64-Tb/s, 8 b/s/Hz, PDM-36QAM Transmission Over 320 km Using Both Pre- and Post-Transmission Digital Signal Processing

Optical Communication: Its History and Recent Progress

“…One can also implement error-correcting codes and employ encoder and decoder chips to improve the bit-error rate at the receiver end. A new record was set in 2011 when 64-Tbit/s transmission was realized over 320 km of a single-mode fiber using 640 WDM channels that spanned both the C and L bands with 12.5-GHz channel spacing [20]. Each channel contained two polarization-multiplexed 107-Gbit/s signals coded with a modulation format known as quadrature amplitude modulation.…”

“…Singlewavelength systems, employing TDM in the electrical domain, started with a capacity of under 100 Mbit/s in the 1980s and were operating at 10 Gb/s around 1990. The advent of WDM in the early 1990 led to a big jump in the system capacity and subsequent adoption of coherent detection with digital signal processing allowed the capacity to reach 64 Tbit/s by the year 2010 [20]. Further increase in system capacity required the adoption of SDM.…”

Transmission and reception of Quad-Carrier QPSK-OFDM signal with blind equalization and overhead-free operation

“…For the phase recovery, Viterbi algorithm is utilized to cancel the phase noise of QPSK signal after 4-point FFT. For the CMMA algorithm, we only select the inner three rings/radii for the error signal calculation to increase equalizer robustness [10,11], which is the same as CMMA algorithm for 9-QAM signal [12,13]. We also analyze the PAPR of Quad-Carrier QPSK-OFDM signal and traditional QPSK-OFDM signal.…”

“…At receiver, after optical to electrical (O/E) conversion, a digital filter is used to separate the 4-subcarrier, and then DSP is applied for each subcarrier [9]. 4-subcarrier OFDM signal shows as a 25-QAM signal in the time domain, and it can be blindly equalized with cascaded multi-modulus algorithm (CMMA) equalization in the time domain [10][11][12][13]. With the blind equalization, channel estimation and equalization, FOE, and phase recovery can be implemented without TS and pilot tones.…”

Massive individual orbital angular momentum channels for multiplexing enabled by Dammann gratings

“…1 In addition to the multiplexing technologies based on amplitude, wavelength [2][3][4] and light polarization 5,6 division, the orbital angular momentum (OAM) of optical vortex (OV) beams [7][8][9][10][11] provides a new degree of freedom for multiplexing to further increase the capacity of optical communications systems. OV beams have helical phase profiles in their electric fields that are proportional to the azimuthal phase term of exp(i'w), where ' is the eigenvalue of the OAM or the so-called topological charge and w is the azimuthal angle.…”