Interferometric Sensor Array Research Articles

Plasmonic interferometers for label-free multiplexed sensing

We report a plasmonic interferometric biosensor based on a simple slit-groove metallic nanostructure that monitors the phase changes of surface plasmon polaritons resulting from biomolecular adsorptions. The proposed sensing scheme integrates the strengths of miniaturized plasmonic architectures with sensitive optical interferometry techniques. Sensing peak linewidths as narrow as 7 nm and refractive index resolutions of 1 × 10(-5) RIU were experimentally measured from a miniaturized sensing area of 10 × 30 µm(2) using a collinear transmission setup and a low-cost compact spectrometer. A high-density array of such interferometric sensors was also fabricated to demonstrate its potential for real-time multiplexed sensing using a CCD camera for intensity interrogation. A self-referencing method was introduced to increase the sensitivity and reduce sensor noise for multiplexing measurements. The enhanced sensing performance, small sensor footprint, and simple instrumentation and optical alignment suggest promise to integrate this platform into low-cost label-free biosensing devices with high multiplexing capabilities.

Highly Scalable Amplified Hybrid TDM/DWDM Array Architecture for Interferometric Fiber-Optic Sensor Systems

We present a distributed amplified hybrid dense wavelength division multiplexing (DWDM) and time division multiplexing (TDM) array architecture for large scale interferometric fiber-optic sensor array systems. This architecture employs a distributed Erbium doped fiber amplifier (EDFA) scheme to decrease the distribution loss among multiplexed wavelengths, and employs TDM at each wavelength to increase the total number of sensors that can be supported. The first experimental demonstration of this system is reported including results which show the potential for multiplexing and interrogating up to 4096 sensors using a single telemetry fiber pair with good system performance. The number of interrogation sensors could be further increased by increasing the number of wavelength channels. These architectures would be of great importance in the application of systems requiring very large number of sensors with limited telemetry cabling.

Plasmonic interferometric sensor arrays for high-performance label-free biomolecular detection

A plasmonic interferometric biosensor that consists of arrays of circular aperture-groove nanostructures patterned on a gold film for phase-sensitive biomolecular detection is demonstrated. The phase and amplitude of interfering surface plasmon polaritons (SPPs) in the proposed device can be effectively engineered by structural tuning, providing flexible and efficient control over the plasmon line shape observed through SPP interference. Spectral fringes with high contrast, narrow linewidth, and large amplitude have been experimentally measured and permit the sensitive detection of protein surface coverage as low as 0.4 pg mm(-2). This sensor resolution compares favorably with commercial prism-based surface plasmon resonance systems (0.1 pg mm(-2)) but is achieved here using a significantly simpler collinear transmission geometry, a miniaturized sensor footprint, and a low-cost compact spectrometer. Furthermore, we also demonstrate superior sensor performance using the intensity interrogation method, which can be combined with CCD imaging to upscale our platform to high-throughput array sensing. A novel low-background interferometric sensing scheme yields a high sensing figure of merit (FOM*) of 146 in the visible region, surpassing that of previous plasmonic biosensors and facilitating ultrasensitive high-throughput detection.

Full-Field Laser Vibrometer for Instantaneous Vibration Measurement and Non-Destructive Inspection

We describe a system for real-time, full-field vibrometry, incorporating features of high-speed electronic speckle pattern interferometry (ESPI) and laser Doppler velocimetry (LDV). Based on a 2D interferometric sensor array, comprising 16×16 parallel illumination and detection channels, the matrix laser vibrometer (MLV), captures full-field data instantaneously, without beam scanning. The instrument design draws on the advantages of scale offered by modern telecommunications fiber optic and digital electronics. The resulting architecture, comprising a compact measurement probe linked by fiber optic umbilical to a remote electronics unit, facilitates practical application to the full-field study of transient vibrations and rapid non-destructive inspection of composite materials.

Tunable Fabry–Perot-resonator-based fiber-optic white-light interferometric sensor array

A tunable Fabry-Perot-resonator-based fiber-optic white-light interferometric quasi-distributed sensing system permitting absolute length measurement in a remote reflective sensor array is proposed and demonstrated. The sensor reflective signals characteristics have been analyzed, and the relationship between light signal intensities and sensors number was given for multiplexing potential evaluation. The proposed sensing scheme will be useful for the measurement of strain distribution. An important application could be deformation sensing in smart structures. Experimentally, a four-sensor array has been demonstrated.

