Experimental and Numerical Simulation of Hot Embossing for Fabrication of Glass Microlens Array

In this work, a hot embossing process for replication of glass microlens array (MLA) on optical glass substrate is proposed. Both numerical simulation and experimental validation were employed to investigate the filling behavior of the glass material into the microstructure mold cavities. The finite element method (FEM) was carried out using Ansys software after the establishment of the model layout and boundary condition. For validation, the K-PG375 optical glass samples were pressed at a temperature above the glass transition temperature Tg, using a home-made hot embossing setup. Then, the correlation between two- dimensional (2D) FEM analysis and experiments were established, which provide a guideline for understanding of the glass filling behavior in the viscoelastic region. The replication quality of the embossed glass was confirmed using scanning electron microscopy (SEM) and atomic force microscope (AFM). Overall, the simulation result gave a very useful insight to predict the optimum processing condition for the thermal replication process primarily the temperature, pressure and holding time

Direct formation of periodic parallel microgrooves on glass using CO2 laser irradiation

Direct laser structuring is an interesting candidate for a rapid, large area and maskless method for formation of various microstructures pattern on glass substrates without the use of mold. Before the desired pattern shape and scale could be obtained, the relationship between the type of laser used, substrate material and laser irradiation parameters must be understood. In this work, direct formation of periodic parallel microgrooves on optical glass substrate using CO 2 laser irradiation is proposed. The effect of the laser scanning speed and initial glass temperature to the formation of periodic micro-grooves with various width and height was investigated. As a result, smooth and crack-free parallel microgrooves were successfully fabricated on KPSFN214-P optical glass with dimension ranging from 287μm to 456μm in width dimension and 4.2μm to 11.9μm in height

Laser-assisted thermal imprinting of glass guided mode resonant (GMR) optical filter

Laser-assisted thermal imprinting of glass nanostructures is demonstrated. Compare to the existing thermal imprinting, this method significantly reduced the contact imprinting time. The quality of the replicated glass nanostructures revealed by field emission scanning electron microscope ( SEM) and atomic force microscope ( AFM) exhibited a very smooth surface finish that closely matched the profile of the silicon mold. As proof-of-concept, the utility of laser-assisted, imprinted glass nanostructures as guided-mode resonant (GMR ) optical filter was evaluated. The peak spectral values obtained were satisfactory; which yielded an average FWHM and PWV of 4.6 nm and 691.39 nm respectively

Rapid Direct Continuous Method for Hot Embossing of Glass Microlens Array Combined with CO2 Laser Irradiation and External Preheating/Cooling

Hot embossing of glass micro structures requires long thermal cycle, generally takes no less than 15 min due to the isothermal heating, pressing and cooling performed inside a closed vacuum chamber. In this paper, a new hot embossing procedure was presented. First, the glass was preheated slightly below its glass transition temperature at the heating station. Then, a thin layer of the glass surface was further raised to high temperature temporarily through CO2 laser irradiation. The glass was then quickly transferred to the embossing station for pattern transfer, demolding and followed by external cooling. This method accelerated the filling of glass material into the microlens array mold cavities and outperforms the conventional method in terms of overall cycle time reduction, lower mold working temperature and embossing pressure. Microlens array with diameter of 135 µm, sag height of 18.5 µm and pitch of 200 µm were faithfully embossed onto the K-PG375 optical glass time in a time scale of about ~3 s. Optical evaluation of the glass MLA was also performed using charge couple device (CCD) camera which showed uniform spot intensity

Feasibility Study of Wafer Scale Laser Assisted Thermal Imprinting of Glass Nanostructures

Major challenges for any direct nanostructuring method on glass substrate is the difficulty to scale up the patterning area to industrial scale. In this work, a rapid and large area direct thermal imprinting of glass nanostructures using silicon mold assisted by CO2 laser irradiation was demonstrated. Pattern transfer was successful for experiment trial of one spot laser irradiation and laser scanning with imprinting area of 100 mm2 and 400 mm2; confirmed by SEM and AFM measurement. When the method was extended to a larger imprinting area (2000 mm2), the glass was cracked and partially imprinted due to the high cooling rate of the glass after laser irradiation and misalignment of the glass during the contact pressing step in our molding setup