频域反射法光纤延时精密测量

本文提出了一种应用于光纤延时系统中实现光纤延时精密测量的新方法,用以提高光纤延时测量的精度和准确性.该方法以1064 nm激光调制信号作为光源,通过测量回波信号的幅值和相位信息得到被测通道的频率响应,采用快速傅里叶逆变换得到被测目标的延时信息,实现光纤延时测量.本文通过理论分析和延时测量实验对频域反射法与传统的时域测量方法进行对比,使用频域反射法在调制频率范围10—200 MHz,采样频率间隔0.5 MHz的实验条件下,实现了3.3 ps延时测量分辨率,并证明了该方法具有比时域方法更高的测量精度,测量结果的准确性更好.     

高精度光链路授时时延估算

授时系统中信号单程传输时延的估算直接影响到授时的精度, 环路时延测试是估算单程传输时延的方法之一。在光缆授时系统中光纤的色散特性将导致不同波长光信号在同一光链路中的传输时延存在差异, 基于G.652光纤的色散特性, 提出的时延差精确估算方法, 能够得到这种传输时延的差异。仿真显示来回链路工作波长在1.55 μm附近时, 此方法能够很好地补偿时延差, 从而精确估算信号传输时延。     

Fiber chromatic dispersion measurement based on wavelength-to-time mapping using a femtosecond pulse laser and an optical comb filter

A novel method for the measurement of chromatic dispersion of an optical fiber based on wavelength-to-time mapping using a femtosecond pulse laser (FSPL) and an optical comb filter is proposed and experimentally evaluated. In the proposed approach, the spectrum of an ultrashort optical pulse generated by an FSPL is sliced by an optical comb filter. The spectrum-sliced optical pulse is then coupled into the optical fiber under test. Thanks to the chromatic-dispersion-induced wavelength-to-time mapping in the optical fiber under test, a time-domain waveform similar to the sliced spectrum is generated at the output of the optical fiber, with different frequency components having different time delays. The time delay vs. frequency data are then recorded for the estimation of the chromatic dispersion by using least square fitting. Chromatic dispersions of two types of optical fibers with different lengths are tested. The measured dispersion values agree well with those measured by the conventional modulation phase shift (MPS) method.     

Character analysis of slow light with communication waveband in fiber optical parametric amplifier

The comprehensive characters of delay time and delay bandwidth with distortion, signal wavelength dependence and delay bandwidth product in fiber optical parametric amplifier are investigated theoretically when the pump locates at anomalous dispersion region. The delay character of single pulse, data stream with certain bit pattern and pseudo random data stream are analyzed comprehensively. In this category of fiber optical parametric amplifier, the delay time and delay bandwidth product vary from signal wavelengths and bit rates. For the same nonlinear coefficient, pump power and fiber length, the diverse dependences of bit pattern in different signal wavelengths are found by numerical simulation. The impacts of pump power and fiber length on the delay character and distortion are also discussed. These relations are conductive to the design of slow light based on fiber optical parametric amplifier in telecommunication waveband.     

Simple and highly accurate technique for time delay measurement in optical fibers by free-running laser configuration

A novel and simple technique for the measurement of time delay in the optical fiber by a free-running laser is proposed and demonstrated. The fiber to be measured was spliced to an erbium-doped fiber so as to form a ring-cavity laser. The mode beating frequency of the laser was measured to determine the round-trip time delay. This precise and efficient technique has an accuracy of 10(-8) for a fiber length of 100 km and of 10(-6) for a several-meters-long one.     

A novel method for measuring optical fiber delay lines based on the optical fiber low-coherence Young's interferometer

According to the principle of double-beam interference imaging using an infrared broadband light source, a novel method based on the optical fiber low-coherence Young's interferometer for the measurement of programmable optical fiber delay line is proposed. By measuring the small length increments of delay fiber through the evaluation of the central positions of zero-order interference fringes, we successfully construct a system with a variety of important functions, such as real-time controlling, measurement and displaying. This system offers the benefit that it can be regulated precisely to generate interference stripes once again after the length of fiber segment changes. When the locations of central stripes are moved to coincide with the original markers, the determination of the corresponding fiber optical delay time becomes really simplified, as just by reading out the tinny displacement of the reference arm. Multiple groups of experimental results demonstrate the outstanding performance of the proposed system since it bears a measuring accuracy of μm and a measuring range from 1 mm to 20 cm.     

Fiber-optic delay line using multicore fiber

A fiber-optic delay line based on a multicore optical fiber is fabricated for the first time. Due to the optical pulse sequential passage over all cores, the time delay of the optical signal of 45.0 μs is obtained at the optical fiber length of only 1300 m. The use of the seven-core optical fiber allows a sevenfold reduction in the used fiber length in comparison with single-core fibers, which is promising for developing lines with long signal delays.     

