A sensitivity-enhanced flexible acoustic sensor using side-polished fiber Bragg grating

Abstract A miniature flexible fiber Bragg grating (FBG) acoustic sensor with enhanced pressure sensitivity was fabricated by using a side-polished configuration of ∼54 μm depth and ∼15 mm length. The photoelectromechanical response of the sensor suspended as a dual-end-fixed beam was characterized based on the acoustic-induced strain interaction with fiber gratings. The opto-mechanical response of the sensor to bending strain was firstly investigated and exhibited about 11 times larger in wavelength shift, in comparison with a conventional bare FBG. Then acoustic testing demonstrated an acoustic pressure-induced wavelength shift of 0.041 nm/Pa and a noise equivalent acoustic signal level of ∼1.66 mPa/Hz 1/2 in the frequency region around 2.5 kHz. Also, a relative flat frequency response with a fluctuation of less than 12.9 dB was achieved in the measurement between 400 Hz and 20 kHz, which is in well agreement with the result obtained by a reference condenser microphone. Along with strain-sensitive nanomaterials, the use of the side-polished FBG could be further extended for highly sensitive acousto-ultrasonic sensors in structural health monitoring and wearable applications.