In this research, we systematically investigated the image classification accuracy of Fourier Ptychography Microscopy (FPM). Multiple linear regression of image classification accuracy (dependent variable), PSNR and SSIM (independent variables) was performed. Notebly, results show that PSNR, SSIM, and image classification accuracy has a linear relationship. It is therefore feasible to predict the image classification accuracy only based on PSNR and SSIM. It is also found that image classification accuracy of the FPM is not universally significantly differed from the lower resolution image under the higher numerical aperture (NA) condition. The difference is yet much more pronounced under the lower NA condition.
In this paper, we study the diffraction properties of tunable cascaded VHGs by using the two-dimensional coupled wave theory and two-dimensional Runge-Kutta methods. The intensity distributions of the diffracted and transmitted beams are given, the total diffraction efficiency is calculated for multiple cascaded finite-sized VHGs. It is shown that the diffraction characteristics depend on the grating parameters such as the number of the cascaded VHGs and the sizes of each VHG, and the effects of the buffer gaps between two cascaded VHGs is also discussed. It demonstrates the possibility of shaping beam and improving the beam quality by controlling the grating parameters and the layers number of the VHGs. The analysis of this paper also will be valuable for novel applications of finite-sized VHGs.
Lossy and near-lossless digital hologram compression methods are investigated to compress different complexities of wafer surface structures. In the lossy compression method, we apply row- and column-based uniform downsampling together with spline interpolation, whereas in the near-lossless compression method, we use wavelet local modulus maxima and spline interpolation. Results have shown that the lossy compression method is able to achieve a compression ratio of up to 100 for simpler wafer surface structures than that for complex surface structures. However, the near-lossless compression method is able to yield almost lossless compression even for complex wafer surface structures with a compression of about two. The proposed compression methods are computationally friendly for wafer surface structures as there is no time-consuming iterative computation involved.
The formation dynamics of crossed-beam photorefractive gratings formed by the in Fe doped LiNbO3 crystal is studied based on jointly solving the material equations and the two-dimensional coupled-wave theory. The numerical calculations of the temporal and the spatial evolutions of the space-charge field and the light modulation depth are given, and the influence of the recording conditions, including the recording wavelength, the two-dimensional sizes of the holographic grating are presented, and the time evolution of diffraction efficiency during holographic recording is also presented.
Volume gratings are of wide interest in many applications because of their properties of high diffraction efficiency, excellent wavelength selectivity and angular selectivity. Ultrashort pulsed laser has many promising applications in the fields such as optical communication, signal and imaging processing. Because of its abundant spectrum and wide bandwidth, the diffraction properties of volume gratings under illumination by ultrashort optical pulse will be different from that of a monochromatic continuous wave. A periodical structure is highly dispersive and such a dispersive property can be used to control the group velocity of light beams. So the spectral properties and dispersive properties of the periodically layered structures such as volume gratings when a linear chirped Gaussian pulse illuminated are very necessary. These properties can be applicable to addressable filter, switching, and controllable optical delay line. In this paper, a detailed study of linear chirped ultrashort pulsed beams diffracted by volume gratings in dispersive media is performed. The group delay characteristics of the diffraction spectrum of the transmitted and reflected volume gratings were studied based on the modified coupled wave theory. The analysis and observation of this paper will be valuable for the designing optical elements based on diffractive structure for the use with linear chirped ultra-short pulsed waves.
Laser beam scanners are important optical elements with a large variety of applications in the measurement techniques, optical communications, laser imaging ladar, etc. Agile beam steering of optical radiation using phased arrays offers significant advantages, such as weight, stability and power requirements over conventional beam steering systems. There are several kinds of optical phased array technology to be developed, such as Lithium tantalite phase shifters, lithium niobate electro-optic prism deflectors, and liquid crystal and ferroelectric liquid crystal phase modulations. However, one of the major drawbacks of these approaches is low light efficiencies because of the side lobes in far-field pattern of the steering beam. In this paper, a new low side lobe optical beam steering technique using phase correction technique is proposed. A stable and fast single-lobed far-field pattern in steering beam can be obtained from the optical phased array with a phase plate by optima design. It can result in a substantially increased light efficiency and beam quality. The quantitative calculation results of typical optical phased array are demonstrated. The low side lobe optical beam steering technology of optical phased array will benefit many practical applications such as laser ladar, laser communications and high resolution displays.
