In this work, we show the conversion of a Gaussian beam into an annular vortex beam (AVB) by means of an optical vortex element (OVE). This is a simple phase plate which generates the AVB at a determined distance without the use of external optical elements such as lenses and axicons. We discuss the interesting features and the advantages of the OVE respect to other methods to generate AVB such as the conventional vortex (CV) and the helical axicon (HA). The OVE presents the highest intensity peak respect to both the CV and the HA. Another important feature is that the OVE and the HA maintain a fixed annular radius; in contrast the CV changes the annular radius, while the topological charge is modified. The OVE is displayed on a spatial light modulator (SLM) in order to generate experimentally the AVBs. We demonstrate the features of the AVB generated and measure the high angular velocities achieved due to the angular momentum transfer to 3 μm particles.
A numerical and experimental comparison between different synthetic holographic codes is presented. Its performance
is evaluated considering the generation of Bessel and Laguerre-Gaussian beams, as examples. Some
reviews of computer generated holograms (CGHs) have been published in the literature but none of them have
included a detailed comparison of their performance in the encoding of structured optical fields. The numerical
evaluation includes an analysis of the theoretical features of each hologram and a calculation of Signal-to-Noise
Ratio of the reconstructed field while the experimental evaluation assume the implementation of the holograms
using a pixelated phase modulator.
The use of spatial light modulators to generate arbitrary optical field distributions has been extensively used to trap and manipulate dynamically a large number of particles. Here we show that by using phase computer generated holograms displayed on a spatial light modulator (SLM) sorting of microparticles can be achieved at relatively low power. The algorithm used for the generation of the PCGH is based on iterative Fourier transform algorithm which generate a spots array in the Fourier plane, then controlling some parameters as: the spot separation, the direction and velocity of the pattern displacement, optical sorting of micron-sized particles can be achieved.
A spatial light modulator (SLM) is a very useful optical tool due its versatility to be manipulated dynamically. We
propose a characterization method for reflective SLMs in quasi-normal configuration. This device can work as either
amplitude-mostly or phase-mostly modulator. To achieve the modulation, the SLM can be accompanied by two
polarizes, or additionally using a quarter-wave plate retarder. By simulating the behaviour of the optical setup for this
device; we establish an experimental Jones matrix that represent the modulator. In this work we present a more realistic
modulator characterization, only assuming that the modulator Jones matrix should be unitary (the modulator do not
absorb light). We report this model for characterization of the Holoeye LCR2500 SLM.
We experimentally investigated the transmission variation of a nonlinear optical loop mirror (NOLM). We analyzed the transmission evolution of the NOLM based on the input intensity. The NOLM is formed by a symmetrical coupler, 500 m of highly twisted low-birefringence fiber and a quarter-wave retarder plate in the loop. If we rotate the quarter-wave retarder plate is possible to change the transmission behavior. Using circular polarization of the input beam is possible to get a high contrast between the maximum and minimum of the transmission. With this characteristic, we have the possibility to reduce the amplitude fluctuations and the pedestal in a train of optical pulses.