柱形微腔回音壁激光光谱模式的精确标定

由柱形微腔中回音壁模式满足的本征值方程,得到确定回音壁模式位置和间距的近似解析公式。以此近似解析公式,首次对直径在215～328 μm间的5个柱形微腔回音壁激光光谱做了模式标定。在用近似解析公式对柱形微腔激光光谱的数值作拟合的计算中,除了回音壁模的径向模式数(l)和角动量模式数(n)外无需其他拟合参数,解析公式的拟合值和实验激光光谱波长值间的偏差小于0.05 nm,拟合结果精确可靠。柱形微腔回音壁激光光谱模式的精确标定在模式的场分布计算以及频移型微腔生物传感器的研究应用中具有重要作用,文章介绍的方法亦可应用于柱形微腔直径和折射率的精密测量。     

光纤回音壁模式的三波段激光辐射研究

将石英光纤浸入低折射率的激光染料溶液中构成圆柱形微腔.采用沿光纤轴向光抽运的消逝波激励增益方式,获得了沿光纤轴向长距离的激光染料增益,受激辐射光在圆柱形微腔中回音壁模式的支持下形成激光振荡.在直径为288 μm的同一根光纤外分三段分别填入罗丹明6G、罗丹明610和罗丹明640激光染料乙二醇溶液,实现了波长分别在567～575 nm、605～614 nm和656～666 nm三个不同波段的回音壁模式激光振荡,用一根光纤同时获得了红、橙、黄三种不同颜色的激光辐射.对实验所获得的回音壁模式激光光谱做了模式标定,依据标定的模式数计算了各种模式以及抽运光在光纤截面的强度分布.计算结果表明,激光增益区域总是局限在圆柱形微腔回音壁模式的模场区域内,由此可以显著地提高抽运效率,增加抽运光沿光纤轴向的增益长度.     

消逝波激励的双波段光纤回音壁模式激光辐射

将石英光纤浸入低折射率的染料溶液中后构成圆柱形微腔.采用轴向光抽运消逝波激励激光增益的方式,使增益区域局限在圆柱形微腔回音壁模式的模场区域内,由此显著地提高了抽运效率,增加了沿光纤轴向的增益长度.在一根石英光纤的轴向分段填入浓度同为2×10^-3mol/L的罗丹明6G和罗丹明B乙醇溶液,在567—576nm 和592—600nm的两个波长范围内同时获得回音壁模式的激光辐射;分段填入浓度为8×10^-4和8×10^-3mol/L的罗丹明B乙醇溶液, 关键词： 消逝波激励 圆柱形微腔 回音壁模式 双波段激光辐射     

光学微盘腔与三能级量子点系统中的模耦合研究

用一种全量子理论方法研究了波导、光学微盘腔与三能级量子点耦合系统的动力学过程,求出其耦合后的透射模和反射模的解析解. 由于微腔表面粗糙引起反向散射,在微腔内形成两简并回音壁耦合共振模,其耦合率为β;量子点的两激发态分别以耦合率g₁,g₂与回音壁耦合共振模产生耦合. 在实数空间里,得出透射光谱和反射光谱的数值解,这些三能级模型结果比二能级模型结果更接近真实光学微盘腔系统,能更好地显示耦合系统的动力学特性. 关键词： 模耦合 光学微盘腔 三能级量子点 全量子理论     

808 nm LD激发下高折射率差光纤锥-硫卤微球耦合系统的荧光回廊模

用熔融淬冷法制备了0.5wt.%掺杂Nd3+:75GeS2-15Ga2S3-0CsI(0.5wt.%Nd-GGSI)硫卤玻璃.在此基础上以玻璃粉料漂浮熔融法制备出粒径为50~300μm高折射率(n≈2.1)玻璃微球,并在显微镜下选出表面质量高的硫卤微球用于后续实验.将火焰法拉制出的直径1~2μm间的双锥形石英微纳光纤与硫系微球进行近场耦合.相位匹配条件下测试结果表明光纤锥倏逝场将激发球内径向高阶回音壁模式.实验测量了在808nm LD激光泵浦下直径110μm微球的荧光光谱特性,结果表明:掺Nd3+硫卤微球在输出端1 075nm波段附近产生了等间距分布的荧光回音壁模式的光学谐振,共振峰间隔为1.80nm.实验结果与微球腔回音壁模式谐振的理论模型有较高的符合度.     

