Detection of nanoscale objects is highly desirable in various fields such as early‐stage disease diagnosis, environmental monitoring and homeland security. Optical microcavity sensors are renowned ...for ultrahigh sensitivities due to strongly enhanced light‐matter interaction. This review focuses on single nanoparticle detection using optical whispering gallery microcavities and photonic crystal microcavities, both of which have been developing rapidly over the past few years. The reactive and dissipative sensing methods, characterized by light‐analyte interactions, are explained explicitly. The sensitivity and the detection limit are essentially determined by the cavity properties, and are limited by the various noise sources in the measurements. On the one hand, recent advances include significant sensitivity enhancement using techniques to construct novel microcavity structures with reduced mode volumes, to localize the mode field, or to introduce optical gain. On the other hand, researchers attempt to lower the detection limit by improving the spectral resolution, which can be implemented by suppressing the experimental noises. We also review the methods of achieving a better temporal resolution by employing mode locking techniques or cavity ring up spectroscopy. In conclusion, outlooks on the possible ways to implement microcavity‐based sensing devices and potential applications are provided.
Single nanoparticle detection is of critical importance in various fields from fundamental research to practical applications. Optical microcavities are excellent candidates to be employed in ultra‐sensitive sensing due to significantly enhanced light‐matter interaction. The sensing performance can be improved by obtaining better spectral resolution and temporal resolution, and techniques can be applied to realize practical and portable sensors using microcavities.
Optical forces, generally arising from changes of field gradients or linear momentum carried by photons, form the basis for optical trapping and manipulation. Advances in optical forces help to ...reveal the nature of light–matter interactions, giving answers to a wide range of questions and solving problems across various disciplines, and are still yielding new insights in many exciting sciences, particularly in the fields of biological technology, material applications, and quantum sciences. This review focuses on recent advances in optical forces, ranging from fundamentals to applications for biological exploration. First, the basics of different types of optical forces with new light–matter interaction mechanisms and near‐field techniques for optical force generation beyond the diffraction limit with nanometer accuracy are described. Optical forces for biological applications from in vitro to in vivo are then reviewed. Applications from individual manipulation to multiple assembly into functional biophotonic probes and soft‐matter superstructures are discussed. At the end future directions for application of optical forces for biological exploration are provided.
Optical forces form the basis for optical trapping and manipulation, and are of critical importance in various disciplines from fundamental research to practical applications. Advances in optical forces have made significant impact for biological exploration both in vitro and in vivo, with applications from individual manipulation and analysis to multiple assembly and detection.
A new label‐free sensing mechanism is demonstrated experimentally by monitoring the whispering‐gallery mode broadening in microcavities. It is immune to both noise from the probe laser and ...environmental disturbances, and is able to remove the strict requirement for ultra‐high‐Q mode cavities for sensitive nanoparticle detection. This ability to sense nanoscale objects and biological analytes is particularly crucial for wide applications.
The law of momentum conservation rules out many desired processes in optical microresonators. We report broadband momentum transformations of light in asymmetric whispering gallery microresonators. ...Assisted by chaotic motions, broadband light can travel between optical modes with different angular momenta within a few picoseconds. Efficient coupling from visible to near-infrared bands is demonstrated between a nanowaveguide and whispering gallery modes with quality factors exceeding 10 million. The broadband momentum transformation enhances the device conversion efficiency of the third-harmonic generation by greater than three orders of magnitude over the conventional evanescent-wave coupling. The observed broadband and fast momentum transformation could promote applications such as multicolor lasers, broadband memories, and multiwavelength optical networks.
Integrated optics provides a versatile platform for quantum information processing and transceiving with photons1–8. The implementation of quantum protocols requires the capability to generate ...multiple high-quality single photons and process photons with multiple high-fidelity operators9–11. However, previous experimental demonstrations were faced by major challenges in realizing sufficiently high-quality multi-photon sources and multi-qubit operators in a single integrated system4–8, and fully chip-based implementations of multi-qubit quantum tasks remain a significant challenge1–3. Here, we report the demonstration of chip-to-chip quantum teleportation and genuine multipartite entanglement, the core functionalities in quantum technologies, on silicon-photonic circuitry. Four single photons with high purity and indistinguishablity are produced in an array of microresonator sources, without requiring any spectral filtering. Up to four qubits are processed in a reprogrammable linear-optic quantum circuit that facilitates Bell projection and fusion operation. The generation, processing, transceiving and measurement of multi-photon multi-qubit states are all achieved in micrometre-scale silicon chips, fabricated by the complementary metal–oxide–semiconductor process. Our work lays the groundwork for large-scale integrated photonic quantum technologies for communications and computations.Four single-photon states are generated and entangled on a single micrometre-scale silicon chip, and provide the basis for the demonstration of chip-to-chip quantum teleportation.
