A tunable comb filter using single-mode/multimode/polarization-maintaining-fiber-based Sagnac fiber loop

A novel tunable comb filter composed of a single-mode/multimode/polarization-maintaining-fiber-based Sagnac fiber loop is proposed and experimentally demonstrated. The filter tunability is achieved by rotating the polarization controller. The spectral shift is dependent on rotation direction and the position of the polarization controller. In addition, the adjustable range achieved by rotating the half-wave-plate polarization controller is twice higher than that of the quarter-wave-plate one.

Amplification and Compression of Ultrashort Fundamental Solitons in An Erbium-Doped Nonlinear Amplifying Fiber Loop Mirror

A nonlinear amplifying loop mirror constructed from erbium-doped fiber is proposed for simultaneous amplification and compression of ultrashort fundamental solitons. Numerical simulations show that, the proposed device performs efficient high-quality amplification and compression of solitons.

Fiber loop ring-down cavity integrated U-bent single-mode-fiber for magnetic field sensing

A novel magnetic field sensing system based on the fiber loop ring-down technique is proposed in this paper. In the fiber loop, a U-bent single-mode-fiber structure coated with magnetic fluid(MF) serves as the sensing head, and an erbium-doped fiber amplifier(EDFA) is introduced to compensate for the intrinsic loss of the cavity. The ring-down time of the system varies with the change of applied magnetic field due to the tunable absorption coefficient and refractive index of the MF. Therefore, measurement of the magnetic field can be realized by monitoring the ringdown time. The experimental results show that the performance of the system is extremely dependent on the interrogation wavelength, because both the gain of the EDFA and the loss of the sensing head are wavelength dependent.We found that at the optimal wavelength, the ratio of the gain to loss attained its maximum. The sensing system was experimentally demonstrated and a sensitivity of-0.5951 μs∕Oe was achieved.

Wavelength-Tunable Single Frequency Ytterbium-Doped Fiber Laser with Loop Mirror Filter

By using a loop mirror filter, a novel wavelength-tunable single-frequency ytterbium-doped fiber laser is developed to select single longitudinal modes in a linear cavity. The output wavelength could be tuned 2.4 nm intervals range from 1063.3 to 1065.Tnrn with the temperature change of the fiber Bragg grating. The maximum output power could reach 32 m W while the pump power increases to 120 m W. The corresponding optical-to-optical conversion efficiency is 26.7% and the slope efficiency is 33.9%, respectively. The output power fluctuation is below 2%, and its highest signal-to-noise ratio is 60 dB.

Recent Progress of Fiber Loop Mirror-Based Sensors in China Jiliang University

作者概述纤维环镜子的最近的进步在中国 Jiliang 基于传感器大学。与各种各样的插入的纤维做的纤维循环镜子的唯一的特征，纤维循环镜子基于传感器有潜力在许多宽应用程序被利用。

Fiber-Loop Ringdown Multi-Function Sensors

We demonstrate a fiber-loop ring down multi-function sensors system, which can be used to measure refractive index and curvature simultaneously. Good agreement has been found between theoretical analyses and experimental results. It has great potential for sensor applications.

Wideband All-Polarization-Maintaining Yb-Doped Mode-Locked Fiber Laser Using a Nonlinear Optical Loop Mirror

We report on a wide-band and stable mode-locked all-polarization-maintaining fiber laser configuration using a nonlinear optical loop mirror. The central wavelength of the laser is 1080.14nm and the 3dB bandwidth is 20.29nm. The repetition rate of the pulse is 3.28 MHz and the pulse width is 848ps. By tuning the pump power, which is centered at 980nrn, from 300mW to 380mW, we obtain a linearly changed output power from 6row to 7.12roW. The all-polarization-mMntaining fiber configuration is fundamental to the stability of the output power.

Fabrication and formation mechanism of closed-loop fibers by electrospinning with a tip collector

Electrospun nanofibers with designed or controlled structures have drawn much attention. In this study, we report an interesting new closed-loop structure in individual cerium nitrate/polyvinyl alcohol（Ce（NO3）3/PVA） and Na Cl/PVA fibers,which are fabricated by electrospinning with a nail collector. The electrospinning parameters such as voltage and Ce（NO3）3（or Na Cl） concentration are examined for the formation of the closed-loop structure. The results suggest that the increase of the spinning voltage or addition of Ce（NO3）3（or Na Cl） is favorable for the formation of the closed-loop structure, and the increase of loop numbers and the decrease of loop size. Further analyses indicate that the formation mechanism of the closed-loop fibers can be predominantly attributed to the Coulomb repulsion in the charged jets.

