320 Gb/s Nyquist OTDM received by polarization-insensitive time-domain OFT

Abstract

Abstract:We have demonstrated the generation of a 320 Gb/s Nyquist-OTDM signal by rectangular filtering on an RZ-OTDM signal with the filter bandwidth (320 GHz) equal to the baud rate (320 Gbaud) and the reception of such a Nyquist-OTDM signal using polarization-insensitive time-domain optical Fourier transformation (TD-OFT) followed by passive filtering. After the time-to-frequency mapping in the TD-OFT, the Nyquist-OTDM signal with its characteristic sinc-shaped time-domain trace is converted into an orthogonal frequency division multiplexing (OFDM) signal with sinc-shaped spectra for each subcarrier. The subcarrier frequency spacing of the converted OFDM signal is designed to be larger than the transform-limited case, here 10 times greater than the symbol rate of each subcarrier. Therefore, only passive filtering is needed to extract the subcarriers of the converted OFDM signal. In addition, a polarization diversity scheme is used in the four-wave mixing (FWM) based TD-OFT, and less than 0.5 dB polarization sensitivity is demonstrated in the OTDM receiver. References and links1. P. J. Winzer, "High-spectral-efficiency optical modulation formats," J. Lightwave Technol. 30(24), 3824-3835 (2012 Schindler, C. Koos, W. Freude, and J. Leuthold, "512QAM Nyquist sinc-pulse transmission at 54 Gbit/s in an optical bandwidth of 3 GHz," Opt. Express 20(6), 6439-6447 (2012 (2011)

High Speed All Optical Nyquist Signal Generation and Full-band Coherent Detection

“…However, the full-band modulation, multiplexing and detection are not investigated in this work. Although Nyquist signal modulation, multiplexing and detection is similar to the optical time-division multiplexing (OTDM) in previous works29303132, some important features are not considered for Nyquist signals. When we look at the previous OTDM works, the most recent experiment has achieved a symbol rate of 1.28 Tbaud and a single-channel bit rate of 10.2 Tb/s with RZ 16-QAM modulation and coherent detection.…”

“…In addition, the OTDM relies on short pulses occupying large bandwidth in the frequency domain which reduces the spectral efficiency2930. The combination of Nyquist pulse generation and OTDM system is reported in31323334. However, these works are mainly on the on-off keying or differential phase-shift keying.…”

“…Higher-order modulation and coherent detection are not mentioned in these works. Again, the receivers in these works31323334 are typical OTDM one with complicated channel demultiplexing setups. In addition, as analyzed in28, the Nyquist pulses in333436 are not an optimal one but with very large roll-off factors (0.4 or even 0.5).…”

“…At the coherent receiver, one free-run continuous wave (CW) local oscillator (LO) laser working at the central frequency of the comb is used for coherent homodyne beating. As mentioned before, the full-band coherent receiver is simpler compared with the typical OTDM receiver reported in29303132333435. The simpler receiver setup mainly shows in two aspects: the reduced number of receivers and the free run LO.…”

“…However, in our experiment, the LO is commercial available, free-run, CW ECL, which is quite easy for implementation. No strict synchronization pulse demultiplexing293031323334 or comb source LO35 is used in the receiver side, while a full-band coherent detection and digital signal processing (DSP) is applied. The DSP is based on regular algorithms and subsystems, which is commonly used in coherent system3738394041.…”