Xiong, Chi
Pernice, Wolfram
Schuck, Carsten
Tang, Hong X.
Integrated optics is a promising optical platform both for its enabling role in optical interconnects and applications in on-chip optical signal processing. In this paper, we discuss the use of group III-nitride (GaN, AlN) as a new material system for integrated photonics compatible with silicon substrates. Exploiting their inherent second-order nonlinearity we demonstrate and second, third harmonic generation in GaN nanophotonic circuits and high-speed electro-optic modulation in AlN nanophotonic circuits.
Photonic miniaturization requires seamless integration of linear and nonlinear optical components to achieve passive and active functions simultaneously. Among the available material systems, silicon photonics holds immense promise for optical signal processing and on-chip optical networks. However, silicon is limited to wavelengths above 1.1 mu m and does not provide the desired lowest order optical nonlinearity for active signal processing. Here we report the integration of aluminum nitride (AlN) films on silicon substrates to bring active functionalities to chip-scale photonics. Using CMOS-compatible sputtered thin films we fabricate AlN-on-insulator waveguides that exhibit low propagation loss (0.6 dB/cm). Exploiting AlN's inherent Pockels effect we demonstrate electro-optic modulation up to 4.5 Gb/s with very low energy consumption (down to 10 fJ/bit). The ultrawide transparency window of AlN devices also enables high speed modulation at visible wavelengths. Our low cost, wideband, carrier-free photonic circuits hold promise for ultralow power and high-speed signal processing at the microprocessor chip level.
The present invention relates to devices which operate on gradient optical forces, in particular, nanoscale mechanical devices which are actuable by gradient optical forces. Such a device comprises a waveguide and a dielectric body, with at least a portion of the waveguide separated from the dielectric body at a distance which permits evanescent coupling of an optical mode within the waveguide to the dielectric body. This results in an optical force which acts on the waveguide and which can be exploited in a variety of devices on a nano scale, including all-optical switches, photonic transistors, tuneable couplers, optical attenuators and tuneable phase shifters. The waveguide can also comprise a gap such that two cantilever bridges are formed.
We apply the Callan-Harvey anomaly-inflow mechanism to the study of QCD (chromoelectric) flux tubes, quark (pair) creation, and the chiral magnetic effect, using new variables from the Cho-Faddeev-Niemi decomposition of the gauge potential. A phenomenological description of chromoelectric flux tubes is obtained by studying a gauged Nambu-Jona-Lasinio effective Lagrangian, derived from the original QCD Lagrangian. At the quantum level, quark condensates in the QCD vacuum may form a vortexlike structure in a chromoelectric flux tube. Quark zero modes trapped in the vortex are chiral and lead to a two-dimensional gauge anomaly. To cancel it, an effective Chern-Simons coupling is needed and, hence, a topological charge density term naturally appears.
Xiong, Chi
Pernice, Wolfram H P
Sun, Xiankai
Schuck, Carsten
Fong, King Y
Tang, Hong X
Silicon photonics has offered a versatile platform for the recent development of integrated optomechanical circuits. However, silicon is limited to wavelengths above 1.1 mum and does not allow device operation in the visible spectrum range where low-noise lasers are conveniently available. The narrow bandgap of silicon also makes silicon optomechanical devices susceptible to strong two-photon absorption and free carrier absorption, which often introduce strong thermal effects that limit the devices' stability and cooling performance. Further, silicon also does not provide the desired lowest order optical nonlinearity for interfacing with other active electrical components on a chip. On the other hand, aluminum nitride (AlN) is a wide-band semiconductor widely used in micromechanical resonators due to its low mechanical loss and high electromechanical coupling strength. In this paper, we report the development of AlN-on-silicon platform for low loss, wide-band optical guiding, as well as its use for achieving simultaneously high-optical-quality-factor and high-mechanical-quality-factor optomechanical devices. Exploiting AlN's inherent second-order nonlinearity we further demonstrate electro-optic modulation and efficient second harmonic generation in AlN photonic circuits. Our results suggest that low-cost AlN-on-silicon photonic circuits are excellent substitutes for complementary metal-oxide-semiconductor-compatible photonic circuits for building new functional optomechanical devices that are free from carrier effects.
Zhang, Ying
Xiong, Chi
Kudelko, Mateusz
Li, Yan
Wang, Cheng
Wong, Yuk Lun
Tam, Vivian
Rai, Muhammad Farooq
Cheverud, James
Lawson, Heather A
Sandell, Linda
Chan, Wilson C W
Cheah, Kathryn S E
Sham, Pak C
Chan, Danny
Intervertebral disc degeneration (IDD) causes back pain and sciatica, affecting quality of life and resulting in high economic/social burden. The etiology of IDD is not well understood. Along with aging and environmental factors, genetic factors also influence the onset, progression and severity of IDD. Genetic studies of risk factors for IDD using human cohorts are limited by small sample size and low statistical power. Animal models amenable to genetic and functional studies of IDD provide desirable alternatives. Despite differences in size and cellular content as compared to human intervertebral discs (IVDs), the mouse is a powerful model for genetics and assessment of cellular changes relevant to human biology. Here, we provide evidence for early onset disc degeneration in SM/J relative to LG/J mice with poor and good tissue healing capacity respectively. In the first few months of life, LG/J mice maintain a relatively constant pool of notochordal-like cells in the nucleus pulposus (NP) of the IVD. In contrast, chondrogenic events are observed in SM/J mice beginning as early as one-week-old, with progressive fibrotic changes. Further, the extracellular matrix changes in the NP are consistent with IVD degeneration. Leveraging on the genomic data of two parental and two recombinant inbred lines, we assessed the genetic contribution to the NP changes and identified processes linked to the regulation of ion transport systems. Significantly, "transport" system is also in the top three gene ontology (GO) terms from a comparative proteomic analysis of the mouse NP. These findings support the potential of the SM/J, LG/J and their recombinant inbred lines for future genetic and biological analysis in mice and validation of candidate genes and biological relevance in human cohort studies. The proteomic data has been deposited to the ProteomeXchange Consortium via the PRIDE [1] partner repository with the dataset identifier PXD008784. Copyright =C2=A9 2018. Published by Elsevier B.V.
Han, Xu
Xiong, Chi
Fong, King Y.
Zhang, Xufeng
Tang, Hong X.
Optomechanical microcavities with high-frequency mechanical resonances facilitate experimental access to mechanical states with low phonon occupation and also hold promise for practical device applications including compact microwave sources. However, the weak radiation pressure force poses practical limits on achievable amplitudes at super-high frequencies. Here, we demonstrate a piezoelectric force-enhanced microcavity system that simultaneously supports microwave, optical and mechanical resonant modes. The combination of the highly sensitive optical readout and resonantly enhanced strong piezoelectric actuation enables us to build a microwave oscillator with excellent phase noise performance, which pushes the micromechanical signal source into the microwave X-band.
Pernice, Wolfram H. P.
Xiong, Chi
Walker, Fred J.
Tang, Hong X.
We propose a novel design concept for compact electro-optic modulators based on a horizontally slotted ridge waveguide using ferroelectric barium titanate (BaTiO3) as the electro-optically active material. A low voltage-length product is achieved by concentrating the propagating electromagnetic fields in the BaTiO3 layer. Thus, high overlap between the modulation electric fields and the guided light is achieved. The proposed waveguide structure features low propagation loss and can be easily fabricated with standard silicon fabrication techniques.
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