Abstract
We investigate 128-level set-partitioning quadrature amplitude modulation (128-SP-QAM) experimentally and compare the performance to polarization-multiplexed 16QAM both at the same bit rate and at the same symbol rate. Using a recirculating loop we study both single channel and wavelength-division multiplexing (WDM) transmission and demonstrate a reach of up to 2680 km at a bit-error rate of 10(-3) for 128-SP-QAM. We confirm that 128-SP-QAM has an increased sensitivity compared to PM-16QAM and show that the maximum transmission distance can be increased by more than 50 % at the same bit rate for both single channel and WDM transmission. We also investigate the performance at the same symbol rate as a possible fall back solution in a degrading link.
Highlights
The optical coherent receiver has enabled fiber optical communication systems using modulation formats which take advantage of both quadratures as well as the two polarization states of the optical field and we have seen a remarkable amount of research on high-speed optical links utilizing such modulation formats in combination with polarization multiplexing
We show that 128-SP-QAM can achieve a 1.9 dB increased back-to-back (B2B) sensitivity over polarization multiplexed (PM)-16QAM for the same bit rate and 2.9 dB for the same symbol rate
We have experimentally demonstrated 128-SP-QAM in single channel and wavelength-division multiplexing (WDM) transmission and compared the results to PM-16QAM both at the same symbol rate and at the same bit rate
Summary
The optical coherent receiver has enabled fiber optical communication systems using modulation formats which take advantage of both quadratures as well as the two polarization states of the optical field and we have seen a remarkable amount of research on high-speed optical links utilizing such modulation formats in combination with polarization multiplexing. The two modulation formats that have been most studied in coherent optical communication systems are polarization multiplexed (PM) quadrature phase shift keying (QPSK) and polarization multiplexed rectangular 16-ary quadrature amplitude modulation (PM-16QAM). The use of phase-tracking, polarization demultiplexing and adaptive equalization in the DSP has made transmission of these two formats and a plethora of other modulation formats possible. PM-QPSK is by far the most studied modulation format in coherent optical links and has been investigated using off-line processing in countless experiments and implemented using real-time DSP [1,2]. PM-16QAM enables higher spectral efficiency at a cost of a reduced transmission reach and has been extensively studied recently [3, 4]
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