Highly sensitive refractive index sensor based on degeneracy in specialty optical fibers: a new approach
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TECHNICAL PAPER
Highly sensitive refractive index sensor based on degeneracy in specialty optical fibers: a new approach Arpan Roy1 • Abhijit Biswas1 • R. K. Varshney2 • Somnath Ghosh3
Received: 2 August 2017 / Accepted: 3 November 2017 Ó Springer-Verlag GmbH Germany, part of Springer Nature 2017
Abstract We study the phenomenon of deliberate intermodal interactions in a specially designed index guided Microstructured Optical Fiber (MOF) by exploiting multipole expansion method (White et al. 2002). The MOF is designed in such a way that the first layer of holes is judiciously filled with a material having refractive index slightly greater than the background material or core and remaining holes are filled with air. Accordingly, we find an interesting phenomenon of mode crossing between the fundamental mode and a targeted defect mode while tuning the wavelength. Exploring this transition wavelength of the mode crossing, we propose a design of a fiber optic sensor for refractive index measurement (Silva et al. 2014) with enhanced sensitivity.
1 Introduction The discovery of photonic crystal fiber or microstructured optical fiber (Russell et al. 1996) opens up tremendous opportunity for the researchers to overcome many constraints of conventional optical fibers, owing to their unique properties such as endlessly single mode operation with large core area (Birks et al. 1997; Knight et al. 1998), low bend-loss sensitivity (Wheeler et al. 2014), polarization & Somnath Ghosh [email protected] 1
Institute of Radio Physics and Electronics, University of Calcutta, Kolkata 700009, India
2
Department of Physics, Indian Institute of Technology Delhi, New Delhi 110016, India
3
Department of Physics, Indian Institute of Technology Jodhpur, Rajasthan 342011, India
maintaining capabilities (Kaczmarek 2014), and many more. The MOF consists of a periodic arrangement of air holes with triangular or hexagonal symmetry running along their entire length, together with a missing air hole or a low refractive index material at the center acting as the core. Due to the special geometry of MOFs, they host a range of unique capabilities which would be exploited especially for enhanced sensing applications such as refractive index sensor, pressure sensor, high-temperature sensor, etc. Lately, refractive index sensors based on MOFs have been explored widely in the field of chemical and biological detection industry; for example, fuel quality measurement (Osorio et al. 2013), measurement of salinity of water (Pereira et al. 2004; Adhikari et al. 2015), etc. Moreover, this technology has also been effectively applied in detection of drugs/DNA interaction, and cell growth (Zibaii et al. 2010a, b). Many of these MOF based sensors rely on photonic bandgap (PBG) properties or generic resonant coupling phenomena in dual core MOF where the concept of dual core was achieved by selectively filling the cladding air holes (Darran et al. 2009; Luan et al. 2016; Town et al. 2010). In 2004, Kim et al. through their numerical investigations establ
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