超短孤子脉冲在色散缓变光纤中的时间抖动

通过微扰理论分析了超短孤子在色散缓变光纤(DDF)中传输的时间抖动。结果发现三阶色散和拉曼散射分别影响了孤子的位置和频率,是决定时间抖动大小的重要因素。在光纤的拉曼系数一定的情况下,选择不同的三阶色散参数,系统的时间抖动存在一个最小值。当DDF的三阶色散参数为接近零的一个负值的时候,系统时间抖动最小,这个负值与拉曼系数和传输距离有关,其绝对值随传输距离的增大而增大。在采用色散缓变光纤进行超短孤子传输的系统设计中应该重点考虑三阶色散的影响,当DDF的三阶色散参数较大的时候,必须对系统的三阶色散进行补偿,使时间抖动达到最小,能够极大地增加了孤子的传输距离。     

Wavelength tuning in optically mode-locked semiconductor fiber ring lasers with linearly chirped fiber Bragg gratings

We demonstrate wavelength tuning in single-wavelength and multiwavelength semiconductor fiber ring lasers that are mode locked with an optically injected control signal. A semiconductor optical amplifier is used to provide gain as well as to function as an optically controlled mode-locking element. Linearly chirped fiber Bragg gratings--single or superimposed--are used to define the lasing wavelengths as well as to provide wavelength tunability and allow for multiwavelength operation. We obtain pulses of tens of picoseconds in duration when we inject a sinusoidal optical control signal into the laser cavity, and we can tune the lasing wavelength(s) over the reflection bandwidth(s) of the grating(s) by simply changing the frequency of the injected control signal.     

Analytic study on soliton amplification in graphene oxide mode-locked Er-doped fiber lasers

Graphene oxide mode-locked Er-doped fiber lasers are investigated in this paper. The generalized nonlinear Schrödinger equation, which can be used to describe the fiber lasers, is studied analytically. Soliton solutions for this equation are obtained, and the stable solitons are generated in the fiber lasers. Physical effects, such as the gain bandwidth, distributed gain, group-velocity dispersion, and nonlinearity of fiber lasers, are analyzed. Soliton amplification techniques are proposed which can effectively restrain the appearance of pedestals during the evolution of solitons in the cavity. These analytic results are compared with the experimental ones. The results of this paper will be valuable to the study of the fiber lasers properties and provide theoretical guidance for the obtaining of high-power ultra-short pulses.     

Analysis and measurement of timing jitter induced by radiated EMI noise in automatic test equipment

This paper deals with the generation, measurement and modeling of the jitter encountered in the signals of a testhead board for automatic test equipment (ATE). A novel model is proposed for the jitter; this model takes into account the radiated electromagnetic interference (EMI) noise in the head of an ATE. The RMS value of the jitter is measured at the output signal of the testhead board to validate the proposed model. For measuring the RMS value, a novel circuitry has been designed on a daughter board to circumvent ground noise and connectivity problems arising from the head environment. An H-field is applied externally at the loop filter of a phase-locked loop (PLL), thus permitting the measurement of the RMS jitter to verify the transfer function between radiated EMI and jitter variation. The error between measured and predicted jitters is within a 15% level at both 200 kHz and 500 kHz.     

High-precision absolute distance and vibration measurement with frequency scanned interferometry

We report high-precision absolute distance and vibration measurements performed with frequency scanned interferometry using a pair of single-mode optical fibers. Absolute distance was determined by counting the interference fringes produced while scanning the laser frequency. A high-finesse Fabry-Perot interferometer was used to determine frequency changes during scanning. Two multiple-distance-measurement analysis techniques were developed to improve distance precision and to extract the amplitude and frequency of vibrations. Under laboratory conditions, measurement precision of approximately 50 nm was achieved for absolute distances ranging from 0.1 to 0.7 m by use of the first multiple-distance-measurement technique. The second analysis technique has the capability to measure vibration frequencies ranging from 0.1 to 100 Hz with an amplitude as small as a few nanometers without a priori knowledge.     

