OTDR: Measurement of “Unconnectorized” Optical Fiber Cables

When evaluating products in the manufacture of optical fiber cable, it is often necessary to measure fiber length and attenuation for an unprocessed fiber, which does not have a connector at either end. Since the Optical Time Domain Reflectometer (OTDR) port requires a connector, an unprocessed fiber cannot be connected directly to it. V-groove is a tool that can join a launch fiber, which has a connector on one end, to an unprocessed fiber. This allows it to be connected to the OTDR and measured.


A fiber coupling tool with V-shaped grooves cut to fit the thickness of the fiber.
Two optical fibers lock along the groove.
Index-matching gels are applied to the contact point to suppress reflection.
A version is also available for multicore fibers (tape or ribbon fiber),
Please note that it is not possible to mate fibers with different outer diameters. Outer diameters must be the same.



If the fiber to be measured is short, or if a precise measurement is desired, use the launch fiber as a dummy fiber. The launch (dummy) fiber length should be longer than the dead zone at the near-end of the fiber. It must be long enough to be detected as an event.

By performing analysis with the “Dummy fiber setting” on the OTDR turned on, the V-groove position becomes [R] point and the far-end of the fiber becomes [E] point. Therefore, only the measured fiber portion (between [R] and [E]) excluding the launch fiber portion is analyzed.

nDummy Fibers setting for AQ 7280
Press the [SETUP] , [F1: Detail],
[F3: Analysis Setup], and [Launch Fiber Setting]
Select [Set on Distance]
Enter a length of launch fiber in the “From Start” section.
OTDR measurement trace

OTDR: Measurement of “Unconnectorized” Optical Fiber Cables

Related Industries

Related Products & Solutions

AQ7280 Modular Optical Time Domain Reflectometer

  • Yokogawa AQ7280 Optical Time Domain Reflectometer (OTDR)
  • Fast and precise measurements with confidence
  • Satisfies broad range of test and measurement needs
  • Analyzing optical networks from access to core

Optical Test Equipment

  • Yokogawa optical test equipment solutions to measure optical components/systems
  • Serves demand for high capacity fiber lines and new component technologies

Optical Time Domain Reflectometer

  • Optical time domain reflectometer precision instrument for access network optical fiber installation and maintenance
  • Locate events or faults along fiber link during OTDR testing procedure

Precision Making