Identifying low value pathology test ordering in hospitalised patients: a retrospective cohort study across two hospitals.

The push to identify low value care has led to scrutiny of pathology test re-ordering. The objective of this study was to identify the patterns of ordering pathology tests among inpatients in teaching hospitals and model strategies to reduce unnecessary testing. This was a retrospective cohort study of all adult medical and surgical inpatients admitted to one major teaching hospital and one rural hospital in the same health district over 2 years. Obstetric, gynaecological, intensive care, elective/day procedures and dialysis admissions were excluded. Orders for electrolytes, urea and creatinine (EUC), full blood count (FBC), thyroid stimulating hormone (TSH), glycated haemoglobin (HbA1c), vitamin D, and troponin, date of order, and value of the resulting test, were obtained from a health district data warehouse. Pathology results were mapped to each inpatient day. EUC and FBC constituted over 90% of all inpatient pathology requests for these six tests. Between 40-45% of inpatients had EUC and/or FBC performed daily. After the first couple of tests, the retest interval was consistently around 24 hours, regardless of the previous value of the test, consistent with a culture of routine ordering. This was less pronounced in the rural hospital compared to the urban teaching hospital. Lockouts (applied when previous tests normal) or minimum retest intervals (applied to previously normal and abnormal tests) of various lengths were tested on the data to find optimal combinations that reduced unnecessary tests without missing too many very abnormal tests. A lockout of 48 hours for EUC and 48 hour lockout combined with a 12 hour minimum retest interval for FBC appear optimal to reduce over ordering and could save approximately AU$400/inpatient bed per year at a single teaching hospital. There is evidence of low value re-ordering of EUC and FBC pathology tests. Implementation of a computerised physician order entry system with inbuilt prompts to restrict unnecessary re-ordering of pathology tests may be a practical solution.

High-speed optical sampling using a silicon-chip temporal magnifier.

We demonstrate a single-shot technique for optical sampling based on temporal magnification using a silicon-chip time lens. We demonstrate the largest reported temporal magnification factor yet achieved (>500) and apply this technique to perform 1.3 TS/s single-shot sampling of ultrafast waveforms and to 80-Gb/s performance monitoring. This scheme offers the potential of developing a device that can transform GHz oscilloscopes into instruments capable of measuring signals with THz bandwidths.

Silicon-chip-based ultrafast optical oscilloscope.

With the realization of faster telecommunication data rates and an expanding interest in ultrafast chemical and physical phenomena, it has become important to develop techniques that enable simple measurements of optical waveforms with subpicosecond resolution. State-of-the-art oscilloscopes with high-speed photodetectors provide single-shot waveform measurement with 30-ps resolution. Although multiple-shot sampling techniques can achieve few-picosecond resolution, single-shot measurements are necessary to analyse events that are rapidly varying in time, asynchronous, or may occur only once. Further improvements in single-shot resolution are challenging, owing to microelectronic bandwidth limitations. To overcome these limitations, researchers have looked towards all-optical techniques because of the large processing bandwidths that photonics allow. This has generated an explosion of interest in the integration of photonics on standard electronics platforms, which has spawned the field of silicon photonics and promises to enable the next generation of computer processing units and advances in high-bandwidth communications. For the success of silicon photonics in these areas, on-chip optical signal-processing for optical performance monitoring will prove critical. Beyond next-generation communications, silicon-compatible ultrafast metrology would be of great utility to many fundamental research fields, as evident from the scientific impact that ultrafast measurement techniques continue to make. Here, using time-to-frequency conversion via the nonlinear process of four-wave mixing on a silicon chip, we demonstrate a waveform measurement technology within a silicon-photonic platform. We measure optical waveforms with 220-fs resolution over lengths greater than 100 ps, which represent the largest record-length-to-resolution ratio (>450) of any single-shot-capable picosecond waveform measurement technique. Our implementation allows for single-shot measurements and uses only highly developed electronic and optical materials of complementary metal-oxide-semiconductor (CMOS)-compatible silicon-on-insulator technology and single-mode optical fibre. The mature silicon-on-insulator platform and the ability to integrate electronics with these CMOS-compatible photonics offer great promise to extend this technology into commonplace bench-top and chip-scale instruments.

