Fig. 1. Schematic of CO-OFDM system

Fig. 2. Schematic of pilot insertion

Fig. 3. Schematic of two-dimensional projection histogram in 16-QAM constellation

Fig. 4. Histograms of two-dimensional projection in constellation. (a) Histogram in in-phase-dimension without CPE; (b) histogram in quadrature-dimension without CPE; (c) histogram in in-phase-dimension with CPE; (d) histogram in quadrature-dimension with CPE

Fig. 5. Schematic of CPE compensation algorithm based on two-dimensional projection histogram and pilots

Fig. 6. System simulation platform of CO-OFDM system based on MATLAB and OptiSystem

Fig. 7. Relationship between EVM performance and received optical power for PA, PH and PA-2PH algorithms with different pilot densities

Fig. 8. Relationship between EVM performance and received optical power. (a) Value of a is determined; (b) value of a matches the received optical power

Fig. 9. Comparison of actual and estimated phase noise. (a) 500 OFDM symbols for PH; (b) estimation error for PH; (c) 500 OFDM symbols for PA-2PH; (d) estimation error for PA-2PH

Fig. 10. Relationship between BER performance and received optical power for PA, PH and PA-2PH algorithms with different pilot densities

Fig. 11. Relationship between BER performance and received optical power for PA-PH and PA-2PH algorithms with different pilot densities