We discuss asymmetric reflectance in surface plasmon Bragg gratings incorporating optical gain, referred to as
active asymmetric surface plasmon Bragg gratings. It is shown that balanced modulation of index and gain/loss with
quarter pitch spatial shift causes unidirectional coupling between contra-propagating modes in long-range surface
plasmon polariton Bragg gratings. Such gratings operate at the breaking threshold of parity-time symmetry
(exceptional point). Two active asymmetric surface plasmon Bragg gratings designs are proposed and their
performance is examined through modal and transfer matrix method computations.
Strong reemission of the surface plasmons through a single subwavelength aperture is mainly caused by in-phase coupling of the surface localized electromagnetic waves to irradiative modes by periodic groove structures. By introducing a linear chirping in the groove period, we enhance the coupling effect for focusing the reemitted light in near-field region. The linear chirping in the groove structures which have monotonically decreasing period, leads to focusing the reemitted light with the length, depth, and width of the focus in order of wavelength. We show numerically that the focusing ability is dramatically affected by amount of the linear chirping, and that efficient relaying of a diverging Gaussian beam to a photonic crystal waveguide can be achieved.
We trapped and manipulated the micro-particles by two beam interference. The micro-particles were pulled toward the bright fringe and were aligned along the periodic interference pattern. We observed the distribution of trapped particles at the various polarization configurations by adjusting the polarization states and measured the optical force acting on the particles. The particles were trapped in bright fringe by intensity gradient in the case of parallel polarization state. In the case of perpendicular polarization state, the particles aligned along periodic pattern even though there was no intensity modulation. Consequently, the results showed that the optical force can be generated from not only the intensity modulation but also no intensity modulation.
Two types of photo-induced gratings, birefringence and surface relief gratings, were formed on an azo polymer film when two orthogonal circularly polarized writing beams irradiated the film. All the diffracted beams from the gratings were measured during irradiation and the surface relief height inscribed on the film was measured by using atomic force microscope (AFM) after the irradiation. The transmitted beam intensities were calculated using a Jones matrix for two gratings. The phase differences for the two gratings were separately determined by fitting the experimental results to the theory. Next, the changes of the phase differences of two gratings were measured in-situ using an exact equations. The results from this method agreed with previous one. The phase difference between two gratings was measured. The phase difference between two gratings converged on about 45 degrees in our case. Diffraction efficiency measurement and analysis revealed that the two gratings were independent of each other and that the mechanisms for the two gratings were different.
We have observed experimentally photonic band gap in dispersion curves of SPPs excited at a 1-D dielectric lattice structure on a flat metal surface. The observation result is compared with theoretical result by using of the well-known calculation method of diffraction, rigorous coupled wave analysis method.
Photonic band gap interaction between surface plasmon (SP) and dielectric gratings is calculated by rigorous coupled wave analysis (RCWA). Results from the RCWA show that the reflectance goes down near to 0%, and the diffraction efficiency increases above 50% even though the modulation depth of the grating layer is less than 100nm. If the grating vector is twice of the wave vector of SP, on the other hand, the reflectance surprisingly increases up to 90% even though the resonance condition of the SP is satisfied. This photonic band gap effect at the SP resonance can be completely analyzed by the RCWA, and verified by experiment.