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1. Heterogeneous balanced photodetector on silicon nitride with 30 GHz bandwidth and 26 dB common mode rejection ratio

   https://doi.org/10.1364/OFC.2023.W2B.2  

   Gao, Junyi; Tzu, Ta Ching; Fatema, Tasneem; Guo, Xiangwen; Yu, Qianhuan; Navickaite, Gabriele; Zervas, Michael; Geiselmann, Michael; Beling, Andreas (January 2023, 2023 Optical Fiber Communications Conference and Exhibition (OFC))

   We demonstrate InGaAs/InP balanced photodiodes onSi₃N₄waveguides with record-high 3-dB bandwidth of 30 GHz, 0.72 A/W responsivity, and high common mode rejection ratio (CMRR) of 26 dB at 30 GHz. 

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2. A Polarimetric Radar Analysis of Ice Microphysical Processes in Melting Layers of Winter Storms Using S-Band Quasi-Vertical Profiles

   https://doi.org/10.1175/JAMC-D-19-0128.1  

   Griffin, Erica M.; Schuur, Terry J.; Ryzhkov, Alexander V. (April 2020, Journal of Applied Meteorology and Climatology)

   Quasi-vertical profiles (QVPs) obtained from a database of U.S. WSR-88D data are used to document polarimetric characteristics of the melting layer (ML) in cold-season storms with high vertical resolution and accuracy. A polarimetric technique to define the top and bottom of the ML is first introduced. Using the QVPs, statistical relationships are developed to gain insight into the evolution of microphysical processes above, within, and below the ML, leading to a statistical polarimetric model of the ML that reveals characteristics that reflectivity data alone are not able to provide, particularly in regions of weak reflectivity factor at horizontal polarization Z_H. QVP ML statistics are examined for two regimes in the ML data: Z_H≥ 20 dB Z and Z_H< 20 dB Z. Regions of Z_H≥ 20 dB Z indicate locations of MLs collocated with enhanced differential reflectivity Z_DRand reduced copolar correlation coefficient ρ_hv, while for Z_H< 20 dB Z a well-defined ML is difficult to discern using Z_Halone. Evidence of large Z_DRup to 4 dB, backscatter differential phase δ up to 8°, and low ρ_hvdown to 0.80 associated with lower Z_H(from −10 to 20 dB Z) in the ML is observed when pristine, nonaggregated ice falls through it. Positive correlation is documented between maximum specific differential phase K_DPand maximum Z_Hin the ML; these are the first QVP observations of K_DPin MLs documented at S band. Negative correlation occurs between minimum ρ_hvin the ML and ML depth and between minimum ρ_hvin the ML and the corresponding enhancement of Z_H(Δ Z_H= Z_Hmax− Z_Hrain). 

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3. Fiber array to chip attach using laser fusion splicing for low loss

   https://doi.org/10.1364/OE.492752  

   Nauriyal, Juniyali; Song, Meiting; Zhang, Yi; Granados-Baez, Marissa; Cardenas, Jaime (June 2023, Optics Express)

   With the ever-increasing need for higher data rates, datacom and telecom industries are now migrating to silicon photonics to achieve higher data rates with reduced manufacturing costs. However, the optical packaging of integrated photonic devices with multiple I/O ports remains a slow and expensive process. We introduce an optical packaging technique to attach fiber arrays to a photonic chip in a single shot using CO₂laser fusion splicing. We show a minimum coupling loss of 1.1 dB, 1.5 dB, and 1.4 dB per-facet for 2, 4, and 8-fiber arrays (respectively) fused to the oxide mode converters using a single shot from the CO₂laser. 

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4. Imaging Dielectric Breakdown in Valence Change Memory

   https://doi.org/10.1002/adfm.202102313  

   Hubbard, William_A; Lodico, Jared_J; Chan, Ho_Leung; Mecklenburg, Matthew; Regan, Brian_C (September 2021, Advanced Functional Materials)

   Abstract Dielectric breakdown (DB) controls the failure, and increasingly the function, of microelectronic devices. Standard imaging techniques, which generate contrast based on physical structure, struggle to visualize this electronic process. Here in situ scanning transmission electron microscopy (STEM) electron beam‐induced current (EBIC) imaging of DB in Pt/HfO₂/Ti valence change memory devices is reported. STEM EBIC imaging directly visualizes the electronic signatures of DB, namely local changes in the conductivity and in the electric field, with high spatial resolution and good contrast. DB is observed to proceed through two distinct structures arranged in series: a volatile, “soft” filament created by electron injection; and a non‐volatile, “hard” filament created by oxygen‐vacancy aggregation. This picture makes a physical distinction between “soft” and “hard” DB, while at the same time accommodating “progressive” DB, where the relative lengths of the hard and soft filaments can change on a continuum. 

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5. Double-Bilayer polar nanoregions and Mn antisites in (Ca, Sr)3Mn2O7

   https://doi.org/10.1038/s41467-022-32090-w  

   Miao, Leixin; Hasin, Kishwar-E; Moradifar, Parivash; Mukherjee, Debangshu; Wang, Ke; Cheong, Sang-Wook; Nowadnick, Elizabeth A.; Alem, Nasim (August 2022, Nature Communications)

   Abstract The layered perovskite Ca₃Mn₂O₇(CMO) is a hybrid improper ferroelectric candidate proposed for room temperature multiferroicity, which also displays negative thermal expansion behavior due to a competition between coexisting polar and nonpolar phases. However, little is known about the atomic-scale structure of the polar/nonpolar phase coexistence or the underlying physics of its formation and transition. In this work, we report the direct observation of double bilayer polar nanoregions (db-PNRs) in Ca_2.9Sr_0.1Mn₂O₇using aberration-corrected scanning transmission electron microscopy (S/TEM). In-situ TEM heating experiments show that the db-PNRs can exist up to 650 °C. Electron energy loss spectroscopy (EELS) studies coupled with first-principles calculations demonstrate that the stabilization mechanism of the db-PNRs is directly related to an Mn oxidation state change (from 4+ to 2+), which is linked to the presence of Mn antisite defects. These findings open the door to manipulating phase coexistence and achieving exotic properties in hybrid improper ferroelectric. 

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