Optical time lens based on four-wave mixing on a silicon chip.

We propose a new technique to realize an optical time lens for ultrafast temporal processing that is based on four-wave mixing in a silicon nanowaveguide. The demonstrated time lens produces more than 100 pi of phase shift, which is not readily achievable using electro-optic phase modulators. Using this method we demonstrate 20x magnification of a signal consisting of two 3 ps pulses, which allows for temporal measurements using a detector with a 20 GHz bandwidth. Our technique offers the capability of ultrafast temporal characterization and processing in a chip-scale device.

Absorption of ultrashort optical pulses in water.

We investigate the linear propagation of 800 and 1530 nm ultrashort optical pulses in water. For all pulse repetition rates studied, we observe pure exponential decay down to a transmission of 2.5 x 10(-5). We further demonstrate that previous observations of nonmonoexponential decay and pulse splitup in broadband pulses are consistent with Beer's law in the purely linear regime.

All-optical regeneration on a silicon chip.

We demonstrate optical 2R regeneration in an integrated silicon device consisting of an 8-mm-long nanowaveguide followed by a ring-resonator bandpass filter. The regeneration process is based on nonlinear spectral broadening in the waveguide and subsequent spectral filtering through the ring resonator. We measure the nonlinear power transfer function for the device and find an operating peak power of 6 W. Measurements indicate that the output pulse width is determined only by the bandwidth of the bandpass filter. Numerical modeling of the nonlinear process including free-carrier effects shows that this device can be used for all-optical regeneration at telecommunication data rates.

Negligible birefringence in dual-mode ion-exchanged glass waveguide gratings.

Polarization dependence of UV-written Bragg gratings in buried ion-exchanged glass waveguides is investigated. A polarization-dependent shift in Bragg wavelength of less than 0.02 nm is measured, both for the even and the odd modes of a laterally dual-mode waveguide. The measured wavelength shift corresponds to a waveguide birefringence of the order of 10(-5), which is negligible for most applications in optical communications. It is observed that the UV-induced birefringence is small, within the limits of the measurement accuracy. The thermal stability of the fabricated gratings is also very good. The results are of particular importance for devices considered here since they require a polarization-independent mode-converting waveguide Bragg grating. Polarization-independent performance of these gratings enables the fabrication of a new class of integrated optical devices for telecommunication applications.

Optical add-drop multiplexers based on the antisymmetric waveguide Bragg grating.

A novel optical add-drop multiplexer (OADM) based on a null coupler with an antisymmetric grating was designed and experimentally demonstrated. The antisymmetric grating exclusively produces a reflection with mode conversion in a two-mode waveguide. This improves the performance compared with previous demonstrations that used tilted Bragg gratings. Our design minimizes noise and cross talk produced by reflection without mode conversion. In addition, operational bandwidth and, versatility are improved while the compactness and simplicity of the null coupler OADM are maintained.

Demonstration of mode conversion using anti-symmetric waveguide Bragg gratings.

We experimentally demonstrate a novel grating which only produces reflection with mode conversion in a two-mode waveguide. That characteristic can improve the performance of optical devices that currently use tilted Bragg gratings to provide the mode conversion. Tilted Bragg gratings produce also reflections without mode conversion which increases noise and crosstalk of the optical device.

Fabrication and comprehensive modeling of ion-exchanged Bragg optical add-drop multiplexers.

Optical add-drop multiplexers (OADMs) based on asymmetric Y branches and tilted gratings offer excellent-performance in wavelength-division multiplexed systems. To simplify waveguide fabrication, ion-exchange techniques appear to be an important option in photosensitive glasses. Optimum OADM performance depends on how accurately the waveguide fabrication process and tilted Bragg grating operation are understood and modeled. Results from fabrication and comprehensive modeling are compared for ion-exchange processes that use different angles of the tilted grating. The transmission and reflection spectra for the fabricated and simulated OADMs show excellent agreement. The OADM's performance is evaluated in terms of the measured characteristics of the Y branches and tilted gratings.