双光梳绝对距离测量实验研究

长度测量作为几何量测量关键共性基础技术之一,在科学研究、高端装备制造及空间探测等领域有着重要的应用。双光梳绝对测距技术充分发挥了光学频率梳的时域超短脉冲和频域高分辨特性,实现了高测量速率的绝对距离测量。目前双光梳测距存在测量范围小、测量精度低的问题,为解决此问题,提出了一种基于双光梳测距技术与相位测距技术相结合的方案,采用双光梳测距技术实现非模糊距离范围内长度的高精度测量,利用相位测距技术实现非模糊距离整数倍测量及指示功能,作为双光梳测距高精度测量的有效补充。搭建实验系统对该方案的可行性进行验证,结果表明在0~70 m的测量范围内,测量误差小于±5 μm。     

Comparison of absolute spectral irradiance responsivity measurement techniques using wavelength-tunable lasers

Independent methods for measuring the absolute spectral irradiance responsivity of detectors have been compared between the calibration facilities at two national metrology institutes, the Helsinki University of Technology (TKK), Finland, and the National Institute of Standards and Technology (NIST). The emphasis is on the comparison of two different techniques for generating a uniform irradiance at a reference plane using wavelength-tunable lasers. At TKK's Laser Scanning Facility (LSF) the irradiance is generated by raster scanning a single collimated laser beam, while at the NIST facility for Spectral Irradiance and Radiance Responsivity Calibrations with Uniform Sources (SIRCUS), lasers are introduced into integrating spheres to generate a uniform irradiance at a reference plane. The laser-based irradiance responsivity results are compared to a traditional lamp-monochromator-based irradiance responsivity calibration obtained at the NIST Spectral Comparator Facility (SCF). A narrowband filter radiometer with a 24 nm bandwidth and an effective band-center wavelength of 801 nm was used as the artifact. The results of the comparison between the different facilities, reported for the first time in the near-infrared wavelength range, demonstrate agreement at the uncertainty level of less than 0.1%. This result has significant implications in radiation thermometry and in photometry as well as in radiometry.     

The effects of timing jitter in sampling systems

Timing jitter generally causes a bias (systematic error) in the amplitude estimates of sampled waveforms. Equations are developed for computing the bias in both the time and frequency domains. Two principle estimators are considered: the sample mean and the so-called Markov estimator used in some equivalent-time sampling systems. Examples are given using both real and simulated data. It is shown that the bias that results from using the sample mean as an estimator can be approximated in the frequency domain by a simple filter function. The Markov estimator is shown to asymptotically converge to the population median. It is therefore an unbiased estimator for monotonic waveforms sampled with jitter distributions having a median of zero     

Birefringence measurement in double-clad fiber lasers with large cross section

We report on birefringence measurements in double-clad fibers with large cross section, doped with neodymium and ytterbium. The experimental results for rectangular double-clad fibers are compared with those for single-clad circular neodymium-doped fibers, taking into account existing models of stress- and geometry-induced birefringence. We demonstrated that the ellipticity of an outer silica cladding has no effect on birefringence in large-area double-clad fibers. The stress-induced birefringence is shown to depend on the ratio between the diameter of an internal silica support and the linear dimensions of the rectangular outer cladding. The stress-distribution pattern is derived to prove the experimental results.     

1.4 ps pedestal-free low timing jitter 10 GHz pulse source using commercial cascaded LiNbO3 modulators and fiber-based compressor

A stable 10 GHz pedestal-free short pulse generation scheme consisting of cascaded commercial LiNbO(3) modulators has been proposed and successfully demonstrated experimentally. Fiber-based pulse compression and reshaping stages have been utilized to obtain a 1.38 ps optical pulse train with very little pedestal and 132 fs timing jitter. Excellent performance of multiplexing from 10 Gbits/s to 160 Gbits/s using this method indicates good potential for application in ultrahigh-speed optical time-division-multiplexing systems.     

Development of an in-fiber white-light interferometric distance sensor for absolute measurement of arbitrary small distances

The fabrication, implementation, and evaluation of an in-fiber white-light interferometric distance sensor that is capable of measuring the absolute value of an arbitrary small distance are presented. Taking advantage of the mode-coupling effect of a long-period fiber grating, an additional cavity distance is added to the optical path difference of the distance sensor; therefore, it can generate a sufficient number of fringes for distance demodulation even if the free-space cavity distance is very small. It is experimentally verified that the distance sensor is capable of measuring small distances that are beyond the capability of a Fabry-Perot interferometric distance sensor.     

