Early efforts developing smart structures started with strain sensors based on interferometeric techniques. It immediately became apparent that structural engineers were used to dealing with conventional electrical strain gages and thermocouples with much shorter gage lengths. The fiber grating offered a competitive solution for the measurement of strain and temperature with the advantages of electrical isolation and improved ruggedness. The principal draw back was cost. So early applications involved high value projects where the unique capabilities of the technology offered superior performance. One area of particular interest involved the usage of fiber gratings to sensor more than one parameter simultaneously. Multi-dimensional strain and the measurement of pressure and temperature were two key examples of multi-parameter sensing. In parallel efforts were conducted to operate at high speed. Early examples in aerospace and civil structures were at speeds in the range of 10 kHz. Ballistic work later dictated increasing speeds to 5 MHz. Much more recent work with burn, deflagration and detonation has involved measurements from more than 100 MHz to multiple GHz. This paper provides a personal history of some of these developments and how fiber grating sensor technology is moving into the future.

An all optical-fiber-based approach to measuring high explosive detonation front position and velocity is described. By measuring total light return using an incoherent light source reflected from a fiber Bragg grating sensor in contact with the explosive, dynamic mapping of the detonation front position and velocity versus time is obtained. We demonstrate two calibration procedures and provide several examples of detonation front measurements: PBX 9502 cylindrical rate stick, radial detonation front in PBX 9501, and PBX 9501 detonation along a curved meridian line. In the cylindrical rate stick measurement, excellent agreement with complementary diagnostics (electrical pins and streak camera imaging) is achieved, demonstrating accuracy in the detonation front velocity to below the 0.3% level when compared to the results from the pin data. In a similar approach, we use embedded fiber grating sensors for dynamic pressure measurements to test the feasibility of these sensors for high pressure shock wave research in gas gun driven flyer plate impact experiments. By applying well-controlled steady shock wave pressure profiles to soft materials such as PMMA, we study the dynamic pressure response of embedded fiber Bragg gratings to extract pressure amplitude of the shock wave. Comparison of the fiber sensor results is then made with traditional methods (velocimetry and electro-magnetic particle velocity gauges) to gauge the accuracy of the approach.

A novel very high speed fiber grating sensor system has been used to support velocity, position, temperature and pressure measurements during burn, deflagration and detonation of energetic materials in Russian DDT tests. For the first time the system has been demonstrated in card gap testing and has allowed real time measurements of the position of the blast front into the card gap and monitoring of pressure at key locations in the card gap test. This paper provides an overview of this technology and examples of its application.

One of the most common fiber optic sensor (FOS) types used are fiber Bragg gratings (FBG), and the most frequently measured parameter is strain. Hence, FBG strain sensors are one of the most prevalent FOS devices in use today in structural sensing and monitoring in civil engineering, aerospace, marine, oil and gas, composites and smart structure applications. However, since FBGs are simultaneously sensitive to both temperature and strain, it becomes essential to utilize sensors that are either fully temperature insensitive or, alternatively, properly temperature compensated to avoid erroneous measurements. In this paper, we introduce the concept of measured “total strain”, which is inherent and unique to optical strain sensors. We review and analyze the temperature and strain sensitivities of FBG strain sensors and decompose the total measured strain into thermal and non-thermal components. We explore the differences between substrate CTE and System Thermal Response Coefficients, which govern the type and quality of thermal strain decomposition analysis. Finally, we present specific guidelines to achieve proper temperature-insensitive strain measurements by combining adequate installation, sensor packaging and data correction techniques.

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.

Fiber-optic ultrasonic transducers are an important component of an active ultrasonic testing system for structural health monitoring. Fiber-optic transducers have several advantages such as small size, light weight, and immunity to electromagnetic interference that make them much more attractive than the current available piezoelectric transducers, especially as embedded and permanent transducers in active ultrasonic testing for structural health monitoring. In this paper, a distributed fiber-optic laser-ultrasound generation based on the ghost-mode of tilted fiber Bragg gratings is studied. The influences of the laser power and laser pulse duration on the laser-ultrasound generation are investigated. The results of this paper are helpful to understand the working principle of this laser-ultrasound method and improve the ultrasonic generation efficiency.

