Abstract
A grating-assisted trimodal interferometer biosensor is proposed and numerically analyzed. A long period grating coupler, for adjusting the power between the fundamental mode and the second higher order mode, is investigated, and is shown to act as a conventional directional coupler for adjusting the power between the two arms. The trimodal interferometer can achieve maximal fringe visibility when the powers of the two modes are adjusted to the same value by the grating coupler, which means that a better limit of detection can be expected. In addition, the second higher order mode typically has a larger evanescent tail than the first higher order mode in bimodal interferometers, resulting in a higher sensitivity of the trimodal interferometer. The influence of fabrication tolerances on the performance of the designed interferometer is also investigated. The power difference between the two modes shows inertia to the fill factor of the grating, but high sensitivity to the modulation depth. Finally, a 2050 2π/RIU (refractive index unit) sensitivity and 43 dB extinction ratio of the output power are achieved.
Highlights
Integrated photonic biosensors have demonstrated their great potential for clinical, chemical and biological diagnostics in the past years
We propose a modified trimodal waveguide interferometric biosensor
Just about 10% power is coupled into the E13 mode for normal trimodal interferometer, which normal trimodal interferometer, which results in bad fringe visibility and limit of detection (LOD)
Summary
Integrated photonic biosensors have demonstrated their great potential for clinical, chemical and biological diagnostics in the past years They have many advantages, such as high sensitivity, compact dimensions, mechanical stability, and immunity to electromagnetic interference [1,2]. The input power is split between the two arms in a conventional MZI, in order to give maximal fringe visibility, which influences the LOD. In order to simplify the fabrication process, a lateral bimodal waveguide interferometer was proposed and demonstrated [17]. As it has the same height everywhere, the two steps of lithography and etching are avoided, which makes the fabrication much simpler. The polymer is functionalized, which is necessary for biosensors [19]
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