Coherence-polarization mixing in resonance gratings

We show, using rigorous diffraction theory, that resonance gratings can be used to transfer partial spatial correlation to partial polarization even if the incident light beam is fully polarized. The phenomenon is based on the fact that either of the two orthogonal polarization components can be coupled into the leaky waveguide mode, leading to a strong phase delay, while the other one is reflected without being coupled into the grating. Numerical demonstrations are based on a Gaussian Schell-model beam and a grating analysis performed by rigorous Fourier modal method.     

Fabrication of blazed gratings by area-coded effective medium structures

Area-coded effective medium structures (ACES) are a recently presented novel type of diffractive structure. Because of their higher stability compared to 2D binary blazed gratings, they have the potential of a broader use in micro-optics applications. The first fabrication with electron-beam lithography validate the theoretical model of blazed ACES. The measured diffraction efficiencies are in very good agreement with the values obtained from rigorous electromagnetic analysis.     

Morphology studies of the metal surfaces with enhanced absorption fabricated using interferometric femtosecond ablation

Recently, the enhancing of bulk metals optical absorption with focused femtosecond pulses was demonstrated. This absorption enhancement is caused by different nano- and micro-structures which are formed during laser ablation with ultrashort pulses. In this paper we study the evolution of the surface structures using interferometric ablation and compare it to normal fs-ablation. Previously we have shown that interferometric femtosecond ablation is an efficient method to fabricate absorbing metal surfaces. In this study we ablated large areas of hole-array structures with different pulse numbers in polished stainless steel and copper samples. The evolution of surface morphology and the depth of the holes for these structured surfaces are presented. In addition, the reflectance of laser generated surface structures are measured at the wavelength range of 200–2300 nm using a standard spectrophotometer.     

Modeling of laser-colored stainless steel surfaces by color pixels

Different colors on stainless steel have been obtained by heating the surfaces with laser. The colors have been modeled as an effective sum of small color pixels, each of them consisting of certain thickness of chromium oxide. We have considered the utilization of the technique into color pixeling and presented a qualitative relation between the energy, the color, and the chromium oxide layer thickness.     

3D printed plano-freeform optics for non-coherent discontinuous beam shaping

Optical Review - The design, fabrication, and characterization of freeform optics for LED-based complex target irradiance distribution are challenging. Here, we investigate a 3D printing technology...     

Inverse metal-stripe polarizers

Received: 18 May 1998/Revised version: 17 August 1998     

Spectral control in anisotropic resonance-domain metamaterials

We introduce a concept to control the spectral and dichroic properties of metamaterials. The approach is based on anisotropic metal nanoparticles and on varying their mutual orientation in a periodic lattice. Even seemingly inconsequential changes in particle ordering strongly modify the dichroic properties of the arrays and result in either very narrow resonances or ultrabroad extinction ranges. The results arise from long-range diffractive coupling between the particles, as determined by the dependence of the array unit cell size on particle ordering.     

Modeling and interference-microscopy characterization of graded index transitions in ion-exchange waveguide integrated elements: transitions between annealed surfaces

We employ interference microscopy to characterize in a direct and local way the graded index transitions at the boundaries of integrated optical elements fabricated by multistep ion-exchange processes, a task not yet possible by other technologies. A particular fabrication method based on purely thermal ion-exchange, which allows local single-mode propagation, is investigated. The refractive-index distribution is modeled on the basis of the linear theory of diffusion and adiabatic transitions of the refractive-index profile. Finally, its validity is analyzed by microinterferometry.     

Phase gratings to couple several input beams into one output beam

Phase gratings with certain continuous grating profiles are shown to be excellent devices for beam coupling, that means to couple N input beams into a single output beam. These gratings are also known as N-to-one-interconnection gratings. We prove in this paper that if the relative phases of the incoming beams are chosen properly coupling efficiencies over 90% are achieved. Only thin phase-only gratings are considered. The input angles of the incoming waves may be freely chosen. The effects of noise in phases and in grating profiles are also numerically calculated and discussed.     

Replicated data-matrix array generators

The fabrication and replication of binary spot array generators using 4 and 16 levels gratings is investigated. The elements are designed using iterative Fourier transform algorithm and fabricated by electron-beam lithography. Finally elements are copied by fabricating nickel shims and using hot embossing technique. In each step the optical signals are measured and signals are characterized using bit error rate as a measure of quality. The results show that although 16 level element gives theoretically superior performance, the bit error rate is much lower (∼0.2%) for replicated 4 level elements than for their 16 level counterparts (∼9%).