Reduction of Laser Frequency Noise and Intensity Noise in Phase-Shifted Fiber Bragg Grating Acoustic-Emission Sensor System

• Published in: IEEE sensors journal Vol. 17; no. 15; pp. 4820 - 4825
• Main Authors: Hu, Lingling, Han, Ming
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.08.2017; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Acoustic emission; Acoustic noise; Cost engineering; diode lasers; Emissions control; fiber gratings; Fiber lasers; Fiber optics; Fiber-optic sensors; Laser noise; Lasers; Measurement by laser beam; Michelson interferometers; Multiplexing; Noise; Noise intensity; Noise levels; Noise reduction; nondestructive testing; Optical fiber sensors; Optical fibers; Phase shift; Sensor systems; Sensors; Signal processing
• ISSN: 1530-437X; 1558-1748
• DOI: 10.1109/JSEN.2017.2716410

The noise performance of a fiber-optic acoustic-emission (AE) sensor system is often limited by the laser intensity noise and the laser frequency noise. Here, we report a novel low-cost, high-performance noise reduction method for fiber-optic AE sensor system based on a π-phaseshifted fiber Bragg grating. This method uses a reference channel built by an all-fiber Michelson interferometer formed by a 3 × 3 fiber-optic coupler and two Faraday mirrors. The reference channel has two outputs whose spectra are two sinusoidal fringes with a relative phase shift of 2π/3. A novel signal processing method is developed to extract both the laser intensity noise and the laser frequency noise from the outputs of the reference channel, which are subsequently removed from the output of the sensing channel. The results show that, for an AE sensor system using a distributed-feedback semiconductor laser as the laser source, this method achieves a noise reduction ratio of more than 20 dB. The reference channel possesses a broad operating spectral width and has the potential to be used in a multiplexed AE sensor system.