[Paper Review] Experimental Analysis on Variations and Accuracy of Crosstalk in Trench-Assisted Multi-core Fibers

Hui Yuan, Alessandro Ottino+9 more|arXiv (Cornell University)|Aug 7, 2020

Optical Network Technologies34 references4 citations

TL;DR

This paper experimentally investigates the dynamic and static inter-core crosstalk (IC-XT) in an 8-core trench-assisted multi-core fiber under varying transmission parameters, validating theoretical IC-XT models and demonstrating that IC-XT fluctuation strength and accuracy are significantly influenced by temperature, wavelength, baud rate, modulation format, and measurement configuration. The study introduces a novel IC-XT step distribution model that enables accurate IC-XT characterization with shorter observation windows and reduced averaging time, outperforming traditional Chi-square fitting.

ABSTRACT

Space division multiplexing using multi-core fiber (MCF) is a promising solution to cope with the capacity crunch in standard single-mode fiber based optical communication systems. Nevertheless, the achievable capacity of MCF is limited by inter-core crosstalk (IC-XT). Many existing researches treat IC-XT as a static interference, however, recent research shows that IC-XT varies with time, wavelength and baud rate. This inherent stochastic feature requires a comprehensive characterization of the behaviour of MCF to its application in practical transmission systems and the theoretical understanding of IC-XT phenomenon. In this paper, we experimentally investigate the IC-XT behaviour of an 8-core trench-assisted MCF in a temperature-controlled environment, using popular modulation formats. We compare the measured results with the theoretical prediction to validate the analytical IC-XT models previously developed. Moreover, we explore the effects of the measurement configurations on the IC-XT accuracy and present an analysis on the IC-XT step distribution. Our results indicate that a number of transmission parameters have significant influence on the strength and volatility of IC-XT. Moreover, the averaging time of the power meter and the observation time window can affect the value of the observed IC-XT, the degrees of the effects vary with the type of the source signals.

Motivation & Objective

• To understand the dynamic behavior of inter-core crosstalk (IC-XT) in trench-assisted multi-core fiber (TA-MCF) under real-world transmission conditions.
• To validate existing analytical IC-XT models against experimental data across diverse modulation formats and system parameters.
• To quantify the influence of transmission parameters—such as temperature, wavelength, baud rate, PRBS length, and number of excited cores—on IC-XT levels and fluctuations.
• To evaluate the impact of measurement configuration (averaging time and observation window) on IC-XT accuracy.
• To propose and validate a new IC-XT step distribution model that improves measurement efficiency and accuracy compared to Chi-square fitting.

Proposed method

• Conducted experimental measurements on an 8-core trench-assisted multi-core fiber in a temperature-controlled environment using CW, ASE, OOK, PAM-4, and QAM signals at 25 Gbaud.
• Varied key transmission parameters: temperature (20–50 °C), wavelength (1480–1630 nm), baud rate, PRBS sequence length, and number of excited cores.
• Measured static and dynamic IC-XT using standard power meters with adjustable averaging time and observation window to assess accuracy trade-offs.
• Compared experimental IC-XT distributions against theoretical models, including Brownian motion-based time-dependent IC-XT and Chi-square distributions.
• Proposed and validated a new IC-XT step distribution model based on empirical fitting, using coefficients μ, σ, and α to describe the distribution shape.
• Performed long-term measurements (up to 12 hours) to evaluate fitting accuracy of IC-XT distributions under different signal types and conditions.

Experimental results

Research questions

• RQ1 How does temperature variation affect the static and dynamic IC-XT in trench-assisted multi-core fibers?
• RQ2 To what extent do modulation format, baud rate, and PRBS length influence IC-XT levels and fluctuation volatility?
• RQ3 How do averaging time and observation window length affect the accuracy of measured IC-XT values?
• RQ4 Can the IC-XT step distribution model provide better fitting accuracy than the Chi-square distribution with shorter measurement windows?
• RQ5 How well do theoretical IC-XT models match experimental results across different signal types and system parameters?

Key findings

• Static IC-XT increases by 0.13 dB/K and 0.113 dB/nm with temperature and wavelength, respectively, and decreases with PRBS length and modulation order.
• Dynamic IC-XT is inversely proportional to temperature and baud rate, with the highest stability observed in 256-QAM signals (1.80 dB dynamic IC-XT) compared to OOK (6.50 dB).
• The speed of IC-XT fluctuation increases by a factor of 7.4 per core as the number of excited cores increases.
• The IC-XT step distribution model achieves over 99.5% fitting accuracy with significantly shorter observation times than required for Chi-square fitting, e.g., 10 minutes with 0.625 s averaging time.
• For CW sources, the IC-XT step model achieves 99.56% accuracy with only 50 minutes of observation when averaging time is 3.5 s, whereas Chi-square fitting requires over 50 minutes with 3.5 s averaging for similar accuracy.
• The IC-XT step model outperforms Chi-square fitting for all signal types—including ASE and QAM signals—where Chi-square fitting fails to converge even after 12 hours of measurement.