This PDF file contains the front matter associated with SPIE Proceedings Volume 8034, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

We present preliminary designs and experimental results for creating a microarray nanoplatform based on twodimensional photonic crystal devices in silicon. Multiple photonic crystal microcavities are coupled along the length of a single photonic crystal waveguide that undergo resonance wavelength shifts when an antibody-antibody binding event occurs in the immediate vicinity of the corresponding photonic crystal microcavity. The microarray nanoplatform enables high throughput measurements of multiple antibody-antibody interactions via a single optical waveguide transmission measurement.

GE Global Research Center, in collaboration with Morpho Detection, Inc. has developed an assay scheme for the identification of biological agents using Surface Enhanced Raman Scattering (SERS). Specifically, unique spectroscopic signatures are generated using SERS tags consisting of individual glass-encapsulated gold nanoparticles and surfacebound reporter molecules. These SERS tags are modified with a capture moiety specific to the antigen of interest, and serve as a spectroscopic label in a bead-based sandwich assay. Assays are being developed for a variety of pathogens and this paper will focus on aspects of assay development, optimization, stabilization and validation. Results on the development of an assay to detect Ricin toxin will be presented, and preliminary feasibility studies for the detection of additional pathogens will be discussed.

Many important bio and chemical molecules have their signature frequency (vibrational resonance) matching the mid infrared region (2-10 μm) of the optical spectrum. But building a bio-sensor, sensitive in this spectral regime, is extremely challenging task. It is because of the weak light-particle interaction strength due to huge dimensional mismatch between the probed molecules (typically ~ 10's of nm) and the probing wavelength (order of micron). We exploit the optical antenna to overcome this problem by squeezing the optical modes. This modal confinement happens only in the near-field region of the antenna and thus we have built an apertureless near-field scanning optical microscope (a-NSOM) to demonstrate it experimentally. Further, we have integrated these plasmonic antennas with mid-infrared sources known as Quantum Cascade Lasers (QCL). Our antenna structure is based on metal-dielectric-metal (MDM) and we have shown how they can generate higher electrical field enhancement compared to single metal design. Antenna integrated QCL operated at room temperature and its wavelength of operation was measured to be ~ 6μm. We have used 3D finite-difference-time-domain (FDTD) simulations to optimize the different component of the MDM antenna. After optimizing, we fabricated the antenna on the facet of QCL using focused ion beam (FIB) and measured using a-NSOM. We have shown that the optical mode can be squeezed down to a few 100's of nm which is much smaller than the incident light wavelength (λ~6μm). We also propose a microfluidic approach to build a typical mid-infrared bio-sensor where the probed molecules can be transferred to the near field region of the antenna through fluidic channels. Such scheme of building bio-sensor can overcome the barrier of weak light-particle interaction and eventually could lead to building very efficient, compact, mid-infrared bio-sensors.

Silicon dioxide surfaces are commonly used in photonic microsensors for bioreceptor attachment. Functionalization of sensor surface with aptamer receptors provides the opportunity to develop low cost, robust, field deployable sensors. Most aptamer sensors are constructed by covalently linking modified aptamers to a derivatized surface. There have been reports of using UV crosslinking to directly immobilize DNA with sequences that end with poly(T)10-poly(C)10 on an unmodified glass surface for hybridization. We have expanded this strategy using thrombin-binding aptamers (TBAs) with three different tail modifications. TBA with PolyT20 tail showed the best performance in terms of sensitivity and dynamic range. PolyTC tailed aptamers did not bind thrombin well, which may be due to that the interactions between the C bases and G-quadruplex affect their target binding capability. When compared to biotinylated aptamer immobilized on a streptavidin surface, polyT aptamer printed directly on plain glass showed comparable affinity. Direct immobilization of TBA on nonfunctionalized silicon dioxide wafer and its binding towards thrombin has also been demonstrated. Our results showed that using polyT-tagged aptamer probes directly immobilized on unmodified glass and SiO₂ surface is a robust, very straightforward, and inexpensive method for preparing biosensors.

