Complex Light Fields Research Articles

边缘复杂光场图像的深度估计散焦响应函数优化

边缘复杂光场图像的深度估计散焦响应函数优化

Deep Recurrent Network for Fast and Full-Resolution Light Field Deblurring

Restoring a sharp light field image from its blurry input has become essential due to the increasing popularity of parallax-based image processing. State-of-the-art blind light field deblurring methods suffer from several issues such as slow processing, reduced spatial size, and a limited motion blur model. In this work, we address these challenging problems by generating a complex blurry light field dataset and proposing a learning-based deblurring approach. In particular, we model the full 6-degree of freedom (6-DOF) light field camera motion, which is used to create the blurry dataset using a combination of real light fields captured with a Lytro Illum camera, and synthetic light field renderings of 3D scenes. Furthermore, we propose a light field deblurring network that is built with the capability of large receptive fields. We also introduce a simple strategy of angular sampling to train on the large-scale blurry light field effectively. We evaluate our method through both quantitative and qualitative measurements and demonstrate superior performance compared to the state-of-the-art method with a massive speedup in execution time. Our method is about 16K times faster than Srinivasan et. al. [22] and can deblur a full-resolution light field in less than 2 seconds.

Creating and controlling complex light

Random light fields—commonly known as speckles—demonstrate Rayleigh intensity statistics and only possess local correlations which occur within the individual speckle grains. In this work, we develop an experimental method for customizing the intensity probability density function (PDF) of speckle patterns while simultaneously introducing nonlocal spatial correlations among the speckle grains. The various families of tailored speckle patterns—created by our method—can exhibit radically different topologies, statistics, and variable degrees of spatial order. Irrespective of their distinct statistical properties, however, all of these speckles are created by appropriately encoding high-order correlations into the phase front of a monochromatic laser beam with a spatial light modulator. In addition to our experimental demonstration, we explore both the theoretical and practical limitations on the extent to which the intensity PDF and the spatial intensity correlations can be manipulated concurrently in a speckle pattern. This work provides a versatile methodology for creating complex light fields and controlling their statistical properties with varied applications in microscopy, imaging, and optical manipulation.

Observation of diffractive-correction and spin-orbit interaction induced effects around the Brewster angle

We report the observation of splitting, rotation and spiraling behavior in the polarization components of the Laguerre–Gaussian beam, reflected around the Brewster angle for a TM-polarized input beam. The measurements carried out using Stokes parameters in addition show that the strength and behavior of the above-mentioned effects depend on the order of the Laguerre–Gaussian beam. These polarization effects appear to be a manifestation of the collaborative behavior of the diffraction-corrective longitudinal Goos–Hänchen and spin-orbit interaction induced transverse spin-Hall shifts, wherein the coupling between these shifts play a critical role. Except for the polarization splitting, other observed effects are absent for a TE polarized input beam. These studies are useful to understand the topological aspect of complex light field in various applications, including optical manipulation, wherein the source optical angular momentum has been point of discussion. Additionally, they can be used as a promising tool in the identification of the thickness of thin layer and optical sensing.

Multiple foci modulation with controllable positions and intensity ratios through decomposed optimization

In this Letter, multiple foci modulation with controllable positions and intensity ratios is presented with a multi-belt binary phase mask in a tightly focusing system. Different from previous methods, the diffractive optical element (DOE) in our model is first virtually decomposed into two or more simple sub-DOEs. Then, after optimization, the sub-DOEs are combined to form the desired DOE through superposition. By such a decomposed optimization, the optimization complexities are greatly reduced, and the calculation becomes simpler and more effective. Furthermore, since the quantities and structures of sub-DOEs can be adjusted according to the original DOE, the method is very flexible and adaptable. As a demonstration, up to nine foci on the optical axis are studied, and the simulation results show that multiple foci can be well modulated. The proposed method may provide a universal strategy for complex light field modulations in a simple way.

Under-Sampled Phase Retrieval of Single Interference Fringe Based on Hilbert Transform

Phase retrieval from single interference fringe is important and effective method in obtaining the real phase distribution. The original phase can be retrieved by the line integral of its gradient expressed as sine and cosine components, which were gained by the Hilbert transform twice from a single interference fringe pattern. However, this method fails when the phase transformation of the interference fringe is too fast. In this paper, a novel method to recover the continuous phase of the whole field is proposed to solve the above problems. The shear interference technique is introduced into the phase retrieval method to build an exponential 2-D complex light field of natural base for the phase slope obtained by the Hilbert transform. Then, the expressions of phase slopes in x- and y-directions are constructed as a discrete Poisson equation. Therefore, the calculation of phase retrieval is equivalent to solve the discrete Poisson equation mathematically. Finally, the real phase is gotten by the weighted discrete cosine transform (WDCT) of the discrete Poisson equation. The simulation results verify the validity of this method and show that the proposed method can achieve the phase retrieval of the phase discontinuity in x- and y-directions, which leads to the under-sampled problem. It can restore the whole field phase distribution rapidly and accurately. Moreover, this method is applied to phase retrieval of interferometric synthetic aperture radar (InSAR) with the under-sampled problem in this paper. The experimental results show that this method can recover the phase of InSAR with the under-sampled problems caused by terrain abrupt change and so on. Compared with other commonly used methods, it achieved satisfactory results. This method provides a new idea for solving the under-sampled problem in the phase retrieval from a single-frame interference fringe.

