Bragg光纤光栅用作滤波器时的输出光脉冲波形分析

对光纤光栅用作接收端光噪音滤波器进行了详细的理论分析,计算了通信系统中矩形光脉冲信号经“强”、“弱”Bragg光纤光栅滤波器后的输出光脉冲波形,同时也计算了矩形光脉冲信号经匹配光滤波器、现行光通信系统中常用F-P滤波器的输出光脉冲波形,对四种滤波器的输出光脉冲波形进行了分析和比较,并分析了输出信号在抽样判决时的码间干扰情况,从输出波形分析认为,光纤光栅用做接收端噪音滤波器比F-P滤波器具有更大的优越性.     

两根大芯双包层光纤激光器获得60 W相干输出

报道了一个相位锁定的光纤激光器阵列获得60W的输出,同相模式输出时的斜率效率为37%。对于两种不同的纤芯距离都观测到稳定的高对比度干涉条纹。整个系统在高功率操作时,所用的空间滤波器没有观察到明显的热问题,这充分说明了采用这种方法能够进一步提高相干输出功率。     

Switchable multi-wavelength fiber laser based on modal interference

A comb fiber filter based on modal interference is proposed and demonstrated in this paper. Here two cascaded uptapers are used to excite the cladding mode, and a core-offset jointing point is used to act as an interference component.Experimental results show that this kind of structure possesses a comb filter property in a range of the C-band. The measured extinction ratio is better than 12 dB with an insertion loss of about 11 dB. A switchable multi-wavelength erbium-doped fiber laser based on this novel comb filter is demonstrated. By adjusting the polarization controller, the output laser can be switched among single-, dual-, and three-wavelengths with a side mode suppression ratio of better than 45 dB.     

Electrically tunable Sagnac filter based on a photonic bandgap fiber with liquid crystal infused

We demonstrate an electrically tunable Sagnac filter based on a photonic bandgap fiber that is realized by infusing liquid crystal into a solid-core air-hole photonic crystal fiber. The filter enables an electrical tuning with a range of about 26 nm for one single interference minimum in the transmission bandgap from 1330 to 1650 nm wavelength. The tuning efficiency is averaged to 0.53 nm/V.     

Study of the amplification characteristics of a coaxial EDF with varying coupling conditions

A coaxial erbium doped fiber (EDF) designed to show inherent gain flattening for one of its propagating modes in general supports two or more modes with different gains. In this paper, we show that when such an amplifying coaxial EDF is spliced to a single mode transmission fiber carrying the signal, in general, more than one mode is excited each with its excitation coefficient strongly dependent on wavelength. Due to the interference between these modes, the amplified output coupled to an output single core transmission fiber can be a very sensitive function of the coaxial EDF length, especially around the phase matching wavelength (PMW), and does not show inherent gain flattening. However, due to interference between the two modes, the coaxial fiber acts as a band reject filter at the phase matching wavelength with attenuation and bandwidth depending on fiber parameters. This property can be employed for inherent gain flattening when both modes are excited.     

Propagating beam analysis of fiber wavelength filters with a depressed-index section

A wavelength filter consisting of single-mode and few-mode fibers is investigated numerically. A simple finite-difference beam-propagation method, in which a transparent boundary condition can be imposed, is developed for circularly symmetric waveguides. After confirming the validity of the numerical method by the mode-mismatch loss, we calculate the propagating field in the fiber wavelength filter, in which interference between LP₀₁, and LP₀₂ modes occurs. To improve the filtering operation, a depressed-index fiber is employed for the few-mode fiber. The effects of the radius and refractive index of the depressed section on the transmission power are revealed and discussed. Power is suppressed to less than 0.1% at 1.3 μm, while maintaining power transmission of more than 85% at 1.55 μm. It is also found that the filtering operation shifts to higher wavelengths as the input power is increased when we choose a self-focusing nonlinear material in the depressed section.     

134-W phase locking of two-dimensional four-fiber lasers with improved self-imaging resonator

We experimentally demonstrate the phase locking of a two-dimensional （2D） array of four fiber lasers using an improved self-imaging resonator with a spatial filter. The high visibility interference round stripes of the coherent beam profile are observed. The coherent output power of the fiber array exceeds 134 W. Tile entire system operates quite stably, and no thermal effects observe in the spatial filter, indicating that the coherent output power can be increased using this method.     