We present a multi-modality optical sensing platform employing integrated Vertical Cavity Surface Emitting Lasers (VCSELs), photodetectors, and filters suitable for portable, real-time analyte detection in aqueous environments. Fluorescence and refractive index sensors designed to utilize visible and near-infrared VCSELs for low background absorption from analyte delivery fluids are described. We demonstrate in vitro fluorescence sensing of Cy5.5 dye with a detection sensitivity of 5 nM and photonic crystal slab refractive index sensing with tunable GaAs-based 670 nm VCSELs. This compact, parallel sensor architecture enables multiplexed, cost-effective on-chip biosensing.

Super-resolution imaging using a three-dimensional metamaterials nanolens has been recently reported [B. D. F. Casse et al. Appl. Phys. Lett. 96, 023114 (2010)]. This nanolens, consisting of bulk gold nanowires embedded in alumina template, can transport with low-loss object details down to λ/4 (λ, wavelength) length scales, over significant distances of the order of 6λ. Here, we present validation of the super-resolution imaging by the nanolens through extensive control experiments. We also analytically show that the nanowire array medium supports a quasi transverse electromagnetic mode (TEM) with flat isofrequency contours, which is a requirement for super-resolution imaging. We numerically compute the optical transfer function to quantify the imaging quality of the lens and show that the theoretical resolution of this nanolens is λ/5. Additionally, we demonstrate the broadband nature of the lens in the spectral region 1510 nm to 1580 nm. Finally, imaging of a large object (~ 52λ in diameter), with subwavelength features, is presented.

The refractive index of magnetic fluid may be changed by external magnetic field. Therefore, through measuring its refractive index, the intensity of the magnetic field can be obtained. Fiber Bragg grating (FBG) is sensitive to the refractive index surrounding its cladding when the diameter of cladding is reduced to a certain degree. In order to prove the sensitivity of the thinned fiber Bragg grating to refractive index, series of experiments, such as the fabrication of thinned FBG, tuning magnetic field and obtaining spectral characterizations, are carried out. After the FBG is etched for 193 minutes by HF solution at 22%, the FBG starts to be sensitive to the surrounding refractive index and the Bragg wavelength decreases sharply with the etching process. The thinned FBG has been packaged to a container filled with MF. Using a tunable magnetic field the refractive index of magnetic fluid could be changed and the Bragg wavelength of FBG shifts correspondingly. Both the wavelength and the light power are sensitive to magnetic field and the sensitivity of wavelength is 2.3 pm/mT at least in the condition of proposed experiment. The obtained results show that the thinned FBG sensor with magnetic fluid could be applicable for magnetic field and current sensing.

In this paper we present computational and experimental results of dust particles that can be tuned to preferentially reflect or emit IR radiation within the 8-14 μm band. The particles consist of thin metallic subwavelength gratings patterned on the surface of a simple quarter wavelength cavity. This design creates distinct IR absorption resonances by combining the plasmonic resonance of the grating with the natural resonance of the cavity. We will show that the resonance peaks are easily tuned by varying either the geometry of the grating or the thickness of the cavity. Here, we present a computational design algorithm along with experimental results that validate the design methodology.

Surface enhanced Raman scattering (SERS) amplifies the small Raman scattering cross section of molecules toward distinguishable signal. It has been advanced into an influential label-free nondestructive method to measure vibrational fingerprints of molecular structures directly. We report here the demonstration of vapor detection of 2,4-dinitrotoluene (2,4-DNT), a typical manufacturing impurity of trinitrotoluene (TNT) based explosives, using reproducible ultrasensitive SERS substrates, i.e., assembled gold nanoparticles (GNPs) synthesized by a UV photoreduction method. The estimated detection limit was achieved 0.4 attogram, which corresponds to a sub-ppb DNT concentration in air. The 2,4- DNT molecules was noticeable within a minute of exposure to the DNT vapor at room temperature. The detection time was as short as only 2 seconds with 12 mW 785 nm laser excitation at the SERS substrate. Our study shows that larger GNPs (~ 117 nm in diameter) with higher density, an enhancement factor of 5.6x10⁶, exhibits the high sensitivity and the fast detection response, as compared to smaller and lower density GNPs. Dynamic depletion by laser heating indicates that our GNP based sensor is possible real time 2,4-DNT detection.

