Investigation of refractive indices of liquids by interferometer with nitrogen-doped diamond film as a mirror

Sandra Pawłowska, Monika Kosowska
Department of Metrology and Optoelectronics, Faculty of Electronics, Telecommunications and
Informatics, Gdańsk University of Technology, 11/12 Narutowicza Street, 80-233 Gdańsk, Poland

Fiber-optic sensors are light and compact devices, so they can be easily installed in
hard to reach places. They assure resistance to electromagnetic interferences, because the
measuring part of the system does not use electricity. They are sensitive to changes in the
measured value of the physical quantities and provide precise and reliable results [1–3]
. Due to
those advantages, we constructed a Fabry-Perot fiber-optic interferometric sensor for
measurements of refractive indices of liquids. In order to extend the possibilities of its use –
we applied nitrogen-doped diamond films (with varying nitrogen content) instead of silver as
an external mirror. We report for the first time the impact of nitrogen-doping level on the
performance of the refractive index sensor.
Diamond structures are a very good alternative to using silver mirrors in optical
sensors as they have better chemical and mechanical properties. They are chemically stable
and resistant to mechanical and chemical damage [4]. They can be used in biological
applications because of the well-known biocompatibility [5]. In addition, they are currently
used in many scientific and industrial applications.
The nitrogen-doped diamond films were deposited on silica substrates by the use of
a Microwave Plasma Assisted Chemical Vapor Deposition System, with varying nitrogen
content in the working gas mixture. We measured refractive indices of liquids in the range
from 1.3 to 1.45 for each nitrogen-doped diamond sample and for silver as a reference. The
measurements were made using a broadband light source with a central wavelength of
1550 nm. The optical signal was transmitted through the single-mode optical fibers and
registered by the optical spectrum analyzer.

[1] K. Karpienko, M. S. Wróbel, M. Jędrzejewska-Szczerska, OE 2014, 53, 077103.
[2] M. Jedrzejewska-Szczerska, M. Gnyba, B. B. Kosmowski, Acta Phys. Pol. A 2011, 120.
[3] M. Jędrzejewska-Szczerska, Sensors 2014, 14.
[4] D. Majchrowicz, M. Kosowska, P. Struk, M. Jędrzejewska‐Szczerska, Physica Status
Solidi (a) 2017, 214.
[5] M. Jędrzejewska-Szczerska, D. Majchrowicz, M. Hirsch, P. Struk, R. Bogdanowicz, M.
Bechelany, V. V. Tuchin, in Nanotechnology and Biosensors (Eds.: D.P. Nikolelis, G.-P.
Nikoleli), Elsevier, 2018.