Spot Array Generator Research Articles

Design of large-angle distortion-free and spot adjustable LED spot array projector based on microlens array and eyepiece

The spot array projector has long been a challenging and intriguing research focus in the fields of projection and lighting applications. In the current literature, there is a lack of a comprehensive and detailed presentation on the design and analysis method for a spot array generator based on the structure of imaging eyepiece and MLA. We present a novel design and optimization method for a large-angle, distortion-free and spot adjustable LED spot array projector that is composed of an eyepiece, two microlens arrays (MLAs), and a micro-LED array (MLEDA). The eyepiece system is optimized using imaging optical methods to project sub-beams to the target plane with a large angle. The sub-lens of condenser MLA is also optimized using imaging optical methods to refocus the collimating beam and match the numerical aperture (NA) with the eyepiece, and the sub-lens of the collimating MLA is acquired by using simulated annealing (SA) global illumination optics optimization method to achieve collimation and far-field homogenization. The predistortion MLEDA and the MLAs are proposed and implemented by the radial basis function (RBF) interpolation method, which correct the large-angle distortion introduced by the eyepiece. Both near-field and far-field applications can be realized by the proposed system. In the near-field applications, different spot geometries at the near-field target plane can be achieved. In the far-field applications, the power matching of the MLEDA is used to improve far-field uniformity of spot array. Moreover, the predefined-geometry arrangement spot array can be realized in both near and far fields. Two design examples with full field of view (FOV) projection of 80° and 100° are provided to validate the proposed method. Overall, the proposed system offers a promising solution for various applications requiring target identification or 3D calibration.

Generation of optical needles and bright spot arrays through reversing the radiation pattern of collinear antenna array

An optimization-free approach is proposed for generating optical needle and bright spot arrays with controllable distributions. This is achieved by inversely focusing the radiation pattern from a collinear antenna array whose elements are placed along an optical axis and whose currents in each element also flow along that direction, situated at the focus of a 4pi configuration. The shape and central location of the nth focusing field only depend on the length ln and coordinate zn of the nth element in collinear array, respectively. The number of focal fields is determined by the number of elements in the array.

Experimental Study of Reconfigurable Visible Light Communications Based on Holographic Spot Array Generations

An experimental study of a reconfigurable visible light communication (VLC) system, using liquid crystal on silicon-based spatial light modulator, which dynamically offers multicast transmission, for indoor optical wireless communication configuration is presented and experimentally demonstrated. The multicast transmission of the system using holographic spot array generation was achieved through an efficient design of near-field computer generated hologram based on Gerchberg–Saxton (GS) algorithm. The system transmission performance, limited by the spot power nonuniformity, was improved through an optimization of GS algorithm, and the results shown that a significant improvement over 11% has been achieved either in a one-dimensional or two-dimensional spot array generations at a transmission distance of 1.25–2.5 m. This paper provides an efficient approach for the direct implementation of a reconfigurable VLC system based on multisport configuration.

Grating- and checkerboard-based zone plates as an optical array generator with a favorable beam shape.

The combination of a grating as a periodic object and a Fresnel zone plate with a quasi-periodic structure leads us to propose some novel array generator elements. It is shown that diffraction performance of the proposed element depends on the grating structure, so that the diffraction performance may efficiently be increased if the grating is replaced with a checkerboard structure. Depending on the kind of zone plate, we have demonstrated that the corresponding array generator is also created. For instance, a focused array of vortices is generated when the zone plate is replaced with a spiral zone plate. We have also clarified that the method allows us to generalize it to the other class of the zone plate-based elements, e.g., a cross zone plate. Namely, when the cross zone plate is used instead of the Fresnel zone plate, a spot array generator is again created whose diffractive performance is improved by modifying its phase structure. Also, it is clearly shown that the focusing feature of the element depends on the grating period. Finally, there is a good agreement between the simulation results and the corresponding experimental works.

Plasma nitrogenation of polymer surfaces with a new type of combinatorial plasma‐printing reactor

A new method for combinatorial area‐selective polymer modification or deposition using DBD‐type plasmas at atmospheric pressure (“plasma‐printing”) is presented. Thereby a gradient of two gases perpendicular to the flow direction is established by triangular‐shaped overlapping gas inlets. Design of this reactor allows generation of spot arrays with controlled gradients of physicochemical surface properties which is first applied by investigating the influence of H2 admixtures to N2‐plasma‐treatment of polymers. Formation of functional groups is quantitatively characterized by ATR FT‐IR with preceding chemical derivatization using nucleophilic and electrophilic chemicals. It is shown that treatments using high gas flow velocities are more efficient than treatments with low gas speed. Also it is shown that direct plasma treatment leads to polymer surfaces with nucleophilic and electrophilic properties and that H2 content influences formation of both types of functionalities.

