Simulation investigation on supercontinuum generation and noise characteristics in the normal dispersion photonic crystal fiber with a flattened dispersion profile

The propagation of picosecond pulses in the normal dispersion photonic crystal fiber(PCF) with a flattened dispersion profile is numerically investigated.The characteristics of the amplitude and phase noise in the supercontinuum generation(SCG) are also analyzed through the coherent sliced supercontinuum(SC).The effects of self-phase modulation(SPM) and four-wave mixing(FWM) on broadening of the pulse spectrum are presented,and the best amplitude and phase noise performance with a specific fiber length is o...     

Design of optimum supercontinuum spectrum generation in a dispersion decreasing fiber

To facilitate the efficient support of quality-of-service(Qo S)for promising free-space optical(FSO)communication systems,it is essential to model and analyze FSO channels in terms of delay Qo S.However,most existing works focus on the average capacity and outage capacity for FSO,which are not enough to characterize the effective transmission data rate when delay-sensitive service is applied.In this paper,the effective capacity of FSO communication systems under statistical Qo S provisioning constraints is investigated to meet heterogeneous traffic demands.A novel closed-form expression for effective capacity is derived under the combined effects of atmospheric turbulence conditions,pointing errors,beam widths,detector sizes and Qo S exponents.The obtained results reveal the effects of some significant parameters on effective capacity,which can be used for the design of FSO systems carrying a wide range of services with diverse Qo S requirements.     

Spectrally Sliced Pulse Source Based on Supercontinuum Generation in Dispersion-Flattened Photonic Crystal Fiber

Designed is dispersion-flattened photonic crystal fiber（PCF） with small normal dispersion for generating flat wideband supercontinuum （SC）, and demonstrated is spectrally sliced pulse source which utilizes supereontinuum generated in dispersion-flattened photonic crystal fiber. The results show that the fiber characterized by flattened dispersion with small normal dispersion is suitable for flat wideband supercontinuum generation. In the process of spectral broadening, self-phase modulation plays a dominant role. By filtering the supercontinuum, multi-wavelength pulses can be obtained over a wide spectral range.     

基于微结构光纤的10 GHz超过1100信道的平坦超连续谱光源

报道了一种基于微结构光纤的宽带、平坦超连续谱(SC)光源。利用锁模半导体激光器产生的1.6ps,重复率为10GHz的光脉冲,通过一段80m的色散平坦高非线性微结构光纤(HNL-MF),在1.55μm波长区域产生了谱宽超过100nm的平坦超连续谱。实验中采用的微结构光纤的非线性系数约为11W-1·km-1。光纤具有小的正常色散和平坦的色散特性,在1550nm波长处,光纤的色散值约为-0.58ps·nm-1·km-1,而在1500～1650nm波长范围内,光纤的色散值变化小于1.5ps·nm-1·km-1。实验中获得的宽带、平坦超连续谱在1503～1593nm宽达90nm的波长范围内,具有±2.5dB的平坦度。该宽带、平坦超连续谱能同时提供波长间隔为10GHz,超过1100路的多波长载波信道。通过对光谱滤波,获得了速率为10Gbit/s的多波长脉冲序列。这样的超连续谱光源在波分复用(WDM)光通信系统、光波长变换等方面都有重要的应用。     

Supercontinuum Generation in Normal-dispersion Photonic Crystal Fiber Using Picosecond Pulse

Studied is the Super-continuum （SC） generation of a normal-dispersion photonic crystal fiber （PCF） using picosecond pulse excitation. In experimental analyses, a 237 nm broadband infrared continuum was generated pumped at 1 550 nm（normal dispersion regime） by 1.6 ps pulses from an erbium-doped fiber laser. In addition, we conduct the numerical analyses of SC based on generalized nonlinear Schr dionger equation. The results have been applied to investigate the dominant physical processes underlie the generation - of SC. We conclude that dispersion, self-phase modulation （SPM）, four-wave-mixing （FWM） and Raman scattering are determinants of SC generation rather than fission of soliton in normal-dispersion PCF.     

Highly nonlinear bismuth-oxide fiber for supercontinuum generation and femtosecond pulse compression

Highly nonlinear normally dispersive bismuth-oxide fiber shows promise for applications such as supercontinuum generation and femtosecond pulse compression in the telecommunications-wavelength range. To generate a wideband and flat supercontinuum spectrum, the balance between fiber nonlinearity and normal group velocity dispersion (GVD) is important. Highly nonlinear bismuth-oxide fiber exhibits a large nonlinearity due to the small effective area and nonlinear index of the host glass material. The fiber also has a relatively flat dispersion profile over a large wavelength range. Utilizing these features, we generate a smooth unstructured supercontinuum between 1200 and 1800 nm. This supercontinuum is passed through a grating pair, and pulses, originally of 150-fs length, are compressed to 25 fs.     

