In recent years, Time-of-Flight (TOF) camera technology is widely adopted for 3D mapping and motion gestures. TOF camera generally consists of light emitting and receiving elements. The micro lens array (MLA) which had been commercialized as a lens for light projection for TOF camera could be made of a resin with a product size of 6 x 5 x 0.85 mm while the projection range was 120 degrees and the light amount unevenness was 10 % or less.
In general, a plurality of lenses in MLA are regularly arranged, and this arrangement causes light interference. Since the light amount unevenness occurred due to the interference, the unevenness could be reduced by arranging the lenses at random in three axes. The light amount unevenness was also caused by transfer errors that occurred in the molding process. The shape error of lens was controlled to nanometer-size by developing a correction process that functioned the shape error and adapted it to mold processing. Although a high refractive resin was used to widen the projection angle, it was difficult to manufacture a thin lens by injection molding because of the high viscosity. This problem was also solved by developing a heating and cooling method in the molding process. As a result, by optimizing the lens arrangement and controlling the error of the lens shape, the light amount unevenness of projection could be suppressed to 10% or less.
Melt transcription molding is one of novel processes suitable for manufacturing large-area thin film with microstructures.
We designed the mold which enables to transfer structures on both surfaces for the melt transcription molding machine
and examined about relations of temperature and pressure on the accuracy of dimension and optical strain. To keep the
high accuracy of relative position between both surfaces, the mold can avoid strain caused by the thermal expansion of
metal and is optimized by three-dimension unsteady heat conduction analysis. As a result, distribution of pressure mainly
affects stress and distribution density, influences shrinkage and accuracy of position. The decenter between both surfaces
was several micrometers. This makes it possible to mass-produce the large-area optical elements which is formed the
micro and nano structures on both surfaces with extremely low birefringence at high productivity.
This paper describes the fabrication of several diverse examples of molding tools designed for high volume production of plastic and glass optical components. The examples shown demonstrate a wide combination of surface shapes and structures all with nanometer level accuracy. The tungsten carbide molding tools were produced using grinding and magnetorheological finishing (MRF), new raster fabrication, and micro-milling. Mold tools were fabricated to produce a glass free-form surface, (profile accuracy of less than 200nm in PV, surface roughness of less than Ra5nm), a radial arrangement of 188-microlens, a microscopic pin (3um in diameter, 100um in height), and a molding tool for DOE with little optical loss. The molding of glass optics requires mold materials which can be used at high temperatures. In addition to tungsten carbide this paper describes molds fabricated from nano-structural sintered material or ceramic with partially stabilized molecular structure.
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