Budget Extension Schemes for Nx10 Gbit/s DPSK-based

TDM/WDM PON

A. Emsia, Q. T. Le, T. von Lerber, D. Briggmann and F. Kueppers

Institute of Microwave Engineering and Photonics, TU Darmstadt, Merckstr. 25, Darmstadt, Germany

Keywords:

Wavelength-Division-Multiplexed Passive Optical Network (WDM PON), Differential-Phase-Shift-Keying

(DPSK), Semiconductor Optical Ampliﬁer (SOA), Delay Line Interferometer (DLI), Saturated Collision

Ampliﬁer (SCA).

Abstract:

We present a new TDM/WDM PON scheme utilizing PSK (phase shift-keying) at 10 Gbit/s per λ-channel as

the modulation format along the feeder line and an SOA (semiconductor optical ampliﬁer) as the amplifying

component at the remote node. One single DLI (Delay Line Interferometer) converts all λ-channels from PSK

to OOK (on-off keying), the modulation format which is used along the access line and one single SOA are

experimentally demonstrated to be sufﬁcient providing a power budget increase of up to 46.8 dB.

1 INTRODUCTION

Fibre-to-the-Home (FTTH) or Building (FTTB) is an

access network technology that delivers the highest

possible speed of Internet connection by using op-

tical ﬁbre that runs directly to the home, building

or ofﬁce. Gigabit-capable Passive Optical Network

(PON) systems, such as GPON standardized by ITU-

T G.984 and G-EPON standardized by IEEE 802.3ah,

are now being mass-deployed in various FTTH/B

markets around the world. These systems use Time-

division multiplexing (TDM) / Time-division Multi-

ple Access (TDMA) to manage the connection of N

users (up to 128) to one optical port, the connection

between end users and Optical Line Terminal(OLT)

(Willner et al., 2009) (Jia et al., 2010) (Davey et al.,

2006). The follow-up PON solutions use 10 Gbit/s for

downstream transmission known as XGPON (ITU-

T G.987) and 10GE-PON (IEEE p802.3) based on

the same TDM technology. With the continuous in-

crease in bandwidth demand generated by consumer

and business applications (HD TV, cloud computing,

online gaming, video-conferencing, etc.), and with

the requirements of high-speed mobile backhaul for

Long Term Evolution (LTE) networks, the need for

a new, higher capacity access architecture becomes

clear. Wavelength-division-multiplexed passive opti-

cal network (WDM-PON), whose simple topology is

shown in Figure 1, is an efﬁcient choice for future

ﬁbre access networks, and one of the most likely to

solve the challenges of next generation access net-

Figure 1: Wavelength-division-multiplexed passive optical

network.

work (NGAN) as it can provide a point-to-point con-

nectivity to multiple remote locations sharing the ma-

jor part of the ﬁbre plan. This WDM-PON architec-

ture provides the most scalable, cost effective, and

future proof solution available to address the capac-

ity, security, and distance capabilities that network

operators require while leveraging the beneﬁts of a

passive infrastructure. All these factors combine to

make WDM-PON poised to become the disruptive

next-generation access solution. It will enable high

speed access for business, mobile backhaul, and even-

tually FTTH, while also enabling operators to build

converged networks and consolidate the access net-

work.

In this paper, we present a new TDM/WDM PON

conﬁguration based on Return to Zero(RZ) phase

shift-keying signal (PSK) at 10 Gbit/s. The network

extension by the use of a single semiconductor optical

ampliﬁer (SOA) for all channels is demonstrated.

373

Emsia A., T. Le Q., von Lerber T., Briggmann D. and Kueppers F..

Budget Extension Schemes for Nx10 Gbit/s DPSK-based TDM/WDM PON.

DOI: 10.5220/0004057603730377

In Proceedings of the International Conference on Data Communication Networking, e-Business and Optical Communication Systems (OPTICS-2012),

pages 373-377

ISBN: 978-989-8565-23-5

 2012 SCITEPRESS (Science and Technology Publications, Lda.)

DLI

Feeder

Access

OLT

Remote node

1:M splitter

ONU

SOA

Figure 2: Downstream WDM PON architecture.

