John C.

Vol 5 Article ID: 0068 DOI: 10.34133/adi.0068
Over the past decade, smartphones and various offshoot wearables have become indispensable consumer devices attracting considerable attention beyond telecommunications providing accessible edge computing and data generation into the Internet. Particularly, sensing technologies are rising, and advanced analytics both at the edge and exploiting online computing and camera imaging are growing. The data generated from these are already being… Show more

Vol 5 Article ID: 0068 DOI: 10.34133/adi.0068
Over the past decade, smartphones and various offshoot wearables have become indispensable consumer devices attracting considerable attention beyond telecommunications providing accessible edge computing and data generation into the Internet. Particularly, sensing technologies are rising, and advanced analytics both at the edge and exploiting online computing and camera imaging are growing. The data generated from these are already being collated, stored, processed, and used by various commercial enterprises, raising considerable regulatory and ethical challenges across multiple sectors. At the core of all this remain simple cost-effective sensor technologies and the work toward that. This review examines these sensor technologies to highlight challenges being solved to achieve full-spectrum Internet of Things (IoT), using advances in sensing and material processing including the pivotal role of additive manufacturing in accelerating deployment testing and understanding of these sensors and diagnostic elements. These sensors are the points from which the intelligent IoT “feels”, detects, and makes ideally real-time assessments, creating a global sensory network founded on light that, to our present knowledge, knows no natural equivalent, potentially turning the earth itself into the skeleton of an intelligent organism. It introduces the sensor side of the coming IoT, and while the focus is on smartphone technologies, the principles apply to the majority of IoT network edge technologies. Show less

Using the flexibility and diversity of material and structure designs possible with 3D printing fiber technology, an all-solid photonic crystal fiber (PCF) is fabricated using borate (B2O3) doping. The geometry, material, and optical properties of this 3D printed PCF are characterized and analyzed using optical microscopy, scanning electron microscopy (SEM), fiber index profilometry, and Fourier transform infrared (FTIR) microscopy. Analysis demonstrates that B2O3 doped in fabricated PCF has… Show more

Using the flexibility and diversity of material and structure designs possible with 3D printing fiber technology, an all-solid photonic crystal fiber (PCF) is fabricated using borate (B2O3) doping. The geometry, material, and optical properties of this 3D printed PCF are characterized and analyzed using optical microscopy, scanning electron microscopy (SEM), fiber index profilometry, and Fourier transform infrared (FTIR) microscopy. Analysis demonstrates that B2O3 doped in fabricated PCF has experienced evaporation leading to mass loss during drawing. In addition, there is no observable difference between the structure of substrate silica (SiO2) and the SiO2 nanoparticles. However, microdomain differences may explain enhanced reflectance. Furthermore, a Mach–Zehnder interferometer (MZI) sensor is constructed with this 3D printed solid PCF and applied to temperature, refractive index, tensile force, and bending sensing. The specially designed 3D printed PCF has maximum temperature sensitivity up to Δλ/ΔT ≈0.075 nm °C−1. When immersed in 76.34 wt.% glycerol-water solution, the sensitivity can be further improved. These results demonstrate that 3D printing fiber technology enables the custom fabrication of highly sensitive optical fiber sensors, increasing opportunities for the development of diverse and flexible sensors and devices for future internet-of-things (IoT) applications. Show less

Compact, magnetic field, 𝐵 sensing is proposed and demonstrated by combining the two Faraday rotation elements and beam displacement crystals within a micro-optical fiber circulator with a fiber reflector and ferromagnets to allow high contrast attenuation in an optical fiber arm. Low optical noise sensing is measured at 𝜆=1550nm as a change in attenuation, 𝛼, of optical light propagating through the rotators and back. The circulator’s double-pass configuration, using a gold mirror as a… Show more

Compact, magnetic field, 𝐵 sensing is proposed and demonstrated by combining the two Faraday rotation elements and beam displacement crystals within a micro-optical fiber circulator with a fiber reflector and ferromagnets to allow high contrast attenuation in an optical fiber arm. Low optical noise sensing is measured at 𝜆=1550nm as a change in attenuation, 𝛼, of optical light propagating through the rotators and back. The circulator’s double-pass configuration, using a gold mirror as a reflector, achieves a magnetic field sensitivity 𝑠=Δ𝛼/Δ𝐵=(0.26±0.02)dB/mT
with a resolution of Δ𝐵=0.01mT, over a detection range 𝐵=0−89mT. The circulator as a platform provides direct connectivity to the Internet, allowing remote sensing to occur. The method described here is amenable to multisensor combinations, including with other sensor technologies, particularly in future integrated waveguide Faraday optical circuits and devices, extending its utility beyond point magnetic field sensing applications. Show less

With the advent of the smart information network, optical fibre is evolving from a telecommunication medium to a network device with multiple functions, from laser amplification to distributed sensing. This increasing added function of optical fibre is posing new challenges for specialty optical fibre manufacture. In this article, twin core bismuth and erbium co-doped silica optical fibre (TCBEDF) was manufactured using 3D printing technology. This approach effectively avoided the tedious steps… Show more

With the advent of the smart information network, optical fibre is evolving from a telecommunication medium to a network device with multiple functions, from laser amplification to distributed sensing. This increasing added function of optical fibre is posing new challenges for specialty optical fibre manufacture. In this article, twin core bismuth and erbium co-doped silica optical fibre (TCBEDF) was manufactured using 3D printing technology. This approach effectively avoided the tedious steps involved with traditional chemical vapour deposition (CVD) technology, such as deposition, doping and drilling, greatly simplifying the manufacturing process of optical fibre preforms. The fabricated TCBEDF has potential emission and sensing applications. The broadband luminescence over wavelength span Δλ ∼ 950–1600 nm was obtained under laser excitation at λ = 830 nm. At the same time, the dual core structure, despite some distortion in profile, provided a polarized ultra-broadband fluorescence. In addition, the dual core structure was used to construct a Mach–Zehnder interferometer (MZI) to demonstrate the sensing of multiple parameters, including temperature, refractive index, stress and bending. Show less

The utilisation of plants directly as quantifiable natural sensors is proposed. A case study measuring surface wettability of Aucuba japonica, or Japanese Laurel, plants using a novel smartphone field interrogator is demonstrated. This plant has been naturalised globally from Asia. Top-down contact angle measurements map wettability on-site and characterise a range of properties impacting plant health, such as aging, solar and UV exposure, and pollution. Leaves at an early age or in the shadow… Show more

The utilisation of plants directly as quantifiable natural sensors is proposed. A case study measuring surface wettability of Aucuba japonica, or Japanese Laurel, plants using a novel smartphone field interrogator is demonstrated. This plant has been naturalised globally from Asia. Top-down contact angle measurements map wettability on-site and characterise a range of properties impacting plant health, such as aging, solar and UV exposure, and pollution. Leaves at an early age or in the shadow of trees are found to be hydrophobic with contact angle θ ~ 99°, while more mature leaves under sunlight are hydrophilic with θ ~ 79°. Direct UVA irradiation at λ = 365 nm is shown to accelerate aging, changing contact angle of one leaf from slightly hydrophobic at θ ~ 91° to be hydrophilic with θ ~ 87° after 30 min. Leaves growing beside a road with heavy traffic are observed to be substantially hydrophilic, as low as θ ~ 47°, arising from increased wettability with particulate accumulation on the leaf surface. Away from the road, the contact angle increases as high as θ ~ 96°. The results demonstrate that contact angle measurements using a portable diagnostic IoT edge device can be taken into the field for environmental detection, pollution assessment and more. Using an Internet connected smartphone combined with a plant sensor allows multiple measurements at multiple locations together in real-time, potentially enabling tracking of parameter change anywhere where plants are present or introduced. This hybrid integration of widely distributed living organic systems with the Internet marks the beginning of a new bionic Internet-of-things (b-IoT). Show less

EXPERT PANEL: P. Cebon, University of Melbourne, Australia; D. Eyman, Creativity + Innovation, Miami University, USA; John W. Altman Inst. For Entrepreneurship, Oxford, Ohio USA; M. B. Graeber, University of Sydney, Australia; B. C. Sanders, University of Calgary, Canada; Panel Chair: J. Canning, Laseire Consulting, Sydney Australia

Commentary on whistleblower protection.

