© 2014 Optical Society of America. We demonstrate two 1Tbit/s superchannel architectures using a compact, FSR-tunable gain-switched comb source. SSMF transmission of 18GBaud Nyquist-WDM shaped PDM-QPSK and PDM-16QAM modulation is reported, with a capacity up to 1.296Tbit/s and SE of 7.2bit/s/Hz.