This PDF file contains the front matter associated with SPIE Proceedings Volume 9362, including the Title Page, Copyright information, Table of Contents, Introduction, Authors, and Conference Committee listing.

Spectral broadening and the generation of supercontinuum are inherent features of nonlinear optics, and have been studied intensively for many years. Supercontinuum generation has been found numerous applications in such various fields as spectroscopy, pulse compression, and the design of tunable ultra-short femtosecond laser sources. Generally, supercontinuum is mainly generated by hyperbolic-secant soliton pulse. It is rarely investigated about the spectral broadening when pumping with pulse of a rectangle or quasi-rectangle shape, which is an interesting direction of supercontinuum generation. In this paper, supercontinuum generation based on soliton, quasi-rectangle, and rectangle pulses are investigated numerically. Firstly, we introduced the general nonlinear Schrödinger equation (GNLSE) to deduce the temporal and spectral evolution of pulse broadening in the photonic crystal fiber. Secondly, with different types of pulses, including hyperbolic-secant, ultra-Gaussian and rectangle pulses, we investigated the generation of new frequency and spectral broadening by numerical methods. Comparisons of characteristics of spectral and temporal evolution with different pulses are made in the following parts of paper. It is found that the generation of dispersive waves and Raman effect play main roles in the spectral broadening and generation of supercontinuum, as the broadband wave is generated by the coupling of Raman soliton and dispersive waves through cross-phase modulation. Apparent side-bands can be observed in our simulation under the condition of quasi-rectangle and rectangle pulses pumping, which affect the smooth of spectrum. Thus, to our acknowledge, a flat supercontinuum can be generated by changing the parameter of pulse to make a better coupling of the side-bands.

We propose a sub-terahertz (THz) illuminator suitable for use with a THz camera when exploring objects within and behind smoke at the scene of a fire. The illuminator contains a photomixer array and each photomixer generates incoherent sub-THz waves from a single-mode laser light and optical noise using photomixing. The incoherency of the generated sub-THz waves enables us to raise their intensity by increasing the number of photomixers in operation, which makes it possible to realize very bright sub-THz illumination. Consequently, objects being under searched for within or behind smoke can be clearly illuminated using the illuminator and visualized by the THz camera even though they are surrounded by thick and/or high-temperature smoke. To verify our concept, we conducted active imaging with coherent and incoherent sub-THz radiation from a photomixer array utilizing reflection geometry. Although the contrast of the image was improved by increasing number of photomixers in operation on the imaging with coherent radiation, the shape of the target was degraded by the interference pattern of the illuminated sub-THz waves. The contrast of the image when using incoherent radiation was improved without obscuring the shape of the target by increasing the number of photomixers. We also confirmed that there was good visibility for active imaging using incoherent sub-THz illumination even though thick smoke was presented. These results indicate that the use of incoherent sub-THz waves and an array of photomixers should enable a sub-THz illuminator with a high level of brightness to be used for active imaging

Since the 1990s the photoconductive material of choice for THz generation has been low-temperature grown GaAs (LTG-GaAs) thanks to its useful mobility (~200 cm²/V.s), high dark resistivity (~10⁷ Ω.cm), and fast carrier lifetime (~0.2 ps). However, due to the band gap energy of GaAs, the usual optical drive wavelength is around 800 nm where suitable lasers, both cw and pulsed, tend to be marginal in output power and rather expensive. Consequently, research has pushed towards the development of InGaAs-on-InP-based ultra-fast photoconductive materials operating at 1550-nm where cw and pulsed lasers are superior in all respects. Recently, we discovered ultrafast extrinsic photoconductivity in ErAs:GaAs at 1550 nm, allowing the generation of both cw and pulsed THz waves. GaAs-based materials have major electrical advantages over InGaAs-based because of their superior dark resistivity and breakdown field. In this paper, we show that 1550-nm-driven ErAs:GaAs is now a promising alternative to InGaAs-based photoconductive material. We focus on the ultrafast photoconductive behavior, and compare the performance of ErAs:GaAs photoconductive switches to those from state-of-the-art ultrafast InGaAs devices.

