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This paper presents a method for characterizing electric field profiles of radio frequency (rf) quadrupole ion trap structures using sensors based on slab coupled optical-fiber sensor (SCOS) technology. The all-dielectric and virtually optical fiber-sized SCOS fits within the compact environment required for ion traps and is able to distinguish electric field orientation and amplitude with minimal perturbation. Measurement of the fields offers insight into the functionality of traps, which may not be obtainable solely by performing simulations. The SCOS accurately mapped the well-known field profiles within a commercially available three-dimensional quadrupole ion trap (Paul trap). The results of this test allowed the SCOS to map the more complicated fields within the coaxial ion trap with a high degree of confidence as to the accuracy of the measurement. Figure ᅟ

In this paper we measure for the first time the full-spectral response of a fiber Bragg grating (FBG) sensor subjected to vibration. We consider two cases: with and without an initial spectral distortion due to non-uniform strain along the length of the FBG. Previous work has measured only the dynamic response at a single wavelength which is valid when no spectral distortion is present. FBG sensors are mounted near the notch tip on a double edge notch specimen that is also subjected to harmonic vibration. We measure the full-spectral response of the FBG at 100 kHz applying an interrogator recently developed by the authors. The measurements of the FBG response with an initial spectral distortion clearly show the transient response and are verified through simulation. Finally, we demonstrate that the use of the high-speed, full-spectral interrogator permits the separation of the spectral distortion and the harmonic vibration from the FBG response signal through classical filtering and can therefore be applied to measure non-uniform strain fields in noisy environments.

We report the development of a temporally stable in-fiber electric field sensor using electro-optic (EO) polymer. The design consists of partially replacing the core of a D-fiber with AJL8/APC EO polymer resulting in a device insertion loss less than 2 dB. The design method is presented for the optimization of the hybrid waveguide. The resulting design is demonstrated to have an Epi of 134.6 MV/m at a modulation frequency of 990 MHz, which exhibited no appreciable temporal decay over a time span of over 200 hours and a sensitivity of 7.76 V/(m sqrt(Hz)). The design of the sensor packaging is also presented, which has an outer diameter of 1.5 mm. Mechanical tests demonstrate that the sensor withstands 17 rotations, a bending radius of 0.11 cm, and a tensile force of 4.5 N, confirming that the sensors are mechanically robust.

This paper shows a method allowing electric field sensing in high vibration environments. The vibration sensitivity is reduced using a push-pull configuration and external phase modulation. This paper provides both theoretical description and experimental verification.

An undergraduate design project is described in which a free-space optical communications link is constructed. The interest and motivation for the students is achieved by using a visible laser and constructing a complete system by using the digital output of a CD/DVD player and an audio receiver to transmit music over the free-space link. In addition to providing a high-level technical experience, the project also teaches multidisciplinary teamwork and emulates a real working environment; it is relatively low cost, divisible into modules, and adaptable. An overview of the project is included with representative designs and information.

One of the most common methods used to measure high voltage is using a voltage divider. While this method is fairly reliable for most low frequency high voltage measurements, the voltage divider encounters difficulty when measuring higher frequency voltage signals. In these instances, the signal measured by the voltage divider becomes susceptible to distortion and inaccuracy. One solution to measuring voltages where a voltage divider would not suffice is using an electrode structure in conjunction with a fiber-based electric field sensor. A high voltage generator was constructed utilizing automotive ignition coils and was used in a capacitor-charging circuit. The voltage on the capacitor was measured using a common resistive voltage divider as well as with a fiber-based electric field sensor. Where a resistor divider was not reliable in characterizing the system, the optical sensor was successful in measuring the charge and discharge voltages of the capacitor circuit.

