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1. Design of a compact atto-joule-per-bit bus-coupled photonic nanocavity switch

   https://doi.org/10.1016/j.photonics.2024.101346  

   Shen, Jianhao; Chakravarty, Swapnajit (February 2025, Photonics and Nanostructures - Fundamentals and Applications)

   We experimentally demonstrate an array of bus-coupled compact one-dimensional photonic crystal nanocavities with large extinction, high-quality factor, and large free spectral range (FSR) exceeding 300 nm centered on the telecom wavelength at 1550 nm. We present designs for an oxide-clad bus-coupled PC switch with 0.96 dB insertion loss, 4.33 dB extinction, and ∼260 aJ/bit switching energy by careful control of the cavity geometry as well as p-n junction doping. We also demonstrate that air-clad bus-coupled PC switches can operate with 1 dB insertion loss, 3 dB extinction, and ∼80 aJ/bit switching energy. We present a design route integrating phase change materials that can undergo a controlled transition between amorphous to crystalline material phases of the PCMs for a large change in refractive index. The large index change can overcome fabrication imperfections to effectively align the PC nanocavity resonance to the source laser wavelength thereby enabling true atto-joule per bit operation without the need for active power-consuming thermal heaters. 

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2. Nonvolatile Electrically Reconfigurable Integrated Photonic Switch Enabled by a Silicon PIN Diode Heater

   https://doi.org/10.1002/adma.202001218  

   Zheng, Jiajiu; Fang, Zhuoran; Wu, Changming; Zhu, Shifeng; Xu, Peipeng; Doylend, Jonathan_K; Deshmukh, Sanchit; Pop, Eric; Dunham, Scott; Li, Mo; et al (June 2020, Advanced Materials)

   Abstract Reconfigurability of photonic integrated circuits (PICs) has become increasingly important due to the growing demands for electronic–photonic systems on a chip driven by emerging applications, including neuromorphic computing, quantum information, and microwave photonics. Success in these fields usually requires highly scalable photonic switching units as essential building blocks. Current photonic switches, however, mainly rely on materials with weak, volatile thermo‐optic or electro‐optic modulation effects, resulting in large footprints and high energy consumption. As a promising alternative, chalcogenide phase‐change materials (PCMs) exhibit strong optical modulation in a static, self‐holding fashion, but the scalability of present PCM‐integrated photonic applications is still limited by the poor optical or electrical actuation approaches. Here, with phase transitions actuated by in situ silicon PIN diode heaters, scalable nonvolatile electrically reconfigurable photonic switches using PCM‐clad silicon waveguides and microring resonators are demonstrated. As a result, intrinsically compact and energy‐efficient switching units operated with low driving voltages, near‐zero additional loss, and reversible switching with high endurance are obtained in a complementary metal‐oxide‐semiconductor (CMOS)‐compatible process. This work can potentially enable very large‐scale CMOS‐integrated programmable electronic–photonic systems such as optical neural networks and general‐purpose integrated photonic processors. 

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3. Low-power quasi-continuous hybrid volatile/nonvolatile tuning of ring resonators

   https://doi.org/10.1063/5.0236098  

   Dutta, Jayita; Chen, Rui; Tara, Virat; Majumdar, Arka (February 2025, APL Photonics)

   Programmable photonic integrated circuits are expected to play an increasingly important role in enabling high-bandwidth optical interconnects and large-scale in-memory computing as needed to support the rise of artificial intelligence and machine learning technology. To that end, chalcogenide-based non-volatile phase-change materials (PCMs) present a promising solution due to zero static power. However, high switching voltage and a small number of operating levels present serious roadblocks to the widespread adoption of PCM-programmable units. Here, we demonstrate an electrically programmable wide bandgap Sb2S3-clad silicon ring resonator using a silicon microheater at a complementary-metal–oxide–semiconductor compatible voltage of <3 V. Our device shows a low switching energy of 35.33 nJ (0.48 mJ) for amorphization (crystallization) and reversible phase transitions with high endurance (>2000 switching events) near 1550 nm. Combining a volatile thermo-optic effect with non-volatile PCMs, we demonstrate 7-bit (127 levels) operation with excellent repeatability and reduced power consumption. Our demonstration of low-voltage and low-energy operation, combined with the hybrid volatile–nonvolatile approach, marks a significant step toward integrating PCM-based programmable units in large-scale optical interconnects. 

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4. Integrated non-reciprocal magneto-optics with ultra-high endurance for photonic in-memory computing

   https://doi.org/10.1038/s41566-024-01549-1  

   Pintus, Paolo; Dumont, Mario; Shah, Vivswan; Murai, Toshiya; Shoji, Yuya; Huang, Duanni; Moody, Galan; Bowers, John E; Youngblood, Nathan (January 2025, Nature Photonics)

   Abstract Processing information in the optical domain promises advantages in both speed and energy efficiency over existing digital hardware for a variety of emerging applications in artificial intelligence and machine learning. A typical approach to photonic processing is to multiply a rapidly changing optical input vector with a matrix of fixed optical weights. However, encoding these weights on-chip using an array of photonic memory cells is currently limited by a wide range of material- and device-level issues, such as the programming speed, extinction ratio and endurance, among others. Here we propose a new approach to encoding optical weights for in-memory photonic computing using magneto-optic memory cells comprising heterogeneously integrated cerium-substituted yttrium iron garnet (Ce:YIG) on silicon micro-ring resonators. We show that leveraging the non-reciprocal phase shift in such magneto-optic materials offers several key advantages over existing architectures, providing a fast (1 ns), efficient (143 fJ per bit) and robust (2.4 billion programming cycles) platform for on-chip optical processing. 

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5. Non-volatile electrically programmable integrated photonics with a 5-bit operation

   https://doi.org/10.1038/s41467-023-39180-3  

   Chen, Rui; Fang, Zhuoran; Perez, Christopher; Miller, Forrest; Kumari, Khushboo; Saxena, Abhi; Zheng, Jiajiu; Geiger, Sarah J.; Goodson, Kenneth E.; Majumdar, Arka (December 2023, Nature Communications)

   Abstract 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. 

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