This PDF file contains the front matter associated with SPIE Proceedings Volume 8376, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

Conventional multi-component gas analysis is based either on laser spectroscopy, laser and photoacoustic absorption at specific wavelengths, or on gas chromatography by separating the components of a gas mixture primarily due to boiling point (or vapor pressure) differences. This paper will present a new gas molecular mass detection method based on thermally modulated nano-trampoline material as smart skin for gas molecular mass detection by fiber Bragg grating-based gas sensors. Such a nanomaterial and fiber Bragg grating integrated sensing device has been designed to be operated either at high-energy level (highly thermal strained status) or at low-energy level (low thermal strained status). Thermal energy absorption of gas molecular trigs the sensing device transition from high-thermal-energy status to low-thermal- energy status. Experiment has shown that thermal energy variation due to gas molecular thermal energy absorption is dependent upon the gas molecular mass, and can be detected by fiber Bragg resonant wavelength shift with a linear function from 17 kg/kmol to 32 kg/kmol and a sensitivity of 0.025 kg/kmol for a 5 micron-thick nano-trampoline structure and fiber Bragg grating integrated gas sensing device. The laboratory and field validation data have further demonstrated its fast response characteristics and reliability to be online gas analysis instrument for measuring effective gas molecular mass from single-component gas, binary-component gas mixture, and multi-gas mixture. The potential industrial applications include fouling and surge control for gas charge centrifugal compressor ethylene production, gas purity for hydrogen-cooled generator, gasification for syngas production, gasoline/diesel and natural gas fuel quality monitoring for consumer market.

The fabrication of surface-enhanced Raman spectroscopy (SERS) substrates that are optimized for use with specific laser wavelength - analyte combinations is addressed. In order to achieve large signal enhancement, temporal stability, and reproducibility over large substrate areas at low cost, only self-assembly and templating processes are employed. The resulting substrates consist of arrays of gold nanospheres with controlled diameter and spacing, properties that dictate the optical response of the structure. We demonstrate the tunability of the extended surface plasmon resonance in the range of 520-1000 nm, helping to match the enhancement profile to the laser line of the Raman instrument. Despite relying on self-organization, we obtain site-to-site SERS enhancement factor variations smaller than 10%.

We describe and demonstrate a physical mechanism that substantially enhances the label-free sensitivity of a Whispering-Gallery-Mode biosensor for the detection of individual nanoparticles in aqueous solution. It involves the interaction of dielectric nanoparticle in an equatorial carousel orbit with a plasmonic nanoparticle bound on the orbital path. As a 60 nm dielectric particle parks on plasmonic hot spots we observe frequency shifts that are considerably enhanced consistent with a simple reactive model. Using the same model the label free detection of a single bovine serum albumin (BSA) molecule is projected.

In whispering-gallery-mode (WGM) microresonator based optical biosensors, the mode shift or splitting induced by biomolecules are typically regarded as the sensing signals. Here we propose several schemes to improve the performance of WGM based biosensing. In the mode shift sensing scheme, we propose to use a novel exterior plasmonic WGM supported by a metal-coated toroidal microresonator, and the detection sensitivity reaches 500 nm/RIU (refraction index unit). In the mode splitting scheme, we study and discuss how to extend the detection range, which is of importance in detecting small-sized biomolecules. Finally, the single nanoparticle detection is realized experimentally by using mode splitting sensing scheme in the aqueous environment.

This paper presents innovations that reduce the dimensions and interrogation complexity of a previously developed multi-axis electric field sensor. These devices are based on slab coupled optical sensor (SCOS) technology. SCOS are sensitive to electric fields that are parallel to the optic axis of the electro-optic slab. Electric fields are measured in two axes by mounting SCOS devices, which have slabs with optic-axes perpendicular to the fiber (z-cut), orthogonal to each other. In order to reduce dimensions of the sensor, the third-axis is measured by having a slab with the optic-axis parallel to the fiber (x-cut). Since the resonant mode coupling of a SCOS device occurs at specific wavelengths whose spectral locations are determined in part by the effective refractive index of the modes in the slab, rotating a z-cut slab waveguide relative to the optical fiber will cause the spectral position of the resonance modes to shift. This method allows the resonance modes to be tuned to specific wavelengths, enabling a multi-axis SCOS to be interrogated with a single laser source.