2 WDM PON ARCHITECTURE

The proposed architecture is shown in Figure 2. It is

comprised of 5 elements: 1) Optical Line Terminal

(OLT), 2) the feeder line, 3) the remote node, 4) split-

ters and the access line, and 5) Optical Network Unit

(ONU). In this architecture, the PSK signal is consid-

ered for downstream transmission as it has many ad-

vantages compared to conventional OOK modulation

format (for instance, better tolerance to ﬁbre disper-

sion and non-linearities). The OLT consists of DPSK

transmitters which offer the wavelengths from 1 to

N for downstream each to its own TDM PON tree

(splitters in the Figure 2 represent the PON trees). In

upstream scenario, TDM technology used to transmit

signals up to OLT. Each user has a dedicated time slot.

At the remote node, only one DLI is used re-

gardless of number of channels.Namely, all six wave-

lengths are converted from DPSK to OOK at the same

time, no need to demodulate the channels separately.

The DWDM signals are then demultiplexed by an

AWG demux and the wavelengths are sent to respec-

tive individual TDM PON trees. At the ONU, the

receivers need no individual demodulators, because

the modulation format transformation from the DPSK

to OOK is performed simultaneously for all ONUs at

the remote node. The proposed downstream PON is

therefore compatible with commercial XGPON1 net-

work terminals. Only DPSK downstream transmis-

sion at the OLT is needed, which could be performed

by cost-efﬁcient direct phase, or frequency modulated

lasers (Vodhanel et al., 1990) (Maher et al., 2010).

The budget extension by the use of a single SOA at

the remote node is experimentally demonstrated and

the possibility to use a saturated collision ampliﬁer

(SCA) (Tervonen et al., 2010) is discussed in the next

sections.

Access

eeder

Remote node

Access budget

10 Gb/s RZ DPSK

Feeder budget

Figure 3: Measurement setup.

3 MEASUREMENTS

3.1 Experimental Setup

The measurement setup is shown in Figure 3 where

six downstream channels of 10 Gbit/s PON are at

1537.388 nm,1542.93 nm ,1543.64 nm,1553.329 nm

,1554,101 nm ,and 1556.55 nm generated by DFB

laser diodes. The channels are combined through

AWG and modulated by Mach Zehnder Modula-

tor. The modulator operates in push-pull mode and

generates RZ-DPSK signals at 10 Gbit/s (PRBS of

-1). In order to have uncorrelated data on each

wavelength, the channels are separated, transmitted

through different ﬁbre lengths and again combined

by a multiplexer. The AWGs have 100 GHz chan-

nel spacing and 50 GHz 3-dB bandwidth. The EDFA

is used to compensate the loss of the multiplexers and

the demultiplexer, each channel has 8 dBm power at

the input of feeder variable optical attenuator. The

line between OLT and the remote node is termed as

feeder line and the one between remote node and

ONU is the access line.

A DLI is employed to convert DPSK into OOK

signal. The receiver is a p-i-n photodiode with sensi-

tivity of -17 dBm at BER 10

−9

and -22 dBm 10

−3

OPTICS2012-InternationalConferenceonOpticalCommunicationSystems

374

Figure 4: BER versus received power for the case without

SOA.

3.2 Experimental Results

The Figure 4 depicts the bit error ratio versus receiver

input power for all six channels for the constructive

output of the DLI as well as corresponding eye dia-

gram of a channel. As mentioned above the sensitiv-

ity range of our receiver at the time of measurements

was from -17 dBm to approximately -22 dBm. The

measurements are done for back-to-back case in the

absence of the SOA.

The Figure 5 demonstrates the spectrum of six

channels with nearly the same power (the spectrum

is acquired after DLI, refer to Figure 2). All six chan-

nels show almost the same performance.

The SOA is now considered in the setup as de-

picted in the Figure 3 to see how it will improve the

power budget of the link. The bias current of SOA is

set to 300 mA at the temperature of 17.2

C. The Fig-

ure 6 displays the gain and noise ﬁgure of the SOA

used in the experiment for vairous channels. The

highest gain of 34.8 dB is achieved at 1554.10 nm

with NF of 8.5 dB.

1500 1520 1540 1560 1580

−70

−60

−50

−40

−30

−20

−10

Wavelength[nm]

P[dBm]

Figure 5: The spectrum of all channels, BWR 0.1nm.

