Binary Phase Diffractive Optical Elements Research Articles

High-resolution interference microscopy of binary phase diffractive optical elements

In this work, we apply the high-resolution interference microscopy technique to investigate the intensity and phase of light transmitted through a binary phase element. Using a combination of simulation and experimental results, we identify specific features in the intensity and phase maps of the transmitted light that are associated with the positions of the edges of the ridges and grooves in the phase element. Specifically, we identify these features to be minima in the intensity recordings, as well as phase jumps and in some cases phase singularities in the phase maps. We focus on the former two features, as they can reliably be observed in a single z-plane intensity or phase image, respectively, focused at the top of the structure ridges. Using the edge locations extracted from the intensity and phase profiles, we estimate the dimensions of the structure ridges and grooves as well as measure the displacement of the sample on a piezo stage. With both methods, the absolute width of the ridges and grooves is measured with an accuracy of approximately 220 nm, and the sample displacement is detected to approximately 50 nm resolution.

Extended focus depth for Gaussian beam using binary phase diffractive optical elements.

A novel technique to improve the focus depth of a Gaussian beam is presented in this paper. The improvement is based on two-step beam shaping using a cascade of binary phase diffractive optical elements (BPDOEs). The first BPDOE transforms the incident Gaussian beam into a high-order radial Laguerre-Gaussian beam (LGp0). Then the second BPDOE rectifies the obtained LGp0 beam and gives rise to a quasi-Gaussian one in the focal plane of a converging lens. This resulting quasi-Gaussian beam exhibits a lower divergence and larger focus depth compared to the pure Gaussian beam having the same beam waist. These results open new possibilities in laser beam manufacturing and micromachining, and in applications that need an extended focus depth.

Generation of Hermite – Gaussian modes of high-power femtosecond laser radiation using binary-phase diffractive optical elements

We present the results of experiments on generation of Hermite – Gaussian modes up to the third order inclusive using binary-phase diffractive optical elements (DOEs) illuminated by subterawatt femtosecond laser pulses. We perform a compariosn of the mode formation using DOEs designed by the kinoform method and the fractional coding technique, when the DOEs are illuminated by both femtosecond radiation and cw laser radiation at close wavelengths.

Axial superresolution of focused radially polarized light using diffractive optical elements

Particle swarm optimization (PSO) was used to design binary phase- and amplitude diffractive optical elements (DOEs) that axially superresolve a tightly focused radially polarized beam. The Pareto front was generated for a fitness-value space that describes the superresolution that can be achieved with the DOEs and radially polarized light versus an allowed upper bound in side lobe intensity. Fitness values for designs obtained via the PSO-, simplex-, and simulated-annealing methods are compared to show that PSO yields globally optimized solutions. Performance of binary phase/amplitude DOEs with different numbers of zones is compared. Binary amplitude DOEs give slightly better superresolution, whereas binary phase DOEs offer the advantage of higher power efficiency. The potential of using DOEs for 4Pi microscopy to further reduce the side lobes and achieve better superresolution is discussed.

Precision measurement system using binary phase computer-generated holograms

We present a novel method of obtaining precision measurement using two binary phase diffractive optical elements, termed the hologram, and phase mask. By encoding multiple views into the hologram, each of which corresponds to a horizontal or vertical relative displacement of the phase mask, the system is able to provide a visual feedback of the measurement without the use of electronics. A probabilistic method for detection of the resultant images, matched to the statistical properties of holographic replay, shows promise for enabling a fully automated measurement system.

Sapphire-GaN-based planar integrated free-space optical system

We report on the design and fabrication of a planar integrated free-space optical system working on the basis of binary phase diffractive optical elements (DOEs) realized in GaN on a sapphire substrate. Group III-nitride/sapphire substrates enable the parallel monolithic integration of passive microoptical elements like lenses and gratings as demonstrated here and optoelectronic devices like light emitters and photodetectors on a single wafer. We present an approach for the simultaneous optimization of the efficiency of transmissive and reflective diffractive optical elements processed in a single lithographic etching step.

Precision measurement with visual feedback using binary phase diffractive optical elements

A novel method for obtaining precision measurements by using two binary diffractive optical elements is presented. The system provides visual feedback of the measurement without the use of electronics.

Review of iterative Fourier-transform algorithms for beam shaping applications

We present a comparison of some of the most used iterative Fourier transform algorithms (IFTA) for the design of continuous and multilevel diffractive optical elements (DOE). Our aim is to provide optical engineers with advice for choosing the most suited algorithm with respect to the task. We tackle mainly the beam-shaping and the beam-splitting problems, where the desired light distributions are almost binary. We compare four recent algorithms, together with the historical error-reduction and input-output methods. We conclude that three of these algorithms are interesting for continuous-phase kinoforms, and two, namely the three-step method proposed by Wyrowski and the over-compensation of Prongué, still perform well with multilevel- and binary-phase DOE.

Optical optimization of binary phase fan-out elements

An optical parallel processor is presented which optimizes binary phase diffractive optical elements using simulated annealing. A liquid crystal television is used to simulate the phase element. Experimental results are presented for the optimization of fan-out elements. The performance of the optical parallel processor is analyzed using Fast Fourier Transform methods.