Experimental study on pulse propagation characteristics at normal dispersion region in dispersion flatted fibers

Pulse propagation characteristics at normal-dispersion region in dispersion-flatted-fibers are experimentally investigated by employing the second-harmonic generation frequency-resolved optical gating (SHG-FROG) method. It is found that the experimental results are consistent with the theoretical prediction. The initial optical pulse with negative chirp is compressed for nonlinear effect in the normal-dispersion fiber, and it evolves into near Gaussian pulse. Temporal width of the optical pulse decreases with the increase of the input power and propagation distance. The output pulse width for small dispersion is less than that for great dispersion at the same input power. The spectrum of the output pulse is still symmetrical about the central wavelength, and is broadened with the increase of input power. The spectral width of the output pulse is much wider than the input spectral width.     

Dispersion Characteristics of Waveguide Arrays in Optical Spectrum Analyzers

Formulas for calculating the spectral characteristics of waveguide arrays, which are incorporated into waveguide spectrum analyzers based on planar waveguides, channel waveguides, and fiber optical waveguides, are derived taking into account the contribution of both the waveguide dispersion and the material dispersion to the dispersion factor. These formulas are used to study the dependence of the dispersion factor on the waveguide-system parameters for specific models of waveguide arrays. It is shown that consideration of contributions of the waveguide dispersion and material dispersion can affect profoundly the spectral characteristics of waveguide arrays.     

Chalcogenide glasses as a medium for controlling parameters of ultrashort IR pulses: II

The propagation of ultrashort optical pulses in planar chalcogenide glass waveguides with uniform or periodic claddings is considered. In comparison with silica waveguides a structure based on chalcogenide glass provides higher nonlinearity. This material has a high normal dispersion in the wavelength range of 1.5–3.5 μm. Periodic waveguide structures can be used to compensate for this dispersion. High-intensity laser pulses propagating in these structures undergo spectral broadening. The influence of the phase self-modulation of a pulse on its spectrum and width is analyzed using numerical simulations.     

Pulse broadening of the femtosecond pulses in a Gaussian beam passing an angular disperser

A general analytical formula has been found to describe the evolution of the pulse width of the femtosecond pulses in a Gaussian beam after passing an angular disperser without the assumption of well collimation. This formula is experimentally verified by measuring the pulse width with an autocorrelator based on two-photon absorption. It is found that the effect of the spectral lateral walk-off and group delay dispersion on the pulse-width evolution, and its dependence on the distance traveled, are substantially different when the beam has not been well collimated than from when it has been collimated. These differences result from the decaying nature of the angular dispersion of the Gaussian beam sent across a distance.     

Effect of metal boundaries on surface-wave spectrum in plasma-vacuum structures

The effect of metal on the surface-wave spectrum in cylindrical metal-plasma-vacuum-metal and metal-vacuum-plasma-metal waveguide structures and waveguides with a single metal boundary is investigated. It is shown that such boundaries can greatly affect the spectral properties of the waveguide and change the nature of surface-wave dispersion. Analytic expressions are obtained for the frequency of symmetrical surface waves in various spectrum intervals. The strong dependence of phase velocity on the size of the internal metal cylinder that is found can be convenient for beam and wave synchronization in a plasma waveguide.     

Slow light pulse propagation in dispersive media

We present a theoretical and numerical analysis of pulse propagation in a semiconductor photonic crystal waveguide with embedded quantum dots in a regime where the pulse is subjected to both waveguide and material dispersion. The group index and the transmission are investigated by finite-difference-time-domain Maxwell–Bloch simulations and compared to analytic results. For long pulses the group index (transmission) for the combined system is significantly enhanced (reduced) relative to slow light based on purely material or waveguide dispersion. Shorter pulses are strongly distorted and depending on parameters broadening or break-up of the pulse may be observed. The transition from linear to nonlinear pulse propagation is quantified in terms of the spectral width of the pulse. To cite this article: T.R. Nielsen et al., C. R. Physique 10 (2009).     

