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Passive Optical Networks for FTTx Applications
                                                         Chang-Hee Lee
including the management and installation costs by using wavelength independent optical network termination
(ONT). Spectru...
[1] M. Zirngibl, C. R. Doerr, and L. W. Stulz, “Study of spectral slicing for local access applications,” IEEE ...
OLT                            RN           ONU
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  1. 1. Passive Optical Networks for FTTx Applications Chang-Hee Lee Department of Electrical Engineering and Computer Science, Korea Advanced Institute of Science and Technology, 373-1 Guseong-dong Youseong-gu, Daejeon, 305-701, Korea Abstract: Applications of passive optical networks, especially WDM-PON, for FTTH and FTTPole are investigated. We also demonstrate a new WDM-PON based on wavelength locked FP-LDs to injected spectrum sliced narrow band ASE. ©2005 Optical Society of America OCIS codes: (060.4250) Networks; (060.4510) Optical communications The demands of broadband access networks are continuously increase with the evolution of new services such as imaged based internet, video on demand, and IP TV. The high definition TV that requires a bandwidth of about 20 Mb/s/channel will be a common video service in near future. We show required bandwidth for the future services in Table 1. We may need about 100 Mb/s bandwidth for down stream data, while 50 Mb/s for upstream data. To meet quality of service (QoS) requirements for these video applications, the minimum guaranteed bandwidth per subscriber should be supported by the access network. In addition, the access network will evolve to support triple-play service, i.e., converged service of voice, data, and video within a single network platform. The access networks based on copper cables (cable modem and many kinds of digital subscriber lines (DSL)) do not provide either enough minimum bandwidth or transmission distance for the future services . To provide triple-play service with high QoS, we need to bring optical fiber directly to the home. Many Passive Optical Networks (PONs) have been demonstrated to provide high bandwidth to the customer premises without any active equipments in the field. Since a single feeder fiber is shared by many user in the PON, we need an appropriate multiple access methods such as a time division multiple access (TDMA) and a wavelength division multiple access (WDMA). In a PON based on TDMA (TDM-PON), each subscriber can access the central office only within a specific time interval. Thus every subscriber has to use a single common communication protocol and their bandwidth is limited by time sharing. Thus it is not easy to guarantee the enough bandwidth required for future video-based services. A PON based on WDMA (WDM-PON) can solve these problems by allocating a different wavelength to each subscriber. Then, each customer can communicate to the central office with a separate wavelength that can carry a different data rate and a different protocol. However, the WDM-PON had been considered as an expensive solution, since it had to use expensive wavelength specific sources, e.g. DFB-lasers, in order to maintain pre-assigned wavelengths. In addition, it had high installation and maintenance costs. Several approaches have been proposed to reduce costs of the WDM-PON
  2. 2. including the management and installation costs by using wavelength independent optical network termination (ONT). Spectrum-slicing using a broadband incoherent light source such as a light emitting diode (LED) may be used to realize the wavelength independent ONT [1-3]. The LED can be fabricated at a low cost and modulated directly. However, its output power and modulation speed are insufficient for high speed operation. The spectrum sliced amplified spontaneous emission (ASE) based on EDFA had been proposed as a WDM source [2]. However, an expensive external modulator is required for transmission of signal. Recently, a wavelength locked Fabry-Perot laser diode (F-P LD) with external spectrum-spliced amplified spontaneous emission (ASE) injection was proposed as a low cost WDM source for wavelength independent operation of the ONT [4]. By injecting spectrum-sliced broadband light source (BLS) into a F-P LD, the laser is forced to operate in a quasi single mode and