Electrically Controlled On-Chip Optical Isolators for Telecommunication Band Photonic Integrated Circuits

ĀOur approach will utilize an asymmetric acoustic pump, consisting of an interdigitated transducer on a piezoelectric material (lithium niobate), that enhances optomechanical coupling between two optical modes in a photonic ring resonator via phonon scattering. Non-reciprocity arises from the fact that efficient phonon-enhanced optomechanical coupling only happens when the scattering process is phase-matched, which is only satisfied for one propagation direction due to the asymmetry of the pump. Isolation is achieved by driving the pump in the strong optomechanical coupling regime to induce phonon-mediated Autler-Townes splitting (p-ATS), which produces strong unidirectional absorption for light critically coupled to one of the p-ATS dressed states. The result is electrically tunable isolation, high peak contrast (>39dB), and low insertion loss (<1 dB). This approach has been demonstrated in part by our consultant, Gaurav Bahl. However, a crucial disadvantage of that design is the narrow bandwidth. Therefore, we propose to increase the operational bandwidth during our Phase I efforts by leveraging the frequency tunability and exceptionally low insertion loss of the existing design. We will fabricate multiple isolators in a cascade configuration and detune the frequency of each isolator electrically via the acoustic pump power. We expect to achieve 30 dB isolation contrast across a bandwidth of >30 MHz while simultaneously meeting the desired insertion loss (< 3 dB) specified in the solicitation, although higher bandwidth is possible at the expense of more insertion loss. Moreover, we intend to reduce the die area by optimizing the dimensions of the optical resonator and reduce power consumption by increasing the conversion efficiency of the pump with an acoustic resonator. Furthermore, we plan to develop a material architecture that is compatible with silicon photonics by wafer bonding lithium niobate on silicon-on-insulator waveguides encased in silica. Phase I efforts will be focused on simulating the acoustic mode displacement from the pump to determine the feasibility of reaching the p-ATS regime with this architecture. If awarded, our Phase I Option efforts will be directed towards developing fabrication protocols for wafer bonding in preparation for Phase II, for which we anticipate optimizing both architectures to determine commercial viability. Both Phase I and Phase I Option efforts will be performed by Digital Optics Technologies, Inc. and the subcontractor, Northwestern University, with consultation from Gaurav Bahl.