Quantification of broadband chromatic drifts in Fabry–Pérot resonators for exoplanet science
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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.
Deep tissue photoacoustic imaging with light and sound
Photoacoustic computed tomography (PACT) can harvest diffusive photons to image the optical absorption contrast of molecules in a scattering medium, with ultrasonically-defined spatial resolution. PACT has been extensively used in preclinical research for imaging functional and molecular information in various animal models, with recent clinical translations. In this review, we aim to highlight the recent technical breakthroughs in PACT and the emerging preclinical and clinical applications in deep tissue imaging.
Digital infrastructure construction and corporate innovation efficiency: evidence from Broadband China Strategy
Adopting the Broadband China Strategy as a quasi-natural experiment, we construct a multi-period Difference-in-Differences (DID) model to examine the impact of digital infrastructure construction on corporate innovation efficiency with panel data from Chinese listed companies between 2010 to 2022. Our findings indicate that the development of digital infrastructure significantly boosts corporate innovation efficiency. Mechanistic analysis reveals that financing constraints negatively moderates this innovation impact, while human capital positively moderates it. The effects of the Broadband China Strategy are particularly pronounced in non-state-owned enterprises, non-high-tech enterprises, and firms located in the non-eastern region of China. Our research provides important insights for enterprises seeking to enhance their innovation efficiency, while also offering strong empirical evidence on the role of digital infrastructure in fostering corporate innovation. Our study contributes to the literature on digital economy and innovation, with practical implications for policymakers and firms aiming to leverage digital infrastructure for sustained competitive advantage.
Broadband transparent Huygens’ spaceplates
Spaceplates have emerged in the context of nonlocal metasurfaces, enabling the compression of optical systems by minimizing the required empty space between their components. In this work, we design and analyze spaceplates that support resonances with opposite symmetries, operating under the so-called Huygens’ condition. Using the temporal coupled-mode theory, we demonstrate that the spatial compression provided by Huygens’ spaceplates is twice that of conventional single-resonance counterparts. Additionally, they can support broader operational bandwidths and numerical apertures, facilitating the reduction of chromatic aberrations. Moreover, Huygens’ spaceplates maintain nearly full transparency over a wide frequency and angular range, allowing their straightforward cascading for multi-frequency broadband operation. Finally, we propose a physical implementation of a Huygens’ spaceplate for optical frequencies based on a photonic crystal slab geometry.
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