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Here, we present the design and simulation of an ultrawide-bandwidth on-chip spectrometer that can be used in various applications, e.g. spectral tissue sensing. It covers 1200 nm wavelength range (400 nm-1600 nm) with 2 nm spectral resolution. The overall design size is only 3 × 3 cm2. The ultra-wide spectral range is made possible by using novel on-chip band-pass filters for the coarse wavelength division. The fine resolution is provided by the arrayed waveguide gratings. The band-pass filter is formed by using bend waveguides and adiabatic full-couplers. The additional loss caused by the band-pass filter is relatively small. The proposed spectrometer covers entire 400 nm-1600 nm range continuously with low crosstalk values. We envision that this design can be used in several different applications including food safety, agriculture, industrial inspection, optical imaging, and biomedical research.

Here, we present a compact, high-resolution, and ultrabroad-bandwidth arrayed waveguide grating (AWG) realized in a silicon nitride (Si3N4) platform. The AWG has a cascaded configuration with a 1×3 flat-passband AWG as the primary filter and three 1×70 AWGs as secondary filters (i.e. 210 output channels in total). The primary AWG has 0.5-dB bandwidth of 45 nm over 190 nm spectral range. The ultrabroad-bandwidth is achieved by using an innovative design that is based on a multiple-input multi-mode interference (MMI) coupler placed at the entrance of the first free propagation region of the primary AWG. The optical bandwidth of the cascaded AWG is 190 nm, and the spectral resolution is 1 nm. The overall device size is only 1.1 × 1.0 cm2. Optical loss at the central channel is 4 dB, which is 3 dB less than a conventional design with the same bandwidth and resolution values but using a primary filter with Gaussian transfer function. To the best of our knowledge, this is the first demonstration of an ultrabroad-bandwidth cascaded AWG on a small footprint. We also propose a novel low-loss (∼ 0.8 dB) design using a small AWG instead of an MMI coupler in the primary filter part, which can be used in applications where the light intensity is very weak, such as Raman spectroscopy.

We report on a novel non-destructive testing method for integrated circuits (ICs) by measuring their response to scanning terahertz and sub-terahertz radiation at the pins. Analyzing the response using artificial intelligence (AI), counterfeit, altered, or damaged ICs can be identified as in-package and in-situ.

Increasing complexity of digital and mixed-signal systems makes establishing the authenticity of a chip to be a challenging problem. We present a new terahertz testing technique for non-destructive identification of genuine integrated circuits, in package, in-situ and either with no or under bias, by measuring their response to scanning terahertz and sub-terahertz radiation at the circuit pins. This novel, patent pending non-invasive nondestructive technology when merged with Artificial Intelligence (AI) engine will evolve and self-improve with each test cycle. By establishing and AI processing of the THz scanning signatures of reliable devices and circuits and comparing this signatures with devices under test using AI, this technology could be also used for reliability and lifetime prediction.

In this letter, we report on the fabrication and DC/RF characterization of a novel Graphene Field-effect Transistor (GFET) with two additional contacts at the access regions. The additional contacts-Field Controlling Electrodes (FCEs), are capacitively coupled to the ungated access regions and independently biased to control the access resistance. The reduced access resistance resulted in an increased current-gain cutoff frequency (fT). The fabricated proposed device could be used for radio frequency (RF) applications.

In this paper, we have proposed and experimentally demonstrated engineering the bandgap of semi-metal zero bandgap single layer chemical vapor deposited graphene by decorating with randomly distributed nanoparticles. Decoration with two types of nanoparticles was investigated: zinc oxide nano-seed grown by sonication of zinc acetate dihydrate, and gold nanoparticles grown by thermal annealing of sputtered gold thin film. The proximity of nanoparticles and graphene break graphene’s sublattice symmetry and opens-up a bandgap. The grown nanoparticles were characterized by scanning electron microscopy and atomic force microscopy. The single layer graphene before and after decoration was characterized with Raman spectroscopy. The bandgap was engineered by simply adjusting the nanoparticle size and density, and the introduced bandgap was measured from the slope of temperature dependent conductivity characteristics. Graphene with significant bandgap introduced by the proposed methods could be used for devices intended for high speed digital and logic applications.

Two dimensional (2D) Molybdenum disulfide (MoS2) has evolved as a promising material for next generation optoelectronic devices owing to its unique electrical and optical properties, such as band gap modulation, high optical absorption, and increased luminescence quantum yield. The 2D MoS2 photodetectors reported in the literature have presented low responsivity compared to silicon based photodetectors. In this study, we assembled atomically thin p-type MoS2 with graphene to form a MoS2/graphene Schottky photodetector where photo generated holes travel from graphene to MoS2 over the Schottky barrier under illumination. We found that the p-type MoS2 forms a Schottky junction with graphene with a barrier height of 139 meV, which results in high photocurrent and wide spectral range of detection with wavelength selectivity. The fabricated photodetector showed excellent photosensitivity with a maximum photo responsivity of 1.26 AW(-1) and a noise equivalent power of 7.8 × 10(-12) W/√Hz at 1440 nm.

