Yingbai Yan

Novel integrated light-guide plates for liquid crystal display backlight

A conventional LCD backlight system is composed of light sources, a light-guide plate (LGP) and optical sheets, such as reflection sheets, diffusion sheets and prism sheets, etc. In order to make the backlight system thinner and brighter, we propose a novel integrated LGP based on micro-prism structures by using traditional transparent polymethyl methacrylate (PMMA) material, which can be designed to control the illumination angle, and to get high uniformity of intensity. So the backlight system will be simplified to use only one LGP and to require no other optical sheets. By using the Monte Carlo ray tracing method, the light scattering phenomenon inside the LGP is analysed. The illumination angle with forward directivity and sufficient intensity uniformity are optimized with the simulation program. Design results reveal that our LGPs can achieve a uniformity of intensity better than 86%, and get a peak illumination angle from +40? to ?20?, without using any optical sheets. Design examples, including 1.8?inch LGPs and 14.1?inch LGPs, are also performed.

High quality light guide plates that can control the illumination angle based on microprism structures

In order to make the backlight system thinner and brighter, we propose a high quality poly(methylmethacrylate) light guide plate (LGP) based on microprism structures, which can be designed to control the illumination angle, and to get enough uniformity of intensity, so the backlight system will be simplified to use only one LGP and requires no other optical sheets. Design results reveal that our LGP can achieve a uniformity of intensity better than 86%, and get an illumination angle between ±25°, without using any optical sheets.

Polarized light-guide plate for liquid crystal display

A novel polarized light-guide plate (LGP) for the illumination of liquid crystal display is proposed in this paper. For the substrate of the LGP, stress-induced birefringence is introduced to achieve the polarization state conversion. An aluminum sub-wavelength grating (SWG) is designed on the top surface as a polarizing beam-splitter (PBS). The structure of the novel LGP is optimized for three wavelengths of LEDs: 625nm, 533nm and 452nm, and high efficiencies of polarization conversion are obtained. The backlight system with the designed LGP does not require prism sheets and quarter wavelength plate. The backlight with the novel LGP achieved large gain in energy efficiency, and the peak luminous intensity is about 2 times higher than that of a conventional backlight.

Broadband polarizing beam splitter based on the form birefringence of a subwavelength grating in the quasi-static domain

We propose a novel broadband polarizing beam splitter with a compact sandwich structure that has a subwavelength grating in the quasi-static domain as the filling. The design is based on effective-medium theory an anisotropic thin-film theory, and the performance is investigated with rigorous coupled-wave theory. The design results show that the structure can provide a high polarization extinction ratio in a broad spectral range.

Improved fast fractional-Fourier-transform algorithm

Through the optimization of the main interval of the fractional order, an improved fast algorithm for numerical calculation of the fractional Fourier transforms is proposed. With this improved algorithm, the fractional Fourier transforms of a rectangular function and a Gaussian function are calculated. Its calculation errors are compared with those calculated with the previously published algorithm, and the results show that the calculation accuracy of the improved algorithm is much higher.

Theories for the design of diffractive superresolution elements and limits of optical superresolution.

We suggest using the theory of linear programming to design diffractive superresolution elements if the upper bound of the intensity distribution on the input plane is restricted, and using variation theory of functional or wide-sense eigenvalue theory of matrix if the upper bound of the radiation flux through the input plane is restricted. Globally optimal solutions can be obtained by each of these theories. Several rules of the structure and the superresolution performance of diffractive superresolution elements are provided, which verify the validity of these theories and set some limits of optical superresolution.

Design of three-dimensional superresolution filters and limits of axial optical superresolution

Theories to design a three-dimensional superresolution filter (TDSF) for confocal microscopy are proposed that can obtain a globally optimal solution through linear programming. The designed TDSF is proved to be a phase-only element introducing a phase delay of 0 or pi. Five design examples of the TDSF are presented to demonstrate the validity of these theories, Regardless of transverse superresolution, a curve of Seu(Ga+/-) defined as the maximum value of Strehl ratio S under the axial resolving power of Ga+/- is calculated to set the fundamental limits of axial optical superresolution. Finally, what is to our knowledge a novel analytic expression of Seu(Ga+/-) is deduced.

Statistic analysis of influence of phase distortion on diffractive optical element for beam smoothing.

In this paper, the diffractive optical element (DOE) is used to realize beam smoothing with the smoothing by spectral dispersion (SSD) technique. The influences of the high and low frequency phase distortions on the DOE for beam smoothing are statistically analyzed based on the spatial frequency spectrum method. The amplitude and initial phase spectra of the far field intensity distribution are modulated by the characteristic of the phase distortion. The relationship between the performance parameters of the beam smoothing and the characteristic of the phase distortion is obtained. This can afford a theoretical tool to determine whether the characteristic of the phase distortion and the performance of the designed DOE for beam smoothing are able to satisfy the requirement of the light efficiency and the non-uniformity simultaneously or not.

Wavelet packet compression for volume holographic image recognition

An optical image recognition system based on the mechanism of crystal volume holography and wavelet packet compression method is proposed and constructed. Volume holographic associative storage in a photo-refractive crystal has some special properties, which can provide a suitable mechanism to develop an optical correlation system for image recognition. The method of wavelet packet is introduced in this optical system to reduce the number of images stored in the crystal. Through best wavelet packet basis selection, a set of best eigenimages, which will be stored in the crystal as the reference images for recognition, are extracted from a large number of training images. Correlation output between these eigenimages and input ones can be applied for classification and recognition according to the different light intensities of angularly separated beams. Experimental results showed this scheme is practical and can significantly compress the data stored in the crystal while the accurate rate of recognition is still high.

Multiobject recognition in a multichannel joint-transform correlator

A multichannel joint-transform correlator that incorporates a Dammann grating as a beam splitter is described. The Dammann grating splits a single incident beam into a two-dimensional array of equal-intensity beams, which form several channels for correlation. Each channel contains both a single target and a single reference. Optical experimental results are presented.