Generalized angle–orbital angular momentum Talbot effect and modulo mode sorting
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Optical sorting: past, present and future
Optical sorting combines optical tweezers with diverse techniques, including optical spectrum, artificial intelligence (AI) and immunoassay, to endow unprecedented capabilities in particle sorting. In comparison to other methods such as microfluidics, acoustics and electrophoresis, optical sorting offers appreciable advantages in nanoscale precision, high resolution, non-invasiveness, and is becoming increasingly indispensable in fields of biophysics, chemistry, and materials science. This review aims to offer a comprehensive overview of the history, development, and perspectives of various optical sorting techniques, categorised as passive and active sorting methods. To begin, we elucidate the fundamental physics and attributes of both conventional and exotic optical forces. We then explore sorting capabilities of active optical sorting, which fuses optical tweezers with a diversity of techniques, including Raman spectroscopy and machine learning. Afterwards, we reveal the essential roles played by deterministic light fields, configured with lens systems or metasurfaces, in the passive sorting of particles based on their varying sizes and shapes, sorting resolutions and speeds. We conclude with our vision of the most promising and futuristic directions, including AI-facilitated ultrafast and bio-morphology-selective sorting. It can be envisioned that optical sorting will inevitably become a revolutionary tool in scientific research and practical biomedical applications.
Programmable electron-induced color router array
The development of color routers (CRs) realizes the splitting of dichromatic components, contributing to the modulation of photon momentum that acts as the information carrier for optical information technology on the frequency and spatial domains. However, CRs with optical stimulation lack active control of photon momentum at deep subwavelength scale because of the optical diffraction limit. Here, we experimentally demonstrate an active manipulation of dichromatic photon momentum at a deep subwavelength scale via electron-induced CRs, where the CRs radiation patterns are manipulated by steering the electron impact position within 60 nm in a single nanoantenna unit. Moreover, an encrypted display device based on programmable modulation of the CR array is designed and implemented. This approach with enhanced security, large information capacity, and high-level integration at a deep subwavelength scale may find applications in photonic devices and emerging areas in quantum information technologies.
A MEMS traveling-wave micromotor-based miniature gyrocompass
Traditional gyrocompasses, while capable of providing autonomous directional guidance and path correction, face limitations in widespread applications due to their large size, making them unsuitable for compact devices. Microelectromechanical system (MEMS) gyrocompasses offer a promising alternative for miniaturization. However, current MEMS gyrocompasses require the integration of motor rotation modulation technology to achieve high-precision north-finding, whereas conventional motors in previous research introduce large volume and residual magnetism, thus undermining their size advantage. Here, we innovatively propose a miniature MEMS gyrocompass based on a MEMS traveling-wave micromotor, featuring the first integration of a chip-scale rotational actuator and combined with a precise multi-position braking control system, enabling high accuracy and fast north-finding. The proposed gyrocompass made significant advancements, reducing its size to 50 × 42.5 × 24.5 mm³ and achieving an azimuth accuracy of 0.199° within 2 min, which is half the volume of the smallest existing similar devices while offering twice the performance. These improvements indicate that the proposed gyrocompass is suitable for applications in indoor industrial robotics, autonomous driving, and other related fields requiring precise directional guidance.
Compact and reciprocal probe-signal-integrated rotational Doppler velocimetry with fiber-sculpted light
In recent years, with the clarification of the mechanism of the rotational Doppler effect (RDE), there has attracted extensive attention to its development of applications, especially in the detection of the angular velocity of rotating objects. On the other hand, optical fiber technology is widely applied in laser velocimetry from beam delivery to scattered light collection, aiding the miniaturization of instruments. Here we report the first all-fiber rotational Doppler velocimetry (AF-RDV) with a single probe based on a fabricated mode-sculpted fiber-optic element. The constructed AF-RDV can be operated in two reciprocal schemes wherein exchanging the illuminating mode and detected mode. Using this, we experimentally demonstrate the mode-changing dependent nature of the RDE. Particularly, the results suggest that the rotational Doppler shift can be observed by mode-filtering the scattered signal even with a non-twisted probe light. We also show the achromatic property of the RDE by scanning the incident wavelength, enabling the AF-RDV within an ultra-broadband operation range. The AF-RDV exhibits favorable performance for detecting spinning rough surfaces. It may provide an exciting new practical sensing instrument with significant prospects for monitoring angular motion in both research and industry.
Observationally derived magnetic field strength and 3D components in the HD 142527 disk
The magnetic fields in protoplanetary disks around young stars play an important role in disk evolution and planet formation. Measuring the polarized thermal emission from magnetically aligned grains is a reliable method for tracing magnetic fields. However, it has been difficult to observe magnetic fields from dust polarization in protoplanetary disks because other polarization mechanisms involving grown dust grains become efficient. Here we report multi-wavelength (0.87, 1.3, 2.1 and 2.7 mm) observations of polarized thermal emission in the protoplanetary disk around HD 142527, which shows a lopsided dust distribution. We revealed that smaller dust particles still exhibit magnetic alignment in the southern part of the disk. Furthermore, angular offsets between the observed magnetic field and the disk azimuthal direction were discovered. These offsets can be used to measure the relative strengths of each component of a three-dimensional magnetic field (radial (Br), azimuthal (Bϕ) and vertical (Bz)). Applying this method, we derived the magnetic field around a 200 au radius from the protostar as ∣Br∣:∣Bϕ∣:∣Bz∣ ≈ 0.26:1:0.23 with a strength of ~0.3 mG. Our observations provide some key parameters of magnetic activities, including the plasma beta, which has had to be assumed in theoretical studies. In addition, the radial and vertical angular momentum transfers were found to be comparable, which poses a challenge to theoretical studies of protoplanetary disks.
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