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A smart metal component with an integrated high temperature sensing capability is presented. The metallic structure in SS316 is manufactured by an additive layer process based on laser powder bed fusion (LPBF). The sensor, a temperature sensitive in-fiber Fabry-Perot element, is encapsulated in a capillary and embedded into the structure during the LPBF build process. It is demonstrated that the sensor can measure the temperature inside the metal up to 1000°C with accuracy better than 10°C for extended periods far in excess of 300 h.

Sensors play a large role in monitoring and ensuring that environmental parameters satisfy industrial requirements. They offer crucial safety measures in the early detection of hazards. Conventional electrical sensors possess several drawbacks that hinder their use in environmental sensing. Research has explored and optimized optical-based sensors because they are more robust, immune to electromagnetic interference and offer multiplexing capabilities for sensor arrays accompanied by ease of modification to cater to different measurands. Fibre Bragg grating is the perturbation of the refractive index imprinted within the core of an optic fibre via an intense UV laser. The gratings, when perturbed by external parameter changes, will induce a shift in their wavelength, indicating detection. With modifications such as hygroscopic coating and different grating profile imprinting, FBG can detect various physical and chemical parameters. Environmental, pharmaceutical and biochemical fields can benefit from FBG sensing because their parameters affect not only their product quality but also the lives of consumers. This review discusses some of the FBG sensors that have been proposed to serve in environmental and biochemical applications.

Focused ion beam (FIB) machining has been demonstrated to be capable of fabricating nano- and micro-scale structures. In this paper we demonstrate techniques to design and fabricate 45° micro-mirrors into the end of multi-core fibres using FIB processing. The mirrors are fabricated by a two-step process: a scanning process which is used to make a rough cut followed by a polishing process to create an optical surface finish mirror. The machined 45° mirrors can be accurately aligned with optical fibre cores, which avoids issues associated with the alignment of external turning mirror components. Proof-of-concept demonstration shows that the fabricated structure is capable of measuring two-axis acceleration interferometrically with a linear response from 0.2 to 4 g and an rms. error of 0.03 g. Acceleration measurements of frequency response up to 700 Hz and cross-sensitivity of ∼4.3% are demonstrated.

Understanding transport phenomena and governing mechanisms of different physical and chemical processes in porous media has been a critical research area for decades. Correlating fluid flow behaviour at the micro-scale with macro-scale parameters, such as relative permeability and capillary pressure, is key to understanding the processes governing subsurface systems, and this in turn allows us to improve the accuracy of modelling and simulations of transport phenomena at a large scale. Over the last two decades, there have been significant developments in our understanding of pore-scale processes and modelling of complex underground systems. Microfluidic devices (micromodels) and imaging techniques, as facilitators to link experimental observations to simulation, have greatly contributed to these achievements. Although several reviews exist covering separately advances in one of these two areas, we present here a detailed review integrating recent advances and applications in both micromodels and imaging techniques. This includes a comprehensive analysis of critical aspects of fabrication techniques of micromodels, and the most recent advances such as embedding fibre optic sensors in micromodels for research applications. To complete the analysis of visualization techniques, we have thoroughly reviewed the most applicable imaging techniques in the area of geoscience and geo-energy. Moreover, the integration of microfluidic devices and imaging techniques was highlighted as appropriate. In this review, we focus particularly on four prominent yet very wide application areas, namely “fluid flow in porous media”, “flow in heterogeneous rocks and fractures”, “reactive transport, solute and colloid transport”, and finally “porous media characterization”. In summary, this review provides an in-depth analysis of micromodels and imaging techniques that can help to guide future research in the in-situ visualization of fluid flow in porous media.

Micro-cantilever sensors have shown great promise in a wide range of applications including chemical medical and biological sensing. However, many of these devices are based upon a sensor ‘chip’ that requires careful alignment between the cantilever and the read-out system, which can be challenging. Furthermore, optical interrogation typically involves a bulky free-space system. Optical fiber addressed cantilevers have been reported previously in the literature and in this paper we propose techniques to design and fabricate polymer micro-cantilevers onto the end of standard single mode fibers using ns-laser machining. The cantilever will deflect and thereby observing biological binding between species of interests and activated cantilevers. Proof-of-concept experiments demonstrate that the sensor is capable of detecting Listeria food pathogen concentrations with a minimum level of less than 105cfu/ml.

