Browsing by Author "Li, Tiantian"
Now showing 1 - 6 of 6
Results Per Page
Sort Options
Item Controlling Microring Resonator Extinction Ratio via Metal-Halide Perovskite Nonlinearity(Advanced Optical Materials, 2021-09-09) Wang, Feifan; Zhao, Lianfeng; Xiao, Yahui; Li, Tiantian; Wang, Yixiu; Soman, Anishkumar; Lee, Hwaseob; Kananen, Thomas; Hu, Xiaoyong; Rand, Barry P.; Gu, TingyiThe exceptionally high optical nonlinearities, wide bandgap, and homogeneity in solution-processed metal-halide perovskite media are utilized as optical nonlinear elements on a silicon photonic platform for low-power-active components, such as all-optical switches, modulators, and lasers. With room temperature back-end-of-line compatible processing, a hybrid metal-halide perovskite (CH3NH3PbI3) microring resonator (MRR) structure is fabricated on a foundry-processed low-loss silicon photonic platform. With in-plane exci-tation near the light intensity of 110 W m−2, strong two-photon absorption and free-carrier absorption saturation are observed. With 103 field enhancements by MRRs, the photorefractive effect in the metal-halide perovskite reduces linear absorption, represented by 102 improvement of the MRR’s intrinsic quality factor and 20 dB enhancement of the extinction ratio.Item Integrated photonic metasystem for image classifications at telecommunication wavelength(Nature Communications, 2022-04-19) Wang, Zi; Chang, Lorry; Wang, Feifan; Li, Tiantian; Gu, TingyiMiniaturized image classifiers are potential for revolutionizing their applications in optical communication, autonomous vehicles, and healthcare. With subwavelength structure enabled directional diffraction and dispersion engineering, the light propagation through multi-layer metasurfaces achieves wavelength-selective image recognitions on a silicon photonic platform at telecommunication wavelength. The metasystems implement high-throughput vector-by-matrix multiplications, enabled by near 103 nanoscale phase shifters as weight elements within 0.135 mm2 footprints. The diffraction manifested computing capability incorporates the fabrication and measurement related phase fluctuations, and thus the pre-trained metasystem can handle uncertainties in inputs without post-tuning. Here we demonstrate three functional metasystems: a 15-pixel spatial pattern classifier that reaches near 90% accuracy with femtosecond inputs, a multi-channel wavelength demultiplexer, and a hyperspectral image classifier. The diffractive metasystem provides an alternative machine learning architecture for photonic integrated circuits, with densely integrated phase shifters, spatially multiplexed throughput, and data processing capabilities.Item Melting-free integrated photonic memory with layered polymorphs(Nanophotonics, 2024-01-31) Ullah, Kaleem; Li, Qiu; Li, Tiantian; Gu, TingyiChalcogenide-based nonvolatile phase change materials (PCMs) have a long history of usage, from bulk disk memory to all-optic neuromorphic computing circuits. Being able to perform uniform phase transitions over a subwavelength scale makes PCMs particularly suitable for photonic applications. For switching between nonvolatile states, the conventional chalcogenide phase change materials are brought to a melting temperature to break the covalent bonds. The cooling rate determines the final state. Reversible polymorphic layered materials provide an alternative atomic transition mechanism for low-energy electronic (small domain size) and photonic nonvolatile memories (which require a large effective tuning area). The small energy barrier of breaking van der Waals force facilitates low energy, fast-reset, and melting-free phase transitions, which reduces the chance of element segregation-associated device failure. The search for such material families starts with polymorphic In2Se3, which has two layered structures that are topologically similar and stable at room temperature. In this perspective, we first review the history of different memory schemes, compare the thermal dynamics of phase transitions in amorphous-crystalline and In2Se3, detail the device implementations for all-optical memory, and discuss the challenges and opportunities associated with polymorphic memory.Item Metasurface on integrated photonic platform: from mode converters to machine learning(Nanophotonics, 2022-07-20) Wang, Zi; Xiao, Yahui; Liao, Kun; Li, Tiantian; Song, Hao; Chen, Haoshuo; Uddin, S. M. Zia; Mao, Dun; Wang, Feifan; Zhou, Zhiping; Yuan, Bo; Jiang, Wei; Fontaine, Nicolas K.; Agrawal, Amit; Willner, Alan E.; Hu, Xiaoyong; Gu, TingyiIntegrated photonic circuits are created as a stable and small form factor analogue of fiber-based optical