In-line microfluidic integration of photonic crystal fibres as a highly sensitive refractometer

Abstract

Photonic crystal fibres appear to be an ideal platform for the realisation of novel optofluidic devices and sensors due to their waveguide nature and microstructured architecture. In this paper, we present the fabrication and characterisation of an in-line photonic crystal fibre microfluidic refractometer enabled by a C-shaped fibre. The C-shaped fibre spliced in-between the photonic crystal fibre and the single-mode fibre allows simultaneous in-line optical signal delivery and analyte fluid feeding. Through an arc discharge pre-treatment technique, we successfully achieve selective exploitation of only the central two channels of the photonic crystal fibre for microfluidic sensing. After constructing a Sagnac interferometer, a highly sensitive refractometer with a sensitivity of 8699 nm per RIU was achieved experimentally; this agrees very well with the theoretical value of 8675 nm per RIU. As a demonstration for label-free optical sensing application, the refractometer was used to measure the concentration of NaCl solution with a sensitivity of 15.08 nm/(1 wt%) and a detection limit of 2.3 × 10(-3) wt% (23 ppm).

Optofluidics Refractometers

“…Many research efforts contribute to design the deliberate structures to achieve the convenient load of liquid sample, and employ special modes to improve the sensitivity of the sensors. For example, C. Wu et al presented the fabrication and characterization of an in-line photonic crystal fiber microfluidic refractometer outfitted with a C-shaped fiber [ 30 ] ( Figure 1 a). The C-shaped fiber, placed between the PCF and single-mode fiber, achieved two functions simultaneously: in-line optical signal coupling and analyte fluid feeding.…”

“… ( a ) Scheme and transverse section graph of the SMF-C-PCF-C-SMF microfluidic device. Reprinted with permission from [ 30 ]. Copyright (2014) RSC; ( b ) Scheme of the in-line optofluidic sensing platform and SEM image of the SC-PCF and Simulated intensity distribution of LP 01 mode and LP 11 mode at the wavelength of 1550 nm.…”

Optofluidic refractive index sensor based on partial reflection

“…The past decade has witnessed the realizations of optofluidic devices including tunable waveguides [3,4], lenses [5,6], switches [7,8], apertures [9,10], reconfigurable lasers [11,12], interferometers [13,14], gratings [15,16], and sensitive sensors with fast response and low sample consumption [17][18][19][20], as well as demonstrations of their applications in chemical and biological analysis [21], energy [22], and photonics [23]. For many biological and chemical applications, the measurement of refractive index (RI) is extremely useful for detecting compounds that are: nonionic, transparent in the UV/vis range, or with no fluorescence, moreover, it has great potential for none invasive and label-free biosensing [24][25][26].…”

All-in-fiber sensing and light generation based on specialty fibers

“…The two channels are in the innermost ring of the fiber cladding, and the RI of liquid is higher than that of silica. [199]. The schematic diagram is shown in Fig.…”

“…As the simulations were carried out over a broad wavelength range, the material dispersion of silica and water also need to be considered in the simulations to ensure the desired accuracy. Therefore, the RI values of the silica and air at different wavelengths were calculated according to their Sellmeier equations [199,249].…”