1864 JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 28, NO. 12, JUNE 15, 2010
Integrating Fiber-to-the-Home and POF In-Door
Routing CATV Transport System
Ching-Hung Chang, Heng-Sheng Su, Hai-Han Lu, Senior Member, IEEE, Peng-Chun Peng, and Hsuan-Wen Hu
Abstract—An integrating fiber-to-the-home and plastic optical fiber (POF) in-door routing CATV transport system is
proposed and demonstrated with good quality of service. In this system, a 1550 nm optical signal is directly transmitted
along with a span of single-mode fiber (SMF) plus POF without wavelength converting or any bridge circuit. The
feasibility of our proposed system is observed and accompanied with good carrier-to-noise ratio, composite secondorder, and composite triple beat performances under various SMF and POF lengths. To be the first one, to the best of
our knowledge, of successfully transporting CATV signals in such integrated access and in-door LAN, this system
reveals prominence in simplicity and cost-effective to provide all-optical CATV service all the way to consumer in-door
devices.
Index Terms—CATV, fiber to the home (FTTH), in-door network, local-area network (LAN), plastic optical fiber
(POF).
I.
O
INTRODUCTION
PTICAL fiber transport systems with high-capacity, low-attenuation, light weight, and electromagnetic noise
interference (EMI) free characteristics are widely employed to deliver broadband CATV signals [1], [2]. The
applications of transmitting and distributing multimedia signals over optical fiber bring a lot of benefits, including
high-performance, wide-service range, and easy management [3]. Nevertheless, the current optical fiber CATV
transport systems are mainly concentrating on the connections among central office (CO) and client premises. The
intrabuilding network is commonly neglected so far but, now, more and more multimedia services, such as
video/voice on demand (VoD), on-line games, and CATV programs, are gradually encapsulated into the access
network. The bandwidth demand may significantly boost up and is highly possible to extend the capacity of current
in-door wire or wireless LAN [4], [5]. So the very last in-door connection becomes a critical bottleneck to
successfully transport high quality of multimedia services all the way from a CO to the home and then to the
consumer devices. To overcome the challenge, a new kind of in-door network medium is required to boost up the
LAN capacity and to replace the presented coaxial cable or twisted pair networks, which are installed to deliver
video, telephone, or internet services, etc. The plastic optical fiber (POF) with its low cost, high capacity, and EMI
free characteristics becomes a main candidate to bridge any arrived optical signal to each room without any extra
interface.
As a communication medium, glass single-mode fiber (SMF) can offer much better performances than that by the
POF and is widely used to distribute extremely large bandwidth with low-power loss in backbone and access
networks [3]. However, the core diameter of an SMF is much smaller than that of a POF. It needs a trained person
with high-precision devices to install SMF inside a house, so its construction is relatively costly. POF on the other
hand has much larger core diameter and has most of the advantages of glass fiber, albeit its transmission distance is
limited by high attenuation. It can offer relative smaller bending radius (5 mm) and is easy to fit connectors. An
amateur can fit connector to a POF with minimal training and cheap tools [6], [7]. The easy setting and low-cost
characteristics is well suited for do-it-yourself home LAN installation. As a result, a POF network with EMI
immunity and no radiation is an ideal medium to conjunction optical fiber-to-the-home (FTTH) services all the way
to consumer in-door devices. Recently, some new POFs, such as perfluorinated graded-index polymer optical fiber
(PF GI-POF), have been developed with better performance and lower cost [8], [9]. Those flash products greatly
promote the POF LAN research enthusiasm and have been utilized to transmit digital baseband, quadratureamplitude modulation (QAM), RF, or discrete multitone modulation signal in-door [10]–[14]. Nevertheless, none
of the aforementioned architectures are designed to transmit optical CATV signal all the way from CO to the home
and then to the consumer in-door devices. The CATV signal with its wide spreading throughout current cable
industry [15], [16] is an important service and should not be ignored in such POF in-door LAN.
