This PDF file contains the front matter associated with SPIE Proceedings Volume 10917, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists.

Rabi splittings are now being routinely measured for condensed phase vibrations interacting with the modes of a parallel plate etalon of wavelength-scale spacing by means of Fourier Transform Infrared (FTIR) spectrometers. Considering that the width of an etalon fringe is a critical parameter in experiments of cavity-vibration interactions, it is noteworthy that the fringes are strongly affected by non-ideal conditions such as the angular spread of the FTIR beam and/or etalon misalignment. This work characterizes how parallel plate etalons are affected by angular spread in our FTIR and presents a method to reconstruct fringes that are strongly affected by vibrations by using those unaffected by strong vibrations.

We have developed two terahertz (THz) polarimetric methodologies based on terahertz time-domain spectroscopy (THz- TDS) incorporating three wire-grid polarizers. They require no change to existing THz-TDS setups and are free of any complicated electronic controls and synchronizations. In addition to the standard quantities measured by THz-TDS such as transmission and optical constants, they provide complete information on the anisotropy and chirality for a generalized material through measurements of the full electric field vector and hence the Jones matrix, and calculating specific quantities. Thus terahertz time-domain polarimetry (THz-TDP) can be considered as an upgrade of the conventional THz- TDS, needed for full characterization of anisotropic and chiral materials. In this paper, we describe the details of the experimental settings, mathematical procedures and property quantifications in these methodologies. We present experimental results on an anisotropic polymer sheet showing the effectiveness of the methods, and preliminary data for chiral DNA molecules for the first time in the THz frequency range.

Frequent measurement can suppress the transitions between different quantum states. This quantum physics phenomenon can play a very good role in the state control. This effect can be helpful to the laser amplification technology. Therefore, this article attempts to use this quantum effect to realize the amplification without population inversion. The article first introduce this phenomenon, and then explain what frequent measurements are. Finally, a simple model is simulated by using hydrogen atom system as a medium for optical amplification without population inversions.

In the last three decades, the terahertz science has achieved great development, possibility to be utilized in a wide variety of fields such as biology, quality control, and security. Especially terahertz time-domain spectroscopy is very useful for nondestructive measurement of materials. Many excellent researchers have approached the commercialization of terahertz technology. However, in the ambient atmosphere, not in the laboratory environment, the signal is distorted due to absorption of water vapor. As a result, unintentional noise is generated in the absorption line, resulting in a great difficulty in spectroscopy. We propose an algorithm that selects a frequency band with no signal distortion and performs spectroscopy. It has an advantage that it can apply algorithms without complex calculation and additional optical components. We measure terahertz time-domain signals of several samples within nitrogen filled chamber, and then the nitrogen was removed to measure the signal in a high relativity humidity environment. We extract optical parameters from the obtained signals. The algorithm is verified by comparison of experimental results and literature value. The values of absorption peaks of samples from our algorithm show good agreement with a literature value. We compared these values and conclude that the thickness was measured and we can check the peak of the absorption line. We find that the proposed algorithm can extract optical parameters even in a high relativity humidity environment.

In this paper, we show the fabrication of metamaterials by 3D printing, metal coating and wet etching. We showcase 3D printed cylindrical metamaterial arrays with Terahertz frequency response around 200 GHz. We use two distinctive methods for metal coating - stamping and another involving sputtering followed by etching. We also represent a novel method of metamaterial fabrication by embedding metamaterial arrays in a curved parabolic substrate. This is achieved by simply printing a curved substrate followed by sanding and Polyurethane coating for smoothness. This followed by shadow printing metamaterial pattern using a stencil. Such a curved parabolic metamaterial shows both focusing and frequency selective performance around 100 GHz. Suite of fabrication approaches listed here will enable fabrication of complex 3D printed metamaterials for high frequency applications.

Dispersion induced power penalty limits the applicability of Double SideBand with Carrier (DSB+C) signals in Radio-over-Fiber type of communication system. The issue is alleviated using Single Sideband with Carrier (SSB+C) modulated signals where either upper or lower order sidebands are retained while suppressing the others. In this work, we propose a fully integrated and configurable solution to suppress one sideband using Micro Ring Modulator (MRM) and a Self-Coupled Micro Ring Resonator (SCMRR) on Silicon. A DSB+C signal is generated by MRM, and the sideband is suppressed using SCMRR. SCMRR works on splitting of cavity resonance by exciting counter-propagating mode in a controlled manner. The split notches are then utilized for selecting the carrier and one sideband. Using the proposed method, we demonstrate generation of SSB+C signal with a bandwidth of 55GHz and an Optical Sideband Suppression Ratio (OSSR) of 56dB. The solutions offer complete reconfigurability of OSSR via thermo-optic tuning and of bandwidth by varying the resonance split. At 15GHz, we report OSSR tunability of 25dB (15db-38dB) using a Peltier heater and bandwidth of 55GHz and 10GHz by engineering the optical power in the counter-propagating mode. Phase noise and polarization parameter measurements of the down-converted RF signal is performed to assess the spectral purity and polarization dependent variations. We also report bit error rate and eye diagram analysis of our device at 12.5Gbps which is only limited by the capability of the instruments involved.

Within advanced driver assistance systems, long-range radar devices with a frequency around 77 GHz are widely used. They have several advantages for automotive use, e.g. the wide bandwidth available improves accuracy and object resolution, combined with small antennas and limited interference with other systems due to atmospheric absorption. Nowadays, these sensors must provide better separation of objects and elevation estimation, translating to a higher angular and velocity resolution, which will be enabled by utilizing cascaded, off-the-shelf, radar front-end devices. In order to guarantee precise beam forming, all modules need to be synchronized. For the distribution of these signals, which are in the range of 20 GHz, optical technologies are of great advantage. They are lightweight, show low loss, are insensitive to electromagnetic interference and have the capability to be integrated. Within the proposed system, the electrical synchronization signal from a central master chip is transferred to the optical domain by a Mach-Zehnder modulator, amplified by an EDFA and distributed with an optical splitter to 4 separate modules. O/E conversion is carried out by a photodiode. Long time stable operation over a wide temperature range is ensured by an external bias voltage regulation of the modulator. First results of the complete system show improved accuracy and object resolution of the targets. The already space-saving design could be made even more compact with special integrated photonic devices. In addition, the realization of a complete optical radar, where the radar signals and echoes are transmitted with optical fibers, would be possible.

In developing terahertz (THz) technologies that are more suitable for industrial applications, we have focused on research on continuous-wave (CW) THz technologies to develop small, low-cost, and multifunctional THz devices and systems. In the course of this research, we have developed several key devices such as widely tunable compact beating sources in the form of dual mode lasers, THz emitters, including nano-electrode-photomixers and uni-traveling carrier photodiode photomixers, and highly sensitive THz detectors, such as Schottky barrier diodes (SBDs). In this study, along with our recently obtained results that demonstrate the enhanced performance of these devices, we also present an example of a practical industrial application of our CW THz system: a nondestructive evaluation (NDE) system. The system described can be applied in the car manufacturing factory as an NDE technique to find process errors. Although further improvements to photonics-based THz technologies are necessary, we believe that efforts in this field will begin an era of THz technologies as a widely-used industrial technique.

