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Review Articles|24 Article(s)
Microcomb technology: from principles to applications
Haowen Shu, Bitao Shen, Huajin Chang, Junhao Han, Jiong Xiao, and Xingjun Wang
Integrated microcombs bring a parallel and coherent optical frequency comb to compact chip-scale devices. They offer promising prospects for mass-produced comb sources in a compact, power-efficient, and robust manner, benefiting many basic research and practical applications. In the past two decades, they have been utilized in many traditional fields, such as high-capacity parallel communication, optical frequency synthesis, frequency metrology, precision spectroscopy, and emerging fields like distance ranging, optical computing, microwave photonics, and molecule detection. In this review, we briefly introduce microcombs, including their physical model, formation dynamics, generation methods, materials and fabrications, design principles, and advanced applications. We also systematically summarize the field of integrated optical combs and evaluate the remaining challenges and prospects in each aspect. Integrated microcombs bring a parallel and coherent optical frequency comb to compact chip-scale devices. They offer promising prospects for mass-produced comb sources in a compact, power-efficient, and robust manner, benefiting many basic research and practical applications. In the past two decades, they have been utilized in many traditional fields, such as high-capacity parallel communication, optical frequency synthesis, frequency metrology, precision spectroscopy, and emerging fields like distance ranging, optical computing, microwave photonics, and molecule detection. In this review, we briefly introduce microcombs, including their physical model, formation dynamics, generation methods, materials and fabrications, design principles, and advanced applications. We also systematically summarize the field of integrated optical combs and evaluate the remaining challenges and prospects in each aspect.
Photonics Insights
- Publication Date: Dec. 31, 2024
- Vol. 3, Issue 4, R09 (2024)
Spatiotemporal optical wavepackets: from concepts to applications|On the Cover , Story Video
Xin Liu, Qian Cao, and Qiwen Zhan
Spatiotemporal optical wavepackets refer to light fields with sophisticated structures in both space and time. The ability to produce such spatiotemporally structured optical wavepackets on demand attracted rapidly increasing interest as it may unravel a variety of fundamental physical effects and applications. Traditionally, pulsed laser fields are treated as spatiotemporally separable waveform solutions to Maxwell’s equations. Recently, more generalized spatiotemporally non-separable solutions have gained attention due to their remarkable properties. This review aims to provide essential insights into sculpting light in the space–time domain to create customized spatiotemporal structures and highlights the recent advances in the generation, manipulation, and characterization of increasingly complex spatiotemporal wavepackets. These spatiotemporally non-separable light fields with diverse geometric and topological structures exhibit unique physical properties during propagation, focusing, and light–matter interactions. Various novel results and their broad potential applications as well as an outlook for future trends and challenges in this field are presented. Spatiotemporal optical wavepackets refer to light fields with sophisticated structures in both space and time. The ability to produce such spatiotemporally structured optical wavepackets on demand attracted rapidly increasing interest as it may unravel a variety of fundamental physical effects and applications. Traditionally, pulsed laser fields are treated as spatiotemporally separable waveform solutions to Maxwell’s equations. Recently, more generalized spatiotemporally non-separable solutions have gained attention due to their remarkable properties. This review aims to provide essential insights into sculpting light in the space–time domain to create customized spatiotemporal structures and highlights the recent advances in the generation, manipulation, and characterization of increasingly complex spatiotemporal wavepackets. These spatiotemporally non-separable light fields with diverse geometric and topological structures exhibit unique physical properties during propagation, focusing, and light–matter interactions. Various novel results and their broad potential applications as well as an outlook for future trends and challenges in this field are presented.
