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1. Widely separated optical Kerr parametric oscillation in AlN microrings

   https://doi.org/10.1364/OL.384317  

   Tang, Yulong ; Gong, Zheng ; Liu, Xianwen ; Tang, Hong X. ( February 2020 , Optics Letters)

   Here, we report${\mathrm{\chi <\#comment/>}}^{(3)}$-based optical parametric oscillation (OPO) with widely separated signal–idler frequencies from crystalline aluminum nitride microrings pumped at$2\text{µ<\#comment/>}\mathrm{m}$. By tailoring the width of the microring, OPO reaching toward the telecom and mid-infrared bands with a frequency separation of 64.2 THz is achieved. While dispersion engineering through changing the microring width is capable of shifting the OPO sideband by$><\#comment/>9\mathrm{T}\mathrm{H}\mathrm{z}$, the OPO frequency can also be agilely tuned in the ranges of 1 and 0.1 THz, respectively, by shifting the pump wavelength and controlling the chip’s temperature. At high pump powers, the OPO sidebands further evolve into localized frequency comb lines. Such large-frequency-shift OPO with flexible wavelength tunability will lead to enhanced chip-scale light sources.

    

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2. 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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3. Diel variability of bulk optical properties associated with the growth and division of small phytoplankton in the North Pacific Subtropical Gyre

   https://doi.org/10.1364/AO.394123  

   Henderikx Freitas, Fernanda ; Dugenne, Mathilde ; Ribalet, François ; Hynes, Annette ; Barone, Benedetto ; Karl, David M. ; White, Angelicque E. ( July 2020 , Applied Optics)

   Cross-platform observing systems are requisite to capturing the temporal and spatial dynamics of particles in the ocean. We present simultaneous observations of bulk optical properties, including the particulate beam attenuation (${\mathit{\text{c}}}_{\mathit{\text{p}}}$) and backscattering ($b_{\text{bp}}$) coefficients, and particle size distributions collected in the North Pacific Subtropical Gyre. Clear and coherent diel cycles are observed in all bulk and size-fractionated optical proxies for particle biomass. We show evidence linking diurnal increases in${\mathit{\text{c}}}_{\mathit{\text{p}}}$and${\mathit{\text{b}}}_{\text{bp}}$to daytime particle growth and division of cells, with particles$<<\#comment/>7\text{µ<\#comment/>}\mathrm{m}$driving the daily cycle of particle production and loss within the mixed layer. Flow cytometry data reveal the nitrogen-fixing cyanobacteriumCrocosphaera($\sim <\#comment/>4-<\#comment/>7\text{µ<\#comment/>}\mathrm{m}$) to be an important driver of${\mathit{\text{c}}}_{\mathit{\text{p}}}$at the time of sampling, whereasProchlorococcusdynamics ($\sim <\#comment/>0.5\text{µ<\#comment/>}\mathrm{m}$) were essential to reproducing temporal variability in${\mathit{\text{b}}}_{\text{bp}}$. This study is a step towards improved characterization of the particle size range represented byin situbulk optical properties and a better understanding of the mechanisms that drive variability in particle production in the oligotrophic open ocean.

    

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4. Picostrain-resolution fiber-optic sensing down to sub-10  mHz infrasonic frequencies

   https://doi.org/10.1364/JOSAB.395397  

   Hoque, Nabil Md Rakinul ; Duan, Lingze ( August 2020 , Journal of the Optical Society of America B)

   High-resolution strain sensing based on long, high-finesse fiber Fabry–Perot interferometers (FFPIs) has been demonstrated with a special focus on the infrasonic frequency range. A novel dual-FFPI scheme allows the large environment-induced background at low frequencies to be suppressed, permitting high strain resolution limited only by excess electronic noise. Noise-equivalent strain resolution of$257\mathrm{p}\text{ε<\#comment/>}/\surd <\#comment/>\mathrm{H}\mathrm{z}$has been achieved at 6 mHz, and the resolution improves to$\sim <\#comment/>200\mathrm{f}\text{ε<\#comment/>}/\surd <\#comment/>\mathrm{H}\mathrm{z}$between 4–20 Hz. Without the use of any additional optical frequency references and with only off-the shelf commercial components, these resolutions are much better than most in the prior reports. Especially, an improvement of a factor of 1.8 is achieved in comparison with the highest resolution reported so far near 5 Hz. The limiting factors of the current scheme have been analyzed in detail, and the application prospects have been demonstrated using an acoustic transducer. The work lays out the potential of using long FFPIs with high finesse for high-resolution fiber-optic sensing in the infrasonic frequency range.

    

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5. Additive manufacturing for the development of optical/photonic systems and components

   https://doi.org/10.1364/OPTICA.451642  

   Berglund, Gregory ; Wisniowiecki, Anna ; Gawedzinski, John ; Applegate, Brian ; Tkaczyk, Tomasz S. ( June 2022 , Optica)

   The ambition of this review is to provide an up-to-date synopsis of the state of 3D printing technology for optical and photonic components, to gauge technological advances, and to discuss future opportunities. While a range of approaches have been developed and some have been commercialized, no single approach can yet simultaneously achieve small detail and low roughness at large print volumes and speed using multiple materials. Instead, each approach occupies a niche where the components/structures that can be created fit within a relatively narrow range of geometries with limited material choices. For instance, the common Fused Deposition Modeling (FDM) approach is capable of large print volumes at relatively high speeds but lacks the resolution needed for small detail ($><\#comment/>100\text{µ<\#comment/>}\mathrm{m}$) with low roughness ($><\#comment/>9\text{µ<\#comment/>}\mathrm{m}$). At the other end of the spectrum, two-photon polymerization can achieve roughness ($<<\#comment/>15\mathrm{n}\mathrm{m}$) and detail ($<<\#comment/>140\mathrm{n}\mathrm{m}$) comparable to commercial molded and polished optics. However, the practical achievable print volume and speed are orders of magnitude smaller and slower than the FDM approach. Herein, we discuss the current state-of-the-art 3D printing approaches, noting the capability of each approach and prognosticate on future innovations that could close the gaps in performance.

    

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