级联声光器件与回音壁模式微腔实现非对称传输

本文提出利用级联声光效应器和耦合回音壁模式微球腔的方案来实现非对称传输效果,并进行理论和实验验证.实验中利用加热拉锥的方式制备了两段式光纤,可同时实现声光效应的激发和回音壁模式的耦合.利用光纤中声光效应将纤芯基模中的矢量模式转换到包层高阶模式,由于基模中不同矢量模式转换包层模式的矢量模式也不同,从而产生类似双折射效果,使输出的包层模式产生偏振变化.而后通过耦合回音壁模式微腔将包层模式转换回纤芯基模.由于回音壁模式的偏振选择效果,使得相反方向入射光能量具有不同的透射特性,其传输隔离度可达17 d B.此外,对两个方向传输的透射率随偏振角度变化进行测试,测得声光效应带来的偏振变化约为80°.本文的非对称传输方案继承了声光器件响应迅速、调谐性良好的优势,同时具有全光纤结构和无工作阈值的特点,在光开关、光隔离器等场景具有重要的应用潜力.     

高Q值薄壁液芯毛细管微腔电场传感器

为提高电场传感器的抗电磁干扰能力、灵敏度和稳定性,将高Q值薄壁液芯毛细管微腔和电泳效应结合,增强回音壁模共振微腔对外加电场的感知能力,并进行了实验验证.基于时域有限差分法得到了液芯毛细管微腔回音壁模式共振特性随毛细管直径、壁厚等结构参数的变化规律,发现随着壁厚变薄灵敏度增加.采用熔融拉锥法制备了直径为86μm,壁厚约为2μm的薄壁毛细管微腔,通过高精度位移平台实现了锥形光纤和毛细管微腔的高效率耦合,测得回音壁模式Q值为2.8×10^6.毛细管微腔内注入不同浓度的蛋白质溶液,利用电泳原理和蛋白质分子在缓冲溶液里带电的特性,实现的最大电场传感灵敏度为10.6 pm/(kV/m).     

圆柱形Bragg微腔的共振模特性

利用圆柱形介质设计了一个Bragg微腔结构,含有圆柱形和环形两个微腔.基于传输矩阵理论,通过研究会聚柱面波的反射相移,根据反射相移在Bragg禁带中的尖锐突变来确定微腔结构的共振模.较之其他计算方法,相移方法操作简单,图像直观,且行之有效.研究表明,随着中心圆柱形微腔的半径增大,方位指数相同的两微腔共振模之间会发生相互作用,在腔模光子能量相近时耦合效应最强,导致双微腔的耦合共振模曲线出现反交叉现象.最后给出了耦合共振模的空间电磁场分布.     

基于回音壁模式微球腔的PDH稳频技术

光学微球腔因其回音壁模式可获得极高的品质因数而受到广泛关注.本文分析了Fabry-Perot腔和微球腔的基本原理,通过CO2激光熔融光纤实验制得了直径为1.2 mm的微球腔,并测试了微球腔和锥形光纤耦合结构的耦合特性.采用典型的PDH稳频系统设计了基于微球腔的稳频系统,分析了用于鉴频的误差曲线的吸收特性和色散特性,对比了不同调制频率、微球腔直径、耦合损耗、传输损耗下与误差曲线斜率的关系.结果表明:耦合状态下最大Q值可达到1.1×108,调节微球腔内横磁模和横电模的转换可优化耦合效率,匹配微球腔和锥形光纤的尺寸得到了径向二阶模式的透射谱,误差曲线效率达到15.4A mW/MHz.球腔在提高PDH稳频技术灵敏度上具有巨大潜力.     

微纳光纤环形腔海水温度的谐振光谱分析

微纳光纤环形腔作为传感器件,具有灵敏度高、响应快的优点,因而越来越广泛地应用在传感领域。环形腔的谐振光谱直接反映外界环境的变化,因此谐振光谱分析对探测环境参数至关重要。从理论和实验研究了微纳光纤环形腔谐振光谱与海水温度的关系。首先,数值计算了基模(HE₁₁)两个垂直偏振态的传播常数随光纤直径和探测波长的变化关系,计算结果表明传播常数随光纤直径增大而增大,随波长增大而减小,同时计算了传播常数随海水温度的变化,海水温度越高,传播常数越大,表明海水温度的变化会影响到模式的传播常数,因而可以通过测量谐振光谱的变化得知海水温度的变化。其次,搭建了海水温度传感实验系统,获得了微纳光纤环形腔海水温度的谐振光谱,实验发现同时存在两套谐振峰,分别对应基模的TE模和TM模,两个偏振模式的传感灵敏度分别为5.54和5.24 pm·℃-1。最后,探讨了基模两个偏振态谐振光谱的产生原因,由于结型耦合区的扭曲耦合使得两个偏振态分离,并对两个偏振模式的谐振强度进行了分析。两个模式的谐振强度不同,而且随着波长的增加,一个模的谐振强度不断增强,另一个模的谐振强度逐渐减弱。这是由于不同耦合态的耦合系数和衰减决定的,而且他们随着波长而改变。实验结果与理论计算相吻合。     

