First Realization of a Three-Channel Lithium-Niobate Photonic Filter for 50G Passive Optical Networks

A high-performance lithium-niobate photonic filter for 50G passive optical networks is proposed and demonstrated for the first time. The present photonic filter consists of three wavelength channels of 1270, 1300, and 1342 nm, realized by introducing two-mode (de)multiplexers as well as multimode waveguide gratings (MWGs) in cascade. In experiments, the presented photonic filters are made of a 400 nm-thick X-cut lithium-niobate-on-insulator, exhibiting box-like spectral responses with ultralow excess losses of <0.2 dB for the wavelength channels. The crosstalk between the two channels of 1270/1300 is as low as ∼−30 dB and the measured sidelobe suppression ratio for the channel of 1342 nm is about 20 dB. Furthermore, all the channels have achieved the channel bandwidths and the center wavelengths as desired. In addition, the temperature sensitivity of the channel wavelength is as low as 35 pm/°C and the measured eye diagrams are open with high quality for 50 Gbps data. The presented high-performance lithium-niobate photonic filter can work with higher bit rates and can also be integrated easily with other lithium-niobate photonic devices, such as optical modulators, showing great potential for high-capacity data transmissions.