Hollow-Core Microstructured Optical Fiber Gas Sensors

Abstract

Recent progress in gas detection with hollow-core microstructured optical fibers (HC-MOFs) and direct absorption/photothermal interferometry spectroscopy are reported. For direct-absorption sensors, the issue of mode interference noise is addressed and techniques to minimize such a noise are experimentally demonstrated. Large-scale drilling of hundreds of low-loss micro-channels along a single HC-MOF is demonstrated, which reduces the diffusion-limited response time from hours to ~40 seconds for sensing HC-MOFs of 2.3 meters. For photothermal inteferometry sensors, novel detection configurations based on respectively a Sagnac interferometer and an in-fiber modal interferometer are proposed and experimentally demonstrated. The Sagnac configuration avoids the need for complex servo-control for interferometer stabilization while the in-fiber configuration simplifies the detection, reducing the size and cost of the sensor system. Sub-ppm gas detection can be achieved easily with photothermal interferometry spectroscopic HC-MOF sensors but is difficult to achieve for direct-absorption sensors with the current commercial HC-MOFs.

Nanofiber enhanced stimulated Raman spectroscopy for ultra-fast, ultra-sensitive hydrogen detection with ultra-wide dynamic range

“…However, it is hard to fill gas into the long and thin hollow core from the fiber ends, even with the help of a pressure differential. Drilling side holes through the cross section of the fiber reduces gas filling time, but it also compromises the mechanical robustness of the fiber and introduces additional propagation loss [13].…”

Towards label-free distributed fiber hydrogen sensor with stimulated Raman spectroscopy

“…Labelfree We demonstrated distributed hydrogen sensing over a 100-m-long HC-PCF with microchannels drilled over a length of 2.2 m. It is feasible to fabricate a large number of microchannels along the entire length of the HC-PCF for real time distributed gas detection. With a femtosecond laser, we have demonstrated the fabrication of hundreds of micro-channels with an average loss below 0.01 dB per channel [27]. Observation of the fabrication process showed that most of the micro-channels have negligible contribution to the fiber loss and a few poorly made micro-channels raised the level of the average loss, which is believed caused by the scrap generated during the femtosecond laser drilling process.…”

“…For the purpose of gas ingress/egress, 56 pairs of micro-channels (i.e., 112 micro-channels) were drilled over a 2.2-m region around the location 88 m along the 100-m-long sensing HC-PCF. The drilling was done with an 800-nm femtosecond laser micro-machining system [27]. The separation between the adjacent pairs of micro-channels is ~4 cm, and the spacing between the two channels forming a pair is 200 µm.…”

Hollow Metal–Organic‐Framework Micro/Nanostructures and their Derivatives: Emerging Multifunctional Materials

“…Here, we first summarize the synthetic strategies of hollow MOFs and their derivatives. Afterward, we discuss their morphological and compositional effects on the applications in catalysis, gas sensors, batteries, supercapacitors, electrocatalysis, and others . Armed with discussions with several representative examples, the design and preparation strategies of hollow MOFs and their derivatives are clarified.…”