In the paper, an integrating FTTH and POF in-door routing CATV transport system is proposed and demonstrated
to transport 77-channels amplitude modulation-vestigial sideband (AM-VSB) CATV signals from a CO all the way
to client premises and then to dedicated rooms. In the proposed structure, the utilized optical carrier is 1550 nm.
Although it is not the best option for POF LAN transmission and may suffer serious attenuation, the 1550 nm
wavelength is commonly employed to transmit CATV signal in access networks. Using a low-attenuation optical
wavelength in POF LAN will require a wavelength converting process between the access network and the in-door
LAN, which will boost up the construction cost. By eliminating this process, our transparent access and in-door
LAN system reveals an outstanding one in structure simplicity and construction cost down. Great performances of
the CATV RF parameters: carrier-to-noise ratio (CNR), composite second order (CSO), and composite triple beat
(CTB) are experimentally demonstrated in our transport system. This is the first time, to the best of our knowledge,
of successfully transporting multiple CATV channels in such integrated access and in-door LAN.
II. NETWORK CONFIGURATION AND DESIGN
Fig. 1 illustrates the schematic diagram of the integrated CATV transport configuration. At the CO, CATV
programs, which come from other service providers, are first electrical to optical converted to multiple 1550 nm
range downstream lightwaves and then fed into a span of SMF for downstream transmission. Each lightwave at the
edge of residential area is consequently separated by an array waveguide grating before routed through another
span of SMF to each dedicate client premise. Since each optical channel is addressed at different wavelengths, the
downstream CATV signals can be effectively transmitted from the CO to every consumer premise without
colliding with each other. When the optical CATV signals arrive at the first house, e.g., the optical video signals are
bridged along with POF in-door LAN to consumer devices.
Since POF has relative smaller bending radius and EMI free characteristics, people can deploy POF along with the
presented electrical cable channels to a specific destination. In this process, the optical signal can be directly
transmitted along in-door LAN without optical wavelength converting or optical to electrical converting. This can
further simplify the very last mile connection as well as increase the end-to-end QoS. Under this all optical
structure, video service providers can conveniently adjust the CATV RF parameters at the CO without sending
people to client premise. In addition, the core sizes of the feeder and distribution fibers among the CO and
consumer premises are small and required high-precision devices to connect. Comparing with conventional coaxial
cable CATV systems, it is very difficult to illegally bridge the CATV programs, so the security issue in the alloptical network can be well ensured as well.
The transmission performance of a CATV system is typically verified by three RF parameters: CNR, CSO, and
CTB. The CNR value is in direct proportion to the optical carrier power. The higher CNR value is obtained, the
clearer picture is presented, so the CO should provide each end user enough optical carrier power to ensure picture
quality. Nevertheless, the higher optical carrier power will also induce higher second-order harmonic distortion and
third-order intermodulation distortion to worse CSO and CTB performances. As a result, a tradeoff among CNR
and CSO/CTB values is necessary. According to National Television System Committee (NTSC) definition, the
worst CNR, CSO, and CTB values at each room device should higher than 43/53/53 dB, respectively, [16].
III. EXPERIMENTAL SETUP
The experimental configuration of our integrated FTTH and POF in-door routing CATV transport system is shown
in Fig. 2. Following with the NTSC definition, a total of 77 AM-VSB signals from a NTSC CATV signal generator
(Matrix SX-16) were used to simulate 77 analog CATV channels (channel 2–78 with 6 MHz bandwidth per
channel) and were fed into the RF port of a 1550 nm CATV transmitter. Inside the transmitter, an external
modulator is employed to modulate those RF signals with a 1550 nm optical lightwave. The modulated lightwave
was consequently amplified by an erbium-doped fiber amplifier (EDFA) before transmitted through a span of 20
km standard SMF (with a dispersion of 17 ps/nm/km) and another span of 25 m PF GI-POF (with core diameter =
50 ± 5 µm, numerical aperture = 0.185 ± 0.015, macroband loss ≤ 0.25 dB for ten turns on a 25 mm radium quarter
circle, and long-term bend radium = 5.0 mm). At the end of the POF LAN, the CATV signal is received and
analyzed by a CATV analyzer. Nevertheless, due to the connector type and core size different between the POF and
our optical receiver adaptor, a short span of 50 µm multimode fiber (MMF) with a physical-contact (PC) connector
in one side and angled PC connector in another side is bridged between them to provide a well connectivity.
