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We experimentally realize a one-way waveguide made from a gyromagnetic photonic crystal (GPC) and a normal dielectric photonic crystal in their common photonic band gap. Due to the time reversal symmetry breaking of the GPC under a dc magnetic field, the edge modes exhibit a one-way property. We investigate the unidirectional propagation character originating from the chiral edge states at different widths of the waveguide. Both the forward modes, which are robust to various obstacles, and the backward modes show an obvious frequency shift for different waveguide widths. Numerical simulations by means of the transfer-matrix method and multiple scattering methods agree well with the experimental data. [ABSTRACT FROM AUTHOR]

We demonstrate the design, fabrication, and characterization of a multichannel filter in a two-dimensional triangular-lattice photonic crystal slab. The output signal channel, which directs in the Γ-M crystalline direction, is orthogonal to the input signal channel that directs in the Γ-K crystalline direction. In each channel, the filtering function is guaranteed by the indirect resonant coupling between the waveguide and the cavity. Four resonant cavities with different sizes provide the mechanism of finely tuning the output wavelength. Our experimental results are in good agreement with simulations. [ABSTRACT FROM AUTHOR]

We have designed and fabricated a lithium niobate (LN) nonlinear photonic crystal (NPC) with a two-dimensional (2D) ellipse structure of inverse poling domains. The structure can offer continuously varying reciprocal lattice vectors in different directions to compensate the phase-mismatching during the second harmonic generation (SHG) for diverse pump wavelengths. We consider three propagation directions with large effective nonlinear susceptibility and measure the nonlinear conversion efficiency of SHG. The experimental data are in good agreement with the quantitative calculation results using the effective susceptibility model with pump depletion. With high-efficiency SHG in multiple propagation direction, the 2D ellipse structure of LN NPC has the potential to realize various broadband nonlinear frequency conversion processes in different propagation direction with a single crystal. [ABSTRACT FROM AUTHOR]

We theoretically and experimentally study the side coupling between guided modes and cavity modes in a one-way waveguide that is composed of a regular photonic crystal and a gyromagnetic photonic crystal. At the cavity resonant wavelength, the backward mode can be completely blocked while the forward mode is only slightly influenced in the transmissivity for a specially designed waveguide. This unique light transport property can be exploited to construct a unidirectional band stop filter and a unidirectional channel-drop filter that can selectively process a light signal propagating only along a particular direction. [ABSTRACT FROM AUTHOR]

The microwave absorption dielectric-spectrum technique was used to study the decay kinetics of the free photoelectrons and shallow-trapped electrons in the sulfur-sensitized T-grain AgBrI crystals prepared under different sensitization times. It was found that, from the dependence of the kinetic behavior of photoelectrons in the sensitized T-grain AgBrI emulsions, the optimal sensitization time was 45 min. With an increase of the sensitization time, the trap effect of the sulfur sensitization centers varies from the hole trap to shallow electron trap, and to deep electron trap, corresponding to the sulfur sensitization centers in the forms of a monomer, dimmer, and cluster of Ag2S, respectively. The range of the shallow electron trap depth traps was determined to be 0.26–0.27 eV. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]