For some time now microring resonator structures have been studied as a way of
enhancing nonlinear optical effects, since they concentrate the light in one
place for a long time.  Our interest is in microring structures constructed
from AlGaAs alloys.  While the fabrication procedures for these structures are
not as well developed as for glass or silicon resonators, they have the
advantage that they possess a second-order nonlinear optical response.  Thus
they can serve as an "on chip" platform for producing entangled states by
spontaneous parametric downconversion.   We look at the possibilities of
nonlinear quantum optics in these structures, and the biphoton states they
should be able to generate.  We will also touch on the properties of some other
structures.