Complete characterization of terahertz (THz) radiation becomes an interesting yet challenging study for many years. In visible optical region, the wavefront assessment has been proved as a powerful tool for the beam profiling and characterization, which consequently requires 2-dimension (2D) single-shot acquisition of the beam cross-section to provide the spatial profile in time- and frequency-domain. In THz region, the main problem is the lack of effective THz cameras to satisfy this need. In this communication, we propose a simple setup based on free-space collinear 2D electrooptic sampling in a ZnTe crystal for the characterization of THz wavefronts.

In principle, we map the optically converted, time-resolved data of the THz pulse by changing the time delay between the probe pulse and the generated THz pulse. The temporal waveforms from different lens-ZnTe distances can clearly indicate the evolution of THz beam as it is converged, focused, or diverged. From the Fourier transform of the temporal waveforms, we can obtain the spectral profile of a broadband THz wave, which in this case within the 0.1-2 THz range. The spectral profile also provides the frequency dependency of the THz pulse amplitude. The comparison between experimental and theoretical results at certain frequencies (here we choose 0.285 and 1.035 THz) is in a good agreement suggesting that our system is capable of THz wavefront characterization. Furthermore, the implementation of Hartmann/Shack-Hartmann sensor principle enables the reconstruction of THz wavefront. We demonstrate the reconstruction of THz wavefronts which are changed from planar wave to spherical one due to the insertion of convex THz lens in the THz beam path. We apply and compare two different reconstruction methods: linear integration and Zernike polynomial. Roughly we conclude that the Zernike method provide smoother wavefront shape that can be elaborated later into quantitative-qualitative analysis about the wavefront distortion.

This paper presents a novel THz optical design that allows the acquisition of THz reflectivity maps of in vivo cornea without the need for a field flattening window and preliminary imaging results of in vivo rabbit cornea. The system’s intended use is to sense small changes in corneal tissue water content (CTWC) that can be precursors for a host of diseases and pathologies. Unique beam optics allows the scanning of a curved surface at normal incidence while keeping the source detector and target stationary. Basic system design principles are discussed and image sets of spherical calibration targets and corneal phantom models are presented. The presented design will enable, for the first time, non-contact THz imaging of animal and human cornea.

Colorectal cancer is the third most commonly diagnosed cancer in the world. The current standard of care for colorectal cancer is the conventional colonoscopy, which relies exclusively on the Physician’s experience. Continuous wave terahertz (THz) imaging has the potential to offer a safe, noninvasive medical imaging modality for detecting cancers. The current study demonstrates the design and development of a prototype terahertz endoscopic system based on flexible metal-coated terahertz waveguides. A CO₂ pumped Far-Infrared molecular gas laser operating at 584 GHz frequency was used for illuminating the tissue, while the reflected signals were detected using liquid Helium cooled silicon bolometer. The continuous-wave terahertz imaging system utilizes a single waveguide channel to transmit the radiation and collect the back reflected intrinsic terahertz signal from the sample and is capable of operation in both transmission and reflection modalities. The two dimensional reflectance images obtained using a prototype terahertz endoscopic system showed intrinsic contrast between cancerous and normal regions of the colorectal tissue, thereby demonstrating the potential impact of terahertz imaging for in vivo cancer detection.

We study theoretically and experimentally the plasmonic THz detection by the asymmetric dual-grating-gate HEMT at room temperature without source-to-drain bias. We derive the analytical expressions of photocurrents due to the plasmonic drag and ratchet effects, and we discuss about their frequency dependences. We also compare the theory to the experimentally obtained frequency dependence. It is demonstrated that they agree qualitatively well.

