Nanometre-resolution three-dimensional tomographic and vectorial near-field imaging in dielectric optical resonators
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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.
Periodically poled aluminum scandium nitride bulk acoustic wave resonators and filters for communications in the 6G era
Bulk Acoustic Wave (BAW) filters find applications in radio frequency (RF) communication systems for Wi-Fi, 3G, 4G, and 5G networks. In the beyond-5G (potential 6G) era, high-frequency bands (>8 GHz) are expected to require resonators with high-quality factor (Q) and electromechanical coupling (({k}_{t}^{2})) to form filters with low insertion loss and high selectivity. However, both the Q and ({k}_{t}^{2}) of resonator devices formed in traditional uniform polarization piezoelectric films of aluminum nitride (AlN) and aluminum scandium nitride (AlScN) decrease when scaled beyond 8 GHz. In this work, we utilized 4-layer AlScN periodically poled piezoelectric films (P3F) to construct high-frequency (~17–18 GHz) resonators and filters. The resonator performance is studied over a range of device geometries, with the best resonator achieving a ({k}_{t}^{2}) of 11.8% and a ({Q}_{{rm {p}}}) of 236.6 at the parallel resonance frequency (({f}_{{rm {p}}})) of 17.9 GHz. These resulting figures-of-merit are (({{{rm {FoM}}}}_{1}={{k}_{t}^{2}Q}_{{rm {p}}}) and ({{{rm {FoM}}}}_{2}={f}_{{rm {p}}}{{{rm {FoM}}}}_{1}{times }{10}^{-9})) 27.9 and 500, respectively. These and the ({k}_{t}^{2}) are significantly higher than previously reported AlN/AlScN-based resonators operating at similar frequencies. Fabricated 3-element and 6-element filters formed from these resonators demonstrated low insertion losses (IL) of 1.86 and 3.25 dB, and −3 dB bandwidths (BW) of 680 MHz (fractional BW of 3.9%) and 590 MHz (fractional BW of 3.3%) at a ~17.4 GHz center frequency. The 3-element and 6-element filters achieved excellent linearity with in-band input third-order intercept point (IIP3) values of +36 and +40 dBm, respectively, which are significantly higher than previously reported acoustic filters operating at similar frequencies.
High-performance magnetostatic wave resonators based on deep anisotropic etching of gadolinium gallium garnet substrates
Magnetostatic wave resonators based on yttrium iron garnet (YIG) are a promising technology platform for future communication filters. Such devices have demonstrated better quality factors than acoustic resonators in the 7 GHz range and above. However, the coupling coefficients of these resonators have been limited to less than 3%, primarily due to the restricted design space that is a result of microfabrication challenges related to the patterning of gadolinium gallium garnet (GGG), the substrate material used for growing single-crystal YIG. Here we report magnetostatic wave resonators created through the anisotropic etching of GGG substrates. Our approach, which is based on the YIG-on-GGG platform, uses a transducer with a hairclip-like structure. It is created by developing a microfabrication methodology that involves thinning and deep etching (up to 100 μm) of the GGG substrate. The resulting magnetostatic wave resonators exhibit a coupling of more than 8% in the 6–20 GHz frequency range.
Comparative analysis of nanomechanical resonators: sensitivity, response time, and practical considerations in photothermal sensing
Nanomechanical photothermal sensing has significantly advanced single-molecule/particle microscopy and spectroscopy, and infrared detection. In this approach, the nanomechanical resonator detects shifts in resonant frequency due to photothermal heating. However, the relationship between photothermal sensitivity, response time, and resonator design has not been fully explored. This paper compares three resonator types – strings, drumheads, and trampolines – to explore this relationship. Through theoretical modeling, experimental validation, and finite element method simulations, we find that strings offer the highest sensitivity (with a noise equivalent power of 280 fW/Hz1/2 for strings made of silicon nitride), while drumheads exhibit the fastest thermal response. The study reveals that photothermal sensitivity correlates with the average temperature rise and not the peak temperature. Finally, the impact of photothermal back-action is discussed, which can be a major source of frequency instability. This work clarifies the performance differences and limits among resonator designs and guides the development of advanced nanomechanical photothermal sensors, benefiting a wide range of applications.
Airborne optical imaging technology: a road map in CIOMP
Airborne optical imaging can flexibly obtain the intuitive information of the observed scene from the air, which plays an important role of modern optical remote sensing technology. Higher resolution, longer imaging distance, and broader coverage are the unwavering pursuits in this research field. Nevertheless, the imaging environment during aerial flights brings about multi-source dynamic interferences such as temperature, air pressure, and complex movements, which forms a serious contradiction with the requirements of precision and relative staticity in optical imaging. As the birthplace of Chinese optical industry, the Changchun Institute of Optics, Fine Mechanics and Physics (CIOMP) has conducted the research on airborne optical imaging for decades, resulting in rich innovative achievements, completed research conditions, and exploring a feasible development path. This article provides an overview of the innovative work of CIOMP in the field of airborne optical imaging, sorts out the milestone nodes, and predicts the future development direction of this discipline, with the aim of providing inspiration for related research.
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