All-Passive Nonreciprocal Power Limiters

OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Integrated Sensing and Cyber; Quantum Science; Advanced Materials; Microelectronics The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), 22 CFR Parts 120-130, which controls the export and import of defense-related material and services, including export of sensitive technical data, or the Export Administration Regulation (EAR), 15 CFR Parts 730-774, which controls dual use items. Offerors must disclose any proposed use of foreign nationals (FNs), their country(ies) of origin, the type of visa or work permit possessed, and the statement of work (SOW) tasks intended for accomplishment by the FN(s) in accordance with the Announcement. Offerors are advised foreign nationals proposed to perform on this topic may be restricted due to the technical data under US Export Control Laws. OBJECTIVE: Design, fabricate and characterize a new category of optical nonlinear metasurfaces operating as asymmetric power limiters. Such devices will be important for the protection of sensitive equipment from external interference, in particular waves from different directions in free space. The use of nonlinear effects will allow the proposed devices to be all passive, without the need of external biasing fields or signals, in contrast to other approaches for designing nonreciprocal devices, which are based on magnetic biasing or modulation with electrical signals. Furthermore, they will be ultra-thin and light-weight, making them suitable for mobile applications. The nonreciprocal response will provide an isolation larger than 10 dB, an insertion loss in the order of 1 dB over a large range of input powers and angles of incidence. DESCRIPTION: Nonreciprocal devices are very important components for civilian and defense communication systems, in order to protect sensitive components from external interferences. Such devices are conventionally realized through magnetic materials under static magnetic fields, but this approach is accompanied by several problems, including the scarcity of magnetic materials, the large size and weight of the magnets required for the magnetic biasing and the incompatibility of magnetic materials with integration technologies. For this reason, the design of magnet-free nonreciprocal devices has recently attracted a lot of attention, with the majority of proposed approaches based on spatiotemporal modulation of appropriately designed circuits. However, these approaches often require external modulation sources, which may not be an option for applications where availability to external power supply is limited. For these cases, reciprocity can be broken by combining spatial asymmetries with nonlinear responses. In particular, including nonlinear effects in asymmetric resonators, it is possible to achieve very large transmission from one side and very small from the opposite one for sufficiently strong input signals. This call explores the application of these concepts to metasurfaces for free space isolation, protection and radiation hardening, and power limiting, operations of great importance for DoD applications. PHASE I: Awardee(s) will explore the modelling and designing of nonlinear optical metasurfaces operating as free-space asymmetric power limiters. Analytical models to understand the underlying physics and full-wave simulations to develop optimum designs will be carried forward. Phase I awards should include preliminary fabrication experiments that demonstrate the feasibility of the approach and benchmarks on the improved properties. PHASE II: In the Phase II effort, the design and fabrication process identified in Phase I will be evolved towards improving several metrics of the devices, including bandwidth, insertion loss, nonreciprocal power range and incident angles range. Towards this direction, different approaches, including multi-layer and multi-resonant metasurfaces will be explored, and realization of an optimal prototype will be carried forward. PHASE III DUAL USE APPLICATIONS: The Phase III work will demonstrate the repeatability of the fabrication process and the feasibility of the proposed approach for large scale fabrication. A partnership with industry to commercialize the technology will be created. Beside the applications across all branches of the armed forces, civilian applications of this technology will be explored, including communication systems, laser protection, etc. Furthermore, exploration of these concepts for the realization of broadband and broad-angle power limiter metasurfaces will be investigated. REFERENCES: Lax B. & Button K. J. Microwave ferrites and ferrimagnetics (McGraw-Hill, 1962). Estep, N., Sounas, D. L., Soric, J. & Alu, A. Magnetic-free non-reciprocity based on parametrically modulated coupled-resonator loops, Nature Physics 10, 923-927 (2014). J. Soric, D. L. Sounas, and A. Al , Non-Magnetic, Non-Linear Radio-Frequency Isolator with Large Isolation and Small Insertion Loss, in 2016 IEEE International Symposium on Antennas and Propagation and USNC-URSI Radio Science Meeting, Fajardo, Puerto Rico, June 26 - July 1, 2016.; KEYWORDS: Power limiter; nonreciprocal; chip scale; nonlinearity; modulation; isolation; interference