flexible devices for detecting small temperature variations, pressure changes, bending, and moistness fluctuations. [21,22] Besides, more recent reports on hydrogel [23,24] show good performance on the material response-based wearable devices. However, such sensing systems have parasitic repercussions, low performance, nonintrinsic electrical security, and electromagnetic interference, which hamper the working efficiency and restrict their wide applications as wearable gadgets. [25] But, optical segments incorporated on adaptable substrates were not explored more. These systems offer exceptional benefits like distant checking capacity, high affectability, nonelectromagnetic disturbances, real-time monitoring, and intrinsic electrical security apart from features like reconfigurability and scalability. One such optical segment is optical microfibers that possess strong evanescent fields [26][27][28][29] and are sensitive to microforce or relocation. [30,31] Furthermore, when light propagates through the optical microfiber, it excites the higher-order modes that interfere with the fundamental modes of single-mode fiber to form an interference pattern whose period can be tailored depending upon the requirement and the interference pattern shifts when subjected to external perturbations.On the other hand, polydimethylsiloxane (PDMS) is an excellent material to embed optical microfiber due to its biocompatibility and robust mechanical stability [32,33] apart from providing mechanical stability to the microfiber, which otherwise is fragile and difficult to use. PDMS-incorporated optical microfiber also exhibits low loss, high-temperature steadiness with high flexibility. Such an encapsulation also solves the demerits of conventional thermometers such as glass breaking, mercury poisoning, long-term affectability, and biocompatibility. These devices can also be directly affixed to the human body to detect small bending of different body joints like the neck, knee, elbow, and arms to name few where most conventional goniometers-based system cannot be utilized like the comfort and ease provided by flexible PDMS-assisted systems. Recent reports on knot resonator, [34] straight, and bend micronanofiber [35] are very delicate due to their miniature diameter, less sensitive, difficult to mount on skin as light enters from one side and comes out from other, nontailorable performance, and uses the change in incident light intensity for monitoring, which make its widely susceptible to light source fluctuations. Hence, it remains a challenge to develop a robust and stable system, which can be skin mountable, reconfigurable with

Utilization of flexible optical systems for real-time comprehensive physiological monitoring has been restricted by their low mechanical robustness and reconfigurability. Here we report a mechanically robust, reconfigurable, flexible, and wearable photonic interferometer system for real-time precision tracking of limb activities, facial motions, respiration, and pulse rate with significant temporal stability and repeatability. Vital health diagnostic parameters have been measured by virtue of a highly sensitive response of the system. The proposed system features curvature sensitivity of 3.1 nm/m–1 over the range of 0–1.71 m–1, temperature sensitivity of 284 pm/°C between 30 and 60 °C, and physical strain sensitivity of 540 pm/1% tensile strain. Such a robust, reconfigurable, and sensitive system would have a wide practical and sustainable utility for real-time dynamic activity monitoring in health, industrial, and various other sectors.

Wearable technologies have achieved tremendous success in medical‐grade human vital signal monitoring. Herein, a unique geometry (balloon shaped) and usage of very economical polymer embedded single mode fiber based modal interferometry that not only overcome the mechanical strength restrictions of most of the fiber wearables but also fulfil the two most important and necessary requirements of any wearable system: flexibility and stretchability are reported. Here, the human pulse rate and respiration rhythm are successfully monitored by placing the wearables at appropriate positions on different human subjects. The wearable system when compared with the other two commercial approaches: piezoelectric and Photoplethysmography shows better results in terms of pulse visibility. The wrist pulse detection by the proposed system shows 72 bpm and can distinguish different human pulse parameters such as main peak, tidal peak, dicrotic wave peak, and dicrotic notch. Further, three volunteers’ heart beat values obtained from the proposed system very well match with the commercial heart‐rate meter thereby showing the alternative and better approach for futuristic health monitoring wearable device.

Optical segments based flexible systems are the key for the development of futuristic advanced wearable devices for health monitoring, robotics, and ultraprecision positioning in industrial applications. Here, we have demonstrated an processed optical microfiber based multifunctional sensing system, which overcomes the various limitations of most widely reported electronics and material-based flexible devices. By optimizing the position of the post processed microfiber configuration in optimized Polydimethylsiloxane (PDMS) thickness and controlling the interference between the fundamental mode and higher order modes of microfiber to form and tunable interference pattern, we are able to make an efficient, simple, flexible and economical optical wearable vector bending system with a sensitivity as high as 1.01nm/degree. In addition, this skinmountable sensing sensor shows a remarkable and ultrasensitivity of -3.07 nm/oC. This ultrahigh sensitivity, mechanical robustness, with the excellent flexible and biocompatible nature also makes this sensing system a dominant candidate for wearable medical devices for elder-care facilities, physioclogical monitoring, athletic training, and rehabilitation program.

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