Femtosecond laser directly writing of apodized fiber Bragg grating

Fiber Bragg gratings boast a wide range of applications, including fiber optic communication, highly sensitive long-distance sensing, and laser devices. To enhance the signal-to-noise ratio of the central wavelength of fiber gratings, the suppression of side lobes reflectivity of Apodized Fiber Bragg Gratings (AFBG) is researched. The article employs femtosecond laser direct writing technology and precise modulation of output pulse energy through attenuators to inscribe AFBG. Controlling over the angle between two half-wave plates within the optical attenuator is required. Additionally, we investigated various apodization modulation functions (i.e., Triangular, Gaussian, and Hamming) and conducted simulations and experimental validations. Simulation and experimental outcomes confirm the method's feasibility and efficiency. The method of energy-apodized gratings controlled by Gaussian functions can effectively suppress side lobes and enhance the contrast of the reflective center wavelength.