The influence of isochronal and isothermal annealing on grating regeneration in single mode silica optical fibers has been investigated. By rapid annealing of Type-I grating under isothermal conditions we demonstrated that the underlying processes in the fiber that contribute toward grating regeneration work best around a certain temperature and there is a turn-around-point or roll-over of strength of grating regeneration. We validate the existence of “regeneration turn-around-point” with… Show more

The influence of isochronal and isothermal annealing on grating regeneration in single mode silica optical fibers has been investigated. By rapid annealing of Type-I grating under isothermal conditions we demonstrated that the underlying processes in the fiber that contribute toward grating regeneration work best around a certain temperature and there is a turn-around-point or roll-over of strength of grating regeneration. We validate the existence of “regeneration turn-around-point” with Type-I gratings inscribed using a 248 nm laser and a 213 nm laser as well. Attaining a “regeneration turn-around-point” may be set as a milestone on the way to optimizing regenerated fiber Bragg gratings (RFBG) and subsequently to develop high quality FBG sensors suitable for use at elevated temperatures. Show less

The government AgriTech Expert Working Group has provided a detailed overview of the practical challenges domestic Australian farmers have to deal with when digitising their farms through the implementation of connected sensor technologies, motivated by the predicted growth of the sector to AUD 100 billion by 2030. In addressing these issues, of which connectivity and access to wireless technologies along with unreliable sensor performances over time remain prominent, domestic regional specific… Show more

The government AgriTech Expert Working Group has provided a detailed overview of the practical challenges domestic Australian farmers have to deal with when digitising their farms through the implementation of connected sensor technologies, motivated by the predicted growth of the sector to AUD 100 billion by 2030. In addressing these issues, of which connectivity and access to wireless technologies along with unreliable sensor performances over time remain prominent, domestic regional specific solutions are sought. A key solution being relied upon are low earth orbital satellites, perhaps the only communication infrastructure that cycles over territorial boundaries and has both regulatory and technical challenges that are not widely considered. The resilience of these solutions is assessed in the context of the agricultural technology, or AgTech, market which is arguably invented and shaped by broader, global interests mostly centred where end-user populations are based. The argument is made that government policy must include the latter within a larger holistic framework, including education, when assessing the future of both agriculture and AgTech markets in Australia. At the core, the AgTech report does highlight some challenges in Australia’s wider research approach. Show less

We report BEDFs with one and seven cores drawn from 3D printed preforms. The capability of 3D printing technology to produce complex and arbitrary fiber structures was demonstrated without the necessary time-consuming separation and integration processes involved in the traditional preform manufacture. In addition, a range of dopants, namely Bi3+, Er3+, Ge4+, Ti4+ and Al3+ are introduced, further proving its diverse materials manufacturing capability. Care is needed in adjusting drawing… Show more

We report BEDFs with one and seven cores drawn from 3D printed preforms. The capability of 3D printing technology to produce complex and arbitrary fiber structures was demonstrated without the necessary time-consuming separation and integration processes involved in the traditional preform manufacture. In addition, a range of dopants, namely Bi3+, Er3+, Ge4+, Ti4+ and Al3+ are introduced, further proving its diverse materials manufacturing capability. Care is needed in adjusting drawing conditions and method as the number of cores increases, leading to effective lower melting points in the preform. Show less

A multichannel smartphone spectrometer exploiting multiple identical diffraction orders of a customized 2D diffractive element is reported. The instrument utilizes diffraction grating holographic imaging to converge and capture the multiple diffraction orders simultaneously within the limited field-of-view of the smartphone’s camera detector. This eliminates the requirement of convergence optics as used in conventional spectrometer systems. Each diffraction order can be utilized as a single… Show more

A multichannel smartphone spectrometer exploiting multiple identical diffraction orders of a customized 2D diffractive element is reported. The instrument utilizes diffraction grating holographic imaging to converge and capture the multiple diffraction orders simultaneously within the limited field-of-view of the smartphone’s camera detector. This eliminates the requirement of convergence optics as used in conventional spectrometer systems. Each diffraction order can be utilized as a single optical channel for spectroscopic analysis. As proof of concept, a customized 2D grating composed of two identical thin-film 1D gratings orthogonally stacked together is utilized to diffract the light rays emanating from a broadband visible source and produce four identical 1st orders dispersive diffraction in two orthogonal axes. The smartphone camera captures the diffraction orders within its solid angle – a quad-channel spectrometer exploiting the 2D properties of a CMOS detector is demonstrated. Mindful of losses, further increases in channel numbers is possible by simply increasing the number of gratings (N) within the stack spatially separated by an angle between successive grating axes. The instrument offers an ultra-low-cost, lightweight, high throughput, rugged and small form factor multichannel spectrometer ideal for field use as well as a laboratory benchtop alternative. To evaluate the performance of the instrument, three chemically and biologically significant parameters are measured simultaneously: - (a) iron concentration [Fe], (b) chlorine concentration [Cl], and (c) pH of the drinking water. Show less

A fused deposition modeling (FDM) 3D printer extruder was utilized as a micro-furnace draw tower for the direct fabrication of low-cost optical fibers. An air-clad multimode microfiber was drawn from optically transparent polyethylene terephthalate glycol (PETG) filament. A custom-made spooling collection allows for an automatic variation of fiber diameter between ϕ ∼ 72 to 397 μm by tuning the drawing speed. Microstructure imaging as well as the 3D beam profiling of the transmitted beam in the… Show more

A fused deposition modeling (FDM) 3D printer extruder was utilized as a micro-furnace draw tower for the direct fabrication of low-cost optical fibers. An air-clad multimode microfiber was drawn from optically transparent polyethylene terephthalate glycol (PETG) filament. A custom-made spooling collection allows for an automatic variation of fiber diameter between ϕ ∼ 72 to 397 μm by tuning the drawing speed. Microstructure imaging as well as the 3D beam profiling of the transmitted beam in the orthogonal axes was used to show good quality, functioning microfiber fabrication with uniform diameter and identical beam profiles for orthogonal axes. The drawn microfiber was used to demonstrate budget smartphone colorimetric-based absorption measurement to detect the degree of adulteration of olive oils with soybean oil. Show less

Single and multi-core preforms doped with Bi and Er are fabricated using additive manufacture and drawing into optical fibre. We observe an increasing trend towards shape distortion with increasing number of cores. This is explained by noting that the composite effective softening point falls as the number of doped cores rises. The use of a silica cladding tube elevates the drawing temperature unnecessarily.

The SARS-Coronavirus-2 (SARS-CoV-2) infectious disease, COVID-19, has spread rapidly, resulting in a global pandemic with significant mortality. The combination of early diagnosis via rapid screening, contact tracing, social distancing and quarantine has helped to control the pandemic. The absence of real time response and diagnosis is a crucial technology shortfall and is a key reason why current contact tracing methods are inadequate to control spread. In contrast, current information… Show more

The SARS-Coronavirus-2 (SARS-CoV-2) infectious disease, COVID-19, has spread rapidly, resulting in a global pandemic with significant mortality. The combination of early diagnosis via rapid screening, contact tracing, social distancing and quarantine has helped to control the pandemic. The absence of real time response and diagnosis is a crucial technology shortfall and is a key reason why current contact tracing methods are inadequate to control spread. In contrast, current information technology combined with a new generation of near-real time tests offers consumer-engaged smartphone-based “lab-in-a-phone” internet-of-things (IoT) connected devices that provide increased pandemic monitoring. This review brings together key aspects required to create an entire global diagnostic ecosystem. Cross-disciplinary understanding and integration of both mechanisms and technologies for effective detection, incidence mapping and disease containment in near real-time is summarized. Available measures to monitor and/or sterilize surfaces, next-generation laboratory and smartphone-based diagnostic approaches can be brought together and networked for instant global monitoring that informs Public Health policy. Cloud-based analysis enabling real-time mapping will enable future pandemic control, drive the suppression and elimination of disease spread, saving millions of lives globally. A new paradigm is introduced – scaled and multiple diagnostics for mapping and spreading of a pandemic rather than traditional accumulation of individual measurements. This can do away with the need for ultra-precise and ultra-accurate analysis by taking mass measurements that can relax tolerances and build resilience through networked analytics and informatics, the basis for novel swarm diagnostics. These include addressing ethical standards, local, national and international collaborative engagement, multidisciplinary and analytical measurements and standards, and data handling and storage protoco Show less

The use of anti-reflection coatings on 3D-printed components to reduce both Fresnel reflections and scattering is explored. Two similar photo-initiated acrylic commercial material structures, known as Standard Clear (SC: T~60% @ λ = 800 nm) and VeroClear (VC: T~90% @ λ = 800 nm), used specifically for optical components, are examined. The refractive indices for slab samples~(5 × 5 × 0.7) cm are measured at λ = 650 nm and averaged over the slab area: n(SC)~(1.49 ± 0.04) and n(VC)~(1.42 ± 0.03)… Show more

