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An investigation of extended depth-of-field camera with optimized phase mask and digital restoration is presented. The goal of this paper is to implement the wavefront coding technique without affecting much of the original design, and the design has taken the complexity of imaging system into consideration. The optimized strength of cubic phase mask (CPM) is based on the analytical optimal solution for the task-based imaging system [J. Opt. Soc. Am. A 25, 1064 (2008)]. The noisy intermediate images of CPM system with highest spatial frequency of interest can be effectively restored by vector-based Richardson-Lucy algorithm. Restoration from the system with generalized CPM produces precise image position than the system with CPM does. In general, the CPM system procures modulation transfer function higher than 0.195 in the whole depth-of-field, and the mean squared error of the restored images are less than 5 %.

Wide, nonperiodic stepped phase structures are studied to correct various parameter-dependent wave-front aberrations in optical systems. The wide nature of these phase structures makes them easy to manufacture with sufficient compensation of the wave-front aberrations. Wave-front aberration correction for both continuous and discrete parameter variations are studied. An analytical method is derived for the discrete parameter variations to find the optimal phase structure. Both theoretical and experimental results show that these nonperiodic phase structures can be used to make (1) lenses athermal (defocus and spherical aberration compensated), (2) lenses achromatic, (3) lenses with a large field of view, (4) lenses with a reduced field curvature, and (5) digital versatile disk objective lenses for optical recording that are compatible with compact disk readout. OCIS codes: 220.1000, 220.4830, 050.1940, 210.4770.

The domain integral equation method for anisotropic inhomogeneous dielectric waveguides is derived, and the spectral properties of the integral operator are discussed. It is explained why spurious modes do not occur when the Galerkin method is applied to the domain integral equation. Furthermore, the convergence of the method is discussed.

The sidewall angle (SWA) of a nanostructure exerts influence on the performance of the nanostructure and plays an important role in processing nano-structural chips. It is still a great challenge to determine steep SWAs from far field measurements especially when the SWAs are close to 90°. Here, we propose a far-field detection system to determine steep SWA of a cliff-shape step structure on a silicon substrate by combining a split detector with a scanning method. The far-field radiation field is asymmetric due to the scattering of the step structure, and further numerical analysis demonstrates the reliability of this far-field measurement method. In the simulations, two key variables, i.e. the polarization state and the focus position of the incident laser beam, are considered to explore their impacts. By scanning over the structure laterally and longitudinally with both TE and TM polarizations, polarization effects on the far-field occur. These effects show higher sensitivity to steep SWA variation for TM polarization as compared to TE. Furthermore, with a comprehensive longitudinal scanning analysis for the TM polarization case, a feasible focus interval can be optimized to retrieve the steep SWA. As the proposed method is fast, highly sensitive and easy to implement, it provides a powerful approach to investigate the scattering behavior of nanostructures. [ABSTRACT FROM AUTHOR]

A scalar readout model is presented to investigate the readout characteristics of the super resolution near field disc. The super resolution effect is described by means of a threshold model, where the super resolution material imparts a phase change on the focused spot if the laser density energy is high enough to trigger the SRens effect. This approach results in a very fast way of computing the basic characteristics of the SRens readout signal, being suitable for large investigations. Moreover, many simulation results have been experimentally confirmed by other groups, which further validates the model. Thus, this simplified model is an useful tool for a better comprehension of the readout signal of the super resolution effect in optical data storage and other super resolution applications.

Lateral resolution enhancement is demonstrated in a confocal imaging system with amplitude-modulated radially polarized (RP) light at the wavelength Annular pupil fields and optimized amplitude distribution functions can be realized with a spatial light modulator. By comparing images obtained with full and amplitude modulated apertures of RP illuminations using a high numerical aperture (NA = 0.9), spatial resolution of has been achieved experimentally. This result agrees very well with theoretical simulation results and will be helpful in improving performance of the non-fluorescent imaging systems. [ABSTRACT FROM AUTHOR]

In the theory of partial coherence, coherence singularities can occur in the spectral degree of coherence (SDOC): in case the fields at two different points are completely uncorrelated, the phase of the SDOC is undefined. For a partially coherent vortex beam, the detection of coherence singularities is linked to the measurement of topological charge, whose magnitude equals the number of ring dislocations in its far field amplitude. However, the phase distribution of coherence singularities is rarely mentioned in the literature and the amplitude distribution can hardly reflect the sign of topological charge. In this letter, we present a phase-analysis method for measuring the coherence singularities by introducing a movable perturbation at a certain point in an illumination window of a finite size. Using the proposed method, we measure experimentally the coherence singularities of a partially coherent vortex beam in the focal plane. From the results, the magnitude and sign of the topological charge can be determined simultaneously from the phase distribution of the coherence singularities. Our results can find application in information transmission. [ABSTRACT FROM AUTHOR]

