Optical reflectance is dealt seriously in high bit rate transmission systems. Optical reflectance is defined as the ratio of the reflected optical power present at a point, to the optical power incident to that point. Control of optical reflections is important. In general, optical reflective points shall be kept at minimum so that it the total reflectance between multipath interface at the source (MPI-S) and receiver (MPI-R) are within the specified limits.
Control of reflections is discussed extensively in ITU- T recommendation G.957. The maximum number of connectors or other discrete reflection points, which may be included in the optical path (e.g. for distribution frames, or WDM components), must be such as to allow the specified overall optical return loss to be achieved. If this cannot be done using connectors meeting the maximum discrete reflections cited here, then connectors having better reflection performance must be employed.
Alternatively, the number of connectors must be reduced. It may also be necessary to limit the number of connectors or to use connectors having improved reflectance performance in order to avoid unacceptable impairments due to multiple reflections. The maximum discrete reflectance between MPI-S and MPI-R is generally limited to –27 dB.