Utilizing short-carrier-lifetime semiconductors as the photo-absorbing substrate of photoconductive terahertz detectors has been considered a necessity to enable ultrafast operation and to recombine the slow photo-generated carriers that increase the detector noise and reduce the detector responsivity. However, most of the techniques used for growing short-carrier-lifetime semiconductors introduce a high density of defects in the semiconductor lattice, degrading the carrier mobility and drift velocity and, thus, the detector responsivity. To eliminate the need for a short-carrier-lifetime semiconductor, we present a novel photoconductive terahertz detector based on a nanocavity-coupled plasmonic nanoantenna array. The presented photoconductive terahertz detector uses an undoped GaAs layer embedded inside a nanocavity as the photoconductive active region. The nanocavity is specifically designed to confine the optical pump photons very tightly inside the undoped GaAs layer so that all the photo-generated carriers concentrate around an array of plasmonic nanoantennas, which are also designed to operate as broadband terahertz antennas. Therefore, the presented nanocavity-coupled plasmonic nanoantenna array maximizes the photo-generated carrier concentration and the induced terahertz electric field in response to an incident terahertz radiation near the plasmonic nanoantenna contact electrodes. This significantly increases the detector responsivity and offers photo-generated carrier transport times comparable to photoconductive terahertz detectors based on short-carrier-lifetime semiconductors. By using the presented detector in a time-domain terahertz spectroscopy system, we demonstrate resolving terahertz spectra with a large dynamic range over the 0.1-5 THz frequency range.

This paper reviews recent advances in the terahertz (THz) graphene-based 2D-heterostructure lasers and amplifiers. The linear gapless graphene energy spectrum enables population inversion under optical and electrical pumping giving rise to the negative dynamic conductivity in a wide THz frequency range. We first theoretically discovered these phenomena and recently reported on the experimental observation of the amplified spontaneous THz emission and single-mode THz lasing at 100K in the current-injection pumped graphene-channel field-effect transistors (GFETs) with a distributedfeedback dual-gate structure. We also observed the light amplification of stimulated emission of THz radiation driven by graphene-plasmon instability in the asymmetric dual-grating gate (ADGG) GFETs by using a THz time-domain spectroscopy technique. Integrating the graphene surface plasmon polariton (SPP) oscillator into a current-injection graphene THz laser transistor is the most promising approach towards room-temperature intense THz lasing.

Three-dimensional semimetals have been predicted and demonstrated to have a wide variety of interesting properties associated with its linear energy dispersion. In analogy to 2D Dirac-materials, such as graphene, Cd3As2 has also shown to exhibit ultra-high mobility, with values exceeding 15,000 cm2/V.s at room-temperature and much higher mobility at low temperatures. Furthermore, based on ARPES data Cd3As2 has been shown to exhibit a very large Fermi velocity, vF ~1.5x106 m/s, which is much higher than that in graphene (~1x106 m/s) or topological insulators. We experimentally demonstrate synthesis of high-quality large-area Cd3As2 thin-films through thermal evaporation and molecular beam epitaxy as well as the realization of plasmonic structures consisting of periodic arrays of Cd3As2 disks and stripes. These arrays exhibit sharp plasmonic resonances at terahertz frequencies (~1 THz) with associated quality-factors ~5. These quality-factors, which to the best of our knowledge are among the largest reported to-date at room-temperature in semiconductor-based plasmonic structures in the terahertz range, is a direct result of the long relaxation-time in Cd3As2, which in our films approaches 1 ps at room-temperature. Moreover, ultrafast tunable response is demonstrated through excitation of photo-induced carriers in optical pump / terahertz probe experiments. Our results evidence that the 3D nature of Cd3As2 provides for a more robust platform for terahertz plasmonic applications than what is otherwise possible in 2D Dirac-materials such as graphene. Overall, these observations can pave a way for the development of a myriad of terahertz optoelectronic devices based on Cd3As2, benefiting from strong coupling of terahertz radiation, ultrafast transient response, magneto-plasmon properties, etc.; moreover, the long Drude scattering time, thus large kinetic inductance in Cd3As2 also holds enormous potential for the re-design of passive elements such as inductors and hence can have a profound impact in the field of RF integrated circuits.

The generation and use of THz radiation for electron acceleration and manipulation of electron bunches has progressed over the last decade to a level where practical devices for THz guns, acceleration and a wide range of beam manipulations have become possible. Here, we present on our progress to generated single-cycle THz pulses at the twohundred micro- Joule level to drive advanced acceleration and beam manipulation devices. Specifically, a segmented terahertz electron accelerator and manipulator (STEAM) capable of performing multiple high-field operations on the 6D-phase-space of ultrashort electron bunches is demonstrated using these pulses. Using this device, powered by single-cycle, 0.3 THz pulses, we demonstrate record THz-acceleration of <60 keV, streaking with <10 fs resolution, focusing with <2 kT/m strength, compression to ~100 fs as well as real-time switching between these modes of operation. The STEAM device demonstrates the feasibility of THz-based electron accelerators, manipulators and diagnostic tools enabling science beyond current resolution frontiers with transformative impact.

We present a nonlinear optical crystal-based terahertz (THz)-microfluidic chip with a few arrays of asymmetric metaatoms, elementary units of metamaterials, for the measurements of trace amount of liquid solutions. A near-field THz emission source that is locally generated in the process of optical rectification at the irradiation spots of fs laser beams induces a sharp Fano resonance and modifies the resonance frequency of the meta-atoms when the channel is filled with solutions with different concentrations. Using this chip, we successfully detected minute changes in the concentration of trace amounts of ion solutions by monitoring the shift in the resonance frequency. The detectable sensitivity of attomole order of solute in a less than 100 pL volume of the solution was achieved.

Since vast frequency range in 300GHz band is available for wireless communication in future generation, near- fiber-optic speed over 100Gbps will be possible. Here, to target at real commercial products, a transceiver with all CMOS technology is promising since digital signal processing including baseband modulation must be with CMOS integrated circuits. However, high-frequency characteristics of silicon MOSFETs used in the CMOS technology are generally inferior to those of advanced InP devices. Recently, a 300GHz CMOS transceiver capable of quadrature-amplitude-modulation (QAM) has been demonstrated. In this presentation, terahertz frontend technologies with CMOS process are explained. Then, performance comparison of 300GHz transceivers with miscellaneous technologies is clarified. Finally, future promising application for terahertz wireless communication is introduced.