Photonics Insights
- Publication Date: Dec. 28, 2024
- Vol. 3, Issue 4, R08 (2024)
Electrically tunable optical metasurfaces|Story Video
Fei Ding, Chao Meng, and Sergey I. Bozhevolnyi
Optical metasurfaces have emerged as a groundbreaking technology in photonics, offering unparalleled control over light–matter interactions at the subwavelength scale with ultrathin surface nanostructures and thereby giving birth to flat optics. While most reported optical metasurfaces are static, featuring well-defined optical responses determined by their compositions and configurations set during fabrication, dynamic optical metasurfaces with reconfigurable functionalities by applying thermal, electrical, or optical stimuli have become increasingly more in demand and moved to the forefront of research and development. Among various types of dynamically controlled metasurfaces, electrically tunable optical metasurfaces have shown great promise due to their fast response time, low power consumption, and compatibility with existing electronic control systems, offering unique possibilities for dynamic tunability of light–matter interactions via electrical modulation. Here we provide a comprehensive overview of the state-of-the-art design methodologies and technologies explored in this rapidly evolving field. Our work delves into the fundamental principles of electrical modulation, various materials and mechanisms enabling tunability, and representative applications for active light-field manipulation, including optical amplitude and phase modulators, tunable polarization optics and wavelength filters, and dynamic wave-shaping optics, including holograms and displays. The review terminates with our perspectives on the future development of electrically triggered optical metasurfaces. Optical metasurfaces have emerged as a groundbreaking technology in photonics, offering unparalleled control over light–matter interactions at the subwavelength scale with ultrathin surface nanostructures and thereby giving birth to flat optics. While most reported optical metasurfaces are static, featuring well-defined optical responses determined by their compositions and configurations set during fabrication, dynamic optical metasurfaces with reconfigurable functionalities by applying thermal, electrical, or optical stimuli have become increasingly more in demand and moved to the forefront of research and development. Among various types of dynamically controlled metasurfaces, electrically tunable optical metasurfaces have shown great promise due to their fast response time, low power consumption, and compatibility with existing electronic control systems, offering unique possibilities for dynamic tunability of light–matter interactions via electrical modulation. Here we provide a comprehensive overview of the state-of-the-art design methodologies and technologies explored in this rapidly evolving field. Our work delves into the fundamental principles of electrical modulation, various materials and mechanisms enabling tunability, and representative applications for active light-field manipulation, including optical amplitude and phase modulators, tunable polarization optics and wavelength filters, and dynamic wave-shaping optics, including holograms and displays. The review terminates with our perspectives on the future development of electrically triggered optical metasurfaces.
Photonics Insights
- Publication Date: Sep. 27, 2024
- Vol. 3, Issue 3, R07 (2024)
Image reconstruction from photoacoustic projections|Story Video
Chao Tian, Kang Shen, Wende Dong, Fei Gao, Kun Wang, Jiao Li, Songde Liu, Ting Feng, Chengbo Liu, Changhui Li, Meng Yang, Sheng Wang, and Jie Tian
Photoacoustic computed tomography (PACT) is a rapidly developing biomedical imaging modality and has attracted substantial attention in recent years. Image reconstruction from photoacoustic projections plays a critical role in image formation in PACT. Here we review six major classes of image reconstruction approaches developed in the past three decades, including delay and sum, filtered back projection, series expansion, time reversal, iterative reconstruction, and deep-learning-based reconstruction. The principal ideas and implementations of the algorithms are summarized, and their reconstruction performances under different imaging scenarios are compared. Major challenges, future directions, and perspectives for the development of image reconstruction algorithms in PACT are also discussed. This review provides a self-contained reference guide for beginners and specialists in the photoacoustic community, to facilitate the development and application of novel photoacoustic image reconstruction algorithms. Photoacoustic computed tomography (PACT) is a rapidly developing biomedical imaging modality and has attracted substantial attention in recent years. Image reconstruction from photoacoustic projections plays a critical role in image formation in PACT. Here we review six major classes of image reconstruction approaches developed in the past three decades, including delay and sum, filtered back projection, series expansion, time reversal, iterative reconstruction, and deep-learning-based reconstruction. The principal ideas and implementations of the algorithms are summarized, and their reconstruction performances under different imaging scenarios are compared. Major challenges, future directions, and perspectives for the development of image reconstruction algorithms in PACT are also discussed. This review provides a self-contained reference guide for beginners and specialists in the photoacoustic community, to facilitate the development and application of novel photoacoustic image reconstruction algorithms.
