Fiber Optic Length and Latency

Luna has refined the use of optical frequency-domain reflectometry (OFDR) to provide ultra-high resolution and accurate measurements of the length and latency of a fiber optic cable, network or assembly.

Luna’s Optical Backscatter Reflectometers (OBRs) operate on a principle known as optical frequency domain reflectometry (OFDR). With OFDR, a tunable laser is swept through an optical frequency range, generating interference fringe data that is collected and analyzed with an interferometer based system, producing a record of reflection events observed as a function of the optical time delay which occurs when light propagates from the instrument to the reflection event and back.

The time delay, or latency, in fiber is related to length by the equation

where L is the length, c is the speed of light in a vacuum and n is the index of refraction for the optical fiber.

Luna’s OBR systems are precisely engineered and calibrated for very accurate length and latency measurements.

For example, the OBR 4600 is able to measure latency or length this way with an accuracy of <0.0034% of the total length (or latency). For a 30 m optical fiber, for example, this corresponds to an overall length measurement accuracy of better than 1 mm or about 5 ps.