Vicente Micó

Synthetic aperture superresolution with multiple off-axis holograms

An optical setup to achieve superresolution in microscopy using holographic recording is presented. The technique is based on off-axis illumination of the object and a simple optical image processing stage after the imaging system for the interferometric recording process. The superresolution effect can be obtained either in one step by combining a spatial multiplexing process and an incoherent addition of different holograms or it can be implemented sequentially. Each hologram holds the information of each different frequency bandpass of the object spectrum. We have optically implemented the approach for a low-numerical-aperture commercial microscope objective. The system is simple and robust because the holographic interferometric recording setup is done after the imaging lens.

Superresolution digital holographic microscopy for three-dimensional samples

An approach that allows superresolution imaging of three-dimensional (3-D) samples by numerical refocusing is presented in the field of digital holographic microscopy. Based on the objects spectrum shift produced by tilted illumination, we present a time multiplexing superresolved approach to overcome the Abbes diffraction limit. The proposed approach uses a microscope in a Mach-Zehnder interferometric architecture with the particularity that the output plane does not coincide with the image plane. Thus, a set of off-axis non-image plane holograms are sequentially recorded for every tilted beam used in the illumination stage. After that and by using simple digital post-processing and numerical reconstruction, a 3-D superresolved sample volume is reconstructed slice-by- slice in terms of the definition of a synthetic aperture (SA) that expands the cutoff frequency of the microscope lens. Experimental results showing the capabilities of the proposed approach are presented.

Superresolved imaging in digital holography by superposition of tilted wavefronts

A technique based on superresolution by digital holographic microscopic imaging is presented. We used a two dimensional (2-D) vertical-cavity self-emitting laser (VCSEL) array as spherical-wave illumination sources. The method is defined in terms of an incoherent superposition of tilted wavefronts. The tilted spherical wave originating from the 2-D VCSEL elements illuminates the target in transmission mode to obtain a hologram in a Mach-Zehnder interferometer configuration. Superresolved images of the input object above the common lens diffraction limit are generated by sequential recording of the individual holograms and numerical reconstruction of the image with the extended spatial frequency range. We have experimentally tested the approach for a microscope objective with an exact 2-D reconstruction image of the input object. The proposed approach has implementation advantages for applications in biological imaging or the microelectronic industry in which structured targets are being inspected.

Superresolution optical system by common-path interferometry

We present a new approach to obtain superresolved images in digital holography by means of synthetic aperture generation using common-path interferometry and off-axis illumination in optical imaging systems. The paper includes two parts. First, we present a simple approach to double the resolution of an optical system using tilted illumination onto the object and an optical element in the image plane to produce the holographic recording. Then we present a novel approach consisting of attaching a diffraction grating in parallel together with the object in the input plane and using off-axis illumination provided by a Vertical Cavity Surface Emitting Lasers (VCSEL) array to allow us achieving a major improvement in the optical resolution limit with an extremely low penalty in the complexity of the resulting system. Experimental investigation based on commercial microscope objectives is presented.

Simultaneous remote extraction of multiple speech sources and heart beats from secondary speckles pattern

The ability of dynamic extraction of remote sounds is very appealing. In this manuscript we propose an optical approach allowing the extraction and the separation of remote sound sources. The approach is very modular and it does not apply any constraints regarding the relative position of the sound sources and the detection device. The optical setup doing the detection is very simple and versatile. The principle is to observe the movement of the secondary speckle patterns that are generated on top of the target when it is illuminated by a spot of laser beam. Proper adaption of the imaging optics allows following the temporal trajectories of those speckles and extracting the sound signals out of the processed trajectory. Various sound sources are imaged in different spatial pixels and thus blind source separation becomes a very simple task.

Single-step superresolution by interferometric imaging.

The use of vertical-cavity surface-emitting laser (VCSEL) arrays for implementation of incoherent source superresolution is presented. The method uses an interferometer setup to obtain superresolution in a single step. The novelty of the method relies on the use of a VCSEL array as the light source, which provides a set of coherent sources which are mutually incoherent. The technique accomplishes the transmission of several spatial frequency bands of the objects spectrum in parallel by use of spatial multiplexing that occurs because of the tilted illumination of the source array. The recording process is done by interference of each frequency band with a complementary set of reference plane waves. After the reconstruction process, the resolution of any optical system can approach the natural lambda/2 limit. The benefit of our system is improved modulation speed and hence more rapid image synthesis. Moreover, any desired synthetic coherent transfer function can be realized at ultrafast rates if we simply change the electrical drive of the VCSEL array.

Synthetic aperture superresolved microscopy in digital lensless Fourier holography by time and angular multiplexing of the object information

The resolving power of an imaging system in digital lensless Fourier holographic configuration is mainly limited by the numerical aperture of the experimental setup that is defined by both the restricted CCD size and the presence of a beam splitter cube in front of the CCD. We present a method capable of improving the resolution in such a system configuration based on synthetic aperture (SA) generation by using time-multiplexing tilted illumination onto the input object. Moreover, a priori knowledge about the imaged object allows customized SA shaping by the addition of elementary apertures only in the directions of interest. Experimental results are provided, showing agreement with theoretical predictions and demonstrating a resolution limit corresponding with a synthetic numerical aperture value of 0.45.

Phase-shifting Gabor holography

We present a modified Gabor-like setup able to recover the complex amplitude distribution of the object wavefront from a set of inline recorded holograms. The proposed configuration is characterized by the insertion of a condenser lens and a spatial light modulator (SLM) into the classical Gabor configuration. The phase shift is introduced by the SLM that modulates the central spot (dc term) in an intermediate plane, without an additional reference beam. Experimental results validate the proposed method and produce superior results to the Gabor method.

Improved noncontact optical sensor for detection of glucose concentration and indication of dehydration level

The ability to extract different bio-medical parameters from one single wristwatch device can be very applicable. The wearable device that is presented in this paper is based on two optical approaches. The first is the extraction and separation of remote vibration sources and the second is the rotation of linearly polarized light by certain materials exposed to magnetic fields. The technique is based on tracking of temporal changes of reflected secondary speckles produced in the wrist when being illuminated by a laser beam. Change in skins temporal vibration profile together with change in the magnetic medium that is generated by time varied glucose concentration caused these temporal changes. In this paper we present experimental tests which are the first step towards an in vivo noncontact device for detection of glucose concentration in blood. The paper also shows very preliminary results for qualitative capability for indication of dehydration.

Superresolution imaging method using phase-shifting digital lensless Fourier holography

A method which is useful for obtaining superresolved imaging in a digital lensless Fourier holographic configuration is presented. By placing a diffraction grating between the input object and the CCD recording device, additional high-order spatial-frequency content of the object spectrum is directed towards the CCD. Unlike other similar methods, the recovery of the different band pass images is performed by inserting a reference beam in on-axis mode and using phase-shifting method. This strategy provides advantages concerning the usage of the whole frequency plane as imaging plane. Thus, the method is no longer limited by the zero order term and the twin image. Finally, the whole process results in a synthetic aperture generation that expands up the system cutoff frequency and yields a superresolution effect. Experimental results validate our concepts for a resolution improvement factor of 3.