Research Projects
Here is a high-level summary of my doctoral research projects and associated publications.
Turbulence-Resilient Free-Space-Optical Communications
Compared with radio, free-space optical (FSO) communications have the potential advantages of higher data capacity and lower probability of interception. However, FSO systems are highly vulnerable to atmospheric turbulence effects, especially for complex modulation formats involving both amplitude and phase encoding, such as quadrature amplitude modulation (QAM). We demonstrated pilot-assisted self-coherent approach to enable turbulence-resilient FSO communications with automatic turbulence degradation compensation.
Related Publications:
- R. Zhang, N. Hu, H. Zhou, K. Zou, X. Su, Y . Zhou, H. Song, K. Pang, H. Song, A. Minoofar, Z. Zhao, C. Liu, K. Manukyan, A. Almaiman, B. Lynn, R. W. Boyd, M. Tur, and A. E. Willner, “Turbulence-Resilient Pilot-Assisted Self-Coherent Free-Space Optical Communications Using Automatic Optoelectronic Mixing of Many Modes,” Nature Photonics, vol: 15, no. 10, pp: 743-750, 2021.
- [Invited] R. Zhang, X. Zhou, H. Song, H. Zhou, M. Tur, and A. E. Willner, “Automatic Turbulence Resilience in Pilot-Assisted Self-Coherent Free-Space Optical Communications,” IEEE/Optica Journal of Lightwave Technology, vol: 42, no. 3, pp: 3760 - 3769, 2024.
- [Invited] R. Zhang, X. Su, H. Song, H. Zhou, M. Tur, and A. E. Willner, “Automatic Turbulence Resilience in Self-Coherent Free-Space Optical Communications,” IEEE/Optica Conference on Optical Fiber Communications (OFC), paper M1J.4, San Diego, CA, USA, 2023.
- [Invited] R. Zhang and A. E. Willner, “Turbulence-Robust Free-Space Optical Transmission Assisted by a Pilot Beam,” Advanced Photonics Congress, paper NeM4B.3, Busan, Republic of Korea, 2023.
Mode-Division-Multiplexed Optical Communications in Random Media
Spectral efficiency and data capacity of optical communications (free-space system or fiber-system) can be enhanced N-fold by mode-division-multiplexing (MDM), in that each mode can carry an independent data stream and differnet spatal modes are orthogonal. Such orthogonal modal sets can be chosen in different modal basis, such as Laguerre-Gaussian, Hermite-Gaussian, and Linearly-polarized spatial modes. Communication media can be in the form of random nature, of which refractive index can interact with and distort the wavefront of spatial modes. We explored light-medium interaction and demonstrated enhanced optical MDM transmission in different random media (atmospheric turbulence, turbudity, and multi-mode fiber).
Related Publications:
- R. Zhang, H. Song, H. Song, Z. Zhao, G. Milione, K. Pang, J. Du, L. Li, K. Zou, H. Zhou, C. Liu, K. Manukyan, N. Hu, A. Almaiman, J. Stone, M. J. Li, B. Lynn, R. W. Boyd, M. Tur, and A. E. Willner, “Utilizing Adaptive Optics to Mitigate Intra-Modal-Group Power Coupling of Graded-Index Few-Mode Fiber in a 200-Gbit/s Mode-Division-Multiplexed Link,” Optics Letters, vol: 45, no. 12, 2020.
- R. Zhang, H. Song, Z. Zhao, H. Song, J. Du, C. Liu, K. Pang, L. Li, H. Zhou, A. N. Willner, A. Almaiman, Y. Zhou, R. W. Boyd, B. Lynn, R. Bock, M. Tur, and A. E. Willner, “Simultaneous Turbulence Mitigation and Channel Demultiplexing for Two 100-Gbit/s Orbital-Angular-Momentum Multiplexed Beams by Adaptive Wavefront Shaping and Diffusing,” Optics Letters, vol: 45, pp: 702-705, 2020.
- R. Zhang, L. Li, Z. Zhao, G. Xie, G. Milione, H. Song, P. Liao, C. Liu, H. Song, K. Pang, A. N. Willner, B. Lynn, R. Bock, M. Tur, and A. E. Willner, “Coherent Optical Wireless Communication Link Employing Orbital Angular Momentum Multiplexing in a Ballistic and Diffusive Scattering Medium,” Optics Letters, vol: 44, pp: 691-694, 2019.
- [Invited] H. Zhou*, R. Zhang*, H. Song, N. Hu, H. Song, K. Zou, X. Su, Z. Zhao, K. Pang, A. Almaiman, C. Liu, A. Minoofar, B. Lynn, D. Park, M. Tur, and A. E. Willner, “Demonstration of Turbulence Resiliency in a Mode-, Polarization-, and Wavelength- Multiplexed Free-Space Optical Link Using Pilot-Assisted Optoelectronic Beam Mixing,” Journal of Lightwave Technology, vol: 40, no. 3, pp: 588-596, 2022. Contributed equally.
High-Capacity Free-Space-Optical Communications for UAVs
Unmanned-aerial-vehicles (UAVs), such as flying drones, have been proliferating for numerous applications, of which data capacity needs have also been increasing dramatically. Free-Space-Optical (FSO) communications aided with mode-division-multiplexing (MDM) can potentially enhance the spectral efficiency and data capacity. In this project, we demonstrated high-capacity FSO communications employing MDM with a flying UAV in the field with a round-trip distance of up to 100 m.
Related Publications:
- L. Li*, R. Zhang*, Z. Zhao, G. Xie, P. Liao, K. Pang, H. Song, C. Liu, Y. Ren, G. Labroille, P. Jian, D. Starodubov, B. Lynn, R. Bock, M. Tur, and A. E. Willner, “High-Capacity Free-Space Optical Communications Between a Ground Transmitter and a Ground Receiver via a UAV Using Multiplexing of Multiple Orbital-Angular-Momentum Beams,” Scientific Reports, vol: 7, no. 1, pp: 17427, 2017. Contributed equally.
- [Editor’s Pick] L. Li, R. Zhang, P. Liao, Y. Cao, H. Song, Y. Zhao, J. Du, Z. Zhao, C. Liu, K. Pang, H. Song, A. Almaiman, D. Starodubov, B. Lynn, R. Bock, M. Tur, A. F. Molisch, and A. E. Willner, “Mitigation for Turbulence Effects in a 40-Gbit/s Orbital-Angular-Momentum-Multiplexed Free-Space Optical Link Between a Ground Station and a Retro-Reflecting UAV Using MIMO Equalization,” Optics Letters, vol: 44, pp: 5181-5184, 2019.