DIFFRACTION-GRATING-BASED BLOCH SURFACE WAVE REFRACTIVE INDEX SENSORS

Transcription

1 DIFFRACTION-GRATING-BASED BLOCH SURFACE WAVE REFRACTIVE INDEX SENSORS E.A. Kadomina,, E.A. Bezus,, L.L. Doskoloich, Image Processing Systems Institute Branch of the Federal Scientific Research Centre Crystalloaphy and Photonics of Russian Academy of Sciences, Samara, Russia Samara National Research Uniersity, Samara, Russia Abstract. A planar optical sensor consisting of a diffraction ating and a onedimensional photonic crystal based on Bloch surface wae excitation effect is proposed. The obtained results can find application in the design of noel onchip refractie index sensors. Keywords: photonic crystal, Bloch surface wae, diffraction ating, optical sensor, Maxwell s equations, rigorous coupled-wae analysis. Citation: Kadomina EA, Bezus EA, Doskoloich LL. Diffraction-ating-based Bloch surface wae refractie index sensors. CEUR Workshop Proceedings, 06; 638: DOI: 0.887/ Introduction Nowadays, resonant optical sensors based on the excitation of surface electromagnetic waes (surface plasmon polaritons (SPP) or Bloch surface waes (BSW)) are widely used for refractie index measurement and for detection of arious micro-objects. SPPbased sensors [ 3] hae a significant drawback, namely, high absorption losses in metals leading to broadening of the SPP resonance, which limits the sensor performance. BSW-based sensors are free from this disadantage because BSW can be supported by all-dielectric structures. Moreoer, BSW can be either TM- or TEpolarized, which adds one more deee of freedom to the sensor design. Recently proposed BSW-based sensors [4 9] possess high sensitiity (the accuracy of the 6 measurement of the refractie index exceeds 0 ). In the existing works, BSW are excited in the Kretschmann configuration, which leads to a relatiely large size of the sensor. A promising approach to miniaturizing the sensors consists in the utilization of ating-based BSW excitation configuration and is studied in the present work. Geometry and parameters of the optical sensor Fig. shows the geometry of the inestigated sensor. The structure comprises a diffraction ating with one-dimensional periodicity and a one-dimensional photonic Information Technology and Nanotechnology (ITNT-06) 49

2 crystal (PC). The PC consists of N periods (N pairs of plane-parallel layers with alternating thicknesses and dielectric permittiities). Let us consider an example with the following parameters: PC layer thicknesses h 96 nm and h 40 nm, 3 dielectric permittiities i (corresponds to TiO at nm ) 4 and i (corresponds to SiO at nm ). At the upper surface of the PC, an additional layer with the thickness h and the dielectric permittiity is located. In the considered example, we set and h h hc, where hc 63.8 nm. The studied structure is intended for the measurement of the refractie index of the superstrate (the medium oer the PC with the unknown refractie index n ). The working refractie index range in the considered example is sup (distilled water and weak NaCl solutions). At the lower surface of the PC, a onedimensional diffraction ating with the period d, ridge height h, ridge width l and dielectric permittiity (in the present example, ) is located. The alues of the parameters d, h, l are chosen so that BSW are excited by a prescribed diffraction order (orders) of the ating. x z n sup h measured medium h N periods h h... h h l d Fig.. Geometry of the inestigated optical sensor consisting of a diffraction ating and a onedimensional photonic crystal The operating principle of the sensor consists in the measurement of the reflection coefficient at different (adually arying) alues of the incident angle or the incident waelength. In the icinity of the resonance that occurs at certain combinations of parameters (e.g., the refractie index of the superstrate and the angle of incidence), BSW is excited at the interface between the PC and the superstrate, which leads to a pronounced dip in the reflectance spectrum. To ealuate the sensor performance, we use the following conentional figure of merit [6, 8]: FoM S D W, (),q where S is the sensor sensitiity, D is the reflectance dip depth, and W is the dip FWHM (full width at half maximum). Depending on the arying parameter (angle of Information Technology and Nanotechnology (ITNT-06) 50 R 0

3 incidence q or waelength ), the sensitiity is calculated using one of the following equations: S qmin n or S min n, where q min and min are the angular and spectral locations of the minimum, respectiely. In order to compare the inestigated structure with the conentional sensor configuration (Kretschmann geometry), a sensor comprising a prism made of BK7 optical glass instead of the diffraction ating was also simulated. Let us note that the FoM alues gien below were obtained on the basis of a rigorous solution of the Maxwell s equations using the Fourier modal method [0, ]. The deriation of the BSW dispersion relation and the conditions of BSW excitation by prescribed diffraction orders of a diffraction ating were described in detail in the preious works of the present authors [, 3]. Performance of the optical sensor at arying angle of incidence The sensing performance of the considered structure was inestigated for the following superstrate media: double-distilled water and %, % and 3% NaCl solutions with the refractie indices equal to.3330,.3347,.3364, and.338, respectiely. The alues of the diffraction ating parameters d 453. nm, h nm, l 0.59d were found using an optimization procedure from the condition of BSW excitation by the first diffraction order at the incidence angle of 0º and the superstrate refractie index of.335. Fig. shows the absolute alue of the reflection coefficient s. the incidence angle for the four measured media. According to Fig., the resonance (the reflection dip) is present for all considered media. Let us note that the angular position of the reflectance dip changes continuously and monotonically with the change in the refractie index of the measured medium. The performance of the ating-based sensor and the sensor based on the Kretschmann geometry is compared in Table. It follows from Table that the FoM alues for the sensor with a diffraction ating are slightly lower than the alues for the sensor based on the Kretschmann configuration. At the same time, these alues are significantly (by almost 5 times) eater than the theoretical limit for SPPbased sensors with a gold film ( FoM 08RIU ) - []. Fig.. The absolute alue of the complex reflection coefficient s. angle of incidence for different superstrate media Information Technology and Nanotechnology (ITNT-06) 5

