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Self-mixing optical coherent detection is a non-contact measurement technique which provides accurate information about the vibration frequency of any test subject. In this research, novel designs of optical homodyne and heterodyne detection techniques are explained. Homodyne and heterodyne setups are used for measuring the frequency of the modulat...
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Citations
We propose a sensor based on the integration of self-mixing interference (SMI) with microfiber, for human health monitoring. Through the power variation of the reflected light from the microfiber which is embedded into polydimethylsiloxane (PDMS), we are able to accurately monitor pulse waves continuously and in real time, and human blood pressure is successfully monitored via the pulse transmission time (PTT). We measured systolic blood pressure (SBP) and diastolic blood pressure (DBP) in volunteers with a measurement error of
$- 0.222\,\,\pm \,\,2.636$
mmHg and
$- 1.056\,\,\pm \,\,2.198$
mmHg, respectively. Long-term health monitoring was also performed for several days, and measurements met the requirements of the American Association for the Advancement of Medical Instrumentation (AAMI). The experimental results show that the sensor is capable of accurately monitoring multiparameter information of human pulse and blood pressure, and has the characteristics of high sensitivity, noninvasive, and long-term monitoring. This application of microfiber to the self-mixing sensor provides an effective solution for smart health monitoring, and has potential applications in disease prevention and healthcare.
Optical coherent detection techniques are important techniques for accurate detection of optical signals. Optical coherent detection consists of Mach-Zehnder interferometer which provides beating between two optical beams. Inside an interferometer an optical signal is divided into two parts with a beam splitter. These two beams travel in test and reference arms of optical interferometer and gets combined at another beam splitter. If the path lengths traveled by test beam and reference beam is equal inside an interferometer, then test beam and reference beam shows constant phase relationship with each other. The constant phase relationship between two beams is the most important characteristics of an interferometer as it enables extraction of modulated frequency components in the test arm. If one of the mirrors in Mach-Zehnder interferometer is mounted on piezo actuator, then it is possible to precisely control the path difference between two beams. In this research paper, a PID controlled closed loop operation of Mach-Zehnder interferometer is demonstrated.KeywordsMach-Zehnder interferometerPID controllerPiezo ActuatorFringes
