A Novel Noise-Insensitive Chromatic Dispersion Estimation Method Based on Fractional Fourier Transform of LFM Signals

We propose a novel chromatic dispersion (CD) estimation method by fractional Fourier transformation of linear-frequency modulation (LFM) signals. This method can measure inband and outband CD without using extra spectrum or timeslot resources. In our method, LFM signals are added on quadrature phase-shift keying (QPSK) and 16 quadrature amplitude modulation (16-QAM) signals with different center frequency offsets. The average estimation error of CD estimation is 0.234%, 0.25%, and 0.41% when the center frequency offset is 0, 15, and 40 GHz after five, 10, 15, and 20 spans standard single-mode fiber transmission. The results demonstrates that the maximum estimation error is always below 80 ps/nm for accumulated CD less than 24 000 ps/nm. For all scenarios, the CD estimation performance barely drops with optical signal-to-noise ratio from 10 to 25 dB and launch power from 0 to 6 dBm of five channel transmission.