A temperature sensor link based on wavelength-multiplexed fiber Bragg grating (FBG) was designed and fabricated for distributed temperature measurement in a jet engine nozzle under field conditions. Eight FBGs with different Bragg wavelengths ranging from 1520 nm to 1560 nm were fabricated along one single-mode fiber which was packaged inside a stainless steel tube. The reflected signal from the sensor link was simultaneously collected by an optical sensing interrogator and converted into temperature information. The steel tube was embedded in a steel flange assembly attached to a jet engine. Three engine cycles were performed from 55% (idle) to 80% of the engine’s full power to test the sensor response under high temperature, vibration and strong exhaust flow conditions. Test results show good survivability of the sensor, and the temperature around the nozzle was measured up to 290 °C. The system has a temperature measurement range from 20 °C to 600 ° and the response time is less than 1 second.

Fiber-optic ultrasonic transducers are an important component of an active ultrasonic testing system for structural health monitoring. Fiber-optic transducers have several advantages such as small size, light weight, and immunity to electromagnetic interference that make them much more attractive than the current available piezoelectric transducers, especially as embedded and permanent transducers in active ultrasonic testing for structural health monitoring. In this paper, a distributed fiber-optic laser-ultrasound generation based on the ghost-mode of tilted fiber Bragg gratings is studied. The influences of the laser power and laser pulse duration on the laser-ultrasound generation are investigated. The results of this paper are helpful to understand the working principle of this laser-ultrasound method and improve the ultrasonic generation efficiency.

We proposed a Brillouin optical fiber time domain analysis (BOTDA)-based fully-distributed temperature system as high as 1000°C and spatial resolution to 5 meters. This technique is prominent for high spatial resolution fully distributed high temperature and stress sensing over long distance.

Optical fiber sensors utilizing Brillouin scattering rely on the principle that the Brillouin frequency shift is a function of the local temperature or strain. Conventional optical fibers, such as standard telecommunications single-mode fibers, have been successfully used in these applications, and most typically in the time domain, such as with BOTDR. Such conventional fibers however are susceptible simultaneously to both temperature and strain, requiring either at least two fibers or specialized cabling to distinguish the effects of a local stress from those of a local change in temperature. Recently, methods utilizing fibers possessing at least two Brillouin frequency shifts, each with different temperature or strain coefficients have been proposed. However, realizing such fibers is challenging, requiring fibers with regions of very different compositions, all of which must have substantial overlap with the optical field, posing significant manufacturing challenges. We present several new specialty optical fibers based on novel and unconventional fabrication techniques with significant potential for use in distributed fiber sensor systems. First, we describe a class of fibers fabricated from materials whose Brillouin frequency shifts are immune to either temperature or strain, with a demonstration of the former using fiber derived from sapphire crystal, and modeling and measurements predicting the latter. The ‘Brillouin-athermal’ fiber enables the measurement of a local strain, independent of the local temperature. Second, we describe and demonstrate a novel group of longitudinally graded (chirped) fibers enabling easily-implemented frequency-domain systems; affording the potential to simplify and reduce the cost of Brillouin-based distributed sensors.

Long-period gratings (LPG) are inscribed in endlessly single mode (ESM) photonic crystal fiber (PCF) and conventional single mode fiber (SMF) with symmetric and asymmetric CO₂ laser irradiation. Transmission measurements and near field imaging indicate that symmetric index perturbation induced by laser irradiation with the aid of a 120° gold-coated reflecting mirror results in LP_0n symmetric mode coupling, while asymmetric irradiation without using the mirror leads to LP_1n asymmetric mode coupling for both fiber types. Symmetric irradiation yields far more reproducible LPG in PCF than asymmetric irradiation. On the other hand, the irradiation symmetry has little effect on the reproducibility of LPG inscribed in SMF due to the isotropy of its all-solid cladding structure. The removal of the outer solid cladding of PCFLPG results in a significant change in its transmission characteristics, which provides rich information on the refractive index perturbation and mode field distribution in the outer solid cladding of PCF-LPG.

It has been proposed that fast-light optical phenomena can increase the sensitivity of a Ring Laser Gyroscope (RLG) of a given size by several orders of magnitude. MagiQ is developing a compact fully-fibered fast light RLG using Stimulated Brillouin Scattering (SBS) in commercial optical fiber. We will discuss our experimental results on SBS pumped lasing in commercial fibers and analyze their implications to the fast light generation. Based on these results, we envision a fast light enhanced Ring Laser Gyroscope (RLG) that will use only a few meters of fiber and require moderate pump power (only a few 100’s of mW). We will present the design that is based on proven, commercially available technologies. By using photonic integrated circuits and telecom-grade fiber components, we created a design that is appropriate for mass production in the near term. We eliminated all free-space optical elements (such as atomic vapor cells), in order to enable a compact, high sensitivity RLG stable against environmental disturbances. Results of this effort will have benefits in existing applications of RLGs (such as inertial navigation units, gyrocompasses, and stabilization techniques), and will allow wider use of RLGs in spacecraft, unmanned aerial vehicles or sensors, where the current size and weight of optical gyros are prohibitive.

