This PDF file contains the front matter associated with SPIE Proceedings Volume 10323, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

We review our recent work on chirped-pulse phase-sensitive optical time-domain reflectometry along optical fibers and its application in the measurement of true nanostrain variations in the kHz frequency range over km-long fibers. We also show how this technique can be used to perform distributed photothermal measurements of gas presence in suitable microstructured fibers

A Distributed Vibration Sensor Based on Phase-Sensitive OTDR is numerically modeled. The advantage of modeling the building blocks of the sensor individually and combining the blocks to analyse the behavior of the sensing system is discussed. It is shown that the numerical model can accurately imitate the response of the experimental setup to dynamic perturbations a signal processing procedure similar to that used to extract the phase information from sensing setup.

A distributed acoustic sensing system (DAS) with low-coherence ASE and Michelson interferometer based on continuous width-band ultra-weak fiber Bragg grating (UW-FBG) array is proposed and experimentally demonstrated. The experimental result shows that the proposed system has better performance in detecting acoustic waves than the conventional hydrophone.

We propose a novel BOTDA that can measure a BFS change appearing on a time axis with a single-shot measurement by using a frequency-swept probe pulse. The proposed method employs a very simple laser control and detection system, without precise test light frequency control, and with an oscilloscope. We demonstrate a fast BFS distribution measurement completed within 0.33 s with 1.8 MHz BFS accuracy for a 10 km range, and discuss its advantages compared with conventional BOTDA.

Long period fiber grating (LPFG) has been actively researched in bio-sensing applications owing to its ability to sense refractive index (RI) of the surrounding medium. We investigate on the adequacy of the present state of the art to quantify adsorption of bio-molecules on the surface of the fiber confined within few tens of nanometers and possible improvements in the design of sensors suitable for bio-sensing applications.

This work presents the proof of concept of the detection of global and surface optical index variations by surface plasmon resonance (SPR) thanks to optical fiber bundles. This work is the first necessary step for the future design of a lab-on-fiber tool dedicated to molecular analysis for endoscopic diagnosis. Our approach is based on nanostructured optical fiber bundles comprising several thousands of individual optical fibers. These nanostructures were coated by a thin gold layer in order to gain interesting optical properties such like SPR. The sensitivity and resolution of the bundle to global optical index changes were measured in retro-reflection. We performed numerical simulations in order to optimize the fiber tip geometry, gold coating thickness and finally enhance their analytical performances. We achieved a resolution of 10^-4 refractive index unit, which is fully compatible with the detection of biological interactions involving large proteins or bacteria. Finally, we proved that our sensor was sensitive to surface optical index variations and able to detect the adsorption of a thin self-assembled molecular layer.

Two novel configurations of multi-parameter fiber-optic sensing systems based on the fiber random grating are reported. The fiber random grating is fabricated through femtosecond laser induced refractive index modification over a 10cm standard telecom single mode fiber. In one configuration, the reflective spectrum of the fiber random grating is directly detected and a wavelength-division spectral cross-correlation algorithm is adopted to extract the spectral shifts for simultaneous measurement of temperature, axial strain, and surrounding refractive index. In the other configuration, a random fiber ring laser is constructed by incorporating the random feedback from the random grating. Numerous polarization-dependent spectral filters are formed along the random grating and superimposed to provide multiple lasing lines with high signal-to-noise ratio up to 40dB, which enables a high-fidelity multi-parameter sensing scheme by monitoring the spectral shifts of the lasing lines. Without the need of phase mask for fabrication and with the high physical strength, the random grating based sensors are much simpler and more compact, which could be potentially an excellent alternative for liquid medical sample sensing in biomedical and biochemical applications.

A multi-port microcoil resonator magnetic field sensor based on a microfiber coupler coil resonator (MMCR) is presented. The microfiber coupler coil is fabricated by coiling a four-port microfiber coupler with a uniform waist region around a low index support rod. The MMCR is embedded in a low refractive index polymer to increase the robustness and operation stability. The enhanced sensor response to the magnetic field is ascribed to the diverse MMCR response to the light polarization state. The MMCR magnetic field sensor is compact and low cost, and exhibits a magnetic field sensitivity of 37.09 dB/T with an estimated minimum detection limit (DL) of ~ 27 μT.