A study on asymmetric coupled waveguides ascompact dispersion compensators

A strong polarization dependence of pulse compression was experimentally observed using an InGaAsP/InP slab-type coupled waveguide structure consisting of two dissimilar waveguides. This polarization dependence strongly demonstrated that the observed pulse compression results from dispersion compensation due to group velocity dispersion (GVD) associated with supermodes. High mode-conversion efficiency over a wide spectral band in mode converters and the possibility of continuous control of supermode GVD by current injection were demonstrated by numerical simulation.     

Optimization of supercontinuum generation in photonic crystal fibers for pulse compression

A theoretical study of super generation in photonic crystal fiber and its application to pulse compression is presented. The evolution of the spectrum can be divided into three stages: initial broadening below a certain threshold propagation distance, dramatic broadening to a supercontinuum at a threshold distance, and, finally, saturation of the spectral width on propagation. It is found that the group delay and group-delay dispersion of the supercontinum are sensitive to the input pulse peak power after further propagation at the third stage. Fluctuations from the input pulse are amplified and translated into fluctuations and time shift of the compressed pulses. There exists an optimum compressed distance at which compressed pulses with negligible fluctuation and time shift can be obtained.     

飞秒脉冲在硅波导中产生超连续谱的研究

利用非线性薛定谔方程对飞秒脉冲在硅波导中的传输以及超连续谱的产生进行了研究,计算和分析了色散参量及非线性损耗在超连续谱的产生过程中的影响.结果表明,孤子分裂是飞秒脉冲在硅波导中产生超连续谱的主要机理.飞秒脉冲中心波长与波导零色散点的相对位置对超连续谱的产生有极大影响.当中心波长位于近零色散点的反常色散区时,孤子分裂现象最明显,谱宽远大于在零色散波长及正常色散处入射时的情况,并且达到稳定展宽所需波导长度最短.其次,高阶色散的大小也会影响光谱展宽,三阶色散绝对值较小时,能够获得较大的展宽.另外,由于双光子吸收效应带来大量损耗,限制了谱宽,并且随着初始脉冲功率的逐渐增大,展宽出现饱和现象. 关键词： 超连续谱 孤子分裂 色散 硅波导     

皮秒级时间分辨超快高能脉冲激光光谱

介绍了一种利用光电摄谱法和条纹管相结合测量ps级时间分辨超快高能脉冲激光光谱的方法。论述了条纹相机工作原理和平面衍射光栅的分光原理,分析指出利用介绍的装置,可以实现波长300 nm ～1 600 nm、脉宽＞2 ps超快高能脉冲激光的光谱测量。采用1 054 nm超快高能脉冲激光器,实验得到了条纹像,对条纹像进行数据处理后得到测量光谱曲线,通过能量标定后,得到了超快高能脉冲激光器实际光谱曲线,验证了ps级时间分辨超快高能脉冲激光光谱方法。讨论了系统中耦合透镜组对光谱测量和光纤色散角对条纹图像的影响,论述了ps级时间分辨超快高能脉冲激光光谱的作用。随着条纹管制造技术的飞速发展,该方法可用于fs级激光光谱的测量。     

Impact of spectral filtering on a weak breathing laser based on AS-Yb-PBGF with large net normal dispersion cavity

We have investigated numerically the effects of the spectral filtering on the temporal and spectral properties of the pulse with large net normal cavity dispersion in a weak breathing passively mode-locked ring laser based on all-solid Yb-doped photonic bandgap fiber (AS-Yb-PBGF), which gives the laser gain and anomalous dispersion simultaneously. The specific range of spectral filter bandwidth is indispensable for obtaining high-peak-power pulse in a given highly chirped pulse laser system under a fixed pump level. The shortening of the pulse durations and the shaving of the sharp peaks at the steep edges of the spectrum by the spectral filter are demonstrated. Moreover, the advantage of the weak breathing fiber laser by introducing the AS-Yb-PBGF for scaling up the peak power and shortening the pulse width is investigated, and the effect of third-order dispersion induced by AS-Yb-PBGF on the pulse shape is also discussed.     