Twin multiplexing strain sensing array based on a low-coherence fiber optic Mach–Zehnder interferometer

A twin multiplexed white light interferometric fiber optic strain sensor array was designed and demonstrated. In this sensing system, based on a low-coherence fiber optic Mach–Zehnder interferometer, an optical path matching technique is used to demodulate each sensor. The strain sensor array consists of 2 × N sensing elements linked by N 3 dB couplers. When one of the fiber sensors has been used to measure the strain, the variation caused by the temperature can be compensated by the other sensor. The multiplexing capacity of the sensing scheme has been analyzed. The results shown that it is depend on the light source power. The maximum number of the twin fiber sensor size is 4 for light source with 35 μW, and 7 for light source with 3 mW, respectively. The experimental result with a two-coupler sensor array was conducted and demonstrated which confirm this. It is useful for temperature compensation of distributed strain measurement in smart materials or structures health monitoring.

AAO Nanowells: Synthesis, in-situ Growth Study, and Applications in Ultra-sensitive Chemical Detection

ABSTRACTAnodized aluminum oxide (AAO) membranes consist of locally highly ordered nanopores. The pore diameter (20-200 nm) and pore-to-pore distance are controlled through the anodizing voltage and the choice of etching solution. High aspect ratio over 1,000 can easily be achieved which makes AAO membranes the ideal templates for making nanowires and nanotubes. In this work, the early stage of nanopore formation was studied in-situ with the use of small angle x-ray scattering (SAXS) and glazing incidence GISAXS techniques. The nanopores were found to grow as a function of the square root of growth time. The resulting short nanopores or nanowells with length below 200 nm were further characterized with use of SEM and AFM. These AAO nanowells showed interference color. Their reflectance UV-Vis spectra indicated strong angular dependence and can be understood with a simple single layer (nanoporous alumina over aluminum) model. These spectra are influenced by the nanowells thickness and diameter. Therefore, large array of interferometric AAO nanowells sensors are possible. When these nanowells are coated with Ag or Au thin films, in addition to enhanced interference color, highly sensitive surface enhanced Raman scattering (SERS) effect has been observed. These results will be presented.

Large-scale remotely pumped and interrogated fiber-optic interferometric sensor array

We report a demonstration of a large-scale remotely interrogated remotely pumped fiber-optic, interferometric sensor array. The system is designed primarily for underwater acoustic applications where each sensor is configured as a hydrophone and a large number of sensors (i.e., up to /spl sim/500) are required to be interrogated through link lengths of several tens of kilometers. A system comprising of 96 sensors combined using time and dense wavelength-division multiplexing and interrogated through a 40-km fiber link is demonstrated. A remotely pumped erbium-doped fiber amplifier is incorporated into the array to increase the distance between the array and interrogation electronics. We describe the performance of our system and validate a previously published model.

Enhancement of multiplexing capability of low-coherence interferometric fiber sensor array by use of a loop topology

A novel technique for enhancing the multiplexing capability of low-coherence interferometric sensor array is proposed. The technique uses a fiber loop topology and allows for twice as many sensors as the conventional low-coherence reflectometry system to be multiplexed. Power budget and signal analyses for different sizes of sensor array are performed. A ten-sensor system was experimentally demonstrated and applied for quasi-distributed temperature measurement. An additional advantage of the technique is that it provides an extra degree of redundancy through the bidirectional interrogation of the sensor array and thus improves the system reliability.

Large-scale remotely interrogated arrays of fiber-optic interferometric sensors for underwater acoustic applications

The fiber-optic interferometric acoustic sensor array has established itself as a potential alternative to the conventional sonar array based on electroceramic transducers. In this paper, we discuss all the aspects of a large-scale fiber-optic interferometric sensor array. We review the basic operating principles of the fiber-optic interferometric sensor, signal processing, and multiplexing techniques, we present results from a noise model for a full size system, and we determine the benefit of incorporating a remotely-pumped optical amplifier in the array. As a practical example we describe the design and construction of a prototype array with 96 hydrophones incorporating a remotely pumped erbium-doped fiber amplifier, called the fiber-optic bottom mounted array, which is based on a dense wavelength division and time division multiplexed architecture. These arrays have applications in military sonar and seismic surveying.

Locating acoustic emission with an amplitude-multiplexed acoustic sensor array based on a modified Mach–Zehnder interferometer

We report on an amplitude-division-multiplexed interferometric sensor array for locating acoustic emission. Preliminary experiments were carried out with a modified Mach-Zehnder interferometer consisting of two sensing arms and a reference arm and demonstrated a one-dimensional location accuracy of a few centimeters. The system can be extended for two- and three-dimensional location of acoustic emissions by the addition of one or two more sensing arms, respectively, in the interferometer.