This paper gives a review of a proposed fully-distributed fiber-optic sensing technique based on a traveling long-period grating (LPG) in a single-mode optical fiber. The LPG is generated by pulsed acoustic waves that propagate along the fiber. Based on this platform, first we demonstrated the fully-distributed temperature measurement in a 2.5m fiber. Then by coating the fiber with functional coatings, we demonstrated fully-distributed biological and chemical sensing. In the biological sensing experiment, immunoglobulin G (IgG) was immobilized onto the fiber surface, and we showed that only specific antigen-antibody binding can introduce a measurable shift in the transmission optical spectrum of the traveling LPG when it passes through the pretreated fiber segment. In the hydrogen sensing experiment, the fiber was coated with a platinum (Pt) catalyst layer, which is heated by the thermal energy released from Pt-assisted combustion of H₂ and O₂, and the resulted temperature change gives rise to a measurable LPG wavelength shift when the traveling LPG passes through. Hydrogen concentration from 1% to 3.8% was detected in the experiment. This technique may also permit measurement of other quantities by changing the functional coating on the fiber; therefore it is expected to be capable of other fully-distributed sensing applications.

Fiber grating laser sensors have been attracting interest because of their high signal-to-noise ratio and narrow linewidth that permit high resolution sensing. According to the working principle, fiber grating laser sensors can be classified into two types: wavelength encoding sensor and polarimetric heterodyning sensor. The former converts measurrand into shift in the operation wavelength of the fiber laser, which is similar to that of fiber grating sensor. The latter converts measurrant into change in beat frequency between the two orthogonal polarization modes from the laser. Because the beat frequency is in radio frequency (RF) range, the polarimetric heterodyning sensor has distinctive advantages of ease of interrogation and avoidance of expensive wavelength measurement that is required for wavelength encoding sensors. In this paper, we report some of our recent works in fabrication of dual-polarization fiber grating lasers, development of polarimetric heterodyning fiber grating laser sensors for measurement of acoustic wave, acceleration, lateral force, displacement, electric current and hydrostatic pressure, and sensor multiplexing in RF domain.

The subject of light transmission through optically thin metal films perforated with arrays of subwavelength nanoholes has recently attracted significant attention. In this work, we present experimental and calculated results on optical transmission/reflection of the U-shaped nanoapertures for enhanced optical transmission and resolution. We propose different structure designs in order to prove the effect of geometry on resonance and enhanced fields. Theoretical calculations of transmission/reflection spectra and field distributions of U-shaped nano-apertures are performed by using 3-dimensional finite-difference time-domain method. The results of these numerical calculations show that transmission through the apertures is indeed concentrated in the gap region. Added to theoretical calculations we also performed a liftoff free plasmonic device fabrication technique based on positive resist electron beam lithography and reactive ion etching in order to fabricate U-shaped nanostructures. After transferring nanopattern on 80 nm thick suspended SiNx membrane using EBL followed by dry etching, a directional metal deposition processes is used to deposit 5 nm thick Ti and 30 nm thick Au layers. Theoretical calculations are supported with experimental results to prove the tunability of resonances with the geometry at the mid-infrared wavelengths which could be used for infrared detection of biomolecules.

A fiber-optic intrinsic Fabry-Perot interferometric (IFPI) sensor was fabricated in single-mode fiber using femtosecond (fs) laser. The fs laser was directly focused into the fiber core to form a local mirror by inducing the refractive index (RI) changes, and the F-P sensor was composed of two local mirrors and the fiber cavity between them. The measured spectrum has a high fringe visibility up to 10 dB. The temperature sensing characteristics of the F-P sensor were studied. Experiment results show that the reflection spectrum linearly shifts against the temperature with the sensitivity of 10.6pm/°C.

