Supercontinuum generation in the irregular point of hollow-core photonic crystal fiber

Broadband supercontinuums (SC) are generated by soliton self-frequency shift (SSFS) of hollow-core photonic crystal fiber (HC-PCF) in our laboratory. With the pump works at 810 nm when the pump power increase from 400 to 600 mW, the Raman Soliton shifts from 2089 to 2215 nm, the bandwidth of SC increases from 2213 to 2320 nm. The ultra-violet part of SC is below 180 nm, and the mid-infrared part of SC exceeds 2500 nm. Moreover, the influence of pump power on SC is also analyzed.     

Highly efficient Cherenkov radiation generation in the irregular point of hollow-core photonic crystal fiber

Highly efficient Cherenkov radiation(CR) is generated by the soliton self-frequency shift(SSFS) in the irregular point of a hollow-core photonic crystal fiber(HC-PCF) in our laboratory.The impacts of pump power and wavelength on the CR are investigated,and the corresponding nonlinear processes are discussed.When the average power of the 120 fs pump pulse increases from 500 mW to 700 mW,the Raman soliton shifts from 2210 nm to 2360 nm,the output power of the CR increases by 2.3 times,the maximum output power ratio of the CR at 539 nm to that of the residual pump is calculated to be 24.32:1,the width of the output optical spectrum at the visible wavelength broadens from 35 nm to 62 nm,and the conversion efficiency η of the CR in the experiment can be above 32%.     

飞秒脉冲在光子晶体光纤中的传输特性

基于广义非线性薛定谔方程,利用分步傅里叶法数值模拟了超高斯时间分布的飞秒脉冲在光子晶体光纤中的传输特性。结果表明：超高斯脉冲比高斯脉冲在更短距离内形成孤子衰变,而且出现比强孤子功率稍低的次峰,孤子自频移更显著;另外,三阶色散会导致脉冲波形及频谱不对称,出现精细结构,并且有形成孤子的趋势;脉冲内拉曼散射对脉冲有平滑作用;自陡改变了主峰与次峰之间的能量分配。     

光子晶体光纤超连续谱产生过程中色散波的孤子俘获研究

基于光子晶体光纤中脉冲演化遵循的非线性薛定谔方程, 用数值模拟的方法分别研究了飞秒脉冲在单零色散点和双零色散点光子晶体光纤中超连续谱的产生和色散波的孤子俘获现象. 结果表明: 与单零色散点光子晶体光纤相比, 双零色散点光子晶体光纤产生的超连续谱既包含了蓝移色散波, 又包含了红移色散波, 且当满足群速度匹配时, 孤子通过四波混频不仅能俘获蓝移色散波, 而且能俘获红移色散波, 从而产生新的俘获波频谱成分. 为了清楚地观察脉冲传输的时频特性, 通过模拟交叉相关频率分辨光学开关技术, 得到了孤子俘获色散波的演化过程. 关键词： 超连续谱 色散波 孤子俘获 光子晶体光纤     

飞秒光脉冲在光子晶体光纤中的非线性传输和超连续谱产生

采用分步傅里叶方法数值模拟了飞秒光脉冲在光子晶体光纤中非线性传输和超连续谱的产生. 计算和分析了高阶色散和非线性效应对超连续谱形状和带宽的影响. 结果表明在光子晶体光纤中产生了孤子自频移现象. 同时也发现脉冲内拉曼散射和自相位调制的联合作用导致了超连续谱中精细结构的出现. 另外，还发现高阶色散和初始光脉冲的峰值功率对超连续谱的带宽和平滑也有直接影响. 关键词： 光子晶体光纤 孤子自频移 超连续谱     

Broadband tunable Raman soliton self-frequency shift to mid-infrared band in a highly birefringent microstructure fiber

Raman soliton self-frequency shifted to mid-infrared band(λ 2 μm) has been achieved in an air-silica microstructure fiber(MF). The MF used in our experiment has an elliptical core with diameters of 1.08 and 2.48 μm for fast and slow axis. Numerical simulation shows that each fundamental orthogonal polarization mode has two wide-spaced λZDW and theλZDW pairs located at 701/2110 nm and 755/2498 nm along the fast and slow axis, respectively. Using 810-nm Ti:sapphire femtosecond laser as pump, when the output power varies from 0.3 to 0.5 W, the furthest red-shift Raman solitons in both fast and slow axis shift from near-infrared band to mid-infrared band, reaching as far as 2030 and 2261 nm. Also, midinfrared Raman solitons can always be generated for pump wavelength longer than 790 nm if output pump power reaches0.5 W. Specifically, with pump power at 0.5 W, the mid-infrared soliton in slow axis shifts from 2001 to 2261 nm when the pump changes from 790 nm to 810 nm. This means only a 20 nm change of pump results in 260 nm tunability of a mid-infrared soliton.     

