A new photon scheme for linear frequency modulation （LFM） signal generation and dechirping is proposed. In the proposed scheme， at the radar transmitter， a double-parallel Mach-Zehnder modulator is used to generate quadruple frequency suppression carrier double-sideband signal. The two sidebands are separated after the fiber grating and modulated by a cyclic phase， and the octave frequency LFM signal is generated by photoelectric conversion through a photodetector. At the receiving end， the echo signal is phase-modulated， the carrier wave and the first-order sideband containing the echo information are filtered through a filter， and the beat frequency is realized to obtain a single-frequency signal. Thus， the dechirp processing of the echo signal is completed. In the analysis and verification by Optisystem， the frequency of the radio frequency signal was set to 10 GHz， the amplitude of the parabolic signal was 1， and the width of the parabolic signal was 10 ns. An LFM signal with a center frequency of 80 GHz， bandwidth of 32 GHz and time bandwidth products of 320 was generated. The tunability and compression performance were verified， and LFM signals with time bandwidth products of 480， 640， and 3200 were generated. At the receiving end， echo signals with delays of 1.0 μs and 0.9 μs were dechirped at the receiver， corresponding to detection distances of 150 m and 135 m， respectively. The scheme is compact and has good reconfigurability.