Improved DFB-FL Sensor Interrogation With Low Harmonic Distortion Based on Extended Kalman Filter

In the distributed feedback fiber laser sensor interrogation based on 3x3 coupler, the asymmetry of the 3x3 coupler and the inconsistency of detectors lead to harmonic distortion in the result. This paper presents an improved method that combines the 3x3 coupler and the extended Kalman filter (3x3-EKF method) to effectively suppress the harmonic distortion in real-time. The coefficients of the three ellipses formed by every two-channel interference fringes were estimated using EKF. The system parameters were corrected based on these coefficients to eliminate the dependence on the idealization of 3x3 coupler and detectors. The result shows that the 3x3-EKF method can update the system parameters with a frequency up to 500 kHz. A total harmonic distortion less than 0.1% can be achieved with signal frequency ranging from 20 Hz to 1 kHz. Besides, the system shows a minimum detectable wavelength shift of 3.1 x 10(-7) pm/root Hz @ 1 kHz, and a large dynamic range of 135 dB @ 100 Hz.

Automated summary

This study introduces an improved method that combines the 3x3 coupler and extended Kalman filter to effectively suppress harmonic distortion in distributed feedback fiber laser sensor interrogation. The method can update system parameters in real-time, leading to a low total harmonic distortion and large dynamic range in signal frequency range of 20 Hz to 1 kHz.