Comparison of pulse evolutions in low and ultra-large anomalous dispersion mode-locked fiber lasers

We have investigated and compared the pulse evolutions in low and ultra-large anomalous dispersion erbium-doped fiber lasers mode-locked by the nonlinear polarization rotation technique. Two lasers deliver the pulses that exhibit quite distinct characteristics such as pulse duration, spectral width, and spectral sidebands. Experimental observations show that the spectral width decreases from several nanometers to less than one nanometer whereas pulse duration extends about three times by changing the cavity dispersion from −0.03 to −15.50 ps². The solitons in ultra-large anomalous fiber laser show dips in the optical spectrum, which is quite distinct from that of conventional solitons observed in low anomalous regime.     

Adjustable dispersion compensating in one dimensional coupled resonator planar optical waveguides

In this paper, the optical properties in finite size one dimensional coupled resonator optical waveguide are investigated. The large dependence of the group velocity, dispersion parameter and its higher order slope such as transmission group delay, third order dispersion and intrinsic waveguide induced loss have been studied. By engineering the optical contrast ratio of the medium by using some accessible and compatible materials, according to the equivalent layers theory, the above mentioned parameters can either be adjusted or enhanced dramatically, according to the configuration of the optical networks and users’ requirements. Also, by setting proper choice of the optical contrast ratio, super flattening of the transmittance group delay, third order dispersion spectrum and reduced intrinsic waveguide induced loss can be realized. Our results show the potential applications of the device for preventing the satellite pulse creating and transmitting pulse information distortion in multichannel lightwave systems.     

GaP波导型发射器产生频率可调谐太赫兹脉冲

报道了利用脉宽可调的光子晶体光纤飞秒激光放大器抽运矩形波导结构的GaP晶体太赫兹(THz) 发射器产生频率可调谐的超快THz脉冲.非线性晶体中光整流过程产生的THz辐射频率随抽运光脉冲宽度而 变化. GaP波导THz发射器可通过波导的几何尺寸来控制色散,以达到增加有效作用长度和提高输出功率的目的. 不同横截面尺寸的波导型发射器的THz辐射峰值频率随相位匹配条件的改变而改变,加以脉宽调节技术, 可以在大频谱范围获得频谱精细可调的THz脉冲.实验中在1 mm×0.7 mm的波导型THz发射器中获得了 频率可调谐的THz脉冲.提出实现THz辐射频率大范围调谐的GaP波导型阵列发射器的实施方案.     

高非线性光纤正常色散区产生超连续谱的数值研究

基于广义非线性薛定谔方程,通过数值计算对高非线性光纤正常色散区产生超连续谱进行了研究.结果表明,抽运脉冲的峰值功率、脉冲宽度以及脉冲初始啁啾对该光纤正常色散区超连续谱的形成有极其重要的影响;在高非线性光纤正常色散区产生超连续谱的过程中,三、四阶群速度色散甚至更高阶群速度色散对超连续谱的影响完全可以忽略,但与其他高非线性效应相比,自陡峭效应对超连续谱产生的影响更为明显.高功率超短光脉冲在高非线性光纤正常色散区,得到了没有泵浦成份残余、－20 dB谱宽达400 nm以上而频谱强度起伏小于10 dB的超宽而平坦超连续谱.     

