10 GHz超连续脉冲光子源的实验研究

利用增益开关(GS)DFB半导体激光器(LD)作初始抽运源,在4．2km左右的普通色散位移光纤(DSF)中获得了10GHz、120nm以上的超连续(SC)谱脉冲。实验研究了抽运光脉冲峰值功率和光纤零色散波长对SC谱宽度的影响,同时还利用0．4nm带宽的可调谐滤波器对从SC谱中滤出脉冲的特性进行了研究。     

光纤中超连续脉冲的频谱展宽

为了产生高重复频率的多波长短光脉冲,利用锁模掺铒光纤激光器作为抽运光源,对色散位移光纤中的超连续脉冲进行了实验研究,成功实现了输出脉冲的频谱展宽.实验也发现,制约这个实验结果的主要因素是光纤激光器的输出脉冲的稳定性不够和功率不高.     

Design and modelling of dispersion-engineered rib waveguide for ultra broadband mid-infrared supercontinuum generation

We report a dispersion-engineered As₂Se₃ chalcogenide glass rib waveguide structure for ultra broadband mid-infrared supercontinuum generation across molecular ‘fingerprint region’. The proposed rib waveguide structure offers non-linear coefficient as high as 18,250 W^?1 km^?1 at 2.5 μm. Supercontinuum spectrum spanning 2–15 μm, which not only covers the both atmospheric transparent windows (3–5 μm and 8–13 μm) in the mid-infrared domain but also covers the important molecular ‘fingerprint domain’, is obtained using only 4 mm-long rib waveguide structure. To the best of our knowledge, such broadband mid-infrared supercontinuum spectrum in As₂Se₃-based chalcogenide waveguide geometry is reported for the first time. The proposed design of rib waveguide has potential for robust, integrated and low-cost supercontinuum sources in various applications including frequency comb generation, chemical sensing, food quality control and early cancer diagnostics.     

Supercontinuum generation in quantum wells facilitated by electromagnetically induced transparency

In this paper, employing numerical simulation, we examine the possibility of generation of optical supercontinuum (SC) in a multiple quantum well (MQW) system facilitated by electromagnetically induced transparency. Within the transparency window created by a control laser beam in a MQW, another probe pulse experiences negligible loss and large optical non-linearity that has been exploited to obtain the optical SC. With 1.0 pico-second ‘sech’ probe pulses of 500 W peak power at wavelength 739.7 nm, the numerically simulated SC spectrum at the end of the 9.377 μm long MQW extends from 550 to 1000 nm. The spectrum is asymmetric, contains large number of oscillations which is attributed to the nonlinearity induced self-phase modulation and modulation instability. This investigation may lead to the fabrication of on-chip SC sources that can be easily integrated with other semiconductor devices.     

一种适合低阈值中红外超连续谱产生的新型微结构光纤

提出并设计了一种适合低阈值中红外超连续谱产生的新型微结构光纤.采用多极法对光纤的传输常数和模场分布进行计算.计算结果表明,光纤在中红外波段具有极高的非线性系数、平坦的色散曲线、极低的模式限制损耗以及良好的单模传输特性,在2.2 μm和3.32 μm处分别有一个零色散点.采用分步傅里叶的数值模拟方法,研究了光纤中超连续谱...     

1.8–13 μm supercontinuum generation by pumping at normal dispersion regime of As–Se–Te glass fiber

Mid-infrared (MIR) band supercontinuum (SC) light source has highly important application prospects in aerospace, biomedicine, MIR sensing, and pollutant monitoring. As–Se–Te glass has high nonlinear refractive index, wide MIR transmission range and weak crystallization ability. As₄₀Se₄₀Te₂₀ glass fiber is suitable for producing wide MIR–SC spectrum. In this study, purified As₄₀Se₄₀Te₂₀ glass was prepared and unclad and step-index fibers were drawn. An unclad As₄₀Se₄₀Te₂₀ glass fiber with minimum loss of 1.7 dB/m at 8.8 μm was obtained. By pumping the unclad fiber in the normal dispersion region at 5 μm, we recorded the broadest SC generation spectrum, which covered 1.8–13 μm with a 30 dB spectral flatness, from a fiber with 15 cm length. Besides, As₄₀Se₄₀Te₂₀/As₄₀Se₄₂Te₁₈ step-index fiber with minimum loss of 5.6 dB/m at 5 μm was drawn from isolation extruded preform. The step-index fiber was pumped in the normal dispersion region at 5 μm, and the SC spectrum, covering 2.1–11.2 μm with a 40 dB spectral flatness, was recorded from a fiber with 15 cm length. The SC spectrum, which was achieved by pumping the As₄₀Se₄₀Te₂₀ fiber, covered almost all the transparent range of material.     

Characteristics of filamentation in ZK7 glass by negatively chirped femtosecond laser pulses

The filamentation characteristics of femtosecond laser pulses in ZK7 glass are investigated experimentally as a function of initial negative chirps. It is found that the filament threshold power grows rapidly and the filament length extends over a long distance with increasing initial temporal chirps. The measurement of supercontinuum reveals that the plasma generation process within filamentation becomes weaker as the initial negative chirp increases, leading to a self-guiding long light channel dominated by Kerr nonlinearity. The interference of transverse rings in multifilamentation of the chirped laser pulses is observed as well. Analyses and discussions give an interpretation of this chirp-induced ionization-free filamentation. These results indicate that initial chirps will play a crucial role in the filament formation of ultrashort laser pulses in transparent media. Supported by the National Natural Science Foundation of China (Grant No. 60637020)     

基于超连续谱产生的光子晶体光纤的特性研究

采用多极法理论研究了光子晶体光纤的非线性和色散特性。数值模拟结果表明:保持孔直径与孔间距比值d/Λ不变,减小孔直径d;或者保持孔直径d不变,增大d/Λ,这两种方法都不仅可以显著提高光子晶体光纤的非线性,而且能够有效地将其零色散点λ0向短波长方向移动。光子晶体光纤的高非线性和灵活可调的色散特性为产生宽带、可见的超连续谱提供了前提条件。     

基于超连续谱的光阈值器的实验研究

光阈值器件能够抑制光码分多址(OCDMA)系统中多址干扰(MAI)噪声,增加用户数量。基于超连续谱(SC)的光阈值器件,对偏振态不敏感,而且结构简单,易于实现。为克服放大器放大倍数和高非线性光纤(HNLF)长度对SC阈值实验研究的限制,本文提出通过改变输入脉冲占空比来改变峰值功率的方法。在通信波长为1 550nm的OCDMA系统中,基于SC的阈值时,最佳阈值脉冲峰值功率为6.195W,所需带通滤波器中心波长为1 558nm,带宽为5nm。     

Generation of Supercontinuum and Spectrum Broadening in Holey Fibers Subjected to Radiation from Continuous Femtosecond Visible and Infrared Lasers

Supercontinuum generation in holey fibers manufactured at the University of Bath (Great Britain) and at the Institute of Radioengineering and Electronics of the Russian Academy of Sciences is produced through use of a Ti:sapphire femtosecond laser. Broadening of the radiation spectrum of a Cr:forsterite femtosecond laser ( = 1250 nm) is observed in these fiber samples. The present study is part of a program intended for the creation of an optical femtosecond synthesizer stabilized relative to a methane optical frequency standard ( = 3390 nm).