Metallic graded photonic crystals for graded index lens

We have designed a flat graded index lens made from a metallic graded 2D photonic crystal. The gradient of index has been obtained by varying the filling factor of a flat slab of photonic crystal in the direction perpendicular to that of the propagation of the electromagnetic field. This gradient has been designed in such a way that the flat slab focuses a plane wave. With applications in the microwave range in view, we considered a photonic crystal which consists of copper strips.     

Light bending and quasi-transparency in metallic graded photonic crystals

Graded photonic crystals (GPhCs) have the remarkable ability to bend the path of light on the wavelength scale. A mirage effect has recently been reproduced experimentally in a two-dimensional structure made of metallic rods operating in the microwave regime (Akmansoy et al., 2008 [7]). This paper is intended to provide some theoretical insight onto the optical properties of metallic GPhCs and to report on the existence of a distinct regime of operation, in which light passes through the structure in a weakly curved trajectory. Experimental results are in good agreement with theoretical predictions, thereby further proving the ability of GPhCs to mold the flow of light in different ways at different frequencies.     

Graded photonic crystals for graded index lens

A graded index lens made from graded 2D photonic crystal has been designed by the means of the Finite Difference Time Domain (FDTD) method. The gradient of index has been obtained by varying the filling factor of a flat slab of photonic crystal in the direction perpendicular to that of the propagation of the electromagnetic field. This gradient has been designed in such a way that the flat slab focuses a plane wave. As only a few layers are necessary, graded photonic crystals show their ability to efficiently control the propagation of light and may apply to various photonic devices, from the microwave range to the optical domain.     

The use of controllable photonic band gap (CPBG) materials: An antenna application

In this paper, we theoretically and experimentally demonstrate the capability to realise controllable photonic band gap (CPBG) materials applied to the conformation of the radiation pattern of a planar antenna at 12 GHz. The CPBG materials studied are variable capacitance and conductance lattices fabricated with high frequency PIN diodes soldered along wires or metallic stripes on dielectric printed boards. Depending on the diode bias, the transmission factor of the lattice is controlled. Then, the emitted radiation of an antenna can be either transmitted or totally reflected by the material. In the transmission state, the antenna radiation is angular filtered by the CPBG material. In that case, it behaves like a controllable electromagnetic lens in the allowed frequency domain of the material.     

Comparative performances of stable-and unstable-resonator TEA CO2 lasers with cw injection

The performances of stable- and unstable-resonator TEA CO₂ lasers with cw injection are experimentally compared. Two types of measurements are reported. First, locking band-widths are measured for a wide range of cw injected powers. It is shown that 5-s 1-J single longitudinal mode pulses can be obtained with unstable resonator lasers for injected powers as low as 200 nW. Second, heterodyne measurements of the intrapulse TEA laser frequency are presented. The use of unstable resonators is experimentally proven to be the most efficient way to achieve reproducible high-power chirpless single-mode pulses at 10m.This work has been supported by Direction des Recherches et Etudes Techniques