Long-Haul Transmission of PM-16QAM-,PM-32QAM-, and PM-64QAM-Based

TerabitSuper channels Over a Field Deployed

Legacy FiberStefano Calabr`o, Erik de Man, Uwe Feiste, Antonio Napoli, Marc Bohn, Ginni Khanna, Norbert Hanik, Claude Le Bou¨ett´e, J´er´emie Jauffrit, Sylvain Bordais, Celine Andr´e, Christian Dourthe, Bruno Ragu´en`es, Chigo M. Okonkwo, and A. M. J. Koonen.

MADE BY : Ammar Abdul Jalil & Zainab Jassim

THE recent advances in social networking, cloud services and media content quality (4k/8k video) is resulting in exponential growth of data traffic.capacity of optical fibers is rapidly approaching its limits expected over next five years.In order to economically enhance the capacity of deployed fiber networks, high-order quadrature amplitude modulation (QAM) formats are considered.Achievable transmission reach of high capacity QAM formats is however limited due to reduced nonlinear tolerance and higher required optical signal to noise ratio (OSNR)So these days employing both erbium doped fiber amplifier (EDFA) and Raman amplifier (RA) have gained significant interest.

INTRODUCTION

Some needed expressions: forward error correction (FEC):or channel coding is a technique used for controlling errors in data transmission over unreliable or noisy communication channels. Bit error rate (BER):is the number of bit errors per unit time. pre-FEC BER: are the bit errors caused by attenuation, ageing, temperature changes of the optical fiber. PRE-FEC: indicates that the signal on the optical fiber is FEC encoded.

long-haul transmission can be achieved by utilizing a fraction of QAM formats’ capacity for stronger FEC codes with overhead (OH) as high as 28%.In this context, soft decision (SD-) low density parity check (LDPC) FEC codes requiring pre-FEC BER as high as 9.88 × 10−2 have been experimentally demonstrated.

Flex-grid networks are specially suited for future generation transponders aiming for data rates as high as 1 Tb/s achievable through superchannels structures. In order to reduce cost per transmitted bit, reduction in number of subcarriers per terabit is desired which necessitates higher symbol rates and higher order QAM format.

G.652 standard single mode fiber used with total length of fiber between Lyon and Marseille was 381 km consisting of five spans, Both transmitter and receiver were set up in Lyon and an optical loopback, without regeneration , was established in Marseille . Consequently, the transmitted signal passed through a total of 762 km of dispersion uncompensated link with a total of ten spans. The span attenuation was compensated completely by hybrid EDFA-Raman amplification for eight spans. The two shortest spans of 60 km (Link 3) were purely EDFA amplified. The total accumulated group velocity dispersion (GVD) at 1550 nm was ∼13 000 ps/nm.The combined pump power was ∼500 mW with an on/off gain of 12 dB.in order to comply with the required gain range of 10–25 dB and maximum output power of 21 dBm , two fixed gain amplifiers combined with variable optical attenuators where used.

The subcarriers under test and rest of the WDM channels were generated by two separate setups.DAC 1, operating at 64 Gsamples/s, was used for neighboring channels while DAC 2, operating at 88 Gsamples/s, was used to generate the subcarrier under test. In order to generate the even and odd neighboring optical m QAM signals, two single polarization LiNbO3 IQ- modulators were used, which were driven by the four amplified electrical signals from DAC 1. DAC 1 outputs independent waveforms on each channel modulating even and odd lasers by independent data. Each modulator was fed in by either sixteen even or sixteen odd continuous wave, 3-dB coupler followed by a split-delay-combine polarization multiplexing emulation stage resulting in a dual polarization signal with 32 channels.

Transmitter process

The symbol rate per subcarrier and the inter subcarrier spectral spacing are different. However, the total number of subcarriers required per terabit is always kept at four. Net data-rate of each subcarrier for PM-16QAM and PM-32QAM configuration was 250 Gb/s and that for PM-64QAM configuration was 300 Gb/s.The minimum symbol-rate required to achieve a given data-rate is constrained by the given PM-mQAM format.

TRANSMISSION CONFIGURATIONS AND BACK-TO-BACK CHARACTERIZATION

A. Quad Subcarrier PM-16QAM 1.0 Tb/s Superchannel• based superchannel was modulated at 41.2 GBd• Limiting the occupied bandwidth of each subcarrier to 49.4 GHz. Spectral spacing between subcarriers was set to 50 GHz• The terabit superchannel occupied a spectral width of 200 GHz• potential C-band capacity of 24 Tb/s.• BER floor of 2 × 10−5• pre-FEC limit of ∼3.8 × 10−2 , achievable at an OSNR0.1 nm of ∼18.4 dB

B. Quad Subcarrier PM-32QAM 1.0 Tb/s

Superchannel

• based superchannel was 33 GBd.

• limit the bandwidth within ≤37.5 GHz

• four flexi-grid slots of 37.5 GHz

• Each superchannel occupied 150 GHz optical bandwidth

• potentially allowing in total 32 × 1 Tb/s superchannels over the C-band

• BER floor at 3.5×10−4• The FEC threshold BER is 3.8 × 10−2 at OSNR0.1 nm of ∼21.2 dB

C. Quad Subcarrier PM-64QAM 1.2 Tb/s Superchannel

• based superchannel was 34 GBd

• occupied an optical bandwidth of 37.4 GHz

• spacing between subcarriers was adjusted to 37.5 GHz

• The superchannel occupied a bandwidth of 150 GHz

• potential C-band capacity was 38.4 Tb/s

• BER floor of 6 × 10−3• pre-FEC limit of 5.7 × 10−2 at OSNR0.1 nm of ∼22.4 dB

As the symbol-rate of each subcarrier is increased, self phase modulation (SPM) effects become more significant independent of the order of modulation. Considering cross phase modulation (XPM) effects, The WDM signal received from the link passed through a waveshaper WS (was used to multiplex the test channel with the neighboring channels and to balance the optical power),The filtered signal and local oscillator (LO) then went into an integrated coherent receiver (ICR))lieaner optical demodulation( which consisted of 2 × 4 90◦ optical hybrids followed by balanced photodiodes that performed optical to electrical conversion.receiver processing consisted of resampling the data to a rate of 2 samples per symbol, then equalizer then located in sample stream then periodically inserted pilot symbols. Finally, the resulting data went into a soft de-mapper and the FEC decoder, with overhead of 24% for FEC.

Receiver process

results & CONCLUSION

-For the first time WDM transmission of PM-64QAM over a field deployed G.652 fiber with the highest symbol-rate over >750 km.- Maximum transmission distance achieved for PM-16QAM case was ∼1571 km and that for PM-32QAM case was ∼1065 km.