Incoherent Optical Image Research Articles

Quantum limit to subdiffraction incoherent optical imaging. III. Numerical analysis

Quantum limit to subdiffraction incoherent optical imaging. III. Numerical analysis

An efficient autofocus method for microscope based on the improved first-order derivative Gaussian filtering operator

This paper introduces an improved filtering operator based on the first-order derivative Gaussian filtering operator. As the defocus distance decreases, the edges of an image transition from being smooth to sharp. Using the operator proposed in this study, a parameter can be obtained to quantify the degree of edge sharpness, where a smaller value indicates sharper edges. By using the characteristic, we can judge whether the object is near the focal plane. Combining this information, we proposed two focus method. Both of them can avoid the problem of the hill climbing algorithm locating at local extremum points and one of them can locate the watershed between “coarse search” and “fine search” before the sharpness value crosses the peak value, so as to realize the transition from “coarse search” to “fine search” before crossing the peak value and improve focusing efficiency. This is different from previous passive focusing strategies. The final experiment shows that the proposed solutions in this paper is effective. However, the methods proposed in this study are only applicable to incoherent optical microscopy imaging systems and are not suitable for coherent light source microscopy imaging systems. Besides, the prerequisite for the successful implementation of the two proposed focusing strategies in this study is that the target exhibits sharp edges when it is within the focal plane.

3D single shot lensless incoherent optical imaging using coded phase aperture system with point response of scattered airy beams

Interferenceless coded aperture correlation holography (I-COACH) techniques have revolutionized the field of incoherent imaging, offering multidimensional imaging capabilities with a high temporal resolution in a simple optical configuration and at a low cost. The I-COACH method uses phase modulators (PMs) between the object and the image sensor, which encode the 3D location information of a point into a unique spatial intensity distribution. The system usually requires a one-time calibration procedure in which the point spread functions (PSFs) at different depths and/or wavelengths are recorded. When an object is recorded under identical conditions as the PSF, the multidimensional image of the object is reconstructed by processing the object intensity with the PSFs. In the previous versions of I-COACH, the PM mapped every object point to a scattered intensity distribution or random dot array pattern. The scattered intensity distribution results in a low SNR compared to a direct imaging system due to optical power dilution. Due to the limited focal depth, the dot pattern reduces the imaging resolution beyond the depth of focus if further multiplexing of phase masks is not performed. In this study, I-COACH has been realized using a PM that maps every object point into a sparse random array of Airy beams. Airy beams during propagation exhibit a relatively high focal depth with sharp intensity maxima that shift laterally following a curved path in 3D space. Therefore, sparse, randomly distributed diverse Airy beams exhibit random shifts with respect to one another during propagation, generating unique intensity distributions at different distances while retaining optical power concentrations in small areas on the detector. The phase-only mask displayed on the modulator was designed by random phase multiplexing of Airy beam generators. The simulation and experimental results obtained for the proposed method are significantly better in SNR than in the previous versions of I-COACH.

Weak Incoherent Optical Signal Amplification Based on Modulation Instability for Imaging Through Fog

Weak optical signal processing based on nonlinear effects offers new approaches for imaging through scattering media. A novel incoherent optical signal amplification method based on spatial modulation instability is proposed for imaging through fog. We experimentally demonstrated the amplification and recovery of degraded weak incoherent optical image signals after passing through dense fog in a photorefractive crystal. Our experimental results indicate that the intensity profiles of the output images can be redistributed from disordered to ordered when the nonlinear strength exceeds the threshold of incoherent modulation instability, which shows that the partially disordered incoherent probe light intensities are orderly transferred to enhance the signal intensity profiles and the residuals become a uniform background. The restored nonlinear output images with high visibility were observed for a proper optical thickness of fog, and weak optical imaging from undetectable to detectable with relatively poor visibility for a larger optical thickness was also realized in the experiment. This incoherent optical signal amplification method based on modulation instability has a potential application for image recovery in atmospheric scattering imagings.

