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1. Optomechanical inertial sensors

   https://doi.org/10.1364/AO.393061  

   Hines, Adam ; Richardson, Logan ; Wisniewski, Hayden ; Guzman, Felipe ( June 2020 , Applied Optics)

   We present a performance analysis of compact monolithic optomechanical inertial sensors that describes their key fundamental limits and overall acceleration noise floor. Performance simulations for low-frequency gravity-sensitive inertial sensors show attainable acceleration noise floors on the order of$1\times <\#comment/>{10}^{-<\#comment/>11}\mathrm{m}/{\mathrm{s}}^2\sqrt{\mathrm{H}\mathrm{z}}$. Furthermore, from our performance models, we devised an optimization approach for our sensor designs, sensitivity, and bandwidth trade space. We conducted characterization measurements of these compact mechanical resonators, demonstrating$\mathit{\text{mQ}}$-products at levels of 250 kg, which highlight their exquisite acceleration sensitivity.

    

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2. Optomechanical lasers for inertial sensing

   https://doi.org/10.1364/JOSAA.396774  

   Wisniewski, Hayden ; Richardson, Logan ; Hines, Adam ; Laurain, Alexandre ; Guzmán, Felipe ( August 2020 , Journal of the Optical Society of America A)

   We have developed an inertially sensitive optomechanical laser by combining a vertical-external-cavity surface-emitting laser (VECSEL) with a monolithic fused silica resonator. By placing the external cavity mirror of the VECSEL onto the optomechanical resonator test mass, we create a sensor where external accelerations are directly transcribed onto the lasing frequency. We developed a proof-of-principle laboratory prototype and observe test mass oscillations at the resonance frequency of the sensor through the VECSEL lasing frequency,$4.18\pm <\#comment/>0.03\mathrm{H}\mathrm{z}$. In addition, we set up an ancillary heterodyne interferometer to track the motion of the mechanical oscillator’s test mass, observing a resonance of$4.194\pm <\#comment/>0.004\mathrm{H}\mathrm{z}$. The interferometer measurements validate the VECSEL results, confirming the feasibility of using optomechanical lasers for inertial sensing.

    

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3. Utilizing adaptive optics to mitigate intra-modal-group power coupling of graded-index few-mode fiber in a 200-Gbit/s mode-division-multiplexed link

   https://doi.org/10.1364/OL.394307  

   Zhang, Runzhou ; Song, Hao ; Song, Haoqian ; Zhao, Zhe ; Milione, Giovanni ; Pang, Kai ; Du, Jing ; Li, Long ; Zou, Kaiheng ; Zhou, Huibin ; et al ( June 2020 , Optics Letters)

   We experimentally demonstrate the utilization of adaptive optics (AO) to mitigate intra-group power coupling among linearly polarized (LP) modes in a graded-index few-mode fiber (GI FMF). Generally, in this fiber, the coupling between degenerate modes inside a modal group tends to be stronger than between modes belonging to different groups. In our approach, the coupling inside the${\mathrm{L}\mathrm{P}}_{11}$group can be represented by a combination of orbital-angular-momentum (OAM) modes, such that reducing power coupling in OAM set tends to indicate the capability to reduce the coupling inside the${\mathrm{L}\mathrm{P}}_{11}$group. We employ two output OAM modes$l=+1$and$l=-<\#comment/>1$as resultant linear combinations of degenerate${\mathrm{L}\mathrm{P}}_{11\mathrm{a}}$and${\mathrm{L}\mathrm{P}}_{11\mathrm{b}}$modes inside the${\mathrm{L}\mathrm{P}}_{11}$group of a$\sim <\#comment/>0.6\text{-}\mathrm{k}\mathrm{m}$GI FMF. The power coupling is mitigated by shaping the amplitude and phase of the distorted OAM modes. Each OAM mode carries an independent 20-, 40-, or 100-Gbit/s quadrature-phase-shift-keying data stream. We measure the transmission matrix (TM) in the OAM basis within${\mathrm{L}\mathrm{P}}_{11}$group, which is a subset of the full LP TM of the FMF-based system. An inverse TM is subsequently implemented before the receiver by a spatial light modulator to mitigate the intra-modal-group power coupling. With AO mitigation, the experimental results for$l=+1$and$l=-<\#comment/>1$modes show, respectively, that (i) intra-modal-group crosstalk is reduced by$><\#comment/>5.8\mathrm{d}\mathrm{B}$and$><\#comment/>5.6\mathrm{d}\mathrm{B}$and (ii) near-error-free bit-error-rate performance is achieved with a penalty of$\sim <\#comment/>0.6\mathrm{d}\mathrm{B}$and$\sim <\#comment/>3.8\mathrm{d}\mathrm{B}$, respectively.