All-fiber multimode interference bandpass filter

A novel design for an all-fiber bandpass filter based on a multimode interference reimaging phenomenon is presented. The filter has achieved low insertion loss with adequate bandwidth and isolation for coarse wavelength-division multiplexing. The filter can easily be made with any central wavelength that is compatible with the single-mode fiber used for its construction. The measured filter performance matches the theoretical predictions well. The filter can have broad applications in fiber-optic telecommunications, spectroscopy, and sensing.     

A stable and tunable linear polarization single longitudinal mode fiber ring laser

A stable and tunable linear polarization single longitudinal mode fiber ring laser is proposed and demonstrated. A high extinction ratio spatial mode interference filter utilizing two-mode graded-index fiber supresses irregular side modes effectively, the combination of fiber polarizer and polarization maintaining fiber act as a polarization dependent comb filter, and tunable bandpass filter is adopted to select proper lasing wavelength. The power fluctuation and wavelength fluctuation at 1549.88 nm are less than 0.05 dB and 0.02 nm in 1 h, respectively. Only one longitudinal mode appears within a free spectral range of 7.5 GHz, and the degree of polarization in percentage is approximately as high as 99.07%.     

Demonstration of high extinction ratio modal interference in a two-mode fiber and its applications for all-fiber comb filter and high-temperature sensor

We show that high extinction ratio (>20 dB) modal interference in a two-mode dispersion compensating fiber can be utilized to build a compact, easy-to-fabricate tunable all-fiber optical comb filter. Wavelength tunability over the full free spectral range of the comb filter is demonstrated with an electrical power of 115mW using an on-fiber thin film micro-heater deposited directly on the fiber. In another configuration, the comb filter is used as a temperature sensor with dynamic range of >300 °C and sensitivity of <0.1 °C. The temperature sensor is capable of measuring a temperature as high as 500 °C.     

光纤光栅传感信号解调技术研究进展

光纤光栅传感器是一种新型传感器,有着非常广泛的应用前景。限制光纤光栅传感器大量实际应用的主要障碍是传感信号解调,因而,光纤光栅传感信号解调是光纤光栅传感器应用的关键技术之一。本文对现有已报道的光纤光栅传感信号的解调方法进行综述,并归类为:边缘滤波法、匹配滤波法、可调谐滤波法、光源波长可调谐扫描法、射频探测法、光栅啁啾法、CCD分光仪法、干涉法。对各种方法的原理及相关改进方法进行了阐述,并对其优缺点做了比较分析,最后,对光纤光栅传感信号的解调技术发展进行了展望。     

光纤网络中的云数据并行调度

光纤网络的通信质量受到云数据调度均衡性影响很大,为了改善光纤网络通信质量,提高网络中云数据传输的吞吐量和保真率,通过云数据并行调度,实现云数据传输均衡,提出一种基于自适应判决反馈均衡的光纤网络云数据并行调度模型。构建光纤网络通信的传输信道模型,采用最小均方误差估计方法进行光纤网络的量化融合估计,运用匹配滤波检测器进行云数据中的干扰滤波处理,结合自适应判决反馈均衡方法进行信道均衡,在均衡的信道中对滤波输出的云数据进行并行调度和多线程输出调制。仿真结果表明,采用该方法进行光纤网络中的云数据并行调度的均衡性较好,输出数据的保真率较高,误码率较低,改善了光纤网络的整体性能。     

All-fiber polarization interference filters based on 45°-tilted fiber gratings

We report all-fiber polarization interference filters, known as Lyot and Lyot-?hman filters, based on alternative concatenation of UV-inscribed fiber gratings with structure tilted at 45° and polarization maintaining (PM) fiber cavities. Such filters generate comb-like transmission of linear polarization output. The free spectral range (FSR) of a single-stage (Lyot) filter is PM fiber cavity length dependent, as a 20 cm long cavity showed a 26.6 nm FSR while the 40 cm one exhibited a 14.8 nm FSR. Furthermore, we have theoretically and experimentally demonstrated all-fiber 2-stage and 3-stage Lyot-?hman filters, giving more freedom in tailoring the transmission characteristics.     

