Magnetic-free non-reciprocal and topological integrated microwave components

OBJECTIVE: Design, fabricate, and demonstrate a new category of subwavelength non-reciprocal circulators, including arrays of them to form photonic topological insulators, operating at microwave frequencies without the need of magnetic materials and/or magnetic bias, which are compatible with integrated circuits technology. In contrast to conventional magnetic-based non-reciprocal components, the proposed components will be based on suitably tailored time-varying networks, they shall be fully integrable within the same substrate of common microwave integrated components, such as filters, mixers, oscillators, etc..., they should be deeply subwavelength in size, and at the same time they should achieve an isolation of at least 20 dB, an insertion loss lower than 1 dB and ensure broadband operation, spanning an octave or more. Arrays of these elements to realize topological insulators should guarantee reconfigurability and inherent robustness to disorder and imperfections, ideally suited for advanced 5G and 6G wireless systems. DESCRIPTION: Non-reciprocal microwave components are the basis of many sensing, defense and communication systems. Their functionality is almost exclusively achieved through magnetic materials, which are incompatible with integrated technology [1]. Recent work has shown that biasing with EM vectors (other than the magnetic field) which are odd under time reversal, such as the electric current [2] or the linear momentum [3], can also produce a non-reciprocal effect, relaxing the requirements on magnetic materials. These alternatives, however, are currently limited by typically weak effects, requiring large volumes of operation, and in some instances large power consumption and/or narrow bandwidths. Recent efforts have shown that temporal variations synthesizing angular momentum bias can actually overcome these problems [4-5], and realize broadband, ultracompact nonreciprocal devices. The ultimate goal of this project is to fabricate and demonstrate microwave devices exhibiting strong non-reciprocal responses in a deeply subwavelength scale, without the need of magnetic materials and with adequate bandwidth for the majority of practical applications. The fabrication methods must allow realization at low cost with conventional integrated technology. We envision arrays of these elements to implement true-time-delay (TTD) beamforming networks in which reconfigurable signal routing and wideband nanosecond-scale delays enable TTD-based beam forming of ultra-wideband signals spanning DC to GHz frequencies. We also envision arrays of integrated nonreciprocal elements to realize full-duplex phased-arrays in which programmable delays within each element enable independent phased-array beam forming in transmit- and receive-modes, and whose isolation features enable full-duplex simultaneous transmission and reception of broadband radio-wave signals. These devices will enable highly reconfigurable antenna systems for e.g. radar and communication systems, enhancing the spectrum efficiency, and drastically reducing weight, cost and avoiding the need of scarce magneto-optical materials. PHASE I: In the Phase I effort, a complete design of the proposed non-reciprocal components will be formulated and fabrication procedures will be developed. The proposed designs should include realistic layouts of the proposed integrated circuitry. Full-wave / circuit simulations should be based on accepted analytical methods or rigorous numerical models. Phase I efforts should also include designs of arrays of these elements to realize topological insulators with robust and reconfigurable nonreciprocal signal transport. PHASE II: In the Phase II effort, the design and fabrication process identified in Phase I will be evolved towards the integration of the proposed non-reciprocal components in realistic circuits, and evaluation of their performance. The robust response of the circulators and topological insulators under harsh environmental conditions and their integration in electronic circuits should also be verified. PHASE III DUAL USE APPLICATIONS: The Phase III work will demonstrate the repeatability of the fabrication process and the system integrability in true-time delay and advanced wireless antenna systems. Besides the applications across all branches of the armed forces, civilian applications of this technology will be explored, including communication systems, high-fidelity circuitry, etc. REFERENCES: [1] Lax B. & Button K. J. Microwave ferrites and ferrimagnetics (McGraw-Hill, 1962). [2] Kodera, T., Sounas, D. L. & Caloz, C. Artificial Faraday rotation using a ring metamaterial structure without static magnetic field. Appl. Phys. Lett. 99, 03114 (2011). [3] Yu, Z. & Fan, S. Complete optical isolation created by indirect interband photonic transitions. Nature Photonics 3, 91-94 (2009). [4] Sounas, D. & Al , A. Non-Reciprocal Photonics Based on Time Modulation, Nature Photonics 11,774-783 (2017) [5] Kord, A., Sounas, D. & Al , A. Magnet-Free Microwave Nonreciprocity, Proceedings of IEEE 108, 1728-1758 (2020) KEYWORDS: Magnetic-free, Non-reciprocal, Topological integrated microwave components