In recent times, we have been studies of broadband coherent THz pulse propagation in a 186-m and 910-m open path under atmospheric weather conditions, which provides information for important applications in the atmosphere. The complexity of the atmosphere requires the use of the complete theory of Essen and Froome to compare the measured time shifts due to both the dry atmosphere and water vapor with theoretical calculations. A new procedure involving the measurement of phase in the frequency domain is introduced and achieves comparable results for the calculated time shifts, compared to the previous direct measurements of time shifts. Meanwhile, the characteristics of the N2O and CO gases are investigated using 2-m long gas chamber which is located 93m away from a THz transmitter and receiver chips. The THz pulse propagates an outside environment of 79 m between two buildings. The natural resonances of the gases are detected in the 0.5 THz bandwidth. Because the resonance spacing between two resonances of N2O gas is 0.025 THz, 14 resonances are detected in the bandwidth. However, only 3 resonances of CO gas are detected in the bandwidth. Unfortunately since the first and third resonances are too small and too close to water resonance, only the second resonance, which is at 0.35 THz, can be used to CO gas sensing frequency. Therefore, the resonances near 0.35 THz can be used to remote gas sensing window for CO and N2O gases.

Recent studies in spintronics have highlighted ultrathin magnetic metallic multilayers as a novel and very promising class of broadband terahertz radiation sources. Such spintronic multilayers consist of ferromagnetic (FM) and non-magnetic (NM) thin films. When triggered by ultrafast laser pulses, they generate pulsed THz radiation due to the inverse spin-Hall effect – a mechanism that converts optically driven spin currents from the magnetized FM layer into transient transverse charge currents in the NM layer, resulting in THz emission. As THz emitters, FM/NM multilayers have been intensively investigated so far only at 800-nm excitation wavelength using femtosecond Ti:sapphire lasers. In this work, we demonstrate that an optimized spintronic bilayer structure of 2-nm Fe and 3-nm Pt grown on 500 μm MgO substrate is just as effective as a THz radiation source when excited either at λ = 400 nm, λ = 800 nm or at λ = 1550 nm by ultrafast laser pulses (pulse width ~100 fs, repetition rate ~100 MHz). Even at low incident power levels, the Fe/Pt spintronic emitter exhibits efficient generation of THz radiation at all three excitation wavelengths. The efficient THz emitter operation at 1550 nm facilitates the integration of such spintronic emitters in THz systems driven by relatively low cost and compact fs fiber lasers without the need for frequency conversion.

Detection of faint fluxes of photons at terahertz frequencies is crucial for various applications including biosensing, medical diagnosis, chemical detection, atmospheric studies, space explorations, high-data-rate communication, and security screening. Heterodyne terahertz spectrometers based on cryogenically cooled superconducting mixers have so far been the only instruments that can provide high spectral resolution and near-quantum-limited sensitivity levels. The operation temperature, bandwidth constraints, and complexity of these terahertz spectrometers have restricted their use to mostly astronomy and atmospheric studies, limiting the overall impact and wide-spread use of terahertz technologies. Here we introduce a spectrometry scheme that uses plasmonic photomixing for frequency downconversion to offer quantum-level sensitivities at room temperature for the first time. Frequency downconversion is achieved by mixing terahertz radiation and a heterodyning optical beam with a terahertz beat frequency in a plasmonics-enhanced semiconductor active region. We demonstrate spectrometer sensitivities down to 3 times the quantum-limit at room temperature. Our presented spectrometry scheme can be applicable to resolve both the high-resolution spectra of gas molecules and mid-resolution spectra of condensed phase samples over a total operable bandwidth of 0.1-5 THz. As an example, we use the presented spectrometer to resolve the spectral information of ammonia, which has a number of narrowband absorption peaks over the 0.1-5 THz frequency range. With a versatile design capable of broadband spectrometry, this plasmonic photomixer has broad applicability to quantum optics, chemical sensing, biological studies, medical diagnosis, high data-rate communication, as well as astronomy and atmospheric studies.

High-power pulsed terahertz radiation sources are highly in demand for time-domain terahertz imaging and spectroscopy systems. A common way to generate pulsed terahertz radiation is exciting a biased ultrafast photoconductor with a femtosecond optical pulse. The photo-generated carriers drift to a terahertz radiating element under the induced bias electric field and a pulsed terahertz radiation is generated. Developing photoconductive terahertz sources operating at telecommunication wavelengths (~1550 nm) is very attractive because of the availability of high-power, narrow-pulse-width, and compact fiber lasers at these wavelengths. However, photoconductors responsive to telecommunication wavelengths often have low resistivity due to their small bandgap energy, resulting in excessive dark current levels under an applied bias voltage. As a result, telecommunication-compatible photoconductive sources experience a premature thermal breakdown under high bias voltages and cannot offer high terahertz radiation powers. To address this limitation, we introduce a new type of telecommunication-compatible photoconductive terahertz source that does not require an externally applied bias voltage and relies on a built-in electric field formed at the interface between the photoconductor and terahertz antenna contact electrodes. By eliminating the bias voltage, the device operates at a zero dark current, enabling a highly reliable operation. We use an array of plasmonic nanoantennas as the terahertz radiating elements to achieve a broad terahertz radiation bandwidth and high optical-to-terahertz conversion efficiency. We demonstrate pulsed terahertz radiation with powers exceeding 100 μW, enabling time-domain terahertz spectroscopy with a 100 dB dynamic range over a 0.1-3 THz bandwidth.

This mathematical model deals with the nonlinear response of a magneto-active plasma to the interaction of frequency chirped laser pulses. The beating lasers produce a nonlinear ponderomotive force due to their oscillatory motion. This force drives a nonlinear current, which is responsible for the THz-wave generation at beat frequency. The influence of the external magnetic field on the optimization process of THz field amplitude is investigated numerically. A linear frequency chirp increases the duration of nonlinear interaction of laser pulse with plasma electrons and hence, enforces the resonance for longer duration. The presence of magnetic field further improves the resonance condition. Our numerical simulations reveal that there is a significant enhancement in the THz field strength for optimized value of chirp parameter and magnetic field.

A gain-boosted terahertz-wave parametric generator (TPG) in high frequency tuning range based on MgO-doped nearstoichiometric LiNbO₃ (MgO:SLN) crystal has been demonstrated with 1064 nm nanosecond pulsed laser pumping. The pulse-seed is provided by nanosecond singly resonant near-degenerated KTP optical parametric oscillator with the wavelength range of 1068.08 nm to 1084.76 nm. The terahertz tuning range of 0.97 THz to 4.07 THz was achieved. The maximum THz wave output signal was 4285mV at 1.82 THz under the pump energy of 180 mJ and pulse-seed energy of 20.2 mJ. During the frequency range of 1.25 THz to 3.43 THz, the THz output energies were larger than 2000mV. Compared with the maximum THz output energy, the THz energy attenuation factors of 0.55 dB, 1.71 dB and 3.31 dB were realized in pulse-seeded TPG at 2.5 THz, 3.0THz and 3.5THz, respectively. The significantly increasing of THz gain in high frequency range (<2.5 THz) was achieved.

