High resolution TCSPC imaging of diffuse light with a one-dimensional SPAD array scanning system.

We report a time-correlated single-photon counting (TCSPC) imaging system based on a line-scanning architecture. The system benefits from the high fill-factor, active area, and large dimension of an advanced CMOS single-photon avalanche diode (SPAD) array line-sensor. A two-dimensional image is constructed using a moving mirror to scan the line-sensor field-of-view (FOV) across the target, to enable the efficient acquisition of a two-dimensional 0.26 Mpixel TCSPC image. We demonstrate the capabilities of the system for TCSPC imaging and locating objects obscured in scattering media - specifically to locate a series of discrete point sources of light along an optical fibre submerged in a highly scattering solution. We demonstrate that by selectively imaging using early arriving photons which have undergone less scattering than later arriving photons, our TCSPC imaging system is able to locate the position of discrete point sources of light than a non-time-resolved imaging system.

pH sensing through a single optical fibre using SERS and CMOS SPAD line arrays.

Full exploitation of fibre Raman probes has been limited by the obstruction of weak Raman signals by background fluorescence of the sample and the intrinsic Raman signal of the delivery fibre. Here we utilised functionalised gold nanoshells (NS) to take advantage of the surface-enhanced Raman spectroscopy (SERS) effect to enhance the pH responsive spectrum of 4-mercaptobenzoic acid (MBA). However, the fibre background is still dominant. Using the photon arrival time-resolving capability of a CMOS single-photon avalanche diode (SPAD) based line sensor, we recover the SERS spectrum without a fibre background in a 10 s measurement. In this manner, pH sensing through a multimode fibre at a low excitation power that is safe for future in vivo applications, with short acquisition times (10 or 60 s), is demonstrated. A measurement precision of ± 0.07 pH units is thus achieved.

Ballistic and snake photon imaging for locating optical endomicroscopy fibres.

We demonstrate determination of the location of the distal-end of a fibre-optic device deep in tissue through the imaging of ballistic and snake photons using a time resolved single-photon detector array. The fibre was imaged with centimetre resolution, within clinically relevant settings and models. This technique can overcome the limitations imposed by tissue scattering in optically determining the in vivo location of fibre-optic medical instruments.

Chip-based quantum key distribution.

Improvement in secure transmission of information is an urgent need for governments, corporations and individuals. Quantum key distribution (QKD) promises security based on the laws of physics and has rapidly grown from proof-of-concept to robust demonstrations and deployment of commercial systems. Despite these advances, QKD has not been widely adopted, and large-scale deployment will likely require chip-based devices for improved performance, miniaturization and enhanced functionality. Here we report low error rate, GHz clocked QKD operation of an indium phosphide transmitter chip and a silicon oxynitride receiver chip-monolithically integrated devices using components and manufacturing processes from the telecommunications industry. We use the reconfigurability of these devices to demonstrate three prominent QKD protocols-BB84, Coherent One Way and Differential Phase Shift-with performance comparable to state-of-the-art. These devices, when combined with integrated single photon detectors, pave the way for successfully integrating QKD into future telecommunications networks.

Endoscopic sensing of alveolar pH.

Previously unobtainable measurements of alveolar pH were obtained using an endoscope-deployable optrode. The pH sensing was achieved using functionalized gold nanoshell sensors and surface enhanced Raman spectroscopy (SERS). The optrode consisted of an asymmetric dual-core optical fiber designed for spatially separating the optical pump delivery and signal collection, in order to circumvent the unwanted Raman signal generated within the fiber. Using this approach, we demonstrate a ~100-fold increase in SERS signal-to-fiber background ratio, and demonstrate multiple site pH sensing with a measurement accuracy of ± 0.07 pH units in the respiratory acini of an ex vivo ovine lung model. We also demonstrate that alveolar pH changes in response to ventilation.

Photon pair generation in a silicon micro-ring resonator with reverse bias enhancement.