Materials that have hygroscopic capabilities are potent sensing elements for humidity sensors. The hygroscopic behaviour of zinc oxide (ZnO) with modified nanostructure was synthesized and characterized. Heterocyclic additive was added on ZnO to improve its hygroscopic capability for humidity sensitization. ZnO capability of water molecule adsorption was tested with a hygroscopic characterization method adapted from American Society for Testing and Materials (ASTM) method for hygroscopic determination. It was found that inclusion of additive improves the water retention and release ZnO, making it more viable for use in sensors that take advantage of mechanical strain due to weight for humidity determination. The hygroscopic behaviour was observed in the steeper gradient on the mass change during humidity exposure to the ZnO compound with the additive compared to non-additive ZnO. Furthermore, the additive loaded ZnO showed greater reliable regression, R2 value (3.56 %) compared to the non-additive ZnO sample. Crystal analysis via X-ray diffraction (XRD) revealed increment on ZnO characteristic peaks (002) and (101) upon addition of the organic compound to the ZnO which influence the nanostructure of the material. Field emission scanning electron microscopy (FESEM) indicates porous and hemispherical nanostructure. Elemental analysis showed minimal impurities present on both ZnO and additive loaded ZnO. The hygroscopic capabilities of ZnO synthesized with low temperature hydrothermal technique allows for implementation in many humidity sensing options required by industries of various fields.

We present a research to determine the long-term stability of intrinsic Fabry–Perot (F–P) optical fiber sensors in high-temperature environments. In-fiber sensors were created in 125 μ m diameter single mode fiber (Corning SMF28 Ultra) and a 125 μm diameter PCF ESM-12B pure SiO2 fiber spliced to a SMF28 fiber with a low reflectivity Cr layer at the interface. The outcome is a low finesse optical cavity either formed by a short length of Ge doped SMF fiber, or a short length of pure and undoped SiO2 core PCF fiber. We demonstrate the manufacturing technique required for these intrinsic F–P sensors as well as the stability of their optical characteristics at temperatures up to the range of 850 °C to 1050 °C. We report on the effect of annealing on stability after exposing sensors to temperatures of 1000 °C above nominal working temperatures. In the temperature range above 900 °C we observe increasing levels of nonreproducible drift characteristics. Stability is demonstrated up to 1000 °C. After extended exposure of sensors to high temperatures we observe deviations from the initial smooth second-order response of phase versus temperature, which has been attributed to a change in core diameter in the fiber leading to the sensor at the distal end due to Ge diffusion at the high temperatures. The down lead is exposed to over a length of 17 cm. The dopant diffusion of an SMF28 ultra fiber has been studied using Energy Dispersive X-rays analysis (SEM/EDX), to measure the radial distribution of Ge concentration before and after being heated for a period of 100 days.

This paper reports the methods of embedding into 3-D printed metal components a fused silica capillary designed to accept an in-fiber Fabry–Perot cavity-based extreme high-temperature sensor. The components are manufactured in stainless steel (SS316) by additive manufacturing using selective laser melting (SLM). The temperature sensor consists of a standard single-mode optical fiber with the F-P sensor located at the distal end of the fiber with the fiber being inserted into the capillary. The capillary is either directly embedded into the structure during the SLM build process or brazed into the structure in between the SLM build process, and the advantages and disadvantages of these two manufacturing approaches are discussed. Temperature sensing of up to 1000 °C inside the metal with an accuracy better than ±10 °C is reported. The capillary can be directly embedded in the component, which needs to be monitored, or it can be embedded in a metal coupon, which can be attached to a component by conventional welding technology, including the use of laser metal deposition (LMD). In the case of LMD, the sensor coupon can also be fully encapsulated by over cladding the coupon.

