Flexible Hollow Core Fiber Photoacoustic Gas Sensor Based on Embedded Acoustic Resonant Structure

In this paper, we demonstrate a flexibleleaky hollowcore fiber(LHCF) photoacoustic (PA) gas sensor based on an embedded acousticresonant structure. The sensor employs a part of a gas conduit asthe buffer chamber to construct an equivalent T-type half-open PAcell. The LHCF is installed inside of the gas conduit and the LHCFis hence replaceable. Also, the flexibility of the LHCF and the gasconduit make the gas sensor flexible to reduce spatial size. The innerdiameter and length of the LHCF are 1.6 mm and 70 mm, respectively.The inner diameter and length of the gas conduit are 4 mm and 210mm, respectively. The total gas volume of the sensor is only & SIM;2.6mL. Trace acetylene (C2H2) is selected as thetarget gas to evaluate the performance of the PA gas sensor. A near-infrareddistributed feedback (DFB) laser is utilized to generate the PA signal,and an electrical micro-electro-mechanical system (MEMS) microphoneis employed to extract the PA signal. The experimental results showthat the minimum detection limit (MDL) can be as low as 21.1 ppb whenthe lock-in integration time is 200 s. And the normalized noise equivalentabsorption coefficient (NNEA) is calculated to be 5.7 x 10(-9)& BULL;W/cm(-1)& BULL;Hz(-1/2).