Subwavelength confinement of light

Transformation optics has recently provided a new method for the design of devices to control electromagnetic fields. Based on the analogy between the macroscopic Maxwell's equations in complex dielectrics and the free-space Maxwell's equations in a curved coordinate system, it offers an elegant approach to exploit the full potential of metamaterials, of which the most exciting examples are invisibility cloaks. In this contribution, we want to show how the technique can be applied to design cavities with extraordinary properties. We have been able to demonstrate theoretically deep subwavelength cavities that do not suffer from fundamental losses.