Resolution Of Optical Imaging System Research Articles

Electric field enhancement of coupled plasmonic nanostructures for optical amplification

Plasmonic effects that enhance electric fields and amplify optical signals are crucial for improving the resolution of optical imaging systems. In this paper, a metal-based plasmonic nanostructure (MPN) is designed to increase the resolution of an optical imaging system by amplifying a specific signal while producing a plasmonic effect via a dipole nanoantenna (DN) and grating nanostructure (GN), which couple the electric field to be focused at the center of the unit cell. We confirmed that the MPN enhances electric fields 15 times more than the DN and GN, enabling the acquisition of finely resolved optical signals. The experiments confirmed that compared with the initial laser intensity, the MPN, which was fabricated by nanoimprint lithography, enhanced the optical signal of the laser by 2.24 times. Moreover, when the MPN was applied in two optical imaging systems, an indistinguishable signal that was similar to noise in original was distinguished by amplifying the optical signal as 106 times in functional near-infrared spectroscopy(fNIRS), and a specific wavelength was enhanced in fluorescence image. Thus, the incorporation of this nanostructure increased the utility of the collected data and could enhance optical signals in optics, bioimaging, and biology applications.

Characteristics of the Image System based on Photon Density Waves in Observing Underwater Objects through a Waved Surface

The wavy surface effect on the resolution of optical imaging systems employing narrow modulated probing beams is studied. Relations are formulated connecting the complex amplitudes of the photon density waves (propagating through the wavy interface and the water layer) to the main parameters of the problem. These relations consider the finite waves height and the change in the photon trajectory length due to random refraction of rays upon entering the water. The optical transfer function of the wavy surface and the beam scattering function averaged over the ensemble of surface waving realizations are introduced. The dependences of these functions on the surface waves integral parameters, namely, the elevations and slopes dispersions, are examined. The contributions of surface waving and water layer to the generation of optical transfer functions and to the overall signal level from an underwater object when it is imaged using photon density waves are estimated. It is shown that in a certain range of depths, spatial frequencies, and illumination beam modulation frequencies, the systems employing photon density waves can demonstrate advantages over the systems with stationary illumination.

Smart quantum statistical imaging beyond the Abbe-Rayleigh criterion

The wave nature of light imposes limits on the resolution of optical imaging systems. For over a century, the Abbe-Rayleigh criterion has been utilized to assess the spatial resolution limits of imaging instruments. Recently, there has been interest in using spatial projective measurements to enhance the resolution of imaging systems. Unfortunately, these schemes require a priori information regarding the coherence properties of “unknown” light beams and impose stringent alignment conditions. Here, we introduce a smart quantum camera for superresolving imaging that exploits the self-learning features of artificial intelligence to identify the statistical fluctuations of unknown mixtures of light sources at each pixel. This is achieved through a universal quantum model that enables the design of artificial neural networks for the identification of photon fluctuations. Our protocol overcomes limitations of existing superresolution schemes based on spatial mode projections, and consequently provides alternative methods for microscopy, remote sensing, and astronomy.

Influence of drift correction precision on super-resolution localization microscopy.

Super-resolution localization microscopy (SRLM) breaks the diffraction limit successfully and improves the resolution of optical imaging systems by nearly an order of magnitude. However, SRLM typically takes several minutes or longer to collect a sufficient number of image frames that are required for reconstructing a final super-resolution image. During this long image acquisition period, system drift should be tightly controlled to ensure the imaging quality; thus, several drift correction methods have been developed. However, it is still unclear whether the performance of these methods is able to ensure sufficient image quality in SRLM. Without a clear answer to this question, it is hard to choose a suitable drift correction method for a specific SRLM experiment. In this paper, we use both theoretical analysis and simulation to investigate the relationship among drift correction precision, localization precision, and position estimation precision. We propose a concept of relative localization precision for evaluating the effect of drift correction on imaging resolution, which would help to select an appropriate drift correction method for a specific experiment.

Far-Field Imaging Beyond the Diffraction Limit Using Waves Interference

Due to the wave nature of light, resolution of optical imaging systems is limited to approximately half of the wavelength. The reason behind this limitation, known as diffraction limit, is the loss of information contained in evanescent waves at the far-field region. Here, we propose a new method to retrieve the information contained in evanescent waves in far field region resulting in a novel sub-wavelength imaging technique which can go beyond the diffraction limit. We theoretically prove that using interference of waves, between the target field and reference and reconstruction waves, one can apply a shift to the angular spectrum of the target field and convert a range of evanescent waves into propagating modes. Moreover, we demonstrate how these converted waves can be distinguished in far-field from other existing modes. Unlike previously developed sub-wavelength imaging techniques, the proposed method does not require either fluorescent materials or complex nano-structures to realize evanescent-to-propagating wave conversion. The performance of the method is numerically investigated illustrating a resolution of one-seventh of the working wavelength, which is much beyond the diffraction limit. The proposed technique can significantly simplify sub-wavelength imaging paving the road to develop practical low cost super-resolution imaging systems.

Three Zone Asymmetric Pupil Filter for Increasing Two-point Resolution of Optical Imaging Systems

In the present study, influence of three zone asymmetric apodizer on the resolution of composite image of two object points with given intensity ratio 'c' has been investigated. The proposed pupil function and its transmittance is for- mulated and studied. Fourier analytical properties of three zone aperture systems are studied by applying the modified sparrow criterion. The results are discussed in terms of sparrow limits obtained as a function of the degree of coherence of the illumination, intensity ratio of two object points and apodization parameters. Additionally, a test for the resolvability of the point sources from various set of observations is presented. It is established that for certain cases of illumination, the presence of amplitude and phase apodizer leads to an improvement in the resolution of optical imaging systems. The dependence of these characteristics on apodization controlling parameters is studied and reported.

Effect of coherence and polarization on resolution of optical imaging system

The effect of coherence properties of illumination on image resolution, well known in a scalar case, is studied for the case of vector electromagnetic illumination. Using an example of vector Gaussian Schell-model illumination, we analyze the dependence of optical system resolution on the transverse correlation lengths of the orthogonal field components and on the ratio of the powers of these components, each taken separately.

Synthetic aperture microscopy using off-axis illumination and polarization coding

A new method to improve the resolution of optical imaging systems beyond the classical Rayleigh resolution limit is presented. The technique relies on synthetic aperture generation in three stages. The first one (encoding stage) uses an illumination procedure that combines both on-axis and off-axis illumination beams with different polarization states onto the object. After the imaging system, a second stage (decoding stage) allows the recovering of the encoded spatial-frequency object information by means of an interferometric configuration based on the polarization coding carried out in the previous stage. Finally, a third stage (digital post-processing stage) is used to generate a synthetic aperture that is three times larger than the conventional aperture of the imaging system. The whole process allows us to obtain a superresolved image of the object. Experimental implementation of the approach for a commercial microscope objective is presented.