Double-Slit and Square-Slit Interferences With Surface Plasmon Polaritons Modulated by Orbital Angular Momentum Beams

We present two kinds of interferences on metallic thin films with orbital angular momentum (OAM) beams, namely, double-slit interference and square-slit interference. When an OAM beam is normally incident upon the metallic thin film with two slits, the fringes on the metallic thin film generated by the interference of two surface-plasmon-polariton waves will twist, and the twist amount depends on the topological charge of the incoming OAM beam. When a square slit is employed, a quasi-square optical lattice will be unveiled, and the arrangement of lattice can be modulated by the OAM beam. The fringes and spots are both at the subwavelength level, which show great potential for superresolution microscopy, OAM detection, and spot-array generation.

Matched filtering Generalized Phase Contrast using binary phase for dynamic spot- and line patterns in biophotonics and structured lighting

This work discusses the use of matched filtering Generalized Phase Contrast (mGPC) as an efficient and cost-effective beam shaper for applications such as in biophotonics, optical micromanipulation, microscopy and two-photon polymerization. The theoretical foundation of mGPC is described as a combination of Generalized Phase Contrast and phase-only correlation. Such an analysis makes it convenient to optimize an mGPC system for different setup conditions. Results showing binary-only phase generation of dynamic spot arrays and line patterns are presented.

Laser Beam Splitting by Diffractive Optics

Recent advances in diffractive optics theory and technology have made it possible to design programmable, multichannel optical systems based on diffraction gratings, lenslet arrays and digital holography algorithms. Spot array generation, multiple and multifocal imaging, matched filtering, laser beam mode selection and simultaneous contour shaping are among the most promising applications of diffractive beam splitting.

Design, fabrication and characterization of subwavelength computer-generated holograms for spot array generation

We report the analysis, design, fabrication and experimental characterization of novel subwavelength computer-generated holograms that produce uniform symmetric spot array. We distinguish between a polarization-sensitive and polarization-insensitive far-field reconstruction and show that a linearly polarized incident illumination is required in the former case in order to generate a symmetric reconstruction. The polarization-insensitive case generates a symmetric response independent of the illumination polarization. We show that this response is equivalent to that of a scalar-based computer-generated hologram but with an additional, independent, term that describes the undiffracted zeroth order. These findings simplify the design and optimization of form birefringent computer-generated holograms (F-BCGH) significantly. We present experimental results that verify our analysis and highlight the advantage of these novel elements over scalar-designed elements.

Design, implementation, and characterization of a folded spot-array generator for a modulator-based free-space optical interconnect.

A folded structured light generator is presented. This spot generator is to be used in a modulator-based free-space optical interconnect. Three cascaded diffractive optical elements produce 4 x 8 clusters on an 800 microm x 1600 microm pitch, in which each cluster is a 4 x 4 array of 13.1-microm-radius spots on a 90-microm pitch. The folded configuration is more compact than an existing linear spot-array generator and replaces 14 optical surfaces with eight surfaces. Details of the optical design, sensitivity analysis, alignment techniques, assembly, and test results are presented.

Effects of feedback from collimating, focusing, and spot-array generating outcoupler gratings in surface-emitting semiconductor lasers

We experimentally demonstrate that a grating outcoupler used for complex beam shaping (spot-array generation) can produce unintentional optical feedback that severely disturbs the integrated in-plane laser that illuminates the coupler. Simulations show that these outcouplers, in contrast to conventional collimating or focusing outcouplers, tend to produce high levels of feedback in spite of the detuning used to suppress feedback. Further, this feedback is focused to high intensity in the laser gain medium. This focused light acts as a seed for the nonlinear self-focusing that causes wave-front distortion and filamentation, which degrades the beam quality.

Non-paraxial array illuminator based on a single low-resolution pixelated lens

The performance of a low-resolution pixelated lens (PL) as a spot array generator is discussed. It is proved that if the lens is encoded onto a typical pixelated spatial light modulator, it will generate a large number of uniform foci only at non-paraxial focal planes. We show, numerically and experimentally, that in such non-paraxial conditions the PL generates a focal plane spot array with acceptable efficiency and uniformity. Moreover, it is shown that the quality of the focal plane spot array improves when the numerical aperture of the PL is increased.

Generation of achromatic and propagation-invariant spot arrays by use of continuously self-imaging gratings

A particular class of Montgomery's self-imaging objects that we call continuously self-imaging gratings (CSIG's) is introduced. When they are illuminated by a plane wave, these objects produce a field whose intensity profile is a propagation- and wavelength-invariant biperiodic array of bright spots. The mathematical construction of these objects and their intrinsic properties are described. On a practical level, CSIG's are compact and achromatic nondiffracting array generators. We show that a good CSIG approximation can be realized by a two-level phase grating that is experimentally tested.

