Biomedical subjects

Jeffrey A Davis

Publications and source records attributed to Jeffrey A Davis.

8 recordsLinked to original sources

PubMed2004

Programmable birefringent lenses with a liquid-crystal display.

We study the properties of a novel birefringent lens constructed by combination of a regular glass lens and a programmable diffractive lens addressed to a liquid-crystal display (LCD). The LCD affects only the vertical polarization state. Consequently the birefringent lens produces two images of an input object with different locations and magnifications for the two orthogonal polarization states. Using a properly oriented analyzer polarizer produces interference fringes. We then show how the imaging system acts as a common-path polarization interferometer for wave-front analysis of objects in the input plane. Finally, we subtract the two images to produce an edge-enhanced version of the input image. All these effects can be controlled because we can program lenses with different focal lengths onto the LCD.

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PubMed2004

Polarizing binary diffraction grating beam splitter.

We report a polarizing beam splitter that uses binary phase gratings written onto a liquid-crystal spatial light modulator. These gratings produce several linearly polarized diffracted orders and a zeroth-order beam whose polarization state can be completely controlled. Experimental results are shown.

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PubMed2004

Focusing properties of fractal zone plates: experimental implementation with a liquid-crystal display.

We report the first experimental results, to our knowledge, with fractal zone plates implemented in a liquid-crystal display. Our results largely agree with theory for the axial irradiance distribution of these lenses. The dependence of the shape and size of the focus points on critical design parameters is discussed. Additional unpredicted features are also described.

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PubMed2004

Optical processing with vortex-producing lenses.

We discuss two types of optical processing using vortex-producing angular phase plates. In the most common spatial-filtering operation, an input object is Fourier transformed (either by Fraunhofer diffraction or with a lens system). The Fourier transform is then multiplied by an angular phase pattern, and the product is again Fourier transformed. The output is a space-invariant, edge-enhanced version of the input object. Alternatively we can directly image the object using a lens multiplied by the angular phase. The space-variant image is severely distorted along the optical axis of the system. We encode the phase plates onto a liquid-crystal display and present experimental results on both systems.

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PubMed2003

Fractional Fourier transform optical system with programmable diffractive lenses.

We present experimental results for a fractional Fourier transform (FRFT) system implemented with programmable lenses written onto a liquid-crystal spatial light modulator (LCSLM). Because the focal length can be changed, different orders of the FRFT can be obtained without changing the optical setup. The LCSLM can very easily implement more complicated operations, including the realization of simultaneous orders of the FRFT and anamorphic transforms.

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PubMed2003

Encoding amplitude and phase information onto a binary phase-only spatial light modulator.

We report what to our knowledge is a new technique for encoding both amplitude and phase information onto a single binary-valued spatial light modulator. In our approach, we spatially modulate the diffraction efficiency of the filter. Light that is not diffracted into the first order is sent into the zero order, effectively allowing amplitude modulation of either the first-order or zero-order diffracted light. This technique has applications in both optical pattern recognition and image processing. Experimental results are included.

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PubMed2002

Selective edge enhancement of images with an acousto-optic light modulator.

We show experimental results for image processing using an acousto-optic light modulator (AOLM) where the image can be edge enhanced with respect to the input object. We can select which edges are enhanced and the degree to which they are enhanced by changing the amplitude of the acoustic wave of the AOLM. We relate this technique to the fractional Hilbert transform and the fractional derivative image-processing operations and discuss its application to phase-only input images.

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PubMed2002

Phasor analysis of eigenvectors generated in liquid-crystal displays.

We analyze optical systems for creating phase-only operation of a liquid-crystal display (LCD). We introduce a new formalism in which any input or output polarization state can be described in terms of a linear combination of the eigenvectors of the LCD. We use a phasor analysis to examine the linear combination of the eigenvectors and show how improved performance can be obtained with a new configuration. We experimentally compare the intensity and phase operation for two configurations with the same spatial light modulator and show the improved performance with the new configuration.

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