Hui Pang

Multi-focus plasmonic lens design based on holography

Multi-focus plasmonic lens with metallic nanoslits of variant widths have great potential applications in optical interconnection, integrated optics and nanophotonics. But the design method with simulated annealing algorithm or Yang-Gu algorithm requires complex calculation and multi focuses are limited to be set on the same output plane. In this paper, we propose a design method based on holography. The desired light field distribution and the incident plane wave can be treated as object wave and reference wave, respectively. So the calculation is relative simple and multi focuses can be located in different output plane. Numerical simulation of multi-focus lens design is performed through finite-difference time-domain (FDTD) method and the result confirms the feasibility of our method.

Non-iterative phase-only Fourier hologram generation with high image quality

We report a novel and non-iterative method for the generation of phase-only Fourier hologram for image projection. Briefly, target image is first added with a special quadratic phase and then padded with zeros. A complex Fourier hologram is generated via the simple fast Fourier transform. Subsequently, the error diffusion algorithm is applied to convert the complex hologram into a phase-only hologram. The numerical, as well as the optical reconstructed images with the proposed method are of higher visual quality and contain less speckle noise compared to the original random phase method, which add the random phase to the target image and then preserve the phase component of the complex hologram. The influences of quadratic phase and zero-padding on the image quality are also discussed in detail.

The Effects of Profile Errors of Microlens Surfaces on Laser Beam Homogenization

Microlens arrays (MLAs) are key optical components in laser beam homogenization. However, due to imperfect surface profiles resulting from microfabrication, the functionalities of MLAs in beam modulation could be compromised to some extent. In order to address this issue, the effects of surface profile mismatches between ideal and fabricated MLAs on beam homogenization were analyzed. Four types of surface profile errors of MLAs were modeled theoretically and numerical simulations were conducted to quantitatively estimate the effects of these profile errors on beam homogenization. In addition, experiments were conducted to validate the simulation results, revealing that profile errors leading to optical deviations located on the apex of microlenses affected beam homogenization less than deviations located further away from it. This study can provide references for the further applications of MLAs in beam homogenization.

High-accuracy method for holographic image projection with suppressed speckle noise.

Iterative Fourier transform algorithms are widely used for creating holograms in holographic image projection. However, the reconstructed image always suffers from the speckle noise severely due to the uncontrolled phase distribution of the image. In this paper, a new iterative method is proposed to eliminate the speckle noise. In the iteration, the amplitude and phase in the signal window in the output plane are constrained to the desired distribution and a special object-dependent quadratic phase distribution, respectively. Since the phase of the reconstructed image is assigned artificially, the speckle noise came from the destructive interference between the sampling points with random and erratic phase distribution can be eliminated. To verify the method, simulations and experiments are performed. And the result shows that high quality, low noise images can be achieved.

Center Off-Axis Tandem Microlens Arrays for Beam Homogenization

Tandem microlens arrays are commonly used in many applications for the beam shaping of an arbitrary input intensity distribution into a top hat. Because of the periodic structure of the regular arrays, the output intensity distribution is modulated by equidistantly located sharp intensity peaks, which reduces the homogeneity of the beam. A new concept is proposed in this paper for tandem microlens arrays incorporating a center off-axis microlens array for the generation of an intensity far-field distribution with improved homogeneity under coherent illumination with the envelope of a top hat. The geometric centers of the sub-apertures are randomly offset by the light axis of the sub-lens in the array to break the periodicity. The influences of the various off-axis amounts on the homogeneity are discussed. The center off-axis microlens array has been fabricated, and the corresponding laser beam homogenizing experiment has been carried out. The results verify that a high homogeneity output intensity distribution can be achieved based on the presented method.

