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1. Mid-IR spectroscopy of Er 3+ doped low-phonon CsCdCl 3 and CsPbCl 3 crystals

   https://doi.org/10.1364/JOSAB.470152  

   Brown, Ei_Ei ; Fleischman, Zackery_D ; McKay, Jason ; Hommerich, Uwe ; Kabir, Al_Amin ; Riggins, Jazmine ; Trivedi, Sudhir ; Dubinskii, Mark ( September 2022 , Journal of the Optical Society of America B)

   The mid-IR spectroscopic properties of${\mathrm{E}\mathrm{r}}^{3+}$doped low-phonon${\mathrm{C}\mathrm{s}\mathrm{C}\mathrm{d}\mathrm{C}\mathrm{l}}_3$and${\mathrm{C}\mathrm{s}\mathrm{P}\mathrm{b}\mathrm{C}\mathrm{l}}_3$crystals grown by the Bridgman technique have been investigated. Using optical excitations at$\sim <\#comment/>800\mathrm{n}\mathrm{m}$and$\sim <\#comment/>660\mathrm{n}\mathrm{m}$, both crystals exhibited IR emissions at$\sim <\#comment/>1.55$,$\sim <\#comment/>2.75$,$\sim <\#comment/>3.5$, and$\sim <\#comment/>4.5\text{µ<\#comment/>}\mathrm{m}$at room temperature. The mid-IR emission at 4.5 µm, originating from the${}^4{\mathrm{I}}_{9/2}\to <\#comment/>{}^4{\mathrm{I}}_{11/2}$transition, showed a long emission lifetime of$\sim <\#comment/>11.6\mathrm{m}\mathrm{s}$for${\mathrm{E}\mathrm{r}}^{3+}$doped${\mathrm{C}\mathrm{s}\mathrm{C}\mathrm{d}\mathrm{C}\mathrm{l}}_3$, whereas${\mathrm{E}\mathrm{r}}^{3+}$doped${\mathrm{C}\mathrm{s}\mathrm{P}\mathrm{b}\mathrm{C}\mathrm{l}}_3$exhibited a shorter lifetime of$\sim <\#comment/>1.8\mathrm{m}\mathrm{s}$. The measured emission lifetimes of the${}^4{\mathrm{I}}_{9/2}$state were nearly independent of the temperature, indicating a negligibly small nonradiative decay rate through multiphonon relaxation, as predicted by the energy-gap law for low-maximum-phonon energy hosts. The room temperature stimulated emission cross sections for the${}^4{\mathrm{I}}_{9/2}\to <\#comment/>{}^4{\mathrm{I}}_{11/2}$transition in${\mathrm{E}\mathrm{r}}^{3+}$doped${\mathrm{C}\mathrm{s}\mathrm{C}\mathrm{d}\mathrm{C}\mathrm{l}}_3$and${\mathrm{C}\mathrm{s}\mathrm{P}\mathrm{b}\mathrm{C}\mathrm{l}}_3$were determined to be$\sim <\#comment/>0.14\times <\#comment/>{10}^{-<\#comment/>20}{\mathrm{c}\mathrm{m}}^2$and$\sim <\#comment/>0.41\times <\#comment/>{10}^{-<\#comment/>20}{\mathrm{c}\mathrm{m}}^2$, respectively. The results of Judd–Ofelt analysis are presented and discussed.

    

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2. Simultaneous turbulence mitigation and channel demultiplexing for two 100  Gbit/s orbital-angular-momentum multiplexed beams by adaptive wavefront shaping and diffusing

   https://doi.org/10.1364/OL.383714  

   Zhang, Runzhou ; Song, Hao ; Zhao, Zhe ; Song, Haoqian ; Du, Jing ; Liu, Cong ; Pang, Kai ; Li, Long ; Zhou, Huibin ; Willner, Ari_N ; et al ( January 2020 , Optics Letters)

   We experimentally demonstrate simultaneous turbulence mitigation and channel demultiplexing in a 200 Gbit/s orbital-angular-momentum (OAM) multiplexed link by adaptive wavefront shaping and diffusing (WSD) the light beams. Different realizations of two emulated turbulence strengths (the Fried parameter$r_0=0.4,1.0\mathrm{m}\mathrm{m}$) are mitigated. The experimental results show the following. (1) Crosstalk between OAM$l=+1$and$l=-<\#comment/>1$modes can be reduced by$><\#comment/>10.0$and$><\#comment/>5.8\mathrm{d}\mathrm{B}$, respectively, under the weaker turbulence ($r_0=1.0\mathrm{m}\mathrm{m}$); crosstalk is further improved by$><\#comment/>17.7$and$><\#comment/>19.4\mathrm{d}\mathrm{B}$, respectively, under most realizations in the stronger turbulence ($r_0=0.4\mathrm{m}\mathrm{m}$). (2) The optical signal-to-noise ratio penalties for the bit error rate performance are measured to be$\sim <\#comment/>0.7$and$\sim <\#comment/>1.6\mathrm{d}\mathrm{B}$under weaker turbulence, while measured to be$\sim <\#comment/>3.2$and$\sim <\#comment/>1.8\mathrm{d}\mathrm{B}$under stronger turbulence for OAM$l=+1$and$l=-<\#comment/>1$mode, respectively.

