Coherent perfect absorption and reflection in slow-light waveguides

We identify a family of unusual slow-light modes occurring in lossy multi-mode grating waveguides, for which either the forward or backward mode components, or both, become degenerate. In the fully-degenerate case, by varying the wave amplitudes in a uniform input waveguide, one can modulate between coherent perfect absorption (zero reflection) and perfect reflection. The perfectly-absorbed wave has anomalously short absorption length, scaling as the inverse 1/3 power of the absorptivity

Semi-analytic method for slow light photonic crystal waveguide design

We present a semi-analytic method to calculate the dispersion curves and the group velocity of photonic crystal waveguide modes in two-dimensional geometries. We model the waveguide as a homogenous strip, surrounded by photonic crystal acting as diffracting mirrors. Following conventional guided-wave optics, the properties of the photonic crystal waveguide may be calculated from the phase upon propagation over the strip and the phase upon reflection. The cases of interest require a theory including the specular order and one other diffracted reflected order. The computational advantages let us scan a large parameter space, allowing us to find novel types of solutions.Comment: Accepted by Photonics and Nanostructures - Fundamentals and Application

ZINC OXIDE NANORODS AS AN INTRACELLULAR pH SENSOR

pH measurements using two kind of samples, namely zinc oxide (ZnO) nanorods of 300nm in diameter and 10µm in length grown on 2D macro-porous periodic structures (2DMPPS) and plane n-Si substrates and ZnO nanorods of 60nm in diameter and 500nm in length grown on the silver coated tip of glass capillary (D=0.7µm). We found that the sensitivity of ZnO nanorods increases with reductions in size from (35mV/pH for D=300nm and L=10µm) to (58mV/pH for D=50nm and L=1µm) using the site binding model. The potential difference for the ZnO nanorods electrode vs. Ag/AgCl electrode showed a high sensitivity range for ZnO nanorods grown on 2DMPPS n-Si, as compared to plane n-Si, and had a sensitivity equal to 51.88mV/pH at 22oC for the ZnO on the capillary tip for pH (4-12) in buffer solutions. Vertically nanoelectrodes of this type can be applied to penetrate a single living cell without causing cell apoptosis

Slow and frozen light in optical waveguides with multiple gratings: Degenerate band edges and stationary inflection points

We show that a waveguide with multiple gratings can have a modal dispersion relation which supports frozen light. This means that light can be coupled efficiently to low group velocity modes of an optical waveguide or can even have finite coupling to zero group velocity modes. These effects are associated with stationary points in the dispersion of the form ω-ωo ⊃(k⊃-ko⊃)m, for integer order m>1, around a center frequency ωo and wave number ko. Stationary points of any order can be created, not only regular band edges (m=2), but also degenerate band edges (m>2 and even) and stationary inflection points (m odd). Using the perturbation theory of matrices in Jordan normal form, the modes and their properties are calculated analytically. Efficient coupling is shown to stem from evanescent modes which must accompany the presence of high-order stationary points with m>2

Bistability suppression and low threshold switching using frozen light at a degenerate band edge waveguide

We predict that nonlinear waveguides which support frozen light associated with a degenerate photonic band edge, where the dispersion relation is locally quartic, exhibit a tunable, all-optical switching response. The thresholds for switching are orders-of-magnitude lower than at regular band edges. By adjusting the input condition, bistability can be eliminated, preventing switching hysteresis.This work was supported by the Australian Research Council programs, including Discovery Project DP1093445 and Future Fellowship FT100100160

Low-power all-optical switching through frozen light at degenerate band edges

We predict that nonlinear waveguides designed to support frozen light at degenerate band edges enable tunable bistable response and orders-of-magnitude lower all-optical switching threshold compared to conventional slow-light at regular band-edges

Degenerate band edges in optical fiber with multiple grating: efficient coupling to slow light

Degenerate band edges (DBEs) of a photonic bandgap have the form (ω − ωD) ∝ k2m for integers m > 1, with ωD the frequency at the band edge. We show theoretically that DBEs lead to efficient coupling into slow-light modes without a transition region, and that the field strength in the slow mode can far exceed that in the incoming medium. A method is proposed to create a DBE of arbitrary order m by coupling m optical modes with multiple superimposed gratings. The enhanced coupling near a DBE occurs because of the presence of one or more evanescent modes, which are absent at conventional quadratic band edges. We furthermore show that the coupling can be increased or suppressed by varying the number of excited evanescent waves.This work was supported by the Australian Research Council

Coherent perfect absorption and reflection in slow-light waveguides

We identify a family of unusual slow-light modes occurring in lossy multimode grating waveguides, for which either the forward or backward mode components, or both, are degenerate. In the fully degenerate case, the response can be modulated between coherent perfect absorption (zero reflection) and perfect reflection by varying the wave amplitudes in a uniform input waveguide. The perfectly absorbed wave has anomalously short absorption length, scaling as the inverse one-third power of the absorptivity.This work was supported by the Australian Research Council (Future Fellowship FT100100160, Discovery Project DP130100086), by the Singapore National Research Foundation under Grant No. NRFF2012-02, and by the Singapore MOE Academic Research Fund Tier 3 Grant MOE2011-T3-1-005

Stationary inflection points in optical waveguides: accessible frozen light

Stationary Inflection Points (SIPs) around a frequency ω 0 are of the form ω - ω 0 ∝ k m for any positive odd integer. We show theoretically that SIPs of order m can be created in optical waveguides such as optical fiber gratings or periodic nanobea

Frozen and broadband slow light in coupled periodic nanowire waveguides

We develop novel designs enabling slow-light propagation with vanishing group-velocity dispersion ("frozen light") and slow-light with large delay-bandwidth product, in periodic nanowires. Our design is based on symmetry-breaking of periodic nanowire waveguides and we demonstrate its vailidy through two- and three-dimensional simulations. The slow-light is associated with a stationary inflection point which appears through coupling between forward and backward waveguide modes. The mode coupling also leads to evanescent modes, which enable efficient light coupling to the slow mode.This work was supported by the Australian Research Council