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Performance Investigation of Back-Compatible
Integrated TWDM/GPON System Using MDM And
Pulse Shapes
To cite this article: Ajmer Singh and Rosepreet Kaur Bhogal 2022 J. Phys.: Conf. Ser. 2327 012036
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4th International Conference on Intelligent Circuits and Systems
Journal of Physics: Conference Series 2327 (2022) 012036
IOP Publishing
doi:10.1088/1742-6596/2327/1/012036
1
Performance Investigation of Back-Compatible Integrated
TWDM/GPON System Using MDM And Pulse Shapes
Ajmer Singh1 , Rosepreet Kaur Bhogal2
School of Electronics and Electrical Engineering, Lovely Professional University,
Punjab.
ajmersinghbhinder@gmail.co1, rosepreetkaur12@gmail.com2
https://orcid.org/0000-0002-5452-11811 , https://orcid.org/0000-0002-1697-44892
Abstract. Optical access networks are the prominent and promising cutting edge technology to
provide high speed, and cost effective operation for meeting the requirements of ever-increasing
demands of users. Multiple access techniques such as Wavelength and time division in passive
optical networks are important innovations to provide high capacity. A mode division
multiplexed back compatible integrated next generation PON2 (TWDM PON) and GPON is
demonstrated with triple play supportability in this work. Proposed system offer pay as you grow
feature and also provide enhanced performance by suppressing the inter-channel interference in
TWDM-PON2. System successfully works on same optical distribution network unit for both
PON standards without extra arrangements and has potential to support 62.5 Gbps in full duplex
mode (Symmetrical downlink/uplink). Moreover, demonstrated back compatible system is
analyzed by incorporating diverse modulations such as NRZ-DPSK, RZ-DPSK, RZ-DQPSK,
NRZ-DPSK and linecodings NRZ, RZ. Received power, Optical signal to noise ratio (OSNR),
BER and Q factor are noted at diverse link lengths and it is noteworthy that LP modes with NRZ
in TWDM PON provide outstanding results.
Keywords. MDM, TWDM, GPON, telecommunication, optical fiber
1. Introduction
With the unpredictable bandwidth requirements due to video on demand, online games, and high-
definition videos, researchers are put forward to enhance the ability of existing optical fiber access
networks [1] [2]. Telecom companies have great opportunities to cater the user with value added services
as the internet traffic is thriving day by day [3]. Optimal way outs to fulfil the user demands by providing
economical and high-speed services, are passive optical networks. PONs has diverse standards
recognized by international telecommunication union and IEEE which are in operation such as ATM-
PON, BPON, GPON, XGPON, GEPON and NG-PONs. There are different data rates, distance, and
users support capacity in each aforementioned PON standards. Fiber to the home networks/premises is
getting attention due to their reliable and cost-effective working using Gigabit passive optical networks.
GPON provide low latency and also guaranteed QOE [4] [5]. GPON basically has three diverse
components such as optical line terminal, transmission medium (optical fiber), and optical network unit
present at user location [6] [7] [8]. Despite the various advantages of GPON, it can provide lesser bit
rates, lesser distances and also lesser users. Numerous research works for enhancing the performance of
4th International Conference on Intelligent Circuits and Systems
Journal of Physics: Conference Series 2327 (2022) 012036
IOP Publishing
doi:10.1088/1742-6596/2327/1/012036
2
passive optical networks are reported so far such as by frequency change [9], power boosters [10], pulse
shapes [11], noise removing filters [12], pulse width shortening [13] etc. However, all of the components
and improvements made to improve PON performance eventually raise the system's cost and
complexity.
Solution to the problem of low data rate and capacity is next generation passive optical network standard
which are separated into two diverse stages such as NGPON1 and NGPON2. Supported data rate of
NGPON1 is symmetrical 10 Gbps and in MGPON2 is symmetrical 40 Gbps or more. With the extensive
literature review, it is perceived that NGPON2 has potential to reuse of ODN, reverse compatibility,
wide bandwidth and mobility of wavelengths [14] [15]. Integration of already deployed GPON with
TWDM PON increase the bandwidth per user, enhance capacity, bit rates and cater the pay as you grow
services which will serve the requirements in near future.