Six-bit all-optical quantization using photonic crystal fiber with soliton self-frequency shift and pre-chirp spectral compression techniques

In this paper,we propose an optical quantization scheme for all-optical analog-to-digital conversion that facilitates photonics integration.A segment of 10-m photonic crystal fiber with a high nonlinear coefficient of 62.8 W 1/km is utilized to realize large scale soliton self-frequency shift relevant to the power of the sampled optical signal.Furthermore,a 100-m dispersion-increasing fiber is used as the spectral compression module for further resolution enhancement.Simulation results show that 317-nm maximum wavelength shift is realized with 1550-nm initial wavelength and 6-bit quantization resolution is obtained with a subsequent spectral compression process.     

Scaling of Yb-doped photonic crystal fiber to 200 μm core diameter for high beam quality laser output

The rare earth-doped active fibers not only have ten thousands of square-micron core-area but also deliver a laser with near-diffraction-limited beam quality. However, they have been studied little. In this paper, we design a 200-μm-corediameter Yb~(3+)-doped photonic crystal fiber with a large pitch in the air-hole cladding region. Simulations demonstrate that only fundamental mode(FM) with a mode field area(MFA) of ～ 28000 μm~2 can be amplified and propagated at the gain saturation, and the beam quality M~2 is about 1.5. It is predicted that almost 105 m J single-pulse energy is available from such a 1.5-meter-length fiber.     

光子晶体光纤中高效的反斯托克斯信号产生

基于四波混频的反斯托克斯变换, 被广泛应用于短波辐射高分辨率成像以及直接激发分子的电子跃迁等方面. 为了实现更加高效的反斯托克斯变换, 利用中心波长为810 nm脉冲宽度为120 fs的钛蓝宝石(Ti: sapphire)飞秒激光器作为抽运光源, 在长度为0.5 m和3 m的光子晶体光纤中分别实现了高阶模和基膜的简并四波混频. 实验中, 采用的光子晶体光纤的零色散波长在820 nm附近. 在基模相位匹配条件下, 在560 nm附近实现了高效地反斯托克斯信号的产生, 反斯托克斯信号与残余抽运信号的最大功率比为33:1; 反斯托克斯信号和斯托克斯信号的最大功率比25:1; 反斯托克斯信号最大功率转换效率P_a/P_p0为34%. 抽运波长从790 nm逐渐增加到810 nm过程中, 在长为3 m的光子晶体光纤中相位从不匹配状态转化为高阶模匹配状态后, 再转化为基模匹配状态. 通过实验研究得出了相位匹配程度随抽运功率、波长和光纤长度的变化规律, 同时分析了造成理论计算与实验结果存在差异的主要因素. 本文为研究在光子晶体光纤基模中实现相位匹配和产生高效反斯托克斯信号提供了理论和实验依据.     

Generation of mid-infrared supercontinuum by designing circular photonic crystal fiber

A circular photonic crystal fiber (C-PCF) based on As₂Se₃ is designed, which has three zero dispersion wavelengths and flat dispersion. Using this fiber, a wide mid-infrared supercontinuum (MIR-SC) can be generated by launching a femtosecond pulse in the first anomalous dispersion region. The simulation results show that the MIR-SC is formed by soliton self-frequency shift and direct soliton spectrum tunneling on the long wavelength side and self-phase modulation, soliton fission on the short wavelength side. Further, optical shocking and four-wave mixing (FWM) are not conducive to the long-wavelength extension of MIR-SC, while the number and intensity of fundamental solitons have a greater effect on the short-wavelength extension of MIR-SC. The generation of optical shocking waves, FWM waves and fundamental solitons can be obviously affected by changing the fiber length and input pulse parameters, so that the spectrum range and flatness can be adjusted with great freedom. Finally, under the conditions of 4000 W pulse peak power, 30 fs pulse width, 47 mm fiber length, and 0 initial chirp, a wide MIR-SC with a coverage range of 2.535 μm-16.6 μm is obtained. These numerical results are encouraging because they demonstrate that the spread of MIR-SC towards the red and blue ends can be manipulated by choosing the appropriate incident pulse and designing optimized fiber parameters, which contributes to applications in such diverse areas as spectroscopy, metrology and tomography.     

