A terahertz-bandwidth non-magnetic isolator

Wideband optical isolators are critical for the robust operation of virtually all photonic systems. However, they have been challenging to realize in the integrated form due to the incompatibility of magnetic media with these circuit technologies. Here we present the first-ever demonstration of an integrated non-magnetic optical isolator with terahertz-level optical bandwidth. The system comprises two acousto-optic beamsplitters that create a non-reciprocal multimode interferometer exhibiting high-contrast, non-reciprocal light transmission. We dramatically enhance the isolation bandwidth of this system by precisely balancing the group delays of the paths of the interferometer. Using this approach, we demonstrate integrated non-magnetic isolators with an optical contrast as high as 24.5 dB, insertion losses as low as −2.16 dB and optical bandwidths as high as 2 THz (16 nm). We also show that the centre frequency and direction of optical isolation are rapidly reconfigurable by tuning the relative phase of the microwave signals used to drive the acousto-optic beamsplitters. With their complementary metal–oxide–semiconductor compatibility, wideband operation, low losses and rapid reconfigurability, such integrated isolators address a key barrier to the integration of a wide range of photonic functionalities on a chip.