Regenerated fibre Bragg gratings are formed when specially pre-treated seed gratings are heated up to several hundred degrees centigrade. During this process, the fibre Bragg grating (FBG) reflectivity vanishes and regrows, forming a regenerated grating, which can survive temperatures of more than 1000 °C. Right from the beginning, it was clear that the extraordinary temperature stability of regenerated FBGs will open new fields of applications for FBGs. Multiple investigations have been made to explore the mechanisms of the regeneration effect, often presenting contradictory explanations of the processes leading to their formation. To date, there is no comprehensive theory which can explain all the observed phenomena regarding the regeneration effect. However, a broad base of knowledge exists, which can be used for tailored manufacturing and application of regenerated FBG. In this article, we present a summary of the breadth of regenerated FBG research, including a critical overview and discussion of the various competing theories published to date. We conclude with an outlook on present and future applications of regenerated FBGs and identify further research necessary to unambiguously identify and explain the key processes occurring during regeneration.

In this paper we report on experiments aimed at the development of a highly responsive sensor based on long period gratings (LPGs) operating at high order cladding modes which exhibit a turn-around-point in their phase matching diagrams. These high order cladding modes are accessed by decreasing the period of the grating within standard optical fiber according to theoretical simulations. The sensors tested detect hydrogen through a Pd coating on the fiber cladding. As expected from simulations these sensors exhibit a near eight fold increase in response to 1% hydrogen when operated near the phase turning point. This increase in response is, however, not selective to hydrogen and a combination of increased thermal noise and broadened resonance condition serves to decrease the signal to noise ratio such that any gain in theoretical sensitivity is counter-acted by a loss in fidelity of the recovered (or recorded) signal. The highest sensitivity (shift of a LPG lossband) recorded was in the order of 470 pm for an exposure to 1% H-2 at 70 degrees C, which represented a shift of similar to 1/150 of the FWHM of the LPG loss band.

The hygroscopic properties of a material allow water retention and release of water vapor from surface of a nanostructure. Most nanostructure exhibit morphological change due to swelling or directional expansion upon water intake. The study focuses on characterizing the hygroscopic properties of additive enhanced zinc oxide via weighing method and testing of its hysteresis free sensing potential. Zinc oxide (ZnO) was prepared along with added additive via modified low temperature hydrothermal synthesis. The growth solution was coated on to glass slides before characterization of hygroscopicity and water adsorption hysteresis. The sample was placed in a sealed chamber with sensitive microbalance to measure mass gain and loss of the sample. The humidity within the chamber was manipulated chemically and temperature was left at constant ambient temperature. Relative humidity range from 40 to 80 % RH was exposed to the samples. The additive enhanced zinc oxide (ZnO-HMT) film has shown superior water retention and release capabilities by having steeper gradient compared to its initial version. ZnO-HMT could maintain its mass at low RH% of 37.5 % and high RH% of 80 % at closely similar value upon exposed to several cycles of incremental and decremental RH%. The mass intake and release of ZnO-HMT was also greater at 1.5 mg per 10 % increment and decrement of RH within 40 RH% - 80 RH% compared to ZnO which only have 0.9 mg mass change at each increment. Microscopic observation has shown apparent morphology change to ZnO-HMT nanostructure upon exposed to increased humidity from lower humidity. ZnO-HMT shown potent candidate as a humidity sensor material to be implemented into optical sensors that requires strain as the sensing mechanism to take advantage of the hygroscopic nature of the material.

Various characterization techniques are used in the study of materials in order to understand their properties. Data and observation recording characterization of a material is done by researchers for various properties within various environments. One of the many properties that make a material attractive for use in certain devices is hygroscopicity. Various techniques for characterizing hygroscopicity have been developed and utilized. However, since these techniques are not usually the highlights of studies, there has been limited acknowledgement of the usefulness of hygroscopicity testing. This review introduces several established characterization techniques allowing researchers to fully characterize materials in terms of their hygroscopicity. The full potential of hygroscopic materials can be seen in their use in various fiber sensors. The deformation of materials upon exposure to water molecules can be utilized to perturb sensing elements in fiber sensors, allowing the user to take full advantage of the hygroscopicity of the material.

