Highly Sensitive Strain Sensor Based on Microfiber Coupler for Wearable Photonics Healthcare

Abstract

Flexible strain sensors are essential components of wearable smart devices that perceive and respond to strain stimulations. However, the sensitivity and response time of most sensors require further improvement to detect subtle strains related to human bodies. Herein, an ultrasensitive flexible optical sensor with fast response time has been built based on a microfiber coupler encapsulated in polydimethylsiloxane. Benefiting from dramatic change of coupling ratio of the microfiber coupler under weak strain, this flexible strain sensor exhibits ultrahigh strain sensitivity (gauge factor, GF = 900), low detection limit (0.001%), ultrafast response time (<0.167 ms), wide sensing range (0.45%), and superior durability and stability (>10 000 cycles). Real‐time capturing and recognizing of respiration, broadband sound signals, and pulse waves at different sites of human body have been demonstrated based on this highly sensitive microfiber coupler sensor. Moreover, simultaneous detection of the wrist pulse and human voice has been achieved based on the frequency division multiplexing technology. This flexible photonics strain sensor could serve as the prototype of ultrasensitive flexible optical sensors with fast response time for the development of high performance and wearable healthcare devices.