We describe a scanning system for shape recovery that employs a pair of one-dimensional interlaced axilenses encoded onto a reflective liquid-crystal spatial light modulator. The design of these axilenses with opposite depth presets allows the generation of a high-quality laser line pattern with extended depth of focus, which is applied in the shape recovery. Other attributes of the system allow the scanning of objects whose lateral dimensions are larger that those of the spatial light modulator itself. The high performance of the scanning system is demonstrated by its application to the shape recovery of ceramic objects.
This work describes the characterization of a quadrant-type silicon photodiode that detect visible light and is designed
using CMOS integrated circuit technology, peaking in 550 nm wavelength. The quadrant detector (QD) derives
photocurrents by projecting a spot of light on four photodiodes placed close to each other on a silicon common substrate.
The photodetector is square shaped with 2.25 mm2 per active area by each quadrant and the size of the device is 9mm2.
Its transition region between the adjacent cells had a narrow width of 30 μm. The technology to develop position
sensitive detectors of four quadrant optimizing geometry to increase sensitivity is described. In addition, the performance
on applying the QD to shape a recovering system is investigated.
KEYWORDS: Diffractive optical elements, Modulation, Ceramics, Numerical simulations, Field programmable gate arrays, Spatial light modulators, Liquid crystal on silicon, Near field diffraction, Transmittance, 3D scanning
We show that long depth of focus can be achieved with a pixelated lens (PL) encoded onto a reconfigurable spatial light modulator (SLM). Our PL has a phase distribution similar to that of a conventional axilens. Additionally, our resulting reconfigurable PL is employed in a novel shape recovering system. A feature of this system is that no moving parts or motors are required to scan a three-dimensional object. Numerical simulations and experimental results are shown.
In a previously reported holographic code for the synthesis of arbitrary complex fields with phase-only modulators, the amplitude is encoded by scaling the phase modulation. For the appropriate performance of this code, it is necessary to employ an ideal phase modulator, which can not be easily obtained with a standard liquid-crystal device. We generalize and improve the above holographic code in such a way that the desired complex function can be obtained by using the restricted phase-mostly modulation provided by a twisted-nematic liquid-crystal display, in a simple setup employing two polarizers and a He-Ne laser. A commercial liquid-crystal device employed in this setup only provides a phase modulation in a range smaller than 1.5π radians, coupled with an amplitude modulation with a significant variance. In spite of these restrictions, the quality of complex signals encoded with the modified holographic code is only affected by a marginal efficiency reduction. We present numerical simulations and experimental results regarding our proposal.
We propose a holographic code for synthesis of fully-complex transmittance, which can be implemented employing a twisted-nematic liquid-crystal display, two linear polarizers, and a He-Ne laser. This simple setup provides a reduced phase range and amplitude modulation with significant variance. Our holographic code efficiently exploits this constrained modulation for the accurate encoding of arbitrary complex transmittance. Two experimental examples illustrate the good performance of the holographic code.
We propose the implementation of improved Fresnel type diffractive optical elements (DOEs) on spatial light modulators with a limited phase modulation capability. For the design of our elements we developed a method of design, that starts with an element formed by the phase function of a pixelated lens (PL), modulated by the phase of a lenslet array. The design is subject to a large number of phase levels in a limited range (smaller than 2π). We show that the undesirable effects produced by the complex modulation of a spatial light modulator (specifically, a twisted nematic liquid crystal display) can be minimized when improved Fresnel type DOEs are used. Simulation and optical reconstructions corroborate our proposal.
We discuss the performance of the double-phase holographic encoding of complex modulation, implemented with a phase-only spatial light modulator (SLM). A macro-pixel formed with two phase-modulated pixels of the SLM is required to encode each sampled value of the desired complex modulation. This complex modulation is obtained in the zero order term of the Fourier series associated to the macro-pixel structure. We discuss the performance of this holographic method with explicit consideration to the pixelated structure of the SLM. We show that an exact copy of the desired complex function, only attenuated by the SLM fill factor, is generated by the holographic code (with some additional high order off-axis terms). We derive a formula for the signal field reconstruction efficiency. This formula shows that the efficiency is dependent on the absorption (or modulus) of the encoded complex modulation. As an application, we show that the holographic code can be adapted (with slight modifications) to implement a highly isotropic edge enhancement filter.
We investigate the encoding of a phase-only filter together with a Fourier transforming lens using a single SLM. We consider the implementation of this composed filter with both phase-only and real-only SLMs. The restrictions on the optical setup parameters in terms of the SLM characteristics are discussed. We corroborate our proposals by presenting numerical simulations.
In this work we present three spatial filters that perform isotropic edge enhancement or recognition. Their design is based on first determining a convolution kernel that performs the desired operation and then, by Fourier transforming, obtaining the filter function. To the authors' best knowledge, these filters have not been proposed in the past. We present numerical simulations that corroborate our proposal. For the optical implementation of one of the proposed filters, a holographic technique capable of representing complex transmittances is required. In this case, the filter is simulated using a double-phase holographic code.
We present a modified simulated annealing algorithm for the design of diffractive optical elements whose basic cell is constrained by a symmetry similar to that of the reconstruction field. Compared with the conventional SA algorithm, our approach permits better designs with reduced computational efforts.