We describe the application of SCOS technology in non-intrusive, directional and spatially localized measurements of high electric fields. When measuring electric fields above a certain threshold, SCOS measurement sensitivity starts varying to a great extent and the linear approximation that assumes sensitivity to be constant breaks down. This means that a comprehensive nonlinear calibration method is required for accurate calibration of both low and high electric fields, while linear calibration can only be accurately applied for low fields. Nonlinear calibration method relies on the knowledge of the variability of sensitivity, while linear calibration relies on approximation of sensitivity with a constant value, which breaks down for high fields. We analyze and compare the two calibration methods by applying them to a same set of measurements. We measure electric field pulses with magnitudes from 1 MV/m to 8.2 MV/m, with sub-300 ns rise time and fall-off time constant of 60 μs. We show that the nonlinear calibration very accurately predicts all measured fields, both high and low, while the linear calibration becomes increasingly inaccurate for fields above 1 MV/m.

This paper presents a simple low-power control circuit intended to manage the power within a remote autonomous microsystem hybrid power supply. A hybrid power supply has only recently been discussed in the literature as a microsystem power source solution. The power management circuitry, which is a key component within a hybrid power supply, has not been adequately explored. Although a variety of components could have been implemented, the control circuit in this paper was designed for a hybrid power supply that utilizes a Ni/Zn microbattery and silicon solar cell. The circuit also employs a shunt architecture powered only by the solar cell to minimize the overall energy consumption of the hybrid power supply. The control circuit consumes a maximum of 7 /spl mu/A and appropriately manages power even when the hybrid power supply is connected to a microsystem and is experiencing environmental variations. Details of the control circuit are discussed and simulations combined with experimental results demonstrate its performance.

The push-pull slab-coupled optical sensor measures a localized single electric field component with the advantage of reducing adverse strain effects for sensing in harsh vibrating environments. Its miniature size makes it ideal for compact environments.

In this paper we investigate the linear displacement bistable mechanism (LDBM) for use in microrelays. The LDBM, thermal actuators and contacts are integrated to demonstrate a relay design. The performance of the relay is characterized using relay performance metrics, including size (1.92 mm2), contact force (23.4 μN), switching time (340 μs), breakdown voltage (>475 V) and isolation (>235 V). The actuation voltage and current are 11 V and 85 mA, respectively. The ac characteristics, including contact-to-contact crosstalk and ac isolation are also measured. The testing results demonstrate that it is feasible to use the LDBM as a microrelay and that it has potential for use in future applications.

This paper describes the characteristics of microbatteries suitable for use in a hybrid micropower supply for powering autonomous MEMS and other microsystems. The hybrid power supply includes an energy conversion device, microscopic batteries for energy storage, and control/interface circuitry. Comparison of the hybrid approach with single power sources (either a battery or energy conversion device alone) shows that it offers several potential advantages including reduced size, increased flexibility, long lifetime and increased reliability. Such an approach is well suited to the expected duty cycles of remote microsensors. Realization of the advantages of a hybrid system depends on the availability of a battery with the required characteristics. Initial experimental results demonstrate the feasibility of fabricating microbatteries with the proper characteristics and the use of these batteries as part of a hybrid micropower supply. It is anticipated that hybrid micropower supplies with suitable microbatteries will play a critical role in the successful implementation of a wide variety of autonomous microsystems.

We demonstrate the measurement of and applications for reflected spectral signatures obtained from FBG sen- sors in dynamic environments. Three uses of the spectral distortion measurements for monitoring of airframe structures are presented: the measurement of the dynamic response of a laminated plate to an impact event; the measurement of damage induced spectral distortion in a thin plate during vibration loading; and the measurement of the change in dynamic response of an adhesively bonded joint with the progression of fatigue damage.

