FTTH Network

Fiber Characterization by Fiber Optic Test Equipment


The following specification is the fiber testers and specification for a cable before delivery.

1. Optical Time-Domain Reflectometer (OTDR) — sends a laser pulse through the fiber and detects the return signal strength as well as the transmitting time. This test shows the overall character of the fiber strand including splice loss, splice numbers, connectors, splices, and fiber loss. Cleaning, re-terminating, or re-splicing can generally correct problems.

2. Optical Insertion Loss (OIL) — measures optical power attenuation that occurs when 2 cables are connected or spliced together. The insertion loss is the value of light lost. In longer distances network transmission, the light loss can cause the signal strength to weaken.

3. Optical Return Loss (ORL) — sends a light pulse down the fiber and measures the amount of light that returns. Some light is lost at all connectors and splices. Dirty or poorly mated connectors cause scattering or reflections, and result in weak light returns.

4. Chromatic Dispersion (CD) — measures the amount of dispersion on the fiber. In single-mode fiber, the light from different wavelengths travels down the fiber at slightly different speeds causing the light pulse to spread. Additionally, when light pulses are launched close together and spread too much, information is lost. Chromatic dispersion can be compensated for with the use of dispersion-shifted fiber (DSF) or dispersion compensation modules (DCMs.)

5. Polarization Mode Dispersion (PMD) — occurs in single-mode fiber and is caused by imperfections that are inherent in the fiber, producing polarization-dependent delays of the light pulses. The end result is the light travels at different speeds and causes random spreading of optical pulses.