Yudong Li

Independently tunable double Fano resonances in asymmetric MIM waveguide structure

In this paper, an asymmetric plasmonic structure composed of a MIM (metal-insulator-metal) waveguide and a rectangular cavity is reported, which can support double Fano resonances originating from two different mechanisms. One of Fano resonance originates from the interference between a horizontal and a vertical resonance in the rectangular cavity. And the other is induced by the asymmetry of the plasmonic structure. Just because the double Fano resonances originate from two different mechanisms, each Fano resonance can be well tuned independently by changing the parameters of the rectangular cavity. And during the tuning process, the FOMs (figure of merit) of both the Fano resonances can keep unchanged almost with large values, both larger than 650. Such, the transmission spectra of the plasmonic structure can be well modulated to form transmission window with the position and the full width at half maximum (FWHM) can be tuned freely, which is useful for the applications in sensors, nonlinear and slow-light devices.

Multilevel phase-type diffractive lenses in silica glass induced by filamentation of femtosecond laser pulses

Multilevel phase-type diffractive lenses were fabricated by translating a filament of a femtosecond laser pulse into three-dimensional space inside synthesized silica. The profile of the lenses was designed by use of a multi-level approximation to a kinoform lens. Two-level diffractive lenses with multiple layers along the optical axis provided a maximum efficiency of 37.6% at a wavelength of 632.8 nm. A four-level diffractive lens provided a maximum efficiency of 56.9%. The lenses fabricated with filamentation were free from birefringence.

All-optical logic gates using bacteriorhodopsin films

We demonstrate all-optical logic gates using bacteriorhodop- sin (bR) film. By studying the transmission of bR film, we advance an all-light-modulated transmission mechanism of bR film: complementary suppression-modulated transmission (CSMT). When a yellow beam (568 nm) and a blue beam (412 nm) illuminate bR film, the two transmitted beams suppress mutually. Based on this mechanism, we design an all- optical operating device in which we implement all 16 kinds of double- variable binary logic operations. The intensity of an incident yellow or blue beam acts as the input to the logic gate and the transmission bears the output of the gate. We can turn this all-optical device into different states using different wavelengths and different intensity illuminations.

Optical Boolean logic based on degenerate multi-wave mixing in bR film

When two coherent beams interfere in bacteriorhodopsin (bR) film with a very small crossing angle, degenerate multi-wave mixing appears. In this paper, the properties of degenerate multi-wave mixing in bR film were studied. By use of degenerate multi-wave mixing in bR film, we realized optical Boolean logic operations.

Tunable Resonances in the Plasmonic Split-Ring Resonator

A nanoscale resonator composed of two metal-insulator-metal (MIM) waveguides and a split ring is investigated numerically. The multipolar plasmonic resonance modes can be excited, weakened, or even cut off by adjusting the split angle. These novel phenomena are due to the electric polarization in the split area. Odd modes exhibit when the electric field is polarized perpendicular to the split. The resonator acts as a LC circuit for the electric field polarized parallel to the split, in which even modes are excited. The capacitance diminished when the split depth is increased, and the resonance wavelengths of even modes exhibit blue shift. Our results imply an extensive potential for tunable multichannel filters and biosensor devices in integrated nano-optics.

Effect of Edge Rounding on the Extinction Properties of Hollow Metal Nanoparticles

The optical responses of metal nanoparticles induced by subtle variations in geometry, especially by the rounding of the edges and corners, have generated great interest at present due to the requirement of fabricating refined structures of metal nanoparticles and theoretical simulations of the real particles. We study the effect of both inner and outer edge rounding on the optical properties of gold nanobox and gold nanobox dimer with small interparticle distances by using the discrete dipole approximation method. The shift of extinction peaks, the electric field distribution, and the variation of refractive index sensitivities by changing the curvature of the inner and outer edges of gold nanobox are investigated. We demonstrate that the optical properties of nanobox are more sensitive to the outer edge rounding than the inner edge rounding. By edge rounding of two very close gold nanoboxes, the blue shift of the dipolar and the quadrupolar plasmonic resonances of nanobox dimer are shown. Comparing with the inner edge rounding of nanobox dimer, we find that rounding of the outer edges causes the larger shift of the quadrupolar mode and approximate shift of the dipole mode.

Fabrication of Dammann Gratings in Silica Glass Using a Filament of Femtosecond Laser

The Dammann grating is one kind of useful binary optical elements. We fabricated a single-layer birefringence-free 5?5 Dammann grating in silica glass using the filamentation of 800 nm femtosecond laser pulses. The diffraction efficiency of the Dammann grating reached 56%, which is close to the theoretical value of 77%.

Simulation of Nanoscale Multifunctional Interferometric Logic Gates Based on Coupled Metal Gap Waveguides

A novel design of ultrasmall multifunctional Boolean logic gates is proposed in this letter. This interferometric logic device is based on the coupled metal waveguides. This structure is a theoretical analysis, and logic performances are proved by using the finite-difference time-domain method. The single device can perform individually four different kinds of basic functions: and, or, xor, and not operations. The device with an extremely small feature size is an attractive candidate for high density nano-photonic integrated circuits.

Quasi 3-dimensional optical trapping by two counter-propagating beams in nano-fiber

Optical forces on a nanoparticle around an absorptive dielectric nano-fiber illuminated by two linear polarized counter-propagating beams were investigated. The results show the scattering force of the two beams causes the steady trapping along the fiber and the gradient force makes the trapping in the transverse plane of the nano-fiber. By altering the intensity ratio between the two incident beams and the polarization direction of the beams, manipulation along the nano-fiber and in the transverse direction can be realized, respectively. The numerical results present a new promising method to realize quasi 3-dimensional optical manipulation.

Plasmonic analog of electromagnetically induced transparency in planar metamaterials: manipulation and applications

In this article, we have investigated an analog of electromagnetically induced transparency (EIT) in planar metamaterials by a metallic regular triangle (RT) embedded in split ring (SR) nanostructure. It is demonstrated that, depending on the different coupling ways between the RT and the SR, the EIT-like spectral response can be actively modulated by simply adjusting the incident light polarization angle. Based on this observation, an on-to-off active modulation of the EIT-like transparency window can be realized, and it can serve as the base for an optical switching with the switching efficiency exceeding 95%. The size of the RT finely controls the coupling strength between the RT and the SR. It is shown that the EIT-like transparency window can be enhanced or suppressed by adjusting the size of the RT, which shows the big modulation to the EIT-like spectral response. Furthermore, the transmission spectra show potential applications in sensing due to high sensitivity of about 600 nm/RIU with figure of merit exceeding 36 to the surrounding environment.