Porous materials offer several advantages for chemical and biomolecular sensing applications. In particular, nanoscale porous materials possess a very large reactive surface area to facilitate the capture of small molecules, and they have the capability to selectively filter out contaminant molecules by size. This paper will provide an overview of the fabrication, functionalization, and application of porous silicon thin films and waveguides, as well as porous gold templates, for the detection of small chemical and biological molecules. Issues of efficient molecule infiltration and capture inside porous materials, binding kinetics in nanoscale pores, the influence of pore size on small molecule detection sensitivity, and the new nanoscale patterning technique of Direct Imprinting of Porous Substrates (DIPS) will be addressed. Additionally, a novel application of porous silicon for detection of x-ray radiation will be introduced.

In this paper, we report an in vivo experimental study of liver tissue during Laser Induced Interstitial Thermotherapy (LITT). Single FBG was used in the experiments to measure the temperature distribution profile of the bio tissue in real time. Ideally, the goal of LITT is to kill pathological tissue thoroughly and minimize its damage to surrounding healthy tissue, especially vital organs. The extent of treated tissue damage in the therapy is mainly dependent on the irradiation time and the laser power density at the tissue surface. Therefore, monitoring the dynamic change of the exact temperature distribution of the tissue is a key point for the safety of this treatment. In our experiments, FBG was embedded in the laser irradiated bio tissues and used as fully distributed temperature sensor. During the therapy, its reflection spectra were recorded and transmitted to PC in real time. The temperature profile along the FBG axial was reconstructed from its reflection spectrum by the spectra inversion program running on the PC. We studied the dependence of the temperature distribution and the laser output power experimentally and compared the results of in vivo and in vitro under similar laser irradiating conditions. Experimental results demonstrate the effectiveness of this method. Due to influence of body temperature, the in vivo measured temperature is higher than the in vitro one with an almost constant temperature difference value, but the slope and trend of the measured temperature curves in vivo and in vitro are almost identical.

Noninvasive detection of glucose has been heavily researched in their roles of offering cost-effective, painless, and bloodless monitoring of glucose concentration. In this work, we describe a novel, label-free, and sensitive approach for detecting the glucose concentration in human interstitial fluid samples using the opto-fluidic ring resonator (OFRR). The OFRR incorporates microfluidics and optical ring resonator sensing technology to achieve rapid label-free detection in a small and low-cost platform. In this study, bulk refractive index measurements are presented. Results show that the OFRR is able to detect glucose at medically relevant concentrations in interstitial fluid ranging from 0 to 25 mM, with a detection limit of 0.32 mM, which is lower than clinical requirement by one order of magnitude. Our work is believed to lead to a device that can be used to frequently monitor glucose concentration in a low-cost and painless manner.

This paper summarizes the recent progress of improving optical fiber sensor interrogation technique by introducing acitve fiber loop into demodulation system. Various types of sensors including multimode interferometer chemical vapor sensor and etc are implemented in the active fiber loop interrogation system. The experiments show an improved signal to noise ratio by active fiber loop.

An interrogation scheme for an in-series double cladding fiber (DCF) sensor is proposed and demonstrated, which can be used for simultaneous refractive index (RI) and temperature measurement. It utilizes two commercial distributed feedback lasers to match two cascade DCF sensors which have two band-rejected filtering spectra at different wavelengths. The two lasers were intensity modulated by different frequencies and demodulated by a lock-in amplifier. Experimental results indicated that a resolution of ±2×10^-5 in RI and ±1.2°Cin temperature were achieved. Based on the simple and low cost interrogation scheme, the dual parameters sensor system will find potential applications in chemical sensors and biosensors.

We reported a high-sensitivity CO₂ gas sensing system based on wavelength scanning absorption spectroscopy. A distributed feedback (DFB) laser was used as the light source in the system, whose wavelength was thermally tuned, by a thermoelectric cooler (TEC), to scan around one CO₂ absorption line near 1572nm. Scanning of the absorption line spectrum is performed over a glass CO₂ gas cell, 16.5 cm long with collimated optical fiber connectors. Different concentrations of CO₂ were prepared by a high-precision gas flow control meter and sealed within the gas cell. A self-designed detection and amplification circuit was employed for absorption spectrum detection. The circuit implements background-cancellation with a two tier amplification scheme. By cancelling the high background signal, we can improve the CO₂ sensitivity by about two orders of magnitude compared with commonly used direct detection methods with high background signals. Reducing the high DC signal permits isolated amplification of the absorption line spectrum. Absorption spectra of different CO₂ concentrations were measured, and the results demonstrated sensing capability of 100% to <0.1% concentrations of CO₂. This sensing system is expected to be used in conjunction with a wireless CO₂ sensor network for large area CO₂ monitoring. Given the very lower power consumption of the DFB laser and the detection circuit this sensing system offers a solution for affordable long term CO₂ monitoring for reliable storage in carbon sequestration.

