This paper investigates the performance of the Spectral Amplitude Coding (SAC) Optical Code Division Multiple-Access (OCDMA) system utilizing the Flexible Double Weight (FDW) code and a newly developed detection technique, the Direct AND (D-AND) detection technique. The newly proposed Direct AND (D-AND) technique comprises three decoder components: a primary decoder, a subtractive decoder (S-decoder), and an addition decoder (A-decoder). The numerous noises investigated in the theoretical research included phase-induced intensity noise, shot noise, thermal noise, and multiple-access interference effects. Bit Error Rate (BER) and signal-to-noise ratio (SNR) were used to gauge the system�s performance. The Detection (DD) and Single-Photodiode Detection (SPD) results were compared to those of the study of the new detection technique. The newly developed detection technique, which was tested using the FDW code, can support more active users and improve system performance when compared to SPD and DD approaches. The simulation experiment demonstrates that the system�s BER performance with the new detection technique is much better than with the earlier techniques. The new detection technique outperforms the previous technique, supporting 284 concurrent users compared to DD 172 concurrent users and SPD 116 concurrent users at a 10 Gbps bit rate. © The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature 2024.