Co propagating pump and probe experiments on Si-nc in SiO2 rib waveguides doped with Er: the role of “dark” ions

We present a study that demonstrates the limits for achieving net optical gain in an optimized waveguide where Si nanoclusters in SiO2 codoped with Er3þ are the active material. By cross correlating absorption losses measurements with copropagant pump (lambda_pump1.48 um) and probe (lambda_probe.54 lm) experiments we reveal that the role of more than 80% of the total Er3þ population present on the material (intended for optical amplification purposes) is to absorb the propagating light, since it is unfeasible to invert it.