Yongkang Guo

Large-area surface-plasmon polariton interference lithography

Large-area surface-plasmon polariton (SPP) interference lithography is presented, which uses an attenuated total reflection-coupling mode to excite the interference of the SPPs. The interference of the SPPs causes a highly directional intensity range in a finite depth of the electric field, which is good for noncontact. Finite-difference time-domain simulations of the interference on a thin resist layer show that broad-beam illumination with a p-polarized light at a wavelength of 441 nm can produce features as small as 60 nm with high contrast, smaller than lambda/7. Our results illustrate the potential for patterning periodic structures over large areas at low cost.

Real-time gray-scale photolithography for fabrication of continuous microstructure

A novel real-time gray-scale photolithography technique for the fabrication of continuous microstructures that uses a LCD panel as a real-time gray-scale mask is presented. The principle of design of the technique is explained, and computer simulation results based on partially coherent imaging theory are given for the patterning of a microlens array and a zigzag grating. An experiment is set up, and a microlens array and a zigzag grating on panchromatic silver halide sensitized gelatin with trypsinase etching are obtained.

High-Power Coherent Beam Combining of Two Photonic Crystal Fiber Lasers

Coherent beam combining of two large mode area photonic crystal fiber (LMA PCF) lasers is studied experimentally by using a self-imaging technique. Steady interference strips with high visibility of 35% are observed in high-power operation, which demonstrates the obvious advantages of the LMA PCF over the conventional double-clad fiber in coherent beam combining. Experiments also show that the reflectivity of coupling output mirror affects the coherent output power. The maximum coherent output power of 80 W with approximate 90% combining efficiency is achieved when the pump power is 130 W and the reflectivity of coupling output mirror is 5%.

Calibration of a portable laser 3-D scanner used by a robot and its use in measurement

A robot scanning system consisting of a portable laser 3-D scanner and an industrial robot is demonstrated. In this system, the scanner is precalibrated by the traditional nonlinear two-step approach. In addition, by using a criterion sphere as the calibration object, a new robot tool center point (TCP) calibration approach is proposed for calibrating the relation between the precalibrated laser 3-D scanner and the robot. In this approach, two different translational motions of the robot are first made to determine the rotation part, and then at least three different rotational motions are made to determine the translation part. During the process, the extrinsic camera parameters are not recalibrated for each robot motion, so the calibration errors brought by camera calibration can be decreased. Moreover, the calibration error due to robot positioning error can be decreased by making use of the differences of different robot positions in calculations. An experiment was performed on a portable laser 3-D scanner and an ABB IRB-4400 industrial robot to test the validity of the proposed calibration approach. The experimental results show that this approach is simple and accurate compared to the conventional robot TCP calibration approach.

Modeling and effects of ion pairs in high-concentration erbium-doped fiber lasers

According to the modeling of ion pairs in high-concentration erbium-doped fiber lasers, a closed form rate and power evolution equations containing isolated ions and ion pairs are constructed. Based on the equations, the effects of ion pairs on the output performance of high-concentration erbium-doped fiber lasers for low Q and high Q laser cavity in three different pump modes are analyzed numerically. The results show that with the increasing percentage of ion pairs, the output power and the slope efficiency decrease, and the threshold increases for each pump mode. Meanwhile, the backward pump mode is proved to be the best pump mode and the deleterious effects of ion pairs for low Q laser cavity is proved to be smaller than that for high Q laser cavity.

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.

Theoretical analysis of the heat dissipation mechanism in Yb3+-doped double-clad fiber lasers

Based on the special structure of high-power Yb3+-doped double-clad fiber lasers, a heat dissipation model and the corresponding steady-state heat equations with consideration of both convective and radiative heat transfer are constructed. The temperature distributions along the radial and axial directions of the fiber for forward pump of 1000 W and two-end pump of 500 W each side are calculated numerically by using the steady-state rate equations and the heat equations. The results show that the temperature distribution for two-end pump mode is more even than that for forward pump mode and the maximum temperature in the fiber decreases by 139.8°C. Finally, a comparison between the temperature distributions with and without consideration of radiative heat transfer is performed, the results of which indicate that radiative heat transfer plays an important role in heat dissipation of high-power fiber lasers. Therefore, radiative heat transfer has to be considered in the thermal, stress, and thermo-optic effects of any type of high-power fiber lasers.

Overview of grey-scale photolithography for micro-optical elements fabrication

The advance in microlithography has greatly helped the development of microoptical elements. Large array of microlenses can now be fabricated in the same fashion as manufacturing of integrated circuits. Because most of the microoptical elements require well-defined and continuous surface relief profile, special methods are needed to supplement to the normal microlithography to produce those relief structures. One of the techniques is greyscale lithography, including electron and laser beam direct write and greyscale photolithography. In this paper, the development of greyscale photolithography is reviewed, in comparison with the direct write techniques. The new development in coding method for greyscale mask is introduced. The importance of correcting non linearity in optical imaging and resist development is discussed. A discussing is also devoted to practical issues in mask fabrication, thick resist patterning and pattern transfer process.

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