Sensor-based optical fibers require thinner cladding for enhanced interaction between the evanescence wave and the environment. Fiber Bragg grated fiber sensors relying on an axial strain require chemical etching to weaken the fiber allowing more sensitivity in terms of strain. Ease of sensor multiplexing can be achieved through etching the mid-section of the fiber which is rarely reported with a custom-made holder. This paper proposes a technique for etching at the middle section of a fiber with a custom fiber holder. Chemical etching of a single-mode silica fiber was done with 48% hydrofluoric acid (HF). Etching proceeds until the fiber was completely etched. The optical spectrum was recorded at an interval of 3 min. Microscope visuals indicated possible etching with the mount design until ∼10 μm at 45 min with the fiber intact compared to a longer etching time. A longer etching duration than 45 min results in the optical spectrum displaying a null spectrum, depicting core damage. Etching of the fiber follows a linear trend and the reaction rate was determined to be 1.699 μm min−1 experimentally. The proposed fiber holder and receptacle were capable of etching a fiber with minimal defects while maintaining the ease of fiber handling.

A micro-cantilever fabricated using a combination of picosecond-laser machining and focused ion beam milling directly onto the end of a standard telecommunications optical fiber is demonstrated as a liquid pH sensor. Conventional pH meters typically require relatively large reaction volumes up to $\sim 50$ mL, which is not always convenient. The micro-scale nature of this sensor offers the potential for pH measurement on a smaller sample volume down to micro-liter. The fiber end-tip cantilever is coated with a pH sensitive layer, and the pH-induced deflection is monitored interfermetically. A detectable pH range from 4.0 to 10.0 is demonstrated for the cantilevers coated with 16-mercapto-hexadecanoic-1-acid as the functional layer, and a detectable pH range from 4.0 to 9.0 is demonstrated for the cantilevers coated with Al2O3 as the functional layer.

The fabrication, characterization and encapsulation of a fiber optic temperature sensor based upon a micro Fabry–Perot (F-P) cavity is presented. The F-P cavity is formed between a reflective in-fiber metallic splice and the air-fiber boundary at the end of the sensor. A change in temperature modifies the optical cavity length, and this is observed as a change in the reflected interference spectrum. The sensor has been demonstrated for high-temperature measurement up to 1100 °C. The stability of the sensor system is ∼10 °C over a period exceeding 300 h at 1100 °C. Furthermore, a sealed capillary is used as a protective enclosure.

Single-mode optical fibers with thin nickel coatings (outer diameter ∼ 350 μm) are successfully embedded into stainless steel (SS) 316 components using bespoke laser-based additive manufacturing technology. In our approach, we manufacture SS 316 components using selective laser melting, incorporating U-shaped grooves with dimensions suitable to hold nickel-coated optical fibers. Coated optical fibers containing fiber Bragg gratings for strain monitoring and temperature sensing are placed in the groove. The embedding is completed by melting subsequent powder layers on top of the fibers. Cross-sectional microscopy analysis of the fabricated components, together with analysis of the Bragg gratings behavior during fabrication indicates a strong substance-to-substance bond between coated fiber and added SS 316 material. Temperature and strain cycling of the embedded sensors demonstrates the ability of gratings to survive the embedding process, and act as sensing elements in harsh environments. In situ strain and temperature measurements from within the component are demonstrated for high dynamic stress levels and elevated temperatures (

The diagnosis of prostate cancer using invasive techniques (such as biopsy and blood tests for prostate-specific antigen) and non-invasive techniques (such as digital rectal examination and trans-rectal ultrasonography) may be enhanced by using an additional dynamic instrumented palpation approach to prostate tissue classification. A dynamically actuated membrane sensor/actuator has been developed that incorporates an optical fibre Fabry–Perot interferometer to record the displacement of the membrane when it is pressed on to different tissue samples. The membrane sensor was tested on a silicon elastomer prostate model with enlarged and stiffer material on one side to simulate early stage prostate cancer. The interferometer measurement was found to have high dynamic range and accuracy, with a minimum displacement resolution of ±0.4 μm over a 721 μm measurement range. The dynamic response of the membrane sensor when applied to different tissue types changed depending on the stiffness of the tissue being measured. This demonstrates the feasibility of an optically tracked dynamic palpation technique for classifying tissue type based on the dynamic response of the sensor/actuator.

