Design of an Efficient Fabry-Perot Biosensor Using High-Contrast Slanted Grating Couplers on a Dual-Core Single-Mode Optical Fiber Tip

Plasmonic Biosensor on the End-Facet of a Dual-Core Single-Mode Optical Fiber

“…As observed, changing n a brings about not only obvious shifts in the transmittance but also slight changes in spectral shape and in the fringes comprising the spectra. These tiny fringes in the optical response of the structure originate from the weak Fabry-Pérot cavity formed between the mirrored PSGCs, as verified by calculating the distance between adjacent fringes (e.g., ∆λ in Figure 7a), which is of the order of the free spectral range (FSR) for such a resonator [13]. Choosing one of the fringes, e.g., the first clear fringe in each spectrum, marked by the solid red dot in Figure 7a, and tracking its wavelength shift vs. n a yields the plot of Figure 7b, from which a bulk sensitivity and FoM of 965 nm/RIU and 10 RIU −1 , respectively, are deduced.…”

“…we propose a straightforward but efficient design approach derived from an intuitive vector geometry accompanied by 1D modal calculations to attain initial design parameters, following a similar method adopted to design Si3N4 slanted gratings [13]. It will be shown that the initial design parameters are in good agreement with the optimized parameters obtained through numerical modeling.…”

“…Contrary to low-contrast gratings for which the grating design can be determined from the phase-matching condition, the design of high-contrast grating couplers is more complex, as the coupling efficiency and (undesired) scattering into radiative modes depend on parameters such as slant angle, fill factor, and pitch. To overcome this challenge, we propose a straightforward but efficient design approach derived from an intuitive vector geometry accompanied by 1D modal calculations to attain initial design parameters, following a similar method adopted to design Si 3 N 4 slanted gratings [13]. It will be shown that the initial design parameters are in good agreement with the optimized parameters obtained through numerical modeling.…”

“…A dual-core single-mode optical fiber (DCSMF), with a biosensor structure formed on its end-facet that also couples the cores, could overcome this challenge [13]. Employing a DCSMF facilitates optical interrogation as one core can be used to launch the incident light to the fiber tip, and the other core can be used to receive the light emerging from the biosensor.…”

“…Such a system operates in transmission, which is advantageous, as it simplifies the interrogation setup, especially for polarization-resolved spectral interrogation. The idea was explored in a previous work, where the biosensor consisted of a Si 3 N 4 grating-coupled Fabry-Pérot waveguide resonator, in which spectral interrogation in transmission was verified, but the design produced a bulk sensitivity of only 50-100 nm/RIU [13].…”