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1. Dual-band Optical Isolation in Thin-film Lithium Niobate Based on Dynamic Modulation

   https://doi.org/10.1364/CLEO_SI.2023.SW3L.6  

   Shah, Manav; Briggs, Ian; Chen, Pao-Kang; Hou, Songyan; Fan, Linran (May 2023, Optica Publishing Group)

   Current integrated optical isolators have limited bandwidths due to stringent phase-matching, resonant structures, or absorption. We demonstrate broadband optical isolation in thin-film lithium niobate that simultaneously achieves∼100 nm isolation bandwidth at visible and telecom wavelengths. 

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2. Design of GaSb-based monolithic passive photonic devices at wavelengths above 2 µm

   https://doi.org/10.1088/2515-7647/ace509  

   Sumon, Md Saiful; Sankar, Shrivatch; You, Weicheng; Faruque, Imad I; Dwivedi, Sarvagya; Arafin, Shamsul (July 2023, Journal of Physics: Photonics)

   Abstract In this paper, we report, for the first time, a theoretical study on passive photonic devices including optical power splitters/combiners and grating couplers (GCs) operating at non-telecom wavelengths above 2 µ m in a monolithic GaSb platform. Passive components were designed to operate, in particular, at around 2.6 µ m for monolithic integration with active photonic devices on the III–V gallium antimonide material platform. The three popular types of splitters/combiners such as directional couplers, multimode interferometer-, and Y-branch-couplers were theoretically investigated. Based on our optimized design and rigorous analysis, fabrication-compatible 1 × 2 optical power splitters with less than 0.12 dB excess losses, large spectral bandwidth, and a 50:50 splitting ratio are achieved. For fiber-to-chip coupling, we also report the design of GCs with an outcoupling efficiency of ∼29% at 2.56 μ m and a 3 dB bandwidth of 80 nm. The results represent a significant step towards developing a complete functional photonic integrated circuits at mid-wave infrared wavelengths. 

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3. An integrated photonic engine for programmable atomic control

   https://doi.org/10.1038/s41467-024-55423-3  

   Christen, Ian; Propson, Thomas; Sutula, Madison; Sattari, Hamed; Choong, Gregory; Panuski, Christopher; Melville, Alexander; Mallek, Justin; Brabec, Cole; Hamilton, Scott; et al (December 2025, Nature Communications)

   Abstract Solutions for scalable, high-performance optical control are important for the development of scaled atom-based quantum technologies. Modulation of many individual optical beams is central to applying arbitrary gate and control sequences on arrays of atoms or atom-like systems. At telecom wavelengths, miniaturization of optical components via photonic integration has pushed the scale and performance of classical and quantum optics far beyond the limitations of bulk devices. However, material platforms for high-speed telecom integrated photonics lack transparency at the short wavelengths required by leading atomic systems. Here, we propose and implement a scalable and reconfigurable photonic control architecture using integrated, visible-light modulators based on thin-film lithium niobate. We combine this system with techniques in free-space optics and holography to demonstrate multi-channel, gigahertz-rate visible beamshaping. When applied to silicon-vacancy artificial atoms, our system enables the spatial and spectral addressing of a dynamically-selectable set of these stochastically-positioned point emitters. 

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4. Plasmonic and photonic isolators based on the spatiotemporal modulation of graphene

   https://doi.org/10.1117/12.2519237  

   Correas-Serrano, Diego; Paul, Nayan; Gomez-Diaz, J. Sebastian (May 2019, Micro- and Nanotechnology Sensors, Systems, and Applications XI, edited by Thomas George, M. Saif Islam, Proc. of SPIE)

   We explore the possibilities enabled by the spatiotemporal modulation of graphene’s conductivity to realize magnetic-free isolators at terahertz and infrared frequencies. To this purpose, graphene is loaded with periodically distributed gates that are time-modulated. First, we investigate plasmonic isolators based on various mechanisms such as symmetric bandgaps and interband photonic transitions and we demonstrate isolation levels over 30 dB using realistic biasing schemes. To lessen the dependence on high-quality graphene able to support surface plasmons with low damping, we then introduce a hybrid photonic platform based on spatiotemporally modulated graphene coupled to high-Q modes propagating on dielectric waveguides. We exploit transversal Fabry-Perot resonances appearing due to the finite-width of the waveguide to significantly boost graphene/waveguide interactions and to achieve isolation levels over 50 dB in compact structures modulated with low biasing voltages. The resulting platform is CMOS-compatible, exhibits an overall loss below 4 dB, and is robust against graphene imperfections. We also put forward a theoretical framework based on coupled-mode theory and on solving the eigenstates of the modulated structure that is in excellent agreement with full-wave numerical simulations, sheds light in the underlying physics that govern the proposed isolators, and speeds-up their analysis and design. We envision that the proposed technology will open new and efficient routes to realize integrated and silicon compatible isolators, with wide range of applications in communications and photonic networks. 

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5. Chip‐Based Optical Isolator and Nonreciprocal Parity‐Time Symmetry Induced by Stimulated Brillouin Scattering

   https://doi.org/https://doi.org/10.1002/lpor.201900278  

   Ma, J.; Wen, J.; Hu, Y.; Ding, S.; Jiang, X.; Jiang, L.; Xiao, M. (April 2020, Laser photonics reviews)

   Realization of chip‐scale nonreciprocal optics such as isolators and circulators is highly demanding for all‐optical signal routing and protection with standard photonics foundry process. Owing to the significant challenge for incorporating magneto‐optical materials on chip, the exploration of magnetic‐free alternatives has become exceedingly imperative in integrated photonics. Here, a chip‐based, tunable all‐optical isolator at the telecommunication band is demonstrated, which is based upon bulk stimulated Brillouin scattering (SBS) in a high‐Q silica microtoroid resonator. This device exhibits remarkable characteristics over most state‐of‐the‐art implements, including high isolation ratio, no insertion loss, and large working power range. Thanks to the guided acoustic wave and accompanying momentum‐conservation condition, bulk SBS also assist in realizing the nonreciprocal parity‐time symmetry in two directly coupled microresonators. The breach of time‐reversal symmetry further makes the design a versatile arena for developing many formidable ultra‐compact devices such as unidirectional single‐mode Brillouin lasers and supersensitive photonic sensors. 

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