Incoherent optical image encryption based on coded aperture correlation holography

We propose an incoherent encoding system for image encryption utilizing the coded aperture correlation holography (COACH) technique. Incoherent imaging is the core component of this proposal, in which the point spread hologram (PSH) of the imaging system serves as the main key to encode the input intensity distribution. The proposal makes full use of PSH which consists of four point spread functions (PSFs) respectively generated by four coded phase masks (CPMs), so that a multidimensional key space is generated to resist illegal attacks. Incoherent illumination of the imaging system ensures that only the intensity information is manipulated. The encoded information is just an intensity distribution which is advantageous for data storage, simplifying the system structure and processing, and suppressing the information expansion involved in general conventional encryption methods. Both numerical and experimental results illustrate the feasibility and effectiveness of the proposed method. This work represents an effective idea for incoherent optical encryption techniques.

3d Single Shot Lensless Incoherent Optical Imaging Using Coded Phase Aperture System with Point Response of Scattered Airy Beams

3d Single Shot Lensless Incoherent Optical Imaging Using Coded Phase Aperture System with Point Response of Scattered Airy Beams

Quantum limit to subdiffraction incoherent optical imaging. II. A parametric-submodel approach

In a previous paper [M. Tsang, Phys. Rev. A 99, 012305 (2019)], I proposed a quantum limit to the estimation of object moments in subdiffraction incoherent optical imaging. In this sequel, I prove the quantum limit rigorously by infinite-dimensional analysis. A key to the proof is the choice of an unfavorable parametric submodel to give a bound for the semiparametric problem. By generalizing the quantum limit for a larger class of moments, I also prove that the measurement method of spatial-mode demultiplexing (SPADE) with just one or two modes is able to achieve the quantum limit. For comparison, I derive a classical bound for direct imaging using the parametric-submodel approach, which suggests that direct imaging is substantially inferior.

Three-dimensional transfer function of optical microscopes in reflection mode.

Three-dimensional (3D) transfer functions build the basis for a comprehensive characterization of optical imaging systems in the spatial frequency domain. Utilizing the projection-slice theorem, the 2D modulation transfer function of an incoherent imaging system can be derived from a 3D transfer function by integration with respect to the axial spatial frequency. For a diffraction limited microscope with homogeneous incoherent pupil illumination, the modulation transfer function equals the 2D autocorrelation function of a circular disc. However, until now to the best of our knowledge no 3D transfer function has been published, which exactly leads to the 2D modulation transfer function of a diffraction limited microscope in reflection mode. In this article, we derive a formula, which after integration with respect to the axial spatial frequency coordinate perfectly fits to the diffraction limited 2D modulation transfer function. The inverse three-dimensional Fourier transform of the 3D transfer function results in a complex-valued 3D point spread function, from which the depth of field, the lateral resolution and, in addition, the corresponding 3D point spread function of both, a conventional and an interference microscope, can beobtained.

System Transfer Function of Incoherent Light Illumination System

Generally, most imaging cases are incoherent light field illumination, and incoherent light illumination system has the advantages of simple installation and no coherent noise, therefore it has received extensive attention. The optical transfer function of illumination system is an effective method to evaluate the imaging quality of such optical system. In order to evaluate the imaging quality of an optical system, the specific form of the system transfer function should be known. However, due to the in-coherent nature of the optical field, both the input function and the impulse response can only be non-negative real functions, it is difficult to deal with lots of bipolar inputs and impulse responses. In this paper, two methods for calculating the system transfer function of incoherent light illumination system under quasi-monochromatic light illumination are given. Method 1: the coherence of incoherent light is defined, and the coherent system transfer function based on the characteristics of the system transfer itself is deduced. Method 2: based on the theory of partially coherent light, started from Kirchoff’s diffraction integral, the quasi-wavefront aberration is introduced, and the spatial coherence of the light field is described by the mutual intensity instead of the mutual coherent function, finally the system transfer function of incoherent illumination is derived. The calculation formula is simple and the transfer function of incoherent light system can be calculated accurately and easily. The work in this paper is helpful to the study of the new phenomena related to incoherent optical imaging.