Investigation of all-optical analog-to-digital quantization using a chalcogenide waveguide: A step towards on-chip analog-to-digital conversion

We have investigated all-optical analog-to-digital quantization by broadening the pulse spectrum in a chalcogenide (As₂S₃) waveguide and subsequently slicing the measured spectrum using an array of filters. Pulse spectral broadening was measured for 8 different power levels in a 6 cm long As₂S₃ waveguide and used to analyze an 8-level all-optical quantization scheme employing filters with full-width at half-maximum (FWHM) bandwidth of 2 nm. A supercontinuum spectrum with −15 dB spectral width up to 324 nm was observed experimentally at large powers. This large spectral broadening, combined with filtering using a 128 channel arrayed waveguide grating (AWG) with 2 nm filter spacing, has the potential for all-optical quantization with 7-bit resolution. In order to encode the quantized signal we propose an encoder scheme which can be implemented using optical Exclusive-OR gates. Demonstrating all-optical quantization using a planar waveguide is an important step towards realizing all-optical A/D conversion on a chip.     

螺旋波导压缩频率调制脉冲的初步研究

利用螺旋波导对频率调制脉冲进行压缩可大幅度提高脉冲峰值功率。利用所编Matlab程序对螺旋波导的色散特性进行了计算和分析,获得了波纹幅度和纵向周期长度等结构参数对其色散特性的影响规律;给出了脉冲功率压缩比的计算公式,对不同脉宽和频带宽度、不同频率调制形式的微波脉冲通过螺旋波导后的功率压缩比进行了计算和分析。计算表明:脉冲的频率调制形式对功率压缩比影响较大;相同频率调制形式下,脉冲长度越长,工作频带越宽,功率压缩比越高。为了获得尽可能高的功率压缩比,需对脉冲的频率变化方式进行调节,使其与螺旋波导色散特性匹配。同时还需要在高的功率压缩比和高的压缩效率之间做出权衡。计算得到,当注入脉冲的脉宽为40ns、工作频带为8.8~9.5GHz、频率调制形式与螺旋波导色散特性匹配时,功率压缩比达到了15,压缩效率约为40%。     

Effect of dark soliton on the spectral evolution of bright soliton in a silicon-on-insulator waveguide

The spectral evolution of bright soliton in a silicon-on-insulator optical waveguide is numerically simulated using the split-step Fourier method. The power and input chirp of the dark soliton and the second-order dispersion are varied to investigate the effect of dark soliton on the spectrum of bright soliton. The simulations prove that the dark soliton modifies the spectral shape of the bright soliton. Further, the variation in the power of dark soliton affects the splitting of bright soliton. Furthermore, the chirped dark soliton can improve the spectral width and flatness. The variation in the dispersion of dark soliton modifies the phase matching of the bright soliton and the dispersive wave emission, thereby affecting the spectral evolution.     

用变分法研究高阶色散和五阶非线性对高斯脉冲在光纤中传输特性的影响

从修正的非线性薛定谔方程出发,采用变分法,导出了在高阶色散和五阶非线性共同作用情况下高斯型脉冲参量随传输距离的演化方程组;求出了振幅与脉宽、频率与啁啾、脉宽与啁啾之间的三个重要约束关系;并进一步得出了脉宽随传输距离演化的解析解和脉冲中心位置随传输距离的演化规律;描绘了高阶色散和五阶非线性下,脉宽随传输距离演化的图形.结果表明:光纤中的高阶色散和五阶非线性都会影响高斯型脉冲各个参量的演化,但脉宽和振幅间的绝热关系并未改变.高阶色散使高斯型脉冲的脉宽展宽,五阶非线性使高斯型脉冲的脉宽压缩,它们对脉宽或初始啁啾的影响可以在一定程度上抵消,从而有可能使脉冲近似实现保形传输.     

High repetition rate all-normal dispersion Yb:fiber laser for minimum pulses

Simulation and experimental results for high repetition rate all-normal dispersion Yb:fiber ring lasers are demonstrated for the cavity dispersion from 0.01 to 0.025 ps 2 .The simulation shows that the pulse spectrum has the potential to reach>30 nm for the dispersion of 0.014 ps 2 under practical pump power. This potential is proved by the experiment.Maximum spectral width of 30 nm is achieved at the repetition rate of 285 MHz under the 850-mW pump power.Average output power is 550 mW and dechirped pulse is 78 fs.