This paper presents an overview of non-intrusive electric field sensing. The non-intrusive nature is attained by creating a sensor that is entirely dielectric, has a small cross-sectional area, and has the interrogation electronics a long distance away from the system under test. One non-intrusive electric field sensing technology is the slab coupled optical fiber sensor (SCOS). The SCOS consists of an electro-optic crystal attached to the surface of a D-shaped optical fiber. It is entirely dielectric and has a cross-sectional area down to 0.3mm by 0.3mm. The SCOS device functions as an electric field sensor through use of resonant mode coupling between the crystal waveguide and the core of a D-shaped optical fiber. 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. An electric field changes the refractive index of the slab causing a shift in the spectral position of the resonant modes. This paper describes an overview of the SCOS technology including the theory, fabrication, and operation. The effect of crystal orientation and crystal type are explained with respect to directional sensitivity and frequency response.

Ion traps are widely used in the field of mass spectrometry. These devices use high electric fields to mass-selectively trap, eject, and count the particles of a material, producing a mass spectrum of the given material. Because of their usefulness, technology pushes for smaller, more portable ion traps for field use. Making internal ion trap field measurements not yet feasible because current electric field sensors are often too bulky or their metallic composition perturbs field measurements. Using slab coupled optical sensor (SCOS) technology, we are able to build sensors that are compatible with the spacing constraints of the ion trap. These sensors are created by attaching a nonlinear crystal slab waveguide to an optical fiber. When a laser propagates through the fiber, certain wavelengths of light couple out of the fiber via the crystal and create “resonances” in the output light spectrum. These resonances shift in proportion to a given applied electric field, and by measuring that shift, we can approximate the electric field. Developing a sensor that can effectively characterize the electric fields within an ion trap will greatly assist in ion trap design, fabrication, and troubleshooting techniques.

We present an optical fiber non-intrusive sensor for measuring high voltage transients. The sensor converts the unknown voltage to electric field, which is then measured using slab-coupled optical fiber sensor (SCOS). Since everything in the sensor except the electrodes is made of dielectric materials and due to the small field sensor size, the sensor is minimally perturbing to the measured voltage. We present the details of the sensor design, which eliminates arcing and minimizes local dielectric breakdown using Teflon blocks and insulation of the whole structure with transformer oil. The structure has a capacitance of less than 3pF and resistance greater than 10 GΩ. We show the measurement of 66.5 kV pulse with a 32.6μs time constant. The measurement matches the expected value of 67.8 kV with less than 2% error.

The teaching laboratory can be an invaluable component of an undergraduate electromagnetics curriculum. This goal of this article is to illustrate several simple but effective microwave-design laboratory projects, involving both system- and component-level design experiences, based upon radar and wireless communications applications. The projects highlighted include a Doppler radar, a simple synthetic aperture radar (SAR), and wireless links using amplitude and frequency-modulation schemes. Students use modern computer-aided design (CAD) tools, coupled with planar technology.

The calculus of differential forms has significant advantages over traditional methods as a tool for teaching electromagnetic (EM) field theory. First, films clarify the relationship between field intensity and flux density, by providing distinct mathematical and graphical representations for the two types of fields. Second, Ampere's and Faraday's laws obtain graphical representations that are as intuitive as the representation of Gauss's law. Third, the vector Stokes theorem and the divergence theorem become special cases of a single relationship that is easier for the student to remember, apply, and visualize than their vector formulations. Fourth, computational simplifications result from the use of forms: derivatives are easier to employ in curvilinear coordinates, integration becomes more straightforward, and families of vector identities are replaced by algebraic rules. In this paper, EM theory and the calculus of differential forms are developed in parallel, from an elementary, conceptually oriented point of view using simple examples and intuitive motivations. We conclude that because of the power of the calculus of differential forms in conveying the fundamental concepts of EM theory, it provides an attractive and viable alternative to the use of vector analysis in teaching electromagnetic field theory.

