Research

We explore both fundamental and technical aspects of photonics, aiming to bridge the gap between fundamental science and future technology. Our research focuses on integrated nanophotonics, developing chip-scale photonic integrated circuits (PICs) that transform bulky optical systems into compact, robust, and scalable platforms. Our work spans from device-level innovation to system-level applications, including AI computing and quantum sensing. The following are research topics that we previously worked on. Each area is strongly correlated, and we always look forward to extending our expertise into other areas to impact the world.

PIC Device Innovation

Keywords: Subwavelength Gratings, Metaphotonics, Exceptional Points, Topological Photonics

We develop novel physics-driven approaches for photonic integrated circuits (PICs) to overcome key limitations of current technologies, including scalability, noise, loss, and fabrication sensitivity.

  • Subwavelength Gratings (SWGs) / Metaphotonics [1-4]: We utilize anisotropic subwavelength grating (SWG) metamaterials to engineer light confinement beyond conventional index-guided approaches. This enables scalable PIC architectures with suppressed crosstalk, improved extinction ratio, and reduced noise. We demonstrated extreme crosstalk suppression with record-high coupling lengths (>500× improvement over conventional waveguides).
  • Exceptional Points (Non-Hermitian Photonics) [5-6]: We explore non-Hermitian photonics based on exceptional points (EPs), which enable non-conventional wave phenomena inaccessible in Hermitian systems. In particular, we demonstrated passive EPs in integrated waveguides, revealing unconventional wave penetration and spatially uniform energy dissipation.
  • Topological Photonics [7]: We investigate topological photonic structures to achieve robust light transport in PIC platforms. These approaches aim to enhance fabrication tolerance and device stability by leveraging topology-protected properties.

These efforts establish next-generation PIC device innovations beyond conventional design paradigms.

[1] S. Jahani†, S. Kim†, et al. "Controlling evanescent waves using silicon photonic all-dielectric metamaterials for dense integration," Nature Communications, 9, 1893 (2018) (†equal contribution)
[2] M. Mia, et al. "Exceptional coupling in photonic anisotropic metamaterials for extremely low waveguide crosstalk," Optica 7, 881-887 (2020)
[3] M. Kabir, et al. "Anisotropic leaky-like perturbation with subwavelength gratings enables zero crosstalk," Light: Science & Applications, 12, 135 (2023)
[4] Y. Shin, et al. "Anisotropic metamaterials for scalable photonic integrated circuits: a review on subwavelength gratings for high-density integration," Nanophotonics, 14(9), 1311 (2025)
[5] A. Yulaev†, S. Kim†, et al. "Exceptional points in lossy media lead to deep polynomial wave penetration with spatially uniform power loss,"  Nature Nanotechnology17, 583–589 (2022) (†equal contribution)
[6] S. Hasanli, et al. "Exceptional points in a passive strip waveguide," Nanophotonics, 14(8), 1301 (2025)
[7] J. You, et al. (in preparation)

Integrated Nonlinear & Quantum Photonics

Keywords: Microcombs, Nonlinear Optics, Quantum Photonics

We investigate nonlinear and quantum optical phenomena enabled by high-Q integrated photonic platforms, with a focus on dispersion-engineered microresonators for on-chip frequency comb generation.

  • Microcombs and Dispersion Engineering [1-4]: We develop integrated microresonators with tailored dispersion to enable efficient and broadband frequency comb generation. We demonstrated dispersion control using concentric resonator geometries and multimode coupling, enabling low-power comb initiation and access to visible and mid-infrared spectral regimes.
  • Nonlinear Wave Mixing and Spectral Engineering [5-6]: We explore nonlinear interactions such as supercontinuum generation and multimode coupling to achieve broadband and flexible spectral control on chip. These approaches enable compact and programmable optical sources for spectroscopy and optical communications.
  • Quantum Photonics with Microcombs: We investigate microcomb-based quantum light sources, including multi-wavelength entangled photon generation and quantum state control. This provides a scalable platform for integrated quantum photonics and quantum information processing.

These efforts establish microcombs as a versatile platform bridging nonlinear optics, precision metrology, and quantum photonics on a chip.