A picosecond laser is used for rapid prototyping of enclosed microfluidic devices from borosilicate glass substrates. The fabrication method and applications of these devices for the investigation of subsurface flow processes in porous media are presented.

In this paper we present long-term stability results for a Fabry-Perot optical fibre sensor in high temperatures environments. We introduce an intrinsic Fabry-Perot type of sensor, which its sensing element is made with an undoped pure fused silica cavity. Furthermore, we will present results detailing dopant diffusion from core to cladding of standard optical fibres demonstrating their inherent unsuitability for high temperature environments. Finally, we display the manufacturing technique required to produce this sensor and we present results of 33 days long stability tests conducted at elevated temperatures of more than 900°C.

In this paper two silica hollow core microstructured fibres (Negative Curvature Fibre and Photonic Bandgap Fibre) are presented with attenuations of 0.06 dB/m and 1.1 dB/m at 2.94 μm wavelengths, respectively. This is an important regime for medical applications, specifically surgery due to the existence of a strong absorption peak for water around 3 μm. The guidance of high energy pulses of the order of 195 mJ and 14.4 mJ respectively has been demonstrated. These energies are sufficient to ablate soft and hard biological tissues. As verification porcine bone was ablated in air and submerged in water to simulate practical application of a surgical device. These fibres open the way to a new and fully flexible delivery system for high energy Er:YAG laser radiation.

In this paper, we describe a technique to characterize long period fiber gratings (LPG) by use of a correlation between the measured transmission spectrum and a theoretical model. The model is robust enough to require only a-priori knowledge of the fiber design and the inscription period. We demonstrate the application of this technique on an example LPG resulting in the calculation of the dispersive core index, length, and strength of the grating to better than experimental error. The technique is further expanded to allow for the modeling of metal jacketed long period gratings by use of an extended version of Erdogan's model.

Smart materials with integrated sensing capabilities are now ubiquitous in many structures and devices manufactured from composite materials and they offer enhanced safety, reliability and efficiency in such smart devices. This paper explores the application of embedded sensors to components manufactured using additive layer manufacturing (ALM) technology. ALM offers the ability to create physical parts with little or no restriction in shape and complexity. In this paper, optical fiber sensors incorporating fiber Bragg gratings are embedded inside a component made by, and during a powder-bed-based, layer-by-layer, additive manufacturing process. A commercial EOS P730 system is used, where a laser is employed to sinter the polymeric powder into a 3D component. The fiber embedding approach is based upon insertion of a “fiber-carrier” component, which replaces a removable “place-holder” component during an interruption of the ALM build process. Tensile test specimens fabricated this way are subjected to extended cyclic tensile loading trials at low strain levels of up to 580 μe . The test specimens demonstrate stable and reproducible responses over a period in excess of 720 days and 311000 load cycles. Polyimide and acrylic jacketed fibers are trialled, and the resulting deformations of the component through internal stresses depending on the fiber jacket type are discussed.

We investigate the effect of temperature on a multicore fibre (MCF) curvature sensor. The curvature sensing element is formed from four Fibre Bragg gratings (FBGs) inscribed in a MCF. A fibre optic coupled fan-out device is used to interface the MCF to standard single core fibre optic technology. The peak positions of the FBGs are measured to determine wavelength shift as a result of the curvature induced strain on the fibre. The differential strain allows the curvature of the fibre in a plane to be extracted. The temperature sensitivities of the FBGs and the fan-out device are examined thoroughly.

We present high temperature (~1100°C) stability tests of, Ge-doped and F-doped, optical fibre sensors. Our analysis includes the variation in their behaviours within high temperature environments and how the dopant diffusion affects their long term stability.

