The rapid growth of new services has led to a significant increase in data traffic, which brings challenges for data centers to support high-speed processing of large volumes of data. Traditional electrical interconnects are becoming increasingly inadequate, leading to increasing attention on 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 paper, 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 1m MMF-1m FSO-1m MMF link is successfully achieved based on a 50-channel WDM VLLC system utilizing DPC and bit-power-loading DMT modulation. To the best of our knowledge, this is the highest data rate and constellation size ever reported for a WDM VLLC system, which proves that VLLC is a promising candidate solution to achieve high-capacity and cost-effective optical interconnects in data centers.