轴向隐失波激励的回音壁模式光纤激光器

采用轴向隐失波激励增益的方式,使激光增益区域局限在光纤回音壁模式的模场区域内,显著地降低了回音壁模式光纤激光辐射的抽运阈值,由此形成一种低阈值的回音壁模式光纤激光器.在微焦耳量级的低抽运能量条件下,用回音壁模式光纤激光器研究了激光染料的浓度效应.实验结果表明,随着激光染料浓度的增加,回音壁模式激光辐射的波长向长波方向移动,激光波长范围变宽.用回音壁模式染料激光的四能级模型得到激光上能级和所有能级上的分子数比值γ(λ)曲线后,很好地解释了实验结果.低抽运阈值的回音壁模式光纤激光器,为研究液体激光现象提供了极为便利的手段.     

Whispering gallery microcavity lasers

Whispering gallery mode (WGM) optical microresonators have attracted intense interests in the past decades. The combination of high quality factors (Q) and small mode volumes of modes in WGM resonators significantly enhances the light‐matter interactions, making them excellent cavities for achieving low threshold and narrow linewidth lasers. In this Review, the progress in WGM microcavity lasers is summarized, and the laser performance considering resonator geometries and materials as well as lasing mechanisms is discussed. Label‐free detection using WGM resonators has emerged as highly sensitive detection schemes. However, the resolution is mainly limited by the cavity Q factor which determines the mode linewidth. Microcavity lasers, due to their narrow laser spectral width, could greatly improve the detection resolution. Some recent developments in sensing using microcavity lasers are discussed.     

聚二甲基硅氧烷微流道中光流控荧光共振能量转移激光

将单一折射率的石英裸光纤植入由聚二甲基硅氧烷构成的基片微流道中,以低折射率的罗丹明B(RhB)和吡啶821(LDS821)乙醇溶液构成的供体和受体对作为激光增益介质.采用沿光纤轴向消逝波抽运方式,首先以波长为532nm的连续波激光器作为激励光,对荧光共振能量转移特性参数进行了研究.然后以波长为532nm的脉冲激光器作为抽运光,通过直接激励供体分子RhB,并将其能量转移给临近的受体分子LDS821,在不改变抽运光波长的条件下,实现了较低阈值(1.26μJ/mm~2)的受体LDS821激光辐射.     

偏斜光线抽运下的回音壁模式光纤激光辐射特性

研究了偏斜光线抽运下的回音壁模式光纤激光辐射特性.实验发现,在抽运光以偏斜光线方式沿光纤的近轴向抽运时,回音壁模式的光纤激光辐射中,既存在光电矢量和光纤径向垂直的横电波(TE),也存在光电矢量和光纤径向平行的横磁波(TM);随增益包层染料溶液折射率的增加,径向模式数和角模式数相同的TE波和TM波之间的波长差单调减小,回音壁模式激光辐射的中心波长向短波方向移动,辐射的波长范围变窄.用回音壁模式激光的辐射理论结合激光染料的四能级模型,满意地解释了实验结果.     

回音壁模式光纤激光器的阈值特性研究

研究了一种新型光纤激光器——消逝波激励的回音壁模式光纤激光器的阈值特性.将不同直径的石英光纤分别浸入低折射率的罗丹明6G乙醇和乙二醇混合溶液中,采用沿光纤轴向光抽运消逝波激励染料增益的方式,发现回音壁模式光纤激光辐射的阈值能量和混合溶液的折射率存在不同的依赖关系.随折射率的增加,对小直径光纤,阈值能量随之增加;对大直径光纤,阈值能量单调缓慢递减;对直径适中的光纤,阈值能量先减后增,存在一个和最小阈值能量对应的最佳折射率.用消逝波激励的回音壁模式激光理论,导出了回音壁模式光纤激光的阈值能量公式.理论计算曲线 关键词： 光纤激光器 回音壁模式 激光阈值 消逝波     

Characteristics of whispering-gallery-mode dye lasers utilizing dye-doped solid microspheres by UV N2-laser pumping

The characteristics of a whispering-gallery-mode (WGM) dye laser using a variety of dye-doped solid microspheres, pumped by a UV N₂-laser, are presented. Experimental results for the WGM dye laser are presented with the spatial distribution and spectral and temporal responses of lasing. The spectral response of a new variety of WGM dye laser is in the blue-green or red spectral regions, and over a wide spectral range.     

