A Terahertz Bandwidth Nonmagnetic Isolator
- Haotian Cheng
- Yishu Zhou
- Freek Ruesink
- Margaret Pavlovich
- Shai Gertler
- Andrew L. Starbuck
- Andrew J. Leenheer
- Andrew T. Pomerene
- Douglas C. Trotter
- Christina Dallo
- Matthew Boady
- Katherine M. Musick
- Michael Gehl
- Ashok Kodigala
- Matt Eichenfield
- Anthony L. Lentine
- Nils T. Otterstrom
- Peter T. Rakich
Integrated photonics could bring transformative breakthroughs in computing,
networking, imaging, sensing, and quantum information processing, enabled by
increasingly sophisticated optical functionalities on a photonic chip. However,
wideband optical isolators, which are essential for the robust operation of
practically all optical systems, have been challenging to realize in 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 is comprised of two acousto-optic frequency-shifting beam splitters
which create a non-reciprocal multimode interferometer exhibiting
high-contrast, nonreciprocal light transmission. We dramatically enhance the
isolation bandwidth of this system by precisely dispersion balancing the paths
of the interferometer. Using this approach, we demonstrate integrated
nonmagnetic isolators with an optical contrast as high as 28 dB, insertion
losses as low as -2.16 dB, and optical bandwidths as high as 2 THz (16 nm). We
also show that the center frequency and direction of optical isolation are
rapidly reconfigurable by tuning the relative phase of the microwave signals
used to drive the acousto-optic beam splitters. With their CMOS compatibility,
wideband operation, low losses, and rapid reconfigurability, such integrated
isolators could address a key barrier to the integration of a wide range of
photonic functionalities on a chip. Looking beyond the current demonstration,
this bandwidth-scalable approach to nonmagnetic isolation opens the door to
ultrawideband (>10 THz) isolators, which are needed to shrink state-of-the-art
imaging, sensing, and communications systems into photonic integrated circuits.