Characterization of Fano resonance in optical biosensors of refractometric type based on ring fiber Bragg gratings with pi-shift. Statement of modeling tasks
Abstract
Characterization of Fano resonance in optical biosensors of refractometric type based on ring fiber Bragg gratings with pi-shift. Statement of modeling tasks
Incoming article date: 14.06.2018A variant of the solution of the problem of characterization of a resonant Fano contour in optical biosensors of refractometric type based on ring fiber Bragg gratings with pi-shift is presented. To solve this problem, the first part of the article proposes a radio-photon method of three-frequency probing of the upper-band and asymmetric Fano contours by symmetric amplitude-modulated radiation with amplitude components unbalanced in amplitude. To characterize the central wavelength, a functional analogous to the modulation coefficient of the beat envelope between the components of the probing radiation is introduced. The requirements for the selection of the frequencies of the side components at which the uniqueness of the functional is preserved and the maximum sensitivity in the measurement range determined by the bandwidth of the Fano contour at half-height are justified. The possibility of extending the range of lateral frequencies and increasing the sensitivity of measurements with the use of two-frequency sounding with a frequency reduced by half and amplitude unbalanced side components with a suppressed carrier is shown. An example is given of a comparison with the two-frequency symmetric probing, previously used by us for solving similar problems, with equal amps of side components and a suppressed carrier. Based on the results of characterizing the Fano contour with fixed probing, it is possible to unambiguously determine the central frequency, the maximum amplitude, and its Q-factor.
Keywords: optical biosensor, refractometry, Bragg fiber grating, phase pi-shift, Bragg annular fiber grating with phase pi-shift, Fano resonance, radio-photon measurement methods, amplitude-balanced three-frequency symmetric probing, two-frequency disbalanced and a