Microfluidic flow direction and rate vector sensor based on a partially gold-coated TFBG

Abstract

In microfluidic chips applications, the monitoring of the rate and the direction of a microfluidic flow is very important. Here, we demonstrate a liquid flow rate and a direction sensor using a partially gold-coated tilted fiber Bragg grating (TFBG) as the sensing element. Wavelength shifts and amplitude changes of the TFBG transmission resonances in the near infrared reveal the direction of the liquid flowing along the fiber axis in the vicinity of the TFBG due to a nanoscale gold layer over part of the TFBG. For a device length of 10 mm (and a diameter of 125 µm for easy insertion into microfluidic channels), the flow rates and the direction can be detectable unequivocally. The TFBG waveguiding properties allow such devices to function in liquids with refractive indices ranging from 1.33 to about 1.40. In addition, the proposed sensor can be made inherently temperature-insensitive by referencing all wavelengths to the wavelength of the core mode resonance of the grating, which is isolated from the fiber surroundings.

Mode-division and spatial-division optical fiber sensors

“…It has been known for a while that the response of a partially immersed, relatively long fiber grating refractometer shows a transmission spectrum that has features corresponding to the two media which surround the grating, in proportions corresponding to the fraction of the grating length in each medium [228]. This idea was recently extended to dynamic measurements of the motion of a fluid boundary along the grating to determine the flow velocity and direction [229,230]. The same principle was used in the measurement of the surface tension of liquids in the milli-Newton range but in this case for partial contact of a water bead around the circumference of the fiber grating [231].…”

Low Acoustic Frequency Sensing Based on Ghost Mode of Small Angle Tilted Fiber Bragg Grating

“…It is worth noting that tilted fiber Bragg gratings (TFBGs) couple light from forward core mode to dozens or even hundreds of backward cladding modes, corresponding to resonant dips of narrow linewidth in the transmission spectrum [20][21][22]. For TFBGs, micro-bending is easy to cause leakage of the cladding modes and changes to their coupling efficiencies.…”

Towards a fast and stable tachypnea monitor: a C60-Lys enabled optical fiber sensor for humidity tracking in breath progress

“…As a result, various fiber manufacturing methods, including fiber tapering [3] , laser etching [4] , side-polishing [5] , and microstructure drawing [6] , were employed to fabricate optical structures aimed at leaking the optical power inside the fiber core into cladding. In contrast to the above structures, gratings encompassing a fiber Bragg grating (FBG) [7] , long-period fiber grating (LPG) [8] , and tilted fiber Bragg grating (TFBG) [9,10] are ultrasensitive and exhibit superior capacities in terms of loss, robustness, practical fabrication attributes, and consistency. Also, considering the environmental disruption, the TFBG proves to be a preferable choice because the core mode in the spectrum is unaffected by the change of refractive index outside fiber and can offset the influences of strain, temperature, and bending, which is important to the RH sensors [11,12] .…”