292 JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 27, NO. 3, FEBRUARY 1, 2009 First Demonstration of Coexistence of Standard Gigabit TDM-PON and Code Division Multiplexed PON Architectures Toward Next Generation Access Network Hideaki Tamai, Masahiro Sarashina, Hideyuki Iwamura, Member, IEEE, Masayuki Kashima, Gyaneshwar C. Gupta, Takashi Ushikubo, Takeshi Kamijoh, Philippe Chanclou, Naveena Genay, Bernard Landousies, Andrzej Mosek, and Michal Gredziak Abstract—World-first coexistence trial of TDM and CDM giga-bit passive optical networks (PONs) was successfully com- pleted. A very shallow minimum isolation of 7 dB between G- and CDM-PON at OLT and ONU in the ITU-T G.984.5 enhancement band was demonstrated. The feasibility of bidirectional transmis- sion on the same wavelength was confirmed. The backscattering optical noise does not seriously affect the maximum reach of CDM-PON. Adding the CDM-PON onto GPON can provide following technical and economical impacts: low-cost coexistence, minimum service outage, and combination of best-effort and guaranteed-bandwidth for efficient and high-quality network services due to CDM feature. Index Terms—Code division multiplexing, coexisting network, passive optical network, Rayleigh backscattering. I. INTRODUCTION P ASSIVE optical network (PON) is one of the most promising optical access network architectures in terms of cost effectiveness. Deployment of Giga-bit PON based on conventional time division multiplexing (TDM) such as IEEE 802.3ah GE-PON and ITU-T G.984 GPON has started, em- powering broadband optical access services including data and voice-over-IP (VoIP) services. Next generation optical access (NGA) technology is now being discussed from various points of view, such as larger bandwidth, bandwidth allocation for multimedia delivery, reach extension, smooth migration on the living Optical Distribution Network (ODN), and so on. Manuscript received June 30, 2008; revised September 30, 2008. Current ver- sion published February 13, 2009. H. Tamai, M. Sarashina, H. Iwamura, M. Kashima, G. C. Gupta, T. Ushikubo, and T. Kamijoh are with the Oki Electric Industry Company, Ltd., Corporate R&D Center, Tokyo 193-8550, Japan (e-mail: tamai677@oki.com; sarashina238@oki.com; iwamura564@oki.com; kashima567@oki.com; ushikubo675@oki.com; kamijoh543@oki.com). P. Chanclou, N. Genay, and B. Landousies are with the France Telecom, Re- search and Development Division, 22307 Lannion, France (e-mail: philippe. chanclou@orange-ftgroup.com; naveena.genay@orange-ftgroup.com; bernard. landousies@orange-ftgroup.com). A. Mosek and M. Gredziak are with the Telekomunikacja Polska, Re- search and Development Centre, 02-691 Warsaw, Poland (e-mail: An- drzej.Mosek@telekomunikacja.pl; Micha.Greziak@telekomunikacja.pl). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/JLT.2008.2009999 Coexistence of legacy and new services architectures is a key issue for NGA. Various types of coexisting, typically hy- brid wavelength division multiplexed (WDM)-PON, have been proposed [1]. Towards economical network as well as higher quality of service and more subscribers, a combination of GPON and guaranteed-bandwidth PON seems to be expected on the living ODN. Code-division multiplexing-access (CDMA) technologies have been widely used and deployed in wireless communication and also studied in Optical CDMA (OCDMA) systems as well as an access network for PON applications [2], [3]. Previously, we reported a novel passive optical network which we called “COF-PON” based on code division multiplexing (CDM) on fiber (COF, multiplexing carried out in electrical domain) [4], [5]. COF-PON has attractive features to satisfy the additional requirements of current gigabit PONs. The demonstration of coexistence with GPON and verification of service-enhance- ment is expected to provide a potential NGA solution. The rest of this paper is organized as follows. Section II presents the concept of GPON and COF-PON coexisting net- work. Features of COF-PON, a typical configuration of hybrid network, and service images are described. In Section III, we show the world-first experimental demonstration of GPON and COF-PON coexisting network using conventional WDM filters. We also show the minimum and maximum required isolation of WDM filters for this hybrid network. Finally, we show the analysis of the back reflection influence that arises in the transmission system using the same wavelength both upstream and downstream like COF-PON. II. CONCEPT OF GPON AND COF-PON COEXISTING NETWORK Fig. 1(a) shows the basic configuration of COF-PON. The most characteristic point is that both encoding and decoding process are carried out in electrical domain, while OCDM does in optical domain using all-optical encoder and decoder. COF-PON is a synchronous CDM system using orthogonal code which offers minimum interference from unwanted users for the desired user. Therefore, it helps to avoid ad- ditional multi-user interference rejection techniques like in OCDM system [9]. The electrical encoder can be realized by conventional digital large scale integrations (LSIs). Analog charge coupled device matched filter (CCD-MF) is used as 0733-8724/$25.00 © 2009 IEEE