Ultrabroadband low-crosstalk dense lithium niobate waveguides by Floquet engineering

Integrated photonic chips have gradually become a significant option for information transmission and processing, in which the integration density will play an increasingly important role similar to that witnessed in integrated circuits. To date, great efforts have been made for silicon-on-insulator wafers to achieve dense integration with low crosstalk, although it remains quite challenging in the emerging lithium-niobate-on-insulator (LNOI) platform. Here, we report a strategy utilizing Floquet-mode-index modulation to realize broadband zero crosstalk with minimal impact on other performance metrics on the LNOI chips. The underlying physics of zero crosstalk is attributed to the collapse of the Floquet quasienergy, which is further experimentally verified by ultrabroadband low-crosstalk transmissions with low excess loss. Moreover, we demonstrate broadband eight-channel light transmissions in a compact LNOI waveguide array, showing an advantage over the conventional ones in comparison. Our work provides an alternative approach for improving the integration density of on-chip photonic circuits, opening up different possibilities for dense waveguide applications in the promising LNOI platform.