Jiajiu Zheng

We present a low-loss, non-volatile optical phase shifter leveraging the phase change material (PCM) Ge₂Sb₂Te₅ (GST) operating at a 1550 nm wavelength. The design is based on the coupling mechanism between a primary silicon strip waveguide and a GST-loaded hybrid waveguide, minimizing direct interaction between the waveguide mode and the PCM. In the amorphous, low-loss state of GST, phase matching between the waveguides enables efficient coupling, allowing light to re-couple into the primary waveguide after a certain length. Upon transitioning to the crystalline state, the GST induces phase mismatch, confining the light within the primary waveguide and circumventing the lossy crystalline GST, thereby preserving low-loss performance. At the central wavelength, the phase shifter exhibits a loss of ~1 dB in both states and achieves a phase shift of π upon phase change. A Mach-Zehnder interferometer incorporating this phase shifter demonstrates optical switching with a low insertion loss of ∼0.6 dB and minimal crosstalk below −20 dB over a 30 nm bandwidth, underscoring the potential of GST-based phase shifters for low-power, high-performance photonic circuits.

We introduce a scalable platform designed for very-large-scale programmable photonics, achieved through the integration of 300-mm-wafer-scale fabrication processes and in-house phase-change material fabrication. This approach enables reversible electrical tuning capabilities up to 50, 000 switching events. Moreover, we demonstrate a deterministic multilevel scheme capable of achieving 2^N optical levels, offering enhanced control and versatility in programmable photonics applications.

Programmability is demanding in integrated photonics, while a suitable photonic platform is still lacking. It should have no static power, easy tuning knobs, high endurance, and many operation levels. We report a wide-bandgap PCM antimony sulfide (Sb2S3)-clad silicon photonic platform, based on which essential building blocks for programmable photonics are demonstrated, including micro-ring resonators, Mach-Zehnder Interferometers, and directional couplers. The fabricated devices simultaneously achieved low loss (10 dB), high cyclability (>1,600 switching events), and 5-bit (32 operation levels) operation.

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 TM₀ and TE₀ mode by modifying the phase of nonvolatile Sb₂Se₃ between amorphous and crystalline. When the Sb₂Se₃ is amorphous, two-mode interference happens in the polarization-rotation section resulting in efficient TE₀-TM₀ conversion. 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 TE₀ and TM₀ modes 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 TE₀ and TM₀ modes.

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 (> 1,600 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 ∼10fJ/nm³. Remarkably, Sb₂S₃ is 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. Our work opens an attractive pathway toward large-scale energy-efficient programmable PICs with low-loss and multi-bit operations.

We demonstrate passive integrated athermal (de)multiplexers showing near 0 pm/°C wavelength shift from 20 to 80 °C on 300 mm silicon photonics wafers. Waferscale data shows its high fabrication tolerance for next-generation optical transceiver systems.

Phase-change materials (PCMs) integrated photonics are generating new paradigms, thanks to their zero static energy consumption, capability of switching reversibly, and drastic optical property contrast. However, electrically switching PCMs is inherently stochastic, hindering reliable multi-level or quasi-continuous operations. Here we propose that reliable quasi-continuous operation can be achieved in GST optical switches, where several GST patches are controlled in a binary fashion by interleaved PIN-diode doped silicon microheaters. We further experimentally demonstrate that the idea works in a tunable attenuator.

Silicon photonics is evolving from laboratory research to real-world applications with the potential to transform many technologies, including optical neural networks and quantum information processing. A key element for these applications is a reconfigurable switch operating at ultra-low programming energy—a challenging proposition for traditional thermo-optic or free carrier switches. Recent advances in non-volatile programmable silicon photonics based on phase-change materials (PCMs) provide an attractive solution to energy-efficient photonic switches with zero static power, but the programming energy density remains high (hundreds of attojoules per cubic nanometre). Here we demonstrate a non-volatile electrically reconfigurable silicon photonic platform leveraging a monolayer graphene heater with high energy efficiency and endurance. In particular, we show a broadband switch based on the technologically mature PCM Ge₂Sb₂Te₅ and a phase shifter employing the emerging low-loss PCM Sb₂Se₃. The graphene-assisted photonic switches exhibited an endurance of over 1,000 cycles and a programming energy density of 8.7 ± 1.4 aJ nm^–3, that is, within an order of magnitude of the PCM thermodynamic switching energy limit (~1.2 aJ nm^–3) and at least a 20-fold reduction in switching energy compared with the state of the art. Our work shows that graphene is a reliable and energy-efficient heater compatible with dielectric platforms, including Si₃N₄, for technologically relevant non-volatile programmable silicon photonics.