The use of anti-reflection coatings on 3D-printed components to reduce both Fresnel reflections and scattering is explored. Two similar photo-initiated acrylic commercial material structures, known as Standard Clear (SC: T~60% @ λ = 800 nm) and VeroClear (VC: T~90% @ λ = 800 nm), used specifically for optical components, are examined. The refractive indices for slab samples~(5 × 5 × 0.7) cm are measured at λ = 650 nm and averaged over the slab area: n(SC)~(1.49 ± 0.04) and n(VC)~(1.42 ± 0.03). Within experimental error, novel Shore D mapping is used to show hardness distribution across the surface flats, with VC slightly harder than SC, where VC = 85.9 ± 0.3 and SC = 84.4 ± 1.3, indicating uniform hardness. A TiO2/MgF2 anti-reflection twin-layer coating is deposited onto one side of an unpolished SC slab and binds well, passing standard peeling and humidity tests. Shore hardness increases to SCCOATED = 87.5 ± 1.5. It is found to reduce the measured Fresnel reflection and surface scatter by~65% without requiring major polishing, paving the way for lower-cost high-quality optics. The demonstration of s Show less

This paper presents an overview of recent developments in smartphone spectrometers focusing on light collection, dispersion, detection and spectral calibration. These spectrometers potentially offer unprecedented field diagnostics that can exploit real-time IoT edge data transfer into the cloud and back. However, there are technical challenges if these are to perform as well, if not better, than laboratory-based instruments. Limitations of traditional spectral calibration are addressed by… Show more

This paper presents an overview of recent developments in smartphone spectrometers focusing on light collection, dispersion, detection and spectral calibration. These spectrometers potentially offer unprecedented field diagnostics that can exploit real-time IoT edge data transfer into the cloud and back. However, there are technical challenges if these are to perform as well, if not better, than laboratory-based instruments. Limitations of traditional spectral calibration are addressed by considering an accurate non-linear wavelength increment over the spatial region of the detector pixels and dispersion associated with the effective refractive index (n) variation of a sample and its holder. To evaluate the performance of novel wavelength calibration, the algorithm was applied to the measurement of absorption spectra of vegetable oils (olive and soybean) using a double beam smartphone spectrometer. In the presence of a significant variation of sample n, the spectrometer measures spectra that overlap well with the spectra obtained using a standard spectrometer. The results also show a significant variation in absorbance spectrum between oil types with distinct absorption bands. This allows one to use the instrument as a straightforward tool for determining the adulteration level of olive oils in the fields and a means of addressing global food fraud more generally. Show less

To address the challenge of appropriate cementitious materials that can support future optical fibre sensors with reduced strains for smart city infrastructure, reducing structural heterogeneity by integrating diatomous earth is proposed. A series of samples made up of commercial grade instant mortar and an increased percentage of diatomous earth are fabricated and characterised. Mindful of the growing importance of “in-the-field” measurements and diagnostics to wider construction technology… Show more

To address the challenge of appropriate cementitious materials that can support future optical fibre sensors with reduced strains for smart city infrastructure, reducing structural heterogeneity by integrating diatomous earth is proposed. A series of samples made up of commercial grade instant mortar and an increased percentage of diatomous earth are fabricated and characterised. Mindful of the growing importance of “in-the-field” measurements and diagnostics to wider construction technology evolution, hardness properties are measured using Mohs scratch test and portable field durometers; the latter was shown to be effective in post-plasticity assessment of these cement composites. Within experimental error low added concentrations improve cement hardness whilst making the cement more plastic. Structural colour is introduced by the diatoms and novel characterisation using a smartphone and polymer lens proposed and demonstrated. The implications for CO2 trapping and intelligent structural health monitoring (ISHM) for internet-of-things (IoT) in smart city infrastructure are discussed. Show less

A robust multichannel smartphone spectrometer exploiting multiorder diffraction imaging on a smartphone camera is reported. The instrument utilizes a thin film diffractive element generating multiple orders of diffracted light from a broadband visible source (white LED, λ = 400-700 nm). The smartphone's CMOS camera captures all the diffraction orders simultaneously, producing a 2-D image. Each of these diffraction orders can be utilized as a single optical channel for dedicated samples enabling… Show more

A robust multichannel smartphone spectrometer exploiting multiorder diffraction imaging on a smartphone camera is reported. The instrument utilizes a thin film diffractive element generating multiple orders of diffracted light from a broadband visible source (white LED, λ = 400-700 nm). The smartphone's CMOS camera captures all the diffraction orders simultaneously, producing a 2-D image. Each of these diffraction orders can be utilized as a single optical channel for dedicated samples enabling simultaneous multiple sample analysis. The wavelength distribution along the diffraction direction produces a tunable spectral resolution of δλ ~1.6 to 3.0 nm/pixel over the bandwidth of Δλ = 300 nm. A customized app processes each diffraction image into spectra. 3-D printing is used to create the entire instrument prototype. As an initial demonstration, simultaneous absorption measurements of reference and sample cells using the first diffraction orders (m = +1 and -1) is shown. Absorption spectra for a laser dye (Rhodamine B) and a pH-responsive buffer (bromothymol blue) are measured. This offers a low cost (<; $30) portable instrument layout comparable to conventional double beam benchtop instruments in performance but more rugged for field use. Show less

This article reports a 3-D printing intelligent insole gait monitoring system based on an embedded fiber Bragg grating (FBG). The smart insole combines 3-D printing technology and FBG sensors providing high sensitivity and end-point low cost. Results using pressure points measured by four FBGs are sufficient to differentiate foot loads and gait types.

Fiber Bragg gratings are embedded within 3D printed polymer packages. Information about both induced and applied stresses, and operator error, can be determined from the observed spectral shifts and chirping. A novel way to produce packaged broadband gratings, with Δ𝜆BW>7nm/cm, is proposed and demonstrated.

The employment of type-I pyrethroids for airplane disinfection in recent years underlines the necessity to develop sensing schemes for the rapid detection of these pesticides directly at the point-of-use. Antibody-gated indicator-releasing materials were thus developed and implemented with test strips for lateral-flow assay-based analysis employing a smartphone for readout. Besides a proper matching of pore sizes and gating macromolecules, the functionalization of both the material's outer… Show more

The employment of type-I pyrethroids for airplane disinfection in recent years underlines the necessity to develop sensing schemes for the rapid detection of these pesticides directly at the point-of-use. Antibody-gated indicator-releasing materials were thus developed and implemented with test strips for lateral-flow assay-based analysis employing a smartphone for readout. Besides a proper matching of pore sizes and gating macromolecules, the functionalization of both the material's outer surface as well as the strips with PEG chains enhanced system performance. This simple assay allowed for the detection of permethrin as a target molecule at concentrations down to the lower ppb level in less than 5 minutes. Show less

The application of self-contained field-portable, internet connected spectroscopic diagnostics in food analysis using a fibre endoscopic smart fluorimeter is reported. A UV-induced fluorescence is used to measure the quality of olive oils, distinguishing between extra virgin and others within a smartphone platform. When excited at λ ~ 370 nm, the extra virgin olive oil fluoresces red at λ ~ 670 nm. Notably, other oils do not fluoresce red but rather blue, consistent with degradation of the… Show more

The application of self-contained field-portable, internet connected spectroscopic diagnostics in food analysis using a fibre endoscopic smart fluorimeter is reported. A UV-induced fluorescence is used to measure the quality of olive oils, distinguishing between extra virgin and others within a smartphone platform. When excited at λ ~ 370 nm, the extra virgin olive oil fluoresces red at λ ~ 670 nm. Notably, other oils do not fluoresce red but rather blue, consistent with degradation of the chlorophyll in the oil. Artificial refinement employed in some of the commercial products removes the red emission providing a simple method for distinguishing extra virgin olive oil from all other oils. A smartphone endoscopic fluorimeter is designed and constructed that measures the emission band Aλ ~ (400 - 700) nm with λ ~ 370 nm excitation. The instrument is used to characterise the fluorescence of the oils. Photo-degradation over time for extra virgin olive oil under room lights is observed, demonstrating the origin for the decomposition of extra virgin olive oil in transparent bottles. Extra virgin olive oils are also susceptible to thermal degradation more than refined oils. Show less

Using induced UV attenuation across a twisted fiber asymmetric core drawn from a 3D printed preform, linear fiber Bragg gratings (FBGs) are produced on one side of the core. By removing the twist, a helical grating with a period matching the twist rate is produced. Balancing the rate with the polarization beat length in a form birefringent fiber allows the production of a combined rocking filter and FBG device with tunable properties. Direct observation of the fiber grating dispersion within… Show more