We present all-fiber resonating Fabry-Perot gas cells made with a piece of hollow-core photonic bandgap fiber (HCPBF) sandwiched by two single mode fibers with mirrored ends. A HC-PBF cavity made of 6.75-cm-long HC-1550-06 fiber achieved a cavity finesse of 128, corresponding to an effective optical path length of 5.5 m. Such HC-PBF cavities can be used as absorption cells for high sensitivity gas detection with fast response. Preliminary experiment with a 9.4-cm-long resonating gas cell with a finesse of 68 demonstrated a detection limit better than 7.5 p.p.m. acetylene.

We propose a novel type of compact multichannel MEMS based spectrometer, where we replace the linear detector with a Digital Micromirror Device (DMD). The DMD is typically cheaper and has better pixel sampling than an InGaAs detector used in the 1550 nm range, which leads to cost reduction and better performance. Moreover, the DMD is a 2D array, which means that multichannel systems can be implemented without any additional optical components in the spectrometer. This makes the proposed interrogator highly cost-effective. The digital nature of the DMD also provides opportunities for advanced programmable spectroscopy.

In this paper, we propose a novel approach to measurements of low relative humidity (RH) levels based on the whispering gallery modes (WGMs) phenomenon in a silica microsphere resonator coated with Agarose. The spectral dips of the WGM resonances excited in the proposed sensor depend strongly on the changes in the refractive index (RI) of the coating material as well as the surrounding RI. A study of the humidity-induced RI changes in a thin Agarose layer, applied to the surface of a 162 μm-diameter silica microsphere was carried out by correlating the experimental results and numerical simulations performed using the perturbation theory. We experimentally demonstrate a linear sensing characteristic in a low-humidity range from 10% to 45% RH. The estimated quality factor of the micro-resonator is 2.82×10⁶ and detection limit for the sensor is 0.057 %RH, corresponding to the RI resolution of 8.4×10^-7 RIU.

In this paper we present an overview of the current efforts towards integration of Fiber Bragg Grating (FBG) sensor interrogators. Different photonic integration platforms will be discussed, including monolithic planar lightwave circuit technology, silicon on insulator (SOI), indium phosphide (InP) and gallium arsenide (GaAs) material platforms. Also various possible techniques for wavelength metering and methods for FBG multiplexing will be discussed and compared in terms of resolution, dynamic performance, multiplexing capabilities and reliability. The use of linear filters, array waveguide gratings (AWG) as multiple linear filters and AWG based centroid signal processing techniques will be addressed as well as interrogation techniques based on tunable micro-ring resonators and Mach-Zehnder interferometers (MZI) for phase sensitive detection. The paper will also discuss the challenges and perspectives of photonic integration to address the increasing requirements of several industrial applications.

One of the major challenges when using fiber Bragg grating sensors (FBGs) to detect Lamb wave or acoustic emission signals in structures is the low sensitivity of these sensors to surface waves propagating in the structure. The authors have previously demonstrated that remote bonding of the optical fiber away from the FBG can increase the measured signal amplitude. In this paper we investigate the potential mechanisms for this increase through finite element simulations and demonstrate that the shear lag effect through the adhesive is the major source of the signal amplitude difference between the direct and remote bonding cases.

A new type of photodetector with an optical sensor is presented, which enables it to operate even in the presence of strong electro-magnetic interference. The optical sensor head consists of cascaded Fabry-Perot etalons coated with a new type of photo-thermal coating comprising of hydrogel-embedded copper-oxide micro-particles. For white-light irradiation, the photodetector exhibits a power sensitivity of 760 pm/mW, a detection limit of 16.4 μW, and an optical damage threshold of ∼100 mW or ∼800 mW/cm². The response and recovery times are 3.0 s (∼90% of change within 100 ms) and 16.0 s.

A fiber-based device for testing mechanical properties of cartilage is presented within this study. The measurement principle is based on stepwise indentation into the tissue and observing of corresponding relaxation of the stress. The indenter tip is constituted of a cleaved optical fiber that includes a fiber Bragg grating which is used as the force sensor. Stress relaxation measurements at 25 different positions on a healthy bovine cartilage sample were performed to assess the behavior of healthy cartilage. For each indentation step a good agreement was found with a viscoelastic model that included two time constants. The model parameters showed low variability and a clear dependence with indentation depth. The parameters can be used as reference values for discriminating healthy and degenerated cartilage.