4 Table. Comparison of the performance of the ating-based sensor and the sensor based on the Kretschmann configuration in the case of arying angle of incidence. ddh O NaCl NaCl NaCl % % 3% Sensor based on the Kretschmann geometry S, / RIU W 0, D FoM, RIU Sensor with a diffraction ating S, / RIU W 0, D FoM, RIU Performance of the optical sensor at arying waelength Let us now study the performance of the considered sensors in the case of arying waelength. As in the preious case, the ating parameters d nm, h nm, l 0.7d were found using an optimization procedure. In the present example, two counter-propagating BSW were excited by ± st diffraction orders at normal incidence of the wae with nm at nsup.335. Similarly to Fig., it is eident from Fig. 3 that the reflection dip is present for all measured media. The comparison of the proposed sensor with the sensor in the Kretschmann configuration is gien in Table. It follows from Table that in the case of arying waelength, the ating-based sensor proides better aerage FoM alue. Fig. 3. The absolute alue of the complex reflection coefficient s. waelength for different superstrate media Information Technology and Nanotechnology (ITNT-06) 5

5 Table. Comparison of the performance of the ating-based sensor and the sensor based on the Kretschmann configuration in the case of arying waelength. ddh O NaCl NaCl NaCl % % 3% Sensor based on the Kretschmann geometry S, nm/riu W,nm D FoM 0,RIU Sensor with a diffraction ating S, nm/riu W,nm D FoM 0,RIU Conclusion In the present work, a planar configuration of an optical refractie index sensor was proposed and numerically inestigated. The sensor contains a diffraction ating with one-dimensional periodicity and a one-dimensional photonic crystal. The working principle of the sensor is based on the excitation of Bloch surface waes. As a arying parameter, the angle of incidence or the waelength can be used. The proposed sensor is compared with the conentional sensor based on the Kretschmann configuration in the case of four measured media: double-distilled water and %, % and 3% NaCl solutions. It is shown that two sensor configurations hae comparable performance, which significantly exceeds the theoretical limit for SPP-based sensors with gold films. The obtained results may find application in the design of noel on-chip refractie index sensors. Acknowledgements This work was funded by the Russian Science Foundation ant References. Piliarik M, Homola J. Surface plasmon resonance (SPR) sensors: approaching their limits? J. Opt. Express, 009; 7(9): Shankaran DR, Gobi KV, Miura N. Recent adancements in surface plasmon resonance immunosensors for detection of small molecules of biomedical, food and enironmental interest. Sens. Actuators B, 007; (): Homola J. Present and future of surface plasmon resonance biosensors. Anal. Bioanal. Chem., 003; 377: Information Technology and Nanotechnology (ITNT-06) 53

6 4. Sinibaldi A, Danz N, Descroi E, Munzert P, Schulz U, Sonntag F, Dominici L, Michelotti F. Direct comparison of the performance of Bloch surface wae and surface plasmon polariton sensors. Sensors and Actuators B, 0; 74: Li Y, Yang T, Pang Z, Pang Z, Du G, Song S, Han S. Phase-sensitie Bloch surface wae sensor based on ariable angle spectroscopic ellipsometry. Opt. Express, 04; (8): Sinibaldi A, Fieramosca A, Rizzo R, Anopchenko A, Danz N, Munzert P, Magistris C, Barolo C, Michelotti F. Combining label-free and fluorescence operation of Bloch surface wae optical sensors. Opt. Lett, 04; 39: Rizzo R, Danz N, Michelotti F, Maillart E, Anopchenko A, Wachter C. Optimization of angularly resoled Bloch surface wae biosensors. Opt. Express, 04; (9): Sinibaldi A, Danz N, Anopchenko A, Munzert P, Schmieder S, Chandrawati R, Rizzo R, Rana S, Sonntag F, Occhicone A, Napione L, Panfilis SD, Steens MM, Michelotti F. Label-Free Detection of Tumor Angiogenesis Biomarker Angiopoietin Using Bloch Surface Waes on One Dimensional Photonic Crystals. J. Lightwae Technology, 05; 33(6): Sinibaldi A, Rizzo R, Figliozzi G, Descroi E, Danz N, Munzert P, Anopchenko A, Michelotti F. A full ellipsometric approach to optical sensing with Bloch surface waes on photonic crystals. Opt. Express, 03; (0): Moharam MG, Gaylord TK, Grann EB, Pommet DA. Formulation for stable and efficient implementation of the rigorous coupled-wae analysis of binary atings. Journal of the Optical Society of America A, 995; : Moharam MG, Gaylord TK, Pommet DA, Grann EB. Stable implementation of the rigorous coupled-wae analysis for surface-relief atings: enhanced transmittance matrix approach. Journal of the Optical Society of America A, 995; : Bezus EA, Doskoloich LL, Byko DA, Soifer VA. Phase modulation of Bloch surface waes with the use of a diffrac-tion microrelief at the boundary of a one-dimensional photonic crystal. JETP Letters, 04; 99(): Kadomina EA, Bezus EA, Doskoloich LL. Spectrally selectie near-field enhancement in a photonic crystal structure with a diffraction ating. Computer Optics, 05; 39(4): DOI: 0.887/ Information Technology and Nanotechnology (ITNT-06) 54