Adaptively loaded SP-offset-QAM OFDM for IM/DD communication systems

Area of Science:

• Optical Communications
• Digital Signal Processing
• Modulation Techniques

Background:

• Intensity-modulation direct-detection (IM/DD) systems are crucial for cost-effective optical communication.
• Existing schemes like carrier-less amplitude phase modulation (CAP) and conventional OFDM have limitations in performance and complexity.
• Set-partitioned quadrature amplitude modulation (SP-QAM) formats offer potential for enhanced data transmission.

Purpose of the Study:

• To propose and evaluate adaptively loaded set-partitioned offset quadrature amplitude modulation (SP-offset-QAM) orthogonal frequency division multiplexing (OFDM) for IM/DD systems.
• To compare the performance of the proposed SP-offset-QAM OFDM with multi-band CAP and conventional OFDM.
• To demonstrate high-speed data transmission capabilities and analyze the scheme's complexity and robustness.

Main Methods:

• Development of an adaptive loading algorithm tailored for SP-QAM formats.
• Implementation and comparison of SP-offset-QAM OFDM, multi-band CAP, and conventional OFDM.
• Experimental transmission of data over 50-km single-mode fiber.

Main Results:

• Demonstrated data transmission exceeding 40 Gbit/s over 50-km single-mode fiber.
• Significant performance improvements observed across all three schemes due to adaptive loading of SP-QAM formats.
• SP-offset-QAM OFDM exhibited reduced complexity compared to SP-QAM based multi-band CAP.
• SP-offset-QAM OFDM outperformed SP-QAM based conventional OFDM in both back-to-back and post-transmission tests.
• Enhanced tolerance to fiber intra-channel nonlinearity and potential for increased communication security were characterized.

Conclusions:

• Adaptive SP-offset-QAM OFDM offers a promising solution for low-cost IM/DD communication systems.
• The proposed scheme provides a balance of high performance, reduced complexity, and robustness.
• It is well-suited for medium- and long-reach optical access networks and data center interconnects.