An efficient full-wave analysis technique for one-dimensional optical domains, known as the recursive Green's function method (RGFM), is presented for evaluation of distributed feedback (DFB) laser cavities with arbitrary material profiles. The method first constructs the Green's function of an inhomogeneous domain and subsequently uses Green's theorem to determine the laser optical field, lasing wavelength, and threshold gain. The technique is applied to investigate the performance of three DFB laser structures: a chirped-grating configuration, a modulated stripe width design, and a reduced duty cycle complex-coupled device. These structures are evaluated in terms of their single-mode lasing behavior and the uniformity of the optical field within the cavity.

We present a new type of fiber Bragg grating (FBG) that can be used in high-temperature sensing applications. We use the flat side of a D-shaped optical fiber as a platform to etch the grating into the surface of the fiber. Because the grating becomes a physical feature of the fiber, it is not erased at high temperatures as are standard FBGs. These surface relief fiber Bragg gratings will operate up to high temperatures. We provide a brief explanation of the fabrication process and present our results for operation up to 1100/spl deg/C.

This paper presents improvements to slab-coupled optical fiber sensors for electric-field sensing. The sensors are comprised of a potassium titanyl phosphate (KTP) crystal mounted on a D-fiber. The improvements are based on changing the crystal orientation, which enhances sensitivity due to a combined increase in the effective electro-optic coefficient and electric-field penetration into the KTP crystal. The paper provides a detailed comparison of the improved sensor, which uses x-cut KTP to the previous sensor design using z-cut KTP. The measurements show an 8.6× improvement in the sensitivity.

One challenging need for inspection capabilities is in adhesively bonded joints between composite components, a common location of premature failure in aerospace structures. In this work we demonstrate that dynamic, full spectral scanning of FBG sensors embedded in the adhesive bond can identify changes in bond quality through the measurement of non-linear dynamics of the joint. Eighteen lap joint specimens were fabricated with varying manufacturing quality. Ten samples also included fiber Bragg grating (FBG) sensors embedded in the adhesive bond for real-time inspection during a simulated flight condition of these single-lap joints. Prior to testing, pulse phase thermography imaging of the pristine specimens revealed defects such as air bubbles, adhesive thickness variations, and weak bonding surface between the laminate and adhesive. The lap joint specimens were then subjected to fatigue loading, with regular interrogation of the FBG sensors at selected load cycle intervals. The FBG data was collected during vibration loading of the lap joint to represent an in-flight environment. Changes in the lap joint dynamic response, including the transition to non-linear responses, were measured from both the full-spectral and peak wavelength FBG data. These changes were correlated to initial manufacturing defects and the progression of fatigue-induced damage independently measured with pulse phase imaging and visual inspections of the failure surfaces.

When fiber Bragg gratings (FBG) are tightly packed in a mesh and their peaks get close at a distance on the order of individual FBG spectrum widths, they start overlapping and there is a distance below which both peaks won’t be detectable anymore using standard peak detection method. Ability to determine locations of individual peaks even after they overlap allows more gratings in a mesh and an increase in shape sensing resolution. We use a linear interpolation method to estimate peak locations when peaks overlap and become undetectable with standard peak finding technique. We test this algorithm on experimentally obtained data and compare peak locations obtained by the algorithm to exact peak locations. We analyze the error to show that algorithm performs well when velocity of peaks stays uniform during peak crossing. However, the error rapidly increases if the velocity changes during crossing and the maximum error can occur in a situation when peaks change direction during peak crossing.

In this study we evaluate the measurements of a fiber Bragg grating (FBG) sensor embedded at the adhesive layer of a single composite lap joint subjected to harmonic excitation after fatigue loading. After a fully-reversed cyclic fatigue loading is applied to the composite lap joint, the full spectral response of the sensor is interrogated in reflection at 100 kHz during two states: with and without an added harmonic excitation. The dynamic response of the FBG sensor indicates strong nonlinearities as damage progresses. The short-time Fourier transform (STFT) is computed for the extracted peak wavelength information to reveal time-dependent frequencies and amplitudes of the dynamic FBG sensor response. Pulse-phase thermography indicates a progression in defect size at the adhesive layer that strongly suggests non-uniform loading of the FBG sensor.

