The rapid growth of new services has led to a significant increase in data traffic, which brings challenges for data centers in supporting high-speed processing of large volumes of data. Traditional electrical interconnects are becoming increasingly inadequate, leading to increasing attention to optical interconnects to achieve high-speed data center interconnects (DCIs). Visible light laser communication (VLLC) inherits the advantages of free-space optics (FSO), allowing it to circumvent the limitations of conventional fiber-based optical interconnects. In addition, VLLC offers other advantages such as high thermal stability, low power consumption, and low packaging cost. In this Letter, a novel differential pilot coding (DPC) scheme is proposed to achieve precise channel estimation and compensation for linear impairments without halving the effective data rate. A data rate of 601.46 Gbps with a constellation size up to 1024QAM over a 1 m multimode fiber (MMF)-1 m FSO-1 m MMF link is successfully achieved based on a 50-channel wavelength division multiplexer (WDM) VLLC system utilizing DPC and bit-power-loading discrete multitone (DMT) modulation. To the best of our knowledge, this is the highest data rate and constellation size ever the reported for a WDM VLLC system, which proves that VLLC is a promising candidate solution for achieving high-capacity and cost-effective optical interconnects in data centers.