A smart metal component having the potential for high temperature strain sensing capability is reported. The stainless steel (SS316) structure is made by selective laser melting (SLM). A fiber Bragg grating (FBG) is embedded in to a 3D printed U-groove by high temperature brazing using a silver based alloy, achieving an axial FBG compression of 13 millistrain at room temperature. Initial results shows that the test component can be used for up to 700°C for sensing applications.

Applications of fibre optic sensors at high temperatures have gained a huge interest recently, as they appeared to be suitable for temperature recording in harsh environments. In this paper, we are demonstrating two intrinsic Fabry-Perot (F-P) fibre optic sensors for high temperature monitoring. The sensors are consisting of a 125μm diameter single mode fibre (SMF28) and a 125μm diameter PCF ESM-12B pure fused silica fibre spliced to a SMF28, respectively. The result was a low finesse optical SMF-Cr-SMF, and SMF-Cr-PCF, sensor with cavity lengths varying from 50μm to 100μm. Both types of Fabry-Perot sensors were tested in a tube furnace over a temperature range from room temperature up to 1100°C. Following a number of annealing cycles, between the above mentioned temperatures range, very good repeatability of the phase response was achieved. During the cycling process, thermal stress relief takes place which makes the sensors suitable for temperature testing at temperatures just in excess of 1000°C. After initial cycling the sensors are subjected to long term stability tests. The phase response is stable, less than 4°C, over a period of 5 days at a temperature of 1050°C for both sensors. The temperature resolution is around 3°C.

We report a compact two-dimensional accelerometer based upon a simple fiber cantilever constructed from a short length of multicore optical fiber. Two-axis measurement is demonstrated up to 3 kHz. Differential measurement between fiber Bragg gratings written in the multicore fiber provides temperature-insensitive measurements.

Proceedings of the 27th Annual International Solid Freeform Fabrication

Hydrogen sensing at low concentrations in the order of tens to hundreds of parts per million (ppm) over extended periods requires highly sensitive and stable sensor technology. Palladium and its alloys are widely used in hydrogen sensing as they show a high and selective affinity for hydrogen. On exposure to hydrogen, Pd experiences a volumetric expansion, roughly proportional to the hydrogen concentration in the environment. This volumetric expansion can be measured either directly by dimensional monitoring or through monitoring of secondary physical effects. Optical sensor technology is a preferred technique for hydrogen sensing because of its inherent safety for use in a potentially explosive environment, and several optical hydrogen sensors have been reported. However, the majority have been designed to measure hydrogen concentrations of a few per cent in air, whereas the sensors described here are capable of operating in concentrations down to hundreds of ppm. Fibre Bragg gratings (FBGs) and interferometric length monitoring are shown to be able to monitor the dimensions of a palladium sensor element. Hydrogenation not only induces physical strain but also changes the electronic configuration resulting in a change in refractive index which can be monitored using a long-period grating (LPG). The paper discusses the respective characteristics of these different optical measurement techniques using Pd and Pd/Ag alloys as sensor elements for hydrogen concentrations between 100 ppm and 1%.

Smart metal having integrated high temperature sensing capability is reported. The SS316 structure is made by additive layer manufacturing via selective laser melting (SLM). Sensor component is embedded in to the structure during the SLM build process. The strain isolated in-fiber Fabry-Perot cavity sensor measures temperature up to 1100 °C inside the metal.

Focused Ion Beam (FIB) machining has been demonstrated to be capable of fabricating nano and micro scale elements onto optical fibres. In this paper we exploit FIB to fabricate core aligned 45° mirrors at the end of multi-core fibres (MCF). The resulting fibre is used as a component in a two dimensional optical fibre accelerometer. The mirror is produced using a two step process: first a scanning process is used to make a rough cut to define the overall mirror structure. This is followed by a polishing process to create an optical surface finish. The machined 45° mirror can be accurately aligned with optical fibre core, which avoids issues associated with the alignment of external turning mirror components. Proof-of-concept tests demonstrate the use of such a fibre as a two axis acceleration sensor that is interrogated interferometrically. The sensor operated between 0.5g and 4.5g with a cross talk of -24.3dB between axes.

