SENSORS: Optical Whispering-Gallery Modes for Diverse Sensing Applications

这个传感器方案的重点是透明的熔融二氧化硅微球，它支持低语通道模式（WGMs）——光被全内反射捕获并在表面下轨道运行。这些模式由相邻锥形光纤的光隧穿激发，具有表面外的倏逝成分和非常尖锐的频率共振（highQ）。模幅和谐振频率可以对微谐振器环境的变化非常敏感，从而能够感知，例如：应变，加速度，热效应，微量气体，化学物质和表面的修改。该项目将：进一步发展和推进以前演示的大气中痕量气体和溶液中的化学物质的wgm倏逝波传感方法；将WGM微传感器在测量热和吸收性能方面的早期应用扩展到透明薄膜的表征；通过将模态干扰等效应与WGM微传感相结合，追求能够提高灵敏度的新技术；并应用于WGM微谐振器的表面制备方法，该方法已被证明在用于气体，化学品和生物制剂的光纤传感器中有用。为了实现这些目标，该项目的各个方面都将受益于：改进控制耦合技术，利用各种冗余测量来表征wgm，研究改变系统配置的影响，以及扩展微传感器的数值模拟。该项目的具体部分将涉及：实现波长调制光谱，将WGM锁定在与频率扫描激光器共振的位置，并通过连接耦合器加固传感器；测量涂覆微谐振器的薄膜的热调节系数和光吸收系数；利用散射光的腔衰荡，并对微谐振器的wgms施加可控多模锥耦合，以提高其吸收检测灵敏度；将表面增强拉曼散射与WGMs相结合，在微谐振器上涂覆含金纳米粒子的薄膜，以及使用干凝胶或抗体表面涂层技术进行生物传感。智力优势：即使是一个被认为很好理解的系统，在极端条件下，或者在与另一个系统交互时，也会表现出新的行为。WGM的高Q值在这里提供了极端条件，WGM与表面或耦合效应之间的相互作用使灵敏度增强因子倍增。更广泛的影响：参与的研究生将学习基础物理学，并在现实世界的应用中扎根；他们还将通过会议报告和同行评议的期刊出版物直接参与成果的传播。这项工作将有利于该大学的多学科光子学学位课程及其跨部门的传感器和传感器技术中心。这里开发的传感技术对社会有许多潜在的好处，俄克拉何马州科学技术进步中心、美国宇航局的马歇尔太空飞行中心和Nomadics公司已经认识到这一点，通过他们对相关工作的支持和合作。

This Sensor proposal focuses on transparent fused-silica microspheres, which supportwhispering-gallery modes (WGMs)- light trapped by total internal reflection and orbiting justbeneath the surface. These modes, excited by optical tunneling from an adjacent tapered fiber,have an evanescent component outside the surface and a very sharp frequency resonance (highQ). The mode amplitude and resonant frequency can be very sensitive to changes in themicroresonator's environment, and thus enable sensing of, for example: strain, acceleration,thermal effects, trace gases, chemicals, and modifications of the surface.This project will: further develop and advance previously-demonstrated methods ofWGM evanescent-wave sensing of trace gases in the atmosphere and chemicals in solution;extend earlier applications of WGM microsensors, in measuring thermal and absorptiveproperties, to the characterization of transparent thin films; pursue novel techniques that enablethe multiplication of sensitivity enhancements, by combining effects such as modal interferencewith WGM microsensing; and apply to WGM microresonators methods of surface preparationthat have proved useful in fiber sensors for gases, chemicals, and biological agents. Inaccomplishing these objectives, all aspects of the project will benefit from: improving controland coupling techniques, utilizing various redundant measurements to characterize WGMs,studying the effects of changing system configurations, and expanding the numerical modelingof the microsensors. Specific parts of the project will involve: implementing wavelength-modulationspectroscopy with the WGM locked to resonance with a frequency-scanning laser,and ruggedizing the sensor by attaching the coupler(s); measuring the thermal accommodationcoefficient and optical absorption coefficient of a thin film coating the microresonator; usingcavity ringdown of the scattered light, and applying controlled multimode-taper coupling to theWGMs of the microresonator, to amplify its absorption-detection sensitivity; and combiningsurface-enhanced Raman scattering with WGMs by coating the microresonator with a thin filmcontaining gold nanoparticles, as well as using the techniques of surface coating with xerogels orantibodies for biosensing.Intellectual Merit: Even a supposedly well-understood system can exhibit novelbehavior under extreme conditions, or when interacting with another system. The exquisitelyhigh Q of a WGM provides extreme conditions here, and interactions between WGMs andsurface or coupling effects give a multiplication of sensitivity-enhancement factors.Broader Impacts: The graduate students involved will be learning fundamental physicsas well as becoming grounded in real-world applications; they will also be directly involved indissemination of results through conference presentations and peer-reviewed journalpublications. This work will benefit the University's multidisciplinary Photonics degreeprograms and its interdepartmental Center for Sensors and Sensor Technologies. The sensingtechniques to be developed here have many potential benefits to society, as has already beenrecognized by the Oklahoma Center for the Advancement of Science and Technology, NASA'sMarshall Space Flight Center, and Nomadics, Inc., through their support of and collaboration onrelated work.