the mode partition noise of the F-P LD is suppressed sufficiently to use as a WDM source. We show optical access network configuration for FTTH based on WDM-PON in Fig. 1. Well known internet protocol (IP) is used as a communication protocol between the central office and each home. Then converged voice, data, and video services can be provided to each home with help of Ethernet switches and routers. At customer’s home, the electrical switch classifies (It may be home gateway.) the traffic based on services and provides data to the corresponding terminal equipments such as a TV set, a phone, or PCs. At the central office, a high capacity electrical switch/router classifies the traffic based on service. Then, classified data were sent to metro core networks. The core of this network is a WDM-PON that connects each subscriber to the central office. Then, each subscriber communicates with the central office through dedicated wavelengths. A single wavelength channel carries 4B5B coded 125 Mb/s Ethernet data to provide 100 Mb/s data to each home. Recently, we have demonstrated feasibility of 50 GHz spaced WDM-PON based on wavelength locked FP-LD. Details of the WDM- PON will be discussed at the conference. Before deployment of the FTTH massively, the access network based on copper cable can be upgraded with many kinds of PONs. A xDSL modem at subscriber’s home brings many operation and management issues, since their fault rate is relatively high and it is not easy to access subscriber’s home. In addition, we have to use optical fiber to extend services area of xDSL. At the termination point of the optical signal, we need a broad band cabinet or a small hut that aggregates incoming traffic from subscribers and optical to electrical signal conversion, or vice versa. It is not easy to find out the land to install the broad band cabinet. These problems can be solved by using a pole mountable small size cabinet that includes a Fast Ethernet Switch (FES) or a L2 Ethernet switch with an optical transceiver. Then, a PC located at subscriber’s home was connected to the FES through an unshielded twisted pair (UTP) cable without the modem. The ONUs mounted on the pole were connected to the central office by using the PON, such as the TDM-PON or the WDM-PON. Fig. 2 shows architecture for FTTPole system based on the WDM-PON. In case of the TDM-PON, we need a media access protocol to share many ONUs in time domain. In conclusion, we investigated application of passive optical networks, especially WDM-PON, for FTTH and FTTPole. The WDM-PON was realized based on wavelength locked FP-LDs for a low cost and wavelength independent operation of ONT/ONU.
  3. 3. References [1] M. Zirngibl, C. R. Doerr, and L. W. Stulz, “Study of spectral slicing for local access applications,” IEEE Photon. Technol. Lett., vol. 8, no. 5, pp. 721-723, 1996. [2] D. K. Jung, S. K. Shin, C. -H. Lee, and Y. C. Chung, “Wavelength-division- multiplexed passive optical network based on spectrum-slicing techniques,” ” IEEE Photon. Technol. Lett., vol. 10, no. 9, pp. 1334-1336, 1996. [3] R. D. Feldman, E. E. Harstead, S. Jiang, T. H. Wood, M. Zirngibl, “An evaluation of architectures incorporating wavelength division multiplexing for broad-band fiber access,” IEEE J. Lightwave Technol., vol. 16, no. 9, pp. 1546-1559, 1998. [4] H. D. Kim, S. -G. Kang, and C. –H. Lee, “A low cost WDM source with an ASE injected Fabry-Perot semiconductor laser,” IEEE Photon. Technol. Lett., vol. 12, no. 8, pp. 1067-1069, 2000. Services Bandwidth (down) Bandwidth (up) Streaming Video (HD) Total 60 Mb/s Live TV 20 M/service VoD 20 M/service EoD/GoD 20 M/service 20 M/service Internet 10 Mb/s 10 Mb/s (P-to-P) Video conference 2 ~ 20 Mb/s 2 ~ 20 Mb/s Remote sensing/control 1 Mb/s 1 Mb/s Total Bandwidth 73 ~ 91 Mb/s 33 ~ 53 Mb/s Table 1. Various services and required bandwidth OLT RN ONTs MUX/ TVs OLT Switch BLS DEMUX Video Router TRx 1 Switch Phone Core TRx 1 PCs Phones A-BLS B-BLS Home 1 L2/L3 switch Metro Coupling optics Core Stream Server TRx 32 TVs Video TRx 32 Switch Management Phone POTS PCs Phones Home 32 Fig. 1 A FTTH configuration based on WDM-PON
  4. 4. OLT RN ONU UTP FES TRx 1 SMF (L2) TRx 1 Pole 1 A-BLS B-BLS L2/L3 switch Router Core Metro Coupling optics Core Tx 16 FES TRx 16 (L2) Pole 16 UTP Management Fig. 2 A FTTPole configuration based on WDM-PON. The OUN was mounted on the pole.