2. Principle of MDM based Reverse compatible GPON/TWDM PON
In order to reduce the inter-channel interference among the channels of TWDM PON, mode division
multiplexing is incorporated in the system. For generating the different intensity profiles, mode
generators having different “azimuthal” and radial number are considered. Eq. 1 represents the mode
number expression
𝑀𝑜𝑑𝑒 𝑁𝑢𝑚𝑏𝑒𝑟 = 𝐴 + 2𝐵 + 1 (1)
Where, B= Radial number, A= azimuthal number
Effect of these different linearly polarized modes is such that these provide extra layering to the
wavelengths which eliminate the wavelength interference effects even if mode coupling takes place.
3. System setup
A high capacity, mode division multiplexed reverse compatible 62.5 Gbps downstream and 61.25 Gbps
upstream system with the incorporation of diverse modulations is depicted in Figure 1. Downstream
TWDM PON has 10 Gbps data rate per channel and total channels of TWDM PON are six in both
upstream and downstream. Triple play services are activated in the system and demonstration is
accomplished without using optical amplifiers. Each transmitter of TWDM PON has binary data
generator, pulse generator, laser and intensity modulator which are then further followed by linearly
polarized mode generator. Similarly, GPON transmitter also has same components as TWDM PON
except the data rate (2.5 Gbps in downstream). Wavelengths assigned to GPON for downstream is 1490
nm and in case of TWDM PON downstream, these assigned wavelengths are λ1=1596 nm to λ6=1601
nm with 1 nm spacing. For video signals, a sine generator pulse is overlaid at 4th channel of TWDM
PON. Linarly polarized modes for TWDM PON are LP01, LP11, LP21, LP12, LP22, LP31 and in the
case of gigabit passive optical network, assigned mode is LP13. Coexistence mux (CEx) is used for
combining both the PON standards and then fed into few mode optical fiber. Signals are then coupled
to FMF of 25 km and all the channels then passed through optical filters for separating TWDM and
GPON channels. After, filtering, photo detectors, low pass filters and BER analyzers are placed to
calculate Q and BER.
For upstream transmission, six channels of TWDM PON at wavelengths λ1=1524 nm to λ6=1529 nm
with 1 nm spacing are used at data rate of 10 Gbps at each channel. GPON has upstream wavelength
1310 nm with bit rate of 1.25 Gbps. Bidirectional few mode fiber is placed in the optical distribution
network and having link length of 25 km. Upstream receiver consists of optical filters for separating
TWDM and GPON channels and after, filtering, photo detectors, low pass filters and BER analyzers are
placed.
3.1. Diverse modulation and linecodings
RZ and NRZ linecodings are basic pulse formats which are also called on off keying and implemented
over developed system for checking the performance of the system. It is perceived that return to zero
modulation format or linecoding has broad spectrum as compared to non return to zero which means
4th International Conference on Intelligent Circuits and Systems
Journal of Physics: Conference Series 2327 (2022) 012036
IOP Publishing
doi:10.1088/1742-6596/2327/1/012036
3
RZ is not as bandwidth efficient as NRZ is. However, return to zero modulation format has prominent
advantage that it is less prone to fber optical phase modulating effects (nonlinear effects). Also, NRZ
and RZ both are less tolerant to dispersion effects and easily introduce errors due to interference of
adjacent bits. However, in the phase shifted modulations this problem is eliminated to maximum extent.
Therefore, DPSK with NRZ and RZ is implemented and analyzed over developed system. DPSK has
many advantages of high dispersion tolerance, bandwidth efficiency due to phase shifting between two
adjacent bits without any reference to preceding bits. Further, from the reported works, it is evident that
higher the phase siftings, higher the dispersion tolerance and therefore NRZ-DQPSK and RZ-DQPSK
are deployed further.
Figure 1. Illustration of proposed system
4. Results and Discussions
Investigation of the demonstrated system is accomplished for diverse link distances in terms of OSNR,
BER and Q factor. An optical spectrum analyzer is employed to check the total wavelengths in the
system and depicted in Figure 2. It represents the power at each carrier sognal with reference of its
center frequency.
Figure 2. Illustration of proposed system
Performance of diverse intensity profiles (LP modes) are investigated at different link lengths of FMF
and results observed in eh form of BER/Q factor. Figure 3 (a) depicts that deterioration increases if
4th International Conference on Intelligent Circuits and Systems
Journal of Physics: Conference Series 2327 (2022) 012036
IOP Publishing
doi:10.1088/1742-6596/2327/1/012036
4
length of the fiber increases which is due to attenuation, dispersion and scattering effects. Results reveal
that best performing mode in terms of Q is LP01 and performance is followed by LP11, LP21
respectively. Minimum Quality is seen in case of LP31 mode.