We present a fiber Bragg grating (FBG) interrogation method using a micro-controller board and optical filter that achieves high strain sensitivity and high dynamic range. This interrogation method allows high sensitivity detection of ultrasonic waves superimposed on low-frequency (on the order of 100Hz) vibrations of arbitrary magnitude. One possible application is in-situ structural health monitoring of windmill blades exposed to strong winds by using FBG sensors for detection of ultrasonic waves. Interrogator operation is based on the edge filtering method using a broadband source, fiber Fabry-Perot filter and a micro-controller board which acts as a control feedback loop that locks the filter wavelength to the mid-reflection point on the FBG spectrum. Wavelength locking method allows high sensitivity for edge filtering of high-frequency waves, while the feedback signal is the measurement of low-frequency vibration with high dynamic range. The concept of the interrogator operation and different implementations are described and discussed with experimental results.

This paper presents improvements to slab-coupled optical fiber sensors (SCOS) for electric-field sensing. The improvements are based on changing the crystal cut and orientation of the slab waveguide in combination with altering the input light polarization. Traditional SCOS are fabricated using z-cut potassium titanyl phosphate crystals and are operated with TM polarized light. They have been shown to detect fields as low as 100 V/m. By using an x-cut crystal and TE polarized light, the sensitivity to electric fields is increased 8x due to, primarily, an increase in electric field penetration into the slab by exploiting a tangential boundary condition, and secondly, an increase to the effective electro-optic coefficient of the slab.

This paper presents a method for calibrating slab coupled optical fiber sensors (SCOS). An automated system is presented for selecting the optimal laser wavelength for use in SCOS interrogation. The wavelength calibration technique uses a computer sound card for both the creation of the applied electric field and the signal detection. The method used to determine the ratio between the measured SCOS signal and the applied electric field is also described along with a demonstration of the calibrated SCOS involving measuring the dielectric breakdown of air.

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.© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

In this study we evaluate the measurements of a fiber Bragg grating (FBG) sensor subjected to a non-uniform static strain state and simultaneously exposed to vibration loading. The full spectral response of the sensor is interrogated in reflection at 100 kHz during two loading cases: with and without an added vibration load spectrum. The static tensile loading is increased between each test, in order to increase the magnitude of the non-uniform strain field applied to the FBG sensor. During steady-state vibration, the behavior of the spectral shape of the FBG reflection varies depending on the extent of non-uniform strain. With high-speed full spectral interrogation, it is potentially possible to separate this vibration-induced spectral change from spectral distortions due to non-uniform strain. Such spectral distortion contains valuable information on the static damage state of the surrounding host material.

We used high-speed full-spectrum interrogation of a Fiber Bragg Grating (FBG) sensor to measure dynamic strain in different sensor packages in real-time. In this effort we performed solenoid impact tests on a variety of sensor mounting structures made with FR4, steel, and carbon fiber composite materials. Full spectrum FBG interrogation at 40 kHz repetition rate was the key that allowed us to measure and compare dynamic strain in the structures, with measurement resolution on the sub-millisecond scale. With this interrogation method we were able to measure the full character of the dynamic strain including the strain non-uniformity and distribution manifested in peak-splitting and spectrum broadening. Results showed that the FR4 board with soft epoxy responded with a maximum dynamic strain on the order of 3000 micro-strain. Adding hard materials such as steel and graphite fiber composite reduced the strain about 7 times. However, the FR4 board mounted in a free-floating configuration using hard epoxy reduced the maximum strain to a value below the noise threshold of the full spectrum interrogation configuration. Here we proposed using edge detection method of FBG interrogation due to its increased strain sensitivity which enabled us to further analyze the critical results obtained by full spectrum interrogation. We also proposed using edge detection to measure sensor strain in real time for the purpose of filtering out the strain noise from useful signal. We will use the results and data obtained with both methods to analyze and enhance the performance of our electric field sensors in environments of high static and dynamic strain.

