MEMS Fiber-Tip Photoacoustic Spectrometer for In Situ Microscale Trace Gas Sensing

Low Cross Sensitivity Fiber-Optic MEMS Pressure Sensor for Water Depth Measurement

To address the demand for high-precision depth detection in intelligent monitoring and sensing applications for the ocean environment, this letter presents a fiber-optic Fabry-Perot (FP) micro-electro-mechanical systems (MEMS) water depth pressure sensor. Its core is a miniaturized FP cavity fabricated via anodic bonding of borosilicate glass and silicon, which ensures robustness and enables wafer-scale production. Experimental results demonstrate a high pressure sensitivity of −68.99nm/MPa over 0.1-1.1MPa (equivalent to 10-110m water depth). When integrated with a high-resolution interrogation system, centimeter-level depth resolution is achieved. The sensor demonstrates a repeatability error of 0.18%Full scale (FS) and stability better than 0.21%FS. Furthermore, owing to the matched thermal expansion coefficients of the bonded materials, the sensor exhibits low temperature cross sensitivity, with a temperature sensitivity of only 0.43nm/°C over the -10-40°C range, ensuring reliable operation in varying temperatures. This work provides a competitive solution for developing high-reliability, low cost optical water depth pressure sensors suitable for marine environments.

An integrated micro-thermometer for mid-infrared photothermal spectroscopy of dense materials built in a CMOS 200 mm pilot line

Indirect photothermal infrared spectroscopy of dense materials typically relies on photoacoustic cells for detecting acoustic waves generated by light-induced heating. This detection approach can be challenging to implement as it is highly sensitive to the sealing quality of the interface between the cavity and the sample, as well as to the properties of the gas within the cavity. Here, we present a simplified and more robust method. This approach relies on direct photothermal temperature measurement using an optimized platinum microsensor fabricated on a thin silicon substrate that acts as a thermally transparent interface with the sample. The sensor design, fabrication in a 200 mm CMOS pilot line, assembly on a readout PCB, and experimental characterization are reported. The component achieves a signal-to-noise ratio close to 1000 making it well-suited for miniaturized and embedded infrared spectroscopic applications.

Anti-Resonant Hollow-Core Fiber Sensor With Microchannel Arrays for Fast CO2 Sensing

A fast carbon dioxide (CO2) sensor utilizing an anti-resonant hollow-core fiber with microchannel arrays is demonstrated, where the microchannel arrays along the fiber cladding are precisely fabricated by a femtosecond laser to enhance the internal gas mass transfer rate to speed up the response. We utilized the method of direct absorption spectroscopy to calibrate the fiber sensor within a CO2 concentration range of 1% to 10% at the $2~\mu $ m wavelength band. A sensitivity of 0.155 a.u./% with a high linearity (R2) of 0.9935 in the experimental detection is characterized at 2004.33 nm. Meanwhile, the design of microchannel arrays along the fiber significantly improves diffusion dynamics, which reduces the response time from 355 s to 185 s at the steady state and achieves a limit of detection of 896.1 ppm. Benefiting from rapid dynamic response and excellent repeatability, the proposed fiber sensor provides a highly efficient in-line gas cell solution for the real-time quantitative monitoring of trace gases.

Fabrication and sensing characteristics of a fiber-optic air pressure sensor based on the Vernier effect

A high-sensitivity fiber-optic pressure sensor is demonstrated, based on the Vernier effect in a cascaded dual Fabry–Pérot interferometer. The sensor incorporates a 343 μm polarization-maintaining fiber and a single-mode fiber, precisely aligned and secured within a ceramic sleeve to form an air cavity. The Vernier effect is realized by precisely controlling the silica cavity length through a fiber polishing process, which significantly enhances the gas pressure sensitivity. The device exhibits a linearity of 99.68% and a sensitivity of 50.93 pm kPa−1 over the range of 50.2 kPa–201.8 kPa. Owing to its compact structure, robust fabrication, and good short-term stability, this sensor holds great potential for gas pressure monitoring applications.

Highly Sensitive Gas Pressure Sensor Based on Fabry-Perot Interferometers and the Vernier Effect

A highly sensitive gas pressure sensor based on the Vernier effect (VE) and Fabry-Perot interferometers (FPIs) has been proposed. The sensing structure was fabricated by fusion-splicing a single-mode fiber (SMF) with two quartz-capillary sections of different inner diameters, followed by coating a polydimethylsiloxane (PDMS) film on the end face of the terminal capillary. The experimental results show that the pressure sensitivities during the pressurization and depressurization processes were -431.4908 and -363.1582 nm/MPa,with linear fitting coefficients of 0.9902 and 0.9758, respectively. The difference between the two sensitivities is mainly attributed to the viscoelastic hysteresis of the PDMS film, delayed stress relaxation, incomplete elastic recovery, and experimental uncertainty. The results indicate that the proposed sensor has the advantages of compact size, relatively simple fabrication, high sensitivity, and favorable linear response, suggesting its potential for slight-pressure monitoring and pressure detection in confined spaces.

Adaptive laser-tagging optofluidic microcavity for single-molecule hydrogen detection across a nine-decade concentration span