A high-sensitivity temperature sensor is demonstrated by coating a layer of polydimethylsiloxane (PDMS) on the surface of a silica toroidal microresonator on a silicon chip. Combining both the advantages of the WGM microcavity (with ultrahigh Q factor) and PDMS (with large thermal effect), the PDMS-coated microresonator is highly sensitive to the temperature change of the surroundings. We find that, when the PDMS layer becomes thicker, the fundamental WGM experiences a transition from red- to blue-shift with temperature increasing due to the negative thermal-optic coefficient of PDMS. The measured sensitivity (0.151 nm/K) is one order of magnitude higher than pure silica microcavity sensors. The ultra-high resolution of the temperature sensor is also analyzed to reach 10^-4 K. With both high sensitivity and resolution, the thermal sensor can be employed to monitor a slight temperature variation which cannot be realized with conventional temperature sensor. Its on-chip feature can also fulfill the demand for integration and miniaturization in optics.

In this paper, we demonstrate high optical quantum efficiency (90%) resonant-cavity-enhanced mid-infrared photodetectors fabricated monolithically on a silicon platform. High quality photoconductive polycrystalline PbTe film is thermally evaporated, oxygen-sensitized at room temperature and acts as the infrared absorber. The cavity-enhanced detector operates in the critical coupling regime and shows a peak responsivity of 100 V/W at the resonant wavelength of 3.5 μm, 13.4 times higher compared to blanket PbTe film of the same thickness. Detectivity as high as 0.72 × 10⁹cmHz^1/2W¹ has been measured, comparable with commercial polycrystalline mid-infrared photodetectors. As low temperature processing (< 160 °C) is implemented in the entire fabrication process, our detector is promising for monolithic integration with Si readout integrated circuits.

The concept of all-optically controlled, remotely actuated and interrogated, ultra-compact nonlinear-optical sensor which can be employed for environmental probing in remote or hostile locations is proposed and the underlying theory is developed. Backwardness of electromagnetic waves propagating in the negative-index metamaterials play critically important role in the proposed concept. Difference-frequency, three- and four-wave mixing processes are investigated and numerically simulated, which utilize uncommon coherent energy transfer from the control optical field to the contra-propagating negative-phase wave. Such conversion leads to parametric amplification of the incident signal and frequency-shifted wave generated in the direction of reflection. Extraordinary features of the proposed microscopic devices applied to sensing applications are discussed. Numerical experiments have been carried out to identify optimum operational requirements and the anticipated properties of the proposed sensor.

Raman spectroscopy has become an established method for determining the composition of gaseous samples at low temperatures (<1000°C). However, the design of a Raman sensor which operates at high temperatures (>1000°C) remains elusive. This work investigates the feasibility of high-temperature Raman spectroscopy utilizing a monolithic sapphire tube as a sample cell and signal collection optic. The insertion loss of small-diameter, single-crystal sapphire tubing is measured to be 0.26-0.40dB/cm, proving its potential for use as a short-distance waveguide. Relevant system losses are characterized for a fiber-based, reflection mode Raman sensor, and expected Raman signal powers are predicted by simulation for the gaseous combustion products of ethylene: N₂, CO, CO₂, H₂, and H₂O. The successful implementation of a Raman sensor as described by this research could enable real-time analysis of exhaust gases from a hydrocarbon combustor. Furthermore, the extension of Raman spectroscopy to high temperatures would be a critical step towards more precisely controlled, fuel-efficient technologies.

Current sensors always play a very important role in the power industry. For example, current sensors can provide the key information for measurement, control and relay protection. However, when the economic further develops and the level of current increases year by year, it is very difficult to meet the demand for current sensors based on conventional technology which is still the main stream. Novel current sensors always are pursued. A research focusing on the current sensor is the technology of fiber optic current sensor, because there is high resistance to electromagnetic interference in fiber optic sensors. Fiber Bragg grating (FBG) sensors have been applied in many fields and have gained great achievements. It is of great help to the current measurement if FBG current sensors are realized. In this paper, a novel FBG high-current sensor is developed based on magnetic coupling. The principle is described, such as the magnetic coupling, the structure of the sensor and the sensing data processing. Experiments are carried out, and the results show at least 60 pm wavelength shift with the change of 100A and 2563 pm wavelength shift when the current is 750A and a good repeatability. The results are in agreement with the principle and indicate that the proposed sensor is capable of measuring both dc and ac current.