All lasers are susceptible to back reflection. Back reflection or as it is sometimes called, optical return loss
(ORL) is a peculiar phenomenon where by a fraction of the transmitted optical power will reflect back toward the
source upon encountering variations in refractive index. Splices, patches and defects in the fiber all can cause back
reflections. Fiber with more than 20dB of back reflection are considered quite high and optical isolators should be
used on laser sources. For example the back reflection of an air-glass interface, as one would see in a broken fiber is
-15 dB. If a laser with –5dBm output power was launched into this broken fiber, then the laser would have –20dBm
optical power reflecting back into the laser cavity disrupting the standing optical wave generating noise in the output
optical signal.