表面粗糙度光纤传感器研究

基于光在粗糙表面的散射原理,利用时间延迟技术,设计了一种快速、非接触测量表面粗糙度的光纤传感器。与同类传感器相比,成本低,系统误差小。     

多束高重复频率全光纤激光脉冲时间波形实时精密测量技术

提出了一种基于时分复用的多束高重复频率全光纤激光脉冲时间波形实时精密测量技术,针对分类成组的多束高重复频率全光纤激光系统不同测量功能需求,分别设计了1×8时分复用器、不同延时量的1×2时分复用器,实现了48路、144个1kHz光纤激光整形脉冲时间波形宽度、上升沿、面积等关键参数的精密测量,同时实现了多束高重复频率全光纤脉冲激光系统运行状态的实时监测。     

A large capacity sensing network with identical weak fiber Bragg gratings multiplexing

A quasi-distributed optical fiber sensing network with large multiplexing capacity, which is based on identical weak fiber Bragg gratings, is proposed, theoretically analyzed and experimentally studied. The key technique is the demodulation technology named “Optical wavelength time-domain reflection (OWTDR),” which utilizes the optical power variation of reflected sensing signal in both time domain and wavelength domain. The influence of reflectivity of fiber grating, interval between adjacent gratings and transmission loss of delay fiber on the multiplexing capacity of sensing system are discussed. Analyzed results demonstrate that this sensing scheme can effectively increase the multiplexing capacity of sensing system up to 1000, implement multi-point synchronous measurement and reduce the cost of signal demodulation. 9 Identical weak fiber Bragg gratings with the same Bragg wavelength of 1536.651 nm, reflectivity of 6%, bandwidth of 0.07 nm are written in series to investigate the performance of the proposed scheme.     

利用高精度时间间隔测量技术实现光速测定方法的研究

为了实现实验室环境下测定光速，采用已知长度及折射率的单模零色散光纤作为传输介质，利用高精度时间间隔测量技术测量了光在该光纤中的传输延时。经过理论推导，求出光速c与作为传输介质的光纤长度L、折射率n及光纤延时τ之间的关系式，从而通过测量得到L，n及τ的值即可计算得到真空中的光速值。与传统的利用天文法及精密仪器测量光速的方法相比，采用比较先进的高精度时间间隔测量技术可使时间分辨率达到125ps，从而在实验室环境下，利用简单仪器得到了高精度的测量结果。最终测量所得光速为299928077m/s，误差为30860m/s。     

适用于光突发交换网的可编程光缓存器

提出了两种适用于光突发交换网的可编程光缓存器结构：交叉型和多端口开关型.两种结构都能满足突发包缓存的超长性和可变性的要求，且结构简单紧凑，成本低，可扩展.交叉型缓存器通过指定信号在每个子缓存模块的光纤环中的循环次数即能实现可变时间的延迟.多端口开关型缓存器通过指定信号在两个多端口开关相应端口与所接光纤延迟线组成的光纤环中的循环次数实现可变时间的延迟.仿真结果表明，两种可编程光缓存器都能对光突发包实现ns级指定时间延迟，可用于解决光突发交换网突发包的冲突问题.     

Single-shot tomography by means of VIPA and spatial phase modulator installed optical interferometer

A VIPA (virtually imaged phased array) installed optical interferometer has been proposed for scanless tomography. Also, a spatial phase modulator and a line-image sensor were installed into the interferometer to realize single-shot measurement by displaying the delay time on a line-image sensor. The correlation peak function was observed on the line-sensor at same time. The envelope of the peak was given by the inverse Fourier transformation of the light source spectrum. The peak position on the image-sensor reflects the sample structure. Furthermore, the correlation peaks are appeared repeatedly along the delay time of the interferometer. The repeated correlation function raise an alignment flexibility of the sample set position, which has been limited in the traditional time-domain interferometry involving the delay time to be zero. The flexibility was experimentally confirmed at 25 mm related to the VIPA coherency. The resolution was experimentally 52.5 μm when the ASE (amplified spontaneous emission) light source of the optical fiber amplifier was used. The single-shot measurement was realized by a line-image sensor of the 30 frames per second. The repeatability of the interfered peak position was 5 μm by the tunable mirror position. The one-dimensional scanless measurement was demonstrated by use of 3-layer glass plates.     