Photonics Insights
- Publication Date: Sep. 26, 2024
- Vol. 3, Issue 3, R06 (2024)
Integrated structured light manipulation|On the Cover
Jian Wang, Kang Li, and Zhiqiang Quan
Structured light, also known as tailored light, shaped light, sculpted light, or custom light, refers to a series of special light beams with spatially variant amplitudes and phases, polarization distributions, or more general spatiotemporal profiles. In the past decades, structured light featuring distinct properties and unique spatial or spatiotemporal structures has grown into a significant research field and given rise to many developments from fundamentals to applications. Very recently, integrated structured light manipulation has become an important trend in the frontier of light field manipulation and attracted increasing interest as a highly promising technique for shaping structured light in an integrated, compact, and miniaturized manner. In this article, we give a comprehensive overview of recent advances in integrated structured light manipulation (generation, processing, detection, and application). After briefly introducing the basic concept and development history of structured light, we present representative works in four important aspects of integrated structured light manipulation, including multiple types of integrated structured light generation, many sorts of integrated structured light processing, diverse forms of integrated structured light detection, and various kinds of integrated structured light applications. We focus on summarizing the progress of integrated structured light manipulation from basic theories to cutting-edge technologies, to key devices, and to a wide variety of applications, from orbital angular momentum carrying light beams to more general structured light beams, from passive to active integration platforms, from micro-nano structures and metasurfaces to 2D photonic integrated circuits and 3D photonic chips, from in-plane to out-of-plane, from multiplexing to transformation, from linear to nonlinear, from classical to quantum, from optical communications to optical holography, imaging, microscopy, trapping, tweezers, metrology, etc. Finally, we also discuss in detail the future trends, opportunities, challenges, and solutions, and give a vision for integrated structured light manipulation. Structured light, also known as tailored light, shaped light, sculpted light, or custom light, refers to a series of special light beams with spatially variant amplitudes and phases, polarization distributions, or more general spatiotemporal profiles. In the past decades, structured light featuring distinct properties and unique spatial or spatiotemporal structures has grown into a significant research field and given rise to many developments from fundamentals to applications. Very recently, integrated structured light manipulation has become an important trend in the frontier of light field manipulation and attracted increasing interest as a highly promising technique for shaping structured light in an integrated, compact, and miniaturized manner. In this article, we give a comprehensive overview of recent advances in integrated structured light manipulation (generation, processing, detection, and application). After briefly introducing the basic concept and development history of structured light, we present representative works in four important aspects of integrated structured light manipulation, including multiple types of integrated structured light generation, many sorts of integrated structured light processing, diverse forms of integrated structured light detection, and various kinds of integrated structured light applications. We focus on summarizing the progress of integrated structured light manipulation from basic theories to cutting-edge technologies, to key devices, and to a wide variety of applications, from orbital angular momentum carrying light beams to more general structured light beams, from passive to active integration platforms, from micro-nano structures and metasurfaces to 2D photonic integrated circuits and 3D photonic chips, from in-plane to out-of-plane, from multiplexing to transformation, from linear to nonlinear, from classical to quantum, from optical communications to optical holography, imaging, microscopy, trapping, tweezers, metrology, etc. Finally, we also discuss in detail the future trends, opportunities, challenges, and solutions, and give a vision for integrated structured light manipulation.
Photonics Insights
- Publication Date: Sep. 17, 2024
- Vol. 3, Issue 3, R05 (2024)
Advanced manufacturing of dielectric meta-devices
Wenhong Yang, Junxiao Zhou, Din Ping Tsai, and Shumin Xiao
Metasurfaces, composed of two-dimensional nanostructures, exhibit remarkable capabilities in shaping wavefronts, encompassing phase, amplitude, and polarization. This unique proficiency heralds a transformative paradigm shift in the domain of next-generation optics and photonics, culminating in the development of flat and ultrathin optical devices. Particularly noteworthy is the all-dielectric-based metasurface, leveraging materials such as titanium dioxide, silicon, gallium arsenide, and silicon nitride, which finds extensive application in the design and implementation of high-performance optical devices, owing to its notable advantages, including a high refractive index, low ohmic loss, and cost-effectiveness. Furthermore, the remarkable growth in nanofabrication technologies allows for the exploration of new methods in metasurface fabrication, especially through wafer-scale nanofabrication technologies, thereby facilitating the realization of commercial applications for metasurfaces. This review provides a comprehensive overview of the latest advancements in state-of-the-art fabrication technologies in dielectric metasurface areas. These technologies, including standard nanolithography [e.g., electron beam lithography (EBL) and focused ion beam (FIB) lithography], advanced nanolithography (e.g., grayscale and scanning probe lithography), and large-scale nanolithography [e.g., nanoimprint and deep ultraviolet (DUV) lithography], are utilized to fabricate high-resolution, high-aspect-ratio, flexible, multilayer, slanted, and wafer-scale all-dielectric metasurfaces with intricate nanostructures. Ultimately, we conclude with a perspective on current cutting-edge nanofabrication technologies. Metasurfaces, composed of two-dimensional nanostructures, exhibit remarkable capabilities in shaping wavefronts, encompassing phase, amplitude, and polarization. This unique proficiency heralds a transformative paradigm shift in the domain of next-generation optics and photonics, culminating in the development of flat and ultrathin optical devices. Particularly noteworthy is the all-dielectric-based metasurface, leveraging materials such as titanium dioxide, silicon, gallium arsenide, and silicon nitride, which finds extensive application in the design and implementation of high-performance optical devices, owing to its notable advantages, including a high refractive index, low ohmic loss, and cost-effectiveness. Furthermore, the remarkable growth in nanofabrication technologies allows for the exploration of new methods in metasurface fabrication, especially through wafer-scale nanofabrication technologies, thereby facilitating the realization of commercial applications for metasurfaces. This review provides a comprehensive overview of the latest advancements in state-of-the-art fabrication technologies in dielectric metasurface areas. These technologies, including standard nanolithography [e.g., electron beam lithography (EBL) and focused ion beam (FIB) lithography], advanced nanolithography (e.g., grayscale and scanning probe lithography), and large-scale nanolithography [e.g., nanoimprint and deep ultraviolet (DUV) lithography], are utilized to fabricate high-resolution, high-aspect-ratio, flexible, multilayer, slanted, and wafer-scale all-dielectric metasurfaces with intricate nanostructures. Ultimately, we conclude with a perspective on current cutting-edge nanofabrication technologies.