Wavefront aberration measurements are required to test an extreme ultraviolet (EUV) imaging system. For a high-NA EUV imaging system, where conventional wavefront-sensing techniques show limitations, ptychography can be used for this purpose. However, at the wavelength region of EUV (i.e., 13.5 nm), the position accuracy of the scanning mask that is defined for ptychography is stringent. Therefore, we propose ptychography combined with mask position correction. The simulated intensity patterns, the ones we use, resemble expected EUV experimental data. Finally, we show the results in the presence of Poisson noise and the tolerance of the position correction method for error in mask positions. [ABSTRACT FROM AUTHOR]

A technique to create aspheric surface shapes on commercially available electrowetting liquid lenses is demonstrated. Based on a previously published surface oscillation model a technique using a Hankel transform is proposed and tested experimentally. An alternating actuation voltage is applied to the liquid lens to stimulate surface oscillations, that temporarily add up to the desired surface shape. The voltage signal can be repeated at video rate. The measurements were taken with a Mach-Zehnder interferometer and confirm the previous results. The capabilities and limitations of the proposed method are demonstrated using the examples of a Bessel surface, spherical aberration, an axicon, and a top hat structure. [ABSTRACT FROM AUTHOR]

The increased usage of liquid lenses motivates us to investigate surface waves on the liquid's surface. During fast focal switching, the surface waves decrease the imaging quality. We propose a model that describes the surface modes appearing on a liquid lens and predicts the resonance frequencies. The effects of those surface modes on a laser beam are simulated using Fresnel propagation, and the model is verified experimentally. [ABSTRACT FROM AUTHOR]

Protecting groups are commonly applied in multi-step molecular syntheses to protect one or multiple functional groups from reacting. After the reaction, they are removed from the molecule. In full analogy to this concept, we report the practical and scalable colloidal synthesis of Au semishells using polyphenylsiloxane protecting patches to prevent part of the surface of polystyrene nanoparticles from being covered with Au. After Au deposition, the patches are removed yielding Au semishells. We anticipate that this strategy can be extended to the synthesis of other types of non-centrosymmetric nanoparticles. [ABSTRACT FROM AUTHOR]

Degenerate two-photon absorption (TPA) is investigated in a 186 nm thick gallium arsenide (GaAs) p-i-n diode embedded in a resonant metallic nanostructure. The full device consists in the GaAs layer, a gold subwavelength grating on the illuminated side, and a gold mirror on the opposite side. For TM-polarized light, the structure exhibits a resonance close to 1.47Vector beams, which have space-variant state of polarization (SOP) comparing with scalar beams with spatially homogeneous SOP, are used to manipulate surface plasmon polarizations (SPPs). We find that the excitation, orientation, and distribution of the focused SPPs excited in a high numerical aperture microscopic configuration highly depend on the space-variant polarization of the incident vector beam. When it comes to vector beam with axial symmetry, multi-foci of SPPs with the same size and uniform intensity can be obtained, and the number of foci is depending on the polarization order n. Those properties can be of great value in biological sensor and plasmonic tweezers applications. [ABSTRACT FROM AUTHOR]

An instrument achieving 100 KHz spectral precision using multiple correlation Fourier transform spectroscopy has been demonstrated. The instrument can measure the individual frequency comb modes of 100 MHz frequency comb lasers in air. The experiments show ∼400,000 resolved modes at linewidths of 85 MHz in the region of 829 nm and ∼ 182,000 resolved modes at linewidths of 28 MHz in the region of 1.5 μm, with a recording time of few minutes. The precision of the instrument, defined by the frequency positioning, attains sub-MHz even when the scan is performed in air. [ABSTRACT FROM AUTHOR]

The longitudinal–differential (LD) phase distribution was investigated near the focus of a high numerical aperture (NA = 0.9) aplanatic lens illuminated with a linearly polarized monochromatic plane wave. The Richards and Wolf method was used to compute field distributions. The LD phase map was obtained by analyzing the deviation of the phase of the simulated wave to the phase of a referential plane wave. The irregular wavefront spacing that is linked to the Guoy phase is discussed and subtle details of the phase features with respect to the spatial domain relative to the focal point are disclosed. The LD phase is used to revisit different definitions of the focal region. The definition is eventually identified that is in agreement with the Gouy phase in the focal region. Our work paves the way towards a coherent notion to quantify the optical action of high NA optical elements that are increasingly important for many applications. [ABSTRACT FROM PUBLISHER]

