This paper presented a high-sensitivity humidity sensor comprised of a side-polished fiber with polymer nanostructure cladding, which was constructed by dehydrating dichromate gelatin film on the polished surface. Due to the intermodal interference of the core mode and cladding mode, two main transmission dips were observed at 1184.4 nm and 1325.6 nm. These two transmission dips showed significant sensitivity to humidity. The position of transmission dip at 1325.6 nm shifted 22 nm while the relative humidity (RH) changed from 30% RH to 50% RH. The humidity sensitivity was up to 1.12 nm/% RH, and its linear correlation was 98.45%. The humidity sensing characteristic of nanostructure cladding fiber was successfully demonstrated. This novel sensor is compatible with optical fiber systems and has high potential in optical sensing applications.
Photoacoustic tomography (PAT), also known as optoacoustic tomography, is an attractive imaging modality that provides optical contrast with acoustic resolutions. Recent progress in the applications of PAT largely relies on the development and employment of ultrasound sensor arrays with many elements. Although on-chip optical ultrasound sensors have been demonstrated with high sensitivity, large bandwidth, and small size, PAT with on-chip optical ultrasound sensor arrays is rarely reported. In this work, we demonstrate PAT with a chalcogenide-based micro-ring sensor array containing 15 elements, while each element supports a bandwidth of 175 MHz (−6 dB) and a noise-equivalent pressure of 2.2 mPaHz−1/2. Moreover, by synthesizing a digital optical frequency comb (DOFC), we further develop an effective means of parallel interrogation to this sensor array. As a proof of concept, parallel interrogation with only one light source and one photoreceiver is demonstrated for PAT with this sensor array, providing images of fast-moving objects, leaf veins, and live zebrafish. The superior performance of the chalcogenide-based micro-ring sensor array and the effectiveness of the DOFC-enabled parallel interrogation offer great prospects for advancing applications in PAT.
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