Complete polarization and phase control with a single spatial light modulator for the generation of complex light fields

We present an optical system for the formation of arbitrary spatial polarization and phase patterns with a single spatial light modulator (SLM). Any such complex light beam can be generated by using three interactions with a computer controlled SLM. We achieved this by bouncing the beam three times in different areas on the SLM surface, and the cumulative interactions provide for any desired polarization and phase state imprinted on the output beam. The system can deliver high output power, since the only light loss arises from imperfect optical elements.

On-chip switchable radially and azimuthally polarized vortex beam generation.

Cylindrical vector vortex (CVV) beams, complex light fields that exhibit a vector nature and carry quantized orbital angular momentum (OAM) states, have been widely investigated due to their rich applications. Current technologies to generate CVV beams using individual polarization and spatial phase manipulations suffer from bulky size and low configurability. In this Letter, we propose and experimentally demonstrate an approach to generate CVV beams with a single integrated device based on a silicon nitride microring resonator and embedded top-gratings. The device allows the manipulation of both the polarization and OAM degrees of freedom of light, and enables the generation of both radially and azimuthally polarized CVV beams. In addition, we develop a method to fabricate the devices of shallow-etched top-gratings with only one-step etching. To the best of our knowledge, this novel method provides new capabilities to develop on-chip integrated devices with great ease and flexibility.

Generation of Radial Polarized Lorentz Beam with Single Layer Metasurface

AbstractA radially polarized Lorentz beam is demonstrated in the terahertz waveband with a single layer metasurface. Composed of cross antennas of various sizes and orientation, the metasurface performs simultaneously a continuous amplitude modulation and a controlled polarization spatial redistribution of incident waves of wavelength 400 µm. The metasurface device is designed and characterized using a terahertz time domain spectral imaging system. Experimental results are consistent with theoretical calculations. With the advantage of compactness and simplicity, this device may be applied to generate various complex light fields and in the reconstruction of computer‐generated polarization hologram.

The effect of stimulated Mandelstam–Brillouin scattering on angular divergence of a laser beam in the air

A quasi-steady-state approximation for the problem of stimulated Mandelstam–Brillouin scattering (SMBS) in the air as in a multimode acoustic medium is formulated. In this approximation, a numerical solution of the equation for the envelope of the complex light field amplitude is implemented. Based on a series of performed numerical experiments, it is established that the SMBS effect can lead to a discernible increase in the angular divergence of laser beams during the propagation of a sufficiently powerful laser radiation with a wavelength λ = 1.315 μm in air.

Dynamic modulation of Poincar\xe9 beams

Generation of complex Poincaré beams is enabled by amplitude and phase modulation accompanied by simultaneous spatially polarization structuring. A holographic system to tailor complex light fields and optical angular momentum structures forecasts promising applications in quantum communication and optical trapping. Experimental results are presented together with simulations of complex Poincaré beams embedding different types of polarization singularities. Additionally, parameters of the dynamic polarization modulation system are discussed and analyzed to demonstrate the enormous capability of the method.

Co-axis digital holography based on sinusoidal phase modulation using generalized lock-in detection.

Sinusoidal phase modulating (SPM) interferometers are used to precisely measure complex light fields with simple interferometric setups. Recently, a generalized lock-in technique has been proposed for optimizing the signal extraction in phase-modulated interferometers. This article shows its applicability in digital holography as well as digital holographic interferometry. A compact homemade setup based on the Michelson interferometer was used to observe the scattering sample surface with a spatial resolution of 32 LP/mm; out-of-plane rotation was measured with a theoretical detection limit of 0.004°. The comparison between the generalized lock-in detection and traditional SPM interferometer method was done theoretically and experimentally.

Resonant evanescent complex fields on dielectric multilayers.

Complex light fields, including evanescent Bessel beams, can be generated at dielectric interfaces by means of oil-immersion optics operating in total internal reflection conditions. Here we report on the observation of evanescent complex fields produced on a dielectric multilayer through the interference of surface modes resonantly sustained by the multilayer itself. The coupling to surface modes is attained by modifying the wavefront of an incident laser beam in such a way that the resulting intensity distribution in k-space matches the dispersion of the surface mode. The phase of surface modes can be further controlled, and two-dimensional vortex beams can also be produced according to the same working principle.

Iterative optimum frequency combination method for high efficiency phase imaging of absorptive objects based on phase transfer function.

