UPM, DIAC. Open Course. March MEASURES 7.1 Attenuation 7.2 OTDR

ATTENUATION (I) Fundamentals Methods – Cutback – Insertion – Backscattering

ATTENUATION (II) Cutback Method – Two powers are compared p 2 : RX power with L(km) fiber p 1 : RX power cutting back to a fiber tail (1-2 m) —calibration – Features Destructive technique Requires access to both fiber ends Precise → homologation

ATTENUATION (III) Insertion Method (I) – Two powers are compared p 2 : RX power inserting L(km) fiber coil + connectors p 1 : RX power without coil —calibration – Features Non-destructive technique Requires access to both fiber ends Tolerance:  0.5 dB

ATTENUATION (IV) Insertion Method (II)

OTDR (I) Backscattering (Rayleigh) – Every point in the fiber scatters light, all directions – A fraction of the scattered light comes back (echo) Reflectometer (I) OPT. SOURCE PHOTODETECTOR OSCILLOSCOPE LIGHT FIBER Optical Time Domain Reflectometer

OTDR (II) Reflectometer (II) – Operation Principles A light pulse is sent Rayleigh backscattered light is received – Measurable Parameters Fiber length Fiber attenuation Faults Splices, connectors – Advantages An only fiber end is needed Very complete method —many measures can be done

OTDR (III) Fiber Attenuation Measure A “2” FACTOR IS DIVIDING SINCE LIGHT TRAVELS  L TWICE

OTDR (IV) Splice/Connector Measure  P 2 HAS GONE TWICE THROUGH THE SPLICE/CONNECTOR  CONNECTORS USUALLY DISPLAY REFLECTIONS (RETURN LOSSES dB)

OTDR (V) Fault-Locating – Based on Reflectometry (Rayleigh) and Echometry (Fresnel)

OTDR (VI) Actual OTDRs (I) – Normalized in t, d, P Slopes =  OF Steps =  s /  c One-way distances Powers in dB – Using tables with typical values, elements are identified

OTDR (VII) Actual OTDRs (II)