High sensitivity dual core photonic crystal fiber sensor for simultaneous detection of two samples

The optical control ability of photonic crystal fiber (PCF) is a distinctive property suitable for improving sensing and plasma performance. This article proposes a dual-core D-channel PCF sensor that can detect two samples simultaneously, which effectively solves the problems of coating difficulty and low wavelength sensitivity. The PCF has four layers of air holes, which dramatically reduces the optical fiber loss and is more conducive to the application of sensors in actual production. In addition, by introducing dual cores on the upper and lower sides of the central air hole, reducing the spacing between the core and the gold nanolayer, a stronger evanescent field can be generated in the cladding air hole. The optical fiber sensor can detect the refractive index of two samples simultaneously with a maximum sensitivity of 21300 nm/RIU. To the best of our knowledge, the sensitivity achieved in this work is the highest sensitivity with the dual sample synchronous detection sensors. The detection range of the refraction index is 1.35-1.41, and the resolution of the sensor is 4.695×10^-6. Overall, the sensor will be suitable for medical detection, organic chemical sensing, analyte detection, and other fields.     

基于闪锌矿晶体中受激电磁耦子散射产生可调谐太赫兹波的理论研究

基于受激电磁耦子散射原理,采用已报道的利用非线性光学参量振荡方法产生可调谐太赫兹波的实验条件作为理论分析的实验模型,以GaAs,GaP, InP,ZnTe晶体为代表,计算分析了在闪锌矿晶体中参量振荡产生太赫兹波的吸收、增益特性,对输出THz波的调谐特性给出了详尽分析.分析太赫兹波高效耦合输出的腔型结构,并与掺氧化镁铌酸锂晶体组成的太赫兹波参量振荡器做对比. 关键词： 太赫兹波 太赫兹波参量振荡 电磁耦子 闪锌矿晶体     

Theoretical research on terahertz wave generation from planar waveguide by optimized cascaded difference frequency generation

A novel scheme for high-efficiency terahertz(THz)wave generation based on optimized cascaded difference frequency generation(OCDFG)with planar waveguide is presented.The phase mismatches of each-order cascaded difference frequency generation(CDFG)are modulated by changing the thickness of the waveguide,resulting in a decrement of phase mismatches in cascaded Stokes processes and an increment of phase mismatches in cascaded anti-Stokes processes simultaneously.The modulated phase mismatches enhance the cascaded Stokes processes and suppress the cascaded anti-Stokes processes simultaneously,yielding energy conversion efficiencies over 25%from optical wave to THz wave at 100 K.     

小型化外腔可调谐THz参量振荡器

基于LiNbO3晶体垂直表面输出技术,设计了一台小型化外腔THz参量振荡器。利用小型化灯1064 nm脉冲激光器泵浦MgO:LiNbO3,通过优化设计三波非共线相位匹配的光学参量振荡腔结构,实现THz垂直晶体表面输出,减少LiNbO3晶体对THz波的吸收,提高了THz波输出光束质量。当在泵浦光能量为128 mJ、重复频率为10 Hz时,获得THz波的调谐范围为0.69~3.01 THz,在1.6 THz处获得THz波最大平均功率为10.8 W,脉冲宽度为10 ns,对应THz波能量转换效率为8.4310-6。     

DFB半导体激光器调谐动态波长特性研究

为了测量半导体激光器在电流调谐下的动态波长,提出了基于光纤延时自外差法的测量方案,阐述了测量原理,研究了拍频与动态波长的递推关系。应用该实验系统测量了分布反馈式半导体激光器调谐的动态波长特性,与由光谱仪测量的稳态波长特性比较。结果表明,动态波长与稳态波长随电流变化特性有着类似的非线性规律,在20~100 mA调谐范围内二者差异小于0.002 nm。此外,通过气体CO₂的两条吸收谱线与HITRAN谱库中标准吸收线位置比对,辨识出半导体激光器调谐的动态波长,该辨识出的动态波长值与由延时自外差法推算出的动态波长值比较,二者误差为1 pm,进而验证了该测量系统的可靠性。     

Intersubband absorption with difference-frequency generation in GaAs asymmetric quantum wells

