CD-tolerant 2-channel OTDM system using alternating-phase pulses and SiP transmitter for data-center networks

Area of Science:

• Optical Communications
• Photonics
• Signal Processing

Background:

• High-speed intensity-modulation and direct-detection systems face transmitter bandwidth limitations.
• In-phase and quadrature (IQ)-interleaved 2-channel optical time-division multiplexing (OTDM) is a potential solution.
• Conventional constant-phase pulses in IQ-interleaved OTDM suffer from chromatic dispersion (CD)-induced power imbalance, limiting transmission reach.

Purpose of the Study:

• To address the CD-induced power imbalance in IQ-interleaved OTDM systems.
• To enhance the transmission reach of 200-Gb/s pulse-amplitude modulation 4-level (PAM4) signals in the C-band.
• To propose and validate a novel pulse generation technique and equalization scheme for robust optical data transmission.

Main Methods:

• Analytical derivation showing CD-induced power imbalance in conventional OTDM.
• Proposal and analytical/simulational validation of sinusoidally modulated alternating-phase pulses.
• Implementation of a two-stage equalization scheme with symbol-timing recovery and adaptive channel equalization.
• Experimental validation using a silicon photonics transmitter chip.

Main Results:

• Alternating-phase pulses eliminate CD-induced power imbalance for IQ-interleaved OTDM signals.
• The +90° phase configuration extends simulated transmission reach to 6 km.
• Experimental demonstration achieved 1.9 km transmission of 200-Gb/s C-band PAM4 signals, validating 2-km data-center network feasibility.
• Simulations indicate potential for future 400-Gb/s/λ operation.

Conclusions:

• Sinusoidally modulated alternating-phase pulses effectively mitigate CD-induced power imbalance in IQ-interleaved OTDM.
• The proposed system and equalization scheme enable extended transmission reach for high-speed PAM4 signals.
• The technology is feasible for C-band data-center networks and holds promise for future higher-speed optical communication systems.