Arbitrary Programming of Racetrack Resonators Using Low-Loss Phase-Change Material Sb₂Se₃

Area of Science:

• Photonics and Optical Engineering
• Materials Science
• Quantum Information Science

Background:

• Programmable photonic integrated circuits (PICs) are crucial for optical interconnects and quantum information processing.
• Current PIC programmability relies on thermo-optic, free carrier, or mechanical tuning, which demand constant power and are inefficient for infrequent switching.
• Nonvolatile phase-change materials (PCMs) offer a promising solution for energy-efficient, 'set-and-forget' PICs.

Purpose of the Study:

• To develop and demonstrate an essential building block for large-scale programmable PICs.
• To create a racetrack resonator with independently controllable coupling and phase using PCMs.
• To achieve high extinction ratio (ER) switching without altering resonance wavelength.

Main Methods:

• Designed a compact, 33-μm-long programmable unit incorporating a directional coupler and a low-loss PCM, antimony selenide (Sb₂Se₃).
• Utilized the PCM's nonvolatile properties to control the optical coupling.
• Fabricated and tested the racetrack resonator unit for performance metrics including insertion loss, ER, operating bandwidth, and endurance.

Main Results:

• Achieved independent control of coupling and phase, enabling ER modulation without affecting resonance wavelength.
• Demonstrated a low insertion loss of approximately 0.36 dB and a high ER of around 15 dB.
• Exhibited an operating bandwidth exceeding 50 nm and excellent endurance (>1000 cycles) across multiple devices.

Conclusions:

• The developed PCM-based directional coupler is a key component for scalable, energy-efficient programmable PICs.
• This 'set-and-forget' switch technology significantly reduces static power consumption.
• Represents a critical advancement towards practical, large-scale photonic integration for future computing and communication systems.