Band gap of hexagonal 2D photonic crystals with elliptical holes recorded by interference lithography.

Two-dimensional hexagonal photonic crystals can be recorded using the simple superimposition of two interference patterns rotated by 60 masculine. Such process generates high contrast masks, however, it generates elliptical cross section structures instead of cylinders. We study the PBG properties of the experimentally feasible geometries, using this technique and we demonstrate that the effect of this asymmetric shape is a reduction in the PBG map area, for TE polarization, in comparison with cylindrical structures. On the other hand, it appears a PBG for TM polarization.

Recording different geometries of 2D hexagonal photonic crystals by choosing the phase between two-beam interference exposures.

2D hexagonal patterns can be generated by the superimposition of two or three fringe patterns that have been formed by two-wave interference and that have rotations of 60 degrees between them. Superimposing three exposures solves the problem of asymmetry in the cross section of structures, which is caused by double exposure. The resulting structure, however, depends on the phase shift of the third fringe pattern in relation to the previous two. We propose a method for controlling the phase shift, and we demonstrate that three different lattice geometries of hexagonal photonic crystals can be recorded when the phase is chosen.

Measurement of phase differences between the diffracted orders of deep relief gratings.

Measurement of the phase difference between the 0th and the 1st transmitted diffraction orders of a symmetrical surface-relief grating recorded on a photoresist film is carried out by replacement of the grating in the same setup with which it was recorded. The measurement does not depend on lateral shifts of thereplaced grating relative to the interference pattern, on environmental phase perturbations or on the wave-front quality of the interfering beams. The experimental data agree rather well with theoretical results calculated for sinusoidal profiled gratings.

Metallized photoresist grating as a polarizing beam splitter.

We propose and demonstrate the use of a simple holographic relief photoresist grating covered with an aluminum film as a reflecting polarizing beam splitter. The polarizing effects were achieved as a result of the nonsinusoidal profile of the grating. The best parameters of the gratings for optimizing the polarizing-beam-splitting properties were found by the introduction of the experimental profiles in diffraction calculation software. Theoretical and experimental results are presented, confirming the feasibility of the element.

Reflecting polarizing beam splitter.

We propose and experimentally demonstrate the use of metal-covered lamellar relief gratings as a polarizing beam splitter operating at a single wavelength near Littrow incidence. We report the characteristics of a grating produced by holography and reactive ion etching that was calculated for operation as beam splitter at lambda = 633 nm (for a He-Ne laser).

Diffractive structures holographically recorded in amorphous hydrogenated carbon (a-C:H) films.

We propose and demonstrate the direct recording of submicrometer relief gratings in amorphous hydrogenated carbon (a -C:H) films by reactive ion etching (RIE) for use as diffractive optical components. The high refractive index of this film and its transparency in the IR make such structures promising candidates for IR-transmission diffractive optical components. The structures are holographically recorded in photoresist and then transferred to a thin aluminum layer that is used as a mask for RIE of the a -C:H films. The diffraction measurements of the structures recorded in these films demonstrated the feasibility of using the materials as diffractive optical components.

Developed profile of holographically exposed photoresist gratings.

A simulation of the profile of holographically recorded structures in photoresists is performed. In addition to its simplicity this simulation can be used to take into account the effects that arise from exposure, photosensitization, development, and resolution of positive photoresists. We analyzed the effects of isotropy of wet development, nonlinearity of the photoresist response curve, background light, and standing waves produced by reflection at the film-substrate interface by using this simulation, and the results agree with the experimentally recorded profiles.

Photoresist resolution measurement during the exposure process.

The index-modulation evolution of a positive photoresist material was measured during the holographic exposure of sinusoidal patterns. The exposures were performed in a stabilized holographic setup that permits easy changes in the period. The results show the lowering of the recorded index modulation when the period decreases.

Holographic quarterwave plates.

Quarterwave plates can be made as holographic gratings in positive photoresist. We studied the effect of the grating period and relief depth on the phase retardation and on the rotation of the polarization of the transmitted light. Experiments were performed with gratings of different periods, which also exhibit an antireflection property.

Adaptive fringe-locked running hologram in photorefractive crystals.

We have recorded running holograms in a photorefractive crystal with an applied electric field, using a 90 degrees phase-shift fringe-locked interference pattern of light. This method provides a simple way to obtain optimal conditions for nonstationary holographic recording. The experiment that we describe allows us to calculate the crystal diffusion length L(D) and provides direct evidence of the occurrence of running holograms in photorefractive crystals. Experimental results for a Bi(12)SiO(20) sample are reported.

Interference-term real-time measurement for self-stabilized two-wave mixing in photorefractive crystals.

We report the real-time direct interference-term measurement for a two-wave-mixing experiment in photorefractive crystals. Knowledge of the interference term may provide information concerning diffraction efficiency, interference pattern-to-recorded hologram phase shift, and optical activity and anisotropic diffraction properties of these materials. This method comprises phase modulation of one of the interfering beams and synchronous detection of the first and second harmonics in the resulting output irradiance modulation. Simultaneous detection of both harmonics enables the measurement to be made even in strongly perturbed conditions, since one harmonic is used for measuring and the other is used for operating Bi(12)TiO(20) are reported.

Analysis of an active stabilization system for a holographic setup.

An active stabilization system for a holographic setup based on detection of phase shift between the interference pattern and a reference hologram is described. Its basic feature is the possibility of operating for 0, pi or +/-pi/2 at will, always in a null-detection mode. The reference hologram may be a previously recorded permanent hologram or a real-time (even reversible) one. The use of the open loop response of the stabilization system is developed for analyzing its performance, which allows closer insight into parameters limiting Its behavior. The effects of different noise sources are analyzed in detail. The real-time effect in a positive resist is successfully employed for operating the stabilization setup for recording an improved grating in this material.

Self-diffraction for intrinsic optical modulation evolution measurement in photoresists.

Two-wave mixing at a holographic grating being recorded in a positive photoresist film is used for simultaneously and independently stabilizing the holographic setup itself and for measuring the real-time optical modulation evolution during recording. The method is more sensitive than directly measuring the diffraction efficiency with a probe beam, being particularly interesting for very low efficiency values. This technique is used here for studying the photoreaction kinetics in a Shipley AZ-1350J positive photoresist, and measurements acree with those made with a well-established spectrophotometric method.

Stabilized holographic recording using the residual real-time effect in a positive photoresist.

The weak real-time effect in a positive-resist film was used for operating an actively stabilized holographic setup in order to carry out the entire recording process in a stabilized mode. Illustrative experimental results are reported. The successive recording in phase of spatially shifted holographic gratings is also shown.