双包层大模场面积保偏掺镱光子晶体光纤研究

采用改进的化学气相沉积法和溶液掺杂法制备出掺镱石英光纤预制棒,以该预制棒为有源纤芯制备芯区直径约为30μm的双包层保偏掺镱光子晶体光纤.模拟计算得到该保偏光纤的模场面积约232μm2,双折射系数B为5×10-5.利用该光纤分别进行了脉冲激光和连续激光的放大测试实验,在国内首次实现了高效率的飞秒激光放大,2 m长的光子晶体光纤可得到1.64 W的激光输出,激光放大斜率效率为49.8%.同时5 m长的光纤还能够实现8.12 W的连续激光放大输出,斜率效率达到55.9%,具有较高的斜率效率.此外,该光纤消光比约10 dB,具有良好的保偏特性.     

Multiwavelength fiber laser based on a photonic crystal fiber loop mirror with cooperative Rayleigh scattering

In this work, a multiwavelength fiber Raman laser based on a highly birefringent photonic crystal fiber loop mirror is presented. A laser resonator is formed when the Raman amplification with cooperative Rayleigh scattering in a dispersion-compensating fiber is used as a distributed mirror and combined with a photonic crystal fiber loop mirror filtering structure. Stable multiwavelength lasing at room temperature is achieved due to the low temperature sensitivity of the highly birefringent photonic crystal fiber.     

Stable SOA-based multi-wavelength fiber ring laser using Sagnac loop mirror incorporating a high-birefringence photonic crystal fiber

Multi-wavelength fiber laser using semiconductor optical amplifier (SOA) and Sagnac loop mirror (SLM) incorporating a newly designed high-birefringence photonic crystal fiber (HB-PCF) is experimentally demonstrated. The modal birefringence of the fabricated HB-PCF is estimated to be 1.1 × 10⁻³. Mainly, by adjusting a polarization controller in the fiber ring laser, the proposed fiber laser can operate at six lasing wavelengths with 2.7 nm intervals, the signal-to-noise ratio (SNR) of around 30 dB. The output power stability is 0.8 dB. In addition, we obtained near-perfect temperature independence in our multi-wavelength fiber laser system. The temperature dependence of the SLM is around 3 pm/°C.     

72-kW high-peak-power linearly-polarized single-mode pulsed fiber laser with 80 kHz repetition rate and 4.5 ns duration

We reported a 26 W linearly polarized single-mode Yb-doped photonic crystal fiber amplifier, working at 80 kHz repetition rate with 4.5 ns duration, corresponding 72 kW peak power. Using a acousto-optic Q-switched Nd:YVO₄ laser as the seed source, the 26 W average power of 1064 nm laser was obtained at a repetition rate of 80 kHz from a Yb-doped photonic crystal fiber amplifier, with 4.5 ns duration, polarization extinction ratio 11 dB and M ² < 1.2.     

激光泵浦碲化物产生中红外超连续谱数值模拟

对2 m波段脉冲激光泵浦碲化物光子晶体光纤产生中红外超连续谱进行了数值研究。通过材料的拉曼增益谱间接求得了对应的拉曼响应函数;由光子晶体光纤的材料折射率和波导结构,通过COMSOL软件获得了碲化物光子晶体光纤中基模等效折射率,计算了相应的色散曲线和限制损耗 ;利用自适应的分步傅里叶算法,模拟了中心波长为1.96m、峰值功率为20 kW的50 fs脉冲光泵浦碲化物光子晶体光纤时超连续谱的产生,当光纤长度为6 cm时,产生的中红外超连续谱波长范围为1.0~4.5 m。     

光子晶体微腔中高偏振单偶极模的研究

三角晶格排列的光子晶体微腔中的偶极模式是简并的,通过改变其晶格的对称性可以消除模式简并.晶格的整体形变破坏了晶格对称性从而影响光场的分布,同时还改变了电磁场的偏振分布.晶格整体形变使得简并的偶极模式分离成x极和y极偶极模式.通过计算分析发现分离后的模式具有良好的偏振特性,从而为实现单偏振光子晶体激光器提供了一种很好的途径.文中针对光子晶体薄板结构的微腔,主要计算了偶极模中x极偶极模式在不同拉伸时以及不同填充因子情况下的Q值,并分别计算了x关键词： 光子晶体 偶极模 品质因子 偏振度     

Radially polarized and passively Q-switched fiber laser

We report, for the first time to our knowledge, a radially polarized and passively Q-switched Yb-doped fiber laser. By using a Cr(4+):YAG crystal as a saturable absorber and a photonic crystal grating as a polarization mirror, a radially polarized pulse is produced, which has 202 W of peak power, 75 ns duration, and ~92% polarization purity at a 56.6 kHz repetition rate. The Q-switched pulse with radial polarization from the fiber laser would facilitate numerous applications.     