We propose a novel Graphene FET (GFET) with two capacitively coupled field-controlling electrodes (FCEs) at the bottom of the ungated access regions between gate and source/drain. The FCEs could be independently biased to modulate sheet carrier concentration and thereby the resistance in the ungated regions. The reduction of source/drain access resistance results in increased cut off frequency compared to those of conventional GFETs with the same geometry. We studied the DC and improved RF characteristics of the proposed device using both analytical and numerical techniques and compared with the baseline designs.

Graphene plasmonics has been introduced as a novel platform to design various nano- and microstructures to function in a wide range of spectrum from optical to THz frequencies. Herein, we propose a tunable plasmonic metamaterial in the THz regime by using metallic (silver) concentric microscale split ring resonator arrays on a multilayer metasurface composed of silica and silicon layers. We obtained an absorption percentage of 47.9% including two strong Fano resonant dips in THz regime for the purely plasmonic metamaterial without graphene layer. Considering the data of an atomic graphene sheet (with the thickness of ~0.35 nm) in both analytical and experimental regimes obtained by prior works, we employed a graphene layer under concentric split ring resonator arrays and above the multilayer metasurface to enhance the absorption ratio in THz bandwidth. Our numerical and analytical results proved that the presence of a thin graphene layer enhances the absorption coefficient of MM to 64.35%, at the highest peak in absorption profile that corresponds to the Fano dip position. We also have shown that changing the intrinsic characteristics of graphene sheet leads to shifts in the position of Fano dips and variations in the absorption efficiency. The maximum percentage of absorption (~67%) was obtained for graphene-based MM with graphene layer with dissipative loss factor of 1477 Ω. Employing the antisymmetric feature of the split ring resonators, the proposed graphene-based metamaterial with strong polarization dependency is highly sensitive to the polarization angle of the incident THz beam.

A novel label free, compact, fast and noninvasive absorbance based optical sensing technique was devised for the first time to detect cortisol, a physical and psychological stress biomarker, using ultraviolet (UV) LEDs. LEDs at three different UV wavelengths were employed to demonstrate cortisol sensing with different cortisol concentration. From the differential photoresponse versus concentration curves, we calculated the sensitivity of the sensors to be 1 mV/μM, 0.15 mV/μM and 0.08 mV/μM at 240 nm, 250 nm and 260 nm wavelength respectively. The developed sensing technique can be easily incorporated with microfluidic system for point-of-care cortisol detection and such developed protocol can be used in personalized health monitoring.

There have been extensive research to systematically tailor terahertz (THz) plasmonics structures to support strong resonant modes as platforms for designing practical nano and microscale devices with high efficiency and tunability. Here, using a symmetric four-member assembly of plasmonic vee-shaped structures, we introduce a quadratic, multiresonant plasmonic THz antenna to support significant resonant modes with high efficiancy. The effect of unique geometrical shape of the structure on the quality of the proposed structure is analyzed to provide ultrasharp resonant modes with high plasmon resonance confinement. Employing both numerical and experimental studies, we investigated and confirmed the tunable plasmonic response of the suggested antenna. In addition, by depositing an atomic graphene monolayer below the antenna, we enhanced the THz response of the proposed structure, including remarkable absorption cross-section correlating with the resonant frequencies. This understanding will contribute to a promising model for practical all-optical and optoelectronic devices operating in the THz spectrum.

In this paper, we have experimentally demonstrated the engineering of semi-metal single layer CVD Graphene’s bandgap by decorating with randomly distributed ZnO nano-seed grown by sonication of Zinc acetate dehydrate. The proximity of nanoparticles and Graphene breaks Graphene’s sublattice symmetry and opens-up a bandgap. The 2-D/G ratio of Raman spectroscopy of decorated Graphene along with a peak at 432.39 cm-1 confirmed presence of ZnO on single layer Graphene. The introduced bandgap was measured from the slope of Arrhenius plot. Graphene with significant bandgap introduced by the proposed methods could be used for devices intended for digital and logic applications.

This work proposes a novel geometry field effect transistor with graphene as a channel—graphene field-effect transistor (GFET), having a hybrid contact that consists of an ohmic source/drain and its extended part towards the gate, which is capacitively coupled to the channel. The ohmic contacts are used for direct current (DC) biasing, whereas their capacitive extension reduces access region length and provides the radio frequency (RF) signal a low impedance path. Minimization of the access region length, along with the paralleling of ohmic contact’s resistance and resistive part of capacitively coupled contact’s impedance, lower the overall source/drain resistance, which results in an increase in current gain cut-off frequency, fT. The DC and high-frequency characteristics of the two chosen conventional baseline GFETs, and their modified versions with proposed hybrid contacts, have been extensively studied, compared, and analyzed using numerical and analytical techniques.

This chapter summarizes the optical and electrical properties of plasmonic photodetectors in the spectral range of UV to the near infrared. Different types of plasmonic photodetectors are described with fundamental operation principles, relative advantages, applications and challenges. The chapter also reviews the state of the art for the plasmonic photodetectors and provides an outlook for the future.

