Ultrasensitive plasmonic sensing in air using optical fibre spectral combs

Abstract

Surface plasmon polaritons (SPP) can be excited on metal-coated optical fibres, enabling the accurate monitoring of refractive index changes. Configurations reported so far mainly operate in liquids but not in air because of a mismatch between permittivities of guided light modes and the surrounding medium. Here we demonstrate a plasmonic optical fibre platform that overcomes this limitation. The underpinning of our work is a grating architecture—a gold-coated highly tilted Bragg grating—that excites a spectral comb of narrowband-cladding modes with effective indices near 1.0 and below. Using conventional spectral interrogation, we measure shifts of the SPP-matched resonances in response to static atmospheric pressure changes. A dynamic experiment conducted using a laser lined-up with an SPP-matched resonance demonstrates the ability to detect an acoustic wave with a resolution of 10−8 refractive index unit (RIU). We believe that this configuration opens research directions for highly sensitive plasmonic sensing in gas.

Recent Advances in Plasmonic Sensor-Based Fiber Optic Probes for Biological Applications

“…LFBGs have been proposed to achieve SPR of a single cladding mode at the gold-coated tip of a single mode fiber [67], as shown in Figure 7e. Recently, sensors based on TFBGs have exhibited a sensitivity of 500 nm/RIU in non-plasmon-assisted refractometry and bulk optic SPR sensors, as shown in Figure 7f [68].…”

Discrete Self-Imaging in Small-Core Optical Fiber Interferometers

“…In fact, the cladding region of an optical fiber can also act as a waveguide and can support multiple cladding modes, which can be excited in a standard SMF by a fiber Bragg grating (FBGs) or a long-period grating [11]. Cladding modes are useful in many applications such as sensing and integrated optical devices [12], [13], for example in sensing, cladding modes can interact much more readily with the surrounding environment. Mathematically the core modes and the cladding modes are characterized by different functions arising from different solutions of the Bessel equation [11], [14], Jm and Km for the core modes and functions Jm, Ym and Km for the cladding modes.…”

Black phosphorus integrated tilted fiber grating for ultrasensitive heavy metal sensing

“…The novel lab-on-fiber technology has been proposed for optical sensing and optical communications [21,22]. Besides the inherent merits of optical fiber, such as compact size, light weight, and electromagnetic interference immunity, in-fiber grating technology provides advantages of real-time, multiplex, high sensitivity, label-free, and inline determination [23][24][25][26][27][28]. Both long period fiber grating (LPG) and tilted fiber grating (TFG) can couple the light from fiber core to the cladding yielding an evanescent wave penetrating outside of the cladding.…”

“…As the evanescent wave can be affected by changes in concentration or composition of the surrounding medium or by molecular interactions occurring on the cladding surface, it is a good candidate for chemical and biochemical sensing [23][24]. In contrast to conventional LPG, TFG owns narrow band resonances demonstrating much higher Q-factor hence high accuracy in optical signal detection [25][26][27][28]. In particular, the excessively tilted fiber grating shows much lower thermal and tension cross-talk effects and higher sensitivity in lower refractive index (RI) region [25].…”