This PDF file contains the front matter associated with SPIE Proceedings Volume 7682, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

Multiplex assays have attracted considerable interest to meet the growing demand for clinical diagnosis, gene expression, drug discovery, and so on. Most of the assays are based on molecular binding or recognition events. In this point, different probe biomolecules could be immobilized to encoded carriers, which can be mixed and subjected to an assay simultaneously and then many binding events can be distinguished by their codes. Herein we summarize our work on photonic beads as novel encoded carriers of biomolecules in multiplex bioassays. We have successfully fabricated different kinds of encoded photonic beads with controlled size and monodispersity by microfluidic device. The beads with opal structure and inverse opal structure could be used in multiplex labeling detection and label-free detection of biomolecules, respectively. These photonic beads provide a new coding strategy of suspension array for low cost, sensitive and simultaneous multiplex bioassay.

This paper reports some of our recent work on in-line devices based on air-silica microstructrue optical fibers. These devices are fabricated by use of a CO₂ laser/a femtosecond infrared laser and include strong long period gratings in index-guiding fibers and air-core photonic bandgap fibers, in-fiber polarizers, polarimeters, and modal interferometers. Applications of such devices for strain, temperature, directional bend, twist, and gas sensing are discussed.

Long period fiber grating (LPFG) has been attracted much attention for use in optical sensing applications and optical communication systems. Compared with a regular LPFG, the phase shift long period fiber grating (PS-LPFG) has shown certain unique advantages such as higher sensitivity and potentials for simultaneous measurements of multiple parameters. This paper presents the fabrication and characterization of PS-LPFG by CO2 laser point-by-point irradiations. We emphasis on the difference between LPFG and PS-LPFG as optical sensors for measurement of strain, temperature and refractive index.

In this work, we describe a novel approach for detecting the HER2/neu extra-cellular domain (ECD) protein in human serum samples using the opto-fluidic ring resonator (OFRR). OFRR sensing technology that incorporates microfluidics and optical sensing methods to achieve rapid label free detection in a small and low cost platform. In this study, HER2 proteins were spiked in PBS running buffer and serum at varying concentrations. Concentrations of the HER2 protein were adjusted in serum to levels typical of breast cancer patients that show over-expression of this particular beast cancer biomarker. The OFRR was modified with a biologically functional layer to efficiently capture the HER2 biomarker and produce a sensing signal through interaction with the evanescent field of the optical resonator. Results show effective capture of HER2 at medically relevant concentrations in serum and was achieved for concentrations as low as 13 ng/mL and ranged to above 100 ng/mL. This work will lead to a device that can be used as a tool for monitoring disease progression in a low cost sensing setup.

Optical microcavities with high quality factors (Q factor) and small mode volumes have shown their potentials in various sensing applications. Here we experimentally demonstrate the real-time detection of single nanoparticles down to 30 nm in radius, using an ultra-high-Q microtoroid on a silicon chip. Mode splitting phenomenon of WGMs caused by their strong interactions with a single nanoparticle is utilized as the sensing signal. Frequency and linewidth information of the split modes is used to accurately derive the size of the particle detected. Theoretical calculations and finite element simulations are in good agreement with the experimental results. The mode splitting technique provides a self-reference scheme that is more immune to noise than the techniques based on the detection of changes of a single mode.

Whispering gallery mode (WGM) optical microcavities trap light in micro-scale volumes by continuous total internal reflection which leads to enhancement of light intensity within a confined region and longer photon lifetime. Consequently, light-matter interaction is enhanced making the WGM resonator an extremely sensitive platform for the detection of perturbations in and around the resonator. Here, we report mode-splitting in monolithic ultra-high-Q WGM microcavities for real-time and in-situ detection of single nanoparticles. We investigate experimentally and theoretically particle detection and sizing at single nanoparticle resolution using the mode-splitting technique. Theoretical calculations are in good agreement with the experimental results. The mode-splitting effect provides a 'self-reference sensing' technique that can overcome the limitations of current resonator-based sensors and in the meantime keep the advantages offered by resonant structures for high-performance sensing.