In this work, we propose a novel Graphene field effect transistor (GFET) with ohmic Source/Drain contacts having capacitive extension towards the Gate. The ohmic contacts of the proposed GFET are used for DC biasing as like as conventional GFETs whereas their extended parts which are capacitively coupled to the channel reduce access region length as well as the access resistance and provide a low impedance route for the high frequency RF signal. Reduction of access resistance along with the paralleling of ohmic contact resistance and real part of capacitive impedance result in an overall lower Source/Drain resistance which eventually increases the current gain cut-off frequency, f T . We have studied and compared the DC and RF characteristics of the baseline conventional GFET and proposed GFET using analytical and numerical techniques.

We propose and extensively analyze a novel graphene-FET (GFET) with two capacitively coupled field-controlling electrodes (FCE) at the access region. The dc and RF characteristics of the proposed device are studied using analytical and numerical techniques and compared with the baseline designs. The independently biased FCEs could control the electric field and sheet carrier concentration at the ungated region, and thus reduce the access resistance effectively. The reduction of source/drain access resistance results in improved fT and fMAX compared with those of conventional GFETs of the same geometry. The proposed device with improved characteristics of GFET can be used for high-frequency applications.

This study reports on a reconfigurable antenna platform based on vanadium dioxide (VO2), a phase-change material (PCM) with low transition temperature, integrated with an addressable microheater matrix. For the first time, it is shown that an entire planar antenna can be thermally reconfigured virtually to any pattern by switching the phase of the selected regions of the VO2 layer from insulator to metallic state by indirect thermal stimuli generated by individually addressable nichrome resistive microheaters. Careful selection of the individual pixels to start the phase transition from insulator (OFF) to metallic (ON) state allows creating different antenna patterns with unique resonance properties. Reconfiguring the antenna into different patterns, operating frequency can be tuned from C-band (4–8 GHz) to X-band (8–12 GHz), and S-band (2–4 GHz) frequencies which cover the entire ultra wideband spectrum (3.1–10.6 GHz). The proposed approach provides a promising platform for designing monolithically integrated reconfigurable antennas, radio frequency devices, and circuits for various applications.

We designed and theoretically investigated nonlinear optical micro-ring resonators for tunable terahertz (THz) emission in 1-10 THz range by using difference frequency generation (DFG) phenomenon with large second order optical nonlinearity (χ(2)). Our design consists of a nonlinear ring resonator and another ring underneath capable of sustaining high-Q resonant modes for infrared pump beams and the generated THz radiation, respectively. The nonlinear ring resonator generates THz through DFG by mixing the input waves carried by a pair of waveguides. The proposed device can be a viable platform for tunable, compact THz emitters and on-chip integrated spectrometers.

We report on sub-wavelength THz plasmonic split ring resonators on 2 dimensional electron gas (2DEG) at AlGaN/GaN hetero-interface and on oxide coated high mobility graphene. The investigated in this study guide THz electric field into deep sub-wavelength scale by plasmonic excitations. Propagation of a broadband pulse of EM waves was simulated by using a commercial FDTD simulation tool. The results show that split ring resonator structures can be used to guide THz into deep sub-wavelength down λ/200 and achieve relatively higher quality factors than grating gate devices by plasmonic confinement which can be used for THz detection, filtering and possibly for THz on-chip-spectrometer. Moreover, ring resonator modes supported by system can be tuned with an applied voltage to gratings.

We propose Terahertz (THz) plasmonic devices based on linearly integrated FETs (LFETs) on Graphene. LFET structures are advantageous for (THz) detection since the coupling between the THz radiation and the plasma wave is strongly enhanced over the single gate devices and accordingly higher-order plasma resonances become possible. AlGaN/GaN heterostructure LFETs with their high sheet carrier concentration and high electron mobility are promising for plasmonic THz detection. Nevertheless, our numerical studies show that room temperature resonant absorption of THz radiation by the plasmons in AlGaN/GaN LFETs is very weak even if the integration density is sufficiently large. Our simulations also demonstrate that similar LFETs on Graphene, which has very large electron mobility, can resonantly absorb THz radiation up to 5th harmonic at room temperature. Additionally, we investigated LFETs with integrated cavities on Graphene. Such Periodic Cavity LFETs substantially enhance the quality factor of the resonant modes.

We report on sub-wavelength THz plasmonic lenses based on 2 dimensional electron gas (2DEG) at AlGaN/GaN interface and also on few-layer graphene sheets. Circular gratings investigated in this study concentrate THz electric field into deep sub-wavelength scale by plasmonic excitations polarization independently. Propagation of a broadband pulse of EM waves in 0.5-10 THz was simulated by using a commercial FDTD simulation tool. The results show that concentric plasmonic grating structures can be used to concentrate THz into deep sub-wavelength down to /350 spot size and achieve very large field enhancements by plasmonic confinement which can be used for THz detection and possibly for sub-wavelength imaging. Electric field intensity under the central point can be orders of magnitude higher than the outer grating area. Moreover, plasmonic lens modes supported by system can be tuned with an applied voltage to gratings.