Effect of light source spectral modulation on wavelength interrogation in fiber Bragg grating sensors and its reduction

In the fiber Bragg grating sensing using a superluminescent diode as the light source and an arrayed waveguide grating as the wavelength interrogator, the wavelength measurement error due to the spectral modulation of the superluminescent diode is theoretically formulated and quantitatively analyzed by computer simulation. It is shown that the wavelength measurement errors produced with the use of real superluminescent diodes are in very good agreement with the theoretical results. In order to reduce the wavelength measurement error due to the spectral modulation of superluminescent diode, two different types of remedies are proposed that utilize the temperature switching of superluminescent diode and that adjust the bandwidths of fiber Bragg grating and arrayed waveguide grating, and their efficacies are experimentally demonstrated together with good quantitative agreement with the theoretical calculation.