Waveguides having a lithium niobate (LiNbO₃) core are investigated for the generation of terahertz (THz) radiation, where second-order nonlinear susceptibility enhancement is utilized to produce the THz radiation via optical rectification. Although reststrahlen band losses are high in the vicinity where the nonlinear susceptibility exhibits enhancement, these losses are avoided by restricting the core to have sub-micron dimensions, thus allowing the generated THz radiation to propagate along the guide with >90% of its intensity outside the lossy LiNbO₃ core. The generated radiation exhibits a spectral distribution having a central frequency of 5.6 THz and a full-width half maximum bandwidth of 1.3 THz. The THz electric field pulse has an amplitude of 2 kV/cm and is produced at the conversion efficiency of 0.025%.

Difference frequency generation (DFG) is one of the most important methods for obtaining monochromatic THz-wave radiation, with the advantages of simplicity, lack of a threshold, room-temperature operation, and wide-range tunability. We previously demonstrated a milliwatt single-longitudinal-mode and tunable THz-wave source based on DFG in a MgO:LiNbO3 (MgO:LN) crystal using a pair of Yb-doped, pulsed fiber lasers [Y. Wada et al., Proc. SPIE 10531, 1053107- 8 (2018)]. In this study, we report the improvement of the THz-wave source by optimizing the collimation optics for THz output and enhancing the pumping fiber laser sources. The modified source produces an average power of 3.6 mW and a peak power greater than 7 W with nanosecond pulses at a pulse repetition frequency of 500 kHz and a tunability range from 0.34 to 1.25 THz. This improved source enables nondestructive 2-D transmission imaging of objects behind materials as thick as 5 mm using a pyroelectric detector operated at room temperature. As a demonstration of our powerful THz source, we present some results of transmission imaging of a train pass and thin objects such as an optical fiber and a human hair. We also demonstrate the direct spectroscopic imaging of medicine tablets.

We have demonstrated a high-energy and broadly tunable monochromatic terahertz (THz) source via difference frequency generation (DFG) in DAST crystal. The THz frequency is tuned randomly in the range of 0.3-19.6 THz, which is much wider than the THz source based on the inorganic crystal and the photoconductive antenna. The highest energy of 2.53μJ/pulse is obtained at 18.9 THz corresponding to the optical-to-optical conversion efficiency of 1.31×10^-4. The THz output spectroscopy is theoretically and experimentally explained by DFG process and Raman spectroscopy. Meanwhile, a phenomenon of blue light from the KTP-OPO with tunable and multiple wavelengths was firstly observed and explained. Based on our THz source, an ultra-wideband THz frequency domain system (THz-FDS) with transmission mode is realized to measure the ultra-wideband THz spectroscopies of typical materials in solid and liquid states, such as Si, SiC, White PE, water, isopropyl myristate, simethicone, atonlein and oleic acid, etc.. Furthermore, we have studied the THz spectral characteristic of biomedical tissue in the ultra-wideband THz frequency range of 0.3-15THz to study the biomedical response in the entire THz frequency range, which contains more abundant spectral information and was rarely focused with the limit of the THz source.

This paper presents a newly developed square law detector array whose NEP is as low as ~ 1 pW/Hz^0:5 for 1.0 THz waves. The detector array using high electron mobility transistor (HEMT) with InGaAs/InAs/InGaAs double hetero-structured channel has been fabricated. The InAs-HEMT was fabricated on a quartz substrate using the layer transfer technology. Also, an array of square law detectors was developed by applying advanced selective etching, atomic layer deposition, and metallization to the transferred hetero-structured layers. The static analysis revealed that the transistor shows electron mobility as high as 3,200 cm²/Vs and low leakage with subthreshold slope as low as ~ 100 mV/dec. Detection performance was characterized by directly inputting 1.0 THz waves thorough a THz probe to each of the arrayed detectors. It is also demonstrated that the detection characteristics were well described by the analytical formulae derived from the channel-carrier behavior model. The experimental results suggested that the developed detector array is a promising candidate for imaging application.

THz imaging and sensing has demonstrated a wide-ranging application potential. However, the transfer of such basic applicability observations to real-world application scenarios is severely obstructed by fundamental limitations imposed by the comparatively long wavelength of this analytic technique. In this presentation, an overview of recent signal processing developments for the enhancement of the analytic performance of THz imaging and sensing systems is presented. The first part of the presentation introduces advanced signal processing techniques to enhance the spectroscopic investigation capability of THz systems. Experiments are performed at particularly difficult application situations, including inter alia very thin material systems or measurements with strongly absorptive features beyond the signal to noise limitations of spectroscopic instrumentation. Model- based numeric procedures for spectroscopic investigation with pulsed THz systems are derived, which enhance the analytic material data quality by two orders of magnitude in comparison to established numeric procedures. Furthermore, computer vision based blind-deconvolution superresolution approaches are introduced, which allow the unassisted increase of imaging resolution beyond the diffraction limit. Experiments performed with a FMCW- based THz imaging system operating from 514 - 640 GHz demonstrate a resolution increase by a factor of 2.3 beyond the diffraction limit, without requiring any prior knowledge on the point-spread function size or shape of the imaging system, but based on a direct analysis of the imaging data of an unknown target sample.

In this paper, we review modern advances in microwave and millimeter-wave computational frequency-diverse imaging, and submillimeter-wave radar systems. We first present a frequency-diverse computational imaging system developed by Duke University for security-screening applications at K-band (17.5-26.5 GHz) frequencies. Following, we show a millimeter-wave spotlight imaging concept and its conceptual integration with the K-band system as interesting example of sensor fusion. We also demonstrate the application of computational frequency-diverse imaging for polarimetric imaging and phase retrieval problems. We show that using the concept of computational frequency-diverse imaging and quasi-random measurement bases, high-fidelity images of objects can be retrieved without the need for any mechanical scanning apparatus and phase shifting circuits. Increasing the frequency-band of operation, we also demonstrate a 340 GHz radar developed by the Jet Propulsion Laboratory and its application for standoff detection. We demonstrate a new technique to characterize the point-spread-function (PSF) of radars operating at submillimeter-wave frequencies.

In this work the potential of THz technology to detect ageing effects in modern armor system is studied. First experiments have been done in pure polymers, a key component in modern armor devices. Artificial ageing in thermooxidative environment has been applied to Polyamide 6 and Polyethylene and their THz response has been recorded. It was found that the THz refractive index indeed undergoes significant changes after the thermal treatment. The direction of the changes and the mechanisms causing these changes are highly dependent on the investigated polymer. Afterwards experiments on more representative devices, made from hard aramid, were conducted. An artificial ageing following the NATO standard STANAG 4370 has been applied. The THz refractive index undergoes significant changes, showing the high potential THz technology has to offer in this novel field of application.