Resonating properties of passive spherical optical microcavities

As an optically pumped device, the lasing characteristics of a spherical microcavity laser depend on the optical pumping processes. These characteristics can be described in term of the Q factor and the optical field distribution in a microsphere. We derived analytical expressions and carried out numerical calculation for Q factor and optical field. The Q factor is found to be oscillatory functions of the radius of a microsphere and the pumping wavelength, and the pumping efficiency for a resonating microsphere is much higher than that for an anti-resonating microsphere. Using tunable lasers as pumping sources is suggested in order to achieve a higher pumping efficiency. Numerical calculation on optical field distribution in spherical microcavities shows that a well focused Gaussian beam is a suitable incident wave for cavity quantum electrodynamics experiments in which strong confinement of optical field in the center of a microsphere is requested, but higher order spherical wave should be used instead for exciting whispering-gallery-mode (WGM) microsphere lasers, for the purpose of favoring optical energy transferring to WGM in optical microspheres.     

Linearly polarised three-colour lasing emission from an evanescent wave pumped and gain coupled fibre laser

A novel Whispering--Gallery--Mode (WGM) fibre laser, emitting linearly polarised three-colour light, is demonstrated by pumping and gain coupling with evanescent waves. The pump light is longitudinally coupled into a bare optical fibre immersed in a dye solution of lower refractive index. The dye molecules around the bare fibre are excited by the evanescent waves of pump light when they propagate along the fibre in a total internal reflection. When the pump beam within the fibre is a meridian beam, the WGM lasing emission from the fibre laser is a linearly polarised transverse electric wave, while it is a mixed wave of the linearly polarised transverse electric and magnetic waves if the pump beam is a skew beam within the fibre. Because the excited molecules are located within the evanescent field of WGM, a good spatial overlap between the dye gain and the evanescent field leads to a high pumping efficiency and a longer gain distance along the fibre. Once the bare fibre is inserted into three glass capillaries filled with Rhodamine 6G, 610 and 640 dye solutions, respectively, WGM laser oscillations at the wavelengths of 567--575, 605--614 and 656--666~nm occur simultaneously, and a linearly polarised three-colour lasing emission is achieved in a single optical fibre.     

Fabrication and characterization of spherical micro semiconductor crystals by laser ablation method

We have been establishing the technique of fabricating spherical semiconductor microcrystals with suitable diameters for whispering gallery mode (WGM) lasing. Concretely, semiconductor microspheres were synthesized by ablating various semiconductor-sintered targets with focused pulsed laser at high fluences. In this report, dependences of fabricated zinc oxide (ZnO) microstructures on laser wavelengths were investigated. Lasing characteristics and photoluminescence of ZnO microspheres were determined, and photoluminescence of Sb-doped ZnO microspheres were determined. Additionally, it was also found that Sb-doped ZnO and aluminum nitride microspheres can be similarly synthesized. By developing this method, which does not require complex processing, it is expected that efforts in the application of WGM lasing are accelerated in many kinds of semiconductors.     

Lasing emission of dye-doped cholesteric liquid crystal microdroplet wrapped by polyglycerol in hollow glass microsphere

In this Letter,a dye-doped cholesteric liquid crystal(DDCLC)-filled hollow glass microsphere is demonstrated to be a resonator with good temperature response.A diglycerol layer is used to wrap the DDCLCs microdroplet to keep it steady and control its orientation.The whispering gallery mode(WGM)lasing and photonic band gap(PBG)lasing caused by two different mechanisms were obtained under the pump of a pulsed laser,and the temperature response of these two kinds of lasing was studied.For the liquid crystal and chiral material used in this Letter,both the WGM lasing and the PBG lasing have a blue shift in wavelength with increasing temperature.     

LD Pumped Q-Switching and Self-starting Mode-locked All Fiber Laser

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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.     

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。     

Whispering‐gallery mode lasing from patterned molecular single‐crystalline microcavity array

Organic single‐crystalline materials have attracted great attention for laser applications. However, the fabrication of laser resonators and pattern of crystals are still intractable problems. Organic single crystals have been limited to fundamental property studies despite their superior photonic characteristics. In this work, whispering‐gallery mode (WGM) resonators of BP1T and BP2T crystalline materials have been fabricated through a combination method with improved lithography and dry etching. Crystalline microresonators with different geometries over a large area are top‐down fabricated with submicrometer spatial resolution. WGM lasing oscillation from circular, hexagonal, pentagonal and square resonators is definitively observed. The BP1T and BP2T crystals are characterized with high refractive index, and stable lasing in aqueous solution is demonstrated besides in the air environment. It is expected that organic crystalline materials would be used for the practical applications in a variety of organic electronic and optical devices.     