In this paper we propose and investigate a novel magnetic field sensor based of a ring erbium-doped fiber laser combined with a fiber Bragg grating and a Sagnac loop containing a microfiber coupler and magnetic fluid. In addition to the magnetic field sensing capability, the proposed structure can simultaneously provide temperature information. Thanks to the dual-ring structure of the MFC-Sagnac loop and the FBG-assisted resonant cavity, the output has two distinct laser peaks. Experimentally demonstrated magnetic field sensitivity of one of the laser peaks is 15 pm/mT in the magnetic field range from 0 to 100 mT. The spectral position of the second laser peak is independent on the magnetic field but shifts towards long wavelengths with a sensitivity of 13 pm/°C.

Coherent fading noise (also known as speckle noise) affects the SNR and sensitivity of Distributed Acoustic Sensing (DAS) systems and makes them random processes of position and time. As in speckle noise, the statistical distribution of DAS SNR is particularly wide and its standard deviation (STD) roughly equals its mean (σ_SNR/⟨SNR⟩ ≈ 0.89). Trading resolution for SNR may improve the mean SNR but not necessarily narrow its distribution. Here a new approach to achieve both SNR improvement (by sacrificing resolution) and narrowing of the distribution is introduced. The method is based on acquiring high resolution complex backscatter profiles of the sensing fiber, using them to compute complex power profiles of the fiber which retain phase variation information and filtering of the power profiles. The approach is tested via a computer simulation and demonstrates distribution narrowing up to σ_SNR/⟨SNR⟩ < 0.2.

Distributed fibre optic acoustic sensing (DAS) can serve as an excellent tool for real-time condition monitoring of a variety of industrial and civil infrastructures. In this paper, we portray a subset of our current research activities investigating the usability of DAS based on coherent optical time-domain reflectometry (C-OTDR) for innovative and demanding condition monitoring applications. Specifically, our application-oriented research presented here aims at acoustic and vibrational condition monitoring of pipelines and piping systems, of rollers in industrial heavy-duty conveyor belt systems and of extensive submarine power cable installations, respectively.

A technique based on a multi-dimensional signal processing approach is here described for performance enhancement of distributed optical fibre sensors. In particular, the main features of linear and nonlinear image denoising techniques are described for signal-to-noise ratio enhancement in Brillouin optical time-domain analysers. Experimental results demonstrate the possibility to enhance the performance of distributed Brillouin sensors by more than 13 dB using a nonlinear image denoising approach, while more than 20 dB enhancement can be obtained with video denoising.

This paper presents new techniques designed to improve the performances of a BOTDR. The first one introduces a second pump to the sensor, thus doubling the Brillouin signal on the receiver. The second one uses image processing with a two-dimensional Gaussian filter whose parameters are defined. The last technique explores the possibilities offered by colour codes. The benefits of each, in terms of signal-to-noise ratio, is presented by comparing measurements over a distance range of 50km with a spatial resolution of 5m. These techniques can easily be combined and the global improvement is estimated at 10dB, compared to conventional sensors.

We report an experimental study on the spectral dependence of depolarized guided acoustic-wave Brillouin scattering (GAWBS) in a silica single-mode fiber (SMF) on acoustic impedance of external materials. The GAWBS spectrum was measured when the acoustic impedance was changed from 1.51 to 2.35 kg/s⋅mm². With increasing acoustic impedance, the linewidth increased; the dependence was almost linear in the range up to ∼2.0 kg/s⋅mm² with an acoustic impedance dependence coefficient of 0.16 MHz/kg/s⋅mm², which is directly applicable to acoustic impedance sensing. Meanwhile, with increasing acoustic impedance, the central frequency nonlinearly decreased, which probably originates from the change in the effective outer diameter of the silica SMF.

Temperature and strain discrimination is experimentally demonstrated in an elliptical-core polarization-maintaining fiber by making use of Rayleigh-based distributed birefringence measurements and the frequency shift of the correlation peak obtained by standard coherent optical time-domain reflectometry. The high sensitivity of coherent Rayleigh sensing and the very distinct behavior of birefringence makes the two quantities clearly discriminated, resulting in temperature and strain accuracies of ~ 40 mK and ~ 0.5 με, respectively, for distributed measurements with a 2 m spatial resolution.