This paper provides a detailed analysis of electric field sensing using a slab-coupled optical fiber sensor (SCOS). This analysis explains that the best material for the slab waveguide is an inorganic material because of the low RF permittivity combined with the high electro-optic coefficient. The paper also describes the fabrication and testing of a SCOS using an AJL chromophore in amorphous polycarbonate. The high uniform polymer slab waveguide is fabricated using a hot embossing process to create a slab with a thickness of 50 μm. The fabricated polymer SCOS was characterized to have a resonance slope of ΔP/Δλ=6.83E5 W/m and a resonance shift of Δλ/E=1.47E-16 m(2)/V.

This paper presents a high repetition rate fiber Bragg grating (FBG) interrogation system that is able to capture the entire reflection spectrum at a rate of up to 300 kHz. The system uses a high speed MEMS based tunable optical filter that is driven with a sinusoidal voltage. The time varying FBG reflection spectrum in transmitted through the tunable filter. The time varying signal is then mapped into time varying reflection spectra. This interrogation system is used during two dynamic strain tests, in which the reflection spectra are measured at a repetition rate of 100 kHz. The first test is the impact of a woven carbon composite and the second test is on an electromagnetic railgun.

Ultra small magnetic field sensors are created using magneto-optic slab waveguides coupled to optical fiber. The magneto-optic material used is bismuth-doped rare earth iron garnet (Bi:RIG). By etching close to the core of D-type optical fiber and attaching a magneto-optic material, light transfers from the fiber to the slab waveguide at specific wavelengths. The wavelengths that couple depend on the refractive index of the slab that changes in the presence of a magnetic field. When a field is applied, the wavelength coupling shifts and a resulting change in power can be detected. The sensors reported in this paper detect magnetic fields as low as 11 A/m.

Modern electronics are often shielded with metallic packaging to protect them from harmful electromagnetic radiation. In order to determine the effectiveness of the electronic shielding, there is a need to perform non-intrusive measurements of the electric field within the shielding. The requirement to be non-intrusive requires the sensor to be all dielectric and the sensing area needs to be very small. The non-intrusive sensor is attained by coupling a slab of non-linear optical material to the surface of a D shaped optical fiber and is called a slab coupled optical fiber sensor (SCOS). The sensitivity of the SCOS is increased by using an organic electro-optic (EO) polymer.

In this study we evaluate the measurements of a fiber Bragg grating (FBG) sensor subjected to a non-uniform static strain state and simultaneously exposed to vibration loading. The full spectral response of the sensor is interrogated in reflection at 100 kHz during two loading cases: with and without an added vibration load spectrum. The static tensile loading is increased between each test, in order to increase the magnitude of the non-uniform strain field applied to the FBG sensor. The spectral distortion due to non-uniform strain is observed to change once the sensor is exposed to a non-transient 150 Hz vibration spectrum. With high-speed full spectral interrogation, it is potentially possible to separate this vibration-induced spectral change from spectral distortions due to non-uniform strain. Such spectral distortion contains valuable information on the static damage state of the surrounding host material.

This paper demonstrates the value of D-type optical fibers (D-fibers) in a variety of sensing applications. The principal advantage of the D-fiber is that it allows for interaction with light traveling in the core of an optical fiber with materials or structures placed in contact with the fiber. This permits stimulus sensitive materials to be placed on the D-fiber to interact with the light in the core of the fiber. The presentation shows that this feature of D-fibers can be used to create alternatives to sensors formed in standard optical fibers for measuring temperature, strain, and shape change. In addition, D-fiber sensors have been fabricated to measure chemical concentrations, and electric fields.

