Relaxing the Optical Signal-to-Noise Ratio (OSNR) requirements of modern Wavelength Division Multiplexing (WDM) transmission systems/networks is essential due to the introduction of high-loss Optical Network Elements (ONE), the large channel numbers, and the very high channel-speeds. Forward Error Correction (FEC) codes are currently used in many applications, but the problem of the bit-rate increase caused by the redundancy will worsen as the channel-speed increases. This paper presents a novel error-controlling scheme that does not increase the bit-rate while offering OSNR relaxation. Error control is achieved by the two kinds of receiver proposed here, both of which are characterized by the diverse detection of dual-mode modulated signals, "consensus" logic for error detection, and multiple threshold selection for data recovery. After describing the "basic" receiver, an enhanced version is presented. Analyses based on the classical Gaussian noise approximation show the performances of these receivers. Experimental results show fair agreement with the analysis results, despite the simplifications used in the analyses. Experiments on the basic receiver show 3dB gain, and 9dB gain was observed with the addition of the standard RS(255,239) FEC code. 4dB gain is observed experimentally from the enhanced version of the receiver, and 10dB gain with the addition of RS(255,239).© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.