−50 −40 −30 −20 −10 0

Pin[dBm]

NF and Gain[dB]

1542.93nm

1537.388nm

1554.10nm

1553.27nm

1556.56nm

1543.94nm

Noise figure

Gain

Figure 6: The noise ﬁgure and gain of SOA.

10 15 20 25

−12

−10

−8

−6

−4

−2

Access budget(dB)

logBER

5.6 dB

15.6 dB

25.6 dB

35.6 dB

Figure 7: BER versus access budget for varying feeder bud-

gets.

The Figure 7 displays the bit error ratio curves over

access budget for different values of optical feeder

budget considering one channel (1543.64nm).As

seen, for larger values of feeder budget, the bit er-

ror ratio decreases. This is due to domination of ASE

noise produced by the SOA. On the other hand lower

values of feeder budget show weaker performance,

this may be a result of non-linearities caused by the

SOA.

The Figure 8 illustrates BER map for 1543.64

nm.Considering use of forward Error Correc-

tion(FEC),the BER of 10

−3

can be selected. In this

case, at the feeder budget of 17.5 dB the access bud-

get is 18.5 dB. Therefore, the total optical budget is

36 dB. An avalanche photodiode (APD) can be used

to further increase the access budget of the system. In

the absence of SOA, the maximum feeder budget can

be 21 dB, however, SOA can result in higher feeder

budget. In other words, the input signal to the feeder

can be attenuated more than without SOA. For in-

stance, in the Figure 8 at feeder budget of 30 dB we

have access budget of 16.8 dB, this gives total optical

BudgetExtensionSchemesforNx10Gbit/sDPSK-basedTDM/WDMPON

375

10 12 14 16 18 20

−3

Access budget(dB)

Feeder

budget(dB)

Figure 8: BER map of 6-wavelength setup.

budget of 46.8 dB.

4 SATURATED COLLISION

AMPLIFIER

The SCA arrangement consists of a delay interferom-

eter, a pair of circulators, and an SOA (see Figure

9). The delay interferometer demodulates the input

DPSK signal into a pair of complementary OOK sig-

nals that are coupled into the circulators, which direct

the opposite polarity signals through the SOA (Ter-

vonen et al., 2010). The signals are ampliﬁed while

they simultaneously traverse the SOA gain medium

from the opposite directions, and ﬁnally the signals

are coupled out via the circulators.

As discussed in (Tervonen et al., 2010), this arrange-

ment permits saturated SOA operation, which results

in the maximized output power, low ASE noise, and

virtual absence of pattern effects. In other words, the

common negatives of an SOA are effectively miti-

gated. We compared the performance when the SOA

was used in the conventional linear regime with the

SCA arrangement and found up to 10-dB power bud-

get improvement from a single output arm. When the

output doubling is taken in account, the power budget

improvement over the linear operation SOA rises up

DLI

Feeder

OLT

Remote node

Access

1:M splitter

ONU

SOA

Figure 9: TDM/WDM using SCA.

to 13 dB. In collaboration with Orange-France Tele-

com Labs we show in (Le et al., 2011) that the SCA

arrangement can even be used for ampliﬁcation of

multiple simultaneous wavelengths without a notice-

able penalty. And the compatibility of the SCA for

reach extension of a commercial single-wavelength

XGPON1 system was experimentally demonstrated

(Saliou et al., 2011).

5 CONCLUSIONS

In this paper, a power budget extension scheme has

been shown. We demonstrated our scheme using

a SOA and one DLI. Optical budget extension of

46.8 dB with in a 10 Gbit/s TDM/WDM PON was

achieved. We showed that there is trade-off between

higher and lower values of the feeder budget. The ex-

periment performed for six-channel case, i.e., for total

transmission of 60 Gbit/s.

6 FUTURE WORKS

The SCA power extension method has been explained

in section 4. The SCA has not been investigated for 60

Gbit/s WDM/PON system. One of the future works

will be to investigate the difference between the sin-

gle SOA and the SCA setup. Additionally, the bit

rate will be increased to see the performance of the

proposed model. Furthermore, power equalization in

burst mode transmission in upstream case is under in-

vestigation in the laboratory.

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