Fiber optic sensor embedded in textiles has been a new direction of researching smart wearable technology. Pulse signal which is generated by heart beat contains vast amounts of physio-pathological information about the cardiovascular system. Therefore, the research for textile-based fiber optic sensor which can detect pulse wave has far-reaching effects on early discovery and timely treatment of cardiovascular diseases. A novel wavelength demodulation method based on photonic crystal fiber (PCF) modal interference filter is proposed for the purpose of developing FBG pulse wave sensing system embedded in smart clothing. The mechanism of the PCF modal interference and the principle of wavelength demodulation based on In-line Mach-Zehnder interferometer (In-line MZI) are analyzed in theory. The fabricated PCF modal interferometer has the advantages of good repeatability and low temperature sensitivity of 3.5pm/°C from 25°C to 60°C. The designed demodulation system can achieve linear demodulation in the range of 2nm, with the wavelength resolution of 2.2pm and the wavelength sensitivity of 0.055nm<sup>-1</sup>. The actual experiments’ result indicates that the pulse wave can be well detected by this demodulation method, which is in accordance with the commercial demodulation instrument (SM130) and more sensitive than the traditional piezoelectric pulse sensor. This demodulation method provides important references for the research of smart clothing based on fiber grating sensor embedded in textiles and accelerates the developments of wearable fiber optic sensors technology.
A sensor head consisting of an all single-mode fiber (SMF) in-line Mach–Zehnder interferometer (MZI) with an embedded fiber Bragg grating (FBG) is proposed and experimentally demonstrated for simultaneous measurement of curvature and temperature. It is fabricated by cascading two bulge-taper fusion structures in a section of SMF including an FBG. The MZI is sensitive to fiber bending and ambient temperature with a sensitivity of −16.59 nm/m−1 in the range of 1.05 to 4.05 m−1 and 58 pm/°C in the range of 30°C to 100°C, respectively. However, the FBG is only sensitive to the latter with a sensitivity of 13 pm/°C. Simultaneous measurement of curvature and temperature is obtained and the cross-sensitivity issue can be solved. The experimental results show that the average relative error of the curvature is 0.38%, which is about 18 times better than that without temperature compensating. The average error of temperature is only 0.21°C.
The fluorescence spectra, delayed luminescence (DL) spectra and DL decay dynamics of human serum were studied
by fluorescence and time resolved emission spectrum technology under different excitation conditions in this paper. The
results we obtained are shown as follows: (1) the DL spectrum is similar to the time resolved fluorescence spectrum
within 50ns after Ps laser pulse excitation. (2) The intensity and decay time of DL from the serum samples are dependent
on excitation power and irradiation time. Under fixed excitation power, the longer irradiation time is, the higher the DL
intensity; after the excitation energy reaches about 200mJ, the DL intensity is nearly unchanged. The change of DL decay
time follows the similar regulation to that of DL intensity. (3) As the excitation energy increases, the spectral distribution
of the relative intensities exhibits an observable change. The higher the excitation energy is, the stronger the relative
intensity at short wavelength region. The results show that the delayed luminescence of human serum is mainly
originated from its delayed fluorescence, phosphorescence, and induced bio-photon emission. These results may be also
useful for the development of serum diagnosis technology.
The photo-induced delayed luminescence (DL) of human serum and its dependence on exciting conditions, including exciting wavelength, exciting energy and exciting power, were studied in this paper. It was found that the DL of serum follows the law of hyperbolic decay rather than exponential decay, exhibiting coherent character. The exciting conditions had affinities with the activation as well as the active reactions of biological molecules, which were sensitive and active under UV-light excitation. Exciting energy mainly decides the activation. More sufficient activation leads to more drastic active reactions and stronger re-emission ability of bio-molecules after illumination, resulting in the more intensive photon emission and lower DL decay speed rate. On the other hand, exciting power also plays an important role in impacting the active reactions. Exciting light with higher power makes the active reactions more drastic, causing the higher photon counts. However, there are few correlations between exciting power and the re-emission ability of bio-molecules. These results may be useful for investigation and application of human serum.