We propose and investigate the performance of integrated photonic isolators
based on non-reciprocal mode conversion facilitated by unidirectional,
traveling acoustic waves. A triply-guided waveguide system on-chip, comprising
two optical modes and an electrically-driven acoustic mode, facilitates the
non-reciprocal mode conversion and is combined with modal filters to create the
isolator. The co-guided and co-traveling arrangement enables isolation with no
additional optical loss, without magnetic-optic materials, and low power
consumption. The approach is theoretically evaluated and simulations predict
over 20 dB of isolation and 2.6 dB of insertion loss with 370 GHz optical
bandwidth and a 1 cm device length. The isolator utilizes only 1 mW of
electrical drive power, an improvement of 1-3 orders of magnitude over the
state-of-the-art. The electronic driving and lack of magneto-optic materials
suggest the potential for straightforward integration with the drive circuitry,
possibly in monolithic CMOS technology, enabling a fully contained `black box'
optical isolator with two optical ports and DC electrical power.Comment: 14 pages, 5 figures, 1 table. Relies on an acoustic-optical
multiplexer introduced in arXiv:2007.11520, which has been separated out in
this updated version of the paper for clarity. Additionally, this updated
version included additional discussion of design considerations of the
isolato
