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Silicon photonics has evolved from lab research to commercial products in the past decade as it plays an increasingly crucial role in data communication for next‐generation data centers and high‐performance computing. Recently, programmable silicon photonics has also found new applications in quantum and classical information processing. A key component of programmable silicon photonic integrated circuits (PICs) is the phase shifter, traditionally realized via thermo‐optic or free‐carrier effects that are weak, volatile, and power hungry. A non‐volatile phase shifter can circumvent these limitations by requiring zero power to maintain the switched phases. Previously non‐volatile phase modulation is achieved via phase‐change or ferroelectric materials, but the switching energy remains high (pico to nano joules) and the speed is slow (micro to milliseconds). Here, a non‐volatile III‐V‐on‐silicon photonic phase shifter based on a HfO₂memristor with sub‐pJ switching energy (≈400 fJ), representing over an order of magnitude improvement in energy efficiency compared to the state of the art, is reported. The non‐volatile phase shifter can be switched reversibly using a single 100 ns pulse and exhibits excellent endurance over 800 cycles. This technology can enable future energy‐efficient programmable PICs for data centers, optical neural networks, and quantum information processing.

Scalable programmable photonic integrated circuits (PICs) can potentially transform the current state of classical and quantum optical information processing. However, traditional means of programming, including thermo-optic, free carrier dispersion, and Pockels effect result in either large device footprints or high static energy consumptions, significantly limiting their scalability. While chalcogenide-based non-volatile phase-change materials (PCMs) could mitigate these problems thanks to their strong index modulation and zero static power consumption, they often suffer from large absorptive loss, low cyclability, and lack of multilevel operation. Here, we report a wide-bandgap PCM antimony sulfide (Sb₂S₃)-clad silicon photonic platform simultaneously achieving low loss (<1.0 dB), high extinction ratio (>10 dB), high cyclability (>1600 switching events), and 5-bit operation. These Sb₂S₃-based devices are programmed via on-chip silicon PIN diode heaters within sub-ms timescale, with a programming energy density of$$\sim 10\,{fJ}/n{m}^{3}$$$~10fJ/n{m}^3$. Remarkably, Sb₂S₃is programmed into fine intermediate states by applying multiple identical pulses, providing controllable multilevel operations. Through dynamic pulse control, we achieve 5-bit (32 levels) operations, rendering 0.50 ± 0.16 dB per step. Using this multilevel behavior, we further trim random phase error in a balanced Mach-Zehnder interferometer.

Phase change materials (PCMs) have long been used as a storage medium in rewritable compact disk and later in random access memory. In recent years, integration of PCMs with nanophotonic structures has introduced a new paradigm for non‐volatile reconfigurable optics. However, the high loss of the archetypal PCM Ge₂Sb₂Te₅in both visible and telecommunication wavelengths has fundamentally limited its applications. Sb₂S₃has recently emerged as a wide‐bandgap PCM with transparency windows ranging from 610 nm to near‐IR. In this paper, the strong optical phase modulation and low optical loss of Sb₂S₃are experimentally demonstrated for the first time in integrated photonic platforms at both 750 and 1550 nm. As opposed to silicon, the thermo‐optic coefficient of Sb₂S₃is shown to be negative, making the Sb₂S₃–Si hybrid platform less sensitive to thermal fluctuation. Finally, a Sb₂S₃integrated non‐volatile microring switch is demonstrated which can be tuned electrically between a high and low transmission state with a contrast over 30 dB. This work experimentally verifies prominent phase modification and low loss of Sb₂S₃in wavelength ranges relevant for both solid‐state quantum emitter and telecommunication, enabling potential applications such as optical field programmable gate array, post‐fabrication trimming, and large‐scale integrated quantum photonic network.

Programmable photonics play a crucial role in many emerging applications, from optical accelerators for machine learning to quantum information technologies. Conventionally, photonic systems are tuned by mechanisms such as the thermo-optic effect, free carrier dispersion, the electro-optic effect, or micro-mechanical movement. Although these physical effects allow either fast (>100 GHz) or large contrast (>60 dB) switching, their high static power consumption is not optimal for programmability, which requires only infrequent switching and has a long static time. Non-volatile materials, such as phase-change materials, ferroelectrics, vanadium dioxide, and memristive metal oxide materials, can offer an ideal solution thanks to their reversible switching and non-volatile behavior, enabling a truly “set-and-forget” programmable unit with no static power consumption. In recent years, we have indeed witnessed the fast adoption of non-volatile materials in programmable photonic systems, including photonic integrated circuits and free-space meta-optics. Here, we review the recent progress in the field of programmable photonics, based on non-volatile materials. We first discuss the material’s properties, operating mechanisms, and then their potential applications in programmable photonics. Finally, we provide an outlook for future research directions. The review serves as a reference for choosing the ideal material system to realize non-volatile operation for various photonic applications.

Increasing the space-bandwidth product of spatial light modulators incurs severe issues in terms of power consumption, mutual crosstalk, and control signal wiring. In this opinion article, we propose a novel system to overcome these challenges by marrying energy-efficient modulators in photonic integrated circuits (PICs) and a meta-optical beam aggregator. This hybrid approach can significantly improve the space-bandwidth product, theoretically up to 10¹³Hz · pixel, which is several orders of magnitude higher than the state-of-the-art.

We report a hybrid phase-change mateial Sb₂S₃-silicon photonic tunable directional coupler, which exhibits low insertion loss (< 1.0 dB), large extinction ratio (> 10 dB), high endurance (> 1,600 switching events), and 32 operation levels.

We demonstrated a nonvolatile electrically reconfigurable metasurface based on low-loss phase-change materials Sb₂Se₃with phase-only (~0.25π) modulation in the free-space. The tunable metasurface is robust against reversible switching over 1,000 times.

We propose and simulate a compact (∼29.5 µm-long) nonvolatile polarization switch based on an asymmetric Sb₂Se₃-clad silicon photonic waveguide. The polarization state is switched between TM₀and TE₀mode by modifying the phase of nonvolatile Sb₂Se₃between amorphous and crystalline. When the Sb₂Se₃is amorphous, two-mode interference happens in the polarization-rotation section resulting in efficient TE₀-TM₀conversion. On the other hand, when the material is in the crystalline state, there is little polarization conversion because the interference between the two hybridized modes is significantly suppressed, and both TE₀and TM₀modes go through the device without any change. The designed polarization switch has a high polarization extinction ratio of > 20 dB and an ultra-low excess loss of < 0.22 dB in the wavelength range of 1520-1585 nm for both TE₀and TM₀modes.