  Immersion optics enable creation of systems with improved optical
concentration and coupling by taking advantage of the fact that the luminance
of light is proportional to the square of the refractive index in a lossless
optical system. Immersion graded index optical concentrators, that do not need
to track the source, are described in terms of theory, simulations, and
experiments. We introduce a generalized design guide equation which follows the
Pareto function and can be used to create various immersion graded index optics
depending on the application requirements of concentration, refractive index,
height, and efficiency. We present glass and polymer fabrication techniques for
creating broadband transparent graded index materials with large refractive
index ranges, (refractive index ratio)^2 of ~2, going many fold beyond what is
seen in nature or the optics industry. The prototypes demonstrate 3x optical
concentration with over 90% efficiency. We report via functional prototypes
that graded-index-lens concentrators perform close to the theoretical maximum
limit and we introduce simple, inexpensive, design-flexible, and scalable
fabrication techniques for their implementation.