In this work, an optimum frequency combination (OFC) method is proposed to reconstruct high quality phase information of the complex light field, which is really valuable for many objects such as optical elements and cells. It is shown that the difference image between two symmetrical separated, larger defocused planes contains a lot of lower frequency components of the phase distribution and the higher frequency components can be easily observed in the difference image between two nearly focused planes. Based on the phase transfer function (PTF), our method combines different frequency components with high Signal-to-Noise Ratio (SNR) together to estimate a more accurate frequency spectrum of the object's phase distribution without any complicated linear or nonlinear regression. Then, we can directly reconstruct a high-quality phase map through inverse Fourier transform. What's more, in order to compensate the phase discrepancy resulted from strong absorption in the intensity, an iterative compensation algorithm is proposed. Both the simulation and experimental results demonstrate that our iterative OFC (IOFC) method can give a computationally efficient and noise-robust phase reconstruction for absorptive phase objects with higher accuracy and fewer defocus planes.

Radially polarized cylindrical vector beams from a monolithic microchip laser

Monolithic microchip lasers consist of a thin slice of laser crystal where the cavity mirrors are deposited directly onto the end faces. While this property makes such lasers very compact and robust, it prohibits the use of intracavity laser beam shaping techniques to produce complex light fields. We overcome this limitation and demonstrate the selection of complex light fields in the form of vector-vortex beams directly from a monolithic microchip laser. We employ pump reshaping and a thermal gradient across the crystal surface to control both the intensity and polarization profile of the output mode. In particular, we show laser oscillation on a superposition of Laguerre–Gaussian modes of zero radial and nonzero azimuthal index in both the scalar and vector regimes. Such complex light fields created directly from the source could find applications in fiber injection, materials processing and in simulating quantum processes.

Position-Dependent Importance Sampling of Light Field Luminaires

The possibility to use real world light sources (aka luminaires) for synthesizing images greatly contributes to their physical realism. Among existing models, the ones based on light fields are attractive due to their ability to represent faithfully the near-field and due to their possibility of being directly acquired. In this paper, we introduce a dynamic sampling strategy for complex light field luminaires with the corresponding unbiased estimator. The sampling strategy is adapted, for each 3D scene position and each frame, by restricting the sampling domain dynamically and by balancing the number of samples between the different components of the representation. This is achieved efficiently by simple position-dependent affine transformations and restrictions of Cumulative Distributive Functions that ensure that every generated sample conveys energy and contributes to the final result. Therefore, our approach only requires a low number of samples to achieve almost converged results. We demonstrate the efficiency of our approach on modern hardware by introducing a GPU-based implementation. Combined with a fast shadow algorithm, our solution exhibits interactive frame rates for direct lighting for large measured luminaires.

The polarization properties of a tilted polarizer

Polarizers are key components in optical science and technology. Thus, understanding the action of a polarizer beyond oversimplifying approximations is crucial. In this work, we study the interaction of a polarizing interface with an obliquely incident wave experimentally. To this end, a set of Mueller matrices is acquired employing a novel procedure robust against experimental imperfections. We connect our observation to a geometric model, useful to predict the effect of polarizers on complex light fields.

Parallax Walls: Light fields from occlusion on height fields

We introduce a simple, inexpensively manufacturable, height field surface geometry that, when appropriately painted, can produce diffuse reflections under ambient lighting approximating a target light field. We demonstrate a light field basis analysis of these surfaces which allows us to formulate the problem as a gamut-mapping, and propose a perceptually motivated metric for bringing complex light fields into gamut while preserving their structure. We show resultant surfaces displaying physical light fields, animations, HDR exposure stacks, and scene relighting.

Measurement system for marine animal reflectance functions

Photonic structures in the skin of pelagic fishes and squids evolved specifically for hiding in the complex light field of the open ocean. To understand the principles under which these structures operate, a detailed characterization of their optical properties is required. An optical scatterometer has been developed to measure one important property, the bidirectional reflectance distribution function (BRDF). The instrument was used to collect reflectance functions from the squid Pterygioteuthis microlampas and fish Sternoptyx sp. Although the animals appear very different to a casual observer, the results reveal interesting similarities in their scattering patterns, suggesting a similar optical strategy for hiding in open water.

Supramolecular Chiral Structures: Smart Polymer Organization Guided by 2D Polarization Light Patterns

AbstractChiral periodic structures and photonic crystals have attracted a great deal of interest due to their applications in advanced photonics. As a consequence, the design and the fabrication of periodic microstructures in photosensitive materials have been widely investigated. Many achievements in the fabrication of such devices have been made over the last decade, but most of the established methods are still restricted to light intensity distribution with different structural shapes and minor attention has been devoted to exploit the vectorial nature of the light coupled with the response of polarization sensitive materials. Here, supramolecular chiral structuring in an amorphous azo‐polymer is demonstrated, coupling the strong and diversified photoresponse of the material with the holographic recording of 2D polarization patterns. The smart polymer organization guided by the complex light field induces periodic chiral microstructures, with spiral‐ or ribbon‐like shape and identical or opposite helicity, characterized by high stability and complete reconfigurability. The holographic structures are theoretically described by means of the Jones matrix method and experimentally investigated, confirming the simultaneous presence of both linear and circular photoinduced anisotropies. These results prove an alternative approach to design a new class of materials with periodic chiral arrangement.