Back Reflection Back reflection occurs when light reflects from a connector, splice, or fibre break and travels back towards the source. In high-power systems this can create dangerous power spikes, potentially overloading transmitters or amplifiers. There is also the possibility of fibre fuse or connector burn. This is quantified as optical return loss (ORL); poor ORL (high reflectance) increases noise and can stress sources—APC terminations mitigate this.
*Even when hot-pluggable is supported, prefer muting/shuttering or disabling the source, and always inspect–clean–inspect before mating. As a rule of thumb, optical levels above 0 dBm demand caution when hot swapping. At levels above +10 dBm, it should never be attempted. Beyond +20 dBm, it is an absolute no-go. The greatest danger lies at the transmitter or EDFA output, where laser levels are highest and both equipment and personal safety are at risk. Once signals pass through splitters, taps, or attenuators, output levels are usually lower and safer—but this should never be assumed. Always refer to system documentation for expected optical levels.
Fig 3. The point of ignition from a back reflection
Transient Effects Transient effects are brief, high-power optical spikes capable of triggering fibre fuse or connector burn. They are usually caused by sudden changes in the network—for example, disconnecting a live fibre near an optical transmitter. Although short-lived, their impact
can be permanently damaging. Hot Swapping Risks
How should fibre distribution or FIRS systems be approached when it is difficult to isolate the optical source? The table below provides a guide to the dangers of hot swapping (disconnecting live laser sources)—a practice strongly discouraged.
Table 1. Assessing the risk
47 CAI Feedback Winter 2025
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