DSP-based CSO cancellation technique for RoF transmission system implemented by using directly modulated laser

Area of Science:

• Optoelectronics
• Optical Communications
• Signal Processing

Background:

• Radio-over-fiber (RoF) systems using directly modulated lasers (DMLs) face performance limitations due to composite second-order (CSO) distortions.
• These distortions arise from the interaction between DML chirp and fiber chromatic dispersion, degrading signal quality.

Purpose of the Study:

• To propose and demonstrate a simple digital signal processing (DSP) based technique for canceling CSO distortions in DML-based RoF systems.
• To theoretically analyze the nonlinear distortions and experimentally verify the effectiveness of the proposed CSO cancellation method.

Main Methods:

• A composite second-order (CSO) cancellation technique utilizing digital signal processing (DSP) was developed.
• Theoretical analysis of nonlinear distortions caused by DML chirp and fiber chromatic dispersion was performed.
• Experimental validation involved transmitting twenty-four 100-MHz filtered orthogonal frequency-division multiplexing (f-OFDM) signals in 64 quadrature amplitude modulation (QAM) format over 20 km of standard single-mode fiber (SSMF).

Main Results:

• The proposed DSP technique successfully suppressed CSO distortion components by over 10 dB.
• Error-vector magnitude (EVM) performance better than 6% was achieved after 20 km of SSMF transmission.
• The technique demonstrated effectiveness in mitigating nonlinear distortions in RoF systems.

Conclusions:

• A simple DSP-based CSO cancellation technique is effective for DML-based RoF systems.
• The method significantly improves signal quality and enables reliable data transmission over standard single-mode fiber.
• This approach offers a practical solution for enhancing the performance of RoF transmission systems.