The goal of this study is to explore the efficacy and safety of near-infrared light combined with lecanemab in patients with mild Alzheimer's disease (AD). This study will employ a randomized, double-blind, sham-controlled method with an open-label extension phase. This trial contains the core phase and an extension phase. During the core phase, eligible subjects were selected and randomized (experimental group: control group = 1:1). The subjects who entered the experimental group received treatment with a near-infrared light therapy device combined with lecanemab for 16 weeks. The subjects who entered the control group received treatment with a near-infrared light therapy device simulator (sham stimulation) combined with lecanemab for 16 weeks. After completing the core phase, patients from both groups of the core phase are eligible to enter the extension phase. In the extension phase, all the participants were treated with a near-infrared light therapy device combined with lecanemab up to week 48.