The focus of this review is recent work to develop microstructured hollow core fibers for two applications where the flexible delivery of a single mode beam is desired. Also, a brief review of other fiber based solutions is included. High power, short-pulsed lasers are widely used for micro-machining, providing high precision and high quality. However, the lack of truly flexible beam delivery systems limits their application to the processing of relatively small planar components. To address this, hollow-core optical fibers for the 1 μm and green wavelength ranges have been developed. The hollow core overcomes the power delivery limitations of conventional silica fibers arising from non-linear effects and material damage in the solid core. The fibers have been characterized in terms of power handling capability, damage threshold, bend loss and dispersion, and practically demonstrated delivery of high peak power pulses from the nanosecond to the femtosecond regime. Such fibers are ideal candidates for industrial laser machining applications. In laser surgical applications, meanwhile, an Er:YAG laser (2.94 μm) is frequently the laser of choice because the water contained in tissue strongly absorbs this wavelength. If this laser beam is precisely delivered damage to surrounding tissue can be minimized. A common delivery method of surgical lasers, for use in the operating theater, is articulated arms that are bulky, cumbersome and unsuitable for endoscopic procedures. To address this need for flexible mid-IR delivery silica based hollow core fibers have been developed. By minimizing the overlap of the light with glass it is possible to overcome the material absorption limits of silica and achieve low attenuation. Additionally, it is possible to deliver pulse energies suitable for the ablation of both hard and soft tissue even with very small bend radii. The flexibility and small physical size of systems based on these fibers will enable new minimally invasive surgical procedures.

Fiber Bragg Grating (FBG) sensors are embedded into Stainless Steel (SS) 316 components using bespoke Selective Laser Melting (SLM) technology. SS 316 material is added on substrates by SLM, incorporating U-shaped grooves with dimensions suitable to hold nickel coated optical fibers. Coated optical fibers containing fiber Bragg gratings for strain monitoring are placed in the groove. Melting subsequent powder layer on top of the fiber completes the embedding. Strain levels exceeding 3 me are applied to specimens and are measured by embedded fiber optic sensors. Elastic deformation of the steel component is reliably measured by the Bragg grating from within the component with high accuracy. During plastic deformation of the steel the optical fiber is slipping due to poor adhesive bonding between fused silica and metal surround.

We describe the implementation of optical absorption spectroscopy in which aT i:sapphire pumped femtosecond optical parametric oscillator based on aperiodically poled lithium niobate was used as a broadband source to directly acquire a mid-infrared absorption spectrum of methane gas. Fourier transform spectroscopy was performed using the idler output from the optical parametric oscillator to directly acquire spectra spanning over 600 nm (14.4 THz or 480 cm −1 )w ith around 2.2 nm (55 GHz or 1. 9c m −1 ) resolution. Data are presented of absorption measurements in methane at pressures of 2 bar, 250 mbar and 25 mbar. This approach combines the advantages of spectroscopy using a broadband thermal source with the high power and excellent beam quality of a modelocked laser source.

In this paper we propose a novel fibre interferometer for the simultaneous measurement of optical phase at multiple wavelengths generated within the spectral envelope of a femtosecond laser. The use of narro wb andwidth fibre Bragg gratings allows particular wavelengths to be selected with sufficiently narrow bandwidth to give the necessary coherence length for interferometric phase measurements over practical distances exceeding 30 mm. Multi-wavelength interferometry provides a means of making absolute measurements by extending the unambiguous measurement range beyond the wavelength of light. Preliminary experimental results are presented for a two-wavelength sensor where an absolute range of 0.13 mm with 3 nm resolution has been achieved producing a dynamic range of 43 000:1. This approach has the potential to be applied to high speed transient events.