We report that by using a single mode coupled microcavity laser, we successfully realized a sensitivity of 80 pg/ml for detecting BSA. The detecting scheme also works for other bio samples. The result proves that active sensing with microcavity laser can achieve ultrahigh sensitivity. Further analysis shows that the ultra-sensitivity comes from the slight change of coupling coefficient between the two coupled microcavities.

We theoretically investigate a sensitivity-enhanced sensing by using a coupled optical microcavities structure in which a sharp asymmetrical Fano resonance is supported. The coupled mcirocavities gives rise to faster changes in output transmission than that from a single cavity.

A mechanical resonator was fabricated on the tip of a standard single mode fiber with outer diameter of 125 μm. The fabrication process involved a single-mode to a multimode fiber splicing, sputtering coating of a submicron gold nanofilm, focused ion beam (FIB) patterning and chemical wet etching. A micro-vibrating disk with suspension arms was formed on the sensing fiber tip, the resonance frequency of the vibrator is sensitive to mass loading on its surface. Vibration was excited by laser excitation via the radiation pressure and the photo-thermal effect and detected by a CW laser beam at another wavelength. The detected intensity of the fundamental and higher order harmonics can be monitored for resonance frequency determination. The excitation and detection beams were multiplexed within a single fiber link, which makes the sensor compact and versatile. The resonator maintained relatively high quality factor in air and was successfully applied to the analysis of layer-by-layer electrostatic self-assembly and immuno-sensing.

Surface Plasmon Resonance imaging (SPRi) is a label-free technique for the quantitation of binding affinities and concentrations for a wide variety of target molecules. Although SPRi is capable of determining binding constants for multiple ligands in parallel, current commercial instruments are limited to a single analyte stream and a limited number of ligand spots. Measurement of target concentration also requires the serial introduction of different target concentrations; such repeated experiments are conducted manually and are therefore time-intensive. Likewise, the equilibrium determination of concentration for known binding affinity requires long times due to diffusion-limited kinetics to a surface-immobilized ligand. We have developed an integrated microfluidic array using soft lithography techniques for SPRi-based detection and determination of binding affinities for DNA aptamers against human alphathrombin. The device consists of 264 element-addressable chambers of 700 pL each isolated by microvalves. The device also contains a dilution network for simultaneous interrogation of up to six different target concentrations, further speeding detection times. The element-addressable design of the array allows interrogation of multiple ligands against multiple targets, and analytes from individual chambers may be collected for downstream analysis.

Detection of pollution gas is important in environmental and pollution monitoring, which can be used widely in mining and petrochemical industry. Fiber optical spectrum absorption (FOSA) at near-IR wavelength is widely used in gas detection due to its essential advantages. It has attracted considerable attention, and there are several types and methods in FOSA. Wavelength modulation technique (WMT) is one of them, which will improve the gas detection sensitivity dramatically. This technique can be realized by detecting the intensity of the second-harmonic component signal. Intra-cavity laser spectroscopy (ICLS) is another alternative technique for high sensitivity absorption measurement. With an absorber directly placed within the laser cavity, a short absorption cell can be transformed into a high sensitivity system. But the practical sensitivity is obviously less than the theoretical value. The authors did some works in these fields and have obtained some remarkable progress. With broad reflectors instead of FBG as mirror of the cavity and wavelength sweep technique (WST), several absorption spectra of detected gas can be collected. And the detection sensitivity can be enhanced sharply by averaging the results of each spectrum, with acetylene sensitivity less than 100 ppm . When ICLS is used combined with WST and WMT, the detection sensitivity of acetylene can be enhanced further. The sensitivity is less than 75 ppm. By using FBGs as wavelength references, the absorption wavelength of the detected gas is obtained, which can be used to realize gas recognition. The system is capable of accessing into fiber intelligent sensing network.

