Khoi Phuong Dao

Curved and conformal optics provide additional geometric degrees of freedom that enable enhanced optical performance while satisfying non-optical constraints such as ergonomics, aerodynamics, and wearability. However, existing fabrication approaches for curved metasurfaces are limited in scalability, geometry control, and alignment accuracy. Here we show a scalable fabrication strategy for curved and conformal metasurface optics based on thermoforming, an industry-standard manufacturing process for thermoplastics. Our approach enables wafer-scale production of highly curved metasurfaces with millimeter-level radii of curvature and micron-level alignment precision. We develop a predictive thermorheological model that accurately captures and compensates for the large deformations induced during thermoforming, preserving the intended optical response and enabling diffraction-limited performance. As demonstrations, we realize freestanding curved metalenses, conformal refractive-metasurface hybrid optics, and an artificial compound eye with a wide field of view, reduced aberrations, and uniform imaging performance. These results establish thermoforming as a scalable manufacturing platform for next-generation conformal photonic systems.

We report a back‐end‐of‐line (BEOL)‐compatible approach for integrating high‐quality vanadium dioxide (VO ₂ ) into silicon photonic platforms using on‐chip doped silicon microheaters as localized thermal processors. VO ₂ is a promising material for reconfigurable photonics due to its large refractive index modulation and fast, energy‐efficient metal‐insulator transition (MIT). However, its integration is hindered by the high thermal budget required for crystallization and the difficulty of patterning. In this work, vanadium metal is deposited at room temperature and patterned via a lift‐off process, followed by microheater‐assisted local oxidation and crystallization to form VO ₂ without exceeding the global BEOL temperature constraints. Structural and spectroscopic characterization confirms the formation of VO ₂ with high crystallinity and accurate stoichiometry. Device‐level integration is demonstrated using silicon racetrack resonators, where the measured switching contrast shows excellent agreement with simulations based on literature optical constants, indicating material quality comparable to that of high‐temperature‐grown films. The microheater platform enables both material synthesis and reversible MIT switching, and is inherently scalable via parallel electrical biasing for wafer‐scale processing. Beyond VO ₂ , this approach provides a general pathway for integrating thermally demanding functional materials into complementary‐metal‐oxide‐semiconductor (CMOS)‐compatible systems.

Active metasurfaces enable dynamic control of light for applications in beam steering, pixelated holography, and adaptive optics, but demonstrations of two-dimensional electrically addressable arrays have so far been limited. Here we introduce a scalable two-dimensional architecture based on phase-change materials integrated metasurfaces and apply it to realize the first transmissive mid-infrared amplitude-only spatial light modulator. The device is fabricated through standard silicon photonic foundry processing combined with backend-of-line integration and employs multilayer backend metal interconnects to implement a crossbar addressing scheme. Each pixel is integrated with a silicon diode selector to suppress sneak-path currents, a feature essential for scaling to large arrays. The result establishes a foundry-compatible route to high-density, large-area active metasurfaces with independently tunable pixels.

Semiconductor innovation is increasingly constrained by the complexity, cost, and time involved in developing and optimizing advanced manufacturing processes. Traditional R&D approaches anchored in sequential experimentation and tool-specific workflows create critical bottlenecks that impede progress across the full spectrum of semiconductor technologies, including deposition, patterning, etching, doping, and integration. In this perspective, we present a new paradigm: leveraging semiconductor platforms themselves as engines for accelerating their own advancement. We introduce the EMPOWEr framework— E xpedited M anufacturing P rocess O ptimization through W afer-scale E xpe r imentation—which reimagines semiconductor wafers not as passive substrates, but as programmable experimental platforms enabling massively parallel process exploration. By embedding controlled process variability and integrated characterization directly into wafer-scale infrastructure, EMPOWEr addresses long-standing bottlenecks in process optimization, expands the materials and methods accessible to backend integration, and opens new pathways toward agile, scalable, and sustainable semiconductor innovation. This perspective outlines how EMPOWEr can transform semiconductor R&D into a self-reinforcing, high-throughput ecosystem, accelerating both the pace and scope of next-generation microfabrication.

Continuously tunable phase-gradient metasurfaces offer powerful capabilities for dynamic and adaptive optics, but their practical realization remains challenging due to the complexity of device control architectures, especially when compared to binary or discretely tunable systems. In this perspective, we outline a unifying framework that leverages inverse design principles to enable scalable implementation of reconfigurable metasurfaces. We begin by reviewing three core innovations from our earlier work on phase change material (PCM) based varifocal metalenses: thermal profile shaping via patterned doping, phase-gradient tuning through direct search optical inverse design, and pixel-level wavefront control using phase-change metasurface arrays. We then highlight recent advances that build upon these foundations: an analytical, geometry-independent thermal inverse design method for microheater profile customization; the generalization of phase-gradient tuning to alternative actuation mechanisms including coherent optical control; and the experimental realization of a mid-infrared two-dimensional spatial light modulator based on diode-integrated PCM metasurfaces. Together, these developments demonstrate a path from architectural insight to scalable implementation, opening new opportunities for high-performance, programmable optical systems in imaging, beam shaping, and beyond.