Using induced UV attenuation across a twisted fiber asymmetric core drawn from a 3D printed preform, linear fiber Bragg gratings (FBGs) are produced on one side of the core. By removing the twist, a helical grating with a period matching the twist rate is produced. Balancing the rate with the polarization beat length in a form birefringent fiber allows the production of a combined rocking filter and FBG device with tunable properties. Direct observation of the fiber grating dispersion within the rocking filter rejection band is possible. Show less

This research aims to promote photocatalysis of endocrine disrupting chemicals (EDCs) in water. Two reactor setups with (i) modified air-clad optical fibres and (ii) waterproof LED strips were utilised to transmit light to photocatalysts P25 TiO2 and gold-modified TiO2 (Au-TiO2). The performances to photodegrade 17α-ethynylestradiol (EE2) and estriol (E3) under Cool White and UVA high efficacy LEDs were examined. Au-TiO2 showed superior photocatalytic activity for EE2 removal over P25 TiO2. The… Show more

This research aims to promote photocatalysis of endocrine disrupting chemicals (EDCs) in water. Two reactor setups with (i) modified air-clad optical fibres and (ii) waterproof LED strips were utilised to transmit light to photocatalysts P25 TiO2 and gold-modified TiO2 (Au-TiO2). The performances to photodegrade 17α-ethynylestradiol (EE2) and estriol (E3) under Cool White and UVA high efficacy LEDs were examined. Au-TiO2 showed superior photocatalytic activity for EE2 removal over P25 TiO2. The pseudo first-order rate constants for EE2 photocatalysis under UVA were 0.55 h−1 and 0.89 h−1 for TiO2 and Au-TiO2, respectively. E3 was effectively degraded by Au-TiO2 in the immersible LED strip reactor (0.13 h−1). Show less

3D printing is a disruptive technology that could revolutionise the fabrication of optical fibre by offering greater flexibility and diversity in material and structure designs. This paper reviews the recent research and development of material and fabrication techniques toward 3D printing-based polymer optical fibre (POF) and silica optical fibre (SOF).

Top-down contact angle (CA) measurements are used to characterize the green leaves and purple flowers of both old and young the Cattleya warneri orchids. The top-down CA allows the characterization of large surfaces away from the leaf edge, avoiding traditional cutting required for side view CA measurement. This allows large area mapping without damaging leaves making the method amenable to fieldwork and useful in environmental diagnostics. Young leaves are found to be hydrophobic whilst old… Show more

Top-down contact angle (CA) measurements are used to characterize the green leaves and purple flowers of both old and young the Cattleya warneri orchids. The top-down CA allows the characterization of large surfaces away from the leaf edge, avoiding traditional cutting required for side view CA measurement. This allows large area mapping without damaging leaves making the method amenable to fieldwork and useful in environmental diagnostics. Young leaves are found to be hydrophobic whilst old leaves become practically hydrophilic across their entirety, mostly as a result of continued exposure to changes in the environment over time. The flowers are hydrophobic because of their visual and tactile attractor function for pollinating animals and the self-cleaning of dirt and pathogens. Real-time measurement and mapping of CA of surfaces open a new tool to assess the long-term impact of plant aging, pollution, and more of organisms in the field. The method has clear applications elsewhere such as in industrial probing of surfaces and products. Show less

Excitation of surface waves on conducting materials provides a near resistance-free interface capable of a material glissade either by plasmon forces or by optical beam tractors. Analogous to an ice hockey rink, as proof-of-principle plasmon-assisted optical traction, or hoovering, of water drops on a gold surface is demonstrated. Changes in the contact angle provide a novel, low-cost nanoscale method of quantifying observable and potentially tunable changes. Variability in thresholds and… Show more

Excitation of surface waves on conducting materials provides a near resistance-free interface capable of a material glissade either by plasmon forces or by optical beam tractors. Analogous to an ice hockey rink, as proof-of-principle plasmon-assisted optical traction, or hoovering, of water drops on a gold surface is demonstrated. Changes in the contact angle provide a novel, low-cost nanoscale method of quantifying observable and potentially tunable changes. Variability in thresholds and movement, including jumps, is observed and can be explained by the presence of significant roughness, measured by scanning electron microscopy, with water tension. The demonstration opens a path to directly integrate various optical and plasmonic traction technologies. Implications of the phenomena and ways of improving transport and potential applications spanning configurable microfluidics, antennas, tunable lenses, diagnostics, sensing, and active Kerr and other devices are discussed. Show less

In this paper, various types of high temperature fibre Bragg gratings (FBGs) are reviewed, including recent results and advancements in the field. The main motivation of this review is to highlight the potential of fabricating thermally stable refractive index contrasts using femtosecond (fs) near-infrared radiation in fibres fabricated with non-conventional techniques, such as the molten core method. As a demonstration of this, an yttrium aluminosilicate (YAS) core and pure silica cladding… Show more

In this paper, various types of high temperature fibre Bragg gratings (FBGs) are reviewed, including recent results and advancements in the field. The main motivation of this review is to highlight the potential of fabricating thermally stable refractive index contrasts using femtosecond (fs) near-infrared radiation in fibres fabricated with non-conventional techniques, such as the molten core method. As a demonstration of this, an yttrium aluminosilicate (YAS) core and pure silica cladding glass optical fibre is fabricated and investigated after being irradiated by an fs laser within the Type II regime. The familiar formation of nanogratings inside both core and cladding regions are identified and studied using birefringence measurements and scanning electron microscopy. The thermal stability of the Type II modifications is then investigated through isochronal annealing experiments (up to T = 1100 °C; time steps, Δt = 30 min). For the YAS core composition, the measured birefringence does not decrease when tested up to 1000 °C, while for the SiO2 cladding under the same conditions, its value decreased by ~30%. These results suggest that inscription of such 'Type II fs-IR' modifications in YAS fibres could be employed to make FBGs with high thermal stability. This opens the door toward the fabrication of a new range of 'FBG host fibres' suitable for ultra-high temperature operation. Show less

Silica optical fibre was drawn from a three-dimensional printed preform. Both single mode and multimode fibres are reported. The results demonstrate additive manufacturing of glass optical fibres and its potential to disrupt traditional optical fibre fabrication. It opens up fibre designs for novel applications hitherto not possible.

Transmission Mueller-matrix spectroscopic ellipsometry is applied to study femtosecond laser induced nanogratings in silica glass in a wide spectral range 250–1800 nm. By using differential decomposition of the Mueller matrix, the circular birefringence and dichroism of femtosecond laser irradiated SiO2 are quantified for the first time in the UV and near-IR range. A maximum value of the effective specific rotation of α ∼ −860°/mm at 290 nm is found. In the near-IR range, we found a linear and… Show more

Transmission Mueller-matrix spectroscopic ellipsometry is applied to study femtosecond laser induced nanogratings in silica glass in a wide spectral range 250–1800 nm. By using differential decomposition of the Mueller matrix, the circular birefringence and dichroism of femtosecond laser irradiated SiO2 are quantified for the first time in the UV and near-IR range. A maximum value of the effective specific rotation of α ∼ −860°/mm at 290 nm is found. In the near-IR range, we found a linear and circular dichroism band peaking around 1240 nm, which might be attributed to the formation of anisotropic species like the formation of oriented OH species and Si-O-Si bond. Show less

This paper presents two in vivo instrumentation techniques to study the different types of gait of horses performing athletics using fiber Bragg gratings (FBG). These techniques can be used as an auxiliary tool in the early diagnosis of injuries related to the horse's locomotor system, mainly in the distal portion of the digit, one of the most common causes of retirement when they are athletes. Therefore, the first technique presented consists of the fixation of FBGs without encapsulation… Show more

This paper presents two in vivo instrumentation techniques to study the different types of gait of horses performing athletics using fiber Bragg gratings (FBG). These techniques can be used as an auxiliary tool in the early diagnosis of injuries related to the horse's locomotor system, mainly in the distal portion of the digit, one of the most common causes of retirement when they are athletes. Therefore, the first technique presented consists of the fixation of FBGs without encapsulation, directly on the dorsal wall of the hoof in each of the limbs. In the second technique presented, the FBG sensor is encapsulated in a prototype developed using a composite material reinforced with carbon fiber in a horseshoe shape. The second technique is associated with digital image processing (DIP) for better visualization of the deformation and compression forces that act upon the limbs. The first method showed sensitivity to detection of the digit compression against the ground, being able to identify walking patterns. The second technique, with the encapsulated sensor elements, also allows the capture of characteristic signals of gait, such as step walk, trot, and gallop under training conditions. Both, FBG sensor interrogation and DIP, analysis techniques have proven good performance and promising results for the clinical and biomechanical study and medical evaluations of horses even during dynamic training and competitions. Show less

