Optical filter requirements in an EML-based single-sideband PAM4 intensity-modulation and direct-detection...

Area of Science:

• Optical Communications
• Integrated Photonics
• Digital Signal Processing

Background:

• Single Sideband (SSB) Pulse Amplitude Modulation with 4 levels (PAM4) is crucial for high-speed optical communication systems.
• CMOS analog-to-digital converters (ADCs) and digital-to-analog converters (DACs) offer cost-effective solutions for these systems.
• Challenges include Electro-absorption Modulated Laser (EML)-induced chirp and dispersion, limiting SSB filter requirements.

Purpose of the Study:

• To experimentally demonstrate the feasibility of an SSB PAM4 IM/DD transmission system utilizing CMOS ADC/DAC.
• To investigate the impact of EML chirp and dispersion on SSB filter requirements.
• To determine the minimum roll-off factor for achieving high-speed, long-distance transmission.

Main Methods:

• Generation of SSB signals using a low-cost EML and passive optical filter.
• Employment of filters with varying roll-off factors to analyze performance tolerance.
• Utilization of high-resolution spectrum analysis to identify system limitations.
• Application of linear feed-forward equalization.

Main Results:

• A 51.84 Gb/s transmission over 40 km was achieved.
• A minimum roll-off factor of 7 dB/10GHz was identified as necessary.
• The system demonstrated tolerance to different transmission distances by adjusting filter roll-off.

Conclusions:

• The experimental demonstration confirms the viability of CMOS-based SSB PAM4 IM/DD systems for >50 Gb/s transmission.
• Careful selection of the SSB filter's roll-off factor is critical for mitigating impairments and achieving extended reach.
• Linear feed-forward equalization is sufficient for compensating impairments in this configuration.