High-performance talbot array illuminators

The performance of two-dimensional Talbot array illuminators is discussed in terms of compression ratio, fabrication cost, and illumination efficiency. By comparing two array-illuminator families, we try to answer the question, "Which Talbot array illuminator provides the best illumination performance and requires the least expenditure in fabrication for a given compression ratio?" We further present experimental results obtained with a quartz-glass four-level surface-relief array illuminator designed for a two-dimensional compression ratio of 16 and fabricated with only two lithographic masks.     

Multilevel phase gratings for array illuminators

We describe a variety of multilevel phase structures that can be used to generate Lohmann's array illuminators. We report several experimental verifications of the synthesis of such multilevel phase structures by using simple binary curves in a conventional optical processor.     

Talbot array illuminators: general approach

I present a general approach for designing Talbot array illuminators (TAIL's). Beyond the scope of conventional TAIL's, in which each period of the replay field contains only one bright spot, I examine complex configurations ensuring various topologies of the output spots. The synthesis problem is stated in terms of constraints and degrees of freedom. Both the one-dimensional and two-dimensional cases are treated, and an example of constraints, namely the binarization of the TAIL, is discussed. For illustration, an application is proposed in which I consider a dynamic multilayer interconnection architecture involving a programmable TAIL.     

Numerical study of Dammann array illuminators

The numerical solutions of binary-phase (0, π) gratings for one-dimensional array illuminators up to 32 are presented. Some fabrication errors, which are due to position-quantization errors, phase errors, dilation (or erosion) errors, and the side-slope error, are calculated and show that even-number array illuminators are superior to odd-number array illuminators when these fabrication errors are considered. One (0, π) binary-phase, 8 × 16 array illuminator made with the wet-chemical-etching method is given in this paper.     

Designing Talbot array illuminators with phase-space optics

The problem of designing Talbot array illuminators is revisited in the context of phase-space optics. It is shown that for Talbot array illuminators with optimum compression ratio the construction of phase-only grating profiles can be simplified significantly by using phase-space representations of optical signals. Based on the Wigner distribution function a graphical procedure is derived for obtaining the complete design of the array generator for a given compression ratio. The application of phase-space optics to other classes of Talbot array illuminators, and its use as part of numerical optimization algorithms, is considered as well.     

Reinterpretation and improvement of Talbot array illuminators

We show that the transmittance of a finite Talbot array illuminator (TAI) can be expressed by the phase distribution of a pixelated lens, modulated by a discrete phase grating (G). Thus the TAI reconstruction field is given by the convolution of the grating's Fourier transform, with the point-spread function of the pixelated lens. On the basis of this approach we propose a method to improve the performance of a finite TAI by modifying the basic cell of the grating factor G.     

Number of phase levels of a talbot array illuminator

The number of phase levels of a Talbot array illuminator is an important factor in the estimation of practical fabrication complexity and cost. We show that the number (L) of phase levels of a Talbot array illuminator has a simple relationship to the prime number. When there is an alternative pi-phase modulation in the output array, the relations are similar.     

Design of array illuminators operating under spherical illumination

The effect of the form of the illuminating wave on array illuminators is investigated. Attention is focused on spherical illumination, and relevant parameters such as spot size and compression ratio are discussed. In addition, a general approach is presented to designing a Talbot array illuminator that operates under spherical illumination. It is shown how spherical illumination can be used as a degree of freedom, and an example of application in the field of human eye aberration correction is given.     

Design of non-paraxial array illuminators by step-transition perturbation approach

Abstract

We introduce an efficient Fourier-domain formulation of an approximate method to model non-paraxial diffractive elements. The method is based on evaluation of local field perturbations caused by abrupt surface-profile transitions. It facilitates fast parametric optimization of binary and four-level diffractive array illuminators in the non-paraxial domain of diffractive optics. Comparison with rigorous electromagnetic theory of gratings shows that optimization with the perturbation method gives accurate results if the smallest feature size in the surface profile is larger than one wavelength. Some binary designs are demonstrated using electron beam lithography.     

Generation of Lohmann images from binary-phase Talbot array illuminators

A systematic analysis has been performed that predicts the existence of 36 cases in which 100% modulated, square-wave irradiance distributions can be generated in the Fresnel regime by simple binary-phase gratings. These types of distributions, referred to here as Lohmann images, have been previously predicted by researchers studying phase gratings known as Talbot array illuminators. Twenty of the cases are reported, to the best of my knowledge, for the first time. Sixteen of these new cases result in Lohmann images with twice the spatial frequency of the original grating. Experimental verifications of the theoretical predictions are presented.     

