Research Progress on Programmable Topological Photonic Chips

Research Background

In recent years, topological insulators (TI) have garnered significant attention in the physics community due to their rich physical mechanisms and the potential applications of topological boundary modes, leading to rapid development in this field. Since the discovery of the quantum Hall effect, substantial progress has been made in the study of topological phases, encompassing dimensions, symmetry, non-Hermiticity, defects, and more. When topology meets photonics, the field of topological photonics has quickly risen, becoming an independent research direction and revolutionarily advancing optical science and technology. Topological photonics systems offer many advantages, including low noise, minimal lattice geometric constraints, a wide variety of optical materials, high controllability of optical devices, and broadly applicable nonlinear optical effects.

Research Problem

Although topological photonic devices have demonstrated numerous topological phenomena and potential practical applications, such as topological optical delay lines, topological lasers, topological single-photon sources, and entangled photon sources, there is an urgent need for high-level programmability in their actual applications. Controlling the topological phase of light allows for the observation of rich topological phenomena and the development of robust photonic devices. Achieving such an advanced level of control requires devices with high programmability.

Research Objective

This research aims to demonstrate a fully programmable, large-scale integrated silicon photonic nano-circuit and microcavity topological photonic chip. By individually addressing and controlling the photonic artificial atoms and their interactions within our composite system, the structural parameters and geometric configurations can be arbitrarily adjusted, enabling the observation of dynamic topological phase transitions and various photonic topological insulators. Our general-purpose topological photonic chip can be rapidly reprogrammed to achieve multiple functions, providing a flexible and versatile platform for fundamental science and the broad applications of topological technology.

Paper Source

The main authors of the paper include Tianxiang Dai, Anqi Ma, Jun Mao, and others, from institutions such as the State Key Laboratory of Mesoscopic Physics at Peking University, the Department of Physics and Applied Physics at Nanyang Technological University, Singapore, and the Institute of Microelectronics, Chinese Academy of Sciences. This research was published in the journal “Nature Materials,” accepted on April 19, 2024, and published online in 2024.

Research Process and Methods

Steps

1. Chip Design and Integration

   • The topological photonic chip is based on cyclic photonic circuits, capable of operating light states in both forward and backward directions.
   • Each microring simulates an “atom,” while the Mach–Zehnder interferometer (MZI) simulates adjustable atom-atom interactions, with the photonic chip simulating an artificial atom lattice.

2. Experimental Setup

   • A 6-cell × 6-cell square lattice embedded with 96 identical-circumference microrings, each with an intrinsic quality factor of about 105.
   • Coupling (strength and phase) between microrings is controllable via the MZI.

3. Topological Phase Transition Testing

   • By adjusting the coupling strength and resonance phase parameters, different types of Floquet topological phase transitions are driven respectively.

4. Statistical Verification of Topological Phenomena

   • Adding random phase perturbations to all microrings generated and tested 100 samples with precisely controlled disorder.

5. Comparison of Various Lattice Structures

   • Testing and simulating electronic state distributions and bandgap structures in different lattice structures (e.g., 1D Su–Schrieffer–Heeger topological insulators, 2D Floquet topological insulators).

Experimental Methods and Equipment Innovations

The topological photonic chip used in the study embeds numerous silicon photonic nano-waveguide circuits and microring resonators, manufactured based on complementary metal-oxide-semiconductor (CMOS) technology. Each microring acts as an artificial atom, with its resonance phase and coupling strength and hopping phase between adjacent atoms independently controllable. The experiment demonstrated high levels of controllability and programmability, enabling dynamic topological phase transitions, statistical topological processes, and diverse topological lattices.

Research Results

1. Floquet Topological Phase Transition

   • By adjusting coupling parameters θ1−4 and resonance phase parameters φ, three-band structure floating phase transitions were successfully achieved.
   • In coupling strength-driven topological phase transitions, the bandgap closes and reopens at the critical point of θ, leading to the disappearance of topological edge modes.
   • Adjusting resonance phase φ and changing phase φs exhibited the disappearance and reappearance of topological edge modes in various bandgaps.

2. Statistical Verification

   • Testing 100 samples under random phase perturbations verified the robustness of topological edge modes.
   • The experimental results showed that disorder had almost no effect on the high-transmission stability of topological edge modes but significantly affected bulk modes.

3. Topological Anderson Transition

   • Under strong disorder, precisely controlling phase disorder observed the topological Anderson transition, showcasing non-trivial transitions emerging in low-transmission bandgaps.

4. Testing Multiple Lattice Structures

   • By reconfiguring the device, successfully demonstrating Floquet topological modes in equivalent hexagonal lattices, observing staggered bandgaps and edge modes.

Significance of the Research

This study showcases a highly programmable topological photonic chip, providing a flexible, efficient platform for realizing dynamic topological phase transitions, observing statistical topological phenomena, and achieving diverse topological lattices. The prototype presented provides a flexible, multifunctional, and instantaneously programmable topological photonic platform, useful for fundamental research in topological optical science and offering new solutions for classical and quantum information processing and computing tasks.

With the unique bidirectional operation functionality of the large-scale optical resonator lattice, it can simulate the complex properties of actual materials, offering a flexible hardware platform for researching and predicting the physical properties of complex topological materials.

In the future, the scalability and integration can be enhanced through more sophisticated cyclic photonic circuit designs and wiring circuits, potentially realizing larger-scale topological chips and advancing broader applications of photonic technology.