WDM系统中利用色散补偿降低脉冲定时抖动的研究

本文对色散管理孤子系统中存在的影响脉冲传输的ASE(放大器自发辐射)致定时抖动进行了研究。利用微扰理论,通过半解析算法推导出ASE致定时抖动的算术表达式,从中得出ASE致定时抖动主要受放大器间距和色散图的影响。在此基础上对通常采用的二级色散图进行拓展,提出三级色散图方案并对色散管理系统进行计算机数值模拟,结果表明,通过选取适当的色散图参数,三级色散图方案比之二级色散图将能更好地减小因ASE噪声致定时扰动的影响。     

Maximum fiber coupling efficiency and optimum beam size in the presence of random angular jitter for free-space laser systems and their applications

Free-space laser communication systems use optical-fiber-based technology such as optical amplifiers, receivers, and high-speed modulators. In these systems using single-mode fibers, the fiber coupling efficiency is one of the most significant issues to be solved. Optimum relationships between a focused optical beam and mode field size of the optical fiber in the presence of random angular jitter are discussed in relation to fiber-coupled optical systems. Maximum fiber coupling efficiency is analytically derived with the optimum Airy disk radius normalized by the mode field radius as a function of random angular jitter. The fade level of fiber-coupled signals at desired fade probability is investigated. It is shown that the average bit error ratio significantly degrades with the random angular jitter normalized by the mode field radius larger than about 0.3 when the Airy disk size is optimally selected.     

Active synchronization and carrier phase locking of two separate mode-locked femtosecond lasers

Two independent mode-locked femtosecond lasers are synchronized to an unprecedented precision. The rms timing jitter between the lasers is 4.3 fs observed within a 160 Hz bandwidth over tens of seconds, or 26 fs within a 50 kHz bandwidth. Novel multi-stage phase-locked loops help to preserve this ultrahigh timing resolution while setting on arbitrary delay between the two pulse trains (0–5 ns). Under such synchronization, phase locking between the carrier frequencies of the two femtosecond lasers has been achieved. It is also demonstrated that the same level of synchronization can be achieved with two lasers at different repetition frequencies.     

Disturbance-free distributed Bragg reflector laser-diode interferometer with a double sinusoidal phase-modulating technique for measurement of absolute distance

A new range-finding technique that uses both double sinusoidal phase modulation and quasi-two-wavelength interferometry is described. Two independent interference signals are generated with respect to two different wavelengths on a time-sharing basis. We clarify that external disturbances of these interference signals are eliminated by both feedback control and differential detection and that the feedback control does not affect the distance measurement. A single distributed Bragg reflector laser diode allows us to simplify the optical setup and to improve the measurement accuracy. After discussing a measurement range, we estimate a measurement error by making several measurements.     

Microchip lasers and their applications in optical microsystems

The microchip lasers are the most compact diode pumped solid state lasers. They are fabricated using collective mass production processes, at low cost. Several hundreds of microchip lasers can be fabricated on one single thin wafer of a laser material. The microchip laser is pumped with a standard GaAlAs or GaInAs diode laser, directly or through a multimode fibre. It is a kind of optical transformer which transforms a poor quality laser diode beam to a diffraction limited TEM00 and single frequency laser beam. Moreover, by Q-switching, very short pulses (∼0.4–2 ns) with very high peak power (0.5–50 kW) can be obtained. Most of the well known laser materials can be used for emissions near 1, 1.3, 1.5 and 2. Visible and UV emissions are obtained using harmonic generations in non-linear crystals. Microchip lasers have many different industrial applications in large markets such as: automotive, laser marking, environmental and medical applications, public works, telecommunications. They should open the domain of solid state lasers to high volume and low cost markets.     

Measurement of timing jitter contributions in a dynamic test setupfor A/D converters

The article provides a new method which permits one to separate and to obtain an accurate estimation of timing jitter contributions appearing in an analog-to-digital (A/D) converter dynamic common test setup. The results are obtained using coherent sampling configuration and are independent of quantization and nonlinearities of the converter     

Modeling and optimization of Q-switched double-clad fiber lasers

The numerical modeling of actively Q-switched fiber lasers is systematically presented. On the basis of typical Q-switched ytterbium-doped double-clad fiber lasers under forward and backward pump, the dynamic characteristics of pulse energy, pulse width, population inversion, and stored energy at tens-of-kilohertz repetition rates are studied by using the traveling-wave method. The laser performance is further investigated for different fiber core diameters, doping rates, cavity lengths, fiber losses, signal and pump wavelengths, reflectivities of output coupler, and switching speed of an acousto-optic modulator; the laser optimization is also quantitatively discussed. Some simulation results are also compared with previous experimental results.     

0.6328μmHe-Ne激光器小数重合法大尺寸绝对距离测量方法的研究

本文介绍了以小数重合法为基础的大尺寸绝对距离干涉测长的原理，并着重分析了两种测量方法：外差法和拍波法。