Joint digital signal processing for superchannel coherent optical communication systems

Abstract

Ultra-high-speed optical communication systems which can support ≥ 1Tb/s per channel transmission will soon be required to meet the increasing capacity demand. However, 1Tb/s over a single carrier requires either or both a high-level modulation format (i.e. 1024QAM) and a high baud rate. Alternatively, grouping a number of tightly spaced "sub-carriers" to form a terabit superchannel increases channel capacity while minimizing the need for high-level modulation formats and high baud rate, which may allow existing formats, baud rate and components to be exploited. In ideal Nyquist-WDM superchannel systems, optical subcarriers with rectangular spectra are tightly packed at a channel spacing equal to the baud rate, thus achieving the Nyquist bandwidth limit. However, in practical Nyquist-WDM systems, precise electrical or optical control of channel spectra is required to avoid strong inter-channel interference (ICI). Here, we propose and demonstrate a new "super receiver" architecture for practical Nyquist-WDM systems, which jointly detects and demodulates multiple channels simultaneously and mitigates the penalties associated with the limitations of generating ideal Nyquist-WDM spectra. Our receiver-side solution relaxes the filter requirements imposed on the transmitter. Two joint DSP algorithms are developed for linear ICI cancellation and joint carrier-phase recovery. Improved system performance is observed with both experimental and simulation data. Performance analysis under different system configurations is conducted to demonstrate the feasibility and robustness of the proposed joint DSP algorithms.

Phase-coherent lightwave communications with frequency combs

“…Having access to multiple channels impaired by the same phase noise means that the phase estimation can be made more efficient in terms of phase tracking capabilities [15][16][17], or power consumption of the digital electronics [18]. It has been suggested that joint phase processing can be implemented with optical frequency comb sources [19][20][21][22] but a proof in a transmission experiment is still outstanding. In the receiver, one even and one odd channel can be picked to be received simultaneously.…”

Frequency Comb-Based WDM Transmission Systems Enabling Joint Signal Processing

“…Instead, our results serve as an indication that the phase coherence between the received channels was good enough to enable joint phase estimation. In phase-noise limited systems, such as low-baud rate and higher-order modulation-format systems, larger performance gains can be expected, which has been demonstrated in other phase-locked systems [104] and predicted using simulations [99,103,105].…”

“…For comb-based spectral superchannels, joint phase tracking was first proposed by Liu et al [103]. Using simulations they showed that the phase noise tolerance increased when processing three channels together.…”

Advanced signaling technologies for high-speed digital fiber-optic links

“…In contrast, Co-OFDM produces a sincshaped carrier in the frequency domain (rectangular pulse in the time domain). In practical systems, the transmitter cannot produce gt to perfectly eliminate ISI and ICI; efforts to reduce the impact of ISI and ICI are areas of active research [15].…”