We demonstrate experimentally the light coupling between two types of optical fiber devices, including the long period fiber gratings (LPFGs) and fiber tapers. Optical power transfer is achieved through evanescent field coupling between the cladding modes. The output spectra from the LPFG couplers exhibit band-pass/band-rejection pattern, which could be used as add/drop filters. The output spectra from the fiber taper couplers show an interference pattern similar to a Mach-Zehnder interferometer. By fixing the fiber devices in a capillary glass tube, we demonstrated a miniaturized coupler for displacement sensing.

A fiber optical sensor has been developed by coating proton conducting perovskite oxide (Sr(Ce_0.8Zr_0.1)Y_0.1O_2.95, SCZY) thin film on the long-period fiber grating (LPFG) for high temperature in situ measurement of bulk hydrogen in gas mixtures relevant to the fossil- and biomass-derived syngas. In this paper, we investigate in the H₂-sensing mechanism of the SCZY-LPFG sensor. The high temperature H₂ adsorbance in the SCZY, the SCZY electric conductivity in H₂, and the resonant wavelength shift of the SCZY-LPFG (Δλ_R,H2) have been experimentally studied to understand the effect of operation temperature on the sensor's sensitivity to H₂. Because of the activation process of the H₂ reaction with the perovskite oxide, increasing temperature benefits the H₂ uptake in the SCZY phase and the sensitivity of the SCZY-LPFG sensor. However, the thermal stability of the LPFG and the microstructure of the SCZY nanocrystalline film limit the application temperature of the fiber optic sensor.

We fabricate optical fiber with the same dimensions as standard communication single mode fiber (SMF) with the glass core surrounded by 40 to 60 nm thick lithium niobate (LiNbO₃) film as schematically shown in Fig 1. Lithium Niobate Cylinder Fiber (LNCF) can be used as strain sensor and sonar detector. We use the LNCF in a mode where the strain causes a change in the light propagating through the fiber.

We present an improved microfabricated sound localization sensor for unobtrusive surveillance systems inspired by the tympanic membranes of the parasitoid fly, Ormia ochracea. The device consists of two silicon diaphragms mechanically coupled by a suspended beam that amplifies the difference in time response, dependent on the incident angle of the sound source. Fabrication techniques were modified to reduce residual stresses and improve device uniformity. Enhanced acoustic cues for devices with central pivoting anchors were measured with laser Doppler vibrometry. Device responses to weak excitations demonstrated good sensitivity over environmental noise. An order of magnitude in time difference amplification was measured at 90° incident angles with a directional sensitivity of .39μs/degree. These results provide a foundation for realizing an accurate bio-inspired MEMS directional microphone.

Optical foveated imaging using liquid crystal spatial light modulators has received considerable attention in the recent years as a potential approach to reducing size and complexity in wide-angle lenses for high-resolution foveated imaging. In this paper we propose a very compact design for an F/2.8 visible monochromatic foveated optical system covering a total field-of-view of 80 degrees and capable of achieving a resolution in excess of 100 MPixels. The diffraction efficiency and image quality of the foveated optical system are estimated. The foveated optical system is compared to equivalent conventional wide-angle lenses in terms of size, complexity and image quality. Fabrication and assembly tolerances as well as limitations of the current transmissive LC SLM technology are taken into consideration.

A new sensor system, whose functionality is not reliant on mass spectrometric or ionization methods, is combined with a substrate technology which allows for separately optimized control circuits and standardized advanced sensors in a simple packaging methodology to foster an entirely new generation of modular optical sensors. These sensors will be based on biologic and chromic compounds. The compounds will utilize reversible reaction chemistry to enable self cleaning. The detector's operation is based on simple changes in absorbance, reflectance, color, or other optical properties. The time to saturation of the sensor will determine the relative concentration in the air. A detection scheme based on these properties will function in high background levels and also be able to pick up low level concentrations as well.