Photon sources are fundamental components for any quantum photonic technology. The ability to generate high count-rate and low-noise correlated photon pairs via spontaneous parametric down-conversion using bulk crystals has been the cornerstone of modern quantum optics. However, future practical quantum technologies will require a scalable integration approach, and waveguide-based photon sources with high-count rate and low-noise characteristics will be an essential part of chip-based quantum technologies. Here, we demonstrate photon pair generation through spontaneous four-wave mixing in a silicon micro-ring resonator, reporting separately a maximum coincidence-to-accidental (CAR) ratio of 602 ± 37 (for a generation rate of 827kHz), and a maximum photon pair generation rate of 123 MHz ± 11 kHz (with a CAR value of 37). To overcome free-carrier related performance degradations we have investigated reverse biased p-i-n structures, demonstrating an improvement in the pair generation rate by a factor of up to 2 with negligible impact on CAR.

A superconducting nanowire single photon detector on lithium niobate.

Superconducting nanowire single photon detectors (SNSPDs) are a key enabling technology for optical quantum information science. In this paper we demonstrate a SNSPD fabricated on lithium niobate, an important material for high speed integrated photonic circuits. We report a system detection efficiency of 0.15% at a 1 kHz dark count rate with a maximum of ~1% close to the critical current at 1550 nm wavelength for a parallel wire SNSPD with front side illumination. There is clear scope for improving on this performance with further materials optimization. Detector integration with a lithium niobate optical waveguide is simulated, demonstrating the potential for high single photon detection efficiency in an integrated quantum optic circuit.

Evaluation of tibial component fixation in specimens retrieved at autopsy.

Fixation of the tibial component was evaluated in eight knees retrieved at autopsy by comparing their radiographs with measurements of micromovement between the component and the tibial plateau. Micromovement in the one cemented Miller-Galante and seven cementless Ortholoc components, which had been implanted for a range of 3 days to 57 months, was measured with linearly variable differential transducers under anteroposterior shear and axial compressive loads. Micromovement between the tibial component and the screws and between the tibial component and the bone after the screws were removed also was measured in the cementless specimens. Minimal micromovement in most of the implants suggests that the tibial components were well fixed. Micromovement between the tibial tray and the screws also was minimal in the cementless components. Removing the screws did not significantly affect micromovement, except in the specimen retrieved 3 days after surgery and in the specimen with a complete radiolucent line under the component. The cementless tibial components fixed with screws, pegs, and stem were as stable as the component secured with cement. Partial radiolucencies were not associated with greater micromotion than that of bone ingrown areas, but the component with complete radiolucency did have greater micromotion than that of all of the other specimens.

Effect of locking mechanism on fluid and particle flow through modular acetabular components.

Six modular acetabular components were evaluated to determine whether screw holes in the metal shell offer a route for fluid and debris into the acetabular bone stock. A 56-mm acetabular shell for each trial was mounted to a sealed chamber and loaded at a 25 degrees angle under axial loads of 270-2,700 N and +/- 2.5-N-m torsional load. Polystyrene microspheres (average diameter, 0.5 microm) were placed in double-deionized water at 300 mmH2O pressure in a sealed chamber above the component. The only channel between the fluid above and the collecting chamber below was through the cup-liner interface and 1 screw hole. Fluid and debris in the collecting chamber were harvested after 1,000,000 cycles. The collected sample was filtered through a 0.2-microm-pore filter and analyzed under electron microscopy for evidence of microspheres. Water and polystyrene microspheres were isolated in the collecting chamber for all trials except the Reflection cup (Smith & Nephew Orthopaedics, Memphis, TN) with a screw hole cover and the Micro-Seal cup (Whiteside Biomechanics, St. Louis, MO) with a peripheral seal. A screw placed in the screw hole of the Reflection cup failed to seal the interface. The peripheral seal around the rim of the Micro-Seal polyethylene prevented fluid and particle flow between the metal shell and polyethylene liner.

Effects of sterilization on wear in total knee arthroplasty.

