Ultrahigh Spectral Density Coherent Optical Transmission Technologies

Novel coherent self-heterodyne receiver based on phase modulation detection

“…The 3dB penalty of PM detection method was primarily caused by the additional ASE beat noise from the EDFAs due to heterodyne demodulation. The accumulated number of noise photons after the EDFAs chain was ( 1) sp m G n − (where sp n is the spontaneous emission factor, m is the number of EDFAs, and G is the amplifier gain), which is much greater than the number of photons from shot-noise (1 photon) [1]. The carrier-to-noise ratio after the EDFAs chain was largely determined by ASE noise, as the shot-noise-limit is negligible in such a system [1]:…”

“…Advanced optical modulation formats that offer high spectral efficiency are being increasingly deployed to cope with this trend [1][2][3]. The state-of-the-art optical coherent receiver employs a 90° hybrid front end and a local oscillator (LO) laser for homodyne demodulation [1,4].…”

First demonstration of digital coherent transmission in a deployed ROADM network with a 120 Gbit/s polarization-multiplexed 64 QAM signal

“…To meet the growing demand for larger transmission capacity, digital coherent transmission technologies with higher-order quadrature amplitude modulation (QAM) are expected to be a promising approach in terms of increasing the spectral efficiency and maximizing the use of available bandwidth resources in backbone optical networks [1]. Spectral efficiency exceeding 10 bit/s/Hz has already been achieved [2,3,4], which has made it possible to realize an ultra-large wavelengthdivision multiplexing (WDM) capacity of > 100 Tbit/s by fully utilizing the finite bandwidth of the C-and L-bands [2].…”

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

“…In recent years, spectrally efficient coherent optical transmission with a multilevel modulation format has been intensively investigated to keep pace with the rapid growth in data traffic in current optical fiber networks [1]. Of the many available modulation formats, quadrature amplitude modulation (QAM), in which the amplitude and phase of an optical carrier are simultaneously modulated, has received considerable attention because of its high spectral efficiency compared with other modulation formats.…”