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phosphosilicate optical fibres through

Electronics Letters. 1995;31(7):576-577

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Demonstration of pulse controlled alloptical switch/modulator. Optics Letters. 2014;39(6):1469-1472

[84] Sivan Y, Rozenberg S, Halstuch A,

[85] Khurgin JB, Sun G, Chen WT, Tsai

nonlinearity. Scientific Reports. 2015;5:

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Coupled-mode theory for

2016;93:144303

41

WY, Tsai DP. Ultrafast thermal

interactions between short pulses of different spatio-temporal extents.

gratings in rare-earth-doped

periodic population inversion.

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Ishaaya AA. Nonlinear wave

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2189-2191

3470-3477

17899

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[75] Sivan Y, Ctistis G, Yüce E, Mosk AP. Femtosecond-scale switching based on excited free-carriers. Optics Express. 2015;23(12):16416-16428

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[77] Johnson JA, Maznev AA, Bulsara MT, Fitzgerald EA, Harman TC, Calawa V, et al. Phase-controlled, heterodyne laser-induced transient grating measurements of thermal transport properties in opaque material. Journal of Applied Physics. 2012;111(2):023503

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produced by the flash condensation technique. Optics Letters. 1995;20(21): 2189-2191

of Selected Topics in Quantum Electronics. 2009;15(1):114-119

and phonon dynamics in

[63] Othonos A. Probing ultrafast carrier

Fiber Optic Sensing - Principle, Measurement and Applications

and opportunities. Journal of Lightwave

[72] van Driel HM. Kinetics of highdensity plasmas generated in Si by 1.06 and 0.53μ m picosecond laser pulses. Physical Review B. 1987;35:8166

[73] Sabbah AJ, Riffe DM. Femtosecond pump-probe reflectivity study of silicon carrier dynamics. Physical Review B.

[74] Eichler HJ, Massmann F. Diffraction efficiency and decay times of freecarrier gratings in silicon. Journal of Applied Physics. 1982;53(4):3237-3242

[75] Sivan Y, Ctistis G, Yüce E, Mosk AP. Femtosecond-scale switching based on excited free-carriers. Optics Express.

[76] Käding OW, Skurk H, Maznev AA, Matthias E. Transient thermal gratings at surfaces for thermal characterization of bulk materials and thin films. Applied

2015;23(12):16416-16428

Physics A: Materials Science & Processing. 1995;61(3):253-261

[77] Johnson JA, Maznev AA, Bulsara MT, Fitzgerald EA, Harman TC, Calawa V, et al. Phase-controlled, heterodyne laser-induced transient grating measurements of thermal transport properties in opaque material. Journal of Applied Physics. 2012;111(2):023503

[78] Graebner JE. Measurement of thermal diffusivity by optical excitation and infrared detection of a transient thermal grating. Review of Scientific Instruments. 1995;66(7):3903-3906

[79] Stepanov S. Dynamic population gratings in rare-earth-doped optical fibres. Journal of Physics D: Applied Physics. 2008;41(22):224002

[80] Canning J, Sceats MG, Inglis HG, Hill P. Transient and permanent

gratings in phosphosilicate optical fibers

Technology. 2005;23:4222

2002;35:165217

semiconductors. Journal of Applied Physics. 1998;83(4):1789-1830

[64] Reif J, Schmid RP, Schneider T. Femtosecond third-harmonic generation: Self-phase matching

through a transient Kerr grating and the way to ultrafast computing. Applied Physics B. 2002;74(7–8):745-748

[65] Deeg FW, Stankus JJ, Greenfield SR, Newell VJ, Fayer MD. Anisotropic reorientational relaxation of biphenyl: Transient grating optical Kerr effect measurements. The Journal of Chemical

Physics. 1989;90(12):6893-6902

212(1):57-64

2007. p. JWA53

[66] Zoweil H, Lit JW. Bragg grating with periodic non-linearity as optical switch. Optics Communications. 2002;

[67] Laniel JM, Bélanger N, Villeneuve A. Nonlinear switching in a Bragg grating with periodic χ (3). In: Conference on Lasers and Electro-Optics. Optical Society of America;

[68] Furtado Filho AFG, de Sousa JRR, de Morais Neto AF, Menezes JWM, Sombra ASB. Periodic modulation of nonlinearity in a fiber Bragg grating: A numerical investigation. Journal of Electromagnetic Analysis and Applications. 2012;4(02):53-59

[69] Ashcroft NW, Mermin N. Solide State Physics. Stamford: Thomson Learning; 1976. p. 13, 26, 80, 119 and 127

[71] Lipson M. Guiding, modulating, and emitting light on silicon—Challenges

[70] Euser TG, Vos WL. Spatial homogeneity of optically switched semiconductor photonic crystals and of bulk semiconductors. Journal of Applied

Physics. 2005;97:043102

40

[81] Canning J, Sceats MG. Transient gratings in rare-earth-doped phosphosilicate optical fibres through periodic population inversion. Electronics Letters. 1995;31(7):576-577

[82] Akin O, Dinleyici MS. An all-optical switching based on resonance breaking with a transient grating. Journal of Lightwave Technology. 2010;28(23): 3470-3477

