What is the Right OTDR I Need?

The OTDR is a critical tool in the characterization and certification of fiber optic links (multimode and single mode LAN / Ethernet). When choosing an OTDR, it is important to select the specific OTDR performance and features needed to qualify these links accurately and to the required specification/standard.

The Optical Time Domain Reflectometer addressing different test and measurement needs: from very simple fiber optic fault finder to advanced OTDRs for link certification. To make the right choice, five fundamental parameters must be considered when purchasing an OTDR, as selecting a unit simply based on overall performance and price will lead to problems if the selected model is inappropriate for the application. A solid understanding of these parameters will help buyers make the right choice for their specific environment, and thus maximize productivity.

Multi-purpose Optical Measuring Instruments

This specification determines the total optical loss that the OTDR can analyze; i.e., the overall length of fiber link that can be measured by the unit. The higher the dynamic range, the longer the distance the OTDR can analyze. The dynamic range specification must be considered carefully for two reasons:

1. OTDR manufacturers specify dynamic range in different ways (playing with specifications like pulse width, signal-to-noise ratio, averaging time, etc.). Therefore, it is important to understand them thoroughly and avoid comparing apples and oranges.

2. Having insufficient dynamic range will result in the inability to measure the complete link length and, in many cases, affect the accuracy of the link loss, attenuation and far-end connector losses. A good rule of thumb is to choose an OTDR whose dynamic range is 5 to 8dB higher than the maximum loss you will encounter.

For example, a single mode OTDR with a dynamic range of 35dB has a useable dynamic range of around 30dB. Assuming typical fiber attenuation of 0.20dB/km at 1550 nm and splices every 2km (loss of 0.1dB per splice) and a unit such this one will be able to accurately certify distances of up to 120 km.

Comparatively, a multimode OTDR with a dynamic range of 26dB has a useable dynamic range of around 21dB. Assuming typical attenuation of 0.5dB/km at 1300 nm and two connector losses of about 1dB each, this unit would be able to accurately certify distances of up to 38 km.

For purchasing more high quality OTDRs or FTTH products with low cost or for more products’ information, please contact a Sopto representative by calling 86-755-36946668, or by sending an email to info@sopto.com.