Optical OFDM Error Floor Estimation by Means of OTDR Enhanced by Front-End Optical Preamplifier.

Area of Science:

• Optical Engineering
• Telecommunications
• Signal Processing

Background:

• Optical time-domain reflectometer (OTDR) is crucial for diagnosing fiber optic link events like breaks and measuring losses.
• High dynamic range (DR) and signal-to-noise ratio (SNR) in OTDR are essential for long-haul fiber visibility and accurate event characterization.
• Reflective events causing significant return loss can dominate the optical bit-error-rate (BER) floor in high SNR scenarios.

Purpose of the Study:

• To complement traditional OTDR tests by introducing a method for estimating the optical BER floor in the field.
• To investigate the relationship between OTDR parameters (DR, SNR) and the optical BER floor, particularly concerning reflective events.
• To propose and validate a technique for improving OTDR performance and BER floor prediction accuracy, especially when high SNR is not met.

Main Methods:

• Utilizing the classical time-dispersion channel model, relating optical BER floor to the root-mean-square (rms) delay spread under high SNR conditions.
• Proposing the integration of a low-noise optical preamplifier into the OTDR front-end to enhance SNR and reduce noise floor.
• Conducting experimental measurements of BER on a fiber link and comparing results with predictions derived from OTDR traces.

Main Results:

• Demonstrated that reflective events significantly impact the optical BER floor under high SNR conditions.
• Validated the applicability of the time-dispersion channel model for predicting optical BER floors determined by rms delay spread.
• Showcased that the addition of a low-noise optical preamplifier effectively improves OTDR performance and leads to accurate BER floor predictions that closely match experimental measurements.

Conclusions:

• The study successfully establishes a method for estimating optical BER floors using OTDR data, enhancing field diagnostics.
• The proposed integration of an optical preamplifier offers a practical solution to overcome limitations posed by insufficient OTDR dynamic range and achieve reliable BER floor estimation.
• The findings provide a valuable tool for network operators to predict and manage optical performance by understanding the interplay between OTDR characteristics and BER floors.