Modifying functionality of variable optical attenuator to signal monitoring through defect engineering

A commercial silicon-based variable optical attenuator has been converted to a low bandwidth (quasi-CW) light monitor through an ion implantation and annealing process. The measured total optical loss of the device is <5 dB while the responsivity per tapped fraction is 1 mA/W/dB. The straightforward manner in which the monitoring functionality is induced suggests a cost-effective route to CW optical monitors using a widely available commercial product.