The special features of photonic crystal fibres (PCFs) are achieved by their air hole structures. PCF structure is determined and formed by its origin preform design and drawing process. Therefore, structure formation dynamics in drawing PCF is important for the fabrication of PCF achieving desirable structure and thus the intended feature. This paper will investigate structure formation dynamics of PCF drawing in relation to key parameters and conditions, such as hole dimension, temperature… Show more

The special features of photonic crystal fibres (PCFs) are achieved by their air hole structures. PCF structure is determined and formed by its origin preform design and drawing process. Therefore, structure formation dynamics in drawing PCF is important for the fabrication of PCF achieving desirable structure and thus the intended feature. This paper will investigate structure formation dynamics of PCF drawing in relation to key parameters and conditions, such as hole dimension, temperature and pressure. Show less

A review of the literature offers an explanation for the large anomalous electro-optic (e.o.) effect reported by Fujiwara et al. in 1994. It is based on the large e.o. coefficient of ordered water at an interface measured in recent years >1000 pm/V. More broadly, the concept of water-based photonics, where water could be a new platform material for devices and systems, is introduced, suggesting that liquid states of matter can allow ready shaping and exploitation of many processes in ways… Show more

A review of the literature offers an explanation for the large anomalous electro-optic (e.o.) effect reported by Fujiwara et al. in 1994. It is based on the large e.o. coefficient of ordered water at an interface measured in recent years >1000 pm/V. More broadly, the concept of water-based photonics, where water could be a new platform material for devices and systems, is introduced, suggesting that liquid states of matter can allow ready shaping and exploitation of many processes in ways not previously considered. This paper is a commentary on the significance of this new understanding and the broader interest of water in photonics, particularly its consideration as a new platform material.A review of the literature offers an explanation for the large anomalous electro-optic (e.o.) effect reported by Fujiwara et al. in 1994. It is based on the large e.o. coefficient of ordered water at an interface measured in recent years >1000 pm/V. More broadly, the concept of water-based photonics, where water could be a new platform material for devices and systems, is introduced, suggesting that liquid states of matter can allow ready shaping and exploitation of many processes in ways not previously considered. This paper is a commentary on the significance of this new understanding and the broader interest of water in photonics, particularly its consideration as a new platform material. Show less

A new approach to fabricating nanobot technology based on charge transfer with
optical excitation is proposed. Some general molecular robotic systems are suggested, including
the possibility of a nanobot with molecular clamps for gripping and tail for locomotion.

A structured optical fibre is drawn from a 3D-printed structured preform. Preforms containing a single ring of holes around the core are fabricated using filament made from a modified butadiene polymer. More broadly, 3D printers capable of processing soft glasses, silica and other materials are likely to come on line in the not-so-distant future. 3D printing of optical preforms signals a new milestone in optical fibre manufacture.

A large dynamic index measurement range (n = 1 to n = 1.7) using surface plasmon resonance (SPR) shifts was demonstrated with a ZnSe prism at 632.8 nm, limited by the available high index liquid hosts. In contrast to borosilicate based SPR measurements, where angular limitations restrict solvent use to water and require considerable care dealing with Fresnel reflections, the ZnSe approach allows SPR spectroscopies to be applied to a varied range of solvents. An uncertainty in angular resolution… Show more

A large dynamic index measurement range (n = 1 to n = 1.7) using surface plasmon resonance (SPR) shifts was demonstrated with a ZnSe prism at 632.8 nm, limited by the available high index liquid hosts. In contrast to borosilicate based SPR measurements, where angular limitations restrict solvent use to water and require considerable care dealing with Fresnel reflections, the ZnSe approach allows SPR spectroscopies to be applied to a varied range of solvents. An uncertainty in angular resolution between 1.5° and 6°, depending on the solvent and SPR angle, was estimated. The refractive index change for a given glucose concentration in water was measured to be n = (0.114 ± 0.007) /%[C6H12O6]. Given the transmission properties of ZnSe, the processes can be readily extended into the mid infrared. Show less

A combined “dual” absorption and fluorescence smartphone spectrometer is demonstrated. The optical sources used in the system are the white flash LED of the smartphone and an orthogonally positioned and interchangeable UV (𝜆ex=370  nm) and blue (𝜆ex=450  nm) LED. The dispersive element is a low-cost, nano-imprinted diffraction grating coated with Au. Detection over a 300 nm span with 0.42 nm/pixel resolution was carried out with the camera CMOS chip. By integrating the blue and UV excitation… Show more

A combined “dual” absorption and fluorescence smartphone spectrometer is demonstrated. The optical sources used in the system are the white flash LED of the smartphone and an orthogonally positioned and interchangeable UV (𝜆ex=370  nm) and blue (𝜆ex=450  nm) LED. The dispersive element is a low-cost, nano-imprinted diffraction grating coated with Au. Detection over a 300 nm span with 0.42 nm/pixel resolution was carried out with the camera CMOS chip. By integrating the blue and UV excitation sources into the white LED circuitry, the entire system is self-contained within a 3D printed case and powered from the smartphone battery; the design can be scaled to add further excitation sources. Using a customized app, acquisition of absorption and fluorescence spectra are demonstrated using a blue-absorbing and green-emitting pH-sensitive amino-naphthalimide-based fluorescent probe and a UV-absorbing and blue-emitting Zn2+-sensitive fluoro-ionophore. Show less

We report the excitation of a surface plasmon resonance (SPR) close to the orthogonal axis of a gold (Au) film on borosilicate glass. Direct spectroscopic measurement of SPR shifts using different liquids are made at ∼5° incidence within a reflection spectrophotometer. The proposed mechanism to establish coupling and plasmon localization is the scattering of light able to penetrate across the film at the interfaces.

Recently, we showed that femtosecond laser induced “nanogratings” consist of thin regions with a low refractive index (Δn = −0.15), due to the formation of nanoporous silica surrounded by regions with a positive index change. In this paper, we investigate a wide range of laser parameters to achieve very high retardance within a single layer; as much as 350 nm at λ = 546 nm but also to minimize the competing losses. We show that the total retardance depends on the number of layers present and… Show more

Recently, we showed that femtosecond laser induced “nanogratings” consist of thin regions with a low refractive index (Δn = −0.15), due to the formation of nanoporous silica surrounded by regions with a positive index change. In this paper, we investigate a wide range of laser parameters to achieve very high retardance within a single layer; as much as 350 nm at λ = 546 nm but also to minimize the competing losses. We show that the total retardance depends on the number of layers present and can be accumulated in the direction of laser propagation to values higher than 1600 nm. This opens the door to using these nanostructures as refined building blocks for novel optical elements based on strong retardance. Show less

Transient changes in the contact angle, Δθ [similar] 10°, of water on gold (Au) reveal reversible wetting of near hydrophobic Au films. The recovery time is temperature dependent. Surface flatness is investigated using AFM and profilometery.

An optical fiber sensor based on long-period gratings (LPG) for selective measurements of flap- and edge-wise bending of a wind turbine blade is presented. Two consecutive LPGs separated by 40 mm interfere to improve resolution and reduce noise in a D-shaped fiber. The mode profile of the device was characterized experimentally to provide a model describing the mode couplings. The sensor was tested on a wind turbine blade.

Advantages for sensor applications of long-period gratings (LPGs) in special optical fibers are reported. Two consecutive LPGs separated by 60 to 100 mm interfere to improve the resolution and reduce noise in a highly doped fiber with inner cladding and in a D-shaped fiber. These gratings provide good contrast to increase the resolution for sensing applications, with or without access to the surroundings along the fiber. The mode profiles of the devices were characterized experimentally to gain… Show more

Advantages for sensor applications of long-period gratings (LPGs) in special optical fibers are reported. Two consecutive LPGs separated by 60 to 100 mm interfere to improve the resolution and reduce noise in a highly doped fiber with inner cladding and in a D-shaped fiber. These gratings provide good contrast to increase the resolution for sensing applications, with or without access to the surroundings along the fiber. The mode profiles of the devices were characterized experimentally to gain deeper insight into the improved functionality. Show less

A novel portable fluorometer combining the attributes of a smartphone with an easy fit, simple and compact sample chamber fabricated using 3D printing has been developed for pH measurements of environmental water in the field. The results were then compared directly with those obtained using conventional electrode based measurements.

We propose a compact multi-parameter fibre sensing module based on a fibre Bragg grating (FBG) in single–multi–single mode fibre structure (FBG-in-SMS). We experimentally demonstrated that the FBG-in-SMS can measure temperature and strain simultaneously. In addition, we found that the process of writing FBG in SMS could be an effective technique for tuning and optimizing SMS spectrum for sensing.