Vector optical field generation based on birefringent phase plate

Vector optical field has recently gained interest in a variety of application fields due to its novel characteristics. Conventional approaches of generating vector optical fields have difficulties in forming highly continuous polarization and suffer from the issue of high energy utilization rates. In order to address these issues, in this study a single optical path was proposed to generate vector optical fields where the birefringent phase plate modulated a linear polarized light into a vector optical field, which was then demodulated to a non-uniform linear polarization distribution of the vector optical field by the polarization demodulation module. Both a theoretical model and numerical simulations of the vector optical field generator were developed, illustrating the relationship between the polarization distribution of the target vector optical field and the depth distribution of the birefringent phase plate. Furthermore, the birefringent phase plate with predefined surface distributions was fabricated by grayscale exposure and ion etching. The generated vector optical field was experimentally characterized, capable of producing continuous polarization with high light energy utilization ratio, consistent with simulations. This new approach may have the potential of being widely used in future studies of generating well-controlled vector optical fields.

The Polarization Multiplexing Image with a Single Diffractive Optical Element

The diffractive optical element (DOE) can modulate the light to image in a fixed distance. However, when the wavelength of the light is single and fixed, the imaging is single. In this paper, we proposed a novel architecture to solve this problem. The birefringent material is used as the substrate of the DOE, and the polarization modulation is added in the design of the DOE. The two orthogonally linear polarized lights with the same wavelength modulated by the DOE image differently at the same distance. The imaging of incident light with different polarization is simulated, and the diffraction efficiency and the uniformity are also calculated to demonstrate the validity of this mew method.

Nanobowl Array Fabrication via Conglutination Process Based on Thiol–Ene Polymer

The technique to fabricate nanostructures with high resolution is of crucial importance to nanosciences and nanotechnology. This paper presented a nonconventional method to fabricate metallic nanobowl arrays via the conglutination process, which relied on the high adhesive material to “stick” nanostructures. The ultraviolet (UV)-curable thiol-ene had low viscosity and was cured under UV light to form a cross-linked polymer with high Youngs modulus and high surface energy via “click chemistry,” which was used as the adhesive material to firmly stick nanostructures from the mold. By using the method, a self-assembly polystyrene (PS) sphere template with a metallic layer was stuck by the cross-linked thiol-ene polymer from the substrate. After removing the PS spheres, the metallic nanobowl structure with the thiol-ene substrate was achieved. In this paper, we fabricated gold nanobowl arrays composed of nanoheaves with the average diameter of ca. 60 nm between nanobowls, which verified the feasibility of the fabrication method.

Fabrication of nano-pillar with sub-100nm resolution based on thiol-ene

This paper demonstrates an approach to fabricate nano-pillar based on thiol-ene via soft-lithography. The template is anodic aluminum oxygen (AAO) with ordered nano-holes with the diameter of 90nm.The nano-pillar consists of rigid thiol-ene features on an elastic poly(dimethylsiloxane) (PDMS) support. It is capable of patterning both flat and curved substrate. The thiol-ene is a new green UV-curable polymer material, including a number of advantages such as rapid UV-curing in the natural environment, low-cost, high resolution, and regulative performance characteristic. Here, we fabricated a two-layer structure, which included rigid thiol-ene nano-pillar with sub-100nm resolution and soft PDMS substrate. The experiment results show that this approach can be used to fabricate high-resolution features and the thiol-ene is an excellent imprint material. The fabrication technique in this paper is simple, low-cost, high-resolution and easy to high throughput, which has broad application prospects in the preparation of nanostructures.

Fabrication of resonant subwavelength grating based on thiol-ene

This paper presents an approach used to fabricate resonant subwavelength grating based on thiol-ene material. First of all, polydimethylsiloxane soft imprint stamp with opposite structure of the subwavelength grating master mold is made by casting. Then, the desired subwavelength grating with UV-curable thiol-ene material grating structure is fabricated using the polydimethylsioxane soft stamp by UV-curable soft-lithography. Here, we fabricate a subwavelength grating with period of 300nm using the approach, which could reflect blue light with wavelength ranging from 448nm to 482nm at a specific angle and presents the excellent resonant characteristic. The experimental results are consistent with the simulation results, demonstrating that the approach proposed in this paper could effectively fabricate the thiol-ene material resonant subwavelength grating structure. The thiol-ene material is a new green UV-curable polymer material, including a number of advantages such as rapid UV-curing in the natural environment, low-cost, high resolution, and regulative performance characteristic. The fabrication technique in this paper is simple, low-cost, and easy to high throughput, which has broad application prospects in the preparation of micro and nano structures.