Abstract
In this work, a hybrid code division multiplexing (CDM) coding and digital filtering method for optical intensity modulation and direct detection (IM-DD) link is investigated to address multipath interference (MPI) and channel bandwidth limitation. CDM signaling already provides robustness to MPI through suppressing the unsynchronized paths by orthogonal (de)coding. As for digital filtering based on square root raised cosine (SRRC) waveforms, its advantage to IM-DD link includes robustness to channel bandwidth limitation due to pulse shaping. Additionally, matching filters achieve the best orthogonality only when they are synchronized well, thus robustness to MPI can be expected on the basis of CDM. We study the performance of such hybrid coding and filtering method over IM-DD link in the presence of MPI and bandwidth limitations through simulation. This is followed by experimental demonstrations of single point-to-point transmission with capacity at 112 Gbps. BER comparison between CDM only and hybrid filtering and coding method is performed by emulating MPI using a Mach-Zehnder interferometer. Furthermore, bidirectional transmission over a single fiber verifies its performance advantage and demonstrates potentials for reducing implementation costs of end-to-end optical communications.
Highlights
Recent years, optical intensity modulation and direct detection (IM-DD) solution exhibits its advantages in short reach optical communication application, with low power consumption and economical implementation [1]
We study the performance of such hybrid coding and filtering method over IM-DD link in the presence of multipath interference (MPI) and bandwidth limitations through simulation
Models developed for optical IM-DD link in this paper are available online [20], including bandwidth channel limitation and MPI modeling, digital implementation of code division multiplexing (CDM)/carrier-less amplitude phase (CAP) signaling and performance evaluations as well
Summary
Optical intensity modulation and direct detection (IM-DD) solution exhibits its advantages in short reach optical communication application, with low power consumption and economical implementation [1]. To address MPI issue in IM-DD systems, proposed solutions include reducing the coherent length of optical carriers [8], constructing a high-pass filter [3], [9] and reconstructing the delayed signal [10]. Another approach is code division multiplexing (CDM) in which using orthogonal codewords to suppress unsynchronized paths whose phase shift are uncertain.
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