  We demonstrate photon noise limited performance in both phase and amplitude
readout in microwave kinetic inductance detectors (MKIDs) consisting of NbTiN
and Al, down to 100 fW of optical power. We simulate the far field beam pattern
of the lens-antenna system used to couple radiation into the MKID and derive an
aperture efficiency of 75%. This is close to the theoretical maximum of 80% for
a single-moded detector. The beam patterns are verified by a detailed analysis
of the optical coupling within our measurement setup.