Terahertz (THz) technology is an active area of research with various applications in non-intrusive imaging and spectroscopy. Very few organic molecules have significant resonances below 1 THz. Understanding the origin of low frequency THz modes in these molecules and their absence in other molecules could be extremely important in design and engineering molecules with low frequency THz resonances. These engineered molecules can be used as THz tags for anti-counterfeiting applications. Studies show that low frequency THz resonances are commonly observed in molecules having higher molecular mass and weak intermolecular hydrogen bonds. In this paper, we have explored the possibility of enhancing the strength of THz resonances below 1 THz through electronegative atom substitution. Adding an electronegative atom helps in achieving higher hydrogen bond strength to enhance the resonances below 1 THz. Here acetanilide has been used as a model system. THz-Time Domain Spectroscopy (THz-TDS) results show that acetanilide has a small peak observed below 1 THz. Acetanilide can be converted to 2-fluoroacetanilide by adding an electronegative atom, fluorine, which doesn’t have any prominent peak below 1 THz. However, by optimally choosing the position of the electronegative atom as in 4-fluoroacetanilide, a significant THz resonance at 0.86 THz is observed. The origin of low frequency resonances can be understood by carrying out Density Functional Theory (DFT) simulations of full crystal structure. These studies show that adding an electronegative atom to the organic molecules at an optimized position can result in significantly enhanced resonances below 1 THz.

We demonstrate video rate THz imaging by detecting a frequency upconverted signal with a CMOS camera. A fiber laser pumped, double resonant optical parametric oscillator generates THz pulses via difference frequency generation in a quasi-phasematched gallium arsenide (QPM-GaAs) crystal located inside the OPO cavity. The output produced THz pulses centered at 1.5 THz, with an average power up to 1 mW, a linewidth of <100 GHz, and peak power of >2 W. By mixing the THz pulses with a portion of the fiber laser pump (1064 nm) in a second QPM-GaAs crystal, distinct sidebands are observed at 1058 nm and 1070 nm, corresponding to sum and difference frequency generation of the pump pule with the THz pulse. By using a polarizer and long pass filter, the strong pump light can be removed, leaving a nearly background free signal at 1070 nm. For imaging, a Fourier imaging geometry is used, with the object illuminated by the THz beam located one focal length from the GaAs crystal. The spatial Fourier transform is upconverted with a large diameter pump beam, after which a second lens inverse transforms the upconverted spatial components, and the image is detected with a CMOS camera. We have obtained video rate images with spatial resolution of 1mm and field of view ca. 20 mm in diameter without any post processing of the data.

Light detection and ranging (lidar) is used for various applications such as remote sensing, altimetry and imaging. Continuous wave frequency modulated (CWFM) lidars rely on linearly ramping the optical frequency of a laser and interfering the delayed echo signal with a reference signal to produce a beat frequency. The range resolution of lidar is determined by the swept frequency range of the linearly chirped continuous light waves in a frequency modulation system. For example, for 1mm range resolution, it needs the frequency sweep range of more than 150 GHz. In this paper a system which can generate a linearly chirped optical waveform within a super broad-wide band of 200 GHz, using cascaded phase modulators (PM) and single side band (SSB) modulator, is designed as a light source in a high resolution lidar system.

We investigate the terahertz (THz) phase imaging using liquid crystal (LC) device. Recently, there have been extensive efforts to measure the refractive indices and transmission losses of some LC materials in THz region. From these results, LC materials show relatively large refractive index anisotropy and they can have a potential application to some control devices similar to the display application. Furthermore, tunable LC THz phase shifter has been reported. In this study, an attempt was made to introduce the LC device into the THz phase imaging which was based on four-step phase-shifting algorithm. Four-step phase-shifting algorithm is one of the most effective methods of phase imaging and moving mirror is needed to introduce phase shift in standard measurements. In addition, we should prepare the two rays with common source, therefor experimental setup becomes complicated. While on the other hand, it is just needed to insert a LC phase shifter into the light path when we adopt LC device. Furthermore, low-voltage application is enough to introduce the phase-shifting, hence it is not necessary to prepare the moving mirror. In this work, we fabricate the electrically tunable LC phase shifter which has sandwich cell structure. The fundamental phase-shifting properties were measured by using an optically pumped gas laser system which can generate continuous wave (CW) THz waves. In addition, we investigated the phase shifting interferometry which was based on four-step phase-shifting algorithm by using LC phase shifter. We also estimate the birefringence of X-cut crystalline quartz at 2.5 THz.

