Optical Fiber Communication

**69**

**Chapter 5**

*and Curtis Knittle*

**Abstract**

Delta-Sigma Digitization and

Fiber Coax Networks

*Jing Wang, Zhensheng Jia, Luis Alberto Campos* 

Negligible MER degradation is observed for BER up to 1.5 × 10<sup>−</sup><sup>6</sup>

**Keywords:** access network, delta-sigma ADC, digitization, DOCSIS 3.1,

Video-intensive services, such as virtual reality and immersive applications are driving the growth of data traffic at user premises in an explosive way, making access networks become a bottleneck of user quality of experience. Various optical and wireless access technologies have been investigated, including passive optical networks (PON) [1–3], cloud-radio access networks (C-RAN) [4–7], and hybrid fiber coax (HFC) networks [8, 9]. In the United States, there are more than 50 million subscribers using cable services for broadband access, which is 40% more than digital subscriber line (DSL) and fiber-to-the-home (FTTH) users [10]. Given the emergence of data over cable service interface specification (DOCSIS)

one-bit and two-bit digitization, respectively.

hybrid fiber coax, OFDM

**1. Introduction**

Optical Coherent Transmission

of DOCSIS 3.1 Signals in Hybrid

We first demonstrate delta-sigma digitization and coherent transmission of data over cable system interface specification (DOCSIS) 3.1 signals in a hybrid fiber coax (HFC) network. Twenty 192-MHz DOCSIS 3.1 channels with modulation up to 16384QAM are digitized by a low-pass cascade resonator feedback (CRFB) delta-sigma analog-to-digital converter (ADC) and transmitted over 80 km fiber using coherent single-λ 128-Gb/s dual-polarization (DP)-QPSK and 256-Gb/s DP-16QAM optical links. Both one-bit and two-bit delta-sigma digitization are implemented and supported by the QPSK and 16QAM coherent transmission systems, respectively. To facilitate its practical application in access networks, the coherent system is built using a low-cost narrowband optical modulator and RF amplifiers. Modulation error ratio (MER) larger than 50 dB is successfully demonstrated for all 20 DOCSIS 3.1 channels, and high order modulation up to 16384QAM is delivered over fiber for the first time in HFC networks. The raw DOCSIS data capacity is 54 Gb/s with net user information ~45 Gb/s. Moreover, the bit error ratio (BER) tolerance is evaluated by measuring the MER performance as BER increases.

and 1.7 × 10<sup>−</sup><sup>4</sup>

, for