We report the first use of a multicore fibre incorporating fibre Bragg grating strain sensors in each core as a fibre optic pitch and roll sensor. A length of four-core fibre supported at one end forms a cantilever. The differential strains between opposite grating pairs depend on the fibre's orientation in pitch (in the vertical plane) and roll (azimuth) with respect to gravity. Resolutions of +/-2degrees in roll and +/-15degrees in pitch were measured.

We have investigated the effects of ionizing radiation-induced changes on dispersion and refractive index in photonic crystal fibre, boron co-doped photosensitive fibre and standard SMF-28 fibre up to a level of 7 MGy of 60Co γ-radiation. We have been unable to observe any changes within an experimental error of ~1% for the dispersion value and

A novel dual-fibre Bragg grating sensor structure is described, incorporating integrated mechanical stress amplification and temperature compensation by common mode rejection. Stress amplification allows the measurement of very low actuator forces, such as generated by small cross section bellows, for operation as a barometric pressure sensor. We demonstrate a pressure sensor range of 800–1100 hPa and a resolution of 0.1 hPa.

The energy difference between the threshold for free ion-pair formation (X+ + Y−) and the molecular ionization energy (XY+) is relatively large in I2 and ICl. Photodissociation to free ion-pairs in this energy region has been probed by vacuum ultraviolet laser radiation generated by four-wave mixing. The negative ion excitation spectra are highly structured and closely follow the one-photon absorption cross-sections. Several Rydberg series are identified, the f series being particularly prominent. Direct absorption to the free ion-pair continuum is negligible in this region and all of the Rydberg states that are accessed act as efficient doorway states to ion-pair production.

We present the fabrication, characterization and encapsulation of a fibre optic temperature sensor based upon a micro Fabry-Perot (F-P) cavity. The F-P cavity is formed between a reflective in-fibre metallic splice and the air-fibre boundary at the end of the sensor. A change in temperature modifies the optical cavity length and this is observed as a shift in the reflected interference spectrum. The temperature resolution of the sensor is

Micro-cantilever sensors have shown great promise in a wide range of application are as including chemical and biological sensing. However, many of these devices are based upon a sensor ‘chip’ that requires careful alignment between the cantilever and the read-out system, which can be challenging. Furthermore, optical interrogation typically involves a bulky free-space system. Optical fibre addressed cantilevers have been reported previously in the literature and in this paper we propose techniques to design and fabricate polymer micro-cantilevers for attachment onto the end of standard single mode fibres using laser machining. Low-cost optical sources and a fibre coupled spectrometer are employed to monitor the cantilever deflection and therefore observe biological binding between a species of interest and an activated cantilever. Proof-of-concept experiments show that the sensor is capable of detecting pathogen concentration with down to a level of 10 5 cfu/ml.

Metal clad single mode optical fibres containing high reflectivity Bragg gratings are successfully embedded into stainless steel components using bespoke laser based additive manufacturing technology. Temperature cycling of the embedded sensor demonstrates the ability of gratings to survive the embedding process, and act as temperature or strain sensors. At extreme temperatures up to 500 °C, discontinuities in the gratings response are observed and these have been attributed to possible delamination issues at the interface between glass fiber and the surrounding metal.

Additive manufacturing or 3D printing of structural components in metals has potential to revolutionise the manufacturing industry. Embedded sensing in such structures opens a route towards SMART metals, providing added functionality, intelligence and enhanced performance in many components. Such embedded sensors would be capable of operating at extremely high temperatures by utilizing regenerated fibre Bragg gratings and in-fibre Fabry-Perot cavities.

A prototype of a scalable and potentially low-cost stacked array piezoelectric deformable mirror (SA-PDM) with 35 active elements is presented in this paper. This prototype is characterized by a 2 μm maximum actuator stroke, a 1.4 μm mirror sag (measured for a 14 mm × 14 mm area of the unpowered SA-PDM), and a ±200 nm hysteresis error. The initial proof of concept experiments described here show that this mirror can be successfully used for shaping a high power laser beam in order to improve laser machining performance. Various beam shapes have been obtained with the SA-PDM and examples of laser machining with the shaped beams are presented.