Terahertz (THz) technology is a competent non-destructive evaluation (NDE) technique, particularly for advanced materials such as Fibre Reinforced Polymer (FRP) composites due to its ability to penetrate most non-metallic and nonpolar substances. Typically, THz NDE studies are carried out using expensive and broadband pulsed THz systems limiting their widespread use in practical applications. In contrast, Continuous wave (CW) THz systems can potentially be a narrowband, cost-effective and scalable solution for NDE applications. However, conventional CW THz systems employ a coherent detection scheme which results in large acquisition time per pixel thus limiting their real-time applicability. In this paper, a CW THz system with incoherent detection scheme using Schottky receiver along with spatial adaptive sampling technique is employed to achieve rapid THz imaging of Glass Fibre Reinforced Polymer (GFRP) composite with artificial defects. Here, an initial coarse scan of 2 mm step size has been done, and gradient based thresholding criterion is used for identifying the regions of interest to progressively scan the sample with finer resolution down to a step size of 0.5 mm. Results demonstrate a total reduction in the image acquisition time by a factor of 50 compared to the coherent CW THz imaging. Further, the THz image acquired through adaptive sampling shows excellent correlation with that of the traditional uniformly sampled THz image with 0.5 mm step size.

We describe an implementation of continuous wave microscopy in the millimeter - terahertz wave region in with phase imaging is realized using a simple low cost detection scheme. Samples are illuminated using a Backward Wave Oscillator system and a detection scheme is presented in which soft or semitransparent samples are imaged in reflection or transmission using an interferometer. The main advantage of this approach is that simple pyroelectric detectors can be used and can in principle be extended to use in near field measurements.

Time-domain terahertz reflectometry has long been of interest to obtain three-dimensional information about objects transparent in the 100 GHz-3 THz frequency range. The application of such techniques has been limited by the conductivity of the materials and by conventional axial resolution criteria. Specifically, I discuss work on detecting subsurface damage in carbon fiber composites and in measuring paint-layer thicknesses down to ~20 microns. We employ a typical commercial broadband time-domain source with bandwidth from ~100 GHz to ~3 THz. Yet terahertz imaging faces two important limitations. (1) The first is that in materials with a significant conductivity, the attenuation of incident terahertz electromagnetic waves is very rapid, limiting the penetration into the object. (2) The second limitation can best be illustrated by a stratified medium. Due to the Fresnel coefficients associated with the variation of the refractive index across material interfaces, one expects a reflected signal that is composed of various echoes associated with the interfaces (as well as multiple reflections which in practice are often weak). If the layers are sufficiently thin, then the echoes from successive layers will overlap, and thus multiple echoes will not be visually evident in the reflected signal. In this talk I discuss my group’s recent work to circumvent these limitations. The approaches rely upon applying advanced signal-processing techniques to extract the maximum information from the detected signals. Specifically, I provide case studies of coatings on metals, fiber composite laminates, and an oil painting on canvas with multiple paint layers.

Over the past decade, the performance of generation and detection schemes for short electromagnetic waveforms in the THz spectral range has been improved at a rapid pace and facilitated the exploration of novel quantum phenomena of solid-state systems. Here, we present a selection of recent key advances and discuss their impact on cutting-edge fundamental research. Widely tunable high-field sources providing atomically strong, phase-locked few-cycle lightwaves with field amplitudes of up to 1 V/A at few-kHz repetition rates have driven dynamical Bloch oscillations in bulk semiconductors, quasiparticle collisions, and control of the valley pseudo-spin in monolayer dichalchogenides. Novel, highly phase-stable sources operating at repetition rates of 190 kHz provide comparably strong fields of up to 13 MV/cm, foreshadowing future applications in ultrabroadband frequency-comb metrology or lightwave scanning tunneling microscopy. Similarly, electro-optic sensors have been pushed to the quantum level, detecting THz waveforms which contain only 0.1 photons, on average, enabling strongly subdiffractional and subcycle tomography of interface polaritons black phosphorus in THz near-field scattering experiments. Moreover, customized FPGA technology has enabled synchronous single-shot detection of incoherent THz electric fields with amplitudes of less than 0.5 V/cm. In combination with femtosecond fiber lasers and an acousto-optical delay line, we have implemented fast-scan THz time-domain spectroscopy with a waveform refresh rate of 36 kHz and a bandwidth of 3 THz. The acquisition time of only 28 µs and signal-to-noise ratio of 27 for a single waveform, or 1.7×10^5/√Hz, may power multidimensional spectroscopy or real-time monitoring of non-repeatable processes in technology or biology.

Even though Terahertz Time Domain Spectroscopy (TDS) setups have been available for decades in laboratories worldwide and possible applications have been shown in many research papers, a breakthrough of applications actively used on an industrial scale is yet to come. Apart from the THz sources, such as photoconductive antennas (PCAs), a conventional TDS system consists of an ultrafast laser source, a mechanical delay line used for the sampling, and a data acquisition system. While the femtosecond laser makes up for the majority of the system cost, the mechanical delay is accountable for the long acquisition time. In order to push pulsed THz systems one step further towards industrial applications, this work addresses both: the optical source and the sampling mechanism. To overcome the necessity of the delay line an asynchronous optical sampling (ASOPS) approach is chosen. Here, the sampling mechanism is obtained by operating two femtosecond lasers with slightly different repetition rates ▵f resulting in an inherent sampling of the THz transient. While this was shown with ultrafast solid state lasers such as Ti:Sapphire or fiber lasers, we use edge emitting mode locked semiconductor quantum well lasers operating in the 830nm wavelength regime. In a first step, two laser diodes operated in compact external cavity configurations are hybridly modelocked at repetition rates around 390MHz with a RF synthesizer each in order to obtain a stable pulse scanning. In a second step, we evaluate hybridly modelocked monolithic edge emitting laser diodes at 12:8 GHz for THz TDS ASOPS.

Time-domain spectroscopy (TDS) is the most prominent technique for fast acquisition of broadband terahertz (THz) spectra with update rates of several ten Hz up to kHz. However, fast tunable continuous-wave (cw) laser sources enable rapid acquisition of broadband THz signals without the well-known drawbacks of THz-TDS systems: mechanical delay lines and femtosecond pulse lasers. In this work, we make use of a fast tunable laser to demonstrate coherent continuouswave THz spectroscopy with unprecedented speed and bandwidth. The system features three different modes of operation exploiting both broad spectral bandwidth and high frequency resolution. In broadband mode, 2 THz-wide spectra with 800 MHz resolution can be acquired at a continuous update rate (UR) of 24 Hz. To our knowledge, this is the highest update rate of a broadband, phase-sensitive cw THz spectrometer. In high-speed mode, 200 GHz wide spectra are acquired with 800 MHz resolution at an UR of 120 Hz, ideal for high-speed spectroscopy of absorption lines. In high-resolution mode, frequency steps of 20 MHz and a scan range of 200 GHz allow for high-resolution gas spectroscopy. In broadband and high-speed mode, the peak dynamic range exceeds 65 dB for single shot measurements. More than 100 dB peak dynamic range and a 3 THz bandwidth are obtained after 7 min. averaging in the broadband mode. Due to its high update rates, in combination with high bandwidth and flexible operation modes, this system paves the way for industry-scale non-destructive testing based on cw THz technology.

Advanced silicon technologies have been used to build digital circuits and answer the global demand of signal processing systems. Traditionally, front end circuits have been dominated by III-V compounds, and silicon confined to the back-end. However novel circuit design techniques have been demonstrated to push the limits of traditional technology platforms, and has demonstrated the feasibility of application in the frontend field. This work will focus on the quasi-optical capability of silicon technologies to reliably demonstrate high-frequency front end building blocks.