In this paper physical quantities were measured using by the fiber optic sensor when a pendulum ball collides to the fixed ball on the wall. Both steel ball dimensions are 1 inch in diameter. The fiber optic Sagnac interferometer was used to detect the impact time. It is made a 1mm penetrated hole and optical fiber in the Sagnac loop passed through the hole. A ball was welded on the steel plate wall as a fixed ball. When the another ball collides to the fixed ball the fiber optic sensor detects the impact force in between them. Based on the experimental result impact time was measured about 0.14ms at the angle of 30 degree. This fiber optic sensor technique can be expanded to the moving bodies.

In this work we proposed the use of free-space-optics (FSO) to transmit and receive the optical signals from optical fiber placed in ground potential to the FBG fiber optics at high voltage potential, using a pair of optical collimators. The technique evaluation was performed in a prototype for the study of sensitivity to optical alignment and in an external environment using emulated sensing systems for both bus bar and overhead transmission line with real isolator chain. It has been shown that the FSO system allows collimators operate at distances of 500 mm to 2.000 mm. This range of distances is similar to the length of insulator’s chain up to 230 kV. It was also shown that the proposed system can be used in real external environment for bus bar temperature monitoring in substations, where, even if the time out of the system is of 45%, with major interruption time of almost 15 hours, the majority of the interruption time was less than 18 minutes long. On the other hand, system has to be improved in order to be used in overhead transmission line. As tested for a real isolator chain the system shown a time out of 80.3%, with significant number of events of interruption acquisition time greater than 150 minutes. It is believed that for overhead power lines, system must be installed in rigid surge arresters or in a line post where it is expected to have similar results as in substation bus bars monitoring.

In this work half the length of the single FBG is chemically etched and the un-etched half is glued on a cantilever. The response of the grating is investigated as a function for buoyancy force on the cantilever due to liquid level and temperature. Simultaneous measurement of liquid level and temperature is achieved from the coefficients of liquid level and temperature sensitivities obtained from the experimental results.

In this paper, an optical fiber corrosion sensor with stepped metal film was designed and fabricated. The principle of the optical fiber sensor for corrosion monitoring was analyzed. The stepped metal film was prepared by magnetron sputtering and electroplating on the core of multimode optical fiber with cladding removed. The optical performance of the sensor with different steps was investigated by optical power measuring. The result showed that a stepped metal film on optical fiber could enhance the properties of sensor, and the detective range was enlarged.

This work has the objective to research and develop a plastic optical fiber biosensor based taper and mPOF LPG techniques to detect Escherichia coli by measurements of index of refraction. Generally, cell detection is crucial in microbiological analysis of clinical, food, water or environmental samples. However, methods current employed are time consuming, taking at least 72 hours in order to produce reliable responses as they depend on sample collection and cell culture in controlled conditions. The delay in obtaining the results of the analysis can result in contamination of a great number of consumers. Plastic Optical Fiber (POF) biosensors consist in a viable alternative for rapid and inexpensive scheme for cells detection. A study the sensitivity of these sensors for microbiological detection, fiber Tapers and Long Period Grating (LPG) both in poly-methyl-methacrylate (PMMA) were realized as possible candidates to take part of a biosensor system to detect Escherichia coli in water samples. In this work we adopted the immunocapture technique, which consists of quantifying bacteria in a liquid sample, attract-ing and fixing the bacteria on the surface of the polymer optical fiber, by the antigen-antibody reaction. The results were obtained by optical setup that consists in a side of the fiber a LED coupled to a photodetector through a POF with the taper in the middle of it. On the other side of the POF a photodetector receives this light producting a photocurrent. The output voltage is fed into the microcontroller A/D input port and its output data is sent via USB to a LabView software running in a microcomputer. The results showed the possibility of the POF in biosensor application capable to detect E. coli for environmental and food industry and for detecting and identifying biological-warfare agents using a very rapid response sensor, applicable to field detection prototypes.

