Contents
2021
Volume: 2 Issue 2
6 Article(s)

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DEEP LEARNING in PHOTONICS
Interfacing photonics with artificial intelligence: an innovative design strategy for photonic structures and devices based on artificial neural networks
Yihao Xu, Xianzhe Zhang, Yun Fu, and Yongmin Liu

Over the past decades, photonics has transformed many areas in both fundamental research and practical applications. In particular, we can manipulate light in a desired and prescribed manner by rationally designed subwavelength structures. However, constructing complex photonic structures and devices is still a time-consuming process, even for experienced researchers. As a subset of artificial intelligence, artificial neural networks serve as one potential solution to bypass the complicated design process, enabling us to directly predict the optical responses of photonic structures or perform the inverse design with high efficiency and accuracy. In this review, we will introduce several commonly used neural networks and highlight their applications in the design process of various optical structures and devices, particularly those in recent experimental works. We will also comment on the future directions to inspire researchers from different disciplines to collectively advance this emerging research field.

Review of Optics: a virtual journal
  • Publication Date: Mar. 31, 2021
  • Vol. 9 Issue 4 0400B135 (2021)
Deep learning in nano-photonics: inverse design and beyond
Peter R. Wiecha, Arnaud Arbouet, Christian Girard, and Otto L. Muskens

Deep learning in the context of nano-photonics is mostly discussed in terms of its potential for inverse design of photonic devices or nano-structures. Many of the recent works on machine-learning inverse design are highly specific, and the drawbacks of the respective approaches are often not immediately clear. In this review we want therefore to provide a critical review on the capabilities of deep learning for inverse design and the progress which has been made so far. We classify the different deep-learning-based inverse design approaches at a higher level as well as by the context of their respective applications and critically discuss their strengths and weaknesses. While a significant part of the community’s attention lies on nano-photonic inverse design, deep learning has evolved as a tool for a large variety of applications. The second part of the review will focus therefore on machine learning research in nano-photonics “beyond inverse design.” This spans from physics-informed neural networks for tremendous acceleration of photonics simulations, over sparse data reconstruction, imaging and “knowledge discovery” to experimental applications.

Review of Optics: a virtual journal
  • Publication Date: Apr. 14, 2021
  • Vol. 9 Issue 5 0500B182 (2021)
Integrated Optics
Electro-optic polymer ring resonator modulators [Invited]
Feng Qiu, and Yu Han
Electro-optic (EO) ring resonator modulators have a number of communications and scientific applications, including analog optical links, optical signal processing, and frequency comb generation. Among the EO materials used to fabricate ring modulators, the EO polymer has many promising characteristics, including a high EO coefficient of 100–200 pm/V (3–7 times larger than that of LiNbO3), an ultrafast EO response time (<10 fs), a low dielectric constant (3 to 4) with very little dispersion up to at least 250 GHz, and a straightforward spin-coating fabrication process. These inherent characteristics will be able to combine excellent EO properties with simple processing in achieving exceptional performance in a variety of high-speed optical modulation and sensing devices. This review focuses on the research and recent development of ring resonator modulators based on EO polymers. The first part describes the operation principle of EO ring resonator modulators, such as modulation mechanism, EO tunability, and 3 dB bandwidth. Subsequently, the emphasis is placed on the discussion of the ring modulators with EO polymers as the waveguide core and the improvement of EO modulation by using an EO polymer/titanium dioxide hybrid core. At the end, a series of EO polymers on silicon platforms including slot modulators, etching-free modulators, and athermal modulators are reviewed.
Review of Optics: a virtual journal
  • Publication Date: Apr. 10, 2021
  • Vol. 19 Issue 4 041301 (2021)
Optoelectronics
Lead–halide perovskites for next-generation self-powered photodetectors: a comprehensive review
Chandrasekar Perumal Veeramalai, Shuai Feng, Xiaoming Zhang, S. V. N. Pammi, Vincenzo Pecunia, and Chuanbo Li
Metal halide perovskites have aroused tremendous interest in optoelectronics due to their attractive properties, encouraging the development of high-performance devices for emerging application domains such as wearable electronics and the Internet of Things. Specifically, the development of high-performance perovskite-based photodetectors (PDs) as an ultimate substitute for conventional PDs made of inorganic semiconductors such as silicon, InGaAs, GaN, and germanium-based commercial PDs, attracts great attention by virtue of its solution processing, film deposition technique, and tunable optical properties. Importantly, perovskite PDs can also deliver high performance without an external power source; so-called self-powered perovskite photodetectors (SPPDs) have found eminent application in next-generation nanodevices operating independently, wirelessly, and remotely. Earlier research reports indicate that perovskite-based SPPDs have excellent photoresponsive behavior and wideband spectral response ranges. Despite the high-performance perovskite PDs, their commercialization is hindered by long-term material instability under ambient conditions. This review aims to provide a comprehensive compilation of the research results on self-powered, lead–halide perovskite PDs. In addition, a brief introduction is given to flexible SPPDs. Finally, we put forward some perspectives on the further development of perovskite-based self-powered PDs. We believe that this review can provide state-of-the-art current research on SPPDs and serve as a guide to improvising a path for enhancing the performance to meet the versatility of practical device applications.
Review of Optics: a virtual journal
  • Publication Date: May. 20, 2021
  • Vol. 9 Issue 6 06000968 (2021)
Physical Optics
Topological photonic states in artificial microstructures [Invited]
Hui Liu, Boyang Xie, Hua Cheng, Jianguo Tian, and Shuqi Chen
Topological photonics provides a new opportunity for the examination of novel topological properties of matter, in which the energy band theory and ideas in topology are utilized to manipulate the propagation of photons. Since the discovery of topological insulators in condensed matter, researchers have studied similar topological effects in photonics. Topological photonics can lead to materials that support the robust unidirectional propagation of light without back reflections. This ideal transport property is unprecedented in traditional optics and may lead to radical changes in integrated optical devices. In this review, we present the exciting developments of topological photonics and focus on several prominent milestones of topological phases in photonics, such as topological insulators, topological semimetals, and higher-order topological phases. We conclude with the prospect of novel topological effects and their applications in topological photonics.
Review of Optics: a virtual journal
  • Publication Date: May. 10, 2021
  • Vol. 19 Issue 5 052602 (2021)
Special Issue on Lithium Niobate Based Photonic Devices
Recent progress of second harmonic generation based on thin film lithium niobate [Invited]
Yang Li, Zhijin Huang, Wentao Qiu, Jiangli Dong, Heyuan Guan, and Huihui Lu
Recently, nonlinear photonics has attracted considerable interest. Among the nonlinear effects, second harmonic generation (SHG) remains a hot research topic. The recent development of thin film lithium niobate (TFLN) technology has superior performances to the conventional counterparts. Herein, this review article reveals the recent progress of SHG based on TFLN and its integrated photonics. We mainly discuss and compare the different techniques of TFLN-based structures to boost the nonlinear performances assisted by localizing light in nanostructures and structured waveguides. Moreover, our conclusions and perspectives indicate that more efficient methods need to be further explored for higher SHG conversion efficiency on the TFLN platform.
Review of Optics: a virtual journal
  • Publication Date: Jun. 10, 2021
  • Vol. 19 Issue 6 060012 (2021)