研究目的
To demonstrate high-spectral-efficiency 600-Gbps/carrier transmission using PDM-256QAM format for data center interconnection applications, overcoming signal quality degradation from device imperfections through a precise calibration method.
研究成果
The study successfully demonstrated single-carrier 48-GBaud PDM-256QAM transmission over 100 km and 10-WDM transmission in a 50-GHz grid, achieving a spectral efficiency of 12.02 bit/s/Hz. The precise calibration method enabled high-baud-rate, high-order modulation despite device limitations. Future research should focus on mitigating nonlinearities and dense-WDM penalties to enhance signal quality and extend transmission distances.
研究不足
The experiment used devices with limited analog bandwidth (13 GHz for Tx, 21 GHz for Rx) and a μITLA with linewidth up to 100 kHz, which may constrain higher performance. The calibration scheme does not precisely separate phase responses for Tx and Rx, and WDM transmission introduced penalties such as cross-phase modulation. Future work is needed to address nonlinear characteristics and improve transmission distance.
1：Experimental Design and Method Selection:
The study used a precise calibration method with fixed equalizers to separately compensate for the linear frequency responses of the transmitter (Tx) and receiver (Rx). This involved offline digital signal processing (DSP) and the use of an arbitrary waveform generator (AWG) for signal generation.
2：Sample Selection and Data Sources:
The experiments utilized 48-GBaud PDM-256QAM signals with a net rate of
3：24 Gbps, generated using pseudorandom binary sequences (PRBS) of 2^18-1 and pilot symbols. List of Experimental Equipment and Materials:
6 Equipment included an AWG (Keysight M8196A), lithium niobate (LN) I/Q-modulator, micro-integrable tunable laser assembly (μITLA) from NeoPhotonics (TTX1995), erbium-doped fiber amplifier (EDFA), optical bandpass filter (OBPF), balanced photodiodes (BPDs), digital storage oscilloscope (DSO), and pure-silica-core fiber (PSCF).
4：Experimental Procedures and Operational Workflow:
Signals were generated offline, pre-equalized, transmitted over fiber (up to 100 km), received, and processed offline. Calibration involved using an ASE source for Rx response estimation and training sequences for Tx and Rx compensation.
5：Data Analysis Methods:
Data was analyzed using fixed equalizers, adaptive equalization with LMS algorithm, pilot-assisted digital phase-locked loop (PLL), and Q-factor measurements to evaluate performance against pre-FEC limits.
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