An approximate solution to the problem of plane‐wave scattering by a finite, hemispherically terminated (end‐capped) cylinder of circular cross section is found via the uniform geometrical theory of diffraction (UTD). Both Dirichlet and Neumann boundary conditions are considered. A scattering model is applied in which a reduced set of geodesic paths or rays is used to obtain the acoustic pressure field at any point in space where the UTD is valid. A standard method for obtaining transfer functions describing the pressure field changes along the geodesic paths is briefly outlined. This method uses asymptotic expansion of the exact solutions to two related problems (plane wave scattering by a sphere and an infinite cylinder) whose ray sets together comprise the total ray set for the end‐capped cylinder problem. An approximation to the total pressure field is then found for the case when an impinging plane wave is scattered by an end‐capped cylinder. The predicted scattered fields demonstrate the expected si...

A mathematical model is presented that predicts birefringence changes in an optical fiber as the cladding is removed. This model approximates a highly elliptical fiber core with a rectangular dielectric waveguide. The birefringence calculations obtained with the model compare well with experimental evidenceobtained with real-time birefringence monitoring during cladding removal by chemical etching. The information is used to control the amount of cladding removed from a D fiber to within approximately 0.05 microm for use in the production of passive optical fiber components.

This paper presents a means for the high repetition rate interrogation of fiber Bragg gratings (FBG's). The new system highlights a method that allows a tradeoff between the full spectrum capture rate and the wavelength range and/or the spectral resolution of the technique. Rapid capture of the entire reflection spectrum at high interrogation rates shows important features that are missed when using methods that merely track changes in the peak location of the spectrum. The essential feature of the new system is that it incorporates a MEMs tunable filter driven by a variable frequency openloop sinusoidal source. The paper demonstrates the new system on a laminated composite system under impact loading.

This paper presents the full-spectral measurement of fiber Bragg grating sensor responses during impact testing of composite laminates. The sensors are embedded in carbon fiber/epoxy laminates which are subjected to multiple low velocity impacts until perforation of the laminate occurs. Applying a recently developed high-speed interrogator, the Bragg grating sensor interrogation is demonstrated at 534 Hz over a 14.9 nm bandwidth. The measurement of the transient response of the grating sensors during impact reveals unique spectral signatures that could not be detected through peak-wavelength monitoring or post-impact full-spectral scanning of the sensors, including local relaxation of the laminate.

Spin casting electro-optic polymers for in-fiber device fabrication is problematic due to the flexibility and high-contrast topography of optical fibers. An ink-jetting method is developed for the deposition of AJL8/APC using a commercially available printer. The method results in more consistent control of film thickness and uses 1000 times less material than the spin-coating method. A D-fiber electric field sensor is fabricated using this deposition method and exhibits a sensitivity of 157 V/(m square root(Hz)) at a modulation frequency of 6 GHz.

Wavelength selective coupling is demonstrated between the core of a D-shaped optical fiber and a multimode planar waveguide. The fabrication process consists of wet chemical etching of the D-fiber and spin coating or molding to produce the planar waveguide. This fabrication process is shown to produce weak coupling and long interaction length, which exhibits transmission dips with narrow wavelength linewidths. A comb filter is demonstrated with peak separations of 12nm, transmission dips of -20dB, and linewidths of 0.25nm. High sensitivity is demonstrated by showing shift in the transmission dips of -3.16 nm/degree C.

This paper presents a new means for collecting fiber Bragg grating (FBG) data during drop tower measurements used to assess damage to composite structures. The high repetition-rate collection process reveals transient features that cannot be resolved in quasi-static measurements. The experiments made at a repetition rate of about 500 Hz show that the detected FBG spectrum broadens for a short period of time and relaxes quickly to a narrower static state. Furthermore, this relaxation time increases dramatically as the strike count increases. The information gained by such measurements will enhance the ability to characterize and distinguish failure modes and predict remaining lifetime in composite laminate structures.

