Why does OFSCN® recommend using genuine patch cords?

OFSCN Global Technical Center OFSCN Technical Knowledge Base
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Summary: Why is high-quality processing the final step in ensuring sensor accuracy?

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In fiber optic sensing systems, fiber patch cords and connectors are not just the ‘connecting wires’ for light path transmission but also crucial optical components within the overall optical interference and measurement loop. The minute physical quantities sensed by the sensor ultimately manifest as wavelength shifts (\\Delta \\lambda), phase changes, or optical intensity modulation. High-quality patch cord processing and packaging techniques are the ‘final step’ in ensuring the ultimate sensing accuracy, with the core physical and engineering mechanisms as follows:

I. Suppressing Parasitic Fresnel Reflections to Ensure Spectral Signal-to-Noise Ratio (SNR)

Fiber Bragg Grating (FBG) interrogators and distributed fiber optic sensors (e.g., OFDR, BOTDA) rely on precise feature extraction from extremely weak reflection peaks or backscattered signals:

  1. End-face Grinding Process and Return Loss (RL): Ordinary or inferior connectors, due to non-compliance with radius of curvature (ROC), apex offset, or fiber undercut/protrusion control, easily generate small air gaps upon mating, leading to intense interfacial Fresnel reflections.
  2. Algorithm Distortion Suppression: High-intensity parasitic reflections can introduce multi-beam interference ripples into the optical path or significantly elevate the noise floor. When disturbed by background stray light or interference noise, the peak-finding accuracy of interrogator algorithms like Gaussian fitting and centroid algorithms can suffer severe deviations (drifts of several to tens of picometers), directly translating into sensing measurement errors. Employing high-quality precision grinding processes (such as the standard FC/APC 8^\\circ angled polish, ensuring return loss \\text{RL} > 60\\ \text{dB}) can effectively eliminate parasitic reflections.

II. Precisely Controlling Concentricity and Mode Field Matching to Avoid Additional Loss and Polarization State Degradation

  1. Core Concentricity Error and Insertion Loss (IL): The core diameter of single-mode fiber is only about 9\\ \mu\\text{m}. Deviations in the ferrule hole diameter or excessive concentricity errors during processing can cause slight axial misalignment of the fiber cores, resulting in significant additional insertion loss (IL). In applications with multiplexed measurement points or long-distance transmission, cumulative loss will severely weaken the returned optical power.
  2. Polarization Mode Dispersion (PMD) and Polarization Dependent Loss (PDL): If asymmetric micro-stresses exist on the connector end-face during assembly crimping or curing, it can induce birefringence in the fiber end-face, leading to random perturbations of the transmitted light’s polarization state. This causes the sensing reflection peak to exhibit double-peak splitting or asymmetrical distortion, severely degrading demodulation accuracy.

III. Eliminating