In this paper, we present a temperature-insensitive refractive index sensor based on π-phase-shifted Bragg gratings fabricated on side-hole fibers processed by wet chemical etching technique. The reflection spectrum of the π-phase shifted gratings on etched side-hole fiber features two notches with large spectral separation, which was used for refractive index (RI) detection in our application. The relative spectral notch separation exhibited a RI sensitivity of −278.5 pm/RIU (RIU: RI unit). Theoretical simulation obtained the temperature sensitivity of −0.00241 pm/°C, and experimental results also showed little sensitivity to temperature of our RI sensor.

The combination of fiber optics with micro-structure technologies and sensitive thin films offers great potential for the realization of novel sensor concepts. Minitured optical fiber sensors with thin films as sensitive elements could open new fields for optical fiber sensor applications. Thin films work as sensitive elements and transducer to get response and feedback from environments, optical fiber here are employed to signal carrier. This paper reviews some works on the integration of thin films with fiber micro-structures for sensing application, which are currently conducted at the National Engineering Laboratory for Fiber Optic Sensing Technologies, Wuhan University of Technology.

Our hybrid plasmonic whispering gallery mode biosensor has recently demonstrated detection and characterization of the smallest known RNA virus. A gold nanoparticle affixed to the resonator surface acts like a nanoscopic antenna, enhancing locally the electric field within the cavity mode. When a target analyte binds with this nanoscopic antenna the result is an enhanced response (spectral shift) of the resonator system to the binding event. We have observed shift enhancements ~70× over the response of the bare resonator, thereby permitting the detection and characterization of all known viral particles and even some large protein molecules.

A novel compact architecture implementing grating-coupled surface plasmon resonance (GCSPR) based on polarization modulation in conical mounting is presented. In this system a plasmonic grating is azimuthally rotated in order to support the excitation of high-sensitivity surface plasmon polaritons (SPPs). At SPP resonance, a scan of the incident polarization is performed before and after the binding event and the phase term of the output trend is exploited as sensing parameter. The mechanical complexity of the SPR system is significantly reduced and a resolution down to 10^-7 refractive index units is assured. In this work a numerical study of the polarization-based grating-coupled SPR technique is performed and analyzed with Chandezon’s method. Therefore an experimental test on an assembled prototype is presented and applied to the detection of binding events on the grating surface (avidin/biotin reaction, DNA/PNA probes).

In this paper, we present an optofluidic SERS microsystem suitable for on-site detection of multiplexed analytics in the field. We show simultaneous detection of three fungicides that are highly regulated in aquaculture. The optofluidic SERS microsystem shows improved portability since it does not require a bulky pump for sample loading. The sample is simply drawn into the microchannel using a pipette. Additionally, two fiber optic cables are inserted into the device for sample excitation and photon collection. The fiber optic cables, aligned into the detection zone, eliminate the need for microscope alignment required in traditional SERS detection. The detection zone of the device consists of a porous matrix of packed silica microspheres that traps silver nanoparticles and adsorbed analyte molecules. The sample is passively concentrated into the matrix as it is loaded by applying negative pressure from the outlet with a pipette. The concentrating matrix has been shown to amplify the SERS signal by up to four orders of magnitude as compared to SERS in an open microfluidic channel. We were able to detect as low as 5 ppm methyl parathion, 0.1 ppb malachite green, and 5 ppb thiram simultaneously.

Rapid DNA analysis systems show promise for reduced DNA analysis times and can be used by untrained operators in point-of-use applications. Throughput improvements can be gained by reducing the polymerase chain reaction (PCR) cycle count, which is used in conventional DNA processing to amplify the DNA to an easily measurable amount. A Photonic Crystal (PhC) can be integrated within a microfluidic channel to enhance fluorescence emission, enabling a reduction in PCR cycling. Most PhCs are fabricated using serial top-down fabrication techniques, resulting in a structure that is challenging to integrate with microfluidic system components. Here, we present a co-integration process for fabricating a Silicon master mold consisting of a visible range PhC lattice and a microfluidic channel. This process can be used to co-fabricate microscale channel and nanoscale lattice structures in polymer or thermoplastic materials. Two dimensional visible range PhCs are fabricated by patterning electron beam resist via E-Beam Lithography (EBL). The patterned features (100-300nm features with 200-450nm pitch) are cured to a glass-like material that is used as a direct etch mask for Reactive Ion Etching. A 200μm wide and 25μm high ridge “strip” is fabricated around the PhC region using Photolithography and Deep RIE etching to form the completed channel and lattice mold. Results indicating the quality of nanoscale features resulting from the molding process in Polydimethylsiloxane (PDMS) will be discussed.