We propose and experimentally demonstrate a pulse compression phase sensitive optical time domain reflectometer (φ- OTDR) with sub-meter resolution. Principle and theoretical analysis on the spatial resolution, the feasibility to obtain the phase information are provided. This technique can break the tradeoff between spatial resolution and measurement range in the traditional φ-OTDR. As example, our verifying experiment achieves 30cm spatial resolution and 20km measurement range, and the signal to noise ratio (SNR) reaches 10dB. To our knowledge, this is the first time that such a high spatial resolution over such a long sensing range is reported in φ-OTDR-based distributed vibration sensing.

Implementation of Optical Frequency Domain Reflectometry (OFDR) requires a source whose instantaneous frequency can be accurately scanned over a sufficiently wide frequency range. Achieving high repetition rates of accurate linear frequency sweeps can be rather challenging. In contrast, fast and accurate Sinusoidal Frequency Scan (SFS-OFDR) can be easily implemented via direct or external optical frequency modulation. While enabling high spatial resolution measurements of a sensing fiber at high scan rates, SFS-OFDR requires a special processing algorithm to convert the detector output to fiber profiles. Previous implementation of the algorithm involved O(N²) complexity and prohibited real time operation. In this work a novel algorithm for processing SFS-OFDR raw data is introduced. Based on two consecutive FFT operations, the algorithm produces the fiber profile with O(NlogN) operations and lends itself for real time applications. The new method was tested via simulation and experiment. It enabled static detection with high resolution (~3m) at 64km and highly sensitive dynamic detection (stretching amplitude of 70nm) near the end of a 64km sensing fiber with spatial resolution <10m and with 400Hz scan repetition rate.

We present an enhanced performance Brillouin optical time-domain analysis sensor that uses dual probes waves with optical frequency modulation and cyclic coding. The frequency modulation serves to increase the probe power that can be injected in the fiber before the onset of non-local effects and noise generated by spontaneous Brillouin scattering. This leads to higher detected signal-to-noise ratio (SNR), which is further increased by the coding gain. The enhanced SNR translates to extended range for the sensor, with experiments demonstrating 1-m spatial resolution over a 164 km fiber loop with a 3-MHz Brillouin frequency shift measurement precision at the worst contrast position. In addition, we introduce a study of the power limits that can be injected in the fiber with cyclic coding before the appearance of distortions in the decoded signal.

This work shows the possibility of using chirped pulse amplification concepts in order to increase the signal-to-noise ratio (SNR) of phase sensitive optical time domain reflectometry (ΦOTDR) sensors. This method allows to increase the SNR of a ΦOTDR sensor without sacrificing spatial resolution. Here, we report a ΦOTDR sensor with a spatial resolution of 3 mm (limited only by the available detection equipment) and an SNR increase of 20 dB over the traditional architecture. To our knowledge, this is the highest-resolution ΦOTDR sensor reported to date.

Discriminative measurement of strain and temperature distribution is experimentally demonstrated by optical time-domain reflectometry of Brillouin dynamic grating (BDG-OTDR) in an elliptical core two-mode fiber (e-core TMF). The acoustic waves generated by the amplified spontaneous Brillouin scattering of LP₀₁ mode in x-polarization are used to reflect the LP₁₁ mode in x- and y-polarizations. Distribution maps of intermodal birefringence between the LP₀₁ and LP₁₁ modes with two different polarizations are measured to separate strain and temperature induced spectral shift of the BDG in a 95 m ecore TMF with 2.0 m spatial resolution. The strain and temperature sensitivities are measured to be ‒0.082 MHz/με and 6.8 MHz/°C for the pair of LP₀₁ ^y-LP₁₁ ^x modes, and ‒0.095 MHz/με and 3.9 MHz/°C for the pair of LP₀₁ ^x-LP₁₁ ^x modes, respectively.

Distributed fiber-optic sensing (DFOS) has drawn great attention in both academic research and industrial applications due to its unique advantages. Recent progress at University of Electronic Science and Technology of China (UESTC) in DFOS, mainly on ultra-long-distance Brillouin optical time-domain analysis (BOTDA) and phase-sensitive optical timedomain reflectometry (Φ-OTDR), is discussed in this paper, including research progress and real-life applications.

We investigate geometries for efficient coupling of single ions to fiber-coupled light fields for applications in quantum sensing, quantum metrology, and quantum information processing. Specifically, we discuss the integration of fiber-tip microcavities into radio-frequency ion traps. The distortions of the trapping fields induced by the presence of the optical fibers are simulated for a range of ion trap geometries and the most promising arrangements are identified. Finally, we investigate the use of fiber-tip microcavities with non-spherical mirrors for enhanced ion-light coupling at the center of the trap by appropriate shaping of the cavity modes.

