On chip glucose sensing using guided waves at terahertz frequencies.

This paper demonstrates an on-chip anhydrous D-glucose sensor using a coplanar stripline (CPS) on a thin (1 [Formula: see text]m) silicon nitride membrane at terahertz (THz) frequencies. A thin layer (≈ 10 [Formula: see text]m) of D-glucose was placed in close proximity to the CPS and the transmission response was measured using a modified THz-TDS setup. The D-glucose introduces frequency-dependent changes to the effective permittivity of the CPS resulting in a modified spectral response at the receiver.

Demonstration of a terahertz coplanar-strip spoof-surface-plasmon-polariton low-pass filter.

There is a growing interest in spoof surface plasmon polariton (SSPP) structures at terahertz (THz) frequencies for applications such as filtering, sensing, and communications. However, to date, there are limited experiments that confirm SSPP characteristics at THz frequencies. The majority of literature focuses on simulation or verification by device scaling to Gigahertz (GHz) frequencies where standard vector network analyzers are readily available.

Demonstration of an Integrated terahertz band-stop filter using an apodized Bragg grating.

This paper presents the demonstration of an on-chip integrated terahertz (THz) apodized Bragg grating (TABG) which functions as band-stop filter with a center frequency of 0.8 THz and a bandwidth of 200 GHz. For experimentation, we integrate the TABG into our THz system-on-chip to enable wideband (DC - 1.

Characterization of a split-ring-resonator-loaded transmission line at terahertz frequencies.

Recently we demonstrated the fabrication and testing of a variety of RF-engineered passive transmission-line-based components designed for operation at terahertz frequencies and fabricated on thin (1 μm) silicon-nitride membranes. In this work we measure the transmission response of a coplanar-strip transmission line loaded with split-ring resonators up to 2.5 THz.

Terahertz low-pass filter based on cascaded resonators formed by CPS bending on a thin membrane.

A membrane-based coplanar-stripline (CPS) transmission-line platform has recently enabled implementation of diverse THz system-on-chip (TSoC) components. In this paper, we demonstrate an elliptic-function THz low-pass filter (TLPF) using cascaded λ/4 resonators between the right-angle bending of a CPS transmission line defined on a 1 μm-thin membrane. We investigated the effect of bending the CPS transmission line with different angles that introduces a frequency response similar to a simple LC low-pass filter (LPF) and facilitates the design of a desired roll-off performance using traditional methods.

Demonstration of a low-distortion terahertz system-on-chip using a CPS waveguide on a thin membrane substrate.

Distortion-free transmission of THz-bandwidth pulses over centimeter-scale distances is desirable for future THz system-on-chip (TSoC) applications. In this work we achieve this by utilizing a coplanar strip (CPS) transmission line fabricated on a thin (1 µm) silicon nitride membrane. To generate and detect the THz-bandwidth pulses we use a well-known lift-off technique to construct thousands of small (20 µm × 40 µm) thin-film LTG-GaAs photoconductive devices from a small (approx.

Plasmon-enhanced LT-GaAs/AlAs heterostructure photoconductive antennas for sub-bandgap terahertz generation.

Photocurrent generation in low-temperature-grown GaAs (LT-GaAs) has been significantly improved by growing a thin AlAs isolation layer between the LT-GaAs layer and semi-insulating (SI)-GaAs substrate. The AlAs layer allows greater arsenic incorporation into the LT-GaAs layer, prevents current diffusion into the GaAs substrate, and provides optical back-reflection that enhances below bandgap terahertz generation. Our plasmon-enhanced LT-GaAs/AlAs photoconductive antennas provide 4.

THz-TDS using a photoconductive free-space linear tapered slot antenna transmitter.

A near-field edge-coupled photoconductive free-space linear tapered slot antenna has been constructed as a planar alternative to the standard photoconductive switch coupled to a silicon substrate lens. The temporal response along the optical axis is investigated to ensure the structure itself does not introduce pulse distortion which would fundamentally limit the usefulness of the structure. Experimental results show that a 1.

Nanoplasmonic terahertz photoconductive switch on GaAs.

Low-temperature (LT) grown GaAs has a subpicosecond carrier response time that makes it favorable for terahertz photoconductive (PC) switching. However, this is obtained at the price of lower mobility and lower thermal conductivity than GaAs. Here we demonstrate subpicosecond carrier sweep-out and over an order of magnitude higher sensitivity in detection from a GaAs-based PC switch by using a nanoplasmonic structure.

Probability based modeling of cross phase modulation in 16-QAM dispersion compensated coherent systems.

A probability-based model is developed to describe cross phase modulation in multichannel multilevel amplitude/phase modulated coherent systems. Standard deviation of nonlinear phase-shift is evaluated in 16-QAM coherent systems accordingly and by numerical simulation for different values of chromatic dispersion and symbol rate. Furthermore, an error analysis is provided to evaluate the accuracy of the model which demonstrates maximum relative error of 12% in the field of interest.

Tuning plasmonic resonances of an annular aperture in metal plate.

We present theory to describe the plasmonic resonances of a subwavelength annular aperture in a real metal plate. The theory provides the reflection, including the amplitude and phase, of radially polarized surface plasmon waves from the end faces of the aperture with a significant departure from the perfect electric conductor case due to plasmonic effects. Oscillations in the reflection amplitude and phase are observed.

Coupling of terahertz waves to a two-wire waveguide.

We calculate theoretically the coupling of a terahertz wave from a dipole into a two-wire waveguide. The field transmission and reflection are obtained using a Single Mode Matching (SMM) technique at the input port of the two-wire waveguide. The results show more than 70 percent coupling efficiency for the waveguide using 500 μm radii wires with 2mm center-to-center separation and the exciting field cross section of 1mm × 1mm.

Expansion of field of view in digital in-line holography with a programmable point source.

We present a technique for programming the source of the spherical reference illumination in digital in-line holography using digital micromirror devices. The programmable point source is achieved by individually addressing the elements of a digital micromirror device to spatially control the illumination of the object located at some distance from the source of the spherical reference field. By moving the location of the "ON" element on the digital micromirror device, translation of both the source of the spherical reference beam and the captured holograms is achieved.

Applications of digital micro-mirror devices to digital optical microscope dynamic range enhancement.

In this paper, we present a method of using digital micro-mirror devices to dynamic range enhancement of a digital optical microscope images. Our adaptive feedback illumination control generates a high dynamic range image through an algorithm that combines the DMD-to-camera pixel geometrical mapping and a feedback operation. The feedback process automatically generates an illumination pattern in an iterative fashion that spatially modulates the DMD array elements on pixel-by-pixel level.

Minimal-bracketing sets for high-dynamic-range image capture.

This paper considers the problem of high-dynamic-range (HDR) image capture using low-dynamic-range (LDR) cameras. We present three different minimal-bracketing algorithms for computing minimum-sized exposure sets bracketing of HDR scenes. Each algorithm is applicable to a different HDR-imaging scenario depending on the amount of target-scene-irradiance information and real-time image processing available at the time of image acquisition.

Design of a continuous-wave tunable terahertz source using waveguide-phase-matched GaAs.

A novel source of continuous-wave terahertz radiation based on difference frequency generation (DFG) in GaAs crystal is proposed. Phase matching is provided using integration of appropriate optical and terahertz waveguides based on dispersive properties of GaAs. The output frequency can be tuned between 0-3.