  We present a way of exciting surface plasmon polaritons along non-patterned
metallic surfaces by means of a flat squeezing slab designed with
transformation optics. The slab changes the dispersion relation of incident
light, enabling evanescent coupling to propagating surface plasmons. Unlike
prism couplers, the proposed device does not introduce reflections at its input
interface. Moreover, its compact geometry is suitable for integration. A
feasible dielectric implementation of the coupler is suggested. Finally, we
show that the angular response of the device can be engineered by using a
non-uniform compression factor. As an example, we design a coupler with a
half-power angular bandwidth 2.5 times higher than that of a conventional
dielectric coupler.
