Hungkei Chow

Energy efficiency of optical transceivers in fiber access networks [invited]

The dramatic growth of Internet traffic is leading to a concern about the future power consumption of the Internet. Energy sustainability of communication networks is becoming a very important goal for the reduction of the global carbon footprint. As optical access networks gain more popularity, their share in the energy consumption of the data network will increase. Developing energy-efficient technologies for optical access networks is therefore crucial for the continuous scaling of the Internet. In this paper, we model the power consumption of different transceivers and demonstrate how various electronic and photonic technologies can help improve energy efficiency. We discuss the impact of different light sources and driver circuits on the transceiver power efficiency. We also show how energy efficiency is related to network topology.

Low energy bit-interleaving downstream protocol for passive optical networks

A novel, low energy protocol for passive optical networks (PON), featuring bit-interleaving of downstream traffic, is described. The bit-interleaving protocol enables decimation of the received frame, which eliminates the processing overhead associated with unrelated traffic by customer premises equipment (CPE), while preserving the flexibility of downstream bandwidth allocation. Measurement results obtained from a bit-interleaving PON prototype at the line rate of 10 Gb/s indicate a reduction of CPE dynamic power consumption by a factor of 30, with respect to the power of a standard PON CPE at the same line rate. Additionally, a significant reduction in CPE hardware complexity, with respect to that of a standard PON CPE, is achieved.

Options for TDM PON beyond 10G

This paper proposes an architecture to increase the downstream transmission of TDM PON from 10-Gbps to 40-Gbps. Challenges like chromatic dispersion tolerance, optical power budget, cost, and coexistence with legacy PONs are discussed.

Demonstration of Symmetrical 25 Gb/s TDM-PON With Multilevel Interleaving of Users

A cost effective symmetrical 25 Gb/s TDM-PON utilizing a novel multilevel user-interleaving scheme based on PAM-4 in the downstream and three-level duobinary modulation in the upstream is demonstrated without using any DSP. At the ONU, we used a commercial off-the-shelf 10 Gb/s EML-based transmitter and a 10 Gb/s APD/TIA-based receiver to keep the cost low. It will be shown that three-level duobinary and PAM-4 modulation are more tolerant to chromatic dispersion compared to NRZ; therefore, it also offers a reach extension. The multilevel user-interleaving scheme enables the use of a half-rate CDR at the ONU as well as the use of a simple NRZ CDR/EDC to improve the optical receiver sensitivity for downstream transmission. We believe that using PAM-4 modulation for the downstream and NRZ to duobinary conversion for the upstream offers a good technical compromise for lowest cost at the ONU for 25 Gb/s TDM-PON.

Energy-Efficient Optical Links: Optimal Launch Power

In an optical link, there is a tradeoff between power consumption of transmitter and that of receiver. This letter investigates this tradeoff by developing a power consumption model for the components of the link. The impact of different photonic technologies is studied. A method to minimize the power consumption by optimizing the optical modulation amplitude is discussed.

Demonstration of symmetrical 25 Gbps quaternary PAM/duobinary TDM-PON with multilevel interleaving of users

A cost effective symmetrical 25 Gbps TDM-PON utilizing a novel multilevel user-interleaving scheme based on PAM-4 in the downstream and 3-level duobinary modulation in the upstream using exclusively 10 Gbps parts at the ONU is demonstrated.

Road to energy-efficient optical access: greentouch final results

The growing energy footprint of communication networks has raised concern about the sustainability of future network development. The GreenTouch consortium was founded to help counter this trend by developing and integrating green network technologies from the access to the core. In order to evaluate these technologies, an end-to-end network power model was developed in the form of the Green Meter, a tool to assess the overall impact and overall energy efficiency benefits of an entire portfolio of solutions. In this paper, we describe the methodology of the Green Meter for the residential fixed access portion, which was extended to include metro aggregation. A baseline architecture for optical access and metro aggregation networks is defined, and is adapted to other scenarios integrating future technologies. The performance is evaluated each time through a mathematical model that captures the energy savings at the component level and has the ability to compute the overall system-level energy savings. We show that energy efficiency can be improved 29-fold over a decade (2010-2020) with businessas- usual trends, and with the added effort of introducing GreenTouch solutions, this could be further improved to achieve a 257-fold increase in energy efficiency. The results confirm that an emphasis on green network design can indeed have a huge impact on reducing the energy consumption of an optical access infrastructure.

Energy-efficient cascaded bit-interleaved converged optical access/in-building network protocol

This paper proposes the cascaded bitinterleaved optical network protocol, an energy-efficient solution aiming at low power consumption in converged optical access/in-building networks while providing high data rates to end users, and a novel network architecture for optical access/in-building networks. In the proposed network architecture, optical-electrical-optical (OEO) regeneration is employed at the interface between access and in-building networks. The downstream frames are generated in the central office using a two-stage bitinterleaving scheme. In the downstream direction, the network nodes only process the data destined for them at a lower clock rate than that of the aggregate passive optical network (PON). In the upstream direction, no word alignment or decoding is performed in the intermediate nodes. Simulation and experimental results show that significant reduction in the power consumption of access/in-building networks can be achieved when the proposed cascaded bit-interleaved protocol is employed in conjunction with the proposed network architecture.

Voltage Controlled Oscillators for 40Gbit/s Cascaded Bit-Interleaving PON

Technologies such as the Internet-of-Things and cloud services demand dynamic bandwidth allocation flexibility, which is not offered by the currently deployed solutions. The Bit-Interleaving PON (BiPON) and its cascaded extension the Cascaded Bit-Interleaving PON (CBI-PON) offer a solution that allows to increase bandwidths, reduce power consumption and have a much more flexible dynamic bandwidth allocation scheme. CBI-PON consists of multiple levels of BiPON with different line rates. For each of these line rates, clock-and-data recovery must be performed, which requires a set of different Voltage Controlled Oscillators (VCOs). This paper presents the VCOs designed for the CABINET chip, an implementation of a CBI-PON network device, allowing clock-and-data recovery for 40Gbit/s, 10 Gbit/s and 2.5 Gbit/s line rates.