Expansive scope of aplanatic concentrators and collimators

Aplanats refer to inherently imaging optics that wholly eliminate both spherical aberration and coma. They typically comprise two refractive and/or reflective surfaces. For radiative transfer (which is typically nonimaging in nature), aplanats can closely approach the thermodynamic bounds for collimation and concentration, especially significant for light-emitting diodes (LEDs), solar energy, and infrared applications. Recently, we identified previously unrecognized basic categories of aplanats and showed how they can offer powerful new possibilities for LED collimation and for concentrating sunlight. Here, we review and elaborate the full scope of aplanat classifications, with illustrative examples of maximum-performance practical optics for all possible combinations of reflective and refractive contours. These examples subsume the latest invention of faceted (Fresnel) aplanats toward achieving greater compactness and lower mass. We also show how hybrid aplanats that combine the basic categories can improve concentrator and collimator performance.