Twenty-nine Ortholoc II ultrahigh molecular weight polyethylene tibial components were retrieved from 27 patients at revision surgery from the same hospital. The polyethylene material grade, method of sterilization, and sterilization dosage for 26 of the tibial components were determined by tracing the material lot number for each component. Each tibial surface was scored for wear using a qualitative scoring system that evaluated delamination, pitting, scratching, cold flow, abrasion, and burnishing. After the wear score analysis, 14 of the 26 components were analyzed to determine the physical and mechanical properties of the polyethylene including toughness and elongation. Seven of these 14 components were sterilized using ethylene oxide and 7 were sterilized using gamma radiation. Tibial components sterilized with gamma radiation had significantly higher wear rates than those sterilized with ethylene oxide. Thirteen of the 18 components sterilized with gamma radiation had delamination of the articular surface compared with 2 of 8 components sterilized with ethylene oxide. Mechanical properties were significantly affected by the sterilization method. Components sterilized with ethylene oxide had significantly higher toughness and percent elongation than those sterilized with gamma radiation. These findings suggest that ethylene oxide sterilization caused less microstructural damage to the polyethylene and resulted in significantly less wear than was found in those components sterilized with gamma radiation.

Effect of polyethylene quality on wear in total knee arthroplasty.

During evaluation of 29 Ortholoc II tibial polyethylene components retrieved at revision surgery, the authors noticed that components with a lot number prefix of CP (Custom Product) consistently had minimal wear and those with a standard lot number had severe wear, regardless of patient age, weight, gender, and activity level. Non-CP components had earlier and more severe wear than CP components in service for the same amount of time. Microscopic evaluation of the polyethylene revealed major differences in the material. Large subsurface cracks, fusion defects, and intergranular cracks were present in the non-CP components, but these defects were minimal or nonexistent in the CP components. The components with defects had a significantly greater delamination rate than those without defects. Gamma irradiation did not seem to accelerate wear or delamination, because irradiated components that had minimal microscopic signs of fusion defects performed as well as nonirradiated components with a similar microscopic appearance. The manufacturing details disclosed that different materials and processing methods were used for the 2 groups. The results from this study suggest that improved quality control of polyethylene material would greatly decrease wear and delamination of total knee arthroplasty components.

An evaluation of new attachment formation using a microfibrillar collagen barrier.

The objective of this study was to evaluate the effectiveness of microfibrillar collagen as a barrier to prevent epithelial migration and allow for guided tissue regeneration. Fourteen study teeth were selected. Mucoperiosteal flaps were elevated and roots were debrided and planed. Avitene was placed over teeth and alveolar bone. Flaps were then sutured over it. At control sites no Avitene was placed. At 90 days, block sections were obtained and processed for histologic and histometric evaluation. Results revealed that all specimens had a long junctional epithelial attachment. New attachment was present within the area of the root notch at the original level of the alveolar bone, and there was no significant difference in mean connective tissue attachment between the control and experimental specimens (P = 0.614). Avitene did not form an effective barrier to epithelial migration nor did it allow for guided tissue regeneration and significant new attachment formation in humans.

Hemispheric specialization in normally and slowly developing children: a tachistoscopic and dichaptic evaluation.

The purpose of the study was a description of hemispheric specialization characteristics of normally developing right- and left-handed children and determination of what differences in such characteristics, if any, existed between young normally developing and older slowly developing children. With dichaptic and tachistoscopic methods, hemispheric specialization characteristics of 15 slowly developing children (5-0 to 9-6 yr.) and 25 normally developing children (6-0 to 6-11 yr.) were assessed. Latencies and the number of correct responses were analyzed. Both right- and left-handed normally developing 6-yr.-olds showed considerable evidence of bilateralization of hemispheric functions for spatial and verbal information processing; slowly developing children exhibited unusual patterns of hemispheric specialization usually opposite those typically expected in children or adults. Response latency measures of performances of slowly developing children suggested a bilateralization of hemispheric function for processing of verbal and spatial information; number of correct responses indicated that lateralization of such functions was present.