We report the extraordinary result of rapid fibre Bragg grating inscription in doped polymer optical fibres based on polymethyl methacrylate in only 7 ms, which is two orders of magnitude faster than the inscription times previously reported. This was achieved using a new dopant material, diphenyl disulphide, which was found to enable a fast, positive refractive index change using a low ultraviolet dose. These changes were investigated and found to arise from photodissociation of the diphenyl disulphide molecule and subsequent molecular reorganization. We demonstrate that gratings inscribed in these fibres can exhibit at least a 15 times higher sensitivity than silica glass fibre, despite their quick inscription times. As a demonstration of the sensitivity, we selected a highly stringent situation, namely, the monitoring of a human heartbeat and respiratory functions. These findings could permit the inscription of fibre Bragg gratings during the fibre drawing process for mass production, allowing cost-effective, single-use, in vivo sensors among other potential uses.

Fiber Bragg grating (FBG) sensors fabricated in silica optical fiber (Silica-FBG) have been used to measure the strain of human arteries as pulse wave signals. A variety of vital signs including blood pressure can be derived from these signals. However, silica optical fiber presents a safety risk because it is easily fractured. In this research, an FBG sensor fabricated in plastic optical fiber (POF-FBG) was employed to resolve this problem. Pulse wave signals were measured by POF-FBG and silica-FBG sensors for four subjects. After signal processing, a calibration curve was constructed by partial least squares regression, then blood pressure was calculated from the calibration curve. As a result, the POF-FBG sensor could measure the pulse wave signals with an signal to noise (SN) ratio at least eight times higher than the silica-FBG sensor. Further, the measured signals were substantially similar to those of an acceleration plethysmograph (APG). Blood pressure is measured with low error, but the POF-FBG APG correlation is distributed from 0.54 to 0.72, which is not as high as desired. Based on these results, pulse wave signals should be measured under a wide range of reference blood pressures to confirm the reliability of blood pressure measurement uses POF-FBG sensors.

The convergence of fiber optic sensing with lithium-ion batteries holds great promise for observing key cell parameters in real time, which is essential to every level of decision making, from design and engineering to finance and management. Optical sensors based on fiber Bragg gratings have recently been demonstrated as an ideal tool for measuring these metrics with sufficient temporal and spatial resolution. In this work, we extend the use of fiber Bragg gratings to polymeric optical fibers which have notably greater thermal and strain coefficients than their common silica counterparts. We demonstrate that a polymer optical fiber sensor paired with a silica-based sensor, both affixed to the external package of a lithium battery, can concurrently generate high fidelity temperature and volumetric expansion data through this non-invasive approach. The quality of this data allows for further assessments as mechanical characteristics associated with dimensional changes of cells may indicate more than simple charging or discharging during cycling. While internal monitoring remains essential for future diagnostics, external monitoring using polymer fiber sensors offers a straightforward, superficial, and cost-effective sensing solution that opens a new avenue for real-time cell assessment, prognostics, and packaging considerations.

There is a need to develop sensors that can measure vital signs such as pulse rate and blood pressure easily; such vital signs can be calculated by measuring arterial strain. To this end, a new method that uses a plastic fiber Bragg grating (FBG) sensor to measure pulsation strain at human fingertips is proposed herein. Plastic fiber has a smaller Young’s modulus than that of the glass fiber. Under the same applied pressure, the plastic FBG sensor deforms more than the silica glass FBG sensor, and the Bragg wavelength shift length becomes longer, which results in higher detection sensitivity. The pulsation strain of the fingertip was measured by the proposed method based on this characteristic. The most sensitive signal detection point in the fingertip was the measurement point 10 or 15 mm from the distal interphalangeal joint in the fingertip direction. Strain signals with periodic peaks were measured from five participants. From the strain signal measured with the cuff attached to the arm, the peak disappeared when the cuff moved, and it reappeared when the cuff was opened. Therefore, the measured signal waveform changes based on the blood flow condition. The pulse rate calculated from the peak interval of the measured signal showed high correlation with the reference pulse rate, and the measurement accuracy was ±5.5 bpm. It may be possible to calculate the blood pressure and pulse rate from the measurement signal of the pulsation strain of the fingertip obtained using the plastic FBG sensor.

Real-time monitoring of both continuous and spontaneous degradation in lithium-ion batteries is challenging due to the limited number of quantitative metrics available during cycling. In this regard, improved sensing approaches enabled by sensors of high accuracy, precision, and durability are key to achieving comprehensive state estimation and meeting rigorous safety standards. In this work, external temperature and strain monitoring in commercial Li-ion button cells was carried out using tandem pairs of polymer-based and silica-based optical fiber Bragg grating sensors. The decoupled data revealed that the sensors can reliably track strain and temperature evolution for over 500 cycles, as evidenced by periodic patterns with no sign of sensor degradation or loss of fidelity. Moreover, monitoring the strain signal enabled early detection of an anomalous cell over ∼60 cycles ahead of an electrochemical signature and abrupt drop in capacity, suggesting that mechanical sensing data may offer unique benefits in some cases. Detailed mechanical monitoring via incremental strain analysis suggests a parallel path toward understanding cell degradation mechanisms, regardless of whether they are continuous or discrete in nature. The accuracy and durability of such a package-level optical fiber sensing platform offers a promising pathway for developing robust real-time battery health monitoring techniques and prognostic strategies.

Research directed toward polymer optical fiber light source generation and polymer optical fiber Bragg gratings to be part of a novel all-polymer sensor system, integrating a light source with a sensor, are reported. It is demonstrated that photo generated fluorescence can be detected 2 m away from the excitation point using a novel fiber design. Furthermore, the research works focused on polymer fiber sensors have proven that Diphenyl Sulfide + Trans-4-stilbenemethanol, which is a core composition used by numerous groups, exhibited very good photosensitivity, allowing FBG inscription.