Yangsu Zeng

Real-time photolithographic technique for fabrication of arbitrarily shaped microstructures

Sichuan UniversityInformation Optics InstituteChengdu 610064, ChinaE-mail: pengqinjun@263.netChongxi ZhouChinese Academy of SciencesState Key Laboratory of Optical Technologyon MicrofabricationChengdu 610209, ChinaZheng CuiRutherford Appleton LaboratoryChilton, DidcotOxon OX11 0QXUnited KingdomAbstract. A new photolithographic technique that combines the advan-tages of a programmable digital liquid crystal display (LCD) system andprojection photolithography system to fabricate arbitrarily shaped micro-structures using LCD panels as real-time masks is reported. Its principleand design method are explained. Based on a partial coherent imagingtheory, the process to fabricate microaxicon arrays and zigzag gratings issimulated. The experiment has been set up using a color LCD as areal-time mask. Microaxicon arrays and zigzag gratings have been fab-ricated by a real-time photolithographic technique. The 3-D surface reliefstructures are made on panchromatic silver-halide sensitized gelatin(Kodak-131) with trypsinase etching. The pitch size of the zigzag gratingis 46.26 mm, and the etching depth is 0.802 mm. The caliber of theaxicon is 118.7 mm, and the etching depth is 1.332 mm.

Principle and application of multiple fractional Fourier transform holography

In this paper, the principle of multiple fractional Fourier transform hologram (FRTH) is presented, and its characteristics based on the particularity in recording and reconstruction are analyzed. With this method, a multiple FRTH of several objects with different fractional transform orders is fabricated on one holographic plate. It requires a matched multiple fractional Fourier transform system to reconstruct the recorded images correctly. The potential application of multiple FRTH in optical security or anti-counterfeiting system is also discussed.

Electron-beam lithography to improve quality of computer-generated hologram

Abstract The quantized errors in computer generated holograms (CGH) have been analysed theoretically. In order to evaluate quantitatively the influence of these errors on the quality of reconstructed image, a signal-to-noise ratio (SNR) is introduced. It is found that the SNR of a reconstructed image is very sensitive to the accuracy of amplitude and phase. Improving the accuracy of amplitude and phase is much more effective for improvement of CGH image quality than simply increasing the sampling cells. The accuracy of amplitude and phase of a sampling cell is represented by the fidelity of sampling cell geometry. CGH plates with the same encoded image have been fabricated by both conventional photoreduction method and e-beam direct write method. The reconstructed images from both plates have been compared. The experimental result has confirmed the theoretical analysis: e-beam direct write can produce CGHs with quality superior to conventional photoreduction technique

One-step lithography for fabrication of multifunction diffractive structures with grey-tone mask

A new method with coding grey-tone mask has been developed to fabricate multifunction diffractive structures. Instead of conducting two different lithography processes to produce multifunction diffractive structures on a substrate, the new method achieves such structures through one-step lithography using a grey-tone mask. Considering the nonlinear nature of aerial image formation and resist development, predistortion is introduced to encode the grey-tone mask. Based on the theory of partial coherent light and resist development model, the intensity distribution through the grey-tone mask and exposure of photoresist have been simulated. The simulated 3D photoresist profiles are in agreement with the intended multifunction diffractive structures.

A microcylindrical lens array made of silver-halide-sensitized gelatin etched by an enzyme with a real-time mask

Abstract A novel method has been developed to fabricate microcylindrical lenses by etching silver-halide-sensitized gelatin (SHSG) with an enzyme solution, and the exposure pattern is produced on SHSG through a real-time mask technique. In this paper the principle of etching SHSG with an enzyme solution is given in detail and the optimum technique parameters of this process are presented; furthermore the theoretical analysis and solving scheme for the nonlinearities which arise from the absorption of light energy by film are given. A good linear relationship is experimentally obtained between the etching depth and time in depth a range up to 4 μm. Finally, the microcylindrical lens is achieved by experiment. The results are evaluated for experiments with a stylus profiling instrument and scanning electron microscope. This method does not require the use of expensive equipment, and it is not sophisticated and time consuming. So it is a practical method to fabricate excellent micro-optical elements.

Simple geometry to record fractional Fourier transform hologram with holographic lens

FRTH is a new kind of hologram, which is different form common Fresnel holograms and Fourier transform holograms. It can be applied for fractional Fourier transform filtering and anti-counterfeiting, etc. Due to the flexibility of holographic lens, we present a method that uses the -1 diffraction wave of holographic lens as the object wave and the 0 diffraction wave as the reference wave to record FRTH. It provides a new simple way to record FRTH. In this paper, the theory of achieving FRT and recording FRTH with holographic lens has been discussed, and the experimental results are also presented.

Micro-optical elements made of silver-halide sensitized gelatin etched by enzyme with real-time mask

In this paper a new method has been developed for fabricating micro-optical element by exposing silver-halide sensitized gelatin (SHSG) through real-time mask and etching SHSG with enzyme solution. The principle of etching SHSG with enzyme solution is given in detail and the optimum technique parameters of this process are presented, furthermore the theoretical analysis and solving scheme for the nonlinearities which come from the absorption of light energy by film are given. It is experimentally obtained a good linear relationship in a range of 4µm deep. At last, the micro-cylindrical lens and micro axicon array are achieved by experiment, and the results are evaluated for experiments by stylus profiling instrument and interference microscope.

Fractional Fourier domain filtering applied to improve image quality in photolithography

In this paper, we present a new method to improve the image quality and resolution of photolithography by filtering in fractional Fourier domain. Introducing a filter into fractional Fourier domain can not only increase the flexibility of the filtering operation, but also enhance the image quality and the depth of focus in photolithography. The corresponding simulation results are illustrated.

Digital implementation of fractional Fourier transform hologram

Digital implementation of fractional Fourier transform hologram (FRTH) is studied. From the definition of fractional Fourier transform (FRT), its discrete form is obtained and then a fast FRT algorithm is generated based on fast Fourier transform (FFT). Therefore, with the algorithm whose numerical efficiency is equal to the FFT, FRT can be quickly calculated and moreover FRTCGH can be efficiently encoded and reconstructed. The digital implementation for FRTH can lead its advantages, such as flexibility of fabrication and variation with recording system parameters, to expanding its application fields in FRT and holography.

Using a phase corrector plate to correct static phase aberrations in high-power laser system

Based on the analysis of phase aberrations in high power laser system, the phase corrector plate is presented to correct the static phase aberration. It can greatly improve the performance of the focal spot and is regarded as the suitable supplement of adaptive optics. In this paper, the performance of phase corrector plate, both continuous structure and multi-steps structure, is analyzed and simulated. The effect of misalignment between the phase corrector plate and the laser beam on the focal spot is also presented and simulated.