512 QAM (54 Gbit/s) coherent optical transmission over 150 km with an optical bandwidth of 4.1 GHz

Polarization-multiplexed, 10Gsymbol/s, 64QAM coherent transmission over 150km with OPLL-based homodyne detection employing narrow linewidth LDs

“…The linewidth of the spectrum was less than 10 Hz, which was below the measurement resolution. The phase noise of the signal calculated by integrating the SSB noise power spectrum was 5.0 degrees (10 Hz∼1 MHz), which is 17 times larger than the experimental result obtained with EFL [8,9,10,11]. This may be attributed to broadening in the tail of the spectrum of the ECLDs and to a narrow FM response bandwidth of the LO.…”

“…To apply an OPLL to higher-order QAM, we have developed a highly precision OPLL circuit for coherent transmission with a frequency-stabilized erbium fiber laser (EFL) with a linewidth of 4 kHz as a transmitter and a frequency tunable EFL with an FM response bandwidth of over 1 GHz as an LO. With the circuit, 128∼512 QAM coherent transmissions were successfully realized, in which the phase noise of the demodulated signal was as low as 0.3 degrees [8,9,10]. We have also demonstrated a real-time 64 QAM coherent transmission with the OPLL [11].…”

Functional integrated modulators and receivers utilizing PLC hybrid integration technology for coherent transmission

“…As for the modulator, to achieve these advanced modulations, multilevel electronics such as arbitrary waveform generators (AWGs) or digitalto-analogue converters (DACs) have been used in many transmission experiments [3,4]. By using them, we can cover various modulation formats with a simple optical setup.…”

Higher Spectral Efficiency Coherent Optical OFDM Transmission With Iterative Polar Modulation

“…Using CO-OFDM [5] with PDM-128-QAM subcarrier modulation, WDM transmission with SE and 165-km (3x55-km)reach has been reported [6]. For single-channel transmission, Nyquist-pulse-shaped PDM-256-QAM [7], PDM-512-QAM [8] and OFDM-PDM-1024-QAM [9] have been used to achieve remarkable ISEs of 16-b/s/Hz, 12.4-b/s/Hz and 11.7-b/s/Hz, respectively, but the achieved transmission reach was limited to 160-km, and the net channel data rates were less than 64-Gb/s. To increase the transmission reach and data rate of high-SE signals, forward error correction (FEC) coding schemes with soft-decision (SD) decoding is being actively studied [10].…”