超密集波分复用无源光网络凭借其信道间隔仅为几个GHz、功率预算高达几十dB等优越性能，可以实现用户数目和传输容量的大幅提升。从频谱效率提高、相干接收机简化、光子集成器件应用、数字信号处理优化等关键研究方向出发，简述了国内外关于超密集波分复用无源光网络相关研究的最新进展情况，探讨了其未来可能的研究方向和发展趋势。

An ultra-dense wavelength division multiplexing passive optical network can substantially increase the number of users and transmission capacity because it exhibits a channel spacing of only a few GHz， power budget of up to tens of dB， and other superior performance characteristics. Herein， the recent progress on the ultra-dense wavelength division multiplexing passive optical networks at home and abroad was comprehensively reviewed based on several key research directions， such as the improved spectral efficiency， simplified coherent receivers， photonic integrated device application， and optimized digital signal processing. Moreover， possible research directions and development trends were discussed.