Microstructured and Photonic Bandgap Fibers for Applications in the Resonant Bio- and Chemical Sensors
Small solid core PBG Bragg fiber-based SPR sensor. (a) Schematic of a sensor. Low refractive index core is surrounded by the concentric photonic crystal reflector. Reflector exterior is goldplated for plasmon excitation. Gold layer is bordered by aqueous analyte. Energy flux distribution across the fiber cross-section is shown as a solid curve for the fundamental core mode, and as a dashed curve for the plasmonic mode. (b) Band diagram of the sensor modes. Dispersion relation of the fundamental core mode (thick solid curve), and plasmonic mode (dashed curve). TE, TM bandgap of a periodic planar reflector is shown as a clear region, while gray regions correspond to the continuum of bulk reflector states. In a small core Bragg fiber, effective refractive index of the fundamental core mode can be much smaller than refractive index of the core material. (c) Upper plot: solid curve shows loss of the fundamental core mode near the phase matching point with plasmon. Modal loss reaches its maximum at the phase matching wavelength. Dashed line corresponds to the shifted modal loss curve when the analyte refractive index is varied. Lower plot: sensor amplitude sensitivity as a function of wavelength.
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