Boyun Wang

Wideband and Low Dispersion Slow Light in Lattice-Shifted Photonic Crystal Waveguides

We propose a new type of photonic crystal waveguide structure to achieve wideband slow light with large group index and low dispersion. The waveguide is based on triangular lattice photonic crystal imposed by simply a selective altering the locations of the holes adjacent to the line defect. Keeping the group index at 31, 44, 61, 71, 94, and 132, respectively, while restricting its variation within a ±10% range, we accordingly attain an available bandwidth of 19.1, 13.0, 9.0, 7.5, 5.5, and 3.6 nm around 1550 nm. The normalized delay-bandwidth product keeps around 0.35 for all cases. Low dispersion slow light propagation is confirmed by studying the relative temporal pulsewidth spreading with the 2-D finite-difference time-domain method.

Low-power and ultrafast all-optical tunable plasmon induced transparency in metal-dielectric-metal waveguide side-coupled Fabry-Perot resonators system

In this paper, low-power and ultrafast all-optical tunable plasmon induced transparency in metal-dielectric-metal (MDM) waveguide side-coupled Fabry-Perot (FP) resonators system with nonlinear optical Kerr medium is investigated both analytically and numerically. High tunability in transparency window magnitude and phase responses is obtained when nonlinear optical Kerr material is embedded in the MDM waveguide. In order to reduce the pump intensity, traditional nonlinear optical Kerr material is replaced by graphene. A shift of 64 nm in the central wavelength of the transparency window is achieved when the FP resonators are covered with monolayer graphene with pump intensity increasing from 9.2 to 10 MW/cm2. An ultrafast response time of the order of 1 ps is reached because of ultrafast carrier relaxation dynamics of graphene. This work not only paves the way towards the realization of on-chip integrated nanophotonic devices but also opens the possibility of the construction of ultrahigh-speed informatio...

A dynamic and ultrafast group delay tuning mechanism in two microcavities side-coupled with a waveguide system

We theoretically propose a dynamic and ultrafast group delay tuning mechanism in two microcavities side-coupled to a waveguide system through external optical pump beams. The optical Kerr effect modulation method is applied to improve tuning rate with response time of subpicoseconds or even femtoseconds. The group delay of an all-optical analog to electromagnetically induced transparency effect can be controlled by tuning either the frequency of photonic crystal microcavities or the propagation phase of line waveguide. Group delay is controlled between 5.88 and 70.98 ps by dynamically tuning resonant frequencies of the microcavities. Alternatively, the group delay is controlled between 1.86 and 12.08 ps by dynamically tuning the propagation phase of line waveguide. All observed schemes are analyzed rigorously through finite-difference time-domain simulations and coupled-mode formalism. Results show a new direction toward microstructure integration optical pulse trapping and all-optical dynamical storage of light devices in optical communication and quantum information processing.

Phase shift multiplication effect of all-optical analog to electromagnetically induced transparency in two micro-cavities side coupled to a waveguide system

We propose phase shift multiplication effect of all-optical analog to electromagnetically induced transparency in two photonic crystal micro-cavities side coupled to a waveguide system through external optical pump beams. With dynamically tuning the propagation phase of the line waveguide, the phase shift of the transmission spectrum in two micro-cavities side coupled to a waveguide system is doubled along with the phase shift of the line waveguide. π-phase shift and 2π-phase shift of the transmission spectrum are obtained when the propagation phase of the line waveguide is tuned to 0.5π-phase shift and π-phase shift, respectively. All observed schemes are analyzed rigorously through finite-difference time-domain simulations and the coupled-mode formalism. These results show a new direction to the miniaturization and the low power consumption of microstructure integration photonic devices in optical communication and quantum information processing.

Plasmon-induced transparency effect in metal-insulator-metal waveguide coupled with multiple dark and bright nanocavities

Abstract. We used bright and dark nanocavities coupled to a metal-insulator-metal waveguide to realize a plasmonic analogue of electromagnetically induced transparency (EIT) in integrated plasmonics. The bright nanocavity is directly coupled to the waveguide, while the dark nanocavity is achieved with the help of evanescent coupling. The numerical simulation shows a typical EIT-like line in the transmission spectrum. Using the model of EIT effect in a three-level atomic system, this phenomenon is well explained. Adding the number of dark nanocavities, we get multiple transparent peaks in the transmission spectrum of plasmon-induced transparency (PIT) effect, and we can realize control of the PIT effect by changing the geometric parameters of the plasmonic structure.