Correlation between the birefringence and the structural parameter in photonic crystal fiber

In order to simply design a highly birefringent photonic crystal fiber (HB-PCF), we numerically simulated the correlation between the birefringence and the structural parameter of photonic crystal fiber with square-lattice or triangle-lattice air-holes by using multipole method. It is shown that the phase birefringence B(λ) and the group birefringence G(λ) can be modulated by the structure parameter of normalized wavelength λ/Λ and the relative air-hole size d/Λ. Numerical results show very high phase and group birefringence of the order of 10⁻². The group birefringence becomes negative in the region where phase birefringence increases with an increase in normalized wavelength that does not appear in traditional highly birefringent fibers.     

Broad and ultra-flattened supercontinuum generation in the visible wavelengths based on the fundamental mode of photonic crystal fibre with central holes

By coupling a train of femtosecond pulses with 100 fs pulse width at a repetition rate of 76 MHz generated by a mode-locked Ti:sapphire laser into the fundamental mode of photonic crystal fibre(PCF) with central holes fabricated through extracting air from the central hole,the broad and ultra-flattened supercontinuum(SC) in the visible wavelengths is generated.When the fundamental mode experiences an anomalous dispersion regime,three phases in the SC generation process are primarily presented.The SC generation(SCG) in the wavelength range from 470 nm to 805 nm does not emerge significant ripples due to a higher pump peak power and the corresponding mode fields at different wavelengths are observed using Bragg gratings.The relative intensity fluctuations of output spectrum in the wavelength ranges of 530 nm to 640 nm and 543 nm to 590 nm are only 0.028 and 0.0071,respectively.     

光子晶体光纤耦合器中的标量调制不稳定性

从光纤耦合器的耦合模方程出发,用偶奇超模对其进行重写,讨论了当输入条件使奇偶超模其中之一被单独激发时,在光子晶体光纤耦合器中的调制不稳定性.结果表明：光子晶体光纤耦合器中在正常和反常色散区均存在调制不稳定性,并且调制不稳定性与三阶色散项无关、与四阶色散项有关,给出了增益谱在不同色散区随输入功率的变化关系;当满足一定条件时,在光子晶体光纤耦合器中传播的准连续波可以分解成脉冲序列,由此可以分离和提取超短脉冲. 关键词： 光子晶体光纤耦合器 偶次超模 奇次超模 标量调制不稳定性     

光子晶体光纤包层可见光及红外宽带色散波产生

对光子晶体光纤包层3个空气孔之间节区的传光特性进行了分析, 对比了纤芯与包层节区传光的模场面积、非线性系数及色散特性, 得到光子晶体光纤包层节区具有小芯、高非线性的特点.在包层空气孔较大的情况下, 得到了双零色散曲线.根据色散曲线, 分析了色散波产生的相位匹配特性, 得到了色散波中心波长随抽运波长及功率的变化规律.制备出了所设计的光子晶体光纤, 实验得到了在可见光及红外大于300 nm的宽带色散波, 并给出了色散波随抽运波长及功率的变化规律.实验和理论分析结果一致, 为波长变换及超连续宽带光源的研究奠定了基础. 关键词： 光子晶体光纤 色散波 相位匹配 非线性     

双折射光子晶体光纤中基于孤子分裂的超连续光谱产生

利用亚纳焦量级、脉冲宽度为100 fs的激光脉冲在双折射光子晶体光纤中获得了450—1050 nm 的超连续光谱,且超连续光谱具有明显的分立峰状结构.分析了光谱中分立峰状结构产生的物理机制,抽运光波长处于接近零色散波长的反常色散区,形成高阶光孤子,由于高阶非线性和高阶色散的影响,高阶孤子分裂成多个基孤子,使初始光谱上演化出红移的光孤子成分和蓝移的色散波成分.理论模拟了飞秒激光脉冲在光纤中的色散特性和传输特性,较好地解释了实验结果. 关键词： 光子晶体光纤 超连续光谱产生 孤子分裂 脉冲俘获     

