Huaming Wu

Flat Band Slow Light in Symmetric Line Defect Photonic Crystal Waveguides

Flat band slow light in symmetric line defect photonic crystal waveguides formed by adding dielectric pillars in the air holes nearest to the waveguide core is investigated. By adjusting the radii of the new dielectric pillars, a linear band in the photonic band structure appears which denotes low group velocity dispersion. High average group index of 74.4 with 2.3-nm bandwidth is demonstrated in an optimized waveguide by finite-difference time-domain simulation.

Wideband slow light in chirped slot photonic-crystal coupled waveguides

Wideband dispersion-free slow light in chirped-slot photonic-crystal coupled waveguides is proposed and theoretically investigated in detail. By systematically analyzing the dependence of band shape on various structure parameters, unique inflection points in the key photonic band with approximate zero group velocity can be obtained in an optimized slot photonic-crystal coupled waveguide. By simply chirping the widths of the photonic-crystal waveguides in the optimized structure, wideband (up to 20 nm) slow-light with optical confinement in the low dielectric slot is demonstrated numerically with relative temporal pulse-width spreading well below 8% as obtained from two-dimensional finite-difference time-domain simulations. The wideband slow-light operation of the proposed structures would offer significant potential for novel compact high-speed optical-signal-processing devices in silicon-based systems.

Low Dispersion Slow Light in Slot Waveguide Grating

A novel and simple one-dimensional waveguide grating with two parallel air slots is proposed to support low dispersion slow light. Due to more structural tuning freedoms provided by introduction of the slots, it is easier to achieve the perfect flat and straight slow light mode dispersion curve. Low group dispersion of only 3.38 ps2/mm with a slow light group index of 13 is obtained in a plane wave expansion calculation, which denotes a wide bandwidth of 13.2 nm. This result is also proved by finite-difference time-domain simulation in which the output pulse relative distortion is only 0.96% towards the input pulse.

Polarizing beam splitter based on a subwavelength asymmetric profile grating

In this paper, we propose a broadband compact polarizing beam splitter (PBS) constructed by only a single layer subwavelength asymmetric profile grating. The properties of the grating PBS are investigated by rigorous coupled-wave analysis. It is shown that, over a broadband spectrum of 1.53–1.62 µm, the grating PBS demonstrates high diffraction efficiencies (>97%) with extinction ratio (ER) greater than 16 dB and a comparatively wide angular bandwidth (about 8 ◦ ). Effects of deviation from the design parameters on the performance of the grating PBS are

Flat Band Slow Light With High Coupling Efficiency in One-Dimensional Grating Waveguides

Flat band slow light with high coupling efficiency is achieved in a simple one-dimensional grating waveguide. An ideal flat band indicating slow light with group index of 18.3 and bandwidth of 10.3 nm is obtained by plane wave expansion calculation. This result is also verified by inputting a Gaussian pulse into a 48.7-μm -long waveguide in a finite-difference time-domain simulation, in which optical pulse delay of 2.85 ps and group index of 17.54 can be observed. Meanwhile, by introducing a step taper, the coupling efficiency could be improved remarkably from below 20% for butt coupling to 70%. The proposed structure is an ideal candidate for wideband and compact low loss slow light delay lines or optical buffers in on-chip signal processing.

Silicon nanophotonic devices based on resonance enhancement

In recent years, silicon nanophotonic devices have attracted more and more attention due to their compactness, low power consumption, and easy integration with other functions. In addition to the higher index of silicon material providing stronger light confinement, the optical resonance associated with the novel structure design also enhances the performance of nanophotonic devices and offers stronger light-matter interaction. Silicon nanophotonic devices such as polarization beamsplitters, mirrors and reflectors, slow light waveguides, and microring sensors are studied, and all of them demonstrate much better performances due to the incorporated optical resonance enhancement.

Wideband Slow Light in One-Dimensional Chirped Holey Grating Waveguide

Wideband slow light away from band edge in one-dimensional (1-D) structure is proposed and theoretically investigated for the first time. With carefully chosen structure parameters of the 1-D holey grating waveguide, an ideal chair shape band with unique inflection points of high group index beyond 1000 can be obtained. By chirping the structure according to the scaling law, wideband up to 31-nm slow light pulse propagation with a moderate group index of 14.6 is demonstrated by finite-difference time-domain simulation, and the relative pulse shape expansion is only 2.34%.

Enhanced bandgap in annular photonic-crystal silicon-on-insulator asymmetric slabs

Photonic band structures of annular photonic-crystal (APC) silicon-on-insulator (SOI) asymmetric slabs with finite thickness were investigated by the three-dimensional plane-wave expansion method. The results show that for a broad range of air-volume filling factors, APC slabs can exhibit a significantly larger bandgap than conventional circular-hole photonic-crystal (PC) slabs. Bandgap enhancements over conventional air hole PC SOI slabs as large as twofold are predicted for low air-volume filling factors below 15%. This desirable behavior suggests a potential for APC SOI slabs to serve as the basis of various optical cavities, waveguides, and mirrors.

Silicon-Based Stress-Coupled Optical Racetrack Resonators for Seismic Prospecting

A silicon-based stress-coupled optical racetrack resonator with a crossbeam mass is proposed to detect acceleration for seismic prospecting. Acceleration applied on the crossbeam mass can result in optical phase changes in one racetrack cycle, which leads to a resonant wavelength shift. By systematically optimizing the resonator structure and mechanical characteristics, a very large wavelength shift of 52 pm under 1 g acceleration is demonstrated by numerical simulation. The maximum frequency of input signal can be up to 200 Hz. This silicon-based compact and high-performance racetrack resonator can have great potential for seismic prospecting.

A Multilayer-Based High-Performance Multisubpart Profile Grating Reflector

In this letter, a multilayer-based high-performance subwavelength multisubpart profile grating reflector (MPGR) is proposed and fabricated. The properties of the reflector are investigated by rigorous coupled-wave analysis for multilayered grating structures. It is shown that with the properly configured profile and strongly modulated grating layer in transverse-electric polarized wave, the MPGR experimentally demonstrates a broadband reflection spectrum from 1.56 to 1.8 ¿m, very high reflectivity (>97%), and good angular insensitivity of about 27.8°.