Hybrid algorithm for twin image removal in optical scanning holography

Optical scanning holography is an incoherent optical image processing system. It is a technique, where the complete information of an object or image will be recorded as a hologram and later reconstructed to get back the original image. In the hologram reconstruction process, a virtual image is formed along with the real image, which appears as a twin image noise. To eliminate such noises, a technique of hybrid algorithm is used while recording the hologram itself. The MATLAB R2012b image processing tool is used for simulation and the simulated values are tabulated and compared with the existing method in terms of peak signal to noise ratio, mean square error. In the reconstruction, the proposed method results are having 26% increment in the MSE and PSNR values. To further improve the MSE and PSNR values a case study using different denoising techniques combined with the proposed hybrid algorithm is used and found considerable improvement of 32%. Hence the image quality is increased.

Hybrid Algorithm for Twin Image Removal in Optical Scanning Holography

Optical scanning holography is an incoherent optical image processing system. It is a technique, where the complete information of an object or image will be recorded as a hologram and later recons...

Quantum limit to subdiffraction incoherent optical imaging

The application of quantum estimation theory to the problem of imaging two incoherent point sources has recently led to new insights and better measurements for incoherent imaging and spectroscopy. To establish a more general limit beyond the case of two sources, here I evaluate a quantum bound on the Fisher information that can be extracted by any far-field optical measurement about the moments of a subdiffraction object. The bound matches the performance of a spatial-mode-demultiplexing (SPADE) measurement scheme in terms of its scaling with the object size, indicating that SPADE is close to quantum-optimal. Coincidentally, the result is also applicable to the estimation of diffusion parameters with a quantum probe subject to random displacements.

Subdiffraction incoherent optical imaging via spatial-mode demultiplexing: Semiclassical treatment

I present a semiclassical analysis of a spatial-mode demultiplexing (SPADE) measurement scheme for far-field incoherent optical imaging under the effects of diffraction and photon shot noise. Building on previous results that assume two point sources or the Gaussian point-spread function, I generalize SPADE for a larger class of point-spread functions and evaluate its errors in estimating the moments of an arbitrary subdiffraction object. Compared with the limits to direct imaging set by the Cram\'er-Rao bounds, the results show that SPADE can offer far superior accuracy in estimating the second and higher-order moments.

Super-resolution in incoherent optical imaging using synthetic aperture with Fresnel elements

We present a new lensless incoherent holographic system operating in a synthetic aperture mode. Spatial resolution exceeding the Rayleigh limit of the system is obtained by tiling digitally several Fresnel holographic elements into a complete Fresnel hologram of the observed object. Each element is acquired by the limited-aperture system from different point of view. This method is demonstrated experimentally by combining three holographic elements recorded with white light illumination which is emitted from a binary grating.

Aliasing-based incoherent optical spatial image processor

We present a configuration for a real-time spatial image processor that is based upon an imaging setup in which a grating with Fourier coefficients with tunable phase is attached to the object plane. The illumination that is used for the proposed concept is spatially incoherent. By proper adjusting of the magnification of the imaging system to the spatial period of the grating and the sampling grid of the camera, the aliasing effect due to the digital sampling realizes a nonuniform and tunable spectral distribution (a filter) that is applied over the spectrum of the object. Preliminary numerical and experimental demonstration of the operation principle is provided with a spatial LiNbO(3) hexagonal grating.

