Imaging and delivering of light in a controlled manner through complex media such as glass diffusers, biological tissue, or multimode optical fibers, is limited by the scattering of light when it propagates through the material. Different methods based on spatial light modulators can be used to prior shaping the light beam to compensate for the scattering, this including phase conjugation, hall-climbing algorithms, or the so-called transmission matrix approach. Here, we develop a machine-learning approach for light delivery through complex media. Using pairs of binary intensity patterns and intensity measurements we train artificial neural networks (ANNs) to provide the wavefront corrections necessary to shape the beam after the scatterer. Additionally, we show that ANNs pave the way towards finding a functional relationship between reflected and transmitted light through the scatterer that can be used for light delivery in transmission by using reflected light. We expect that our approach showing the versatility of ANNs for light shaping will open new doors towards efficiently and flexibly correcting for scattering, in particular by only using reflected light.
Gathering information of objects hidden from the field of view is an extremely relevant problem in many areas of science and technology. Some state-of-the-art techniques are able to detect and image an object behind an obstacle at the cost of high computational and processing times. Alternatively, other methods can track the object in real-time without giving information on the objects shape. Here we make use of a non-scanning ultrashort pulsed light source, a Single-Photon Avalanche Diode (SPAD), and artificial neural networks (ANNs) to demonstrate a system that can detect, identify, and track objects hidden from view. SPAD technology, characterised by a temporal resolution of 100 ps, provides us with the time traces of the light back-scattered by the environment (including the hidden object). By using different known objects placed at different known positions, we generate a library of time traces that are used to train the ANN algorithm. The application of the trained ANN algorithm in an experimental scenario allow us to identify unknown objects hidden from view in real time with cm resolution. These results open new routes for exciting novel machine learning applications with high impact in the fields of machine vision, self-driving cars, and defence.
This paper is devoted to investigating the application of different dynamic light structures generated by a self-calibrated Liquid Crystal on Silicon (LCoS) display for microparticle manipulation. Two major studies based on implementing different DOEs, to thoroughly characterize the LCoS display and to achieve optical-inspired particle manipulation, are proposed, respectively. On the one hand, we dynamically introduced two diffractive lens based patterns (the Billet-lens configuration and the micro-lens array pattern) on the LCoS display, from which the self-calibration of the studied device is implemented. In this case, both the phase-voltage relation and the surface profile were determined and optimized to the optimal performance for microparticle manipulation. On the other hand, we performed the optical manipulation of microparticles by addressing configurable three-dimensional light structures obtained from different phase driven split-lens configurations initiated by the same but optimized LCoS display. Experimental results demonstrated that, by addressing certain phase distributions on the LCoS display, the microparticle can be trapped in the light cones and manipulated by providing certain continuous split-lens configurations.
High-order harmonic generation (HHG) has been recently proven to produce harmonic vortices carrying orbital angular momentum (OAM) in the extreme-ultraviolet (XUV) region from the nonlinear up-conversion of infrared vortex beams. In this work we present two methods to control and extend the OAM content of the harmonic vortices. First, we show that when a driver combination of different vortex modes is used, HHG leads to the production of harmonic vortices with a broad OAM content due to its nonperturbative nature. Second, we show that harmonic vortices with two discrete OAM contributions –so called fractional OAM modes– are generated when HHG is driven by conical refraction beams. Our work offers the possibility of generating tunable OAM beams in the XUV regime, potentially extensible to the soft x rays, overcoming the state of the art limitations for the generation of OAM beams far from the visible domain.
We propose two different in-line optical schemes for the implementation of Biaxial Crystal (BC) based polarimeters. Unlike already existing BC polarimeters prototypes, our proposed architectures only require of a single BC and only one CCD camera, this leading to more feasible and cheaper prototypes. The first scheme is restricted to linear metrology and we provide its interest to be applied under low-intensity conditions. The second architecture is suitable for complete polarimetry, this being achieved by including an optical module to properly split and steer the input light. The BC polarimeters were implemented and tested by measuring different known input polarizations and we obtained excellent results in terms of accuracy and repeatability.
Laser beams with cone-refracted output from the plane mirror is demonstrated for the first time in lasers based on intracavity conical refraction (CR) phenomenon. Transverse profile of such lasers comprises a crescent ring of CR-like distribution, where any opposite points are of orthogonal linear polarizations. We confirm the existence of such mode of CR lasers by two observations. First, cascaded CR in reflection geometry has been demonstrated for first time and it provides experimental prove that a light beam passed along optic axis of a biaxial crystal, reflected back from a plane mirror and passed again through the crystal is restored. Second, CR cavity mode with CR-like pattern through the plane mirror is experimentally and theoretically demonstrated for the first time.
Conical refraction (CR) is proposed to increase the channel capacity for free space optical communication applications.
We present the first investigations of cascaded CR with a linearly polarized input beam and experimentally prove that
two oppositely oriented consecutive identical biaxial crystals perform a forward-backward transformation of the incident
light beam. This forward-backward transformation is reported for different input beams with Gaussian, elliptical and
angularly modulated transverse intensity profiles and is the basis for our novel proposal on multiplexing and
demultiplexing of optical beams. We present experimental proof of usefulness and perspective of the CR multiplexing
technique by increasing in one order of magnitude the channel capacity at optical frequencies. The technique is
applicable to any wavelength in optical and telecommunication bands. It can be also properly upgraded with the WDM