Spatial filter for increasing the depth of focus

Ojeda‐Castañeda, J.; Berriel‐Valdos, L. R.; Montes, Emma L.

doi:10.1364/ol.10.000520

Cited by 61 publications

(23 citation statements)

References 10 publications

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“…Annular pupils produce an increase both of the DOF and the resolution [5][6][7] at the expense of an increase in sidelobes and loss of light. Non-uniform transmission filters have been also proposed to increase DOF [8][9][10][11], also with polychromatic illumination [12]. In that line, a zone plate with a prespecified number of foci [13], which are separated axially by Rayleigh's limit of resolution was proposed to create arbitrarily high DOF.…”

Section: Introductionmentioning

confidence: 99%

Depth of focus increase by multiplexing programmable diffractive lenses

Iemmi¹,

Campos²,

Escalera³

et al. 2006

Opt. Express

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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. References and links 1.H. Fukuda, "A new pupil filter for annular illumination in optical lithography," Jpn. J. Appl. Phys. 31, 4126-4130 (1992). 2.R. Hild, M. J. Yzuel and J. C. Escalera, "High focal depth imaging of small structures," Microelectron. Eng. 34, 195-214 (1997). 3.G. G. Yang, "An optical pickup using a diffractive optical element for a high-density optical disc," Opt. Commun. 159, 19-22 (1999). 4.H. Wang and F. Gan, "High focal depth with a pure-phase apodizer," Appl. Opt. 40, 5658-5662 (2001). 5.W. T Welford, "Use of annular aperture to increase focal depth," J. Opt. Soc. Am. A 50, 749-753 (1960). 6. Z. S Hegedus, "Annular pupil arrays. Application to confocal scanning," Opt. Acta. 32, 815-826 (1985). 7.J. C. Escalera, M. J. Yzuel and J. Campos, "Control of the polychromatic response of an optical system through the use of annular color filters," Appl. Opt. 34, 1655-1663 (1995).

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Section: Introductionmentioning

confidence: 99%

Depth of focus increase by multiplexing programmable diffractive lenses

Iemmi¹,

Campos²,

Escalera³

et al. 2006

Opt. Express

View full text Add to dashboard Cite

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“…The reason is that a small focal spot is usually implemented by reducing the wavelength of the laser or by increasing the numerical aperture NA ͑here defined as NAϭr 0 / f 0 , where r 0 is the radius of the optical aperture of the optical system, and f 0 is the focal length͒, which decreases the DOF rapidly because DOF ϭ/(NA) 2 . In order to solve this problem, several techniques for achieving large DOF in optical storage systems have been reported, including use of some specially designed apodizers, [1][2][3] image-processing methods, 4,5 and quasi-bifocus birefringent lens methods. 6 Unfortunately, these specially designed apodizers have complicated phase and amplitude transmissivity dependences, which make their fabrication difficult.…”

Section: Introductionmentioning

confidence: 99%

Tunable focal depth of an apodized focusing optical system

et al. 2005

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Abstract. The axial intensity distribution and focal depth of an apodized focusing optical system are theoretically investigated with two kinds of incident light fields: a uniform-intensity-distribution beam and a Gaussian beam. Both a low-numerical-aperture and a high-numerical-aperture optical system are considered. Numerical results show that the depth of focus can be adjusted by changing the geometrical parameters and transmissivity of the apodizer in the focusing optical system. When a Gaussian beam is employed as the incident beam, the waist width also affects the depth of focus. The tunable range of the focal depth is very considerable.

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“…The purpose of the apodization process is to produce the suppression of the secondary maxima, or side lobes, of a di raction pattern in order to enhance the resolving power of the optical system. It is a classical problem and it has been widely studied [1,2]. In the apodization method proposed by Cheng and Siu [3], the aperture is modi®ed in an asymmetric mode.…”

Section: Introductionmentioning

confidence: 99%

Short Communication Analysis of the asymmetric apodization using the fractional Fourier transform

Granieri¹,

Zalvidea²,

Sicre³

1999

Journal of Modern Optics

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Abstract.The e ect of asymmetric apodization is analysed using the fractional Fourier transform. The focusing properties of an apodizing pupil mask are investigated by means of a simple display in a generalized phase-space (or x±p domain). Some comparative computer simulations are performed and curves displaying the Strehl ratio versus defocus are presented in order to illustrate the possibilities of our approach. IntroductionSeveral e orts to improve the quality of the point spread function (PSF) of an optical imaging system have been done by using apodizer apertures. The purpose of the apodization process is to produce the suppression of the secondary maxima, or side lobes, of a di raction pattern in order to enhance the resolving power of the optical system. It is a classical problem and it has been widely studied [1,2]. In the apodization method proposed by Cheng and Siu [3], the aperture is modi®ed in an asymmetric mode. This asymmetric aperture function produces the suppression of the secondary maxima at a side of the central peak of the di raction pattern at the cost of increasing the lobes at the opposite side [4].The fractional Fourier transform (FRT) was introduced in optical signal processing by Ozaktas and Mendlovic [5] and Lohmann [6]. Two di erent optical de®nitions of the FRT have been given. In the ®rst, the FRT was de®ned based on light propagation in quadratic graded index media. In the second de®nition, the FRT of fractional order p results from a phase-space rotation of the input Wigner distribution function by an angle of pº=2. The FRT is a generalization of the classical Fourier transform and the information content stored in the FRT changes from spatial to spectral as the fractional order varies from pˆ0 to pˆ1. The relation between a FRT of order p and the free-space di raction [7,8] allows the analysis of the tolerance of optical imaging systems to focus errors and/or aberrations. There are several criteria to analyse the performance of an optical imaging system based on the on-axis irradiance. The Strehl ratio (SR), de®ned as the intensity values on axis at the di raction focus conveniently normalized, is an important image quality parameter [9]. The purpose of this letter is to analyse the

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Spatial filter for increasing the depth of focus

Abstract: The Strehl ratio, in the form of McCutchen's theorem, is employed to design a spatial filter that increases the depth of focus. Computer-simulated images show the increment in focal depth.

Cited by 61 publications

References 10 publications

Depth of focus increase by multiplexing programmable diffractive lenses

Depth of focus increase by multiplexing programmable diffractive lenses

Tunable focal depth of an apodized focusing optical system

Short Communication Analysis of the asymmetric apodization using the fractional Fourier transform

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