Precision Glass Molding of High Filling Factor Micro Lens Arrays

Glass micro lens arrays (GMLAs) have several advantages such as a high transmission rate, anti-environment, and can be used for special wavelength applications. Precision glass molding (PGM) has been used to mass produce high-accuracy aspherical glass lenses. Ultra-precision diamond grinding (UPDG) is a fundamental part of the precision glass molding process. Using UPDG, grinding spherical and aspherical to sub-micrometer form and nanometer surface roughness is simple. However, asymmetrical surface MLAs are difficult to generate using the UPDG process. UPDG, together with the wheel-forming method and a strategy used to separate the entire surface generation process into several grinding loops, were studied and developed to generate high filling factor MLAs on the mold surface. The GMLA material used was K-CSK120, made by Sumita Inc., Japan. Finally, GMLAs with an approximately 100% filling factor were generated using PGM with form accuracy and surface roughness that were respectively less than 0.3 μm and 10 nm. The tolerance of each single micro lens figure was greater than 95%.

Fabrication of a Micro Lens Array with a High Filling Factor Using a Direct Molding Method

In recent years, micro lens arrays have played a crucial role in optical illumination systems. The function of micro lens arrays (MLAs) is to create a uniform light intensity or shape the light profile. Polymers that are commonly used as MLAs have several advantages, such as cost effectiveness, light weight, and easy formation. In general, the ultra-precision diamond-turning technique and plastic injection molding technique have been combined to fabricate MLAs with polymer materials. However, residual stress and non-balance injection pressure are produced on MLAs during injecting processing. Therefore, this paper presents the fabrication of MLAs using a direct molding method (DMM). The STAVAX with electroless nickel coating and PMMA were used as the mold and polymer preform, respectively. First, a mold of MLA with 100% filling factor was fabricated using the ultra-precision diamond-turning technique. A high filling factor can decrease the non-effective area of the MLA in an optical system. Subsequently, an MLA was formed on the PMMA surface using DMM processing. This paper shows the DMM process parameters, including molding temperature, molding force, and cooling rate. Moreover, the profile of the MLA was measured using a laser confocal microscope. Finally, a high filling factor MLA with a diameter of 11.5 mm, and lenses with a height of 8.5 μm and a radius of 470 μm were formed on PMMA.