The demand for larger bandwidth to carry high capacity data in optical networks is increasing. Thus, it is expected to replace all digital logic with optical logic soon. Privacy and data security are also of utmost importance in all-optical networks. Generally, all-optical encryption has been carried out using (i) highly nonlinear fiber (HNLF) and (ii) Semiconductor Optical Amplifier (SOA) with interferometric structures. However, the former is limited by the requirement of a lengthy fiber and the latter one with more number of nonlinear components. In this work, an all-optical encryption process using nonlinear effects and four-wave mixing (FWM) in SOA without interferometric structure is presented for different number systems. The basic idea of the proposed system is to use delay operations which are carried out by duo binary modulation units whereas the encryption using single SOA is possible by FWM nonlinear effect. This combination of novel design for different number systems is optimized through SOA structural parameters, pump and probe signal power, and wavelength. Through optimization, the performance improvement is assured by a good extinction ratio of 11.5 dB for the active region length of less than 200 μm. Compared to the existing techniques, the quality factor is 2.28 times and 1.52 times better than HNLF and SOA-MZI, respectively. © 2020 Walter de Gruyter GmbH, Berlin/Boston 2020.