光纤中超连续谱产生机理研究

从非线性薛定谔方程出发,分析了自相位调制(SPM)和群速度色散(GVD)效应对超连续(SC)谱的贡献。利用主动锁模光纤激光器作为泵浦光源。对色散位移光纤(DSF)中的SC谱展宽进行了实验研究。理论和实验结果表明,光纤中,SC谱的产生主要是SPM和GVD共同作用的结果：对于皮秒泵浦脉冲和常规光纤,仅考虑SPM和GVD效应,就可以较精确地描述光纤中SC谱的产生过程。     

基于超连续谱产生的波长转换实验研究

本文对基于超连续谱产生的波长转换进行了实验研究。实验中首先搭建了主动锁模掺铒光纤激光器,然后将其产生的脉冲放大后注入色散位移光纤,利用双通结构获得了超连续光谱,最后用光纤光栅滤波实现了波长转换。实验得到了宽度为80nm的超连续谱,用光纤光栅滤波得到了峰值功率为-37.27dBm,信噪比是26.83dB,脉冲宽度为3ns的转换脉冲。     

The dynamics of pulse compression in synchronously pumped fiberRaman lasers

Dynamical equations describing the amplification and propagation of an initial Stokes seed pulse in a synchronously pumped fiber Raman laser configuration are formulated, and analytic solutions are derived. A train of Stokes shifted pulses is produced. Their individual characteristics eventually evolve on successive round trips through the fiber into subpicosecond pulses having constant fluence and decreasing temporal duration. Raman pulse compression stops when it is counterbalanced by the effects of group velocity dispersion and phase modulation in the normal dispersion regime. Pulse breakup due to soliton formation can occur in the anomalous dispersion regime. Simple expressions for the rate of pulse compression, the steady-state pulse fluence, and the minimum steady-state pulse duration are obtained     

Investigation of wave breaking in the normal dispersion region of nano-structured photonic crystal fibers

The propagation of femtosecond laser pulses with wavelengths of 1550 nm, 1064 nm, 800 nm and 700 nm, respectively, which are in the normal dispersion region of the nano-structured photonic crystal fiber (N-PCF) with interesting broadband normal dispersion and highly nonlinear properties, is studied. For the effect of chirp variation mainly induced by group velocity dispersion (GVD) and self-phase modulation (SPM), after propagation over a short length, the wave breaking occurs. Namely, oscillatory structures are presented near pulse edges and sidelobes appear in the pulse spectrum. In the case of 800 nm, after the propagation of 20 mm, a super flat spectrum is obtained. The bandwidth of the super flat spectrum is associated with the dispersion length and the nonlinear length. By choosing N-PCF and laser pulse with appropriate parameters, a broadband super flat spectrum in a short length can be achieved.     

40GHz皮秒光脉冲序列光谱展宽的实验研究

实验采用具有较大正常色散值的高非线性光纤（HNLF）,应用脉冲啁啾补偿压缩技术的改进方案实现了40GHz、1．2ps光脉冲序列光谱的更大展宽。在该方案中,脉冲首先通过一定长度的HNLF,成为光谱展宽的线性正啁啾脉冲;然后经过相应长度的普通单模光纤（SMF）进行啁啾补偿压缩以重新提高峰值功率;最后进人第2段HNLF实现脉冲光谱的进一步展宽。实验结果表明,在使用相同长度HNLF（150m）和相同抽运脉冲输入条件下,改进方案10dB带宽增加了3．28nm,并且相干特性保持良好。实验表明,对于40GHz皮秒光脉冲序列,在其峰值功率受自身高重复频率限制不能被光功率放大器充分放大的情况下,该方案是实现脉冲光谱在此类HNLF中展宽的有效途径。     

Complete dispersion compensation for 400-fs pulse transmission over10-km fiber link using dispersion compensating fiber and spectral phaseequalizer

We have demonstrated essentially complete dispersion compensation for 400-fs pulses over a 10-km fiber link using dispersion compensating fiber and a programmable femtosecond pulse shaper functioning as a spectral phase equalizer. The pulse shaper impresses adjustable quadratic and cubic phases onto the spectrum and removes all the residual dispersion and dispersion slope in the dispersion compensated fiber link. Our work shows that the pulse shaper technique provides a powerful and convenient tool for programmable fiber dispersion compensation over broad optical bandwidth. This allows distortion-free femtosecond pulse transmission over a fiber link in excess of 10 km without requiring the exact trimming of the dispersion-compensating fiber     

High-speed picosecond optical pulse compression from gain-switched 1.3-µm distributed feedback-laser diode (DFB-LD) through highly dispersive single-mode fiber

Picosecond optical pulse compression characteristics of chirped pulses from gain-switched distributed feedback-laser diodes (DFB-LD) transmitting through highly dispersive media are studied theoretically and experimentally. It is clarified theoretically that gain-switched chirped pulses can be compressed to about a 0.7-time bandwidth product by normal dispersion of the dispersive media and that the optimum dispersion value to obtain a minimum compressed pulse is proportional to the square of original pulsewidth. Through a dispersion, shifted single-mode fiber with -48-ps/nm normal dispersion at a 1.3-μm wavelength, gain-switched 30-ps (FWHM) pulses from a directly modulated 1.3-μm DFB-LD at a 4.4-GHz repetition rate have been successfully compressed to 6.4-ps optical pulses with a 0.86-time bandwidth product. Experimental results agree with the theoretical analysis.     

