Low-Cost FBG Interrogator Using Random Nanoparticle-Doped Fiber Laser and Fiber Optic Interferometer
The use of fiber Bragg gratings (FBGs) is widespread in a broad range of applications. However, one of the main drawbacks is the cost and practicality of FBG interrogation systems, which are generally bulky and more expensive than electronic sensors or alternative optical fiber sensing approaches. This article presents a novel, low-cost FBG interrogator that employs a random laser based on a nanoparticle-doped fiber (RNPFL) and an unbalanced Mach–Zehnder fiber interferometer (MZI). The system uses the RNPFL connected to an unbalanced interferometer to convert Bragg wavelength shifts into phase changes, enabling precise interferometric detection with higher resolution than conventional spectral methods. Experimental results obtained with four FBGs of varying reflectivity, spectral width, and sidelobe suppression ratio (SLSR) demonstrate that, when operated with the RNPFL, the interrogator achieves up to 30 dB higher optical power (OP) and interference visibility of 60%–90%, substantially outperforming a standard superluminescent light-emitting diode (SLED) source. The relative error (RE) in phase demodulation remains below 0.2% for optimal configurations, characterizing the precision and phase-noise performance of the demodulation rather than the absolute accuracy of the system. The method is effective for FBGs with a wide range of parameters, provided that the SLSR is at least 15 dB. The main advantages of this approach are its compatibility with standard FBGs, high measurement resolution, and reduced cost, while the primary limitations are the requirement for a star topology in multichannel setups and the sensitivity of the resonator to external disturbances.