Etude des nouveaux formats de modulation pour la montée en débit dans le réseau d'accès optique 28/03/2008 – Journée de doctorant ENSTB DUONG Thanh Nga Encardrant à FT: GENAY Naveena Directeur de thèse: SIMON Jean-Claude

Outline 1 2 3 Introduction Experimentation Conclusion and perspective Contexte Experimentation Low-cost MB-OFDM for remote modulation of colorless ONU Direct modulation of 2.5GHz DFB laser at a bit rate of 10Gbit/s Conclusion and perspective 2 3

Outline 1 2 3 Introduction Experimentation Conclusion and perspective Contexte Experimentation Low-cost MB-OFDM for remote modulation of colorless ONU Direct modulation of DFB laser at a bit rate of 10Gbit/s Conclusion and perspective 2 3

1. Introduction (1) Interest of OFDM for the optical access network Application Débit requis Téléchargement des données 2 Mb/s VoIP, Video-telephony, Videoconferencing 1 Mb/s Musique à la demande (contenu multimédia) Jeux en ligne TV numérique SD 3 Mb/s TV numérique HD 10 Mb/s TV numérique HD canaux additionnels (2 HD DTV) 20 Mb/s

1. Introduction (2) Interest of OFDM for the optical access network Increase the capacity and decrease the cost of the system in optical access network Increase the bit rate up to 10Gbit/s and more Increase the transmission distance up to 100km without chromatic dispersion compensation Fiber chromatic dispersion Rayleigh Backscattering in architecture colorless ONU Cost of system Solution Low-cost ONU module Direct modulation of laser To use advanced modulation format which is robust to fiber chromatic dispersion like DB, DPSK or OFDM modulation format

Spectre de DB, NRZ, DPSK et RZ Interest of OFDM Spectre de DB, NRZ, DPSK et RZ Duo-binary (DB) Un spectre est plus comprimé que celui du NRZ Plus tolérance à la dispersion chromatique Détection simple Complexité de l'émetteur DPSK/DQPSK Appliquer la technique remodulation La complexité du récepteur → coût élevé DPSK/DQPSK-ASK Forte tolérance à la DC La complexité de l'émetteur et du récepteur Faible sensibilité au récepteur OFDM Technique de transmission multi-porteuses Utiliser l'algorithme FFT/IFFT Chaque sous-porteuse est modulé par un format de modulation numérique différent Le signal modulé DPSK

1. Introduction (3) Interest of OFDM for the optical access network What is OFDM ? Widely use in the radio communication DAB (Digital Audio Broadcasting) DVB-T (Digital Video Broadcasting-Terrestrial) DRM (Digital Radio Mondiale) Wireless system Multi-carriers modulation format which uses a large number of closely-spaced orthogonal sub-carriers Use FFT/IFFT algorithm Each sub-carrier is modulated with a conventional modulation (QPSK, m-QAM, etc…)

1. Introduction (5) Interests of OFDM for optical access network Why we use OFDM for optical access network? High density of information (Bit/s/Hz) → increase the bit rate without increasing RF cost (using low bandwidth component) More tolerant to fiber chromatic dispersion (multi-path resilience) and we can optimize the transmission performance by adjusting the modulation format on each sub-carrier → 10G compatible Could be implemented with DSP technique on fast and low cost devices Reuse existing development in radio system (ISO/IEC DIS26908 UWB standard for MB-OFDM) Improve the transmission performance with the help of FEC (BER = 10-4 without FEC)

Outline 1 2 3 Introduction Experimentation Conclusion Contexte Low-cost MB-OFDM for remote modulation of colorless ONU Direct modulation of DFB laser at a bit rate of 10Gbit/s Conclusion 2 3

2. Experimentation (1) Low-cost MB-OFDM for remote modulation of colorless ONU CW 1xN ONU Rx 20km OLT 1.92Gbit/s OFDM CW laser CWDM Splitter Remote modulation Bidirectional transmission on 20km single-fiber hybrid WDM/TDM-PON architecture CW laser at 1550nm sent downstream Upstream data was generated by MB-OFDM at 1.92Gbit/s (3 OFDM bands at a bit rate of 640Mbit/s for each band)

2. Experimentation (2) Low-cost MB-OFDM for remote modulation of colorless ONU, EAM solution SOA1 CWDM EAM OFDM Signal SOA2 CW signal l1 Modulated upstream signal l1 Filter: CWDM having 0.6dB insertion losses and bandwidth of 20nm EAM: 14dB insertion losses, 10dB extinction ratio and bandwidth of 12GHz 2SOAs: 18dB optical gain 3 OFDM bands centred at 744MHz, 1272MHz and 1800MHz. 128 sub-carriers modulated by QPSK format each band

2. Experimentation (3) Low-cost MB-OFDM for remote modulation of colorless ONU, EAM solution BTB transmission, upstream transmission for 1x16 splitting ratio Received signal's constellation

2. Experimentation (4) Low-cost MB-OFDM for remote modulation of colorless ONU, EAM solution BTB 1x8 1x16 2dB 6dB Remote modulation was possible on a single fiber hybrid architecture There are 2dB penalty for 1x8 splitting ratio and 6dB for 1x16 splitting ratio

