Fiber Optic Signal Measuring

Part
01
of two
Part
01

Methods and Equipments for Measuring Fiber Optic Signals

Visual fault locators, connector inspection (using microscopes), light sources and power meters, optical-fiber identifiers, and OTDRs are five examples of methods and equipments that can be used to measure fiber optic signals for troubleshooting purposes.

Visual Fault Locator

  • A visual fault locator or fiber tracer is used to inject visible light into a fiber optic cable to visually trace the cable from the transmitter to the receiver to check orientation and continuity.
  • Continuity testing can be used to test if a terminated cable is damaged. The test is carried out by attaching the fiber cable to the fiber visual fault locator.
  • If visible light can be seen at the other end, then the fiber cable is not damaged.
  • To trace a fiber cable, the cable is connected to the equipment's output connector. The light output can be seen at the far end of the cable.
  • This allows a particular fiber cable in a multifiber cable system to be easily identified.
  • A visual fault locator costs as low as $42.46.

Connector Inspection (Microscope)

  • A fiber inspection microscope allows fiber connectors to be safely inspected for contamination which can cause network outages and to confirm that fiber cleaning procedures are effective.
  • Some microscopes allow the connector to be inspected from different angles, either by angle illumination or tilting of the connector.
  • Fiber microscopes are usually fitted with protective infrared filters to reduce the risk associated with viewing live fiber cables.
  • Some video inspection equipment do not have a direct optical path from the fiber cable to the user's eye.
  • These equipments use a video signal path (similar to a camcorder viewfinder) which converts the optical image from the fiber cable to a high resolution, safe video image.
  • A fiber inspection microscope costs as low as $143.

Light Source and Power Meter

  • A light source and power meter is used to measure the optical power from a transmitter or receiver in order to determine power loss.
  • A transmitter's optical power by attaching a fiber cable to the signal source while the power is measured at the far end.
  • The optical power of a receiver is measured by disconnecting the fiber cable connected to the receiver receptacle while the output is measured with the meter.
  • The loss reading is then compared to an estimated loss, known as a loss budget, which was calculated for the fiber link.
  • A light source and power meter costs as low as $245.

Fiber identifier

  • An optical-fiber identifier or a live fiber detector (or optical-fiber detector) is used to detect the presence or absence of optical transmissions in a fiber cable.
  • It is a non-intrusive equipment which is used by clamping it to a fiber cable.
  • It then measures several indicators including "traffic direction, presence (or absence) of modulation and, on some units, a core power reading".
  • The measurements enable the user to quickly assess the status of the fiber network.
  • An optical-fiber identifier costs as low as $913.08.

Optical Time Domain Reflectometer (OTDR)

  • An OTDR injects optical pulses into a fiber cable and extracts light scattered or reflected back from different points along the length of the fiber cable.
  • The equipment measures the strength of the returned pulses and is used to determine the quality of the optical fiber cable.
  • An OTDR costs as low as $2037.50.

Part
02
of two
Part
02

Installation and Testing of Fiber Optic Cables: Best Practices

The best practices for installation and testing of fiber optic cables include cleanliness, proper planning and preparation, and personal safety.

Cleanliness

  • According to Cabling Installation & Maintenance, 85% of attenuation loss issues are attributed to dirty fiber end faces. Dirty end faces affect testing by causing inconsistent results after several measurements.
  • Contamination may occur in many forms, including as dust particles attracted to connectors by moisture ingress or static electricity. Dust particles may cause scratching on connectors by being rubbed on the surfaces.
  • Test equipment connections and cables should be kept clean. To verify the cleanliness of connecting ferrules and the core, fiber optic microscopes can be used.
  • Fiber optic connectors should be cleaned using recommended specialized cleaning materials.
  • The National Electrical Conductors Association, recommends working in clean areas, use of protective dust caps, not touching connector ends, and use of lint-free swipes and "pure reagent-grade isopropyl alcohol" for connector cleaning.

Proper Planning and Preparation

  • A detailed plan of installation helps to eliminate about 95% of issues installers encounter. This should include fiber cable specification, equipment and supplies, location of equipment, installation methods, data forms for testing, potential areas of problems, testing requirements, and safety issues.
  • Documenting should be part of the planning process. According to The Fiber Optic Association, documenting the installation saves materials and time during installation and "allows better planning for upgrading".
  • Preparation for testing of fiber optic cables should include pre-testing and cleaning equipment, studying layouts proposed, checking to ensure that equipment is calibrated, and assembling a comprehensive complete test tool kit.
  • Foreseeable problems can be determined by talking to local employees. These problems can be averted by careful planning.

Personal safety

  • During installation and testing of fiber optic cables, safety precautions should be taken. Thin pieces of glass should be handled properly, mishandling them may cause internal hemorrhaging and stomach irritation when injected.
  • General safety precautions for installing and testing fiber optic cables include avoiding light radiation exposure, safe handling of chemicals, wearing safety glasses, disposing of small scraps of fiber according to regulations, the work area should be thoroughly cleaned after work, not eating and drinking near the work area, and washing hands.
  • Eye safety is important while working with VFL for fault location. The source and illuminated fiber core should not be "viewed directly with the naked eye".
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