[1] S. Kim, et al., "Dispersion Engineering and Frequency Comb Generation in Thin Silicon Nitride Concentric Microresonators," Nature Communications, 8, 372 (2017)
[2] G. Moille, et al., "Phased-Locked Two-Color Single Soliton Microcombs in Dispersion-Engineered Si3N4," Optics Letters, 43, 2772-2775 (2018)
[3] Y. Xuan, et al., "High-Q Silicon Nitride Micro-Resonators Exhibiting Low Power Frequency Comb Initiation," Optica, 3, 1171-1180 (2016)
[4] M. Hasan, et al., "Modeling method for concentric ring resonators with dispersion engineering," Optics Express, 33(24), 51499–51512 (2025)
[5] S. Fatema, et al., "Multiple mode couplings in a waveguide array for broadband near-zero dispersion and supercontinuum generation," Journal of Lightwave Technology, 39, 216–222 (2021)
[6] T. Kim, et al., "Dual-bus resonator for multi-port spectral engineering," Laser & Photonics Reviews, e02935 (2026)

Hybrid PICs for Quantum & Sensing

Keywords: Hybrid Integration, Quantum Sensing, Atomic-Integrated PICs, Ion-Trap PICs, LiDAR

We develop hybrid-integrated photonic platforms that combine PICs with atomic, ionic, and microfluidic systems to expand the capabilities of chip-scale photonics beyond conventional standalone devices.

  • Hybrid Integration and Optical Interfaces [1-2]: We develop advanced mode converters and beam shaping components to bridge the large mode mismatch between PICs and external systems. We demonstrated extreme waveguide-to-free-space Gaussian beam conversion and are expanding it for further applications.
  • Atomic-Integrated PICs for Quantum Sensing [1,3]: We integrate PICs with atomic systems to realize compact and robust platforms for precision measurement and quantum sensing. For example, chip-based laser stabilization to atomic vapor, enabling high-precision frequency references on chip, was demonstrated.
  • Emerging Hybrid Systems (LiDAR & Ion-trap PIC) [4]: We develop hybrid PIC architectures for sensing applications such as chip-scale LiDAR, leveraging advanced optical beam shaping and phased-array techniques. These approaches can be further extended to emerging quantum systems, including ion-trap PICs.

These efforts establish hybrid PICs as a versatile platform for quantum systems, sensing, and future integrated photonic applications.

[1] S. Kim, et al., "Photonic waveguide to free-space Gaussian beam extreme mode converter," Light: Science & Applications, 7, 72 (2018)
[2] N. Jaidye, et al., "In-plane beam focusing via integrated photonic gradient-index subwavelength grating metalens," Optics Express, 32, 46225–46238 (2024)
[3] M.T. Hummon, et al., "Photonic chip for laser stabilization to an atomic vapor at a precision of 10-11," Optica, 5, 443–449 (2018)
[4] L. Zhang, et al., "Time-lens-based optical phased array LiDAR for ranging and accuracy enhancement," APL Photonics, 10(11), 116102 (2025)

PICs for AI Accelerators & CPO

Keywords: Programmable PICs, AI Accelerators, Co-Packaged Optics (CPO), Pulse Shaping

We explore system-level PIC architectures for AI and data-centric computing, where scalable bandwidth and energy efficiency are critical challenges beyond the limits of conventional electronic systems.

  • Photonic AI Accelerators: We explore photonic approaches for accelerating AI workloads using parallelism in wavelength and space. Leveraging dense PIC integration, these architectures aim to enable high-throughput and energy-efficient computing beyond conventional electronic accelerators.
  • Co-Packaged Optics (CPO): We investigate photonic–electronic integration for high-bandwidth optical interconnects co-packaged with electronic processors. This approach addresses communication bottlenecks in large-scale AI systems and data centers.
  • Integrated Pulse Shaping and Spectral Control: We develop programmable PIC-based pulse shapers and spectral control systems for precise manipulation of optical signals. These capabilities support applications ranging from optical communications to advanced computing and quantum systems.

These efforts aim to establish PICs as a scalable platform for next-generation AI systems and high-performance optical infrastructures. This is a rapidly emerging focus of our research, where we are intensively exploring system-level PIC architectures and expect significant advances and impactful results in the near future.