Preface

To enable conversion between optical and electrical signals, optoelectronic devices that rely on light-matter interactions are gaining much attention and are ubiquitous in modern society. Typically, they can be fabricated using either conventional Si and compound semiconductors (like GaAs, InP, and GaN) or emerging materials, such as graphene, transition-metal dichalcogenides (TMDs), and perovskites, or even using a combination of these materials. Optoelectronic devices for imaging and sensing are integral components of many photon-involved applications, such as optical communications, public security warning, smart city monitoring, clinical imaging, and personal healthcare checking. Considering the rapid development of the Internet of Things, 5G-based techniques, and beyond, optoelectronic imaging and sensing devices are ever increasingly important for these applications. Thereupon, they are facing tough challenges and high demands in terms of device properties and parameters.

High-performance optoelectronic imaging and sensing devices, such as optical sensors, photodetectors, light-emitting diodes (LEDs), lasers, and flexible devices, are indeed desired for practical use. For instance, photodetectors and optical sensors in the near-infrared (IR) and mid-infrared (MIR) regions have a huge number of applications, ranging from telecommunications to molecular spectroscopy. Nowadays, the quest for high photoresponsivity, high detectivity, high photogain, low dark noise, fast photoresponse, and complementary metal-oxide semiconductor (CMOS)-compatible room temperature photodetectors in these spectral regions is ongoing. Moreover, recently there have been significant developments in on-chip integration using emerging two-dimensional (2D) materials and/or plasmonic structures to extend the wavelength range of silicon-based photodetectors beyond 1100 nm. There has also been a lot of interest in building MIR detectors based on 2D material design. In order to achieve further developments based on traditional materials and device structures, new concepts regarding emerging materials and device configuration design can also be adopted. Accordingly, this book covers topics including nanomaterial-based photodetector arrays for imaging, plasmonic photodetectors, optical resistance switches for optical sensing, optical interferometric sensing, novel materials for super-resolution imaging techniques, and nanomaterial advances and on-chip integration.

Chapter 1 describes the material systems and heterostructures for optoelectronics, device components, challenges, and prospects of nano-optoelectronic devices. 2D materials are an expanding family of atomically thin crystals, represented by semimetallic graphene, semiconducting black phosphorus, metallic and semiconducting transition-metal (di)chalcogenides, insulating boron nitride, and so on. They exhibit fascinating characteristics, including tunable bandgap, high carrier mobility, efficient light absorption, good structural stability, and mechanical flexibility. In particular, their excellent photodetecting properties render them attractive for optoelectronic devices. Different strategies have been investigated to further enhance the photodetection capabilities of 2D materials, such as chemical doping, surface modification, defect and strain engineering, and plasmonic nanostructure assisting. Moreover, 2D van der Waals heterostructures have been developed to enrich the optical functionalities, such as fast response over a broad spectral range. Advanced synthesis techniques are desired to realize industrial-scale integration. Chapter 2 focuses on the design and performance of 2D material-based photodetectors for imaging applications.

IR photodetectors and imaging focal plane arrays (FPAs) are critical devices for sensing and imaging applications. Various techniques have been developed to enhance the performance of IR photodetectors and FPAs, including resonant cavities, surface gratings, surface plasmonic resonances (SPRs), optical antennas, and plasmonic perfect absorbers. Chapter 3 reviews the concepts of SPR, its excitation (i.e. resonant conditions), dispersion relations, and near-field profiles and enhancement. The applications of SPR resonance in IR photodetection will also be discussed. Specifically, various SPR structures are discussed, including the metallic 2D sub-wavelength hole array (2DSHA) and localized SPRs in metallic circular disks and nanowires. Plasmonic perfector absorbers (PPA) and their enhancement effect on IR photodetectors will be discussed as well. In Chapter 4, representative publications regarding optical switches for optical sensing applications have been studied. The main properties of the structures are given. Such features are the setup and topology of the optical devices, their mechanism operation, dimensions (2D/3D), and isolated waveguides. Also, whether the time-domain simulations are performed has been investigated. In summary, based on the mentioned properties, these structures have the potential to be used as optical sensors.

In Chapter 5, the nonlinear interferometer is discussed, including experimental implementation of phase locking, enhancement of phase sensitivity, experimental realization of entanglement enhancement, and quantum noise cancellation (QNC). Meanwhile, other types of nonlinear interferometers are described, including a nonlinear Sagnac interferometer, a hybrid interferometer consisting of a nonlinear four-wave mixing (FWM) process and a linear beam splitter, a phase-sensitive FWM process acting as a nonlinear beam splitter, and interference-induced quantum-squeezing enhancement. Afterwards, a nonlinear interferometric SPR sensor has been theoretically proposed and its sensing advantages were demonstrated by using sensing parameters such as degree of intensity-difference squeezing, estimation precision, and signal noise ratio. In Chapter 6, recent achievements of this emerging and fast-growing field have been reviewed. The diffraction limit substantially impedes the resolution of the conventional optical microscope. Under traditional illumination, the high-spatial-frequency light corresponding to the subwavelength information of objects is located in the near-field in the form of evanescent waves and thus not detectable by conventional far-field objectives. Recent advances in micro/nanomaterials and metamaterials provide new approaches to break this limitation by utilizing large-wavevector evanescent waves with the spatial frequency shift (SFS) method. The current super-resolution imaging techniques based on evanescent-waves-assisted SFS method, using nanomaterials, photonic waveguides, wafers, and metamaterials, are illustrated. They are promising in investigating unobserved details and processes in fields such as medicine, biology, and material research.

Recent advances in monolithically integrated multisection semiconductor lasers (MI-MSSLs) have propelled microwave photonic (MWP) technologies to new potentials with a compact, reliable, and green implementation. Much research has examined that MI-MSSLs can realize the same or even better MWP functions compared to discrete lasers by taking advantages of enhanced light-matter interactions. Here, we review these recent advances in this emerging field and discuss the corresponding photonic microwave applications. Three main kinds of MI-MSSL structures are demonstrated in general, including passive feedback laser, active/amplified feedback laser, and monolithically integrated mutually injected semiconductor laser. The focus of this paper is on MWP techniques based on the nonlinear dynamics of MI-MSSLs. The primary MWP applications considered in this paper cover from electro-optic conversion characteristics enhancement, photonic microwave generation, MWP filter, to multiwavelength laser array for wavelength division multiplexing radio-over-fiber (WDM-RoF) networks. Especially, the four special dynamic states of free-running oscillation, mode-beating self-pulsations (MB-SPs), period-one (P1) oscillation, and sideband injection locking are considered and demonstrated in detail for photonic microwave generation. In Chapter 7, the authors take a look at the future prospects of the research directions and challenges in this area.

We acknowledge all the contributors and sincerely hope this book can help readers better understand materials, devices, and applications for optical imaging and sensing.

Chengdu, China
28 December 2022

Hao Xu                                                    

Jiang Wu                                                

University of Electronic Science and

Technology of...