Fuhua Gao

Refractive micro lens array made of dichromate gelatin with gray-tone photolithography

A novel method is proposed to fabricate refractive micro lens array using dichromate gelatin (DCG) and an enzyme. DCG has optical properties similar to glass but is sensitive to UV light. The enzyme solution is used to develop the optically exposed DCG instead of a conventional water-isopropanol developer, which greatly enhances the surface relief depth. The continuous surface relief structure is realized by a coded grey-tone mask. A computer program has been developed to code an arbitrary 3D surface relief shape into a grey-tone mask design. The DCG properties and the lithography process are described. The grey-tone coding principle is presented. Unlike the current processes where patterned photoresist relief structure has to be transferred to a substrate material, the fabricated DCG micro lens array can be directly used as an optical element. The new process opens a new route of micro lens fabrication, which is simple and low cost

Coding gray-tone mask for refractive microlens fabrication

A new method has been developed to design gray-tone masks for microlens fabrication. Unlike previous methods which modulate the light intensity by changing the cell size or cell pitch only, the method relays on adjusting both the shape and position of a cell which gives an extra freedom to control the design accuracy. Based on the theory of partial coherent light and the resist development model, the intensity distribution through the gray-tone mask and exposure of photoresist have been simulated. Nonlinear effects in aerial image and resist development have been take into account to correct the mask design. A grey tone mask for microlens array has been fabricated and printed by a g-line stepper. Hemispherical photoresist structures have been achieved.

Design and Fabrication of Three-Dimensional Chiral Nanostructures Based on Stepwise Glancing Angle Deposition Technology

The chiral structures have displayed some inevitable and fascinating properties in many research fields, such as chemistry, biology, mathematics, and physics. In this Article, we report the use of stepwise glancing angle deposition technology to produce the 3D chiral nanostructures. Through the optimization of deposition parameters (such as the orientation angle of poly styrene spheres (PSs) array, the deposition angle, thickness, and number), a great number of chiral structures have been achieved, and their size depends on the diameter of PS spheres. These chiral structures all can be simulated and predesigned through the use of a 3D geometrical model, which greatly improves the efficiency of this method. In addition, the circular dichroism spectrum shows that these chiral structures own an obvious Cotton effect, indicating their potential application as 3D chiral metamaterials.

Determination of magneto-optical constant of Fe films with weak measurements

In this letter, a detecting method for the magneto-optical constant is presented by using weak measurements. The photonic spin Hall effect (PSHE), which manifests itself as spin-dependent splitting, is introduced to characterize the magneto-optical constant, and a propagation model to describe the quantitative relation between the magneto-optical constant and the PSHE is established. According to the amplified shift of the PSHE detected by weak measurements, we determinate the magneto-optical constant of the Fe film sample. The Kerr rotation is measured via the standard polarimetry method to verify the rationality and feasibility of our method. These findings may provide possible applications in magnetic physics research.

Incident-polarization-sensitive and large in-plane-photonic-spin-splitting at the Brewster angle.

In this Letter, we report a phenomenon of large in-plane-photonic-spin-splitting (IPPSS) in the case of a linear polarized Gaussian light beam reflected from an air-glass interface at the Brewster angle. The IPPSS-induced displacement reaches ∼12.4  μm, which is quite larger than the previously reported value. Particularly, the IPPSS is extremely sensitive (∼70  μm/deg) to the incident polarization. We also find that the direction of the spin accumulation can be switched by adjusting the incident polarization slightly. These findings may have useful applications in spin manipulation and precise polarization metrology.

Design of hybrid micro optical elements with coded gray-tone mask

A new method to fabricate hybrid micro-optical elements in one-step lithography is proposed in this paper. A gray-tone coding method has been developed to achieve one step photolithography of achromatic hybrid micro-optical elements. Design and simulation of hybrid lens with grey-tone mask are presented. The aberrations of optical elements are pre-corrected in the lithography process. The operating range of the hybrid optical element is in infrared band (8.0∼12.0 μm) with the central wavelength at 10.6 μm.

Imaging simulation of maskless lithography using a DMD

A maskless lithography imaging simulation using digital micromirror device (DMD) was investigated. The DMD acts as a reflective spatial light modulator. The micro-mirrors on DMD can be instructed by the computer to tilt them ±12° off their normal position which produces a mask pattern, and then the mask pattern can be carried onto the surface of wafer by the imaging system. Because the imaging of the maskless lithography is a complex process, it is necessary to simulate and analyze its practical process. In this paper, we present a partial coherent imaging model of maskless lithography considering the practical projection characterization of DMD. With the model, it is convenient to simulate the lithography of arbitrarily shaped microstructure using DMD. Through calculation, the spatial image in maskless lithography process based on gray scale photolithography with DMD real-time masks was obtained.

Diffraction-dependent spin splitting in spin Hall effect of light on reflection

We report on a diffraction-dependent spin splitting of the paraxial Gaussian light beams on reflection theoretically and experimentally. In the case of horizontal incident polarization, the spin splitting is proportional to the diffraction length of light beams near the Brewster angle. However, the spin splitting is nearly independent with the diffraction length for the vertical incident polarization. By means of the angular spectrum theory, we find that the diffraction-dependent spin splitting is attributed to the first order expansion term of the reflection coefficients with respect to the transverse wave-vector which is closely related to the diffraction length.

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