Low-cost vertical taper for highly efficient light in-coupling in bimodal nanointerferometric waveguide biosensors

Abstract

There is still the need for a compact and cost-effective solution for efficient light in-coupling in integrated waveguides employed in photonic biosensors, especially when these waveguides are of submicron dimensions and operate at visible wavelengths. The employment of a vertically stacked taper with a larger input area is proposed to meet this need. The design of the taper is divided into two stages: in the first stage, light is guided downwards by two vertically stacked tapers; in the second stage, an inverted taper directly confines the light inside the waveguide. The design parameters are optimized using commercial software, obtaining a total theoretical light coupling efficiency of 72.25%. The taper is manufactured using SU-8 polymer as the main material, employing standard photolithography techniques at wafer level. After characterization, the results show the practicality of the taper when coupling light from macrometric sources to nanometric waveguides, obtaining an experimental coupling efficiency of 55%. With this vertical taper, a compact, easy-to-couple and cost-effective solution is achieved for waveguide-based biosensors operating at visible wavelengths, opening the way for a truly portable point-of-care biosensor for low-cost and label-free diagnostics.

High-Order Multimode Waveguide Interferometer for Optical Biosensing Applications

“…Knowing how the two propagating modes will behave with this change in the cladding, and measuring how much the phase difference between the two modes has been altered, it is, therefore, possible to evaluate the devariation in the refractive index of the cladding with high precision. If the sensing waveguide is subject to biofuncionalization, this interferometer may be employed as a biosensing device [16][17][18]27,28,30]. The motivations for using the second-order propagating mode for the TriMW in [28], in contrast with the first-order mode for the BiMW in [27,30], were: less confinement of the high-order mode and an increase in the region of interaction between the evanescent tail of this mode and the sensing area.…”

“…Our last step in this analysis was to compare our results with the performances of BiMW and TriMW presented in the literature at this point, as shown in Figure 5. The designs compared in this Figure are the Si 3 N 4 BiMW rib type from [16,27], the Si 3 N 4 and ma-P 1205 BiMW/TriMW of [28], and the Si 3 N 4 4th order MMW of this work. In terms of intrinsic bulk sensitivity, the Si 3 N 4 4th order MMW is far superior to all of its peers, being 23.4% more sensitive than the Si 3 N 4 TriMW channel type @n clad = 1.33, 58.5% more sensitive than the ma-P 1205 TriMW channel type @n clad = 1.40 and 34.6% more sensitive than the ma-P 1205 TriMW channel type @n clad = 1.46.…”

“…Among these various sensor classes, which present desirable characteristics for supporting the early detection and diagnosis of diseases, the optical sensors correspond to a potential technology that can be used to achieve the goal. They can be designed to be compact, rapid/real-time, very sensitive, and label-free detection devices [4,[15][16][17][18]. Optical transducers also present several different types of construction and operating principles, among which we may cite: Surface Plasmon Resonance (SPR) [19][20][21], Localized Surface Plasmon Resonance (LSPR) [22], Raman Spectroscopy [23], Resonators [24], and Interferometers [14,25].…”

“…In 2011, Zinoviev et al proposed the bimodal waveguide interferometer (BiMW) using the TE 00 -TE 01 modes as a biosensing device [27]. Since then, several works have been presented, with the aim of developing the original device by means of utilizing a different set of modes in the interferometer (the trimodal waveguide interferometer (TriMW)) [17,28] and by improving the efficiency of light-coupling into the chip itself [16] or the desired waveguide modes [18,25,29]. These works contributed to the development of the sensor, adding incremental improvements to sensitivity and signal-to-noise ratio.…”

Label-free detection of nosocomial bacteria using a nanophotonic interferometric biosensor

“…This sensing configuration provides an excellent sensitivity with a resolution (minimum detectable change of refractive index) of only 10 -8 RIU. 29,30 The BiMW biosensor device has been successfully employed for the rapid detection of Escherichia coli and Bacillus cereus. 31 We have now modified the silanization protocol to improve even more the surface-repelling properties of the biosensor surface and its usefulness has been demonstrated with the capture and detection of two highly prevalent nosocomial bacteria in a label-free way.…”