It was predicted a few years ago that a medium with negative index of refraction would allow for perfect imaging. Although no material has been found so far that behaves as a perfect lens, some experiments confirmed the theoretical predictions in the near-field, or quasi-static, regime where the behaviour of a negative index medium can be mimicked by a thin layer of noble metal, such as silver. These results are normally attributed to the excitation of surface plasmons in the metal, which only leads to the restoration of p-polarized evanescent waves. In this work, we show that the restoration of s-polarized evanescent waves and, correspondingly, sub-wavelength imaging by a single dielectric slab are possible. Specifically, we show that at λ = 632 nm a thin layer of GaAs behaves as a superlens for s-polarized waves. Replacing the single-metal slab by a dielectric is not only convenient from a technical point of view, it being much easier to deposit and control the thickness and flatness of dielectric films than metal ones, but also invites us to re-think the connection between surface plasmon excitation and the theory of negative refraction. [ABSTRACT FROM AUTHOR]

We present an accurate and fast 3-D simulation scheme for out-of-plane grating couplers, based on 2-D rigorous [finite difference time domain (FDTD)] grating simulations, the effective index method, and the Rayleigh–Sommerfeld diffraction formula. In comparison with full 3-D FDTD simulations, the rms difference in electric field is below 5% and the difference in power flux is below 3%. A grating coupler for coupling from a silicon-on-insulator photonic integrated circuit to an optical fiber positioned 0.1 mm above the circuit is designed as an example. [ABSTRACT FROM PUBLISHER]

In previous work, we have introduced the Hamiltonian method which enables to calculate the ray paths of light rays in inhomogeneous anisotropic media in the geometrical-optics approach. With this method we are able to simulate the effect of optical anisotropy in three dimensions. In this manuscript, we simulate the optical properties of multiple liquid-crystal configurations. We demonstrate the resemblance between the optical properties of a gradient-index fiber and a liquid-crystal layer with a Freedericksz alignment. In addition, we investigate the optical properties of artificial liquid-crystal profiles induced by the electric field of a set of point charges. Altogether, we conclude that, in the geometrical-optics approach, we are able to assess the optical properties of any arbitrary anisotropic optical system. [ABSTRACT FROM AUTHOR]

The super resolution near-field effect has attracted the attention of many researchers since it offers a relatively simple way to overcome the diffraction limit of optical systems. Although the technique has been widely applied in optical data storage, it can be promptly used in other fields, once some problems are solved. There is an open question of what happens to the focused spot after passing through an activated super resolution layer. In addition, there is a need for a model that can accurately describe the super resolved spot. Hence, in this work, we analyze and discuss these issues, both numerically and experimentally. Coherent far-field scatterometry and near-field scanning microscopy techniques are employed to both monitor the phase transition of the sample and to measure the transmitted super-resolved spots; Rigorous electromagnetic simulations based on the finite element method are used to model the effect. A direct comparison between experiment and simulation is provided. [ABSTRACT FROM AUTHOR]

A detailed study on the influence of the focusing lens numerical aperture on the InSb super resolved spot is presented. The super resolution effect is described using the threshold model, where the material permittivity locally changes under laser exposure, being rigorously simulated in a finite element method program. The superresolved InSb focused spot is investigated for a wide range focusing lenses systems, from high to low numerical apertures. An extension of the model to account for disc motion is discussed. Such dynamic super-resolution near-field structure (Super-RENS) threshold model is suitable for readout signal analysis when combined with a “quasi-scalar” readout program, also described. Interesting properties of the InSb Super-RENS focused spot, such as sub-diffraction limited spot size and the general conditions to achieve it, are shown. An analysis on the Super-RENS readout signal is also given, with useful applications in optical data storage. Thus, this work greatly helps in understanding the InSb scatterer type of Super-RENS effect for optical data storage and other super resolution applications. [ABSTRACT FROM AUTHOR]

A rigorous electromagnetic computational model is presented to simulate the near field characteristics of the focused spot in an embedded super rens medium. The super resolution effect is described using a threshold model, where the material refractive index is changed instantaneously under laser exposure above a certain threshold. The simulations reveal interesting features of the Super Rens focused spot and demonstrate how super resolution is achieved. This model is useful for a better understanding of the super resolution effect in optical data storage and other super resolution applications. [ABSTRACT FROM AUTHOR]

Carrying orbital angular momentum per photon, the optical vortex has elicited widespread interest. Here, we demonstrate that dual coaxial longitudinal polarization vortices can appear upon a nonparaxial propagation of a tightly focused Pancharatnam-Berry tailored Laguerre-Gaussian beam. Most importantly, it is capable of accessing arbitrary independent topological charges for both vortices, as well as predesigned tunable spacing distances between them. [ABSTRACT FROM AUTHOR]