Jesús Lancis

Achromatic fourier transforming properties of a separated diffractive lens doublet: theory and experiment.

The strong chromatic distortion associated with diffractive optical elements is fully exploited to achieve an achromatic optical Fourier transformation under broadband point-source illumination by means of an air-spaced diffractive lens doublet. An analysis of the system is carried out by use of the Fresnel diffraction theory, and the residual secondary spectrum (both axial and transversal) is evaluated. We recognize that the proposed optical architecture allows us to tune the scale factor of the achromatic Fraunhofer diffraction pattern of the input by simply moving the diffracting screen along the optical axis of the system. The performance of our proposed optical setup is verified by several laboratory results.

Scale-tunable optical correlation with natural light

We describe two different scale-tunable optical correlators working under totally incoherent light. They behave as spatially incoherent wavelength-independent imaging systems with an achromatic point-spread function (PSF). In both cases it is possible to adapt the scale of the achromatic PSF, i.e., to modify the scaling factor of the PSF and preserve the chromatic compensation, by ones shifting the input along the optical axis. The remarkable properties of these systems allow us to carry out a scale-tunable color pattern-recognition experiment with natural light.

Multiple incoherent 2D optical correlator

Abstract A nonconventional setup, based on the Lau effect, is employed for implementing a lensless version of an incoherent object-space correlator of 2D signals with compact support. Experimental results are also shown.

White-light implementation of the Wigner-distribution function with an achromatic processor

A temporally incoherent optical processor that combines diffractive and refractive components is proposed for performing two different operations simultaneously: an achromatic image along an axis and an achromatic one-dimensional Fourier transformation along the orthogonal axis. These properties are properly employed to achieve the achromatic white-light display of the Wigner-distribution function associated with a one-dimensional real signal, with high redundancy and variable scale.

Structured illumination enables image transmission through scattering media

Precise control of light propagation through highly scattering media is a much desired goal with major technological implications. Since interaction of light with turbid media results in partial or complete depletion of ballistic photons, it is in principle impossible to transmit images through distances longer than the extinction length. In biomedical optics, scattering is the dominant light extinction process accounting almost exclusively for the limited imaging depth range. In addition, most scattering media of interest are dynamic in the sense that the scatter centers continuously change their positions with time. In our work, we employ single-pixel systems, which can overcome the fundamental limitations imposed by multiple scattering even in the dynamically varying case. A sequence of microstructured light patterns codified onto a programmable spatial light modulator are used to sample an object and measurements are captured with a single-pixel detector. Acquisition time is reduced by using compressive sensing techniques. The patterns are used as generalized measurement modes where the object information is expressed. Contrary to the techniques based on the transmission matrix, our approach does not require any a-priori calibration process. The presence of a scattering medium between the object and the detector scrambles the light and mixes the information from all the regions of the sample. However, the object information that can be retrieved from the generalized modes is not destroyed. Furthermore, by using these techniques we have been able to tackle the general problem of imaging objects completely embedded in a scattering medium.

Diffractive optics for spectral tuning of second harmonic and supercontinuum generated in nonlinear crystals

It is shown that diffractive lenses can tune the spectrum of femtosecond pulses after nonlinear optical processes. We focus on spectra of second-order pulses generated in birefringent crystals and supercontinuum in sapphire crystals. The tunability is achieved by changing the relative distance between the nonlinear crystal and the diffractive lens.

Diffractive optics for processing ultrashort light pulses

In this work we combine, in principle, two disjoint optical fields, diffractive optics and ultrashort light radiation. This combination allows us to manipulate in a very unconventional manner femtosecond pulses and, on the other hand, to implement a set of novel applications. In our case we have focused our attention on material processing and biophotonics applications.

High-contrast Lau fringes with white light

A novel optical set-up that allows a totally incoherent Lau effect is demonstrated. It is based on dispersion-compensated techniques that employ strong dispersive elements. In this way, three commercially available diffractive lenses and a refractive objective are used for achromatic Lau fringes production with spatial and temporally incoherent illumination.

Quantitative phase imaging by using a position sensitive detector

We present a phase imaging system using a novel non-interferometric approach. We overcome the limitations in spatial resolution, optical efficiency, and dynamic range that are found in Shack-Hartmann sensors. To do so, we sample the wavefront using a digital micromirror device. A single lens forms a time-dependent light distribution on its focal plane, where a position detector is placed. Our approach is lenslet-free and does not use any kind of iterative or unwrap algorithm to recover the phase information. The validity of our approach is demonstrated by performing both aberration sensing and phase imaging of transparent samples.

Vision through turbid media by Fourier filtering and single-pixel detection

We present a novel approach for imaging through turbid media that combines the principles of Fourier spatial filtering with single-pixel imaging. We compare the performance of our single-pixel imaging setup with that of a conventional system. We conclude that the introduction of Fourier gating improves the contrast of images in both cases. Furthermore, we show that single-pixel imaging fits better than conventional imaging in vision through turbid media by Fourier filtering.