Mode characteristics of silver-coated inverted-wedge silica microdisks

The characteristics of whispering gallery modes(WGM) in silver-coated inverted-wedge silica microdisks are theoretically investigated by using finite element method. Dielectric TE mode always exists in silver-coated inverted-wedge resonators; dielectric TM mode tends to couple with SPP modes; only pure interior surface plasmonic polariton(SPP) mode but not pure exterior SPP mode is observed in contrast to the metal-coated cylindrical and toroidal resonators. The dependence of quality factor of different kinds of WGMs on the radius of the resonator and the thickness of the coated silver layer are systematically analyzed. We find that the quality factors of the hybrid WGMs associated with SPP mode can reach 104. The maximum light intensity enhancement in ambient for a hybrid mode consisting of a dielectric TM mode and an exterior SPP mode can be obtained when a silver film of thickness ~40 nm is deposited. The silver-coated inverted-wedge silica resonators may be widely applied in sensing and surface enhanced Raman scattering.     

Whispering gallery mode microlasers and refractive index sensing based on single polymer fiber

The realization of whispering gallery mode (WGM) lasing in polymer fibers is hindered by an appropriate method to dissolve the polymer and the gain material. In this work, microfibers fabricated by directly drawing from a dye doped polymer solution are exhibited as high quality microlasers and microsensors. Multi‐mode and even single‐mode lasing is observed from the fiber under optical pumping at room temperature. The linewidth of lasing mode is narrower than 0.09 nm. The lasing mechanism is unambiguously verified by comprehensive spectroscopic analysis and ascribed to WGMs. Diameter‐ and polarization‐dependent lasing characteristics are systematically investigated, showing good agreement with the theoretical calculation. Particularly, application of the fiber laser for refractive index sensing based on resonant shift of lasing mode is demonstrated and the sensitivity up to about 300 nm/RIU is achieved. The promising potential of high quality polymer microfibers as optical sensors and multi‐function components for flexible photonic integrated systems is highly expected.     

Higher order mode propagation in an optical nanofiber

The propagation of higher modes, such as the LP₁₁ mode, in optical nanofibers using the exponentially tapered optical fiber as a basic model is investigated. In order to preserve the LP₁₁ mode in the downtaper as far as the nanofiber waist, the effect of varying the cladding-core radius ratio on the LP₁₁ adiabatic criterion is modeled. A Laguerre-Gaussian beam is created in free space using a spatial light modulator (SLM) and coupled to a few-mode fiber. This device allows convenient switching between the fundamental and LP₁₁ fiber modes. By selecting a few-mode fiber with a relatively low cladding-core ratio, the propagation of the LP₁₁ mode down to a submicron waist has been maintained. Furthermore, by observing the transmission profile during tapering, it is possible to decisively terminate the pulling process in order to eliminate the two degenerate HE₂₁ modes of the LP₁₁ mode. As a result, a nanofiber can be fabricated through which only the TE₀₁ and TM₀₁ components of the LP₁₁ mode propagate. Such a nanofiber has promising applications in the area of mode interference for controlled particle trapping sites.     

