Diffraction of light of a visible spectral range by subwavelength metal gratings is investigated theoretically and experimentally. The diffraction efficiencies of the gratings made of various metals (Ni, Ag, Al, etc.) with different depths of the profile are calculated and measurements are carried out. It is demonstrated that under certain conditions an effect of plasmon resonance occurs, at which a complete absorption of the incident light takes place. It is demonstrated, that the influence of the incident beam width on the diffraction efficiency and the electric field profile of the reflected beam is significant for the incident angles, at which the plasmon resonance occurs. It is shown that the incident beam width must be larger than the propagation distance of the surface plasmon in order to couple energy effectively into the plasmon mode.
Special features of light-induced scattering of radiation (λ = 0.44 μm) with extraordinary polarisation in the SBN-75
photorefractive crystal are studied in detail and an efficient technique is proposed for exciting surface waves in this
crystal. In the experiment carried out the efficiency of the surface wave excitation was ~ 30%, which is 50 times greater
than that achieved earlier in exciting nonlinear surface waves in the optical region. The patterns of the near and far fields
of the surface wave are presented. It is found that at small excitation angles (0-1.5°) the presence of a metal changes the
character of arising surface waves. Using method of images for calculation of electrostatic fields a model is proposed
explaining the peculiarities of light propagation close to the crystal-metal boundary.
Fabry-Perot interferometer with two identical waveguide gratings mirrors is studied. Earlier we studied the case of
oblique light incidence and in this paper normal incidence is considered. Normal incidence case is special because two
waveguide modes propagating in the opposite directions are excited simultaneously. It is found that for the filter having
small distance between the waveguide grating mirrors the reflection spectrum depends on the phase shift between the
gratings. One or two additional resonances appear in the case of phase shift not being equal to 0 or π. We attribute the
appearance of these resonances to the symmetry breakdown in the waveguide system and coupling between the waveguides.
We describe a new approach to achieving high brightness emission from laser diodes using a compound waveguide containing an unusual high order mode. This mode is predominantly single lobed and unusually localized in the low index region of the waveguide. To examine the utility of this mode we calculated the single-mode fiber butt coupling efficiency for an AlGaAs/GaAs compound waveguide of 61 micrometer aperture width, emitting at a wavelength of (lambda) equals 980 nm. Our results show a 2.3 times enhancement of the fiber coupling efficiency when compared with a simple broad area waveguide. Furthermore the coupling efficiency is still almost a factor of two greater than the coupling efficiency of the emission from a single mode ridge waveguide.
The simulation of the coupling efficiency of fluorescence sources immobilized in the evanescent field of a waveguide mode has allowed the dimensioning of a sensing waveguide platform based on a silicon substrate exhibiting maximum fluorescence efficiency. The incoupling of the excitation light and the outcoupling of the fluorescence signal are performed by means of a corrugation grating. The presence of the highly reflective silicon surface under the waveguide grating causes interferences in the fluorescence output signal which depend on the wavelength and on the radiation angle. A theoretical modeling of the grating coupling under these conditions has led to the achievement of high incoupling efficiency at the excitation wavelength, and simultaneously to high outcoupling efficiency at the wavelength of the fluorescence peak. An experiment was performed with fluorescein at the surface of a 160 nm thick silicon nitride waveguide film on a silicon substrate with a 2100 nm thick buffer layer of silica. The measured outcoupled spectra fit well with the calculated spectra taking into account the output grating coupling, the fluorescence spectrum, and fluorescence coupling. These waveguide grating structures are applied to the detection of immunological reactions.
The blazing effect of parallelogramic grooves is analyzed theoretically and demonstrated experimentally in the case of TE and TM modes in large guidance waveguides. A novel fabrication method is proposed, modellized and demonstrated.
The spectral properties of corrugated waveguide structures comprising a thin high index waveguiding layer, and a thick lower index slab volume are reported. It is shown that a wavelength filter based on this structure can be realized. Laser generation in the structure with an active thick slab is experimentally demonstrated. Several possible schemes of distributed feedback are discussed.
A system of two radiationally coupled corrugated waveguides is proposed for remote coupling. Coupling is achieved owing to diffraction of the waveguide mode on the corrugated waveguide surface. Using Rayleigh-Fourier-Kiselev method, we calculated the dispersion curves of the system and the coupling length on their basis. Coupling length changes periodically when waveguide separation increases, this fact makes the remote coupling possible. Optimum distances between the waveguides are also determined. It is shown that the coupling length is related to the radiation loss coefficient of the single waveguide.
A system of two radiationally coupled waveguides is proposed for remote coupling implementation. Radiation loss coefficient and coupling length are determined for two different designs of radiationally coupled waveguides: corrugated and leaky. Remote coupling over a 95 micrometers distance in a pair of radiationally coupled waveguides is demonstrated experimentally for the first time.