An asymmetric quantum well(AQW) is designed to emit terahertz(THz) waves by using difference frequency generation(DFG) with the structure of GaAs/Al 0.2 Ga 0.8 As/Al 0.5 Ga 0.5 As.The characteristics of absorption coefficients are analysed under the parabolic and non-parabolic energy-band conditions in detail.We find that the absorption coefficients vary with the two pump optical intensities,and they reach the maxima when the pump wavelengths are given as λ p1 = 9.70 μm and λ p2 = 10.64 μm,respectively.Compared with non-parabolic conditions,the total absorption coefficient under parabolic conditions shows a blue shift,which is due to the increase in the energy difference between the ground and excited states.By adjusting the two pump optical intensities,the wave vector phase-matching condition inside the AQW is satisfied.     

高双折射的混合格子太赫兹光子晶体光纤的设计与研究

提出了一种新型高双折射的混合格子太赫兹光子晶体光纤,通过对芯区亚波长尺寸的空气孔进行多种格子组合排列,增加结构的非对称性实现高的模式双折射. 全文仿真建模采用专业的有限元计算软件COMSOL Multiphysics 4.0,结果表明:混合格子太赫兹光子晶体光纤在很宽的频率范围内都具有较高的双折射(达到10^-2)和低的限制损耗,且通过改变光纤的某些参数可以灵活地控制其双折射或限制损耗特性. 相比于同类光通信波段光纤,由于太赫兹波波长较大,能够降低芯区微结构加工的难度,具有可行性. 关键词： 双折射 混合格子 太赫兹光子晶体光纤 限制损耗     

Creation of multi-frequency terahertz waves by optimized cascaded difference frequency generation

A new scheme which generates multi-frequency terahertz (THz) waves from planar waveguide by the optimized cascaded difference frequency generation (OCDFG) is proposed. A THz wave with frequency ω_T1 is generated by the OCDFG with two infrared pump waves, and simultaneously a series of cascaded optical waves with a frequency interval ω_T1 is generated. The THz wave with a frequency of M-times ω_T1 is generated by mixing the m-th-order and the (m+M)-th-order cascaded optical wave. The phase mismatch distributions of cascaded difference frequency generation (CDFG) are modulated by changing the thickness of planar waveguide step by step, thereby satisfying the phase-matching condition from first-order to high-order cascaded Stokes process step by step. As a result, the intensity of THz wave can be enhanced and modulated by controlling the cascading order of OCDFG.     

金属纳米薄膜对大孔径光子晶体光纤传感特性的影响

基于全矢量有限元法研究了金属纳米薄膜对大孔径光子晶体光纤(PCF)传感特性的影响.针对所设计的大孔径PCF传感模型,数值模拟了PCF材料中金属纳米薄膜厚度不同以及不均匀时所表现的吸收特性:当金属纳米薄膜的厚度为均匀的30 nm和40nm时,分别在0.535 μm和0.565 μm处出现非常明显的吸收峰,且HEX11和HEy11两个模式完美简并;当有一个空气孔中的金属纳米薄膜厚度为30 nm,其他空气孔中的金属纳米薄膜厚度为40nm时,HEx11和HEy11模式的损耗曲线明显不简并,能够表现出两种金属纳米薄膜厚度的吸收特性;模拟计算了所设计传感器不同测量方法所表达的灵敏度与分辨率.研究结果为PCF传感器中金属纳米镀膜的实际操作和使用提供了理论依据.     

级联参量振荡产生太赫兹辐射的理论研究

针对光学参量振荡产生太赫兹波转换效率低的缺点, 提出了级联参量振荡产生太赫兹波的新机理以提高转换效率. 以周期极化铌酸锂晶体为例, 对级联参量振荡产生太赫兹波的原理和过程进行了理论研究. 分析了抽运光波长、周期极化铌酸锂晶体极化周期和工作温度对产生一阶、二阶闲频光频率的影响. 推导了三波共线相互作用条件下太赫兹波的增益特性和吸收特性. 计算结果表明, 通过级联参量振荡可以有效提高太赫兹波的转换效率, 并可以得到宽调谐的太赫兹波输出. 基于分析结果, 设计了周期极化铌酸锂晶体级联参量振荡产生高效率、宽调谐、窄线宽、连续太赫兹波的实验. 关键词： 太赫兹波 太赫兹波参量振荡 级联参量振荡