2D FDTD simulation of low loss small angle bend and Y branch configurations in a photonic crystal waveguide layout with a Mach–Zehnder device design configuration

A technique to produce low loss small angle bends in photonic crystal waveguides is presented. The technique consists of bridging parallel input and output waveguide segments with an inclined waveguide region of the same basic design that has a lateral dielectric shift. Results are presented for waveguides produced by enlarging the silicon gap along the central line, separating air holes in a square array photonic crystal for the TE polarization and an operating wavelength of λ_o = 1.55 μm. This low loss waveguide bending technique is applied to the design of Y branch and Mach–Zehnder photonic crystal structures. Simulation of the performance of the dielectric structures is achieved using 2-D FDTD, similar results are anticipated when applied to 3-D waveguide configurations and for other photonic crystal layouts.     

空气包层大模场面积掺镱光子晶体光纤研究

采用改进的化学气相沉积法和气相液相混合掺杂技术制备大芯径掺镱石英光纤预制棒, 以此作为有源纤芯制备了纤芯直径约90 μm的掺镱双包层光子晶体光纤, 纤芯组分为镱铝磷共掺.双包层光子晶体光纤的模场面积约1330 μm², 纤芯数值孔径0.065,包层数值孔径0.5.首次实现了国产掺镱光子晶体光纤的高功率高效率激光输出, 1 m长的光子晶体光纤激光器实现102 W 激光输出,斜率效率76%.     

Efficient input and output fiber coupling to a photonic crystal waveguide

The efficiency of evanescent coupling between a silica optical fiber taper and a silicon photonic crystal waveguide is studied. A high-reflectivity mirror on the end of the photonic crystal waveguide is used to recollect, in the backward-propagating fiber mode, the optical power that is initially coupled into the photonic crystal waveguide. An outcoupled power in the backward-propagating fiber mode of 88% of the input power is measured, corresponding to a lower bound on the coupler efficiency of 94%.     

Temperature tuning of polarization mode dispersion in single-core and two-core photonic liquid crystal fibers

In this paper we present numerical and experimental results of propagation and polarization properties of the photonic liquid crystal fibers (PLCFs) in which only selected micro holes were filled with nematic liquid crystal (LC) guest materials. As a host photonic crystal fiber (PCF) structure, we used a commercially available highly birefringent PCF (Blazephotonics, UK). A tunable laser operated at infrared has powered the PLCFs under investigation infiltrated by the 1550 nematic LC synthesized at the Military University of Technology. Temperature induced changes of the polarization mode dispersion (PMD) as well switching between fundamental and higher order modes and also single-core and two-core propagation were successfully demonstrated.     

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.     

偶极子位置及偏振对激发光子晶体H1微腔的影响

光子晶体微腔和量子点的集成是实现量子信息处理非常具有潜力的平台之一,利用微腔和量子点的耦合可以制备纠缠光子对,实现对量子态的操控.因为光子晶体微腔具有品质因子高、模场体积小等优点,可以极大地增强光与物质之间的相互作用,从而易于实现量子态在不同物理体系之间的转换.通过单量子点和光子晶体H1微腔的耦合可以产生纠缠光子对,因为H1微腔具有简并的、模式偏振正交的基态模式.通常微腔模式的激发随着量子点在微腔中的位置变化而改变,本文用时域有限差分方法研究了偶极子光源的位置及偏振对激发光子晶体H1微腔模式的影响.结果表明:通过改变偶极子光源位置可以选择性地激发H1微腔简并模式中的一个;具有某一偏振的偶极子光源只能激发相应偏振的微腔模式;模式激发强度的大小也是由偶极子光源在微腔中的位置决定的.鉴于目前量子点在微腔中的位置尚不能精确控制,所以微腔模式受激发光源位置的影响的研究具有重要意义.     

Numerical Analysis of Highly Birefringent Photonic Crystal Fibers with Bragg Reflectors

We analyze theoretically the coupling properties of Bragg gratings written in highly birefringent photonic crystal fibers with doped core and show how they can be tuned by the parameters of a microstructured fiber. We apply the coupled mode theory combined with a fully vectorial mode solver based on the plane-wave method. The results indicate large differences in interaction with the grating for the two linearly polarized fundamental modes. We show fiber designs, which provide single-mode operation with high birefringence and at the same time a high coupling efficiency of the grating. Such features can be used in fiber sensors, fiber laser configurations or to introduce a polarization dependent feedback in a long external cavity system with a semiconductor laser.     

Design and fabrication of Gires�CTournois interferometers for?Yb-doped photonic crystal fiber laser system

A Gires?CTournois interferometer (GTI) with large dispersion compensation was designed and fabricated according to the requirement of the Yb-doped photonic crystal fiber laser system. The designed GTI can provide an average group delay dispersion (GDD) of ?1500 fs² and a high reflectance (>99.7%) from 1030 to 1050 nm. The Ion-assisted Deposition (IAD) technique was utilized to manufacture the mirror. Good agreement between the measured and designed results both for reflectance and GDD was achieved. The reflectance during 1030?C1050 nm was above 99.5% and the GDD ripple was less than ±300 fs². The GTI was used both in the intracavity dispersion compensation and extracavity pulse compression for the Yb-doped photonic crystal fiber laser system. A mode-locked soliton pulse with a 506-fs duration was recorded. An extracavity pulse compression test showed that the GTI had identical pulse compression capability as the conventional grating pairs while the energy loss was obviously reduced. Our results demonstrated that the HDM, which was able to provide quite a large amount of negative dispersion (???8×10⁴ fs²), could be an ideal alternative to replace the dispersive compensating grating pairs for the dispersion compensation of the Yb-doped photonic crystal fiber laser system.     

