###### Abstract  
This paper proposes a novel method to improve the anti-dispersion ability of the all-optical orthogonal frequency division multiplexing (AO-OFDM) system. By replacing the Sinc-shaped filter with a Gauss-shaped filter for sub-carrier generation and inserting a cyclic prefix (CP), the impact of dispersion on the system can be significantly mitigated. Formula derivation and numerical analysis of the pulse-shaping function of the AO-OFDM system in the time domain for each cycle indicated that the pulse-shaping function generated by the Gauss-shaped filter was less affected by the dispersion effect than that of the Sinc-shaped filter. Meanwhile, less inter-carrier crosstalk between carriers was also observed. After carrying out system transmission simulations employing these two different filters, we found that the AO-OFDM system based on the Gauss-shaped filter could greatly improve the anti-dispersion ability compared with the system based on a Sinc-shaped filter. When the parameter settings in both schemes were identical, that is, the number of subcarriers was 32 and the power of a single subcarrier was \(-13\) dBm, the bit error rate (BER) of the system based on the proposed Gauss-shaped filter after 60 km SMF transmission was only \(1.596\times 10^{-3}\), while the BER of the traditional Sinc-shaped filter based system scheme was as high as \(8.545\times 10^{-2}\). all-optical orthogonal frequency division multiplexing; Sinc-shaped filter; chromatic dispersion; Gauss-shaped filter +
Footnote †: journal: _Photonics_control the splitting and recombination of input light by controlling the LCoS and then adding additional delay to produce multiple Sinc-shaped filters [15]. Controlling the liquid crystal to achieve the above function is to control the diffraction of the liquid crystal by loading the phase diagram generated by the complex algorithm on the liquid crystal. The main factor limiting the promotion of this scheme is the excessively high cost of LCoS. The complex liquid crystal phase diagram also requires a large number of optimization algorithms and digital signal processing (DSP), thus further increasing the application burden. Therefore, other AO-OFDM schemes also have great application potential in scenarios where economic costs need to be underlined and the carriers are not required to be flexibly allocated. The AO-OFDM system based on WSSs in Ref. [9] used 252 orthogonal sub-carriers to complete 857.4 km optical fiber transmission with a transmission rate of 10.08 Tbit/s. In Ref. [10], the data rate of AO-OFDM exceeded 26 Tbit/s, and the spectrum efficiency reached 6 bit/s/Hz. At the same time, Ref. [11] also reported that the AO-OFDM system based on AWG was applied to passive optical networks far exceeding Tbit/s. It should be pointed out that AO-OFDM systems, whether applied to large-capacity long-distance transmission or large-capacity passive optical networks, rely heavily on dispersion compensation. As reported in Refs. [7; 16], the AO-OFDM system had very poor anti-dispersion ability and was limited to less than 20 km on a single-mode fiber (SMF) for the reason that chromatic dispersion caused the sub-carrier's intensity peaks to shift from the null points of the other sub-carriers, and the relative time delay among the subcarriers broke their orthogonality, which led to crosstalk. In order to compensate for the fiber dispersion on the system, numerous solutions have been proposed, such as adding CP, fractional Fourier transformation, dispersion compensation fiber, and other optical domain dispersion compensation schemes, where dispersion monitoring is introduced at the receiving end to achieve adaptive dispersion compensation. The main problem of the above method is that the longer the transmission distance, the lower the accuracy of dispersion measurement. The dispersion compensation by the digital signal processing technique can also be used.