Depth of focus increase by multiplexing programmable diffractive lenses.

A combination of several diffractive lenses written onto a single programmable liquid crystal display (LCD) is proposed for increasing the Depth of Focus (DOF) of the imaging system as a whole. The lenses are spatially multiplexed in a random scheme onto the LCD. The axial irradiance distribution produced by each lens overlaps with the next one producing an extended focal depth. To compare the image quality of the multiplexed lenses, the Modulation Transfer Function (MTF) is calculated. Finally we obtain the experimental Point Spread Functions (PSF) for these multiplexed lenses and experimental results in which an extended object is illuminated under spatially incoherent monochromatic light. We compare the images obtained in the focal plane and in some defocused planes with the single lens and with three multiplexed lenses. The experimental results confirm that the multiplexed lenses produce a high increase in the depth of focus.

Amplitude Apodizers Encoded onto Fresnel Lenses Implemented on a Phase-Only Spatial Light Modulator.

We show that both a lens and a nonuniform amplitude transmission filter can be encoded simultaneously onto a twisted nematic liquid-crystal spatial light modulator (SLM) working in the phase-only mode. The inherent equivalent apodization that is due to the pixelated structure of the SLM is compensated for. In addition, different types of nonuniform transmission pupil such as transverse apodizing, transverse hyperresolving, and axial hyperresolving (multifocusing) filters are implemented. The excellent agreement between numerical and experimental results shows the capability of this method to encode amplitude apodizers on a phase-only SLM.

Inherent apodization of lenses encoded on liquid-crystal spatial light modulators.

Focusing diffractive optical elements encoded in liquid-crystal spatial light modulators yields an inherent equivalent apodization of the focused spot as a result of the pixelated nature of these devices and the finite extent of each pixel. We present a theoretical explanation for and experimental evidence of this effect. We demonstrate an experimental procedure for measuring the apodization and a method to compensate for this effect.

Programmable axial apodizing and hyperresolving amplitude filters with a liquid-crystal spatial light modulator.

Amplitude-transmitting filters for apodizing and hyperresolving applications can be easily implemented by use of a two-dimensional programmable liquid-crystal spatial light modulator operating in a transmission-only mode. Experimental results are in excellent agreement with theoretical predictions. This approach can permit the analysis of various filter designs and can allow the filters to be changed rapidly to modify the response of an optical system.

Control of the polychromatic response of an optical system through the use of annular color filters.

The use of annular color filters as a tool to modify the polychromatic response of an optical system is investigated. The introduction of filters with transmission that depends on the wavelength produces a significant modification of the chromaticity response. In contrast, the position in the pupil of the annuli in which the color filters are placed modifies mainly the illuminance response. The influence of different types of annular color filter on the transverse and axial responses of the aberration-free system is studied.

Polychromatic axial behavior of axial apodizing and hyperresolving filters.

The polychromatic behavior in defocused planes produced by different types of axial apodizing and hyperresolvingfilter is studied. The image quality is determined by comparing the illuminance and chromaticity distributions of the aberration free system with different filters and without a filter. The comparison is done in equivalent planes according to the normalized illuminance.