Extending the spectrum of fully integrated photonics to submicrometre wavelengths.

Integrated photonics has profoundly affected a wide range of technologies underpinning modern society1-4. The ability to fabricate a complete optical system on a chip offers unrivalled scalability, weight, cost and power efficiency5,6. Over the last decade, the progression from pure III-V materials platforms to silicon photonics has significantly broadened the scope of integrated photonics, by combining integrated lasers with the high-volume, advanced fabrication capabilities of the commercial electronics industry7,8. Yet, despite remarkable manufacturing advantages, reliance on silicon-based waveguides currently limits the spectral window available to photonic integrated circuits (PICs). Here, we present a new generation of integrated photonics by directly uniting III-V materials with silicon nitride waveguides on Si wafers. Using this technology, we present a fully integrated PIC at photon energies greater than the bandgap of silicon, demonstrating essential photonic building blocks, including lasers, amplifiers, photodetectors, modulators and passives, all operating at submicrometre wavelengths. Using this platform, we achieve unprecedented coherence and tunability in an integrated laser at short wavelength. Furthermore, by making use of this higher photon energy, we demonstrate superb high-temperature performance and kHz-level fundamental linewidths at elevated temperatures. Given the many potential applications at short wavelengths, the success of this integration strategy unlocks a broad range of new integrated photonics applications.

Ultra-precise optical-frequency stabilization with heterogeneous III-V/Si lasers.

The demand for low-noise, continuous-wave, frequency-tunable lasers based on semiconductor integrated photonics has advanced in support of numerous applications. In particular, an important goal is to achieve a narrow spectral linewidth, commensurate with bulk-optic or fiber-optic laser platforms. Here we report on laser-frequency-stabilization experiments with a heterogeneously integrated III/V-Si widely tunable laser and a high-finesse, thermal-noise-limited photonic resonator. This hybrid architecture offers a chip-scale optical-frequency reference with an integrated linewidth of 60 Hz and a fractional frequency stability of 2.5×10-13 at 1 s integration time. We explore the potential for stabilization with respect to a resonator with lower thermal noise by characterizing laser-noise contributions such as residual amplitude modulation and photodetection noise. Widely tunable, compact and integrated, cost-effective, stable, and narrow-linewidth lasers are envisioned for use in various fields, including communication, spectroscopy, and metrology.

Integrated microwave photonic phase shifter with full tunable phase shifting range (> 360°) and RF power equalization.

We report a novel microwave photonic phase and amplitude control structure based on a single microring resonator with a tunable Mach Zehnder interferometer reflective loop, which enables the realization of a continuously tunable microwave photonic phase shifter with enhanced phase tuning range while simultaneously compensating for the RF power variations. The complimentary tuning of the phase and amplitude presents a simplistic approach to resolve the inherent trade-off between maintaining a full RF phase shift while eliminating large RF power variations. Detailed simulations have been carried out to analyze the performance of the new structure as a microwave photonic phase shifter, where the reflective nature of the proposed configuration shows an effective doubling of the phase range while the amplitude compensation module provides a parallel control to potentially reduce the RF amplitude variations to virtually zero. The phase range enhancement, which is first verified experimentally with a passive only chip, demonstrates the capability to achieve a continuously tunable RF phase shift of 0-510° with an RF amplitude variation of 9 dB. Meanwhile, the amplitude compensation scheme is incorporated onto an active chip with a continuously tunable RF phase shift of 0-150°, where the RF power variations is shown to be reduced by 5 dB while maintaining a constant RF phase shift.

Integrated optical driver for interferometric optical gyroscopes.

We present the first chip-scale "integrated optical driver" (IOD) that can interrogate with a sensing coil to realize an interferometric optical gyroscope. The chip comprises a light source, three photodiodes, two phase modulators and two 3-dB couplers within an area of 4.5 mm2. This allows for a significant reduction in size, weight, power consumption and cost of optical gyroscopes.

Integrated chip-scale Si3N4 wavemeter with narrow free spectral range and high stability.

We designed, fabricated, and characterized an integrated chip-scale wavemeter based on an unbalanced Mach-Zehnder interferometer with 300 MHz free spectral range. The wavemeter is realized in the Si3N4 platform, allowing for low loss with ∼62 cm of on-chip delay. We also integrated an optical hybrid to provide phase information. The main benefit of a fully integrated wavemeter, beside its small dimensions, is increased robustness to vibrations and temperature variations and much improved stability over fiber-based solutions.

Frequency modulated lasers for interferometric optical gyroscopes.

We study the use of frequency modulated lasers in interferometric optical gyroscopes and show that by exploiting various frequency modulation signals, the laser coherence can be controlled. We show that both angle random walk and bias stability of an interferometric optical gyroscope based on laser sources can be improved with this technique.

Geographical variation in the management of urolithiasis in Australia.

BACKGROUND: To examine any geographical variation in the management of urolithiasis amongst the Australian states and territories. METHODS: Retrospective study with data obtained from the Medicare Australia database, the Royal Australasian College of Surgeons and the Urological Society of Australia and New Zealand. RESULTS: Minimally invasive stone treatment with shock wave lithotripsy (SWL) and ureteroscopy (URS) accounted for the majority of stone treatments in Australia (98%). Variation of stone treatment modalities exists amongst the Australian states and territories with an inverse relationship between the use of SWL and URS. We compared Western Australia (WA) and Queensland (QLD) which have a comparable geographical area. SWL accounts for 1% and 22% of stone treatments in WA and QLD, respectively. In WA, urologists are concentrated in two cities with no SWL available in the private sector. In QLD, urologists are distributed in 11 cities with SWL available in both the public and private sector. The three largest states or territories by geographical area - the Northern Territory, WA and QLD - have stone treatment rates of 1:1337, 1:1110 and 1:2432 per capita of privately insured patients, respectively. In comparison, smaller Australian states/territories such as Tasmania and Victoria have stone treatment rates of 1:619 and 1:765 per capita of privately insured patients, respectively. CONCLUSION: The distribution of urologists and treatment modalities available in each state or territory appear to play a contributory role in choice of treatment modality. In addition, inequality to stone treatment access exists in geographically large Australian states/territories.