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Passive Optical Networks for FTTx ApplicationsChang-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
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.
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.
33 ~ 53 Mb/s
1 Mb/s
2 ~ 20 Mb/s
10 Mb/s (P-to-P)
20 M/service
Bandwidth (up)
73 ~ 91 Mb/sTotal Bandwidth
2 ~ 20 Mb/sVideo conference
10 Mb/sInternet
1 Mb/sRemote sensing/control
Streaming Video (HD)
Live TV
VoD
EoD/GoD
Services
Total 60 Mb/s
20 M/service
20 M/service
20 M/service
Bandwidth (down)
33 ~ 53 Mb/s
1 Mb/s
2 ~ 20 Mb/s
10 Mb/s (P-to-P)
20 M/service
Bandwidth (up)
73 ~ 91 Mb/sTotal Bandwidth
2 ~ 20 Mb/sVideo conference
10 Mb/sInternet
1 Mb/sRemote sensing/control
Streaming Video (HD)
Live TV
VoD
EoD/GoD
Services
Total 60 Mb/s
20 M/service
20 M/service
20 M/service
Bandwidth (down)
Table 1. Various services and required bandwidth
B-BLSA-BLS
TRx 1
BLS
Switch
RN ONTs
TRx 32
MUX/DEMUX
TRx 1
OLT Switch
OLT
Metro Core
Management
Co
reR
ou
ter
L2/
L3
swit
ch
Str
eam
S
erv
er
PO
TS
TVsVideoPhonePCs
Phones
TVsVideoPhonePCs
Phones
TVsVideoPhonePCs
Phones
TRx32 Switch
TVsVideoPhonePCs
Phones
TVsVideoPhonePCs
Phones
TVsVideoPhonePCs
PhonesHome 1
Home 32
Coupling optics
B-BLSA-BLS
TRx 1
BLS
Switch
RN ONTs
TRx 32
MUX/DEMUX
TRx 1
OLT Switch
OLT
Metro Core
Management
Co
reR
ou
ter
L2/
L3
swit
ch
Str
eam
S
erv
er
PO
TS
TVsVideoPhonePCs
Phones
TVsVideoPhonePCs
Phones
TVsVideoPhonePCs
Phones
TVsVideoPhonePCs
Phones
TRx32 Switch
TVsVideoPhonePCs
Phones
TVsVideoPhonePCs
Phones
TVsVideoPhonePCs
Phones
TVsVideoPhonePCs
PhonesHome 1
Home 32
Coupling optics
Fig. 1 A FTTH configuration based on WDM-PON
Coupling optics
A-BLS
SMF
RN ONUOLT
UTP
FES(L2)TRx 16
FES(L2)
TRx 1
Metro Core
Co
reR
ou
ter
L2/
L3
swit
ch
TRx 1
Tx 16
B-BLS
Management
Pole 1
Pole 16
UTP
Coupling optics
A-BLS
SMF
RN ONUOLT
UTP
FES(L2)TRx 16
FES(L2)
TRx 1
Metro Core
Co
reR
ou
ter
L2/
L3
swit
ch
TRx 1
Tx 16
B-BLS
Management
Pole 1
Pole 16
UTP
Fig. 2 A FTTPole configuration based on WDM-PON. The OUN was mounted on the pole.
