Integrated Photonic Nanofences: Combining Subwavelength Waveguides with an Enhanced Evanescent Field for Sensing Applications

Abstract

Photonic nanofences consisting of high aspect ratio polymeric optical subwavelength waveguides have been developed for their application into photonic sensing devices. They are up to millimeter long arrays of 250 nm wide and 6 μm high ridges produced by an advanced lithography process on a silicon substrate enabling their straightforward integration into complex photonic circuits. Both simulations and experimental results show that the overlap of the evanescent fields propagating from each photonic nanofence allows for the formation of an effective waveguide that confines the overall evanescent field within its limits. This permits a high interaction with the surrounding medium which can be larger than 90% of the total guided light intensity (approximately 20000 times larger than the evanescent field of a standard waveguide with equivalent dimensions). In this work, we not only investigate the photonic properties of these structures but also demonstrate their successful integration into a photonic sensor. An absorbance-based sensor for the determination of lead in water samples is therefore achieved by the combination of the photonic nanofences with an ion-sensitive optical membrane. The experimental results for lead detection in water show a sensitivity of 0.102 AU/decade, and a linear range between 10(-6) M and 10(-2) M Pb(II). A detection limit as low as 7.3 nM has been calculated according to IUPAC for a signal-to-noise ratio of 3.

Integrating cell on chip—Novel waveguide platform employing ultra-long optical paths

“…information. [18][19][20][21] Several approaches have been considered to increase the optical path in such a waveguide configuration. Densmore et al proposed a refractive index sensor employing a folded strip waveguide which confines light in a planar structure achieving an optical path of 2 mm.…”

High-aspect-ratio nanoimprint process chains

“…An array of 5 PNFs distributed in 10 μm with a refractive index (n) of 1.55, a width of 200 nm and different heights (d) was considered for this concrete example. The PNFs were simulated on top of an antiresonant reflective substrate composed of silicon, silicon oxide (n = 1.456, d = 240 nm) and silicon nitride (n = 2.001, d = 100 nm) to enhance the coupling of light into the PNF array 38 .…”

“…An example of nanostructures requiring an HAR for a strong optimization of their performance is the recent report demonstrating photonic nanofences (PNFs) 38 . PNFs consist of long nanoridges with lateral dimensions smaller than half of the working wavelength (that is, o 300 nm) and a height in the range of a few microns (Figure 1a).…”

“…While there is a range of different solutions, for example, for guiding and sensing applications, an optimal PNF waveguide would consist of 5 to 9 ridges, that is, with periods of 5 to 0.5 μm (Ref. 38), propagation distances from a few hundred μm to a few millimeters and an AR of at least 10, but concrete applications will lead to concrete geometries and distributions. In this work, three different approaches, that is, thermal nanoimprint lithography (T-NIL), ultraviolet light assisted nanoimprint lithography (UV-NIL), and micromoulding in capillaries (MIMIC), using masters fabricated with two different methods, that is, silicon etching and 2-photon polymerization (2PP) DWL, are considered, tested and compared in order to produce HAR sub-micrometric structures.…”

Polymer integrated waveguide optical biosensor by using spectral splitting effect

“…Integrated waveguide optical biosensors have broad applications in environmental monitoring, food safety, and healthcare with the advantages of the low cost, compact structure, real-time detection, and label-free sensing [1][2][3][4]. Among various structures for integrated waveguide optical biosensors [5][6][7][8], Mach-Zehnder interferometers (MZIs) have been attracting much attention due to their simple structure, easiness for fabrication.…”