We report on photonic crystal electro-optic devices formed in engineered thin film lithium niobate (TFLN™) substrates. Photonic crystal devices previously formed in bulk diffused lithium niobate waveguides have been limited in performance by the depth and aspect ratio of the photonic crystal features. We have overcome this limitation by implementing enhanced etching processes in combination with bulk thin film layer transfer techniques. Photonic crystal lattices have been formed that consist of hexagonal or square arrays of holes. Various device configurations have been explored, including Fabry Perot resonators with integrated photonic crystal mirrors and coupled resonator structures. Both theoretical and experimental efforts have shown that device optical performance hinges on the fidelity and sidewall profiles of the etched photonic crystal lattice features. With this technology, very compact photonic crystal sensors on the order of 10 μm x 10 μm in size have been fabricated that have comparable performance to a conventional 2 cm long bulk substrate device. The photonic crystal device technology will have broad application as a compact and minimally invasive probe for sensing any of a multitude of physical parameters, including electrical, radiation, thermal and chemical.

Cathodoluminescence (CL) spectroscopy is performed on conducting 1- and 2-dimensional gratings of metals, semimetals and semi-conductors of varying periods from 0.5 to 20 microns for a range of grating amplitudes from 0.1 to 4.6 microns. The overall emission spectrum consists of a 400 nm wide band centered at ~600 nm which depends little on the grating period, grating amplitude, material, e-beam energy, or temperature. CL intensity increases and the center wavelength blue shifts with increasing excitation beam current. For the larger amplitude 1-dimensional gratings fringes appear in the emission spectrum, which is due to interference between emission from grating bars and grooves. Surface corrugation is necessary to the emission as none is observed from smooth surfaces. The same band appears weakly in CL of a Cu sample with random ~1 micron surface roughness, but this emission is strongly reduced when the same sample is highly polished. The CL signal appears even when the ~10 nm electron-beam is at least 2 mm away from the grating edge, suggesting electron-beam induced currents are important to the emission, whose precise mechanism remains unclear. Previously suggested mechanisms--electron collision with image charge, transition radiation, surface contamination, and inverse photoemission effect--all fail to explain the observed spectrum and its lack of beam-energy dependence.

An analysis of 1-dimensional quantum device is presented by comparing between two possible mathematical methods. The first is a continuous scheme where both the mass and the potential vary along the Z-axis, while the second one presents segmentation in three main sections where the mass remains constant along each phase. These analysis where made with the help of a Computer Algebra Software (CAS) due to its extensive mathematical development. A discussion about both schemes and its possible applications to photonic devices are presented.

Optical detection is an often used technique for recognition of potentially dangerous materials. Hydrogenated amorphous silicon (a-Si:H) technology provides an inexpensive alternative material compared to crystalline silicon for being used in photonic devices operating in the visible spectrum. Further materials' key benefits are the high light absorption, the voltage-tunable spectral sensitivity and the high space efficiency. Present research efforts concentrate on the determination of the color information in a-Si:H photodiodes. This work presents an approach to improve color recognition of a-Si:H photodiodes by modifying the layer sequence. The maximum of the spectral response (SR) of a single i-layer a-Si:H photodiode can be shifted by varying its bias voltage. In this case, the shift is not more than some nanometers. Precise color recognition requires different SR maxima (e.g. RGB-model). One possibility to accomplish a separation of the SR is to engineer the bandgap; another idea, which is presented here, is based on a layer sequence modification. Normally, the SR at higher reverse bias voltages, with the maximum at longer wavelengths, encloses that at lower voltages. Splitting the SR leads to an improvement of color recognition and is achieved by depositing an additional interior anode. The SR maximum shift amounts to 100nm, from 570nm by contacting the interior anode, to 670nm at the top anode. Furthermore, the curves are clearly split. The presented approach should lead to a tunable multi-spectral photodiode for high quality color recognition. Such a diode can be used in photonic devices, e.g. for safety and security applications.