Direct digitization of long, wideband chirped RF signals in the GHz band requires power hungry ADCs and produces large data sets. Here we present an optical scheme to perform multi-coset sampling of such signals with reduced power consumption and smaller data sets. In our scheme a repetitively pulsed femtosecond laser is dispersed to the interpulse time, the RF is modulated on the optical field, and the field is directed to a pair of wavelength-division demultiplexers (WDM). The channels of the WDM are attenuated with a pseudo-random sequence to form a coset pattern that repeats at the laser repetition rate. After a photodiode, the photocurrent is integrated for the duration of the dispersed optical pulse so that the coset pattern non-uniformly samples the RF signal. Since the laser repetition rate is uncorrelated with the RF, each coset provides an independent measurement of the RF. Experimental and numerical results show that 4 properties of the RF chirp pulse can be determined from the multiple coset samples: carrier frequency, chirp rate, start time, and pulse duration. Results are presented for a 20MHz chirp on a 13 microsecond pulse at a carrier of 2.473 GHz.

Many important astrophysical processes occur at wavelengths that fall within the far-infrared band of the EM spectrum, and over distance scales that require sub-arc second spatial resolution. It is clear that in order to achieve sub-arc second resolution at these relatively long wavelengths (compared to optical/near-IR), which are strongly absorbed by the atmosphere, a space-based far-IR interferometer will be required. We present analysis of the optical system for a proposed spatial-spectral interferometer, discussing the challenges that arise when designing such a system and the simulation techniques employed that aim to resolve these issues. Many of these specific challenges relate to combining the beams from multiple telescopes where the wavelengths involved are relatively short (compared to radio interferometry), meaning that care must be taken with mirror surface quality, where surface form errors not only present potential degradation of the single system beams, but also serve to reduce fringe visibility when multiple telescope beams are combined. Also, the long baselines required for sub-arc second resolution present challenges when considering propagation of the relatively long wavelengths of the signal beam, where beam divergence becomes significant if the beam demagnification of the telescopes is not carefully considered. Furthermore, detection of the extremely weak far-IR signals demands ultra-sensitive detectors and instruments capable of operating at maximum efficiency. Thus, as will be shown, care must be taken when designing each component of such a complex quasioptical system.

The detection and measurement of electromagnetic fields have attracted significant amounts of attention in recent years. Traditional electronic electromagnetic field sensors use large active conductive probes which perturb the field to be measured and also make the devices bulky. In order to address these problems, integrated photonic electromagnetic field sensors have been developed, in which an optical signal is modulated by an RF signal collected by a miniaturized antenna. In this work, we design, fabricate and characterize a compact, broadband and highly sensitive integrated photonic electromagnetic field sensor based on a silicon-organic hybrid modulator driven by a bowtie antenna. The large electro-optic (EO) coefficient of organic polymer, the slow-light effects in the silicon slot photonic crystal waveguide (PCW), and the broadband field enhancement provided by the bowtie antenna, are all combined to enhance the interaction of microwaves and optical waves, enabling a high EO modulation efficiency and thus a high sensitivity. The modulator is experimentally demonstrated with a record-high effective in-device EO modulation efficiency of r₃₃=1230pm/V. Modulation response up to 40GHz is measured, with a 3-dB bandwidth of 11GHz. The slot PCW has an interaction length of 300μm, and the bowtie antenna has an area smaller than 1cm². The bowtie antenna in the device is experimentally demonstrated to have a broadband characteristics with a central resonance frequency of 10GHz, as well as a large beam width which enables the detection of electromagnetic waves from a large range of incident angles. The sensor is experimentally demonstrated with a minimum detectable electromagnetic power density of 8.4mW/m² at 8.4GHz, corresponding to a minimum detectable electric field of 2.5V/m and an ultra-high sensitivity of 0.000027V/m Hz^-1/2 ever demonstrated. To the best of our knowledge, this is the first silicon-organic hybrid device and also the first PCW device used for the photonic detection of electromagnetic waves. Finally, we propose some future work, including a Teraherz wave sensor based on antenna-coupled electrooptic polymer filled plasmonic slot waveguide, as well as a fully packaged and tailgated device.

