Microwave photonic self-interference cancellation system using a slow and fast light delay line

We demonstrate a microwave photonic system to perform wideband, radio-frequency self-interference cancellation. The tunable optical time delay is implemented using a novel semiconductor slow and fast light delay line that enables fast electrical control. Introduction. By 2018, mobile data traffic is expected to increase by an enormous 1100% [1]. Such exponential growth in the demand for bandwidth requires, new, highly efficient methods to allocate and manage radio-frequency (RF) spectrum. Self-interference cancellation (SIC) is a method that not only recovers valuable spectrum real estate, but also has a tremendous impact on future wireless networks [2]. Self-interference occurs when a system simultaneously transmits and receives on the same channel; the system naturally and strongly interferes with itself. Cancelling self-interference enables key spectrum-saving technologies such as in-band full-duplex communications, which immediately doubles the throughput of half-duplex systems. SIC also alleviates pesky global spectrum management issues, and is essential in applications such as military jamming [2]. Most SIC systems are comprehensive, involving antenna, analog, and digital cancellation [3-6]. Electrical analog cancellation uses RF components and phase shifters, which are inherently frequency specific. As a result, electronic SIC typically has constrained bandwidths (~20 MHz) [3,4,6]. Microwave photonics is a natural alternative to bandwidth-limited RF electronics: optics is wideband, immune to noise, and precise [7]. Microwave photonic SIC systems have demonstrated >30 dB analog cancellation across 40 MHz bandwidth with widely tunable center frequency [8]. However, the lack of a fast ( light delay line for quickly tunable optical delay. The system can achieve ~40 dB interference cancellation across ~40 MHz bandwidth. The slow and fast light delay line is electrically controlled, making it suitable for fast convergence and locking of the system to an interference minimum, neutralizing environmental fluctuations. In addition, because all the components are semiconductor based, such a system also has potential to be integrated. References [1] “Cisco Visual Networking Index: Global Mobile Data Traffic Forecast Update, 2013-2018,” Cisco Systems, Inc. Feb. 5, 2014. [2] S. Hong et al., “Applications of Self-Interference Cancellation in 5G and Beyond.” IEEE Commun. Mag., vol. 52, pp. 114–121, Feb. 2014. [3] J. I. Choi et al., “Achieving Single Channel, Full Duplex Wireless Communication,” in MobiCom’10, Chicago, Il, 2010, pp. 1-12. [4] M. Jain et al., “Practical, Real-time, Full Duplex Wireless,” in MobiCom’11, Las Vegas, NV, 2011, pp. 301-312. [5] D. Bharadia, E. McMilin, and S. Katti, “Full Duplex Radios,” in SIGCOMM’13, Hong Kong, China, 2013, pp. 375-386. [6] M. Duarte and A.Sabharwal, “Full-Duplex Wireless Communications Using Off-The-Shelf Radios: Feasibility and First Results,” in 2010 Conf. Record of the 44 Asilomar Conf. on Signals, Systems, and Computers, Pacific Grove, CA, 2010, pp.1558-1562. [7] J. Capmany, B. Ortega, and D. Pastor, “A tutorial on microwave photonic filters,” J. Lightwav. Technol., vol. 24, pp. 201-229, Jan. 2006. [8] M. Chang, M. Fok, A. Hofmaier, and P. R. Prucnal, “Optical Analog Self-Interference Cancellation Using Electro-Absorption Modulators,” IEEE Microw. Compon. Lett., vol. 23, pp. 99-101, Feb. 2013. [9] M. Chang and P. R. Prucnal, “Amplitude-invariant fast Light in a Semiconductor Optical Amplifier for Microwave Photonics,” in CLEO: 2013, San Jose, CA, 2013, paper QM4E.3. [10] M. S. Bigelow, N. N. Lepeshkin, and R. W. Boyd, “Observation of Ultraslow Light Propagation in a Ruby Crystal at Room Temperature,” Phys Rev. Lett., vol. 90, no. 11, 2003. DOI: 10.1103/PhysRevLett.90.113903. Figure 2. Experimental results. (a) Interference cancellation achieved for six different states of the slow and fast light delay line. More negative values correspond to greater cancellation. (b) Relative delay shift and (c) amplitude shift incurred under the six states in (a).