A 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. The use of biosensors of this type makes it possible to increase the sensitivity of detecting changes in the refractive index of the medium under investigation to the level (1-2) x10-9 RIU. These sensitivity values are achieved due to the formation in the lattice of a high-quality Fano resonance with a loop width at half-height equal to 1-5 pm. However, the possibility of obtaining a significant gain in metrological characteristics on the one hand, poses the problem of characterizing such narrow-band resonances on the other, since the existing optical spectrum analyzers do not have the appropriate resolution. To solve this problem, we propose a radio-photon method of three-frequency probing of a high-band and an asymmetric Fano contour by symmetric amplitude-modulated radiation with side-amplitude components unbalanced in amplitude. In contrast to the previously used for solving similar problems of two-frequency symmetric sounding with equal amplitudes of side components and a suppressed carrier, we have uniquely determined the central frequency, the maximum amplitude and Q of the Fano circuits, as well as the possibility of greatly simplifying the technique of collecting information on their parameters. The article consists of two parts, which consistently reflect the posing of modeling problems and discussing its results with confirmation of the results of physical experiments.
Keywords: optical biosensor, refractometry, Bragg fiber grating, phase pi-shift, Bragg annular fiber grating with phase pi-shift, Fano resonance, refractive index change, sensitivity, resolving power, radiophoton measurement methods, two-frequency symmetric balance
An overview of the basic schemes, characteristics, and directions of development of microwave photonics systems is presented in this paper in terms of requirements defining the parameters of external amplitude-phase modulation of laser radiation as a key process for the formation of radio frequency signals in the optical range for systems with polarization multiplexing of polyharmonic signals.
Keywords: microwave photonics; external amplitude and phase modulation, optical generation of radio frequency signals; generation of poly-harmonic optical signals with microwave frequency components