Abstract: Abstract: To address the industry pain point that infrared void detectors in cigarette production cannot simultaneously detect both "small voids" and "large voids", this paper proposes a dual-channel infrared reflection detection method based on single-source modulation and demodulation. The method uses a single infrared emitter to emit modulated infrared light to uniformly illuminate the cigarette end face. Two sets of receivers are used to focus on the shallow field of view (0–4 mm) and the deep field of view (4–8 mm), respectively, and lock-in amplification technology is employed to frequency-demodulate the two reflected signals, achieving dual-channel detection with shared optics and separate electronics. Channel 1 retains the traditional detection logic to ensure the detection accuracy of small voids. Channel 2 adopts a judgment method combining a threshold and a comparison with the value of Channel 1, effectively identifying moderate large voids and severe large voids. After independent threshold judgments, the two channel signals generate a final rejection command through a logical "OR" operation. The paper elaborates on the optomechanical structure, modulation-demodulation signal processing flow, and defect determination logic. To validate the effectiveness of the proposed scheme, a proof-of-principle experiment based on dual-sensor disassembly and reassembly was designed. By measuring static voltage signals of cigarettes with different defect types, it is demonstrated that this method can increase the detection rate of moderate large voids from 34% to 94% and that of severe large voids from 0% to 78%, without reducing the detection rate of small voids.