Exploring High–Order Distortions Associated with Directly Modulated Laser Diodes in Analog Optical Fiber Systems: The Role of Modulation Depth and Fiber Length

Document Type : Original Article

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1 Department of Physics, Faculty of Science, King Abdulaziz University, Jeddah, 80203 Saudi Arabia

2 Laser Institute for Research and Applications, Beni-Suef University, Beni-Suef, 62511 Egypt

Abstract

This study investigates the impact of modulation depth and fiber length on high-order distortions in analog optical fiber systems employing directly modulated laser diodes with two-tone. High-order distortions, including 2nd– and 3rd–order harmonic distortions (HDs) and 3rd–order intermodulation distortions (IMD3), are modeled and analyzed in both time and frequency domains. The numerical simulation relies on the rate equations of laser diodes driven by an injection current containing two sinusoidal waves, spaced by a low radio frequency of 10 MHz. The results reveal the interplay between modulation depth and fiber length in minimizing distortions and identifying optimal operating ranges. The 2HD demonstrates the highest distortion level for modulation depth up to 0.4. Beyond this threshold, IMD3 becomes the predominant source of signal distortion. In contrast, 3HD exhibits the lowest distortion levels across the entire range of modulation depth. Fiber lengths shorter than 5 km minimize IMD3, while lengths around 5 km and 3 km minimize 2HD and 3HD, respectively These findings contribute to enhancing the performance of analog fiber communication systems, particularly in applications requiring high signal fidelity

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