基于光子晶体光纤中多抽运四波混频效应的新型光层组播技术

光层组播是未来透明光子网络中一项重要的全光信号处理功能,提出并实验证实了一种基于色散平坦高非线性光子晶体光纤中多抽运四波混频效应的光层组播方法,将一束信号光与两束连续抽运光同时输入高非线性光子晶体光纤中,通过多抽运四波混频过程,产生四个携带该数据信息的闲频光,从而实现了单一信号的四信道光层组播功能,组播信道波长在35.2 nm范围可调谐,组播信道最大间距4.4 THz,最大转换效率-22 dB,最优Q因子为5.3,该方法的特点在于基于光纤中的四波混频效应工作,因而具有对调制格式和比特率透明的 关键词： 光层组播 多抽运四波混频 光子晶体光纤     

Theoretical simulation of a novel birefringent photonic crystal fiber with surface plasmon resonance around 1300 nm

In this paper, a novel birefringent photonic crystal fiber(PCF) with the silver-coated and liquid-filled air-holes along the vertical plane is designed. Simulation results show that the thickness of silver layer, the sizes of holes, and the refractive index of liquid strongly strengthen the gaps between two polarized directions. The surface plasmon resonance peak along y axis can be up to 675.8 d B/cm at 1.33 μm. The proposed PCF has important application in polarization devices, such as filters and beam splitters.     

用阶跃有效折射率模型研究光子晶体光纤色散特性

在采用阶跃有效折射率模型研究光子晶体光纤的可行性方面，提出了将普通单模光纤、色散位移光纤、色散平坦光纤作为一定极限条件下的折射率引导型光子晶体光纤特例的观点.通过编程计算，并与文献报道的实验数据对比，表明应用本模型可以揭示光子晶体光纤所具有的奇异的色散机理.特别是应用本模型具有更快的计算速度.还用本模型分析了空气孔直径、周期及芯径对色散特性的影响. 关键词： 折射率引导型光子晶体光纤 阶跃有效折射率模型 色散     

Generation of a mid-infrared broadband polarized supercontinuum in As2Se3 photonic crystal fibers

A simplified structure of birefringent chalcogenide As 2 Se 3 photonic crystal fiber（PCF） is designed.Properties of birefringence,polarization extinction ratio,chromatic dispersion,nonlinear coefficient,and transmission are studied by using the multipole method,the finite-difference beam propagation method,and the adaptive split-step Fourier method.Considering that the zero dispersion wavelength of our proposed fiber is about 4 μm,we have analysed the mechanism of spectral broadening in PCFs with different pitches in detail,with femtosecond pulses at a wavelength of 4 μm as the pump pulses.Especially,mid-infrared broadband polarized supercontinuums are obtained in a 3-cm PCF with an optimal pitch of 2 μm.Their spectral width at 20 dB reaches up to 12 μm.In the birefringent PCF,we find that the supercontinuum generation changes with the pump alignment angle.Research results show that no coupling between eigenpolarization modes are observed at the maximum average power（i.e.,37 mW）,which indicates that the polarization state is well maintained.     

光子晶体光纤带隙及模场的一种综合模拟分析方法

提出直接由MATLAB读入光纤端面图实现复杂结构光子晶体光纤(PCF)模型的快速建立,并综合平面波法(PWM)和频域有限差分(FDFD)法,模拟分析带隙型光子晶体光纤(PBG-PCF)的带隙和模场分布.利用PWM计算得到了在PBG-PCF中传输的光波频率及模式有效折射率范围;基于FDFD法在给定波长及模式有效折射率范围情况下,模拟得到了PBG-PCF中可能存在的模场分布及其他特性.以市售的PBG-PCF为例,验证了数值模拟的正确性,随后系统地分析了结构参数(晶格结构、"原子"占有率、背景材料折射率及"原子 关键词： 光子晶体光纤(PCF) 光子带隙(PBG) 平面波法(PWM) 频域有限差分法(FDFD)