Nonlinear effects of phase blurring on Fourier transform holograms

Liquid-crystal light valves can have intensity-dependent resolution. We find for a nematic liquid-crystal light valve that this effect is well modeled as a phase that has been blurred by a linear space-invariant filter. The phase point-spread function is measured and is used in simulations to demonstrate that it introduces intermodulation products to the diffraction patterns of computer-generated Fourier transform holograms. Also, the influence of phase blurring on a pseudorandom-encoding algorithm is evaluated in closed form. This analysis applied to a spot array generator design indicates that nonlinear effects are negligible only if the diameter of the point-spread function is a small fraction of the pixel spacing.

Multispot diffusing configuration for wireless infrared access

In order to combine the advantages and to overcome the drawbacks of a direct line-of-sight or a diffuse configuration for wireless infrared access, a multispot diffusing concept utilizing a holographic spot array generator is presented. Simulation results are presented and compared with those for a pure diffuse configuration in terms of link characteristics, when a single-element or a multibranch composite receiver is employed. The multispot transmitter ensures a more uniform signal power distribution. Improvements of about 2 dBo (optical decibels) can be achieved compared to a Lambertian pattern illumination. The increased power path loss at the edges of the communication cell is accompanied with a decrease in the delay spread resulting in an extension of the coverage range. Utilization of angle diversity detection improves the signal-to-noise ratio by more than 7 dB when selecting the best receiver branch and more than 10.5 dB in the case of maximal-ratio combining. Use of a multibeam transmitter and an angle diversity receiver reduces the likelihood of shadowing of the receiver due to an obstacle standing along the path between the receiver and the transmitter.

Design, implementation, and characterization of a kinematically aligned, cascaded spot- array generator for a modulator-based free-space optical interconnect

The design and the implementation of a modular spot-array generator for a modulator-based free-space optical interconnect is presented. Two cascaded diffractive optical elements produce 4 x 8 clusters on a 1600 microm x 800 microm pitch, where each cluster is a 4 x 4 array of (1/e(2)) 13.1-microm-radius spots on a 90-microm pitch. The spot-array generator is kinematically aligned to the interconnect system such that no realignment is necessary between removal and reinsertion. Characterization results are presented.

High-diffraction-efficiency pseudorandom encoding

Pseudorandom encoding (PRE) is a statistics-based procedure in which a pure-phase spatial light modulator (SLM) can yield, on the average, the prescribed diffraction pattern specified by the user. We seek to combine PRE with the optimization of an aperture-based target function. The target function is a fully complex input transmittance, unrealizable by a phase-only SLM, that generates a prescribed light intensity. The optimization is done to increase the diffraction efficiency of the overall process. We compare three optimization methods-Monte Carlo simulation, a genetic algorithm, and a gradient search-for maximizing the diffraction efficiency of a spot-array generator. Calculated solutions are then encoded by PRE, and the resulting diffraction patterns are computer simulated. Details on the complexity of each procedure are furnished, as well as comparisons on the quality, such as uniformity of the output spot array.

Design, implementation, and characterization of an optical power supply spot-array generator for a four-stage free-space optical backplane

The design and implementation of a robust, scalable, and modular optical power supply spot-array generator for a modulator-based free-space optical backplane demonstrator is presented. Four arrays of 8 x 4 spots with 6.47-mum radii (at 1/e(2) points) pitched at 125 mum in the vertical direction and 250 mum in the horizontal were required to provide the light for the optical interconnect. Tight system tolerances demanded careful optical design, robust optomechanics, and effective alignment techniques. Issues such as spot-array generation, polarization, power efficiency, and power uniformity are discussed. Characterization results are presented.

Single- and multimode VCSELs operating with continuous relief kinoform for focussed spot-array generation

We report the use of both single- and multimode VCSELs operating at 850 nm as the illumination source for a continuous-relief diffractive optical element (DOE) fabricated in resist on quartz. The system produces a 4/spl times/4 array of focussed spots from a single optical input. The uniformity error was found to be /spl sim/10% in all cases, and the overall system efficiency /spl sim/35% A single spot-coupling efficiency of 70% into a multimode fiber placed 20 mm from the DOE was also measured.

Acousto-optic generation of two-dimensional spot arrays

We demonstrate, through the use of an acousto-optic system, the generation of two-dimensional uniform spot arrays with high diffraction efficiency. The system consists of two acousto-optic cells oriented orthogonally to each other and driven by an arbitrary waveform generator. Determination of the acousto-optic drive signal is discussed, as well as techniques for generating arbitrary spot arrays.