The room temperature deposition of self-assembling silica nanoparticles onto D-shaped optical fibres (“D-fibre”), drawn from milled preforms fabricated by modified chemical vapour deposition (MCVD), is studied. Vertical dip-and-withdraw produces tapered layers, with one end thicker (surface coverage >0.85) than the other, whilst horizontal dip-and-withdraw produces much more uniform layers over the core region. The propagation of induced fracturing over the core region during drying is… Show more

The room temperature deposition of self-assembling silica nanoparticles onto D-shaped optical fibres (“D-fibre”), drawn from milled preforms fabricated by modified chemical vapour deposition (MCVD), is studied. Vertical dip-and-withdraw produces tapered layers, with one end thicker (surface coverage >0.85) than the other, whilst horizontal dip-and-withdraw produces much more uniform layers over the core region. The propagation of induced fracturing over the core region during drying is overcome using a simple protrusion of the inner cladding. Thick coatings are discernible through thin film interference colouring, but thinner coatings require scanning electron microscopy (SEM) imaging. Here, we show that fluorescence imaging, using Rhodamine B, in this example, can provide some qualitative and speedy assessment of coverage. Show less

Percolation diffusion into long (11.5 cm) self-assembled, ordered mesoporous microfibres is studied using optical transmission and laser ablation inductive coupled mass spectrometry (LA-ICP-MS). Optical transmission based diffusion studies reveal rapid penetration (<5 s, D > 80 μm2∙s−1) of Rhodamine B with very little percolation of larger molecules such as zinc tetraphenylporphyrin (ZnTPP) observed under similar loading conditions. The failure of ZnTPP to enter the microfibre was… Show more

Percolation diffusion into long (11.5 cm) self-assembled, ordered mesoporous microfibres is studied using optical transmission and laser ablation inductive coupled mass spectrometry (LA-ICP-MS). Optical transmission based diffusion studies reveal rapid penetration (<5 s, D > 80 μm2∙s−1) of Rhodamine B with very little percolation of larger molecules such as zinc tetraphenylporphyrin (ZnTPP) observed under similar loading conditions. The failure of ZnTPP to enter the microfibre was confirmed, in higher resolution, using LA-ICP-MS. In the latter case, LA-ICP-MS was used to determine the diffusion of zinc acetate dihydrate, D~3 × 10−4 nm2∙s−1. The large differences between the molecules are accounted for by proposing ordered solvent and structure assisted accelerated diffusion of the Rhodamine B based on its hydrophilicity relative to the zinc compounds. The broader implications and applications for filtration, molecular sieves and a range of devices and uses are described. Show less

Following on from our invention of the lab-in-a-fibre in 2006, we now extend the concept to the nanoscale in the lab-in-a-microfibre.

We demonstrate a source of 554 nm pulses with 2.7 ps pulse duration and 1.41 W average power, at a repetition rate of 300 MHz. The yellow-green pulse train is generated from the second harmonic of a 1.11 μm fiber laser source in periodically-poled stoichiometric LiTaO3. A total fundamental power of 2.52 W was used, giving a conversion efficiency of 56%.

Atomic force microscopy (AFM) of microfibres fabricated from the self-assembly and fracturing of silica nanoparticles reveals mesoporous structure with hcp packing. Pore size distribution for (20 – 30) nm sized particles are calculated to lie within rtet ~(2.2 – 3.3) nm and roct ~(4.2 – 6.2) nm for the octahedral and tetrahedral sites. The experimentally measured distribution, using N2 adsorption, is r ~(2 - 6) nm, in excellent agreement suggesting a highly controllable and periodic porosity… Show more

Atomic force microscopy (AFM) of microfibres fabricated from the self-assembly and fracturing of silica nanoparticles reveals mesoporous structure with hcp packing. Pore size distribution for (20 – 30) nm sized particles are calculated to lie within rtet ~(2.2 – 3.3) nm and roct ~(4.2 – 6.2) nm for the octahedral and tetrahedral sites. The experimentally measured distribution, using N2 adsorption, is r ~(2 - 6) nm, in excellent agreement suggesting a highly controllable and periodic porosity using these structures. The potential for a number of material and device applications is discussed. Show less

Magnetic induction heating of optical fibers packaged with a steel plate is studied using a fiber Bragg grating. The dependence on the induced wavelength shift with magnetic field is obtained for a commercially available induction heater. More than a 300°C temperature rise is observed within seconds. The potential of magnetic induction as an efficient and rapid means of modulating devices and as a novel approach to potential optical based magnetic field and current sensing is proposed and… Show more

Magnetic induction heating of optical fibers packaged with a steel plate is studied using a fiber Bragg grating. The dependence on the induced wavelength shift with magnetic field is obtained for a commercially available induction heater. More than a 300°C temperature rise is observed within seconds. The potential of magnetic induction as an efficient and rapid means of modulating devices and as a novel approach to potential optical based magnetic field and current sensing is proposed and discussed. The extension of the ideas into micro and nanophotonics is described. Show less

UV laser irradiation (λ = 193 nm), below and above damage thresholds, is used to both alter and pattern the surface properties of borosilicate slides to tune and control the contact angle of a water drop over the surface. Large variation exceeding 25° using laser processing alone, spanning across both sides of the original contact angle of the surface, is reported. An asymmetric contact angle distribution, giving rise to an analogous ellipsoidal-like drop caplet, is shown to improve convective… Show more

UV laser irradiation (λ = 193 nm), below and above damage thresholds, is used to both alter and pattern the surface properties of borosilicate slides to tune and control the contact angle of a water drop over the surface. Large variation exceeding 25° using laser processing alone, spanning across both sides of the original contact angle of the surface, is reported. An asymmetric contact angle distribution, giving rise to an analogous ellipsoidal-like drop caplet, is shown to improve convective self-assembly of silica nanoparticles into straighter optical microwires. Show less

Listed as 2nd author

Confirmation of glass relaxation underpinning ultra high temperature glass components is demonstrated using inert Helium.

The great silica challenge, one of the most pressing problem in material science, is solved! Nanoparticle self-assembly allows the complete integration of anything into silica, including single-photon emitting nanodiamonds demonstrated in this work.

Waveguides are inscribed through densification of the surrounding region of a damage induced channel created by femtosecond irradiation within silica. Single mode propagation at 1.5 μm is obtained below the damage region whilst at shorter wavelengths guidance is only observed away on either side of the region. The quasi-periodic nanostructure that is induced can explain the mode profile elongation observed with polarised light at 45°. The origin of this guidance area is explored using SEM… Show more

Waveguides are inscribed through densification of the surrounding region of a damage induced channel created by femtosecond irradiation within silica. Single mode propagation at 1.5 μm is obtained below the damage region whilst at shorter wavelengths guidance is only observed away on either side of the region. The quasi-periodic nanostructure that is induced can explain the mode profile elongation observed with polarised light at 45°. The origin of this guidance area is explored using SEM analysis, which reveals nanoporous regions within laser track structure above and below the densified region where 1.5 μm propagates. Shorter wavelength light is not supported in this area. Show less

Controlling the evanescent field within platform waveguide technologies underpins waveguide nanophotonics and is critical to optimising the interaction with integrated specialised materials or devices under test. Unfortunately, this interaction is often small since the evanescent field is a fraction of the total optical field. Here we propose and demonstrate, through simulation and experiment, how the waveguide evanescent field can be enhanced substantially by using high index interface layers,… Show more

Controlling the evanescent field within platform waveguide technologies underpins waveguide nanophotonics and is critical to optimising the interaction with integrated specialised materials or devices under test. Unfortunately, this interaction is often small since the evanescent field is a fraction of the total optical field. Here we propose and demonstrate, through simulation and experiment, how the waveguide evanescent field can be enhanced substantially by using high index interface layers, which draw out the optical field in the probe vicinity taking advantage of field localisation. This can be further enhanced by extended resonant and gallery modes within the channels of a structured cylindrical waveguide. Several orders of magnitude increased sensitivity with minimal added insertion loss is obtained using self-assembled layers of TiO2 (B) nanoparticles and porphyrin within a silica structured optical fibre. The combination of novel photonics with specialty material integration highlights the potential scope for physics, chemistry, sensing and materials research. Show less

Using a time-resolved interferometric technique, we study the laser-induced carrier-trapping dynamics in SiO2 and Ge-doped SiO2. The fast trapping of electrons in the band gap is associated with the formation of self-trapped excitons (STE). The STE trapping is doping dependent in SiO2. The mean trapping time of electrons excited in the conduction band was found to be significantly lower in Ge-doped silica (75 ± 5 fs) when compared to pure silica (155 ± 5 fs). At our concentration level, this… Show more

Using a time-resolved interferometric technique, we study the laser-induced carrier-trapping dynamics in SiO2 and Ge-doped SiO2. The fast trapping of electrons in the band gap is associated with the formation of self-trapped excitons (STE). The STE trapping is doping dependent in SiO2. The mean trapping time of electrons excited in the conduction band was found to be significantly lower in Ge-doped silica (75 ± 5 fs) when compared to pure silica (155 ± 5 fs). At our concentration level, this indicates that the plasma properties are determined by the presence of easily ionizable states such as the presence of Ge atoms in the glass network. Therefore, we suggest that in Ge-doped silica there exist an additional trapping pathway that leads to a significantly faster excitons
trapping and a higher plasma density when compared to undoped silica. Show less

Grating writing in structured optical fibers is reviewed. Various laser sources have been used including UV and near IR nanosecond and femtosecond lasers, each enabling different material processing regimes. The issue of scattering is modeled through simulation and compared with experiment. Good agreement has been established.