Photonics Insights
- Publication Date: Jun. 30, 2024
- Vol. 3, Issue 2, R04 (2024)
Recent progress on structural coloration|On the Cover , Story Video
Yingjie Li, Jingtian Hu, Yixuan Zeng, Qinghai Song, Cheng-Wei Qiu, and Shumin Xiao
Structural coloration generates colors by the interaction between incident light and micro- or nano-scale structures. It has received tremendous interest for decades, due to advantages including robustness against bleaching and environmentally friendly properties (compared with conventional pigments and dyes). As a versatile coloration strategy, the tuning of structural colors based on micro- and nanoscale photonic structures has been extensively explored and can enable a broad range of applications including displays, anti-counterfeiting, and coating. However, scholarly research on structural colors has had limited impact on commercial products because of their disadvantages in cost, scalability, and fabrication. In this review, we analyze the key challenges and opportunities in the development of structural colors. We first summarize the fundamental mechanisms and design strategies for structural colors while reviewing the recent progress in realizing dynamic structural coloration. The promising potential applications including optical information processing and displays are also discussed while elucidating the most prominent challenges that prevent them from translating into technologies on the market. Finally, we address the new opportunities that are underexplored by the structural coloration community but can be achieved through multidisciplinary research within the emerging research areas. Structural coloration generates colors by the interaction between incident light and micro- or nano-scale structures. It has received tremendous interest for decades, due to advantages including robustness against bleaching and environmentally friendly properties (compared with conventional pigments and dyes). As a versatile coloration strategy, the tuning of structural colors based on micro- and nanoscale photonic structures has been extensively explored and can enable a broad range of applications including displays, anti-counterfeiting, and coating. However, scholarly research on structural colors has had limited impact on commercial products because of their disadvantages in cost, scalability, and fabrication. In this review, we analyze the key challenges and opportunities in the development of structural colors. We first summarize the fundamental mechanisms and design strategies for structural colors while reviewing the recent progress in realizing dynamic structural coloration. The promising potential applications including optical information processing and displays are also discussed while elucidating the most prominent challenges that prevent them from translating into technologies on the market. Finally, we address the new opportunities that are underexplored by the structural coloration community but can be achieved through multidisciplinary research within the emerging research areas.
Photonics Insights
- Publication Date: Apr. 22, 2024
- Vol. 3, Issue 2, R03 (2024)
Optical microfiber or nanofiber: a miniature fiber-optic platform for nanophotonics|Story Video
Jianbin Zhang, Hubiao Fang, Pan Wang, Wei Fang, Lei Zhang, Xin Guo, and Limin Tong
An optical micro/nanofiber (MNF) is a quasi-one-dimensional free-standing optical waveguide with a diameter close to or less than the vacuum wavelength of light. Combining the tiny geometry with high-refractive-index contrast between the core and the surrounding, the MNF exhibits favorable optical properties such as tight optical confinement, strong evanescent field, and large-diameter-dependent waveguide dispersion. Meanwhile, as a quasi-one-dimensional structure with extraordinarily high geometric and structural uniformity, the MNF also has low optical loss and high mechanical strength, making it favorable for manipulating light on the micro/nanoscale with high flexibility. Over the past two decades, optical MNFs, typically being operated in single mode, have been emerging as a miniaturized fiber-optic platform for both scientific research and technological applications. In this paper, we aim to provide a comprehensive overview of the representative advances in optical MNFs in recent years. Starting from the basic structures and fabrication techniques of the optical MNFs, we highlight linear and nonlinear optical and mechanical properties of the MNFs. Then, we introduce typical applications of optical MNFs from near-field optics, passive optical components, optical sensors, and optomechanics to fiber lasers and atom optics. Finally, we give a brief summary of the current status of MNF optics and technology, and provide an outlook into future challenges and opportunities. An optical micro/nanofiber (MNF) is a quasi-one-dimensional free-standing optical waveguide with a diameter close to or less than the vacuum wavelength of light. Combining the tiny geometry with high-refractive-index contrast between the core and the surrounding, the MNF exhibits favorable optical properties such as tight optical confinement, strong evanescent field, and large-diameter-dependent waveguide dispersion. Meanwhile, as a quasi-one-dimensional structure with extraordinarily high geometric and structural uniformity, the MNF also has low optical loss and high mechanical strength, making it favorable for manipulating light on the micro/nanoscale with high flexibility. Over the past two decades, optical MNFs, typically being operated in single mode, have been emerging as a miniaturized fiber-optic platform for both scientific research and technological applications. In this paper, we aim to provide a comprehensive overview of the representative advances in optical MNFs in recent years. Starting from the basic structures and fabrication techniques of the optical MNFs, we highlight linear and nonlinear optical and mechanical properties of the MNFs. Then, we introduce typical applications of optical MNFs from near-field optics, passive optical components, optical sensors, and optomechanics to fiber lasers and atom optics. Finally, we give a brief summary of the current status of MNF optics and technology, and provide an outlook into future challenges and opportunities.