(a)
(b)
Figure 3. Justify the caption. Analysis of diverse LP modes/wavelengths for (a) Quality factor
(b) Log BER at different distance of FMF
Figure 3(b) represents different LP modes and wavelength channels of TWDM and GPON BER at
varied link lengths. It is perceived that minimum BER is observed in LP01 and performance is followed
by LP11, LP21 respectively. Maximum BER is seen in case of LP31 mode. It is observed that basic
linear modes lower order exhibits best performance. Figure 4 depicts the different LP modes for TWDM
PON and GPON. All the LP modes are taken by changing the azimuthal and radial numbers.
(a)
(b)
(c)
(d)
(e)
(f)
4th International Conference on Intelligent Circuits and Systems
Journal of Physics: Conference Series 2327 (2022) 012036
IOP Publishing
doi:10.1088/1742-6596/2327/1/012036
5
(g)
Figure 4. FMF Representation of LP profiles in TWDM PON (a) LP01 (b) LP11 (c) LP21 (d) LP12
(e) LP22 (f) LP31 and for GPON (g) LP13
Table 1 provides the values of different optical signal to noise ratio for diverse modulations and
linecodings and from the results it is evident that OSNR is highest in RZ-DQPSK due to bandwidth
efficient spectrum of DQPSK and non linear tolerance of RZ and second highest OSNR is of RZ-DPSK
signal. In terms of received power NRZ-DQPSK is best with power 2.50 dB.
Table 1. Values of OSNR and received power for diverse modulations and linecodings
Modulations/Linecodings
OSNR
Received Power dB
NRZ
41.57
1.20
RZ
39.13
-1.89
NRZ-DPSK
28.16
2.40
RZ-DPSK
50.69
0.40
NRZ-DQPSK
34.36
2.50
RZ-DQPSK
57.21
1.40
Further, Q factor investigation of different modulations and linecodings has been done at diverse link
lengths. It is evident that with the increase in the transmission distance, Q of the system decreases due
to attenuations, dispersion and scattering. Modulations which are investigated are RZ-DPSK, NRZ-
DPSK, RZ-DQPSK, RZ-DQPSK. It is reported that due to bandwidth efficiency and less inter symbol
interference, DQPSK is optimal to use. However, it lowers the power of the system due to various
insertion losses of many components which are used to generate phase shiftings. Also it is true for
differentia phase shift keying which has two phase shifts.
Figure 5 depicts the Q factor performance of different modulations and linecodings at diverse link
lengths. Results revealed that due to simple architecture, low losses and bandwidth efficiency, NRZ
comes out to be best in terms of Q factor.
5. Conclusion
A back compatible integrated mode division multiplexed next generation PON2 (TWDM PON) and
GPON is demonstrated with triple play supportability. Enhanced performance is obtained by
suppressing the inter-channel interference in TWDM-PON2 and provides pay as row services. System
successfully works on same optical distribution network unit for both PON standards without extra
4th International Conference on Intelligent Circuits and Systems
Journal of Physics: Conference Series 2327 (2022) 012036
IOP Publishing
doi:10.1088/1742-6596/2327/1/012036
6
arrangements and has potential to support 62.5 Gbps in full duplex mode (Symmetrical
downlink/uplink). Performance of LP01 mode is observed best due to less more coupling and TWDM
PON performs better than GPON. Further different modulations and linecodings are investigated in the
form of OSNR, Q and received power. Results revealed that Q factor is best in case of NRZ among all
modulations and followed by RZ-DQPSK. However, maximum power is received in case of NRZ-
DQPSK.
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Acknowledgement
I would like to express my very great appreciation to Manoj Sindhwani, Shippu Sachdeva, Javed
Dhillon, Raghav Gupta (School of Electronics and Electrical Engineering, Lovely Professional
University, Phagwara, Punjab, India.) for their valuable and constructive suggestions during the
planning and development of this research work. Their willingness to give their time so generously
have been very much appreciated.
4th International Conference on Intelligent Circuits and Systems
Journal of Physics: Conference Series 2327 (2022) 012036
IOP Publishing
doi:10.1088/1742-6596/2327/1/012036
7
[15] Luo Y, Zhou X, Effenberger F, Yan X, Peng G, Qian Y and Ma Y 2013 Time-and wavelength
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