Abstract
Chirped radio-frequency (RF) pulse generation based on optical spectral
shaping and nonlinear wavelength-to-time mapping in a nonlinearly chirped
fiber Bragg grating (NLCFBG) is investigated. In the proposed approach, the
spectrum of a femtosecond pulse generated by a mode-locked fiber laser is
shaped by an optical filter that has a sinusoidal frequency response. The
spectrum-shaped optical pulse is sent to the NLCFBG, to implement nonlinear
wavelength-to-time mapping. A chirped electrical pulse with the central frequency
and chirp rate determined respectively by the first- and second-order dispersions
of the NLCFBG is then obtained at the output of a high-speed photodetector.
An approximate model that describes the chirped RF pulse generation is derived,
which is verified by numerical simulations. Chirped pulse generation with
a pulse compression ratio as high as 450 is demonstrated. The key device in
the chirped RF pulse generation system is the NLCFBG, which is investigated
in detail with an emphasis on the influence of its group delay ripples on
the performance of the pulse generation system. Techniques to design and fabricate
the NLCFBG are also discussed. The proposed approach provides a potential
solution for the generation of chirped RF pulse with a high central frequency
and large chirp rate for applications in pulse compression radar systems.
© 2008 IEEE
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