2. Experimentation (7) Comparison with NRZ signal SOA1 CWDM EAM NRZ SOA2

2. Experimentation (8) Comparison with NRZ signal Remote modulation was also possible on a single fiber hybrid architecture Only a splitting ratio of 1x8 was achieved for EAM solution and no splitter could be added for R-EAM solution (at 1.3Vp-p input at R-EAM)-error floor for 1x2 splitting ratio at 2Vp-p EAM solution R-EAM solution 1x8 1x16 No splitter 1x4 1x2 (pour 2Vp-p)

2. Experimentation (9) Comparison with NRZ signal For EAM solution Measured factor OFDM remote modulation NRZ remote modulation Architecture WDM/TDM-PON Launched power laser 2dBm Bit rate 1.92Gbit/s 2Gbit/s SNR 19dB (BER<10-9) 19dB (BER>10-6) Achieved splitting Ratio (BER<10-9) 1x16 (SNR = 19dB) 1x8 (SNR = 23dB)

Discussion Increase the bit rate in optical access network GPON → 10G in access Fiber chromatic dispersion Expensive component Chirp of components Low cost infrastructure and low cost ONU module Low cost components Colorless ONU RF cost vs optical cost Fiber single architecture Rayleigh Backscattering OFDM modulation is a good candidate as a cost effective solution for colorless ONU OFDM format is more tolerant to Rayleigh backscattering than NRZ format in a bidirectional link

Outline 1 2 3 Introduction Experimentation Conclusion Interest of OFDM modulation for the optical access network Experimentation Low-cost MB-OFDM for remote modulation of colorless ONU Direct modulation of low-cost laser at a bit rate of 10Gbit/s Conclusion 2 3

2. Experimentation (1) Direct modulation of DFB laser at a bit rate of 10Gbit/s Direct modulation of 2.5GHz DFB laser by 10Gbit/s AMOOFDM signal 64 sub-carriers The m-QAM mapping varies from 4-QAM to 32-QAM Transmission distance was taken to be 20km, 50km and 110km No dispersion compensation Encoded data out Optical receiver A/D converter DSP demodulation Negotiation between Tx and Rx S/P M-QAM mapper IFFT P/S AWG DFB laser Encoded data in 20km, 50km, 110km SMF DSP modulation AOV

2. Experimentation (2) Direct modulation of DFB laser at a bit rate of 10Gbit/s Sub No.1 Sub No.31 Sub No.23 Sub No.10

2. Experimentation (3) Direct modulation of low-cost laser at a bit rate of 10Gbit/s – DFB laser BERk is the bit error rate of kth sub-carrier ND is the number of sub-carrier which contain the real data The transmission is possible on 110km SMF A BER of 10-3 was obtained at a received optical power of -16dBm The penalties for 20km and 50km optical links are negligible (the sensibility is considering at BER of 10-4) The penalty on 110km optical link was approximately 2dB because of chromatic dispersion

2. Experimentation (4) Comparison with NRS modulation – DFB laser Modulate directly with signal NRZ-OOK at a bit rate of 10Gb/s using the same DFB laser and receiver There was an error-floor at a bit rate of 9x10-4 for BTB curve and at a bit rate of 3x10-2 for 20km transmission. Transmission over 50km and 110km SMF were impossible due to the effect of chromatic dispersion AMOOFDM is more tolerant to fiber chromatic dispersion than NRZ-OOK signal

2. Experimentation (5) Comparison with NRZ modulation – 2 2. Experimentation (5) Comparison with NRZ modulation – 2.5GHz DFB laser Considering factors Direct modulation with AMOOFDM signal Direct modulation with NRZ-OOK signal Architecture TDM-PON Launch power 9.6dBm Bit rate 10Gb/s Transmission distance possible 110 km

Discussion Increase the capacity in optical access network GPON → 10G in access Transmission distance → 100km Fiber chromatic dispersion Expensive component Chirp of components AMOOFDM modulation is a good candidate as a cost effective solution for optical access network in order to increase the capacity (bit rate and transmission distance) AMOOFDM format is more tolerant to fiber dispersion chromatic than NRZ format

Outline 1 2 3 Introduction Experimentation Conclusion and perspective Contexte Experimentation Low-cost MB-OFDM for remote modulation of colorless ONU Direct modulation of DFB laser at a bit rate of 10Gbit/s Conclusion and perspective

3. Conclusion A remote modulation scheme was presented for upstream transmission in hybrid WDM/TDM-PON single fiber architecture A solutions are proposed for the colorless ONU: EAM solution. A bit rate of 1.92Gbit/s was archived for each wavelength Comparison between NRZ and OFDM remote modulation for both solutions was performed OFDM format is more robust to Rayleigh Backscattered light than NRZ-OOK modulation 10Gb/s transmission is experimentally demonstrated over 110km SMF by direct modulation of 2GHz bandwidth DFB laser without dispersion compensation A comparison between NRZ-OOK format and AMOOFDM format was performed at a bit rate of 10Gb/s AMOOFDM modulation format is more tolerant with fiber chromatic dispersion than NRZ-OOK format

Thank you for your attention This work was performed in the framework of E-Photon One network of excellence and the French ANTARES project Thank you for your attention Any question ?

Annexe (1) Definition of EVM

1. Introduction (4) Interest of OFDM for the optical access network