Pound-Drever-Hall (PDH) technique has been widely adopted for ultrahigh resolution fiber-optic sensors, but its performance degenerates seriously as the light power drops. To solve this problem, we developed a coherent PDH technique for weak optical signal detection, with which the signal-to-noise ratio (SNR) of demodulated PDH signal is dramatically improved. In the demonstrational experiments, a high resolution fiber-optic sensor using the proposed technique is realized, and n"-order strain resolution at a low light power down to -43 dBm is achieved, which is about 15 dB lower compared with classical PDH technique. The proposed coherent PDH technique has great potentials in longer distance and larger scale sensor networks.

The use of photonic sensors to monitor horses is presented and reviewed. Results are very promising and can be used in other areas to monitor animals, machines or industrial processes.

We report the development of an optical fibre probe which could find use as an aid for margin detection during surgery. A fluorophore doped polymer is coated on an optical fibre tip, allowing for pH values of unknown tissue to be measured and compared to healthy tissue, to discriminate between healthy and cancerous tissue.

This probe is integrated within a portable system, requiring no alignment or access to specialised vibration damped optical tables. A miniature spectrometer allows for measurements to be performed on-site, opening up the potential for use of these probes within the operating theatre for in-vivo measurements.

We have developed a chip-scale optofluidic sensor for biomolecular detection, by tapering laterally aligned silica microfiber and capillary to form a modal interferometer. With the pre-immobilization of DNA probes, the sensor is capable of selectively detecting single-stranded microRNA-let7a (molecular weight: 6.5 k) by measuring the spectral shift of the interferometric spectrum. A log-linear response from 2 nM to 20 μM and a minimum detectable concentration of 212 pM (1.43 ng/mL) have been achieved. The sensor is promising for future diagnosis applications due to its high sensitivity, resistance to environmental perturbations, improved portability, and intrinsic connection to fiber optic measurement.

A compact fiber grating laser has been exploited as an ultrasound sensor to probe optically induced spherical elastic waves, taking advantage of its response in beat-frequency variation of the laser output. Optical-resolution photoacoustic microscopy (PAM) is further implemented with such a sensor by raster scanning the excitation light with a 2-axis galvo scanner. A PAM image of mouse ear with a field width of 2 mm is demonstrated. The wide field-of-view of the sensor allows the implementation of fast-scanning PAMs which is attractive for in vivo imaging applications.

Degradation of olive oil under light and heat are analysed using an optical fibre based low-cost portable smartphone spectrofluorimeter. Visible fluorescence bands associated with phenolic acids, vitamins and chlorophyll centred at λ ∼ 452, 525 and 670 nm respectively are generated using near-UV excitation (LED λ_ex ∼ 370 nm), of extra virgin olive oil are degraded more likely than refined olive oil under light and heat exposure. Packaging is shown to be critical when assessing the origin of degradation.

A frequency-domain method is proposed to measure the inertial response of forward stimulated Brillouin scattering, so that the acoustic impedance of a liquid medium outside an uncoated 30 m standard single-mode fibre can be sensed. The proposed technique overcomes the linewidth distortion present in the time-domain approach due to Kerr effect and reduce time and complexity for data post-processing. Experimental results demonstrate that acoustic impedances of water and ethanol agree well with the expected values.

A magnetic field fiber optic sensor based on Nano-magnetic fluid and Hi-Bi non-adiabatic tapered optical fiber in fiber loop mirror (HB-TFLM) is proposed and theoretically explained. As compared to the reported magnetic fluid (MF) based sensors, the achieved sensitivity of the proposed sensor is 255 pm/mT, which is enhanced by 3.6 times of magnitude relative to in line non-adiabatic tapered optical fiber sensor, used only 0.1% of the volume concentration of MF nanoparticles. Detection limit of the HB-TFLM to external magnetic field in range from 0 to 21 mT and 22 to 50 mT was 7.8 μT and 39.2 μT, respectively.

