Abstract
As the demand for high data volumes keeps increasing in optical access networks, transmission capacities and distance are becoming bottlenecks for passive optical networks (PONs). To solve this problem, a novel scheme based on multi-twin single sideband (SSB) modulation with direct detection is proposed and investigated in this paper. At the central office, two SSB signals are generated simultaneously with the same digital-to-analog converters (DACs). The twin-SSB signal is not only robust against frequency selected power fading introduced by chromatic dispersion (CD), but also improves the spectral efficiency (SE). By combining a twin-SSB technique with multi-band carrier-less amplitude/phase modulation (multi-CAP), different optical network units (ONUs) can be supported by flexible multi-band allocation based on software-reconfigurable optical transceivers. The Kramers–Kronig (KK) scheme is adopted on the ONU side to effectively mitigate the signal–signal beat interference (SSBI) induced by the square-law detection. The proposed system is extensively studied and validated with four sub-bands using 50 Gbps 16 quadrature amplitude modulation (QAM) modulation for each sub-band using numerical simulations. Digital pre-equalization is introduced at the transmitter-side to balance the performance of different ONUs. After system optimization, a bit error rate (BER) threshold for hard decision forward error correction (HD-FEC) code with 7% redundancy ratio (BER = 3.8 × 10−3) can be reached for all ONUs over 50-km standard single-mode fiber.
Highlights
Emerging services such as 4K/8K, 5G and virtual reality (VR)/ augmented reality (AR)have imposed challenging demands on passive optical networks (PONs) [1,2,3,4,5,6]
We propose and investigate a novel scheme based on a combination of multi-carrier-less amplitude/phase modulation (CAP)
J=1,j6=ii =1 where A is a constant from the optical carrier, si (t) denotes the i-th optical network units (ONUs)’s single sideband (SSB) signal and n is the number of ONUs in the LSB sideband
Summary
Emerging services such as 4K/8K, 5G and virtual reality (VR)/ augmented reality (AR). Sci. 2019, 9, 748 and the carrier-less amplitude/phase modulation (CAP) [2,3,4,10,11,12] Among these different methods, multi-band CAP (multi-CAP) using intensity modulation and direct detection was proposed as a feasible solution for generation PON due to its low cost and simple structure. By combining the dynamic software-reconfigurable embedded digital orthogonal filters in the digital signal processing (DSP) unit of optical transceivers, the functionality, upgradability and flexibility of the PON transmission link can be considerably enhanced through a centralized SDN controller. At the optical network unit (ONU) side, KK-receiver is adopted to mitigate the SSBI effects from the square-law detection due to its predominant SSBI mitigation capability and low computation complexity. The downlink signal can be separated in the digital domain with cost-effective digitally filters as a conventional multi-CAP signal
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