Distributed feedback (DFB) laser diodes nowadays provide stable single mode emission for many different applications covering a wide wavelength range. The available output power is usually limited because of catastrophical optical mirror damage (COD) caused by the small facet area. For some applications such as trace gas detection output powers of several ten milliwatts are sufficiently high, other applications like distance measurement or sensing in harsh environments however require much higher output power levels. We present a process combining optimizations of the layer structure with a new lateral design of the ridge waveguide which is fully compatible with standard coating and passivation processes. By implementing a large optical cavity with the active layer positioned not in the middle of the waveguide layers but very close to the upper edge, the lasers' farfield angles can be drastically reduced. Furthermore, the travelling light mode can be pushed down into the large optical cavity by continuously decreasing the ridge waveguide width towards both laser facets. The light mode then spreads over a much larger area, thus reducing the surface power density which leads to significantly higher COD thresholds. Laterally coupled DFB lasers based on this concept emitting at wavelengths around 976 nm yield hitherto unachievable COD thresholds of 1.6 W under pulsed operation. The high mode stability during the 50 ns pulses means such lasers are ideally suited for high precision distance measurement or similar tasks.

Spatial Domain Multiplexing (SDM) is a novel technique in optical fiber communications. Single mode fibers are used to launch Gaussian beams of the same wavelength into a multimode step index fiber at specific angles. Based on the launch angle, the channel follows a helical path. The helical trajectory is explained with the help of vortex theory. The electromagnetic wave based vortex formation and propagation is mathematically modeled for multiple channels and the results are compared against experimental and simulated data. The modeled output intensity is analyzed to show a relationship between launch angle and the electric field intensity.

Spatial Domain Multiplexing (SDM) is a novel optical fiber multiplexing technique where multiple channels of the same wavelength are launched at specific angles inside a standard step index multimode carrier fiber. These channels are confined to specific locations inside the fiber and they do not interfere with each other while traversing the length of the fiber. Spatial filtering techniques are employed at the output end to separate, route and process the individual channels. These skew ray channels inside the SDM system follow a helical trajectory along the fiber. The screen projection of the skew rays resembles a circular polygon. A ray theory based mathematical model of the SDM system is presented and simulated as well as experimental data is compared to the model predictions. This ray theory model utilizes launch point, input incidence angle, and point of incidence on fiber to explain the behavior of the individual channels. Thus the vector approach to propagation allows us to predict the effects of pulse spreading in the SDM system. The results showed that the skew ray trajectory is sensitive to input incidence angle. Similarly changing the launch point, while maintaining the angle of incidence constant with the z axis, can drastically affect the skew ray trajectory.

The article was based on the technology and principle of DWDM, which was widely used in optical fiber communication systems, and made use of filter curve and technology of WDM into multichannel dynamic measurements. The technology of the investigation was based on the passive demodulation technologies. The samling rate of the real-time high-speed mutilchannel fiber Bragg grating monitoring system can reach 200KHz, which can both meet the needs of static and dynamic measurement and achieve the monitoring in dynamic environment. In order to adapt the requirement of static and dynamic measurement, increasing the sampling and transmission speed of the fiber grating demodulation is needed. In this article, the wavelength demodulation range of the system is about 0.7 nm, the precision can be 10~17 pm, and transmission interface is based on the USB 2.0, which speed is fast enough for the use of our monitoring system.

We report an approach to achieve simultaneous measurement of refractive index and temperature by using a Mach- Zehnder interferometer realized on a tapered single-mode optical fiber with the advantages of low-cost simple fabrication technique. Electrical arc method has been adopted to fabricate the abrupt tapers. The attenuation peak wavelength of the interference with specific order in the transmission spectrum shifts with the changes in the environmental refractive index and temperature. Experiments indicated the corresponding sensitivities of -23.188 nm/RIU (refractive index unit) (blue-shift) and 0.071 nm/°C (red-shift) for the interference orders of 169, respectively.