What are the mainstream manufacturers of wavelength division multiplexers?

Wavelength Division Multiplexer (WDM) is a low-cost WDM transmission technology used in the access layer of MAN. In principle, CWDM multiplexes optical signals of different wavelengths into a single optical fiber for transmission by using an optical multiplexer. At the receiving end of the link, the mixed signal in the optical fiber is decomposed into signals with different wavelengths by optical demultiplexer and connected to the corresponding receiving equipment. The requirements for technology are also relatively high. As far as I know, Huawei, North Yitong /F-tone Networks and Cisco are relatively mainstream manufacturers, while North Yitong /F-tone Networks focuses on cost performance.