In an optical fiber transport system, optical signals may suffer from various distortions during transmission. The
stimulated Brillouin scattering (SBS), e.g., is a kind of nonlinear effect in optical fiber and may seriously degrade
the CSO and CTB performances. To avoid serious SBS effect, the CO output power should not higher than 17
dBm. In addition, different core sizes between the SMF and POF as well as high attenuation of POF will also
significantly worse connection loss and power budget issue, which limit the deployed SMF or POF length. In the
experiment, the output power of the EDFA was kept at 15.5 dBm, and the transmission losses of the 20 km SMF
and 25 m POF are 5.2 dB and 7.9 dB, respectively. In the system, the core size of the optical CATV receiver is 9
µm, which is much smaller than that in the POF and MMF. When the optical signal is transmitting through the
MMF to the CATV receiver, only a small portion of the optical signal can go into the CATV receiver, so a serious
7.5 dB connection loss is presented between the MMF and CATV receiver. Fortunately, this loss can be eliminated
by utilizing a bigger core receiver. The saved power budget can then be used to support additional two or three
POF cables directed to different rooms. The measured CNR, CSO, and CTB performances are presented in Fig.
3(a)–(c), respectively. It is clear that the CNR values always keep at around 50 dB under every NTSC channel
number. Comparing with back-to-back (BB) case, the measured CNR values are roughly 6.5 dB degraded by power
degradation and nonlinear effects of the SMF and POF, such as SBS effect and mode dispersion; nevertheless, the
measured 50 dB still meets the standard demand.
From Fig. 3(b) and (c), we can also observed that roughly 5.5 dB degradation for CSO value and 5.2 dB
degradation for CTB value are presented by the attribute of fiber dispersions, but ≥ 64 dB under every NTSC
channel number is always practically achieved. All of the advanced CNR, CSO, and CTB values are higher than
the standard requirements. This phenomenon presents a possibility to further extend either the SMF or POF length.
To dig out every potential of our proposed system, the SMF length is varied from 10–30 km, and the POF length is
adjusted between 25 and 50 m. The relative experimental results are recorded in Fig. 4. From these results, we can
find that the values of the CATV RF parameters are gradually reduced with the increased of SMF or POF length
except the CSO/CTB values in the 20 km SMF plus 25 m POF scenario. These two values are slightly increased
when the SMF length is enlarged from 10 to 20 km. This situation is a special phenomenon in CATV transport
systems and is a result of inverse correlation between the CNR and CSO/CTB values. When the CNR value is
reduced with the extension of the SMF, the composed second-order harmonic distortion and third-order
intermodulation distortion are reduced as well, so the overall CSO/CTB performance is improved slightly [16].
Once the optical power is under the acceptable receiver power range, all of the CATV RF parameters will suffer
from serious degradation. Nevertheless, either we double the POF length from 25 to 50 m or extend the 20 km SMF
length to 30 km, the measured CNR, CSO, or CTB values are all acceptable. If we look closer into the Fig. 4, we
can obtain that the CNR value in the 30 km SMF plus 25 m POF scenario is roughly reach the lower limitation.
Keep increasing the POF length from 25 to 50 m would cause extra attenuation, which will significantly worsen
CATV RF parameters. As a result, the critical limitation is presented at 20 km SMF plus 50 m POF or 30 km SMF
plus 25 m POF scenarios.
