Burst-Mode Digital Signal Processing for Coherent Optical Time-Division Multiple Access

Abstract

As the 50G optical access gradually matures, it is time to discuss Beyond 50G optical access. According to the evolution rules of optical access standards, Beyond 50G optical access data rate may achieve 200Gb/s. Direct detection faces great challenges for Beyond 50G optical access, which makes coherent detection a potential solution. Similar to 50G optical timing-division-multiple access (TDMA), burst-mode digital signal processing (BM-DSP) is also required for Beyond 50G coherent optical TDMA (CO-TDMA). This paper proposes coherent BM-DSP (Co-BM-DSP) based on approximately 10ns designed preambles to process the burst signal for 200G CO-TDMA, which can fast estimate the state of polarization, frequency offset, sampling phase offset, synchronization position, and equalizer coefficients. Meanwhile, for obtaining the equalizer coefficients based on the designed preamble, the channel estimation based on the minimum-mean-square-error criterion is theoretically proven to have a unique solution for ensuring reliability. In conclusion, the proposed Co-BM-DSP based on the designed preambles paves the way for the applications of Beyond 50G CO-TDMA.

Figures (11)

• Figure 1: (a) Schematic diagram of CO-TDMA based on Co-BM-DSP. ONU: optical network unit, OLT: optical line terminal, LO: local oscillator, ICR: integrated coherent receiver, ADC: analog-to-digital converter.
• Figure 2: (a) Frame structure for burst signal of CO-TDMA. (b) Structure of designed preambles including Preambles A and B. (c) The spectra of Preamble A for X polarization and Y polarization with two different frequency tones. (d) Constellation diagrams of the Preamble B for X polarization and Y polarization with two different seeds.
• Figure 3: Block diagram of Co-BM-DSP based on the designed preambles at the receiver side. FOE: frequency offset estimation, CDC: chromatic dispersion compensation, ZF: zero forcing, DD-LMS: decision-direct least-mean-square, MIMO: multiple-input-multiple-output, CPR: carrier phase recovery.
• Figure 4: (a) Experimental setups of the 200G CO-TDMA with two ONUs. (b) Two received burst signals with a guard interval.
• Figure 5: Spectra of the received Preamble A (a) without and (b) with the one-tap SOP estimation and recovery. (c) The power sum of two frequency tones at $R_\text{s}/2$ for the X polarization and at $R_\text{s}/4$ for the Y polarization versus $\theta$ in Eq. (\ref{['Eq1']}).