Photonics Insights
- Publication Date: Mar. 01, 2024
- Vol. 3, Issue 1, R02 (2024)
Optical bound states in the continuum in periodic structures: mechanisms, effects, and applications|On the Cover , Story Video , Author Presentation
Jiajun Wang, Peishen Li, Xingqi Zhao, Zhiyuan Qian, Xinhao Wang, Feifan Wang, Xinyi Zhou, Dezhuan Han, Chao Peng, Lei Shi, and Jian Zi
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 (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.
Photonics Insights
- Publication Date: Feb. 26, 2024
- Vol. 3, Issue 1, R01 (2024)
Diffractive optical elements 75 years on: from micro-optics to metasurfaces|On the Cover , Story Video , Author Presentation
Qiang Zhang, Zehao He, Zhenwei Xie, Qiaofeng Tan, Yunlong Sheng, Guofan Jin, Liangcai Cao, and Xiaocong Yuan
Diffractive optical elements (DOEs) are intricately designed devices with the purpose of manipulating light fields by precisely modifying their wavefronts. The concept of DOEs has its origins dating back to 1948 when D. Gabor first introduced holography. Subsequently, researchers introduced binary optical elements (BOEs), including computer-generated holograms (CGHs), as a distinct category within the realm of DOEs. This was the first revolution in optical devices. The next major breakthrough in light field manipulation occurred during the early 21st century, marked by the advent of metamaterials and metasurfaces. Metasurfaces are particularly appealing due to their ultra-thin, ultra-compact properties and their capacity to exert precise control over virtually every aspect of light fields, including amplitude, phase, polarization, wavelength/frequency, angular momentum, etc. The advancement of light field manipulation with micro/nano-structures has also enabled various applications in fields such as information acquisition, transmission, storage, processing, and display. In this review, we cover the fundamental science, cutting-edge technologies, and wide-ranging applications associated with micro/nano-scale optical devices for regulating light fields. We also delve into the prevailing challenges in the pursuit of developing viable technology for real-world applications. Furthermore, we offer insights into potential future research trends and directions within the realm of light field manipulation. Diffractive optical elements (DOEs) are intricately designed devices with the purpose of manipulating light fields by precisely modifying their wavefronts. The concept of DOEs has its origins dating back to 1948 when D. Gabor first introduced holography. Subsequently, researchers introduced binary optical elements (BOEs), including computer-generated holograms (CGHs), as a distinct category within the realm of DOEs. This was the first revolution in optical devices. The next major breakthrough in light field manipulation occurred during the early 21st century, marked by the advent of metamaterials and metasurfaces. Metasurfaces are particularly appealing due to their ultra-thin, ultra-compact properties and their capacity to exert precise control over virtually every aspect of light fields, including amplitude, phase, polarization, wavelength/frequency, angular momentum, etc. The advancement of light field manipulation with micro/nano-structures has also enabled various applications in fields such as information acquisition, transmission, storage, processing, and display. In this review, we cover the fundamental science, cutting-edge technologies, and wide-ranging applications associated with micro/nano-scale optical devices for regulating light fields. We also delve into the prevailing challenges in the pursuit of developing viable technology for real-world applications. Furthermore, we offer insights into potential future research trends and directions within the realm of light field manipulation.
Photonics Insights
- Publication Date: Dec. 29, 2023
- Vol. 2, Issue 4, R09 (2023)
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