Abstract
Abstract In a wide range of applications such as healthcare treatment, environmental monitoring, food processing and storage, and semiconductor chip manufacturing, relative humidity (RH) sensing is required. However, traditional fiber-optic humidity sensors face the challenges of miniaturization and indirectly obtaining humidity values. Here, we propose and demonstrate an optical barcode technique by cooperating with RH meta-tip, which can predict the humidity values directly. Such RH meta-tip is composed of fiber-optic sensor based on surface plasmon resonance (SPR) effect and graphene oxide film as humidity sensitizer. While SPR sensor is composed of multimode fiber (MMF) integrated with metallic metasurface. Dynamic time warping (DTW) algorithm is used to obtain the warp path distance (WPD) sequence between the measured reflection spectrum and the spectra of the precalibrated database. The distance sequence is transformed into a pseudo-color barcode, and the humidity value is corresponded to the lowest distance, which can be read by human eyes. The RH measurement depends on the collective changes of the reflection spectrum rather than tracking a single specific resonance peak/dip. This work can open up new doors to the development of a humidity sensor with direct RH recognition by human eyes.
Highlights
Humidity plays a vital role in many physical, chemical, and biological processes [1,2,3,4,5,6]
The refractive index (RI) response of those dips appearing in the reflection spectrum depends on the mode occupying the principal component, which will lead to the different resonance wavelength shift trends [24]
We have demonstrated an optical barcode technique combined with an relative humidity (RH) meta-tip for RH direct reading
Summary
Humidity plays a vital role in many physical, chemical, and biological processes [1,2,3,4,5,6]. The monitoring parameters of a specific resonant peak/dip may have nonlinear changes or inflexion points, especially in fiber-optic sensors based on multimode interference. This problem can be solved by increasing the number of resonance peaks/dips monitored, it significantly increases the difficulty and workload of spectrum demodulation and reduces the utilization of spectral resonance peaks/dips. We can directly read the RH value from the optical bar code obtained by processing the collective behavior of multiple resonance dips in the reflection spectrum. Such imaging-based barcodes with RH meta-tip may pave the way towards a versatile miniaturized visual humidity sensor
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