Compact, remote optical waveguide magnetic field sensing using double-pass Faraday rotation-induced optical attenuation.

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=1550n m 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=Δ α/Δ B=(0.26±0.02)d B/m T with a resolution of Δ B=0.01m T, over a detection range B=0-89m T. 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.

Realization of optical fiber regenerated gratings by rapid cooling and split annealing.

Rapid cooling, or quenching, during regeneration of seed gratings in standard single-mode silica optical fiber is explored. It is shown that regeneration can be broken up into stages in time. The novel, to the best of our knowledge, method of "split annealing" offers a unique tool for optimizing regeneration and studying fundamental glass science within a one-dimensional bi-material system. We demonstrate regeneration at temperatures as high as T = 1200°C for the first time as well as opening up an approach suited to batch processing of regenerated gratings.

Chirping fiber Bragg gratings within additively manufactured polymer packages.

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 $\Delta {\lambda _{\rm BW}}\gt {7}\;{\rm nm/cm}$ΔλBW>7nm/cm, is proposed and demonstrated.

Helical distributed feedback fiber Bragg gratings and rocking filters in a 3D printed preform-drawn fiber.

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.

Development of a lateral flow test for rapid pyrethroid detection using antibody-gated indicator-releasing hybrid materials.

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.

Silica optical fiber drawn from 3D printed preforms.

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

Large area optical mapping of surface contact angle.

Top-down contact angle measurements have been validated and confirmed to be as good if not more reliable than side-based measurements. A range of samples, including industrially relevant materials for roofing and printing, has been compared. Using the top-down approach, mapping in both 1-D and 2-D has been demonstrated. The method was applied to study the change in contact angle as a function of change in silver (Ag) nanoparticle size controlled by thermal evaporation. Large area mapping reveals good uniformity for commercial Aspen paper coated with black laser printer ink. A demonstration of the forensic and chemical analysis potential in 2-D is shown by uncovering the hidden CsF initials made with mineral oil on the coated Aspen paper. The method promises to revolutionize nanoscale characterization and industrial monitoring as well as chemical analyses by allowing rapid contact angle measurements over large areas or large numbers of samples in ways and times that have not been possible before.

Time-resolved and temperature tuneable measurements of fluorescent intensity using a smartphone fluorimeter.

A smartphone fluorimeter capable of time-based fluorescence intensity measurements at various temperatures is reported. Excitation is provided by an integrated UV LED (λex = 370 nm) and detection obtained using the in-built CMOS camera. A Peltier is integrated to allow measurements of the intensity over T = 10 to 40 °C. All components are controlled using a smartphone battery powered Arduino microcontroller and a customised Android application that allows sequential fluorescence imaging and quantification every δt = 4 seconds. The temperature dependence of fluorescence intensity for four emitters (rhodamine B, rhodamine 6G, 5,10,15,20-tetraphenylporphyrin and 6-(1,4,8,11-tetraazacyclotetradecane)2-ethyl-naphthalimide) are characterised. The normalised fluorescence intensity over time of the latter chemosensor dye complex in the presence of Zn2+ is observed to accelerate with an increasing rate constant, k = 1.94 min-1 at T = 15 °C and k = 3.64 min-1 at T = 30 °C, approaching a factor of ∼2 with only a change in temperature of ΔT = 15 °C. Thermally tuning these twist and bend associated rates to optimise sensor approaches and device applications is proposed.

Polarization mode coupling and related effects in fiber Bragg grating inscribed in polarization maintaining fiber.

Polarization mode coupling (PMC) and related effects from writing fiber Bragg gratings in polarization maintaining fiber (FBGs-in-PMF) are observed experimentally for the first time by optical fiber coherence domain polarimetry (OCDP) using a broadband light source. PMC is another useful aspect of FBG-in-PMF besides Bragg wavelength and its possible potential is evaluated and discussed. A localized and long range temperature measurement based on the PMC and Bragg wavelength is given as an example.

Optical fiber smartphone spectrometer.

An optical fiber-based smartphone spectrometer incorporating an endoscopic fiber bundle is demonstrated. The endoscope allows transmission of the smartphone camera LED light to a sample, removing complications from varying background illumination. The reflected spectra collected from a surface or interface is dispersed onto the camera CMOS using a reflecting diffraction grating. A spectral resolution as low as δλ∼2.0 nm over a bandwidth of Δλ∼250 nm is obtained using a slit width, ωslit=0.7 mm. The instrument has vast potential in a number of industrial applications including agricultural produce analysis. Spectral analysis of apples shows straightforward measurement of the pigments anthocyanins, carotenoid, and chlorophyll, all of which decrease with increasing storage time.

Exciting surface plasmons on metal-coated multimode optical waveguides using skew rays.

Multipoint surface plasmon resonance (SPR) excitation using a skew ray within a multimode plastic optical waveguide coated with gold, Au, is reported. The effect of skew rays on the performance of SPR has been studied both theoretically and experimentally. The approach also entails a novel method of measuring the SPR angle that is in agreement with theoretically predicted values.

Drawing optical fibers from three-dimensional printers.