The development of low cost and compact biological agent identification and detection systems, which can be employed in place-and-forget applications or on unmanned vehicles, is constrained by the photodetector currently available. The commonly used photomultiplier tube has significant disadvantages that include high cost, fragility, high voltage operation and poor quantum efficiency in the deep ultraviolet (240-260nm) necessary for methods such as fluorescence-free Raman spectroscopy. A III-Nitride/ SiC separate absorption and multiplication avalanche photodiode (SAM-APD) offers a novel approach for fabricating high gain photodetectors with tunable absorption over a wide spectrum from the visible to deep ultraviolet. However, unlike conventional heterojunction SAM APDs, the performance of these devices are affected by the presence of defects and polarization induced charge at the heterointerface arising from the lattice mismatch and difference in spontaneous polarization between the GaN absorption and the SiC multiplication regions. In this paper we report on the role of defect density and interface charge on the performance of GaN/SiC SAM APDs through simulations of the electric field profile within this device structure and experimental results on fabricated APDs. These devices exhibit a low dark current below 0.1 nA before avalanche breakdown and high avalanche gain in excess of 1000 with active areas 25x larger than that of state of the art GaN APDs. A responsivity of 4 A/W was measured at 365 nm when biased near avalanche breakdown.

We report a novel, compact design of high speed Ge photo detector integrated with an echelle demultiplexer on a large cross-section SOI platform with low insertion loss and low fiber coupling loss. A narrow Ge photo detector waveguide is directly butt-coupled to a Si waveguide to ensure low loss and high speed operation. With a Ge detector size of only 0.8×15 μm², the device achieves greater than 30 GHz modulation speed. The results indicate that the device speed is transit time limited and that the detector performance benefits from the high electron and hole drift velocity of germanium. The dark current of the detector is less than 0.5μA at -1V. This small footprint high speed Si-based WDM receiver can be fabricated using CMOS processes and used for multichannel terabit data transmission with low manufacturing cost.

Common security CCD and CMOS imaging systems are not able to distinguish colorimetrically between dangerous chemical substances, for example whitish powders [1]. Hydrogenated amorphous silicon (a-Si:H) with profiled bandgaps can be found in solar cells to optimize the collection of incoming photons [2]. We developed multicolor photodiodes based on a-Si:H with different spectral response characteristics for a reliable, fast, cheap and non-destructive identification of potentially dangerous substances. Optical and I-V measurements were performed to explore the effect of combining linearly graded a-SiC:H-/a-SiGe:H layers with low reflective aluminum doped zinc oxide (ZnO:Al) cathodes. We determined absorption coefficients and mobility-lifetime products (μτ) of graded and non-graded absorbers to calculate the penetration depth of photons at different energies into the device structure. This set of parameters enables an optimization of the intrinsic layers so that charge accumulations are generated precisely at defined device depths. Significant color separation improvements could be achieved by using ZnO:Al cathodes instead of commonly used ZnO:Al/Chromium (Cr) reflectors. As a result, we obtained multicolor diodes with highly precise adjustment of the spectral sensitivity ranging from 420 nm to 580 nm, reduced interference fringes and a very low reverse bias voltage of -2.5 V maximum. Three terminal device architectures with similar absorbers exhibit a shift from 440 nm to 630 nm by applying reverse voltages of, for instance, -11.5 V at 580 nm [3]. Present research efforts concentrate on further improvements of the absorption region to reduce the bias without affecting the optical sensor performance, using extensive bandgap engineering techniques.

It is well-known that the conventional lens design suffers from the aberration, which will lead to imperfect imaging. One way to solve this problem is to use gradient index (GRIN) lenses such as Luneburg lens. However, the spherical geometry of Luneburg lens imposes difficulty for manufacturing. Also, it is desired to design the Luneburg lens with arbitrary focal length. To address these issues, in this paper, we propose to apply the transformation optics techniques to the general Luneburg lens design. In this way, the spherical lens surface will be transformed to flattened shapes, which can be practically fabricated on a flat substrate. Specifically, three-dimensional (3D) Luneburg lenses with different focal lengths will be studied. Moreover, discussion on the fabrications of proposed lens has been included. It is desired to ensure that the modified design lies within the available material properties of various polymer photoresists.