This paper reports on the development of micromachined pillar arrays for the filtering of terahertz radiation. These pillar
arrays are fabricated using ultraviolet based processing of thick SU8. This micromachining technique enables the array
patterns, dimensions, and consequently the filter characteristics, to be readily defined. In particular, we demonstrate that
by combining individual filter arrays with either different periods or pillar diameters we can isolate individual pass bands
in the 1 to 2 THz region.
A plane-wave complex photonic bandstructure approach is used to calculate the pass bands as a function of rod diameter
for a system consisting of circular metallic rods in a 2-D square lattice. In addition, FDTD calculations are employed to
calculate the transmission properties of a finite 6-layer structure of the same form. The results of the two methods are
compared and found to be consistent. The effective plasma frequency, the lowest frequency at which propagation can
occur in the infinite lattice, is extracted from the bandstructure calculations, and is in the region of 1 THz for the 200 μm
period structures considered. The results for the effective plasma frequency are compared to those predicted by several
We report on the development of a surface micromachined process for the fabrication of coaxial apertures surrounded by periodic grooves. The process uses a combination of copper electroforming and the negative epoxy based resist, SU8, as a thin flexible substrate. The device dimensions are suitable for the implementation of filters at THz frequencies, and measurements show a pass band centred around 1.5 THz. These devices could form the basis of the next generation of THz biosensors.
At the present time the interaction of Terahertz (THz) radiation with random structures is not well understood. Scattering effects are particularly relevant in this spectral regime, where the wavelength, and the size and separation of scattering centres are often commensurable. This phenomenon can both be used to advantage in imaging and sensing, but conversely can have adverse effects on the interpretation of a "fingerprint" spectrum. A new mathematical method, the Phase Distribution Model, is reported here for the calculation of attenuation and scattering of THz radiation in random materials. This uses a Phase Distribution Function to describe the effect of the non-absorbing scatterers within the media. Experimental measurements undertaken using previously published results, data obtained from specially constructed phantoms and from everyday textiles have been compared with the theory. These experimental results encompass both cylindrical and spherical scattering situations. The model has also been compared with exact calculations using the Pendry code.
A new mathematical method, the Phase Distribution Model, is devised for the calculation of attenuation and scattering of THz radiation in random materials. The accuracy of the approximation is tested by comparison with exact calculations and with experimental measurements on textiles and specially constructed phantoms.
We report the results of calculations of the optical properties of strained InGaAs/InP quantum wells based on realistic band structure. Emphasis is placed on those features relevant to the operation of quantum well lasers. A k. p model including spin and strain is used to calculate the electronic states of the quantum well. The optical matrix elements as well as the dispersion of the conduction and valence subbands are obtained directly from the model and used to calculate gain and spontaneous emission spectra to study some aspects of intervalence band absorption and to model the behaviour of multiquantum well lasers. The results show that interband mixing causes substantial departures from the predictions of simple models including the failure of band edge selection rules for optical transitions. It is demonstrated how the combined effect of alloy composition spatial confinement and strain can can be used to influence the optical properties of quantum wells and improve the performance of lasers based on these structures.