Optical surface modes of photonic crystals for dual-polarization waveguide

In this study, the design of a polarization-independent (dual-polarization) waveguide is presented by utilizing surface modes of photonic crystals. The waveguide structure operates in a frequency interval that is commonly shared by both transverse-electric (TE) and transverse-magnetic (TM) polarizations. The numerical calculations based on plane wave expansion and finite-difference time-domain methods are carried out to design and demonstrate a surface mode waveguide that provides confinement and guiding for both TE and TM modes. Once the relevant modes are properly excited, the high transmission efficiency of the photonic crystal surface waveguide is ensured. The demand to have polarization-insensitive devices makes our proposed design an important component for the photonic integrated circuit applications. Finally, we also propose a broadband surface mode photonic crystal waveguide with a bandwidth value of 28% for only TE polarization.     

非截面二维光子晶体排列矩形波导的全模式分析

在对周期性结构进行谐波分析的基础上，导出了非截面二维光子晶体排列矩形波导的本征值方程. 基于此方程，可以对该类光子晶体波导的所有可能模式进行分析. 分析认为，非截面二维光子晶体排列矩形波导内能存在的模式包括E_(y)，TE_y，H_(y)和TM_y模式；改变波导高度，可以实现E_(y)模式和H_(y)模式与其他模式通带的完全分离. 然而改变任一结构参数，都不能使E_(y)和H_(y)的各个模式通带，以及E_(y)1模式和H_(y)1模式的通带完全隔离. 波导单模工作的带宽由E_(y)1和E_(y)2模式的低端截止频率决定. 关键词： 波导 光子晶体 本征值方程 模式     

Well-confined Yb:GdVO4 laser waveguide formed by MeV C ion implantation

The planar waveguide in x-cut Yb:GdVO₄ crystal has been fabricated by 6.0 MeV carbon ion implantation with the fluence of 1 × 10¹⁴ ions/cm² at room temperature. The modes of the waveguide were measured by the prism-coupling method with the wavelength of 633 nm and 1539 nm, respectively. An enhanced ordinary refractive index region was formed with a width of about 4.0 μm beneath the sample surface to act as a waveguide structure. By performing a modal analysis on the observed transverse magnetic polarized modes, it was found that all the transverse magnetic polarized modes can be well-confined inside the waveguide. Strong Yb-related photoluminescence in Yb:GdVO₄ waveguide has been observed at room temperature, which reveals that it exhibits possible applications for integrated active photonic devices.     

Angular tuning of defect modes spectrum in the one-dimensional photonic crystal with liquid-crystal layer

A one-dimensional ZrO₂/SiO₂ photonic crystal with a 4-n -pentyl-4' -cyanobiphenyl (5CB) nematic defect layer was used to investigate the transmission spectra of light polarized parallel and perpendicular to the liquid-crystal director at different angles of incidence. The spectra of the photonic crystal were shown to split into four polarized components T_ij at oblique incidence. When the incident angle increased, the bandgap edges and the defect modes shifted towards short wavelengths, while the amplitudes of the defect modes increased for the transverse magnetic polarization and decreased for the transverse electric polarization. The observed discrepancy between the defect mode amplitudes in the center and near the edges of the photonic bandgap was found to be related to the radiation losses inside the defect layer of a non-ideal photonic crystal. The simulated transmission spectra obtained using recurrence relations and taking into account the decay of defect modes are in good agreement with the experimental data.     

Variational analysis of Er:Ti:LiNbO3 waveguide lasers based on Gaussian/two-half Gaussian mode field distribution

Starting with two dimensional, scalar wave equation, a variational equation was established for the fundamental TE and TM modes guided in Ti:LiNbO₃ waveguides on the basis of assuming a symmetric Gaussian mode field function in the width direction and two-half Gaussian trial functions in the depth direction. The controllable waveguide fabrication parameters, including channel width, diffusion temperature, initial Ti-strip thickness and diffusion time, dependent of fundamental mode size, effective pump area, coupling efficiency between pump and laser modes, and the coupling loss between a Ti:LiNbO₃ waveguide and a fiber were numerically calculated for Z-cut Er:Ti:LiNbO₃ channel waveguide lasers at three possible emission wavelengths 1532,1563 and 1576 nm and two possible pump wavelengths 1480 and 980 nm. The calculated results were compared with those of Gaussian/Hermite–Gaussian mode field distribution in detail.