Millimeter-wave technologies for the automotive industry are driving inexpensive source/receiver hardware solutions for a wide variety of applications. In order to accurately assess signature characteristics of various scenes, we tested the appropriateness of using an artificial torso in controlled environments and compared the results to data from live subjects. High-range resolution (HRR) backscatter Radar Cross Section (RCS) data from targets and in-scene calibration objects were obtained using a 75GHz transceiver with 8GHz bandwidth. Data was collected for both the artificial torso and live subjects at varying aspects in controlled environments – this included studying the RCS response at different illumination angles while calibrating the response using in-scene calibration targets. Comparing the HRR profiles has allowed UML/UMMS researchers to accurately assess and demonstrate the utilization of artificial constructs in scenes for testing the system response characteristics.

We propose and demonstrate a new technique of generating microwave frequency comb using single mode Fabry-Pérot laser diode (SMFP-LD). The SMFP-LD is obtained by modifying the commercially available FP-LD by adding an external cavity, which provides only single longitudinal mode at the output and has a tunability range of about 10 nm. The basic principle involve with this technique is the injection of the modulating beam to any of the side modes of the SMFP-LD in such a way that one of the sideband is locked with the corresponding injected mode. The injected beam has negative wavelength detuning to the corresponding mode whether it is the dominant mode or the side mode of a SMFPLD. By heterodyning the injected modulated beam and the corresponding side mode, frequency comb is generated using SMFP-LD that has the capability of tuning frequency comb spacing. The tuning of comb frequency spacing is obtained through changing the modulating frequency. The additional modulator is used to increase the power flatness and the bandwidth of comb generation. We measured and compared the output performance of the generated RF comb with and without additional modulator in terms of power flatness, and power and frequency stability.

High frequency analog RF photonic links are desirable to reduce the size, weight and power of RF systems by offering the replacement of lossy, bulky coaxial RF cabling for lightweight, low loss and broadband optical fiber, particularly in applications such as avionics and naval RADAR systems, electronic warfare and distribution of low-jitter clocks or local oscillator signals. Freedom Photonics and the University of Virginia have developed high power, wide-bandwidth optical photodetectors operating in the 1550-nm wavelength range. These photodetectors are based on vertically illuminated modified uni-traveling carrier (MUTC) photodiode technology. The devices have been developed into fully packaged, fiber-pigtailed modules with optimization for high powers or high speeds. This paper will present the architecture and experimental results of our range of photodiodes. One family of devices focuses on high power applications. These include high-power photodiodes with 3-dB bandwidths of 25 GHz coupled with output powers in excess of 23 dBm, as well as 35 GHz photodiodes with output powers greater than 19 dBm. Another family of devices focuses on high speed applications, including photodiodes with 3-dB bandwidths of >65 GHz and >100 GHz. These photodiodes, used in a photonic link, have a major impact on peak performance. The high power-handling capability and high speeds of these devices support high link gain and large bandwidths, while the high linearity of these devices minimizes noise and signal distortion, maximizing spurious-free dynamic range (SFDR).

This paper reviews some recent research progress in superconducting nanowire single-photon detectors (SNSPDs) at the infrared spectrum range, with particular emphasis on detection efficiency and timing jitter. For detection efficiency, we present fractal SNSPDs with reduced polarization sensitivity; for timing jitter, we present two mechanisms of device timing jitter – vortex-crossing-induced timing jitter and spatial-inhomogeneity-induced timing jitter.

Since the first photon counting systems in the visible, developped by Boksenberg and his collabortors in 1972, many groups around the world improved photon counting techniques. In the 2000's in the visible, EMCCDSs (electron multiplying charge coupled devices) allowed to replace the classical image intensifier photon counting systems by solid state devices and improved a lot the QE. But EMCCDs suffer from several issues, and the most important of them is the excess noise factor which prevents to know what is the exact incoming number pf photons in the case of multiple photons per pixel. In the infrared there was no equivalent to EMCCDs up to the development of e-APD sensors and cameras made with HgCdTe material (electron initiated avalanche photo diode). We will present the concepts of photon counting in the infrared with such devices and the main properties and advantages of infrared e-APDs compared to their visible counterpart, EMCCDs and the possibility to detect the photon energy (color) with such devices.

The MIR wavelength regime promises lower gas detection limits than the NIR or the VIS region due to higher absorption levels as one can read for simulation listed in HITRAN. Methane shows moderate absorbance below 3 μm which results into detection limits in the range of low ppm. IC and QC based lasers emit higher wavelengths, where the absorbances of methane are higher. TDLAS and QEPAS measurements to the trace gas CH₄ are shown to display the spectroscopy performance of the different lasers with and without influences from the detector material. In this manuscript only QEPAS measurements will be presented. Scope of this paper is a quantitative comparison of the absorption and QEPAS behaviour of Methane in four important spectral regimes.

Laser interferometry is recognized as an extremely sensitive measurement technique, capable of detecting quantities that conventional sensors usually cannot. However, such advantage also brings a challenge, the interferometer detects, beyond the interest measurements, the environmental disturbances, causing the signal fading which usually leads to a nontrivial process to extract the relevant signal, making the interferometer operation more difficult. Thus, the challenge of interferometry is to be able to measure physical quantities whose values are extremely small, in the presence of external environmental disturbances whose magnitudes are several orders of magnitude higher. Objecting to mitigate this drawback, this work presents the implementation of a digital controller based on variable structures and sliding modes (VS/SM) method, applied to two beams interferometry. The VS/SM technique is a powerful technique in the nonlinear control area because it is simple to implement, presents high performance and provides robustness characteristic. In this work, its digital implementation is made by using the myRI0-1900 (National Instruments) embedded platform, which allows easy configuration and the visualization of system when working online. The results showed that the proposed digital implementation allows the system to log the data from experimental tests, which enables the assembly of an embedded system. As additional advantages, it allows to digitally configure the control gain, allowing high gains, and consequently, a fast response. Applications of this closed loop interferometer to piezoelectric actuators are presented.

Performance of optical heterodyning and external modulation by using an electro-optical modulator technique is evaluated. The first approach is carried out by beating two optical signals with a wavelength spacing corresponding to the desired microwave or millimeter-wave frequency continually tuned. The second technique requires only a single laser source along with a Mach-Zehnder Intensity Modulator (MZ-IM). Due to the available electrical bandwidth of the photodetector used, the experimental results are limited to the frequency range of 13 GHz. All experimental results are validated by a series of simulations using the VPI software. Signal-to-Noise ratio (SNR) and Phase-Noise parameters are measured.

