超高品质因子片上微腔光子学研究进展

光学微腔能够同时在空间和时间维度上约束光场,从而增强光与物质相互作用,被广泛用于基础光物理和光子学应用研究.其中,回音壁光学微腔具有超高的品质因子和很小的模式体积,是当前微腔研究的学术前沿.随着光学材料微纳加工和半导体芯片制备工艺的发展,超高品质因子回音壁光学微腔研究的重要趋势之一是片上集成化.例如,超高品质因子片上光学微腔已经在光子学芯片、集成光计算、片上光互联、光学精密测量等众多领域发挥着重要作用.本文重点介绍了片上回音壁光学微腔在微型激光器、非线性光学、集成光子学回路和高灵敏光学传感等研究中的基本原理、发展历程和最新进展;进一步展望了超高品质因子片上微腔光子学未来研究的发展方向.

Laser particles with omnidirectional emission for cell tracking

The ability to track individual cells in space over time is crucial to analyzing heterogeneous cell populations.Recently,microlaser particles have emerged as unique optical probes for massively multiplexed single-cell tagging.However,the microlaser far-field emission is inherently direction-dependent,which causes strong intensity fluctuations when the orientation of the particle varies randomly inside cells.Here,we demonstrate a general solution based on the incorporation of nanoscale light scatterers into microlasers.Two schemes are developed by introducing either boundary defects or a scattering layer into microdisk lasers.The resulting laser output is omnidirectional,with the minimum-to-maximum ratio of the angle-dependent intensity improving from 0.007(-24 dB)to>0.23(-6dB).After transfer into live cells in vitro,the omnidirectional laser particles within moving cells could be tracked continuously with high signal-to-noise ratios for 2 h,while conventional microlasers exhibited frequent signal loss causing tracking failure.

Optically sizing single atmospheric particulates with a 10-nm resolution using a strong evanescent field

Although an accurate evaluation of the distribution of ultrafine particulate matter in air is of utmost significance to public health,the usually used PM2.5 index fails to provide size distribution information.Here we demonstrate a low-profile and cavity-free size spectrometer for probing fine and ultrafine particulate matter by using the enhanced particle-perturbed scattering in strong optical evanescent fields of a nanofiber array.The unprecedented size resolution reaches 10 nm for detecting single 100-nm-diameter nanoparticles by employing uniform nanofibers and controlling the polarizations of the probe light.This size spectrometry was tested and used to retrieve the size distribution of particulate matter in the air of Beijing,yielding mass concentrations of nanoparticles,as a secondary exercise,consistent with the officially released data.This nanofiber-array probe shows potential for the full monitoring of air pollution and for studying early-stage haze evolution and can be further extended to explore nanoparticle interactions.

An encapsulated optical microsphere sensor for ultrasound detection and photoacoustic imaging

Optical whispering-gallery microresonators have attracted considerable interest for ultrasensitive ultrasound detection and photoacoustic imaging because of the combination of high quality factors and small cavity sizes.In the last decade,ultrasonic sensors with on-chip microcavities have been extensively developed;however,they are unsuitable for the near-field photoacoustic microscopy of micro/nanoscale objects in complex biological environments and endoscopic imaging.In this work,we developed ultrasonic sensors using two types of encapsulated microsphere resonators with different cavity materials.A noise equivalent pressure of as low as 160 Pa at 20 MHz was achieved with the acoustic response up to 70 MHz at-6 d B.Furthermore,the microsensor was used for photoacoustic microscopy in which we successfully performed 3 D imaging of hairs and leaf veins.The microsphere ultrasonic sensor has considerable potential as a probe-type ultrasonic detector for near-field photoacoustic microscopy of micro/nanoscale objects such as subcellular structures and high-resolution endoscopic photoacoustic imaging with its high sensitivity and wide bandwidth.

Whispering-gallery optical microprobe for photoacoustic imaging

Optical ultrasonic probes,exemplified by Fabry–Perot cavities on optical fibers,have small sizes,high sensitivity,and pure optical characteristics,making them highly attractive in high-resolution ultrasonic/photoacoustic imaging,especially in near-field or endoscopic scenarios.Taking a different approach,we demonstrate an ultrasensitive and broadband ultrasound microprobe formed by an optical whispering-gallery-mode polymer microcavity coupled to a U-shaped microfiber.With the h/√igh-quality(Q)factors(>10^(6)),the noise equivalent pressure of the ultrasound microprobe reaches 1.07 m Pa∕Hz with a record broadband response of 150 MHz and a large detection angle of 180°.Our results show that this optical microprobe can overcome the strong decay resulting from ultrasound diverging and medium absorption through short working distances.We further demonstrate high-quality in vivo whole-body photoacoustic imaging of a zebrafish larva.Our implementation provides a new strategy for developing miniature ultrasound detectors and holds great potential for broad applications.

Submonolayer biolasers for ultrasensitive biomarker detection

Biomarker detection is key to identifying health risks.However,designing sensitive and single-use biosensors for early diagnosis remains a major challenge.Here,we report submonolayer lasers on optical fibers as ultrasensitive and disposable biosensors.Telecom optical fibers serve as distributed optical microcavities with high Q-factor,great repeatability,and ultralow cost,which enables whispering-gallery laser emission to detect biomarkers.It is found that the sensing performance strongly depends on the number of gain molecules.The submonolayer lasers obtained a six-order-of-magnitude improvement in the lower limit of detection(LOD)when compared to saturated monolayer lasers.We further achieve an ultrasensitive immunoassay for a Parkinson's disease biomarker,alpha-synuclein(α-syn),with a lower LOD of 0.32 pM in serum,which is three orders of magnitude lower than theα-syn concentration in the serum of Parkinson's disease patients.Our demonstration of submonolayer biolaser offers great potentials in high-throughput clinical diagnosis with ultimate sensitivity.

Tailoring laser colors for super-multiplexed cell tagging

The miniaturization of lasers has opened up a wide variety of new applications,including on-chip optical communications,laser displays,medical imaging,and sensing.A representative example is the cell laser that emerged in 2011,in which a single biological cell expressing green fluorescent protein generated laser emission under optical pumping with nanojoule pulse inside a Fabry–Pérot microcavity.