Photonic Generation of Linearly Frequency-Modulated Waveform with Improved Time-Bandwidth Product

Linear frequency-modulated (LFM) waveforms can be photonically generated by introducing a parabolic phase difference to two phase-correlated optical wavelengths followed by optical heterodyning, but the maximal achievable time-bandwidth product (TBWP) is limited by the modulation index of the electro-optic modulator, which is independent of the bandwidth or duration of the input signal. In this paper, a novel approach to increase the TBWP is proposed and demonstrated by splitting the electrical parabolic signal into N pieces with identical amplitudes. Although the bandwidth or the time duration of the input signal is increased by N times, the TBWP of the generated LFM waveform is improved by N times. A proof-of-concept experiment is carried out. As compared with the scheme using conventional parabolic signal, the TBWP is improved by more than 45 times.