The earlier discussions present that the CATV RF parameters are significantly limited by received electrical signal
power at receiver. In other words, if there is a need to extend the connection length, boosting up the transmitted
signal power is a main direction to work on. However, simply increasing the transmitted optical power will suffer
from higher SBS, second-order harmonic distortion, and third-order intermodulation distortion. Transmitting fewer
channels with higher electrical power in each one is therefore becoming a suitable direction to extend the
transmission length. This process cannot only improve the CNR performance but also reduce fiber nonlinear and
dispersion effects. This is because that major part of second-order distortion can be automatically removed. For
example, the carrier frequency for CH 9, CH 25, and CH 56 is 187.25, 229.25, and 415.25 MHz. The composite of
CH 9 and CH 25 is
187.25 MHz + 229.25 MHz = 415.5 MHz (1).
This composition is located at CH 56 (416.5 MHz–415.25 MHz = 1.25 MHz). Similarly, the carrier frequency for
CH 68, CH 55, and CH 5 is 487.25, 409.25, and 77.25 MHz, respectively. The composite of CH 68 and CH 55 is
487.25 MHz -409.25 MHz = 78 MHz (2)
This composition is located at CH 5 (78 MHz–77.25 MHz = 0.75 MHz). These results illustrate that by reducing
the transmitted channel number, the composited distortion effect can be reduced. Fig. 5(a) and (b) recodes CNR,
CSO, and CTB performances under 40 and 20 CATV channel numbers, 10–30 km SMF lengths, and 25 or 50 m
POF lengths. In the 40-channels scenario, the RF parameters are still unacceptable in 30 km SMF plus 50 m POF
case. Nevertheless, comparing these values with the same SMF and POF lengths case in the Fig. 4, the CNR, CSO,
and CTB values are increased from 38.9, 50.5, and 47.8 dB to 40.2, 53.1, and 50.8 dB, respectively. A notable
improvement has been observed to proof our statement mentioned earlier. In the 20-channels scenario, the
measured CNR, CSO, and CTB performances in each case all satisfy the required 43, 53, and 53 dB.
The aforementioned discussions present a strong evident to successfully transmit 1550 nm optical CATV signals all
the way from a CO to client premises and then go through a span of POF to their destinations without any optical
transceiver and bridge circuit between the optical access network and the in-door LAN. In the proposed transport
system, the 1550 nm optical carrier may suffer from serious attenuation in the POF in-door LAN, but the
aforementioned experimental results have shown the successful of our integrated system to deliver high quality of
CATV signals all the way from a CO to consumer devices.
IV. CONCLUSION
We have proposed an integrated FTTH and POF in-door routing CATV transport system to directly deliver 77channels AM-VSB CATV signal all the way from a CO to client premises and then to consumer devices. Different
with current POF LAN schemes, which concentrate on short-distance POF transmission only, our novel system is
the first one to transmit widespread CATV signals from a CO to client premises and then to the in-door devices. In
this system, a 1550 nm optical carrier is directly transmitted along with a span of SMF and POF links. No
wavelength converting or any bridge circuit is needed between the SMF access network and the POF in-door LAN.
Generally, the PF GI-POF is not cheaper than twisted pair/coaxial cable and is not popular to be installed into
houses now. Nevertheless, the fiber length we need to install into a house is quite short, and an amateur can deploy
it with minimal training and cheap tools. Instead of employing a trained person and high-precision devices to install
SMF inside consumers’ house, the POF with do-it-yourself characteristic will be an economic candidate for
installing intrabuilding LAN. Furthermore, the POF cost will be reduce when it is widely accept as well. To sum up
the installation cost and CAPEX, the PF GI-POF will be an economic medium for future optical intrabuilding
LAN. To verify the proposed structure, the feasibility of our proposed system is observed and accompanied with
good CNR, CSO, and CTB performances over a span of 20 km SMF plus 25 m POF. In addition, by varying the
SMF lengths among 10–30 km and POF lengths between 25 and 50 m, the critical limitation of our system presents
at 20 km SMF plus 50 m POF or 30 km SMF plus 25 m POF scenarios. In case longer transmission distance is
required, we also experimentally demonstrate a method to extend the limitation with good CATV RF parameters as
well. Since our proposed system does not need any transceiver circuit or bridge circuit at the SMF and POF
connection point, it is an economic and straightforward solution to provide all optical CATV service all the way
from a CO to consumer in-door devices.