Fundamentally new classes of aplanatic lenses

We identify fundamentally new classes of aplanatic lenses where the focus resides inside the lens. These new aplanatic designs comprise a primary contoured dielectric entry, and a secondary contoured profile that, in general, is mirrored, but also admit solutions satisfying total internal reflection. We show that these aplanatic lenses engender 8 basic, distinct design categories, of which 6 yield physically admissible solutions. Flux concentration for far-field small-angle sources such as the sun and, conversely, narrow-field collimation of wide-angle emitting light sources such as LEDs can approach the thermodynamic limit. Losses due to chromatic aberration are smaller than in conventional lenses of comparable f-number, primarily due to the focus being in the lens. By the same token, exit numerical aperture can be increased by a factor of n (the dielectric's refractive index) - and hence flux concentration can be increased by a factor of n² - relative to common lenses where the focus resides outside the lens.