The bowtie antenna is a topic of growing interest in recent years. In this paper, we design, fabricate, and characterize a modified gold bowtie antenna integrated on a transparent glass substrate. We numerically investigate the antenna characteristics, specifically its resonant frequency and enhancement factor. We simulate the dependence of resonance frequency on bowtie geometry, and verify the simulation results through experimental investigation, by fabricating different sets of bowtie antennas on glass substrates utilizing CMOS compatible processes and measuring their resonance frequencies. Our designed bowtie antenna provides a strong broadband electric field enhancement in its feed gap. The far-field radiation pattern of the bowtie antenna is measured, and it shows dipole-like characteristics with large beam width. Such a broadband antenna will be useful for a myriad of applications, ranging from wireless communications to electromagnetic wave detection.

In the previous work we presented results demonstrating the ability of transmission mode terahertz time domain spectroscopy (THz-TDS) to detect doping profile differences and deviations in silicon. Here we report follow up work demonstrating doping profile measurement by first precisely removing a thin layer (currently ~ 20 nm) from the junction by anodization followed by selective oxide etching. The anodization-etching step is followed by measuring the terahertz transmission using THz-TDS. The anodization and terahertz measurement steps are then alternated. The doping profile can then be reconstructed using the resultant dataset. In this work we share results obtained on phosphorus doped silicon wafers. We find good agreement between the measured transmitted terahertz spectra and the simulated terahertz spectra for all etching cycles when the doping profile used in the simulations agrees with SIMS analysis. We conclude that anodization combined with THz-TDS can potentially be a high resolution destructive doping profile mapping method.

We report an investigation on optoelectronic oscillators based on a combination of a fiber delay line and a whispering gallery mode resonator. We analyze the dynamical processes which are key for the understanding of the spectral purity of these oscillators. We therefore show how combining both optical elements leads to significant improvement of the spectral purity of the oscillator, as it leads to a spurious rejection rate higher than 50 dB.

High-performance photodetectors (PDs) for radio over fiber (RoF) applications over 60 GHz were designed and fabricated. The RF output was investigated while a high linearity was observed for two designs: a low carrier concentration InGaAs absorption layer in a PIN structure and a low carrier concentration collection layer in a unitravelling- carrier (UTC) structure. The RF output performances of both PIN and UTC structures were studied at 67 GHz and 100 GHz respectively. High photocurrent densities could be obtained from both structures (21.7 kA/cm² in the PIN structure and 35.4 kA/cm² in the UTC structure). The PIN structure exhibited a slightly higher current density of 1.6 times than the UTC structure. The frequency response of the UTC-PD exhibited excellent flatness up to 110 GHz, with a 3 dB bandwidth beyond 110 GHz. In addition, maximum RF output powers of +6.8 dBm at 67 GHz and -5 dBm at 100 GHz was successfully obtained. The space charge effect could be ruled out for the output linearity, but avoiding overheating in the p-contact metal had to be considered. By modifying impedance matching circuit designs, the maximum RF output power level of 3 dB can be improved.

This paper introduces the continuously tunable THz radiation through sideband generation of a free running and solidnitrogen- cooled THz quantum cascade laser. The 2.324 THz QCL operating in a single longitudinal mode (SLM) in continuous-wave (cw) was mixed with a swept synthesized microwave signal by a THz Schottky-diode-balanced mixer. Through sideband generation, two frequency branches were observed at low and high frequency, characterized with a Fourier-transform spectrometer. At low frequency, the sideband generates frequencies from -50 GHz to +50 GHz. At high frequency, it generates sideband frequencies from 70 GHz to 115 GHz. The total ±100 GHz tuning range can be further expanded with higher frequency millimeter wave amplifier/multiplier source. The sideband generates total 1 μW of output power at both upper and lower frequency with 200 μW of driven power from the THz QCL, showing a power conversion efficiency of 5 × 10^-3. The demonstration of this SM, continuously tunable THz source enables its applications where SM, spatially coherent beam is required.

