1. Sandis Spolitis, Inna Kurbatska, Vjaceslavs Bobrovs
Comparison of C-band and L-band WDM-PON systems performance with PAM-4 modulation format
Sandis Spolitis, Inna Kurbatska, Vjaceslavs Bobrovs
Institute of Telecommunications, Riga Technical University, LV-1048, Riga, Latvia
FOAN 2017, Munich

2. Outline Benefits of the PAM-4 modulation format
Brief overview of NG-PON2 solutions
The structure of the research
Simulation technique
Simulation model of the investigated transmission system
Setup
Parameters
Results
Conclusions

3. Benefits of the PAM-4 modulation
Four-level pulse amplitude (4-PAM) modulation
Advantages for high-speed transmission:
Ensures twice higher spectral efficiency than traditionally used NRZ.
Has a higher dispersion tolerance than NRZ.
Requires a narrower bandwidth of the equipment than NRZ.
Has a lower cost and implementation complexity in comparison with other advanced modulation formats.
One of the intensively studied solutions for the realisation of 40 Gbit/s per-wavelength data rate for NG-PON2.

4. Brief overview of NG-PON2 solutions
Rec. ITU-T G (12/2014)
TWDM-PON
Up to 4 wavelengths with up to 10 Gbit/s.
PtP WDM-PON (optional)
Up to 8 wavelengths with up to 10 Gbit/s.
The increase to 40 Gbit/s is widely studied.
nm for downstream
nm for downstream
The investigation of utilization of L-band becomes crucial.

5. The structure of the research
The aim of our research:
To evaluate the difference between the transmission utilizing frequencies of C-band and L-band.
1st stage. Reference transmission systems.
Comparison of BER dependance on the transmission distance.
2nd stage. The impact of filtering on the BER.
Comparison of the impact of the optimizing of optical and electrical filters’ bandwidths.
3rd stage. The impact of filtering on the received optical signal power.

6. Simulation technique
Results are obtained in VPItransmissionMaker Optical Systems simulation software.
BER of received signals is evaluated performing statistical analysis applying Gaussian statistical model.
*1 D. N.Nguyen, M. Elsherif, A. Malekmohammadi, “Investigations of high-speed optical transmission systems employing Absolute Added Correlative Coding (AACC)”, Optical Fiber Technology, 30, 23-31, 2016.
The part of the BER results was evaluated also by applying direct error counting utilizing co-simulation with MATLAB.

7. Simulation model
Simulation setup of investigated PAM-4 modulated WDM-PON transmission system operating in optical C and L bands.

8. Utilized frequencies of C –band * Utilized frequencies of L –band**
Number of the channel
Frequency
(THz) 1.
192.8 2.
192.9 3.
193.0 4.
193.1 5.
193.2 6.
193.3 7.
193.4 8.
193.5
Utilized frequencies of L –band**
Number of the channel
Frequency
(THz) 1.
184.7 2.
184.8 3.
184.9 4.
185.0 5.
185.1 6.
185.2 7.
185.3 8.
185.4
*according to ITU-T G.694.1
** according to ITU-T G.989.2, frequencies for PtP WDM

9. Optical signal power
Optical interface parameters of downstream direction with 40 Gbit/s per channel data rate are not standardized.
ITU-T G.989.2
PtP WDM: Optical interface parameters for line rate class 3 (from Gbit/s to Gbit/s) downstream direction, N1 power class.
Channel launch power, MIN
7.5 dBm
Channel launch power, MAX
11 dBm
Optical path loss,
MIN
14 dB
Laser output power:
13 dBm
Two optical attenuators,
attenuation of each:
4 dB

10. 1st stage. Reference transmission systems
The BER of the reference system in dependence on the length of transmission distance.
C-band
L-band
Maximal transmission distance with BER<10-3 : 11 km
Maximal transmission distance with BER<10-3 : 8 km
Maximal transmission distance with BER<10-9 : 8 km
Maximal transmission distance with BER<10-9 : 5 km

11. 2nd stage. Filtering vs BER
The dependence of BER on the bandwidths of the filters for C and L bands.
C-band
BW of electrical filter: 20 GHz
BW of optical filter: 75 GHz
BW of electrical filter: 30 GHz
BW of optical filter: 60 GHz

12. 2nd stage. Filtering vs BER
The dependence of BER on the bandwidths of the filters for C and L bands.
L-band
BW of electrical filter: 20 GHz
BW of optical filter: 75 GHz
BW of electrical filter: 30 GHz
BW of optical filter: 60 GHz

13. 2nd stage. Filtering vs BER
The dependance of BER on transmission distance for the different combinations of optical and electrical filters bandwidths
For both frequency bands the optimization of the filters bandwidths is prerequisite for the increase of the transmission distance and the decrease of the BER.

14. 2nd stage. Filtering vs BER
The dependance of BER on transmission distance for the different combinations of optical and electrical filters bandwidths
For both frequency bands the optimization of the filters bandwidths is prerequisite for the increase of the transmission distance and the decrease of the BER.

15. 2nd stage. Filtering vs BER
The dependance of BER on transmission distance for the different combinations of optical and electrical filters bandwidths
For both frequency bands the optimization of the filters bandwidths is prerequisite for the increase of the transmission distance and the decrease of the BER.
Maximal transmission distances for C-band are longer than for L-band.

16. 3rd stage. Filtering vs optical signal power
The dependance of BER on transmission distance for the different combinations of optical and electrical filters bandwidths
For both frequency bands, the optimization of the filters bandwidths allows to decrease the minimal necessary received signal power.
The combination of the bandwidth of optical filter equal to GHz and bandwidth of the electrical filter equal to 20 GHz is the most successful.

17. Conclusions The impact of filtering on the BER
For both, optical C and L frequency bands, the impact on the BER is similar:
The wider bandwidth of the optical filter allows using narrower bandwidth of the electrical filter.
The optimal combination is the combination of optical filter equal to GHz and bandwidth of the electrical filter equal to 20 GHz.
The optimization of the bandwidths increased maximal transmission distance and decreased BER.
The impact of filtering on the received optical signal power
For both, optical C and L frequency bands, the impact on the optical signal power is similar:
The optimization allows to decrease the minimal necessary received signal power.
In comparison with C-band, L-band demonstrates shorter transmission distance and requires higher signal power at longer transmission distances.

18. Thank you for your attention!
FOAN 2017, Munich