Experimental study of performance enhanced IM/DD transmissions based on constellation switching

Area of Science:

• Optical communications
• Digital signal processing

Background:

• Intensity Modulation/Direct Detection (IM/DD) systems are crucial for high-speed data transmission.
• Standard Pulse Amplitude Modulation (PAM) systems use a single constellation, limiting performance gains.
• Bandwidth limitations in components like Digital-to-Analog Converters (DACs) pose challenges for high bit rates.

Purpose of the Study:

• To experimentally investigate the performance improvements of Constellation Switching (CS) in IM/DD systems.
• To demonstrate the effectiveness of CS in enhancing receiver sensitivity and reducing required power.
• To evaluate CS performance across different bit rates and transmission distances.

Main Methods:

• Implementation of Constellation Switching (CS) by encoding extra bits on PAM constellation pattern selection.
• Experimental setup utilizing bandwidth-limited components, including a 14 GHz DAC.
• Performance evaluation at Hard Decision Forward Error Correction (HD FEC) threshold (BER = 4 × 10^-3).
• Simulations to assess CS performance over a range of transmitter bandwidths.

Main Results:

• CS improved receiver sensitivity in 112 Gbit/s PAM4 by 0.8 dB (B2B) and 1.1 dB (3 km fiber).
• CS improved receiver sensitivity in 84 Gbit/s 2D-PAM4 by 1.05 dB (B2B) and 3.5 dB (5 km fiber).
• Simulations confirmed performance benefits of CS across various transmitter bandwidths.

Conclusions:

• Constellation Switching (CS) offers a simple, low-complexity method to significantly improve IM/DD system performance.
• CS enables achieving higher bit rates or reducing required power, particularly beneficial in bandwidth-constrained scenarios.
• The demonstrated performance gains highlight the potential of CS for future high-speed optical communication systems.