Hysteresis and balance of backaction force on dielectric particles photothermally mediated by photonic nanojet

Packaged WGM MBR sensor for high-performance temperature measurement using CNN-based multimode barcode images

The whispering gallery mode (WGM) optical microresonator sensors are emerging as a promising platform for precise temperature measurements, driven by their excellent sensitivity, resolution and integration. Nevertheless, challenges endure regarding stability, single resonant mode tracking, and real-time monitoring. Here, we demonstrate a temperature measurement approach based on convolutional neural network (CNN), leveraging the recognition of multimode barcode images acquired from a WGM microbottle resonator (MBR) sensor with robust packaged microresonator-taper coupling structure (packaged-MTCS). Our work ensures not only a high sensitivity of -14.28 pm/℃ and remarkable resolution of 3.5 × 10-4 ℃ across a broad dynamic range of 96 ℃ but also fulfills the demands for real-time temperature measurement with an average detection accuracy of 96.85% and a speed of 0.68s per image. These results highlight the potential of high-performance WGM MBR sensors in various fields and lay the groundwork for stable soliton microcomb excitation through thermal tuning.

Topologically protected optical pulling force on synthetic particles through photonic nanojet

A dielectric microsphere concentrates light into a photonic nanojet (PNJ), and swims towards the near-infrared laser in response to the nanojet-mediated force. In contrast, a Janus particle with an opaque metal layer was thought to be impossible to concentrate light into a stable nanojet. However, the Janus particle may experience optical torque owing to the inhomogeneous composition on both sides even in linearly polarized non-resonant light. Herein, we report on topologically protected PNJ produced by a synthetic Janus particle, and observed the backaction force on the Janus particle. Due to symmetry, the counter-propagating beams can both form PNJ on the respective opposite sides, and pull Janus particles towards respective sources. Furthermore, we unveil that the hysteresis on backaction force with respect to the injection power also exists on synthetic Janus particle compared with their dielectric counterparts. Additionally, the magnitude of the backaction force varies between power increase and decrease stages even with the same laser power. We anticipate that the observation offers great possibilities to pull irregular particles by concentrating light with the particle, and such scheme may be applied for parallel particle manipulation and classification.

Temperature-Controlled Switchable Photonic Nanojet Generated by Truncated Cylindrical Structure

We propose a novel micro-nano structure that can realize a photonic nanojet (PNJ) switch by adjusting the temperature, which is composed of a truncated cylinder coated with a thin vanadium dioxide (VO2) film. The influence of temperature on the maximum strength, full width at half maximum (FWHM), working distance, and focal length of the PNJ were studied by finite-difference time-domain (FDTD) method. The results demonstrate that the structure can adjust the open and close state of the PNJ by changing the temperature. A PNJ with varying characteristics can be obtained at both high and low temperatures, and the maximum intensity ratio of the PNJ can reach up to 7.25. This discovery provides a new way of optical manipulation, sensing and detection, microscopy imaging, optoelectronic devices, and other fields.

An opto-thermal approach for assembling yeast cells by laser heating of a trapped light absorbing particle

Cell assembly has important applications in biomedical research, which can be achieved with laser-heating induced thermal convective flow. In this paper, an opto-thermal approach is developed to assemble the yeast cells dispersed in solution. At first, polystyrene (PS) microbeads are used instead of cells to explore the method of microparticle assembly. The PS microbeads and light absorbing particles (APs) are dispersed in solution and form a binary mixture system. Optical tweezers are used to trap an AP at the substrate glass of the sample cell. Due to the optothermal effect, the trapped AP is heated and a thermal gradient is generated, which induces a thermal convective flow. The convective flow drives the microbeads moving toward and assembling around the trapped AP. Then, the method is used to assemble the yeast cells. The results show that the initial concentration ratio of yeast cells to APs affects the eventual assembly pattern. The binary microparticles with different initial concentration ratios assemble into aggregates with different area ratios. The experiment and simulation results show that the dominant factor in the area ratio of yeast cells in the binary aggregate is the velocity ratio of the yeast cells to the APs. Our work provides an approach to assemble the cells, which has a potential application in the analysis of microbes.