Fibre Bragg gratings were written in large diameter (~300-400 um) air-clad optical fibre using an amplified Ti:Sapphire femtosecond laser (800 nm, 100 fs, 0.3 uJ/pulse) with the point-by-point method. Utilising multiphoton absorption, we induced modifications in the core of the air-clad fibre. By focusing the femtosecond laser close to the diffraction limit with a 20x oil immersion microscope objective lens, the glass modification region is of the order of I um in the fibre, which has a 5 um… Show more

Fibre Bragg gratings were written in large diameter (~300-400 um) air-clad optical fibre using an amplified Ti:Sapphire femtosecond laser (800 nm, 100 fs, 0.3 uJ/pulse) with the point-by-point method. Utilising multiphoton absorption, we induced modifications in the core of the air-clad fibre. By focusing the femtosecond laser close to the diffraction limit with a 20x oil immersion microscope objective lens, the glass modification region is of the order of I um in the fibre, which has a 5 um core diameter. A technique to avoid the scattering effect of the large air-silica index contrast, on the femtosecond radiation, was implemented. Grating rejection strengths of 20 dB were achieved with an accompanying insertion loss of 3-4 dB at 1085 nm. Show less

Fibre Bragg gratings were written in large diameter (~300-400 um) air-clad optical fibre using an amplified Ti:Sapphire femtosecond laser (800 nm, 100 fs, 0.3 uJ/pulse) with the point-by-point method. Utilising multiphoton absorption, we induced modifications in the core of the air-clad fibre. By focusing the femtosecond laser close to the diffraction limit with a 20x oil immersion microscope objective lens, the glass modification region is of the order of I um in the fibre, which has a 5 um… Show more

Fibre Bragg gratings were written in large diameter (~300-400 um) air-clad optical fibre using an amplified Ti:Sapphire femtosecond laser (800 nm, 100 fs, 0.3 uJ/pulse) with the point-by-point method. Utilising multiphoton absorption, we induced modifications in the core of the air-clad fibre. By focusing the femtosecond laser close to the diffraction limit with a 20x oil immersion microscope objective lens, the glass modification region is of the order of I um in the fibre, which has a 5 um core diameter. A technique to avoid the scattering effect of the large air-silica index contrast, on the femtosecond radiation, was implemented. Grating rejection strengths of 20 dB were achieved with an accompanying insertion loss of 3-4 dB at 1085 nm. Show less

Fibre Bragg gratings were written in large diameter (~300-400 um) air-clad optical fibre using an amplified Ti:Sapphire femtosecond laser (800 nm, 100 fs, 0.3 uJ/pulse) with the point-by-point method. Utilising multiphoton absorption, we induced modifications in the core of the air-clad fibre. By focusing the femtosecond laser close to the diffraction limit with a 20x oil immersion microscope objective lens, the glass modification region is of the order of I um in the fibre, which has a 5 um… Show more

Fibre Bragg gratings were written in large diameter (~300-400 um) air-clad optical fibre using an amplified Ti:Sapphire femtosecond laser (800 nm, 100 fs, 0.3 uJ/pulse) with the point-by-point method. Utilising multiphoton absorption, we induced modifications in the core of the air-clad fibre. By focusing the femtosecond laser close to the diffraction limit with a 20x oil immersion microscope objective lens, the glass modification region is of the order of I um in the fibre, which has a 5 um core diameter. A technique to avoid the scattering effect of the large air-silica index contrast, on the femtosecond radiation, was implemented. Grating rejection strengths of 20 dB were achieved with an accompanying insertion loss of 3-4 dB at 1085 nm. Show less

Multiple precision selective micro-filling of a structured optical fibre using three luminescent dyes enables the simultaneous capture of red, blue and green luminescence within the core to generate white light. The technology opens up a new approach to integration and superposition of the properties of multiple materials to create unique composite properties within structured waveguides.

A Bragg grating in a photonic crystal fiber was written and its dependence with temperature and strain analyzed. The two observed Bragg wavelengths correspond to a fundamental and a higher-order mode in the optical fiber. The temperature and strain calibration curves for both modes are measured and found to be distinct. The general properties of gratings in these fibers, and their implications, are enunciated.

A Bragg grating in a photonic crystal fiber was written and its dependence with temperature and strain analyzed. The two observed Bragg wavelengths correspond to a fundamental and a higher-order mode in the optical fiber. The temperature and strain calibration curves for both modes are measured and found to be distinct. The general properties of gratings in these fibers, and their implications, are enunciated.

A water core photonic crystal Fresnel fiber exploiting a hole distribution on zone plates of a cylindrical waveguide was developed and characterized. This fiber has similar guiding properties as the pristine air-hole guiding fiber although a large loss edge ~900nm is observed indicating that the bandgap associated with Fresnel guidance has shifted to longer wavelengths. The absorption bands of the water in the region of the NIR were observed. The application to biosensing is discussed.

In this paper we review recent results describing the generation of optical modes within waveguides based on coherent scattering from artificially structured interfaces. The generation of optical waveguide propagation similar to free space propagation enables possible solutions to controlling and shaping optical field generation in free space using coherent scattering of multiple sources. It is shown that the controlled fabrication of such sources can be done simply with air-material structured… Show more

In this paper we review recent results describing the generation of optical modes within waveguides based on coherent scattering from artificially structured interfaces. The generation of optical waveguide propagation similar to free space propagation enables possible solutions to controlling and shaping optical field generation in free space using coherent scattering of multiple sources. It is shown that the controlled fabrication of such sources can be done simply with air-material structured waveguides such as air-silica structured fibres. Further, the technique of coherent superposition is well known in Fresnel optics, exploiting zone plates to correct the necessary phase adjustments for a desired lens performance. Similarly, in waveguide form this allows fine control of the interference process resulting in the desired mode field and its properties within the waveguide, at the end of the waveguide in the near field regime and well beyond the waveguide into the far field. A factor that can contribute significantly to the coherent scattering within the Fresnel waveguide is resonant-like scattering inside the low index regions since the critical angle of propagation can be very small, increasing Fresnel reflections between interfaces. The results presented here open up a range of hitherto unexplored possibilities in controlling and shaping at first glance disparate phenomena, including free space diffraction. Show less

We report on grating writing in air–silica structured optical fibers with pure silica cores by use of two-photon absorption at 193 nm. A decrease in propagation loss with irradiation was observed. The characteristic growth curves were obtained.

We report on grating writing in air–silica structured optical fibers with pure silica cores by use of two-photon absorption at 193 nm. A decrease in propagation loss with irradiation was observed. The characteristic growth curves were obtained.

We report on grating writing in air–silica structured optical fibers with pure silica cores by use of two-photon absorption at 193 nm. A decrease in propagation loss with irradiation was observed. The characteristic growth curves were obtained.

We report on grating writing in air–silica structured optical fibers with pure silica cores by use of two-photon absorption at 193 nm. A decrease in propagation loss with irradiation was observed. The characteristic growth curves were obtained.

We report on grating writing in air–silica structured optical fibers with pure silica cores by use of two-photon absorption at 193 nm. A decrease in propagation loss with irradiation was observed. The characteristic growth curves were obtained.

We report on grating writing in air–silica structured optical fibers with pure silica cores by use of two-photon absorption at 193 nm. A decrease in propagation loss with irradiation was observed. The characteristic growth curves were obtained.

We report on grating writing in air–silica structured optical fibers with pure silica cores by use of two-photon absorption at 193 nm. A decrease in propagation loss with irradiation was observed. The characteristic growth curves were obtained.