Label-free biosensing using optical long-period gratings (LPGs) induced in optical fiber and coated with biological compound enables for detection and monitoring the kinetics of reactions taking places on the sensor’s surface. The labelfree detection effect for the LPG biosensor working near the dispersion turning point (DTP) of higher order cladding modes can be observed as resonance wavelength shift induced by binding of biomolecules to fiber surface. In this study we analyzed shift of the resonance wavelength for LPG after its functionalization with DNA layer and during DNA hybridization. It has seen found that the LPG is able to be functionalized with DNA oligonucleotide, acting as a probe and after the functionalization can selectively bind specific complementary DNA oligonucleotides in a very low concentration. DNA-coated LPG can be used as a probe capturing specific DNA sequences with wide ranges of concentrations from 0.1 to 10 pM. Hybridization of the DNA on the fiber surface has also been verified with Midorii Green florescent marker.

In this work is discussed an effect of nanocoating long-period grating (LPG) with an aluminum oxide (Al2O3) on its refractive index (RI) and temperature (T) sensitivity. For comparison two LPGs, namely one before and after the nanocoating process were optimized towards working at dispersion turning point (DTP) of higher order cladding modes. The DTP was reached with two methods, i.e., by wet etching of LPG’s cladding and by optimized deposition of Al₂O₃ thin overlay using atomic layer deposition (ALD) method. For both the cases we show significant increase in RI sensitivity at DTP. When Al₂O₃ is deposited the RI sensitivity reaches 9270 nm/RIU for traced only one resonance out of the pair and RI in range 1.33-1.34 RIU, what is over 4-fold higher than for the bare LPG. Moreover, T sensitivity for both the structures was compared and the one for Al₂O₃-coated sample was found to be only up to 12% higher than for the bare sample. Higher RI sensitivity and low temperature cross-sensitivity effects allow for more accurate RI measurements than in case of bare LPGs. The Al2O3-nanocoated LPGs can further find applications in label-free biosensing, due to their optimized sensitivity in RI in range close that of water.

Optical fiber sensors are very useful to monitor the internal strain and temperature in composites during manufacturing and assembly as well as in practical operations. The authors have been using both multi-point and distributed strain monitoring techniques to characterize the internal state of composite structures. This paper reports some recent developments of life cycle monitoring and quality control of aerospace composite structures. Specifically, distributed sensing for large-scaled parts, through-thickness strain monitoring for complex-shaped parts, and direction-dependent cure shrinkage monitoring are described, highlighting wide applicability of embedded optical fiber sensors for intelligent process monitoring and quality assessment of composite parts.

The extrusion nozzles of three low cost desktop 3D printers are characterised using optical fibre Bragg gratings. Temperature profiles show remarkably consistent distributions pointing to operation as good quality micro-furnaces potentially not only for 3D printing but also optical fibre drawing.

Dynamic fibre-optic curvature sensing is demonstrated by interrogating chains of fibre segments, separated by broadband Bragg grating reflectors, using range-resolved interferometry (RRI). Four fibre strings, containing four fibre segments each of gauge length 20 cm, are attached to the opposing sides of a support structure and the resulting differential strain measurements allow inference of lateral displacements of a cantilever test object. Dynamic tip displacement resolutions in the micrometre range at an interferometric bandwidth of 21 kHz demonstrate the suitability of this approach for highly sensitive and cost-effective fibre-optic directional vibration measurements of smart structures.

Distributed sensing by means of polarimetric analysis of the Rayleigh scattering has been among the first distributed optical fiber sensors ever proposed. Despite offering some unique features, like distributed sensing of magnetic fields and torsion, the method has not yet achieved full commercial maturity. The talk will review the present state of art, highlighting limits and potentialities.

A high-finesse silica waveguide ring resonator (WRR) is designed and a new record is demonstrated experimentally. The finesse and the resonant depth of the silica WRR with a length of 7.9 cm and a diameter of 2.5 cm are 196.7 and 98%, respectively. In addition, the silica WRR is pigtailed with single-polarization fiber to improve the polarization extinction ratio thus to reduce the polarization error. With the application of this high-finesse and high polarization extinction ratio WRR to the resonant micro-optic gyroscope (RMOG), a bias stability of 0.004°/s was observed over a one-hour timeframe.

We demonstrate operation of an interferometric optical gyroscope that uses an on-chip 3m ultra-low-loss silicon nitride waveguide coil. The measured minimum waveguide loss of the waveguide coil fabricated using lithographic die stitching was 0.78 dB/m. The angle random walk and bias instability of the gyroscope were characterized to be 8.52 deg/hr^1/2 and 58.7 deg/hr respectively.

