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Carrierless amplitude and phase (CAP) modulation is generating increasing interest for short reach optical communications. In this letter, we present the use of a decision-directed least mean square (DD-LMS) adaptive equalization algorithm for CAP128/256 transmission systems. A novel preconvergence scheme using aided threshold decision is proposed, called decision-assisted modified cascaded multimodulus algorithm. With the help of a DD-LMS-based equalizer, we demonstrate for the first time transmission of 10-Gb/s CAP128/256 signal over 40-km standard single mode fiber using low-cost directly modulated lasers.