CWDM OVERLAY ON AN EPON SYSTEM: A DEMONSTRATION AND ECONOMIC RAMIFICATIONS FOR FTTH

In this paper, we present results of a proof-of-concept laboratory demonstration where the new ITU-T wavelength grid for Coarse Wavelength Division Multiplexing (CWDM) is applied to a Passive Optical Network (PON) for metro access. The investigated demonstration network simulates an architecture described best as a CWDM overlay to a generic gigabit PON that is in accordance with ITU-T G.983/984 and IEEE 802.3ah specifications at the physical layer. Above the physical layer, we use Ethernet protocol and adapt a TDMA scheme similar to what is described in the IEEE 802.3ah pre-standard working draft. We also look beyond performance capabilities to model economic ramifications. The use of low-cost EPON electronics and the potential of the entire set of 20-nm-spaced Full-Spectrum CWDM wavelengths for transmission over zero water peak fiber (ZWPF) provides an economic path to revenue opportunities, both in business wavelength services and in residential voice, video, and data. PON architecture Rather than focusing on commercial systems, we demonstrate an upgrade path for PON access networks on the level of laboratory experiments. With the simplified set-up described in this paper we will investigate the value of this approach both experimentally and in economic terms. The demonstrated architecture is based on a proposal first described in an NFOEC paper from 2002, where we explored the economics of a CWDM overlay to augment a PON access network (1). The concept of CWDM uses the entire optical spectrum from 1260 to 1610 nm for signal transmission where a 20-nm grid standard is established per ITU-T G.694.2. This low-cost transmission standard takes advantage of a new class of zero water peak AllWave® fiber (2) that conforms to ITU G.652.C&D. With no loss peak around 1385 nm, this fiber opens the E Band from 1360 to 1480 nm for additional wavelength services and thus increases the capacity to 16 CWDM channels or more per fiber. Conventional standard single-mode fibers (SSMF) can only carry 12 channels or less. This new spectral region in the E-Band avoids wavelength allocation conflicts of the CWDM channels with other parts of the optical spectrum already used by PON standards (3). Therefore, the two parts of this network can be operated completely independently, resulting in greater flexibility and enhanced security. The target commercial application for such a PON system with CWDM overlay is shown in Figure 1. At the central office (CO), the wavelengths from the PON-OLT and the CWDM OLT are combined using an E-Band optical add- drop multiplexer (OADM) and both sub-bands are transmitted over a single optical fiber to a second OADM where the E-Band CWDM channels are separated from the remaining PON wavelengths. Business users receive dedicated wavelengths services carried by the individual CWDM channels. Separate wavelengths for downstream (from the CO) and upstream (towards the CO) ensure flexibility in transmission protocols, and the full capacity is available for each CWDM channel without sharing its bandwidth. The conventional PON channels are distributed with a power splitter (PS) among the N end users by N separate fibers (PS-PON). Unlike in the CWDM section of this access system, both upstream and downstream traffic are carried over the same fiber, and data for all users is time- interleaved on the same wavelength.