一种全光纤型窄带梳状滤波器的特性分析

分析了由双光纤定向耦合器组成的梳状滤波器的透射特性。根据传输矩阵,推导出了该滤波器的输出光谱与有关参数之间的关系式。分析结果表明:该滤波器具有法布里_珀罗腔多光束干涉的特点,是一种窄带宽梳状滤波器;耦合器的耦合系数与法布里_珀罗腔中的反射率类似,通过控制耦合系数可以调节滤波器的通带半宽度、消光比、隔离度、输出光强等。     

新型波长解调技术在干涉型光纤传感器输出解调中的应用

提出了一种改进型边缘滤波波长解调技术,解决干涉型或谐振型光纤传感器输出的干涉谱波长的快速解调问题。该波长解调技术基于啁啾光栅和长周期光栅的光谱特点,以啁啾光栅作为矩形滤波器,提取传感器输出干涉谱的一个干涉峰;以长周期作为边缘滤波器,将干涉峰的波长信息转化为光强信息进行检测。该波长解调技术波长解调范围为传感器输出干涉谱的一个自由光谱范围(FSR),解调速度快,克服了当前波长解调技术中存在的测量范围与测量速度难以同时提高的问题,同时还具有系统成本低 ,体积小,能够灵活多路扩展的特点。详细介绍了解调系统的工作原理以及系统结构,并将其实际应用于一种干涉型光纤电流传感器输出干涉谱的波长解调中。通过实验证明电流传感器工作在工频及脉冲电流(脉冲宽度25 μs)情况下,该解调系统对传感器输出干涉谱具有准确、快速的解调效果。该研究对推进干涉或谐振型光纤传感器的实际工程化水平的提高具有重要意义。     

Multimode interference filter for tuning of a mode-locked all-fiber erbium laser

We present a mode-locked all-fiber erbium laser that can be tuned in wavelength while in pulsed operation. A low-cost multimode interference bandpass filter based solely on standard fibers was employed in a sigma-shaped cavity design. By bending the fiber filter, the spectrum could be continuously shifted by up to 11.6 nm without interrupting pulsed operation, and output powers of more than 3.3 mW at pulse durations below 350 fs were achieved.     

All-optical microwave notch filter with flat passband based on semiconductor optical amplifier

An all-optical filter structure for interference mitigation of microwave signals is proposed and demonstrated. The structure is based on a recirculating delay line loop (RDLL) and a fiber Bragg grating. The RDLL is comprised of a semiconductor optical amplifier (SOA) followed by a tunable narrowband optical filter and an optical variable delay line. Negative tap is generated using wavelength conversion based on the cross-gain modulation of amplified spontaneous emission spectrum of the SOA. A negative band-pass filter and a broadband all-pass filter are synthesized to achieve a narrow notch filter with flat passband which can excise interference with minimal impact on the wanted signal over a wide microwave range. Experimental results show the notch rejection ratio of 30 dB, good shape factor and tunability.     

光纤背向激光自发喇曼散射的温度效应研究

从理论和实验上研究了光纤背向激光自发喇曼散射的温度效应.光纤背向激光自发反斯托克斯喇曼散射、斯托克斯喇曼散射光的相对强度正比于光纤分子上、下能级粒子数的布居,依赖于温度.由于实际系统中,作为分光用的干涉滤光片不可能完全隔离背向瑞利散射光,因此,实际系统温度曲线比理论曲线低,本文给出了理论修正公式,提出了附加修正项,它与隔离度和波长有关.     

级联长周期光纤光栅对的干涉谱分析及其在多信道滤波器中的应用

分析了由光纤级联的两个相同的长周期光纤光栅形成的干涉谱。根据设计中的关键技术,利用粒子群优化算法设计了长周期光纤光栅传输损耗为50％的平坦传输损耗谱.将相同的两个优化设计的长周期光纤光栅级联,可以实现一种实用的可调谐多信道隔离滤波器.讨论了级联长周期光纤光栅对之间光纤的偏振特性对干涉谱的影响.     

基于偏振模干涉的可变系数微波光子滤波器

基于偏振调制和光的干涉原理,设计了同时具有正系数和负系数特性的微波光子滤波器,并通过搭建实验模型证实了方案的可行性。利用偏振调制及光的偏振特性实现载波和一阶边带的正交偏振,并通过改变偏振调制器的偏置电压分别对载波和一阶边带引入相移。当载波和一阶边带的相位差为0或90时,利用保偏光纤快慢轴上两正交偏振光在同一偏振态上的干涉效应,分别对应实现具有负系数或正系数特性的微波光子滤波器。最后,测量并验证了0~15 GHz频率范围内滤波器的频率响应。