In recent years, whispering gallery mode devices have extended their functionality across a number of research fields from photonics to sensing applications. Here, we will discuss environmental sensing applications, such as pressure, flow, and temperature using ultrahigh Q-factor microspheres fabricated from ultrathin optical fiber and microbubbles fabricated from pretapered glass capillary. We will discuss device fabrication and the different types of sensing that can be pursued using such systems. Finally, we will introduce the concept of using cavity ring-up spectroscopy to perform dispersive transient sensing, whereby a perturbation to the environment leads to a frequency mode shift, and dissipative transient sensing, which can lead to broadening of the mode, in a whispering gallery mode resonator.

We present novel optical fiber designs to improve performance of distributed optical fiber sensors based on Rayleigh and Brillouin scatterings, including hybrid core fiber for increasing Rayleigh backscattered signal, dual core fiber for simultaneous measurement of temperature and stain, few mode fiber for enhancing sensitivity and spatial resolution and Brillouin frequency managed fiber for increasing sensing range.

We review the unique properties of a so-called optical fiber fuse phenomenon in plastic optical fibers (POFs), including its slow propagation velocity (1–2 orders of magnitude slower than that in silica fibers) and threshold power density (1/180 of the value for silica fibers). We also show that an oscillatory continuous curve instead of periodic voids is formed after the passage of the fuse, and that the bright spot is not a plasma but an optical discharge, the temperature of which is ~3600 K. We then discuss its impact on distributed Brillouin sensing based on POFs.

A spider uses up to seven different types of silk, all having specific functions, to build its web. For scientists, native silk - directly extracted from spiders - is a tough, biodegradable and biocompatible thread used mainly for tissue engineering and textile applications. Blessed with outstanding optical properties, this protein strand can also be used as an optical fibre and is, moreover, intrinsically sensitive to chemical compounds. In this communication, a pioneering proof-of-concept experiment using spider silk, in its pristine condition, as a new type of fibre-optic relative humidity sensor will be demonstrated and its potential for future applications discussed.

A new instrumentation system for FBG interrogation is proposed. It combines the use of a VCSEL as a tunable laser and an optical frequency comb generator as a selective broadband source. Features such as auto-calibration and wave-length tracking are provided with this interrogation system. First a fast sweep searches for the FBG spectral position, its reflection profile and finds the best set of operating points for the optical comb. Then, the VCSEL is tuned with the FBG through a feedback loop to withstand large-range slow changes (strain and temperature) and, at the same time, the faster phenomena (vibrations and ultrasounds) are measured by the optical frequency comb generator. In practice, a dual comb is proposed to interrogate actively the FBG reflection in order to obtain radio frequency signals that contain the FBG dynamic-strain due to applied vibrations.

Optical fibres have been explored widely for their sensing capability to meet increasing industrial needs, building on their success in telecommunications. This paper provides a review of research activities at City University of London in response to industrial challenges through the development of a range of fibre Bragg grating (FBG)-based sensors for transportation structural monitoring. For marine propellers, arrays of FBGs mapped onto the surface of propeller blades allow for capturing vibrational modes, with reference to simulation data. The research funded by EU Cleansky programme enables the development of self-sensing electric motor drives to support ‘More Electric Aircraft’ concept. The partnership with Faiveley Brecknell Willis in the UK enables the integration of FBG sensors into the railway current-collecting pantographs for real-time condition monitoring when they are operating under 25kV conditions.

In this paper a sensor system for multi-parameter electrical machine condition monitoring is reported. The proposed FBG-based system allows for the simultaneous monitoring of machine vibration, rotor speed and position, torque, spinning direction, temperature distribution along the stator windings and on the rotor surface as well as the stator wave frequency. This all-optical sensing solution reduces the component count of conventional sensor systems, i.e., all 48 sensing elements are contained within the machine operated by a single sensing interrogation unit. In this work, the sensing system has been successfully integrated into and tested on a permanent magnet motor prototype.

Blade tip timing is an upcoming technology to research possibilities of working point identification and phenomena like stall and blade vibrations for axial compressors. This method determines blade bendings for each individual compressor blade. Due to their high timing resolution optical sensors are often used in this field. Real blade bendings are often of very small amplitudes in the range of micrometers. So it's important to have a reference system that is as accurate as possible. This paper describes a method which guarantees a high resolution and high precision reference system to improve the results of blade tip timing.