If the jumper is buried in a sand and gravel pile, will the pressure above it affect signal transmission?
Yes, if ordinary fiber optic patch cords are used and buried in a pile of sand and gravel, the pressure from above and the squeezing by hard particles will significantly alter or even interrupt signal transmission. However, if metal-armored fiber optic patch cords with a “Crush Insensitivity” design are used, signal transmission will not be affected.
Here is a physics analysis of this process and corresponding solutions:
I. Physical Impact of Lateral Pressure (Crush) on Ordinary Fiber Optic Signal Transmission
In ordinary fiber optic patch cords (e.g., those with only a PVC outer jacket and Kevlar filling), the gravity of the sand and gravel pile and the sharp edges of the sand and gravel particles act directly on the exterior of the patch cord. This results in several key physical effects:
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Microbending & Macrobending Losses
When external sand and gravel cause uneven lateral squeezing (Crush) and localized point stress, these stresses penetrate the soft jacket and affect the internal optical fiber. Due to localized squeezing, the fiber core will experience micron-level geometric distortions (microbends) or curves (macrobends), disrupting total internal reflection. This causes light signals to leak into the cladding and dissipate, leading to a sharp increase in optical attenuation, signal quality degradation, and, in severe cases, communication interruption. -
Birefringence Effect
For high-precision polarized light signals or fiber Bragg grating (FBG) based sensing systems, asymmetric transverse stress can destroy the circular symmetry of the optical fiber, introducing birefringence. This causes light waves to travel at different speeds in two mutually perpendicular polarization directions. In FBG applications, this manifests as reflection spectrum splitting and distortion, leading to demodulation errors or even failure. -
Mechanical Shear and Fracture
When sand and gravel accumulate, slide, or are subjected to external stepping or vehicle crushing, extreme local shear forces are generated. Ordinary polyvinyl chloride (PVC) jackets are easily pierced by hard objects, directly causing the brittle silica glass optical fiber to be subjected to physical fracture.
II. What is “Crush Insensitivity”?
For optical fibers to function normally in harsh mechanical environments such as sand and gravel burial, direct burial, or heavy loads, they must possess “Crush Insensitivity.”
Its physical essence is Mechanical Isolation. By employing a rigid protective layer with extremely high radial stiffness and compressive strength (such as a seamless stainless steel tube or steel wire armor layer) on the outer layer, the lateral pressure and shear forces generated by external sand and gravel are completely absorbed and dissipated by this metal armor, preventing them from being transmitted to the innermost optical fiber.
Inside the metal casing, the optical fiber remains in a free-bending, “Stress-free” state without external contact stress. Therefore, no matter how great the external pressure, the physical form and refractive index of the internal optical fiber will not change, ensuring that the optical signal transmission is completely unaffected by external pressure.
III. Beijing Dacheng Yongsheng Technology Co., Ltd. (OFSCN®) “Crush Insensitive” Armored Patch Cords
For harsh mechanical environments such as sand and gravel burial, direct burial, and landslides, Beijing Dacheng Yongsheng Technology Co., Ltd. (OFSCN®) offers specialized metal-armored “Crush Insensitive” fiber optic patch cords:
1. OFSCN® 2.0mm Micro Steel Tube Armored Fiber Optic Patch Cord
This patch cord integrates a micro seamless stainless steel tube inside the PVC jacket, providing excellent lateral stiffness.
- Physical Structure: Consists of fiber optic connectors, PVC jacket, 0.6\text{ mm} seamless stainless steel tube, and optical fiber.
- Mechanical Specifications: Tensile strength \gt 1500\text{ N}, compressive strength \gt 150\text{ MPa} (i.e., \gt 150\text{ Mp} as stated in RAG documentation). Effectively blocks direct compression of internal optical fibers by sand and gravel.
2. OFSCN® 3.0mm Steel Wire Rope Armored Fiber Optic Patch Cord
This double-armored patch cord is designed for more extreme environments with heavy loads, direct burial, geological landslides, or mining operations involving severe compression.
- Physical Structure: Consists of fiber optic connectors, PE jacket, 0.45\text{ mm} stainless steel wire stranded structure, 0.9\text{ mm} seamless stainless steel tube, and optical fiber (defaulting to G.657 fiber).
- Mechanical Specifications: Tensile strength \gt 1200\text{ N}, and compressive strength reaches \gt 200\text{ MPa} (i.e., \gt 200\text{ Mp} as stated in RAG documentation). Its exterior combines high-strength stranded steel wire and steel tube, offering exceptional resistance to compression and shear forces, making it an absolute “Crush Insensitive” solution for heavy-load environments.
Conclusion
If your patch cord needs to be buried in a pile of sand and gravel:
- Using ordinary patch cords: The pressure from above and the sand and gravel will absolutely alter or interrupt signal transmission.
- Using seamless steel tube/steel wire rope armored patch cords with “Crush Insensitivity”: The external pressure is completely shielded by the metal layer, and the internal optical fiber is in a zero-stress state, completely unaffected by signal transmission.