In optical networks where action on a message or signal is time critical, latency becomes a critical design element. Latency in communications networks is comprised of the networking and processing of messages, as well as the transmission delay through the physical fibre. Measuring and optimising this optical transmission delay can be critical in diagnosing latency issues in a data centre or maintaining quality control in the production of precision fibre links. Fortunately, the Luna OBR 4600 can measure this latency with picosecond accuracy.

Specifically, latency is the time delay of a light signal to travel, or propagate, in an optical transmission medium. The latency is related to the length of an optical fibre 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 fibre.

Because the Luna OBR can measure loss and reflections in short fibre networks with ultra-high resolution (sampling resolution of 10 µm) and no dead zones, it is straightforward to extract the exact length or latency of a segment of fibre or waveguide by analysing the time delay between reflection events. In fact, 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 fibre, for example, this corresponds to an overall length measurement accuracy of better than 1 mm, which is equivalent to a latency measurement accuracy of about 5ps for standard fibre. Note that this is the absolute accuracy; actual measurement resolution will be much higher.

The example illustrates a typical application of measuring any differences in the length or latency of two fibre segments, each approximately 50 m in length. An OBR 4600 scans both segments and the latency of each segment is indicated by the distance between the two reflections at the beginning and end connectors of the segments. In this example, the difference in latency is found to be 95ps. For this fibre, this is equivalent to a difference of about 19.3 mm in length.

Measuring length and latency is only one application of the versatile OBR reflectometer. For an overview of the OBR and common applications for ultra high resolution optical reflectometry, download Luna’s OBR white paper below.

Fibre Optic Test & Measurement with Optical Backscatter Reflectometry (OBR)

Optical communications technology is rapidly evolving to meet the ever-growing demand for ubiquitous connectivity and higher data rates. As signalling rates increase and modulation schemes become more complex, guaranteeing a high-fidelity optical transmission medium is becoming even more critical.

Additionally, modern networks are relying more on photonic integrated circuits (PICs) based on silicon photonics or other developing technologies, introducing additional variables into the design and deployment of robust high bandwidth optical systems.

Measurement and full characterisation of loss along the light path is a fundamental tool in the design and optimisation of these components and fibre optic networks.

While different types of reflectometers are available to measure return loss, insertion loss, and event location for different types of optical systems, Optical Backscatter Reflectometry (OBR) is a very high resolution, polarisation-diverse implementation of optical reflectometry that dramatically improves sensitivity and resolution.

See what you’ve been missing with traditional optical instrumentation in this white paper.

Topics include:

  • Reflectance And Return Loss
  • Measuring Return Loss
  • Optical Backscatter Reflectometry (OBR)
  • Luna OBR Reflectometers

Click here to download the white paper.

For more information please email or call 01582 764334.

Lambda Photometrics is a leading UK Distributor of Characterisation, Measurement and Analysis solutions with particular expertise in Electronic/Scientific and Analytical Instrumentation, Laser and Light based products, Optics, Electro-optic Testing, Spectroscopy, Machine Vision, Optical Metrology, Fibre Optics and Microscopy.