The phase-locking of the cavity modes induced by this backscattering is a well-known example that notoriously afflicts laser gyroscopes and similar active systems. We experimentally show how backscattering can be circumvented in a unidirectionally operated ring cavity either by an appropriate choice of the resonant cavity mode or by active feedback control. PACS 42.60.Da; 45.40.Cc; 42.79.Bh; 42.55.-f     

Complex-number asymmetry parameters of the optical Fano effect in ring resonators

We studied the sharp asymmetric Fano line shape in fiber ring resonator systems and provided an explicit expression for asymmetry parameters using the physical parameters of the system. The fiber ring system was controllable and reconfigurable, allowing us to produce a variety of Fano line shapes in different configurations. Experimentally observed asymmetric spectral structures were fully reproduced using the complex-number asymmetry parameters, validating the approximations used to reduce the analytical expression for the line shape to the phenomenological Fano formula. The results may be useful in the design of on-chip application systems.     

Multifunctional design of inertially-actuated velocity feedback controllers

The vibration of a structure can be controlled using either a passive tuned mass damper or using an active vibration control system. In this paper, the design of a multifunctional system is discussed, which uses an inertial actuator as both a tuned mass damper and as an element in a velocity feedback control loop. The natural frequency of the actuator would normally need to be well below that of the structure under control to give a stable velocity feedback controller, whereas it needs to be close to the natural frequency of a dominant structural resonance to act as an effective tuned mass damper. A compensator is used in the feedback controller here to allow stable feedback operation even when the actuator natural frequency is close to that of a structural mode. A practical example of such a compensator is described for a small inertial actuator, which is then used to actively control the vibrations both on a panel and on a beam. The influence of the actuator as a passive tuned mass damper can be clearly seen before the feedback loop is closed, and broadband damping is then additionally achieved by closing the velocity feedback loop.     

Active vibration control using an inertial actuator with internal damping

Collocated direct velocity feedback with ideal point force actuators mounted on structures is unconditionally stable and generates active damping. When inertial actuators are used to generate the control force, the system can become unstable even for moderate velocity feedback gains due to an additional -180 degree phase lag introduced by the fundamental axial resonant mode of the inertial actuator. In this study a relative velocity sensor is used to implement an inner velocity feedback loop that generates internal damping in a lightweight, electrodynamic, inertial actuator. Simulation results for a model problem with the actuator mounted on a clamped plate show that, when internal relative velocity feedback is used in addition to a conventional external velocity feedback loop, there is an optimum combination of internal and external velocity feedback gains, which, for a given gain margin, maximizes vibration reduction. These predictions are validated in experiments with a specially built lightweight inertial actuator.     

精密排线系统的设计方法研究

根据绕线机的精密排线要求,设计了一种三闭环的排线系统,该排线系统由位置环、速度环和电流环组成。位置环用来将给定位置和电机实际反馈位置比较,通过滚轴丝杠完成张力支撑部分的排线移动工作,以达到最小误差要求。速度环根据收线架的给定速度计算排线运行系统的速度,结合反馈量实时调节电机电流,即电机速度。速度环的速度决定了整个系统的动态响应速度。电流环主要用来计算电机传动的力矩,可以根据提前保存的电机数据自动优化设置参数;该系统利用高精度的编码器构成位置闭合回路,该系统具有两个同步运行的排线平移系统,为张力支撑部分的排线平移系统和放线轮的排线平移系统。经实验验证,该控制系统两个平移系统同步性能好,密排效果满足技术要求。     

The theoretical study of a new multi-bunch damping mechanism

The most efficient method to damp multi-bunch oscillations in a storage ring is to install an active feedback loop. However, the technical problem of such a device is connected with the high bandwidth which is defined by the inverse of the time of flight between adjacent bunches. It can be shown theoretically that the bandwidth can be reduced drastically if a narrow-band feedback system is combined with frequency splitting between bunches. The bandwidth of such a damper system is then defined only by the damping rate needed. This seems to be reasonable from a pure mathematical point of view.     

Beat-note jitter suppression in a dual-frequency laser using optical feedback

An efficient locking technique based on optical feedback is demonstrated to suppress jitter on the rf beat note between the two modes of a dual-frequency Yb:Er glass laser. The method consists of a self-injection process in which one selected mode serves as a master oscillator to lock and stabilize the second mode via a frequency-shifted optical feedback. The beat note adjusted near 170 MHz was stabilized with an accuracy of 250 mHz using an optical feedback loop with a double pass through an acousto-optic modulator. The beating note can be tuned over 300 kHz by controlling the reference oscillator. The extensions and limitations of the technique are discussed.     

Frequency Stabilization of a Microsecond Pulse Sodium Guide Star Laser with a Tilt-and Temperature-Tuned Etalon

A frequency stabilization approach is introduced for the microsecond pulse sodium beacon laser using an intracavity tilt-and temperature-tuned etalon based on a computer-controlled feedback system connected with a fast high-precision wavelength meter. The frequency stability of the sodium beacon lasers is compared with and without feedback loop controlling. The output wavelength of the laser is locked to the sodium D_(2 a) absorption line(589.159 nm) over 12 h with the feedback loop controlling technology. As a result, the sodium laser guide star is successfully observed by the telescope of National Astronomical Observatories at Xinglong. This approach can also be used for other pulses and continuous-wave lasers for the frequency stabilization.     

圆环振动拍的调整实验

根据非对称圆环点冲击下拍的理论模型分析拍的分布特性,该文提出了一种调整圆环拍周期和清晰度的方法。阐明圆环结构拍的发生原理,从而控制清晰度;在圆环上添加质量或研磨可以改变非对称性进而调整拍频。引入等效圆环的概念,通过在轴对称圆环上添加一个质量,建立与非轴对称圆环振动特性相同的等效圆环模型。利用该模型,计算要在非轴对称圆环添加质量的大小和位置,以便获得拍的最佳周期及清晰度。用实验和有限元法验证了该方法的有效性。