arXiv subjects

Chuanyu Lian

Publications and source records attributed to Chuanyu Lian.

6 recordsLinked to original sources

arXiv2026

Photonic Theta Cavity: Engineering Bound States in the Continuum in Topological Resonators Beyond the Limitations of Near Field Coupling

The Theta Cavity is a unique topological resonator architecture which utilizes interferometric coupling to overcome fundamental design limitations associated with near-field evanescent coupling which currently dominates the design space for integrated photonics. The defining device physics is established by the mirror symmetric cross junctions which preserves efficient power transfer between a waveguide and ring resonator creating a strongly correlated phase relationship between the multiple paths. The unique mode selection physics allows for interference driven suppression of radiative pathways enabling strong cavity confinement and the emergence of Bound States in the Continuum (BICs). Analytical models reveal non-Hermitian optical band structure displaying non-trivial topological transitions between BIC and quasi-BIC modes that are robust to attenuation, temperature variations, and typical fabrication non-idealities, which is critical for overcoming intrinsic limitations associated with silicon based integrated photonics. The Theta Cavity architecture also circumvents limitations that arise from proximity requirements of the physical gap used in near-field coupled waveguides which enables a flexible design space for new devices. In this study, we demonstrate phase mediated long-range strong coupling of multiple ring resonators in the Nested Theta Cavity architecture showcasing band structure hybridization resulting in the formation of anti-crossing bandgaps, Dirac crossings, and Fano resonances. The photonic Theta Cavity architecture provides a scalable, topologically robust platform for engineering modes across a multidimensional parameter space with high resilience to perturbation and attenuation, enabling a new approach for the designing of integrated cavity devices.

physics.optics↗

arXiv2026

Ultrawide-angle diffraction-limited 2D beam steering via hybrid integrated metasurface-photonic circuit

Two-dimensional (2D) wide field-of-view (FOV) beam steering is a key enabling capability for emerging free-space optical systems, including inter-satellite optical links, airborne LiDAR, point-to-point optical wireless communications, and collaborative robotic platforms. These applications require rapid acquisition and tracking across both azimuth and elevation; architectures that offer wide scanning in only one dimension while maintaining limited coverage in the orthogonal direction constrain link availability, coverage uniformity, and system agility. Here, we demonstrate a chip-scale platform for ultrawide-angle, diffraction-limited 2D beam steering based on hybrid integration of a silicon photonic integrated circuit (PIC) and an optical metasurface. A free-form micro-optical reflector efficiently transforms the guided waveguide mode into an expanded free-space beam that illuminates an analytically optimized ultrawide-FOV metasurface. The integrated system achieves a measured FOV exceeding 160° while maintaining diffraction-limited beam quality over a broad angular range at telecom wavelengths. This hybrid PIC-metasurface architecture provides a compact and scalable route to high-quality 2D beam steering and establishes a practical pathway toward integrated optical projectors for space-based optical communications and other applications requiring agile, wide-angle, high-fidelity beam control.

physics.optics↗

arXiv2025

Incorporating Si into Sb2Se3: Tailoring Optical Phase Change Materials via Nanocomposites

Chalcogenide-based optical phase change materials (OPCMs) exhibit a large contrast in refractive index when reversibly switched between their stable amorphous and crystalline states. OPCMs have rapidly gained attention due to their versatility as nonvolatile amplitude or phase modulators in various photonic devices. However, open challenges remain, such as achieving reliable response and transparency spanning into the visible spectrum, a combination of properties in which current broadband OPCMs (e.g., Ge2Sb2Se4Te1, Sb2Se3, or Sb2S3) fall short. Discovering novel materials or engineering existing ones is, therefore, crucial in extending the application scope of OPCMs. Here, we use magnetron co-sputtering to study the effects of Si doping into Sb2Se3. We employ ellipsometry, X-ray diffraction, Raman spectroscopy, and scanning and transmission electron microscopy to investigate the effects of Si doping on the optical properties and crystal structure and compare these results with those from first principles calculations. Moreover, we study the crystallization and melt-quenching of thin films via nano-differential scanning calorimetry (NanoDSC). Our experiments demonstrate that 20% Si doping increases the transparency window in both states, specifically to 800 nm (1.55 eV) in the amorphous phase, while reducing power consumption by lowering the melting temperature. However, this reduction comes at the cost of reducing the refractive index contrast between states and slowing the kinetics of the phase transition.

cond-mat.mtrl-sci↗

arXiv2024

High-Speed Multifunctional Photonic Memory on a Foundry-Processed Photonic Platform

The integration of computing with memory is essential for distributed, massively parallel, and adaptive architectures such as neural networks in artificial intelligence (AI). Accelerating AI can be achieved through photonic computing, but it requires nonvolatile photonic memory capable of rapid updates during on-chip training sessions or when new information becomes available during deployment. Phase-change materials (PCMs) are promising for providing compact, nonvolatile optical weighting; however, they face limitations in terms of bit precision, programming speed, and cycling endurance. Here, we propose a novel photonic memory cell that merges nonvolatile photonic weighting using PCMs with high-speed, volatile tuning enabled by an integrated PN junction. Our experiments demonstrate that the same PN modulator, fabricated via a foundry compatible process, can achieve dual functionality. It supports coarse programmability for setting initial optical weights and facilitates high-speed fine-tuning to adjust these weights dynamically. The result showcases a 400-fold increase in volatile tuning speed and a 10,000-fold enhancement in efficiency. This multifunctional photonic memory with volatile and nonvolatile capabilities could significantly advance the performance and versatility of photonic memory cells, providing robust solutions for dynamic computing environments.

physics.optics↗

arXiv2024

Microheater hotspot engineering for repeatable multi-level switching in foundry-processed phase change silicon photonics

Nonvolatile photonic integrated circuits employing phase change materials have relied either on optical switching mechanisms with precise multi-level control but poor scalability or electrical switching with seamless integration and scalability but mostly limited to a binary response. Recent works have demonstrated electrical multi-level switching; however, they relied on the stochastic nucleation process to achieve partial crystallization with low demonstrated repeatability and cyclability. Here, we re-engineer waveguide-integrated microheaters to achieve precise spatial control of the temperature profile (i.e., hotspot) and, thus, switch deterministic areas of an embedded phase change material cell. We experimentally demonstrate this concept using a variety of foundry-processed doped-silicon microheaters on a silicon-on-insulator platform to trigger multi-step amorphization and reversible switching of Sb$_{2}$Se$_{3}$ and Ge$_{2}$Sb$_{2}$Se$_{4}$Te alloys. We further characterize the response of our microheaters using Transient Thermoreflectance Imaging. Our approach combines the deterministic control resulting from a spatially resolved glassy-crystalline distribution with the scalability of electro-thermal switching devices, thus paving the way to reliable multi-level switching towards robust reprogrammable phase-change photonic devices for analog processing and computing.

physics.app-ph↗

arXiv2023

Nonvolatile Tuning of Bragg Structures Using Transparent Phase-Change Materials

Bragg gratings offer high-performance filtering and routing of light on-chip through a periodic modulation of a waveguide's effective refractive index. Here, we model and experimentally demonstrate the use of Sb2Se3, a nonvolatile and transparent phase-change material, to tune the resonance conditions in two devices which leverage periodic Bragg gratings: a stopband filter and Fabry-Perot cavity. Through simulations, we show that similar refractive indices between silicon and amorphous Sb2Se3 can be used to induce broadband transparency, while the crystalline state can enhance the index contrast in these Bragg devices. Our experimental results show the promise and limitations of this design approach and highlight specific fabrication challenges which need to be addressed in future implementations.

physics.optics↗