systems, from wavelength-division multiplication transceivers to more recent mode-division multiplexing components. Silicon nanowire waveguides guide the light in a way that single and few mode fibers define the direction of signal flow. Beyond communication tasks, on-chip cascaded interferometers and photonic meshes are also sought for optical computing and advanced signal processing technology. Here we review an alternative way of defining the light flow in the integrated photonic platform, using arrays of subwavelength meta-atoms or metalines for guiding the diffraction and interference of light. The integrated metasurface system mimics free-space optics, where on-chip analogues of basic optical components are developed with foundry compatible geometry, such as low-loss lens, spatial-light modulator, and other wavefront shapers. We discuss the role of metasurface in integrated photonic signal processing systems, introduce the design principles of such metasurface systems for low loss compact mode conversion, mathematical operation, diffractive optical systems for hyperspectral imaging, and tuning schemes of metasurface systems. Then we perceive reconfigurability schemes for metasurface framework, toward optical neural networks and analog photonic accelerators.Item Spontaneous Detachment of Colloids from Primary Energy Minima by Brownian Diffusion(Public Library of Science (PLOS), 2016-01-19) Wang, Zhan; Jin, Yan; Shen, Chongyang; Li, Tiantian; Huang, Yuanfang; Li, Baoguo; Zhan Wang, Yan Jin, Chongyang Shen, Tiantian Li, Yuanfang Huang, Baoguo Li; Jin, YanThe Derjaguin-Landau-Verwey-Overbeek (DLVO) interaction energy profile has been frequently used to interpret the mechanisms controlling colloid attachment/detachment and aggregation/disaggregation behavior. This study highlighted a type of energy profile that is characterized by a shallow primary energy well (i.e., comparable to the average kinetic energy of a colloid) at a small separation distance and a monotonic decrease of interaction energy with separation distance beyond the primary energy well. This energy profile is present due to variations of height, curvature, and density of discrete physical heterogeneities on collector surfaces. The energy profile indicates that colloids can be spontaneously detached from the shallow primary energy well by Brownian diffusion. The spontaneous detachment from primary minima was unambiguously confirmed by conducting laboratory column transport experiments involving flow interruptions for two model colloids (polystyrene latex microspheres) and engineered nanoparticles (fullerene C60 aggregates). Whereas the spontaneous detachment has been frequently attributed to attachment in secondary minima in the literature, our study indicates that the detached colloids could be initially attached at primary minima. Our study further suggests that the spontaneous disaggregation from primary minima is more significant than spontaneous detachment because the primary minimum depth between colloid themselves is lower than that between a colloid and a collector surface.Item Structural Phase Transitions between Layered Indium Selenide for Integrated Photonic Memory(Advanced Materials, 2022-04-18) Li, Tiantian; Wang, Yong; Li, Wei; Mao, Dun; Benmore, Chris J.; Evangelista, Igor; Xing, Huadan; Li, Qiu; Wang, Feifan; Sivaraman, Ganesh; Janotti, Anderson; Law, Stephanie; Gu, TingyiThe primary mechanism of optical memoristive devices relies on phase transitions between amorphous and crystalline states. The slow or energy-hungry amorphous–crystalline transitions in optical phase-change materials are detrimental to the scalability and performance of devices. Leveraging an integrated photonic platform, nonvolatile and reversible switching between two layered structures of indium selenide (In2Se3) triggered by a single nanosecond pulse is demonstrated. The high-resolution pair distribution function reveals the detailed atomistic transition pathways between the layered structures. With interlayer “shear glide” and isosymmetric phase transition, switching between the α- and β-structural states contains low re-configurational entropy, allowing reversible switching between layered structures. Broadband refractive index contrast, optical transparency, and volumetric effect in the crystalline–crystalline phase transition are experimentally characterized in molecular-beam-epitaxy-grown thin films and compared to ab initio calculations. The nonlinear resonator transmission spectra measure of incremental linear loss rate of 3.3 GHz, introduced by a 1.5 µm-long In2Se3-covered layer, resulted from the combinations of material absorption and scattering.