Two-dimensional Diffractive Optical Elements Research Articles

Formation of two-dimensional photopolymer diffractive optical elements for converting light beams with two-beam interactions taken into account

Bessel light beams are used in many fields, such as nonlinear optics, optical metrology, design of atmospheric wireless telecommunication lines, nanoscale objects manipulating, etc. Bessel beams do not diffract, they have restoration properties, they retain high intensity in the axial region at large distances. Thus, the search for an affordable method of forming such beams seems very relevant. In this paper, we study the process of two-dimensional diffractive optical elements (DOEs) holographic formation in photopolymer materials (PPM) with allowance for two-beam interactions. DOEs is intended for converting light beams with a Gaussian distribution into a Bessel-like ones.

Completely passive method of speckle reduction utilizing static multimode optical fibre and two-dimensional diffractive optical element

ABSTRACTIn this paper, we present experimental results on speckle noise suppression using a completely passive method. The passivity of the method is achieved owing to the absence of any mechanical, electronic, or other dynamic influences on the optical scheme elements. In the experiment, a multimode semiconductor 520 ± 5-nm laser with a spectral bandwidth of 2 nm, static two-dimensional (2D) and 2 × 1D diffractive optical elements (DOEs), as well as multimode single-core optical fibre and multimode optical fibre bundle were used. The dependence of the speckle reduction efficiency as a function of the optical fibre type and optical fibre length was measured for different DOEs. A speckle contrast of 0.148 and speckle reduction coefficient of 2.38 were obtained for a 2.5-m-long multimode optical fibre bundle. The experimental results confirmed that it is possible to construct completely passive optical circuits with reduced speckle noises using static multimode optical fibres and diffraction optical elements.

Design of two-dimensional diffractive optical elements for beam shaping of multicolor light-emitting diodes.

To achieve a cellular network in visible light communication, the illumination areas covered by red, green, and blue light-emitting diodes (LEDs) forming a white LED should be of the same size with uniform intensity distribution. In this paper, the iterative algorithm for the design of multicolor-oriented two-dimensional diffractive optical elements (DOEs) is improved. Simulation results indicate that almost the same size of the diffraction patterns of the DOE illuminated by multicolor LEDs is achieved with good uniformity of the intensity distribution.

Precise design of two-dimensional diffractive optical elements for beam shaping.

Diffractive optical elements (DOEs) for beam shaping are widely used in many fields, and there are many kinds of optimization algorithms to design the DOEs for beam shaping. However, only the intensity distribution of the selected sampling points is controlled by these optimization algorithms. The intensity distribution of other points on the output plane is always far away from the ideal distribution. The reason is that the sampling interval on the output plane is not small enough. In this paper, a new modified GS algorithm is presented with a small enough sampling interval on the output plane. A two-dimensional DOE for beam shaping is designed, and the simulation results and the experimental results demonstrate the good performance of this algorithm.

Flexible fabrication of three-dimensional optical-domain photonic crystals using a combination of single-laser-exposure diffractive-optics lithography and template inversion

We demonstrate inversion of three-dimensional photonic crystal templates fabricated in a large area with diffractive-optics lithography. A custom-designed two-dimensional diffractive optical element was used to generate highly uniform, bicontinuous, three-dimensional photonic crystal templates in a single-laser exposure. Chemical vapor deposition successfully infiltrated the thick periodic polymer structure to deposit amorphous silica and thereby define an all-silica inverted photonic crystal after polymer removal, as confirmed by focused ion-beam milling and energy-dispersive x-ray spectroscopy. The diffractive-optics lithography permitted a large number of uniform layers to form that manifested in the recording of a strong -28 dB stopband in the telecom band.

Single-frame measurement of the complete spatiotemporal intensity and phase of ultrashort laser pulses using wavelength-multiplexed digital holography

We show that a simple (few-element) arrangement for wavelength-multiplexed digital holography allows the measurement of the electric field E(x,y,t) of a femtosecond laser pulse on a single shot. A slightly rotated two-dimensional diffractive optical element and a variable-wavelength filter together generate multiple spectrally resolved digital holograms that are simultaneously captured in a single frame by a digital camera. An additional simultaneous measurement of the spectral phase for a spatially filtered replica of the pulse with frequency-resolved optical gating completes this three-dimensional measurement. An experimental implementation of the technique is presented and its current limitations are discussed.

Phase tunable multilevel diffractive optical element based single laser exposure fabrication of three-dimensional photonic crystal templates

The fabrication of diamond-like three-dimensional photonic crystal templates using a single laser exposure through a diffractive optical element has been demonstrated. An orthogonal combination of two linear phasemasks was used to define a two-dimensional diffractive optical element of multiple phase levels. By adjusting the gap between two phasemasks, a variable phase shift is shown by theory and demonstrated experimentally to control the interlacing position of two orthogonally rotated periodic structures. The transition of formation of diamond-like woodpile structures having tetragonal symmetry to structures having body-centered-tetragonal symmetry and variations in between has been demonstrated.

Applying a mapped pseudospectral time-domain method in simulating diffractive optical elements

A new technique for the analysis of two-dimensional diffractive optical elements, by use of the pseudospectral time-domain (PSTD) method, is presented. In particular, the method uses a nonuniform (NU) grid and a mapping technique to obtain very accurate spatial derivatives in an efficient manner. To this end, we present the formulation of the PSTD method by using a NU grid and compare its application to the analysis with that of the finite-difference time-domain (FDTD) method. Using only a fraction of the memory and a fraction of the computation time used by FDTD, the mapped PSTD was able to obtain very close results to FDTD.

Low-data simulation of diffractive optical elements based on the zones geometry

Design and simulation of two-dimensional diffractive optical elements are often limited by the amount of data required to represent the element in the computer's memory. We present a technique based on a geometrical description of the element, which requires fewer data than the traditional pixel description. Moreover, the element is being described more accurately and consequently the pixel-related artefacts are suppressed. This technique can be used for both periodic and non-periodic structures of large dimensions under Fraunhofer or Fresnel approximations. We apply the method to analysis of far-field beam-shaping elements and discuss possible extensions and refinements of the technique.