Optical fiber Bragg grating sensors exhibit specialized sensing characteristics for harsh environments. The most common interrogation methods for FBGs require high resolution spectrometers that are not well suited to some embedded test situations. We have developed a compact, high speed, Ethernet-enabled interrogator that consumes less than 10 Watts. We describe the conventions used to convert from the optical domain to a sensor network, then present integrated system test data acquired from sensors in dynamic temperature and strain environments. Fiber optic system and sensor performance signal a maturity level capable of mainstream usability.

The authors use a fiber sensor integrated monitor (FSIM) as a fully functioning system to characterize the temporal response of a surface-relief fiber Bragg grating (SR-FBG) to temperature heating above 1000 degrees C. The SR-FBG is shown to have a rise time of about 77 ms for heating and a fall time of about 143 ms for cooling. The FSIM also provides full spectral scans at high speed that can be used to gain further insights into the temperature dynamics of a given system.

An electric-field sensor is specially fabricated with an optical D-fiber that utilizes weak evanescent coupling with a lithium niobate slab waveguide. Resonant modes with a Q-factor of ~13,000 yield high sensitivity for detecting electric fields.

A fiber Brag grating sensor interrogator has been developed which is capable of gathering vectors of information from individual fiber Bragg gratings by capturing the full optical spectrum 3 kHz. Using a field programmable gate array with high speed digital-to-analog converters and analog-to-digital components, plus a kilohertz rate MEMS optical filter, the optical spectrum can be scanned at rates in excess of 10 million nanometers per second, allowing sensor sampling rates of many kilohertz while maintaining the necessary resolution to understand sensor changes. The autonomous system design performs all necessary detection and processing of multiple sensors and allows spectral measurements to be exported as fast as Ethernet, USB, or RS232 devices can receive it through a memory mapped interface. The high speed - full spectrum - fiber Bragg grating sensor interrogator enables advanced interrogation of dynamic strain and temperature gradients along the length of a sensor, as well as the use of each sensor for multiple stimuli, such as in temperature compensation. Two examples are described, showing interrogation of rapid laser heating in an optical fiber, as well as complex strain effects in a beam that had an engineered defect.

The Surface Relief Fiber Bragg Grating (SR-FBG) is a viable alternative to the thermocouple for high temperature measurements in industry. To fabricate the SR-FBG we etch a grating into the flat surface of an elliptical-core D-fiber. At high temperature (1000 °C) the optical fiber becomes brittle. To overcome brittleness we thread the fiber through a preheated 0.020 inch diameter stainless steel tube. We insert the small tube into a larger one with a diameter of 0.125 inches. The smaller tube rests on ceramic inserts to prevent contact with the large tube. The end of the D-fiber is fitted with a standard fiber optic connecter. With this packaging scheme we conduct a series of test at high temperature. The sensor is robust with no power loss or Bragg wavelength shift, even after heating for 24 consecutive hours.

A fiber-optic electric field sensor was developed to measure electric field up to 18 MV/m. The sensor uses resonant coupling between an optical fiber and a nonlinear electro-optical crystal. The sensing system uses high dielectric strength materials to eliminate dielectric breakdown. A postprocessing nonlinear calibration method is developed that maps voltage change to wavelength shift and then converts the wavelength shift to electric field using the transmission spectrum. The nonlinear calibration method is compared against the linear method with electric field pulses having magnitudes from 1.5 to 18 MV/m.

A fiber-optic sensor used to detect volatile organic compounds is described. The sensor consists of a single-mode D-fiber with a 2.5 microm polydimethylsiloxane layer. The layer is applied to the fiber flat after removal of a section of the fiber's cladding to increase evanescent interaction of the light with the layer. Absorption of volatile organic compounds into the polymer alters the refractive index of the layer, resulting in a birefringent change of the fiber. This change is observed as a shift in polarization of the light carried by the fiber. The sensor has a short length of 3 cm and a response time of around 1 s. The sensor is naturally reversible and gives an exponential response for gas and liquid concentrations of dichloromethane and acetone, respectively.