Spectral Analysis Using a Dispersive Microwave Photonics Link Based on a Broadband Chirped Fiber Bragg Grating

We report on the use of a dispersive microwave photonics analog optical link for spectral analysis and wavelength measurement in optical fiber sensors. The system is built on the concept of wavelength to group-delay mapping, with a scale determined by the dispersion of the link. In our demonstration, the dispersive channel is a chirped fiber Bragg grating for dispersion compensation of 10 km of single-mode fiber and low third-order dispersion, with a reflection band in the range 1540-1560 nm. The spectral analysis is performed by a vector network analyzer with time-domain analysis software, as in incoherent optical Fourier-domain reflectometry. The spectrum is reproduced as the time-domain impulse response of the fiber-optics link, and the system operates over a wide range of input power and acquisition parameters. As a spectrometer, the system shows sensitivities up to -23.3 dBm, measured at the input of the link, resolutions up to 170 pm, and dynamic range up to 34 dB after windowing the radio frequency response. As a wavelength meter, picometer resolution is demonstrated for laser lines within a 40 pm range, and also an uncertainty of ±4 pm for Bragg wavelength shifts of FBG when the reflected power is -10 dBm.