Optical MIMO Communication Using Holographic Spectral Multiplexing of Pulsed Ultrashort Laser

In this paper, we introduce Holographic Spectral Multiplexing (HSM) as a novel technique to enable multiple-input multiple-output (MIMO) communication in optical networks. HSM uses the spectral space of ultrashort laser pulses to create line codes in the form of 2D holograms. The pulse processing is performed in the temporal Fourier domain by spatially dispersing the pulse frequency components in a spectral processing device (SPD). The 2D holograms are composed of the patterns of intensity disparities that an SLM inscribes on the spectrally-decomposed Fourier plane of the pulse. The holographic line codes defined in this way transform the ultrashort laser pulses into high-entropy data symbols, hence, enhance the communication's spectral efficiency. Unlike conventional optical multiplexing schemes (e.g., TDM, WDM, or SDM), HSM does not physically or abstractly separate the communication propagation space into subchannels. Rather, HSM realizes a MIMO communication paradigm by allowing the photonic waves under the pulse envelope to propagate in the same space so they scatter and interfere by chromatic dispersion. This allows HSM to form beams between the pixels of SLM at the sender and receiver sides and optimize the beam to adapt to channel scattering situations. In this way, HSM delivers a rate gain that in the best case exponentially increases the information rate of communication.