Encoding of arbitrary micrometric complex illumination patterns with reduced speckle

In nonlinear microscopy, phase-only spatial light modulators (SLMs) allow achieving simultaneous two-photon excitation and fluorescence emission from specific regionof-interests (ROIs). However, as iterative Fourier transform algorithms (IFTAs) can only approximate the illumination of selected ROIs, both image formation and/or signal acquisition can be largely affected by the spatial irregularities of the illumination patterns and the speckle noise. To overcome these limitations, we propose an alternative complex illumination method (CIM) able to generate simultaneous excitation of large-area ROIs with full control over the amplitude and phase of light and reduced speckle. As a proof-of-concept we experimentally demonstrate single-photon and second harmonic generation (SHG) with structured illumination over large-area ROIs

Lossless equalization of frequency combs

Frequency combs obtained by sinusoidal phase modulation of narrow-band continuous-wave lasers are widely used in the field of optical communications. However, the resulting spectral envelope of the comb is not at. In this Letter, we propose a general and eficient approach to achieve at frequency combs with tunable bandwidth. The idea is based on a two-step process. First, eficient generation of a train with temporal at-top-pulse profile is required. Second, we use large parabolic phase modulation in every train period in order to map the temporal intensity shape into the spectral domain. In this way, the resulting spectral envelope is at and the size is tunable with the chirping rate. Two diferent schemes are proposed and verified through numerical simulations

Use of principal states of polarization of a liquid crystal device to achieve a dynamical modulation of broadband beams

A spatially resolved polarization switcher operating over a bandwidth of 200 nm is demonstrated. The system is based on liquid crystal technology and no specific-purpose birefringent element is required. The procedure is founded on the polarization mode dispersion theory of optical fibers, which provides a convenient framework for the design of broadband polarization systems. Our device benefits from the high resolution of off-the-shelf twisted nematic liquid crystal displays and is well suited for spatial modulation of the intensity of broadband beams, such as those coming from few-cycle femtosecond laser

Encoding complex fields by using a phase-only optical element

We show that the amplitude and phase information from a two-dimensional complex field can be synthesized from a phase-only optical element with micrometric resolution. The principle of the method is based on the combination of two spatially sampled phase elements by using a low-pass filter at the Fourier plane of a 4 - f optical system. The proposed encoding technique was theoretically demonstrated, as well as experimentally validated with the help of a phase-only spatial light modulator for phase encoding, a conventional CMOS camera to measure the amplitude of the complex field, and a Shack-Hartmann wavefront sensor to determine its phase.This work was funded by the Generalitat Valenciana through the programme (PROMETEO/2012/021), and by University Jaume I through the project P1·1B2013-53. The authors are also very grateful to the SCIC of the Universitat Jaume I for the use of the femtosecond laser

Single-pixel imaging of the retina through scattering media

Imaging the retina of cataractous patients is useful to detect pathologies before the cataract surgery is performed. However, for conventional ophthalmoscopes, opacifications convert the lens into a scattering medium that may greatly deteriorate the retinal image. In this paper we show, as a proof of concept, that it is possible to surpass the limitations imposed by scattering applying to both, a model and a healthy eye, a newly developed ophthalmoscope based on single-pixel imaging. To this end, an instrument was built that incorporates two imaging modalities: conventional flood illumination and single-pixel based. Images of the retina were acquired firstly in an artificial eye and later in healthy living eyes with different elements which replicate the scattering produced by cataractous lenses. Comparison between both types of imaging modalities shows that, under high levels of scattering, the single-pixel ophthalmoscope outperforms standard imaging methods

Centroid propagation through optical systems with ABCD kernels and nonuniform or finite apertures

If the propagation of a light field can be satisfactorily described by a diffraction integral with an ABCD kernel, the propagation of its irradiance centroid is completely determined by the corresponding ABCD ray-transfer matrix in exactly the same way as if the centroid path were a conventional geometrical ray. However, potentially significant deviations from this geometrical propagation rule may arise in the presence of finite or nonuniform apertures truncating or otherwise modifying the input beam irradiance distributionThis work has been supported by the Spanish Ministerio de Ciencia e Innovación (MICINN), grants FIS2008-03884 and FIS2010-1574

Diffractive digital lensless holographic microscopy with fine spectral tuning

We experimentally demonstrate an all-diffractive optical setup for digital lensless holographic microscopy with easy wavelength line selection and micrometric resolution. In the proposed system, an ultrashort laser pulse is focused with a diffractive lens (DL) onto a pinhole of diameter close to its central wavelength to achieve a highly spatially coherent illumination cone as well as a spectral line with narrow width. To scan the complete spectrum of the light source the DL is displaced with respect to the pinhole plane. The proposed microscopy setup allows us to spectrally separate contributions from different sections of a sample, which may be attractive for several applications in life sciences

Coherence revivals in two-photon frequency combs

We describe and theoretically analyze the self-imaging Talbot effect of entangled photon pairs in the time domain. Rich phenomena are observed in coherence propagation along dispersive media of mode-locked two- photon states with frequency entanglement exhibiting a comblike correlation function. Our results can be used to remotely transfer frequency standards through optical fiber networks with two-photon light, avoiding the requirement of dispersion compensation

Electromagnetic arbitrary waveform generation with broadband incoherent light sources

Optical engineering: new waveform generation provides the experimentalist with interesting new tool

Reconfigurable RF-Waveform Generation Based on Incoherent-Filter Design

Radio-frequency (RF) waveform generators are key devices for a variety of applications, including radar, ultra-wideband communications, and electronic test measurements. Following advances in broadband coherent pulsed sources and pulse-shaping technologies, reconfigurable RF waveform generators operating at bandwidths 1 GHz have become a reality. In this work, we demonstrate reconfigurable RF waveform generation using broadband spectrally incoherent optical sources. This is achieved in two steps. First, we implement an RF incoherent filter. The energy spectrum of the optical source is conveniently apodized using a commercially available computer-controlled D-WDM channel selector with 100-GHz resolution. The channel controller provides high flexibility for shaping the optical source energy spectrum and, hence, high reconfigurability capabilities in terms of the RF filter. Second, we show that by applying a short baseband electrical waveform to the input of the RF filter, the output RF spectrum of the electrical signal is a mapped version of the designed RF filter transfer function. Specifically, we illustrate the capabilities of our technique by generating RF signals with 10 GHz bandwidth and tunable repetition rate. Finally, we discuss how this method can be scaled up to the millimeter-wave range with current technolog