Martin Schmitz

Gratings in the resonance domain as polarizing beam splitters.

Polarization-selective gratings in the resonance domain of diffractive optics are calculated by use of rigorous electromagnetic diffraction theory. The polarizing effects are attained by special surface-relief structures, and the profile of binary surface-relief gratings is optimized with a nonlinear Newton algorithm to design diffractive polarizing beam splitters.

Phase gratings with subwavelength structures

Polarization-selective gratings are designed by use of rigorous electromagnetic diffraction theory. The polarizing effects are attained by special surface-relief structures. We present a scheme for coding two different optical functions in one diffractive element. It is based on a combination of the scalar diffraction theory and the effective-medium theory. The diffractive element may be regarded as a combination of a phase element and a subwavelength grating.

Rigorous concept for the design of diffractive microlenses with high numerical apertures

Cylindrical dielectric diffractive microlenses are designed by the use of rigorous electromagnetic diffraction theory, and their performances are compared with microlenses based on a conventional scalar design concept. Microlenses with a relief of four depth levels are considered as well as binary microlenses with subwavelength structures. We show that the density of energy in the focus of high-numerical-aperture microlenses can be significantly increased if the phase distribution of the transmitted electrical field is optimized.

Beam displacement at diffractive structures under resonance conditions

A beam of light incident upon a diffractive structure can under resonance conditions be subject to a rather large lateral displacement. The effect is demonstrated with a Gaussian profile beam and two geometries based on a waveguide grating and a single-mode waveguide.

Pulse delay at diffractive structures under resonance conditions.

An optical pulse incident upon a diffractive structure under resonance conditions may undergo a temporal delay. The effect is demonstrated with a pulse of Gaussian profile at two geometries: a waveguide grating and a single-mode waveguide. It is shown that the order of magnitude of the delay can be controlled by the parameters of the structures.

Superluminal propagation of optical pulses inside diffractive structures

Inside diffractive structures, the intensity maximum of optical pulses can travel with a velocity exceeding the vacuum speed of light. This effect is due to the occurrence of evanescent waves, and is accompanied by strong attenuation. It is emphasized that, due to the attenuation, causality is not violated.

Rigorous analysis and design of diffractive cylindrical lenses with high numerical and large geometrical apertures

Abstract A concept is presented for the analysis of diffractive cylindrical lenses with apertures larger than 100 wavelengths which are denoted as large geometrical apertures throughout this paper. The transmitted field of a cylindrical lens is calculated by the use of rigorous electromagnetic diffraction theory. Large geometrical apertures are subdivided into smaller overlapping areas that are treated in sequence. The wave propagation from the lens plane to the focal plane is calculated with the spectrum of plane waves. A design concept is presented which ensures that the performance of diffractive cylindrical lenses with high numerical apertures (NA≥0.3) is almost independent of the polarization of the illuminating light. The design concept is based on the local grating model in combination with the phase detour principle. As an example we design and analyze a F /0.5 cylindrical lens (NA=0.71) with a geometrical aperture of 600 wavelengths.

Comment on numerical stability of rigorous differential methods of diffraction

The rigorous coupled wave method and the rigorous modal method are frequently used to analyze lamellar, multilevel gratings. Both methods result in a system of linear equations that has to be solved to obtain the transmitted and reflected amplitudes. An algorithm is presented to increase the numerical stability in the evaluation of these amplitudes. Numerical examples and comparisons with recently published results are given.