In an OTDR trace, what does a sharp reflection spike typically indicate?

In an OTDR trace, what does a sharp reflection spike typically indicate?

• A. A long region of uniform backscatter
• B. A discrete reflection at a discontinuity such as a connector, splice, or end-face
• C. Noise floor spike
• D. A sudden drop in backscatter

Answer: (B)

A sharp reflection spike on an OTDR trace signals a discrete boundary where there is a sudden refractive index mismatch, such as at a connector, splice, or end-face. When the OTDR’s pulse reaches that boundary, part of the light is reflected directly back toward the source, creating a localized, tall spike at the distance corresponding to that location. The rest of the fiber shows a more gradual backscatter level due to attenuation, so a long region of uniform backscatter would appear as a steady level rather than a spike. A noise floor spike is random and not tied to a specific physical boundary, and a sudden drop in backscatter indicates loss along a section rather than a reflection at a boundary.

A sharp reflection spike on an OTDR trace signals a discrete boundary where there is a sudden refractive index mismatch, such as at a connector, splice, or end-face. When the OTDR’s pulse reaches that boundary, part of the light is reflected directly back toward the source, creating a localized, tall spike at the distance corresponding to that location. The rest of the fiber shows a more gradual backscatter level due to attenuation, so a long region of uniform backscatter would appear as a steady level rather than a spike. A noise floor spike is random and not tied to a specific physical boundary, and a sudden drop in backscatter indicates loss along a section rather than a reflection at a boundary.