OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Integrated Sensing and Cyber OBJECTIVE: Develop mission capability of secure free-space mid-wave infrared communications that optimize data transfer rates and bit error rate (BER) while achieving physical-layer security such that eavesdroppers cannot decipher intercepted messages. DESCRIPTION: Free-space optical (FSO) communication in the mid-wave infrared (MWIR) allows the transmission of signal in non-optimal atmospheric conditions with the presence of optical obscurants such as fog, rain or snow, taking advantage of the low-absorption windows in the 3 5 m and 8 12 m spectral ranges. Quantum Cascade Lasers (QCLs) have attained performance levels, which make them attractive as transmitter sources for FSO communication. The extremely fast carrier dynamics and pico-second scale upper-level photon lifetimes present the potential for high bandwidth with relatively low-temperature dependence and a small-package footprint. Semiconductor lasers with distributed feedback have shown strong longitudinal-mode selection, and are ideal candidates for communication applications. Although the narrow-beam, direct link between the FSO transmitter and receiver makes it more difficult to intercept an FSO signal than RF-wireless communication, the FSO is still not impervious to interception. Advances in high-speed computing threaten the ability of data encryption to prevent deciphering of intercepted messages. Additional measures to ensure data security are needed when absolute security is a requirement. Various methods of securing data at the physical level have been studied extensively for telecom lasers and wavelengths, but while these methods may conceivably be extended to mid-IR QCLs, the device dynamics for QCLs are much more complex. One method for secure communication is using lasers operating within the chaotic regime. Researchers using chaos in the fiber-optic telecom wavelength range have been able to theoretically show data transfer rates on the order of 4 10 Gbit/s while using chaos [Refs 1, 2]. Recent work [Refs 3-6] has shown that, similar to their interband (diode) semiconductor laser counterpart, QCLs exhibit chaotic behavior in both the temporal and frequency domains. However, this work has shown a relatively high BER for larger data transfer rates owing to a reduced correlation between the leader and follower lasers. In interband devices, the linewidth enhancement factor, which can influence chaotic behavior, is dependent on the feedback ratio, as well as the drive current and output power [Ref 7]. Further work is needed to control the onset of chaos in QCLs and demonstrate the feasibility of a QCL-based communication link using chaos to ensure security of high-data rate communications. For FSO communication over longer distances and in adverse weather conditions such as rain or haze, high-power MWIR sources are required. Furthermore, the degree of chaos is expected to increase with output power since for QCLs it has been found [Ref 8] that the linewidth enhancement factor increases as the drive current above threshold increases. Characterization of chaos at high-output powers will be necessary for the development and use of secure mid-IR FSO communications. To ensure security, an eavesdropper BER can be used as guidance with values above 25% [Ref 9]. PHASE I: Establish the feasibility of the proposed method to improve chaos bandwidth beyond 100 MHz and link distance beyond 100 m from an MWIR source operating within the ~ 10 m low-absorption window. Support the analysis with QCL experimental data at any wavelength. Design a leader and follower laser to meet Phase II goals. The Phase I effort will include prototype plans to be developed under Phase II. PHASE II: Demonstrate a transmitter and receiver using chaos in the 10 m wavelength region to mask a signal with a BER of less than 4% and a data transfer rate greater than 100 Mbit/s at a link distance > 1 km. An eavesdropper should have an error rate of > 25%. PHASE III DUAL USE APPLICATIONS: Develop a prototype based on the design from Phase II for transition to an operational test asset, which will be determined in Phase III. Issues related to test platform integration will be addressed in cooperation with the Government. Focus on risk management and mitigation (versus the test plan and schedule). Other Government applications within the Drug Enforcement Agency and the Intelligence Community for use with non-RF, covert communication under adverse weather conditions are also considerations. Private sector use in telecommunication and local, urban communication (communication nodes line of sight) would benefit from this technology due to its high-security and high-bandwidth capabilities even in adverse weather conditions. REFERENCES: 1. Sanchez-Diaz, A., Mirasso, C. R., Colet, P., & Garcia-Fernandez, P. (1999). Encoded Gbit/s digital communications with synchronized chaotic semiconductor lasers. IEEE journal of quantum electronics, 35(3), 292-297. https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=748833&casa_token=JYXvDVKW-oIAAAAA:PXYM-6EjBFoZuDzCMpol3WrKfK6cta1WEdnjDocHPCoYynHnasavbzUKcFMYQPsMQ55oEzUs&tag=1 2. Yang, Z., Yi, L., Ke, J., Zhuge, Q., Yang, Y., & Hu, W. (2020). Chaotic optical communication over 1000 km transmission by coherent detection. Journal of Lightwave Technology, 38(17), 4648-4655. https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=9091335&casa_token=Fzy7w4DPJ9YAAAAA:0Tx7Htbet_1WTr7cxty7OYhYJ8TopKj8kzUIm0ht6Qyl9Zq3yzxMIsT9NSdfaet1ukkW513l 3. Jumpertz, L., Carras, M., Schires, K., & Grillot, F. (2014). Regimes of external optical feedback in 5.6 m distributed feedback mid-infrared quantum cascade lasers. Applied Physics Letters, 105(13), 131112. https://perso.telecom-paristech.fr/grillot/60.pdf 4. Jumpertz, L., Schires, K., Carras, M., Sciamanna, M., & Grillot, F. (2016). Chaotic light at mid-infrared wavelength. Light: Science & Applications, 5(6), e16088-e16088. https://www.nature.com/articles/lsa201688.pdf?origin=ppub 5. Spitz, O., Wu, J., Herdt, A., Carras, M., Els sser, W., Wong, C. W., & Grillot, F. (2019). Investigation of chaotic and spiking dynamics in mid-infrared quantum cascade lasers operating continuous-waves and under current modulation. IEEE Journal of Selected Topics in Quantum Electronics, 25(6), 1-11. https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=8815933&casa_token=bmv4S9nQZJ4AAAAA:0TnT1oFXIQZFWYqh4_umcAbtsJ1rQYBTA-vigD5GNwIPK0_6M_z7t1uYHBPyBXEmEnTgbC7j 6. Spitz, O., Herdt, A., Wu, J., Maisons, G., Carras, M., Wong, C. W., Els er, W., & Grillot, F. (2021). Private communication with quantum cascade laser photonic chaos. Nature communications, 12(1), 1-8. https://www.nature.com/articles/s41467-021-23527-9.pdf?origin=ppub 7. Takiguchi, Y., Ohyagi, K., & Ohtsubo, J. (2003). Bandwidth-enhanced chaos synchronization in strongly injection-locked semiconductor lasers with optical feedback. Optics letters, 28(5), 319-321. http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.1084.7122&rep=rep1&type=pdf 8. Jumpertz, L., Michel, F., Pawlus, R., Els sser, W., Schires, K., Carras, M., & Grillot, F. (2016). Measurements of the linewidth enhancement factor of mid-infrared quantum cascade lasers by different optical feedback techniques. AIP Advances, 6(1), 015212. https://aip.scitation.org/doi/full/10.1063/1.4940767 9. Bogris, A., Argyris, A., & Syvridis, D. (2010). Encryption efficiency analysis of chaotic communication systems based on photonic integrated chaotic circuits. IEEE journal of quantum electronics, 46(10), 1421-1429. https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=5565358&casa_token=OOOMv4lQJm8AAAAA:3cLWbaq1nTCPEdFTeDacRI-t14rfpDUdzyis78GeZlPpYYpPn8cTmUywl0N8GTKTbSG0suLQ KEYWORDS: Secure; mid-wave; infrared; free-space; optical communication; chaotic laser Mode
