  We use an optical fiber taper waveguide to probe PbS quantum dots (QDs) dried
on Si photonic crystal cavities near 1.55 $\mu$m. We demonstrate that a low
density ($\lesssim 100 \mu$m$^{-2}$) of QDs does not significantly degrade
cavity quality factors as high as $\approx3\times10^4$. We also show that the
tapered fiber can be used to excite the QDs and collect the subsequent
cavity-filtered photoluminescence, and present measurements of reversible
photodarkening and QD saturation. This method represents an important step
towards spectroscopy of single colloidal QDs in the telecommunications band.