Plasmon-induced transparency effect in a single circular split-ring core ring resonator side-coupled to a metal-isolator-metal waveguide

We theoretically and numerically investigated the plasmon-induced transparency (PIT) effect in a single circular split-ring core ring resonator (CSRCRR) side coupled to a metal–isolator–metal waveguide, in which we can realize a single PIT effect window. The transmission line theory and the coupled mode theory are used. The results (transmission peak varies from 10% to 75%) show that the PIT window results from the destructive interference between the resonance modes in the CSRCRR. Then, the limit of wavelength detuning of the two modes in CSRCRR is studied. This work provides a new structure to realize the PIT effect and shows a new way to judge whether the phenomenon is the real PIT effect or not.

Slow light with large group index–bandwidth product in ellipse-hole photonic crystal waveguides

In this study, we propose a new type of slow light photonic crystal waveguide structure to achieve wideband slow light with low dispersion. The waveguide is based on a triangular lattice ellipse-hole photonic crystal imposed simply by a selective altering of the locations of the holes adjacent to the line defect. Under a constant group index criterion of ±10% variation, when group indices are nearly constants of 54, 69, and 80, their corresponding bandwidths of the flat band reach 12.7, 10.0, and 8.6 nm around 1550 nm, respectively. A nearly constant large group index-bandwidth product of 0.44 is achieved for all cases. Low dispersion slow light propagation is confirmed by studying the relative temporal pulse-width spreading with the two-dimensional finite-difference time-domain method.

Low-power, ultrafast, and dynamic all-optical tunable plasmonic analog to electromagnetically induced transparency in two resonators side-coupled with a waveguide system

We theoretically and numerically investigate a low-power, ultrafast, and dynamic all-optical tunable plasmonic analog to electromagnetically induced transparency (EIT) in two nanodisk resonators side-coupled to a metal-insulator-metal plasmonic waveguide system. The optical Kerr effect is enhanced by the slow light effect of the plasmonic EIT-like effect and the plasmonic waveguide based on graphene-Ag composite material structures with giant effective Kerr nonlinear coefficient. The optical Kerr effect modulation method is applied to improve tuning rate with response time of subpicoseconds or even femtoseconds. With dynamically tuning the propagation phase of the plasmonic waveguide, π-phase shift of the transmission spectrum in the plasmonic EIT-like system is achieved under excitation of a pump light with an intensity as low as 5.85 MW/cm2. The group delay is controlled between 0.09 and 0.4 ps. All observed schemes are analyzed rigorously through finite-difference time-domain simulations and coupled-mo...

Wideband slow light with improved NDBP values in asymmetric photonic crystal waveguides

New procedure of designing slotted photonic crystal waveguides (SPCW) is proposed to achieve slow light with improved normalized delay-bandwidth product (NDBP) and low group velocity dispersion, which is suitable for both the W1 defect mode and the slot mode. The lateral symmetry of the waveguide in our study is broken by shifting the air holes periodically along the slot axis . The conversion of the “flat band” from band-up slow light to band-down slow light is achieved for W1 defect mode. The group index curves of W1 mode change from U-like to step-like and the group index of 47, 67 and 130 are obtained with the bandwidth over 7.2, 4.8, and 2.3nm around 1550nm, respectively. We also obtain the group index of 42, 55, and 108 for the slot mode with the bandwidth over 6.2, 5.6, and 2.2nm. Then the low dispersion slow light propagation is numerically demonstrated by the finite-difference time-domain method.

Novel kind of slow light photonic crystal waveguides with enhanced delay-bandwidth product

The proposed slow light waveguides are based on photonic crystal imposed by a selective altering the locations of the holes adjacent to the line defect. The Normalized Delay-Bandwidth Product keeps around 0.37 for all cases.