**6. Conclusions**

The paper reports on a comparative study of four pulse wave fiber-optic sensors, based on Fabry–Perot interferometer, fiber Bragg grating, optical coherence tomography and singlemode-multimode-singlemode intermodal interferometer. In order to compare the sensors performance, several metrics, evaluating the quality of the obtained PW signals were proposed. According to the scores produced by the proposed metrics, the OCT approach turned out to be the most advantageous. Additional experiment, involving PW measurement of a moving subject also showed that the OCT approach is the most robust against the motion artifacts among the compared ones. However, as follows from the analysis presented in discussion, FPI sensors, having slightly lower scores, are better suited for implementation of portable sensing systems. In turn, the OCT approach of pulse wave monitoring can be successfully implemented for more unique tasks, such as scientific research of pulse wave propagation and cardiovascular system function and be used in specialized clinics.

It should be further noted that configurations of FPI [16,19] and FBG [18,89,90] pulse wave sensors, different from the ones used in our study, have been reported, which might demonstrate different sensing characteristics. Performance of the *ϕ*-OCT approach can be further increased by incorporating micro- and nano-optics for higher light confinement and reduction of light loss inside biological tissues [38,91,92].

**Author Contributions:** Conceptualization, A.M. and N.U.; methodology, A.M. and N.U.; software, D.K. and A.M.; validation, A.M.; formal analysis, A.M.; investigation, A.M. and D.K.; resources, L.L.; data curation, D.K., A.M. and N.U.; writing—original draft preparation, A.M. and N.U.; writing— review and editing, A.M. and N.U.; visualization, A.M. and N.U.; supervision, L.L. and N.U.; project administration, L.L. and N.U.; funding acquisition, N.U. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was supported by the Russian Science Foundation under Grant 19-72-00051.

**Institutional Review Board Statement:** The study was conducted according to the guidelines of the Declaration of Helsinki, and approved by the Institutional Review Board of Higher School of Applied Physics and Space Technologies (protocol #1 of 12 Februbry 2021).

**Informed Consent Statement:** Informed consent was obtained from all subjects involved in the study. Written informed consent has been obtained from the Subjects to publish this paper.

**Data Availability Statement:** Obtained experimental data are available from the corresponding author upon reasonable request.

**Conflicts of Interest:** The authors declare no conflict of interest.
