Observation of broadband unidirectional transmission by fusing the one-way edge states of gyromagnetic photonic crystals.

We experimentally demonstrate a broadband one-way transmission by merging the operating bands of two types of one-way edge modes that are associated with Bragg scattering and magnetic surface plasmon (MSP) resonance, respectively. By tuning the configuration of gyromagnetic photonic crystals and applied bias magnetic field, the fused bandwidth of unidirectional propagation is up to 2 GHz in microwave frequency range, much larger than either of the individual one-way bandwidth associated with Bragg scattering or MSP resonance. Our scheme for broadband one-way transmission paves the way for the practical applications of one-way transmission.

High-Efficiency Broadband High-Harmonic Generation from a Single Quasi-Phase-Matching Nonlinear Crystal.

Nonlinear frequency conversion offers an effective way to expand the laser wavelength range based on birefringence phase matching (BPM) or quasi-phase-matching (QPM) techniques in nonlinear crystals. So far, efficient high-harmonic generation is enabled only via multiple cascaded crystals because of the extreme difficulty to simultaneously satisfy BPM or QPM for multiple nonlinear up-conversion processes within a single crystal. Here we report the design and fabrication of a chirped periodic poled lithium niobate (CPPLN) nonlinear crystal that offers controllable multiple QPM bands to support 2nd-8th harmonic generation (HG) simultaneously. Upon illumination of a mid-IR femtosecond pulse laser, we observe the generation of an ultrabroadband visible white light beam corresponding to 5th-8th HG with a record high conversion efficiency of 18%, which is high compared to conventional supercontinuum generation, especially in the HG parts. Our CPPLN scheme opens up a new avenue to explore and engineer novel nonlinear optical interactions in solid state materials for application in ultrafast lasers and broadband laser sources.

Reducing radiation losses of one-dimensional photonic-crystal reflectors on a silica waveguide.

Interferometric behaviours in radiation generation process of a one-dimensional photonic-crystal (PhC) reflector are investigated on a silica waveguide. An analytical model, which can calculate total radiation losses, is presented after analysing eigen-mode properties and radiation pattern characteristics. Our model takes into account the interference of component radiated waves generated at interfaces between different waveguide sections and is verified by comparing with numerical simulations of periodic and non-periodic one-dimensional PhC reflectors. Its capability to quickly find minimum-radiation tapering geometries helps circumvent time-consuming numerical simulations. Our model negates the conventional knowledge that a gradually tapered transition from uniform waveguide to PhC waveguide yields lower radiation loss. In one example, the gradually tapered transition produces 2.3dB more radiation than the optimum geometry.

Waveguide coupler in three-dimensional photonic crystal.

A waveguide coupler is designed and realized in a three-dimensional woodpile photonic crystal at microwave regime. This waveguide coupler shows good energy transfer property, which is confirmed through measurement of transmission spectrum, internal field distribution and surface field distribution using Agilent microwave network analyzer.

Gamma-Mu waveguides in two-dimensional triangular-lattice photonic crystal slabs.

We propose a line defect waveguide structure along the Gamma-Mu direction in two-dimensional triangular lattice silicon photonic crystal slabs. The modal dispersion relation and the transmission spectra of this waveguide are studied. The results show that by perturbing the width of the line defect and the diameter of the air holes adjacent to the waveguide core, one can control the width of the single mode transmission window and make it far broader than the original one. The proposed Gamma-Mu waveguide will help to build a more flexible network of interconnection channel of light in two-dimensional photonic crystal slabs.

Near-field studies of microwave three-dimensional photonic crystals with waveguides.

By utilizing a vector network analyzer, the field distributions on the surface of a three-dimensional woodpile photonic crystal with a straight waveguide or a bend waveguide buried under the surface were measured in the microwave regime. The information of field profile and propagation characteristics of the guided modes can be successfully extracted from the surface near-field measurement. This work indicates that the near-field detection can become a promising means for experimental characterization of three-dimensional photonic crystal devices in supplement to the usual transmission spectrum measurement.