Abstract
We propose an asymmetric self-coherent detection scheme (ASCD) based on Mach-Zehnder interferometers (MZI) for the field reconstruction of self-coherent (SC) complex double-sideband (DSB) signals. The MZI-ASCD scheme approaches the high electrical spectral efficiency (ESE) of homodyne coherent detection via a direct detection (DD) receiver having only two photodiodes (PD) and two analog-to-digital converters. The incoming SC-DSB signal is split into two parts at the receiver in this approach, one of which is delayed and beats with the other part at the outputs of an MZI. We show that the field reconstruction can be performed from the two tributaries of photocurrents. In addition, we present a modified MZI-ASCD scheme referred to as AUX-ASCD which introduces an auxiliary DD branch to improve the SNR of the detected signal. It is found that both the MZI-ASCD scheme and the AUX-ASCD scheme achieve higher OSNR sensitivity compared to the Kramers-Kronig scheme and in the meantime increases the ESE by a factor of 2 using a cost-effective DD receiver. These advantages make the ASCD scheme attractive for short-reach optical communications including edge cloud connections and mobile X-haul systems.
Highlights
Coherent detection (COHD) systems revived in the late 2000s due to the rapid development of very-large-scale integration (VLSI) circuits [1,2,3,4]
We analyze the effect of signal-signal beating interference (SSBI) enhancement due to the transfer function singularities associated with the Mach-Zehnder interferometers (MZI)-asymmetric self-coherent detection (ASCD) scheme and discuss appropriate signaling schemes to allocate the signal bands within the spectral intervals
A numerical analysis follows to evaluate the theoretical performance of the MZI-ASCD scheme by loading additive spontaneous noise (ASE)-noise
Summary
Coherent detection (COHD) systems revived in the late 2000s due to the rapid development of very-large-scale integration (VLSI) circuits [1,2,3,4]. The KramersKronig (KK) detection scheme removes the guard band using a high carrier to signal power ratio (CSPR) in order to satisfy the minimum phase condition [17,18,19,20] Another problem of SCSSB-DD schemes is a more complex transmitter subsystem required to generate SC-SSB signals relative to IMDD systems. In order to reconstruct the full electric field, we break the symmetry of this DD receiver by adding a delay element in one of the MZI branches such that i1 (t ) − i2 (t ) ≠ 0 , which, as will be shown later, contain additional information for the retrieval of the imaginary part of the signal We refer to this detection scheme as the MZI-based asymmetric self-coherent detection (ASCD).
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