Our recent studies in regards of developing portable THz scanner for imaging and spectroscopy systems are presented. In the course, high power tunable continuous wave (CW) THz emitter and high sensitivity THz receiver platforms are presented. Those platforms can be realized with tunable optical beating source, broadband photomixer, arrayed photomixer and Schottky barrier diode, evanescently-coupled photodiodes with high saturation current, and semiconductor optical amplifier (SOA) integrated optical beating source. On the system level, our recent THz thickness measurement systems and the THz line scanner imaging system are presented.

Recently, microwave photonic techniques have emerged to address the challenges that microwave systems face under high-frequency or wideband conditions. To a large extent, the performance of microwave photonic systems depends on the performance of individual optoelectronics devices, such as high power photodiodes. Here, we report a fullypackaged photodetector module based on InGaAs/InP modified uni-traveling carrier (MUTC) photodiode. The modules demonstrated a 3-dB bandwidth up to 50GHz and a record-high output power of 14.0 dBm at 50GHz.

Three types of electroabsorption modulators (EAMs) based on III-V semiconductor multiple quantum wells (MQW) are presented in this work. One is a novel monolithic integration traveling-wave EAM for an analog optical transmitter/transceiver to achieve integrated photonic mm-wave functions for broadband connectivity. Another one is composed of an integrated EAM 1D array in a photonic beam-former as a Ku-band phased array antenna for seamless aeronautical networking through integration of data links, radios, and antennas. The third one addresses the use of MQW EAMs in free space optical links through biological tissue for transcutaneous communication.

Cement is mixed with water in an optimum ratio to form concrete with desirable mechanical strength and durability. The ability to track the consumption of major cement constituents, viz., Tri- and Dicalcium Silicates (C3S, C2S) reacting with water along with the formation of key hydration products, viz., Calcium-Silicate-Hydrate (C-S-H) which gives the overall strength to the concrete and Calcium Hydroxide (Ca(OH)₂), a hydration product which reduces the strength and durability, using an efficient technique is highly desirable. Optimizing the amount of water to be mixed with cement is one of the main parameters which determine the strength of concrete. In this work, THz spectroscopy has been employed to track the variation in hydration kinetics for concrete samples with different water-cement ratios, viz., 0.3, 0.4, 0.5 and 0.6. Results show that for the sample with water-cement ratio of 0.3, significant amount of the C3S and C2S remain unreacted even after the initial hydration period of 28 days while for the cement with water-cement ratio of 0.6, most of the constituents get consumed during this stage. Analysis of the formation of Ca(OH)₂ has been done which shows that the concrete sample with water-cement ratio of 0.6 produces the highest amount of Ca(OH)₂ due to higher consumption of C3S/C2S in presence of excess water which is not desirable. Samples with water-cement ratio of 0.4 and 0.5 show more controlled reaction during the hydration which can imply formation of an optimized level of desired hydration products resulting in a more mechanically strong and durable concrete.

In this paper, hybrid optical delay line (HODL) which is demanded on automotive radar test system (RTS) is proposed and demonstrated. HODL is composed with coaxial cable in short delay time (< 32 nsec) and optical fiber in long delay time (≥ 32 nsec) which are considering the volume, loss and frequency characteristics. Also, the optical transceiver that has the bandwidth of 1 GHz is designed for frequency modulated continuous wave (FMCW). Experimental results show that the S21 is ± 0.5 dB in the optical transceiver and ± 1.7 dB in the whole system at 3.7 GHz ~ 4.7 GHz. The resolution of delay time is 1 ns and the delay flatness is ± 0.23 ns.