Propagation of light at 1.5 μm with peak intensity in an air hole is achieved within an air–silica-structured Fresnel waveguide. Thus a simpler fiber design alternative to photonic crystal fibers is possible for high-peak-power propagation with reduced nonlinear interactions. Multiple foci are observed in the far field.

Propagation within optical waveguides is re-examined in terms of diffraction-free propagation. The concept of the general diffraction-free mode is introduced. It is suggested that the optimised photonic bandgap waveguide must generate such a mode for loss-free propagation to be achieved. The invention of the “Fresnel” waveguide is described. Nowadays this technology has been reinvented as Bessel fibres and waveguides.

The structure and physical properties of a thin titania sol-gel layer prepared on silicon and silica surfaces were examined. Spectroscopic (FTIR, UV-VIS spectroscopy), refractive index (ellipsometry) and microscopic (light microscopy and SEM/EDS) tools were used to examine both chemical uniformity and physical uniformity of the sol-gel glass layers. The conditions for the fabrication of uniform layers were established, and room temperature dopant incorporation was examined. The absorption bands… Show more

The structure and physical properties of a thin titania sol-gel layer prepared on silicon and silica surfaces were examined. Spectroscopic (FTIR, UV-VIS spectroscopy), refractive index (ellipsometry) and microscopic (light microscopy and SEM/EDS) tools were used to examine both chemical uniformity and physical uniformity of the sol-gel glass layers. The conditions for the fabrication of uniform layers were established, and room temperature dopant incorporation was examined. The absorption bands of porphyrin-containing titania sol-gel layers were characterized. By addition of a metal salt to the titania layer, it was possible to metallate the free-base porphyrin within and change the UV-VIS absorbance of the porphyrin, the basis of metal detection using porphyrins. The metalloporphyrins were detected by localized laser ablation inductive coupled mass spectroscopy (LA-ICP-MS), indicating fairly uniform distribution of metals across the titania surface. Show less

This work presents a short review of the current research on the acousto-optic mechanism applied to optical fibers. The role of the piezoelectric element and the acousto-optic modulator in the excitation of flexural and longitudinal acoustic modes in the frequency range up to 1.2 MHz is highlighted. A combination of the finite elements and the transfer matrix methods is used to simulate the interaction of the waves with Bragg and long period gratings. Results show a very good agreement with… Show more

This work presents a short review of the current research on the acousto-optic mechanism applied to optical fibers. The role of the piezoelectric element and the acousto-optic modulator in the excitation of flexural and longitudinal acoustic modes in the frequency range up to 1.2 MHz is highlighted. A combination of the finite elements and the transfer matrix methods is used to simulate the interaction of the waves with Bragg and long period gratings. Results show a very good agreement with experimental data. Recent applications such as the writing of gratings under the acoustic excitation and a novel viscometer sensor based on the acousto-optic mechanism are discussed. Show less

We report the first (to our knowledge) development of a Bi/Er/Al/P codoped germanosilica optical fiber showing ultrabroadband luminescence between 1000 and 1570 nm, covering O-, E-, S-, C-, and L-bands, when pumped by 532, 808, or 980 nm lasers. The fluorescence profiles are found highly pump wavelength dependent, closely associated with different combinations of excitations from both Bi centers and Er ions as active centers. With a proper selection of pump wavelength(s), this Bi/Er codoped… Show more

We report the first (to our knowledge) development of a Bi/Er/Al/P codoped germanosilica optical fiber showing ultrabroadband luminescence between 1000 and 1570 nm, covering O-, E-, S-, C-, and L-bands, when pumped by 532, 808, or 980 nm lasers. The fluorescence profiles are found highly pump wavelength dependent, closely associated with different combinations of excitations from both Bi centers and Er ions as active centers. With a proper selection of pump wavelength(s), this Bi/Er codoped fiber could be used as an ultrabroadband gain medium for ultrabroadband amplified spontaneous emission sources, fiber lasers, or amplifiers in telecommunications and in other fields. Show less

The reliability and reproducibility of regenerated gratings for mass production is assessed through simultaneous bulk regeneration of 10 gratings. The gratings are characterized and variations are compared after each stage of fabrication, including seed (room-temperature UV fabrication), regeneration (annealing at 850°C), and postannealing (annealing at 1100°C). In terms of Bragg wavelength (λB), the seed grating variation lies within ΔλB=0.16  nm, the regenerated grating within ΔλB=0.41  nm… Show more

The reliability and reproducibility of regenerated gratings for mass production is assessed through simultaneous bulk regeneration of 10 gratings. The gratings are characterized and variations are compared after each stage of fabrication, including seed (room-temperature UV fabrication), regeneration (annealing at 850°C), and postannealing (annealing at 1100°C). In terms of Bragg wavelength (λB), the seed grating variation lies within ΔλB=0.16  nm, the regenerated grating within ΔλB=0.41  nm, and the postannealed grating within ΔλB=1.42  nm. All the results are within reasonable error, indicating that mass production is feasible. The observable spread in parameters from seed to regenerated grating is clearly systematic. The postannealed spread arises from the small tension on the fiber during postannealing and can be explained by the softening of the glass when the strain temperature of silica is reached. Show less

The temperature profile of the reaction zone inside the silica substrate tube during thermal heating with a H2/O2 flame under conditions identical to those used in the fabrication of optical fibre preforms using a modified chemical vapour deposition lathe has been characterised with ultra-high temperature stable regenerated optical fibre Bragg gratings. Experimental and theoretical results indicate a significant drop in temperature – up to several hundred degrees – across the tube wall from… Show more

The temperature profile of the reaction zone inside the silica substrate tube during thermal heating with a H2/O2 flame under conditions identical to those used in the fabrication of optical fibre preforms using a modified chemical vapour deposition lathe has been characterised with ultra-high temperature stable regenerated optical fibre Bragg gratings. Experimental and theoretical results indicate a significant drop in temperature – up to several hundred degrees – across the tube wall from outside to inside. These results are in contradiction with the broadly accepted assumption that there is no significant thermal gradient across the tube itself. An array of regenerated gratings demonstrates that optical fibre grating based sensing can achieve distributed ultra-high temperature mapping and monitoring in harsh environments. Show less

A focused ion beam is used to mill side holes in air–silica structured fibers. By way of example, side holes are introduced in two types of air-structured fiber, (1) a photonic crystal four-ring fiber and (2) a six-hole single-ring step-index structured fiber.

Consigned to the shadows of telecommunications, optical sensing has often taken a back seat in a young person’s mind when considering the importance of photonics, or optics, to the advancement of the society and of knowledge. Here, I touch on briefly how broad optical sensing and sensing generally has become and how and why it is becoming the catalyst for the convergence of many technologies and in the process raising significant philosophical questions about the transformation of our society… Show more

Consigned to the shadows of telecommunications, optical sensing has often taken a back seat in a young person’s mind when considering the importance of photonics, or optics, to the advancement of the society and of knowledge. Here, I touch on briefly how broad optical sensing and sensing generally has become and how and why it is becoming the catalyst for the convergence of many technologies and in the process raising significant philosophical questions about the transformation of our society and indeed ourselves. In doing so I touch on many of the complexities in real life that influence the breakthroughs we see today, including a healthy speculation and critique on our society and an awareness of the motivations to improve it that drive many of them. Show less

We constructed a type of sensor by depositing a solgel layer within the interior holes of a silica-structured fiber and, subsequently, coating this with an acid-responsive porphyrin. Protonation of the porphyrin by an acidic gas (HCl in this case), is detected by a large change in the visible spectrum. Compared to previous work on a liquid-core sensor in a structured optical fiber, the signal-to-noise ratio of this gas sensor shows a reduced signal strength, but the detection rate is increased… Show more

We constructed a type of sensor by depositing a solgel layer within the interior holes of a silica-structured fiber and, subsequently, coating this with an acid-responsive porphyrin. Protonation of the porphyrin by an acidic gas (HCl in this case), is detected by a large change in the visible spectrum. Compared to previous work on a liquid-core sensor in a structured optical fiber, the signal-to-noise ratio of this gas sensor shows a reduced signal strength, but the detection rate is increased about fortyfold. Show less

Both temperature and strain characterization of seed and regenerated gratings with and without post annealing is reported. The high temperature regeneration has significant impact on thermal characterization and mechanical strength of gratings while the post annealing has little effect. The observed difference is evidence of viscoelastic changes in glass structure.

The thermal stability of Type I gratings is increased by postthermal tuning of the grating. Optimization of the procedure leads to gratings that can withstand temperatures as high as 600°C . Aging tests lead to lifetime predictions as high as 25 years with <3 dB reduction at 400°C . Single exponential relaxation is observed. Above 800°C regeneration is obtained.