Understanding OTDR (Optical Time Domain Reflectometry)

The optical time domain reflectometer (OTDR) injects an optical pulse into one end of the fiber and analyzes the backscattered and reflected signal that returns. An operator at one end of a fiber span can measure and localize attenuation, event loss, reflectance, and ORL.

What does an OTDR measures?

An OTDR detects, locates, and measures events on fiber links. It requires access to only one end of the fiber.

  • Attenuation (also called fiber loss). Expressed in dB or dB/km, this represents the loss or the rate of loss between two points along the fiber span.
  • Event Loss. The difference in the optical power level before and after an event, expressed in dB.
  • Reflectance. The ratio of reflected power to incident power of an event, expressed as a negative dB value.
  • ORL (Optical Return Loss). The ratio of the reflected power to the incident power from a fiber optic link or system, expressed as a positive dB value.

How to configure the main OTDR setting?

  • Pulse Width

The pulse width controls the amount of light injected into a fiber. 
A short pulse width enables high resolution and short dead zones but less dynamic range.
A long pulse width enables high dynamic range but less resolution and large dead zones.

  • Acquisition time

The time during which the OTDR acquires and averages data points from the fiber under test. Increasing the acquisition time improves the dynamic range without affecting resolution or dead zones.

  • Index of Refraction (loR)

The IoR converts the time that the OTDR measures to distance and displays it on the trace.Entering the appropriate value for the fiber under test will ensure accurate measurements of fiber length.

WARNING: To obtain accurate measurements, always clean connectors prior to OTDR testing.


For a detailed information, please download the JDSU poster or visit our OTDR devices category page.

About Samm Teknoloji

Samm Teknoloji is a manufacturing and engineering company with services in different sectors, especially fiber optic systems and IoT. It has many patents in fiber to the home infrastructure (FTTH) and Data Center equipment, and has developed a wide variety of products in its own field and presented it to the use of the industry.

In addition, it is among the leading companies with its services in turnkey electrical contracting works, heat tracing, and informatics sectors.


Samm, Samm Teknoloji, Foyer, FOTAS are registered Trademarks of SAMM Teknoloji A.S. Other names may be trademarks of their respective owners.