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Electromagnetic-Attack-Resistant Electro-Optic Modulator


OBJECTIVE: Develop and demonstrate engineering prototypes of a wideband, high-sensitivity, high RF power handling optical modulator suitable for use in low-noise microwave photonic links associated with military and commercial antenna applications. DESCRIPTION: Electronic systems connected to RF and microwave antennas by metal connections cannot be fully shielded from HPM and EMP signals because there must be a continuous path from the antenna to the system for the desired signals to be received. Current electronic protection devices and circuits have issues associated with insertion loss, bandwidth, turn-on/turn-off times, power handling, and lifetime. Unlike any electronic protection devices, photonics can provide complete isolation of electronics from the antenna via the electrical-to-optical and then the optical-to-electrical conversion processes associated with RF photonic transmission links. However, existing high-speed electro-optic modulators can be damaged by extremes of current and voltage [1]. A modulator that can withstand the power levels coupled into it by an antenna during an electromagnetic attack is required. The exact power and time profile is highly dependent upon the type of antenna and the type of attack, but for this SBIR topic a nominal goal is to withstand a 1-second burst of 3-microsecond pulses with a 0.1% duty cycle at 0.1 to 10 GHz center frequency, with 10 kW peak power coupled into the modulator by means of an appropriate RF coaxial cable. Because an electronic low-noise amplifier (LNA) cannot be interposed between the antenna and optical modulator in this application, the wideband modulator must have optical power handling, insertion loss and switching voltage/efficiency characteristics that support a photonic link with a noise figure<10 dB at up to 10 GHz [2]. In addition, it is desirable that the modulator recover to normal operation quickly after the end of the pulse train (<<1 mS). State of the Art: The primary electronic protection device against electromagnetic attack is a plasma limiter. These devices still provide a continuous electrical path from the antenna to the electronics so that there is a possibility of damage if the limiter fails during the years it is installed but untested. They are also susceptible to damage at high power levels and the leading edge of a pulse leaks through. Existing high-speed optical modulators can be damaged by pulsed power levels as low as 100W, making them unsuitable as Electronic Protection devices. PHASE I: Develop the concept and design for an electro-optic modulator and RF photonic link that can meet the cited performance levels. Validate the design with rigorous modeling and/or simple proof-of-concept experiments. PHASE II: Develop, construct, test, and demonstrate an optical modulator and prototype RF photonic link that meets the cited performance goals. Multiple copies of the electromagnetic-attack-resistant front-end component(s) (e.g., the modulator) should be tested against a simulated attack (somewhere in the 0.1-10 GHz range) to provide, at least, a small set of statistical data. Delivery of an optical modulator prototype for independent government testing is required in this phase. PHASE III: Build field-deployable RF photonic link prototypes and demonstrate them in operational environments against a variety of electromagnetic attack types. Transition the demonstrated technology to dual-use production and products. PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: The electromagnetic-attack-resistant RF photonic links developed under this SBIR topic can be used in any military or civilian antenna system where an RF or microwave receiver system must be protected from potential attack [3]. Critical civilian systems such as cellular communication infrastructures are candidates for these products. REFERENCES: 1. Bucholtz, F., Villarruel, C.A., Knapp, P.F., Shue, J., Andreadis, T.D., Schermer, R.T., Gil Gil, and J., Williams, K.J. 2009."Susceptibility of Lithium Niobate Modulator to High Power Microwave Pulses."Electronics Letters, vol. 45, pp. 272-273. DOI:10.1049/el:20090009. 2. Ackerman, E.I., G.E., Burns, W.K., Campbell, J.C., Cox, C.H., Ning Duan, Prince, J.L., Regan, M.D., Roussell, H.V. 2007."Signal-to-Noise Performance of Two Analog Photonic Links Using Different Noise-Reduction Techniques."IEEE/MTT-S International Microwave Symposium Technical Digest, pp. 51-54. DOI: 10.1109/MWSYM.2007.380216. 3. Report of the Commission to Assess the Threat to the United States from Electromagnetic Pulse (EMP) Attack: Critical National Infrastructures, April 2008.
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