    

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3. Sparse decomposition light-field microscopy for high speed imaging of neuronal activity

   https://doi.org/10.1364/OPTICA.392805  

   Yoon, Young-Gyu ; Wang, Zeguan ; Pak, Nikita ; Park, Demian ; Dai, Peilun ; Kang, Jeong_Seuk ; Suk, Ho-Jun ; Symvoulidis, Panagiotis ; Guner-Ataman, Burcu ; Wang, Kai ; et al ( October 2020 , Optica)

   One of the major challenges in large scale optical imaging of neuronal activity is to simultaneously achieve sufficient temporal and spatial resolution across a large volume. Here, we introduce sparse decomposition light-field microscopy (SDLFM), a computational imaging technique based on light-field microscopy (LFM) that takes algorithmic advantage of the high temporal resolution of LFM and the inherent temporal sparsity of spikes to improve effective spatial resolution and signal-to-noise ratios (SNRs). With increased effective spatial resolution and SNRs, neuronal activity at the single-cell level can be recovered over a large volume. We demonstrate the single-cell imaging capability of SDLFM within vivoimaging of neuronal activity of whole brains of larval zebrafish with estimated lateral and axial resolutions of$\sim <\#comment/>3.5\text{µ<\#comment/>}\mathrm{m}$and$\sim <\#comment/>7.4\text{µ<\#comment/>}\mathrm{m}$, respectively, acquired at volumetric imaging rates up to 50 Hz. We also show that SDLFM increases the quality of neural imaging in adult fruit flies.

    

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4. Large-area, high-numerical-aperture multi-level diffractive lens via inverse design

   https://doi.org/10.1364/OPTICA.388697  

   Meem, Monjurul ; Banerji, Sourangsu ; Pies, Christian ; Oberbiermann, Timo ; Majumder, Apratim ; Sensale-Rodriguez, Berardi ; Menon, Rajesh ( March 2020 , Optica)

   Flat lenses enable thinner, lighter, and simpler imaging systems. However, large-area and high-NA flat lenses have been elusive due to computational and fabrication challenges. Here we applied inverse design to create a multi-level diffractive lens (MDL) with thickness$<<\#comment/>1.35\text{µ<\#comment/>}\mathrm{m}$, diameter of 4.13 mm, and$\mathrm{N}\mathrm{A}=0.9$at wavelength of 850 nm (bandwidth$\sim <\#comment/>35\mathrm{n}\mathrm{m}$). Since the MDL is created in polymer, it can be cost-effectively replicated via imprint lithography.

    

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5. Ultra-high extinction ratio polarization beam splitter with extreme skin-depth waveguide

   https://doi.org/10.1364/OL.420824  

   Ahmed, Syed_Z ; Ahmed, Ishtiaque ; Mia, Md_Borhan ; Jaidye, Nafiz ; Kim, Sangsik ( April 2021 , Optics Letters)

   In this Letter, we present a high extinction ratio and compact on-chip polarization beam splitter (PBS), based on an extreme skin-depth (eskid) waveguide. Subwavelength-scale gratings form an effectively anisotropic metamaterial cladding and introduce a large birefringence. The anisotropic dielectric perturbation of the metamaterial cladding suppresses the TE polarization extinction via exceptional coupling, while the large birefringence efficiently cross-couples the TM mode, thus reducing the coupling length. We demonstrated the eskid-PBS on a silicon-on-insulator platform and achieved an ultra-high extinction ratio PBS ($\approx <\#comment/>60\mathrm{d}\mathrm{B}$for TE and$\approx <\#comment/>48\mathrm{d}\mathrm{B}$for TM) with a compact coupling length ($\approx <\#comment/>14.5\text{µ<\#comment/>}\mathrm{m}$). The insertion loss is also negligible ($<<\#comment/>0.6\mathrm{d}\mathrm{B}$). The bandwidth is$><\#comment/>80$(30) nm for the TE (TM) extinction ratio$><\#comment/>20\mathrm{d}\mathrm{B}$. Our ultra-high extinction ratio PBS is crucial in implementing efficient polarization diversity circuits, especially where a high degree of polarization distinguishability is necessary, such as photonic quantum information processing.

    

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