Nonvolatile electrically reconfigurable integrated photonic switch (1912.07680v1)

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 a large footprint and high energy consumption. As a promising alternative, chalcogenide phase-change materials (PCMs) exhibit strong modulation in a static, self-holding fashion. Here, we demonstrate nonvolatile electrically reconfigurable photonic switches using PCM-clad silicon waveguides and microring resonators that are intrinsically compact and energy-efficient. With phase transitions actuated by in-situ silicon PIN heaters, near-zero additional loss and reversible switching with high endurance are obtained in a complementary metal-oxide-semiconductor (CMOS)-compatible process. Our work can potentially enable very large-scale general-purpose programmable integrated photonic processors.

Nonvolatile Electrically Reconfigurable Integrated Photonic Switch

The paper explores the design and fabrication of nonvolatile electrically reconfigurable photonic switches employing phase-change materials (PCMs), specifically Ge2Sb2Te5 (GST), integrated with silicon photonics. This paper presents significant advancements in the domain of photonic integrated circuits (PICs), addressing the critical need for scalable, energy-efficient switching capabilities required for fields such as neuromorphic computing, quantum information, and microwave photonics.

Key Insights and Contributions

The central contribution of this research is the development of photonic switches with low-energy consumption and high endurance, surpassing existing photonic switches that rely on volatile thermo-optic or electro-optic modulation effects. By leveraging GST's ability to undergo reversible phase transitions, the researchers achieved nearly zero additional loss and more than 1,000 phase transitions, setting a precedent for robustness and performance.

Technical Innovations:

• The integration of GST onto silicon PIN junctions allows precise electrical control over phase transitions through Joule heating, avoiding the high loss and complexity of traditional optical heating methods.
• The demonstrated process is compatible with CMOS fabrication techniques, promising large-scale integration capabilities for future optical FPGA development.

Strong Numerical Results

The paper highlights several pivotal results:

• The photonic switches exhibited a near-zero additional insertion loss of approximately 0.02 dB/µm, ensuring minimal impact on optical signal integrity.
• High optical modulation effects were achieved, with demonstrated extinction ratios of 1.25 dB/µm for waveguides and up to 14.7 dB in microring resonators.
• Endurance tests showed stable operations over 1,000 switching cycles, indicating robust device longevity and reliability.

Implications and Future Directions

This research holds significant implications for the evolution of programmable photonic processors. The demonstrated scalability and energy efficiency offer promising avenues for integrating photonics with electronics at the chip scale, potentially alleviating bottlenecks associated with electron-based systems such as the von Neumann architecture.

Potential Developments in AI and Photonics:

• The scalable integration supports advancements in large-scale optical signal processing, needed for AI systems dependent on real-time data processing and high bandwidth.
• Further optimization might enhance extinction ratios and support multi-level operations, broadening the application spectrum beyond binary switching and into complex data modulation landscapes.

Theoretical and Practical Impact

From a theoretical standpoint, this paper contributes to the understanding of phase transitions in PCMs within photonic frameworks, enhancing the predictive modeling approaches critical for designing future PIC architectures. Practically, the work validates the feasibility of integrating PCMs in photonic systems subjected to high thermal and optical loads, paving the way for more durable and reliable photonic systems central to emerging applications.

The research has laid the groundwork for scalable and efficient photonic switches, posing significant implications and opportunities for future developments in integrated photonics, AI, and optical computing technologies.