This study aimed to determine the levels of health-related behaviours (physical activity, screen exposure and sleep status) among Chinese students from primary, secondary and high schools during the ...pandemic of COVID-19, as well as their changes compared with their status before the pandemic. A cross-sectional online survey of 10,933 students was conducted among 10 schools in Guangzhou, China, between 8th and 15th March, 2020. After getting the informed consent from student's caregivers, an online questionnaire was designed and used to obtain time spending on health-related behaviours during the pandemic of COVID-19, as well as the changes compared with 3 months before the pandemic, which was completed by students themselves or their caregivers. Students were stratified by regions (urban, suburban, exurban), gender (boys and girls), and grades (lower grades of primary school, higher grades of primary schools, secondary schools and high schools). Data were expressed as number and percentages and Chi-square test was used to analyse difference between groups. Overall, the response rate of questionnaire was 95.3% (10,416/10,933). The median age of included students was 13.0 (10.0, 16.0) years and 50.1% (n = 5,219) were boys. 41.4%, 53.6% and 53.7% of total students reported less than 15 min per day in light, moderate and vigorous activities and 58.7% (n = 6,113) reported decreased participation in physical activity compared with the time before pandemic. Over 5 h of screen time spending on online study was reported by 44.6% (n = 4,649) of respondents, particular among high school students (81.0%). 76.9% of students reported increased screen time compared with the time before pandemic. Inadequate sleep was identified among 38.5% of students and the proportion was highest in high school students (56.9%). Our study indicated that, during the COVID-19 pandemic, the school closure exerted tremendous negative effects on school-aged children's health habits, including less physical activity, longer screen exposure and irregular sleeping pattern.
Since its invention, optical frequency comb has revolutionized a broad range of subjects from metrology to spectroscopy. The recent development of microresonator-based frequency combs (microcombs) ...provides a unique pathway to create frequency comb systems on a chip. Indeed, microcomb-based spectroscopy, ranging, optical synthesizer, telecommunications and astronomical calibrations have been reported recently. Critical to many of the integrated comb systems is the broad coverage of comb spectra. Here, microcombs of more than two-octave span (450 nm to 2,008 nm) is demonstrated through χ
and χ
nonlinearities in a deformed silica microcavity. The deformation lifts the circular symmetry and creates chaotic tunneling channels that enable broadband collection of intracavity emission with a single waveguide. Our demonstration introduces a new degree of freedom, cavity deformation, to the microcomb studies, and our microcomb spectral range is useful for applications in optical clock, astronomical calibration and biological imaging.
The removal of C2H2 and C2H6 from C2H4 streams is of great significance for feedstock purification to produce polyethylene and other commodity chemicals but the simultaneous adsorption of C2H6 and ...C2H2 over C2H4 from a ternary mixture has never been realized. Herein, a robust metal–organic framework, TJT‐100, was designed and synthesized, which demonstrates remarkably selective adsorption of C2H2 and C2H6 over C2H4. Breakthrough experiments show that TJT‐100 can be used as an adsorbent for high‐performance purification of C2H4 from a ternary mixture of C2H2/C2H4/C2H6 (0.5:99:0.5) to afford a C2H4 purity greater than 99.997 %, beyond that required for ethylene polymerization. Computational studies reveal that the uncoordinated carboxylate oxygen atoms and coordinated water molecules pointing towards the pore can trap C2H2 and C2H6 through the formation of multiple C−H⋅⋅⋅O electrostatic interactions, while the corresponding C2H4–framework interaction is unfavorable.
A robust porous metal–organic framework was synthesized and utilized for the highly selective separation of C2H4 from a ternary mixture of C2 hydrocarbons. After a single operation, the C2H4 purity of the outlet was greater than 99.997 %.
Dissipative Kerr soliton (DKS) featuring broadband coherent frequency comb with compact size and low power consumption, provides an unparalleled tool for nonlinear physics investigation and precise ...measurement applications. However, the complex nonlinear dynamics generally leads to stochastic soliton formation process and makes it highly challenging to manipulate soliton number and temporal distribution in the microcavity. Here, synthesized and reconfigurable soliton crystals (SCs) are demonstrated by constructing a periodic intra-cavity potential field, which allows deterministic SCs synthesis with soliton numbers from 1 to 32 in a monolithic integrated microcavity. The ordered temporal distribution coherently enhanced the soliton crystal comb lines power up to 3 orders of magnitude in comparison to the single-soliton state. The interaction between the traveling potential field and the soliton crystals creates periodic forces on soliton and results in forced soliton oscillation. Our work paves the way to effectively manipulate cavity solitons. The demonstrated synthesized SCs offer reconfigurable temporal and spectral profiles, which provide compelling advantages for practical applications such as photonic radar, satellite communication and radio-frequency filter.
Optical whispering‐gallery mode (WGM) microcavities featuring ultrahigh Q factors and small mode volumes enhance significantly the interaction between light and matter, becoming an excellent platform ...for achieving ultralow‐threshold microlasers. However, the emission of traditional WGMs is isotropic due to the rotational symmetry of cavity geometries, which hinders the potential photonics applications. In this review, the progress in WGM microcavities towards unidirectional laser emission is summarized. When a subwavelength scatterer is placed on the boundary of the microcavity, the unidirectional emission occurs due to the collimation effect of the microcavity‐enhanced scattering field. Furthermore, microcavities deformed from the circular shapes can not only produce the chaos‐assisted unidirectional emission, but also maintain high Q factors by special design and fabrication processes. Finally, gratings along the circumference of the WGM microdisk or microring can scatter the WGMs in the vertical direction. The review also lists several important applications of these types of microcavities, such as wide‐band laser illumination source, free‐space coupling, evanescent‐field enhancement, optical energy storage, and sensing.
In this review, the progress in whispering‐gallery mode microcavities towards unidirectional laser emission is summarized. Three types of mechanisms have been introduced, including scatterer‐induced unidirectional emission, chaos‐induced unidirectional emission and grating‐induced vertical emission. Besides, several important applications of these whispering‐gallery microcavities are introduced, such as wide‐band laser illumination source, free‐space coupling, evanescent field enhancement, optical energy storage, and sensing.
PDF