Theoretical prediction of a dramatic Q-factor enhancement and degeneracy removal of whispering gallery modes in symmetrical photonic molecules

Coupled-microdisk photonic molecules with high-symmetry geometries that support nondegenerate whispering gallery modes with high quality factors are numerically designed, based on a two-dimensional model. Dramatic enhancement of calculated Q factors of nondegenerate modes as compared with single-microdisk whispering gallery modes of the same radial order is achieved by tuning the intercavity coupling distances. Potential applications of this work to the design of single-mode coupled-microdisk structures with large spontaneous emission factors and low threshold lasing operation and to random laser simulations are discussed.     

Low threshold laser cavities of two-dimensional photonic crystal line defect mode

Two-dimensional (2D) rod-type photonic crystal (PC) line defect waveguide (LDW) laser cavities based on three types of line defect modes with zero group velocity are studied by using finite-difference time-domain (FDTD) method. These laser cavities have high quality (Q) factor, better localization of light, non-uniform gain distribution and small overlap between gain medium and light field. Therefore, they have the advantages over conventional and air-bridge PC cavities with uniform gain, such as low threshold, single mode lasing and effectively avoiding thermal effect. From their comparison, one can find the mode at middle Brillouin zones (BZ) is the best one to be used as lasing mode. Its dynamic lasing process and lasing features are demonstrated by the numerical experiment where the FDTD method coupling Maxwell's equations with the rate equations of electronic population is used.     

Cavity-Q-driven phenomena in an evanescent-wave pumped and gain coupled whispering-gallery-mode fiber laser

We study cavity-Q-driven lasing wavelength shift and line-width widening in an evanescent-wave pumped and gain coupled Whispering-Gallery-Mode (WGM) fiber lasers. A bare optical fiber is immersed in a lower refractive index (RI) dye solution, pumped and gain coupled by evanescence waves, and linearly polarized WGM lasing emission is observed from the rim of the fiber. We find that both lasing wavelengths and line width of WGM peaks are sensitive to the RI of the dye solution and the fiber diameter, with the increase of the RI of the dye solution or decrease of the fiber diameter, a blue shift of the lasing spectrum and a widening on the spectral line width are observed. The observed phenomena have been attributed to the change of quality factor of a circular cavity built in the fiber cross section, the achieved experimental data agree well with the calculated values of the quality factor.     

染料掺杂液晶填充毛细管的激光发射特性研究

本文提出利用染料掺杂液晶填充PI光控取向膜毛细管获得可调谐激光.采用532 nm YAG倍频脉冲激光器抽运,实验及理论研究了有聚酰亚胺(PI)取向膜和无PI取向膜毛细管的激光发射特性,对比分析了两种情形的激光产生阈值以及随温度变化的特性.结果表明:经PI光控取向处理的染料掺杂胆甾相液晶毛细管的激光发射模式具有分布反馈模式和回音壁模式,同时,激光产生阈值为4.5 m J·mm~(-2);发现当温度升高时,发射光谱发生"蓝移",中心波长调谐范围为5.9 nm,温度升高到43℃时,形成质量非常好的回音壁模式,其自由光谱范围为1.05 nm.经PI光控取向处理的染料掺杂向列相液晶激光发射模式为随机激光,并且较无PI取向时激光发射峰减少.     

基于飞秒激光直写的单向单模耦合微腔

对具有高Q值的回音壁模式微腔进行调制来获得单向单模输出,对研究腔光力学和开发高质量的微激光具有重要意义.本文对利用飞秒激光直写加工的耦合回音壁模式微腔的研究进行了简要回顾,具体介绍了微腔结构设计、加工过程、激射和耦合机制研究等.利用飞秒激光直写加工的强大三维图案化能力,灵活地设计实现了具有集成功能的单个微腔和具有不同空间组合位置的多个耦合微腔.基于耦合微腔的微激光具有低阂值,同时显示出良好的单模特性和单向性.结合理论模拟可以证实,微腔与微腔/光栅之间的耦合,一方面支持游标效应和集成滤波两种选模方式,另一方面能够破坏微腔的旋转对称性从而获得单向输出,从而实现了对微腔输出的有效调控.