Contents lists available at ScienceDirect Photonics and Nanostructures - Fundamentals and Applications journal homepage: www.elsevier.com/locate/photonics Design of MO-SPR sensor element with photonic crystal P. Otipka a, ⁎ , J. Vlček a , M. Lesňák b , J. Sobota c a Dept. of Mathematics and Descriptive Geometry, VŠB - Technical University of Ostrava, 17. listopadu 15, 708 33, Ostrava-Poruba, Czech Republic b Institute of Physics, VŠB - Technical University of Ostrava, 17. listopadu 15, 708 33, Ostrava-Poruba, Czech Republic c Institute of Scientific Instruments of the ASCR, Královopolská 147, Brno, 612 64, Czech Republic ARTICLE INFO Keywords: Magneto-plasmonics Planar nanostructures MO-SPR response ABSTRACT Magneto-plasmonic response in planar multilayer with prism coupling composed from Fe/Au bi-layer supplied by photonic crystal (Ta 2 O 5 / SiO 2 bi-layers) is studied. Modeled structure is intended as a sensor unit combining magneto-optical (MO) and surface-plasmon-resonance (SPR) effects. The sensitivity of MO-SPR system by small variations of analyte refractive index is tested to obtain optimal resolution ability. The non-reciprocal MO-SPR response is studied by means of the function ρ(φ)=(R p (+) - R p (-) )/(R p (+) + R p (-) ), where the reflectance R p depends on the incidence angle φ and external magnetic field orientation by a fixed wavelength. The detection ability is characterized by the angular shift Δφ 0 between the null-points of the function ρ that corresponds to the change Δn a of analyte refractive index. Besides the key role of metallic layers thicknesses the number and size of Ta 2 O 5 /SiO 2 bi-layers of photonic crystal are discussed. The magneto-plasmonic response in planar multilayer with prism coupling composed from Fe and Au bilayer supplied by photonic crystal (Ta 2 O 5 / SiO 2 ) is studied. Modeled structure is intended as a sensor unit combining MO and SPR effects. 1. Introduction Even though the sensitivity of conventional SPR-based optical sen- sors is very high, is still not enough for some applications as detection of chemical and biological compounds, investigation of biomolecular in- teractions or medical diagnostics pharmacological treatment. Decrease the detection threshold of the corresponding substances via the SPR- sensor sensitivity improvement is an important problem of further SPR- sensor development. One of the ways to significantly increase the SPR- sensor sensitivity almost by an order of magnitude is the exploitation of the magnetic layers in the plasmonic structures and tracking of the magneto-optical Kerr effect (MOKE) resonance instead of the reflection one [1–3]. Especially, the transverse MOKE has stronger resonance and its magnitude is improved compared to the case of the isolated mag- netic interface since the excitation of the surface waves leads to the increase of the effects associated with gyrotropic properties of the media [4]. The quality factor of the plasmonic or magneto-plasmonic re- sonance is determined by the absorbing of the SPP waves excited at the interface. For this cause the magnetic metals (e.g., cobalt, nickel or iron) that have high optical losses are usually used in a combination with the noble ones (such as gold) in the plasmonic structure [3]. When the sensor plasmonic structures are designed to support long-range propagating SPP modes [5,6] the sensitivity is enhanced due to the increase of the optical resonance quality factor. However, usually the refractive index of the analyte is smaller than the refractive index of the dielectric layers on which plasmonic structure is deposited on. This makes the structure asymmetric and prevents the long-range propa- gating modes existence. At the same time, 1D photonic crystal (1D PC) can be designed to have almost any predetermined effective refractive index and therefore the structure 1D PC-metal-analyte can support long-range SPP modes [6]. Among other, the PC’s composed from Ta 2 O 5 and SiO 2 bilayers [7] or from TiO 2 / SiO 2 ones exhibit promising properties [8]. In this work we discuss magneto-plasmonic activity of optical multilayer structure intended as a bio-sensor unit. The coupling prism (SF10 glass) with Fe/Au bi-layer in Kretschmann configuration is con- sidered, where the reflection response is enforced by supplied photonic crystal composed from Ta 2 O 5 /SiO 2 bilayers; the analyte is considered on the basis of H 2 O(Fig. 1). We analyze the structural parameters of proposed MO-SPR chip with given material properties. Besides the PC architecture (the number and size of its layers) the thicknesses of me- tallic compounds are optimized. Presented numerical outputs were obtained using matrix form of RCWA implemented in own Matlab code with the incidence angle step Δφ = 0.001 related to the prism/PC interface. Optical functions of isotropic materials were established at the wavelength 633 nm as fol- lows: n g = 1.7231 (SF10 glass), n Au = 0.1838–3.4310i [9], tantalum pentoxide n T = 2.1358 [10], silica oxide n s = 1.5 with the data of iron film n Fe = 2.87–3.46i, Q Fe = 0.0386 + 0.0034i (Voigt parameter). The https://doi.org/10.1016/j.photonics.2018.06.007 Received 7 February 2018; Received in revised form 28 May 2018; Accepted 20 June 2018 ⁎ Corresponding author. Photonics and Nanostructures - Fundamentals and Applications 31 (2018) 77–80 Available online 21 June 2018 1569-4410/ Published by Elsevier B.V. T