Dynamic Free-Spectral-Range Measurement for Fiber Resonator Based on Digital-Heterodyne Optical Phase-Locked Loop

We propose a novel scheme, based on digital-heterodyne optical phase-locked loop with whole-fiber circuit, to dynamically measure the free-spectral-range of a fiber resonator. The optical phase-locked loop is established with a differential frequency-modulation module consists of a pair of acousto-optic modulators. The resonance-tracking loop is derived with the Pound-Drever-Hall technique for locking the heterodyne frequency of the OPLL on the frequency difference between adjacent resonance modes. A stable locking accuracy of about 7 × 10?9 and a dynamic locking accuracy of about 5 × 10?8 are achieved with the FSR of 8.155 MHz, indicating a bias stability of the resonator fiber optic gyro of about 0.1?/h with 10 Hz bandwidth. In addition, the thermal drift coefficient of the FSR is measured as 0.1 Hz/?C. This shows remarkable potential for realizing advanced optical measurement systems, such as the resonant fiber optic gyro, and so on.

10 MHz氢钟信号传递系统

为满足同一科研园区内不同建筑之间10 MHz氢钟信号(HCS)长期稳定度共享的需求,提出了一种低成本、集成化的基于光纤链路的10 MHz HCS传递完整解决方案。该方案采用1 GHz的射频信号对激光光强进行调制,利用光纤实现信号传递。通过将远端反射信号与本地信号和频后直接与待传递的HCS分频鉴相,输出误差信号反馈控制1 GHz信号的频率,实现远端1 GHz信号与本地HCS之间的相位锁定,从而使远端1 GHz信号具有与本地HCS相同的频率稳定度;之后再通过分频器在远端生成10 MHz信号,作为射频参考输出。实验验证了该方案的频率传递保真度,该系统在200 m往返光纤上的附加频率稳定度(艾伦偏差)为1 s平均时间2.4×10^(-13)和10000 s平均时间5.7×10^(-17);在20 km传递距离上,附加频率稳定度(艾伦偏差)为1 s平均时间4.8×10^(-13)和10000 s平均时间2.1×10^(-16)。研究结果表明该系统的长时间频率传递稳定度优于HCS的频率稳定度,可以满足千米范围内氢钟信号共享的需求。

全保偏飞秒光纤激光器异步锁定技术研究

基于全保偏掺铒光纤激光器、锁相环系统和太赫兹测距光路搭建了一套太赫兹双光梳测距系统。所采用的全保偏掺铒光纤激光器重复频率为79.261 MHz。利用压电陶瓷(piezoelectric ceramics,PZT)和步进电机(stepper motor,SM)双级反馈控制的方案,实现了重复频率锁定和重复频率1.54 MHz可调。使用频率计数器对双光梳重复频率锁定效果进行监测,重复频率锁定的峰峰值抖动为±1.5 mHz,抖动标准差为0.4 mHz。将双光梳重频差设置在10 Hz,10 min内重复频率差最大抖动为3 mHz,标准差为0.6 mHz。进一步将异步采样双光梳系统应用于太赫兹测距,测量移动距离的误差为3µm。该系统具有锁定精度高,稳定性强等优势,有望应用于生物无损检测和工业精密加工中。

光纤激光器中矩形类噪声多脉冲的行为研究

报道了基于非线性光纤环形镜(NOLM)锁模的掺铒光纤激光器中矩形类噪声多脉冲演化行为.在基频重复率为2.19 MHz下,可以获得稳定的矩形类噪声脉冲,脉冲宽度从1.25 ns到4.35 ns可调,单脉冲能量可达7.72 nJ.通过改变泵浦功率和偏振状态,矩形类噪声可分裂成多脉冲,并随着腔参数的不同演化成多种形态,如脉冲间距不等的矩形类噪声脉冲簇,脉冲间距相等的矩形类噪声脉冲簇以及各阶谐波类噪声脉冲.实验结果表明,类噪声脉冲具有与孤子脉冲类似的脉冲分裂特性,并随着腔内脉冲数的增加,单个矩形类噪声脉冲宽度逐渐减小.实验结果有助于进一步理解矩形类噪声脉冲的产生机理与多脉冲的动力学特性.

Combined optical fiber interferometric sensors for the detection of acoustic emission

A type of combined optical fiber interferometric acoustic emission sensor is proposed. The sensor can be independent on the laser source and make light interference by matching the lengths of two arms,so it can be used to monitor the health of large structure. Theoretical analyses indicate that the system can be equivalent to the Michelson interferometer with two optical fiber loop reflectors,and its sensitivity has been remarkably increased because of the decrease of the losses of light energy. PZT is powered by DC regulator to control the operating point of the system,so the system can accurately detect feeble vibration which is generated by ultrasonic waves propagating on the surface of solid. The amplitude and the frequency of feeble vibration signal are obtained by detecting the output light intensity of interferometer and using Fourier transform technique. The results indicate that the system can be used to detect the acoustic emission signals by the frequency characteristics.

