Abstract
We investigate optical prefiltering for 56Gbaud (224Gbit/s) electrical time-division multiplexed (ETDM) dual polarization (DP) quaternary phase shift keying (QPSK) transmission. Different transmitter-side optical filter shapes are tested and their bandwidths are varied. Comparison of studied filter shapes shows an advantage of a pre-emphasis filter. Subsequently, we perform a fiber transmission of the 56Gbaud DP QPSK signal filtered with the 65GHz pre-emphasis filter to fit the 75GHz transmission grid. Bit error rate (BER) of the signal remains below forward error correction (FEC) limit after 300km of fiber propagation.
Highlights
One of the possible solutions to temporarily postpone fiber bandwidth exhaustion is to increase transmission symbol rates and spectral efficiency
Filter shapes under consideration are subsequently applied to the 67% duty cycle return-to-zero (67%RZ)-shaped channel under test (CUT) while maintaining 23 dB optical signal-to-noise ratio (OSNR)
We start the investigation with a BW of 105 GHz for all filter shapes which is the minimum at which filter influence on the Bit error rate (BER) is negligible
Summary
One of the possible solutions to temporarily postpone fiber bandwidth exhaustion is to increase transmission symbol rates and spectral efficiency. Moving to dual polarization (DP) quaternary phase shift keyed (QPSK) transmissions at symbol rates of 56 Gbaud and beyond obtained by electrical time-division multiplexing (ETDM) is very demanding. This is due to a wideband nature of the transmitted signals, which set very high bandwidth (BW) requirements towards electrical components. The wide optical spectrum of high symbol rate signals is facing increased penalties due to cascaded filtering in fixed-grid reconfigurable optical add-drop multiplexers (ROADMs) [6].
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