Large-scale interferometric fiber sensor arrays with multiple optical amplifiers

We report what we believe to be the first laboratory prototype of a fiber sensor array using multiple low-gain (5dB) remotely pumped amplifiers in a 10-rung ladder structure. Incorporating amplifiers improves the system noise figure to less than 20dB, compared with 32dB in an optimized passive array of the same size. Scalability to more than 300sensors per fiber pair while a high dynamic range (1microrad/ sensitivity) is maintained is demonstrated.

Polarization-induced fading in fiber-optic sensor arrays

The statistics of polarization-induced visibility fading is studied for fiber-optic interferometric (Michelson or Mach-Zehnder) sensor arrays made of either regular single-mode fibers or polarization-maintaining fibers. Performance is measured in terms of the probability to observe visibilities, all of which exceed a given value, for all members of the array. Very poor performance is obtained for arrays made of nonpolarization maintaining fibers, unless the input state of polarization is dynamically controlled to optimize the visibility of the worst sensor of the array. While the use of the more costly polarization-maintaining fibers could, in principle, solve this polarization-related fading problem, finite extinction ratios of couplers and splices make the performance of such arrays comparable to that of nonpolarization maintaining arrays with optimally controlled input-polarization.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Polarisation-induced visibility limits in interferometric fibre-optic sensor arrays

Polarisation-induced fading is analysed in Mach–Zehnder type interferometric fibre-optic sensor arrays. Given a sensor array configuration and the polarisation properties of individual elements, a procedure is presented to find an optimal input state of polarisation which maximises overall sensor visibility. It is shown that for both serial and parallel arrays with N sensor elements, the visibility of the worst-case sensor configuration can be maximised to a value of sin (π/2N).

Experimental investigation of polarisation-induced fading in interferometric fibre sensor arrays

The results of an experimental investigation of polarisation induced fading in multiplexed optical fibre interferometric sensor arrays is presented. Measurements, made on a ten-element all-fibre time-division multiplexed array, are analysed in terms of a general N-sensor system and compared with a simple theoretical model.

Demonstration of a hybrid time/wavelength division multiplexed interferometric fibre sensor array

A 14-element interferometric sensor array based on a hybrid time/wavelength division addressing scheme is reported. The system uses two time-division addressed sub-arrays operating at 790 nm and 835 nm which are addressed via common input/output fibres using WDM couplers. Preliminary results obtained show crosstalk levels < −50 dB electrical.

Multiplexed Mach-Zehnder ladder array with ten sensor elements

We report the first experimental demonstration of a tenelement interferometric fibre sensor array. The system topology is based on a ladder network of Mach-Zehnder sensor elements which are time-division multiplexed. Phase shift detection sensitivities ranging from 12 to 18μrad/√Hz at a frequency of 1 kHz are reported for the array.

Gross talk in a fiber-optic Fabry–Perot sensor array with ring reflectors

We demonstrate a fiber-optic interferometric sensor array based on the in-line Fabry-Perot configuration, which uses fiber ring reflectors to effect the low-reflectivity elements required between each sensor section. The intrinsic optical cross talk that occurs between the sensor sections owing to multiple reflections is analyzed and compared with experimental results obtained with a four-sensor system.

Demonstration of an eight-element time-division multiplexed interferometric fibre sensor array

We report the demonstration of an eight-element multiplexed interferometric fibre-optic sensor array based on timedivision addressing. The configuration gives rise to intrinsic optical crosstalk between sensor elements of the system, which is analysed and compared with experimental results.

Time-domain addressing of remote fiber-optic interferometric sensor arrays

This paper describes and analyzes a particular application of high duty-cycle time-division multiplexing to the separation and identification of signals from an interferometric sensor array. Using the method discussed here, the coherence length of the laser is no longer a severe design constraint. Also, the source phase-induced intensity noise which limits some other multiplexing methods may be overcome, leading to a higher sensitivity. The arrays of all-passive remote sensors exhibit minimal crosstalk between sensors, and have downlead insensitivity. A synthetic heterodyne demodulation technique prevents environmentally induced signal fading. Analysis includes coupling ratios for all directional couplers in the system, signal and noise spectra, minimum detectable phase shift, and the effect of ac coupling on noise and crosstalk. An experimental all-fiber implementation of a two sensor array has yielded a measured sensitivity of approximately 10 μrad/ \sqrt{Hz} over a range of signal frequencies, and a crosstalk level of better than 55 dB.