Femtosecond soliton generation over a 32-nm wavelength range usinga dispersion-flattened dispersion-decreasing fiber

The compression characteristics at femtosecond durations are compared for dispersion-decreasing fibers (DDF's) constructed out of standard step index fibers and fibers designed to have low third-order dispersion (dispersion-flattened fibers). It is shown that the dispersion slope of a standard fiber causes the compressed pulse spectrum to vary substantially with wavelength. Furthermore, the peak of the compressed pulse spectrum can appear in a different wavelength band than the input pulse. Both of these problems are substantially reduced by using a dispersion-flattened DDF. The compression of 3-3.6-ps pulses to durations less than 180 fs was achieved between 1533-1565 nm at a repetition rate of 10 GHz. The shortest pulses obtained were 98 fs with peak-to-pedestal ratios in excess of 20 dB     

Experimental study of sideband generation in femtosecond fiberlasers

We present a thorough experimental investigation of the phenomenon of soliton resonance sideband generation in femtosecond fiber lasers. The dependence of the sideband wavelengths on the dispersion and pulse length is confirmed. Third order dispersion is found to play a significant role in determining the sideband spectrum. We show that the minimum pulse length obtained in a fiber laser is determined by the cavity dispersion and relate this to loss into the sidebands. We show how the sideband spectrum can be used as a diagnostic of the fiber parameters and of the formation of ultrashort pulses in the laser     

微结构光纤正常色散区飞秒激光脉冲传输光谱展宽的功率饱和效应

利用自制的微结构光纤进行了飞秒激光脉冲传输实验,输入激光脉冲的中心波长为800 nm,位于微结构光纤的正常色散区。随着输入激光脉冲的平均功率从220 mW逐渐增大到300 mW,输出光谱同时向长波和短波方向展宽,光谱中的反斯托克斯线对应的能量逐渐占据主导地位。平均功率达到280 mW时,光谱的展宽范围不再增大,显示出了一种功率饱和效应。在微结构光纤的正常色散区实现了波长从560~960 nm的20 dB展宽谱。     

C+L波段掺铒光纤被动锁模激光器

提出并证明了一种宽光谱被动锁模掺铒光纤激光器,为光学频率梳和光纤飞秒脉冲的产生奠定了基础。该激光器基于非线性偏振旋转的锁模机理,同时在大的正常色散区合理地将C波段和L波段掺铒光纤结合,确保激光器具有C+L波段的增益谱覆盖。当泵浦功率为350mW时,脉冲稳定的以基频4.32MHz运转,3dB带宽为60nm,20dB覆盖了1522~1630nm,实现了增益带宽内光谱的完全覆盖。这种利用增益拼接加宽光谱的方法可以有效避免光谱成分的非线性相位噪声,并且有利于进一步压窄脉冲。     

Generation of pedestal-free 22-fs ultrashort pulse using highly nonlinear fiber and reverse-dispersion fiber

We present an all-fiber system for generating pedestal-free 22-fs ultrashort pulses with a single-peak spectrum. High-power Raman soliton pulses and a normally dispersive highly nonlinear fiber are used to generate a smooth, broadened single-peak spectrum. Then, the higher order dispersion is compensated for using a hybrid fiber composed of a reverse-dispersion fiber and a standard single-mode fiber, which allows pedestal-free ultrashort pulses to be successfully generated. To our knowledge, this is the first demonstration of pedestal-free 20-fs-class ultrashort pulse generation without spectral distortion using an all-fiber configuration.     

Generation of bound states of three ultrashort pulses with a passively mode-locked high-power Yb-doped double-clad fiber laser

We report the generation of high-power ultrashort bound states of three pulses in an ytterbium-doped double-clad fiber laser. The laser is mode-locked through nonlinear polarization rotation technique in a unidirectional cavity configuration. A pair of diffraction grating is incorporated in the cavity to compensate for the normal dispersion of the fiber. The laser generates chirped bound states of three pulses with either equal or different time separations, with more than 500-pJ energy per pulse. These pulses are subsequently compressed to 100 fs with a compression factor of more than 40.     

一种新型的高功率双波长自相似抛物线脉冲激光器

基于正色散单模光纤、掺Yb3+增益光纤和多模光纤光栅,提出了一种可调高功率双波长自相似抛物线脉冲激光器。采用非线性薛定谔方程描述双波长自相似抛物线脉冲的传输和演化过程,并利用分步傅里叶方法进行数值模拟。输入脉冲在正色散单模光纤与掺镱增益光纤中产生自相似抛物线脉冲,多模光纤布拉格光栅对激光器进行双波长选择,通过调节偏振控制器实现双波长稳定运行。数值模拟分析结果表明该激光器的运行是可行且有效的。