The temperature distribution within extrusion nozzles of three low-cost desktop 3D printers is characterized using fiber Bragg gratings (FBGs) to assess their compatibility as micro-furnaces for optical fiber and taper production. These profiles show remarkably consistent distributions suitable for direct drawing of optical fiber. As proof of principle, coreless optical fibers (φ=30 µm) made from fluorinated acrylonitrile butadiene styrene (ABS) and polyethylene terephthalate glycol (PETG) are drawn. Cutback measurements demonstrate propagation losses as low as α=0.26 dB/cm, which are comparable with standard optical fiber losses with some room for improvement. This work points toward direct optical fiber manufacture of any material from 3D printers.

Step-index optical fiber drawn from 3D printed preforms.

Optical fiber is drawn from a dual-head 3D printer fabricated preform made of two optically transparent plastics with a high-index core (NA∼0.25, V>60). The asymmetry observed in the fiber arises from asymmetry in the 3D printing process. The highly multimode optical fiber has losses measured by cut-back as low as α∼0.44 dB/cm in the near IR.

Smartphone laser beam spatial profiler.

A simple, low-cost, portable, smartphone-based laser beam profiler for characterizing laser beam profiles is reported. The beam profiler utilizes a phosphor silica glass plate to convert UV light into visible (green) light that can be directly imaged onto an existing smartphone CMOS chip and analyzed using a customized app. 3D printing enables the ready fabrication of the instrument package. The beam's diameter, shape, divergence, beam quality factor, and output power are measured for two UV lasers: a CW 244 nm frequency-doubled Ar ion laser and a pulsed 193 nm ArF exciplex laser. The availability of specialized phosphor converters can extend the instrument from the UV to the near infrared and beyond, and the smartphone platform extends the Internet of Things to map laser beam profiles simultaneously in different locations.

Combined "dual" absorption and fluorescence smartphone spectrometers.

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.

Air-structured optical fiber drawn from a 3D-printed preform.

A structured optical fiber 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 fiber manufacture.

A comparative study for image quality and radiation dose of a cone beam computed tomography scanner and a multislice computed tomography scanner for paranasal sinus imaging.

OBJECTIVES: To evaluate image quality and radiation dose of a state of the art cone beam computed tomography (CBCT) system and a multislice computed tomography (MSCT) system in patients with sinonasal poliposis. METHODS: In this retrospective study two radiologists evaluated 57 patients with sinonasal poliposis who underwent a CBCT or MSCT sinus examination, along with a control group of 90 patients with normal radiological findings. Tissue doses were measured using a phantom model with thermoluminescent dosimeters (TLD). RESULTS: Overall image quality in CBCT was scored significantly higher than in MSCT in patients with normal radiologic findings (p-value: 0.00001). In patients with sinonasal poliposis, MSCT scored significantly higher than CBCT (p-value: 0.00001). The average effective dose for MSCT was 42% higher compared to CBCT (108 µSv vs 63 µSv). CONCLUSIONS: CBCT and MSCT are both suited for the evaluation of sinonasal poliposis. In patients with sinonasal poliposis, clinically important structures of the paranasal sinuses can be better delineated with MSCT, whereas in patients without sinonasal poliposis, CBCT turns out to define the important structures of the sinonasal region better. However, given the lower radiation dose, CBCT can be considered for the evaluation of the sinonasal structures in patients with sinonasal poliposis. KEY POINTS: • CBCT and MSCT are both suited for evaluation of sinonasal poliposis. • Effective dose for MSCT was 42% higher compared to CBCT. • In patients with sinonasal poliposis, clinically important anatomical structures are better delineated with MSCT. • In patients with normal radiological findings, clinically important anatomical structures are better delineated with CBCT.

Ultrahigh-Temperature Regeneration of Long Period Gratings (LPGs) in Boron-Codoped Germanosilicate Optical Fibre.

The regeneration of UV-written long period gratings (LPG) in boron-codoped germanosilicate "W" fibre is demonstrated and studied. They survive temperatures over 1000 °C. Compared with regenerated FBGs fabricated in the same type of fibre, the evolution curves of LPGs during regeneration and post-annealing reveal even more detail of glass relaxation. Piece-wise temperature dependence is observed, indicating the onset of a phase transition of glass in the core and inner cladding at ~500 °C and ~250 °C, and the melting of inner cladding between 860 °C and 900 °C. An asymmetric spectral response with increasing and decreasing annealing temperature points to the complex process dependent material system response. Resonant wavelength tuning by adjusting the dwell temperature at which regeneration is undertaken is demonstrated, showing a shorter resonant wavelength and shorter time for stabilisation with higher dwell temperatures. All the regenerated LPGs are nearly strain-insensitive and cannot be tuned by applying loads during annealing as done for regenerated FBGs.

Near orthogonal launch of SPR modes in Au films.

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.

Toward an ultra-broadband emission source based on the bismuth and erbium co-doped optical fiber and a single 830nm laser diode pump.

We demonstrate a broadband optical emission from Bi/Er co-doped fiber and a single 830nm laser diode pump. The ultra-broadband mechanism is studied and discussed in details based on a combination of experimental measurements, including luminescence, differential luminescence and ESA, on fiber samples of different Bi and Er concentrations. The Er co-doping in Bi doped fiber is found to be effective for broadband emission, by enhancing not only luminescence at C and L bands but also that at O and shorter wavelength bands. The luminescence intensity between 1100 and 1570nm is over -45dBm/5nm in single mode fiber using a few meters of Bi/Er co-doped fiber and offers a modest ~40dB dynamic range and a broad bandwidth of ~470nm for an OSA based spectral measurement.