Application to Optically Controlled Spatial Light Modulator Using Organic Photorefractive Composite

Optically controlled spatial light modulator was demonstrated as application of photorefractive polymeric material. Photorefractive composites based on photoconducting carbazole-substituted polysiloxane matrix (PSX-Cz) show an excellent stability against phase separation, compared to poly(N-vinyl carbazole) based composite. 2-[3-[(E)-2-(piperidino)-1-ethenyl]-5,5-dimethyl-2-cyclohexenyliden] malononitrile (P-IP-DC) has large dipole moment and large polarizability anisotropy. A photorefractive sample in which a chromophore (P-IP-DC) was dispersed showed a high diffraction efficiency of 85% at an external field of 28 V/μm. Application of photorefractive material for the optically controlled spatial light modulator which can convert incoherent optical image imposed in Xe-lamp light into coherent image in He–Ne laser wavelength is demonstrated using this composite.

Comparative analysis of the resolving power of optoelectronic imaging systems upon incoherent and coherent illumination of objects

Results of calculations of the resolving power (according to Foucault) of optoelectronic imaging systems with incoherent and coherent illumination under the conditions of atmospheric phase distortions are presented. It is suggested that incoherent optical images are formed in the case of incoherent illumination and speckle images are formed in the case of coherent illumination. The shape of objects observed is estimated from these images. The resolving powers are shown to be practically the same in the formation of incoherent optical images and speckle images in the case of strong phase distortions and smoothing of images by a matrix photodetector. At the same time, the limiting resolving power in the formation of incoherent optical images is twice as large as in the formation of speckle images.

Compression of complex-valued SAR images

Synthetic aperture radars (SAR) are coherent imaging systems that produce complex-valued images of the ground. Because modern systems can generate large amounts of data, there is substantial interest in applying image compression techniques to these products. We examine the properties of complex-valued SAR images relevant to the task of data compression. We advocate the use of transform-based compression methods but employ radically different quantization strategies than those commonly used for incoherent optical images. The theory, methodology, and examples are presented.

Incoherent optical XOR logic gate and image subtractor with series self-pumped phase conjugators

A simple setup that is capable of performing the function of an optical XOR logic gate is proposed. The setup consists of two BaTiO3 self-pumped phase conjugators as its principal elements. The mechanism of the gate is based on the phenomenon of self-pumped phase conjugation and the suppression of it by ordinarily polarized beams. In this way, the two input channels of the system are not required to be mutually coherent. In addition to its use as an XOR gate, the setup can be used as an image subtractor. And, as in the case in which it is used as a logic gate, the two input images do not need to be mutually coherent.

Introduction to Fourier Optics

This is the second edition of the extremely sucessful and much acclaimed original. It deals with the extensive and fast growing field of Fourier Optics from the viewpoint of the electronics engineer or applied physicist who wishes not only to understand the underlying theoretical background (which is the basis of scalar diffraction theory), but also how optical processing can be applied. It is ideal for the student wishing to learn about Fourier Optics, as well as for the reseacher looking for an extensive summary of the relevant background, basic principles and device technology. The book can be read largely as a self contained text, but also includes an extensive and up-to-date list of references. The major changes to the original edition are a wide ranging up-date of the background chapters and the inclusion of recent advances in processing architectures and device technology. The background sections cover all the main aspects of the field including two-dimensional, space-invariant linear systems, diffraction theory, analysis of coherent and incoherent optical processing and imaging systems. The application related text addresses wavefront modulation using a variety of spatial light modulators, descriptions of passive components, information processing techniques and architectures, holography and other related recent device technology. The author, following the pattern of the first edition, presents a fresh and easy to read explanation of basic principles that describe how familiar optical components such as lenses can be treated as processing and transforming elements. He then describes how these elements can be used for signal processing including a frank and clear explanation of their scope and limitations. In a logical and flowing manner designed to enable the reader to understand the significance of the text, he regularly punctuates the explanations with real world examples to identify both the strengths and weaknesses of the techniques and technologies discussed. Each chapter includes an extensive set of questions at the end to aid learning and stimulate thought.