G. Tuttle

Micromachined millimeter-wave photonic band-gap crystals

We have developed a new technique for fabricating three‐dimensional photonic band‐gap crystals. Our method utilizes an orderly stacking of micromachined (110) silicon wafers to build the periodic structure. A structure with a full three‐dimensional photonic band gap centered near 100 GHz was measured, with experimental results in good agreement with theoretical predictions. This basic approach described should be extendable to build structures with photonic band‐gap frequencies ranging from 30 GHz to 3 THz.

Photonic crystal-based resonant antenna with a very high directivity

We investigate the radiation properties of an antenna that was formed by a hybrid combination of a monopole radiation source and a cavity built around a dielectric layer-by-layer three-dimensional photonic crystal. We measured a maximum directivity of 310, and a power enhancement of 180 at the resonant frequency of the cavity. We observed that the antenna has a narrow bandwidth determined by the cavity, where the resonant frequency can be tuned within the band gap of the photonic crystal. The measured radiation patterns agree well with our theoretical results.

Experimental demonstration of negative index of refraction

We introduce an improved and simplified structure made of periodic arrays of pairs of H-shaped metallic wires that offer a potentially simpler approach in building negative-index materials. Using simulations and microwave experiments, we have investigated the negative-index n properties of these structures. We have measured experimentally both the transmittance and the reflectance properties and found unambiguously that a negative refractive index with Re(n)<0 and Im(n)<Re(n). The same is true for e and μ. Our results show that H-shaped wire pairs can be used very effectively in producing materials with negative refractive indices.

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.

DEFECT STRUCTURES IN METALLIC PHOTONIC CRYSTALS

We have investigated metallic photonic crystals built around a layer‐by‐layer geometry. Two different crystal structures (face‐centered‐tetragonal and tetragonal) were built and their properties were compared. We obtained rejection rates of 7–8 dB per layer from both metallic crystals. Defect modes created by removing rods resulted in high peak transmission (80%), and high quality factors (1740). Our measurements were in good agreement with theoretical simulations.

Optimized dipole antennas on photonic band gap crystals

Photonic band gap crystals have been used as a perfectly reflecting substrate for planar dipole antennas in the 12–15 GHz regime. The position, orientation, and driving frequency of the dipole antenna on the photonic band gap crystal surface, have been optimized for antenna performance and directionality. Virtually no radiated power is lost to the photonic crystal resulting in gains and radiation efficiencies larger than antennas on other conventional dielectric substrates.

Structures with negative index of refraction

Rapidly increasing interest in the left-handed materials (LHM) started after Pendry et al. predicted that certain man-made composite structure could possess, in a given frequency interval, a negative effective magnetic permeability meff [1]. Combination of such a structure with a negative effective permittivity medium – for instance the regular array of thin metallic wires [2–7] – enabled the construction of meta-materials with both effective permittivity and permeability negative. This was confirmed by experiments [8, 9]. Structures with negative permittivity and permeability were named ‘‘left-handed” by Veselago [10] over 30 years ago to emphasize the fact that the intensity of the electric field E, the magnetic intensity H and the wave vector k are related by a left-handed rule. This can be easily seen by writing Maxwell’s equation for a plane monochromatic wave: k E 1⁄4 wm c H and k H 1⁄4 wE c E : ð1Þ

DIPOLE ANTENNAS ON PHOTONIC BAND-GAP CRYSTALS : EXPERIMENT AND SIMULATION

The radiation patterns of dipole antennas on three-dimensional photonic crystal substrates have been measured and calculated with the finite-difference-time-domain method. The photonic band-gap crystal behaves as a perfectly reflecting substrate, and all the dipole power is radiated into the air side when driven at frequencies in the stop band. The radiation pattern is found for dfferent positions and orientations of the dipole antenna. Antenna configurations with desirable patterns are identified.

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.

Resonant cavity enhanced detectors embedded in photonic crystals

Summary form only given. We demonstrate the resonant-cavity-enhanced effect by placing microwave detectors in a layer-by-layer photonic crystal. We used the output of a network analyzer as the microwave source, and fed the output to a horn antenna to obtain EM waves. The crystal was then replaced in the beam-path of the EM wave, and the electric field inside the cavity was measured by a probe that consisted of a monopole antenna. The output of the antenna was measured by use of two different techniques: network analyzer and microwave detector within the cavity. The first cavity structure was similar to a one-dimensional Fabry-Perot resonator made of two mirrors separated by a distance.