Abstract. Optical bound states in the continuum (BICs) have recently stimulated a research boom, accompanied by demonstrations of abundant exotic phenomena and applications. With ultrahigh quality (Q) factors, optical BICs have powerful abilities to trap light in optical structures from the continuum of propagation waves in free space. Besides the high Q factors enabled by the confined properties, many hidden topological characteristics were discovered in optical BICs. Especially in periodic structures with well-defined wave vectors, optical BICs were discovered to carry topological charges in momentum space, underlying many unique physical properties. Both high Q factors and topological vortex configurations in momentum space enabled by BICs bring new degrees of freedom to modulate light. BICs have enabled many novel discoveries in light–matter interactions and spin–orbit interactions of light, and BIC applications in lasing and sensing have also been well explored with many advantages. In this paper, we review recent developments of optical BICs in periodic structures, including the physical mechanisms of BICs, explored effects enabled by BICs, and applications of BICs. In the outlook part, we provide a perspective on future developments for BICs.

Optical bound states in the continuum in periodic structures: mechanisms, effects, and applications

We study the role of topological singularities like Bound States in a Continuum (BICs) or Circularly Polarized States (CPSs) in determining ellipticity of the far-field polarization in dielectric metasurfaces. Using finite-difference time-domain as well as rigorous coupled-wave analysis simulations, we determine the behavior of the Stokes parameter S3 in the whole k space above the light cone, with special regard to the region close to the singularities. Moreover, we clarify the relation between the topological singularities and the circular dichroism in reflectivity.

Polarization states and far-field optical properties in dielectric photonic crystal slabs

Grating couplers that interconnect photonic chips to off-chip components are crucial for various optoelectronics applications. Despite numerous efforts in past decades, the existing grating couplers are still far from optimal in energy efficiency and thus hinder photonic integration toward a larger scale. Here, we propose a strategy to achieve ultralow-loss grating couplers by using unidirectional guided resonances (UGRs), suppressing the useless downward radiation with no mirror on the bottom. By engineering the dispersion and apodizing the geometry of grating, we experimentally realize a grating coupler with a record-low loss of -0.34 dB and 1-dB bandwidth exceeding 30 nm at the telecom wavelength of 1550 nm and further demonstrate an optic via with a loss of only -0.94 dB. Given that UGRs ubiquitously exist in a variety of grating geometries, our work sheds light on a systematic method to achieve energy-efficient optical interconnect and paves the way to large-scale photonic integration. 

Ultralow-loss optical interconnect enabled by topological unidirectional guided resonance

Bound states in the continuum (BICs) with exceptionally high quality factors (<inline-formula><tex-math notation="LaTeX">$Q$</tex-math></inline-formula> factors) have become focal points in photonic device research, finding applications in nonlinear enhancement, laser generation, sensing, and beyond. In this study, we systematically investigate the intricate relationship between the in-plane symmetry groups of photonic crystals and symmetry-protected BICs (SP-BICs) using a rigorous group theory approach. By modifying the spatial distribution of refractive indices to perturb the <inline-formula><tex-math notation="LaTeX">$C_{2}$</tex-math></inline-formula> and <inline-formula><tex-math notation="LaTeX">$C_{3}$</tex-math></inline-formula> symmetries within a <inline-formula><tex-math notation="LaTeX">$C_{6v}$</tex-math></inline-formula> photonic crystal slab, we introduce a novel method to enable precise tuning of BIC resonances, including the BIC frequency, <inline-formula><tex-math notation="LaTeX">$Q$</tex-math></inline-formula> factor, and polarization state. The proposed group theory approach and tuning mechanism establish a pioneering pathway for the design and tunability of BICs, opening avenues for the development of advanced photonic devices with tailored functionalities such as tunable lasers and optical sensors with enhanced performance.

Evolution of degenerate pairs of bound states in the continuum with broken symmetry

The intriguing properties of bound states in the continuum (BICs) have attracted a lot of attention in photonics. Besides being effective in confining light in a counter-intuitive way, the correspondence between the near-field mode pattern and the far-field radiation of BICs manifests the fascinating topological characteristics of light. Early works on photonic BICs were mainly focused on designing artificial structures to facilitate their realization, while recent advances have shifted to exploring their exceptional properties in applications. In this review, we survey important breakthroughs and recent advances in this field. We detail the unique properties of BICs, including light confinement enhancement, sharp Fano resonances, and topological characteristics. We provide insights into the unique phenomena derived from BICs and the impact of BICs on various applications. We also discuss the paradigm shift enabled or facilitated by BICs in several emerging research frontiers, such as parity-time symmetric systems, higher-order topology, exciton-photon coupling, and moir\'e superlattices. 

/pdf/applications-of-bound-states-in-the-continuum-in-photonics-2iq9okl9.pdf

Applications of Bound States in the Continuum in Photonics

Radiations towards the continuum not only brings non-Hermicity to photonic systems but also provides observable channels for understanding their intrinsic physics underneath. In this article, we review the fundamental physics and applications of topological polarization singularities, which are defined upon the far-field radiation of photonic systems and characterized by topological charges as the winding numbers of polarization orientation around a given center. A brief summarizing of topological charge theory is presented. A series of applications related to topological polarization singularities are then discussed.

Fundamentals and Applications of Topological Polarization Singularities

Handle everyday research tasks with reliable, citation-backed results

Your personal Research Agent to handle research tasks with citation-backed results

Popular Tasks used by Researchers

How can I help with your research?

Meet SciSpace

Get more enhanced response by uploading the PDFs you want me to reference.

No relevant PDFs in your library

SciSpace is the AI research assistant for academics. Run systematic literature reviews on 280M+ papers, and write papers with cited sources. Trusted by 1M+ students, PhDs & researchers.

SciSpace | AI for Research

Analyze PDFs

Code & Manuscripts

Funding & Grants

Literature & Patents

Medical & Clinical Data

Systematic Review

Visualize & Present

Web & Data

Build a Google Scholar-like website for your research.

Build a website

Create charts and images for your research

Create a Chart

Write a paper for submission to a journal

Draft a manuscript

Patent Search

Design eye-catching scientific posters in minutes.

Scientific Poster Generation

Systematic Literature Review

One task is running at the moment. Your messages will be shown right after.

Drag and drop or click here to browse

Loved by <highlight>1 million+</highlight> researchers

Extract a list of specific topics and their sources from unstructured text

Topics

Compare and analyze relevant papers that matches with your search

Papers

Get insights from PDFs and bookmarked papers from your library

My library

Recent searches

Try searching for:

Catch AI-generated content in scholarly and non-scholarly content

{ai} Detector

Ai Writer

Get PDF Summaries, highlighted text explanations 

Chat with PDF

Effortlessly create in-text citations and bibliographies in APA and 2,500 other formats

Citation generator

Get explanations, summaries, and answers on academic papers

Ease up your research workflow with {scispace}'s cohort of exciting AI tools

Elevate your academic writing skills and convey your ideas the way you want

Paraphraser

Explore our range of reading and writing tools

Your file is being prepared and should be ready in a few minutes. If it's a large file, it might take a bit longer. You can close this window, and we'll email you the file when it's done.

You have reached a maximum limit of <strong>{limit}</strong> columns in the table. Remove at least <strong>1</strong> column to add or create another one.

Feifan Wang

Author Tools

Chat about Author

Papers

Fundamentals and Applications of Topological Polarization Singularities