Scientists have made a breakthrough in fiber-optic sensing technology, offering a new method to detect strain and displacement with unprecedented precision. This innovative approach, detailed in a recent study published in IEEE Sensors Journal, utilizes a polymer optical fiber-based single-mode-multimode-single-mode (SMS) structure to read interference patterns directly in the electrical spectrum of a photodetected signal. This method not only streamlines the sensing process but also enhances its accuracy and speed, potentially revolutionizing various industries that rely on optical fiber sensors.
The key to this advancement lies in the SMS structure, which leverages multimode propagation to create relative modal delays. These delays manifest as measurable dips in the electrical frequency domain, providing a direct and efficient way to interpret sensor signals without the need for conventional optical-spectrum interrogation. Associate Professor Yosuke Mizuno of YOKOHAMA National University emphasizes the significance of this development, stating, 'The key point of this work is that the interference pattern appears directly in the electrical domain, giving us a new way to read out fiber-optic sensor signals.'
The research team, which includes Ryo Takano from YOKOHAMA National University and Professor Marcelo A. Soto from the Universidad Técnica Federico Santa María, demonstrated the method's effectiveness through a series of experiments. By transmitting light through a polymer optical fiber-based SMS structure and analyzing the resulting electrical spectrum, they observed distinct interference dips when using a light source centered around 1070 nm. These dips disappeared when a 1550-nm laser was employed, confirming the role of multimode propagation and modal beating during photodetection.
The team further showcased the method's versatility by applying axial strain to a 57-cm polymer optical fiber segment, resulting in clear and reversible shifts in the interference dips. They also extended the principle to displacement sensing by introducing a variable air gap between silica fibers, achieving a sensitivity of approximately 3.7 MHz/µm for larger air gaps. This sensitivity is a significant improvement over conventional systems, opening up new possibilities for fast and compact measurements.
Looking ahead, the research team aims to optimize the fiber structure and light source conditions and evaluate the temperature response. They believe that this electrical-domain readout could make multimode-interference fiber sensors more practical and accessible, potentially transforming their role in various industries. As Professor Mizuno notes, 'We believe that this electrical-domain readout could make multimode-interference fiber sensors more practical for fast and compact measurements.'
This breakthrough in fiber-optic sensing technology not only enhances the precision and speed of strain and displacement detection but also paves the way for more efficient and cost-effective sensing solutions. As the research team continues to refine their method, the potential applications in fields such as structural health monitoring, civil engineering, and robotics become increasingly promising.