Tilted fiber Bragg grating sensors

Optical fiber gratings have developed into a mature technology with a wide range of applications in various areas, including physical sensing for temperature, strain, acoustic waves and pressure. All of these applications rely on the perturbation of the period or refractive index of a grating inscribed in the fiber core as a transducing mechanism between a quantity to be measured and the optical spectral response of the fiber grating. This paper presents a relatively recent variant of the fiber grating concept, whereby a small tilt of the grating fringes causes coupling of the optical power from the core mode into a multitude of cladding modes, each with its own wavevector and mode field shape. The main consequence of doing so is that the differential response of the modes can then be used to multiply the sensing modalities available for a single fiber grating and also to increase the sensor resolution by taking advantage of the large amount of data available. In particular, the temperature cross‐sensitivity and power source fluctuation noise inherent in all fiber grating designs can be completely eliminated by referencing all the spectral measurements to the wavelength and power level of the core mode back‐reflection. The mode resonances have a quality factor of 10⁵, and they can be observed in reflection or transmission. A thorough review of experimental and theoretical results will show that tilted fiber Bragg gratings can be used for high resolution refractometry, surface plasmon resonance applications, and multiparameter physical sensing (strain, vibration, curvature, and temperature).     

新型抗弯曲大模场面积光子晶体光纤

研制出一种新型抗弯曲大模场面积石英光子晶体光纤. 利用光子晶体光纤结构设计的灵活性, 通过规划缺陷的位置及空气孔的尺寸, 实现了大模场面积单模及低弯曲损耗特性.应用建立的实际光子晶体光纤特性分析模型, 研究了研制光纤的模式特性和弯曲特性, 在波长1064 nm处, 平直状态下光纤的模场面积可以达到2812 μm², 基模限制损耗为0.00024 dB/m, 高阶模限制损耗高于1.248 dB/m. 基模和高阶模之间的高传输损耗差, 保证了在获得大模场面积的同时实现单模传输. 弯曲半径和弯曲方向角所带来弯曲损耗变化的研究结果显示, 即使在弯曲半径小到5 cm时, 弯曲损耗也在10^-3 dB/m量级以下, 而且在弯曲半径为30 cm时光纤可承受的弯曲方向角范围扩展至-60°–60°. 研制的光纤具有良好的低弯曲损耗特性, 可有效解决非对称结构所带来的光纤弯曲特性对弯曲方向角敏感的问题. 该光纤在高功率光纤激光器、放大器及高功率传输等技术领域具有重要的应用价值. 关键词： 光子晶体光纤 大模场面积 低弯曲损耗 弯曲方向角     

新型全固态准晶体结构大模场光纤特性研究

大模场单模光纤在高功率激光器、高功率光传输和高灵敏度传感器等领域具有重要意义.设计了一种新型超低损耗大模场单模光纤,包层空气孔由掺氟硅玻璃棒代替,掺氟硅玻璃棒排列呈六重准晶体结构.基于有限元法对光纤的传输特性进行了数值模拟.研究了光纤结构参量变化对模式特性和有效模场面积的影响.结果表明:波长在1064 nm处,有效模场面积高达5197μm2,基模的限制性损耗低于10-5dB/km,解决了大模场与低损耗之间的冲突;在1064—2000 nm波段内,基模与二阶模的限制性损耗相差7个量级,实现单模传输;半径为10 cm时,弯曲损耗小于0.01 dB/m,具有良好的低弯曲损耗特性.此光纤能够提高光纤热损伤阈值,减少接续损耗,全固态结构有效避免了空气孔塌陷,简化制备工艺,对高功率激光传输、光纤激光器和光纤放大器的发展具有重要意义.     

Mode coupling between first- and second-order whispering-gallery modes in coupled microdisks

The mode characteristics for two coupled microdisks are investigated by the finite-difference time-domain technique. In the two coupled micodisks, mode coupling between the same order whispering-gallery modes (WGMs) results in coupled WGMs with split mode wavelengths. The numerical results show that the split mode wavelengths of the coupled first- and second-order WGMs can have a crossing point in some cases, which can induce anticrossing mode coupling between them and greatly reduce the mode Q factor of the coupled first-order WGMs. The time variation of mode field pattern shows the transformation between the coupled first- and second-order WGMs.     

Novel Design Method for Single-Mode Bend-Insensitive Fiber Appropriate for Fiber-to-the-Home Application

Abstract

A proposal for a new single-mode optical fiber design technique with ultra-low bending loss applicable in fiber-to-the-home operation is presented. The suggested design method is based on reverse problem engineering, which evaluates the refractive index profile. The most remarkable feature of this methodology is designing a bend-insensitive fiber without core radius and mode field diameter reductions. The designed structures exhibit ultra-low bending loss and high effective area simultaneously. Meanwhile, the residual stress of the designed structures is small due to gradual variation of the refractive index in the core region. Simulation results show a bending loss of 4.3 × 10^?4 dB/turn at 1.55 μm for a single turn of 5-mm radius.