The diffraction properties of ultrashort pulsed by the volume gratings with arbitrary boundaries are studied based on the
extended two-dimensional coupled wave theory for volume grating readout by ultrashort pulsed beam. The intensity
distributions of the diffraction and transmitted pulsed beams in spectral and temporal domains are given. And the total
diffraction efficiency is also presented. Our study presents a possibility of shaping a broad band UPB by controlling the
boundary of the local volume hologram grating.
A new type of photorefractive volume holographic lenses for converting a plane wave to a lateral-spread spherical wave
with different wavelength has been suggested, which are recorded at 632.8nm wavelength and reconstructed at 800nm
wavelength. Using the coupled-wave theory, the wave-front conversion by photorefractive volume holographic lenses
between spherical and plane waves is studied. The off-Bragg parameter values of the holographic lenses in the
reconstruction process are analyzed. The dependence of diffraction efficiencies on the focal length of recording spherical
wave and the geometric sizes of the photorefractive holographic lenses are discussed in detail. In addition the intensity
distributions of the diffracted beam are analyzed also.
Using the two-dimensional coupled-wave theory, the diffraction characteristics of volume holographic gratings (VHGs)
with finite size planar are studied for the ultrashort pulsed beam (UPB) readout. Numerical simulations are show for the
special case of the overlapping VHGs reconstructed by a Gaussian-shaped UPB in temporal domain. The effects of the
material dispersion and the finite size of the grating on the intensity distributions of the diffracted and transmitted pulsed
beams, and the total diffraction efficiency are given. Our study also shows the differences between the diffraction
characteristics of the finite size planar VHG for the UPB readout and those for the CW readout. And, comparison of the
diffraction characteristics between the finite size VHGs and the one dimensional VHGs under the UPB readout is given.
The photorefractive volume holographic cylindrical lens taking on the wavelength conversion and the wave-front conversion synchronously was designed. Based on coupled wave theory, the wave-front conversion by local photorefractive volume holograms between cylindrical and plane waves which recoded at 632.8 nm and reconstructed at 800 nm is studied. The off-Bragg parameter at arbitrary point of the hologram in the reconstruction process is analyzed. The dependences of diffraction efficiency on the focal length of recording cylindrical wave and on the geometric size of the gratings on the hologram are discussed in detail. The amplitude distribution of the diffracted beam at the output boundary is also analyzed. Furthermore, the effect of selectivity of different on-Bragg reference point for recording hologram on the diffraction efficiency of the grating is discussed.
In this paper, the theory model in which both the two-center material equations and two-dimensional two-wave coupled equations were solved jointly based on two-center holographic recording method is presented to analysis the dynamic formation of the crossed-beam photorefractive gratings in two doped LiNbO3 crystals. The influence of the light intensity on the basic holographic properties of the crossed-beam photorefractive gratings in LiNbO3:Fe:Mn crystals is explored. The numerical simulation results are presented. The investigation yields quantitative predictions of the expected behavior of the dynamics of these gratings, which can be useful for the design of finite boundary photorefractive holographic optical elements.
With digital holographic interferometry, we have investigated the phase differences of a plane wave transmitting through
a partly-poled RuO2:LiNbO3 crystal sample. The holograms recorded by a CCD array are reconstructed by both the
Fresnel transform method and the angular spectrum backward propagation algorithm. Comparison of the reconstructed
results shows a higher resolution can be achieved by the angular spectrum backward propagation algorithm.
In this paper, effect of polarization of light on photorefractive grating formulation with any light modulation in birefringent photorefractive material is studied in detail. The diffraction efficiency with various modulations and different polarization mode is calculated. Theoretical analytic results are presented. It is shown that both the ratio of the initial intensity and the incident angle of the writing waves are selective when the polarization of mode of the readout wave and that of diffracted wave are different. But these two recording conditions are not selective for the isotropic diffraction. On the other hand, it is also found that the length of the grating is selective for anisotropic diffraction.
A Bragg grating focusing device composed of electro-optically induced refractive index grating in periodically poled lithium niobate was designed for integrated optics systems. The device are induced and controlled by the application of an external electric field. The theoretical analysis of the proposed optical device is carried out using two-dimensional coupled wave theory. The focusing properties and the diffraction intensity are investigated at the focal plane. It is shown that the designed device has good performance of focusing when a plane wave incidents on it at a certain angle. This type of Bragg diffraction devices can be act as a focusing lens and will have many potential applications such as in integrated optics and opto-electronics.
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