Recently, there has been a growing interest in deploying smart materials as sensing components of structural health monitoring systems. In this arena, piezoelectric materials offer great promise for researchers to rapidly expand their many potential applications. The main goal of this study is to review the state-of-the-art piezoelectric-based sensing techniques that are currently used in the structural health monitoring area. These techniques range from piezoelectric electromechanical impedance and ultrasonic Lamb wave methods to a class of cutting-edge self-powered sensing systems. We present the principle of the piezoelectric effect and the underlying mechanisms used by the piezoelectric sensing methods to detect the structural response. Furthermore, the pros and cons of the current methodologies are discussed. In the end, we envision a role of the piezoelectric-based techniques in developing the next-generation self-monitoring and self-powering health monitoring systems.

Reconfigurable photonic integrated devices and circuits are very important for many applications. Among various mechanisms for realizing reconfigurability, thermo-optic effect is popular because of the availability for many materials, the design simplicity and the fabrication ease. In particular, silicon has a large thermo-optic coefficient as well as a high heat conductivity, and thus it is promising to realize efficient thermally-reconfigurable silicon photonic integrated devices and circuits. Recent progress is reviewed in this paper. First, thermally-tunable silicon photonic filters based on different structures are summarized, including microring resonators (MRRs) and MRRs-assisted Mach-Zehnder interferometers (MZIs). Second, silicon photonic switches based on MZIs and MRRs are reviewed. Finally, a review is given for thermally-reconfigurable silicon photonic integrated circuits developed for the applications in quantum photonics, microwave photonics, and optical interconnects.

Silicon photonic signal processors promise a new generation of signal processing hardware with significant advancements in processing bandwidth, low power consumption, and minimal latency. Programmable silicon photonic signal processors, facilitated by tuning elements, can reduce hardware development cycles and costs. However, traditional programmable photonic signal processors based on optical switches face scalability and performance challenges due to control complexity and transmission losses. Here, we propose a scalable parallel signal processor on silicon for versatile applications by interleaving wavelength and temporal optical dimensions. Additionally, it incorporates ultra-low-loss waveguides and low-phase-error optical switch techniques, achieving an overall insertion loss of 10 dB. This design offers low loss, high scalability, and simplified control, enabling advanced functionalities such as accurate microwave reception, narrowband microwave photonic filtering, wide-bandwidth arbitrary waveform generation, and high-speed parallel optical computing without the need for tuning elements calibration. Our programmable parallel signal processor demonstrates advantages in both scale and performance, marking a significant advancement in large-scale, high-performance, multifunctional photonic systems.

Matrix-vector multiplication is a fundamental operation in modern signal processing and artificial intelligence. Developing a chip-scale photonic matrix-vector multiplication processor (MVMP) offers the potential for notably enhanced computing speed and energy efficiency beyond microelectronics. Here, we propose and demonstrate a 16-channel programmable on-chip coherent photonic processor capable of performing complex-valued matrix-vector multiplication at a computing speed of 1.28 tera-operations per second (TOPS). Low phase error Mach-Zehnder interferometers mesh and ultralow-loss broadened photonic waveguide delay lines are firstly combined for optical computing, enabling the encoding of amplitude and phase information, along with high-speed coherent detection. The proposed MVMP demonstrates high flexibility in implementing various functions, including arbitrary matrix transformation, parallel image processing, and handwritten digital recognition. Our work demonstrates the MVMP’s advantages in scalability and function flexibility, enabled by the low-loss and low phase error designs, making a substantial advancement in high-speed and large-scale photonic computing technologies.

A design rule for a Mach-Zehnder interferometer (MZI) sensor is presented, allowing tunable sensitivity by appropriately choosing the MZI arm lengths according to the formula given in this paper. The present MZI sensor designed by this method can achieve an ultra-high sensitivity, which is much higher than any other traditional MZI sensors. An example is given with silicon-on-insulator (SOI) nanowires and the device sensitivity is as high as 10⁶ nm/refractive-index -unit (or even higher), by choosing the MZI arms appropriately. This makes it possible for one to realize a low-cost optical sensing system with a detection limit as high as 10⁻⁶ refractive-index-unit, even when a cheap optical spectrum analyzer with low-resolution (e.g., 1 nm) is used for the wavelength-shift measurement.

Chip‐scale integrated optical signal processors promise to support a multitude of signal processing functions with bandwidths beyond the limit of microelectronics. Previous research has made great contributions in terms of demonstrating processing functions and device building blocks. Currently, there is a significant interest in providing functional reconfigurability, to match a key advantage of programmable microelectronic processors. To advance this concept, in this work, we experimentally demonstrate a photonic integrated circuit as an optical signal processor with an unprecedented combination of two key features: reconfigurability and terahertz bandwidth. These features enable a variety of processing functions on picosecond optical pulses using a single device. In the experiment, we successfully verified clock rate multiplication, arbitrary waveform generation, discretely and continuously tunable delays, multi‐path combining and bit‐pattern recognition for 1.2‐ps‐duration optical pulses at 1550 nm. These results and selected head‐to‐head comparisons with commercially available devices show our device to be a flexible integrated platform for ultrahigh‐bandwidth optical signal processing and point toward a wide range of applications for telecommunications and beyond.