This paper proposes an inverse design scheme for resistive heaters. By adjusting the spatial distribution of a binary electrical resistivity map, the scheme enables objective-driven optimization of heaters to achieve pre-defined steady-state temperature profiles. The approach can be fully automated and is computationally efficient since it does not entail extensive iterative simulations of the entire heater structure. The design scheme offers a powerful solution for resistive heater device engineering in applications spanning electronics, photonics, and microelectromechanical systems.

Chalcogenide optical phase change materials (PCMs) have garnered significant interest for their growing applications in programmable photonics, optical analog computing, active metasurfaces, and beyond. Limited endurance or cycling lifetime is however increasingly becoming a bottleneck toward their practical deployment for these applications. To address this issue, a systematic study elucidating the cycling failure mechanisms of Ge ₂ Sb ₂ Se ₄ Te (GSST) is performed, a common optical PCM tailored for infrared photonic applications, in an electrothermal switching configuration commensurate with their applications in on‐chip photonic devices. Further a set of design rules building on insights into the failure mechanisms is proposed, and successfully implemented them to boost the endurance of the Ge ₂ Sb ₂ Se ₄ Te (GSST) device to over 67 000 cycles.

Ferrimagnetic iron garnets enable magnetic and magneto‐optical functionality in silicon photonics and electronics. However, garnets require high‐temperature processing for crystallization which can degrade other devices on the wafer. Here bismuth‐substituted yttrium and terbium iron garnet (Bi‐YIG and Bi‐TbIG) films are demonstrated with good magneto‐optical performance and perpendicular magnetic anisotropy (PMA) crystallized by a microheater built on a Si chip or by rapid thermal annealing. The Bi‐TbIG film crystallizes on Si at 873 K without a seed layer and exhibits good magneto‐optical properties with Faraday rotation (FR) of −1700 deg cm⁻¹. The Bi‐YIG film also crystallizes on Si and fused SiO₂ at 873 K without a seed layer. Rapidly cooled films exhibit PMA due to the tensile stress caused by the thermal expansion mismatch with the substrates, increasing the magnetoelastic anisotropy by 4 kJ m⁻³ versus slow‐cooled films. Annealing in the air for 15 s using the microheater yields fully crystallized Bi‐TbIG on the Si chip.

The on-chip photonic switch is a critical building block for photonic integrated circuits and the integration of phase change materials (PCMs) enables non-volatile switch designs that are compact, low-loss, and energy-efficient. Existing switch designs based on these materials typically rely on weak evanescent field interactions, resulting in devices with a large footprint and high energy consumption. Here, we present a compact non-volatile 2×2 switch design leveraging optical concentration in slot waveguide modes to significantly enhance interactions of light with PCM, thereby realizing a compact, efficient photonic switch. To further improve the device’s energy efficiency, we introduce an integrated single-layer graphene heater for ultrafast electrothermal switching of the PCM. Computational simulations demonstrate a 2×2 switch crosstalk (CT) down to −24 dB at 1550 nm wavelength and more than 55 nm 0.3 dB insertion loss (IL) bandwidth. The proposed photonic switch architecture can constitute the cornerstone for next-generation high-performance reconfigurable photonic circuits.

The on-chip photonic switch is a critical building block for photonic integrated circuits (PICs) and the integration of phase change materials (PCMs) enables non-volatile switch designs that are compact, low-loss, and energy-efficient. Existing switch designs based on these materials typically rely on weak evanescent field interactions, resulting in devices with a large footprint and high energy consumption. Here we present a compact non-volatile 2 by 2 switch design leveraging optical concentration in slot waveguide modes to significantly enhance interactions of light with PCMs, thereby realizing a compact, efficient photonic switch. To further improve the device's energy efficiency, we introduce an integrated single-layer graphene heater for ultrafast electrothermal switching of the PCM. Computational simulations demonstrate a 2 by 2 switch with crosstalk (CT) down to -24 dB at 1550 nm wavelength and more than 55 nm 0.3 dB insertion loss (IL) bandwidth. The proposed photonic switch architecture can constitute the cornerstone for next-generation high-performance reconfigurable photonic circuits.