Photonic integrated interrogators for wearable fiber-optic sensing

Wearable technology, thanks to its substantial economic and social impact, has garnered widespread public attention. For a long time, the commercialization of wearable fiber-optic sensing has been limited by the cost and size of bulky optics-based optical interrogators, which serve to measure and analyze optical signals. This limitation can be addressed by introducing photonic integrated circuit (PIC) technology to develop optical interrogators, which can be referred to as photonic integrated interrogators. A gap exists between these two domains: fiber-optic sensing researchers lack familiarity with PICs, and conversely, PIC researchers may not be well-versed in fiber-optic sensing. The objective of this review is to bridge and minimize this knowledge gap. A brief summary of different sensing principles is provided. The recent progress and advantages of photonic integrated interrogators and their applications in wearable fiber-optic sensing systems are summarized herein. An overview of different strategies for photonic integrated interrogators including polarimetric, spectroscopic, and hybrid-measurement ones, is presented. We also introduce how light sources and photodetectors can be integrated with photonic integrated interrogators to achieve more compact, lower-cost devices. Moreover, the challenges of photonic integrated interrogators used in wearable fiber-optic sensing systems are briefly discussed and highlighted.