Chalcogenide phase-change materials (PCMs) offer paradigms for programmable photonic integrated circuits thanks to their zero static energy and significant refractive index contrast. However, prototypical PCMs, such as Ge2Sb2Te5 (GST), are lossy in their crystalline phase, albeit transparent in the amorphous state. Moreover, electrically switching PCMs to intermediate states is a stochastic process, limiting programming accuracy. As a result, achieving both low-loss and deterministic multilevel operations with GST remains challenging. Although low-loss PCMs, such as Sb2S3 and Sb2Se3, have been discovered in recent years, they are much less technologically mature. We propose a design with multiple GST segments to overcome the challenge of deterministic multilevel operation. GST segments are individually controlled by interleaved silicon p++-doped-intrinsic-n++-doped diode heaters in a binary but reliable fashion, and multiple levels are encoded in their phase sequence. A 1×1 programmable unit with two unequal GST segments is experimentally demonstrated, showcasing four distinct operation levels and negligible thermal crosstalk with only one pair of metal contacts. We then extend the design to 1×2 and 2×2 programmable units. For the 2×2 programmable unit design, we propose a phase-detuned three-waveguide directional coupler structure to mitigate the absorption and radiation loss, showing <1.2 dB loss and three splitting ratios. We provide a new path toward low-loss and multilevel optical switches using lossy PCMs.

The development of functional chalcogenide optical phase change materials holds significant promise for advancing optics and photonics applications. Our comprehensive investigation into the solution processing of Sb2Se3 thin films presents a systematic approach from solvent exploration to substrate coating through drop-casting methods and heat treatments. By employing characterization techniques such as scanning electron microscopy, dynamic light scattering, energy-dispersive X-ray spectroscopy, Raman spectroscopy, and X-ray diffraction, we reveal crucial insights into the structural, compositional, and morphological properties of the films as well as demonstrated techniques for control over these features to ensure requisite optical quality. Our findings, compared with currently reported deposition techniques, highlight the potential of solution deposition as a route for scalable Sb2Se3 film processing.

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 dynamic color control of solid-state electrochromic (EC) devices has sparked broad interest in both academia and industry. In this work, we report a combination of an optical stack of a Bragg reflector and Fabry–Pérot cavity into a solid-state EC device that achieves high brightness and saturation. The Bragg reflector and Fabry–Pérot optical stacks are designed as multi-color selectors through dynamically varying the optical constants (n and k) of the EC layer, allowing selective reflection of different wavelengths. By employing EC-inactive mixed-tungsten-vanadium oxide as the counter electrode, high reflectivity and contrast can be ensured. The demonstrated combination of the Bragg reflector and Fabry–Pérot cavity into a solid-state EC device offers a practical approach to designing and fabricating high-performance reflective EC devices.

Metasurfaces have attracted immense interest across various scientific disciplines due to their ability to manipulate light wave parameters with numerous functionalities. However, these functionalities have historically been static, lacking the capability for dynamic, real-time control. In this study, we introduce a highly efficient, tunable waveplate by incorporating a thin layer of the phase change material Sb2Se3 into a silicon all-dielectric metasurface. This structure demonstrates the ability to transition from a half-waveplate to a quarter-waveplate as Sb2Se3 shifts from an amorphous to a crystalline state at the telecom wavelength of 1.55 μm. Remarkably, it maintains consistent performance across a range of rotation angles. In addition, we have performed comprehensive electro-thermal simulations to validate the phase change process, confirming the practical feasibility of this technology. This tunable metasurface represents a significant advancement in adaptive photonics, offering customizable and sophisticated functionalities.