Ultra-Stable and Real-Time Demultiplexing System of Strong Fiber Bragg Grating Sensors Based on Low-Frequency Optoelectronic Oscillator

Wide-area and multi-point remote sensing technology plays an important role in the fields of disaster monitoring and locating. We demonstrate a demultiplexing method for quasi-distributed identical strong fiber Bragg grating (FBG) sensors based on optoelectronic oscillator (OEO). When the FBG sensor is affected by environmental changes, the wavelength of the FBG will shift. An oscillation will be stimulated in the OEO since the laser power is reflected by the FBG. The demultiplexing system utilizes the oscillating frequency of the OEO to encode the location information of grating series. Compared with other schemes, the proposed system has three superior advantages. First, as a digital discrete position encoding system, it has a strong anti-interference ability and does not require continuous sweeping wavelength and rapid digital signal processing, which can achieve high speed and high stability. Second, it can demodulate identical FBGs with strong reflectivity, thus ensuring long-distance and large capacity. Third, it can work in a low-frequency range without using high-frequency devices, which has the potential to be a low-cost interrogator in practical applications. The theoretical capacity of the system is 62 multiplexed points in one line and the experimental results show that the sensing area can range from 1 m∼1 km with the response time of ∼0.61 s and the oscillating frequency stability of <28 kHz. The linear relationship between the wavelength of the laser and the alarm strain/temperature, corresponding to 1.3 μϵ/pm or 0.1 °C/pm, can be used to set alarm threshold values.