SBIR-STTR Award

The emerging class of epsilon-near-zero materials (ENZ) is a promising candidate for use in non-linear optical applications including optical limiting. The Army is soliciting proof-of-concept efforts to investigate whether limiting devices can be fabricated based on this novel class of materials. Third Floor Materials, Inc. proposes a feasibility study of such a limiting device, based on its expertise surrounding the highest performing ENZ material in the mid-wave IR (3-5 µm wavelength), donor-doped CdO. The proposed effort seeks to demonstrate the Army’s required specifications (one order of magnitude modulation depth, linear transmission) by coupling the non-linear properties of CdO with a resonant antenna system. Using this coupled-resonator approach, the combined optical properties of the system will leverage CdO’s demonstrated non-linear optical effects. The effort will combine FDTD simulations with experimentally derived non-linear optical properties of CdO. The proposal includes simulation methods to capture the energy dependent optical behavior of candidate structures and optimize the device characteristics, particularly modulation depth and linearity of transmission. This approach will allow efficient screening of device structures based on real-world optical properties. If successful, a potential Phase 1 option effort will experimentally demonstrate a proof-of-concept device.

The emerging class of epsilon-near-zero (ENZ) materials are promising candidates for non-linear optical (NLO) applications like optical limiting. In ENZ materials, large NLO effects, particularly in the infrared, have been demonstrated at much lower optical fluxes than have been shown in traditional NLO materials. The effect has been linked to the unique electric field concentration that occurs in ENZ materials near their zero permittivity frequency. In addition to producing extraordinary NLO effects, many groups have demonstrated that the property change is an ultrafast (fs) phenomena. These shared properties, ultrafast response and low threshold for NLO change, lend themselves to use in optical limiting applications, where ultrashort pulsed lasers are becoming an evermore concerning threat. During a recent Phase 1 feasibility study, Third Floor Materials demonstrated that the NLO effect in ENZ materials designed to operate in the MWIR, could be effectively leveraged by combining them with optical antenna structures. The antenna structure allows coupling to the ENZ mode from free-space and concentrates electric field intensity within the ENZ material further augmenting the NLO effect. Some of these hybrid meta-material/ENZ structures showed better than 2 orders of magnitude limiting at a 3 µm wavelength. To extend the usefulness of the hybrid antenna/ENZ approach, Third Floor Materials will pursue two principle objectives in the Phase 2 follow on program; an effort to broaden the response of the ENZ limiting structure across the entire MWIR (3-5 µm) and a parallel thrust designed to increase ‘off-state’ transmission. Similar to the Phase 1 study, our team will use real, measured ENZ material properties to develop a NLO FDTD model of an ENZ limiting system – and build a prototype for Army AvMC evaluation. We believe that the proposed approach will significantly expand Army understanding of ENZ materials and providing a compelling early use case in the form of an ultra-fast optical limiting solution.