Mihail M. Sigalas

Infrared filters using metallic photonic band gap structures on flexible substrates

Metallic photonic band gap (MPBG) filter structures operating at far infrared wavelengths have been designed, fabricated, and characterized. The MPBGs are multilayer metallic meshes imbedded in a flexible polyimide dielectric. Depending on the periodic pattern of the metal grids, the filters have either simple high-pass or more complex transmission characteristics. The critical frequencies of the filters depend on the spatial periodicity of the metal grids and the interlayer separation. Optical transmission measurements on a high-pass structure show cutoff frequency of 3 THz and attenuation of more than 35 dB in the cutoff region, in good agreement with predicted results. Band-reject filters show similarly good attenuation and large fractional bandwidths. The filters maintain their optical characteristics after repeated bending, demonstrating mechanical robustness of the MPBG structure.

A layer‐by‐layer metallic photonic band‐gap structure

A new photonic band‐gap structure has been developed using a periodic array of metallic rods. Structures have been designed and built that operate in the 75–110 GHz frequency range. A periodic structure shows a high‐pass transmission characteristic, while the addition of a defect to the structure adds a bandpass response. Measured responses show good agreement with theoretical simulations. A defect mode operated in the reflection mode showed a quality factor Q of 461. This new metallic structure is considerably smaller than comparable dielectric photonic band‐gap structures, and should be useful for building compact, inexpensive filters with operating frequencies ranging from 1 GHz to 1 THz.

Dielectric waveguides in two-dimensional photonic bandgap materials

We investigate the performance and guiding properties of waveguides fabricated in a finite two-dimensional (2-D) photonic bandgap (PBG) structure. Confinement in the direction perpendicular to the plane of periodicity is achieved by fabricating the 2-D PBG structure in a high dielectric layer enclosed by two lower dielectric layers. Simulations using the finite-difference time-domain (FDTD) method are performed to investigate the energy transport in such waveguides. Good qualitative agreement is found with the experimental observations.

Optical photonic crystals synthesized from colloidal systems of polystyrene spheres and nanocrystalline titania

We have developed a novel ceramic processing technique to fabricate photonic crystals (PCs) with close-packed lattices of air pores in a dielectric background. The ordering of colloidal spheres and incorporation of the titania is performed simultaneously, in contrast to other approaches. Excellent ordering of the lattice of air pores is achieved over domains extending over 100 /spl mu/. The PCs exhibit a uniform color and a corresponding sharp peak in the reflectivity at the wavelength of the first stopband. The position of the reflectivity peak scales very well with the size of the air pores, providing strong evidence for photonic crystal effects.

Band-reject infrared metallic photonic band gap filters on flexible polyimide substrate

Metallic photonic band gap (MPBG) structures are multi-layer metallic meshes imbedded in a dielectric medium. We report the successful design, fabrication, and characterization of infrared band-reject filters using MPBG structures in a flexible polyimide substrate. The metal layers of the MPBG have square grid patterns with short perpendicular cross-arm defects added halfway between each intersection. The transmission characteristics of these filters show a higher order band-reject region in addition to a lower order band gap that extends from zero to particular cut off frequency. The critical frequencies of the filters depend on the spatial periodicity of the metal grids and length of the cross-arm defects. Optical transmission measurements of the bandreject filters show lower edge cutoff frequency of about 2 THz and the higher order bandgap region centered around 4.5THz with attenuation of more than 35 dB in the bandgap region. This is in good agreement with the theoretical calculations. The filters maintain their optical characteristics after repeated bending, demonstrating mechanical robustness of the MPBG structure and have minimal dependence on angle of incidence.