Subwavelength Resolution in a Two-Dimensional Photonic-Crystal-Based Superlens

We experimentally and theoretically demonstrate single-beam negative refraction and superlensing in the valence band of a two-dimensional photonic crystal operating in the microwave regime. By measuring the refracted electromagnetic waves from a slab shaped photonic crystal, we find a refractive index of $-1.94$ that is very close to the theoretical value of $-2.06$. A scanning transmission measurement technique is used to measure the spatial power distribution of the focused electromagnetic waves that radiate from a point source. The full width at half maximum of the focused beam is measured to be $0.21\lambda$, which is in good agreement with the finite difference time domain method simulations. We also report a subwavelength resolution for the image of two incoherent point sources, which are separated by a distance of $\lambda /3$.

Figure 1

(a) Band diagram for our structure for TM polarization. (b) Equal frequency contours of air and PC at 13.698 GHz. Here $\theta$ denotes the incidence angle from air to PC. (c) Experimental setup. For the refraction measurements a horn antenna is used as the transmitter, and a monopole antenna is used for focusing measurements. For both cases a monopole antenna is used as a receiver.

Figure 2

Comparison of measured (●) and calculated (solid line) angles of refraction versus angles of incidence at 13.698 GHz.

Figure 3

Measured power distribution (●) and calculated average intensity (solid line) at the image plane. Full width at half maximum of the measured image is $0.21\lambda$. Spatial power distribution without PC is also shown (dashed line).

Figure 4

Measured power distribution (●) and calculated average intensity (solid line) at 0.7 mm away from the second interface (a) for two coherent sources and (b) for two incoherent sources. Calculated average intensities at these points with dielectric slabs are also shown (dashed lines).