光纤激光模场及表征技术进展

在光纤通信、光纤激光器和光纤传感等领域的实际应用中,需要重点关注光纤中的模式问题。模分复用是提高光通信信息容量的有效方法,模间干涉是大多数光纤传感的基本方法,高功率光纤激光的光束质量控制的关键技术之一就是模式控制,因此,对光纤模式理论、模式产生及转换、模式表征技术开展研究具有重要的研究意义和实际应用价值。论文讨论了光纤的模式及光束质量,分析了多种模式发生及转换的方法,将模式表征方法归结为非相干、相干和低相干测量法。光纤模式表征是目前的研究热点,在多种表征方法中,空间和频谱成像法（S2）和双重傅里叶变换法（F2）具有显著的优越性,可不需要提前知道光纤的几何参数,就可获得模场分布、模式功率占比、群时延等特性。研究表明F2法更适合于表征高功率光纤激光的模场特性。     

损耗可控条件下掺铒光纤中光速减慢现象的研究

由于相干布居振荡效应,光脉冲通过处于吸收状态的掺铒光纤介质时,将导致群速度传输减慢. 由掺铒光纤的吸收特性可知,此时必伴随着强烈的吸收损耗,这势必会给实际的慢光信号测量及光通信领域带来诸多的困难. 从铒离子基态粒子速率方程出发,对损耗可控条件下的光速减慢传输进行了数值仿真研究,并加以实验验证. 研究表明：抽运光强度越高,信号光损耗系数越小;抽运掺铒光纤长度越长,信号光损耗系数越小. 通过优化抽运光强度、掺铒光纤长度等参量,可以实现损耗可控条件下的光脉冲群速度减慢传输. 关键词： 时间延迟 吸收损耗 掺铒光纤     

马赫-曾德光纤干涉光谱测量系统的设计

光纤干涉光谱仪由于其体积小、分辨率高、抗电磁干扰和耐高温的特点,广泛应用于各种领域的物质检测中。设计了一种使用电动光纤延迟线实现光程差调制的基于Mach-Zehnder光纤干涉仪的光谱测量系统。介绍了系统的构成,推导了基于该系统的光谱计算公式以及分辨率计算公式。搭建了实验平台,对一宽谱光源进行测试,并采集其干涉信号,解调出了相应的光谱图。对结果进行分析,当最大光程差变为0.479 5 cm时,光谱分辨率为2.085 4 cm-1。电动光纤延迟线的性能在很大程度上决定了最终解调出的光谱的分辨率、精度,尤其是速度和延时时间的精度和线性度。     

High-Accuracy Measurement of the Dispersion of Chirped Fiber Gratings

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掺铒光纤中亚稳态粒子振荡和慢光时间延迟关系研究

由于光纤慢光在实际中的应用价值引起广泛关注. 技术手段上利用相干布居振荡效应实现光速可控更具有优势. 本文主要介绍了利用相干布居振荡效应 (CPO) 实现掺铒光纤中的光速减慢传输, 通过改变掺杂浓度、光纤长度、入射信号光及抽运光功率等参量, 具体研究了亚稳态粒子振荡和时间延迟的关系. 研究结果表明: 选择高浓度光纤、增加光纤长度、关闭抽运光源, 选择适当强度的信号光可以有效地增大时间延迟. 关键词： 掺铒光纤 时间延迟 相干布居振荡 慢光     

Spectrally resolved reflectometric measurement of polarization mode dispersion in an optical fiber link with polarization-dependent loss

In an optical fiber link with polarization-dependent loss (PDL), we demonstrate that although the complex polarization mode dispersion vector cannot be fully obtained by the reflectometric measurement, the spectrally resolved differential group delay (DGD) and differential attenuation slope (DAS) can be explicitly determined by such measurements performed simultaneously in the optical frequency domain and the fiber length domain. In principle, this technique can be used to realize the spectrally resolved and spatially resolved measurement of DGD and DAS in an optical fiber link having PDL based on distributed Rayleigh backscattering. We report the experimental result based on the far-end Fresnel reflection to confirm the validity of the proposed method.     

Short-term frequency characteristics of 2 µm single frequency Solid-state lasers

The Short term frequency stability characteristics of 2 μm single frequency Solid-state lasers was investigated. The two laser systems of 2 μm single longitudinal mode oscillation Tm, Ho:YLF microchip laser and Ho:YAG NPRO laser were designed and constructed. The Short term frequency stability of these two laser were measured with the fiber delay self-beating heterodyne method. The 3dB width of the relative frequency fluctuation of Tm, Ho:YLF microchip laser and Ho:YAG NPRO laser were measured to be 895 and 736 Hz with 500 m fiber optical (2.5 μs delay). The proportional relation between the lasing fluctuation and the delay time were 358 and 263 Hz/μs, respectively. The vibration experiment was presented and it indicated that the NPRO Ho:YAG was more terrible to the influence of vibration, which is important in the practical application of wind measurement lidar.