Optical Time-Domain Reflectometers (OTDRs)

Frequently Asked Questions About An Optical Time Domain Reflectometer

An optical time domain reflectometer, or OTDR, is a device that tests the integrity of a fiber optic cable, as well as the loss and reflectance of fiber splices, by measuring its various characteristics using Rayleigh scattering and Fresnel reflection effects. It consists of a laser that generates a high-speed pulse of light down the length of the fiber cable. This light is then scattered or reflected back to the reflectometer device to reveal any faults or damage in the cable.

What are the different types of OTDRs?

The affordable OTDRs on eBay can be categorized by their size and function. Each type can calculate the attenuation of a fiber, uniformity, and splice and connector losses.

  • Full-sized: These devices are relatively large and designed to mostly stay in one place. They can be placed on top of a desk or a bench, or they can be mounted on a rack with other electronic equipment. They can also measure several different optics parameters at the same time.
  • Handheld: These devices are designed with portability in mind. By measuring fiber links in the field, they can locate fiber breaks or points of high loss. However, they are less feature rich than the full-sized devices.
  • Remote control unit: These units are operated by a computer in a central location. They can test vital points in the fiber network automatically.
Does the type of optical fiber matter?

Yes, these nifty OTDRs are designed to work with either single-mode cables or multi-mode cables, although some devices can work with both. Single-mode cables have a small core diameter and allow for long transmission distances. Multi-mode cables have a larger core diameter and need to be graded or stepped. Make sure that the OTDR you are purchasing is compatible with your desired type of cable.

What determines the quality of the OTDR device?

There are two main factors you should consider when selecting a new or pre-owned OTDR device on eBay: the measurement range and the instrument resolution.

  • Measurement range: The range represents the maximum fiber distance it can measure within acceptable accuracy limits.
  • Instrument resolution: The instrument resolution represents the minimum distance required for two separate events to be differentiated from each other, meaning that they can be recognized as distinct events.

There is typically a trade-off between the range and the resolution. A shorter pulse will create a higher resolution but a lower range, and vice versa. Size, feature set, and the accuracy of the measurement are also important factors to consider in an OTDR device.