Multilayer array illuminators with binary phase plates at fractional Talbot distances

We describe a Talbot array illuminator made of cascaded binary phase plates located at fractional Talbot distances. We compare the performance of such an illuminator with a conventional single-layer Talbot array illuminator in terms of compression ratio and technical feasibility.     

Fourier array illuminators with 100% efficiency: Analytical Jones-matrix construction

Abstract

Fourier-type spot-array illuminators are designed for electromagnetic fields in the paraxial domain of diffractive optics. An analytical construction of the periodic, spatially variable Jones matrix is presented, which produces 100% conversion efficiency from an arbitrarily polarized incident plane wave into M × N=2 ^P × 2 ^Q (P and Q are integers) diffraction orders. Such perfect performance is not possible within the scalar theory of paraxial diffractive optics.     

Planar-integrated optical vector-matrix multiplier

We present the design of a planar-integrated optoelectronic vector-matrix multiplier. The inherent parallel-processing potential is fully exploited by optical implementation of multiplications and summations. Planar integration makes the free-space optical system compatible with electronic VLSI technologies. It is composed of phase-only diffractive optical elements, which implement lens and multiple-beam-splitter functions. A demonstrator version of the optical system for a matrix of size 10 x 10 was fabricated on quartz glass by means of multimask lithography and reactive ion etching. It shows low cross talk and good uniformity of the signals.     

Thermal illuminators for far-infrared and submillimeter astronomical instruments

Astronomical instruments operating in the infrared-millimeter region often require internal sources for detector monitoring, instrument calibration, and health checking. We describe the design, modeling, and experimental evaluation of thermal emitters with a fast speed of response and low-power dissipation, suitable for the far-infrared-submillimeter region. The development of an internal illuminator for the Herschel Spectral and Photometric Imaging Receiver (SPIRE) satellite instrument is used as an example of the optimization of the design to meet particular requirements. A prototype illuminator design for SPIRE has been developed that, for a power dissipation of 1.5 mW, provides an equivalent blackbody temperature of 45 K with a 90% settling time of 220 ms.     

Reconfigurable two-dimensional diffractive phase element with the fractional talbot effect

We investigate the technical feasibility of the optical implementation of a four-phase-level diffractive element with two {0, pi}-phase spatial light modulators in a fractional Talbot configuration. The space-bandwidth product of the spatial light modulators is seen as the main theoretical limitation of the proposed approach. We investigate the robustness of technological and geometrical parameters on the diffraction efficiency of the whole system. Ferroelectric liquid-crystal silicon backplane spatial light modulators are chosen because of their high reconfiguration rates and good electro-optics interface. Similarly, we assess the influence of liquid-crystal technical parameters on system performance.     

Phase-locking of multicore fibre laser due to talbot self-reproduction

Abstract

The multicore fibre laser (MCFL), containing an array of single-mode microcores in a circle inside the pump core, is a promising compact laser source. The problem is to synchronize the radiation of microcores with different propagation constants at a given radiation frequency. The theory of phase-locking of an MCFL with an external mirror and an annular waveguide matched to the multicore fibre and having a length some fraction of the Talbot distance is developed. Collective mode selection appears to occur due to spatial filtering at fractional Talbot distances, while the radiation frequency self-adjusts within the spectral gain range to minimize losses. Parallel coupling between microcores is achieved in the limit of a small fill factor. The maximum number of microcores that can be coupled is found. Good agreement is achieved between the theory and previously published experimental results.     

Optical performance of axisymmetric edge-ray concentrators and illuminators

The optical performance of axisymmetric radiation concentrators and illuminators that are derived when two-dimensional edge-ray designs are rotated about their optic axis is investigated. Of particular interest are devices with spherical and cylindrical absorbers or light sources, for which the inherent ray rejection can be substantial. From the principle of etendue (phase-space) conservation, a lower bound for ray rejection can be established. With computer ray tracing, we demonstrate that this bound underestimates the actual ray rejection by only a few percent at most. Hence, to a good approximation, it can be used as an equality in analytic predictions of characteristic efficiency-concentration curves. By designing for absorbers or sources with a bald spot, the full range of efficiency and flux concentration values can be realizedand the trade-off between them can be quantified. The optical performance of these edge-ray designs is also compared against fundamental upper bounds on the flux concentration and efficiency of axisymmetric devices.     

非合作无源探测技术研究进展与发展趋势

从非合作无源探测原理和特点出发,对非合作无源探测技术的研究进展和发展趋势进行了综述。介绍了国内外非合作无源探测理论与实验研究的发展与现状,评述了非合作无源探测技术的研究热点与关键技术,包括辐射源信号分析与选择,参考信号提纯,干扰抑制及目标检测、定位与跟踪等。最后对非合作无源探测技术的发展趋势进行了展望。