What Is FHC? Why Do We Need FHC?

Why Do We Need FHC?

As data communication networks evolve rapidly, fiber communication has become the backbone technology of modern communication networks. However, fiber networks are encountering many challenges, such as contamination, loose connections, and fiber cuts. These problems affect network stability and reliability while increasing O&M costs. Traditional fiber fault detection methods mainly rely on onsite manual detection, which is inefficient and error-prone. As a result, they cannot meet the requirements of modern networks for fast fault response and high reliability.

In key industries such as finance, telecommunications, and healthcare, service continuity and data transmission reliability are critical. If a fiber link is faulty, services may be interrupted, causing huge losses. As such, a technology that can quickly and accurately detect and locate fiber faults is urgently needed to improve network stability and O&M efficiency, reduce the fault rectification time, and ensure service continuity.

FHC technology meets this need and brings the following benefits:

• High-precision fault locating: A meter-level fault locating precision can be achieved, preventing and rectifying faults in advance to ensure network stability and reliability.
• Automatic alarm reporting: Automatic alarm reporting upon fiber cuts can quickly detect faults and notify users, eliminating the need for onsite manual detection and therefore greatly reducing costs.
• Periodic inspection: Periodic intelligent inspection ensures the long-term stability of fiber links. If a fault is detected, it can be promptly rectified.
• Visualized fault management: iMaster NCE-IP is used to implement the visualized management of fiber faults. This helps quickly and accurately locate faults and link damage information, provide guidance for engineering repair, and restore services.

How Does FHC Work?

FHC technology is implemented using the FHC module deployed on a device. The module sends 1490 nm probe pulses to the connected fiber, and receives and analyzes Rayleigh backscattering and Fresnel reflection generated during transmission. In this way, the module can accurately locate fault points and measure link loss on the fiber. The FHC module works with iMaster NCE-IP to implement real-time monitoring and visualized display of fault information.

Fiber link fault detection by FHC modules

Rayleigh backscattering: Rayleigh scattering is an intrinsic scattering phenomenon in fibers, arising from microscopic fluctuations in material density and refractive indexes. These are caused by non-uniformity in atomic compressibility due to thermal agitation during the fiber manufacturing process. Such non-uniform structures are fixed as the fiber cools, forming randomly distributed scattering points with sizes much smaller than the light wavelength. The phenomenon where a portion of the scattered light travels back along its original path is known as Rayleigh backscattering. Since Rayleigh scattering points are continuously distributed throughout the fiber, the FHC module can precisely analyze the attenuation degree and fault location of the fiber link by measuring the arrival time and intensity of Rayleigh backscattering.

Fresnel reflection: This usually occurs at discontinuous interfaces (such as connectors or adapters) and results from factors like air gaps, misalignment, or refractive index mismatch. Fresnel reflection is a discrete type of reflection generated at specific points along the fiber. Typical reflection points include fiber connectors (with gaps of air between glass), smooth mirror-like cross-sections of cut fibers, and fiber endfaces.

What Are the Deployment Modes of FHC?

FHC modules are mainly used to detect fiber link quality before deployment commissioning and to locate and report fiber faults during O&M. They can be deployed in the following modes:

• Deployment with single-fiber bidirectional (BIDI) service optical modules

  The following figure shows a scenario where one FHC module is deployed. The L port of the FHC module connects to the Tx/Rx port of BIDI service module 1 on the local device, and the R port of the FHC module connects to BIDI service module 2 on the remote device.

  When deployed with BIDI service optical modules, the FHC module supports manual detection and automatic fiber cut detection, but does not support online periodic detection.

  
  Deployment with single-fiber bidirectional (BIDI) service optical modules
• Deployment with two-fiber bidirectional service optical modules in Rx concatenation mode

  The following figure shows a scenario where two FHC modules are deployed. The L port of an FHC module connects to the Rx port of the service module on the local device, and the R port of the FHC module connects to the Tx port of the service module on the remote device.

  FHC module 1 is used to detect fiber link 1, and FHC module 2 is used to detect fiber link 2. Both FHC modules support manual detection, automatic fiber cut detection, and online periodic detection.

  
  Deployment with two-fiber bidirectional service optical modules in Rx concatenation mode
• Deployment with two-fiber bidirectional service optical modules in Tx/Rx concatenation mode

  The following figure shows a scenario where two FHC modules are deployed. The L port of FHC module 1 connects to the Tx port of service optical module 1 on the local device, and the R port of FHC module 1 connects to the Rx port of service optical module 2 on the remote device. The L port of FHC module 2 connects to the Rx port of service optical module 1 on the local device, and the R port of FHC module 2 connects to the Tx port of service optical module 2 on the remote device.

  FHC module 1 supports only manual detection for fiber link 1. It does not support automatic fiber cut detection or online periodic detection. FHC module 2 supports manual detection, automatic fiber cut detection, and online periodic detection for fiber link 2.

  
  Deployment with two-fiber bidirectional service optical modules in Tx/Rx concatenation mode