Limitation in thin-film detection with transmission-mode terahertz time-domain spectroscopy

In transmission-mode terahertz time-domain spectroscopy (THz-TDS), the thickness of a sample is a critical factor that determines an amount of the interaction between terahertz waves and bulk material. If the interaction length is too small, a change in the transmitted signal is overwhelmed by fluctuations and noise in the system. In this case, the sample can no longer be detected. This article presents a criterion to determine the lower thickness boundary of a free-standing film that can still be detectable by free-space transmission-mode THz-TDS. The rigorous analysis yields a simple proportional relation between the sample optical length and the system SNR. The proposed criterion can help to decide whether an alternative terahertz thin-film sensing modality is necessary.Comment: 5 pages, 1 figur

3D Modeling from Multiple Projections: Parallel-Beam to Helical Cone-Beam Trajectory

Tomographic imaging is a technique for exploration of a cross-section of an inspected object without destruction. Normally, the input data, known as the projections, are gathered by repeatedly radiating coherent waveform through the object in a number of viewpoints, and receiving by an array of corresponding detector in the opposite position. In this research, as a replacement of radiographs, the series of photographs taken around the opaque object under the ambient light is completely served as the projections. The purposed technique can be adopted with various beam geometry including parallel-beam, cone-beam and spiral cone-beam geometry. From the process of tomography, the outcome is the stack of pseudo cross-sectional image. Not the internal of cross section is authentic, but the edge or contour is valid

Classification of osteosarcoma T-ray responses using adaptive and rational wavelets for feature extraction

Copyright 2007 Society of Photo-Optical Instrumentation Engineers. This paper was published in Complex Systems II, edited by Derek Abbott, Tomaso Aste, Murray Batchelor, Robert Dewar, Tiziana Di Matteo, Tony Guttmann, Proc. of SPIE Vol. 6802, 680211 and is made available as an electronic reprint with permission of SPIE. One print or electronic copy may be made for personal use only. Systematic or multiple reproduction, distribution to multiple locations via electronic or other means, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited.In this work we investigate new feature extraction algorithms on the T-ray response of normal human bone cells and human osteosarcoma cells. One of the most promising feature extraction methods is the Discrete Wavelet Transform (DWT). However, the classification accuracy is dependant on the specific wavelet base chosen. Adaptive wavelets circumvent this problem by gradually adapting to the signal to retain optimum discriminatory information, while removing redundant information. Using adaptive wavelets, classification accuracy, using a quadratic Bayesian classifier, of 96.88% is obtained based on 25 features. In addition, the potential of using rational wavelets rather than the standard dyadic wavelets in classification is explored. The advantage it has over dyadic wavelets is that it allows a better adaptation of the scale factor according to the signal. An accuracy of 91.15% is obtained through rational wavelets with 12 coefficients using a Support Vector Machine (SVM) as the classifier. These results highlight adaptive and rational wavelets as an efficient feature extraction method and the enormous potential of T-rays in cancer detection.Desmond Ng, Wong Fu Tian, Withawat Withayachumnankul, David Findlay, Bradley Ferguson and Derek Abbot

Analysis of measurement uncertainty in THz-TDS

Copyright 2007 Society of Photo-Optical Instrumentation Engineers. This paper was published in Photonic Materials, Devices, and Applications II, edited by Ali Serpengüzel, Gonçal Badenes, Giancarlo Righini Proc. of SPIE Vol. 6593, 659326 and is made available as an electronic reprint with permission of SPIE. One print or electronic copy may be made for personal use only. Systematic or multiple reproduction, distribution to multiple locations via electronic or other means, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited.Measurement precision is often required in the process of material parameter extraction. This fact is applicable to terahertz time-domain spectroscopy (THz-TDS), which is able to determine the optical/dielectric constants of material in the T-ray regime. Essentially, an ultrafast-pulsed THz-TDS system is composed of several mechanical, optical, and electronic parts, each of which is limited in precision. In operation, the uncertainties of these parts, along with the uncertainties introduced during the parameter extraction process, contribute to the overall uncertainty appearing at the output, i.e. the uncertainty in the extracted optical constants. This paper analyzes the sources of uncertainty and models error propagation through the process.W. Withayachumnankul, H. Lin, S. P. Mickan, B. M. Fischer, and D. Abbot

Dielectric resonator nanoantennas at visible frequencies

Drawing inspiration from radio-frequency technologies, we propose a realization of nano-scale optical dielectric resonator antennas (DRAs) functioning in their fundamental mode. These DRAs operate via displacement current in a low-loss high-permittivity dielectric, resulting in reduced energy dissipation in the resonators. The designed nonuniform planar DRA array on a metallic plane imparts a sequence of phase shifts across the wavefront to create beam deflection off the direction of specular reflection. The realized array clearly demonstrates beam deflection at 633 nm. Despite the loss introduced by field interaction with the metal substrate, the proposed low-loss resonator concept is a first step towards nanoantennas with enhanced efficiency. The compact planar structure and technologically relevant materials promise monolithic circuit integration of DRA