The application using the frequency range from 100 GHz to 10 THz has attracted much attention, especially in broadband and higher data-rate wireless communication. In the THz broadband wireless devices, photo mixing by using the uni-traveling carrier photodiode (UTCPD) on the indium phosphide (InP) substrate is a crucial component. UTCPD can down-convert the optical signal to THz wave. To reduce the loss of the connection area between the optical section and the THz section, THz-band antennas and transition lines should be fabricated on the same substrate as the optical section. In our previous research, 1 x 4 and 4 x 4 planar array antennas using one-sided directional slot dipole antenna elements and branched coplanar waveguide (CPW) are connected to the output of UTCPD on the InP substrate for the 300 GHz application. In this presentation, wideband 600 GHz one-sided directional slot antenna was designed. The antenna is based on the slot antenna on the top with the bottom floating metal layer. To enhance the bandwidth, round shape of the edge of the top metal layer was introduced. Moreover, 2 kinds of the antenna element with different resonance frequencies are designed. Antenna 1 (Ant1) has a center frequency = 600 GHz and gain = 2.23dBi. Antenna 2 (Ant2) has a center frequency = 650 GHz and gain = 3.28dBi. The whole size of the antenna elements is 290 um x 230 um and 280 um x 290 um, respectively. Each antenna element is connected to the UTCPD and optical waveguide through a coplanar waveguide (CPW) feed line. Next, we designed a 2-dimensional antenna array with 12 antenna elements. To enhance the bandwidth 4 Ant1s and 8 Ant2s are combined on the InP substrate. From the electromagnetic simulation, this array antenna has antenna gain = 11.89 dBi, 3-dB bandwidth =130 GHz and front-to-back ratio = 15.73 dB. The array size is 1,500 um x 1,500 um. The relative bandwidth can be enhanced from 5 % (reference array antenna) to 20 %. Moreover, by changing the delay line attached to the optical fiber, it is easy to obtain the phase difference of each antenna element. From the results, our proposed phased array antenna has a wideband, high gain and beam tilt characteristics.

A multiple frequency-swept source based on a recirculating frequency shifter loop (RFSL) is established. Three distributed feedback (DFB) lasers are used as a seed source and sweep in the RFSL synchronously. The swept spectra of the separate DFB lasers are precisely controlled and stitch together without overlap. The key significance of this technique is that the swept range increases as the number of the multiple seed wavelengths increase. Experimentally, the swept range of our system can broaden to 4.5 nm/3.9 nm with an 8.6 GHz/7.5 GHz swept step. The swept rate is 200 kHz. The output of the source is sent into a Mach-Zehnder interferometer and the interference signal is detected to measure the length difference of interferometer arms.

Nafion membranes, known for their excellent proton conductivity, are widely used in Proton Exchange Membrane Fuel Cells (PEMFC), a promising clean energy source. Proton conductivity is highly dependent on membrane hydration. Water has strong absorption in the Terahertz (THz) frequency range and hence THz spectroscopy can be potentially used to understand the water dynamics in fuel cell membranes. In this study, Terahertz spectroscopy has been employed to track the water retention in a hydrated Nafion membrane by measuring the transmitted THz time domain pulses through the hydrated membrane for every minute up to 25 minutes. In addition, the complex permittivity has been extracted for each measurement by considering multiple reflections in the sample and is fitted with the double-Debye model. From these calculations, the dielectric constant and relaxation timescale have been extracted which provides more information on the population of bulk and ‘free’ water in the hydrated membranes. Results show 45 % decrease from the initial bulk-like water population by the end of 25 minutes which confirms reasonable water retention of Nafion for the measurement duration.

We report on our recent experiments involving tight packaging of RF photonic oscillators based on optical Kerr frequency combs generated in nonlinear optical microresonators. The devices with volume not exceeding one cubic centimeter characterized with phase noise approaching -120 dBc/Hz at 10 kHz frequency offset are demonstrated at 26 GHz and 28 GHz. Possibilities of tuning the oscillators with a piezo-actuator are discussed.

Introducing a magnetic dopant into a topological insulator can give rise to ferromagnetic ordering which can break timereversal symmetry, realizing dissipationless electronic states in the absence of an external magnetic field. Assessment and control of the magnetic state can translate into novel future applications in quantum computing. We provide a detailed study of the magnetic state in Cr doped Sb₂Te₃ thin films using terahertz time-domain spectroscopy (THz-TDS) and electrical transport. The temperature dependent behavior of the THz conductance of Cr_xSb_2-xTe₃ thin films with x = 0.15 exhibits a clear insulator-metal transition at 40 K, indicating the onset of ferromagnetic order in the Cr_xSb_2-xTe₃ at the TC (40 K). Moreover, the magneto-transport measurements showed anomalous Hall behavior below 40 K, demonstrating the consistency between the electrical and optical measurements. The direct correlation obtained between the carrier density and ferromagnetism in the magnetically doped topological insulators films, using the THz optical technique, strongly suggests a carrier-mediated RKKY coupling scenario. Our non-contact method of using THz radiation to investigate ferromagnetism and the consistency between optical and electrical measurements pave the way to realise exotic quantum states for spintronic and low energy magneto-electronic device applications.

A pixel-based approach to design of metaatoms was implemented on graphene absorbers of terahertz radiation. The top surface of each metaatom was conceived as a square array of square pixels, some patched with graphene but not the others. This patterned graphene was separated from a continuous layer of graphene by an insulator, the entire assembly on top of a metal-backed dielectric substrate. When the chemical potential of graphene was taken to be sufficiently high, simulations indicate almost perfect peak absorptance can be obtained with a significant reduction in the need for graphene, depending upon the arrangement of the graphene pixels.

The common approximations used in the ionized donor density calculations of terahertz quantum cascade lasers (TQCL’s) are investigated. Each approximation is computationally analyzed in order to determine its impact on the accuracy and speed of the doping calculations. The analyses are repeated across all of the lattice temperatures and donor densities that are typical in TQCL’s (T = 1 to 300 K, N_D = 1.00 to 5.00 × 10¹⁶ cm^-3 ). Additionally, an original optimized approximation is proposed and analyzed. This optimized approximation is found to out-perform the common approximations in both accuracy and speed in all cases.

Here, we have presented the first design of a bottom to in-plane grating coupler with a high coupling efficiency and directionality. The grating coupler consists of a high contrast grating (HCG) and an etched silicon-on-insulator (SOI) grating device. The final coupling efficiency is 82.2% at 1.55µm, with a 57nm 3dB bandwidth, and the directionality is 14:1 (left to right ratio). This grating coupler can be further optimized with different low index materials. This grating coupler could work as the vertical to in-plane coupler for the label free silicon photonic bio-sensor.

I report a seamless method to convert a high-speed single-channel signal in the terahertz (THz)-band into an optical signal by using heterodyne detection, optical intensity modulation, and optical filtering. A spectral-efficient singlechannel 40 Gbit/s signal in the THz-band, which was generated from a 40 Gbit/s optical signal shaped with a Nyquist filter, was converted into an optical signal. A sideband of the converted optical signal was extracted with another filter, and the extracted signal was transmitted to a fiber-optic link. I explain the characteristics of the optical signal passed through a single-mode fiber. The signal could be transmitted to a 9 km-long fiber without chromatic dispersion compensation.

