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"Liang, Feng"
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Non-Hermitian photonics based on parity–time symmetry
Nearly one century after the birth of quantum mechanics, parity–time symmetry is revolutionizing and extending quantum theories to include a unique family of non-Hermitian Hamiltonians. While conceptually striking, experimental demonstration of parity–time symmetry remains unexplored in quantum electronic systems. The flexibility of photonics allows for creating and superposing non-Hermitian eigenstates with ease using optical gain and loss, which makes it an ideal platform to explore various non-Hermitian quantum symmetry paradigms for novel device functionalities. Such explorations that employ classical photonic platforms not only deepen our understanding of fundamental quantum physics but also facilitate technological breakthroughs for photonic applications. Research into non-Hermitian photonics therefore advances and benefits both fields simultaneously.
General concepts and recent developments of parity–time symmetry in classical photonics are reviewed.
Journal Article
Non-Hermitian photonics promises exceptional topology of light
The band degeneracy, either the exceptional point of a non-Hermitian system or the Dirac point associated with a topological system, can feature distinct symmetry and topology. Their synergy will further produce more exotic topological effects in synthetic matter.
Journal Article
Photonic zero mode in a non-Hermitian photonic lattice
Zero-energy particles (such as Majorana fermions) are newly predicted quasiparticles and are expected to play an important role in fault-tolerant quantum computation. In conventional Hermitian quantum systems, however, such zero states are vulnerable and even become vanishing if couplings with surroundings are of the same topological nature. Here we demonstrate a robust photonic zero mode sustained by a spatial non-Hermitian phase transition in a parity-time (PT) symmetric lattice, despite the same topological order across the entire system. The non-Hermitian-enhanced topological protection ensures the reemergence of the zero mode at the phase transition interface when the two semi-lattices under different PT phases are decoupled effectively in their real spectra. Residing at the midgap level of the PT symmetric spectrum, the zero mode is topologically protected against topological disorder. We experimentally validated the robustness of the zero-energy mode by ultrafast heterodyne measurements of light transport dynamics in a silicon waveguide lattice.
Zero-energy states such as Majorana fermions could improve quantum computation, but they are not stable under strong coupling conditions. Here, Pan et al. demonstrate a photonic implementation of a topologically protected, non-Hermitian-enhanced, thus stable, zero mode in a non-Hermitian lattice.
Journal Article
Topological hybrid silicon microlasers
Topological physics provides a robust framework for strategically controlling wave confinement and propagation dynamics. However, current implementations have been restricted to the limited design parameter space defined by passive topological structures. Active systems provide a more general framework where different fundamental symmetry paradigms, such as those arising from non-Hermiticity and nonlinear interaction, can generate a new landscape for topological physics and its applications. Here, we bridge this gap and present an experimental investigation of an active topological photonic system, demonstrating a topological hybrid silicon microlaser array respecting the charge-conjugation symmetry. The created new symmetry features favour the lasing of a protected zero mode, where robust single-mode laser action in the desired state prevails even with intentionally introduced perturbations. The demonstrated microlaser is hybrid implemented on a silicon-on-insulator substrate, and is thereby readily suitable for integrated silicon photonics with applications in optical communication and computing.
Topological effects, first observed in condensed matter physics, are now also studied in optical systems, extending the scope to active topological devices. Here, Zhao et al. combine topological physics with non-Hermitian photonics, demonstrating a topological microlaser on a silicon platform.
Journal Article
Orbital angular momentum microlaser
Structured light provides an additional degree of freedom for modern optics and practical applications. The effective generation of orbital angular momentum (OAM) lasing, especially at a micro- and nanoscale, could address the growing demand for information capacity. By exploiting the emerging non-Hermitian photonics design at an exceptional point, we demonstrate a microring laser producing a single-mode OAM vortex lasing with the ability to precisely define the topological charge of the OAM mode. The polarization associated with OAM lasing can be further manipulated on demand, creating a radially polarized vortex emission. Our OAM microlaser could find applications in the next generation of integrated optoelectronic devices for optical communications in both quantum and classical regimes.
Journal Article
Single-mode laser by parity-time symmetry breaking
Effective manipulation of cavity resonant modes is crucial for emission control in laser physics and applications. Using the concept of parity-time symmetry to exploit the interplay between gain and loss (i.e., light amplification and absorption), we demonstrate a parity-time symmetry–breaking laser with resonant modes that can be controlled at will. In contrast to conventional ring cavity lasers with multiple competing modes, our parity-time microring laser exhibits intrinsic single-mode lasing regardless of the gain spectral bandwidth. Thresholdless parity-time symmetry breaking due to the rotationally symmetric structure leads to stable single-mode operation with the selective whispering-gallery mode order. Exploration of parity-time symmetry in laser physics may open a door to next-generation optoelectronic devices for optical communications and computing.
Journal Article
Direct Lithography for Regulating Multiple Properties of Organic Semiconductors via Photo‐Crosslinkers
Photo‐crosslinkers, as materials with negative photoresist characteristics, are applied in the direct lithography process of organic semiconductor devices. Compared to commonly used organic lithography processes, the direct lithography process only requires three steps: spin‐coating, exposure, and development, to achieve optical patterning of the organic semiconductor channel, eliminating the need for complex procedures such as protection, baking, etching, and transfer. Furthermore, during this process, the photo‐crosslinker remains in the blended film, subsequently influencing the crystalline structure and morphology of the semiconductor film. These alterations will further impact multiple properties of the organic film. By utilizing this characteristic, the design of photo‐crosslinker can effectively regulate and enhance the tensile properties, charge carrier mobility, stability, and dielectric properties of the device. This approach effectively enables high‐precision patterning of organic integrated circuits while synchronously enhancing their various performance attributes. Although there are some relevant reports, a systematic summary and organization of the impact of these photo‐crosslinkers on semiconductors remains absent. For the future development of direct lithography, systematic organization is crucial. Therefore, this review systematically classifies and summarizes the functions of photo‐crosslinkers in organic thin film devices, providing guidance for the design of novel photo‐crosslinkers in direct lithography and improve multiple properties of semiconductor devices. The technique of patterning polymers using photo‐crosslinkers has attracted considerable attention in organic electronics. Owing to the retention of photo‐crosslinkers in the blended films after development, various properties of the films will be affected. In this review, the diverse functions of photo‐crosslinkers are summarized, aiming to deepen researchers' understanding of these essential compounds.
Journal Article
Nanomaterial-Based Tumor Photothermal Immunotherapy
In recent years, photothermal therapy (PTT) particularly nanomaterial-based PTT is a promising therapeutic modality and technique for cancer tumor ablation. In addition to killing tumor cells directly through heat, PTT also can induce immunogenic cell death (ICD) to activate the whole-body anti-tumor immune response, including the redistribution and activation of immune effector cells, the expression and secretion of cytokines and the transformation of memory T lymphocytes. When used in combination with immunotherapy, the efficacy of nanomaterial-based PTT can be improved. This article summarized the mechanism of nanomaterial-based PTT against cancer and how nanomaterial-based PTT impacts the tumor microenvironment and induces an immune response. Moreover, we reviewed recent advances of nanomaterial-based photothermal immunotherapy and discussed challenges and future outlook.
Journal Article