title: Orthogonal time-frequency domain multiplexing with multilevel signaling.
abstract: In this paper, we propose and investigate an optical multiplexing technique, called orthogonal time-frequency domain multiplexing (OTFDM) with multilevel signaling, that enables ultrafast, high-spectral-efficiency transmission. On the transmitter side, optical rectangular combs generated from electro-optic modulators are data modulated and multiplexed into the time-frequency domain. On the receiver side, the OTFDM signal is demultiplexed and coherently demodulated by coherent matched detection in which multi-frequency homodyne mixing with a locally generated comb down-converts a target OTFDM tributary channel into baseband frequencies. These multiplexing and demultiplexing processes are fully performed in the optical domain using optoelectronic devices, without the use of fast Fourier transform circuits or optical channel selection filters. It is analytically and numerically proved that multilevel signals such as nPSK and nQAM can be OTFDM-multiplexed and demultiplexed while retaining orthogonality between tributaries. The spectral efficiency of this method reaches as high as 1 Baud/Hz per single polarization, i.e., the Nyquist limit, enabling high-bandwidth operation unrestricted by an electronic response in the transmitter or receiver.
authors: Takahide
authors: T
authors: Sakamoto