Effective-medium-clad Bragg grating filters

We propose a series of integrated Bragg grating filters with performance enhancement via the concept of effective medium. The bandstop filters are built in a high-resistivity silicon wafer and operated over the WR-3.4 band (220–330 GHz) with in-plane polarization. The proposed designs use an additional degree of freedom in controlling the effective refractive index so as to fully use the potential of the Bragg grating structures. As a result, the high insertion loss typically observed at the low-frequency bound of the filters due to weak wave confinement can be reduced, while radiation caused by the leaky-wave effect at the high-frequency bound is minimized, allowing for a 40% operation fractional bandwidth. These features are not achievable with conventional waveguide Bragg grating filters. All-silicon prototypes of filter samples are experimentally validated, demonstrating promising performance for a wide range of terahertz applications. The techniques to improve the filter characteristics by controlling the effective medium can be adopted in both microwave and optics domains.Weijie Gaoa, Wendy S. L. Leeb, Christophe Fumeaux and Withawat Withayachumnankul

Gratingless integrated tunneling multiplexer for terahertz waves

The arrayed waveguide grating (AWG) is a versatile and scalable passive photonic multiplexer that sees widespread usage. However, the necessity of a waveguide array engenders large device size, and gratings invariably commute finite power into undesired diffraction orders. Here, we demonstrate AWG-like functionality without a grating or waveguide array, yielding benefits to compactness, bandwidth, and efficiency. To this end, we exploit optical tunneling from a dielectric waveguide to an adjacent slab in order to realize a slab-confined frequency-scanning beam, which is manipulated using in-slab beamforming techniques that we have developed in order to separate distinct frequency bands. In this way, we devise an all-intrinsic-silicon integrated 4×1 frequency-division terahertz multiplexer, which is shown to support aggregate data rates up to 48 Gbit/s with an on–off-keying modulation scheme, operating in the vicinity of 350 GHz. Our investigation targets the terahertz range, to provide a critical missing building block for future high-volume wireless communications networks.Daniel Headland, Withawat Withayachumnankul, Masayuki Fujita and Tadao Nagatsum

Practical method for determining inductance and capacitance of metamaterial resonators

A practical approach to determining the distributed capacitance and inductance of individual metamaterial resonators is demonstrated. By loading a set of lumped capacitors onto the resonator, the resonance frequency can be measured as a function of the load capacitance. The capacitance and inductance values of the resonator are then determined by relating the equivalent circuit model to the measurements. Although the measurement is limited to the microwave region owing to the availability of suitable lumped capacitors, the concept is useful in simulations over a wider frequency range. The obtainable parameters are useful for further metamaterial analyses or syntheses.J.N. Li, W. Withayachumnankul, S.J. Chang and D. Abbot

Beam deflection lens at terahertz frequencies using a hole lattice metamaterial

The design and simulation of a dielectric lens for beam deflection in the terahertz range is presented. The device consists of a lattice of sub-wavelength holes in a rectangular dielectric slab, and by varying the radii of the holes with respect to position, a gradient index (GRIN) lens can be realised. Beam deflection is achieved by giving the refractive index a ramp-like characteristic. The lens has a flat-profile, and is likely to be more compact than lenses based on geometric optics. A Fresnel lens-like design is used to expand the lens aperture. Additionally, this lens is expected to have lower loss, higher bandwidth, and be less sensitive to polarisation than similar lenses constructed from resonant metamaterials

Microfluidic-based Split-Ring-Resonator Sensor for Real-time and Label-free Biosensing

AbstractIn this report, a split ring resonator (SRR), the most important building block of metamaterial, is fabricated and integrated with a microfluidic chamber for biosensing. The SRR is produced on a microwave printed circuit board while the microfluidic chamber is fabricated by casting of polydimethylsiloxane (PDMS). SRR was immobilized with Anti- Immunoglobulin G (IgG) for IgG detection by a standard covalent immobilization using Cystamine. The PDMS chamber was aligned and clamped on the circuit board and the electromagnetic response of the SRR sensor was continuously monitored when IgG analytes was flowed through the chamber. The reaction of Immunoglobulin G (IgG) and Anti-IgG results in a shift of resonance frequency. It was found that the response of the resonance frequency is sensitive to the IgG concentrations. Therefore, the SRR microfluidic scheme can be effectively used as an advanced bio-sensing device