We present a method for full distortion elimination in phase-modulated analog optical links using the nonlinear optical process of four-wave mixing (FWM). Phase-modulated links consist of a laser and phase modulator in the transmitter and an interferometer (or local oscillator) and photodiode in the receiver. Phase modulation is a linear process, so distortion is introduced in the interferometric detection process. Quadrature biasing eliminates even-order distortion products, leaving only odd-order distortion. Here we introduce a method for eliminating these odd-order distortion products in the receiver. A small portion of the phase-modulated signal is tapped and combined with an unmodulated CW laser to seed a cascaded FWM comb source. This process generates an array of lightwaves with integer multiples of the signal’s phase modulation. By suitably scaling and combining these lightwaves with the original signal the overall transfer function of the interferometric receiver can be linearized (or given another tailored shape) through a Fourier synthesis approach. By combining a single lightwave from the generated comb with the original signal, we demonstrate the complete elimination of third-order distortion from the phase-modulated link leaving fifth-order distortion as the dominate source of distortion. We show a 17.6-dB SFDR improvement (1-Hz bandwidth) for a 6 GHz link operating at 5-mA total photocurrent and a 16.4-dB SFDR improvement (1-Hz bandwidth) for a 15 GHz link operating at 10-mA total photocurrent. By appropriately combining additional lightwaves from the generated comb, higher-order distortion products can be eliminated to produce an ideal linear (or custom shaped) transfer function.

Previously, we introduced a novel and an etch-free solution based procedure utilizing a combination of imprinting and inkjet printing for developing polymer photonic devices to overcome the limitations of conventional polymer photonic device fabrication techniques, such as RIE or direct pattern writing. In this work, we demonstrate the feasibility of developing very large-area photonic systems on both rigid and flexible substrates. Specifically, a complete reconfigurable 4-bit true-time-delay module, comprising of an array of five interconnected TO switches and polymer delay lines, with a dimension of 25 mm × 18 mm is developed. Because of the roll-to-roll (R2R) compatibility of the employed solution processing techniques, photonic system development over large areas at high-throughput on rigid or flexible substrates is possible, which will lead to tremendous cost savings. Moreover, these devices can be integrated with other printed photonic and electronic components, such as light sources, modulators, antennas, etc., on the same substrate, thus enabling integrated systems that can be conformably integrated on any platform.

Molecular rotational resonance (MRR) spectroscopy gives spectral signatures with high chemical selectivity. At room temperature, the peak intensity of the MRR spectrum occurs in the 100 GHz – 1 THz frequency range for volatile species with mass ≤ 100 amu. Advances in high-power sub-mm-wave light sources has made it possible to implement time-domain Fourier transform (FT) spectroscopy techniques that are similar to FT nuclear magnetic resonance (FT-NMR) measurements. In these measurements, the gas sample is excited by a short (200 ns) excitation pulse that creates a macroscopic sample polarization. The electric field of the subsequent transient molecular emission is detected using a heterodyne receiver and a high-speed digitizer. FT-MRR spectroscopy offers speed and sensitivity improvements over absorption spectroscopy. For chemical analysis, FT-MRR spectrometers combine the benefits of broad chemical coverage typical of gas chromatography – mass spectrometry (GC-MS) instruments and the direct measurement capabilities of infrared gas sensors all in a reprogrammable platform. Pulse sequence measurements can be implemented for advanced spectroscopic analysis. Trace level quantitation of volatile species at ppbv concentration can be performed on the time scale of a minute. In cases where the sample is a complex mixture, a double-resonance pulse sequence can be used to achieve chemical selectivity even in cases where spectral overlap occurs. These measurement capabilities are illustrated using the application of FT-MRR spectroscopy to residual solvent analysis of pharmaceutical products.

A novel optical power monitoring method based on optoelectronic oscillators incorporating semiconductor optical amplifiers is presented and a prototype of two nodes distributed online optical power monitor with dynamic measuring range of 6dB and accuracy of 0.25dB is experimentally demonstrated.

We investigate gain equalization of a four-mode-group and six-mode-group erbium-doped fiber amplifiers with a genetic algorithm for mode division multiplexing transmission systems by optimizing rare earth dopant profile and pump modes powers, respectively. The optimizing gains are calculated to be > 28 dB between 1520 nm – 1565 nm with a maximum differential modal gain of ~ 2 dB among the mode groups only by optimizing the rare earth ring doping profile in the few-mode erbium-doped fiber.