Abstract
A novel method for fabricating lens arrays and other non-rotationally symmetric free-form optics is presented. This is a diamond machining technique using 4 controlled axes of motion - X, Y, Z, and C. As in 3-axis diamond micro-milling, a diamond ball endmill is mounted to the work spindle of a 4-axis ultra-precision computer numerical control (CNC) machine. Unlike 3-axis micro-milling, the C-axis is used to hold the cutting edge of the tool in contact with the lens surface for the entire cut. This allows the feed rates to be doubled compared to the current state of the art of micro-milling while producing an optically smooth surface with very low surface form error and exceptionally low radius error.
Highlights
Novel high performance lens array based optical systems have been emerging over the last decade that are pushing the limits of current lens fabrication techniques
Roughing using 4-axis SPDM would have required a tool with both positive and negative sweep, similar to tools used in Single point diamond turning (SPDT)
A novel diamond machining technique known as 4-axis single point diamond machining has been presented
Summary
Novel high performance lens array based optical systems have been emerging over the last decade that are pushing the limits of current lens fabrication techniques. Several microlens array fabrication techniques have been well established and are in widespread use for imaging applications such as plenoptic light field sensors [5] and three dimensional imaging systems [6], which do not have full aberration correction, as well as non-imaging application such as light emitting diode (LED) illumination [7] All of these techniques are capable of producing lenses with state of the art form and surface finish, but each of these techniques has a limitation that makes it unsuitable or undesirable to meet the demands of emerging miniature lens array imaging systems (Table 1). Other similar diamond turning techniques such as slow tool servo (STS) and fast tool servo (FTS) synchronize the motion of the X and Z axes of SPDT with the work spindle using a spindle encoder, called a C-axis This extra degree of freedom enables 3-D fabrication of non-rotationally symmetric objects like lens arrays. Grayscale lithography can produce high quality lenses of arbitrary shapes and with nearly
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