Is it possible to use the Dual-Fiber Micro-OTDR SFP to monitor single-fiber optical links? This is a question that we are often asked by our CSP and OEM Customers who want to monitor lengths of optical fiber (SMF-28 and similar), but do not need to send data. That is, they do not want to make a data link, but they do want to monitor a span of optical fiber with our Micro-OTDR feature. Why do they ask such a question?
Usually this asked when the optical fiber spans are relatively long, and the best performing Micro-OTDR is desired. The figure of merit for the performance of the Micro-OTDR feature is Dynamic Range (DR). The DR indicates the number of “dBs” available to detect an optical fiber fault over a span of optical fiber. Recall the Micro-OTDR Rule of Thumb:
Our Single-Fiber iSFC Micro-OTDR SFPs need to share their receiver between the data transport and Micro-OTDR functions. The receiver must be optimized for data transport, so by necessity, the receiver is suboptimal for the Micro-OTDR feature. (In general, data “wants” wide bandwidth, while the Micro-OTDR “wants” narrow bandwidth.)
However, this problem does not exist for our Dual-Fiber iDFC Micro-OTDR SFPs. Since they have separate receivers for the two functions, each receiver is optimized for its function – data transport or Micro-OTDR.
For the iSFC Fast Ethernet Micro-OTDR SFP (which is 80 Km Class for data transport), the DR is 60 dB. For the iDFC Fast Ethernet Micro-OTDR SFP (which is 100 Km Class for data transport), the DR is 65 dB. So how much difference does this 5 dB make?
To illustrate the performance difference, we will compare two 1511 nm SFPs, using our simple Micro-OTDR model, which calculates the Probability of Detection of an unknown fault (unknown location and unknown reflectance) over a specified optical fiber span.
Here are the results of the model if we “force” each unit analysis to a 95% Probability of Detection:
The key result is that the iDFC Dual-Fiber model can monitor a significantly longer optical fiber span (40.5 Km versus 25.8 Km), with a Probability of Detection of an unknown fault over the span of optical fiber of 95%. The additional 5 dB of DR does make a significant difference.
This is why we are often asked this question by our CSP and OEM Customers.