[83] Akin O, Dinleyici MS. Demonstration of pulse controlled alloptical switch/modulator. Optics Letters. 2014;39(6):1469-1472

[84] Sivan Y, Rozenberg S, Halstuch A, Ishaaya AA. Nonlinear wave interactions between short pulses of different spatio-temporal extents. Scientific Reports. 2016;6

[85] Khurgin JB, Sun G, Chen WT, Tsai WY, Tsai DP. Ultrafast thermal nonlinearity. Scientific Reports. 2015;5: 17899

[86] Yu Z, Margulis W, Tarasenko O, Knape H, Fonjallaz PY. Nanosecond switching of fiber Bragg gratings. Optics Express. 2007;15(22):14948-14953

[87] Sivan Y, Pendry JB. Broadband time-reversal of optical pulses using a switchable photonic-crystal mirror. Optics Express. 2011;19:14502-14507

[88] Sivan Y, Rozenberg S, Halstuch A. Coupled-mode theory for electromagnetic pulse propagation in dispersive media undergoing a spatiotemporal perturbation: Exact derivation, numerical validation, and peculiar wave mixing. Physics Review B. 2016;93:144303

[89] Karenowska A, Gregg J, Tiberkevich V, Slavin A, Chumak A, Serga A, et al.

Oscillatory energy exchange between waves coupled by a dynamic artificial crystal. Physical Review Letters. 2012; 108:015505

[90] Sivan Y, Pendry JB. Time reversal in dynamically tuned zero-gap periodic systems. Physical Review Letters. 2011; 106:193902-1-193902-4

[91] Sivan Y, Pendry JB. Theory of wavefront reversal of short pulses in dynamically tuned zero-gap periodic systems. Physical Review A. 2011;84: 033822-1-033822-13

[92] Chumak A, Tiberkevich V, Karenowska A, Serga A, Gregg J, Slavin A, et al. All-linear time-reversal by a dynamic artificial crystal. Nature Communications. 2010;1:141

[93] Wu AQ, Chowdhury IH, Xu X. Femtosecond laser absorption in fused silica: Numerical and experimental investigation. Physical Review B. 2005; 72(8):085128

[94] Shamir A, Ishaaya AA. Effect of femtosecond photo-treatment on inscription of fiber Bragg gratings. Optics Letters. 2016;41(4):765-768

[95] Shamir A, Halstuch A, Sivan Y, Ishaaya AA. Ns-duration transient Bragg gratings in silica fibers. Optics Letters. 2017;42(22):4748-4751

[96] Combis P, Cormont P, Gallais L, Hebert D, Robin L, Rullier JL. Evaluation of the fused silica thermal conductivity by comparing infrared thermometry measurements with twodimensional simulations. Applied Physics Letters. 2012;101(21):211908

**43**

**Chapter 4**

**Abstract**

**1. Introduction**

Vital Sign Measurement Using

FBG Sensor for New Wearable

In this study, we measured the vital signs of a living body using an FBG sensor by installing it at a pulsation point such as the radial artery. We developed a biological model to demonstrate the capability of an FBG sensor. The FBG sensor signal was found to correspond to the changes in diameter of the artery caused by the pressure of the blood flow. Vital signs such as pulse rate, respiratory rate, stress load, and blood pressure were calculated from the FBG sensor signal. While pulse rate and respiration rate were calculated by peak detection of FBG sensor signal. Blood pressure was calculated from the waveform shape of one beat of the FBG sensor signal by PLS regression analysis. All vital signs were calculated with high accuracy. The study helps establish that these vital signs can be calculated continuously and simultaneously. Considering that an FBG sensor can detect a strain with high sensitivity using a small optical fiber, it is expected to be adopted widely as a novel wearable vital sign sensor.

**Keywords:** FBG sensor, pulse rate, respiration rate, blood pressure, wearable sensor

In Japan, there is surge in demand for medical care of the elderly as their population continues to increase [1]. This is causing a serious concern especially considering the prevailing shortage of medical staff. Meanwhile, since the Tokyo Olympic Games will be held in 2020, there is a high need for self-healthcare management among healthy people. A simple home health system to monitor the vital signs in elderly people is becoming an absolute necessity, as there is increasing demand for their self-health management on a daily basis. Vital signs are fundamental indicators of human health. These indicators include heart rate, respiration rate, blood

In order to meet such needs, wearable sensors are being developed by manufacturers to monitor vital signs [2–4]. These sensors are glasses or wristwatch type, they have a characteristic that can measure vital signs continuously. Most of these sensors are of photoelectric pulse wave type measuring the changes in light absorption caused by hemoglobin in blood vessels. These sensors are compact, portable, and easy to install on a human body. However, there are a few issues with these sensors: moisture noise caused by perspiration, skin damage due to the probe pressure [5], and dependence of signal strength on probe mounting position [6]. In addition, people have psychologically stressful for people who do not use wrist watches or

Sensor Development

*Shouhei Koyama and Hiroaki Ishizawa*

pressure, body temperature, level of consciousness.