    

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4. Planck Dust Polarization Power Spectra Are Consistent with Strongly Supersonic Turbulence

   https://doi.org/10.3847/1538-4357/ad571b  

   Stalpes, Kye_A ; Collins, David_C ; Huffenberger, Kevin_M ( August 2024 , The Astrophysical Journal)

   The polarization of the cosmic microwave background is rich in information but obscured by foreground emission from the Milky Way’s interstellar medium (ISM). To uncover relationships between the underlying turbulent ISM and the foreground power spectra, we simulated a suite of driven, magnetized, turbulent models of the ISM, varying the fluid properties via the sonic Mach number,${\mathcal{M}}_{\mathcal{S}}$, and magnetic (Alfvén) Mach number,${\mathcal{M}}_{\mathrm{A}}$. We measure the power spectra of density (ρ), velocity (v), magnetic field (H), total projected intensity (T), parity-even polarization (E), and parity-odd polarization (B). We find that the slopes of all six quantities increase with${\mathcal{M}}_{\mathcal{S}}$. Most increase with${\mathcal{M}}_{\mathrm{A}}$, while the magnetic field spectrum steepens with${\mathcal{M}}_{\mathrm{A}}$. By comparing spectral slopes ofEandBto those measured by Planck, we infer typical values of${\mathcal{M}}_{\mathcal{S}}$and${\mathcal{M}}_{\mathrm{A}}$for the ISM. As the fluid velocity increases,${\mathcal{M}}_{\mathcal{S}}>4$, the ratio of BB power to EE power increases to approach a constant value near the Planck-observed value of ∼0.5, regardless of the magnetic field strength. We also examine correlation coefficients between projected quantities, and find thatr^TE≈ 0.3, in agreement with Planck, for appropriate combinations of${\mathcal{M}}_{\mathcal{S}}$and${\mathcal{M}}_{\mathrm{A}}$. Finally, we consider parity-violating correlationsr^TBandr^EB.

    

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5. Modifications of ion beam sputtered tantala thin films by secondary argon and oxygen bombardment

   https://doi.org/10.1364/AO.59.00A150  

   Yang, Le ; Randel, Emmett ; Vajente, Gabriele ; Ananyeva, Alena ; Gustafson, Eric ; Markosyan, Ashot ; Bassiri, Riccardo ; Fejer, Martin ; Menoni, Carmen ( January 2020 , Applied Optics)

   Amorphous tantala (${\mathrm{T}\mathrm{a}}_2{\mathrm{O}}_5$) thin films were deposited by reactive ion beam sputtering with simultaneous low energy assist${\mathrm{A}\mathrm{r}}^{+}$or${\mathrm{A}\mathrm{r}}^{+}/{\mathrm{O}}_2^{+}$bombardment. Under the conditions of the experiment, the as-deposited thin films are amorphous and stoichiometric. The refractive index and optical band gap of thin films remain unchanged by ion bombardment. Around 20% improvement in room temperature mechanical loss and 60% decrease in absorption loss are found in samples bombarded with 100-eV${\mathrm{A}\mathrm{r}}^{+}$. A detrimental influence from low energy${\mathrm{O}}_2^{+}$bombardment on absorption loss and mechanical loss is observed. Low energy${\mathrm{A}\mathrm{r}}^{+}$bombardment removes excess oxygen point defects, while${\mathrm{O}}_2^{+}$bombardment introduces defects into the tantala films.

    

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