Fiber Optic Sensors and Sensor Networks Using a Time-domain Sensing Scheme

Fiber loop ringdown (FLRD) has demonstrated to be capable of sensing various quantities, such as chemical species, pressure, refractive index, strain, temperature, etc.;and it has high potential for the development of a sensor network. In the present work, we describe design and development of three different types of FLRD sensors for water, cracks, and temperature sensing in concrete structures. All of the three aforementioned sensors were indigenously developed very recently in our laboratory and their capabilities of detecting the respective quantities were demonstrated. Later, all of the sensors were installed in a test grout cube for real-time monitoring. This work presents the results obtained in the laboratory-based experiments as well as the results from the real-time monitoring process in the test cube.

Optic Fiber-Based Dynamic Pressure Sensor

Weigh-in-Motion（WIM） technique is the process of measuring the dynamic tire forces of a moving vehicle and estimating the corresponding tire loads of the static vehicle. Compared with the static weigh station, WIM station is an efficient and cost effective choice that will minimize unneccessary stops and delay for truckers. The way to turn birefringence of single-mode fiber into a prime quality for a powerful and reliable sensor is shown. Preliminary results for the development of a weigh-in-motion （WIM） technique based on sagnac-loop sensor are presented. After a brief description of the sensor and its principle of operation, the theoretical model characterization made in is developed. Then, a full static conditions is presented.

Pump-induced carrier envelope offset frequency dynamics and stabilization of an Yb-doped fiber frequency comb

In this paper, we demonstrate a carrier envelope phase-stabilized Yb-doped fiber frequency comb seeding by a nonlinear-polarization-evolution（NPE） mode-locked laser at a repetition rate of 60 MHz with a pulse duration of 191 fs.The pump-induced carrier envelope offset frequency（ f0） nonlinear tuning is discussed and further explained by the spectrum shift of the laser pulse. Through the environmental noise suppression, the drift of the free-running f0 is reduced down to less than 3 MHz within an hour. By feedback control on the pump power with a self-made phase-lock loop（PLL）electronics the carrier envelope offset frequency is well phase-locked with a frequency jitter of 85 m Hz within an hour.

基于离散傅里叶变换的光纤陀螺电路串扰自检测

光纤陀螺由于构造限制,电路输出信号中易受驱动信号串扰,导致输出结果精度难以满足现实需求,影响了电路工作的安全性和效率。为此,提出基于离散傅里叶变换的光纤陀螺电路串扰自检测方法。首先,分析光纤陀螺电路串扰的原理,对光纤陀螺电路进行闭环检测,获取到电路信号变化规律。其次,根据得到的干扰信号函数,建立电路串扰模型,由于电路串扰间存在互容特性,针对串扰线路使用基尔霍夫电压定律,结合电流的连续性,建立串扰电路信号变化函数;根据光纤陀螺检测中的振动频率,依据电路串扰的时间序列以及电路零均值、非高斯、统计非零峰度,使用离散傅里叶变换解析串扰信号,完成电路串扰的自动检测。经实验验证:所提方法能够节省大量提取时间,平均耗时节省35 min,检测精度提高34%,能高效地完成串扰检测。

复杂非对称不动环全纤维成形不均匀变形的仿真分析

针对传统复杂非对称7075铝合金不动环模锻件切削加工后易造成抗疲劳性能降低的问题,基于体积不变原理获得了预成形件。然后提出了先预成形再终成形的全纤维成形工艺。采用Deform-3D软件建立了复杂非对称不动环的全纤维预成形三维有限元模型,通过实验验证了所建模型的可靠性。基于所建立的仿真模型对该成形过程中金属流动、温度场、等效应力场和等效应变场等进行了分析,获得了加载载荷随成形过程变化规律,揭示了不均匀变形的产生、发展和演变规律。结果表明:随着成形温度的升高,成形载荷逐渐下降,但400~440℃时变化趋势放缓且载荷值较为接近;等效应力逐渐下降,即变形抗力随着温度升高逐渐下降。

基于SWNT可饱和吸收体结合Sagnac滤波的调Q掺铒光纤激光器

提出并搭建了一种基于单壁碳纳米管可饱和吸收体结合Sagnac环的被动调Q掺铒光纤激光器,对其输出激光特性进行实验研究。采用光沉积法制备了单壁碳纳米管可饱和吸收体,其透射率为75%。基于单壁碳纳米管的可饱和吸收特性,搭建调Q激光器,实现谐振腔Q值调节。将Sagnac环形滤波器插入光纤环形腔,Sagnac环结构产生的滤波效应可以对调Q脉冲实现精细度滤波,该激光器工作阈值为800 mW。当泵浦功率为830 mW时,激光器可实现稳定的1 530.4 nm激光输出,输出功率为12.3 mW,重复频率为210.7 kHz,对应的脉冲周期为4.76μs,脉冲宽度为2.19μs,其最大脉冲能量为58.37 nJ。