In this paper, a novel method of precise dispersion measurement is proposed by exploiting the high sensitivity of the notch frequency shift and stopband rejection in microwave photonic notch filters (MPNF) based on stimulated Brillouin scattering (SBS) in optical fibers. The MPNF principle is based on an amplitude unbalance and π phaseshift between two probe wave sidebands. In case of an SBS interaction on one of the sidebands, the unbalance is eliminated. Thus, the notch filter will be formed at a specific notch frequency by the signal cancellation at the receiver. A slight dispersion mismatch leads to a notch frequency shift and a significant reduction of the notch suppression. Due to the linear dependence of the notch frequency shift on the dispersion in the vicinity of proper compensation value, even two measurements are sufficient for a precise dispersion determination.

This paper discusses the use of double-sideband suppressed-carrier (DSB-SC) modulation and radio frequency mixer as phase detector to extract phase information for methane detection in chirped laser dispersion spectroscopy (CLaDS). The 1.66 μm light from narrow-linewidth laser was modulated by electro-optic modulator (EOM) working on DSB-SC mode. These two sidebands passed through gas chamber and formed interference on photodetector. The phase change from gas absorption in beating signal can be extracted by using passive RF mixer with another input as reference signal which is achieved by doubling RF drive signal of EOM. In RF mixer, two inputs with identical frequency but various phase shift corresponds to DC bias voltage variation of output. The phase change is proportional to refractive index change and can be referred to gas concentration by using Kramers-Kronig relations. The advantage of phase sensitive CLaDS is wide dynamic range for gas detection. It compensates the deficiency of wavelength modulation spectroscopy (WMS) on high concentration circumstances. And the passive scheme pushes the system requirement to the lowest level.

In this paper, we first employ CMOS-compatible integrated optical combs to demonstrate a broadband RF channelizer. By using an on-chip nonlinear micro-ring resonator, a broadband 200GHz-spacing Kerr comb with a large number of comb lines are generated, providing a record large number of wavelength channels (over 60 in the C- and L- band) as well as over 100GHz potential RF operation bandwidth for RF channelizers with greatly reduced size, potential cost, and complexity. Record-high spectral slice resolution of 124.94 MHz is achieved through an on-chip MRR featuring a high Q factor up to 1.549×10⁶. As a result, broadband channelization of RF frequencies ranging from 1.7 GHz to 19 GHz is experimentally demonstrated, verifying our approach’s feasibility and effectiveness towards the realization of broadband RF channelizer with large channel number and high resolution, as well as reduced cost and footprint.

A highly sensitive and high resolution Interrogation setup for Fiber Bragg Grating (FBG) based sensing to measure low strain variation (i.e ~100με) effectively is being proposed in this manuscript. This system uses edge detection interrogation scheme using two optical signals generated through carrier compressed modulation scheme. Here, Dual Drive Mach-Zehnder Modulator (DD-MZM) is employed to generate carrier suppressed first order sidebands, which are then used as two optical signals and detected on two different power meters. Differential power measurement technique is used to calculate change in wavelength or applied strain at detector end. This system can provide system sensitivity as high as 0.3193 dBm.με^-1 and resolution upto 31.31nε in term of strain or 37.2fm in terms of wavelength. Which is much higher than present commercially available interrogation system (~0.8με). The proposed interrogation system can be employed in biomedical sensing to monitor cardiac and respiratory activity even during Magnetic Resonance Imaging (MRI) scanning condition as they are not prone to any electromagnetic interference.

Using liquid crystals (LC) to tune terahertz (THz) metamaterials has been investigated over the past decade with some limited success. The issue has been that the range of tuning has been significantly lower than theoretically anticipated high tuning capabilities, the changes in properties are subject to the orientation of the LC molecules with respect to modulated electromagnetic field. In other words, the design of the alignment of the LC must be optimized specifically for each metamaterial design. The simple first order model must be replaced with representing the LC as an orientation changing, anisotropic uniaxial layer. By optimizing the LC alignment, significant advances will be possible in agile system for chemical and biological sensor, antenna designs, cloaking, and optical signal processing.

III-V semiconductors have broad uses in optoelectronics due to their direct band gaps and high carrier motilities. GaAs_{(1- x)}Bi_x and Tl_xGa_(1-x)As ternary alloys are of interest for light emitting, light absorbing and other applications (e.g. communication lasers, photovoltaics, and high speed transistors) in the infrared spectrum due to their decreased bandgap relative to GaAs. While GaAs has been extensively studied, the optical properties of GaAsBi and TlGaAs are less documented and show significant variation with Bi and Tl content respectively. This study characterized the optical properties of GaAsBi and TlGaAs films of varying Bi and Tl composition using variable angle spectroscopic ellipsometry (VASE) in a range of temperatures from 25 °C – 300 °C. GaAsBi films were grown between 3.3% and 6.5% bismuth. TlGaAs films were grown between 1.7% and 2.7% thallium. Modeling using a superposition of Gaussian oscillators fit to the dielectric functions of sample layers was used to separate film optical properties from the pseudooptical properties of the sample. The analysis in this study directly compares the inclusion of the two largest III-V constituent atoms, Bi and Tl. Comparison of the refractive index and absorption coefficient of samples was done over a spectral range of 0.5 eV to 5 eV (250 nm to 2500 nm). This region displays the absorption edge corresponding to the bandgap of the material, which is then correlated to the incorporation of Bi and Tl in the samples. This characterization allows for better modeling of these alloys for both a fundamental understanding of their properties and for their inclusion in future devices.

Transmission measurements of 11 different garments composed of different materials and different thickness under different conditions were measured. The setup consisted of a 100 Gigahertz camera system which used an IMPATT diode (66mW power output) as the source, a 32x32 image sensor array (1.5x1.5mm pixels, 1 nW/√Hz Noise Equivalent Power) focused with PTFE lens (50mm focal length). The camera system was configured for reflection imaging by placing the source emitter and imaging array at an off-axis angle and focused on a large flat mirrored surface. To simulate reflection of the emitted signal off human skin after transmission through the garments, we placed the garments over the mirrored surface. We then calculated the transmission loss, in terms of signal strength (amplitude), as the ratio of the recorded images with and without the garments. The materials and make-up of the garments were recorded, such as colors, accents, and thickness. To increase the realism of the data, we added several conditions for each garment transmission recording that included overlapping wrinkles and multiple garment layers. We were able to confirm transmission results reported from other research groups, but found that variations such as wrinkles and multiple layers can change the transmission ratios significantly.

I report on Nyquist wavelength division multiplexing (WDM) communication in the terahertz (THz)-band for improving the transmission capacity, whose received signal is processed with high-speed optical technology. The Nyquist WDM signal in the THz-band is generated from an optical Nyquist WDM signal by photo-mixing. The received THz-wave Nyquist WDM signal is down-converted into a radio-frequency signal, and is again transferred to an optical signal through an optical intensity modulator. Then, the desired Nyquist WDM channel in the reproduced optical signal is demultiplexed with an optical filter. I present the operating principle of the proposed procedure and its some preliminary experimental results using a 2 × 40 Gbit/s Nyquist WDM signal.