To solve the problems of complicated structure and rate limiting in conventional format conversion system, 40 Gbps all-optical format conversion from return-to-zero to non-return-to-zero modulation format converter was proposed and demonstrated with a single semiconductor optical amplifier and an optical band-pass filter. The format converter consists of a single semiconductor optical amplifier which is acted as a nonlinear element to broaden the spectrum of input signal and the optical band-pass filter which is used to extract the special spectrum from the broadened spectrum. By adopting the ultra-fast semiconductor optical amplifier model, the 40 Gbps return-to-zero to non-return-to-zero format conversion was demonstrated with simulation. The proof of the principle experiment at 40 Gbps was demonstrated by using the test semiconductor optical amplifier and optical band-pass filter converter. Experimental results show that the power penalty induced by the pattern converter is about 2 dB, which is well coincidence with simulated results. The proposed scheme is robust and potential for applications in future optical networks.