First demonstration of lithium niobate photonic chip for dense wavelength-division multiplexing transmitters

Modern optical communications rely heavily on dense wavelength-division multiplexing (DWDM) technology because of its capability of significantly increasing transmission channels. Here, we demonstrate, for the first time to the best of our knowledge, a compact photonic chip for DWDM transmitters on lithium-niobate-on-insulator (LNOI) by introducing the array of 2×2 Fabry–Perot (FP) cavity electro-optic (EO) modulators. A four-channel LNOI photonic chip for DWDM is designed and realized with a channel spacing of 1.6 nm (which is the narrowest one reported until now for LNOI optical transmitters), exhibiting a total excess loss of 1.3 dB and high 3-dB EO bandwidths of >67 GHz for all channels. Specifically, these four 2×2 FP cavities are designed with broadened LNOI photonic waveguides in the cavity sections, and they are placed very closely on the chip so that their resonance wavelengths are aligned precisely with the desired channel-spacing of ∼1.6 nm. Finally, the generation of 4×80-Gbps on–off keying and 4×100-Gbps PAM4 signals is demonstrated successfully with four channels, and the power consumption is as low as ∼5.1 fJ/bit. The present photonic chip has a compact footprint of about 0.78 mm×0.58 mm, showing great potential to work with more than four channels and to be very useful for future large-capacity optical links.